SYSTEM AND METHOD FOR CHARACTERIZATION OF GASES AND
MATERIAL FOR CHEMICAL VAPOR DEPOSITION OF POLYSILICON

Technical filed

The present subject matter relates to a system for characterization of gases and material for chemical vapour deposition of polysilicon and a method thereof in accordance with the preamble of independent claims.

Background

Polysilicon is generally produced by depositing polysilicon in a Chemical Vapour Deposition (CVD) reactor. In this method, polysilicon is deposited in the CVD reactor on hot, high-purity thin silicon rods known as "slim rods". In view of the high purity of these rods, it can be extremely difficult to heat the silicon rods using electric current, while starting the process. Accordingly, prior to the application of current to these silicon rods, they have to be heated beforehand, so that the resistance of the rods drops to allow a current to pass through it to reach the desired process temperature. The process temperature is then maintained by passing the current through the rod and the reactant gases are let into the reactor which breaks down and deposits silicon on the hot surface of these silicon rods.

Typically a number of rods are heated in a closed reactor in which ultra pure gases are let into. These production reactors are quite big and they cannot be opened till the process is over which can vary from 4 to 6 days or more. Once the batch is made, the end product is removed before the commencement of the next batch.

Normally, on a production floor there will be a number of reactors operating simultaneously, which will have a common source of reaction gases. The quantities of material deposited on the rods will depend on the diameter deposited on the seed rod. Many modern reactors can produce over a ton of material in one batch operation which may last about 5 days.

In light of the above requirements, the current CVD reactors require a complex array of subsystems, including a variety of power supplies and sophisticated controls. In case of
silicon rods being used for deposition, there is a requirement of heaters for raising the initial temperature of the rods.

In another known technique, thin metal rods in place of silicon rods are used since, it is easier to heat the metal rods. This is generally known as Rogers-Heinz method. This technique uses tungsten rods as they can be obtained at high purity levels. During the polysilicon deposition, the metal rods become metal-silicides and typically fall off from the polysilicon core when broken. However, each polysilicon, when broken has to be inspected at the core to see if there are any specs of metal. This requires significant grinding, washing and etching at the core before using the polysilicon. Further, this technique is generally not used due to suspected contamination and also due to the semiconductor industry requiring higher purity levels of polysilicon.

Any impurity inclusion in the deposited material (polysilicon) can come from the gases or the reactor itself. If such a thing were to happen, then the entire batch of material needs to be scrapped. This is true for all the reactors, wherever the gas is contaminated. In addition, since the purity levels of these gases lie in the parts per billion range, it assumes a gigantic task to maintain such purity levels, Consequently, a user incurs substantial loss of revenue considering the high cost of the material.

In view of the above, it is necessary to provide a system that continuously monitors the purity of the gases, so that the deposition of polysilicon in a reactor is of the desired high purity and a system with optimum power consumption and management of gases.
Summary

The present subject matter provides a system for characterization of gases and material for Chemical Vapour Deposition of polysilicon, comprising a poly test reactor having a reaction chamber, a pair of electrodes disposed in the reaction chamber, at least an electrical and heat conducting pin mounted on said electrodes, to form a base for the deposition of polysilicon, a gas feed assembly with a feed nozzle arranged in the reaction chamber, a closely integrated inlet and outlet conduits disposed in the gas feed assembly.

The present subject matter also provides a method for characterization of gases and material for Chemical Vapour Deposition of polysilicon by using the reactor of the present invention.

These and other features, aspects, and advantages of the present subject matter will become better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

Brief description of the drawings

The novel features of the subject matter are set forth in the appended claims hereto. The subject matter itself, however, as well as a preferred mode of use, further objectives, and advantages thereof, will best be understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein the same numbers are used throughout the drawings to reference like features, and wherein:

Fig 1 is a cross-sectional view of the system for characterization of gases and material for chemical vapour deposition comprising a polysilicon reactor according to an embodiment of the present subject matter.

Fig 2 is a cross-sectional view of the gas feed assembly with an integrated inlet and outlet conduits according to an embodiment of the present subject matter.

Fig 3 is a cross-sectional view of the feed nozzle of the gas feed assembly in accordance with an aspect of the present subject matter.

Fig. 4 is a schematic view of power source and management assemblies of the system of the present invention.

Detailed description

The embodiments of the present subject mater are initially described by referring to Figs. 1,2 & 3 of the accompanied drawings. Accordingly, the present subject matter provides a system for characterization of gases and material for Chemical Vapour Deposition of polysilicon comprising a polysilicon reactor with a reaction chamber (7). A metallic wall (8), which is double-walled and having space between the walls, is provided to envelope said reaction chamber (7). A coolant medium, such as liquid, water or gas, is circulated inside the space between the walls, to keep the outer surface of the reaction chamber (7), at a room temperature.

At least two electrodes (9) disposed inside said reaction chamber (7), which are in turn connected to corresponding electrical power source (10), to enable the heating of the electrodes (9). The constructional assembly of the elements of said power source (10) is as described hereinafter.

At least an electrical and heat conducting pin (6) mounted inside the reaction chamber (7) and connected to said electrodes (9). The pin (6) is shaped in the form of a hairpin, which can also be used in conjunction with other shapes. It is also within the purview of the present subject matter, to adopt an electrical and heat conducting pin of other types of rigid materials such as Tungsten, Tantalum and Silicon that facilitate the deposition of polysilicon.

In the present subject matter, as an exemplary embodiment a pair of electrical and heat conducting pin (6) is shown for the deposit of polysilicon. However, a plurality of electrical and heat conducting pins (6) can be incorporated, inside reaction chamber (7) as required.

A gas feed assembly (3) including an inlet (1) and outlet (2) conduits, wherein one end of the gutter fids assembly the reaction chamber (7) and the other end is connected to gas supply sources. A feed nozzle (5) connected to the inlet conduit (i) to permit the gas flow through the inlet conduit (1). The gases enter and leave the reaction chamber (7) through said feed nozzle (5). The feed nozzle (5) includes a base portion (14) and a gas mixing portion (13). The combination of said base (14) and gas mixing portions (13) is used to generate the desired turbulence of the inlet gas. The turbulence is generated to facilitate the reaction process and to purge the gases from the reaction chamber (7) through the outlet (2).

The inlet (1) is a pipe, which is concentrically disposed inside the outlet (2) so as to form an intervening gap (11) between the outer surface of the inlet (1) and the inner surface of the outlet (2). The inlet (1) is disposed to permit input of gases that generate the desired Polysilicon. Normally, during the reaction process the reaction temperature is in the range of 1050-1100°C. Therefore, the gases inside the reaction chamber are heated and the heated gases are permitted to purge through the outlet (2).

The spatial arrangement, i.e. the gap (11) between said inlet (1) and outlet (2) conduits ensures transfer of heat by convection from the gases exiting through the outlet (2) on to the gases passing through the inlet (1).

The present subject matter also provides a system for characterization of gases and material for Chemical Vapour Deposition of polysilicon comprising a poly test reactor as described above and a power source and management assemblies.

By referring to Fig. 4 of the drawings, the power source and management assemblies of the system of the present subject matter are described. The assemblies include electrical and electronic segments disposed to manage and monitor the reaction conditions in the reaction chamber (7). The assembly includes a power transformer (16) that is connected to the reactor through power sensors (17). A power controller (15) connected to said power transformer (16) to monitor the power of the transformer (16) into the reaction chamber (7). The electronic circuitry is provided for power management. The power management assembly is supported by a Processor, PLC Controllers and the corresponding application software. The Power Control Configuration of the system of the present subject matter provides an inherent insulation in order to improve the power factor. The power transformer (16) is designed for a smooth variation in the voltages and the power controls to maximize the power factor and also to provide a smooth variation in the power supplied to the load. The power management assembly offers flexibility in power control of the individual phases and also imbalances occurring due to failures in filaments. The process control mechanism of the present system provides an automatic execution of the process sequence and also the regulation of the filament temperature.

The mechanism also helps identifying fault predictions.

The present subject matter also provides a method for characterization of gases in a reactor, said method comprising the steps of;

(a) evacuating reaction chamber and flushing by using an inert gas,

(b) generating desired temperature for the electrodes disposed inside the reaction chamber,

(c) passing inlet gases comprising Tri-Chloro-Silane (TCS) and Hydrogen (H2) through the inlet,

(d) reacting the inlet gases inside the reaction chamber,

(e) depositing the Polysilicon on the pins,

(f) purging the reaction gases from the reaction chamber through an outlet, and

(g) heating the inlet gases through convection from the gases of the outlet.

In an embodiment of the present subject matter, the deposited polysilicon is tested for impurities and further connected to main reactor for production of polysilicon.

The reaction scheme of the present subject matter is described below:

Polysilicon is prepared by the decomposition of Tri-Chloro-Silane (TCS) on a hot bed body at a temperature around 1100° C. TCS (which has the chemical formula SiHCB) is reacted with hydrogen to produce silicon (Si) according to the chemical reaction, SiHCl3+H2"> S1+3HC1

The above reaction is reversible and hence the temperature of the process and the residence time of the gases inside the reaction chamber requires to be closely monitored or else major portion of the reactants will proceed backwards i.e. silicon will get etched back by HC1 according to the reaction, Si+3 HC1 SiHCl3+H2

The chemistry also permits other reactions to take place at these temperatures i.e.
2SiHC13 —>SiHCl2+SiCl4 which means that TCS will break up into di-chlorosilane & silicon tetra-chloride.

As di-chloro-silane is unstable at these temperatures, it will break up into Si & HC12.
The other reaction that takes place in the reactor is between TCS & HC1 i.e.
HCl+SiHC13 --> S1C14+H2

Thus unreacted TCS, H2, SiCLj & HC1 will be coming out of the reactor as effluents. By recycling these effluents most of these are reacted & converted into polysilicon and deposited. Thus conversion efficiency of TCS into polysilicon is very low initially and in order to improve the conversion efficiency and also power consumption an R&D activity is initiated and successfully accomplished.

The previously described versions of the subject matter and its equivalent thereof have many advantages, including those which are described below.

The present subject matter provides a system and method to detect the quality of the material produced quickly before the gases are set to the main polysilicon reactors. It further provides a system and method to deposit a sample material and characterizing the same before the actual production is commenced.

A system and method with a rapid deposition rates (typically an inch per hour), which can be stopped in about few hours and the material removed and characterized is provided. Further a system and method with reduced power consumption is provided. Typically, number of units of electricity is reduced to 100-150 units/kg of polysilicon from the conventional 250 units/kg. The power control configuration is such that it offers an inherent insulation to the main lines from dominant harmonics due to the non-linear loads, thus contributing to improvement in the power factor. The transformer is designed for a smooth variation in the voltages and the power controls are programmed to maximize the power factor and also provide a smooth variation in the power supplied to the load. As a result the average PF is in the range of 0.8 - 0.9, The configuration offers flexibility in power control of the individual phases, and also ensures that the imbalances occurring due to failures in filaments are not very distinctly appearing in the main line.

Intelligent power controllers that are provided, adapt to the changes in behavior of the loads.

Further, the present subject matter provides a system and method with integrated inlet and outlet conduits that ensures an increased growth rate of polysilicon. The reactor is provided with one or more electrical and heat conducting pins that can quickly be evaluated for deposition of polysilicon. The system is further provided with automatic execution of the process sequence and regulation of the filament temperature. Fault predictions and alarming of the abnormally behaving parameters are also provided. The present system is constructed in such a way that it is easy to integrate with the plant networks and DCS.

Other advantages of the inventive system and method for characterization of gases and material for chemical vapour deposition of polysilicon will become better understood from the description and claims of an exemplary embodiment of such a unit.

The inventive system and method for characterization of gases and material for chemical
vapour deposition of polysilicon of the present subject matter is not restricted to the embodiments that are mentioned above in the description.

Although the subject matter has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternate embodiments of the subject matter, will become apparent to persons skilled in the art upon reference to the description of the subject matter. It is therefore contemplated that such modifications can be made without departing from the spirit or scope of the present subject matter as defined.

We claim:

1. A system for characterization of gases and material for chemical vapour deposition of polysilicon, the system comprising; a polysilicon reactor with a reaction chamber (7), a pair of electrodes (9) disposed in said chamber (7), at least a pin (6) mounted on said pair of electrodes (9) facilitating the deposition of polysilicon, a gas feed assembly (3), disposed in said reaction chamber (7), comprises a feed nozzle (5), an inlet conduit (1), an outlet conduit (2), wherein said outlet conduit (2) is arranged over said inlet conduit (1), with an intervening gap (11) between said inlet and outlet conduits (1) and (2).

2. The system as claimed in claim 1, wherein said feed nozzle (5) comprises a gas mixing portion (13) and a base portion (14).

3. The system as claimed in claim 1, wherein reaction temperature of said reaction chamber (7) is in the range of 1050-1100°C.

4. The system as claimed in claim 1, wherein said pin (6) is an electrical and heat conducting pin.

5. The system as claimed in claim 1, wherein said pair of electrodes (9) is connected to an electrical power source (10).

6. The system as claimed in claim 1, wherein said system connected to a power source assembly and a power management assembly.

7. The system as claimed in claim 6, wherein said power source assembly comprises a power controller (15), power transformer (16) and power sensors (17).

8. The system as claimed in claim 6, wherein said power management assembly comprises a processor, and at least one PLC controller.

9. A method for characterization of gases for chemical vapour deposition of polysilicon, the method comprising:

evacuating a reaction chamber (7) of a polysilicon reactor and flushing by an inert gas, generating a desired temperature for maintaining a pair of electrodes (9) mounted with at least one pin (6) and disposed within said reaction chamber (7), passing inlet gases comprising tri-chloro-silane and hydrogen through an inlet conduit (1) and a feed nozzle (5) of a gas feed assembly (3) connected to said reaction chamber (7), reacting said inlet gases inside said reaction chamber (7) and maintaining a reaction temperature, depositing the polysilicon on said pin (6), purging reaction gases from said reaction chamber (7) through an outlet conduit (2) of said gas feed assembly (3), and heating said inlet gases through convection by means of said reaction gases passing through said outlet conduit (2).

10. The method as claimed in claim 9, wherein the method further comprises testing
said pin (6) deposited with polysilicon for impurities.

11. The method as claimed in claim 9, wherein said reaction temperature is maintained in the range of 1050-1100°C.