Plasma generating apparatus

A plasma generating appartus according to the present invention generates a plasma by cyclotron movement of electrons. The apparatus features microwave introducing guides for introducing microwaves, a reaction chamber in which a plasma is generated based on introduced microwaves, a magnetic field generating section, and solenoid coils. The magnetic field generating section features at least a pair of magnetic poles having mutually facing concave surfaces, and a yoke for coupling the magnetic poles to constitute a loop of magnetic force lines. The magnetic poles are arranged to face each other with the microwave introducing guides and the reaction chamber interposed, and the magnetic poles generate a magnetic field of a predetermined magnetic flux density consisting of magnetic force lines directed vertically to a major surface of a sample placed on a support table in the reaction chamber. The solenoid coils can vary the magnetic field of a predetermined magnetic flux density generated by the magnetic field generating section to a magnetic field of a desired magnetic flux density.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a plasma generating apparatus 
and more particularly to a plasma generating apparatus wherein a plasma is 
generated by microwaves and a magnetic field to etch a sample such as a 
semiconductor wafer or to form a film on the sample. 
2. Description of the Related Art 
In general, in accordance with the higher integration density of an 
integrated circuit formed on a semiconductor substrate, etc., it is 
necessary to reduce the size of circuit elements constituting the 
integrated circuit and the thickness of wires for connecting these circuit 
elements, with high reliability. 
In an example of the apparatus for manufacturing the integrated circuit, 
there is employed a plasma generating apparatus wherein a magnetic field 
is applied in a low-vacuum atmosphere into which a process gas is 
introduced, and microwaves are applied to the magnetic field to accelerate 
electrons in a cyclotron, thus generating a plasma. A typical example of 
this apparatus is an ECR (Electron Cyclotron Resonance) apparatus. 
The ECR apparatus is generally divided into a plasma generating chamber and 
a reaction chamber. A plasma generated in the plasma generating chamber is 
taken out of the chamber in the form of a beam and is radiated to a sample 
placed in the reaction chamber directly or via a target. Thus, the sample 
is etched, or a film is formed on the sample. A coil for generating the 
magnetic field in the plasma generating chamber is parallel to a major 
surface of a semiconductor wafer of the sample, and the coil is wound 
around the plasma generating chamber in a ring-shape. 
The plasma generated by the plasma generating apparatus employed in the ECR 
apparatus has a high density. In addition, since ions travel straight 
along a magnetic field in a direction in which a magnetic field is 
attenuated, the plasma has a relatively anisotropic property and a low 
temperature. 
Accordingly, when the ECR apparatus is employed as an etching apparatus, a 
straight anisotropic beam plasma is radiated onto a major surface of the 
wafer to carry out fine processing; on the other hand, if the ECR 
apparatus is employed as a thin-film forming apparatus, burying of contact 
holes can be effectively performed by virtue of anisotropy in the 
direction of formation of thin-film. 
However, the above ECR apparatus has a two-chamber structure, and the size 
thereof is large. In order to effectively take out ions from the plasma in 
the electric field and radiate the ions on the wafer, a high voltage 
(several hundred voltage) must be applied. In this case, there is problem 
that the ion energy increases due to the application of high voltage. The 
consumption of power can be reduced and ion energy is reduced, for 
example, by placing the sample in the plasma; however, with this 
structure, the sample absorbs microwaves as heat or high-energy electrons 
collide with the sample, and therefore the temperature thereof increases. 
Consequently, the quality and characteristic of the formed film are 
damaged, and the quality of the film is degraded. 
As is well known, when an electric current is supplied to a coil for 
generating a magnetic field, a magnetic field is formed such that the 
lines of magnetic force extend from the inside of the coil, run along the 
outer periphery of the coil, and return to the inside of the coil. 
When the sample is situated such that the lines of magnetic force emitted 
from the inside of the coil are made incident perpendicularly onto the 
major surface of the wafer, the lines enter the center part of the major 
surface perpendicularly but do not enter the outer peripheral part of the 
major surface. Specifically, the lines are inclined from the center of the 
sample towards the outer periphery thereof. 
When the above ECR apparatus is employed for etching, the plasma enters in 
the direction of the lines of magnetic force, and the lines do not 
perpendicularly enter the entire surface of the sample. Thus, vertical 
etching cannot be performed. As a result, fine processing cannot be 
carried out, owing to side etching effected on the outer peripheral part 
of the sample and a difference in etching rate (the center part is etched 
at a higher rate than the outer peripheral part). 
In particular, in accordance with the increase in area of the sample, the 
influence due to the above problems increases. 
More specifically, as the area of the semiconductor wafer of the sample 
increases, the size of the coil increases accordingly and a large electric 
power for generating a necessary magnetic field is required. For example, 
when microwaves of 2450 MHz are employed, the magnetic field of 875 gauss 
is required in the ECR region. When the diameter of the wafer is 10 
inches, the size of the magnetic field generating coil increases such 
that, for example, the inside diameter is 500 mm, the outside diameter is 
660 mm and the height is 80 mm. In this case, in order to generate an 
intense magnetic field of 875 gauss in the entire ECR region, an electric 
current of 40,000 ampere's turn or more must be supplied to the magnetic 
field generating. The electric power to be required is 16 KWh or more. In 
addition, when the diameter of the wafer is 12 inches or more, the size of 
the apparatus increases and a large power is required. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a plasma generating 
apparatus having a smaller size while power consumption is reduced. The 
apparatus is capable of easily carrying out fine processing and highly 
efficient plasma treatment, while preventing a sample from being heated by 
microwaves. 
A plasma generating apparatus according to this invention comprises: 
microwave introducing means for introducing microwaves; plasma generating 
means for generating a plasma based on microwaves introduced into the 
microwave introducing means, and storing a sample so that the sample can 
be freely removed; at least a pair of magnetic field generating means each 
having a magnetic pole, said magnetic field generating means being 
arranged to face each other with the plasma generating means interposed 
and generating a magnetic field of a predetermined magnetic flux density 
consisting of lines of magnetic force which vertically enter a major 
surface of the sample; coupling means for coupling the paired magnetic 
poles of the magnetic field generating means, and forming a loop of lines 
of magnetic force; and magnetic field generation correcting means for 
varying a magnetic field of a predetermined magnetic flux density 
generated by the magnetic field generating means to a magnetic field of a 
desired magnetic flux density. 
Additional objects and advantages of the invention will be set forth in the 
description which follows, and in part will be obvious from the 
description, or may be learned by practice of the invention. The objects 
and advantages of the invention may be realized and obtained by means of 
the instrumentalities and combinations particularly pointed out in the 
appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the present invention will now be described with reference 
to the accompanying drawings. 
FIG. 1 is a view for illustrating the concept of a plasma generating 
apparatus according to the present invention. 
In the plasma generating apparatus, a magnetic pole piece 1 and a magnetic 
lower pole piece 2 (both formed of, e.g. soft iron) are arranged to face 
each other. A plasma space 3 where a plasma is generated is provided 
between the pole pieces 1 and 2. 
The pole pieces 1 and 2 have mutually facing concave surfaces (upper 
opposite surface 1a and lower opposite surface 2a). 
By virtue of the shapes of the surfaces 1a and 2a, a magnetic flux 4a 
generated from the center part of the upper opposite surface 1a travels 
towards the center part of the lower opposite surface 2a. Magnetic fluxes 
4b generated from the peripheral part of the upper opposite surface 1a 
travel towards the peripheral part of the lower opposite surface 2a 
substantially linearly. 
Rear surfaces 1b and 2b of the pole pieces 1 and 2, which are opposed to 
the facing opposite surfaces 1a and 2a, are connected to and integrated 
with magnetic bodies 5 and 6 (formed of, e.g. soft iron). Each of the 
magnetic bodies 5 and 6 has a smaller diameter than the corresponding 
opposite surface 1a, 2a. 
Solenoid coils 7 and 8 capable of controlling (e.g. varying) the intensity 
of the magnetic field in the plasma space 3 are provided around the 
magnetic bodies 5 and 6. 
The magnetic body 5 is connected to one end of a permanent magnet 10 for 
generating a magnetic field via a highly magnetic yoke 9, and the magnetic 
body 6 is connected to the other end of the magnet 10 via a similar yoke 
11. The conductors 5 and 6, yokes 9 and 11 and magnet 10 constitute a 
C-shaped structure. The C-shaped structure functions as a magnetic field 
forming section, and a closed loop of magnetic fluxes is formed via the 
plasma space 3 (magnetic fluxes 4). 
The solenoid coils 7 and 8 serving as magnetic field forming auxiliary 
parts are employed to control the intensity of the magnetic field 
generated by the permanent magnet 10, etc. thereby setting the density of 
magnetic flux in the generation area 14 of the ECR to 875 gauss. 
Hereinafter, the combination of the magnetic field forming section and the 
magnetic field forming auxiliary parts is referred to as "magnetic field 
forming section." 
In order to set the density of magnetic flux of the generation area 14 of 
the ECR to 875 gauss in the manufacture of the apparatus, the density of 
magnetic flux is corrected by the solenoid coils 7 and 8 very slightly. 
For example, a power consumption is only about 0.2 KWh or less. 
Suppose that the distance between the ferromagnetic pole pieces 1 and 2 is 
20 cm, the diameter of each pole piece is 30 cm, the inside diameter of 
each solenoid coil 7, 8 is 17 cm, the outside diameter of each solenoid 
coil is 25 cm, the height of each solenoid coil is 4 cm, and the two 
solenoid coils 7 and 8 are arranged vertically. In this case, the electric 
current needed to obtain the density of magnetic flux of 875 gauss is 
about 14,000 ampere's turn even if no permanent magnet is used. The volume 
of each solenoid coil is much smaller than that of a conventional one, and 
the electric power consumed by the solenoid coils is only 1.6 KWh. 
In the present invention, the permanent magnet and the solenoid coils are 
combined; however, it is easy to obtain a desired density of magnetic flux 
of 875 gauss by using only the solenoid coils. 
A vacuum chamber 15 for treating wafers is situated within the plasma space 
3, and an introducing port 16 for introducing microwaves of 2450 MHz is 
provided on one side of the vacuum chamber 15. In FIG. 1, the port 16 is 
provided in the side wall of the chamber 15 for the purpose of 
convenience; actually, the port is provided so as to introduce microwaves 
in a direction vertical to the major surface of a sample, e.g. a 
semiconductor wafer (hereinafter called "wafer"). 
A support table 18 for supporting a wafer 17 is provided within the vacuum 
chamber 15. 
In the plasma generating apparatus having the above structure, a vacuum is 
erected in the vacuum chamber 15 and thereafter a process gas is 
introduced and microwaves 19 of 2450 MHz are introduced from the 
introducing port 16. A magnetic field having a density of magnetic flux of 
875 gauss is generated in the ECR generation region 14 above the wafer 17. 
Then, electrons in the ECR generation region and near the ECR generation 
region resonate and start to rotate. The electrons collide with the 
process gas and are ionized. Thus, a plasma is generated to treat the 
sample. 
The concave shapes of the facing surfaces of the pole pieces 1 and 2 are 
determined by computer simulation in order to obtain a uniform density of 
magnetic flux. 
FIG. 2 shows a structure of a first embodiment in which the plasma 
generating apparatus of this invention has been applied. In the second and 
subsequent embodiments of the invention, common structural elements are 
denoted by like reference numerals. 
The main part of the first embodiment is constituted by a rectangular 
waveguide 20 serving as a microwave introducing section, a magnetic field 
forming section 21, and a reaction chamber 22 in which a support table 18 
for supporting a sample or a semiconductor wafer 17 is provided. 
The reaction chamber 22 has a cavity resonator structure for exciting 
electron cyclotron resonator structure. The electronic cyclotron resonator 
structure comprises a container or apparatus body 23 of a non-magnetic 
material such as aluminum alloy or stainless steel, the rectangular 
waveguide 20 mounted on an upper opening of the body 23 via a 
microwave-permeable quartz glass 24, and an electrically conductive 
support table 18 having a mount surface 18a on which wafer 17 is mounted. 
The support table 18 is opposed to an upper opening plane 26 with 
microwave discharge ports 25 of the rectangular waveguide 20. 
In the above structure, suppose that the distance between the upper opening 
plane 26 and mount surface 18a is (.lambda.g/2).times.n (integer) when the 
wavelength of microwave is .lambda. g. In this case, electron cyclotron 
resonance of TE mode or TEM mode can be effected in the reaction chamber 
22. 
Accordingly, since the wafer 17 is situated on the microwave reflection 
surface, heating by microwaves can be prevented. 
As is shown in FIG. 3, microwave and electrons (electron behavior) resonate 
at a maximum level in a region located .lambda. g/4 above the mount 
surface 18a, and a plasma with the highest intensity is generated there. 
The reaction chamber 22 has supply ports 27a and 27b for supplying a 
process gas or a reaction gas such as Cl.sub.2, SF.sub.6 and CF.sub.4 into 
the chamber, and an exhaust port 29 communicating with an exhaust system 
28. Thereby, a predetermined vacuum atmosphere is maintained in the 
reaction chamber 22. 
The quartz glass 24 is mounted on the apparatus body 23 with an O-ring 
interposed in order to maintain a vacuum in the reaction chamber 22. The 
exhaust port 29 is provided with a filter 31 formed of a non-magnetic, 
electrically conductive mesh, thereby preventing leakage of microwaves 
from the apparatus body 23. 
The apparatus body 23 is provided with an openable gate 23a for 
loading/unloading the sample. It is possible to connect the gate 23a to a 
load-lock chamber, an unload-lock chamber and a convey mechanism and 
combine the reaction chamber with another process apparatus (chamber), 
thereby carrying out different processes continuously. 
The apparatus body 23 is provided with a heating mechanism for baking the 
inside wall, in order to attain a predetermined vacuum degree and prevent 
a product, occurring during the process treatment, from adhering to the 
inside wall. The support table 18 is provided with a temperature control 
mechanism for heating/cooling the sample in order to control the 
temperature of the sample. 
FIG. 4 shows a specific structure of the rectangular waveguide 20. The 
rectangular waveguide 20 has a flat hollow rectangular shape and is 
connected to a magnetron 32 serving as a microwave supply source. The 
lower surface of the waveguide 20 is provided with a plurality of 
slit-like microwave supply ports 25 at predetermined intervals. 
An end portion of the waveguide 20 is provided with a microwave absorbing 
body 21a. The microwave absorbing body 21a absorbs reflected waves 
generated in the waveguide 20, and the waves are not returned to the 
magnetron. By cooling the microwave absorbing body 21a from outside, the 
heating of the waveguide 20 by microwaves can be prevented. Where the 
wavelength of microwaves is ".lambda. t", the microwave supply ports 25 
are formed at an interval of 1 cm.times.(.lambda. t/2). 
Referring back to FIG. 2, the magnetic field forming section 21 comprises 
upper and lower magnetic poles 33 and 34, magnetic field generating coils 
35 and 36, and a yoke 39. The poles 33 and 34 face each other along the 
vertical axis of the apparatus body 23. The coils 35 and 36 are wound, 
respectively, around the poles 33 and 34. The yoke 39 is made of a highly 
magnetic body, e.g. soft iron. The yoke 39 is integrally coupled to the 
outside surfaces of the magnetic poles 33 and 34 with permanent magnets 37 
and 38 interposed. 
The magnetic field generating coils 35 and 36 and permanent magnets 37 and 
3 of the magnetic field forming section 21 are excited to generate a 
magnetic field of, e.g. 875 gauss when the frequency of microwaves is 2450 
MHz. And vertical lines A of magnetic force are applied to the major 
surface of the wafer 17 situated in the reaction chamber 22. Microwaves 
propagated from the magnetron 32 shown in FIG. 4 to the rectangular 
waveguide 20 are introduced from the microwave supply ports 25 into the 
reaction chamber 22. 
As is shown in FIG. 3, using a process gas fed into the reaction chamber 
22, a plasma is efficiently produced in a region located .lambda. g/4 
above the support table 18 for supporting the wafer 17. Thereafter, ions 
in the plasma are vertically directed to the major surface of the wafer 
17, i.e. in the direction of the lines A of magnetic force. In this case, 
as shown in FIG. 2, a high-frequency source 52 is connected to the support 
table 18 to apply a negative potential to the support table 18, thereby 
extracting ions form the plasma more efficiently. 
FIG. 5 shows a structure of a plasma generating apparatus according to a 
second embodiment of the present invention. 
In the above first embodiment, the upper opening plane 26 is put in contact 
with the quartz plate 24. Thus, two maximum plasma intensity points are 
present at a region (1/4).times..lambda. g above the supporting plate 18 
and a region (3/4).times..lambda. g above the plate 18 where the amplitude 
of microwave has a maximum value. 
Accordingly, in the second embodiment, if the quartz plate 24 is situated 
(1/2).times..lambda. g above the wafer 17, as shown in FIG. 5, the highest 
intensity point of process gas exists only at a region located 
(1/4).times..lambda. g above the supporting table 18. Thus, the plasma is 
formed in a plane-shape on the wafer 17, and excellent etching is carried 
out. 
FIG. 6 shows a structure of a plasma generating apparatus according to a 
third embodiment of the present invention, which plasma generating 
apparatus has been applied to an etching apparatus. FIG. 7 is a plan view 
of the etching apparatus of FIG. 6, and FIG. 8 is a partial 
cross-sectional view of the microwave introducing section used in the 
third embodiment. 
In the third embodiment, a radial waveguide 40 is mounted on the upper 
opening portion of the apparatus body 23 with quartz glass 24 interposed. 
A plurality of microwave supply ports 41 are radially formed in the radial 
waveguide 40, as shown in FIG. 8. A coaxial cable 43 connected to a 
magnetron (not shown) similar to that of FIG. 4 is inserted into an 
opening 42 provided at the upper central part of the radial waveguide 40. 
A microwave absorbing body 40a similar to the absorbing body of the 
aforementioned rectangular waveguide 20 is mounted around the radial 
waveguide 40. 
The microwave supply ports 41 are formed, for example, at an interval of 1 
cm.times.(.lambda. g/2), when the wavelength of microwave is ".lambda. g". 
Specifically, when the wavelength of microwave is ".lambda. t", the 
distance between a microwave introducing plane 44 and a mount plane 18a of 
the support table 18 is found as (.lambda. t/2).times.n (integer). A TE 
mode or TEM mode electron cyclotron resonance is caused in the reaction 
chamber 22. 
As is shown in FIG. 7, upper and lower circular magnetic poles 45 and 46 
are coupled to a plurality of yokes 47 made of a highly magnetic material 
such as soft iron. The yokes 47 are formed in four parts symmetrical with 
respect to the vertical center of the apparatus body 23, thereby 
constituting a plurality of magnetic circuits. Thus, a magnetic field of 
uniform, vertical magnetic flux is produced on the major surface of the 
wafer 17. 
Magnetic field generating coils 48 and 49 are wound around the upper and 
lower magnetic poles 45 and 46 and yokes 47a and 47b coupled to the 
magnetic poles. Each of the openings of the upper and lower magnetic poles 
can be utilized as an insertion guide for the coaxial cable 43 of the 
radial waveguide 40. 
According to the plasma generating apparatus of the third embodiment, an 
ECR plasma is generated by microwaves (e.g. 2.45 GHz) supplied from the 
magnetron situated outside the apparatus into the radial waveguide 40, and 
the magnetic field of 875 gauss is produced by the magnetic field 
generating coils 48 and 49. 
The process gas supplied into the reaction chamber 22 is changed to a 
high-density plasma, and ions in the plasma are radiated vertically to the 
wafer 17. Thereby, etching of wafer 17 is effected. 
An actual example of the plasma apparatus was employed to obtain 
measurement data. The distance between the upper magnetic pole 45 and the 
lower magnetic pole 46 was 30 cm, the diameter of each of upper and lower 
magnetic poles 45 and 46 was 50 cm, the inside diameter of each of 
magnetic field generating coils 48 and 49 was 44 cm, the outside diameter 
of each coil was 52 cm, and the height of each coil was 6 cm. It was found 
that in order to obtain a magnetic flux density of 875 gauss, about 30000 
ampere's turn needed to be fed to the magnetic field generating coils 48 
and 49. The electric power consumed by the coils 48 and 49 was 7 KWh. 
In the third embodiment, the microwave introducing section is composed of 
the radial waveguide; however, a rectangular waveguide may be used. Any 
type of microwave introducing section capable of radiating microwaves 
vertically to the major surface of the sample may be used, and the 
direction in which microwaves are input to the waveguide and the shape of 
the waveguide are not limited. In addition, it is possible to use the 
waveguide in the state in which a dielectric substance is filled. 
In the third embodiment, the yoke 47 of the magnetic field generating 
section is divided into four parts; however, the number of divided parts 
is not limited only if these parts are symmetrical with respect to the 
vertical line passing through the center of the reaction chamber 22. 
FIG. 9 shows a structure according to a fourth embodiment of the invention, 
in which the plasma generating apparatus is applied to an etching 
apparatus. 
The fourth embodiment is an improvement of the third embodiment, and the 
magnetic flux density is increased while the power consumption is reduced. 
Each magnetic field generating section 21 comprises upper and lower 
magnetic poles 45 and 46 facing each other along the vertical axis of the 
apparatus body 23, magnetic field generating coils 35 and 36 mounted 
around the magnetic poles 45 and 46, and a yoke 39 coupled to the rear 
parts of the magnetic poles with permanent magnets 50 and 51 interposed. 
In the magnetic field generating section, errors in manufacture of the 
permanent magnets 50 and 51 and other magnetic circuits can be corrected 
by controlling the electric current flowing through the magnetic field 
generating coils 35 and 36. 
In the fourth embodiment, 90% of a desired intensity of magnetic field can 
be obtained only by the permanent magnets 50 and 51. Thus, it is 
sufficient that the remaining 10% of the intensity is obtained by the 
magnetic field generating coils 35 and 36, and the consumed power of the 
coils 35 and 36 can be reduced. 
Since the permanent magnets 50 and 51 are provided near the reaction 
chamber 22, the magnetic field leaking from the magnets 50 and 51 can be 
reduced, and the adverse effect on the surroundings of the apparatus can 
be reduced. 
A specific example of the plasma generating apparatus according to the 
fourth embodiment will now be described. In this example, it is supposed 
that the distance between the mutually facing upper and lower magnetic 
poles 45 and 46 is 30 cm, the diameter of each magnetic pole is 50 cm, the 
inside diameter of each of magnetic field generating coils 35 and 36 is 44 
cm, the outside diameter of each coil is 52 cm, and the height of each 
coil is 4 cm. In this case, the electric current, which need be supplied 
to the coils 35 and 36 in order to obtain the density of magnetic flux of 
875 gauss, is about 3,500 ampere's turn. The electric power consumed by 
the coils 35 and 36 is only 0.7 KWh. 
The above embodiments are not limited to etching apparatuses; these 
embodiments can easily be applied to a film forming apparatuses such as 
plasma CVD apparatuses. 
As has been described above, the following advantages can be obtained by 
the plasma generating apparatus of the present invention: 
(1) Electron cyclotron resonance occurs in the region between the plane at 
which the microwave supply ports are formed and the plane of the 
electrically conductive support table on which the sample is placed. Thus, 
the support table functions as a reflection plate in the cavity in which 
electron cyclotron resonance is caused. Microwaves are not absorbed in the 
sample as heat, and the heating of the sample can be prevented. 
(2) The position of the maximum intensity of plasma is set at 1/4 
wavelength of microwave above the support table on which the sample is 
placed; therefore, plasma treatment can be carried out with use of a 
high-density plasma generated there. 
(3) The sample placed on the support table is situated at a level 
corresponding to an integer number of times of 1/2 wavelength of microwave 
in the reaction chamber from the microwave inlet. Thus, the adverse effect 
on the sample by microwaves can be prevented, and the plasma treatment of 
the sample can be carried out more efficiently. 
(4) The magnetic field generating sections arranged to face each other 
comprise a plurality of magnetic circuits constituted by magnetic field 
generating coils wound around the magnetic poles arranged to face each 
other, and a plurality of yokes divided in a direction perpendicular to 
the axis connecting the coils. Thus, a magnetic field is generated in a 
direction perpendicular to the sample to be treated in the reaction 
chamber. In addition, a uniform magnetic field is created in the region 
where the sample is grounded. Therefore, the efficiency of fine processing 
and plasma treatment can be increased. 
(5) The permanent magnets are arranged near the reaction chamber in the 
magnetic field generating section. Thus, the power consumption of the 
magnetic field generating coils can be reduced, and the leak of magnetic 
field from the permanent magnets to the surroundings of the apparatus can 
be prevented. 
(6) The opening is formed at the center part of each of the mutually facing 
magnetic field generating sections; therefore, devices such as a microwave 
introducing section or a sample holding device can easily be assembled in 
the apparatus, and the size of the apparatus can be reduced. 
Additional advantages and modifications will readily occur to those skilled 
in the art. Therefore, the invention in its broader aspects is not limited 
to the specific details, and representative devices, shown and described 
herein. Accordingly, various modifications may be made without departing 
from the spirit or scope of the general inventive concept as defined by 
the appended claims and their equivalents.