U.S. patent application number 13/590242 was filed with the patent office on 2014-01-09 for plasma processing apparatus and method.
This patent application is currently assigned to Hitachi High-Technologies Corporation. The applicant listed for this patent is Tooru ARAMAKI, Norihiko IKEDA, Yasuhiro NISHIMORI, Naoki YASUI. Invention is credited to Tooru ARAMAKI, Norihiko IKEDA, Yasuhiro NISHIMORI, Naoki YASUI.
Application Number | 20140011365 13/590242 |
Document ID | / |
Family ID | 49878837 |
Filed Date | 2014-01-09 |
United States Patent
Application |
20140011365 |
Kind Code |
A1 |
YASUI; Naoki ; et
al. |
January 9, 2014 |
PLASMA PROCESSING APPARATUS AND METHOD
Abstract
To improve processing uniformity by improving a working
characteristic in an edge exclusion region. Provided is a plasma
processing apparatus for processing a sample by generating plasma
in a vacuum vessel to which a processing gas is supplied and that
is exhausted to a predetermined pressure and by applying a radio
frequency bias to a sample placed in the vacuum vessel, wherein a
conductive radio frequency ring to which a radio frequency bias
power is applied is arranged in a stepped part formed outside a
convex part of the sample stage on which the wafer is mounted, and
a dielectric cover ring is provided in the stepped part, covering
the radio frequency ring, the cover ring substantially blocks
penetration of the radio frequency power to the plasma from the
radio frequency ring, and the radio frequency ring top surface is
set higher than a wafer top surface.
Inventors: |
YASUI; Naoki; (Kudamatsu,
JP) ; IKEDA; Norihiko; (Hiroshima, JP) ;
ARAMAKI; Tooru; (Kudamatsu, JP) ; NISHIMORI;
Yasuhiro; (Hikari, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
YASUI; Naoki
IKEDA; Norihiko
ARAMAKI; Tooru
NISHIMORI; Yasuhiro |
Kudamatsu
Hiroshima
Kudamatsu
Hikari |
|
JP
JP
JP
JP |
|
|
Assignee: |
Hitachi High-Technologies
Corporation
|
Family ID: |
49878837 |
Appl. No.: |
13/590242 |
Filed: |
August 21, 2012 |
Current U.S.
Class: |
438/712 ;
156/345.48 |
Current CPC
Class: |
H01J 37/32082 20130101;
H01J 37/32192 20130101; H01J 37/32642 20130101; H01L 21/3065
20130101 |
Class at
Publication: |
438/712 ;
156/345.48 |
International
Class: |
H01L 21/3065 20060101
H01L021/3065 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 6, 2012 |
JP |
2012-152005 |
Claims
1. A plasma processing apparatus that generates plasma in a
processing chamber that is supplied with a processing gas and is
exhausted to reduce its pressure to a predetermined pressure and
processes a sample placed on a sample stage by applying a radio
frequency bias to the sample stage provided in the processing
chamber, wherein a conductor ring to which the radio frequency bias
is applied is provided outside an outer periphery of the sample on
the sample stage to which the radio frequency bias is applied, the
conductor ring is covered with a dielectric cover that makes a
plasma ion sheath formed above it have substantially a plasma ion
sheath potential produced only by plasma generation, and the height
of an equipotential surface of a lowermost part in the plasma ion
sheath above the conductor ring is set higher than a top surface of
the sample placed on the sample stage.
2. A plasma processing apparatus that has a processing chamber that
is arranged in a vacuum vessel and whose interior is decompressed,
a sample stage that is arranged in this processing chamber and
holds a wafer to be processed mounted on its top surface, and an
electrode that is arranged in the sample stage and to which a radio
frequency bias power is applied by being connected with a radio
frequency power generator, and processes the wafer by using plasma
formed in the processing chamber while applying the radio frequency
bias power thereto, the plasma processing apparatus comprising: a
ring-shaped part made of a conductor that is arranged in a step
part arranged to encircle the wafer on an outer peripheral side of
a plane holding the wafer on the sample stage and to which the
radio frequency bias power applied to the electrode in the sample
stage is applied; and a cover comprised of a dielectric material
that covers a top surface and an inner peripheral side of the
ring-shaped part and is arranged in the stepped part; wherein the
radio frequency bias power applied to the ring-shaped part is not
coupled to the plasma, and a top surface of the ring-shaped part is
set higher than a top surface of the wafer.
3. The plasma processing apparatus according to claim 2, wherein
the top surface of the ring-shaped part is set higher than the
wafer top surface, being raised by a range of 5.0 mm or less.
4. The plasma processing apparatus according to claim 2, wherein an
inner peripheral edge of the ring-shaped part is larger than an
outer peripheral edge of the wafer by a range of 1.0 to 10 mm.
5. The plasma processing apparatus according to claims 2, wherein
the thickness of the dielectric material of the cover above the top
surface of the ring-shaped part is in a range of 1.0 mm to 5.0
mm.
6. A plasma processing method for processing a sample placed on a
sample stage, comprising: generating plasma in a processing chamber
to which a processing gas is supplied and that is exhausted to
decrease its pressure to a predetermined pressure; and at the same
time applying a radio frequency bias to the sample stage provided
in the processing chamber, wherein a plasma ion sheath formed
outside the sample outer periphery on the sample stage to which the
radio frequency bias is applied is controlled to substantially have
the plasma ion sheath potential produced only by the plasma
generation, and the height of the equipotential surface in the
lowermost part in the plasma ion sheath outside the sample outer
periphery is set higher than a top surface of the sample to effect
the processing of the sample.
7. A plasma processing method, comprising: placing and holding a
wafer to be processed on a top surface of a sample stage placed in
a processing chamber whose interior is decompressed; forming plasma
in the processing chamber; and processing the wafer while applying
a radio frequency bias power to an electrode placed in the sample
stage from a radio frequency power generator, wherein the sample
stage has a ring-shaped part placed in a stepped part arranged
encircling the wafer on an outer periphery side of a plane holding
the wafer and made of a conductor to which the radio frequency bias
power applied to an electrode in the sample stage is applied, and a
cover comprised of a dielectric that covers a top surface and an
inner periphery side of the ring-shaped part and is arranged in the
stepped part, the top surface of the ring-shaped part is set higher
than a top surface of the wafer, and the radio frequency bias power
applied to the ring-shaped part is uncoupled to the plasma.
8. The plasma processing method according to claim 7, wherein the
top surface of the ring-shaped part is set higher than the wafer
top surface, being raised by a range of 5.0 mm or less.
9. The plasma processing method according to claim 7, wherein an
inner peripheral edge of the ring-shaped part is in a range of 1.0
to 10 mm, inclusive.
10. The plasma processing method according to claims 7, wherein the
thickness of the dielectric material of the cover above the top
surface of the ring-shaped part is in a range of 1.0 to 5.0 mm.
11. A plasma processing method for processing a wafer, comprising:
generating plasma in a vacuum vessel to which a processing gas is
supplied and that is exhausted to reduce its pressure to a
predetermined pressure; and at the same time applying a radio
frequency bias to a sample stage on which a sample is mounted in
the vacuum vessel and a conductor ring provided encircling the
sample outside a sample mounting plane of the sample stage wherein
the conductor ring is covered with a dielectric cover, an electric
potential of the plasma ion sheath formed above the conductor ring
by application of the radio frequency bias is controlled to be
substantially an electric potential by plasma generation, the
thickness of the plasma ion sheath is thinned, and the height of
the equipotential surface of the plasma ion sheath is set higher
than the height of the equipotential surface of a processing
surface of the sample to effect the processing of the sample.
Description
CLAIM OF PRIORITY
[0001] The present application claims priority from Japanese patent
application JP 2012-152005 filed on Jul. 6, 2012, the content of
which is hereby incorporated by reference into this
application.
FIELD OF THE INVENTION
[0002] The present invention relates to a plasma processing
apparatus and a processing method for processing a sample, and more
specifically, to a plasma processing apparatus for processing a
sample while applying a radio frequency bias to the sample in an
etching processing of the sample using plasma.
BACKGROUND OF THE INVENTION
[0003] Generally, dry etching using plasma is performed in a
semiconductor manufacturing process. The plasma processing
apparatus for performing dry etching uses various systems.
[0004] On the other hand, with an improvement in integration degree
of the recent semiconductor devices, improvement of micro
fabrication, i.e., working accuracy is required, and at the same
time, improvement of in-wafer uniformity of an etching rate or
in-wafer uniformity of the CD (Critical Dimension) value in an
etched shape, and the like are required.
[0005] Moreover, along accelerating miniaturization in a
manufacture process of the semiconductor device, uniformity of the
etching characteristic as much as an order of nanometer or
subnanometer is being required. Especially, in etching of
multilayer films, degrees of influences that a large number of
parameters (for example, an excitation power of plasma, the kind of
processing gas, a mixing ratio of the processing gases, a gas
pressure, a RF bias power, temperature setting of an electrode, a
reactor wall, etc., and the like) affect a etched profile as a
device performance are serious. For this reason, it becomes more
and more difficult to achieve in-wafer uniformity of a high
accuracy in the etching rate and the etched profile (for example,
the CD) after etching of the multilayer films.
[0006] In the etching process as described above, especially in a
surrounding of a wafer outer peripheral part has a larger
difference in a performance of the process as compared with a
central part of the wafer because of electromagnetic and
thermodynamic factors, which makes nonuniformity in a plane of the
wafer notably appear, which becomes a problem to be solved. For
example, a processed profile in a surrounding of the outer
peripheral part that is obtained after the processing is such that
a difference of a size from that in the central side portion
becomes out of an allowable range, and therefore the semiconductor
devices obtained by processing in the outer edge part of the wafer
cannot be provided.
[0007] Such a region that is the wafer outer edge part and is not
used in semiconductor device manufacture is called an edge
exclusion (E. E.), and a size of this E. E. region has becomes a
factor that decides a price of the semiconductor device largely in
manufacture of memory devices in recent years. Because of this,
reduction of the E.E. region is especially required in recent
years; specifically, the length of a radial direction of the E.E.
region is required to be equal to or less than 2 mm, or further to
be equal to or less than 1 mm.
[0008] As an improvement technology of improving wafer plane
uniformity in the plasma processing apparatus in order to reduce
this E.E. region as small as possible, and thus to increase the
number of chips obtainable from a wafer, for example, what are
disclosed in Japanese patent No. 3881290 and Japanese Patent
Application Laid-Open Publication No. 2005-260011 are known.
[0009] Japanese Patent No. 3881290 discloses a plasma processing
apparatus that has an object of performing uniform processing over
a wafer surface and that has a processing chamber for processing a
sample, a vacuum exhaustion unit to reduce a pressure of the
processing chamber, a processing gas supply unit to supply a
processing gas into the processing chamber, a sample holding unit
to hold the sample to be processed in the processing chamber, a RF
bias applying unit to apply a RF bias potential to the sample
holding unit, and a plasma generating unit to generate plasma in
the processing chamber in which a top surface of the sample holding
unit has a step, the sample is mounted on its uppermost stage, a
ring-shaped part made of a dielectric to which a bias electric
potential can be applied is provided on a surface lower than a
sample mounting surface, a top surface of the ring-shaped part is
equal to or lower than the top surface of the sample, and a part
made of a dielectric covers the top surface of the ring-shaped
part.
[0010] Japanese Patent Application Laid-Open Publication No.
2005-260011 discloses a wafer processing apparatus that has an
object of processing the etched profile vertically as far as the
wafer outer periphery and performs a processing on a semiconductor
wafer using plasma, in which a wafer stage for mounting a wafer is
made of a conductive material having a convex shape as a wafer
mounting part, and is configured to have a disk to which a radio
frequency electric field is applied and a ceramic-made dielectric
film attached to a surface of the disk, the convex part has a
smaller diameter than a diameter of the wafer, and a ring-shaped
part made of a conductor whose inside diameter is larger than a
diameter of the convex part and is smaller than a diameter of the
wafer, whose thickness is less than or equal to the height of the
convex part, and at least to whose top surface a ceramic-made
dielectric film is fixed is attached on the outer periphery of the
convex part.
SUMMARY OF THE INVENTION
[0011] These conventional technologies described above relate to an
electromagnetic problem in a surrounding of the wafer outer
peripheral part in order to reduce an E. E. region, especially to a
technology of improving a curvature of an equipotential surface
formed on the wafer. These conventional technologies are
technologies so as to achieve an uniform etching result by
arranging a ring-shaped conductor, called a radio frequency edge
ring, on an outer peripheral side of the wafer and making a plasma
ion sheath distribution on the wafer uniform from the center to the
outer periphery through adjustment of an electric field
distribution with a conductive part to which electric power is
supplied.
[0012] Through further repeated investigations on the conventional
technological constitution described above, the inventors have
acquired a finding that although a limitation of improvement in the
uniformity is recognized in the surrounding of the wafer peripheral
part, there can be enumerated the following point as its cause.
[0013] That is, in configurations of Japanese patent No. 3881290
and Japanese Patent Application Laid-Open Publication No.
2005-260011, it is premised that a radio frequency bias power
applied to a sample stage couples with plasma through a cover ring
provided on an outer peripheral part of the sample stage, and the
height of a top surface of the radio frequency edge ring arranged
at the outer periphery of the wafer is set to be equal to or lower
than a top surface of the sample. That is, the RF bias power is
coupled with the plasma though the cover ring, the curvature of the
equipotential surface in a surrounding of a wafer outer peripheral
part is corrected by a plasma ion sheath forming on a top surface
of the cover ring.
[0014] Such a cover ring has material and size (thickness) decided
considering several conditions on a design (in view of part shape,
manufacturability, lifetime, etc. on performance) and is provided
on the outer peripheral part of the sample stage. However, there is
a case where the material is limited in consideration of an etching
process, and even if the shape is the optimum, in some cases, the
applied radio frequency bias power cannot transfer the cover ring
that is formed a certain finite thickness, that is, the electric
power for bias supplied to the cover ring and the plasma cannot
couple with each other, and it may be impossible to form an
expected plasma ion sheath on the top surface of the cover ring,
namely, to form the plasma ion sheath having the same thickness as
that of the plasma ion sheath on the wafer surface.
[0015] In such a case, since the plasma ion sheath is not formed
with a desired thickness on the surrounding of the wafer outer
periphery, it is difficult to correct the curvature of the
equipotential surface to a desired shape. Therefore, it is
difficult to make a trajectory of charged particles from the plasma
that is induced towards a wafer top surface in the E.E. region be
in an allowable range including perpendicularity to the wafer top
surface by correcting the curvature of the equipotential surface in
the wafer outer edge part and its surrounding in the E.E. region.
Thus, the conventional technology is insufficient to fully improve
the uniformity of an etching rate in an E.E. part, and how to
further make small the E.E. region is not considered
thoroughly.
[0016] FIG. 5A shows a structure using the conventional technology.
A longitudinal section of a sample stage 111 has a convex shape
towards the above in its upper part, and a diameter of the top
surface is made smaller than the diameter of a wafer 112 by about a
few mm. An outer periphery side of the sample stage 111 has a
stepped part (a concave part) that is made lower than the convex
part by one step. On surfaces of the convex part and the stepped
part of the sample stage 111, a dielectric film for electrostatic
chuck whose illustration is omitted is formed.
[0017] On the top surface of the stepped part (the concave part) of
the sample stage 111, a conductive radio frequency ring 117a whose
inside diameter is still larger than the diameter of the wafer 112
is provided with a distance provided from the convex part side face
on the dielectric film. The height of a top surface of the radio
frequency ring 117a is set equal to or lower than that of a wafer
112 top surface.
[0018] Moreover, in order to prevent the convex part outer
peripheral side face of the sample stage 111 and the top surface of
the stepped part (the concave part) of the radio frequency ring
117a from contacting with the plasma, a cover ring 118a made of a
dielectric material is arranged on the stepped part. The cover ring
118a is formed in a tapered shape such that an upper part of its
inner side face opposing an outer periphery of the wafer 112
expands towards the above. An inner side lower part of a cover ring
118a, i.e., a lower portion of the tapered part engages with the
convex part outer periphery of the sample stage 111 and is set
equal to or slightly lower than a wafer mounting surface, so that
when the wafer is mounted on the sample stage, it is positioned
underneath the back side of outer periphery the wafer.
[0019] When the wafer 112 is mounted during plasma processing, this
cover ring 118a reduces, an area of the top surface and side face
of the sample stage 111 in direct contact with the plasma, and
suppresses damage of an electrode surface and depletion of the
electrode surface caused by the plasma. Incidentally, the cover
ring 118a is made of the dielectric material having plasma
resistance, such as quartz and ceramic materials of alumina, etc.
It is thought that the cover ring 118a made of the dielectric acts
as a capacity component to the radio frequency bias applied to the
sample stage 111, and its impedance for the radio frequency bias is
reduced like a conductor.
[0020] When the plasma is generated, a space charge layer called
the plasma ion sheath is formed on a surface of a substance that
comes in contact with the plasma resulting from a mass difference
between electron and ion. By the radio frequency power for bias
being supplied to the wafer 112 from a radio frequency power
generator whose illustration is omitted through the sample stage
111, the radio frequency power make a larger negative electric
potential at the sample stage 111, in other words, the plasma ion
sheath thickness is thicker with applying the radio frequency power
than without applying one. Here, a symbol 201a shown in the figure
shows the equipotential surface in the electric field in the plasma
ion sheath. A symbol 202a shows the trajectory of the ions drawn by
the electric field. A symbol 203a shows a plasma ion sheath region,
and a symbol 204a shows a plasma region.
[0021] In this case, since the cover ring 118a acts as a conductor
to the radio frequency bias, when the top surface of the radio
frequency ring 117a is the same height as the wafer 112 top
surface, the same plasma ion sheath as that on the wafer 112 is
formed also over the cover ring 118a on the radio frequency ring
117a to the plasma. For this reason, as shown in the figure, the
equipotential surface 201a becomes almost parallel to the wafer
112, and in connection with this, the trajectory 202a becomes
almost perpendicular to the wafer 112. Thereby, an etching
processed profile is improved in a surrounding of an outer
peripheral part of the wafer 112.
[0022] However, since the ion also incident to the cover ring 118a
with the same energy as that of the wafer surface, there still
remain problems that particles are generated from the cover ring
118a and depletion of the cover ring 118a is increasing.
[0023] Moreover, depending on a material and a thickness of the
cover ring 118a, there is a case where it cannot be regarded as a
conductor for the radio frequency bias, which is shown in FIG. 5B.
The same symbol as that of FIG. 5A shows the same component, and
its explanation is omitted. A point in which FIG. 5B differs from
FIG. 5A is a point that a cover ring 118b is specified to be one
through which a radio frequency electric field cannot penetrate, or
is difficult to transfer. In this case, since the radio frequency
bias does not transfer above the cover ring 118b on the radio
frequency ring 117a, it does not act to the electrons and ions in
the plasma. For this reason, the potential of the plasma ion sheath
over the cover ring 118b becomes equal to a plasma ion sheath
potential produced only by the plasma, and the plasma ion sheath is
a thin thickness. Thereby, as shown in the figure, an equipotential
surface 201b in the electric field in the plasma ion sheath curves
downward and becomes low in the outer peripheral part of the wafer
112. By this gradient of the equipotential surface, a trajectory
202b of the ions drawn by the electric field is bending obliquely
from the outside on the surrounding of the outer peripheral part of
the wafer 112.
[0024] Thereby, the etching profile is impaired in the surrounding
of the outer peripheral part of the wafer 112. That is, since the
ions are not incident perpendicularly on the wafer 112 in an outer
peripheral edge of the wafer 112 but are incident on the wafer 112
with a certain angle, an etched profile cannot keep the vertical
shape. Moreover, when comparing with that of the center side (a
region other than the outer peripheral part) of the wafer 112, the
number of the ions incident on the outer peripheral part (E. E.
part) of the wafer 112 increases, and the etching rate of the outer
peripheral part (E. E. part) of the wafer 112 increases. For this
reason, the etching rate in the outer peripheral part (E. E. part)
of the wafer 112 is different from the etching rate of the central
side portion of the wafer 112, and in-wafer uniformity of a
processing characteristic of the wafer 112 will be degreased.
[0025] Moreover, since the height of the equipotential surface in
the radio frequency ring part is set equal to or lower than the
wafer top surface, when the radio frequency bias power supplied to
the sample stage varies, the plasma ion sheath potential on the
wafer varies accordingly, and the plasma ion sheath potential
difference between on the wafer and the radio frequency ring part
outside the wafer outer periphery, as it is, affects the
equipotential surface in the plasma ion sheath, i.e., a shape of
the whole equipotential surface above the wafer is bended by each
power setting, it is getting more difficult to set process recipe
under different power setting at each etching step.
[0026] The object of the present invention is to provide a plasma
processing apparatus and its method that can improve uniformity of
a fine processing performance and improving an etching performance
of the edge exclusion (E. E.) region.
[0027] The above-mentioned object is achieved by a plasma
processing apparatus for processing a sample placed on the sample
stage by generating plasma in the processing chamber to which a
processing gas is supplied and that is exhausted to reduce its
pressure to a predetermined pressure and at the same time by
applying the radio frequency bias to the sample stage provided in
the processing chamber, in which a conductor ring to which the
radio frequency bias is applied is provided outside the sample
outer periphery on the sample stage to which the radio frequency
bias is applied, the conductor ring is covered with a dielectric
cover that controls the plasma ion sheath formed above it to
substantially have the plasma ion sheath potential produced only by
plasma generation, and the height of the equipotential surface in
the lowermost part in the plasma ion sheath above the conductor
ring is set higher than the top surface of the sample placed on the
sample stage.
[0028] Moreover, the above-mentioned object is achieved by a plasma
processing apparatus that has the processing camber that is placed
in the vacuum vessel and whose interior is decompressed, and the
sample stage that is placed in this processing chamber and holds a
wafer to be processed mounted on its top surface, and processes the
wafer using plasma formed in the processing chamber while applying
the radio frequency bias power thereto, in which the apparatus has
a ring-shaped part made of a conductor that is arranged in a
stepped part arranged encircling the wafer placed on the sample
stage on an outer periphery side of a plane holding the wafer and
to which the radio frequency bias power applied to an electrode in
the sample stage is applied, and the cover that is arranged in the
stepped part covering the top surface and the inner periphery side
of the ring-shaped part and is comprised of a dielectric material,
the radio frequency power applied to the ring-shaped part is not
coupled to the plasma, and a top surface of the ring-shaped part is
set higher than the wafer top surface.
[0029] Moreover, the above-mentioned object is achieved by a plasma
processing method having the steps of: generating plasma in a
processing chamber to which a processing gas is supplied and that
is exhausted to reduce its pressure to a predetermined pressure,
applying a radio frequency bias to the sample stage provided in the
processing chamber, and therefore processing a sample placed on the
sample stage, in which the plasma ion sheath formed outside a
sample outer periphery of the sample stage to which the radio
frequency bias is applied is controlled to substantially have the
plasma ion sheath potential produced only by the plasma generation,
and the height of an equipotential surface at a lowermost part in
the plasma ion sheath outside a sample periphery is set higher than
the top surface of the sample to effect the processing of the
sample.
[0030] Moreover, the above-mentioned object is achieved by a plasma
processing method having the steps of: placing and holding the
wafer to be processed on a top surface of a sample stage arranged
in the processing chamber whose interior is decompressed, and
applying the radio frequency bias power to an electrode arranged in
the sample stage from the radio frequency power supply, in which
the sample stage has a ring-shaped part made of a conductor that is
arranged in the stepped part arranged encircling the wafer on the
outer periphery side of the plane holding the wafer and to which
the radio frequency bias applied to an electrode in the sample
stage is applied, and a cover comprised of the dielectric material
arranged in the stepped part covering a top surface and an inner
periphery side of the ring-shaped part, the top surface of the
ring-shaped part being set higher than the wafer top surface, and
the radio frequency bias power applied to the ring-shaped part is
uncoupled to the plasma.
[0031] Moreover, the above-mentioned object is achieved by a plasma
processing method of processing a sample, having the steps of:
generating plasma in a vacuum vessel that is exhausted to
decompress its pressure to a predetermined pressure, and at the
same time applying the radio frequency bias to the sample stage on
which a sample is mounted in the vacuum vessel and a conductor ring
provided to encircle the sample outside the sample mounting surface
of the sample stage, in which the conductor ring is covered with a
dielectric cover, an electric potential of the plasma ion sheath
formed above the conductor ring by application of the radio
frequency bias is substantially set to an electric potential
produced by the plasma generation, the thickness of the plasma ion
sheath is thinned, the height of the equipotential surface below
the plasma ion sheath is set higher than the equipotential surface
of a processing surface of the sample to effect the processing of
the sample.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a vertical sectional view schematically showing an
outline of a configuration of a plasma processing apparatus that is
one embodiment of the present invention.
[0033] FIG. 2 is a vertical sectional view schematically showing an
electric field distribution in the vicinity of a wafer outer edge
part of a sample stage in the apparatus shown in FIG. 1.
[0034] FIG. 3 is a graph showing a relationship (lower limit) of a
height of a radio frequency ring top surface from a top surface of
the sample stage to a distance between a wafer outer peripheral
edge of the apparatus and an inner peripheral edge of a radio
frequency ring shown in FIG. 1.
[0035] FIG. 4 is a graph showing an etching rate distribution of
the outer peripheral part when the wafer is processed by the
apparatus shown in FIG. 1.
[0036] FIGS. 5A and 5B are longitudinal sectional view
schematically showing an electric field distribution in the
vicinity of a wafer outer edge part of the sample stage in the
plasma processing apparatus by the conventional technology.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0037] The present invention makes a plasma ion sheath formed
outside a wafer outer periphery of a sample stage to which a radio
frequency bias is applied substantially have a plasma ion sheath
potential produced only by plasma generation, and sets the height
of an equipotential surface by an electric field in the plasma ion
sheath outside the wafer outer periphery higher than a wafer top
surface. That is, the thickness of the plasma ion sheath outside
the wafer outer periphery is set to be constant irrespective of a
magnitude of a radio frequency bias power, and in this state, the
equipotential surface is set higher than the wafer top surface, so
that depression of the equipotential surface is suppressed in a
wafer outer peripheral part. By this, an influence of alteration of
the radio frequency bias power is reduced, and an incident angle of
ions incident on the wafer outer peripheral part (E. E. region) is
kept substantially perpendicularly.
[0038] Hereafter, an embodiment carried out by the present
invention will be explained using drawings.
Embodiment
[0039] Below, an embodiment of the present invention will be
explained using FIG. 1 to FIG. 4. FIG. 1 is a longitudinal
sectional view schematically showing an outline of a configuration
of a plasma processing apparatus according to the embodiment of the
present invention. The plasma processing apparatus of this
embodiment shows an etching processing apparatus for forming plasma
(microwave ECR plasma) using ECR (Electron Cyclotron Resonance) by
microwave.
[0040] The plasma processing apparatus is constructed as follows in
this case. A disk-shaped dielectric window 102 made of, for
example, quartz is provided in an upper opening of a vacuum vessel
101 whose interior is of a cylindrical shape. A shower plate 103
made of a dielectric (for example, made of quartz) in which
multiple through holes for introducing a gas for etching were
provided is arranged below the dielectric window 102. A supply path
of a gas is formed between the shower plate 103 and the dielectric
window 102, and is linked with a gas supply device 104. A vacuum
exhaust port 105 is arranged in a lower part of the vacuum vessel
101 and is connected with a vacuum exhaust system 106.
[0041] Above the dielectric window 102, a waveguide 107 for
transmitting a microwave electromagnetic field into the vacuum
vessel 101 is arranged. A magnetron 108 for oscillating a microwave
is arranged at an end of the waveguide 107. A magnetic field
generating coil 109 for forming a magnetic field in its interior is
arranged in the outer peripheral part of the vacuum vessel 101. The
electromagnetic field oscillated by the magnetron 108 is converted
into a predetermined electric field mode in an expanded waveguide
part for resonance that is formed at an other end after propagating
through the waveguide 107, which subsequently transfers the
dielectric window 102 and the shower plate 103 and is introduced
into a processing chamber 110 formed between the shower plate 103
and a sample stage 111.
[0042] Although the frequency of the microwave is not limited in
particular, this embodiment uses 2.45-GHz microwave. The electric
field of the microwave introduced into the processing chamber 110
excites a gas for etching that was supplied to the processing
chamber 110 through the shower plate 103 by an interaction with the
magnetic field produced by the magnetic field generating coil 109
to generate plasma in the processing chamber 110.
[0043] In the interior of the vacuum vessel 101, the sample stage
111 that faces the dielectric window 102 is arranged to have a
distance below the shower plate 103 so that the processing chamber
110 may be formed. In the sample stage 111, its top surface is
covered with a coat (illustration being omitted) of a dielectric
material that is formed by thermal spraying, and a sample to be
processed, in this case a wafer 112, is mounted and held on the top
surface of the coat. A mounting surface on which the wafer 112 is
mounted faces the dielectric window 102 and the shower plate
103.
[0044] The sample stage 111 is formed in a convex shape whose top
surface has a slightly smaller outside diameter than the wafer
diameter and has a substantially circular plane. Although
illustration is omitted, inside the coat made of the dielectric on
a top surface of the convex part, a sheet-shaped electrode for
electrostatic attraction comprised of a conductor material is
arranged. A direct current power generator 116 is connected to the
electrode for electrostatic chuck through a radio frequency filter
circuit 115. Furthermore, the sample stage 111 forms an
approximately cylindrical shape, and is arranged with its axis
aligned with an axis of the vacuum vessel 101, and there is an
electrode for radio frequency bias application below the coat made
of the dielectric. A radio frequency power generator 114 is
electrically connected to the electrode for radio frequency bias
application through a matching circuit 113. In this case, the radio
frequency bias power supplied from the radio frequency power
generator 114 has a frequency in a range of about a few hundreds Hz
to 50 MHz, more preferably, in a range of 400 Hz to 40 MHz.
[0045] FIG. 2 shows a detailed structure of surroundings of a wafer
mounting part of the sample stage 111. In this figure, the same
symbol shows the same component in FIGS. 5A, 5B, and its
explanation is omitted. A point in which this figure is different
from FIG. 5B is that as compared with a case where the height of
the top surface of a radio frequency ring 117 of FIG. 5B is set
equal to or lower than a top surface of the wafer 112, the height
of a top surface of the radio frequency ring 117 is set higher than
the wafer top surface, having a distance of height h from the wafer
mounting surface of the sample stage 111. Moreover, the inside
diameter of the radio frequency ring 117 is larger than the outside
diameter of the convex part of the sample stage 111, and is
arranged having a distance d from an outer periphery of the wafer
112. The radio frequency ring 117 is arranged forming a shape that
is a circle or is a set of multiple arcs linked together so that it
may encircle the convex part of the sample stage 111 when seeing
from the above. For a material of this radio frequency ring 117, a
metal having conductivity, for example, aluminum, can be used. On
the surface of the radio frequency ring 117, anodizing (alumite
etc.) in order to suppress a surface reaction, abnormal discharge,
etc. and a surface treatment of covering a body with a coating film
of a dielectric, such as by flame spraying, is performed.
[0046] By the radio frequency ring 117 being conductive, the radio
frequency bias power applied on the sample stage 111 is also
transferred to the radio frequency ring 117 (the conductor ring),
and the electric potential produced on the top surface of the radio
frequency ring 117 (the conductor ring) becomes equal to the
electric potential of the top surface of the convex part of the
sample stage 111.
[0047] In order to make the sample stage 111 and the radio
frequency ring 117 have the same potential, an electrode part of
the sample stage 111 that is connected with the radio frequency
power generator 114 and the radio frequency ring 117 are
electrically connected in this case. As a method for electric
connection, there are multiple methods as follows: the two
conductive materials are made to connect with each other (being
metal touched); the radio frequency ring 117 is fastened to the
sample stage 111 with a bolt comprised of a conductive part; a
conductive part contacting with these surfaces is arranged between
the two parts; etc. Incidentally, although the radio frequency ring
117 was electrically connected with the electrode of the sample
stage 111 in this case, it is important to transfer the radio
frequency power to the radio frequency ring. As the one of the
method, there is an insulating material between the radio frequency
ring and the sample stage. Furthermore, the radio frequency ring
117 does not need to be a separate part, and it may be a
single-piece type such that an outside part of the convex part of
the sample stage 111, i.e., a part of the stepped part (convex
part) may be protruded to be a ring shape.
[0048] In the stepped part outside of the convex part of the sample
stage 111, a cover ring 118 (a dielectric cover) that covers the
radio frequency ring 117 and is a ring-shaped part made of a
dielectric having a material or thickness that does not allow the
radio frequency bias from the radio frequency ring 117 to transfer
is arranged. In this case, the cover ring 118 is comprised of
quartz. Incidentally, the inner periphery side of the cover ring
118 that faces the wafer 112 has the same shape as that of the
cover ring 118b in FIG. 5B.
[0049] In the apparatus constructed as described above, the wafer
112 is conveyed into the vacuum vessel 101 by a conveying device
whose illustration is omitted, and is mounted on the sample stage
111. The wafer 112 placed and held on the sample stage 111 is
etching processed by plasma generated in the processing chamber 110
and by the radio frequency bias applied to the sample stage
111.
[0050] In doing this, when the plasma is formed in the processing
chamber 110 above the sample stage 111, at the same time a radio
frequency power is applied to an electrode for radio frequency bias
application of the sample stage 111 from the radio frequency power
generator 114, and the radio frequency bias is applied to the wafer
112 through a dielectric film on a top surface of the sample stage
111; the plasma ion sheath is formed between the wafer 112 and the
plasma, and a self bias potential is generated at the wafer 112.
The ions (charged particles) in the plasma are drawn towards a
wafer 112 top surface by this self bias electric potential, and
etching layers on the wafer 112 is etching processed by the ions
colliding the wafer 112. Incidentally, although not illustrated,
while the etching process, a gas for heat transfer for promoting
heat transmission, such as helium, is introduced between the
backside of the wafer 112 and the sample stage 111 controlled to a
prescribed temperature.
[0051] According to the radio frequency ring 117 (the conductor
ring) and the cover ring 118 (the dielectric cover) of this
apparatus, plasma is generated in the processing chamber 110, the
radio frequency bias is applied to the sample stage 111, and a
plasma region 204 and a plasma ion sheath region 203 as shown in
FIG. 2 are formed. That is, by the radio frequency bias applying on
the wafer 112, there is a large electric potential difference at an
ion sheath, in other words, the ion sheath is thick, at over the
cover ring 118 that is an outer peripheral part of the wafer 112
and among the radio frequency ring 117, there is a small electric
potential difference at the ion sheath, in other words, the sheath
thickness is thin. The equipotential surface in this ion sheath is
shown by a symbol 201. In this plasma ion sheath region 203, the
ions are accelerated perpendicularly to the equipotential surface
201, which makes an ion trajectory shown by a symbol 202. A density
of the equipotential surfaces 201 becomes a large density on the
wafer 112, and becomes a small density over the cover ring 118. For
this reason, if a top surface height h of the top surface of the
radio frequency ring 117 is lower than the wafer top surface, the
depression (curvature) of an upper equipotential surface in the
wafer outer peripheral part will become large.
[0052] Here, by the height of the top surface of the radio
frequency ring 117 higher than the wafer 112 top surface, the
depression of the whole equipotential surface in the outer
peripheral part of the wafer 112, in other words, a curvature of
the equipotential surface is suppressed (relaxed). Moreover, in
this embodiment, there is a distance d between the wafer 112 outer
periphery and the radio frequency ring 117, a position of the
equipotential surface falls in the gap of the distance d, but this
can be improved by making the height of the top surface of the
radio frequency ring 117 higher: the position is improved so as to
get closer to the wafer 112 top surface in parallel. For example,
in order to suppress the curvature of the equipotential surface in
the vicinity of an outer peripheral edge of the wafer 112 and to
make it become parallel to the wafer 112, the height of the top
surface of the radio frequency ring 117 of this embodiment is made
such that its height h from the top surface of the sample stage 111
shall be higher than the wafer 112 top surface and less than or
equal to 5.0 mm.
[0053] Incidentally, when the top surface of the radio frequency
ring 117 is lower than the wafer 112 top surface, the hanging (the
depression) of the equipotential surface in the vicinity of the
outer peripheral edge of the wafer 112 cannot be suppressed, and
therefore it becomes difficult to bring the wafer 112 and the
equipotential surface closer in parallel in a wafer 112 outermost
periphery. By setting the inside diameter of the radio frequency
ring 117 to be within a predetermined distance to the outside
diameter of the wafer 112, it is possible to suppress the hanging
of the equipotential surface in the vicinity of the outer
peripheral edge of the wafer 112. In this case, the distance d
between the inner peripheral edge of the radio frequency ring 117
and the outer peripheral edge of the wafer 112 is set to be not
less than 1.0 mm and not more than 10 mm. This is because if it is
smaller than 1.0 mm, it is easy to discharge at the distance d; if
it exceeds 10 mm, the depression of the equipotential surface will
become large and an effect of the radio frequency ring will become
impossible to be expected.
[0054] Since the equipotential surface 201 is curved slightly
towards the stepped part (a concave part) of the sample stage 111
(in a downward direction of the figure) in the gap of the distance
d, the equipotential surface 201 is curved slightly in the outer
peripheral edge of the wafer 112, which makes the trajectory 202 of
the charged particles, such as the ions, incident on the wafer 112
not perpendicular to the wafer, becoming slightly inclined. Since
when the gap distance d becomes larger, the curvature of the
equipotential surface 201 also increases, in order to bring the
trajectory 202 close to be more perpendicular, it is necessary to
increase the height h of the top surface of the radio frequency
ring 117 from the top surface of the sample stage 111.
[0055] In this case, thickness of the dielectric part of the cover
ring 118 that covers the top surface of the radio frequency ring
117 is set in a range of 1.0 to 5.0 mm inclusive. This is because,
if the thickness of the cover ring 118 above the radio frequency
ring 117 is smaller than 1.0 mm, it will be undesirable that the
radio frequency bias power will transfer the cover ring 118 and
couples with the plasma and the cove ring has degradation strength
in the point of materials view and manufacturing view. Moreover,
this is because, if the thickness is equal to or less than 5.0 mm,
the covering 118 will act as a step to the wafer 112 and disturb
gas flow on the wafer surface, which will easily cause a problem,
such as byproducts generated from the wafer surface by etching
reaction has a long residence time. As an upper limit to form this
step, it is desirable that the height of a top surface of the cover
ring 118 to the wafer 112 surface is 10 mm or less.
[0056] In this embodiment, since there is a distance d between the
wafer 112 outer periphery and the radio frequency ring 117, a
position of the equipotential surface in the vicinity of the wafer
112 falls slightly in the wafer outer peripheral part. Moreover,
the plasma ion sheath over the cover ring 118 becomes thin. For
this reason, the top surface of the radio frequency ring 117 is set
higher than the wafer 112 top surface, so that the equipotential
surface in the vicinity of the wafer 112 may be raised in the wafer
outer peripheral part and the depression of the equipotential
surface above the plasma ion sheath region 203 may be lessened.
Thereby, a gradient of the ions accelerated in the upper part of
the plasma ion sheath region 203 of the outer peripheral part of
the wafer 112, in other words, the incident ion from the outside
has small gradient. That is, the equipotential surface in the
vicinity of the wafer 112 is aligned parallel to the wafer, and an
incident direction of the ions accelerated in the plasma ion sheath
region 203 becomes substantially more perpendicular to a processing
surface of the wafer 112.
[0057] Moreover, in the etching process, the radio frequency bias
power is altered according to processing conditions. If the radio
frequency bias power is large, the plasma ion sheath will become
thick; if the electric power becomes small, the plasma ion sheath
will become thin. Since in accordance with this, when the radio
frequency bias power is large, a difference of the plasma ion
sheath thickness between the inner side and the outer side on the
wafer 112 becomes large; therefore, the gradient of an oblique
component of the ions incident perpendicularly to the equipotential
surface in the upper part of the plasma ion sheath region 203 of
the outer peripheral part of the wafer 112 becomes large. Moreover,
since when the radio frequency bias power is small, the difference
of the plasma ion sheath thickness between the inner side and the
outer side on the wafer 112 becomes small, the gradient of the
oblique component of the ions incident perpendicularly on the
equipotential surface in the upper part of the plasma ion sheath
region 203 of the outer peripheral part of the wafer 112 becomes
small. Therefore, when the radio frequency bias power is small, the
ions incident on the wafer 112 top surface become almost
perpendicular, but when the radio frequency bias power becomes
large, the ions incident on the wafer 112 top surface become easy
to have a gradient component.
[0058] In this embodiment, by setting the top surface of the radio
frequency ring 117 higher than the wafer 112 top surface as shown
in FIG. 2, a difference between the height of the equipotential
surface of the plasma ion sheath region 203 above the wafer 112 and
the height of the equipotential surface above the radio frequency
ring 117 becomes small compared with a case where the top surface
of the radio frequency ring 117 is the same as the wafer 112 top
surface; therefore, the influence of alteration of the radio
frequency bias power can be reduced.
[0059] In consideration of these respects and in addition through
an electric field analysis in the vicinity of the outer peripheral
edge of the wafer 112 and an evaluation of an etching rate, a
height of the top surface of the radio frequency ring 117 is
optimized, and an evaluation by the present inventors makes clear a
relationship between the height h and the distance d about the
radio frequency ring 117 described above. FIG. 3 shows this. It is
found that taking the distance d between the inner peripheral edge
of the radio frequency ring 117 and the outer peripheral edge of
the wafer 112 on the X-axis and taking the height h of the top
surface of the radio frequency ring 117 from the top surface of the
sample stage 111 on the Y-axis, an optimum value of the top surface
height h of the radio frequency ring 117 to bring the equipotential
surface above the outer peripheral edge of the wafer 112 close to
the wafer 112 top surface in parallel varies in proportion to the
distance d, and in this case, the present inventors have found that
it is good just to vary an incremental size of the height h with a
gradient of 1/2 with respect to the incremental size of the
distance d. This optimum value is shown by a line 301.
[0060] Incidentally, in the case where the height h of the radio
frequency ring is lower than the optimum value with respect to the
distance d, if the radio frequency bias power becomes large, the
gradient angle by which the equipotential surface above the plasma
ion sheath region 203 of the outer peripheral part of the wafer 112
depresses to the outside will take a direction of becoming large,
namely, the curvature of the equipotential surface of the outer
peripheral part of the wafer 112 will become large and many of the
ions incident having a gradient will tend to gather on the outer
peripheral part of the wafer 112.
[0061] For this reason, the ions act so that the etching rate in
the outer peripheral part of the wafer 112 may become high. On the
other hand, in the case where the height h of the radio frequency
ring is higher than the optimum value with respect to the distance
d, if the radio frequency bias power becomes small, the
equipotential surface in the lower part of the plasma ion sheath
region 203 of the outer peripheral part of the wafer 112 will have
a gradient angle taking a direction of raising towards the outside,
and the ions incident towards the wafer top surface 112 will be
guided to the outside of the wafer 112 outer periphery, so that the
ions incident on the outer peripheral part of the wafer 112 will
tend to decrease. For this reason, the ions act so that the etching
rate in the outer peripheral part of the wafer 112 may
decrease.
[0062] FIG. 4 shows one example of an etching rate result in the
case where the wafer 112 is processed using a plasma processing
apparatus having the radio frequency ring 117 and the cover ring
118 that are thus optimized. In this case, a material to be etched
was specified to be a silicon nitride film, and tetrafluoromethane
gas, oxygen gas, and trifluoromethane gas were used as etching
gases, for example.
[0063] A curve 401 shows an in-wafer distribution of the etching
rate when the etching is processed with a conventional structure of
the wafer peripheral part shown in FIG. 5B, especially that of the
wafer outer peripheral part (E. E. part). A curve 402 shows an
in-wafer distribution of the etching rate when the etching is
processed with a structure of this embodiment, especially, that of
the wafer outer peripheral part (E. E. part).
[0064] As shown by the curve 401, when the etching is performed
with the conventional structure, the etching rate of the outer
peripheral part of the wafer 112 increases rapidly and in-wafer 112
uniformity decreases. On the other hand, it is shown that by
adopting a structure of this embodiment as shown by the curve 402,
rapid increase of the etching rate in the peripheral part of the
wafer 112 is suppressed and the in-wafer 112 etching rate
uniformity is improved.
[0065] As described above, according to this embodiment, by using
the radio frequency ring 117 that has the top surface higher than
the wafer top surface placed on the sample stage and the cover ring
118 that does not allow the radio frequency bias to transfer to the
plasma substantially, the plasma ion sheath formed outside the
wafer outer periphery of the sample stage to which the radio
frequency bias is applied is made to have substantially the plasma
ion sheath potential produced only by the plasma generation, the
thickness of the plasma ion sheath outside the wafer outer
periphery is set to be constant irrespective of largeness of the
radio frequency bias power, and the equipotential surface is made
higher than the wafer top surface in this state. By this, as
compared with a case where the height of the top surface of the
radio frequency ring is equal to that of the wafer top surface, it
is possible to make small the difference between the height of the
equipotential surface above the wafer in the plasma ion sheath
region and the height of the equipotential surface above the radio
frequency ring, so that the influence of alteration of the radio
frequency bias can be reduced, and it is possible to suppress the
depression of the equipotential surface in the wafer outer
peripheral part. By this, it is possible to make substantially
perpendicular the incident angle of the ions incident on the wafer
outer peripheral part (E. E. region) with a reduced influence of
alteration of the radio frequency bias power, and to better the
uniformity of device performance by improving an etching
performance of the edge exclusion (E.E.) region. That is, by making
the radio frequency ring 117 have a top surface higher than the
wafer top surface, it is possible to let the equipotential surface
above the wafer 112 to have a smaller curvature angle towards the
lower side to the radio frequency ring 117 in the outer peripheral
edge of the wafer 112 and its outer peripheral side, namely, it is
possible to suppress the curvature and to align parallel to the
wafer 112 top surface. In other words, by raising the equipotential
surface above the radio frequency ring 117 to a higher position
than that above the wafer surface in the vicinity of the wafer 112
outer periphery, it is possible to let the equipotential surface
above the wafer 112 to have a smaller curvature angle showing
depression downward between the outer peripheral edge of the wafer
112 (including its outer periphery side) and the radio frequency
ring 117. Moreover, by using the cover ring 118 that does not allow
the radio frequency bias to transfer to the plasma, it is possible
to thin the thickness of the plasma ion sheath over the cover ring
118. Thereby, the equipotential surface outside the wafer 112 outer
periphery can be made constant (fixed) to the radio frequency bias,
and it becomes easy to set the height of the top surface of the
radio frequency ring 117 without being affected by processing
conditions, especially by the radio frequency bias power.
[0066] By this, as shown in FIG. 2, the equipotential surface 201
is kept parallel to the wafer 112 from a wafer 112 central part to
its outer peripheral edge, and it is possible to make the
trajectory 202 of the ions that are incident perpendicularly on the
equipotential surface substantially perpendicular to the wafer 112
on its top surface as far as the outside of the outer peripheral
edge of the wafer 112. Therefore, the number of the ions incident
on the outer peripheral edge from the wafer 112 central part can be
made uniform, and the etching rate can be made uniform in a wafer
112. That is, the uniformity of the etching rate from the wafer 112
central part to the outer peripheral edge (E. E. part) is
improvable.
[0067] Moreover, the ions are incident on the wafer 112
perpendicularly also in the outer peripheral edge of the wafer 112
and an etched profile becomes a vertical shape. By this, the etched
profile can be controlled with high precision, and impairment of
electric characteristics and performance of the semiconductor
device in the outer peripheral edge of the wafer 112 is suppressed,
which brings about an effect of raising a yield.
[0068] Moreover, according to this embodiment, the electric
potential on the wafer 112 and the surface potential of the radio
frequency ring 117 are always equal, and the curvature of the
equipotential surface of the outer peripheral part of the wafer 112
can be suppressed even when the processing conditions to the wafer
112, especially the radio frequency bias power, may change. That
is, even when the processing conditions alter, it is possible to
make the equipotential surface in the vicinity of the outer
peripheral part of the wafer 112 parallel to the wafer 112 even if
the size of the radio frequency ring 117 is not optimized each
step, which improves an efficiency of the plasma etching.
[0069] Moreover, in this embodiment, the thickness and material
(dielectric constant) of the dielectric part of the cover ring 118
are decided so that the radio frequency bias power applied to the
radio frequency ring 117 may not couple with the plasma through the
cover ring 118 and may not form the plasma ion sheath without
applying the radio frequency bias power on the surface of the
dielectric part. Thereby, not the plasma ion sheath formed when the
radio frequency bias is applied but the plasma ion sheath that has
about plasma potential produced only by the plasma generation is
formed on the surface of the cover ring 118 above the radio
frequency ring 117 of this embodiment. The thickness of this plasma
ion sheath becomes the same thickness as the thickness of the
plasma ion sheath formed on the wafer 112 top surface when the
plasma is formed in the processing chamber 110 with the radio
frequency bias power being not supplied to the sample stage 111. By
this, a sputtering and an etching by ions on the cover ring 118 top
surface are reduced, and depletion of the cover ring 118 lessens,
which prolongs the lifetime.
[0070] Incidentally, in the above-mentioned embodiment, when a
ratio of an impedance to the plasma of the radio frequency bias
power supplied to the electrode part in the sample stage 111
through the mounting surface on which the wafer 112 is mounted and
the wafer 112 and an impedance to the plasma through a radio
frequency ring 117 and a cover ring 118 made of a dielectric above
it (a ratio of the latter to the former) is five or more, it can be
considered that there is no coupling with the plasma of the latter,
that is, the radio frequency bias power from the radio frequency
ring 117 does not transfer to the plasma practically.
[0071] Moreover, this embodiment is a plasma processing apparatus
that has the vacuum vessel forming a processing chamber into which
a processing gas is supplied and whose interior is exhausted to
reduce its pressure to form plasma of the processing gas, the
sample stage that is placed in this processing chamber and holds a
wafer to be processed on its top surface, and the convex-shaped
electrode that constitutes a wafer holding part of the sample stage
and is connected with the radio frequency power generator and to
which the radio frequency bias power is applied, and processes the
wafer using the plasma generated in the processing chamber while
applying the radio frequency bias power thereto, characterized in
that the plasma processing apparatus has the ring-shaped part made
of the conductor that is arranged in a stepped part formed on an
outer periphery side of the wafer holding surface of the electrode
encircling the convex part of the electrode and applies the radio
frequency bias power applied to the electrode, and the cover made
of the dielectric that is arranged in the stepped part covering a
top surface and an inner periphery side of the ring-shaped part,
the cover substantially blocking transition of the radio frequency
power from the ring-shaped part to which the radio frequency power
is applied to the plasma, and the top surface of the ring-shaped
part is set higher than the wafer top surface placed on the sample
stage.
[0072] Moreover, this embodiment is a plasma processing method
having the steps of: placing and holding the wafer to be processed
on the top surface of the sample stage arranged in the processing
chamber whose interior is decompressed, forming plasma of a
processing gas in the processing chamber, and processing the wafer
while applying the radio frequency bias power to the sample stage
from the radio frequency power generator, characterized in that in
a stepped part formed on an outer peripheral side of the wafer
holding surface of the sample stage, the ring-shaped part made of
the conductor that encircles a convex part that is its inside and
has a top surface higher than the top surface of the wafer held on
a wafer holding surface and the cover made of the dielectric
material that covers a top surface and an inner periphery side of
the ring-shaped part are arranged, the radio frequency bias is
applied to the wafer through the sample stage, the cover cut off a
transition of the radio frequency bias to the plasma during etching
process.
[0073] Although, in the above embodiment, the etching apparatus
using the microwave ECR electric discharge was explained as an
example, the same action effect is achieved also in dry etching
apparatuses using other electric discharges (effective magnetic
field UHF electric discharge, capacity coupling type electric
discharge, inductive coupling type electric discharge, magnetron
electric discharge, surface wave excitation electric discharge,
transfer coupled electric discharge). Moreover, in the
above-mentioned embodiment, although the etching apparatus was
described, the same action and effect are given to other plasma
processing apparatuses performing the plasma processing using the
radio frequency bias, for example, a plasma CVD apparatus, an
ashing apparatus, and a surface reforming apparatus, etc.
[0074] Incidentally, the present invention is not limited to the
above-mentioned embodiment, and may include various modifications.
For example, the embodiment described above was explained in
detailed just to give comprehensible explanations of the present
invention and they are not necessarily limited to one that has the
entire configuration being explained.
* * * * *