Plasma apparatus

The present invention relates to a plasma apparatus, in which a plasma is generated by the use of an electron cyclotron resonance, said plasma being introduced into a sample chamber where a sample is housed through a plasma outlet window by the use of a magnetic field for use in the electron cyclotron resonance, and said sample being subjected to a film-formation or an etching, characterized by that the distribution of magnetic flux density on a surface of the sample can be improved to uniform the plasma density, whereby subjecting the sample with the film-formation of uniformly thick or a uniform etching, by disposing a magnetic field forming means capable of forming a magnetic filed, wherein the magnetic flux density at the peripheral edge portion of the sample is higher than that at the central portion of the sample, on a side opposite to the plasma outlet window relatively to the sample.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a plasma apparatus used as a CVD (Chemical 
Vapor Deposition) apparatus, an etching apparatus and the like. 
2. Description of the Prior Art 
Since a plasma apparatus utilizing an electron cyclotron resonance can form 
a plasma having a high activity at a low gas pressure and bring out a 
plasma flow having a large diameter, it can be applied to the formation of 
a thin film, etching and the like in a highly integrated semi-conductor 
element and the like. And, its investigation and development are 
progressing. 
FIG. 1 is a longitudinal sectional view showing a conventional plasma 
apparatus constructed as a thin film forming apparatus. Reference numeral 
31 designates a plasma chamber. Said plasma chamber 31 is provided with a 
microwave inlet 31c sealed up with a silica glass plate 31b at a center of 
an upper wall thereof and a plasma outlet window 31d at a position 
opposite to said microwave inlet 31c at a center of a lower wall thereof, 
said microwave inlet 31c being connected with one end of a wave guide 32, 
which is connected with a microwave generator (not shown) at the other 
end, a sample chamber 33 being arranged so as to face to the plasma outlet 
window 31d, and an exciting coil 34 being arranged concentrically with 
said sample chamber 33 so as to surround from the plasma chamber 31 to one 
end portion of the wave guide 32 connected with the plasma chamber 31. 
The sample chamber 33 is provided with a sample stage 35 arranged at a 
position opposite to the plasma outlet window 31d, a sample 100, such as a 
disc wafer, being placed on the sample stage 35 as it is or detachably by 
means of a static absorption and the like, and the sample chamber 33 being 
provided with an exhaust port 33a, which is connected with an exhauster 
(not shown), opened at a lower wall thereof. In addition, reference 
numerals 31g, 33g designate material gas supply pipes, reference numeral 
31e designating a water-supply system of a cooling water, and reference 
numeral 31f designating a drain system of the cooling water. 
With such a thin film forming apparatus, the plasma chamber 31 and the 
sample chamber 33, which have been set at a desired vacuosity, are 
supplied with a material gas, a high-frequency electric field due to a 
microwave being applied in the plasma chamber 31 while forming a magnetic 
field by the exciting coil 34, to form a plasma, the resulting plasma 
being led out to the vicinity of the sample 100 on the sample stage 35 
within the sample chamber 33 from the plasma chamber 31 through the plasma 
outlet window 31d by a divergent magnetic field formed by the exciting 
coil 34, and a surface reaction due to ions and radical particles in the 
plasma flow being brought on a surface of the sample 100 to form a film on 
the surface of the sample 100 (Japanese Patent Application Laid-Open No. 
155535/1981). 
However, with such the conventional plasma apparatus, the plasma brought 
about in the plasma chamber 31 is extracted to a side of the sample 100 
within the sample chamber 33 through the plasma outlet window 31d along a 
line of magnetic force of the divergent magnetic field formed by the 
exciting coil 34 but the plasma generated in the plasma chamber 31 is not 
uniform, that is, a plasma density at a central portion of the plasma 
chamber 31 becomes higher than that at a periphery of the plasma chamber 
31. This uneven distribution of plasma density has an enlarged influence 
upon the sample 100 by the divergent magnetic field as it is. In the case 
where the sample 100 is arranged in a concentrical manner with the plasma 
outlet window 31d, a difference occurs between the central portion and the 
periphery of the sample 100 in deposition rate, whereby making a film 
thickness uneven. 
It is a reason why the uneven distribution of the plasma generated in the 
plasma chamber 31 is projected toward the sample 100 by the divergent 
magnetic field as it is that electrons in the plasma take a cyclotron 
movement (Larmor movement) having a cyclotron radius of several tens 
microns to several hundreds microns around the divergent magnetic field 
while ions in the plasma follow the electrons by an electric field having 
an amphoteric polarity generated between them and the electrons, so that 
the plasma is restricted by the line of magnetic force as a whole. 
FIG. 2 is a diagram showing a positional relation between the divergent 
magnetic field formed by the exciting coil 34 and the sample 100. As 
obvious from FIG. 2, the line of magnetic force of the divergent magnetic 
field formed by the exciting coil 34 is expanded as it approaches to the 
sample 100 through the plasma outlet window 31d, so that the uneven 
distribution of the plasma generated in the plasma chamber 31 is projected 
on the sample 100 in an enlarged manner. Accordingly, in the case where a 
film is deposited, the uneven film thickness can not be avoided. 
Such an uneven film thickness or etching depth has been found not only in 
the thin film forming apparatus but also in the case where it is used as 
an etching apparatus (Japanese Patent Application Laid-Open No. 
47728/1984). 
SUMMARY OF THE INVENTION 
The present invention was achieved in order to solve the above described 
problems. 
A first object of this invention is to provide a plasma apparatus, in which 
a magnetic field forming means for forming a magnetic field so that a 
density of magnetic field at a periphery of a sample may be higher than 
that at a central portion of the sample is arranged on a side opposite to 
a plasma outlet window relatively to the sample to make a density of 
plasma above the sample to be uniform. 
A second object of this invention is to provide a plasma apparatus, in 
which a coil is disposed around a magnetic body as a magnetic field 
forming means to achieve a fine regulation of magnetic flux density. 
A third object of this invention is to provide a plasma apparatus, in which 
a magnetic flux density at a peripheral portion of a sample and that at a 
central portion of the sample are independently controlled by a magnetic 
field forming means to easily improve the distribution of magnetic flux 
density on a surface of the sample. 
A fourth object of this invention is to provide a plasma apparatus, in 
which a magnetic field formed by an exciting coil, a magnetic field of the 
same direction and a magnetic field of an opposite direction are 
simultaneously formed by a magnetic field forming means to remarkably 
increase a magnetic flux density at an appointed position. 
A fifth object of this invention is to provide a plasma apparatus, in which 
a magnetic field forming means comprises exciting coils integrally 
disposed on an inside circumference and an outside circumference of a 
cylindrical magnetic body to simplify the magnetic field forming means in 
construction and form an ideal magnetic field. 
A sixth object of this invention is to provide a plasma apparatus, in which 
a magnetic field forming apparatus comprises a permanent magnet and a 
magnetic body in combination to make a power supply facility for the 
magnetic field forming means unnecessary, thereby, simplifying 
construction. 
The above and further objects and features of the invention will more fully 
be apparent from the following detailed description with accompanying 
drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments, in which the present invention is constructed as 
a thin film forming apparatus, are concretely described below with 
reference to the drawings. 
FIG. 3 is a longitudinal sectional view showing a plasma apparatus 
according to the present invention. Referring to FIG. 3, reference numeral 
1 designates a plasma chamber, reference numeral 2 designating a wave 
guide, reference numeral 3 designating a sample chamber, and reference 
numeral 4 designating an exciting coil. 
The plasma chamber 1 is provided with a microwave inlet 1c closed by a 
silica glass plate 1b at a center of an upper wall thereof and a circular 
plasma outlet window 1d at a position opposite to said microwave inlet 1c 
of a center of a lower wall thereof, said microwave inlet 1c being 
connected with one end of the wave guide 2, the sample chamber 3 being 
arranged so as to face to the plasma outlet window 1d, and the exciting 
coil 4 being arranged around said sample chamber 3 so as to surround from 
the plasma chamber 1 to one end portion of the wave guide 2 connected with 
the plasma chamber 1. 
The other end portion of the wave guide 2 is connected with a microwave 
generator (not shown) to introduce the microwave into the plasma chamber 1 
through the microwave inlet 1c. The exciting coil 4 is connected with a 
direct current power source (not shown) to form a magnetic field by 
passing a direct current through the exciting coil 4 so that a plasma may 
be formed by introducing a microwave into the plasma chamber 1. This 
magnetic field is a divergent magnetic field with a magnetic flux density 
reduced toward a side of the sample chamber 3. The plasma formed in the 
plasma chamber 1 is introduced into the sample chamber 3. 
A sample stage 5 is disposed at a position opposite to the plasma outlet 
window 1d at a center of a lower portion within the sample chamber 3 so 
that a sample 100, such as a wafer, may be placed on the sample stage 5 as 
it is or detachably by means of a static adsorption and the like. In 
addition, an exhaust port 3a connected with an exhauster (not shown) is 
opened at a bottom wall. 
Reference numerals 1g, 3g designate a material gas supply pipe, reference 
numeral 1e designating a water-supply system of a cooling water, and 
reference numeral 1f designating a drain system of the cooling water. 
And, in a plasma apparatus according to the present invention, a 
cylindrical magnetic body 6 as the magnetic field forming means is 
disposed almost concentrically with the plasma outlet window 1d, the 
sample stage 5 and the sample 100 placed on the sample stage 5 below the 
sample stage 5. An outside diameter D of this magnetic body 6 is set at a 
value almost equal to a diameter of the sample 100 or more. In addition, 
an inside diameter d of this magnetic body is set at a value other than 0, 
that is to say, so that 0&lt;d&lt;D may be held good. 
FIG. 4 is a diagram showing a line of magnetic force in the case where the 
above described discoid sample 100 and the cylindrical magnetic body 6 
having the outside diameter D. The line of magnetic force of the divergent 
magnetic field formed by the exciting coil 4 is drawn toward the magnetic 
body 6. That is to say, the line of magnetic force expanded outside of the 
magnetic body 6 is pulled back while the line of magnetic force within the 
magnetic body 6 is spread outward. As a result, the distribution of 
density of the plasma drawn out of the plasma chamber 1 on a surface of 
the sample 100 is made uniform. 
The above described will be described below in more detail. 
It is important in the present invention that a magnetic field forming 
means capable of increasing a magnetic flux density at a peripheral 
portion of a sample in comparison with that at a central portion of the 
sample, that is, a cylindrical magnetic body 6 in the above described 
preferred embodiment, is used. 
An etching apparatus, in which a plasma is generated by a microwave and a 
magnetic field in the same manner as in the present invention, has been 
disclosed in Japanese Patent Publication No. 13627/1983. A magnet is 
disposed on a side opposite to a coil for generating the above described 
magnetic field or a plasma outlet window relatively to a sample to form a 
mirror magnetic field. FIG. 5 is a schematic diagram showing a line of 
magnetic force in the case where the mirror magnetic field is formed. 
Referring to FIG. 5, reference numeral 61 designates a coil for forming a 
divergent magnetic field and reference numeral 62 designates a magnet for 
forming the mirror magnetic field. In such the mirror magnetic field, a 
magnetic flux formed by the coil 61 does not diverge but is converged due 
to the existence of the magnet 62. However, such conditions cause the 
magnetic flux density to be higher at the central portion and lower at a 
peripheral portion. In the case where the sample 100 is placed within this 
magnetic field, even though the plasma can be economically used, it can 
not be expected to make uniform the plasma density on the surface of the 
sample 100. 
FIG. 6 is a graph showing a relation between a distance r in a radial 
direction from the center of the sample (refer to FIG. 5) and the 
distribution of the magnetic flux density Bz, which is a component in the 
direction vertical to the sample stage at the sample stage 5, for the 
divergent magnetic field [broken line (a)], mirror magnetic field 
[one-dotted oblique line (b)] and the magnetic field [full line (c)] 
obtained by a magnetic field forming means according to the present 
invention. In FIG. 6, the distance r (cm) from the center of the sample is 
taken on an axis of abscissa while the vertical component of the magnetic 
flux density Bz (Gauss) is taken on an axis of ordinate. 
As obvious from FIG. 6, the plasma apparatus according to the present 
invention can correct the projection of the distribution of plasma density 
(lower in the peripheral portion) within the plasma chamber as it is in 
the divergent magnetic field or mirror magnetic field by heightening the 
peripheral portion of the sample than the central portion of the sample. 
In short, in the plasma apparatus according to the present invention, since 
the magnetic field forming means (magnetic body 6) is disposed on a side 
opposite to the plasma outlet window 1d relatively to the sample 100, of 
line of magnetic force of the divergent magnetic field formed toward a 
side of the sample chamber 3, line of magnetic force in the peripheral 
portion of the sample 100 or the vicinity thereof are bent in a direction 
intersecting the peripheral portion of the sample 100, that is, in the 
inside and outside direction to heighten the magnetic flux density in the 
peripheral portion of the sample 100, whereby uniforming the distribution 
of magnetic flux density on the surface of the sample 100. As a result, a 
thin film having a uniform thickness can be formed on the surface of the 
sample by using the plasma apparatus according to the present invention. 
With the above described plasma apparatus according to the present 
invention and the conventional apparatus shown in FIG. 1, respectively, 
oxygen gas was introduced into the plasma chamber 1 and SiH.sub.4 gas into 
the sample chamber 3, respectively, as the material gas to generate the 
plasma and deposit them on a Si wafer having a diameter of 5 inches 
disposed on the sample stage 5. The umiformity of film thickness was 
measured with the results that it was .+-.10% in the conventional 
apparatus but it was reduced as much as .+-.5% in the apparatus according 
to the present invention. 
The uniformity of film thickness was determined by the following formula 
(1): 
##EQU1## 
In addition, FIG. 7 is a sectional view showing another construction of the 
magnetic field forming means in which a fine electrically conductive wire 
7 insulatively coated is densely wound around a cylindrical peripheral 
surface of the magnetic body 6 many times without forming any gap, a 
direct current power source (not shown) being connected between end 
portions of said fine electrically conductive wire 7, and a direct current 
of a desired magnitude being passed through the fine electrically 
conductive wire 7 to finely regulate the distribution of magnetic flux 
density on the surface of the sample 100. 
In addition, the fine electrically conductive wire 7 insulatively coated 
may be disposed around the magnetic body 6 in a circular shape instead of 
being directly wound around the peripheral surface of the magnetic body 6. 
FIG. 8 is a longitudinal sectional view showing another preferred 
embodiment of the plasma apparatus according to the present invention in 
which the magnetic field forming means is composed of two cylindrical 
magnets. 
Two (large and small) cylindrical magnets 8, 9 constructing the magnetic 
field forming means are disposed on a side opposite to the plasma chamber 
1 relatively to the sample stage 5, that is, below the sample stage 5, 
within the sample chamber 3 with the same central line as that of the 
microwave inlet 1c, the plasma outlet window 1d, the sample stage 5 and 
the like. 
Respective cylindrical magnets 8, 9 comprise a cylindrical core 8a, 9a, 
respectively, of which periphery is wound by a lead wire so that the 
cylindrical magnet 8 and the cylindrical magnet 9 may be concentrically 
disposed with the former being arranged inside and the latter being 
outside and the former being slightly shifted from the latter in an up and 
down direction, that is, the former being disposed at a higher position 
while the latter is disposed at a lower position in a direction of axis 
shaft line. The cylindrical magnet 9 is adapted to form lines of magnetic 
force in the same direction as those formed by the exciting coil 4 on the 
central line of the magnetic field formed by the exciting coil 4. In 
addition, the cylindrical magnet 8 is adapted to form lines of magnetic 
force in a direction opposite to that of the lines of magnetic force of 
the magnetic field formed by the exciting coil 4 on the central line. The 
value of magnetic flux density of the magnetic field formed by the 
respective cylindrical magnets 8, 9 is not specially limited but every 
value capable of uniforming the distribution of plasma on the surface of 
the sample 100 can be selected. 
In addition, the construction other than the magnetic field forming means 
is same as that shown in FIG. 3, so that its description is omitted here. 
FIG. 9 is a graph showing a relation between a distance r (cm) in the 
radial direction from the center of the sample and a vertical component of 
the magnetic flux density Bz (Gauss) in the plasma apparatus according to 
the preferred embodiment shown in FIG. 8. Referring to FIG. 9, the full 
line (a) shows the distribution of density of the present preferred 
embodiment. Also the distribution of density in the conventional apparatus 
is shown in FIG. 9 [broken line (b)] for comparison. 
As obvious from this diagram showing the distribution of the vertical 
component of the magnetic flux density, in the conventional apparatus the 
magnetic field is formed substantially merely by the exciting coil 4. That 
is to say, the vertical component of the magnetic flux density Bz of the 
divergent magnetic field shows a maximum value at the central portion of 
the sample stage 5 and is gradually reduced as it is separated from there. 
On the contrary, in the present invention the magnetic flux density Bz 
shows a maximum value above the outside cylindrical magnet 9 and is 
rapidly reduced both outward and inwardly from there. 
This seems to be a result of that the lines of magnetic force diverging 
outside of the sample stage 5 of the divergent magnetic field formed by 
the exciting coil 4 are drawn toward a side of the peripheral edge portion 
of the sample stage 5 by the outside cylindrical magnet 9 while the lines 
of magnetic force in the vicinity of the central portion of the sample 
stage 5 is diverged toward a side of the peripheral edge portion of the 
sample stage 5 by the inside cylindrical magnet 8 in an opposite manner. 
In such the preferred embodiment, the inside plasma is locked in by the 
outside cylindrical magnet 9 during the process of introducing the plasma 
generated in the plasma chamber 1 into the sample chamber 3 through the 
plasma outlet window 1d using the divergent magnetic field formed by the 
exciting coil 4 while the central plasma is diverged toward the peripheral 
edge portion of the sample stage 5 by the magnetic field formed by the 
inside cylindrical magnet 8, whereby relatively increasing the density of 
plasma in the peripheral edge portion of the sample 100. That is to say, 
the distribution characteristics of plasma density, which are reduced 
toward the peripheral edge portion from the central portion of the sample 
100, as seen in the case where the magnetic field is formed merely by the 
exciting coil 4 can be improved in unevenness on the surface of the sample 
100 by the action of both the cylindrical magnet 8 and the cylindrical 
magnet 9. 
Accordingly, it is necessary only to dispose the peripheral edge portion of 
the sample 100 on the sample stage 5 so as to correspond to portions 
having a higher magnetic flux density on both sides shown in FIG. 9 and 
suitably set an electric current and the like passing through the outside 
cylindrical magnet 9 and the inside cylindrical magnet 8 so as to uniform 
the dispersion of plasma. 
In the present preferred embodiment, the magnetic flux density at the 
peripheral edge portion of the sample 100 is controlled mainly by the 
outside cylindrical magnet 9 while the magnetic flux density at the 
central portion of the sample 100 is controlled mainly by the inside 
cylindrical magnet 8. Accordingly, the respective cylindrical magnets 8, 9 
control the magnetic flux density at the central portion and the 
peripheral edge portion of the sample 100 independently, whereby easily 
uniforming the magnetic flux density on the surface of the sample. 
With the preferred embodiment shown in FIG. 8 and the conventional 
apparatus shown in FIG. 1, respectively, N.sub.2 gas (flow rate of 35 
sccm) was introduced into the plasma chamber 1 and SiH.sub.4 gas (flow 
rate of 28 sccm) into the sample chamber 3, respectively, as the material 
gas to generate the plasma at a microwave power of 600 W and form a 
silicon nitride film on a silicon wafer having a diameter of 5 inches on 
the sample stage 5 using the generated plasma. The uniformity of film 
thickness and the deposition rate were measured. With the conventional 
apparatus, the uniformity of film thickness was .+-.9.8% and the 
deposition rate was 2400 .ANG./min while with the present preferred 
embodiment, the uniformity of film thickness was able to be reduced as 
much as .+-.4%. In addition, the plasma could be efficiently used by the 
plasma-locking effect by the cylindrical magnet 9. As a result, the 
deposition rate was able to be increased as fast as 2700 .ANG./min. In 
addition, the uniformity of film thickness was calculated by the above 
described formula (1). 
Although in the present preferred embodiment a direct electric current is 
passed through the cylindrical magnet 9 so that the lines of magnetic 
force may be formed in the same direction as that of the lines of magnetic 
force formed by the exciting coil 4 on the central line of the magnetic 
field formed by the exciting coil 4 while a direct electric current is 
passed through the cylindrical magnet 8 in the same manner so that the 
lines of magnetic force may be formed in the direction opposite to that of 
the lines of magnetic force of the magnetic field formed by said exciting 
coil 4 on the central line, if the above described is reversely carried 
out, that is, a direct electric current is passed through the cylindrical 
magnet 9 so that the lines of magnetic force may be formed in the 
direction opposite to that of the lines of magnetic force formed by the 
exciting coil 4 on the central line of the magnetic field formed by the 
exciting coil 4 while a direct electric current is passed through the 
cylindrical magnet 8 so that the lines of magnetic force may be formed in 
the same direction as that of the lines of magnetic force of the magnetic 
field formed by the exciting coil 4 on the central line, the vertical 
component of the magnetic flux density Bz on the sample sample stage shows 
a maximum value above the cylindrical magnet 8 and is rapidly reduced both 
outward and inward from there, whereby being capable of obtaining a 
distribution equivalent to the distribution of magnetic flux density Bz 
shown in FIG. 9. In addition, it goes without saying that even though the 
combination of the core 8a of the cylindrical magnet 8 and the coil and 
the combination of the core 9a of the cylindrical magnet 9 and the coil 
are replaced by one piece of cylindrical permanent magnet respectively, 
the same effect as in the above described preferred embodiment can be 
attained. 
In addition, although the case where the cylindrical magnets 8, 9 are 
formed of the respective cores 8a, 9a wound by lead wires was shown in the 
above described preferred embodiment, the core may not be used but merely 
a lead wire wound in a circular shape may be used for the cylindrical 
magnet through which a direct electric current is passed so as to form the 
lines of magnetic force in the opposite direction on the central line to 
lines of magnetic force of the magnetic field formed by the exciting coil 
4. 
In addition, although the construction, in which the cylindrical magnets 8, 
9 are disposed immediately below the sample stage 5, was shown in said 
preferred embodiment, the position of disposing the cylindrical magnets 8, 
9 is not specially limited but every position, at which a magnetic field 
having an appointed magnetic flux density can be formed on the surface of 
the sample 100, that is, for example, they may be disposed outside of the 
sample chamber 3 or they may be formed integrally with the sample stage 5 
or they may be adapted to serve also as the sample stage 5. 
FIGS. 10, 11 are enlarged longitudinal sectional views showing 
modifications of the magnetic field forming means according to the 
preferred embodiment shown in FIG. 8. In the magnetic field forming means 
shown in FIG. 10, a magnet positioned inside is solid and columnar and 
constructed in the form of a columnar magnet 18 with a lead wire wound 
around a peripheral surface of a core 18a formed by expanding an end face, 
which is positioned on a side of the sample 100, upward so as to form a 
spherical surface. 
In such the magnetic field forming means, the lines of magnetic force 
formed by the columnar magnet 18 exhibit a higher permeability toward the 
central portion side from the peripheral edge portion and the divergent 
effect for the plasma is higher toward the central line of the sample 100. 
In other words, it is possible to reduce the vertical component of the 
magnetic flux density Bz on the central line of the sample 100, whereby 
still more uniforming the plasma distribution. 
In the magnetic field forming means shown in FIG. 11, a magnet 28 
positioned inside has a construction with a columnar portion 28c disposed 
at a center of one surface of a disc bottom plate portion 28b and a 
cylindrical portion 28d disposed at a position closer to the peripheral 
edge portion so that they may concentrically stand with a desired interval 
therebetween and a lead wire wound around a peripheral surface of said 
cylindrical portion 28d. 
With such the magnetic field forming means, the lines of magnetic force 
formed by the cylindrical magnet 28 selectively exhibit a higher 
permeability than other portions due to the magnetic passage formed by the 
columnar portion 28c at the central portion and the magnetic passage 
formed by the cylindrical portion 28d at the peripheral edge portion, 
whereby increasing the magnetic flux density, so that the divergent effect 
for the plasma at the central portion of the sample 100 can be heightened 
and the vertical component of the magnetic flux density Bz can be reduced 
and as a result, the plasma can be uniformed in the same manner as in the 
preferred embodiment shown in said FIG. 10. 
In addition, other constructions and effects shown in FIGS. 10, 11 are 
substantially same as in the magnetic field forming means according to the 
preferred embodiment shown in said FIG. 8 and the corresponding parts are 
marked with same numerals, so that their description is omitted. 
FIG. 12 is a longitudinal sectional view showing another preferred 
embodiment of the plasma apparatus according to the present invention. A 
magnetic field forming means 6 disposed below a sample stage 5 in the 
present preferred embodiment is integrally provided with exciting coils 
6b, 6c stuck to an inside circumferential surface and a periphery of a 
cylindrical core 6a. An inside diameter of the cylindrical core 6a is set 
so as to be slightly larger than an outside diameter of the sample stage 
5. The cylindrical core 6a is disposed at a position closer to the bottom 
of the sample stage 5 within a sample chamber 3 with making an axial 
direction thereof coincident with a direction of width of the sample 100 
under the condition that an upper end portion thereof is put on the sample 
stage 5. 
In addition, the constructions other than the magnetic field forming means 
6 are same as those shown in FIG. 3, so that their description is omitted 
here. 
FIG. 13 is a graph showing a relation between a distance r (cm) in a radial 
direction from the center of the sample and the vertical component of the 
magnetic flux density (Gauss) in the plasma apparatus according to the 
preferred embodiment shown in FIG. 12. Referring to FIG. 13, a full line 
(a) shows the case where the distance between the sample 100 and the 
cylindrical core 6a is 9 mm while a broken line (b) shows the case where 
said distance is 29 mm. In addition, a white arrow shows a position of the 
cylindrical core 6a. 
It is found from this FIG. 13 that a magnetic field, in which a magnetic 
flux density in a peripheral edge portion of a sample 100 is sufficiently 
higher than that at a central portion of the sample 100, can be obtained 
by a magnetic field forming means disposed closer to the sample 100. It 
can also be found from FIG. 13 that a simple and ideal magnetic field, in 
which the direction of the magnetic field is same all over the area, is 
obtained. 
As the result of the attainment of such the magnetic field, the 
distribution of plasma density led onto the surface of the sample 100 can 
be uniformed. 
In the preferred embodiment shown in FIG. 12, the magnetic field forming 
means 6 is integrally constructed, so that it is handy and can be easily 
incorporated in the plasma apparatus. Accordingly, the assembling 
operation in the vicinity of the sample stage 5 of the plasma apparatus 
becomes easy. 
FIGS. 14 to 17 are enlarged longitudinal sectional views showing the 
modifications of the magnetic field forming means according to the 
preferred embodiment shown in FIG. 12. The preferred embodiment shown in 
FIG. 16 relates to the case where an outside diameter of a core 6a is 
nearly equalized to an outside diameter of a sample stage 5 and the core 
6a is surely housed below the sample stage 5. The preferred embodiment 
shown in FIG. 15 relates to the case where a lower portion of a core 6a is 
slightly shortened in diameter and the shortened-diameter portion is 
provided with coils 6b, 6c. The preferred embodiment shown in FIG. 16 
relates to the case where a lower portion of a core 6a is slightly 
enlarged in diameter and the enlarged-diameter portion is provided with 
coils 6b, 6c. The preferred embodiment shown in FIG. 17 relates to the 
case where a core 6a is provided with sponson portions in both the 
enlarged-diameter direction and the shortened-diameter direction at a 
lower portion thereof to additionally expand the core 6a. In every 
modification, it is sufficient to obtain such the distribution of magnetic 
flux density shown in FIG. 13 in the vicinity of the sample 100 by the 
magnetic field forming means 6 comprising the core 6a provided with the 
coils 6b, 6c. 
FIG. 18 is a longitudinal sectional view showing another preferred 
embodiment of the plasma apparatus according to the present invention. In 
the present preferred embodiment, a magnetic field forming means 6 
disposed below a sample stage 5 comprises a permanent magnet and a 
paramagnetic member in combination. That is to say, in the present 
preferred embodiment, the magnetic field forming means 6 is provided with 
a rod-like core 6d made of a paramagnetic material at a center thereof and 
a circular core 6e made of a paramagnetic material disposed around a 
periphery of said rod-like core 6d concentrically with it, and a plurality 
of permanent magnets 6f are disposed in a circular space between the 
rod-like core 6d and the circular core 6e so that said space may be filled 
up. 
FIG. 19 is a plan view showing the magnetic filed forming means according 
to the present preferred embodiment and FIG. 20 is a longitudinal 
sectional view showing the magnetic field forming means 6 according to the 
present preferred embodiment. Each permanent magnet 6f is fan-shaped. Its 
central side is a N-pole while its peripheral edge side is a S-pole and a 
plurality of permanent magnets are arranged in a closely engaged manner 
under the condition that the N-pole is positioned on a side of the central 
portion, that is, the rod-like core 6d side, while the S-pole is 
positioned on a side of the peripheral edge portion, that is, the circular 
core 6e side. 
Materials of the rod-like core 6d, circular core 6e and permanent magnet 6f 
are not specially limited but the known materials are suitably selected. 
In addition, the constructions other than the magnetic field forming means 
6 are same as those shown in FIG. 3, so that their description is omitted 
here. 
FIG. 21 is a diagram showing the distribution of the lines of magnetic 
force formed by the exciting coil 4 and the magnetic field forming means 
6, in which the line of magnetic force M.sub.1 forming a divergent 
magnetic field turning toward a side of the sample chamber 3 formed by the 
exciting coil 4 is formed so as to pass the positions closer to the 
peripheral edge portion of the sample stage 5 while almost of the magnetic 
force M.sub.2 of the magnetic field formed by the permanent magnets 6f of 
the magnetic field forming means 6 is formed so as to turn toward the side 
of the peripheral edge portion of the sample stage 5 from the central 
portion of the sample stage 5 through the rod-like core 6d from the N-pole 
on the side of the central portion and then arrive at the S-pole on the 
side of the peripheral edge portion through the circular coil 6e from the 
peripheral edge portion. The line of magnetic force immediately arriving 
at the S-pole from the N-pole of the permanent magnet 6f without passing 
through the coils 6d, 6e is remarkably reduced. 
Accordingly, the magnetic flux density in the peripheral portion of the 
sample 100 is relatively heightened while the magnetic flux density at the 
control portion of the sample 100 is relatively lowered by the existence 
of the magnetic field forming means 6. 
FIG. 22 is a graph showing a relation between a distance r (cm) in the 
radial direction from the center of the sample and a vertical component of 
the magnetic flux density Bz (Gauss) in the plasma apparatus according to 
the present preferred embodiment shown in FIG. 18. Referring to FIG. 24, a 
full line (a) shows the distribution of density on the surface of the 
sample stage 5 while a broken line (b) shows the distribution of density 
at a distance of 1 cm above the surface of the sample stage 5. 
It is obvious from FIG. 22 that the condition that the magnetic field 
forming means 6 is not disposed, that is, the combination of a 
distribution pattern of magnetic flux density formed by the divergent 
magnetic filed generated by the exciting coil 4 and the distribution of 
magnetic flux density formed by the magnetic field forming means 6, leads 
to the possibility of obtaining a magnetic field in which the magnetic 
flux density at the peripheral edge portion of the sample 100 is 
sufficiently higher than that at the central portion of the sample 100. 
Thus, the plasma density on the surface of the sample 100 can be 
uniformed. 
In this preferred embodiment, since the magnetic field forming means 
comprises the permanent magnets and the paramagnetic member in 
combination, no power supply facility is required, whereby the magnetic 
flux density on the surface of the sample can be uniformed in a simple 
construction. 
With the preferred embodiment shown in FIG. 18 and the conventional 
apparatus shown in FIG. 1, a silicon wafer having a diameter of 6 inches 
was placed on the sample stage 5 concentrically with the sample stage 5 
and SiH.sub.4 gas was introduced into the sample chamber 3 at a flow rate 
of 28 sccm while N.sub.2 gas was introduced into the sample chamber at a 
flow rate of 35 sccm to form a silicon oxide film on the silicon wafer at 
a microwave power of 600 W. As a result, the deposition rate of 
2100.ANG./min and the uniformity of film thickness was .+-.3.5% were 
obtained. On the contrary, with the conventional apparatus, the deposition 
rate was 2100.ANG./min and the uniformity of film thickness was .+-.20%. 
The uniformity of film thickness was calculated by the above described 
formula (1). 
FIG. 23 is an enlarged longitudinal sectional view showing a modification 
of the magnetic field forming means 6 according to the preferred 
embodiment shown in FIG. 18. The periphery of the magnetic field forming 
means 6 shown in FIGS. 19, 20 is surrounded by a second circular core 6g 
made of a paramagnetic material disposed concentrically with a circular 
core 6e of the magnetic field forming means 6 made of a paramagnetic 
material likewise and this second circular core 6g is movable in the 
direction of an axis shaft line thereof, in other words, in the direction 
of approaching to and going away from the sample stage 5. 
In addition, an assembly comprising a rod-like core 6d, circular core 6e 
and permanent magnets 6f may be integrally ascended and descended instead 
of moving the second circular core 6g. 
In such the preferred embodiment, the distribution of magnetic flux density 
immediately above the surface of the sample stage 5 or still further above 
there can be regulated to still further uniform the plasma distribution in 
the vicinity of the surface of the sample 100. 
In addition, other constructions and operations shown in FIG. 23 are 
substantially same as those in the FIGS. 19, 20 and corresponding parts 
are marked with the same numerals, so that their description is omitted. 
FIGS.24, 25 and FIGS. 26, 27 show the modifications of the magnetic field 
forming means according to the preferred embodiment shown in FIG. 18. 
FIGS. 24, 26 are plan views showing each magnetic field forming means 
while FIGS. 25, 27 are longitudinal sectional views showing each magnetic 
field forming means. 
The magnetic filed forming means 16 shown in FIGS. 24, 25 comprises 
rod-like permanent magnets 16f disposed radially in the circumferential 
direction at almost regular angular intervals between the rod-like core 
16d and the circular core 16e made of a paramagnetic material with 
positioning the N-pole thereof on the central side and the S-pole thereof 
on a side of the peripheral edge portion. 
In such the preferred embodiment, an advantage occurs in that the permanent 
magnet 16f itself is simplified in construction. 
The magnetic field forming means 26 shown in FIGS. 26, 27 comprises a 
rod-like permanent magnet 26d with a sample stage side as a N-pole and a 
circular permanent magnet 26e with the sample stage side as a S-pole 
disposed around said rod-like permanent magnet 26d concentrically with the 
rod-like permanent magnet 26d, said rod-like permanent magnet 26d and said 
circular permanent magnet 26e being concentrically disposed on a disc core 
26f made of a paramagnetic material. 
In such the preferred embodiment, the lines of magnetic force are formed 
toward an upper end as the S-pole of the circular permanent magnet 26e 
from an upper end as the N-pole of the rod-like permanent magnet 26d 
positioned at the center and the plasma moved along the direction of the 
lines of magnetic force is dispersed from a side of the rod-like permanent 
magnet 26d to a side of the circular permanent magnet 26e, in other words, 
from a side of the central portion of the sample stage 5 to a side of the 
peripheral edge portion, whereby uniforming the plasma distribution. In 
addition, almost of the lines of magnetic force arriving at the rod-like 
permanent magnet 26d from the N-pole of the circular permanent magnet 26e 
pass through the disc core 26f, whereby effectively improving the 
distribution of magnetic flux density. 
In addition, other constructions and operations are substantially same as 
those shown in FIGS. 19, 20 and corresponding parts are marked with the 
same numerals, so that their description is omitted. 
As this invention may be embodied in several forms without departing from 
the spirit of essential characteristics thereof, the present embodiment is 
therefore illustrative and not restrictive, since the scope of the 
invention is defined by the appended claims rather than by the description 
preceding them, and all changes that fall within the meets and bounds of 
the claims, or equivalence of such meets and bounds thereof are therefore 
intended to be embraced by the claims.