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Claims  |
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What is claimed is:
1. A plasma processing apparatus comprising:
a chamber having a gas inlet port and a gas discharge port;
supporting means, disposed in said chamber, for supporting an object to be
processed which has a surface to be processed;
a flat coil provided to oppose the surface to be processed of the object
which is supported by said supporting means, with a gap therebetween;
RF power supply means for supplying an RF current to said coil, thereby
generating a plasma in said chamber between said coil and said supporting
means; and
directing means, provided to said supporting means to surround the object
to be processed, and having a projecting portion projecting toward said
coil past the surface to be processed of the object to be processed, and
including an electrical insulator or a high resistance, for focussing the
plasma in a direction substantially parallel to the surface of the object
to be processed;
wherein said directing means has an outer annular member consisting of an
electrical insulator or a high ohmic resistance, and an inner annular
member arranged between said outer annular member and the object to be
processed and consisting of a conductor.
2. An apparatus according to claim 1, wherein said outer annular member
projects more toward said coil than said inner annular member.
3. An apparatus according to claim 1, further comprising:
temperature adjusting means for adjusting a temperature of said supporting
means;
gas supply means for supplying a heat transfer gas, that transfers heat of
said temperature adjusting means to the object to be processed, to a
portion between said supporting means and the object to be processed;
pressure detecting means for detecting a pressure of the supplied gas and
generating a signal corresponding to the pressure; and
control means for adjusting a gas supply amount of said gas supply means
based on the signal from said pressure detecting means, thereby
controlling heat transfer of the gas to the object to be processed.
4. An apparatus according to claim 3, wherein said control means controls
the gas supply amount such that the temperature of the object to be
processed is constant during processing.
5. An apparatus according to claim 3, further comprising temperature
detecting means for detecting the temperature of said supporting means and
generating a signal corresponding to the detected temperature, wherein
said control means adjusts the gas supply amount of said gas supply means
based on the signals from said temperature detecting means and said
pressure detecting means.
6. An apparatus according to claim 1, wherein said supporting means
comprises an electrostatic chuck for supporting the object to be processed
by electrostatic chucking said electrostatic chuck having an outer layer
consisting of a material having a high resistance against a reactive ion
and an electrode provided in said outer layer.
7. An apparatus according to claim 6, wherein said outer layer of said
electrostatic chuck consists of one member selected from the group
consisting of a ceramic, quartz, and an insulating polymer.
8. An apparatus according to claim 1, wherein said supporting means has a
housing counter electrode, and an RF bias energy having a frequency of 1
to 3 MHz is applied to said electrode.
9. An apparatus according to claim 1, comprising means for cooling said
supporting means to -50.degree. to -150.degree. C. during processing of
the object to be processed.
10. An apparatus according to claim 1, comprising means for supplying a gas
mixture containing CH.sub.4 gas, CF.sub.4 gas, and O.sub.2 gas in an
amount of not more than 10% or Ar gas in an amount of not more than 50% in
the ratio of flow rates, or a gas mixture containing NF.sub.3 gas,
CH.sub.4 gas, and O.sub.2 or Ar gas to said chamber through said gas inlet
port, thereby etching the object to be processed.
11. An apparatus according to claim 10, comprising means for heating an
inner surface of said chamber to 50.degree. to 100.degree. C. during
etching.
12. A plasma processing apparatus comprising:
a chamber having a gas inlet port and a gas discharge port;
supporting means, disposed in said chamber, for supporting an object to be
processed which has a surface to be processed;
a flat coil provided to oppose the surface to be processed of the object
which is supported by said supporting means, with a gap therebetween;
RF power supply means for supplying an RF current to said coil, thereby
generating a plasma in said chamber between said coil and said supporting
means; and
directing means, provided to said supporting means to surround the object
to be processed, and having a projecting portion projecting toward said
coil past the surface to be processed of the object to be processed for
focussing the plasma in a direction substantially parallel to the surface
of the object to be processed;
wherein said directing means has an annular plasma focus ring consisting of
an electrical insulator or a high ohmic resistance;
wherein said focus ring has a projecting surface which forms a step farther
from said coil as it is closer to the object to be processed.
13. An apparatus according to claim 12, wherein the step of said projecting
surface of said focus ring has a lower surface and an upper surface
extending from said lower surface toward said coil at an angle of about 90
degrees with respect to said lower surface.
14. A plasma processing apparatus comprising:
a chamber having a gas inlet port and a gas discharge port;
supporting means, disposed in said chamber, for supporting an object to be
processed which has a surface to be processed;
a flat coil provided to oppose the surface to be processed of the object
which is supported by said supporting means, with a gap therebetween;
RF power supply means for supplying an RF current to said coil, thereby
generating a plasma in said chamber between said coil and said supporting
means; and
directing means, provided to said supporting means to surround the object
to be processed, and having a protecting portion projecting toward said
coil past the surface to be processed of the object to be processed for
focussing the plasma in a direction substantially parallel to the surface
of the object to be processed;
wherein said directing means has an annular plasma focus ring consisting of
an electrical insulator or a high ohmic resistance;
wherein said focus ring has a projecting surface which forms a curved
contour;
wherein said curved contour of said projecting surface of said focus ring
has a lower surface which is farther away from said coil as it is closer
to the object to be processed, and an upper surface extending from said
lower surface toward said coil.
15. A plasma processing apparatus comprising:
a chamber having a gas inlet port and a gas discharge port;
supporting means, disposed in said chamber, for supporting an object to be
processed which has a surface to be processed;
an electrode provided to oppose the surface to be processed of the object
which is supported by said supporting means, with a gap therebetween;
RF power supply means for supplying an RF current to said electrode,
thereby generating a plasma in said chamber between said electrode and
said supporting means; and
directing means, provided to said supporting means to surround the object
to be processed, and having a projecting portion projecting toward said
electrode past the surface to be processed of the object to be processed
for focussing the plasma in a direction substantially parallel to the
surface of the object to be processed;
wherein said directing means has an outer annular member consisting of an
electrical insulator or a high ohmic resistance, and an inner annular
member arranged between said outer annular member and the object to be
processed and consisting of a conductor. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma processing apparatus employing
the RF induction technique.
2. Description of the Related Art
In semiconductor wafer processing steps, dry etching is performed for,
e.g., isolation of capacitors and elements and formation of contact holes.
A parallel plate type plasma processing apparatus is known as a
representative of conventional apparatuses that perform dry etching, as
described in Jpn. Pat. Appln KOKAI Publication No. 61-119686.
In this processing apparatus, a rest table or susceptor serving also as a
lower electrode is disposed in an air-tight chamber, and an upper
electrode serving also as a gas supply section is disposed above the rest
table to oppose it.
In this plasma processing apparatus, first, a semiconductor wafer as an
object to be processed is placed on the rest table, and a process gas is
supplied from the gas supply section into the chamber. Simultaneously, an
RF power is applied across the two electrodes by an RF power supply in
order to generate a plasma between these electrodes, thereby etching the
wafer by reactive ions in the plasma.
Recently, the line width of patterns of a semiconductor device is more and
more decreasing. When a plasma is generated in the above apparatus, the
pressure in the chamber is 100 mTorr to 1 Torr. Under this high pressure,
since the mean free time of ions is short, micropatterning is difficult to
perform. Also, although the diameters of wafers are increasing, when the
mean free time of ions is short, a high uniformity of the plasma
distribution over a wide surface cannot be ensured, and thus it is
difficult to uniformly process a wafer having a large diameter.
For this reason, recently, employment of the RF induction method has been
studied. According to this method, as described in European Pat. Appln
KOKAI Publication No. 379828 and Jpn. Pat. Appln KOKAI Publication No.
3-79025, the upper wall of the chamber opposing the rest table is
constituted by an insulating member, e.g., a quartz glass member, and a
flat coil is mounted on the outer surface of the insulating member. An RF
current is supplied to this coil to form an electromagnetic field in the
chamber. The electrons flowing in the electromagnetic field are caused to
collide against neutral particles in the process gas, thereby generating a
plasma.
According to this method, a substantially concentric electric field is
induced in accordance with the shape of the coil, thereby providing a
plasma confining effect. When compared to the conventional parallel plate
type plasma processing apparatus, the plasma can be generated with a
comparatively low pressure. Accordingly, the mean free time of ions in the
generated plasma is long. Therefore, etching by means of this plasma is
suitable for micropatterning. The plasma is diffused from a high-density
area to a low-density area. Since the mean free time of ions is long, the
plasma density distribution is smooth. Thus, the uniformity of the plasma
on a plane parallel to the flat surface of the wafer is high, thereby
increasing the uniformity within a plane of plasma processing for a wafer
having a large diameter.
In this manner, the RF induction method attracts attention as a method
suitable for micropatterning and processing of wafers with large
diameters. However, this method still has many factors that are yet
unknown. Studies are required as to, e.g., how to generate a plasma having
a higher density without much increasing the RF power. As a way of
generating a high-density plasma, an insulator may be arranged around the
wafer, thereby concentrating the plasma. In this case, studies are
required as to how to adjust the degree of concentration of the plasma and
how to ensure the flatness of the lower surface of the plasma at the
peripheral portion of the wafer. The above RF induction method can be
realized only after these points are sufficiently studied.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a plasma processing
apparatus which, when processing an object to be processed with a plasma
obtained by applying an RF power to an antenna made of a coil, can
concentrate the plasma and can obtain a high flatness in the lower surface
of the plasma.
Additional objects and advantages of the invention will be set forth in the
description which follows, and in part will be obvious from the
description, or may be learned by practice of the invention. The objects
and advantages of the invention may be realized and obtained by means of
the instrumentalities and combinations particularly pointed out in the
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part
of the specification, illustrate presently preferred embodiments of the
invention, and together with the general description given above and the
detailed description of the preferred embodiments given below, serve to
explain the principles of the invention.
FIG. 1 is a sectional view showing the overall arrangement of a plasma
processing apparatus according to the first embodiment of the present
invention;
FIG. 2 is a schematic perspective view showing the outline of the overall
arrangement of the first embodiment of the present invention;
FIG. 3 is an exploded perspective view showing the support structure for a
wafer;
FIG. 4 is an exploded perspective view showing a rest table and a focus
ring;
FIG. 5 is a diagram for explaining the positional relationship between the
rest table and the focus ring;
FIG. 6 is a diagram for explaining the shape of a plasma;
FIGS. 7A to 7C are sectional views showing other arrangements of the focus
ring;
FIG. 8 is a sectional view showing the main part of another arrangement of
the present invention;
FIG. 9 is a diagram showing an arrangement employed for preventing an
object to be processed from being damaged by an electric field;
FIG. 10 is a sectional view showing a plasma processing apparatus according
to the second embodiment;
FIG. 11 is a diagram schematically showing a system for supplying wafers to
the plasma processing apparatus according to the second embodiment;
FIG. 12A is a flow chart for explaining steps before start of etching;
FIG. 12B is a flow chart for explaining steps from end of etching to wafer
extraction;
FIG. 13 is a view showing a modification of the apparatus shown in FIG. 10
which has a different RF coil;
FIG. 14 is a view showing a modification of the apparatus shown in FIG. 10
to which a bias electrode is added;
FIG. 15 is a view showing a modification of the apparatus shown in FIG. 10
to which a control electrode is added;
FIG. 16 is a view showing a modification of the apparatus shown in FIG. 10
to which another RF antenna is provided to the outer surface of the
processing chamber;
FIG. 17 is a view showing a modification of the apparatus shown in FIG. 10
to which another RF antenna is provided in the rest table;
FIG. 18 is a view showing a modification of the apparatus shown in FIG. 10
to which another RF antenna is provided around the focus ring;
FIG. 19 is a perspective view schematically showing a plasma processing
apparatus suitable for plasma processing of a large-sized object to be
processed;
FIG. 20 is a sectional view showing a plasma processing apparatus in which
a plasma processing space is formed below an object to be processed;
FIG. 21 is a sectional view showing a plasma processing apparatus in which
a plasma processing space is formed on a side of an object to be
processed;
FIG. 22 is a sectional view showing a plasma processing apparatus in which
a rest table is provided to be vertically movable;
FIG. 23 is a view schematically showing an experiment equipment;
FIG. 24 is a graph showing plasma diffusion states obtained by calculation;
FIG. 25 is a graph showing the pressure dependencies of the electron
density and the electron temperature obtained by experiments;
FIG. 26 is a graph showing the power dependencies of the electron density
and the electron temperature obtained by experiments;
FIG. 27 is a graph showing the distributions of the ion saturation currents
in the radial directions of wafers, which are obtained by experiments;
FIG. 28 is a graph showing the pressure dependency of the emission spectrum
of argon, which is obtained by experiments;
FIG. 29 is a graph showing the pressure dependency of the emission
intensity, which is obtained by experiments;
FIG. 30 is a partially cutaway perspective view showing a modification of a
discharge system;
FIG. 31A is a view showing the wiring of a spiral coil used in the
embodiments; and
FIG. 31B is a view showing a modification of the wiring of the spiral coil.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a sectional view showing the overall arrangement of a plasma
processing apparatus according to an embodiment of the present invention,
e.g., an etching apparatus, and FIG. 2 is a partially cutaway schematic
perspective view of the same. Referring to FIGS. 1 and 2, reference
numeral 2 denotes a cylindrical air-tight chamber or processing chamber
constituted by a conductive material, e.g., aluminum, excluding part of
its upper wall, i.e., its central portion. A rest table as susceptor 3
made of a conductive material, e.g., aluminum, is arranged at the central
bottom portion in the chamber 2.
The rest table 3 is constituted by separably coupling, with a bolt or bolts
33, a rest section 31 as an upper portion and a support section 32 as a
lower portion that supports the rest section 31 thereon. An insulator 34
is interposed between the bottom surface of the support section 32 and the
bottom wall of the chamber 2 in order to electrically separate the support
section 32 and the chamber 2 from each other. An electrostatic chuck sheet
4 is provided on the upper surface of the rest section 31 to cover the
upper surface of the rest section 31 excluding the peripheral portion
thereof. The electrostatic chuck sheet 4 is constituted by covering a
conductive film 41 serving as an electrostatic chuck sheet electrode made
of, e.g., a copper foil, from the two sides with insulating films 42 made
of a material, e.g., an insulating polymer such as a polyimide film,
ceramic, or quartz, which has a high resistance against reactive ions. The
conductive film 41 is electrically connected to a DC power supply 43
outside the chamber 2 through a switch 44.
A large number of vertical through holes 51 for back-side gases (gases for
heat conduction) are formed in the rest section 31 with a uniform
distribution to have upper ends open in the upper surface of the rest
section 31. The lower ends of the holes 51 communicate with, e.g., a vent
chamber 52 which extends horizontally. The vent chamber 52 is connected to
a gas supply source 69 of, e.g., He gas, through a gas supply path 53 for
the back-side gases, which extends to outside the chamber 2 through the
support section 32, the insulator 34, and the bottom wall of the chamber
2. A pressure adjusting unit 54, e.g., a butterfly valve, is provided
midway along the gas supply path 53. Vertical through holes 45 (shown in
FIG. 3) are similarly formed in the electrostatic chuck sheet 4 at
positions corresponding to the respective holes 51. The back-side gases
supplied from the through holes 51 are fed to the upper surface of the
electrostatic chuck sheet 4 through the holes 45 in the electrostatic
chuck sheet 4 and are blown against the lower surface of a wafer W as an
object to be processed which is placed on the electrostatic chuck sheet 4.
The gas supply path 53 is connected to the gas supply source 69.
The vent chamber 52 is provided with a pressure detector 55 for detecting
the pressure of the back-side gases in the vent chamber 52 and for
generating an electrical signal corresponding to the detected pressure. A
controller 56 included in the control system of the apparatus of the
present invention is connected to the output of the pressure detector 55.
The controller 56 adjusts the opening degree of the pressure adjusting
unit 54, the butterfly valve, based on the pressure detected by the
pressure detector 55 such that the pressure of the back-side gases blown
from the holes 51 toward the lower surface of the wafer W is maintained at
a predetermined value, e.g., about 10 Torr.
A plasma focus ring or directing ring 6 is provided on the upper surface of
the rest table 3 to surround the wafer W. The focus ring 6 is made by an
insulator, e.g., ceramic or quartz, or is constituted by an outer annular
member 6a made of an insulator as described above and an inner annular
member 6b made of a conductive material, e.g., carbon, as shown in FIG. 5
in detail. The inner circumferential surface of the focus ring 6 is formed
to be similar to the outer circumferential surface of the wafer W, so that
the clearance between the circumferential surface is uniformly kept at
every points and is inclined to be raised from the inner peripheral edge
toward the outer peripheral edge. When the focus ring 6 is made only of an
insulator, assuming that an 8-inch wafer is to be processed, the ring
width of the focus ring 6 is set to 30 mm, the height of the outer
peripheral edge of the focus ring 6 with respect to the surface of the
wafer W is set to 2 mm, the clearance between the wafer W and the inner
edge of the focus ring 6 is set to 0.5 mm, and the height of the inner
peripheral edge of the focus ring 6 with respect to the surface of the
wafer W is set to 1.5 mm. When the focus ring 6 is made of the outer
annular member 6a and the inner annular member 6b, it is preferable that
they be slightly separated from each other. The insulating member of the
focus ring 6 serves to cause the lines of electric force in the chamber 2
to be attracted by the central portion of the chamber 2 so as to be
substantially parallel to the wafer W. In this embodiment, the focus ring
6 is made of an insulator. However, the focus ring 6 is not limited to an
insulator but can be constituted by a high resistor (including a
conductive high resistor and a material having a resistance corresponding
to that of a semiconductor).
When the focus ring 6 is constituted by the outer and inner annular members
6a and 6b, as described above, the plasma is oriented upward by the outer
annular member 6a. However, since the lines of electric force spread
outward where the inner annular member 6b is placed, the lower surface
region of the plasma is spread laterally. Thus, the flatness at the
peripheral portion of the wafer W is improved, thereby increasing the
in-plane uniformity of plasma processing (this will be described later in
detail with reference to FIG. 8).
A coolant reservoir 35 is formed in the support section 32 in order to
circulate a coolant therein, thereby cooling the wafer W through the rest
table 3. The coolant reservoir 35 is provided with an inlet pipe 36A
connected to a coolant supply source 70, and a discharge pipe 36B
connected to the source 70 through cooling means which is not shown. The
coolant supplied into the coolant reservoir 35 through the inlet pipe 36A,
e.g., liquid nitrogen having a temperature of -190.degree. C., cools the
rest table 3 to -50.degree. to -150.degree. C., and is discharged to
outside the apparatus through the discharge pipe 36B, as indicated by an
arrow in FIG. 1.
The central portion of the upper wall of the chamber 2 opposing the rest
table 3 is constituted by an insulating member, e.g., an insulating plate
21 made of quartz glass or ceramic, and an RF antenna 7 made of a flat
coil, such as a spiral coil, which is made of copper, aluminum, stainless
steel, or the like is fixed to the upper surface of the insulating plate
21. An RF voltage having, e.g., 13.56 MHz and 1 kW, is applied across the
two terminals (inner and outer terminals) of the RF antenna 7 from a
plasma-generating RF power supply 71 through a matching circuit 72. Thus,
an RF current flows through the RF antenna 7, and a plasma is generated in
the space in the chamber 2 immediately under the RF antenna 7, as will be
described later.
An RF power supply 22 is connected between the rest table 3 and the ground
in order to apply a bias voltage having a frequency lower than the
frequency of the RF voltage to be supplied to the RF antenna 7, e.g., 1 to
3 MHz and more preferably 2 to 3 MHz, to the rest table 3. The chamber 2
is connected to ground. Thus, an electric field is generated between the
rest table 3 and the chamber 2. As a result, the perpendicularity of
incidence of reactive ions in the plasma in the chamber 2 with respect to
the wafer W is increased.
A gas supply pipe 23 is provided in the upper portion of the side wall of
the chamber 2. A process gas to be supplied into the chamber 2 through the
gas supply pipe 23 differs depending on the type of processing. For
example, when etching is to be performed, an etching gas, e.g., CHF.sub.3
or CF.sub.4, is supplied. In FIG. 1, only one gas supply pipe 23 is shown.
However, an appropriate number of gas supply pipes arranged in a
predetermined interval may be connected to the chamber 2 in order to
uniformly supply a process gas.
One end of each of a plurality of discharge pipes 81 is connected to the
bottom surface of the chamber 2 at such a position that the discharge
pipes 81 are equidistant in the circumferential direction of the chamber
2. In FIG. 1, one end of each discharge pipe 81 is connected, such that
the two discharge pipes 81 are symmetrical with respect to the axis of the
chamber 2. The other end of each discharge pipe 81 is connected to a
common discharge pipe 84 having a pressure adjusting unit 82, e.g., a
butterfly valve, and a vacuum pump 83, as shown in FIG. 2. A mechanical
shutter (not shown) is preferably provided to the discharge pipe 84, so
that the opening degree of the pressure adjusting unit 82 is adjusted by
an external operation. In this embodiment, a discharge controller 86
adjusts the pressure adjusting unit 82 based on a detected pressure value
obtained by a pressure detector 85 provided in the chamber 2, so that the
discharge system slowly performs discharge in the initial state of
evacuation so as not to scatter particles and performs rapid discharge
after evacuation is performed to a certain degree.
The operation of this device will be described. First, an object to be
processed, e.g., a semiconductor wafer W, is loaded into the chamber 2 and
placed on the electrostatic chuck sheet 4 by a convey arm (not shown). The
interior of the chamber 2 is evacuated by the vacuum pump 83 through the
discharge pipes 81 to a predetermined vacuum atmosphere. Evacuation of the
interior of the chamber 2 is performed through the discharge pipes 81,
while supplying an etching gas, e.g., CF.sub.4, from the gas supply pipe
23 into the chamber 2, in order to maintain the interior of the chamber to
a vacuum degree of, e.g., several mTorr to several tens mTorr.
Simultaneously, an RF voltage is applied to the RF antenna 7 by the RF
power supply 71. When an RF current flows through the RF antenna 7 upon
application of the RF voltage, an alternating magnetic field is generated
around the antenna conductor, and most of the magnetic fluxes run through
the central portion of the RF antenna 7 in the vertical direction, thereby
forming a closed loop. An alternating electric field is induced by this
alternating magnetic field immediately under the RF antenna 7 almost
concentrically in the circumferential direction. The electrons accelerated
in the circumferential direction by the alternating electric field collide
against the neutral particles in the process gas to ionize the gas,
thereby generating a plasma. The reactive ions in the plasma generated in
this manner etch the surface of the wafer W.
Since the focus ring 6 having an insulator or a high resistor is provided
around the wafer W, the lines of electric force are apt to separate from
the focus ring 6, so that the plasma is concentrated to the center of the
wafer W. Since the upper surface of the focus ring 6 is inclined to be
raised toward its outer side, high concentration of the plasma can be
achieved, as indicated by a broken line in FIG. 6. At the same time, since
the lower surface of the plasma is not attracted by the inner side
abruptly, but is attracted by it in an arcuated manner, the flatness of
the lower surface of the plasma at the peripheral portion of the wafer W
can be ensured. As a result, high-efficiency plasma processing having a
high in-plane uniformity can be performed. When the height of the upper
surface of the focus ring 6 and the angle of the inclined surface are
adjusted, the degree of concentration of the plasma and the shape of the
lower surface of the plasma can be adjusted.
When a silicon-based film made of, e.g., silicon dioxide or polysilicon, is
etched, a compound of a halogen and silicon attaches as a reaction product
to the discharge system, e.g., to the interior of a discharge pipe. In
this etching, after a predetermined number of wafers W are processed,
ClF.sub.3 gas may be supplied from the process gas supply pipe 23 into the
chamber 2 at, e.g., a flow rate of 10 to 5,000 sccm and a pressure of 0.1
to 100 Torr, and thereafter the interior of the chamber 2 may be
evacuated. Then, the reaction product attaching to the discharge system
can be cleaned with the ClF.sub.3 gas.
In this embodiment, the insulator portion of the focus ring or directing
means 6 has an inclined surface. However, even if a plurality of stepped
portions are formed to be lowered toward the inner side of the focus ring
6, as shown in FIG. 7A, an L-shaped focus ring 6 is formed, as shown in
FIG. 7B, or the outer portion of the focus ring 6 is inclined while the
inner portion of the focus ring 6 is formed flat, as shown in FIG. 7C, the
same effect can be obtained. The inner portion of the focus ring 6 may be
lower than or level with the surface of the wafer W. It suffices if the
height of the directing ring 6 is appropriately set in accordance with the
density of the plasma and the like so that the flatness at the peripheral
portion of the wafer W can be ensured.
If the insulator portion of the focus ring 6 is formed such that its outer
side is higher than its inner side, it is preferable because the flatness
of the peripheral portion of the lower surface of the plasma is improved.
However, the present invention does not necessarily limit the relationship
in height between the outer and inner sides of the upper surface of the
focus ring 6 as described above. From the viewpoint of obtaining a high
plasma concentration effect, the upper surface of the focus ring 6 may be
a flat surface parallel to the wafer W as far as it is higher than the
surface of the wafer W.
FIG. 8 shows an arrangement of a focus ring in which the upper surface of
an inner annular member 6b of the insulator forms a stepped portion and an
outer annular member 6a of the conductor is set to be lower than the
surface of the wafer with this arrangement, the plasma is oriented upward
by the inner annular member 6b. However, at a portion where the outer
annular member 6a is placed, since the lines of electric force spread
outwardly, the lower surface of the plasma is spread laterally, as
indicated by a solid line (a broken line indicates the shape of a plasma
obtained when the outer annular member 6a is constituted by an insulator
for the purpose of comparison), so that the flatness at the peripheral
portion of the wafer W is improved. As a result, the in-plane uniformity
of plasma processing can be improved.
In utilization of the RF induction method, its preferable embodiment for
preventing the wafer W from being damaged by an electric field will be
described. When the plasma is upright, an electric field generated by the
RF antenna 7 does not reach the wafer W due to the skin effect. However,
when the plasma is not upright, this electric field reaches the wafer W,
and the surface of the wafer W can be damaged by the electric field
component in the vertical direction. Therefore, as shown in FIG. 9, a
mechanical shutter 8 having a size which is the same as or larger than
that of the wafer W may be provided to be reciprocal. Alternatively, a
rest table 3 may be formed to be vertically movable. When an electric
field is generated, the rest table 3 is retreated downward so that the
electric field does not reach the wafer W. Alternatively, an RF power may
be supplied to an RF antenna only after the process gas atmosphere in the
chamber 2 reaches a predetermined pressure.
Plasma processing apparatuses according to different embodiments will be
sequentially described with reference to FIGS. 10 to 23. In these
embodiments, members which are substantially the same as those in the
above embodiment will be denoted by the same reference numerals, and a
detailed description thereof will be omitted.
In an apparatus shown in FIG. 10, a gas supply pipe 23 is provided to
extend through an insulating plate 21 in order to supply a gas into a
chamber 2. The gas supply pipe 23 is associated with a gas supplying means
60 provided above a rest table 3. The gas supplying means 60 is
constituted by a disk having almost the same area as that of the upper
surface of the rest table 3, and a peripheral plate projecting upward from
the outer peripheral portion of the disk and having an upper end mounted
to the insulating plate 21. The inner surfaces of the disk and the
peripheral plate, and the inner surface of the insulating plate 21 define
a gas buffer chamber. The gas supply pipe 23 extends through the
insulating plate 21 to correspond to the central portion of this disk and
is open in the buffer chamber. A large number of small through holes 63
are formed in the disk of the gas supplying means 60 to have a
predetermined distribution. A buffer disk 66 having a diameter slightly
smaller than that of the above disk is coaxially disposed in the buffer
chamber so as to maintain a gap between its upper, lower, and
circumferential surfaces and the inner surface of the buffer chamber. A
hill-like projecting portion 65 is formed on the central portion of the
upper surface of the buffer disk 66 to oppose the gas supply pipe 23.
The gas supply pipe 23 is connected to gas sources (etching gas sources in
this embodiment) 67a and 67b, provided outside the chamber 2, through a
mass flow controller 68. Gases supplied from the gas sources enter the
buffer chamber as their flow rates are adjusted by the mass flow
controller 68. Mixing of the gases is promoted in the buffer chamber, and
the gases are supplied into the chamber 2 at equal flow rates through the
small through holes 63. An annular projection 69 is formed on the
peripheral portion of the lower surface of the gas supplying means 60 such
that it projects downward. This annular projection 69 directs the gases,
supplied into the chamber 2 through the small through holes 63, toward the
wafer.
A temperature-adjusting heater 92 housed in a heater fixing box 91 is
provided between a rest section 31 and a support section 32, and is
connected to a power supply 73. The power supply 73 is controlled to
adjust power supply to the heater 92, in order to control cooling of the
rest table 3 by a coolant reservoir 35, thereby temperature-adjusting the
surface to be processed of a wafer W.
The control system of the processing apparatus having the above arrangement
will be described.
A transmitting window 74 made by a transparent material, e.g., quartz
glass, is attached in an opening formed in one side wall of the chamber 2.
Light emitted from the plasma in the processing chamber passes the window
and is incident on an optical sensor 76 through an optical system 75. The
optical sensor 76 sends a signal concerning the emission spectrum of the
incident light to a controller 77.
A pressure sensor 78 for detecting the pressure in the processing chamber
is mounted on the side wall of the chamber 2. The pressure sensor 78 sends
a signal concerning the pressure to the controller 77. As a result, during
etching, the controller 77 constantly sends control signals to the mass
flow controller 68, RF power supplies 22 and 71, a gas supply source 69,
the power supply 73, and the coolant supply source 70 based on the output
signals from the sensors 76 and 78 and a preset reference signal, thereby
controlling them to perform optimum etching.
A system for supplying wafers to the plasma processing apparatus will be
described with reference to FIG. 11.
A load-lock chamber 96 is connected to one side wall of the processing
chamber 2 through a first gate valve 95 which can open/close freely. The
load-lock chamber 96 is provided with a convey unit 97, e.g., a convey arm
obtained by coating an aluminum arm with conductive Teflon for
electrostatic shielding. The convey arm can be extended and pivoted by a
known mechanism. A discharge pipe 101 is connected to the load-lock
chamber 96 through a discharge port formed in the bottom wall of the
load-lock chamber 96, and the discharge pipe 101 is connected to a vacuum
pump 83 through a vacuum discharge valve 102. As a result, the interior of
the load-lock chamber 96 can be evacuated to a vacuum state by the vacuum
pump 83.
A cassette chamber 99 is connected to a side wall of the load-lock chamber
96, opposite to the side wall where the first gate valve 95 is provided,
through a second gate valve 98 which can open/close freely. A rest table
104 for placing a cassette 100 thereon is provide | | |
