U.S. patent number RE34,106 [Application Number 07/690,541] was granted by the patent office on 1992-10-20 for semiconductor manufacturing apparatus.
Invention is credited to Tadahiro Ohmi.
United States Patent |
RE34,106 |
Ohmi |
October 20, 1992 |
Semiconductor manufacturing apparatus
Abstract
A semiconductor manufacturing for depositing an insulating thin
film on a surface of a semiconductor substrate in a vacuum vessel
at an atmosphere of reduced pressure, wherein radiofrequency powers
each having different first and second radiofrequencies are applied
respectively to a target electrode composed of a material for an
insulating thin film and a succeptor electrode for holding said
semiconductor substrate. The first frequency is selected to be
lower than said second frequency, whereby a high quality insulating
film having a surface excellent in flatness can be assured without
damaging the substrate.
Inventors: |
Ohmi; Tadahiro (Sendai-shi,
Miyagi-ken 980, JP) |
Family
ID: |
16319764 |
Appl.
No.: |
07/690,541 |
Filed: |
April 23, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
85157 |
Aug 14, 1987 |
04824546 |
Apr 25, 1989 |
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Foreign Application Priority Data
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Aug 20, 1986 [JP] |
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61-194151 |
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Current U.S.
Class: |
204/298.08;
204/192.12; 204/298.06; 204/192.3 |
Current CPC
Class: |
B65B
3/28 (20130101); B67C 3/202 (20130101) |
Current International
Class: |
B67C
3/20 (20060101); B67C 3/02 (20060101); B65B
3/00 (20060101); B65B 3/28 (20060101); C23C
014/34 () |
Field of
Search: |
;204/192.12,192.3,298.08,298.06,298.16,298.19 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
J L. Vossen and J. J. O'Neill, Jr. Ultra Stable System for RF
Sputtering With RF-Induced Substrate Bias. .
H. Norstrom Experimental And Design Information For Calculating
Impedance Matching Networks For Use In RF Sputtering And Plasma
Chemistry..
|
Primary Examiner: Nguyen; Nam
Attorney, Agent or Firm: Baker & Daniels
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. A .[.semiconductor.]. manufacturing apparatus for depositing
.[.an insulating.]. .Iadd.a .Iaddend.thin film on the surface of a
.[.semiconductor.]. substrate in a vacuum vessel at an atmosphere
of reduced pressure, comprising:
a target composed of a material for said .[.insulating.]. thin film
or of at least one of constituent elements of said material for the
.[.insulating.]. thin film;
wherein the .[.semiconductor.]. substrate is adapted to be disposed
spaced apart from the target in a confronting relation therewith
for permitting the .[.insulating.]. film of the target to be
deposited thereon;
a first radiofrequency power source for generating first
radiofrequency power of a first frequency for application to the
target;
a succeptor electrode adapted to support the .[.semiconductor.].
substrate thereon;
a second radiofrequency power source for generating second
radiofrequency power of a second frequency for application to the
succeptor electrode; and
said first frequency being selected to be lower than said second
frequency.
2. A semiconductor manufacturing apparatus according to claim
.[.1.]. .Iadd.13.Iaddend.comprising,
a target electrode provided adjoining said target and mounted on
the target for applying first radio-frequency power of the first
frequency to said target;
a first matching circuit provided between said target electrode and
said first radiofrequency power source for matching the target
electrode to said first radiofrequency power source;
a first band reject filter disposed between the matching circuit
and the target electrode for selectively permitting only the first
radiofrequency power to be transmitted to the target electrode;
a second matching circuit disposed between the succeptor electrode
and the second radiofrequency power source for matching the
succeptor electrode to the second radiofrequency power source;
and
a second band reject filter disposed between the succeptor
electrode and the matching circuit for selectively permitting only
the second radiofrequency power to be transmitted to the succeptor
electrode.
3. A semiconductor manufacturing apparatus according to claim 2,
wherein said first frequency is 13.56 MHz while said second
frequency is not less than 100 MHz.
4. A semiconductor manufacturing apparatus according to claim 2,
wherein said second band reject filter used for said succeptor
electrode comprises:
a parallel L-C circuit presenting a maximum impedance at a
resonance frequency of ##EQU4## where L.sub.1 is the inductance of
an inductor L and C.sub.1 is the capacitance of a capacitor C
connected in parallel with the inductor L.
5. A semiconductor manufacturing apparatus according to claim 2,
comprising:
permanent magnets in said vacuum vessel for use in magnetron
discharge effected in the vicinity of the semiconductor substrate
for promoting the rate of sputtering.
6. A semiconductor manufacturing apparatus according to claim 2,
wherein said second radiofrequency power source for use in the
radiofrequency discharge provides a radiofrequency having a
wavelength at least twice the size of the semiconductor substrate
for assuring uniform film making.
7. A semiconductor manufacturing apparatus according to claim
.[.2.]. .Iadd.5.Iaddend., wherein said magnet for magnetron
discharge comprises an elongated closed loop magnet.
8. A semiconductor manufacturing apparatus according to claim 2,
comprising:
magnets provided on the side of the semiconductor substrate for
improving the efficiency of the resputtering.
9. A semiconductor manufacturing apparatus according to claim 2,
wherein the second radiofrequency power source comprises:
means for generating and applying to the succeptor powers of two
different frequencies f.sub.1 and f.sub.2, said frequency f.sub.1
being higher than said frequency f.sub.2, said
frequency f.sub.1 being changed over to f.sub.2, wherein
radiofrequency power of said frequency f.sub.1 is first applied to
said succeptor electrode in making a thin film, and thereafter said
radiofrequency of said frequency f.sub.2 is applied to form a
further thick film on said thin film.
10. A semiconductor manufacturing apparatus according to claim 2,
wherein said succeptor electrode has a plurality of radiofrequency
powers of a plurality of different radiofrequencies corresponding
to said powers applied from a plurality of the radiofrequency power
sources thereto for reducing any damage on the substrate, the
radiofrequency power first applied to the succeptor having a
radiofrequency higher than the radiofrequencies of the other power
sources.
11. A semiconductor manufacturing apparatus according to claim 10,
wherein said plurality of radiofrequencies are selected so that not
one of said plurality of radiofrequencies is an integer multiple of
the radiofrequency of another radiofrequency in order to avoid
nonlinear interaction among said plurality of radiofrequencies.
12. A semiconductor manufacturing apparatus according to claim 2,
wherein said insulating thin film of the target is a material
selected from the group consisting of SiO.sub.2, BPSG, silicon
nitride, Al.sub.2 O.sub.3, and AlN. .Iadd.
13. A manufacturing apparatus according to claim 1, wherein said
substrate is a semiconductor substrate, and wherein said thin film
is an insulating thin film. .Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor manufacturing
apparatus, and more particularly to a bias sputtering apparatus for
depositing an insulating thin film on a substrate.
2. Discussion of Background
Presently, a sputtering method is widely employed for formation of
wiring materials and insulating thin films for use in integrated
circuits. Such a sputtering method makes a thin film by introducing
Ar gas into a vacuum vessel and applying direct current or
radiofrequency power to a cathode including a target material
mounted thereon to cause glow discharge. As a result of this glow
discharge, a target surface is negatively biased (called a self
bias) with respect to the plasma, and Ar ions accelerated by this
bias voltage collide with the target surface to subject the target
material to sputtering and etching. Material particles so etched
are deposited on a wafer located in opposition to the target for
film making. In contrast, there is known the so called
radiofrequency bias sputtering process wherein radiofrequency power
is applied to a succeptor itself including the wafer mounted
thereon as well as target to deposit a film on the wafer surface,
while sputtering and etching are effected by the self bias formed
on the wafer surface simultaneously with the film deposition on the
wafer surface.
FIG. 5 is a schematic cross-sectional view of a typical
conventional bias sputtering apparatus. Designated at 501 is a
target composed of a material such as SiO.sub.2, Si.sub.3 N.sub.4,
Al.sub.2 O.sub.3, AlN and the like for example, and 502 designates
a target electrode including the target mounted thereon. Moreover,
designated at 503 and 504 are respectively a semiconductor wafer
and a succeptor electrode. Radiofrequency power is supplied to the
target electrode 502 and the succeptor electrode 504 via a matching
circuit, and a vacuum vessel 505 is grounded. For this application,
a radiofrequency (RF) power source having an oscillation frequency
of 13.56 MHz is typically employed. Moreover, for an actual
apparatus, besides those members described above, a vacuum exhaust
unit, a gas introduction inlet, and a mechanism for taking the
wafer into and out of the apparatus are provided, but are not shown
in the figure for the sake of brevity.
The surfaces of the semiconductor wafer 503 and the succeptor 504
are negatively biased with respect to the plasma by the RF power
applied to the succeptor, with which the Ar ions accelerated by an
electric field caused by the self bias collide to permit the
deposited film to be partly resputtered. Such a radiofrequency bias
sputtering method assures a thin film excellent in mechanical
strength. In addition, this radiofrequency bias sputtering method
also enables a flat surface film to be formed by making use of a
property of the film, that film formed at a stepped portion is
likely to be sputtered. This method however suffers from a severe
problem during manufacturing a semiconductor integrated circuit in
that the substrate of the semiconductor wafer is damaged due to the
collision of the Ar ions accelerated by the self bias with the
semiconductor wafer resulting in deteriorated characteristics of
the constituent elements. These problems hinder the bias sputtering
apparatus from being put into practical use.
SUMMARY OF THE INVENTION
In view of the drawbacks of the prior techniques, it is an object
of the present invention to provide a semiconductor manufacturing
apparatus capable of forming a high quality insulating thin film
without damaging an underlying substrate.
The above object, and other objects, are achieved according to the
present invention by providing a bias sputtering apparatus for
depositing an insulating thin film on the surface of a
semiconductor substrate in an atmosphere of reduced pressure,
including a target composed of a material for the insulating thin
film or of at least one of constituent elements of the material for
the insulating thin film, a target electrode provided mounted on
and adjoining the target for applying first radiofrequency power of
a first frequency to the target, a first radiofrequency power
source for generating the first radiofrequency power of the first
frequency to supply that power to the target electrode, a first
matching circuit provided between the target electrode and the
first radiofrequency power source for matching the target electrode
to the first radiofrequency power source, a band reject filter
disposed between the matching circuit and the target electrode for
selectively permitting only the first radiofrequency signal to be
transmitted to the target electrode, a semiconductor substrate
disposed spaced away from the target in a confronting relation
therewith for permitting the insulating film of the target to be
deposited thereon as a result of sputtering, a succeptor electrode
for supporting the semiconductor substrate thereon, a second
radiofrequency power source for generating second radiofrequency
power of a second frequency to the succeptor thereby to permit a
self bias to be applied to the surfaces of the semiconductor wafer
and the succeptor for thereby resputtering the deposited film in
part, the self bias being negative in potential with respect to the
plasma, a second matching circuit disposed between the succeptor
electrode and the second radiofrequency power source for matching
the succeptor electrode to the second radiofrequency power source,
a second band eliminator disposed between the succeptor electrode
and the matching circuit for selectively permitting the second
radiofrequency signal to be transmitted to the succeptor electrode,
and a vacuum vessel for enclosing the target electrode, target,
semiconductor substrate, and succeptor, the first frequency being
selected to be lower than the second frequency.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the
attendant advantages thereof will be readily obtained as the same
becomes better understood by reference to the followed detailed
description when considered in connection with the accompanying
drawings, wherein:
FIGS. 1(a), (b) and (d) are schematic diagrams respectively
illustrating a first embodiment of a semiconductor manufacturing
apparatus according to the present invention;
FIG. 1c is a graph illustrating the filter characteristic of a band
reject filter;
FIG. 2 is a schematic diagram illustrating a measuring unit for
measuring a volt-ampere characteristic of a succeptor
electrode;
FIG. 3 is a graph illustrating experimental data concerning the
volt-ampere characteristic of the succeptor electrode;
FIGS. 4(a) and 4(b) are schematic diagrams respectively
illustrating second and third embodiments of the semiconductor
manufacturing apparatus according to the present invention;
FIG. 5 is a schematic diagram illustrating a conventional
semiconductor manufacturing apparatus; and
FIG. 6 is an isometric view of a powerful magnet of racing track
type.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings, wherein like reference numerals
designate identical or corresponding parts throughout the several
views, FIG. 1(a) illustrates a first embodiment of a bias
sputtering apparatus for forming an insulating thin film according
to the present invention. In FIG. 1(a), designated at 101 is a
target of a material such as SiO.sub.2, for example, mounted on a
target electrode 102. Radiofrequency power of, for example, 13.56
MHz is applied to the target electrode via a matching circuit in
the same fashion as the conventional apparatus (FIG. 5). Moreover,
radiofrequency power having a higher frequency than that applied to
the target, for example 100 MHz, is applied to a silicon wafer 103
and a succeptor 104 via a matching circuit.
In addition, band reject filters 102' and 104' are respectively
provided for the target electrode 102 and the succeptor electrode
104 so as to permit only high frequencies of 13.56 MHz and 100 MHz
to be supplied thereto. The band reject filters used for the
succeptor electrode 104 may take an arrangement as illustrated in
FIG. 1(b) for example. A parallel L-C circuit has the maximum
impedance at its resonance frequency of ##EQU1## (FIG. 1(c)), and
is substantially short-circuited at frequencies other than that of
the resonance frequency, and hence it can select only a high
frequency of a prescribed one (.function.1=100 MHz in the present
case) to supply it to the succeptor electrode. Hereupon, the
arrangement of FIG. 1(b) strictly shows the fundamental principle
of the present invention, to which various modifications for
improvement may be applied, as a matter of course.
For example FIG. 1(d) shows such an improvement. In FIG. 1(d),
although a circuit 104b is DC grounded, when it is desired to float
the circuit, a capacitor C.sub.S may be added, like capacitor 104d
in FIG. 1(d), to cut off the DC path, for example. It is needed
thereupon to make C.sub.S sufficiently high such that it satisfies:
to prevent shifting of the resonance frequency from f.sub.l.
In this case, the L.sub.1 -C.sub.S series circuit is adapted to
have zero impedance at the resonance frequency of ##EQU2## and this
is short-circuited at that frequency. Provided
this resonance frequency f.sub.o is set to be equal to the
aforementioned frequency of 13.56 MHz applied to the target, the
succeptor can effectively prevent the radiofrequency of 13.56 MHz
from interfering therewith.
Again referring to FIG. 1(a), a vacuum vessel 105 is electrically
grounded. In addition, a permanent magnet 106 is provided for
enhancing the electrical discharge inside the vacuum vessel 105 by
making use of magnetron discharge. Moreover, the apparatus includes
an exhaust unit, a gas introduction mechanism, and a mechanism for
taking in and out of the silicon wafer 103, which are omitted for
brevity's sake.
Here, the bias sputtering apparatus of the present invention
arranged as described above assures film making of an insulating
thin film by bias sputtering without damaging the underlying
semiconductor wafer. The reason is explained with the aid of FIGS.
2 and 3.
FIG. 2 is a schematic diagram illustrating a device for measuring
the volt-ampere characteristic of the succeptor electrode. A bias
sputtering apparatus employed here is the same as that shown in
FIG. 1. But, a DC power source 201 and an ammeter 202 are connected
to one of the aforementioned electrodes (the succeptor electrode
204 in this figure) via a low pass filter 203 which has a high
impedance at high frequency signals to be applied to the succeptor
and which is substantially short-circuited for DC signals.
FIG. 3 is a graph plotting a relationship between DC voltage V to
be applied to the succeptor electrode and a current flowing
therethrough as obtained upon introduction of Ar gas at pressure of
5.times.10.sup.-3 Torr into the vacuum vessel 105 to cause
electrical discharge therein. Thereupon, the frequency of the
radiofrequency power source 205 is made variable with results
plotted in the figure for three frequencies 14 MHz, 40.68 MHz, and
100 MHz. Currents flowing into the electrode are assumed there to
be positive.
For example, referring to the characteristic of 100 MHz, I=0 holds
when V is approximately -95 V (this value is expressed by
v.sub.SB); 1<0 when V>V.sub.SB ; and I>0 when
V<V.sub.SB. This value of V.sub.SB is called a self-bias which
is DC bias voltage naturally appearing when the electrode is
floating. That is, when the electrode has this potential, numbers
of ions and electrons flowing from the plasma into the electrode
are equal to and cancel out each other to result in zero current
flow. The current is thereupon allowed to flow by controlling the
potential of the electrode by making use of a DC bias applied from
the outside. For example V>V.sub.SB causes many electrons to
flow into the electrode to result in I<0.
Against this, when V<V.sub.SB holds, a potential barrier against
the electrons is made high such that, the number of electrons
flowing into the electrode is reduced, whereby the ion current is
made higher to permit a positive current to flow through the
electrode. With V being further increased negatively, the current
is saturated at V=V.sub.o up to a constant. This is equal to the
current carried only by the ions. In view of the above-described
investigation, the slope of the I-V characteristic when
V>V.sub.o corresponds to the width of energy distributions of
those electrons. That is, a larger slope means a narrow energy
distribution width. FIG. 3 clearly shows the width of the energy
distribution at 100 MHz is reduced to about 1/10 of that at 14 MHz.
Assuming the width of the energy distribution of the ions to be
.DELTA.E.sub.ion and that of the electrons to be .DELTA.E.sub.e,
there is substantially a proportional relationship, and hence the
width of the energy distribution of the ions is also reduced to
about 1/10.
Furthermore, V.sub.SB is also reduced by 1/4 or less in terms of
absolute values from -400 V at 14 MHz to about -95 V at 100
MHz.
Prior methods of bias sputtering suffered as described above from
the fact that the underlying substrate was damaged to deteriorate
the characteristics of the resultant semiconductor device. This
occurred because the electric discharge was produced at the
frequency of 13.56 MHz to result in .vertline.V.sub.sub
.vertline.=400 V to 6000 V, whereby those ions accelerated by this
high voltage collide against the semiconductor substrate. In
addition, the energy distribution of the ions is broadened to
permit many ions to have sufficiently higher energy than the mean
value of the energy even if that mean value is controlled. Such
high energy ions bombard, the substrate to damage the same.
However, the first embodiment of the present invention is adapted
to apply a radiofrequency wave of 100 MHz to the wafer succeptor
electrode 104 to reduce .vertline.V.sub.S .vertline. to about 1/4
to 1/5 and to reduce .DELTA.E.sub.ion to 1/10 or less as compared
with the prior case in which FR power at 13.56 MHz was used. Thus,
the first embodiment of the present invention can prevent the
semiconductor substrate from being damaged.
The self-bias voltage V.sub.SB is further reduced as the frequency
of the radiofrequency power source is increased. Accordingly, such
a frequency capable of providing a DC bias necessary and sufficient
to effect the RF bias sputtering may be selected so as to be
applied to the succeptor.
In FIG. 1(a), 13.56 MHz is applied to the target electrode 102 in
the same manner as in the prior case to cause a greater self-bias
for thereby promoting sputtering owning to higher ion energy,
whereby the rate of sputtering for the target is prevented from
being decreased. Furthermore, the embodiment of FIG. 1(a) is
adapted to include a magnet 106 provided in the vacuum vessel 105
to concentrate ions produced by magnetron discharge in the vicinity
of the target substrate thereby further to increase the rate of
sputtering.
According to the RF bias sputtering apparatus of the present
invention, as described above, the RF bias sputtering for an
insulating film can be assured with the rate of film making kept
higher without damaging the substrate.
Moreover, the energy of the ions entering the succeptor can be
controlled by applying a DC bias to the succeptor electrode as
illustrated in FIG. 2, but this is not effective in forming an
insulating thin film associated with the present invention. The
reason is that the surface potential of such an insulating film is
fixed to V.sub.SB at all times independently of that of the
electrode. It is therefore impossible to finely control the energy
of the ions entering the substrate without any reliance on the
present invention.
Although the frequencies of the RF power to be supplied to the
target and the succeptor were 13.56 MHz and 100 MHz in the above
description, they are not limited thereto as a matter of course.
Briefly, the frequency for the latter succeptor may be made higher
than that for the former target, and actual values of those
frequencies may be determined in consideration of a required rate
of film making and a coated shape of a formed film at the stepped
portion, etc., which rely on respective particular purposes.
However, the use of a microwave power having a frequency such as
2.45 GHz, for example, undesirably causes non-uniform film
thickness because the wavelength of the electromagnetic wave
becomes less than the size of the wafer.
In order to make a uniform film, the RF wavelength from the RF
power source for use in the RF discharge needs to be at least twice
the wafer diameter or more. This frequency preferably ranges from
100 MHz to 1 GHz. But, it is needless to say that another frequency
out of this range may be employed depending on the wafer
diameter.
In addition, the magnet 106 mounted on the back of the target
electrode 102 is not limited to the arrangement shown in FIG. 1. As
disclosed for example in the second embodiment of the present
invention shown in FIG. 4(a), a powerful magnet 409 of racing track
type of which example is shown in FIG. 6 may be installed and
scanned to assure a more uniform magnetic filed. Thereupon,
provided a scanning system 410 is disposed outside a vacuum vessel
405 as shown in FIG. 4(a), for example, a reaction system is
favorably prevented from being contaminated by any dust produced
owning to mechanical operation thereof. Moreover, the magnet 106
may be omitted, of course, if necessary without departing from the
scope of the present invention.
It is furthermore permitted to install a magnet also on the side of
the succeptor to improve the efficiency of resputtering. In
addition, the magnet employed there may be stationarily mounted
such as 106 of FIG. 1, or may be movably mounted, such as the
magnet 410 of FIG. 4(a).
Moreover, in order to reduce further any damage on the
semiconductor substrate, the following method, for example, may
also be useful. That is, in depositing an insulating film such as
SiO.sub.2 directly on the exposed surface of silicon, RF power
supplied to the silicon substrate is first set to zero without
resputtering when a first film of thickness from about several tens
.ANG. is formed, and thereafter the system is changed over to the
bias sputtering. This prevents the surface of the silicon substrate
from being damaged because of no resputtering occurring where the
silicon surface is exposed and because of the initiation of
sputtering for film making after a thin film is formed on the
silicon surface.
FIG. 4(b) illustrates a third embodiment of the present invention,
capable of freely selecting energy for resputtering with reduced
damage onto the semiconductor substrate. This is different from the
first embodiment shown in FIG. 1(a) because the FIG. 4(b)
embodiment is adapted to selectively apply any of two different
frequencies of f.sub.1 and f.sub.2 to the succeptor by changeover
thereof with a new band eliminator 401 for which the previous one
is exchanged, depending on the frequency employed between f.sub.1
and f.sub.2.
Designated at 402 and 403 are respectively LC resonance circuits
having resonance frequencies of f.sub.1 and f.sub.2. ##EQU3##
A band eliminator 401 including the two resonance circuits 402 and
403 connected in series is adapted to have high impedances only at
the two frequencies of f.sub.1 and f.sub.2 and short-circuited at
frequencies other than those two frequencies, and hence serves to
selectively supply only the RF waves of these two kinds to the
succeptor.
For example f.sub.0 =13.56 MHz, f.sub.1 =100 MHz, and f.sub.2 =40
MHz. In addition, in depositing an insulating film such an
SiO.sub.2 directly on the exposed surface of silicon, for example,
the RF frequency applied to the succeptor 104 is made f.sub.1 (100
MHz) when a first film having the thickness of from several tens
.ANG. to 100 .ANG. is formed. Thereafter, the frequency is changed
over to f.sub.2 (40 MHz) to permit a thick film (0.5 to 1 .mu.m for
example) to be formed. Such arrangement permits resputtering to be
effected at a small self bias of about 95 V corresponding to 100
MHz when the silicon surface is exposed further to reduce any
damage on the semiconductor substrate. The changeover of the
frequency to 40 MHz upon completion of covering of the surface with
SiO.sub.2 to the thickness of about 100 .ANG. increases the
self-bias to 250 V and assures an enhanced effect of the
resputtering. However, since the surface of the silicon has already
been covered with SiO.sub.2, the substrate is protected from
damage.
Such a technique is particularly important in controlling the
surface flatness of the insulating film deposited by the method of
the bias sputtering, because such a change in the frequency enables
energy of the Ar ions to be controlled for the most effective
resputtering and the optimum energy to be selected without fear of
damage to the substrate.
Although here only the case of the two different frequencies of
f.sub.1 and f.sub.2 were described, three frequencies of f.sub.1,
f.sub.2 and f.sub.3 may be employed as a matter of course. But, in
this situation, for a frequency f.sub.1 to be first applied to th e
electrode, it is important that f.sub.1 have a frequency higher
than f.sub.2 and f.sub.3 to prevent damage to the substrate. In
addition, upon the use of a plurality of frequencies, it is
desirous to select those frequencies, f.sub.1, f.sub.2 . . .
including the frequency f.sub.0 for the target such that they do
not satisfy a relationship of higher harmonics with respect to each
other, because a nonlinear discharge space may cause RF waves of
harmonic frequencies f.sub.0, f.sub.1, f.sub.2 . . . to interfere
with each other depending on the discharge conditions to result in
inaccurate settlement of a desired condition.
Although the embodiments of the present invention are mainly
illustrated for the disposition of the SiO.sub.2 film in the
foregoing description, they are not limited thereto as a matter of
course. For example, the present invention may be applied to film
making from materials such as PSG, BPSG, nitrided silicon, Al.sub.2
O.sub.3, and AlN, etc.
In addition, although the present invention is described by
exemplary application to the technique of RF bias sputtering with
use of Ar ions, it is also applicable to reactive RF bias
sputtering wherein upon making of a film of Si.sub.3 N.sub.4 for
example, a Si substrate is employed as the target with N.sub.2 or
NH.sub.3 employed as the introduction gas to make a film of
Si.sub.3 N.sub.4. In making a film of AlN, Al may be employed as
the target substrate together with N.sub.2 or NH.sub.3 as the
introduction gas.
Moreover, the present invention is applicable as needed to the
formation of macromolecular materials such as polyimide films and
resists, for example.
Furthermore, it is a matter of course that the substrate for use in
film making is not limited to the semiconductor wafer.
According to the semiconductor manufacturing apparatus of the
present invention, as described above, a high quality insulating
film excellent in surface flatness can be manufactured with ease
without causing any damage onto the substrate.
Obviously, numerous additional modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *