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BACKGROUND OF THE INVENTION
This invention generally relates to a plasma processing apparatus used for
the fabrication of semiconductor devices and the like in the semiconductor
industry, and, more particularly, to a plasma processing apparatus
suitable for performing, within a short period of time, such processings
as uniform injection of impurities into a large area semiconductor device
and a large area semiconductor thin film and uniform formation and etching
of a large area semiconductor thin film.
For performing doping of a desired amount of impurities in the form of ions
into a semiconductor thin film and the like at a desired depth, or
formation and etching of a thin film, there have hitherto been available
various methods including:
(1) a method using an inductance coupling RF ion source, as disclosed in
Review of Scientific Instruments, vol. 33 (1962), pp. 649-652, by C. J.
Cook et al, and illustrated in FIG. 9 of the present application;
(2) a method using a compact ion injector, as disclosed in Proceeding of
the European Community Photovoltaic Solar Energy Conference (Luxembourg),
September 1977, pp. 897-909, by J. C. Muller et al, and illustrated in
FIG. 10 of the present application, wherein an ion source utilizing DC
glow discharge supplies electrons which are not caused to pass through a
mass separation unit, but are accelerated through an ion accelerator unit
so as to be injected into a semiconductor substrate or the like; and
(3) a method such as illustrated in FIG. 11 of the present application
which uses a plasma CVD apparatus wherein capacitance coupling RF
electrodes disposed in a vacuum chamber are energized to cause chemical
vapour reaction through RF glow discharge, with a DC voltage further
applied to the R. F. electrodes by being superimposed on the RF
energization voltage.
In the above-described prior art methods of doping impurities in the form
of ions into a semiconductor thin film or the like, the first method (1)
using the inductance coupling RF ion source shown in FIG. 9 specifically
performs ion injection, etc. by forming a focused ion beam which is
focused through an ion source aperture of 1 cm or less. However, due to
the small diameter of the focused ion beam, electrical scanning of the ion
beam, for example, becomes necessary to perform large area processing of a
semiconductor thin film, etc. Further, RF power leaks externally and an
induced current caused by the RF power leakage flows through the external
electromagnetic coil. Consequently, when the RF power is increased, the
magnetic field generated by the magnetic coil becomes unstable, giving
rise to unstable and nonuniform discharge, and hence it becomes difficult
to perform large area processing uniformly within a short period of time.
An example of the compact ion injector used in the second method (2) is
shown in FIG. 10. In FIG. 10, reference numeral 600 designates a discharge
chamber, 601 a DC power supply for discharging, 602 an anode electrode for
causing DC glow discharge, 603 an acceleration electrode, 604 an
acceleration power supply, 605 a substrate stand or supporting table, 606
a substrate or like material, 607 a gas inlet conduit, 608 a gas
evacuation pipe, and 609 an insulating member.
In the compact ion injector shown in FIG. 10, impurity ions from the ion
source utilizing DC glow discharge, which is caused by the application of
a DC voltage from the DC power supply 601 across the anode electrode 602
and the acceleration electrode 603, are accelerated by the ion accelerator
unit, which effects ion acceleration by a potential difference between the
acceleration electrode 603 and the substrate stand 605 provided by the
acceleration power supply 604. Then, the impurity ions are injected into a
semiconductor substrate or the like without being subjected to mass
separation performed by a mass separation unit. In this compact ion
injector, however, it is necessary to use a complicated mechanism such as
a differential evacuation system to thereby maintain the pressure of the
ion source at a reduced pressure of 1 to 0.01 Torr necessary for the ion
source to fulfil its function for sustaining DC glow discharge and to
maintain a substrate chamber at a pressure of 10.sup.-3 Torr or less at
which pressure the mean free path of the ions can exceed the distance
between the ion source and a substrate. Further, when the discharge
electrodes are made larger to increase the impurity injection area, there
occurs nonuniform and unstable discharge due to creeping discharge, etc.,
which makes it difficult to attain impurity doping with high precision.
An example of the plasma CVD apparatus used in the third method (3) is
shown in FIG. 11. In FIG. 11, reference numeral 610 designates a vacuum
chamber, 611 an RF electrode, 612 a matching box, 613 an RF oscillator,
614 a DC power supply, 615 a gas inlet conduit, 616 a gas evacuation pipe,
617 a substrate or like material, and 618 a substrate stand.
In the plasma CVD apparatus shown in FIG. 11, the capacitance coupling type
RF electrode 611 contained in the vacuum chamber 610 is supplied with RF
power from the RF oscillator 613 and gives rise to a chemical vapour
reaction by RF glow discharge within the vacuum chamber 610. Further, the
substrate stand 618 acting as the other capacitance coupling type RF
electrode is supplied with an acceleration DC voltage from the DC power
supply 614. With the above-mentioned structure, impurity ions generated by
the RF glow discharge are doped into the substrate 617. In this plasma CV
apparatus, the internal pressure of the vacuum chamber 610 is maintained
at 1 to 0.01 Torr in order to sustain the RF glow discharge occurring
therein, and the upper value of the applicable DC voltage is as low as 100
to 1000 volts. As a result, neutral particles other than desired ions are
deposited on the surface of the substrate 617 and high precision impurity
doping with a prescribed concentration of impurities has been difficult to
attain. In addition, since the discharge electrodes 611 and 618 act also
as the acceleration electrodes, discharge becomes unstable. Accordingly,
it becomes difficult to perform plasma processing such as impurity doping
or etching of a substrate having a large area in a uniform manner.
SUMMARY OF THE INVENTION
An object of this invention is to provide a plasma processing apparatus
capable of solving the problems described hereinbefore.
To accomplish the above object, in the present invention, a gas is
introduced into a vacuum chamber, thereby forming an ion source, an RF
signal is applied to two opposite electrodes having their surfaces opposed
to each other through the gas to thereby generate plasma therebetween, and
a magnetic field source is disposed at a required position to apply a
magnetic field to the plasma, where the intensity of the magnetic field is
set to be more than 1.5 times the magnetic field intensity which causes
electron cyclotron resonance to occur. In a specified case where RF power
has a frequency f of 13.56 MHz, the magnetic field intensity is set to be
in the range from 25 gausses to 35 gausses.
The present invention is advantageous in that plasma processing such as
doping of highly purified inpurities into a substrate having a large area
and etching of a substrate can be performed uniformly and with high
precision.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic drawing illustrating a plasma processing apparatus
according to a first embodiment of this invention.
FIG. 2 is a schematic drawing illustrating a plasma processing apparatus
according to a second embodiment of this invention.
FIG. 3 is a cross-sctional view showing the discharge chamber C of the
second embodiment.
FIG. 4 is a graph illustrating the optical emission intensity of the light
emitted from excited nitrogen ions (N.sup.+.sub.2 <0, 0>) at a wavelength
of 392 nm obtained by the plasma optical emission spectroscopy measurement
of nitrogen gas (N.sub.2) plasma generated in the discharge chamber C of
the second embodiment.
FIG. 5 is a schematic drawing showing a plasma processing apparatus
according to a third embodiment of this invention.
FIG. 6 is a perspective drawing schematically illustrating a supplemental
modification of the apparatus of the third embodiment.
FIG. 7 is a schematic drawing illustrating a plasma processing apparatus
according to a fourth embodiment of this invention.
FIG. 8 is a graph showing the relation of the ion current density versus
the intensity of an applied magnetic field.
FIG. 9 is a schematic diagram showing a prior art inductance coupling RF
ion source.
FIG. 10 is a schematic drawing showing a prior art compact ion injector
wherein ions from an ion source utilizing DC glow discharge are
accelerated through an ion accelerator, without being caused to pass
through a mass separation unit, so as to be injected into a semiconductor
substrate or the like.
FIG. 11 is a schematic drawing illustrating a prior art plasma CVD
apparatus which produces chemical vapour reaction through RF glow
discharge caused by capacitance coupling RF electrodes disposed in a
vacuum chamber, the RF electrodes further having a DC voltage applied
thereto by the superimposition thereof on the RF energization voltage.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Before proceeding to the detailed description of preferred embodiments of
this invention, a general description of this invention will be given
hereunder.
In the practical construction of a plasma processing apparatus of the
present invention, an ion source comprises a first vacuum chamber having a
surface made of an insulating material, RF electrodes disposed outside the
first vacuum chamber and along the insulating surface thereof, a magnetic
field source disposed outside the RF electrodes, and a grounded conductor
disposed between the respective RF electrodes and the magnetic field
source when an electromagnetic coil or electromagnetic coils are used as
the magnetic field source. A substrate stand carrying a substrate to be
subjected to plasma processing such as impurity doping and etching of the
substrate is disposed in a second vacuum chamber.
The same effect can be obtained by an apparatus comprising a vacuum chamber
in which RF electrodes, a first conductive porous plate or conductive
mesh, a second conductive porous plate or conductive mesh and a substrate
stand are disposed in parallel with each other, and further comprising a
magnetic field source disposed outside the vacuum chamber for generating a
magnetic field having a magnetic field component perpendicular to an
electric field applied by the RF electrodes.
The magnetic field generated in the discharge chamber by the magnetic field
source effects the confinement of electrons and excitation of cyclotron
gyration of electrons, which allows RF power supplied to the RF electrodes
to be used efficiently so that stable and uniform discharge can be
effected even at a low gas pressure of 10.sup.-3 to 10.sup.-4 Torr.
Because of the highly efficient discharge, the vacuum chamber, in which
plasma is generated, can be constructed to have a surface formed of an
insulating material, and the capacitance coupling RF electrodes having
opposite surfaces are disposed outside the vacuum chamber and along the
surface thereof formed of an insulating material to make discharge occur
therethrough. The discharge caused by the RF power supplied from the RF
electrodes having the opposite surfaces and by the applied magnetic field
generated by the magnetic field source is highly uniform. This fact
permits generation of a uniform charged particle flow or a uniform plasma
flow having a desired cross-sectional form such as an elongated slit or a
circle, as will be explained later.
In this case, in order for electrons to effect cyclotron gyration at a
frequency for industrial use of 13.56 MHz, for example, the application of
a magnetic field, whose intensity is 4.8 gausses, is required. However,
this magnetic field intensity is about 10 times the intensity of a
terrestrial magnetic field, and this magnetic field intensity has not been
practical, because a magnetic field of this intensity is difficult to
control. Under the circumstances, the inventors of the present invention
have found that the efficiency of discharge can be improved even at a
magnetic field intensity of 4.8 gausses or more. The efficiency can be
demonstrated by applying RF power of the frequency of 13.56 MHz to an
N.sub.2 gas to generate plasma and by drawing out ions from the plasma.
FIG. 8 graphically illustrates the relation of the ion current density
versus the intensity of an applied magnetic field. It will be seen from
FIG. 8 that an increase of the ion current caused by the application of a
magnetic field was observed in the range exceeding the magnetic field
intensity of about 1.5 times the magnetic field intensity for causing
electron cyclotron resonance. It will also be noted from FIG. 8 that the
ion current density has a maximum point near a magnetic field intensity of
30 gausses which is about 6 times the electron cyclotron resonance
magnetic field intensity. In addition, the inventors observed that the ion
current density decreases in the range of the magnetic field intensity of
500 gausses or more. In this manner, the efficiency of discharge can be
improved by optimizing the intensity of an applied magnetic field, thereby
stabilizing discharge and generating ions with high efficiency.
When an electromagnetic coil is used as the magnetic field source, a
grounded conductor is interposed between the respective RF electrodes and
the electromagnetic coil to prevent RF power from leaking to the outside
so that an induced current caused by RF power does not flow through the
electromagnetic coil. This stabilizes the applied magnetic field and makes
the discharge very stable and uniform even when RF power is increased. As
a result, it becomes possible to obtain a plasma flow or a charged
particle flow of a large diametric dimension to thereby perform plasma
processing which can be effected uniformly over a large substrate area
without necessitating electrical scanning of the beam.
As described previously, the application of RF power and a magnetic field
makes it possible to sustain stable and uniform discharge even at a gas
pressure of 10.sup.-3 to 10.sup.-4 Torr. The mean free path of ions at the
10.sup.-3 to 10.sup.-4 Torr gas pressure approximates or exceeds the
distance (about 10 cm) between the discharge chamber and the substrate
stand, though there is a difference dependent on the kind of ions and
their energy. Therefore, with the simplified construction including the
first and second electrodes disposed in the discharge chamber, the charged
particles can be drawn out and accelerated so as to be transmitted to a
semiconductor substrate mounted on the substrate stand and to irradiate
the substrate. By virtue of the reduction of the pressure inside the
apparatus to less than 10.sup.-3 Torr and the separated provision of the
RF electrodes for discharging and the electrodes for acceleration,
abnormal discharge such as creeping discharge and avalanche discharge,
which would be caused by high pressure and high DC voltage, can be
prevented, and a large diameter charged particle beam or a large diameter
plasma flow can be accelerated to have 1000 eV or more. The reduction of
the interior pressure to 10.sup.-3 Torr or less is also advantageous in
that deposition of neutral particles other than the desired ions on the
substrate surface can be avoided and high precision plasma processing such
as high precision doping of impurities at a prescribed impurity
concentration and high precision etching of a substrate can be performed.
The embodiments of the present invention will now be described in more
detail with reference to the accompanying drawings.
Referring to FIG. 1, there is illustrated, in a schematic diagrammatic
form, a plasma processing apparatus according to a first embodiment of the
present invention. A discharge chamber A comprises a vacuum chamber 100
having a form of a cylindrical tube which is made of an insulating
material such as quartz, glass or a ceramic. A gas is introduced into the
vacuum chamber 100 through a gas inlet conduit 101. Capacitance coupling
RF electrodes 102-a and 102-b are made of a metal having high conductivity
such as copper or stainless steel and disposed outside the vacuum chamber
100 along a surface thereof. One capacitance coupling RF electrode 102-a
is connected to an RF oscillator 104 of the frequency of 13.56 MHz via a
matching box 103 with the other electrode 102-b grounded, thus supplying
RF power to the interior of the vacuum chamber 100. A permanent magnet 105
is disposed outside the capacitance coupling RF electrodes 102-a and 102-b
to apply a magnetic field in the tube axis direction of the cylindrical
tube. Since the magnetic field effects excitation of cyclotron gyration of
electrons and confinement of electrons, RF power can efficiently be used
to generate plasma stably within the vacuum chamber 100 even at a
relatively low pressure of 10.sup.-3 to 10.sup.-4 Torr. The intensity of
this magnetic field inside the vacuum chamber 100 may be of the order of
10 to 200 gausses. The discharge chamber A is connected to a substrate
chamber B through an electrode 107 having an aperture 106 and an
insulating flange 108 made of, for example, teflon, a ceramic, or a vinyl
chloride. The electrode 107 is connected to a power supply 109 to apply DC
or AC bias. A conductive mesh 110 is applied to cover the aperture 106 and
uniform capture or drawing-out of charged particles is effected over the
aperture 106 by the conductive mesh 110. The substrate chamber B is in
communication with a gas evacuation pipe 111 and maintained at a pressure
of 10.sup.-3 to 10.sup.-4 Torr. Within the substrate chamber B, a
conductive substrate stand 112 made of, for example, stainless steel,
aluminum or copper is disposed and a substrate or a like material 113 such
as a semiconductor substrate is mounted on the substrate stand 112. In
this embodiment, the substrate stand 112 is fixedly supported within the
substrate chamber B by means of an insulating flange 114 made of, for
example, teflon, a ceramic or a vinyl chloride. The substrate 113 is
heated by a heater 115 to raise the efficiency of plasma processing such
as deposition, etching or ashing. A plasma flow 116, which is drawn out
from a plasma cloud generated uniformly in the vacuum chamber 100 and is
distributed uniformly over the aperture 106, irradiates the substrate 113
carried by the substrate stand 112 to perform plasma processing such as
deposition of a desired amount of impurities, etching or ashing of the
substrate 113.
Referring to FIG. 2, a plasma processing apparatus according to a second
embodiment of the invention is schematically illustrated. The sectional
view of a discharge chamber C of the second embodiment taken along line
III--III, is shown in FIG. 3. The discharge chamber C comprises a vacuum
chamber 200 having a form of a cylindrical tube which is made of an
insulating material such as quartz, glass or a ceramic. Capacitance
coupling electrodes 201-a and 201-b for RF glow discharge made of a high
conductivity metal such as copper or stainless steel are disposed outside
the vacuum chamber 200 along a surface thereof. One capacitance coupling
RF glow discharge electrode 201-a is connected to an RF oscillator 203 of
the frequency of 13.56 MHz via a matching box 202 with the other electrode
201-b grounded, thereby supplying RF power to the interior of the vacuum
chamber 200. An electromagnetic coil 204 is disposed outside the
capacitance coupling RF glow discharge electrodes 201-a and 201-b to apply
a magnetic field. Since the magnetic field effects excitation of electron
cyclotron gyration and electron confinement, RF power can be used
efficiently to generate plasma stably within the vacuum chamber 200 even
at a relatively low pressure of 10.sup.-3 to 10.sup.-4 Torr. The intensity
of this magnetic field may be of the order of 10 to 200 gausses inside the
vacuum chamber 200. The RF electrodes 201-a and 201-b are covered with
insulating members 205 made of, for example, teflon and a conductive mesh
206 made of, for example, copper, aluminum or stainless steel is provided
to be in contact with the outer surface of the insulating members 205 so
that the RF electrodes 201-a and 201-b are insulated from the conductive
mesh 206. This conductive mesh 206 is grounded so as to shield RF power.
Instead of using the conductive mesh 206, it is possible to use a hermetic
enclosure, which is made of a nonmagnetic conductor such as stainless
steel, etc. and which is grounded, for enclosing the discharge chamber C
therein. The use of such a hermetic enclosure is advantageous not only in
shielding RF power but also in assuring safety to provide against possible
breakage of a cylindrical tube which is made of an insulating material
such as quartz, glass, a ceramic, etc. and which forms the discharge
chamber C.
A conductive mesh 207-a made of, for example, molybdenum, stainless steel,
aluminum, titanium or tantalum and acting as a first electrode is provided
to cover an aperture 209 of an insulating flange 208 made of, for example,
a ceramic, teflon, acryl, a vinyl chloride or quartz. A conductive plate
207-b made of, for example, stainless steel, aluminum, titanium or
tantalum and acting as a second electrode is disposed in the vacuum
chamber 200 to oppose the conductive mesh 207-a through plasma 210
generated by discharge. The conductive plate 207-b is fixed to the vacuum
chamber 200 by means of insulating rods 211 made of, for example, a
ceramic, teflon or quartz. The conductive mesh 207-a acting as the first
electrode and the conductive plate 207-b are connected across a DC high
voltage power supply 212 and a voltage necessary for pushing forward and
accelerating charged particles inside the discharge chamber C into a
substrate chamber D is applied across the first electrode 207-a and the
second electrode 207-b. A material gas is introduced into the discharge
chamber C through a gas inlet conduit 213. The substrate chamber D
communicates with a gas evacuation pipe 214 and is maintained at a
pressure of 10.sup.-3 to 10.sup.-4 Torr. Disposed within the substrate
chamber D is a conductive substrate stand 215 made of stainless steel,
aluminum or copper, for example, on which a substrate or a like material
216 such as a semiconductor substrate is mounted. The substrate 216 is
heated by a heater 217 to raise the efficiency of plasma processing such
as impurity doping and etching. A charged particle beam 218 drawn out from
plasma 210 generated uniformly within the vacuum chamber 200 has a uniform
charged particle density over the aperture 209 and has kinetic energy
determined by a potential difference between the first electrode 207-a and
the substrate stand 215, and irradiates the substrate 216 mounted on the
substrate stand 215 to apply to the substrate 216 plasma processing such
as doping of a desired amount of impurities or etching.
The optical emission intensity of the light emitted from excited nitrogen
ions (N.sup.+.sub.2 <0, 0>) at a wavelength of 392 nm obtained by the
plasma optical emission spectroscopy measurement (See "The Identification
of Molecular Spectra" by R. W. B. Pearse and A. G. Gaydon, Chapman and
Hall, London, 1984, p. 227) of nitrogen gas (N.sub.2) plasma generated in
the discharge chamber C of the second embodiment of the present invention
is illustrated in the graph of FIG. 4. In this measurement, a vacuum
chamber 200 having a tube diameter of 450 mm was used, and RF power of the
frequency of 13.56 MHz and of 100 W input level and a magnetic field of
the intensity of 30 Gausses were used for both the case (I) without using
the conductive mesh 206, shown by small circles, and the case (II) using
the conductive mesh 206, shown by black circular dots. With the conductive
plate 207-b removed, a bird's eye measurement of the vacuum chamber 200
was carried out for five points A, B, C, D and E illustrated in FIG. 3.
Thus, the present inventors have found that, in the case (I) without using
the conductive mesh 206, the optical emission intensity becomes irregular
to a great extent and the discharge is unstable, whereas, in the case (II)
using the conductive mesh 206, irregularity in the optical emission
intensity is suppressed and the discharge is stable. This accounts for the
fact that the grounded conductive mesh 206 shields RF power to prevent an
induced current caused by RF power from flowing through the
electromagnetic coil so that the magnetic field inside the discharge
chamber C does not vary, thereby giving rise to the generation of stable
and uniform plasma. In this manner, the grounded conductive member
interposed between the respective RF electrodes and the electromagnetic
coil greatly contributes to the generation of stable and uniform plasma
and the uniform plasma processing by the plasma processing apparatus of
this invention.
Further, the inventors confirmed that, when the magnetic field intensity
was raised to 50 gausses or more or reduced to 20 gausses or less, the
uniformity of the optical emission intensity of the plasma was
deteriorated. Especially, it was almost impossible to observe optical
emission from the plasma at the measurement point E shown in FIG. 3, and
this showed that uniform plasma processing could not be attained in such a
condition. As a result, it was confirmed finally that the magnetic field
intensity of around 30 gausses was an optimum value for performing uniform
plasma processing of a substrate having a large area.
A third embodiment of a plasma processing apparatus according to this
invention will now be described with reference to FIGS. 5 and 6. In the
schematic illustration of FIG. 5, a discharge chamber E comprises a vacuum
chamber 400 generally made of a material which is inexpensive, has high
strength, and yet is easily workable, such as stainless steel, for
example. However, the side wall of the vacuum chamber 400 is partly made
of an insulating material permeable to RF power at surfaces 402-a and
402-b thereof covering the portions of the wall of the vacuum chamber 400
confronting capacitance coupling RF electrodes 401-a and 401-b and the
neighbouring portions thereof. One of the capacitance coupling RF
electrodes 401-a is connected to an RF oscillator 404 via a matching box
403, with the other capacitance coupling RF electrode 401-b grounded, thus
supplying RF power into the vacuum chamber 400. Disposed respectively
outside the two capacitance coupling RF electrodes 401-a and 401-b are two
insulating members 405-a and 405-b, two conductive members 406-a and
406-b, and two electromagnetic coils 407-a and 407-b. Since a composite
magnetic field generated by the two electromagnetic coils 407-a and 407-b
effects excitation of electron cyclotron gyration and confinement of
electrons, plasma 408 can be generated stably even at a low pressure of
10.sup.-3 to 10.sup.-4 Torr. The magnetic field intensity may be of the
order of 10 to 200 gausses within the vacuum chamber 400. Alternatively,
magnets may be used as the magnetic field source and in this case the
insulating members 405-a and 405-b and the conductive members 406-a and
406-b can be eliminated. A first electrode 410-a has an elongated
slit-like aperture 409 and is interposed between the discharge chamber E
and a substrate chamber F through insulating flanges 411 and 412. Within
the vacuum chamber 400, a second electrode 410-b is disposed to oppose the
first electrode 410-a through the plasma 408 generated by the discharge.
The second electrode 410-b is secured to the vacuum chamber 400 through an
insulating flange 413. The first and second electrodes 410-a and 410-b are
connected across a DC high voltage power supply 414, and a voltage for
pushing forward and accelerating charged particles inside the discharge
chamber E into the substrate chamber F is applied across the electrodes
410-a and 410-b. A material gas is introduced into the discharge chamber E
through a gas inlet conduit 415 shown in FIG. 6. The substrate chamber F
is a vacuum chamber which is in communication with a gas evacuation pipe
416 and maintained at a pressure of 10.sup.-3 to 10.sup.-6 Torr. Disposed
within the substrate chamber F is movable substrate stand 417 made of, for
example, stainless steel, aluminum or copper on which a substrate or like
material 418 such as a semiconductor substrate is placed. The substrate
418 is heated by a heater 419 to raise the efficiency of plasma processing
such as doping of impurities or etching. A charged particle beam 420,
which is drawn out from the plasma 408 generated uniformly between the
capacitance coupling RF electrodes 401-a and 401-b and in the longitudinal
direction along an X--X axis shown in FIG. 6 within the vacuum chamber
400, has a charged particle density which is uniform over the elongated
slit-like aperture 409 in the X--X axis direction and has kinetic energy
determined by a potential difference between the first electrode 410-a and
the substrate stand 417. This charged particle beam 420 irradiates the
substrate 418 mounted on the substrate stand 417 to perform plasma
processing of the substrate 418, such as doping therein a desired amount
of impurities and etching thereof.
Further, by moving the movable substrate stand 417 in both directions
(indicated by the arrows in FIG. 5) perpendicularly to the longitudinal
direction of the irradiation surface of the charged particle beam 420,
namely, in the directions perpendicular to the X--X axis direction, plasma
processing such as doping of impurities or etching can be applied very
uniformly to a substrate having a large area.
A supplemental modification of the third embodiment will now be described
with reference to the schematic perspective view shown in FIG. 6. In this
supplemental modification of the third embodiment, the construction of an
upper portion of this apparatus including the discharge chamber E is
identical with the corresponding portion of the apparatus shown in FIG. 5.
Only, however, the substrate chamber F communicates with another vacuum
chamber G and another plasma processing apparatus H through gate valves
421 and 422, respectively. By moving the substrate stand 417 from the
substrate chamber F to the vacuum chamber G or the plasma processing
apparatus H, it is made possible to perform pre-processing or
post-processing of the plasma processing such as impurity doping and
etching of the substrate 418, other plasma processings such as doping of
different impurities and etching, loading and unloading of a substrate,
etc. can be carried out without substantially deteriorating the evacuated
condition of the discharge chamber E and the substrate chamber F.
Referring to FIG. 7, there is illustrated schematically a plasma processing
apparatus according to a fourth embodiment of the present invention. A
first electrode 501 made of a high conductivity metal such as copper,
nickel, aluminum or stainless steel is supported within a vacuum chamber
500 made of a conductor, such as stainless steel, etc., and is connected
to an RF oscillator 503 via a matching box 502. A grounded first
conductive mesh 505 is spaced apart from the first electrode 501 in
parallel therewith through a predetermined space 504. The electrode 501
and the first conductive mesh 505 act as capacitance coupling RF
electrodes to supply RF power to the space 504. Two electromagnetic coils
506-a and 506-b are disposed respectively outside the vacuum chamber 500.
Since a composite magnetic field generated by the two electromagnetic
coils 506-a and 506-b performs excitation of electron cyclotron gyration
and confinement of electrons, plasma 507 can be generated stably within
the space 504 even at a low pressure of 10.sup.-3 to 10.sup.-4 Torr. The
magnetic field intensity within the vacuum chamber 500 may be of the order
of 10 to 200 guasses. RF power in this case can be shielded by the vacuum
chamber, so that the flow of an induced current through the
electromagnetic coils can be prevented, thereby allowing the magnetic
field intensity to be controlled at a desired value with high precision so
as to assure stable discharge. Alternatively, permanent magnets may be
used as the magnetic field source in place of the electromagnetic coils
506-a and 506-b. A second conductive mesh 515 made of a high conductivity
metal such as copper, nickel, aluminum or stainless steel is disposed in
parallel with the first conductive mesh 505 in an electrically insulated
state. The second conductive mesh 515 is connected to a power supply 516
and is applied with a DC or AC bias. The applied bias is effective for
performing capture or drawing out of charged particles 517 uniformly over
the second conductive mesh 515. The charged particles 517 are transmitted
passing through the second conductive mesh 515 and irradiate a substrate
508 having a large area mounted on a substrate stand 509 to thereby
perform plasma processing such as uniform impurity doping and etching of
the substrate 508 having a large area. The introduction of a gas into the
vacuum chamber 500 is effected through a gas inlet opening 512 of a gas
inlet conduit 511. Reference numerals 510 and 514 designate a heater for
heating the substrate 508 and an evacuation pipe, respectively.
Further, a protective surface coating made of silicon oxide, silicon
nitride, etc. is provided on a surface of each of the first electrode 501,
the first conductive mesh 505 and the second conductive mesh 515 which
surface is exposed to charged particles generated in the vacuum chamber
500. This protective surface coating serves to prevent the substrate 508
from being contaminated by the spattering of electrode metal particles
from the respective electrodes.
Meritorious effects obtainable by the plasma processing apparatus of the
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