U.S. patent application number 16/888732 was filed with the patent office on 2021-01-14 for plasma spreading apparatus and system.
The applicant listed for this patent is YIELD ENGINEERING SYSTEMS, INC.. Invention is credited to Craig Walter McCoy, William Moffat.
Application Number | 20210013013 16/888732 |
Document ID | / |
Family ID | 1000005107604 |
Filed Date | 2021-01-14 |
United States Patent
Application |
20210013013 |
Kind Code |
A1 |
Moffat; William ; et
al. |
January 14, 2021 |
Plasma Spreading Apparatus And System
Abstract
A device and method of spreading plasma which allows for plasma
etching over a larger range of process chamber pressures. A plasma
source, such as a linear inductive plasma source, may be choked to
alter back pressure within the plasma source. The plasma may then
be spread around a deflecting disc which spreads the plasma under a
dome which then allows for very even plasma etch rates across the
surface of a substrate. The apparatus may include a linear
inductive plasma source above a plasma spreading portion which
spreads plasma across a horizontally configured wafer or other
substrate. The substrate support may include heating elements
adapted to enhance the etching.
Inventors: |
Moffat; William; (San Jose,
CA) ; McCoy; Craig Walter; (San Jose, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
YIELD ENGINEERING SYSTEMS, INC. |
Livermore |
CA |
US |
|
|
Family ID: |
1000005107604 |
Appl. No.: |
16/888732 |
Filed: |
May 31, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15898178 |
Feb 15, 2018 |
10840068 |
|
|
16888732 |
|
|
|
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62459210 |
Feb 15, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J 37/32715 20130101;
H01J 37/32623 20130101; H01J 2237/335 20130101; H01J 37/32357
20130101; H01L 21/02274 20130101; H01J 2237/334 20130101; H01L
21/3065 20130101; H01J 37/32009 20130101; H01J 37/3244 20130101;
H01J 37/321 20130101; H01J 2237/3342 20130101; H01J 2237/327
20130101; H01J 37/32834 20130101; H01J 2237/3343 20130101 |
International
Class: |
H01J 37/32 20060101
H01J037/32; H01L 21/02 20060101 H01L021/02; H01L 21/3065 20060101
H01L021/3065 |
Claims
1. A plasma etching process chamber, said plasma etching process
chamber comprising: a plasma source, said plasma source comprising
a first end and a second end, said first end comprising a gas input
portion, said plasma source coupled to a process chamber at a
second end; a process chamber; a constricting plate adapted to
constrict the flow of plasma from said plasma source, said
constricting plate at said second end of said plasma source, said
constricting plate comprising an annulus; a spreading disc, said
spreading disc adapted to spread the flow of plasma after the
plasma has flowed through said constricting plate, said spreading
disc disposed between said constricting plate and the substrate
support, said spreading disc centered below said annulus of said
constricting plate; a substrate support, said support adapted to
support a substrate in the spread plasma flow, said substrate
support residing within said process chamber, said substrate
support centered below said spreading disc; and a vacuum system,
said vacuum system adapted to evacuate said process chamber.
2. The plasma etching process chamber of claim 1 wherein said
plasma source is a linear-inductive plasma source.
3. The plasma etching process chamber of claim 2 wherein said
plasma source has a cylindrical plasma chamber.
4. The plasma etching process chamber of claim 3 wherein said
constricting plate comprises a disc with an annulus, said disc
extending from an inner surface of said cylindrical plasma
chamber.
5. The plasma etching process chamber of claim 4 wherein the ratio
of the diameter of the annulus in the constrictor plate to the
interior diameter of the cylindrical plasma chamber is in the range
of 1:8 to 1:3.
6. The plasma etching process chamber of claim 4 wherein the ratio
of the diameter of the annulus in the constrictor plate to the
interior diameter of the cylindrical plasma chamber is in the range
of 1:5 to 1:2.5.
7. The plasma etching process chamber of claim 1 further comprising
a gas input showerhead, said gas input showerhead at the first end
of said plasma source.
8. The plasma etching process chamber of claim 4 further comprising
a gas input showerhead, said gas input showerhead at the first end
of said plasma source.
9. The plasma etching process chamber of claim 4 wherein said
spreading disc is circular, and wherein the diameter of the
spreading disc is larger than the diameter of the annulus in the
constrictor plate.
10. The plasma etching process chamber of claim 5 wherein said
spreading disc is circular, and wherein the diameter of the
spreading disc is larger than the diameter of the annulus in the
constrictor plate.
11. The plasma etching process chamber of claim 10 wherein said
spreading disc comprises a curved surface facing said constrictor
plate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 15/898,178, to Moffat et al., which claims priority to
U.S. Provisional Patent Application No. 62/459,210 to Moffat et
al., filed Feb. 15, 2017, which are hereby incorporated by
reference in their entirety.
FIELD OF THE INVENTION
[0002] This invention relates to plasma etching, namely a device
and method for even distribution of plasma across a surface.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] FIG. 1A is a front view with partial cross section of a
system according to some embodiments of the present invention.
[0004] FIG. 1B is a side view of a system according to some
embodiments of the present invention.
[0005] FIG. 1C is a raised perspective view of a system according
to some embodiments of the present invention.
[0006] FIG. 1D is a cross sectional view of the process chamber
portion of a system according to some embodiments of the present
invention.
[0007] FIG. 1E is a cross sectional view of the process chamber
portion of a system according to some embodiments of the present
invention.
[0008] FIG. 2A is a view of the plasma source and beam spreading
portion according to some embodiments of the present invention.
[0009] FIG. 2B is a cross sectional view of the plasma source and
beam spreading portion according to some embodiments of the present
invention.
SUMMARY
[0010] A device and method of spreading plasma which allows for
plasma etching over a larger range of process chamber pressures. A
plasma source, such as a linear inductive plasma source, may be
choked to alter back pressure within the plasma source. The plasma
may then be spread around a deflecting disc which spreads the
plasma under a dome which then allows for very even plasma etch
rates across the surface of a substrate. The apparatus may include
a linear inductive plasma source above a plasma spreading portion
which spreads plasma across a horizontally configured wafer or
other substrate. The substrate support may include heating elements
adapted to enhance the etching.
DETAILED DESCRIPTION
[0011] In some embodiments of the present invention, as seen in
FIGS. 1A-D, the plasma etching system 200 is comprised of plasma
source 101 mounted above a process chamber 205. A main housing 204
includes the associated equipment and electronics to support the
system. A wafer stack housing 202 contains substrates 203, which
may be semiconductor wafers undergoing processing to become
semiconductor products. A wafer moving robot 201 is adapted to
insert and remove substrates 203 to and from the process chamber
205.
[0012] The plasma source 101 may be a linear-inductive plasma
source. This linear-inductive plasma source may be an inductively
coupled plasma source with an integrated power delivery system,
producing a high density plasma that dissociates inert process gas
into reactive species which flow out of the unit and perform work
on substrates placed downstream. The performance of such a plasma
source may be constrained in prior industrial uses, such that the
chamber pressure may need to be constrained within a narrow range,
or that the plasma etch rates on substrates downstream from such a
source may be overly variable across a substrate.
[0013] A linear-inductive plasma source may be utilized in such a
way to overcome prior deficiencies, as seen in embodiments of the
present invention. As seen in cross-section in FIG. 1D, a plasma
source 101 is mounted atop a lower process chamber 205. The plasma
source 101 may be a linear inductive plasma source which has a
cylindrical chamber within it along a vertical axis. A first zone
114 within the cylindrical chamber within the plasma source is
representative of the environment within the plasma source
cylindrical chamber. At the bottom of the cylindrical chamber
within the plasma source is a constrictor 102 which may be a
circular disc. The constrictor 102 may have an opening 116 which
may be a circular opening. A spreading disc 103 resides below the
opening 116 in the constrictor 102. Standoffs 104 are used to
locate the spreading disc 103 below constrictor 102 and to
facilitate attachment of the spreading disc 103. The bottom surface
of the spreading disc 103 may be flat and the upper surface of the
spreading disc 103 may be rounded.
[0014] The target of a plasma process is a substrate 108, which may
be a silicon wafer undergoing processing for semiconductor
applications. The wafer may reside on a substrate support 106
within the lower process chamber 205. The substrate support may
have an upper plate layer and a layer plate layer and have a heater
element 107 routed in recesses between the two plate layers of the
substrate support 106. Lift pins 109 may be used to support wafer
removal. The heater element 107 may be a stainless steel clad
element with electrical connection routed out of the process
chamber with a heater coupling 111.
[0015] A vacuum line 112 resides below the substrate support 106
allowing for chamber exhaust at the bottom of the chamber. With the
plasma input at the top of the process chamber, and then the plasma
first constricted and then spread above the substrate, and then a
vacuum exhaust at the bottom of the chamber, this sequence defines
the flow route through the chamber.
[0016] The lower process chamber 205 has a chamber door 110 which
allows for insertion and removal of the wafer 108 into the chamber
housing 113. A chamber roof 105 is adapted to facilitate the flow
of the plasma around the spreading disc 103 and down onto the top
surface of the wafer 108. The chamber roof 105 maybe begin as a
vertically aligned cylinder and then fan out as a cone to
facilitate radial distribution of the plasma flow. A second zone
115 is illustrative of the environment within the process chamber
205 above the wafer 108.
[0017] In an illustrative embodiment, the plasma source 101 has an
interior space cylindrical diameter of 3 inches, narrowed by the
constrictor 102 with a circular opening of 3/4 inches diameter. The
spreading disc 103 resides below spacers 104 which are 3/4 inch
high. The outside diameter of the spreading disc 103 is 1 and 3/8
inches and is nominally 1/8 inch thick, with a domed top surface
with a 0.78 inch radius. The bottom surface of the constrictor 102
is 3 and 15/16 above the surface of the substrate support 106. The
constrictor 102, the spacers 104, and the spreading disc 103 may be
of a ceramic material. An exemplary substrate 108 is a silicon
wafer 8 inches in diameter and 0.030 inches thick.
[0018] With the use of a constrictor 102 a back pressure can
develop in the plasma source central opening which allows the
plasma to properly develop, even with the lower process chamber 205
at a different or lower pressure. For example, using the
illustrative embodiment described above, a process chamber pressure
of 250 mTorr to 1.2 Torr may be used during an etching process.
After the plasma flows through the constrictor, the spreading disc
103 then spreads the plasma such that the surface of the wafer is
very evenly etched during processing. The substrate support 106
with its heating element 107 allows for heating of the wafer, for
example to 250 C, allowing for enhancement of the etching in some
applications.
[0019] FIG. 1E further illustrates gas flow and pressure regions in
some embodiments of systems and methods of the present invention.
An inductive plasma source 101 has a cylindrical chamber 313 and a
constrictor plate 102. The constrictor plate 102 has an opening
116. In some aspects, the plasma source 101 may be a Litmas.RTM.
Remote Plasma Source 3001 by Advanced Energy of Fort Collins,
Colo.
[0020] In an exemplary embodiment, gas input 312 flows into the
plasma chamber 313 as a combination of O2 and N2. The O2 may flow
in at a rate of 1200 sccm and N2 may also flow in concurrently at a
rate of 120 sccm. The inflow gas flows into the plasma chamber 313
and may occupy a space 301 where plasma firing may occur. As there
is continuous flow during a plasma process, beginning with the gas
input 312 at the upper end of the plasma source 101, and ending
with exit flow 310 through the vacuum exit line 112, there will be
differing pressures along this flow path. In prior systems, the
process efficiency, and process uniformity, may be negatively
impacted due to pressure variations in the process chamber. These
pressure variations may be due to a variety of factors, such as
vacuum pump stability, aspects of the vacuum throttle valve, the
gas distribution itself, accuracies of sensors, and other
factors.
[0021] Using a chamber pressure point 311 as a guidepost for
chamber pressure measurement, to achieve plasma firing in the
firing space 301 the chamber pressure point may be needed to be
kept within a 100 mTorr range, which may be 800-900 mTorr. In some
systems the factors listed above which may lead to pressure
variations may make it difficult to remain within such a tight
pressure range. Excursions outside the pressure range may lead to
incomplete plasma firing, or the cessation of firing. Process
efficiency may be significantly lower when suffering from these
effects. When using a 3/4 inch inside diameter 116 constrictor 102
with the 3 inch cylinder 313 at the flow rates listed above, full
firing in the firing space 301 may occur over a range of pressure
difference an order of magnitude higher, from 250 mTorr to 1.2
Torr, for example. Without a constrictor there may not be full, or
any, plasma firing in such a configuration. With too much of a
constriction, plasma efficiency may also be impacted.
[0022] In some aspects, the interior diameter of the plasma chamber
313 is 3 inches. In some aspects, the interior diameter 116 of the
constrictor 102 is 3/4 inch. In some aspects, the interior diameter
116 of the constrictor 102 is in the range of 3/8 inch to 1 inch.
In some aspects, the interior diameter 116 of the constrictor 102
is in the range of 3/8 inch to 1.25 inches. In some aspects, the
interior diameter 116 of the constrictor 102 is in the range of 1/8
of the diameter of the interior diameter of the plasma chamber 313
to 1/3 of the interior diameter of the plasma chamber. In some
aspects, the interior diameter of the plasma chamber 313 is in the
range of 2 to 4 inches.
[0023] As the plasma flows through 302 the interior annulus 116 of
the constrictor 102, the flow is moderated by the spreading disc
103. The flow is routed 303 outwards around the spreading disc 103.
The plasma then resides within a central zone 304 within the
chamber 205 constrained from above by the chamber roof 105. The
plasma works downward 305 on the top surface of the substrate 108.
Another advantage of systems according to embodiments of the
present invention is that there is more even plasma distribution
onto the top surface of the substrate 108. In some aspects, the
etch rate uniformity is within 6%. In some aspects, the uniformity
is within 10%. Exemplary data is seen in Table 1.
TABLE-US-00001 TABLE 1 Resist Wafer RF Total Thickness Size Temp
Pressure Power O2 Flow N2 Flow Time Rate *Unif 4.mu. 150 200 C. 370
3 kW 1200 120 sscm 30 sec 5.03 .mu./min 4.50% mm mTorr sccm 4.mu.
150 200 C. 370 3 kW 1200 120 sccm 30 sec 5.18 .mu./min 5.90% mm
mTorr sccm 4.mu. 150 200 C. 370 3 kW 1200 120 sccm 30 sec 5.22
.mu./min 3.60% mm mTorr sccm 4.mu. 150 200 C. 370 3 kW 1200 120
sccm 30 sec 5.29 .mu./min 4.30% mm mTorr sccm 4.mu. 150 200 C. 370
3 kW 1200 120 sccm 30 sec 5.28 .mu./min 3.90% mm mTorr sccm *Unif.
= (Max - Min.)/2 Mean .times. 100
[0024] As the plasma and/or gasses flow past the central zone 304
it routes 306, 307 around the exterior of the substrate 108. The
gas flow continues 308, 309 and then the exit flow 310 then routes
out of the chamber. As discussed above, the use of a constrictor
plate and the beam spreader results in processing with the combined
advantages of maintaining plasma, and plasma efficiency, over a
wider range of chamber pressure variations and also results in a
more uniform processing of the substrate.
[0025] In some embodiments of the present invention, as seen in
FIGS. 2A and 2B, the system is also moderated by a gas input
showerhead 351. A gas inlet line 350 may supply the process gasses,
which may O2 and N2, for example, as discussed above. The gas
routes into a gas input showerhead 351, which spreads the gas flow
over the circular area at the upper end of the plasma chamber 313
of the plasma source 101. The gas input showerhead 351 may have a
disc 352 with gas exit holes 353 arranged around the bottom surface
of the disc 352. The gas exit holes 353 may be sized such that
there is some flow resistance within the gas flow as it exits
through the gas exit holes 353, evening out the gas flow through
the different gas exit holes. With the moderated, even, gas input
at the input end of the plasma source 101, which may be a
linear-inductive plasma source, and the moderated gas exit through
the interior 116 of the constrictor 102, very high plasma
efficiency may be obtained. Coupled with the gas spreading disc 103
under the conical chamber top 105, the system then facilitates
extremely even plasma processing on a substrate, as discussed
above, and as seen in Table 1.
[0026] As evident from the above description, a wide variety of
embodiments may be configured from the description given herein and
additional advantages and modifications will readily occur to those
skilled in the art. The invention in its broader aspects is,
therefore, not limited to the specific details and illustrative
examples shown and described. Accordingly, departures from such
details may be made without departing from the spirit or scope of
the applicant's general invention.
* * * * *