U.S. patent application number 12/124455 was filed with the patent office on 2008-11-27 for device for doping, deposition or oxidation of semiconductor material at low pressure.
This patent application is currently assigned to Centrotherm Photovoltaics AG. Invention is credited to Robert Michael Hartung, Alexander PIECHULLA, Claus Rade.
Application Number | 20080292430 12/124455 |
Document ID | / |
Family ID | 39877314 |
Filed Date | 2008-11-27 |
United States Patent
Application |
20080292430 |
Kind Code |
A1 |
PIECHULLA; Alexander ; et
al. |
November 27, 2008 |
DEVICE FOR DOPING, DEPOSITION OR OXIDATION OF SEMICONDUCTOR
MATERIAL AT LOW PRESSURE
Abstract
A device for doping, deposition or oxidation of semiconductor
material at low pressure in a process tube, is provided with a tube
closure as well as devices for supplying and discharging process
gases and for generating a negative pressure in the process tube. A
closure of the process chamber that is gas tight with respect to
the process gases and the vacuum tight seal of the end of the tube
closure are spatially separated from each other in relation to the
atmosphere and are arranged on a same side of the process tube in
such a manner that a bottom of a stopper, sealing the process
chamber, rests against a sealing rim of the process tube and the
tube closure end is sealed vacuum tight by means of a collar, which
is attached to the process tube and against which a door rests
sealingly.
Inventors: |
PIECHULLA; Alexander;
(Blaubeuren, DE) ; Rade; Claus; (Allmendingen,
DE) ; Hartung; Robert Michael; (Blaubeuren,
DE) |
Correspondence
Address: |
HESLIN ROTHENBERG FARLEY & MESITI PC
5 COLUMBIA CIRCLE
ALBANY
NY
12203
US
|
Assignee: |
Centrotherm Photovoltaics
AG
Blaubeuren
DE
|
Family ID: |
39877314 |
Appl. No.: |
12/124455 |
Filed: |
May 21, 2008 |
Current U.S.
Class: |
414/147 |
Current CPC
Class: |
C30B 31/10 20130101;
H01L 21/67109 20130101; F27B 17/0025 20130101; C30B 31/16 20130101;
H01L 21/67103 20130101; H01L 21/67115 20130101; H01L 21/67098
20130101; H01L 21/67757 20130101 |
Class at
Publication: |
414/147 |
International
Class: |
B66C 17/08 20060101
B66C017/08 |
Foreign Application Data
Date |
Code |
Application Number |
May 21, 2007 |
DE |
10 2007 023 812.8 |
Dec 28, 2007 |
DE |
10 2007 063 363.9 |
Claims
1. Device for doping, deposition or oxidation of semiconductor
material at low pressure in a process chamber of a process tube,
wherein: the process tube is provided with a tube closure as well
as with devices for supplying and discharging process gases and for
generating a negative pressure in the process tube, a closure of
the process chamber that is gas tight with respect to the process
gases and a vacuum tight seal of the end of the tube closure are
spatially separated from each other in relation to atmosphere and
are arranged on a same side of the process tube in such a manner
that a bottom of a stoppers, sealing the process chamber, rests
against a sealing rim of the process tube and the tube closure end
is sealed vacuum tight by means of a collar, which is attached to
the process tube and against which a door rests sealingly.
2. Device, as claimed in claim 1, wherein the collar projects
beyond the process tube on a face side so that inside the collar
there is a collar chamber, which can be closed in a vacuum tight
manner by the door.
3. Device, as claimed in claim 2, wherein the vacuum tight sealing
of the tube closure end is carried out with the doors, applied to
the rim of the collar on the face side with the interposition of a
seal.
4. Device, as claimed in claim 1, wherein the stopper is attached
in a detachable and spring loaded manner to an inside of the
door.
5. Device, as claimed in claim 4, wherein the stopper is attached
to the door by bayonet closure.
6. Device, as claimed in claim 1, wherein the stopper is made of
quartz, SiC or another material that is adequately temperature
stable and medium resistant.
7. Device, as claimed in claim 1, wherein the stopper is coated
with quartz, SiC or another material that is adequately temperature
stable and medium resistant.
8. Device, as claimed in claim 1, wherein the door comprises
aluminum.
9. Device, as claimed in claim 8, wherein the door is water
cooled.
10. Device, as claimed in claim 9, wherein the door is provided
with a cooling water inlet Hand a cooling water outlet for the
through passage of a coolant.
11. Device, as claimed in claim 10, wherein a ring-shaped groove in
the door is provided for distribution of the coolant.
12. Device, as claimed in claim 2, wherein the door His provided
with a flushing gas inlet for introducing a flushing gas into the
collar chamber and exhibits includes a flushing gas outlet.
13. Device, as claimed in claim 12, wherein the flushing gas outlet
is connected by way of a hose line to a gas conveying tube and a
pump for pumping the flushing gas out of the collar chamber and for
pumping the process gases out of the process chamber.
14. Device, as claimed in claim 13, wherein the gas inlet is
connected to a source for nitrogen.
15. Device, as claimed in claim 2, wherein the collar chamber
exhibits an overpressure in relation to the process chamber in the
process tube.
16. Device, as claimed in claim 15, wherein a pressure differential
ranges from zero to approximately 50 mbar.
17. Device, as claimed in claim 2, further comprising a common pump
for evacuating the process chamber and the collar chamber and for
generating a pressure differential between the process chamber and
the collar chamber.
18. Device, as claimed in claim 17, wherein for the purpose of
generating the pressure differential, the connection of the collar
chamber to the pump comprises a line that is long in comparison to
a process tube extraction and which exhibits a smaller cross
section.
19. Device, as claimed in claim 17, wherein a cooling trap is
disposed upstream of the pump.
20. Device, as claimed in claim 17, wherein the pump is comprises a
diaphragm pump, screw pump or jet pump.
21. Device, as claimed in claim 18, wherein, in order to form the
pressure differential, a suitable leak rate of a contact point of
the stopper and the sealing rim of the process tube is set by a
flat finish of surfaces that meet.
22. Device, as claimed in claim 1, wherein a process gas outlet for
carrying away the process gases is located on an end of the process
tube that lies opposite the tube closure.
23. Device, as claimed in claim 22, wherein the process gas outlet
is provided with a spherically ground joint.
24. Device, as claimed in claim 22 wherein the process gas outlet
is either downwardly sloped or horizontal.
25. Device, as claimed in claim 24, wherein the process gas outlet
is sloped downwardly by approximately 5 degrees.
26. Device, as claimed in claim 22, wherein a spherically ground
joint won the gas outlet is configured for attachment and for
through passage of a gas outlet lance (18).
27. Device, as claimed in claim 2, wherein the collar chamber is
evacuated by a gas conveying tube via a T-piece, through which the
gas conveying tube is run.
28. Device, as claimed in claim 1, wherein process gas inlet into
the process chamber by coaxial tube as a component of a gas inlet
lance takes place on a side of the process gas outlet that extends
as far as up to the stopper on an other side of the process tube
without touching said stopper.
Description
[0001] The invention relates to a device for doping, deposition or
oxidation of semiconductor material at low pressure in a process
tube, which is provided with a tube closure as well as with devices
for supplying and discharging process gases and for generating a
negative pressure in the process tube.
[0002] In comparison to diffusion at atmospheric pressure,
diffusion at low pressure makes it possible, as well known, to
decrease the spacing between the wafers and, thus, to load the
process tube with a higher number of silicon disks while
simultaneously retaining or improving the homogeneity of the doping
operation. The prerequisite is that it must be possible to evacuate
the process tube or the furnace, which has to be vacuum tight, so
that an adequately low processing pressure is reached. For example,
a processing pressure of about 200 mbar may be regarded as an
adequately low processing pressure.
[0003] Furthermore, the output and reaction products may not come
into contact with materials that would be attacked thereby; and
these products may not accumulate in this reaction
tube/furnace.
[0004] The past prior art devices (for example, EP 1 393 351 A1)
for phosphorus doping at low pressure with phosphorychloride as the
dopant exhibit considerable problems. For example, a condensation
of phosphorus oxide occurs on the surfaces and, in particular, in
the region of the tube closure as well as on the end of the process
tube, to which a pump is connected, and also in the waste gas zone
between the process tube and the pump as well as in the pump
itself. The reason lies in the fact that the temperature in these
regions is significantly lower than the processing temperature.
[0005] The contact with water, in particular of atmospheric
humidity following aeration of the device with pure nitrogen and
pure oxygen upon opening the tube closure causes the phosphorus
oxide to convert into phosphoric acid. The fatal consequences are
corrosion of the metallic components of the device, such as the
tube closure, and the subsequent contamination of the process tube
with the corrosion products and the contamination of the products,
which are processed in the device, for example due to the iron
contamination in silicon.
[0006] Furthermore, there is the risk that the phosphoric acid will
escape from the process tube or that the reaction products may
accumulate in the process tube and the components of the device
that are connected to said process tube. The components that are
connected to the process tube may coalesce; and there is the risk
of decomposition of the process tube and the components that are
connected to said process tube. Finally the accumulation may unfold
an undesired doping effect.
[0007] Moreover, the reaction products, like chlorine, hydrochloric
acid, phosphorus oxide and phosphoric acid, may cause corrosion,
including quartz corrosion.
[0008] In a device of the "cantilever" construction the paddle
stays in the process tube during the process, is consequently
heated to the processing temperature and is then removed again at a
high temperature after the end of the process. For example, in the
cantilever design the rear end of the paddle exhibits a cylinder,
the surface of which is enveloped by a sealing ring.
[0009] The invention is based on the problem of providing a device
for doping, deposition and oxidation of semiconductor material at
low pressure in a process tube. With this device the aforementioned
drawbacks are to be avoided.
[0010] This object is achieved in that a closure of the process
chamber that is gas tight with respect to the process gases and the
vacuum tight seal of the end of the tube closure are spatially
separated from each other in relation to the atmosphere and are
arranged on the same side of the process tube in such a manner that
the bottom of a stopper, sealing the process chamber, rests against
a sealing rim of the process tube and that the vacuum tight sealing
of the tube closure end is carried out by means of a collar, which
is attached to the process tube and against which a door rests
sealingly.
[0011] Thus, the object concerns a two step closure of the process
tube, comprising a gas tight high temperature closure with a low
leak rate and a vacuum tight closure.
[0012] The collar projects beyond the process tube on the face side
so that inside the collar there is a collar chamber, which can be
closed outwardly in a vacuum tight manner by means of the door.
[0013] The vacuum tight sealing of the tube closure with the door
takes place with the interposition of a seal, which can be applied
to the collar on the face side.
[0014] The stopper is made preferably of quartz, SiC or any other
suitable material that is adequately stable to temperature and
resistant to mediums or is coated with such a material and is
attached in a detachable and spring loaded manner to the inside of
the door so that it is possible to replace said stopper with
ease.
[0015] The stopper is attached to the door ideally with a bayonet
closure.
[0016] In order to achieve a door design that is as lightweight as
possible, the door is fabricated of aluminum or another light
metal.
[0017] One special advantage of the inventive two step seal lies in
the fact that the door may be designed so as to be water cooled
without thereby affecting the processing temperature in the process
chamber. Therefore, in addition, a door seal can be achieved with
thermoplastic or flexible materials.
[0018] For this purpose the door is provided with a cooling water
inlet and a cooling water outlet for the through passage of a
coolant. In this case the coolant is distributed by means of a
ring-shaped groove in the door.
[0019] In order to be able to fill the collar chamber with flushing
gas, the door is provided with a flushing gas inlet for introducing
a flushing gas into the collar chamber and exhibits a flushing gas
outlet/pump-out connector. The flushing gas outlet/pump-out
connector may be connected to a separate pump.
[0020] A simpler construction is characterized in that the flushing
gas outlet is connected by way of a hose line to a gas conveying
tube and a pump for pumping the flushing gas out of the chamber and
simultaneously the process gases out of the process chamber.
[0021] The flushing gas inlet is connected to a source for nitrogen
or another suitable gas.
[0022] In order to prevent the process gas fractions from escaping
into the collar chamber, the collar chamber exhibits an
overpressure in relation to the process chamber in the process
tube.
[0023] The pressure differential ranges from zero to approximately
50 mbar.
[0024] In order to evacuate the process chamber and the collar
chamber and in order to simultaneously generate the pressure
differential between the process chamber and the collar chamber, it
is practical to provide a common pump.
[0025] Another embodiment of the invention provides for the purpose
of generating the pressure differential that the connection of the
collar chamber to the pump is designed with a line that is long in
comparison to the process tube extraction and exhibits a smaller
cross section.
[0026] In order to reduce the load on the pump, a cooling trap is
disposed upstream of the pump; and the extracted process gases and
flushing gases are cooled in said cooling trap.
[0027] The pump may be designed as a diaphragm pump, screw pump or
jet pump--that is, as a liquid jet pump.
[0028] Furthermore, in order to form the pressure differential a
suitable leak rate of the contact point of the quartz stopper and
the sealing rim of the process tube is set by a flat finish of the
surfaces that meet.
[0029] In another embodiment of the invention the process gas
outlet for carrying away the process gases is disposed on the end
of the process tube that lies opposite the tube closure.
[0030] The process gas outlet is provided preferably with a
spherically ground joint in order to guarantee, on the one hand, an
adequate tightness and, on the other hand, a certain leakiness so
that it is guaranteed that the connecting point will be flushed by
the surrounding air that is sucked in. Thus, this process prevents
with certainty any process gas residues from being able to settle
out.
[0031] The process gas outlet may be configured so as to be either
downwardly sloped or horizontal.
[0032] Preferably the process gas outlet is sloped downwardly by
approximately 5 degrees.
[0033] Furthermore, the spherically ground joint on the gas outlet
is configured for the attachment and for the through passage of a
gas outlet lance.
[0034] The collar chamber is evacuated by means of the gas
conveying tube via a T-piece, through which the gas conveying tube
is run.
[0035] For the process gas inlet into the process chamber a coaxial
tube is provided as the component of a gas inlet lance on the side
of the process gas outlet that extends up to the quartz stopper on
the other side of the process tube without touching said
stopper.
[0036] The invention is explained below in detail by means of one
embodiment. In the related drawings:
[0037] FIG. 1 is a schematic rendering of an inventive process tube
with extraction and gas inlet (on the left in the drawing).
[0038] FIG. 2 is a perspective view of a door for closing the
process tube, according to FIG. 1.
[0039] FIG. 3 is a side view of the port with the quartz
stopper.
[0040] FIG. 4 depicts a detail of a bayonet closure on the inside
of the quartz stopper.
[0041] FIG. 5 depicts a coaxial gas inlet tube for the gas inlet
into the process tube, according to FIG. 1.
[0042] FIG. 6 depicts a detail of a gas outlet lance for the
evacuation of the process tube, according to FIG. 1.
[0043] FIG. 7 is a schematic drawing of an overview of the
inventive device.
[0044] The core of the invention is that the closure of the process
chamber 1 to the surrounding atmosphere and the seal of the tube
closure end 2 are designed so that they are spatially separated
from each other in a coaxial or successive arrangement. The process
tube 3, which is made of quartz, exhibits a collar 4 on the tube
closure end 2. That is, the process tube exhibits a coaxial tubular
segment, which is glass sealed onto the inner tube, thus, on the
process tube 3, and projects a ways beyond said tube (FIG. 1). The
collar 4 is glass sealed onto the process tube 3 or attached
elsewhere and, in addition, may be enveloped by insulating material
(not illustrated). The tube closure itself is designed in two steps
and comprises a door 5 made of metal for the purpose of ensuring
the vacuum tightness. Attached to this door is a "sunk" stopper
made of quartz (quartz stopper 6) (FIGS. 2-4). In the closed state
of the door 5 the rim of the bottom of the quartz stopper 6 rests
in a spring loaded manner against the sealing rim 3' of the process
tube 3. The stopper is made of quartz, SiC and/or another material
that is adequately temperature stable and medium resistant. The
stopper may also be coated with one of these materials or
additionally coated.
[0045] In the open state, that is, when the door 5 is open, the
tube closure end 2 is used to move in and out the semiconductor
material, which is set side by side or stacked in a boat and which
has the form of wafers W or the like, which are to be treated in
the process chamber 1 (FIG. 7).
[0046] The interior of the quartz stopper 6 is filled with an
insulating material, like shaped parts made of ceramic fibers,
plates or loose wool on the basis of aluminum silicate fibers. The
quartz stopper may have an opaque bottom. The filling with the
insulating material serves to generate a temperature gradient in
the direction of the door 5, in such a manner that the temperature
decreases from the bottom of the quartz stopper 6 in the direction
of the door 5.
[0047] The quartz stopper 6 is fastened to the door 5 of the tube
closure with a plurality of spring elements 7 (FIGS. 3, 7). The
spring elements 7 may be made of stainless steel or another
material that is adequately temperature stable.
[0048] The spring force of the spring elements 7, that is, the
force with which the bottom of the quartz stopper 6 can be applied
to the sealing rim 3' of the process tube 3, may be adjusted from
the outside by means of screws or other setting means that are
covered in a vacuum tight manner when the process tube 3 is
operating. For example, stainless steel springs are used as the
spring elements.
[0049] The interior of the cylinder of the quartz stopper 6
exhibits a bayonet closure 8 on the side facing the door 5 (FIG.
4). The corresponding counter-piece on the door 5 is made of
stainless steel. The bayonet closure 8 is secured and clamped with
the aid of a quartz cord (not illustrated). Therefore, if
necessary, the quartz stopper 6 may be quickly replaced.
[0050] The outer door 5 of the tube closure is made of aluminum and
is water cooled. To this end the interior exhibits boreholes and
channels, through which the cooling fluid flows. Furthermore, the
door 5 exhibits a cooling water inlet 9 and a cooling water outlet
10. In this case the cooling water is distributed over a
ring-shaped groove in the door 5 (FIGS. 2, 3). In addition, a
pressure sensor may be attached to the door 5. The pressure in the
collar chamber 11 can be measured with this pressure sensor.
[0051] The process tube 3 is surrounded by a heating unit H (FIG.
7) and insulation (not illustrated). Furthermore, the left end of
the process tube 3 (as shown in the drawing) is provided with a
central process gas outlet 12 in the form of an intake manifold for
pumping out the process gases (FIGS. 1, 6). Under said process gas
outlet is located a plurality of pipe connections 13, into which a
quartz lance with a thermoelement as well as the necessary gas
inlet lances (coaxial tube 14, FIG. 5) can be inserted. The gas
inlet lances may be designed so long that they extend almost as far
as to the bottom of the quartz stopper 6 on the side of the process
tube 3 that is depicted on the right in the drawing (FIG. 7). A
coaxial tube 14 may also be used for the gas inlet. The process
gases may be conveyed by choice through the inner tube 14' and the
outer tube 14 into said coaxial tube (FIG. 6).
[0052] The process gas is admitted via one pipe connection 13 and
is conveyed to the opposite end of the process tube 3. From there
the process gas flows to the other end of the process tube 3, where
it is extracted by means of a central nozzle--the process gas
outlet 12.
[0053] For a vacuum tight closure of the process tube 3, the door 5
is pushed with a seal 15 against the face rim of the collar 4.
Internally the ground rim 6' of the quartz stopper 5 pushes in a
spring loaded manner so as to seal against the sealing rim 3' of
the process tube 3 so that the process chamber 1 is surrounded in
its entirety by quartz and simultaneously is closed in a vacuum
tight manner (FIGS. 3, 7).
[0054] For flushing and evacuating the tube closure, for example,
with nitrogen, the door 5 is provided with a flushing gas inlet 16
and a flushing gas outlet 20. The flushing gas outlet 20 serves
simultaneously as the pumping-out connector (FIG. 3), with which
the region-collar and quartz stopper and door (that is the collar
chamber 11--can be evacuated.
[0055] Upon loading the process tube 3 and closing the door 5, the
flushing gas inlet and outlet 16, 20 are used for flushing out the
air and during low pressure application for flushing out the
reaction products that have diffused into the collar chamber
11.
[0056] During the process, the collar chamber 11 is flushed with
nitrogen so that an overpressure in relation to the process chamber
1 is formed in the process tube 3. In this way the output products
and the reaction products are prevented from issuing from the
process chamber 1 as far as up to the door 5 that is made of metal
(FIGS. 2, 7).
[0057] A pressure differential of, for example, 50 mbar, should
prevail between the process chamber 1 and the collar chamber 11.
However, the pressure difference may not be too great, since,
otherwise, the bottom of the quartz stopper 6 may break. In this
case a higher strength may offer a bottom of the quartz stopper 6
that is arched in the direction of the process chamber 1.
[0058] The overpressure in the collar chamber 11 helps push the
quartz stopper 6 against the process tube 3. The unavoidable
leakage between the quartz stopper 6 and the process tube 3, that
is, between the ground sealing rim 3' and the ground rim 6', may
lead to an undesired flushing effect at this point.
[0059] The evacuation of the process chamber 1 and the collar
chamber 11 is carried out with the same pump P with simultaneous
generation of a pressure differential between the process chamber 1
and the collar chamber 11. In this case a suitable pump P is a
diaphragm pump and/or a screw pump or a jet pump. A cooling trap K
may be disposed upstream of the pump P for its protection. At the
same time a decrease in the waste gas and liquid downstream of the
pump P is achieved (FIG. 7).
[0060] For the purpose of generating the pressure differential, the
connection of the pumping-out connector 20 of the collar chamber 11
to the pump P is carried out with a line 23 which is long in
comparison to the process tube extraction and which exhibits a
small cross section (FIG. 7). The suction capacity, which is
decreased to such an extent owing to the line 23, for example a
hose line, makes it possible to generate the desired pressure
differential between the process chamber 3 and the collar chamber
11 at a low nitrogen flow rate. The prerequisite for the evolution
of this pressure differential is a suitable leakage rate of the
contact point of the quartz stopper 6 and the process tube 3, a
feature that can be achieved by means of a flat finish of the
surfaces that touch each other (sealing rim 3' and rim 6').
[0061] The necessary process gas outlet 12 from the process chamber
1 in the form of an intake manifold is located in the middle of the
process tube 3 on the side opposite the tube closure 2 and is
provided with a spherically ground joint 17 and is either sloped
downwardly, for example, 5 degrees or configured horizontally
(FIGS. 1, 7). The advantage of the downwardly sloped process gas
outlet 12 lies in the fact that the liquid reaction products or the
reaction products that liquefied upon aeration of the device and
the deposits, like phosphoric acids, may flow away. As a result the
process gas outlet 12 is prevented from clogging. Furthermore, the
object is achieved that as few substances as possible can bind that
can influence the process results.
[0062] A special gas outlet lance 18 (FIG. 6), which is made of
quartz, SiC or another suitable material, may be clamped, for
example, in a spring loaded manner, to the spherically ground joint
17 (FIGS. 1, 7). The gas outlet lance 18 is inserted with a gas
conveying tube 19 into the outlet 12 of the process tube 3 (FIGS.
1, 7) and sealed with a spherically ground joint 21. A T-piece 18'
is connected to the pumping-out connector 20 of the door 5 via a
hose 23 (FIG. 7). In this case an outer tube 22 of the T-piece 18'
surrounds the gas conveying tube 19 at a predefined distance.
Basically a conically ground joint or even a screw connection can
also be used, instead of the spherically ground joint 17.
[0063] The gas outlet lance 18 fulfills a plurality of functions.
First of all, this function would be the evacuation of the process
chamber 1 through the tube 19, which is situated internally and
which extends into the process chamber 1, so that substances from
the process chamber 1, like phosphoric acid, do not flow past the
spherically ground joint 17, 21 of the process gas outlet 12 and,
thus, cannot settle there.
[0064] Furthermore, the spherically ground joint 17, 21 is flushed
with ambient air by means of a design-induced leakage of the
spherically ground joint 17, 21, so that owing to the pressure
differential a little air always gets in from the outside.
[0065] The gas, which flows from the collar chamber 11 through the
T-piece 18 into the outer tube 22, insulates this gas thermally
from the inner tube, conveying the hot waste gases (gas conveying
tube 19), so that the outer tube 22 can be attached to the
additional waste gas line with a thermoplastic seal.
[0066] Finally the gas conveying tube 19, which is situated
internally and which exhibits the extracted process gases, is
thermally insulated by means of the gas flowing in the outer tube
22. In addition, the inner tube 22 may also be heated in order to
avoid condensation phenomena.
[0067] Therefore, owing to the invention a process pressure of, for
example, 50 mbar--thus, far below 200 mbar--can be run. Oxygen,
nitrogen and POCl.sub.3 with nitrogen as the carrier gas are used
as the process gases.
[0068] Essential for the invention is, on the one hand, the spatial
separation of the two seals for the process chamber 1 and the door
5 and that the seal and the wall, that is, the bottom of the quartz
stopper 6, which seals the process chamber 1, are located as near
as possible to the heated region of the process tube 3 and, as a
result, exhibit a temperature near the process temperature. In this
way the condensation of the process gases and their reaction
products and their reactions, which run at the walls at an
adequately low temperature, in particular the settling out of the
phosphorus oxide, in the process chamber 1, is avoided.
[0069] Owing to the spatial separation the seal, which provides for
the vacuum tightness, which is necessary for reaching the desired
process pressure, may be attached adequately far away and owing to
the insulation and thermal radiation protection shielded from the
heated region of the process tube 3. The seal 15 and the door 5 may
be actively cooled without any negative effects on the process and
the process chamber. As a result, the temperature at the vacuum
seal 15 and the door 5 is significantly lower than the process
temperature, a state that makes it possible to use suitable
materials for the seal 15 between the process tube (made, for
example, of quartz) and the door (made, for example, of
aluminum)--in this case, made of silicone and PTFE and for the door
5 itself (for example aluminum). An adequately cold door 5 is also
a prerequisite for attaching the hoses, for example, hose 23, and
for the additional function of the mechanics for actuating the
door, as well as for the thermal dynamics of the system that is
altogether appropriate.
[0070] The core of the inventive device for doping, deposition and
oxidation of semiconductor material or other substrates at low
pressure is the vacuum suitable closure of the process tube 3 with
two "gas tight" seals. The first seal is a spring loaded, ground
quartz-quartz seal between the sealing rim 3' of the process tube 3
and the ground rim 6' of the quartz stopper 6. This seal is
temperature stable and, thus, can seal the process chamber 1 at a
very hot point. In this way a condensation of the process gases can
be prevented with certainty.
[0071] Such a seal is only conditionally tight, that is, at high
differential pressures there is a relatively high leak rate; and
this seal can be designed pressure-proof only with effort. The
maximum differential pressure is about 1 bar. Beyond this amount a
very thick quartz plate has to be used, but the risk of a fracture
still remains.
[0072] Both problems are solved by means of the inventive second
seal between the rim of the door 5 and the face rim of the collar
4, thus a flexibly sealing metal-quartz seal. Since such a seal is
not stable to corrosion, the collar chamber 11 is flushed through
the door 5 with a flushing gas, for example, nitrogen, as described
above.
LIST OF REFERENCE NUMERALS AND SYMBOLS
[0073] 1 process chamber [0074] 2 tube closure end [0075] 3 process
tube [0076] 3' sealing rim [0077] 4 collar [0078] 5 door [0079] 6
quartz stopper [0080] 6' ground rim [0081] 7 spring element [0082]
8 bayonet closure [0083] 9 cooling water inlet [0084] 10 cooling
water outlet [0085] 11 collar chamber [0086] 12 process gas outlet
[0087] 13 pipe connection [0088] 14 coaxial tube [0089] 15 seal
[0090] 16 flushing gas inlet [0091] 17 spherically ground joint
[0092] 18 gas outlet lance [0093] 18' T-piece [0094] 19 gas
conveying tube [0095] 20 flushing gas outlet/pumping-out connector
[0096] 21 spherically ground joint [0097] 22 outer tube [0098] 23
hose line [0099] W wafer [0100] H heater [0101] K cooling trap
[0102] P pump
* * * * *