referring to fig1 , a microwave assisted plasma - cvd apparatus in accordance with the present invention is illustrated . in the figure , the apparatus comprises a reaction vacuum chamber 1 defining a resonating space therein , a loading chamber 8 connected with the vacuum chamber 1 , a substrate holder 3 capable of carrying a substrate 2 to be treated , helmholtz coils 5 around the reaction chamber 1 , an auxiliary electro - magneto 6 located inside of the helmholtz coils around the reaction chamber , a microwave generator 4 connected to the reaction chamber 1 through a waveguide 7 , an evacuating system 9 , and gas feeding systems 10 and 11 . the holder 3 is made of a highly thermal conductive material , such as aluminum nitride , which less disturb the microwave transmission from a microwave introduction window 12 . the auxiliary magnet 6 consists of two electromagnetos providing ioffe bars which extend in the direction of the microwave propagation ( fig2 ( a ) and 2 ( b )). in fig2 ( a ), the end marks of arrow denote the current passing direction of each bar . the object of the provision of the ioffe bars is to strengthen the strength of magnetic field near the cylindrical wall of the reaction chamber 1 . fig3 is a graphical diagram showing the surfaces on each of which the strength of the magnetic field is constant . the abscissa is the distance ( r ) from the axis of the cylindrical reaction chamber and the ordinate is the axial distance from the center plane of the helmholtz coils 5 . the figure given to each surface denotes the strength ( gauss ) of the magnetic field on that surface . as shown in the diagram , the strength of the magnetic field takes a larger value at a nearer position to the cylindrical wall , so that the drifted force exerted on the plasma is always centrifugal . the magnetic field is weakest on the axis of the cylindrical reaction chamber . fig4 is a graphical diagram showing the surfaces on which the magnetic field is constant when the auxiliary magnet is not used . next , the deposition process with this apparatus will be described . a substrate i is mounted on the holder 3 and disposed at an appropriate position in the reaction chamber 1 where the microwave and the magnetic field satisfy the ecr condition . after evacuating the reaction chamber 1 , the substrate 1 is heated to 500 degree c . and hydrogen gas is leaked into the chamber 1 at 10 sccm through the gas feeding system 11 . the introduced hydrogen gas is energized into a plasma gas by virtue of a 2 . 45 microwave emitted from the generator 4 and a magnetic field induced by both the helmholtz coils 5 and the auxiliary magnet 6 . the strength of the portion of the magnetic field that is induced by the coils 5 is about 2 k gauss at the resonating space ( a portion of the reaction chamber ). the pressure in the resonating space is maintained at 0 . 1 pascal . the surface of the substrate is cleaned by virtue of the plasma . then , the introduction of hydrogen is halted and a carbon compound gas such as c 2 h 2 or ch 4 is introduced into the reaction chamber 1 and excited in the same way as hydrogen as explained above . by this process , a diamond or i - carbon film is deposited on the substrate which has been heated to about 500 ° c . according to experimental , diamond films were deposited particularly when the substrate temperatures were not higher than 650 ° c . in accordance with the electron beam diffraction analysis , a halo pattern was observed at a relative low temperature together with a spot pattern which is peculiar to amorphous structures . such an image indicates the presence of i - carbon . the halo pattern gradually became distinct as the substrate temperature was elevated . when the substrate temperature was elevated higher than 650 ° c ., the deposited film became composed mainly of diamond . the diamond film was confirmed by obtaining its raman spectrum . the spectrum includes a moderate peak near 1500 cm − 1 and a sharp peak near 1333 cm − 1 . for reference , the same process was repeated without inducing a magnetic field in the reaction chamber . the film thus deposited was made of graphite . even with the presence of magnetic field , no i - carbon film could not be deposited on a substrate at a temperature lower than 150 ° c . the above process can be applied to a method of depositing polycrystalline silicon carbide films by making use of silicon carbide gaseous compounds as the reactive gas , to a method of depositing aluminum nitride films by making use of a reactive gas consisting of an aluminum compound gas and ammonia , and a method of depositing films having a high melting point , e . g . films made of tungsten , titanium and molybdenum or their silicon compounds . in the same way , the present invention can be applied for the deposition of bn , cn , tin and bp . fig5 a schematic view showing another type of plasma processing apparatus . this apparatus is largely same as the above explained apparatus besides the relationship between the helmholtz coils 5 and the connection position of the waveguide 7 to the reaction chamber 1 . in the arrangement , it is very important that a microwave is mixed with a reactive gas only in the left side of the center surface c between the helmholtz coils 5 , so that the reactive gas is subjected to the magnetic field that is monotonically decreases toward the left in the resonating space . the magnetic field functions to drift the plasma gas to the substrate 2 and prevent the gas from producing deposition on the right side wall . the ioffe magnet may be another type magnet . fig6 ( a ) and 6 ( b ) are drafted in correspondence with fig2 ( a ) and 2 ( b ) to show another type of ioffe magnet suitable for use in accordance with the invention . as shown in the figure , a plurality of rod - shaped permanent magnets is arranged immediately inside of the helmholtz coils 5 with their magnetic moments directed to the circumferential direction as indicated by arrows . the magnetic moments can be arranged in the axial direction as shown in fig7 . while a description has been made for several embodiments , the present invention should be limited only by the appended claims and should not be limited by the particular examples . what follow are some examples of modifications and variation according to the invention . by adding oxygen , water or the like to the reactive gas , the crystallinity of the deposited film can be enhanced . by irradiating the exciting plasma gas with ultraviolet rays between the resonating space and the substrate to be coated , the exciting plasma gas can hold its energy even substantially distant from the resonating space . for instance , a diamond or i - carbon film can be deposited on a large area . also , by applying a dc bias voltage to the exciting plasma , a larger amount plasma reaches the substrate enabling a high deposition speed . also , as easily understood by those skilled in the art , the present invention is effective when used for plasma etching , particularly by making use of ecr . the etchant gas is confined by virtue of the magnetic field in the same way as explained above .