Description:FIELD OF THE INVENTION
This invention relates to a Chemical Vapor Deposition (CVD) system and method for growing diamonds. This invention more particularly relates to a Microwave Plasma Chemical Vapor Deposition (MPCVD) System and method for growing gem quality diamonds using the same in which Methane in combination with waste Carbon Dioxide gas sourced from the cement, pharmaceutical and other industries is used as a source of carbon in the reaction chamber.
In the present system and process, Carbon Dioxide is directly used along with other gases in to the Chemical Vapor Deposition (CVD) reaction chamber for growing diamond. This eliminates costly and time-consuming method of converting Carbon Dioxide into hydrocarbons. Present system and process utilizes the waste Carbon Dioxide from the various industries as a carbon source otherwise which would have been released to the environment causing greenhouse effect and related environmental concerns. Further, as the waste Carbon Dioxide from the various industries is utilized as a carbon source, it eliminates cost of carbon dioxide capture from the atmosphere and its conversion into hydrocarbon.
Present system and process is capable of growing high-quality CVD diamonds suitable for jewelry with minimum piece to piece and batch to batch variations by precisely controlling feed gas mixture composition, feed and exhaust gas mixture flow dynamics and various other process parameters. Present system and process is capable of growing high-quality CVD diamonds without Z-axis (i.e. vertical) movement of the substrate holder.
BACKGROUND OF THE INVENTION
Diamond is a form of carbon which can be manufactured in laboratories by two methods. First method named as High Pressure and High Temperature (HPHT) replicate the natural process of High Pressure and High Temperature. The natural diamonds are formed in earth’s crust under High Pressure and High Temperature. Similar environment created in the laboratory can be used to manufacture diamonds. This process however has its limitations as the purity cannot be controlled beyond some point. The HPHT process there are possibilities small patches of incomplete transition from graphite to diamond. The probability of the incomplete transition increases with the increase in the size of the diamond. In order to manufacture pure and ultra-pure grade diamonds, Chemical Vapor Deposition method is most suitable. Chemical Vapor Deposition uses carbon containing gases to deposit the carbon atoms over an already exiting Diamond Substrate.
By controlling the purity of the gases and configuring the reactor dynamics, extremely pure diamonds can be made. The impurities of the diamond can be controlled up to ppb (parts per billion) level using Chemical Vapor Deposition. Electrical and Optical Grade Diamonds can be created using Chemical Vapor Deposition.
The primary requirement for Chemical Vapor deposition is to have a plasma source to which the Diamond Substrate is exposed in order to generate free radicals that would deposit on the substrate. Unlike Physical Vapor Deposition, Chemical Vapor Deposition converts gases to plasma. Plasma being fourth state of matter contains free radicals. The chemical vapor in Chemical Vapor Deposition contains cations and anions generated from gas by some source of energy. Plasma is generated using an energy source which can be direct current (DC) arc, Microwave, Hot Filament or radio frequency (RF). All the different sources of plasmas have different regimes of operation, each with its advantages and disadvantages.
DESCRIPTION OF THE RELATED ART
European patent application EP3597596A1 discloses a method of producing a synthetic diamond, the method comprising chemical vapor deposition (CVD) of methane and hydrogen, wherein the methane is obtained by reacting carbon dioxide with water or hydrogen, and the hydrogen is obtained by electrolysis of water.
Patent application publication ES2934893A1 discloses a process for obtaining sustainable synthetic diamonds through the reuse of carbon dioxide, consisting of the combination of the carbon captures and uses technique (CUC) from carbon dioxide generated by industries and the high-pressure technique and high temperature (HPHT) for the crystallization of carbon into diamond.
Patent application publication US20210285125 discloses a method of manufacturing synthetic diamond material using a chemical vapor deposition process, and a diamond obtained by such a method comprises providing a freestanding synthetic single crystal diamond substrate wafer having a dislocation density of at least 107 cm-2.
Patent no. US11371162B2 discloses system and method for generating synthetic diamonds via atmospheric carbon capture. As per the method: ingesting an air sample captured during an air capture period at a target location for collection of a first mixture including carbon dioxide and a first concentration of impurities; conveying the first mixture through a liquefaction unit to generate a second mixture including carbon dioxide and a second concentration of impurities less than the first concentration of impurities; in a methanation reactor, mixing the second mixture with hydrogen to generate a first hydrocarbon mixture comprising a third concentration of impurities comprising nitrogen, carbon dioxide, and hydrogen; conveying the first hydrocarbon mixture through a separation unit configured to remove impurities from the first hydrocarbon mixture to generate a second hydrocarbon a fourth concentration of impurities less than the third concentration of impurities; and depositing the second hydrocarbon mixture in a diamond reactor containing a set of diamond seeds to generate a first set of diamonds.
Patent application publication US20150222087 discloses a method of fabricating a polycrystalline CVD synthetic diamond material having an average thermal conductivity at room temperature through a thickness of the polycrystalline CVD synthetic diamond material of at least 2000 Wm-1K-1, the method comprising: loading a refractory metal substrate into a CVD reactor; locating a refractory metal guard ring around a peripheral region of the refractory metal substrate, the refractory metal guard ring defining a gap between an edge of the refractory metal substrate and the refractory metal guard ring having a width 1.5-5.0 mm; introducing microwaves into the CVD reactor at a power such that the power density in terms of power per unit area of the refractory metal substrate is in a range 2.5-4.5 W mm-2; introducing process gas into the CVD reactor wherein the process gas within the CVD reactor comprises a nitrogen concentration in a range 600 ppb to 1500 ppb calculated as molecular nitrogen N2, a carbon containing gas concentration in a range 0.5% to 3.0% by volume, and a hydrogen concentration in a range 92 – 98.5 % by volume; controlling an average temperature of the refractory metal substrate to lie in a range 750-950 °C and to maintain a temperature difference between an edge and a centre point on the refractory metal substrate of no more than 80 °C; growing polycrystalline CVD synthetic diamond material to a thickness of at least 1.3 mm on the refractory metal substrate; and cooling the polycrystalline CVD synthetic diamond material to yield a polycrystalline CVD synthetic diamond material having a thickness of at least 1.3 mm, an average thermal conductivity at room temperature through the thickness of the polycrystalline CVD synthetic diamond material of at least 2000 Wm-1K-1 over at least a central area of the polycrystalline CVD synthetic diamond material, wherein the central area is at least 70 % of a total area of the polycrystalline CVD synthetic diamond material, a single substitutional nitrogen concentration no more than 0.80 ppm over at least the central area of the polycrystalline CVD synthetic diamond material, and wherein the polycrystalline CVD synthetic diamond material is substantially crack free over at least the central area thereof such that the central area has no cracks which intersect both external major faces of the polycrystalline CVD synthetic diamond material and extend greater than 2 mm in length.
OBJECT OF THE INVENTION
Principal object of the present invention is to provide a Chemical Vapor Deposition (CVD) system in which microwaves are used to ignite plasma and a method for growing gem quality diamonds using the same.
Further object of the present invention is to provide a microwave plasma Chemical Vapor Deposition (CVD) system and method for growing gem quality diamonds using the same in which Methane in combination with Carbon Dioxide is used as a source of carbon directly into the reaction chamber of the said system.
Further object of the present invention is to provide a microwave plasma Chemical Vapor Deposition (CVD) system that uses waste carbon dioxide gas sourced from the cement, pharma and other industries along with methane directly into the reaction chamber of the said system as a source of carbon eliminating costly and time-consuming method of conversion of Carbon Dioxide into the hydrocarbon mixture
Further object of the present invention is to provide a microwave plasma Chemical Vapor Deposition (CVD) system that uses waste carbon dioxide gas sourced from the cement, pharma and other industries along with methane preventing release of the waste Carbon Dioxide from the various industries to the environment and thereby preventing greenhouse effect and related environmental concerns.
Further object of the present invention is to provide a microwave plasma Chemical Vapor Deposition (CVD) system and a method that uses the waste Carbon Dioxide from the various industries as a carbon source eliminating cost of carbon dioxide capture from the atmosphere and its purification.
Further object of the present invention is to provide a microwave plasma Chemical Vapor Deposition (CVD) system and a method that is capable of growing high-quality CVD diamonds suitable for jewelry with minimum piece to piece and batch to batch variations by precisely controlling feed gas mixture composition, feed and exhaust gas mixture flow dynamics and various other process parameters.
Further object of the present invention is to provide a microwave plasma Chemical Vapor Deposition (CVD) system in which Z-axis (i.e. vertical) movement of the substrate holder is eliminated and plasma dynamics, electromagnetics and gas phase chemistry (i.e. gas composition, substrate temperature, substrate holder’s design, reactor pressure, reactor water flow and overall stability of the MPCVD system) is used to have the similar effects as the Z-axis movement of the substrate holder thereby eliminating difficulties in maintaining ultra-high-level vacuum which can ultimately compromise the quality of the diamond grown. Thereby also reducing the manufacturing and maintenance costs associated with Z axis movement.
Microwave Plasma uses microwaves to ignite the plasma. The positioning of the plasma can be controlled in the microwave plasma chemical vapor deposition (MPCVD) such that external impurities can be minimized as compared to other sources such as Hot Filament or Direct Current (DC) Arc. The source being in the vicinity of the plasma makes it difficult to create diamonds without impurities from the source. Microwaves can be directed to a separate chamber and as per the requirement in order to avoid any impurities that may arise from the source. The microwave plasma is the best method which avoids impurities from the source.
Although Magnetron is separated from the reaction chamber, it is important to create conditions favorable for clean diamond growth. The Chemical Vapor Deposition has its limitations such that during the growth, there are byproduct entities which must not be allowed to get deposited on the substrate and should be removed through the exhaust in a streamlined fashion.
High quality diamond can be grown by; (i) accurately maintaining composition, purity, uniformity and flow pattern of feed gas mixture fed to the reaction chamber, (ii) controlling uniformity, kinetics, temperature distribution profile and electromagnetic profile of Plasma, (iii) controlling exhaust gas mixture flow dynamics and its stability from the reaction chamber, (iv) removal of the non-diamond entities and byproducts of chemical reactions over the substrate from reaction chamber, (v) controlling dimensions of the substrate holder, purity of the materials used for substrate holder, surface finish of the substrate holder, quality of the substrates (seeds), positioning of the substrates on the subset holder, temperature of the substrate holder and the substrates and, operating procedure used for pre-treatment and post treatment of substrate holders and the substrates, (vi) controlling and maintaining operating pressure of the reaction chamber, (vii) controlling input microwave power and (viii) quality of the water used in terms of TDS and PH.
Prior art uses only Methane as a source of carbon. Instead, methane and carbon dioxide is used as a source of carbon along with other reaction gases such as Hydrogen, Nitrogen, Oxygen and Argon in present invention.
SUMMARY OF THE INVENTION
Present invention relates to a Microwave Plasma Chemical Vapor Deposition (MPCVD) System and method for growing gem quality diamonds using the same in which Methane in combination with Carbon Dioxide gas sourced from the cement, pharmaceutical and other industries is used as a source of carbon fed into reaction chamber.
A Microwave Plasma Chemical Vapor Deposition (MPCVD) System utilizes mixture of Hydrogen, Methane, Carbon Dioxide, Nitrogen, Oxygen and Argon gases in a reaction chamber for growing gem quality diamond using the microwave plasma chemical vapor deposition. The Microwave Plasma Chemical Vapor Deposition System for growing diamonds comprises of a reaction chamber, a two stage rotary vane pump in fluid communication with the reaction chamber for generating and maintaining vacuum as per requirement in the reaction chamber, a microwave generator attached to the reaction chamber for supplying microwaves as a source for generating plasma to the reaction chamber, a feed gas mixing chamber in fluid communication with the reaction chamber for supplying feed gas mixture to the reaction chamber, a hydrogen inlet in fluid communication with the feed gas mixing chamber for supplying hydrogen gas to the feed gas mixing chamber, a methane inlet in fluid communication with the feed gas mixing chamber for supplying methane gas to the feed gas mixing chamber, a carbon dioxide inlet in fluid communication with the feed gas mixing chamber for supplying carbon dioxide gas to the feed gas mixing chamber, a nitrogen inlet in fluid communication with the feed gas mixing chamber for supplying carbon dioxide gas to the feed gas mixing chamber, an oxygen inlet in fluid communication with the feed gas mixing chamber for supplying carbon dioxide gas to the feed gas mixing chamber, an argon inlet in fluid communication with the feed gas mixing chamber for supplying carbon dioxide gas to the feed gas mixing chamber, a nitrogen inlet in fluid communication with the feed gas mixing chamber for supplying carbon dioxide gas to the feed gas mixing chamber, a hydrogen generator in fluid communication with the feed gas mixing chamber via. the hydrogen inlet for generating and supplying it to the feed gas mixing chamber, a copper stage along with a cooling arrangement in the form of a water filled cavity and an internal closed loop water flow channel housed inside the reaction chamber and a substrate holder mounted on the copper stage for holding substrates.
Present system and process is capable of growing high-quality CVD diamonds suitable for jewelry with minimum piece to piece and batch to batch variations by precisely controlling feed gas mixture composition, feed gas mixture and exhaust gas flow dynamics and various other process parameters such as temperature of the substrates and its variation over the substrate holder, temperature variation of plasma, microwave power and frequency, cooling media flow rate and temperature, vacuum in the reaction chamber. Various dimensions and geometry of microwave plasma chemical vapor deposition (MPCVD) system plays important role in controlling gas flow dynamics. Present system and process is capable of growing high-quality CVD diamonds without Z-axis (i.e. vertical) movement of the substrate holder.
BRIEF DESCRIPTION OF THE DRAWINGS
The features of the invention as per the present patent application are described with reference to the following drawings in which like elements are labeled similarly. The present invention will be more clearly understood from the detailed description and the accompanying drawings, wherein:
FIG. 1 is a schematic diagram showing a Microwave Plasma Chemical Vapor Deposition (MPCVD) System.
FIG. 2 is a schematic diagram showing supply of Hydrogen, Methane, Carbon Dioxide, Nitrogen, Oxygen and Argon gases to a gas mixing chamber along with hydrogen generator.
FIG. 3 is a schematic diagram showing a reaction chamber along with various dimension variable of a feed gas mixture zone, an entry zone, a reaction zone and an exhaust zone.
FIG. 4 is a schematic diagram showing a reaction chamber along with a copper stage and various dimension variables of the copper stage and an exhaust zone.
FIG. 5 is a schematic diagram showing a quartz ring, exhaust holes and a microwave input channel along with associated dimension variables.
FIG. 6 is a schematic diagram showing a top cover.
FIG. 7 is a schematic diagram showing a base plate along with exhaust holes in it.
FIG. 8 shows a Raman Spectra for the diamond grown using a Microwave Plasma Chemical Vapor Deposition (MPCVD) System, mixture gas composition and other process parameters as per example.
List of designations/ reference numbers in figure
1. a Microwave Plasma Chemical Vapor Deposition (MPCVD) system
2. a reaction chamber
3. a two-stage rotary vane pump
4. a microwave generator
5. a feed gas mixing chamber
6. a hydrogen gas inlet
7. a methane gas inlet
8. a carbon dioxide gas inlet
9. a nitrogen gas inlet
10. an oxygen gas inlet
11. an argon gas inlet
12. a substrate holder
13. a mass flow controller
14. a top cover
15. a feed gas mixture inlet port-1
16. a feed gas mixture flow channel
17. a plurality of feed gas mixture inlet holes
18. a plurality of exhaust holes
19. a feed gas mixture inlet pipe
20. an exhaust gas outlet pipe
21. an internal surface of the feed gas mixture inlet pipe (19)
22. an internal surface of the exhaust gas outlet pipe (20)
23. a main power supply
24. a diaphragm valve
25. a hydrogen generator
26. a substrate
27. an exhaust system
28. a waveguide and Mode Converter
29. a copper stage
30. a water filled cavity
31. an internal closed loop water flow channel
32. a pressure controller
33. a diaphragm valve
34. a pirani gauge
35. a diaphragm valve
36. a diaphragm valve
37. a diaphragm valve
38. a diaphragm valve
39. a diaphragm valve
40. a diaphragm valve
41. a mass flow controller
42. a mass flow controller
43. a mass flow controller
44. a mass flow controller
45. a mass flow controller
46. a mass flow controller
47. a feed gas mixture zone
48. an entry zone
49. a reaction zone
50. an exhaust zone
51. a microcontroller unit
52. a quartz ring
53. a plurality of temperature sensors
54. a plurality of pressure sensors
55. a gas detector
56. an angle of the feed gas mixture inlet hole with horizontal
57. a microwave input channel
58. a base plate
59. a hydrogen inlet pipe
60. a methane inlet pipe
61. a carbon dioxide inlet pipe
62. a nitrogen inlet pipe
63. an oxygen inlet pipe
64. an argon inlet pipe
DETAILED DESCRIPTION OF THE INVENTION
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
The description of illustrative embodiments according to principles of the present invention is intended to be read in connection with the accompanying drawings, which are to be considered as a part of the entire written description. In the description of embodiments of the invention disclosed herein, any reference to direction or orientation is merely intended for convenience of description and is not intended in any way to limit the scope of the present invention. Relative terms and directives thereof are for convenience of description only and do not require that the apparatus be constructed or operated in a particular manner unless explicitly indicated as such. Terms such as “attached,” “affixed,” “connected,” “coupled,” “interconnected,” and similar refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise. Moreover, the features and benefits of the invention are illustrated by reference to the exemplified embodiments. Accordingly, the invention expressly should not be limited to such exemplary embodiments illustrating some possible non-limiting combination of features that may exist alone or in other combinations of features; the scope of the invention being defined by the claims appended hereto.
FIG. 1 shows a schematic diagram of a Microwave Plasma Chemical Vapor Deposition (MPCVD) System (1) and FIG. 2 shows supply of Hydrogen, Methane, Carbon Dioxide, Nitrogen, Oxygen and Argon gases to a feed gas mixing chamber (5) along with a hydrogen generator (25). As shown in FIG. 1-2, the Microwave Plasma Chemical Vapor Deposition System (1) for growing diamonds comprises of a reaction chamber (2), a two stage rotary vane pump (3) in fluid communication with the reaction chamber (2) for generating and maintaining vacuum as per requirement in the reaction chamber (2), a microwave generator (4) attached to the reaction chamber (2) for supplying microwaves as a source for generating plasma to the reaction chamber (2), a feed gas mixing chamber (5) in fluid communication with the reaction chamber (2) for supplying feed gas mixture to the reaction chamber (5), a hydrogen inlet (6) in fluid communication with the feed gas mixing chamber (5) for supplying hydrogen gas to the feed gas mixing chamber (5), a methane inlet (7) in fluid communication with the feed gas mixing chamber (5) for supplying methane gas to the feed gas mixing chamber (5), a carbon dioxide inlet (8) in fluid communication with the feed gas mixing chamber (5) for supplying carbon dioxide gas to the feed gas mixing chamber (5), a nitrogen inlet (9) in fluid communication with the feed gas mixing chamber (5) for supplying carbon dioxide gas to the feed gas mixing chamber (5), an oxygen inlet (10) in fluid communication with the feed gas mixing chamber (5) for supplying carbon dioxide gas to the feed gas mixing chamber (5), an argon inlet (11) in fluid communication with the feed gas mixing chamber (5) for supplying carbon dioxide gas to the feed gas mixing chamber (5), a nitrogen inlet (9) in fluid communication with the feed gas mixing chamber (5) for supplying carbon dioxide gas to the feed gas mixing chamber (5), a hydrogen generator (25) in fluid communication with the feed gas mixing chamber (5) via. the hydrogen inlet (6) for generating hydrogen gas and supplying it to the feed gas mixing chamber (5), a copper stage (29) along with a cooling arrangement in the form of a water filled cavity (30) and an internal closed loop water flow channel (31) housed inside the reaction chamber (2) and a substrate holder (12) mounted on the copper stage (29) for holding substrates (26).
As shown in FIG. 1, the reaction chamber (2) is divided into a feed gas mixture zone (47), an entry zone (48), a reaction zone (49) and an exhaust zone (50).
FIG. 6 shows a top cover. The reaction chamber (2) is closed using a top cover (14). The top cover (14) is provided with a feed gas mixture inlet port-1 (15), a feed gas mixture flow channel (16) and a plurality of feed gas mixture inlet holes (17). The feed gas mixture inlet port-1 (15) is in fluid communication with the plurality of feed gas mixture inlet holes (17) via the feed gas mixture flow channel (16). The feed gas mixture from the feed gas mixing chamber (5) is supplied to the reaction chamber (2) using a feed gas mixture inlet pipe (19) which is in fluid communication with the feed gas mixture inlet port-1 (15).
FIG. 7 is a schematic diagram showing a base plate (58). A plurality of exhaust holes (18) are provided in the base plate (58). The reaction chamber (2) is closed from the bottom using the base plate (58).
As shown in FIG. 5, a quartz ring (52) is mounted between the copper stage (29) and the base plate (58) for sealing the reaction chamber (2) to prevent the leakage of exhaust gases from the reaction chamber while allowing entry of the microwaves from the microwave generator (4) to the reaction chamber (2).
As shown in FIG. 1, the two-stage rotary vane pump (3) is in fluid communication with the reaction chamber (2) using an exhaust gas outlet pipe (20) via a plurality of exhaust ports (18), a pressure controller (32), a diaphragm valve (33) and a Pirani gauge (34) for generating, monitoring and maintaining vacuum as per requirement in the reaction chamber (2) as well as for controlled discharge of exhaust gases from the reaction chamber (2).
As shown in FIG. 2, quantity and flow rate of the feed gas mixture supplied to the reaction chamber (2) from the feed gas mixing chamber (5) is controlled using a mass flow controller (13) installed on a feed gas mixture inlet pipe (19). A diaphragm valve (24) is installed on the feed gas mixture inlet pipe (19) between the feed gas mixture inlet port (15) and the mass flow controller (13) for preventing back fire and related damages in case of any accidents and to cut-off the feed gas mixture supply to the reaction chamber (2) for maintenance purpose.
As shown in FIG. 2, quantity and flow rate of hydrogen, methane, carbon dioxide, nitrogen, oxygen and argon supplied to the feed gas mixing chamber is precisely controlled by using the mass flow controllers (41-46) installed in a hydrogen inlet pipe (59), a methane inlet pipe (60), a carbon dioxide inlet pipe (61), a nitrogen inlet pipe (62), an oxygen inlet pipe (63) and an argon inlet pipe (64) respectively. The diaphragm valves (35-40) are installed in the inlet pipes (59-64) respectively which act as an on-off value for various feed gas supply and will be helpful in preventing back fire and related damages in case of any accidents and to cut-off the gas supply to the feed gas mixing chamber (5) for maintenance purpose.
A microcontroller unit (51) is used to control various process parameters. The microcontroller unit (51) is in electrical and electronic communication with the mass flow controllers (13, 41-46), the microwave generator (4), the cooling arrangement (17) and the pressure controller (32) and can be configured to control various process parameters in a real time as per requirement using the program.
A main power supply (23) is in electrical communication with the microcontroller unit (51) and supply electrical power to the Microwave Plasma Chemical Vapor Deposition System (1).
A plurality of temperature sensors (53), a plurality of pressure sensors (54) and a gas detector (55) are attached to the Microwave Plasma Chemical Vapor Deposition System (1) at various strategic locations. The temperature sensors (53) and the pressure sensors (54) sense temperature distribution and pressure distribution in the reaction chamber (2) and communicate the same to the microcontroller unit (51). The gas detector (55) sense the gas composition in the feed gas mixing chamber (5) and in the feed gas mixing zone (47) of the reaction chamber (2) and communicate the same to the microcontroller unit (51). Based on this data, the microcontroller unit (51) controls the various mass flow controllers (13, 41-46), the microwave generator (4), the cooling arrangement (17) and the pressure controller (32) in a real time using the program to set parameters as per requirement.
There are large numbers of parameters that are of importance which govern the final quality of grown diamond. Not only the individual parameters affect the system but the permutation and combination of the values of these parameters also affect the final quality of the grown diamonds. Even if one parameter is altered, the output gets altered. The important factors affecting quality of grown diamonds are listed in a chronological order of their importance. All the factors must be very rigorously taken care of in a stringent manner in order to obtain the desired quality of the grown diamonds.
There are many parameters as listed below in an overall design of the Microwave Plasma Chemical Vapor Deposition (MPCVD) system that decide the suitability of the system for achieving high quality grown diamond.
Overall design and process parameters of the Microwave Plasma Chemical Vapor Deposition (MPCVD) system affecting quality of grown diamonds include:
• stability of the input microwave power
• power quality of the mains power supply
• power factor of the mains power supply
• stability, repeatability and accuracy of the mass flow controllers used to control the quantity and flow rate of feed gases and fees gas mixture
• electromagnetic coupling and the efficiency of the coupling
• efficiency of the power delivery system to the reactor.
• internal surface finish of the gas piping
• material quality of the gas piping system both in the supply side and in the system
• purity of the materials (and internal surface finish) used to manufacture the system including the reaction chamber, gas manifold, distribution manifold, vacuum manifold, bellows, vacuum fittings, MFCs, pressure controllers, pneumatic diaphragm valves, manual diaphragm valves, pressure gauges, KF Fittings, quartz glass, quartz windows and the copper stage including the substrate holder
• leak integrity of the overall system as well as individual components
• accuracy and repeatability of the pressure gauges
• quality and efficiency of the gas line filters
• stability and accuracy of the control mechanism of the pressure controllers
• flow dynamics of the system
• temperature distribution profile of the plasma
• plasma kinetics and the uniformity of the plasma
• gas flow as well as electromagnetic profile of the plasma
• stability of the plasma at set vacuum level and input power
• gas distribution of the feed gas mixture and its exhaust design
• uniformity of the feed gas mixture fed to the reaction chamber and its flow pattern
• exhaust mechanism of the gas and its stability
• temperature distribution of the plasma
• accuracy and repeatability of the temperature and pressure sensors
• stability of the vacuum pump and its capacity
• dimensions of the substrate holder and the purity of the materials used
• surface finish of the substrate holder
• gas piping and its leak integrity on the supply side
• purity of the feed gases
• feed gases used, their proportions and total feed gas quantity
• quality of the substrates (seeds) used and the positioning of the substrates on the substrate holder
• temperature of the substrate holder and the substrates
• operating pressure in the reaction chamber
• input microwave power
• stability of the system over longer operation hours
• efficiency of the gas regulators and gas distribution panels
• leak integrity of the Gas distribution panels
• quality of air inside the premises including the moisture and suspended particle count
• standard operating procedure (SOP) followed for pre and post processing of the substrates
• routine maintenance of the systems and the standard operating procedure (SOP) followed for the same
• water flow, pressure and temperature maintained for the various parts of the MPCVD system
• quality of the water used in terms of TDS and PH
Feed gases used in the present invention include Hydrogen, Methane, Carbon Dioxide, Oxygen, Nitrogen, and Argon. These feed gases are used in combination as a feed gas mixture and this feed gas mixture is fed to the reaction chamber (2) via the feed gas mixing cylinder (5). The conventional source of carbon is hydrocarbons as they are economical and readily available as a byproduct of the oil and gas industry. The most widely used carbon source is the most basic hydrocarbon, Methane (CH4). Other gases act as catalyst and supporting gases with each playing its own role individually as well as in combination with other gases. Present invention uses Methane in combination with Carbon Dioxide as a source of carbon to grow diamonds. The feed gas mixture consists of total six gases in controlled proportion. Carbon Dioxide is sourced from the suppliers who basically collect the gas right at its source where the source being the byproduct of cement, pharmaceutical and other industries. This eliminates process of capturing and purification of carbon dioxide from the atmosphere as well as conversion of the same into the hydrocarbons. Instead, the present invention uses the carbon dioxide gas which is a waste gas from the cement, pharmaceutical and other industries which might ultimately get fully or partially left out in the open atmosphere.
The reaction chamber (2) dimensions and geometry are very crucial for controlling quality of grown diamond. Hence, the reaction chamber (2) is designed considering electromagnetic simulations, thermodynamic analysis, gas flow simulations and empirical data of flow dynamics, actual temperature profiles of plasma on the substrate holder (12), actual trials of growth of diamond on the substrate (26) and data gathered by several hundred deposition runs in the actual reaction chamber (2) used for continuous improvement and reach the optimal design.
The reaction chamber (2) is designed based on the flow dynamics calculated using empirical data as well as mathematical simulations. Electromagnetic simulations are performed to analyze and overcome limitations of the conventional Microwave Plasma Chemical Vapor Deposition (MPCVD) systems. The biggest limitation of conventional Microwave Plasma Chemical Vapor Deposition (MPCVD) systems is the non-uniformity of the plasma density. The non-uniform plasma density is very challenging for mass production of diamonds as well as large area thin films. Any application that requires growth over a large area needs to have a uniform plasma density throughout the substrate (26). Uniform temperature distribution up to 75 mm diameter of the substrate holder (12) is achieved using 2.45 GHz microwave frequency. Even though 915 MHz can be used get even larger areas of uniform deposition, however the costs associated with 915 MHz components is very high as compared to 2.45GHz.
Dimension and radial position of the feed gas mixture port-1 (15), dimension of the feed gas mixture flow channel (16) and dimension, radial position and number of exhaust holes (18) are provided such that the regeneration time for attaining the reactor’s composition in the reaction zone (49) is in a range of 5-6 minutes. Dimension and radial position of the feed gas mixture port-1 (15), dimension of the feed gas mixture flow channel (16) and dimension, radial position and number of exhaust holes (18) are provided for uniform distribution of the feed gas mixture supplied from the feed gas mixing chamber (5) through the feed gas mixture inlet port-1 (15) into the feed gas mixture zone (47) of the reaction chamber (2). The flow is designed in such a way that the substrates (26) gets the maximum feed rate and refresh rate is maximized so that substrates (26) are exposed to the new entities at a faster rate. Another advantage of such a flow is the removal of the non-diamond entities and byproducts of chemical reactions over the substrates (26). However, the gas chemistry plays a major role in the growth of high-quality diamonds; flow dynamics of the reactor does have an impact on it.
The feed gas mixture inlet holes (17) are angled such that the laminar vortex is created over the substrate holder (12) in order to help in increasing the growth rate of the diamond as well for improving the quality of the grown diamond. As shown in FIG. 6, the plurality of feed gas mixture inlet holes (17) are angled at an angle in a range of 50-60 degree (shown as (56) in FIG. 6) with the horizontal in a radially inward direction to create a laminar vortex over the substrate holder (12) in order to help in increasing the growth rate of the diamond as well for improving the quality of the Diamond
As shown in FIG. 2, Hydrogen, Methane, Carbon Dioxide, Nitrogen, Oxygen and Argon gases are supplied at an inlet pressure in a range of 2-7 bar from the gas inlets (6-11) via the mass flow controllers (41-46) respectively to the gas mixing chamber (5) for proper mixing and maintaining laminar flow. After the mass flow controllers (41-46), pneumatically controlled diaphragm valves (35-40) are installed in the inlet pipes (59-64) respectively to act as an ON-OFF switch to cutoff feed supply to the feed gas mixing chamber (5) to prevent backfire in case of accident and for maintenance purpose.

The inlet of the feed gases to the feed gas mixing chamber (5) creates a temporary turbulence of the gas stream before entering the reaction chamber (2) for making the feed gas mixture more uniform. The positioning and size of the feed gas mixing chamber (5) is very critical. It should not be too close to the reaction chamber (2). If the feed gas mixing chamber (5) is too close to the reaction chamber (2), the feed gas mixture flow would be turbulent even before it reaches the reaction chamber (2).
An internal surface (20) of a feed gas mixture inlet pipe (19) supplying the feed gas mixture to the reaction chamber (2) and the exhaust gas outlet pipe (20) exhausting exhaust gas mixture from the reaction chamber (2) are electropolished for maintaining laminar flow of the feed gas mixture entering the reaction chamber (2) and exhaust gases exiting the reaction chamber (2). All feed gas inlet pipes (59-64), are electropolished on their internal surfaces. All feed gas inlet pipes (59-64), the feed gas mixture inlet pipe (19) supplying the feed gas mixture to the reaction chamber (2) is having a diameter of 6.35 mm or 12.7 mm.
The turbulence of the feed gas mixture is undesirable at the point of entry into the reaction chamber (2). This makes it a necessary to separate the feed gas mixing chamber (5) from the reaction chamber (2) by a distance of at least 30-500 cm.
The exhaust of the reaction chamber (2) is designed in such way that it causes no ringing effect as well as the gas flow path does not generate flow resistance. The design, size and location of the exhaust ports (18) is selected such that the vortex generated by the inlet feed gas mixture is not countered rather is in co-ordination with the feed. The mismatch between the inlet feed gas mixture flow and the exhaust gas flow can lead to turbulent flow which is not desired for high quality growth. The exhaust must not be to narrow nor it should be too wide. Range of the diameter of the exhaust gas holes (18) must be from 4-18 mm in diameter.

Exhaust gases from the reaction chamber (2) are exhausted through the pressure controller (32), the diaphragm valve (33) and the Pirani gauge (34) and fed into an exhaust system (27) from the two-stage rotary vane pump (3).
Stability of Microwave power is of key importance in the Microwave Plasma Chemical Vapor Deposition (MPCVD) system. In order to maintain the stability of the temperature of the substrate (26), the stability of microwave power is critical. The variation of the input power must be less than a certain range. The acceptable limit is less than +/- 1 Watt. Moreover, the change in microwave power must be in the count of 0.6-1 Watt. The increment of the microwave power must be within the range of 0.6-1 watt. This is critical for stability of the growth conditions. The microwave power waveform must be continuous in nature. Maximum microwave power must be in the range of 6000-15000 Watts. The waveguide and power delivery assembly are capable of delivering 15000 Watts of power without the need of water cooled three stubs tuner. The reaction chamber (2) cavity is electromagnetically coupled with a waveguide and Mode Converter (28) for a longer and stable run of the growth cycles.
Temperature of water in the water filled cavity (30) is maintained in a range of 12 – 30 0C, flow rate of water in the water filled cavity (30) is maintained in a range of 2-12 LPM, TDS of water in the water filled cavity (30) is maintained less than 100 and pH is maintained in a range of 7-8. The copper stage consists of water filled cavity (30) with the internal closed loop water flow channel (31) is used to maintain the temperature of the substrate holder (12) within the desired range. The copper stage (29) is made up of an ETP grade copper. Impurities in the copper can cause electromagnetic losses as well as those impurities can eventually contaminate the diamond during growth conditions. The Contamination would depend on the type and level of impurities present in the copper material used. The surface roughness of the final copper surface of the copper stage (29) must be maintained within 20 Ra.
There have been chemical vapor deposition (CVD) systems used in practice wherein Z axis movement of the substrate holder is provided in order to move the substrate along vertical axis. In present Microwave Plasma Chemical Vapor Deposition (MPCVD) system (1), the substrate holder (12) is fixed in its position. In the present Microwave Plasma Chemical Vapor Deposition (MPCVD) system (1), focus is on plasma dynamics, electromagnetics and gas phase chemistry (includes gas composition, substrate temperature, substrate holder’s design, pressure in the reaction chamber, water cooling of the substrate holder and substrate and overall stability of the MPCVD system (1)) which can be used to have the similar effects as the Z-axis movement. One of the major drawbacks of Z-axis movement of the substrate holder is that the moving parts create difficulties in maintaining ultra-high-level vacuum which can ultimately compromise the quality of the diamond grown. It also increases the cost of the Chemical Vapor Deposition (MPCVD) systems due to the manufacturing complexity associated with the Z-axis movement mechanism.
Using the Microwave Plasma Chemical Vapor Deposition (MPCVD) system (1) better quality growth of diamonds without Z-axis movement of the substrate holder (12) is achieved. Further, carbon dioxide is used as an added source of Carbon atoms for our Diamond Growth in the Microwave Plasma Chemical Vapor Deposition (MPCVD) system (1).
Conventional Chemical Vapor Deposition (CVD) system uses basic hydrocarbons as the source of Carbon for Diamond Growth. There have been many claims in the past regarding the same. However, in the Microwave Plasma Chemical Vapor Deposition (MPCVD) system (1) as per present invention, a mixture of carbon dioxide and Methane is used as a source of Carbon. Use of Methane along with Hydrogen is the well-known combination of gas for the growth of Diamonds. For Gem Quality, controlled amount of Nitrogen at 1-20 PPM have been studied in the past. Use of carbon dioxide in Microwave Plasma Chemical Vapor Deposition (MPCVD) for growing gem quality diamonds is not yet explored. The main reasons for carbon dioxide is not being explored so for as a carbon source for the Microwave Plasma Chemical Vapor Deposition (MPCVD) diamond growth are: availability of alternate economical source of carbons such as Methane, Butane; Methane being a byproduct of petrochemical industry, it is readily available across different countries and thus minimizes transportation costs from source to destination; No other hydrocarbon source is available at such a convenience; Oxygen from carbon dioxide can reduce the growth rate of the diamonds if not used with proper additional gases; the etching effect of Oxygen from carbon dioxide needs to be countered with appropriate gases in the feed along with major changes in the plasma dynamics of the Microwave Plasma Chemical Vapor Deposition (MPCVD) system. Since the growth rate for gem quality diamonds is less, number of trials would be numerous in order to achieve good results without compromising the growth rate by too much margin; since the growth is hampered even after necessary changes to some extent; it is commercially expensive to use carbon dioxide for growing diamonds of any quality.
Apart from the source of Carbon, there are other gases which are used to speed up the growth and achieve a good quality diamond. Oxygen, Argon and Nitrogen widely used across different applications in different proportions bases on the end product and the Microwave Plasma Chemical Vapor Deposition (MPCVD) system configuration. In present invention, carbon dioxide from industrial sources is used to grow gem quality diamonds. Carbon dioxide has been sourced from industry where it is a byproduct and filled in cylinders. Carbon dioxide produced as a waste gas from the industries is ultimately used by some other industries eventually to be released in the atmosphere. In present invention, carbon dioxide is converted into diamonds in literal sense and thereby, avoiding that much carbon dioxide from being released in the atmosphere.
flow rate of the hydrogen, methane, carbon dioxide, nitrogen, oxygen and argon gas to the feed gas mixing chamber (5) is maintained in a range of 400-700, 30-60, 5-75, 0.002-5, 0.2-10 and 80-200 standard cubic centimeter per minute (SCCM) respectively. All the gases of the feed gas mixture are of grade 5.0
Temperature distribution in a range of 1000±100 0C is maintained up to 65-75 mm diameter of the substrate holder (12).
Microwave power for a substrate holder of 65-75 mm in diameter, filled to its maximum capacity, is used for all the carbon dioxide runs. The runs are carried out with the substrate (26) temperature maintained at 1000±100 0C up to 65-75 mm diameter of the substrate holder (12). The thickness of the substrate holder is in the range of 3-15 mm. 24 pieces of square shaped Diamond substrates of 8 mm x 8 mm are used to completely fill the molybdenum substrate holder (12). The thickness of the substrates (26) is kept in the range of 0.50-0.8 mm. The substrates are polished on a scaife procured from the industry. Natural Diamonds are polished on this scaife which is readily available in the open market. All the cleaning procedures are followed post polishing process before the substrates (26) are placed on to the substrate holder (12) made up of molybdenum.
Process followed for cleaning of the substrates (26) includes steps:
A. Heating the substrates (26) in Hydrofluoric Acid at 60 C for about 15 min in order to remove any inorganic impurities.
B. Cleaning the substrates (26) from step A in deionized (DI) water.
C. Keeping the substrates from the step B in a glass beaker with DI water in an ultrasonic batch for 25 minutes.
D. Placing the substrates from step C in a Nitric Acid and Sulphuric Acid mixture congaing both the acids in 1:1 ratio. Heating the substrate in the acid mixture at 70 0C for 25 minutes. This is specifically done to remove any organic impurities and metallic impurities. The seeds are cooled slowly in order to avoid cracking.
E. Cleaning the substrates (26) from step D with DI water.
F. Placing the substrates (26) from step E in DI water Ultrasonic bath for 45 minutes.
G. Cleaning the substrates (26) from step F Iso-propyl Alcohol in Ultrasonic bath for 45 minutes.
H. Cleaning the substrates (26) from step G in DI water for another 10 minutes in the ultrasonic bath.
I. Placing the substrates (26) from the step H on the cleaned Molybdenum Substrate holder by drying them using a nitrogen or dry air gun.
The substrate holder (12) must have the surface roughness with a finish of 20 Ra or better. The substrate holder (12) is kept in ultrasonic batch for 45 minutes in DI water. Lastly, the substrate holder (12) is dried at 90 0C in a vacuum furnace for 60 minutes.
The mass flow controllers (13, 41-46) used in the Microwave Plasma Chemical Vapor Deposition (MPCVD) System (1) for controlled feed gas flow and had the highest accuracy based on differential temperature principle. The accuracy of the MFCs are +/- 1 % of set point if the set point is less than 30 % of full scale. The accuracy is +/- 0.3% of full scale if the set point is more than 30 % of Full Scale. The high accuracy of the mass flow controllers (MFC) ensures repeatability in the Microwave Plasma Chemical Vapor Deposition (MPCVD) process especially for the dopant gas. The mass flow controllers (MFC) had been undergone a 5 point calibration as against industry standards of 3 point calibration. 5-point Calibration is more reliable than 3-point calibration.
Various dimensions of the Microwave Plasma Chemical Vapor Deposition (MPCVD) system (1) play crucial role. The most critical part is dimensions of the reaction chamber (2). For clarity and simplicity, only the internal dimensions of the reaction chamber (2) which affect the process dynamics are shown in FIG. 2. Outer dimensions do not affect the electromagnetic coupling and the gas phase chemistry and other process dynamics. The outer dimensions are irrelevant for flow patterns and thermodynamics. Thermodynamics can be affected by the water flow inside the water filled cavity (30) of the copper stage (29) through the internal closed loop water flow channel (31). Those are not discussed as their influence is not critical. Proper water flow throughout the reaction chamber (2) ensures proper heat transfer thereby avoiding the excessive heating of O-rings. Excessive heating of the O-rings may compromise the vacuum integrity of the system. However, specifics of the water flow throughout the different parts of the system are not discussed in the report as it is not as critical as the internal dimensions.
Internal dimensions of the reaction chamber (2) are optimized for growing gem quality diamonds by using carbon dioxide as a second source of carbon along with methane. The intensity of the plasma is adjusted to compensate the effects of Oxygen that would come from carbon dioxide used directly inside the reaction chamber (2).
FIG. 3-7 shows various dimensions of the Microwave Plasma Chemical Vapor Deposition (MPCVD) System (1). FIG. 3 is a schematic diagram showing a reaction chamber along with various dimension variable of a feed gas mixture zone, an entry zone, a reaction zone and an exhaust zone. FIG. 4 is a schematic diagram showing a reaction chamber along with a copper stage and various dimension variables of the copper stage and an exhaust zone. FIG. 5 is a schematic diagram showing a quartz ring, exhaust holes and a microwave input channel along with associated dimension variables. FIG. 6 is a schematic diagram showing a top cover. FIG. 7 is a schematic diagram showing a base plate along with exhaust holes in it.
As shown in FIG. 3, the reaction chamber (2) is divided into a feed gas mixture zone (47), an entry zone (48), a reaction zone (49) and an exhaust zone (50). The range of the various dimensions shown in FIG. 3-7 in mm as well as in proportion to the dimension F of the reaction zone (49) are reported as per following details.
Dimensions E and F of the reaction zone (49) and the exhaust zone (50) are in a range of 40 – 83 mm and 350 – 450 mm respectively.
Dimensions A and B of the feed gas mixture zone (47) are in a range of 90 - 130 mm and 30 - 95 mm respectively, which is 0.257- 0.289 and 0.086 – 0.211 times dimension F respectively.
Dimensions C, D, H and G of the entry zone (48) are 2 – 20 mm, 5 – 25 mm, 120 – 220 mm and 200 – 280 mm respectively which is 0.0057-0.033, 0.0021-0.033, 0.342-0.49 and 0.571-0.622 times dimension F respectively.
Dimensions I, J, K and M of the copper stage (29) are in a range of 20 – 43 mm, 110 – 190 mm, 19 – 41 mm, 200 – 251 mm respectively which is 0.057-0.096, 0.314-0.422, 0.054-0.091 and 0.571-0.558 times dimension F respectively.
The feed gas mixture inlet port-1 (15) is provided at a pitch circle diameter in a range of 85 - 130 mm i.e. 0.242 - 0.288 times the dimension F.
The feed gas mixture flow channel (16) is provided at a pitch circle diameter in a range of 84 - 125 mm i.e. 0.240 - 0.280 times the dimension F.
The feed gas mixture inlet holes (17) are provided at a pitch circle diameter in a range of 80 – 120 mm i.e. 0.230- 0.270 times the dimension F.
The exhaust holes (18) are provided at a pitch circle diameter (R) of 205 – 230 mm which is 0.511-0.586 times the dimension F.
Dimensions N, P and Q of the quartz ring (52) are in a range of 5 – 100 mm, 152 – 198 mm and 30 – 76 mm which is 0.014 – 0.024, 0.434 – 0.418 and 0.086 – 0.169 times the dimension F respectively.

Microwave power delivery system is of crucial importance. Efficiency of the microwave power deliver system consists of various parts. Here the inner dimensions are of critical importance. The external dimensions are not disclosed as the internal dimensions play critical role in the electromagnetics. The outer dimensions do not play any role in the Electromagnetic coupling. The Quartz windows (not shown in FIG.) used in the viewport of the chamber is of a special grade for temperature measurement. The infrared (IR) grade quartz has been used for an accurate measurement of the temperature of the substrates (26). The transparency of the quartz used is more than 90 % for IR wavelengths in the range of 1 micrometer to 2.6 micrometer.

The IR grade quartz contains low OH content. Higher OH content causes absorption of IR wavelengths. Measurement of temperature of the substrate (28) is very critical for the MPCVD process. Absorption of IR wavelength beyond 25 % can drastically alter the measurement of the temperature of the substrate (25).
Vacuum Pump used for the system is the Two Stage Rotary Vane Pump (3). Capacity of the Two Stage Rotary Vane Pump (3) is at has been used is more than 3 meter cube per hour. The higher capacity of vacuum pump is beneficial for initial evacuation of the reaction chamber (2). It reduces the time required to reach the desired (-3 level) vacuum. Vacuum in the reaction chamber (2) is maintained in a range of 100-150 torr.
BEST METHOD OF PERFORMING THE INVENTI ON
A Microwave Plasma Chemical Vapor Deposition System and Method for Growing Diamonds as per present invention are implemented as per the following sample example. This example given is not intended to limit the scope of present invention as discussed in the detail description of the invention in any way.
Dimensions and other physical parameters of the Microwave Plasma Chemical Vapor Deposition (MPCVD) System (1)
Dimensions E and F of the reaction zone (49) and the exhaust zone (50): 75.2 mm and 366.5 mm respectively
Dimensions A and B of the feed gas inlet zone (47): 120.4 mm and 90.5 mm respectively
Dimensions C, D, H and G of the entry zone (48): 19.3 mm, 21.6 mm, 162.9 mm and 168.8 mm respectively
Dimensions I, J, K and M of the copper stage (29): 36.0 mm, 188.6 mm, 22.9 mm and 200.0 mm respectively
Pitch circle diameter of the feed gas mixture inlet port-1 (15): 88.5 mm
The feed gas mixture flow channel (16) is provided at a pitch circle diameter of 85 mm i.e. 0.232 times the dimension F.
The feed gas mixture inlet holes (17) are provided at a pitch circle diameter of 86 mm i.e. 0.235 times the dimension F.
The exhaust holes (18) are provided at a pitch circle diameter of 220 mm i.e. 0.6 times the dimension F.
Dimensions N, P and Q of the quartz ring (52): 5 mm, 16 mm and 46 mm i.e. 0.0137, 0.436 and 0.1255 times the dimension F respectively.
Feed gas feed gas mixture flow rate
Hydrogen: 450 SCCM
Methane: 31.5 SCCM
Carbon Dioxide: 14 SCCM
Nitrogen: 0.9 SCCM
Oxygen: 0.2 SCCM
Argon: 106 SCCM
Feed gas mixture: 602.6 SCCM

Microwave power
Input power of the microwave generator (4): 4700 W
Frequency of microwave: 2.45 GHz
Variation and increment of the microwave input power: in a range of 0.6 – 1 Watt
Waveform of the microwave power: continuous nature with the maximum microwave power in a range of 6000-15000 Watts

Vacuum in the reaction chamber (2): 125 torr

FIG. 8 shows a Raman spectrum for a diamond grown using the Microwave Plasma Chemical Vapor Deposition (MPCVD) System, mixture gas composition and other process parameters as per example. The said diamond has a carbon–carbon vibration Raman spectrum showing a single Raman shift at 1333 cm-1, confirms the purity of diamond. , Claims:We claim:
1. A Microwave Plasma Chemical Vapor Deposition System and Method for Growing Diamonds comprising:
a reaction chamber (2) housing a copper stage (29) along with a cooling arrangement in the form of a water filled cavity (30) and an internal closed loop water flow channel (31);
a substrate holder (12) mounted on the copper stage (29);
a two stage rotary vane pump (3) in fluid communication with the reaction chamber (2) via a pressure controller (32), a diaphragm valve (33) and a pirani gauge (34) for generating and maintaining vacuum as per requirement in the reaction chamber (2);
a microwave generator (4) attached to the reaction chamber (2) for supplying microwaves as a source for generating plasma to the reaction chamber (2);
a feed gas mixing chamber (5) in fluid communication with the reaction chamber (2) via a mass flow controller (13) and a diaphragm valve (24) for supplying a controlled quantity of gas mixture at a controlled flow rate into the reaction chamber (2);
a hydrogen generator (25) in fluid communication with the gas mixing chamber (5) via a hydrogen inlet (6), the mass flow controller (41) and a diaphragm valve (35) for generating and supplying controlled quantity of hydrogen gas at a controlled flow rate to the gas mixing chamber (5);
a methane inlet (7) in fluid communication with the gas mixing chamber (5) via the mass flow controller (42) and a diaphragm valve (36) for supplying controlled quantity of methane gas at a controlled flow rate to the gas mixing chamber (5);
a carbon dioxide inlet (8) in fluid communication with the gas mixing chamber (5) via the mass flow controller (43) and a diaphragm valve (37) for supplying controlled quantity of carbon dioxide gas at a controlled flow rate to the gas mixing chamber (5);
a nitrogen inlet (9) in fluid communication with the gas mixing chamber (5) via the mass flow controller (44) and a diaphragm valve (38) for supplying controlled quantity of nitrogen gas at a controlled flow rate to the gas mixing chamber (5);
an oxygen inlet (10) in fluid communication with the gas mixing chamber (5) via the mass flow controller (45) and a diaphragm valve (39) for supplying controlled quantity of oxygen gas at a controlled flow rate to the gas mixing chamber (5);
an argon inlet (11) in fluid communication with the gas mixing chamber (5) via the mass flow controller (46) and a diaphragm valve (40) for supplying controlled quantity of argon gas at a controlled flow rate to the gas mixing chamber (5);
a top cover (14) closing the reaction chamber (2) and provided with a feed gas mixture inlet port-1 (15) in fluid communication with the feed gas mixing chamber (5) and a plurality of feed gas mixture inlet holes (17) in fluid communication with the feed gas mixture inlet port-1 (15) via. a feed gas mixture flow channel (16) for feeding of feed gas mixture from the feed gas mixing chamber (5) to the reaction chamber (2);
a base plate (58) closing the reaction chamber (2) from the bottom;
a plurality of exhaust ports (18) provided in the base plate (58) and in fluid communication with the two stage rotary vane pump (3) via the pressure controller (32), the diaphragm valve (33) and the pirani gauge (34) for monitoring of vacuum and controlled discharge of exhaust gases from the reaction chamber (2);
a quartz ring (52) mounted between the copper stage (29) and the base plate (58) for sealing the reaction chamber (2) to prevent the leakage of exhaust gases from the reaction chamber while allowing entry of the microwaves from the microwave generator (4) to the reaction chamber (2);
a quartz window (not shown in FIG.) as a viewport provided on the reaction chamber (2);
a microcontroller unit (51) in electrical and electronic communication with the mass flow controllers (13, 41-46), the microwave generator (4), the cooling arrangement (17) and the pressure controller (32) for controlling various process parameters as per the program;
a main power supply (23) in electrical communication with the microcontroller unit (51) for supply of electrical power to the Microwave Plasma Chemical Vapor Deposition System (1); and
a plurality of temperature sensors (53), a plurality of pressure sensors (54) and a gas detector (55) attached to the Microwave Plasma Chemical Vapor Deposition System (1) at various strategic locations;
characterized in that, wherein
the reaction chamber (2) is divided into a feed gas mixture zone (47), an entry zone (48), a reaction zone (49) and an exhaust zone (50),
dimensions E and F of the reaction zone (49) and the exhaust zone (50) are in a range of 40 – 83 mm and 350 – 450 mm respectively,
dimensions A and B of the feed gas mixture zone (47) are in a range of 0.257- 0.289 and 0.086 – 0.211 times dimension F respectively,
dimensions C, D, H and G of the entry zone (48) are in a range of 0.0057-0.033, 0.0021-0.033, 0.342-0.49 and 0.428-0.622 times dimension F respectively,
dimensions I, J, K and M of the copper stage (29) are in a range of 0.057-0.096, 0.314-0.422, 0.054-0.091 and 0.571-0.558 times dimension F respectively,
the feed gas mixture inlet port-1 (15) is provided at a pitch circle diameter of 0.242 - 0.288 times the dimension F,
the feed gas mixture flow channel (16) is provided at a pitch circle diameter of 0.240 - 0.280 times the dimension F,
the plurality of feed gas mixture inlet holes (17) are provided at a pitch circle diameter of 0.230- 0.270 times the dimension F,
the plurality of exhaust holes (18) are provided at a pitch circle diameter of 0.511-0.586 times the dimension F,
Dimensions N, P and Q of the quartz ring (52) are 0.014 – 0.024, 0.434 – 0.418 and 0.086 – 0.169 times the dimension F respectively,
dimension and radial position of the feed gas mixture port-1 (15), dimension of the feed gas mixture flow channel (16) and dimension, radial position and number of exhaust holes (18) are provided for uniform distribution of the feed gas mixture supplied from the feed gas mixing chamber (5) through the feed gas mixture inlet port-1 (15) into the feed gas mixture zone (47) of the reaction chamber (2),
dimension and radial position of the feed gas mixture port-1 (15), dimension of the feed gas mixture flow channel (16) and dimension, radial position and number of exhaust holes (18) are provided for the regeneration time in a range of 5-6 minutes for attaining the reactor’s composition in the reaction zone (49),
vacuum in the reaction chamber (2) is maintained in a range of 100-150 torr,
temperature distribution in a range of 1000 ± 100 0C is maintained up to 65-75 mm diameter of the substrate holder (12),
thickness of the substrate holder is in the range of 3-15 mm,
thickness of the substrates (26) is kept in the range of 0.50-0.8 mm,
feed gas flow is designed so that the substrate gets the maximum feed rate, refresh rate is maximized so that substrate is exposed to the new entities at a faster rate and the non-diamond entities and byproducts of Chemical reactions over the substrate are removed,
the plurality of feed gas mixture inlet holes (17) are angled at an angle in a range of 50-60 degree with the horizontal in a radially inward direction to create a laminar vortex over the substrate holder (12) in order to help in increasing the growth rate of the diamond as well for improving the quality of the Diamond,
the feed gas mixing chamber (5) creates a temporary turbulence of the feed gas stream before entering the reaction chamber (2) making the feed gas mixture more uniform and positioned 30-500 cm away from the reaction chamber (2) to maintain laminar flow of the feed gas mixture entering the reaction chamber (2),
a feed gas mixture inlet pipe (19) supplying the feed gas mixture to the reaction chamber (2) is having a diameter of 6.35 mm or 12.7 mm,
an internal surface (20) of a feed gas mixture inlet pipe (19) supplying the feed gas mixture to the reaction chamber (2) and the exhaust gas outlet pipe (20) exhausting exhaust gas mixture from the reaction chamber (2) are electro polished for maintaining laminar flow of the feed gas mixture entering the reaction chamber (2) and exhaust gases exiting the reaction chamber (2),
the exhaust gas outlet (18) of the reaction chamber (2) is designed to prevent ringing effect and flow resistance,
the exhaust gas outlet’s (18) design, size and location is selected so that the vortex generated by the inlet feed gas is not countered and remains in co-ordination with the exhaust gas stream elimination mismatch between the inlet and the exhaust leading to turbulent flow,
diameter of the exhaust holes (18) is in a range of 4 – 18 mm,
exhaust gases from the reaction chamber (2) are exhausted through a pressure controller (32) and a diaphragm valve (33) and is fed into an exhaust system (27) from the two stage rotary vane pump (3),
Hydrogen, Methane, Carbon Dioxide, Nitrogen, Oxygen and Argon gases are supplied at an inlet pressure in a range of 2-7 bar from the gas inlets (6-11) via the mass flow controllers (41-46) respectively to the gas mixing chamber (5) for proper mixing and maintaining laminar flow,
the pneumatically controlled diaphragm valves (24, 35-40) are installed at an outlet of the mass flow controllers (13, 41-46) which is operated as an ON OFF switch for the system maintenance and preventing backfire in case of any accident,
flow rate of the hydrogen, methane, carbon dioxide, nitrogen, oxygen and argon gas to the feed gas mixing chamber (5) is maintained in a range of 400-700, 30-60, 5-75, 0.002-5, 0.2-10 and 80-200 standard cubic centimeter per minute (SCCM) respectively,
input power of the microwave generator (4) is maintained in a range of 4000-12000 W with a variation and increment in a range of 0.6-1 W,
frequency of microwave of 2.45 GHz is used,
variation and increment of the microwave input power is maintained in a range of 0.6 – 1 Watt,
a waveform of the microwave power is of continuous nature with the maximum microwave power in a range of 6000-15000 Watts,
the reaction chamber (2) cavity is electromagnetically coupled with a waveguide and Mode Converter (28) for a longer and stable run of the growth cycles,
the waveguide and mode converter (28) are capable of delivering 15000 Watts of power without the need of water cooled three stub tuner,
the copper stage (29) is made up of an Electrolytic tough pitch (ETP) grade copper,
temperature of water in the water filled cavity (30) is maintained in a range of 12 – 30 0C, flow rate of water in the water filled cavity (30) is maintained in a range of 2-12 LPM, TDS of water in the water filled cavity (30) is maintained less than 100 and pH is maintained in a range of 7-8,
surface roughness of the substrate holder (12) is maintained less than 10-20 Ra,
an infrared (IR) grade quartz having more than 90 % transparency for IR wavelength in the range of 1 – 2.6 micrometer is used for the quartz window for accurate measurement of the temperature of the substrates (26),
accuracy of the mass flow controller (13, 41-46) is +/- 1 % of set point if the set point is less than 30 % of full scale and is +/- 0.3 % of full scale if the set point is more than 30 % of full scale,
quality of the grown diamond is controlled by plasma dynamics, electromagnetics and gas phase chemistry and,
carbon dioxide (CO2) gas used is a waste carbon dioxide gas from the cement, chemical and other industries.
2. The Microwave Plasma Chemical Vapor Deposition System and Method for Growing Diamonds as claimed in claim 1, wherein the substrate holder (12) is made up of a Molybdenum.
3. The Microwave Plasma Chemical Vapor Deposition System and Method for Growing Diamonds as claimed in claim 1, wherein process followed for cleaning of the substrates (26) is comprising the steps of:
(a) Heating the substrates in Hydroflouric Acid at 60 C for about 15 min in order to remove any inorganic impurities. (26);
(b) cleaning of the substrates (26) so obtained after step (a) using deionized (DI) water. (26);
(c) placing the substrates (26) obtained from step (b) in a Nitric Acid and Sulphuric Acid mixture congaing both the acids in 1:1 ratio and heating the substrates (26) in the Nitric Acid and Sulphuric Acid mixture at 70 0C for 25 minutes followed by natural cooling of the substrates (26) to avoid cracking;
(d) cleaning the substrates (26) so obtained from step (c) by placing it in DI water Ultrasonic bath for 45 minutes;
(e) cleaning the substrates (26) so obtained from step (d) in an Iso-propyl Alcohol and Ultrasonic bath for 45 minutes;
(f) cleaning the substrates (26) so obtained from step (e) in DI water for another 10 minutes under ultrasonic bath; and
(g) placing the substrates (26) so obtained from step (f) on the substrate holder (12).
4. The Microwave Plasma Chemical Vapor Deposition System and Method for Growing Diamonds as claimed in claim 1, wherein the substrate holder (12) is kept in an ultrasonic batch for 45 minutes in DI Water followed by drying at a temperature in a range of 70-90 0C in a vacuum furnace for 60 minutes.