Method for the supply of fluorine
This application claims priority to European application
No. 10157904.3 filed March 26th, 2010, the whole content of this application
being incorporated herein by reference for all purposes.
The invention concerns a method for the supply (delivery) of elemental
5 fluorine under elevated pressure in a method for the manufacture of electronic
devices. Elemental fluorine (F2) has no GWP and no impact on the ozone layer
and is often produced electrolytically from HF. In the presence of an electrolyte
salt, HF releases fluorine if a voltage of at least 2.9 Vis applied. Practically, the
voltage is often kept in a range of 8 to 10 or 11 Volt.
10 A molten HF adduct ofKF, often having the formula KF·(1.8-2.3)HF, is
15
the preferred electrolyte salt. HF is fed into the reactor containing the molten
electrolyte salt, and F2 is electrolytically formed from the HF according to the
equation (1) by applying a voltage and passing electric current through the
molten salt :
2HF -7Hz+ Fz (1)
Elemental fluorine is useful as fluorinating agent, e.g. for the manufacture
of polymers which are fluorinated on the surface, for the manufacture of
fluorinated solvents especially for Li ion batteries, as chamber cleaning agent
and etchant for the manufacture of electronic devices, especially semiconductors,
20 photovoltaic cells, micro-electromechanical systems ("MEMS"), TFTs (thin film
transistors for flat panel displays or liquid crystal displays), and the like.
As to the use as etchant for the manufacture of electronic devices,
especially semiconductors, photovoltaic cells, MEMS and TFTs, several
consecutive steps of deposition oflayers and etching a part of them are
25 necessary. Fluorine can be used for etching oflayers constituted of very
different constitution, for example, for etching silicon containing layers or other
layers of compounds which form volatile reaction products, e.g. tungsten.
Etching can be performed thermally or plasma-assisted.
As to the use for chamber cleaning, usually, during deposition processes
30 performed in treatment chambers- often CVD chambers (chambers wherein
layers are deposited on items via chemical vapor deposition, e.g. plasmaenhanced
CVD, metal organic CVD or low pressure CVD)- undesired deposits
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form on the walls and on inner constructive parts of the chamber and must be
regularly removed. This is achieved by treating the deposits thermally or
plasma-enhanced with elemental fluorine as chamber cleaning agent.
Especially for the use of elemental fluorine as an etchant, but also when
5 used as chamber cleaning agent, it is desirable that the elemental fluorine be very
pure. The intrusion of water, carbon dioxide, nitrogen and oxygen is considered
as undesired.
After the fluorine is manufactured by the electrolytic manufacture (or any
other method), it can be stored in pressurized cylinders and transported to the site
10 of use. In plants with higher F2 demand, it is preferred to produce the F2 directly
on site.
Thus, US 6,602,433 discloses an apparatus for treating a substrate, the
apparatus comprising a chamber, a support for a substrate, and a delivery system
for delivering an etchant and/or deposition gas into the chamber wherein the
15 delivery system is positioned locally to the chamber. The gas generator operates
at or near atmospheric pressure. In US 6,926,871, the same patentee states that
the generator operates from several torr to atmospheric pressure.
WO 2003/046244 discloses the generation, distribution and use ofF2
within a fabrication facility. According to one embodiment, F2 is produced at a
20 pressure of8 mbar in the electrolytic cells and stored at 15 psig (about
1.03 bar abs or 103 kPa); the pressure at delivery is not indicated. According to
another embodiment, F2 is stored in a negative pressure bulk storage tank,
delivered under a negative pressure to individual tool compressors, compressed
therein and delivered to the tools.
25 WO 2004/009873 discloses an apparatus and a method for fluorine
production. The fluorine is produced by electrolysis from HF in a fluorine
generating cassette. The fluorine may be used in the manufacture of electronic
devices, e.g. in the production ofTFTs. Produced fluorine can be stored in
holding tanks safely withstanding 5 bar pressure of fluorine although such
30 pressures are not generally employed with fluorine in the interests of safety.
WO 2006/043125 discloses a fluorine gas generator disposed in the gas
feed system of a semiconductor plant. The apparatus described contains a flow
management section which is connected to a buffer tank, to a gas storage section
that has a plurality of gas sources that store various active and inert gases, and to
35 a gas generating system comprising a cathode compartment and an anode
compartment which generates F2 . The pressure in the buffer tank is set, for
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example, to 0.18 MPa above atmospheric pressure (i.e. to about 2.8 Bara) while
the pressure in the gas generating system (the electrolytic cell) is between
atmospheric pressure and 820 torr (approximately 109 kPa) No data are given as
to the pressure of gases delivered to the semiconductor tool.
5 US 2006/0130929 discloses a method of supplying F2 to a processing
system wherein an on-site F2 generator supplies high purity F2 to the processing
system. A transportable gas storage vessel can be applied with F2 stored at
typically less than 35 psig (2.4 bar abs or 240 kPa). A fixed storage tank is
operated at a pressure of 5 to 25 psig (0.34 to 1. 7 bar abs or 34 kPa to 170 kPa).
10 The delivery pressure is not indicated.
Object of the present invention is to provide an improved process for
delivery of fluorine to processes wherein it is desirable to use pure fluorine.
The invention concerns a method for the manufacture of electronic devices,
especially semiconductors, photovoltaic cells, MEMS, or TFTs, comprising
15 etching of items in a chamber or cleaning a chamber using elemental fluorine as
etching agent or chamber cleaning agent comprising at least a step of
manufacture of the elemental fluorine, a step of delivery of the fluorine to the
point of use, and optionally at least one further step selected from the group
consisting of a step of purification and a step of storage, wherein the elemental
20 fluorine is kept at least in the step of delivery to the point of use under a pressure
which is greater than ambient pressure.
The chamber is generally a chamber wherein electronic devices are etched,
or which is to be cleaned from time to time or according to a schedule to remove
undesired deposits.
25 Thus, at least the step of delivery of the fluorine to the point of use is
performed under a pressure which is greater than ambient pressure. It is
especially preferred that the method of the present invention further comprises at
least one step selected from the group consisting of purification and storage, and
that the elemental fluorine is kept at least in the steps of delivery to the point of
30 use and in at least one of the steps of purification and storage under a pressure
which is above ambient pressure. In another preferred embodiment, the method
comprises at least one step of each of purification, storage and delivery and is
kept in all three steps under a pressure which is higher than ambient pressure.
The word "a", e.g. in an expression like "a step", is not intended to limit the
35 expression to a single step. The term "comprising" includes the meaning
"consisting of'. Advantage of maintaining the fluorine under a pressure which is
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above ambient pressure at least during the step of delivery to the point of use,
and especially during the steps of purification, storage and delivery is that no air,
nitrogen, oxygen, carbon dioxide, moisture and other impurities can intrude into
the fluorine and thus, contaminate it.
5 In one embodiment which concerns the manufacture ofF2 by the
electrolysis ofHF in the presence ofKF as electrolyte, the F2 is kept under
pressure even in the electrolytic cells. Preferably, the F2 is kept under pressure
right from the start of its generation by electrolysis in electrolytic cells, during
purification, delivery to the point of use and, if performed, during its storage.
10 The content of oxygen is below 750 ppm by volume and often even below
300 ppm by volume and remains at that low level. Due to the elevated pressure,
the level of oxygen, but also of oxygen containing impurities, nitrogen and
carbon dioxide remains very low. The content of nitrogen is in the range of only
some hundreds of ppmv, and even lower, and remains at that low level during
15 delivery. The content of carbon dioxide, for example, is often equal to or lower
than 10 ppmv and remains during delivery at that low level. The content of
water is often equal to or lower than 1 ppmv, and remains at that low level
during delivery. Thus, the process of the invention allows to maintain a low
level of gases, e.g. of oxygen, nitrogen, water and carbon dioxide, prevents the
20 intrusion of these compounds from the gas atmosphere surrounding the means of
delivery such as pipes, valves, manifolds etc., and thus allows to maintain the
low level of such gases.
In the following, the delivery is explained in more detail.
The generation ofF2 can be performed in one or several electrolytic cells.
25 If one electrolytic cell is applied, this cell may deliver F2 to one or more tools.
IfF2 is generated by means of two or more electrolytic cells, the F2 generated in
one cell may be delivered to one or more tools separately from the F2 generated
in other cells which may be delivered to another tool or other tools.
Alternatively, the F2 generated in the two or more cells can be passed into a
30 common line and distributed to the tools where it is applied. This embodiment is
preferred because most often, the F2 generated will be purified before being used,
and it is of course technically more advantageous to pass the F2 in a common line
through a respective purification apparatus, and not to pass the F2 generated
through a multitude of parallel arranged purification apparatuses.
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Often, the process is performed using an apparatus with several electrolytic
cells ; the F2 produced is fed from the individual cells into a common F2 line. In
view of this preferred embodiment, the invention will be explained in detail.
It is advantageous to provide valves which can isolate a specific
5 electrolytic cell or a group of electrolytic cells from others in case a shutdown of
respective cells for repair or maintenance is necessary.
The F2 produced is then delivered via the common line to a means to purify
it. In this step of purification, solids and/or HF may be removed.
The step or steps of purification can be performed before or after storage
1 0 (if a step of storage is foreseen). If desired, the fluorine can be purified before
and after storage ; in this case, preferably both purification steps are performed
under a pressure which is higher than ambient pressure. The purification can be
performed in a manner principally known. For example, entrained solids which
are mainly composed of solidified electrolyte salt (adduct ofHF and KF in
15 varying composition) can be removed in a frit made from Fz-resistant material,
especially Monel metal or nickel. Alternatively or additionally, solids can be
removed by contacting the F2 with liquid HF, e.g. in a jet scrubber. Entrained
HF can be removed by passing the fluorine through NaF. Alternatively or
additionally, HF can be removed in a cooled trap, e.g. a trap cooled to equal to or
20 lower than about -60°C, e.g. to a temperature in the range from -60°C to -80°C.
The purification means can be redundant so that a part of the means can be
regenerated while other means operate. Valves are useful also here to shut off
individual means from the F2 produced.
After the step or steps of purification, the treated F2 can be delivered via a
25 line to the tool. If the F2 is intended to be delivered to several tools, a
distribution system may be applied. In this distribution system, desirable
quantities ofF2 can be delivered to the respective tools. If desired, the F2 can be
mixed with other suitable gases, e.g. noble gases like Ar or Xe before being
introduced into the tool.
30 If desired, the F2 is passed after the purification to a storage tank where it is
preferably kept under the pressure mentioned above.
The process of the invention may be supported by other commonly used
components, e.g. regulator valves, seal pots, pressure transducers, thermo
couples, filters or a valve control system.
35 The tools may be process chambers applied for the manufacture of
semiconductors, a chamber for producing MEMS, a chamber for the manufacture
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ofTFTs or flat panel displays. The tool may for example be a chemical or
physical vapor deposition chamber. Often, the tool includes a plasma generator.
In a preferred embodiment, the fluorine is pressurized by means of
compressors, and no pressurizing gas is applied, unless elemental fluorine.
5 The pressure of the fluorine is preferably equal to or greater than
1.5 bar abs. (150 kPa abs.). The pressure is preferably equal to or lower
than 15 bar abs. (1500 kPa abs.), more preferably, equal to or lower
than 12 bar abs. (1200 kPa abs). The preferred range is from 2 to 3 bar abs.
(200 to 300 kPa abs.). Preferably, the pressure of the fluorine is maintained
10 within the indicated upper levels and lower levels during purification and
delivery and, if performed, also during storage. Especially preferably, the
pressure of the fluorine is maintained within the indicated upper levels and lower
levels, notably from 2 to 3 bar abs, during its electrolytic generation, during its
purification and during its delivery to the point of use and, if performed, also
15 during its storage. The advantage is that a risk of contamination by air or
moisture is further reduced, and that no compressor is needed.
The step of the manufacture of elemental fluorine is preferably performed
as described above by the electrolysis of HF using the adduct of KF and HF as an
electrolyte salt ; alternatively, it can be split off from a metal fluoride with high
20 valency. For example, MnF4 can be heated to split offF2 forming MnFx wherein
x is approximately 3.
The step of purification, if foreseen, comprises for example a step of
distillation in which especially HF can be removed ; instead or additionally, the
fluorine can be contacted with NaF to remove HF.
25 The step of storage, if foreseen, preferably denotes the storage of the
elemental fluorine in suitable tanks, e.g. stainless steel bottles.
The step of delivery preferably denotes passing the fluorine from the
manufacturing apparatus to the point of use through pipes.
The method of the present invention allows for the delivery of elemental
30 fluorine to the point of use with a content of carbon dioxide, nitrogen and oxygen
which is not higher than the carbon dioxide, nitrogen and oxygen content
immediately after the manufacture.
In the apparatus used to generate and deliver F2, double isolation valves
having a vacuum connection in between improve safety.
35 The advantage of the process of the present invention is that F2 produced
keeps its degree of purity when delivered to the point of use. Thus, once the F2
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produced was purified as given above, it may be delivered to the point of use.
After its delivery, no additional step or steps for purification of the delivered F2
is or are necessary. Consequently, a preferred embodiment of the present
process is characterized in that no step or steps of purification, respectively, are
5 performed to purify F2 after its delivery to the point of use. Especially
preferably, no step or steps of purification of the F2 to remove nitrogen, oxygen,
air, humidity or carbon dioxide are performed after the delivery of the F2 to the
point of use. It has to be noted that humidity (H20) is expected to react with F2
under the formation ofOF2 and HF. Thus, the term "humidity" includes the
10 reaction products ofH20 with F2, especially HF and OF2 ; since they are not
formed, they must not be removed.
The method of the invention is especially suitable for the on-site
production of fluorine. In an on-site production, the fluorine is manufactured on
a site and, directly delivered, if desired, without any storage step, to the point of
15 use on the same site. Preferably, the point of use is a plant wherein the elemental
fluorine is used as thermal or plasma-assisted etching agent in the manufacture of
semiconductors, MEMS, solar cells and TFTs (flat panel displays), or for thermal
or plasma-assisted cleaning of treatment chambers used in the manufacture of
semiconductors, MEMS, solar cells and TFTs, (flat panel displays), or both for
20 said manufacture and chamber cleaning. The plasma is local plasma produced
directly in the etching chamber, or remote plasma produced in a separate
chamber with a plasma source.
Thus, preferably, the elemental fluorine is produced and delivered on-site
for use in the manufacture of semiconductors, MEMS, solar cells and TFTs.
25 More preferably, the elemental fluorine is produced by electrolysis ofHF in the
presence of an adduct ofKF and HF, purified and delivered on-site under a
pressure of2 to 3 bar (abs.) into an etching chamber as etchant in the
manufacture of semiconductors, MEMS, solar cells and TFTs, or as a chamber
cleaning agent into a thermal or plasma-assisted etching chamber used for the
30 manufacture of semiconductors, MEMS, solar cells and TFTs, especially when
the chamber is a plasma etching chamber. Especially preferably, even during its
electrolytic generation, the F2 is under said pressure.
The fluorine can be manufactured, if desired, in a fluorine generating
cassette as described in WO 2004/009873. If desired, each cassette can be
35 allocated to one or more process chambers wherein etching is performed ; or a
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plurality of fluorine generating cassettes is connected to a fluorine gas
distribution system which is connected to the chambers.
The fluorine is preferably generated on site of its point ofuse via
electrolysis in an apparatus which is in fluid communication with the process
5 chamber or process chambers, especially preferably via a purification unit
comprising means for removal of solids, e.g. a frit as described above, and/or a
canister or tower comprising an adsorbent for HF or a cooled separator for HF
separation. If desired, the fluorine generator is located near the process chamber
as the point of use, e.g. the distance can be 500 m or less, and is often sometimes
10 50 m or less, and can be in close proximity to the process chamber, e.g. in a
distance of 10 m or less. Thus, preferably, the generated elemental fluorine is
not filled into a tank or into pressurized bottles, which are then disconnected
from the delivery line. If desired, the fluorine is stored in tanks or bottles only
which remain connected to the delivery line. The process can be performed, for
15 example, in a plant according to the skid concept as described in
US provisionals 61/383533 filed September 15, 2010, and 61/383204 filed
September 16, 2010. The plant described therein provides fluorine gas to a tool
which applies fluorine gas as reactant to perform chemistry in this tool which
apparatus comprises skid mounted modules including at least one skid mounted
20 module selected from the group consisting of
- a skid mounted module comprising at least one storage tank for HF, denoted
as skid 1,
- a skid mounted module comprising at least one electrolytic cell to produce F2,
denoted as skid 2,
25 - a skid mounted module comprising purification means for purifying F2,
denoted as skid 3,
- a skid mounted module comprising means to deliver fluorine gas to the point
of use, denoted as skid 4,
- a skid mounted module comprising cooling water circuits, denoted as skid 5,
30 - a skid mounted module comprising means to treat waste gas, denoted as
skid 6,
- a skid mounted module comprising means for the analysis ofF2, denoted as
skid 7, and
- a skid mounted module comprising means to operate the electrolysis cells,
35 denoted as skid 8.
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The advantage of skids is, for example, that they are manufactured, piped,
wired and assembled together before shop testing. It is preferred if they are
constructed such that the interfaces between the skids are minimized and that all
parts in the respective skid are accessible as easily as possible for maintenance,
5 inspection or repair.
The method of the invention allows providing elemental fluorine to be
produced and delivered, especially when applied on-site, without the danger of
intrusion of air, i.e. oxygen, nitrogen, carbon dioxide and humidity and
respective contamination of the F2 .
10 Should the disclosure of any patents, patent applications, and publications
which are incorporated herein by reference conflict with the description of the
present application to the extent that it may render a term unclear, the present
description shall take precedence.
The following examples is intended to explain the invention in detail
15 without limiting it.
Example 1 : Delivery of elemental fluorine on-site
1. Manufacture of elemental fluorine :
KF·2HF is filled into an electrolysis cell, heated to about 80- 120°C and
molten therein. HF is fed into the electrolysis cell, voltage in the range of8
20 to 12 Vis applied, and current is passed through the composition ofHF and the
molten electrolyte salt which is kept in a temperature range between 80
and 1 00°C. Elemental fluorine and elemental hydrogen form in the respective
electrode compartments. The elemental fluorine is passed through a Monel
metal frit to remove solids, compressed in a compressor to a pressure of
25 about 2.5 bar abs. (about 250 kPa) and passed through a bed ofNaF to
remove HF.
2. Delivery of pressurized fluorine
The compressed fluorine is passed under said pressure in a pipe directly to
a facility located on-site. In this facility, the elemental fluorine is applied for the
30 cleaning of a plasma chamber from silicon-containing residues deposited during
the PECVD (plasma-enhanced vapor deposition) layers in a process for the
manufacture of semiconductors.
Since the fluorine is kept under a pressure above ambient pressure from the
manufacturing apparatus to the facility where it is applied, no air contaminates
35 the fluorine, and the low level of oxygen, oxygen containing impurities, nitrogen
and carbon dioxide remains essentially the same.
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Example 2 : Production and delivery of elemental fluorine under pressure
1. Manufacture of elemental fluorine :
KF·2HF is filled into an electrolysis cell, heated to about 80- 120°C and
molten therein. HF is fed into the electrolysis cell, voltage in the range of8
5 to 12 Vis applied, and current is passed through the composition ofHF and the
molten electrolyte salt which is kept in a temperature range between 80
and 1 00°C. Elemental fluorine and elemental hydrogen form in the respective
electrode compartments. The F2 is kept in the cell under a pressure of
approximately 2.5 bar abs (about 250 kPa). It is passed through a Monel metal
10 frit and contacted in a jet scrubber with liquid HF kept at a temperature of
about -80°C to remove solids (mainly entrained solidified electrolyte salt with
the approximate composition KF·2HF), and passed through a trap cooled
to -80°C and then through a bed ofNaF to remove HF.
2. Delivery of fluorine
15 The F2 is passed under said pressure of about 2.5 bar abs in a pipe directly
to a facility located on-site. In this facility, the F2 is applied for the cleaning of a
plasma chamber from silicon-containing residues deposited during the PECVD
(plasma-enhanced vapor deposition) layers in a process for the manufacture of
semiconductors.
20 Since the fluorine is kept under a pressure above ambient pressure from the
manufacturing apparatus to the facility where it is applied, no air contaminates
the fluorine, and the low level of oxygen, oxygen containing impurities, nitrogen
and carbon dioxide remains essentially the same during the step of delivery.

CLAIMS
1. A method for the manufacture of electronic devices comprising
etching of items in a chamber or cleaning a chamber using elemental fluorine as
etching agent or chamber cleaning agent comprising at least a step of
5 manufacture of the elemental fluorine, a step of delivery of the fluorine to the
point of use, and optionally at least one further step selected from the group
consisting of a step of purification and a step of storage wherein the elemental
fluorine is kept at least in the step of delivery to the point of use under a pressure
which is greater than ambient pressure.
10 2. The method of claim 1 wherein the electronic devices are selected
from the group consisting of semiconductors, photo voltaic cells, MEMS,
and TFTs.
3. The method of claim 1 or 2 wherein the method comprises at least the
step of manufacture of the elemental fluorine, the step of delivery of the fluorine
15 to the point of use, and at least one further step selected from the group
consisting of a step of purification and a step of storage of the elemental fluorine
wherein the elemental fluorine is kept under a pressure which is greater than
ambient pressure in the steps of its delivery to the site of use and storage and/or
purification.
20 4. The method of anyone of claims 1 to 3 wherein the elemental fluorine
is kept under a pressure which is greater than ambient pressure in the steps of its
purification and its delivery to the site of use.
5. The method of anyone of claims 1 to 4 wherein the elemental fluorine
is kept under a pressure which is greater than ambient pressure in the steps of its
25 purification, storage and delivery to the site of use.
6. The method of anyone of claims 1 to 5 wherein the elemental fluorine
is kept under a pressure which is greater than ambient pressure in the steps of its
electrolytic generation, purification, storage and delivery to the site of use.
7. The method of anyone of claims 1 to 6 wherein the elemental fluorine
30 is kept at a pressure of about 2 to 3 bar (abs.).
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8. The method of anyone of claims 1 to 7 wherein the elemental fluorine
is produced by electrolysis ofHF in the presence of an adduct ofKF and HF as
electrolyte salt, or by thermally splitting off fluorine from high valency metal
fluorides.
5 9. The method of anyone of claims 1 to 8 wherein the elemental fluorine
is produced on-site.
10. The method of anyone of claims 1 to 9 wherein the elemental fluorine
is produced and delivered on-site for use in the manufacture of semiconductors,
MEMS, solar cells and TFTs.
10 11. The method of anyone of claims 1 to 10 wherein the elemental
fluorine is produced by electrolysis ofHF in the presence of an adduct ofKF and
HF as electrolyte salt, purified and delivered on-site under a pressure of2
to 3 bar (abs.) into an etching chamber as etchant in the manufacture of
semiconductors, MEMS, solar cells and TFTs.
15 12. The method of anyone of claims 1 to 10 wherein the elemental
fluorine is produced by electrolysis ofHF in the presence of an adduct ofKF and
HF as electrolyte salt, purified and delivered on-site under a pressure of2
to 3 bar (abs.) as chamber cleaning agent into a thermal or plasma-assisted
etching chamber used for the manufacture of semiconductors, MEMS, solar cells
20 and TFTs.
13. The method of claims!, 11 or 12 wherein the etching chamber is a
plasma etching chamber.
14. The method of anyone of claims 1 to 13 wherein the elemental
fluorine is manufactured by electrolysis in a fluorine generator which is in fluid
25 communication with the chamber.
15. The method of claim 14 wherein the fluorine generator is located in
proximity of the chamber.