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BACKGROUND OF THE INVENTION
This invention relates to a plasma operation apparatus and more
particularly to a plasma operation apparatus suitable for performing thin
film deposition on a specimen (or substrate) surface or etching,
sputtering or plasma oxidation for the specimen surface by utilizing
plasma generated by microwave discharge.
The plasma operation apparatus utilizing plasma generated by microwave
discharge prevailing in a magnetic field has, within a discharge tube
(also called a plasma generation chamber) forming a part of discharge
space, a position at which electron cyclotron resonance (ECR) is caused by
the magnetic field and a microwave and has a magnetic flux density
distribution which decreases from the ECR conditioning position toward a
specimen stand disposed within a specimen chamber. Consequently, plasma
generated near the resonance position is decreased in density by an order
of one to two or more during its transport from the discharge tube to the
specimen stand and the plasma operation can not be done with high
efficiency.
FIG. 1 illustrates an apparatus disclosed in "CVD utilizing ECR plasma",
Transactions of 31st Semiconductor Integrated Circuit Technology Symposium
held on December 3 and 4, 1986, pp. 49-54 and referred to as prior art
example A hereinafter.
In the prior art example A, when a microwave 4 is introduced, through a
wave guide 3 and an incident window 5, into a discharge tube 2 surrounded
by an external magnetic field coil 1 and the electron cyclotron motion in
a magnetic field due to the magnetic coil 1 resonances with the microwave
4 at the resonance position, resonant electrons collide with and ionize a
gas 6 for plasma, thus generating plasma. Under the influence of a
magnetic field divergence, the generated plasma is then pushed out into a
specimen chamber 9 coupled to the discharge tube 2 and housing a specimen
stand 8 for carrying or holding a specimen 7. This plasma alone or along
with atoms or molecules of a material gas 10 additionally introduced into
the specimen chamber 9 and excited or ionized by that plasma is used for
plasma operation of a surface of the specimen 7.
FIG. 2 shows a magnetic flux density distribution occurring between the
microwave incident window 5 and the specimen stand 8, where a value along
the axis ordinate represents the distance in the direction of the central
axis measured from the origin located at the boundary between discharge
tube 2 and specimen chamber 9 and abscissa axis represents the magnetic
flux density. In the case of this prior art example A, the magnetic flux
density Be effective to cause electron cyclotron resonance at a frequency
of 2.45 GHz of the incident microwave 4 is 875 Gausses and FIG. 2
indicates that the resonance conditioning position is axially about 3 cm
distant from the microwave incident window 5. Then, taking into account
the characteristic of propagation of the microwave through the plasma and
the resonance absorption condition for microwave energy, only a region
inside the discharge tube 2 and which is within 3 cm distant from the
microwave incident window 5 proves to be effective for plasma generation.
Plasma generated in this region is transported over a distance of about 35
cm toward the specimen stand 8 under the influence of force due to the
magnetic field divergence and of polarity diffusion. In this transport,
the long transport distance and an abrupt decrease in the magnetic field
(magnetic flux density) cause a loss and because of this loss, the density
of plasma reaching the surface of the specimen 7 through transport tends
to be smaller than that of plasma near the resonance position at which the
electron cyclotron resonance occurs.
FIG. 3 illustrates another apparatus disclosed in "Films of a - Si:H
prepared by ECR plasma enhanced CVD", Transactions of 31st Semiconductor
Integrated Circuit Technology Symposium held on December 3 and 4, 1986,
pp. 61-66 and referred to as prior art example B hereinafter, and FIG. 4
shows magnetic flux density distributions in the FIG. 3 apparatus. In FIG.
3, elements corresponding to those of FIG. 1 are designated by identical
reference numerals. When compared to the magnetic flux density
distribution of the prior art example A, the level of the magnetic flux
density distributions shown in FIG. 4 is higher as a whole. It will also
be seen from FIG. 4 that the position for 875-Gauss magnetic flux density
corresponding to the ECR position still lies within the discharge tube 2
and magnetic flux density exceeding 875 Gausses also prevails within the
discharge tube 2, indicating that a region effective for the resonance
absorption of microwave measures about 2/3 of the discharge tube 2 at its
maximum. In addition, the magnetic flux density is abruptly decreased
toward the specimen stand 8. Consequently, as in the case of prior art
example A, the density of plasma generated near the resonance position
tends to suffer from a loss and decrease during diffusion of the plasma
toward the surface of the specimen 7.
FIG. 5 illustrates still another apparatus disclosed in JP-A-59-3018 and
referred to as a prior art example C hereinafter, and FIG. 6 shows a
magnetic flux density distribution in the FIG. 5 apparatus. In FIG. 5,
elements corresponding to those of FIG. 1 are designated by identical
reference numerals. The prior art example C is directed to the
configuration of a mirror magnetic field type frequently used in the
plasma confinement method with the view of raising the plasma density and
additionally has a complemental permanent magnet 13 for raising magnetic
flux density near the surface of the specimen 7 housed in the specimen
chamber 9. In this prior art example C, the incident microwave 4
propagates through a region designated at (I) in FIG. 6 in which the
magnetic flux density is higher than that at the resonance position, and
the microwave 4 then undergoes resonance absorption by the plasma near a
first resonance position designated at s in FIG. 6. And, it is difficult
for the microwave reaching the first resonance position to pass
therethrough and propagate into a smaller magnetic flux density region
designated at (II) in FIG. 6 because this tendency of the microwave is
resisted by the plasma. If the propagation leaks for approaching a second
resonance position designated at t in FIG. 6 which is near the specimen 7
on the specimen stand 8 and plasma is generated at the second resonance
position, the plasma will be forced to direct toward the discharge tube
owing to a magnetic field divergence appearing near the second resonance
position, with the result that as in the case of prior art examples A and
B, the density of plasma incident upon the specimen 7 tends to be smaller
than that of the plasma near the first resonance position.
Disclosed in JP-A-56-155535 is still another apparatus wherein, as in the
prior art example A, a plasma activated species is generated in a plasma
generation chamber and a plasma flux stemming from the activated species
under the application of a divergent magnetic field is bombarded for
operation upon a substrate to be operated which is sufficiently distant
from a region of the maximal production efficiency of activated species.
Further, a known plasma operation method as disclosed in JP-A-57-79621
intends to improve efficiency and employs a magnet disposed externally of
a substrate operation chamber and which restricts the radius of plasma
flux to raise plasma density.
All of the prior art described hereinbefore does not thoroughly consider
the problem that the density of plasma generated by the microwave subject
to the electron cyclotron resonance in the magnetic field suffers from a
loss during transport of the plasma to the specimen surface, that is, the
problem concerning life of the plasma activated species or deactivation
thereof during transport of the plasma activated species to the substrate
to be operated, and they can not always succeed in improving efficiency of
the plasma operation. Also, in the prior art, excellent characteristics of
the produced films e.g., densification, crystallinity and stoichiometry of
the deposited films can not be obtained.
Another article relevant to the present invention is "Low Temperature
Chemical Deposition Method Utilizing an Electron Cyclotron Resonance
Plasma" by S. Matsuo and K. Kiuchi, Jpn. J. Appl. Phys. 22(4), L210, 1983.
SUMMARY OF THE INVENTION
A first object of this invention is to provide a plasma operation apparatus
which can improve characteristics of films prepared by the operation and
can increase operation speeds by improving utilization efficiency of the
generated plasma.
A second object of this invention is to provide a plasma operation
apparatus which can attain a highly efficient plasma operation by taking
into account deactivation of a plasma activated species.
A third object of this invention is to attain a highly efficient plasma
operation which can attain excellent characteristics of produced films
such as represented by densification, crystallinity and stoichiometry of
deposited films.
A first feature of this invention resides in that in a plasma operation
apparatus, the magnetic flux density distribution starting from a plasma
generation chamber (discharge tube) toward a specimen stand is so
configured as to monotonously decrease, thereby providing a divergent
magnetic field and that a position at which an ECR conditioning magnetic
field is generated and at which the probability of generation of plasma is
high is located at least partially within a specimen chamber to decrease
the distance between the position at which high-density plasma is
generated and a surface of a specimen.
A second feature of this invention resides in that in a plasma operation
apparatus, the divergent magnetic field is provided and that a substrate
to be operated on is displaced by 150 mm at the maximum or less,
preferably less than 70 mm, from an ECR position at which the generation
of a plasma activated species is maximized. The distance between the ECR
position and the substrate to be operated can be adjusted by increasing
magnetic flux density within the plasma generation chamber or controlling
the magnetic flux density with high accuracy.
A third feature of this invention resides in that in a plasma operation
apparatus, the divergent magnetic field is provided and that a range in
which the magnitude of magnetic flux density is about 1.0 to 1.1 times
that of magnetic flux density cooperating with the TE.sub.01 mode
(circular polarization) of a microwave to cause electron cyclotron
resonance to extend continuously in the direction of plasma flux over a
distance of degree of the mean free path of an activated species, i.e., at
least 50 mm or more, or a distance range which requires the activated
species to take a longer time than its mean life time to pass through the
distance range. The range of the magnetic flux density having the above
magnitude can be formed by disposing a plurality of divisional magnets
aligned in the central axis direction of a vacuum system chamber or
controlling the magnetic flux density with high accuracy.
According to the invention, high-density plasma can be transported to the
surface of the specimen to be operated and a thin film of high quality can
be formed on the specimen surface within a short period of time. Further,
operation efficiency dependent on film deposition rate and the like can be
improved to improve throughput of manufacture process. In addition, even
on the substrate to be operated upon at low temperatures, films having
characters such as crystallinity and densification which are comparable to
those of films prepared through an operation utilizing chemical reactions
at high temperatures can be formed.
Other objects and features of the present invention will become apparent
from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmentary sectional view illustrating a plasma operation
apparatus according to a first prior art example.
FIG. 2 is a diagram showing a magnetic flux density distribution in the
central axis direction in the apparatus of FIG. 1.
FIG. 3 is a fragmentary sectional view illustrating a plasma operation
apparatus according to a second prior art example.
FIG. 4 is a graphic representation showing magnetic flux density
distributions in the central axis direction in the FIG. 3 apparatus.
FIG. 5 is a schematic diagram illustrating a plasma operation apparatus
according to the third prior art example.
FIG. 6 is a graphic representation showing a magnetic flux density
distribution in the central axis direction in the FIG. 5 apparatus.
FIG. 7 is a schematic diagram illustrating a plasma operation system
according to a first embodiment of the present invention.
FIG. 8 is a graph showing magnetic flux density distributions in the axis
direction in the FIG. 7 apparatus.
FIG. 9 is a graph showing the relation of deposition rate ratio obtained
during deposition with the FIG. 7 apparatus with respect to the shape of
the magnetic flux distributions and the electron density ratio related
thereto.
FIG. 10 is a graph showing the relation between etching rate ratio for
deposited thin films obtained with the FIG. 7 apparatus and magnetic flux
density.
FIG. 11 is a shematic diagram illustrating a plasma operation system
according to a second embodiment of the present invention.
FIG. 12 is a graph showing a magnetic flux density distribution in the FIG.
11 apparatus.
FIG. 13 is a schematic diagram illustrating a plasma operation system
according to a third embodiment of the present invention.
FIG. 14 is a graph showing a magnetic flux density distribution in the
apparatus of FIG. 13.
FIG. 15 is a schematic diagram illustrating a plasma operation system
according to a fourth embodiment of the present invention.
FIG. 16 is a similar diagram of a fifth embodiment of the invention.
FIG. 17 is a similar diagram of a sixth embodiment of the present
invention.
FIG. 18 is a similar diagram of a seventh embodiment of the present
invention.
FIG. 19 is a similar diagram of an eighth embodiment of the present
invention.
FIG. 20 is a graph showing magnetic flux density distributions in the axis
direction in the FIG. 19 apparatus.
FIGS. 21a to 21h are graphs showing various experimental data obtained with
the FIG. 19 apparatus to prove characteristics thereof.
FIGS. 22a to 22h are graphs showing other experimental data obtained with
the FIG. 19 apparatus.
FIGS. 23a and 23b, 24a and 24b, 25a and 25b and 26a and 26b are graphs
showing further experimental data obtained with the FIG. 19 apparatus.
FIG. 27 is a schematic diagram showing a plasma operation system according
to a fourteenth embodiment of the invention.
FIGS. 28a and 28b are graphs showing axial magnetic flux density
distributions in the apparatus of FIG. 27.
FIGS. 29a to 29h are graphs showing experimental data obtained with the
FIG. 27 apparatus to prove characteristics thereof.
FIGS. 30a to 30d are graphs showing other experimental data obtained with
the FIG. 27 apparatus.
FIGS. 31a and 31b are graphs showing further experimental data obtained
with the FIG. 27 apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Generally, a microwave propagating through a magnetic field to cause
electron cyclotron resonance is of clockwise circular polarization and
this microwave is cut off by a magnetic field having the magnitude of
magnetic flux density smaller than that of magnetic flux density necessary
for causing the electron cyclotron resonance and consequently can not
propagate through the magnetic field. The present invention takes
advantage of this phenomenon and is constructed such that the magnitude of
magnetic flux density at the incident edge of a discharge tube is made
larger than that of magnetic flux density at the ECR position and the
former magnetic flux density has a distribution which gradually decreases,
starting from the discharge tube, toward a specimen stand, that a position
at which the magnetic field and microwave cooperate together to cause the
electron cyclotron resonance is located within a specimen chamber to
provide a range which extends into the specimen chamber and in which the
magnitude of magnetic flux density is larger than that of the resonance
conditioning magnetic flux density to thereby generate high-density
plasma, and that the distance over which plasma, pushed out under the
influence of a magnetic field divergence is transported to the specimen
stand is minimized or zeroed in an extremity. With the above construction,
in order to avoid the disadvantage of the plasma density abruptly
decreasing within a region in which the magnitude of magnetic flux density
is smaller than that of the resonance conditioning magnetic flux density,
the distance between resonance position and specimen stand can be
minimized sufficiently, making it possible to transport high-density
plasma to a surface of a specimen.
FIRST EMBODIMENT
A plasma operation apparatus according to a first embodiment of the
invention which is relevant to the aforementioned first feature will be
described with reference to FIGS. 7, 8, 9 and 10.
This embodiment of plasma operation apparatus is constructed as shown in
FIG. 7 to perform a specimen surface operation (deposition) based on
magnetic field/microwave discharge. In operation, a microwave 4 is
introduced through a wave guide 3 into a discharge tube 2 surrounded by an
external magnetic field coil 1 and a gas 6 for plasma is excited or
ionized under the influence of electron cyclotron resonance caused by the
electron cyclotron motion in a magnetic field due to the magnetic field
coil 1 and the microwave 4, thereby generating plasma. Under the influence
of a divergence of the magnetic field generated by the magnetic field coil
1, the generated plasma is then pushed out into a specimen chamber 9
coupled to the discharge tube 2 and housing a specimen stand 8 for
carrying or holding a specimen 7 to be operated upon. This plasma, along
with a material gas 10 additionally admitted toward the front of the
specimen 7 inside the specimen chamber 9 and excited or ionized by the
plasma flux, is transported to the surface of the specimen 7 so as to
deposit a thin film having constituents of the plasma gas 6 and material
gas 10 on the surface of the specimen 7.
FIG. 8 shows magnetic flux density distributions in the axis direction of
the FIG. 7 apparatus between the discharge tube 2 and the specimen stand
8, where ordinate represents the distance in the axis direction and
abscissa represents the magnetic flux density. In FIG. 8, the shape of
distributions indicated by curves .circle.1 and .circle.2 is
characteristic of this invention, the shape of magnetic flux density
distribution indicated by curve .circle.3 is obtained with an instance
where the position of the ECR conditioning magnetic field is located at
the boundary between discharge tube 2 and specimen chamber 9, and an
example of magnetic flux density distribution indicated by curve
.circle.4 is for the aforementioned literature by S. Matsuo and K.
Kiuchi.
Returning to FIG. 7, the position (position a in FIG. 7) corresponding to
the resonance conditioning magnetic flux density (Be=875 Gausses) pursuant
to the curve .circle.1 is located within the specimen chamber 9 and
therefore, the microwave 4 (2.45 GHZ) introduced into the discharge tube 2
through the wave guide 3 propagates through a region inside the discharge
tube 2 in which the magnetic flux density exceeds the resonance
conditioning magnetic flux density. As the microwave enters the specimen
chamber 9 and approaches the resonance conditioning position, ionization
and excitation become active under the influence of electron cyclotron
resonance and in proportion thereto, the plasma density at the specimen
position is increased, providing the plasma generation probability which
is maximized at the resonance position. And, because of the nature of
clockwise circular polarization effective for causing electron cyclotron
resonance, the microwave tending to pass through the high magnetic flux
density region and propagate into a magnetic field having the magnetic
flux density smaller than the resonance conditioning magnetic flux density
(in this embodiment, 875 Gausses) is cut off and prevented from
propagating, with the result that part of the microwave which has not been
absorbed by resonance into the plasma is reflected at the resonance
condition position. It therefore follows that almost no plasma generation
takes place in the low magnetic flux density region which is offset from
the resonance position toward the specimen stand 8. The plasma reaching
the surface of the specimen 7 contains plasma transported by polarity
diffusion attendant on the magnetic field gradually decreasing, starting
from the resonance position, toward the specimen stand 8 as well as atoms
and molecules of the material gas 10 admitted near the resonance position
and ionized and excited by the plasma flux. Accordingly, the plasma
density distribution starting from the resonance position toward the
specimen stand 8 exhibits an abrupt decrease. However, according to the
present embodiment, the distance between the resonance position and the
specimen surface can be adjusted so as to be minimized or zeroed in an
extremity, so that the specimen surface may be located to precede a
position at which the plasma density begins to decrease abruptly. As a
result, the operation rate, substantially proportional to the electron
density near the surface of the specimen 7, will not be decreased and
besides the ion density contributing to ion bombardment affecting the
densification of deposited films can be selected properly, thus ensuring
that a thin film of high quality can be deposited within a short period of
time. Obviously, the magnitude of magnetic flux due to the magnetic field
coil 1 of the present embodiment is so selected as to provide the
resonance condition position which lies within the specimen chamber 9.
FIG. 9 shows deposition rate for depositing thin films on the specimen
surface with the apparatus of the present embodiment. Values are measured
under the condition that film composition is constant. In FIG. 9, the
lower abscissa represents the shape of the magnetic flux density
distribution in terms of curves .circle.1 to shown >.circle.4 in FIG.
8, the upper abscissa represents, in arbitrary scale, electron density
ratio on the specimen surface corresponding to the respective points 1
.circle.1 to .circle.4 , and ordinate represents deposition rate ratio
in arbitrary scale. FIG. 9 clearly demonstrates that when the resonance
position is located within the specimen chamber as indicated by points
.circle.1 and .circle.2 in FIG. 9, the electron density is increased to
increase the deposition rate ratio, especially, in proportion to the
degree to which the resonance position to the surface of the specimen 7.
FIG. 10 shows etching rate ratio representative of densification of thin
films deposited on the specimen surface with the apparatus of this first
embodiment, where the lower abscissa represents the shape of the magnetic
flux density distribution in terms of curves .circle.1 to .circle.4
shown in FIG. 8, the upper abscissa represents the magnetic flux density
at the edge of discharge tube 2 which lies at the boundary between
discharge tube 2 and specimen chamber 9, in terms of the magnitude of the
magnetic flux density at the resonance condition position being Be, and
the ordinate represents etching rate ratio in arbitrary scale. FIG. 10
clearly demonstrates that when the resonance position is drawn into the
specimen chamber 9 as indicated by points .circle.1 and .circle.2 in
FIG. 10, the etching rate ratio is small proving that highly dense films
are prepared and the plasma density near the specimen surface is high
bringing about sufficient ion bombardment effect during film deposition.
As described above, according to the present embodiment, by providing the
monotonously decreasing shape for a magnetic flux density distribution
starting from the discharge tube toward the specimen stand and by locating
the position at which the ECR conditioning magnetic field is generated at
least partially within the specimen chamber, the high-density plasma can
be generated near the specimen surface and highly dense thin films can be
prepared at high deposition rates.
SECOND EMBODIMENT
Referring to FIG. 11, there is illustrated a plasma operation apparatus
according to a second embodiment of the invention. In comparison with the
FIG. 7 embodiment, this second embodiment of FIG. 11 additionally
comprises a complemental magnetic field generation means 21, disposed
externally of the specimen chamber 9, for generating within the specimen
chamber 9 a magnetic field which aids in locating the position at which
the ECR conditioning magnetic field is generated within the specimen
chamber 9. FIG. 12 shows a magnetic flux density distribution in the axis
direction of the FIG. 11 apparatus. In FIG. 12, broken-line curve
.circle.6 indicates a magnetic flux density distribution obtained with
only the magnetic field coil 1 shown in FIG. 11 and broken-line curve
.circle.7 indicates a magnetic flux density distribution obtained with
only the complemental magnetic field generation means 21. Accordingly, in
the apparatus of FIG. 11, the curves .circle.6 and .circle.7 are
superimposed together to provide a magnetic flux density distribution
indicated by solid-line curve .circle.5 in FIG. 12 by which the position
of the ECR conditioning magnetic field is drawn in an arrow direction in
FIG. 12 so as to be located within the specimen chamber 9. The
complemental magnetic field generation means 21 is required to supply
magnetic flux density of a magnitude of about 50 Gausses or more which is
effective to locate the resonance condition position within the specimen
chamber 9. Advantageously, in this embodiment, the magnetic field coil 1
can be reduced in size to attain the same effect as that attained with the
FIG. 7 embodiment and in addition, by adjusting the complemental magnetic
field generation means 21, the position of the resonance conditioning
magnetic field can be adjustably moved without greatly affecting the
magnetic field distribution inside discharge tube 2 established by the
magnetic field coil 1 and the radius and density of the plasma drawn by
the complemental magnetic field generation means 21 can be controlled.
THIRD EMBODIMENT
FIG. 13 illustrates a plasma operation apparatus according to a third
embodiment of the invention wherein the same complemental magnetic field
generation means 21 as that used in the FIG. 11 embodiment is disposed
externally of the specimen chamber 9 at a substantially intermediate
position between discharge tube 2 and specimen chamber 9. FIG. 14 shows a
magnetic flux density distribution in the axis direction of the FIG. 13
apparatus. In this embodiment, a magnetic field due to the magnetic field
coil 1 only as indicated by broken-line curve .circle.9 in FIG. 14 and a
magnetic field due to the complemental magnetic field means 21 only as
indicated by broken-line curve .circle.10 in FIG. 14 are superimposed
together to provide a magnetic flux density distribution as indicated by
solid-line curve .circle.8 in FIG. 14. Thus, the third embodiment
attains the same effect as that attained by the second embodiment
illustrated in FIG. 11.
FOURTH EMBODIMENT
As shown in FIG. 15, a fourth embodiment of the invention comprises a
complemental magnetic field generation means 21 disposed inside the
specimen chamber 9 to attain the same effect as that by the foregoing
embodiments.
FIFTH EMBODIMENT
As shown in FIG. 16, a fifth embodiment of the invention comprises a
complemental magnetic field generation means 21 disposed at the back of
the specimen stand 8 within the specimen chamber 9, attaining the same
effect as that by the foregoing embodiments.
SIXTH EMBODIMENT
As shown in FIG. 17, a sixth embodiment of the invention comprises a
complemental magnetic field generation means 21 playing the part of the
specimen stand 8 within the specimen chamber 9 and serving as a specimen
stand 8a with complemental magnetic field generation means. The sixth
embodiment constructed as above can also attain the same effect as that by
the foregoing embodiments.
SEVENTH EMBODIMENT
A seventh embodiment of the invention as illustrated in FIG. 18 acts as an
etching apparatus. The gas 6 for plasma also serves as an etching gas.
Since the position of the resonance conditioning magnetic field at which
the probability of plasma generation is high can be controlled by means of
the complemental magnetic field generation means 21 so as to be located
within the specimen chamber 9, especially, between positions .circle.a
and .circle.b shown in FIG. 18, the proper etching condition can
advantageously be set for the specimen 7 to be operated upon.
In the foregoing embodiments, the magnetic field has been described as
having the shape of magnetic flux density distribution which substantially
monotonously decreases starting from the discharge space into which the
microwave is introduced toward the specimen stand but more briefly, the
distribution may be so configured as to permit the resonance condition
position to lie on a curved surface within the specimen chamber. In an
alternative, the distance between the specimen and the resonance condition
position may be lessened by moving the specimen stand. In the apparatus of
the foregoing embodiments, the pressure within the plasma generation
chamber is not limited to 1.times.10.sup.-2 Torr or less in contrast to
the prior art apparatus described in connection with FIGS. 1 to 6.
Since in the plasma operation apparatus according to the previous
embodiments the magnetic flux density distribution is so configured as to
monotonously decrease and the position of the ECR conditioning magnetic
field at which the probability of plasma generation is high is located
within the specimen chamber and besides the distance between the position
for high-density plasma generation and the specimen surface is lessened, a
very efficient plasma operation can be achieved wherein the high-density
plasma can be transported to the specimen surface to prepare thin films of
high quality at high operation speeds.
An embodiment of the invention which is relevant to the aforementioned
second feature will now be described.
The reaction gas is activated by microwave plasma discharge, especially,
most efficiently activated near the ECR position. An activated species
thus created then loses its activity on account of energy dispersion or
sometimes it is deactivated on account of interparticle interaction due to
its collision with other particles. Accordingly, a decreased distance
between the substrate or specimen surface to be operated on and the ECR
position can permit the plasma activated species to reach the substrate
while keeping activity of the plasma activated species high. This leads to
a highly efficient plasma operation and inproved plasma operation
characteristics. When taking deposition of a film on the substrate, for
instance, the higher the vibrational force between electron energy bonded
atoms and rotation and translation energy of molecules or atoms to be
deposited, the higher is the probability that in the plasma the molecules
or atoms are not ganged or that individual molecules or atoms remain as
single particle. Under this condition, a deposited film advantageously
approaches a film prepared by thermal chemical reaction. Further, because
of the high kinetic energy, the activated species deposited on the
substrate has a high probability of its reconfigurational and
reorientational motion toward a molecular layer preexistent on the
substrate until the energy of the activated species is minimized at a
destination of the reconfigurational and reorientational motion.
Therefore, the deposited film can be increased in densification and
crystallinity. In addition, stoichiometric ratio of the deposited film
approaches that of a film prepared by thermal chemical reaction.
If, otherwise, the magnetic field distribution B(Z), where Z is a
coordinate position on a vacuum-chamber-center-axis coordinate system
which is positive in the direction of plasma flux, is not monotonously
decreasing, there exists a position satisfying dB/dZ>0 and at which the
microwave is prevented from propagating and the generation or production
efficiency of the plasma activated species is disadvantageously degraded.
EIGHTH EMBODIMENT
A plasma operation apparatus according to an eighth embodiment of the
invention is schematically illustrated in FIG. 19. The apparatus comprises
a plasma generation chamber 104, a microwave guide 107 (an oscillator for
a microwave is not illustrated), ECR magnetic field coils 109 and 113, an
operation (specimen) chamber 102, an evacuation conduit 112 (an evacuation
system is not illustrated), reaction gas supply nozzles 105 and 111 (a
reaction gas supply system is not illustrated) and a substrate holder
(specimen stand) 103. The plasma generation chamber 104 is made of
colorless quartz and has a diameter of 240 mm and a length of 250 mm with
its top cone serving as a microwave incident window 108. The ECR magnetic
field coils 109 and 113 respectively surround the plasma generation
chamber and the operation chamber and are operable to provide a maximum of
magnetic flux density of 2.6 K Gausses within the plasma generation
chamber. The coils 109 and 113 are respectively divided into three and two
sub-coils which can be adjusted separately to control the magnetic flux
density. The operation chamber 102 is made of stainless and has a diameter
of 240 mm. The substrate holder 103 having a diameter of 120 mm and placed
in the operation chamber is made of alumina and its position is variable
along the direction of plasma flux (in the right and left directions in
the drawing). FIG. 20 graphically exemplifies magnetic flux density
distributions in the direction of microwave propagation. Various
distributions .circle.j to .circle.m can be established by adjusting
the ECR magnetic field coils 109 and 113, and the distance between the
substrate and the ECR position can be controlled by adjustably setting the
position of the substrate holder 103.
As the substrate 101 to be operated on, a silicon wafer having a diameter
of 100 mm is used and a silicon oxide film is formed on the wafer. Oxygen
is admitted at a flow rate of 40 ml/min into the plasma generation chamber
104 through the first gas inlet pipe 105 and a microwave 106 of 2.45 GHz
propagating through the wave guide 107 is introduced into the plasma
generation chamber 104 through the microwave incident window 108. Then, a
magnetic field of 875 Gausses or more is generated from the static
magnetic field generation coils 109 and 113 both disposed externally of
and concentrically with the plasma generation chamber to generate a plasma
flux 110 and monosilane (SiH.sub.4) is admitted at a flow rate of 6 ml/min
through the second gas inlet pipe 111 into the operation chamber 102 which
is evacuated by the evacuation system to a reduced pressure of 1 m Torr.
The magnetic flux density distribution is controlled by adjusting the
amount of current passed through the static magnetic field generation
coils 109 and 113 or the distance between the ECR position and the
substrate to be operated is adjustably changed by adjusting the position
of the substrate holder. With respect to the ECR position/substrate
distance d, the SiO.sub.2 film deposition rate and the amount of scatter
of the deposition rate within the substrate are graphically depicted in
FIGS. 21a and 21b, the etching rate for the deposited film under etching
with a buffer etching solution (a mixture of 1-mol HF and 6-mol NH.sub.4
F) and the amount of scatter of the etching rate within the substrate | | |
