U.S. patent application number 09/804593 was filed with the patent office on 2002-09-12 for atmospheric pressure plasma etching reactor.
Invention is credited to Henins, Ivars, Selwyn, Gary S., Snyder, Hans.
Application Number | 20020124962 09/804593 |
Document ID | / |
Family ID | 25189357 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020124962 |
Kind Code |
A1 |
Selwyn, Gary S. ; et
al. |
September 12, 2002 |
Atmospheric pressure plasma etching reactor
Abstract
An atmospheric pressure plasma etching reactor has a table
holding a wafer to be processed and which moves the wafer to be
processed under at least one electrode that is mounted in close
proximity to the table and defines an entry of a gas mixture. With
a radio-frequency voltage connected between the table and the at
least one electrode, a plasma is created between the at least one
electrode and the wafer to be processed processing the wafer to be
processed as it is moved under the at least one electrode by the
table.
Inventors: |
Selwyn, Gary S.; (Los
Alamos, NM) ; Henins, Ivars; (Los Alamos, NM)
; Snyder, Hans; (Los Alamos, NM) |
Correspondence
Address: |
Milton D. Wyrick
Los Alamos National Laboratory
LC/BPL, MS D412
Los Alamos
NM
87545
US
|
Family ID: |
25189357 |
Appl. No.: |
09/804593 |
Filed: |
March 12, 2001 |
Current U.S.
Class: |
156/345.47 |
Current CPC
Class: |
H01L 21/67069 20130101;
H01J 37/32082 20130101; H01J 37/32825 20130101 |
Class at
Publication: |
156/345.47 |
International
Class: |
C23F 001/00 |
Goverment Interests
[0001] This invention was made with Government support under
Contract No. W-7405-ENG-36 awarded by the U.S. Department of
Energy. The Government has certain rights in the invention.
Claims
What is claimed is:
1. An atmospheric pressure plasma etching reactor comprising: a
table for holding and moving a wafer to be processed; at least one
atmospheric pressure plasma processor, said at least one
atmospheric pressure plasma processor having an electrode situated
in close proximity to said table, and defining an entry for
introduction of a gas mixture; wherein with a radio-frequency
voltage connected between said table and said electrode of said
least one atmospheric pressure plasma processor and said gas
mixture introduced into said at least one atmospheric pressure
plasma processor, a plasma is created between said wafer to be
processed and said electrode of said at least one atmospheric
pressure plasma processor for processing said wafer to be processed
as it is moved under said at least one atmospheric pressure plasma
processor by said table.
2. The atmospheric pressure plasma etching reactor described in
claim 1 further comprising temperature control channels in said
least one atmospheric pressure plasma processor.
3. The atmospheric pressure plasma etching reactor described in
claim 1 further comprising baffles for distributing said gas
mixture throughout said least one atmospheric pressure plasma
processor.
4. The atmospheric pressure plasma etching reactor described in
claim 1 further comprising controllable heating elements in said
table.
5. The atmospheric pressure plasma etching reactor described in
claim 1 further comprising a motor for moving said table under said
at least one electrode.
6. The atmospheric pressure plasma etching reactor as described in
claim 1 wherein said least one atmospheric pressure plasma
processor comprises one atmospheric pressure plasma processor.
7. The atmospheric pressure plasma etching reactor as described in
claim 1 wherein said at least one atmospheric pressure plasma
processor comprises two atmospheric pressure plasma processors.
8. The atmospheric pressure plasma etching reactor as described in
claim 1, wherein said gas mixture comprises helium and carbon
tetrafluoride.
9. The atmospheric pressure plasma etching reactor as described in
claim 1, wherein said gas mixture comprises helium and oxygen.
10. The atmospheric pressure plasma etching reactor as described in
claim 1, wherein said gas mixture comprises helium and hydrogen.
Description
[0002] The present invention generally relates to plasma generation
for use in material etching processes, and, more specifically to a
reactor for generating a plasma at atmospheric pressure.
BACKGROUND OF THE INVENTION
[0003] Integrated circuits have become pervasive components of
myriad products the world uses everyday. They are found in
household products, cell phones, computers, radios and virtually
thousands of additional application. Because of the demand for
these products, it is imperative that the manufacture of integrated
circuits produces efficacious and reliable devices in the most
efficient and cost effective manner possible.
[0004] One of the critical steps in the manufacture of integrated
circuits is the step of plasma ashing of photoresist. Photoresist
is a thin film compound that is applied to a wafer in order to
photographically transfer a circuit pattern to the surface of a
wafer. The photoresist is "developed" with the circuit pattern and
then the developed photoresist is used as a mask to selectively
define regions of the wafer that will be etched using a
chemically-reactive plasma. After the silicon etching process is
complete, the residual photoresist mask must be removed, or "ashed"
off the surface of the wafer, in preparation for the next process
step. It is important that removal of all the photoresist material
from the wafer be done in this ashing step, to avoid contamination
in subsequent process steps.
[0005] Present systems for providing the wafer ashing process
include wet processes, done using solvents, and dry processes
accomplished by oxidation of the photoresist layer using ozone or
oxygen-containing plasmas. Wet photoresist removal steps generate
chemical waste, which must be disposed of properly. And dry
processes, such as plasma ashing, involve the use of a vacuum
chamber in which the plasma is generated, which increases the cost
of the equipment. A drawback in the use of ozone for photoresist
removal is the danger and toxicity of this relatively unstable,
noxious gas.
[0006] Plasma ashing is the generally preferred means of
photoresist removal. However, because the wafers are individually
processed in vacuum, each step requires a separate vacuum chamber
so that a single process chemistry can be effected in a single
chamber, in order to avoid chemical contamination between the
steps. This means that, should multiple process steps be necessary,
multiple vacuum chambers are required. Naturally, with multiple
vacuum chambers, a wafer must be moved from one chamber to the
next. This increases the cost and complexity of the process.
Multiple process steps are often desirable to use in photoresist
ashing as described herein. While the use of multiple processing
steps is possible using the prior art, the need for separate vacuum
process chambers to accommodate the different chemistries adds to
the cost and complexity of the present method.
[0007] The present invention simplifies this process, and provides
cleaning ability far superior to the present processes. The
invention does this at less cost than the conventional technology
because of the much higher efficiency attained. It accomplishes
these improvements through an atmospheric pressure system that
permits it to complete several process steps without the need for
vacuum transfers and without the risk of cross contamination. It
therefore is an object of the present invention to provide a
substrate processing system capable of providing multiple
processing steps to a given substrate within a single process
enclosure. For purposes of discussion herein, a vacuum chamber is
defined as a vacuum-tight, sealed unit capable of being pumped down
to a low base pressure and refilled with the process gas for the
purpose of generating a plasma. It also would be fitted with
necessary vacuum pumps and vacuum gauges and would be constructed
of material compatible with vacuum operation. An enclosure is
defined as leak-tight box that can contain a mix of process gas
without contamination from outside air. An enclosure does not need
the structural stability required for vacuum operation and does not
require vacuum pumps, vacuum gauges or load-locks capable of
transferring substrates from room air to a vacuum chamber.
[0008] The present invention is loosely related to a recently filed
U.S. patent application Ser. No. 09/776,086, filed Feb. 2, 2001,
for Processing Materials Inside an Atmospheric-Pressure Radio
Frequency Nonthermal Plasma Discharge.
[0009] It is an object of the present invention to provide
substrate processing that is capable of processing multiple
substrates in sequence.
[0010] It is another object of the present invention to provide
substrate processing that is capable of using different plasma
chemistries within the same enclosure.
[0011] Additional objects, advantages and novel features of the
invention will be set forth in part in the description which
follows, and in part will become apparent to those skilled in the
art upon examination of the following or may be learned by practice
of the invention. The objects and advantages of the invention may
be realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
SUMMARY OF THE INVENTION
[0012] To achieve the foregoing and other objects, and in
accordance with the purposes of the present invention, as embodied
and broadly described herein, an atmospheric pressure plasma
etching reactor comprises a table for holding and moving a wafer to
be processed, with at least one electrode being situated in close
proximity to the table and defining an entry for introduction of a
gas mixture. Wherein, with a radio-frequency voltage connected
between the translatable table and the at least one electrode and
the gas mixture introduced into the at least one electrode, a
plasma is created between the wafer to be processed and the at
least one electrode for processing the wafer to be processed as it
is moved under the at least one electrode by the table.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The accompanying drawings, which are incorporated in and
form a part of the specification, illustrate the embodiments of the
present invention and, together with the description, serve to
explain the principles of the invention. In the drawings:
[0014] FIG. 1 is a schematical side view of the one embodiment of
the present invention showing two processing stations.
[0015] FIG. 2 is an end view of an embodiment of the present
invention.
[0016] FIG. 3 is a top view of an embodiment of the present
invention.
DETAILED DESCRIPTION
[0017] The present invention provides plasma processing of
substrates and allows each substrate to undergo sequential
processing by multiple plasma processors using a single enclosure
and a robotic stage. The invention can be understood most easily
through reference to the drawings.
[0018] In FIG. 1, a schematical plan view of one embodiment of the
invention is shown where plasma-etching reactor 10 has wafer table
11 for transporting wafer 12 to be processed by an atmospheric
pressure plasma jet. This atmospheric pressure plasma 13a is
created in atmospheric pressure plasma jet processors 13, in this
figure showing two atmospheric plasma jet processors 13.
Atmospheric pressure plasma processors 13, each contain an
electrode 14, shown in side-view in FIG. 1. Each electrode 14 has
optional temperature control channels 16 and gas baffles 17. An
appropriate processing gas is introduced between the two electrodes
14 through gas inlets 18. With the application of a voltage between
either electrode 14 and wafer table 11, and introduction of an
appropriate gas through gas inlets 18, a plasma 13a will be created
for processing wafer 12 as it is carried through the plasma by
wafer table 11. Appropriate temperature control fluids such as air,
water or oil, at some desired temperature, are circulated through
temperature control channels 16 when necessary to regulate the
temperature of electrode 14. In some cases, it also might be
desirable to heat the electrodes 14, by passing a heated fluid
through the fluid channels 16. In either case, fluid channels 16
are used together with a circulating fluid to control the
temperature of gas striking the wafer 12.
[0019] Wafer table 11 incorporates electric heating rods 19.
Heating rods 19 serve to heat wafer 12 to an appropriate
temperature for processing when such action is required. Wafer
table 11 is supported by ceramic thermal insulators 20, which, in
turn, are attached to slide carriage 21. Slide carriage 21 slides
along translating slide rails 22 when slide carriage 21 is moved as
described below.
[0020] Referring now to FIG. 2, there can be seen an illustration
of an end view of this embodiment of the present invention, where
many elements are shown that were hidden in FIG. 1. Here, it can be
seen that wafer table 11 with wafer is moved under electrode 14 by
conventional slide drive screw 23. Slide drive screw 23 can be
turned in any convenient manner such as by hand or by a
variable-speed motor. Also shown, here in cross section, are
electric heating rods 19, which can be controlled by a thermostat
(not shown) to regulate the temperature of wafer 12 for a
particular processing regimen.
[0021] Turning now to FIG. 3, there can be seen a top view of this
embodiment of the present invention in which two atmospheric
pressure plasma processors are shown. This FIG. 3 shows clearly how
wafer table 11 transports wafer 12 under electrodes 14. This
transport of wafer table 11 is provided by slide drive screw 23,
while sliding along slide rails 22. Also shown are the protective
electrically conductive shields 15 inside which the processing of
wafer 12 is accomplished.
[0022] Although the FIGS. 1-3 illustrate an embodiment of the
present invention utilizing two electrodes 14, the invention is not
limited to two electrodes 14. Any appropriate number could be
utilized, from one to many, depending on the processes to be
employed for a particular wafer 12. These electrodes 14 could be
employed along with subsequent process steps, including wet rinses,
all within the traverse of slide carriage 21.
[0023] In the present invention, electrode 14 is one electrode and
wafer table 11 is the other electrode for connection of the RF
energy for creation of a plasma. Either one may be rf-powered, and
typically, one is grounded. In most cases, it is convenient to have
electrode 14 be rf-powered and wafer table 11 be grounded for
safety reasons. The specific frequency of the RF energy and its
voltage level are to be determined for the particular process step
to be employed for a particular wafer 12.
[0024] It is to be understood that in utilizing individual
electrodes 14, each electrode 14 can be controlled independently,
both with respect to RF energy and process chemistry, while wafer
12 is moved below each electrode 14. A true plasma, including ions
and electrons, as well as reactive chemical neutral species, exists
in the space between electrodes 14 and wafer 12 (FIGS. 1 and
2).
[0025] It is a clear advantage of the present invention that
individual electrodes 14 can be powered differently than others,
and can employ different process gas mixtures for particular
etching situations. For example, one electrode 14 could have a
He/CF.sub.4 gas mixture introduced through its gas inlet 18 (FIGS.
1 and 2), while a second electrode 14 could have a He/O.sub.2 gas
mixture introduced through its gas inlet 18. As wafer 12 is moved
under each electrode 14 it is processed for two process steps
instead of the one step in the conventional reactor. In this
embodiment, a third electrode 14 could be used for passivation of
wafer 12, with use of a gas mixture of He/H.sub.2 for the plasma.
Such an arrangement may be useful for removal of photoresist that
has been "hardened" or carbonized, by exposure to an ion
implantation step. The intense energy of the ion beam causes a hard
"skin" to form on the surface of the photoresist. This surface film
must be removed using a chemically-aggressive plasma, such as
fluorine-containing feedgas (i.e., CF.sub.4) and He feedgas plasma,
but it is desirable to avoid the use of such plasmas after the
surface skin has been removed, and instead use an O.sub.2 and
He-based plasma to finish ashing the photoresist. The oxygen plasma
has better selectivity to silicon (i.e., it will preferentially
etch the photoresist without etching the silicon under the
photoresist, whereas the fluorine-based plasma will etch both). In
conventional plasma systems operating in vacuum, this requires two
processes chambers (one for the fluorine plasma and one for the
oxygen plasma to avoid cross contamination. This invention improves
operation of the ashing process by eliminating the need for
separate process chambers.
[0026] Also, because the present invention processes a single wafer
12, it is not subject to the accumulation of particles and etch
products, as might occur in a solvent cleaning process, such as wet
chemical etching systems. Thus the present invention is inherently
both dry and clean. Operational savings result because there is no
need to dry wafer 12 or to dispose of solvents. In addition, the
present invention can perform multiple process steps nearly
simultaneously, a feat that is not possible with wet processes, and
can do so with lower capital equipment cost and with a smaller
footprint, or equipment size.
[0027] The present invention offers other advantages over the prior
art. First, it eliminates the need for any vacuum equipment,
simplifying maintenance of the equipment. Second, it etches or
cleans wafers or substrates faster because of high reactive species
gas density and in-situ exposure to the plasma, so its throughput
is greater. Third, it has the ability to run multiple process steps
almost simultaneously, even those requiring different process
chemistries, so it results in reduced equipment and process
complexity.
[0028] As previously mentioned, it was desirable in the use of
prior art vacuum-based plasmas, to operate a single process in a
single vacuum chamber for each wafer or substrate. This was done
because the use of different process chemistries in the same vacuum
chamber causes particle contamination to occur, which is a leading
cause of defects during wafer processing. As previously mentioned,
the use of different process chemistries was helpful in removing
hardened, or carbonized, photoresist. Thus, to use different
process chemistries and to avoid contamination problems requires
that multiple vacuum chambers be used. When multiple vacuum
chambers are used, it means that the wafer must be moved from one
chamber to the next, requiring extra handling in addition to the
extra process steps and the associated time and expense.
[0029] The present invention does not require different vacuum
chambers or any vacuum chamber at all. It utilizes a single
manipulator to move the wafer through multiple process units, each
having the same or different plasma chemistry, and without the
associated need for vacuum loadlocks in between. A single process
enclosure is used. However, the effect of multiple vacuum chambers
is achieved through the use of multiple independently controlled
electrodes 14. The close proximity of electrodes 14 to wafer 12
allows wafer 12 to receive multiple process steps as it progresses
under each electrode 14. Because the gas pressure in the plasma
region of each process unit is slightly in excess of atmospheric
pressure (to achieve gas flow) the likelihood of cross
contamination resulting from gas flow in one process unit entering
the adjacent process unit is minimal. Diffusion is slow in this
situation, owing to the high pressure operation of each process
unit, so cross contamination problems are avoided.
[0030] Applications of the present invention are many and varied.
For example, it can be used to etch photoresists, silicon and metal
from semiconductor wafers. It can also be used to deposit thin
films, including especially large area deposition for thin-film
transistor passivation, coatings used for architectural window
glass, and deposition of hermetic coatings on magnetic media.
Additional applications exist and still others are likely to be
discovered through use of the present invention.
[0031] The foregoing description of the embodiments of the
invention has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed, and obviously many
modifications and variations are possible in light of the above
teaching. The embodiments were chosen and described in order to
best explain the principles of the invention and its practical
application to thereby enable others skilled in the art to best
utilize the invention in various embodiments and with various
modifications as are suited to the particular use contemplated. It
is intended that the scope of the invention be defined by the
claims appended hereto.
* * * * *