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Claims  |
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What is claimed is:
1. A plasma treatment apparatus comprising:
means constituting a vacuum treatment chamber;
an upper electrode and a lower electrode located within said vacuum
treatment chamber so as to be spaced apart from each other;
means for supplying and exhausting a treatment gas into and from said
vacuum treatment chamber;
a chuck provided on said lower electrode for holding an object to be
treated;
high-frequency electric power supply means for supplying a high-frequency
electric power between said upper and lower electrodes to generate in the
treatment gas a plasma for treating said object being held by said chuck;
electrically conducting means associated with said lower electrode by way
of electrically insulating means, said electrically conducting means
having a potential different from that of said lower electrode;
backside gas supply means including a gas supply conduit for supplying a
heat transfer backside gas, through said electrically conducting means and
said electrically insulating means, to a backside of said object to be
treated being held by said chuck on said lower electrode; and
flowpath means made of an electrically insulating material and fitted in
said gas supply conduit, said flowpath means having a multiplicity of
flowpath holes which are formed in electrically insulating material of
said flowpath means.
2. A plasma treatment apparatus according to claim 1, wherein:
said flowpath means comprises a plurality of flowpath elements divided in a
longitudinal direction of said gas supply conduit.
3. A plasma treatment apparatus according to claim 1, wherein:
said flowpath means is of a cylindrical shape, and said flowpath holes
extend longitudinally through the interior of the flowpath means.
4. A plasma treatment apparatus according to claim 3, wherein:
said flowpath means comprises a plurality of flowpath elements divided in a
longitudinal direction of said gas supply conduit, and said flowpath holes
of adjacent flowpath elements are offset positionally with one another
with respect to the longitudinal direction thereof.
5. A plasma treatment apparatus according to claim 3, wherein:
said flowpath means comprises a plurality of flowpath elements divided in a
longitudinal direction of said gas supply conduit, and each of said
flowpath elements includes at its surface in contact with an adjacent
flowpath element a recess having a diameter slightly smaller than the
outer diameter of each element; and wherein:
said flowpath holes are formed in the region of said recess.
6. A plasma treatment apparatus according to claim 1, wherein:
said flowpath means comprises a porous body.
7. A plasma treatment apparatus according to claim 1, further comprising:
electrically conducting flowpath means fitted in said gas supply conduit so
as to abut against said flowpath means at the side of said backside gas
supply means.
8. A plasma treatment apparatus according to claim 7, wherein:
said electrically conducting flowpath means is in the form of a cylinder
having a flowpath hole in its central portion.
9. A plasma treatment apparatus according to claim 1, wherein
said flowpath means of electrically insulating material is positioned in
the vicinity of said electrically insulating means.
10. A plasma treatment apparatus according to claim 1, wherein:
said backside supply means further includes:
supply pump means for supplying a backside gas onto the backside of said
object to be treated by way of said gas supply conduit; and
exhaust pump means for exhausting the backside gas from said backside of
said object by way of said gas supply conduit.
11. A plasma treatment apparatus comprising:
means constituting a vacuum treatment chamber;
an upper electrode and a lower electrode located within said vacuum
treatment chamber so as to be spaced apart from each other;
means for supplying and exhausting a treatment gas into and from said
vacuum treatment chamber;
an electrostatic chuck provided on said lower electrode for holding an
object to be treated;
high-frequency electric power supply means for supplying a high-frequency
electric power between said upper and lower electrodes to generate in the
treatment gas a plasma for treating said object being held by said chuck;
electrically conducting means associated with said lower electrode by way
of electrically insulating means, said electrically conducting means
having a potential different from that of said lower electrode; and
backside gas supply means including a gas supply conduit for supplying a
heat transfer backside gas, through said electrically conducting means and
said electrically insulating means, directly to a backside of said object
to be treated being held by said chuck on said lower electrode;
said backside gas supply means further including supply pump means for
supplying a backside gas onto the backside of said object by way of said
gas supply conduit, exhaust pump means for exhausting the backside gas
from said backside of said object by way of said gas supply conduit, and
control means for actuating said supply pump means in relation to an
operation of said high-frequency electric power supply means and for
actuating said exhaust pump means in relation to a lowering of power in
said high-frequency electric power supply means.
12. A plasma treatment method comprising the steps of:
placing an object to be treated on an electrostatic chuck provided on a
lower electrode within a vacuum treatment chamber, and thereby
electrostatically holding the object;
introducing a treatment gas into said vacuum treatment chamber;
Supplying a high-frequency electric power between an upper electrode and
said lower electrode within said vacuum treatment chamber to produce in
said treatment gas a plasma to thereby plasma-treat said object;
supplying a heat transfer backside gas through said lower electrode to a
backside of said object being held on said lower electrode, during the
plasma treatment;
exhausting said backside gas from the backside of said object to be
treated, after completion of said plasma treatment;
stepwisely reducing the supply of the high-frequency electric power upon
the completion of said plasma treatment step; and
evacuating said vacuum treatment chamber of said treatment gas; and
said step of exhausting the backside gas is initiated in unison with a
first reduction stage in the stepwise reduction of the high-frequency
electric power.
13. A plasma treatment apparatus comprising:
means constituting a vacuum treatment chamber;
an upper electrode and a lower electrode located within said vacuum
treatment chamber so as to be spaced apart from each other;
means for supplying and exhausting a treatment gas into and from said
vacuum treatment chamber;
an electrostatic chuck provided on said lower electrode for holding an
object to be treated;
high-frequency electric power supply means for supplying a high-frequency
electric power between said upper and lower electrodes to generate in the
treatment gas a plasma for treating said object being held by said chuck;
electrically conducting means associated with said lower electrode by way
of electrically insulating means, said electrically conducting means
having a potential different from that of said lower electrode; and
backside gas supply means including a gas supply conduit for supplying a
heat transfer backside gas, through said electrically conducting means and
said electrically insulating means, directly to a backside of said object
to be treated being held by said chuck on said lower electrode;
said backside gas supply means further including flow changeover means
provided in said gas supply conduit, supply pump means for supplying a
backside gas onto the backside of said object by way of said flow
changeover means and said gas supply conduit, a number of backside gas
holes connecting said gas supply conduit and the backside of said object,
exhaust pump means for exhausting the backside gas from said backside of
said object by way of said gas supply conduit and said flow changeover
means, and control means for actuating said supply pump means in relation
to an operation of said high-frequency electric power supply means and for
actuating said exhaust pump means in relation to a lowering of power in
said high-frequency electric power supply means.
14. A plasma treatment method comprising the steps of:
placing an object to be treated on an electrostatic chuck provided on a
lower electrode within a vacuum treatment chamber, and thereby
electrostatically holding the object;
introducing a treatment gas into said vacuum treatment chamber;
supplying a high-frequency electric power between an upper electrode and
said lower electrode within said vacuum treatment chamber to produce in
said treatment gas a plasma to thereby plasma-treat said object;
supplying a heat transfer backside gas through said lower electrode to a
backside of said object being held on said lower electrode, during the
plasma treatment;
exhausting said backside gas from the backside of said object to be
treated, after completion of said plasma treatment;
stepwisely reducing the supply of the high-frequency electric power upon
the completion of said plasma treatment step; and
evacuating said vacuum treatment chamber of said treatment gas.
15. The plasma treatment apparatus as recited in claim 11 wherein said
lowering of power is a complete shut off of power provided by said
high-frequency electric power supply means.
16. A plasma treatment apparatus comprising:
means constituting a vacuum treatment chamber;
an upper electrode and a lower electrode located within said vacuum
treatment chamber so as to be spaced apart from each other;
means for supplying and exhausting a treatment gas into and from said
vacuum treatment chamber;
an electrostatic chuck provided on said lower electrode for holding an
object to be treated;
high-frequency electric power supply means for supplying a high-frequency
electric power between said upper and lower electrodes to generate in the
treatment gas a plasma for treating said object being held by said chuck;
electrically conducting means associated with said lower electrode by way
of electrically insulating means, said electrically conducting means
having a potential different from that of said lower electrode; and
backside gas supply means including a gas supply conduit for supplying a
heat transfer backside gas, through said electrically conducting means and
said electrically insulating means, directly to a backside of said object
to be treated being held by said chuck on said lower electrode;
said backside gas supply means further including supply pump means for
supplying a backside gas onto the backside of said object by way of said
gas supply conduit, exhaust pump means for exhausting the backside gas
from said backside of said object by way of said gas supply conduit, and
control means for actuating said supply pump means in relation to an
operation of said high-frequency electric power supply means and for
actuating said exhaust pump means in relation to a lowering of power in
said high-frequency electric power supply means, and
wherein said lowering of power is a stepwise reduction in power provided by
said high-frequency electric power supply means. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The present invention relates to a plasma treatment apparatus for
subjecting an object to be treated, for example, a semiconductor wafer to
a treatment such as film etching or film formation.
A plasma treatment is widely used in manufacturing processes for
semiconductor wafers due to its high accuracy in process control. Plasma
treatment apparatuses include a wafer-by-wafer treatment type and a batch
type. A wafer-by-wafer etching apparatus, by way of example, comprises a
vacuum treatment chamber, and upper and lower electrodes vertically
confronting each other within the vacuum chamber. A semiconductor wafer is
mounted on the lower electrode, and a high-frequency or RF (radio
frequency) electric power is supplied between the two electrodes. In such
a plasma treatment the wafer is required to be uniformity maintained at a
predetermined temperature, and the apparatus therefore has, on the side of
the lower electrode, temperature control means and means for supplying a
heat transfer backside gas.
The known plasma treatment apparatus further comprises a grounded member
which is provided below the lower electrode and is continuous with a wall
of the vacuum treatment chamber by way of an electrically insulating
member. The lower electrode is electrically connected to a RF power source
while the grounded member is connected to the earth. The upper electrode
is electrically connected to the grounded member, whereby an RF electric
power can be applied between the upper and lower electrodes.
A gas supply conduit for a backside gas, made of an electrically insulating
material is provided so as to extend from below the grounded member, that
is, from below the vacuum treatment chamber, through the grounded member
and electrically insulating member, to the underside of the lower
electrode. The top end of the gas supply conduit communicates, via an
accumulator passage and an accumulator space provided within the lower
electrode, with a multiplicity of gas emission holes. Within the lower
electrode there is also provided a cooling medium reservoir allowing
passage of the cooling medium therethrough.
At the time of etching treatment, the wafer is attracted onto the lower
electrode with the aid of an electrostatic chuck, and a backside gas, for
example, He gas from the gas supply conduit is blown onto the backside of
the wafer through the gas emission holes, thereby providing a uniform
distribution of temperature over the wafer surface. After the completion
of the etching, the electrostatic chuck is turned off, while
simultaneously sucking the backslide gas through the gas supply conduit so
as to prevent the wafer from being blown off by the pressure of the
backside gas remaining within the gas supply conduit.
In the above-described etching apparatus, however, there was a fear of an
electric discharge occurring between the lower electrode and the grounded
member by way of the gas supply conduit for a reason which will be
described later. The occurrence of such electric discharge makes it
impossible to secure a predetermined electric power energy, which will
lead to a reduction in the etching rate. Thus, unawareness of an electric
discharge will result in an insufficient etching treatment. Further,
unstabilized plasma may prevent a matching of the impedance, and due to
the electric discharge a damage to the parts such as the gas supply
conduit and electrically conducting sections will occur. It is to be
appreciated that if the gas supply conduit is of small diameter to lower
the voltage at which electric discharge occurs, the conductance will
become small and it will take a considerable amount of time to suck the
backside gas, thus resulting in a reduced throughput.
In this type of plasma treatment apparatus, the electrostatic chuck for
holding an object to be treated such as a semicnductor wafer is provided
with an electrostatic attraction sheet having a multiplicity of openings
through which a backside gas, for example, He gas is supplied and filled
between the object to be treated and the electrostatic attraction sheet.
Such filling of the gas ensures a uniform heat transfer between the object
to be treated and the electrostatic attraction sheet. This type of plasma
treatment apparatus has the problems stated below, in particular, when a
mount supporting the electrostatic chuck is cooled to restore the
temperature within the treatment chamber to the room temperature from an
ultra lower temperature at which the object to be treated undergoes a
plasma treatment.
Within a tank as the source of supply of the backside gas, moisture may be
mixed into the backside gas such as He gas to be filled between the object
to be treated and the electrostatic sheet. This moisture is caused to
return to the liquid phase as the temperature approaches the room
temperature, the moisture having been condensed in the gas accumulation
sparse and gas passage during the plasma treatment under low temperature
conditions. As long as this liquid phase water remains on the inner wall
surface of the gas accumulation space, there arises no problem. However,
there is a large possibility for the liquid phase water to be emitted onto
the attraction surface between the electrostatic chuck and the object to
be treated. Thus, in the case of the liquid phase water depositing on the
attraction surface, there occurs a residual electric charge on the surface
of the electrostatic chuck under the influence of the presence of hydroxyl
groups (OH.sup.-, OH.sup.+) involved in the water. The occurrence of the
residual electric charge on the electrostatic chuck will naturally induce
a residual electric charge on the object to be treated immediately
confronting and abutting against the electrostatic chuck.
It is therefore necessary when unloading the object to be treated that any
such residual electric charge and any electric charge remaining after the
induction by the application of voltage to the electrostatic chuck be
eliminated to assist in unloading the object to be treated. To this end,
the elimination of the electric charge has hitherto been effected when
pushing up the object to be treated by pusher pins which are commonly used
in this type of apparatus and which serve as grounded members.
In case there exists a large amount of residual charge, however, the above
constitution will result in an increase in the number of times by which
the object to be treated is pushed up by the pins. Accordingly, it takes a
considerable time to complete the unloading of the object to be treated,
resulting in a poor throughput. Apart from this, there is a fear of
damaging or impairing the surface of the object to be treated with
increased number of times of the push up. Furthermore, the presence of the
hydroxyl groups will induce a deposition of an unnecessary oxide film on
the surface of the semiconductor wafer, which brings about unfavorable
results in view of the characteristics of the semiconductor wafer.
In the case of filling a gas such as He gas, a uniform heat transfer can be
accomplished between the electrostatic chuck and the object to be treated,
whereas such gas may possibly leak from the filling space to the exterior.
Should leakage occur, liquid phase water which is produced upon the return
to the room temperature and contained in the gas will be scattered within
the plasma treatment chamber or will adhere to the wall surface thereof.
Thus, when evacuating the interior of the plasma treatment chamber, removal
must be performed of the filling gas which has leaked out as well as the
liquid phase water which has been produced with the return to the room
temperature, which inevitably elongates the time taken for the evacuation.
An incomplete removal of the water will adversely affect the conditions of
the plasma treatment to be subsequently executed.
SUMMARY OF THE INVENTION
The present invention was conceived to solve the above problems, and its
major object is to provide a plasma treatment apparatus free from any
electrical discharge through a flow path for a backside gas which is
supplied to an object to be treated.
It is another object of the present invention to provide a plasma treatment
apparatus and method, capable of shortening the time required for the
evacuation after the plasma treatment, and suppressing the generation of a
residual electric charge to prevent any damage or breakage of the object
to be treated.
According to a first aspect of the present invention, there is provided a
plasma treatment apparatus comprising means constituting a vacuum
treatment chamber; an upper electrode and a lower electrode located within
the vacuum treatment chamber so as to vertically confront each other;
means for supplying and exhausting a treatment gas into and from the
vacuum treatment chamber; a chuck provided on the lower electrode for
holding an object to be treated; high-frequency electric power supply
means for supplying a high-frequency electric power between the upper and
lower electrodes to generate in the treatment gas a plasma for treating
the object being held by the chuck; electrically conducting means
associated with the lower electrode by way of electrically insulating
means, the electrically conducting means having a potential different from
that of the lower electrode; backside gas supply means including a gas
supply conduit for supplying a heat transfer backside gas, through the
electrically conducting means and the electrically insulating means, to a
backside of the object to be treated being held by the chuck on the lower
electrode; and flowpath means made of an electrically insulating material
and fitted in the gas supply conduit, the flowpath means having a
multiplicity of conduction holes having a small diameter.
The above feature ensures maintaining a uniform temperature over an object
to be treated by subjecting a backside of the object to the backside gas
during the plasma treatment of the object. Since the diameter of the gas
flow paths is small between the electrically conducting member and the
lower electrode, the voltage required for the initiation or start of the
electrical discharge is increased, which prevents a possible electric
discharge through these gas flow paths. The provision of a multiplicity of
gas flow paths having a small diameter allows a large conductance, which
enables a prompt evacuation in the case of the evacuation through these
gas flow paths. Further, in the case where the gas flowpath means is
divided into a plurality of flow path members, pressure resistance,
conductance and so on can be varied depending on combinations thereof.
In the plasma treatment apparatus according to the present invention, the
backside gas supply means may include supply pump means for supplying a
backside gas onto the backside of the object to be treated by way of the
gas supply conduit, exhaust pump means for exhausting a backside gas from
the backside of the object to be treated by way of the gas supply conduit,
and means for actuating the supply pump means in relation to the operation
of the high-frequency electric power supply means and for actuating the
exhaust pump means in relation to the completion of the operation of the
high-frequency electric power supply means.
By virtue of the above feature, a backside gas is exhausted from the
backside of the object to be treated after the plasma treatment while
simultaneously removing water contained in the gas. This lightens the work
to remove the backside gas and the water when evacuating the interior of
the vacuum treatment chamber.
According to the second aspect of the present invention, there is provided
a plasma treatment method comprising the steps of placing an object to be
treated on a chuck provided on a lower electrode within a vacuum treatment
chamber, and thereby chucking the object; introducing a treatment gas into
the vacuum treatment chamber; supplying a high-frequency electric power
between an upper electrode and the lower electrode within the vacuum
treatment chamber to produce in the treatment gas a plasma to thereby
plasma treat the object; supplying a heat transfer backside gas through
the lower electrode to a backside of the object being chucked on the lower
electrode, during the plasma treatment; exhausting the backside gas from
the backside of the object to be treated, after completion of the plasma
treatment; and evacuating the vacuum treatment chamber of the treatment
gas.
The above method enables a complete removal of the backside gas and the
water mixed therewith at the time when the vacuum treatment chamber is
evacuated, which serves to shorten the time required for the evacuation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical sectional view of a plasma treatment apparatus
constructed in accordance with the present invention;
FIG. 2 is an enlarged sectional view of a part of the apparatus shown in
FIG. 1;
FIG. 3 is an exploded perspective view of flowpath members;
FIG. 4 is a top plan view of a first flowpath member;
FIG. 5 is a top plan view of a second flowpath member;
FIG. 6 is a top plan view of a third flowpath member;
FIG. 7 is a perspective view showing a modification of the first and second
flowpath members;
FIG. 8 is a characteristic diagram showing a relationship between a gas
pressure within a backside gas supply conduit and a discharge start
voltage in a conventional plasma etching apparatus;
FIG. 9 is a characteristic diagram showing a relationship between the
discharge start voltage and the backside gas pressure, with the number of
flowpath members taken as a parameter;
FIG. 10 is a vertical sectional view showing another embodiment of the
present invention; and
FIG. 11 is a timing chart for explaining the operation of a control unit
shown in FIG. 10.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will now be described with
reference to the accompanying drawings.
Referring to FIG. 1 which depicts the entire configuration of a plasma
treatment apparatus embodying the present invention, there is shown a
vacuum treatment chamber generally designated by reference numeral 2. The
vacuum treatment chamber 2 includes a sidewall having on its opposite side
surfaces gate valves G1 and G2 for openably closing wafer
loading/unloading ports g1 and g2, respectively. The chamber 2 has a
bottom with an exhaust conduit 20 which is coupled to a vacuum pump 24 for
exhausting. The chamber has a top provided with an upper electrode 21
serving also as a treatment gas supply section. The electrode 21 has a gas
ejection plate 22 with a multiplicity of ejection holes through which a
treatment gas from a treatment gas supply conduit 23 is introduced into
the vacuum treatment chamber 2 in the direction as indicated by arrows.
The vacuum treatment chamber further includes a lower electrode 3 serving
as a susceptor and located below the upper electrode 21 in vertically
confronting relation with the electrode 21. The lower electrode 3 is made
of a metal such as aluminum, and divided into an upper wafer mount 31 and
a support 32 underlying the mount 31. The upper surface of the mount 31 is
provided with a known electrostatic chuck not shown.
The support 32 has a cooling medium reservoir 35 formed therewithin for
circulation of a cooling medium, for example, liquid nitrogen by way of a
cooling medium supply conduit 34 and a discharge conduit 33. The side and
bottom of the lower electrode 3 are covered with an electrically
insulating member 4 made of, for example, ceramics. Furthermore, the side
and bottom of the electrically insulating member 4 are covered with a
grounded member 41 made of, for example, aluminum and forming a part of
the wall of the vacuum treatment chamber 2.
The lower electrode 3 is electrically connected via an internal conductive
rod 42 to a high-frequency power source 43 lying below the vacuum
treatment chamber 2, while the grounded member 41 is connected to the
earth by way of an external conductive pipe 44 surrounding the internal
conductive rod 42.
From below the vacuum treatment chamber 2 extends upward a backside gas
supply conduit 5 for a heat transfer backside gas, formed of a pipe of
polytetrafluoroethylene (Teflon, brand name of E. I. Du Pont de Nemours &
Co. Inc.) so as to pass through the grounded member 41 and the
electrically insulating member 4, the upper end of the gas supply conduit
5 being joined to the lower surface of the support 32 through an O-ring 51
as shown in FIG. 2. The flow path of the gas supply conduit 5 communicates
at its upper end with a gas flow path 52 formed within the support 32, the
gas flow path 52 communicating via an accumulator space 53 formed within
the mount 31 with a multiplicity of gas emission holes 54 opening into the
upper surface of the mount 31 as shown in FIG. 1.
The gas supply conduit 5 has two branches on the side of its lower end. A
branch conduit 5A on one hand is coupled via a valve V1 to a pressure
control unit 55, and further to an upstream supply source 56 for a
backside gas, for example, He gas. The other branch conduit 5B is intended
to exert a suction to the upper side of the mount 31 through the gas
supply conduit 5 as will be described later, and is coupled via a valve V2
to an exhaust pump 57. In FIG. 2, reference numeral 58 denotes a joint for
joining together the inside and outside conduits of the vacuum treatment
chamber 2.
The gas supply conduit 5 has at its portion located within the electrically
insulating member 4 a first flowpath member 6, a second flowpath member 7,
and a third flowpath member 8 fitted thereinto. The three flowpath members
are each of a length of 10 mm or less and provided with a multiplicity of
flow paths having small diameters. The flowpath members 6 to 8 and
combinations thereof will be described in detail with reference to FIGS. 2
to 4. The first and second flowpath members 6 and 7 are each made of a
cylinder of an electrically insulating material, for example, Teflon
(brand name of E. I. Du Pont de Nemours & Co. Inc.) and having at its one
end a recess 61, 71 with a diameter slightly smaller than its outer
diameter and a depth of the order of, for example, 1 mm. From the bottom
of the recess 61, 71 to the other end extend axially a multiplicity of
conduction holes 62, 72 having a small diameter of, for example, 1 mm or
less.
The conduction holes 62 and 72 may be arranged along, for example, a
plurality of circles concentric with the outer diameter of the flowpath
members 6 and 7. However, the conduction holes 62 of the first flowpath
member 6 differ in the arrangement pattern from the conduction holes 72 of
the second flowpath member 7 so that when the flowpath members 6, 7 are
axially aligned with each other, the positions of the holes 62 and 72 do
not coincide, and in other words, when the second flowpath member 7 is
viewed axially through the conduction holes 62, the conduction holes 72
cannot be seen.
The third flowpath member 8 is made of a cylinder of an electrically
conducting material, for example, aluminum and having at its one end a
recess 81 similar to the recess 61, 71. From the bottom of the recess 81
to the opposite end extends axially a conduction hole 82, for example,
having the same diameter as the bore diameter of the gas supply conduit 5
located outside the vacuum treatment chamber 2.
Within the gas supply conduit 5 are inserted first flowpath members 6 and
second flowpath members 7 alternately from the underside of the lower
electrode 3 (the support 32) with their respective recesses 61, 71 facing
upward. Further, a plurality of third flowpath members 8 are disposed in
series below the vicinity of the interface between the electrically
insulating member 4 and the grounded member 41, with their recesses 81
facing upward so as to be continuous with the arrangement of the flowpath
members 6 and 7 and in close contact with the lowermost flowpath member 6
or 7. In this embodiment, the gas supply conduit 5 and the flowpath
members 6 to 8 constitute backside gas flowpath means.
At a position vertically opposite to a semiconductor wafer W on the mount
and above the chamber 2, as can be seen in FIG. 1, a permanent magnet 90
may be placed rotatably around an axis 91. The permanent magnet 90 is
rotated to form a magnetic field in the vicinity of the semiconductor
wafer W and parallel to the major surface thereof, thus constituting a
magnetron etching apparatus.
The function of the above embodiment will be described below.
First, by means of a transfer arm not shown, a semiconductor wafer W which
is an object to be treated is loaded into the vacuum treatment chamber 2
through the loading port g1 with the gate valve G1 opened, and is placed
on the mount 31 whose temperature is regulated to be within a range of,
for example, 10.degree. C. to -100.degree. C. by the cooling medium in the
cooling medium reservoir 35 and a heater not shown. Then, the wafer W is
attracted and fixed by an electrostatic chuck not shown, and the backside
of the wafer W is subjected to He gas which is supplied through the gas
supply conduit 5 and emitted from the gas emission holes 54 and whose
pressure is controlled to, for example, about 10 Torr by the pressure
control unit 55, whereby the temperature of the wafer W is made uniform.
The vacuum treatment chamber 2 is supplied with a treatment gas from the
treatment gas supply conduit 23 through the holes in the gas ejection
plate 22, while being evacuated by the vacuum pump 24 by way of the
exhaust conduit 20 so as to maintain the pressure within the vacuum
treatment chamber 2 at a predetermined value. Furthermore, a
high-frequency electric power of, for example, 13.56 MHz, 1 KW derived
from the high-frequency power source 43 is applied between the upper
electrode 21 and the lower electrode 3 to produce a plasma for etching the
wafer W. Afterwards, the vacuum treatment chamber 2 is evacuated by the
exhaust pump 57 by way of the branch conduit 5B of the gas supply conduit
5 so as to prevent the wafer W from being blown off the mount 31 by the
pressure of the backside gas remaining within the gas flow path, and then
the electrostatic chuck is deenergized.
In conventional plasma treatment apparatus, the gas supply conduit 5 is
comprised of a mere integral straight pipe, including the portion lying
within the grounded member 41 and the electrically insulating member 4.
With this conventional structure there is a fear of electrical discharge
occurring between the lower electrode 3 and the grounded member 41 through
the gas supply conduit 5. The reason will be described on points noticed
by the inventors and experimental data. The relationship between the
backside gas pressure and the electrical discharge start voltage can be
expressed as an upwardly widening parabola curve, in coordinates with the
axis of abscissas representing the gas pressure and the axis of ordinates
representing the discharge start voltage. The shape of the curve depends
on what kind of gas is used. If the above relationship is analyzed with
the electrodes arranged on both ends of a conduit, the discharge start
voltage is not much influenced by the length of the conduit as long as the
length lies within a certain range, but is liable to be lower as the
diameter of the conduit becomes larger.
Here, He gas being used as the backside gas is sealed into the conduit of 4
mm diameter while variously changing the gas pressure to examine the
relationship between the pressure (Torr) and the discharge start voltage.
FIG. 8 shows the results. In wafer etching apparatus, the high-frequency
voltage and the He gas pressure are typically set at, for example, 1 KV
and about 10 Torr, respectively. As can be seen from the characteristic
curve shown in FIG. 8, the discharge start voltage is less than 1 KV at
the pressure of 10 Torr. It is thus to be appreciated in the case of the
use of only the gas supply conduit 5 that there are conditions readily
causing an electrical discharge between the lower electrode 3 and the
grounded member 41 through the He gas contained in the conduit 5.
Once such electrical discharge occurs, a predetermined electric power
energy cannot be secured, and hence the etching rate is lowered. Thus, the
result of the etching treatment may be insufficient if the electrical
discharge is not detected. Further, unstabilized plasma may prevent the
matching of impedance, and the electrical discharge may damage the gas
supply conduit 5 and other components such as electrically conducting
portions. Where the gas supply conduit 5 is made slender to lower the
discharge start voltage, the conductance becomes small so that a
considerable amount of time must be taken to suck the backside gas,
resulting in a reduced throughput.
According to the present invention, the above problems can be solved by the
provision of the flowpath members 6, 7. The portion of the gas supply
conduit 5 circumscribed by the lower electrode 3 and the grounded member
41 having different potentials accommodates the flowpath members 6, 7
fitted thereinto so as to define a flow path for He gas having a small
diameter of 1 mm or less. As a result, the curve representing the
electrical discharge start voltage, shown in FIG. 8, is upwardly shifted,
that is, the discharge start voltage for each pressure is increased. The
reason why the discharge start voltage increases is supposed to be in that
most of the electrons, when emitted, impinge against the wall and
disappears due to the narrow gas flow path.
Since the conduction holes 62 of the first flowpath member 6 do not
coincide in the arrangement pattern with the conduction holes 72 of the
second flowpath member 7, the gas flow path is caused to bend at the
transition from one flowpath member 6 (7) to the other flowpath member 7
(6) through the recesses 61, 71 each defining a buffer portion, whereby
the electrons are m | | |
