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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma processing apparatus for
supplying a process gas into a process vessel in which an object to be
processed is placed to perform plasma processing for the object.
2. Description of the Related Art
In general, in the steps in manufacturing a semiconductor, various
processes, e.g., a film forming process, are performed for a semiconductor
wafer serving as an object to be processed. As this film forming method, a
plasma CVD (Chemical Vapor Deposition) method using both chemical and
physical methods is known.
In a plasma processing apparatus for performing this process, for example,
two plate-like electrodes are located parallel to each other in a process
vessel, and a semiconductor wafer is placed on the lower electrode. An RF
voltage of, e.g., 13.56 MHz, is applied from an RF power supply across
these electrodes to generate a plasma, thereby performing a film forming
process for the surface of the wafer.
The plasma generated between the parallel-plate electrodes as described
above becomes an alternating magnetic field having an electric field
extending from one electrode to the other electrode. For this reason,
electrons and ions are moved by a magnetic force along this electric
field, and the charged particles collide with gas molecules while the
charged particles are moved. Therefore, a gas which is not easily
thermally excited is activated, thereby performing desired film formation.
In order to increase the yield of semiconductor products, it is important
to form a film having a uniform thickness in a wafer plane. The thickness
of the formed film is considerably influenced by a source or process gas
supply method.
The following process gas supply methods are known. First, a supply nozzle
is inserted from the circumferential wall of a process vessel into the
process vessel, and a source gas is supplied from the supply nozzle toward
the upper surface of a wafer. Second, an upper electrode has a plate-like
shower head structure, and a process gas is supplied from the upper
electrode toward the upper surface of a wafer.
However, when only a process gas is supplied from the circumferential wall
of a process chamber as described above, reactive species contributing to
film formation do not easily reach the center of the wafer, and thus a
film having a uniform thickness cannot be easily formed in a wafer plane.
In addition, even when a plate-like shower head structure is simply used,
the flow of a supplied gas may be inadequately disturbed. In this case,
the uniformity of a film thickness in a wafer plane cannot be easily
assured.
The present inventors proposed, in a preceding application (Japanese Patent
Application No. 5-317375), a so-called inductive coupling plasma forming
method in which an antenna member is arranged in the upper portion in a
process vessel or outside the ceiling portion of the process vessel, and a
plasma is induced by an electromagnetic wave from the antenna member.
According to this inductive coupling plasma forming method, a plasma can be
generated at a low pressure of 1.times.10.sup.-3 Torr or less, and the
uniformity of the plasma can be improved. For this reason, the process
characteristics of a plasma etching process or a plasma film forming
process can be improved. However, when the shower head structure is
employed in the inductive coupling plasma processing apparatus, an
electromagnetic wave from the antenna member is partially absorbed by the
shower head structure consisting of a dielectric, thereby decreasing
plasma generation efficiency. For this reason, in the inductive coupling
plasma processing apparatus, a process gas or the like must be supplied
from the circumferential wall of the process vessel to prevent the plasma
generation efficiency from being degraded. Therefore, the in-plane
uniformity of a film thickness cannot be sufficiently assured as described
above.
In particular, when a semiconductor wafer is increased in diameter, for
example, when an 8-inch wafer is used, the uniformity of gas
concentrations at the central and edge portions of the wafer poses a
problem to be solved.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a plasma processing
apparatus capable of improving the in-plane uniformity of a film thickness
even when an object to be processed is increased in diameter.
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 schematic perspective view showing a plasma processing
apparatus according to a first embodiment of the present invention;
FIG. 2 is a sectional view showing the processing apparatus shown in FIG.
1;
FIG. 3 is a plan view showing the processing apparatus shown in FIG. 1;
FIG. 4 is a view showing the positional relationship between a nozzle and a
wafer to evaluate film formation for a gas supply nozzle position;
FIG. 5 is a graph showing the in-plane uniformity of a film thickness as a
function of the distance between the distal end of the nozzle and the
wafer in a direction of height;
FIG. 6 is a graph showing the in-plane uniformity of a film thickness as a
function of the length of the nozzle;
FIGS. 7A to 7C are graphs for explaining the result obtained by the graph
shown in FIG. 6;
FIG. 8 is a schematic sectional view showing an apparatus according to the
second embodiment of the present invention;
FIG. 9 is an enlarged view showing a modification of part of the apparatus
shown in FIG. 8;
FIG. 10 is a perspective view showing a gas supply head having a tapered
gas injection surface according to the third embodiment;
FIG. 11 is a sectional view showing the gas supply head shown in FIG. 10;
FIG. 12 is a schematic sectional view showing an apparatus, according to
the present invention, in which a gas supply head itself is formed to have
a dome-like shape;
FIG. 13 is a schematic sectional view showing an apparatus, according to
the present invention, in which a gas supply head itself is formed to have
a tapered shape;
FIG. 14 is a schematic sectional view showing an apparatus, according to
the present invention, in which the gas injection surface of a gas supply
head suspended from a ceiling portion is formed to have a dome-like shape;
FIG. 15 is a sectional view showing a plasma processing apparatus according
to still another embodiment of the present invention;
FIG. 16 is a plan view showing an antenna member in the apparatus shown in
FIG. 15;
FIG. 17 is a plan view showing a 1-turn antenna member;
FIG. 18 is a sectional view showing a plasma processing apparatus according
to still another embodiment of the present invention;
FIG. 19 is a sectional view showing a plasma processing apparatus according
to still another embodiment of the present invention;
FIG. 20 is a view showing a change in a processing rate curve when the
positional state of an antenna member is changed;
FIG. 21 is a sectional view showing a plasma processing apparatus according
to still another embodiment of the present invention;
FIG. 22 is an enlarged sectional view showing an antenna member in the
processing apparatus shown in FIG. 21;
FIG. 23 is a sectional view showing a plasma processing apparatus according
to still another embodiment of the present invention;
FIG. 24 is a sectional view showing a plasma processing apparatus according
to still another embodiment of the present invention;
FIG. 25 is a sectional view showing a plasma processing apparatus according
to still another embodiment of the present invention; and
FIG. 26 is a sectional view showing a plasma processing apparatus according
to still another embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of a plasma processing apparatus according to the present
invention will be described below with reference to the accompanying
drawings.
FIG. 1 is a schematic perspective view showing the plasma processing
apparatus according to a first embodiment of the present invention, FIG. 2
is a sectional view showing the processing apparatus shown in FIG. 1, FIG.
3 is a plan view showing the processing apparatus shown in FIG. 1, FIG. 4
is a view showing the positional relationship between a nozzle and a wafer
to evaluate film formation with respect to a gas supply nozzle position,
FIG. 5 is a graph showing the in-plane uniformity of a film thickness as a
function of the distance between the distal end of the nozzle and the
wafer in a direction of height, FIG. 6 is a graph showing the in-plane
uniformity of the film thickness as a function of the length of the
nozzle, and FIG. 7 is a view for explaining a result obtained by the graph
shown in FIG. 6.
In this embodiment, a case wherein the plasma processing apparatus
according to the present invention is applied to a plasma CVD apparatus.
A process vessel 4 (including its flat ceiling and bottom portions) of a
plasma CVD apparatus 2 consists of a conductive material such as aluminum
or stainless steel, and has a cylindrical shape. The process vessel 4 is
grounded. An upper electrode and an object to be processed or a wafer
mounting table or a susceptor 6 are concentrically arranged inside the
process vessel 4. This susceptor 6 is arranged to support the wafer whose
surface to be processed faces upward. However, the wafer may be supported
such that the surface to be processed faces in another direction, e.g.,
sideward or downward.
The susceptor 6 consists of, e.g., anodized aluminum or the like, and has
an almost circularly cylindrical shape. The upper portion of the susceptor
6 projects sideward and has a flat upper surface or an upper surface
having a curvature to be slightly curved downward toward the edge of the
upper surface, thereby forming a disk-like wafer support plate (not
shown). The lower portion of the susceptor 6 is supported by a susceptor
support table 8 consisting of aluminum like the susceptor 6 and having a
circularly cylindrical shape. The susceptor support table 8 is arranged on
the bottom portion of the process vessel 4 through an insulator 10. In
this manner, the susceptor 6 electrically insulated from the process
vessel 4 is supported in the process vessel 4.
The susceptor 6 can be selectively connected to an RF power supply 16 and
the ground outside the process vessel through a switch 14 by a power
supply path 12 extending from the bottom wall of the process vessel and
insulated therefrom.
The wafer support plate of the susceptor 6 is designed such that a
semiconductor wafer W serving as an object to be processed is placed on
the wafer support table and held by an electrostatic chuck mechanism or
the like.
Between the susceptor 6 and the susceptor support table 8, for example, a
ceramic heater 18 for heating the wafer supported on the susceptor 6 and
for controlling the temperature of the wafer is arranged. A cooling jacket
20 for flowing, e.g., cooling water is formed in the susceptor support
table 8 to cool the heated wafer. This ceramic heater 18 is connected to a
power supply (not shown) and a temperature controller (not shown) arranged
outside the process vessel and heated at a predetermined temperature by
the power supply and the temperature controller. The cooling jacket 20 is
connected to a cooling water source and a cooler arranged outside the
process vessel, and circulates cooling water having a predetermined
temperature.
An antenna member 22 consisting of metal, e.g., copper and wound to have a
1- or 2-turn spiral shape is arranged in the upper portion in the process
vessel 14 concentrically with the process vessel 4 and the susceptor 6.
This antenna member 22 is sandwiched by upper and lower insulating plates
24 and 26 consisting of, e.g., quartz to insulate the antenna member 22
from the ceiling portion of the vessel and to prevent the antenna member
22 from being contaminated by a heavy metal generated by plasma
sputtering. The antenna member 22 is attached and fixed to the ceiling
portion by the members 24 and 26. A matching box or matching circuit 30
and an RF power supply 32 for generating an electromagnetic wave are
connected across the ends of the antenna member 22 through a power supply
line 28 extending from the ceiling portion and insulated therefrom. As a
result, when the RF power supply 32 causes an RF current to flow in the
antenna member 22, an electromagnetic wave can be radiated toward a
process space S in the process vessel 4.
A plurality of discharge ports 33 connected to a vacuum pump (not shown)
are formed in the bottom portion of the process vessel 4. These discharge
ports, for example, four discharge ports, are formed at predetermined
intervals along the circumferential direction of the bottom portion. A
gate valve (not shown) which can be opened or closed and used to
load/unload the wafer W in/from the process vessel 4 is arranged on a
portion of the circumferential wall of the process vessel 4.
Eight source gas supply nozzle assemblies or means 34 for supplying a
source gas, e.g., silane gas, serving as a process gas from the
circumferential wall of the process vessel 4 are radially inserted into
the process vessel 4 at equal angular intervals from eight directions.
The number of nozzle insertion directions is not limited to eight, and the
number of nozzle insertion directions may be 2 or more. The nozzles are
arranged at almost equal angles with respect to the circumferential
direction of the vessel.
More specifically, the supply nozzle means 34 constitute supply paths for
supplying a process gas. Each nozzle means includes three horizontally
extending nozzles 34A, 34B, and 34C consisting of an insulator, e.g.,
quartz, formed to have pipe-like shapes and attached at a plurality of
levels, e.g., three levels in FIG. 2, vertically arranged along the
circumferential wall, and airtightly arranged by a seal member or the like
(not shown). The number of levels of the nozzles is not limited to three,
and the nozzles may be arranged at two or four or more levels. The number
of levels is determined by process conditions such as a wafer size.
The proximal end portion of each of the nozzles 34A, 34B, and 34C is
connected, through a gas supply tube 38, to a process gas source 40 for
storing a source gas such as a silane gas as a process gas. The process
gas source 40 may be arranged for each nozzle means, or may be commonly
arranged for all the nozzle means. As will be described later, the nozzles
34A, 34B, and 34C have different lengths. For this reason, when a process
gas is supplied to these nozzles at once, initial injection timings of the
process gas injected from the nozzles into the process space S are
different from each other. When the difference in timing is
disadvantageous, a valve is arranged in each of the branched supply tubes
of the gas supply tube 38 which are respectively connected to the nozzles,
and the opening/closing timings of the valves can be set in accordance
with the lengths of the nozzles.
Of process gas injection holes 36A, 36B, and 36C at the distal ends of the
three nozzles 34A, 34B, and 34C of each nozzle means 34, a process gas
injection hole or port located at an upper level is closer to the center
of the process vessel than a process gas injection hole or port located at
a lower level. Therefore, the process gas injection hole 36B of the
intermediate supply nozzle 34B located at a level (intermediate level)
higher than that of the process gas injection hole 36C of the lowermost
supply nozzle 34C is closer to the center of the vessel than the process
gas injection hole 36C, and the process gas injection hole 36A of the
supply nozzle 34A located at a level (upper level) higher than that of the
injection hole 36B is closer to the center of the vessel than the
injection hole 36B. That is, the uppermost nozzle 34A is longest, and the
lowermost nozzle 34C is shortest.
The gas injection hole 36C of the lowermost supply nozzle 34C is formed to
be located between the inner surface of the circumferential wall of the
process chamber and the edge of the wafer W supported on the susceptor 6.
A horizontal distance L1 between the vertical end face of the process gas
hole 36C and the wafer edge is set to be about 25 mm. Therefore, a source
gas can be uniformly supplied into the process space above the wafer
surface to improve the in-plane uniformity of film formation.
Eight additive gas supply nozzles 42 consisting of quartz like the supply
nozzle means 34, arranged in correspondence with the radial nozzles and
horizontally extending, are horizontally inserted in the circumferential
wall of the process vessel 4 such that the additive gas supply nozzles 42
are located above the uppermost process gas supply nozzles 34A. The
proximal end portions of the nozzles 42 are connected, through a gas
supply tube 46, to an Ar gas source 48 for storing an additive gas, e.g.,
an Ar gas, and an oxygen gas source 50. Additive gas injection holes 44
serving as the distal end portions of the nozzles 42 are located above the
process gas injection holes 36A, 36B, and 36C. An additive gas such as an
Ar or oxygen gas injected from the additive gas injection holes 44 can be
uniformly mixed with the source gas injected from the process gas holes
36A, 36B, and 36C at a high efficiency. In this embodiment, although the
length of each additive gas supply nozzle 42 is set to be equal to that of
each process gas supply nozzle 34A, these lengths may be different from
each other.
The process gas injection holes 36A, 36B, 36C are positioned at a plurality
of levels as described above, and, of the process gas injection holes 36A,
36B, and 36C, a process gas injection hole located at an upper level is
closer to the center of the vessel than a process gas injection hole
located at a lower level, thereby improving the in-plane uniformity of
film formation. A reason why the in-plane uniformity can be improved will
be described below with reference to FIGS. 4 to 7C.
Referring to FIG. 4, a vertical distance G between the upper surface of the
wafer W and the central axis of a source gas supply nozzle (denoted by
reference numeral 52 different from that of the supply nozzle described
above for descriptive convenience) was changed, and a length L of the
source gas supply nozzle 52 was changed to change the distance between the
distal end face of the nozzle and the wafer edge. In these cases, the
in-plane uniformity of film formation was examined. Note that the distance
between the inner surface of the circumferential wall of the vessel and
the wafer edge was set to be 100 mm, and a wafer size was set to be 5
inches. A nozzle inner-diameter was set to be 3.2 mm, and a silane gas and
an oxygen gas were used as source gases.
The in-plane uniformity obtained when film formation was performed while
the distance G in the vertical direction of the nozzle was changed was
evaluated. At this time, the distance between the distal end of the nozzle
and the wafer edge was set to be 25 mm by fixing the length L of the
nozzle to 75 mm. At this time, the in-plane uniformity of a film thickness
with respect to the distance G was measured. The obtained result is shown
in FIG. 5. Referring to FIG. 5, white circles indicate measurement results
obtained when a silane gas serving as a source gas and an oxygen gas have
flow rates of 10 sccm and 13 sccm, respectively, and black circles
indicate measurement results obtained when the flow rate of the silane gas
is changed to 15 sccm.
As is apparent from FIG. 5, as the distance G in the vertical direction of
the nozzle is increased, the in-plane uniformity is improved. For this
reason, it is found that the uniformity of a film thickness is almost
constant by setting the distance G to be 75 mm or more. In this case,
although the in-plane uniformity is improved, this improvement is not
shown in the graph. However, since the deposition rate of the film
formation is decreased with an increase in distance G, it is not
preferable that the distance G be excessively increased.
In-plane uniformity was evaluated when film formation was performed such
that the distance G in the vertical direction of the nozzle was fixed to
75 mm, and the length L of the nozzle was variously changed. The
measurement results of the in-plane uniformity of the film thickness at
that time are shown in FIGS. 6 and 7A to 7C.
As is apparent from FIG. 6, as the length of the nozzle 52 is increased,
i.e., as the injection port of the nozzle is close to the center of the
vessel, the in-plane uniformity is improved until the length L of the
nozzle reaches 75 mm. When the length L is 75 mm, (when the distance
between the distal end of the nozzle and the wafer edge is about 25 mm),
the best in-plane uniformity can be obtained. When the length L of the
nozzle 52 is further increased, the in-plane uniformity is degraded.
When the film thicknesses of a wafer plane were actually measured at three
points where the distance, were set as L=0, L=75, and L=100, the results
shown in FIGS. 7A, 7B, and 7C were obtained.
As shown in FIG. 7A, when the distance L=0 mm, the thickness near the
center of the wafer is excessively thin. As shown in FIG. 7B, when the
distance L=75 mm, the film thickness is almost uniformed along the radial
direction of the wafer, and a preferable result is obtained. As shown in
FIG. 7C, when the distance L=100 mm, the film thicknesses near the center
and edge of the wafer are thin, and the film thickness of the intermediate
portion between the center and edge of the wafer is thick.
Therefore, in order to increase the film thickness near the center of the
wafer, it is found that the following arrangement is preferably employed.
That is, the distal end of the nozzle is inserted into the vessel to
almost reach the center of the vessel, i.e., the length L is increased,
and the distal end of the nozzle is spaced apart from the wafer surface by
a long distance to suppress an influence on the portion except for the
central portion, i.e., the distance G is increased. In addition, in order
to increase the film thickness of the edge portion of the wafer to some
extent, the distal end of the nozzle is preferably located at a position
horizontally spaced apart from the wafer edge by a short distance and
having a level lower than the level of the nozzle near the center of the
vessel.
For this reason, the following fact is clarified. As described above, when
process gas injection holes are arranged at a plurality of levels, and an
injection hole located at an upper level is closer to the center of the
vessel than an injection hole located at a lower level, the in-plane
uniformity of film formation can be improved while keeping a high film
formation efficiency.
An operation of this embodiment arranged as described above will be
described below.
The semiconductor wafer W is loaded into the process vessel 4 by an arm
(not shown) through a gate valve (not shown), and the semiconductor wafer
W is placed and held on the susceptor 6.
The process vessel 4 is evacuated through the discharge ports 33 to have a
vacuum state. A source gas, e.g., a silane gas is supplied from the source
gas supply nozzles 34A, 34B, and 34C, and an additive gas obtained by
mixing an Ar gas and an oxygen gas is supplied from the additive gas
supply nozzles 42 located above the nozzles 34A, 34B, and 34C. The
pressure in the process vessel 4 is set to be a process pressure, e.g., a
low pressure of about 1.times.10.sup.-3 Torr, and, at the same time, the
RF power supply 32 for generating a plasma applies an RF wave of, e.g.,
13.56 MHz, to the antenna member 22.
At this time, an electromagnetic wave is emitted to the process space S by
the induction function of the inductance component of the antenna member
22, and, at the same time, an alternating electric field is generated in
the process space S by the function of a capacitive component between the
antenna member 22 and the process vessel 4. As a result, the Ar gas is
excited in the process space S, thereby generating a plasma. Therefore, a
source gas or an oxygen gas which is not easily excited by heat is
activated, and reactive species are generated, thereby depositing an
SiO.sub.2 film on the wafer surface.
In this case, unlike in a conventional parallel-plate electrode apparatus,
a plasma is generated at a relatively low pressure falling within the
range of 1.times.10.sup.-2 Torr to 1.times.10.sup.-6 Torr and preferably
1.times.10.sup.-3 Torr to 1.times.10.sup.-5 Torr. For this reason,
reactive species are slightly scattered and have the same directivity
during film formation, and a film having a uniform thickness can be
formed.
More specifically, according to the present invention, the source gas
supply nozzles 34A, 34B, and 34C for supplying a source gas are arranged
at a plurality of levels, the length of a nozzle located at an upper level
is increased, and the process gas injection hole in the distal end of the
nozzle is located on the central side of the process space S. For this
reason, a source gas from a process gas injection hole, e.g., the hole
36C, mainly contributes to film formation near the circumferential portion
of the wafer, and a source gas from process gas injection holes, e.g., the
holes 36B and 36A, mainly contribute to film formation near the
intermediate portion between the edge and central portions of the wafer
and to film formation near the central portion of the wafer. As a result,
film formation can be performed over the wafer plane with a good balance,
and the in-plane uniformity of the film thickness can be considerably
improved.
In this case, as a process gas injection hole becomes close to the center
of the process space S, the process gas injection hole is arranged at a
high position further from the wafer surface because the nozzles are
arranged at a plurality of levels. For this reason, the source gas from
the process gas injection hole, e.g., the hole 36A, located on the central
side of the wafer is prevented from excessively contributing to film
formation. As a result, as described above, the in-plane uniformity of the
film thickness can be considerably improved.
In addition, the additive gas supply nozzles 42 for an Ar or oxygen gas
having a larger molecular weight than that of the source gas are located
above the source gas supply nozzles 34A, 34B, and 34C. For this reason,
the supplied source gas and the additive gas are sufficiently mixed with
each other. Therefore, according to this point, the in-plane uniformity of
the film thickness can be further improved.
Therefore, even if the wafer is increased in diameter, the present
invention can cope with this. For example, the in-plane uniformity of the
film thickness of a large-diameter wafer having a diameter of eight or
more inches can be improved.
The supply nozzles are radially inserted from the circumferential wall, and
the distal ends of the supply nozzles are not easily located below the
antenna member 22. For this reason, the supply nozzles do not easily
absorb an electromagnetic wave from the antenna member 22, and the power
of the electromagnetic wave can effectively contribute to generation of a
plasma.
According to the above embodiment, as shown in FIG. 3, a case wherein the
nozzles are radially inserted from eight directions is exemplified.
However, the present invention is not limited to this embodiment. When
nozzles are uniformly arranged along the circumferential direction of the
cylindrical process vessel, the number of directions is not limited to
three, four, five, six, seven, or the like.
In this embodiment, a case wherein source gas supply nozzles 34A, 34B, and
34C are arranged at three levels is exemplified. However, the number of
levels is not limited to three, and the number of levels may be set to be
two or four or more.
In addition, in the above embodiment, a gas mixture of an Ar gas and an
oxygen gas serving as additive gases is supplied from the additive gas
supply nozzles 42 into the vessel. However, the additive gases may be
independently supplied from different nozzles without being mixed with
each other.
Furthermore, since the antenna member 22 is arranged in the process vessel
4, an emitted electromagnetic wave is reflected by the wall of the vessel
and used as a power for producing a plasma. For this reason, energy
efficiency can be improved.
In the above embodiment, the supply nozzle means 34 and the additive gas
supply nozzles 42 are formed such that pipe-like nozzles consisting of
quartz are inserted into the vessel. However, the present invention is not
limited to this embodiment, and the following arrangement may be employed.
Note that the same reference numerals as in FIG. 2 denote the same parts
in FIG. 8, and a description thereof will be omitted.
FIG. 8 shows a CVD apparatus according to the second embodiment, and FIG. 9
is a view showing another source gas supply means.
In the upper portion in a process vessel 4, a gas supply head 54 consisting
of quartz glass like the insulating plates 24 and 26 and having a gas
injection surface 54A formed on the lower surface of the gas supply head
54 to have a dome-like shape is arranged below an antenna member 22
covered with insulating plates 24 and 26 consisting of quartz glass. That
is, the central portion of the gas injection surface 54A is at the highest
level, and the level of the gas injection surface 54A is gradually lowered
toward the edge of the gas injection surface 54A. In the gas supply head
54, sets of source gas supply paths 56A and 56B vertically arranged at a
plurality of levels, two levels in FIG. 8, are horizontally formed, and a
plurality of source gas supply means, e.g., eight source gas supply means,
are radially arranged. The distal ends of the paths are exposed to a
process space S on the gas injection surface 54A as process gas injection
holes 58A and 58B. Therefore, in this case, the process gas injection hole
58A of the source gas supply path 56A located at the upper level is closer
to the center of the process vessel than the process gas injection hole
58B of the source gas supply path 56B located at the lower level.
As in the embodiment described above, additive gas supply paths 60 for
supplying an additive gas are formed above the source gas supply paths 56A
located at the upper level. On the gas injection surface 54A, the distal
ends of the additive gas supply paths 60 are constituted as additive gas
injection holes 62 above the process gas injection holes 58A at the upper
level. In this case, the process gas injection holes 58A at the upper
level are closer to the center of the process vessel than the process gas
injection holes 58B at the lower level. For this reason, the same
functional effect as that of the apparatus shown in FIG. 2 can be
obtained, and the in-plane uniformity of the thickness of film formation
can be improved. In addition, this embodiment can cope with an increase in
diameter of a wafer.
In the apparatus shown in FIG. 8, the source gas supply paths 56A and 56B
and the additive gas supply paths 60 which are formed in the gas supply
head 54 are directly constituted as gas paths. The apparatus is not
limited to this arrangement. For example, as shown in an enlarged view of
FIG. 9, metal pipes 64A and 64B may be inserted into the gas supply paths
56A and 56B, respectively, and a gas may flow in the metal pipes 64A and
64B. In this case, in order to prevent plasma sputtering to the metal
pipes 64A and 64B, the distal ends of the pipes are located at positions
slightly withdrawn from the process gas injection holes 58A and 58B in the
distal ends of the gas supply paths 56A and 56B not to project from the
process gas injection holes 58A and 58B toward the process space S. The
metal pipes 64A and 64B are grounded to prevent plasma discharge from
occurring in the metal pipes 64A and 64B. Note that, although not shown in
FIG. 9, in the additive gas supply paths 60, the same arrangements as that
in the source gas supply paths 56A and 56B are constituted, respectively,
as a matter of course.
In each of the above embodiments, each gas supply path is almost
horizontally formed. However, the gas supply path may be formed such that
the gas supply path is bent downward to cause the distal end portion of
the gas supply path to face toward the center of the susceptor.
In each of the examples shown in FIGS. 8 and 9, a case wherein the gas
injection surface 54A of the gas supply head 54 is formed to have a
dome-like shape has been described. The present invention is not limited
to these examples. For example, as shown in FIGS. 10 and 11, the gas
injection surface 54A may be tapered. FIG. 10 is a perspective view
showing a modification of the gas supply head, and FIG. 11 is a sectional
view showing the gas supply head shown in FIG. 10.
In this embodiment, a gas injection surface 54A serving as the inner
circumferential surface of a gas supply head 54 consisting of quartz glass
is tapered to form part of the inclined surface of a shape of pyramid or
circular cone but a dome-like shape. In this gas supply head 54, as in the
head shown in FIG. 8, source gas supply paths 56A and 56B constituting a
plurality of levels, e.g., two levels, and additive gas supply paths 60
are arranged. In particular, in the embodiment, the gas supply paths 56A,
56B, and 60 are obliquely bent downward such that their distal ends face
toward the center of a susceptor, and the gas is efficiently injected
toward a process space S above the susceptor. According to this point, the
in-plane uniformity of the thickness of a film formed on a wafer, i.e., a
surface to be processed, can be further improved.
In each of the embodiments described above, the antenna member 22 covered
with the insulating plates 24 and 26 is arranged in the upper portion in
the process vessel. However, the present invention is not limited to these
embodiments, and, as shown in FIGS. 12 and 13, an antenna member may be
buried in an insulating member constituting a gas supply head to cover the
antenna member with the insulating member. Referring to FIG. 12, a gas
supply head 54 consisting of quartz glass is formed to have a dome-like
shape having a predetermined thickness, and the head 54 can be vertically
separated into an upper head portion 66A and a lower head portion 66B. The
lower semispherical surface of the lower head portion 66B is used as a gas
injection surface 54A.
A spiral groove 68 capable of storing an antenna member 22 is formed in
each of the joint portions of the upper and lower head portions 66A and
66B, and the upper and lower head portions 66A and 66B are joined with
each other while the antenna member 22 is stored in the grooves. The
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