U.S. patent application number 13/128265 was filed with the patent office on 2011-11-10 for plasma processing apparatus and method for the plasma processing of substrates.
This patent application is currently assigned to OERLIKON TRADING AG, TRUEBBACH. Invention is credited to Ulrich Kroll, Boris Legradic.
Application Number | 20110272099 13/128265 |
Document ID | / |
Family ID | 40792878 |
Filed Date | 2011-11-10 |
United States Patent
Application |
20110272099 |
Kind Code |
A1 |
Kroll; Ulrich ; et
al. |
November 10, 2011 |
PLASMA PROCESSING APPARATUS AND METHOD FOR THE PLASMA PROCESSING OF
SUBSTRATES
Abstract
A plasma processing apparatus (30, 50) comprises a process
chamber with process chamber walls (35), process gas inlet means
and process gas distribution means in said process chamber, exhaust
means for removal of residual gases and a substrate mount (34) for
a substrate (33). In a first embodiment a conductive plate (51) is
arranged within said process chamber, electrically connectable with
at least one RF power source (39) facing said conductive plate
(51), exhibiting a pattern of openings and arranged at a distance
to a backside wall (53) of said process chamber so that a process
gas delivered to a gap (55) between the conductive plate (51) and
said backside wall (53) does not ignite a plasma in the gap (55)
during operation. In a second embodiment a first and second
electrode are arranged within said process chamber adjacent each
other with a gap in-between. The first electrode is connectable to
a RF power source and the second electrode is connected to ground.
The second electrode exhibits a pattern of openings and is arranged
at a distance such that a process gas delivered to said gap does
not ignite a plasma during operation.
Inventors: |
Kroll; Ulrich; (Corcelles,
CH) ; Legradic; Boris; (Lausanne, CH) |
Assignee: |
OERLIKON TRADING AG,
TRUEBBACH
Truebbach
CH
|
Family ID: |
40792878 |
Appl. No.: |
13/128265 |
Filed: |
April 30, 2009 |
PCT Filed: |
April 30, 2009 |
PCT NO: |
PCT/EP2009/055302 |
371 Date: |
May 9, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61049899 |
May 2, 2008 |
|
|
|
Current U.S.
Class: |
156/345.33 ;
118/723E |
Current CPC
Class: |
H01J 2237/0206 20130101;
H01J 37/32357 20130101; H01J 37/32541 20130101; H01J 37/32091
20130101 |
Class at
Publication: |
156/345.33 ;
118/723.E |
International
Class: |
C23F 1/08 20060101
C23F001/08; C23C 16/458 20060101 C23C016/458; C23C 16/509 20060101
C23C016/509; C23C 16/455 20060101 C23C016/455 |
Claims
1. A plasma processing apparatus (30) comprising a process chamber
with process chamber walls (35), process gas inlet means and
process gas distribution means, exhaust means for removal of
residual gases, at least a first and second electrode (31, 32)
arranged adjacent to each other thus forming a gap (38) in-between,
at least one RF power source (39) electrically connectable with
said electrodes (31, 32), and a substrate mount (34) for a
substrate (33) facing second electrode (32), characterized in that
the second electrode (32) exhibits a pattern of openings (36) and
is arranged at such a distance to the first electrode (31) that a
process gas delivered to the gap (38) between the electrodes (31,
32) does not ignite a plasma in the gap (38) during operation and
wherein the second electrode is grounded.
2. An apparatus according to claim 1, wherein the distance between
first electrode (31) and second electrode (32) is essentially
between 1 to 3 mm.
3. An apparatus according to claim 1 or 2, wherein the second
electrode is designed as a plate with a thickness between 1-15
mm.
4. An apparatus according to claims 1 or 2, wherein the substrate
mount (34) is connectable to a second RF power supply (40).
5. A plasma processing apparatus (50) comprising a process chamber
with process chamber walls (35), process gas inlet means and
process gas distribution means in said process chamber, exhaust
means for removal of residual gases, a conductive plate (51)
arranged within said process chamber, electrically connectable with
at least one RF power source (39) and a substrate mount (34) for a
substrate (33) facing said conductive plate (51), characterized in
that the conductive plate (51) exhibits a pattern of openings and
is arranged at a distance to and facing a backside wall (53) of
said process chamber so that a process gas delivered to a gap (55)
between the conductive plate (51) and said backside wall (53) does
not ignite a plasma in the gap (55) during operation.
6. An apparatus according to claim 5 wherein the substrate mount
(34) is connectable to a second RF power supply (40).
Description
[0001] The present invention refers to a plasma processing
apparatus or system with improved (low energy) ion bombardment
properties and to a method for processing substrates in an
apparatus of said kind. Plasma processing refers to deposition-
and/or etching processes, heating, surface conditioning and other
treatments of substrates.
BACKGROUND OF THE INVENTION
[0002] Many plasma processing systems known in the art are
construed according to the so-called parallel plate reactor
principle. A plasma processing apparatus of that kind is shown in
FIG. 1. It comprises a process chamber 7 with walls defining an
enclosure, a first plane electrode 1, a second plane electrode 2,
both arranged within said process chamber 7, electrically
connectable with at least one RF power source. Electrodes 1 and 2
define a plasma generation region 6. A substrate 5 to be processed
is placed on a substrate holder or, as shown, directly on one of
the electrodes. Thus the substrate is exposed to the effects of the
plasma during processing. Process gas inlet means 3 as well as
exhaust means 4 for removal of residual gases are shown
schematically in FIG. 1. Process gas distribution means have been
omitted.
[0003] Typically thin film silicon layers (amorphous,
nano/microcrystalline material etc.) and its alloys with C, N, O
etc. are deposited by the PECVD (plasma enhanced chemical vapor
deposition) technique using this parallel plate setup and
capacitive RF power coupling. Usually the substrates are placed on
a grounded electrode whereas the other electrode serves as the RF
powered electrode and as a gas distribution shower head (process
gas distribution means). Using such a setup, homogeneous
depositions of amorphous and nano/microcrystalline layers over
large areas in the square meter range have been obtained
successfully.
RELATED ART
[0004] In the classical parallel plate configuration the maximal
possible ion energy is correlated in a well known manner (Kohler et
al. J. Appl. Phys. 57 (1985), p. 59 and J. Appl. Phys. 58 (1985),
p. 3350) with the applied RF peak/to/peak voltage which is closely
correlated with the RF power applied. Ion bombardment with ions
accelerated towards a substrate over a certain threshold voltage
value in the process chamber creates defects in the deposited bulk
material and damages sensitive interfaces and, hence, deteriorates
the material quality and interface performance. Several attempts
using VHF and/or high pressure deposition regime, triode
configuration etc. were carried out to reduce this bombardment
especially for the deposition of microcrystalline layers. Triode
configurations lead to excellent material, but reduce the
deposition rates because a recombination of radicals in the zone
between grid and substrate takes place. Increased plasma
excitations frequencies into the VHF/UHF regime reduces the
necessary peak-to-peak voltage for a given power of the plasma, but
again the ion-bombardment increases with the RF power and, hence,
can not be controlled independently and adjusted alone.
[0005] An efficient manner to control the ion bombardment
independently of the RF power could be realized by placing the
substrates on a floating electrode. In this case only the floating
potential, which is much lower than the plasma power dependent
plasma potential, would accelerate ions towards the substrate
leading to a considerable reduction of the maximum possible ion
energies. However, simply allowing the grounded electrode to become
electrically floating in the parallel plate setup would remove most
of the electrical ground especially at large area applications due
to the absence of the electrode ground potential. Only the grounded
chamber walls in electrical contact with the plasma would remain as
ground for the plasma.
[0006] There are Prior Art applications addressing this problem.
FIG. 2 (cited from U.S. Pat. No. 7,090,705) shows a plasma
processing apparatus comprising an electrode configuration facing a
substrate 21 with a first electrode 24 and a second electrode 22
spaced apart by insulators 23. The second electrode 22 is arranged
in a stripe pattern in a parallel plane to the first electrode 24,
resulting in a structure of parallel trenches 26 with a part of the
first electrode 24 acting as the trench base 27 and electrode 22
acting as trench shoulder. Electrical power, preferably RF power 25
is being applied between electrodes 22 and 24, such that plasma is
generated in the trench 26 and adjacent to electrode(s) 22.
Technically this trench 26 could be described as elongated cavity
and might even be using a hollow cathode effect.
[0007] Process gas is being delivered to the trenches 26 via holes
in the trench base 27. The smooth and even distribution of the
process gas is essential for an effective operation and in order to
achieve a homogeneous result of the processing, e.g. layer
deposition or etching step.
[0008] The stripe pattern of electrode bars allows control of the
plasma generation areas, however, the manufacturing effort is
considerable, since the elements of second electrode 22 and
insulators 23 have to be assembled individually; furthermore many
drill holes are required in order to achieve a smooth and even
process gas distribution.
[0009] For large area plasma deposition systems based on the
parallel plate reactor principle the standing wave phenomenon will
occur. This is due to the fact that with increasing RF/VHF
frequency (>13.56 MHz and electrode diameters >1 m) the free
space wavelength decreases and thus a standing wave in the reactor
develops, starting from the point of delivery, the connecting point
of the RF power to the electrode. The design shown in FIG. 2 tries
to avoid this by multiple points of delivery for the RF power, one
per electrode 22. However, this means that a costly and elaborate
wiring is necessary in order to achieve at least partial
independence of said phenomenon. The cost for such wiring will
increase with increasing size of the electrode according to FIG. 2.
However, the design according to FIG. 2 does not resolve the
problem of the standing wave completely. Standing waves may still
occur along the parallel trenches 26, especially for large area
electrodes.
[0010] A further general problem of the parallel-plate reactor
design, especially for large surfaces, lies in the fact, that the
electrical current flow properties are not equal for all areas of
the electrode(s). Regions close to the edges of the electrodes
perceive "more" effective anode area than central areas of the
electrodes due to the fact that the walls of the process chamber
usually have ground connection and therefore will also act as an
anode. A design as described in FIG. 2 cures this problem at least
partially, because electrode surfaces are distributed and arranged
in close relationship so this inhomogeneity, especially for the
central regions of large areas electrodes will be reduced.
[0011] It is therefore an objective of the invention to avoid the
disadvantages of the Prior Art designs, to demonstrate a
lightweight, costeffective and scalable design of an electrode to
be used in a plasma processing apparatus. It is further an object
of the invention to provide for a method for plasma treatment of
substrates with increased flexibility in terms of deposition rate,
influence on crystallinity of deposited layers and layer
homogeneity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a parallel plate reactor design (simplified)
according to Prior Art.
[0013] FIG. 2 shows a reactor as described in Prior Art document
U.S. Pat. No. 7,090,705
[0014] FIG. 3 shows a first embodiment of the invention in side
view
[0015] FIG. 4 shows a top view on a perforated electrode according
to the invention
[0016] FIG. 5 shows photographs made from a small scale reactor
following the principles of the invention.
[0017] FIG. 6 shows a second embodiment of the invention in side
view.
SOLUTION ACCORDING TO THE INVENTION
[0018] A plasma processing apparatus 30 comprises a process chamber
with process chamber walls 35, process gas inlet means and process
gas distribution means in said process chamber, exhaust means for
removal of residual gases, at least a first and second electrode
31, 32 arranged within said process chamber, electrically
connectable with at least one RF power source 39. Further a
substrate mount 34 for a substrate 33 to be processed is being
provided for. The second electrode 32 exhibits a pattern of
openings and is arranged at a distance to the first electrode 31 so
that a process gas delivered to the gap 38 between the electrodes
31, 32 does not ignite a plasma in the gap 38 during operation.
[0019] In an alternative embodiment a plasma processing apparatus
50 comprises a process chamber with process chamber walls 35,
process gas inlet means and process gas distribution means in said
process chamber, exhaust means for removal of residual gases, at
least a perforated (conductive) RF plate 51 arranged within said
process chamber, electrically connectable with at least one RF
power source 39. Further a substrate mount 34 for a substrate 33 to
be processed is provided for. The RF plate 51 exhibits a pattern of
openings and is arranged at a distance to backside wall 53 so that
a process gas delivered to a gap 55 between the RF plate 51 and
backside wall 53 does not ignite a plasma in the gap 55 during
operation.
[0020] A method for plasma processing of substrates comprises
introducing a substrate 33 into a plasma processing apparatus 30,
placing the substrate 33 on a substrate holding means 34 facing an
electrode 32 with openings 36 therein, setting appropriate process
conditions (pressure, process gases, temperature) and igniting
localized plasmas 37 in the openings 36 of said electrode 32 and
processing said substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0021] The inventive solution is based on a modified electrode
configuration for a plasma processing system (or plasma reactor) 30
as shown as a first embodiment's side view in FIG. 3.
[0022] A grounded plate 32 with holes or openings 36 (perforated
ground plate) is arranged adjacent to an electrode 31 operatively
connectable to a RF power source 39. Gas inlet means (not shown)
are preferably provided for delivery of process gases into the gap
38 between grounded plate 32 and powered electrode 31. A commonly
used gas shower-head can be also implemented in this setup by e.g.
providing for holes in the powered electrode 31 located opposite
the holes of the grounded electrode. The distance between said
electrode 31 and grounded plate 32 is chosen such that in the gap
38 between electrode 31 and plate 32 no plasma will ignite
(effective dark-space shielding). The distance can vary depending
on the voltage and the RF frequency applied and the gas pressure
and nature of gas set in the gap 38. Technically the distance can
be set by the use of isolating spacers, such as ceramic screws,
this way defining the separation distance between electrodes 32 and
31. In one embodiment the distance between the RF electrode 31 and
the grounded plate 32 is arranged to be at around 1 to 3 mm.
[0023] By disposing the grounded plate 32 in vicinity to electrode
31 the plasma is forced to burn in the holes 36 of the electrically
grounded plate 32. This way localized plasma(s) 37 can be
generated. The spatial distribution of radicals produced in the
burning localized plasma(s) 37 and the ratio of grounded/powered
electrode area can be adjusted by a proper design of the
distribution of the holes, the holes' diameters, the shape of the
holes and their area density. This way it is additionally possible
to achieve on substrate 33 a uniform layer with an excellent
thickness uniformity and superior etch rate uniformity,
respectively.
[0024] Moreover, the hollow cathode principle can be extended to
these holes to even further enhance the plasma dissociation. In
this case a preferred embodiment would comprise holes with a
diameter of 1-30 mm, preferably 8-15 mm, further preferred 10 mm.
The thickness of the perforated ground plate/electrode 32 can be
selected between 1-15 mm, preferably 5-15 mm and 10 mm further
preferred. Such "thick" electrode could then also be used to act as
gas distribution means to allow dosing of process gas to the gap
between electrodes 31 and 32.)
[0025] A substrate 33 can be located on a substrate holder 34,
which again can be designed to be electrically floating, i.e.
separated from the perforated ground electrode plate, the powered
RF electrode 32 and the process chamber walls 35 by an appropriate
distance (approx. 5 mm to 100 mm, depending on pressure, hole
geometry etc.).
[0026] In a further embodiment an additional, separate, second RF
power supply 40 can be connected between substrate holder 34 and
ground, which will allow an independent bias and, hence, control of
the moderate but sometimes still beneficial ion bombardment. By
this crystallinity and/or density of a deposited layer can be
varied to a larger degree, because the ions generated by the
localized plasmas can be directed towards the substrate.
[0027] FIG. 4 shows a top view on perforated ground plate/electrode
32 with holes 36. Here a regular pattern of holes is being shown;
however, the density of holes could be varied in order to
compensate e. g. edge effects, standing wave effects etc. Electrode
32 can be manufactured from a single sheet of metal with a few mm
thickness. Then, the holes can be easily laser-cut, which will also
ease variations of the diameter of the holes and avoid the efforts
of drilling including the problem of drill-breakage.
[0028] The products to be processed with an inventive plasma
processing system include large area (>1 m.sup.2), essentially
flat substrates, such as solar panels on glass and glass ceramics
as well as other material (plastic, stainless steel), further
display panels for TFT or other applications. The range of
applications includes deposition and/or etching processes, heating,
surface conditioning and other treatments of aforementioned
substrates. Process gases useful in etching processes are CF.sub.4,
SF.sub.6, Cl.sub.2, HCl, BCl.sub.3, O.sub.2 or others. For
deposition of layers, especially semiconductor layers, gases
like
[0029] Silane SiH.sub.4, disilane, dichlorosilane, SiF.sub.4, GeH4
etc. plus eventual dopants, ammonium NH.sub.3, nitrogen N.sub.2,
Hydrazin etc. (for silicon nitride layers), N.sub.2O, CO.sub.2 and
O.sub.2 etc. (for silicon oxide layers), hydrogen H.sub.2 (as
dilutant for many deposition processes) are used with
preference.
[0030] The plasma processing apparatus according to the invention
can be used for RF/VHF frequencies between several hundred kHz to
several hundred MHz. By far preferred are the industrially used
13.56 MHz plus its harmonics like 40 MHz, and more. A small-scale
reactor in operation is shown in FIG. 5 a) and b), the localized
plasmas are visible as bright spots.
[0031] In a third embodiment, the inventive principle can be
further simplified, as shown in FIG. 6. Instead of using a powered
electrode 31 in conjunction with a grounded, perforated plate 32
(FIG. 3) a perforated (conductive) RF plate 51 is being used. Plate
51 is connected to RF power source 39. The process chamber wall 53
just behind will act through the holes as anode. The distance
between RF plate 51 and backside wall 53 (=part of process chamber
walls 35) is chosen such that in the gap 55 no plasma will ignite
(effective dark-space shielding). However, this space will, in
connection with a gas distribution system (not shown) provide each
localized plasma with process gases.
[0032] Localized plasmas 37 will ignite in the openings of RF plate
51. The perforated RF plate 51 allows compensating the effect of
the standing wave effect in the same way as grounded plate 32 for
the embodiment in FIG. 3 by adjusting size, density and
configuration of the localized plasmas. The options and limitations
cited above can be seamlessly applied also for this embodiment,
unless indicated to the contrary.
[0033] In this third embodiment a plasma 52 adjacent to perforated
RF plate 51, facing the processing region 54 might occur. This is
due to the fact that not only between plate 51 and backside wall 53
an electric field is being established, but also between powered
plate 51 and the other regions of process chamber walls 35.
[0034] A second RF power supply 40 can be advantageously connected
between substrate holder 34 and ground, which will allow an
independent bias and, hence, control of the moderate but sometimes
still beneficial ion bombardment as described above for FIG. 3.
[0035] In order to avoid that substrate 34 is affected in unwanted
manner by ion bombardment it should be taken care that no or at
least minimal capacitively coupling occurs between substrate holder
34 and the residual process chamber wall 35.
Further Advantages of the Invention
[0036] By using a reactor setup according to the invention's first
to third embodiment, one RF generator is used to generate locally
the reactive radicals. This RF voltage generates a high
bombardment, but this bombardment will be directed onto the RF
electrode 31 or 51 and its corresponding ground connection
(perforated ground plate 32 and backside wall 53) and not to a
floating electrode or substrate holder 34 where the substrate 33 is
placed and the soft deposition conditions should occur. Technically
this means plasma generation and creation of radicals are being
decoupled from the deposition, especially if a separate (RF)
substrate bias voltage 40 is being used. Thus, the deposition rate
can be increased by using higher frequencies and/or higher voltages
without risking damage to the substrate.
[0037] Since the main and strong bombardment will not take place on
the substrate the latter will be less heated up by the bombardment
and, hence, will remain less affected by heating up during the
deposition.
[0038] In contrast to the design of FIG. 2, where the standing wave
effect is partially avoided by complex electrical wiring and
arrangement of segmented electrodes 22, the inventive design takes
the phenomenon into account and allows to compensate it by the hole
pattern design as described above (diameter, arrangement, density
etc. . . . ). This allows keeping the wiring simple, using only one
or 2-4 connection points to one electrode and at the same time the
constructional and assembly efforts for the electrodes are
minimized.
[0039] It is possible to extend (scale up) the inventive design to
an arbitrary size (very large area reactors, >3 m.sup.2) without
an immense technological constructive effort.
* * * * *