Thin film forming apparatus and ion source utilizing plasma sputtering

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to apparatuses for forming thin films on specimen substrates and apparatuses for extracting ions for forming thin films on specimen substrates, etching the surface of a thin film or improving the quality of the surface of a thin film, and more particularly a novel film forming apparatus capable of forming thin films of various materials at a high film growing rate with a high efficiency and stability for a long period of time by utilizing high-density plasma and a novel sputtering type ion source cable of extracting various ions of high current density with a high efficiency and stability for a long period of time. Furthermore, the present invention relates to a plasma generating apparatus which is capable of generating high-density plasma in a gas under a low pressure and which can be utilized with the film forming apparatus and the ion source.

2. Description of the Prior Art

In various types of LSI production processes, the techniques regarding to the formation of thin films and to ion sources presently occupy very important positions.

The sputtering apparatuses for forming thin films by sputtering targets in a plasma have been widely used for the formation of thin films of various materials and among them the so-called two-electrode (rf, dc) sputtering apparatus in which a target and a substrate are disposed in opposing relationship and are spaced apart from each other by a predetermined distance (for instance, as is disclosed by F. M. D'Heurle, Metallurgical Transactions, Vol. 1, (1970), pp.725-732) is most popular among those skilled in the art. Referring to FIG. 1, this apparatus comprises a vacuum chamber 4 in which are disposed a target 1 and a substrate 2 over the upper surface of which a thin film is grown, a gas introduction system 5 and an exhaust system 6 and a thin film is formed over the surface of the substrate by sputtering the target 1 by plasma 3 generated within the vacuum chamber 4.

In the cases of the conventional sputtering apparatuses, in order to increase the deposition rate of a thin film, plasma must inevitably be maintained in a high density state. In the case of the sputtering apparatus as shown in FIG. 1, the higher the density of plasma, the more rapidly the voltage applied to the target rises, so that the substrate is quickly heated and thin films formed are damaged by the impact due to the incidence of high-energy particles or (high-energy) electrons in the plasma. As a result, high-rate sputtering deposition can be carried out only with special heat-resisting substrates, materials and compositions of thin films.

Furthermore, in the conventional sputtering apparatuses, the discharge cannot be maintained in a stable manner in a low gas pressure range less than 10.sup.-3 Torr and plasma is generated only at a gas pressure of the order of 10.sup.-2 Torr or higher, so that there arises the problem that a large amount of impurities is penetrated into the thin film.

The particles which contribute to the growth of a thin film are almost neutral and it has been difficult to control the energy of such neutral particles.

Meanwhile, the magnetron sputtering apparatuses (for instance, as disclosed by R. K. Waits, J. Vac. Sci. Technol., Vol. 15 (1978), pp.179-187) and the facing targets sputtering apparatuses (for instance, as disclosed by M. Matsuoka et al., J. Appl. Phys., Vol. 60 (1986), pp.2096-2102) which permit a high-rate sputtering in a gas under a low pressure have been devised and demonstrated.

In the magnetron sputtering apparatuses, the high-energy secondary electrons are trapped over the surface of the target by the effects of the magnetic field closed over the surface of the target and the electric field over the surface cf the target so that high-density plasma can be generated in a gas at a low pressure. However, they have the problem that the qualities of the portions of a grown film corresponding to the eroded portions of the target to the not eroded portions, respectively, are widely different from each other. Furthermore, when the target is made of a magnetic material such as Fe, the magnetic flux does not leak to the surface of the target so that high-density plasma cannot be generated and the kinds of thin films to be formed are limited.

In the facing targets sputtering apparatuses, as shown in FIG. 2, the magnetic fields produced by permanent magnets 7 are applied between the targets 1 arranged in opposing relationship with each other so that the high-energy secondary electrons are confined between the targets to generate high-density plasma therebetween. They have the special feature that almost all kinds of thin films can be formed over the surface of the substrate 2 at a high deposition rate. The substrate 2 can be heated by a heater 8. In this apparatus, the impingement of the high-energy particles on the surface of the substrate is decreased so that this apparatus is regarded as one of the better apparatuses for forming a high quality thin film at low temperatures. However, the targets 1 are disposed in opposing relationship and are spaced apart from each other by a suitable distance, so that the substrate 2 must be located at a horizontal position and the deposition rate of the sputtered particles deposited over the surface of the substrate 2 is low. Furthermore, in the case of coating a large surface of a large-sized disc or the like, there arises the problem that the deposition rate or efficiency is essentially low when the targets are disposed in the manner described above.

Meanwhile, the ion sources which utilize an ion extracting mechanism such as a grid to extract the ions produced in plasma have been widely used for forming thin films of various materials, etching the surface of a formed thin film, processing the formed thin films and so on. Among them, the Kaufman type ion source provided with a filament for emitting thermal electrons so as to produce plasma (for instance, as disclosed by R. H. Kaufman et al., J. Vac. Sci. Technol., Vol. 21 (1982), pp.764-767) has been especially widely used. As shown in FIG. 3, in the Kaufman type ion source, disposed within the plasma generating chamber (vacuum chamber) 4 is a filament 9 for emitting thermal electrons. The filament 9 is used as a cathode so as to trigger the discharge in the magnetic field produced by an electromagnet 10 adapted to produce the magnetic field in order to stabilize plasma so that plasma 11 is produced. The ions in the plasma 11 are extracted by a plurality of ion extracting grids 12, as an ion beam 13.

The conventional ion sources which are typically represented by the Kaufman type ion source utilize the thermal electrons emitted from the filament to generate plasma so that the material of the filament itself is also sputtered and is included in the ions being extracted. Furthermore, when a reactive gas such as oxygen is used as a gas for generating plasma, it chemically reacts with the filament so that the ion extraction cannot be continued for a long period of time. In addition, the ion extraction is limited only to the use of gases such as Ar.

As the metal ion sources, the evaporation type ion sources and the sputtering type ion sources are well known to those skilled in the art. However, the evaporation type ion source must maintain the temperature within its furnace at high temperature, so that the vaporized particles are ionized and consequently impurities most frequently tend to be contained in a thin film being grown. Furthermore, the extraction of ions of a material having a high melting point is difficult (for instance, as disclosed by M. A. Hasan et al., J. Vac. Sci. Technol., Vol. B5 (1987), pp.1332-1339). In the cases of the sputtering type ion sources, metal ions obtained by sputtering a target in plasma are selectively extracted, but it is difficult to extract high-current ions over a large area (for instance, as reported by B. Gavin, IEEE Trans. Nucl. Sci., Vol. NS-23 (1976), pp.1008-1012).

In order to realize a high-current ion source by utilizing sputtering, the plasma density must be maintained at a high level with a high efficiency. To this end, the secondary electrons emitted from the target must be efficiently confined, but the conventional ion sources cannot satisfactorily confine the secondary electrons.

An ion extracting method with a high-efficiency and a large-area is disclosed by, for instance, N. Terada et al., Proc. Int'l Ion Engineering Congress, ISIAT'83 and IPAT'83, Kyoto (1983), pp.999-1004. According to this method, a negative potential is applied to a pair of opposing targets so that the high-energy secondary electrons are confined between the targets by the magnetic field produced therebetween. As a result, high-density plasma can be generated and the extraction of metal ions can be realized with a high efficiency. However, according to this method, the ion extracting holes are formed through the target so that the target itself has a function of a grid means for extracting ions. As a result, it is difficult to extract ions in a stable manner for a long period of time.

As described above, the conventional film forming methods cannot satisfy the following conditions simultaneously:

(a) A thin film is formed at a high deposition rate without causing damage to the thin film being grown and the substrate and an extreme temperature rise;

(b) The energy of each particle incident on the substrate is low;

(c) The ionization ratio of plasma must be maintained at a high value;

(d) The discharge can be carried out in a gas under a low pressure; and

(e) The efficiency of the deposition of atoms or ions sputtered from the target over the surface of the substrate must be high.

In like manner, the conventional sputtering type ion source techniques cannot satisfy the following conditions simultaneously:

(a) Ions with a significant current density can be extracted in a large area, hence the yield of the ion must be high;

(b) The thin film formed must have a high purity;

(c) The control of the ion energy must be carried out in a simple manner;

(d) The extraction of almost all the ions including those of the materials having a high melting point can be carried out;

(e) The ion production process must exclude a heating and vaporizing step; and

(f) The ion extraction can be continued for a long period of time in a stable manner.

SUMMARY OF THE INVENTION

In view of the above, one of the objects of the present invention is to provide a film forming apparatus which can substantially solve the above and other problems encountered in the conventional apparatus, can carry out the sputtering process by utilizing high-density plasma generated in a low pressure gas, and can attain formation of a high-quality thin film continuously at a high deposition rate and with a high efficiency by sputtered particles with a high ionization ratio and low energy while maintaining a substrate at a low temperature and preventing damage to the substrate and the thin film being grown.

Another object of the present invention is to provide a sputtering type ion source which can extract a large yield of high-purity ions from almost all kinds of materials such as metals, inert gases, reaction gases and so on over a wide energy range for a long period of time in a stable manner.

A further object of the present invention is to provide an apparatus which can generate high-density plasma in a low pressure gas and which is adapted to be applied to the film forming apparatus and the ion source.

In the first aspect of the present invention, a thin film forming apparatus comprises:

a plasma generating chamber into which a gas is introduced to generate plasma;

a first target and a second target made of materials to be sputtered and disposed at both end portions of interior of the plasma generating chamber, respectively, at least one of the first and second targets having the form of a tube;

at least one power supply for applying a negative potential to the first and second targets;

magnetic means for establishing a magnetic field within the plasma generating chamber and inducing the magnetic flux leaving one of the first and second targets and entering the other target; and

a specimen chamber communicated with the plasma generating chamber on the side of the tubular target and incorporating therein a substrate holder.

Here, one of the first and second targets may be in the form of a tube while the other is in the form of a flat plate.

Both of the first and second targets may be in the form of a tube.

Two specimen chambers may be communicated with both ends of the plasma generating chamber, respectively.

The first and second targets may be the opposite end portions, respectively, of one tubular target.

The tubular target may be a polygonal tubular target.

The thin film forming apparatus may further comprise an auxiliary magnetic field producing means for correcting the magnetic field established by the magnetic means.

In the second aspect of the present invention, an ion source comprises:

a plasma generating chamber into which is introduced a gas to generate plasma;

an ion extracting mechanism disposed in the vicinity of one end of the plasma generating chamber;

a first target and a second target made of a material to be sputtered, and disposed at both end portions of interior of the plasma generating chamber, respectively, at least one of the first and second targets having the form of a tube;

at least one power supply for applying a negative potential with respect to the plasma generating chamber to the first and second targets; and

means for establishing the magnetic field within the plasma generating chamber and inducing the magnetic flux leaving one of the first and second targets and entering the other target.

Here, one of the first and second targets may be in the form of a tube while the other is in the form of a flat plate.

Both of the first and second targets may be in the form of a tube.

Two specimen chambers may be communicated with both ends of the plasma generating chamber, respectively.

The first and second targets may be the opposite end portions, respectively, of one tubular target.

The tubular target may be a polygonal tubular target.

The ion source may further comprise an auxiliary magnetic field producing means for correcting the magnetic field established by the magnetic means.

The ion source may further comprise a plasma control electrode disposed within the plasma generating chamber.

The ion extracting mechanism may comprise two perforated grids.

The ion extracting mechanism may comprise a single perforated grid.

In the third aspect of the present invention, a thin film forming apparatus, comprises:

a plasma generating chamber into which is introduced a gas to generate a plasma;

an ion extracting mechanism disposed in the vicinity of one end of the plasma generating chamber;

a first target and a second target made of a material to be sputtered and disposed at both end portions of interior of the plasma producing chamber, respectively, at least one of the first and second targets having the form of a tube;

at least one power supply for applying a negative potential with respect to the plasma generating chamber to the first and second targets;

means for establishing the magnetic field within the plasma generating chamber and inducing the magnetic flux leaving one of the first and second targets and entering the other target; and

a specimen chamber communicated with the plasma generating chamber on the side of the tubular target and incorporating therein a substrate holder.

Here, the thin film forming apparatus may further comprise an auxiliary magnetic field producing means for correcting the magnetic field established by the magnetic means.

The thin film forming apparatus may further comprise a plasma control electrode disposed within said plasma generating chamber.

The ion extracting mechanism may comprise two perforated grids.

The ion extracting mechanism may comprise a single perforated grid.

In the fourth aspect of the present invention, a plasma generating apparatus, comprises:

a plasma generating chamber into which is introduced a gas to generate a plasma;

a first target and a second target made of a material to be sputtered and disposed in the vicinity of both end portions of interior of the plasma generating chamber, respectively, at least one of the first and second targets having the form of a tube;

at least one power supply for applying a negative potential to the first and second targets; and

means for establishing the magnet field within the plasma generating chamber and inducing the magnetic flux leaving one of the first and second targets and entering the other target.

The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings .

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view illustrating a conventional two-electrode type sputtering apparatus;

FIG. 2 is a schematic sectional view illustrating a conventional facing-targets type sputtering apparatus;

FIG. 3 is a schematic view illustrating a conventional Kaufman type ion source;

FIG. 4 is a sectional view illustrating a first embodiment of a film forming apparatus in accordance with the present invention;

FIG. 5 illustrates the distribution of the strength of the magnetic field in the direction of magnetic fluxes in the embodiment shown in FIG. 4;

FIG. 6 is a view used to explain the mechanism of generating high-density plasma in a film forming apparatus in accordance with the present invention;

FIG. 7 illustrates one example of discharge characteristics when a target is made of aluminum in a film forming apparatus in accordance with the present invention;

FIG. 8 is a sectional view illustrating a second embodiment of a film forming apparatus in accordance with the present invention;

FIG. 9 illustrates the distribution of the strength of the magnetic field in the direction of magnetic flux in the embodiment shown in FIG. 8;

FIG. 10 is a view used to explain the mechanism of generating high-density plasma in the embodiment shown in FIG. 8;

FIG. 11 illustrates one example of the dependence of the thin film deposition rate on power applied to a target;

FIGS. 12-15 are sectional views illustrating a third, a fourth, a fifth and a sixth embodiment, respectively, of a film forming apparatus in accordance with the present invention;

FIG. 16 illustrates the distribution of the strength of the magnetic field in the direction of magnetic flux in the embodiment shown in FIG. 15;

FIG. 17 is a sectional view illustrating a seventh embodiment of a film forming apparatus in accordance with the present invention;

FIG. 18 is a sectional view of a first embodiment of an ion source in accordance with the present invention;

FIG. 19 is a sectional view of a film forming apparatus to which is applied the ion source shown in FIG. 18;

FIG. 20 illustrates one example of the ion extraction characteristics;

FIG. 21 is a sectional view of a film forming apparatus to which is applied a second embodiment of an ion source in accordance with the present invention;

FIG. 22 illustrates one example of ion extraction characteristics;

FIGS. 23 is a sectional view illustrating a film forming apparatuses to which is applied a third embodiment of an ion source in accordance with the present invention;

FIG. 24 is a sectional view illustrating a fourth embodiment of an ion source in accordance with the present invention;

FIG. 25 is a sectional view illustrating a film forming apparatus to which is applied a fifth embodiment of an ion source in accordance with the present invention;

FIG. 26 is a sectional view of a sixth embodiment of a sputtering type ion source in accordance with the present invention;

FIG. 27 illustrates the motion of .gamma. (gamma) electrons and the spatial potential distribution in the ion source shown in FIG. 26;

FIG. 28 is a diagram illustrating the dependence of the extracted ion current on the sputtering power;

FIG. 29 is a diagram illustrating the dependence of the extracted ion energy on the anode potential;

FIG. 30 is a sectional view of a film forming apparatus to which is applied the sputtering type ion source shown in FIG. 26;

FIG. 31 illustrates an example of ion extraction characteristics;

FIG. 32 is a sectional view of a film forming apparatus to which is applied a seventh embodiment of a sputtering type ion source in accordance with the present invention; and

FIG. 33 is a diagram illustrating the relationship between the energy of the extracted ions and the ion current.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, the present invention will be described in detail hereinafter.

FIG. 4 is a sectional view illustrating a first embodiment of a thin film forming apparatus in accordance with the present invention. The thin film forming apparatus is a combination of a plasma generating apparatus and a specimen chamber. A gas for generating plasma is introduced through a gas inlet 15 into the plasma generating chamber 14. A target 16 in the form of a flat plate is disposed at a position in the vicinity of the inner surface of the top of the plasma generating chamber 14 while a target 17 in the form of a cylinder is disposed therein at the lower portion thereof. Alternatively, the cross-section of the target 17 may have a polygonal ring shape. Further, the target 17 may be continuous or discontinous in its circumferential direction. The target 16 is removably mounted on a metal supporting body 16A which is cooled by water and is securely attached to the plasma generating chamber 14 by screwing an internally-threaded cover 16B at the top of the upwardly extended portion of the plasma generating chamber 14; that is, the upper wall 14b thereof. The supporting body 16A is insulated from the wall 14B through an insulating body 16C. In like manner, the cylindrical target 17 is removably mounted on a metal supporting body 17A which is cooled by water and is securely attached to the wall 14C of the plasma generating chamber 14 through an insulating body 17C by screwing on an internally-threaded cover 17B. A projection 16D extended upwardly from the supporting body 16A as well as a projection 17D horizontally extended from the supporting body 17A function as electrodes to which are applied negative voltages from DC power sources 18 and 19, respectively. The negative voltages may be applied from one of the DC power sources 18 and 19 to the targets 16 and 17. At least one electromagnet 20 surrounds the outer surface of the plasma generating chamber 14 so that the magnetic field may be produced therein. Alternatively, the electromagnet 20 may be disposed within the plasma generating chamber 14. The positions of the targets 16 and 17 and the electromagnet 20 are so determined that the magnetic flux 21 produced by the electromagnet 20 traverses the surfaces of the targets 16 and 17 and that the magnetic flux is extended from the surface of one target to the surface of the other target. It is preferable that the plasma generating chamber is so designed and constructed that it may be cooled by water and furthermore that shields 14D and 14E are preferably disposed within the plasma. generating chamber 14 in order to protect the side surfaces of the targets 16 and 17 from plasma

The interior of the plasma generating chamber is evacuated to a high vacuum and then a gas is introduced therein through the-gas inlet 15. Thereafter, when the negative voltages applied to the targets 16 and 17 are increased, a discharge is effected and plasma is generated in the magnetic field established by the electromagnet 20. Sputtered particles 22 consisting of ions and neutral particles can be extracted from the plasma. The magnetic flux extended between the targets 16 and 17 can prevent the secondary electrons (.gamma. (gamma) electrons) emitted from the surfaces of the targets 16 and 17 from dispersing in the direction perpendicular to the magnetic field and furthermore have the function of confining the plasma. As a result, a high-density plasma is now generated under a low gas pressure. The specimen chamber 23 is communicated with the plasma generating chamber 14. A gas can be introduced into the specimen chamber 23 through a gas inlet 24 and the specimen chamber 23 can be evacuated to a high vacuum by means of an exhaust system 25. A substrate holder 27 for supporting a substrate 26 is disposed within the specimen chamber 23 and a shutter 28 which can be opened or closed is disposed above the substrate holder 27. It is preferable that a heater is incorporated into the substrate holder 27 so as to heat the substrate thereon and furthermore, it is preferable that the specimen chamber 23 is so designed and constructed that AC or DC voltage may be applied to the substrate 26 so that a bias voltage may be applied to the substrate 26 over the surface of which is being grown a thin film and furthermore, it becomes possible to clean the substrate 26 by sputtering.

The factors which influence the generation of plasma are gas pressure in the plasma generation chamber 14, voltages applied to the targets 16 and 17, respectively, the magnetic field distribution, the distance between the targets 16 and 17 and so on.

FIG. 5 illustrates one example of the distribution of the strength of the magnetic field in the direction of magnetic flux in the film forming apparatus shown in FIG. 4. The magnetic field is a divergent magnetic field.

Next, referring to FIG. 6, the underlying principle of the generation of high density plasma in a thin film forming apparatus in accordance with the present invention will be described in detail.

A gas is introduced into the plasma generating chamber and the negative voltages are applied to the targets 16 and 17, respectively, so that the gas is discharged and ionized. When the high-energy ions impinge on the surfaces of the targets 16 and 17 to which are applied a negative voltage Va and a negative voltage Va', respectively, high-energy secondary electrons (.gamma. electrons) are emitted from the surfaces of the targets 16 and 17. The .gamma. electrons emitted from the surfaces of the targets 16 and 17 are reflected by the electric field established on the targets 16 and 17 and make a reciprocal motion while making a cyclotron motion about the magnetic flux 21 extended between the targets 16 and 17. That is, the electric field established on the targets 16 and 17 acts as a mirror for the .gamma. electrons 29. The .gamma. electrons 29 are confined between the targets 16 and 17 until the energy of the .gamma. electrons becomes lower than the electron confining energy of the magnetic flux, and during the confinement of the .gamma. electrons, the ionization is accelerated mainly due to the collision of the electrons with the neutral particles. Furthermore, the high-energy electron beam reciprocating between the targets 16 and 17 interacts with the plasma, so that the ionization of the neutral particles is further accelerated. Hence, a high-density plasma can be generated in a low pressure gas.

The neutral particles reach the surface of the substrate without being adversely influenced by the electric and magnetic field. The electrons which have lost their energies reach the surface of the substrate along the diverging magnetic field so that the surface of the substrate has a negative potential. As a result, ions as well as neutral particles are deposited over the surface of the substrate.

In the apparatus according to the present invention, the discharge can be effected in a stable manner at a low gas pressure of the order of 10.sup.-5 Torr and furthermore can realize the formation of a thin film having better crystal structures over the low temperature substrate at a high-rate in a relatively high pressure gas in which neutral radicals play an important role in the growth of the thin film.

Next, the results of the formation of an A1 film by the apparatus in accordance with the present invention will be described. After the specimen chamber was evacuated to a vacuum of 5.times.10.sup.-7 Torr, in a first example, Ar gas was introduced at a flow rate of 2.5 cc per minute, and within the plasma generating chamber 14, a discharge was effected at a gas pressure of 5.times.10.sup.-4 Torr. And in a second example, Ar gas was introduced at a flow rate of 5 cc per minute and a discharge was effected at a gas pressure of 1.times.10.sup.-3 Torr. FIG. 7 illustrates the discharge characteristics obtained from the above-described experiments in which the voltage applied to the planar target 16 was maintained at -300 V. Each experiment showed constant voltage discharge characteristics wherein the discharge current increases in an avalanche manner from a certain voltage. With the film forming apparatus in accordance with the present invention, even when the negative voltages applied to the planar target 16 and the cylindrical target 17 are the same, sufficiently high-density plasma can be generated. The power supplied to the cylindrical A1 target 17 was between 300 and 600 W and the thin film growth was carried out without heating the substrate holder, that is, the temperature of the substrate is room temperature. The result is that the A1 films could be deposited at a stable manner at a deposition rate within a range between 10 and 100 nm/min for a long period of time.

FIG. 8 illustrates a second embodiment of a film forming apparatus in accordance with the present invention which is different from the embodiment described above with reference to FIG. 4 in that the sputtering targets are two cylindrical targets 17 and 30. The target 30 is removably secured to a metal supporting body 30A which can be cooled by water and which is securely attached to the wall 14C by an internally-threaded cover 30B in such a way that the target supporting body 30A, is insulated from the wall 14C through an insulating body 30C. A projection 30D extended horizontally from the supporting body 30 is used as an electrode to which is applied a negative voltage supplied from a power source 31. The magnetic flux 21 produced by the electromagnet 20 leaves the surface of one target and enters the surface of the other target.

FIG. 9 illustrates an example of the distribution of the strength of magnetic field in the direction of magnetic flux in the embodiment shown in FIG. 8.

As shown in FIG. 10, like the above-described embodiment, according to this embodiment, when the high-energy ions impinge upon the surfaces of targets to which are applied negative voltages Va and Va', respectively, the high-energy secondary electrons (.gamma. electrons) 29 are emitted from the surfaces of the targets and are reflected by the electric field established on the targets so that the .gamma. electrons make a reciprocal motion between the targets while making a cyclotron motion around the magnetic flux 21. The second embodiment can generate high-density plasma even at a low gas pressure in a manner substantially similar to that described above.

Next, the results of the formation of A1 films by this embodiment will be described hereinafter. After the specimen chamber 23 was evacuated to a vacuum of 5.times.10.sup.-7 Torr, Ar gas was introduced into the specimen chamber 23 at a flow rate of 5 cc/min and a discharge was effected in the plasma generating chamber in which the gas pressure was maintained at 5.times.10.sup.-5 Torr, and Ar gas was introduced at a flow rate of 1 cc/min and a discharge was effected at a gas pressure of 0.8.times.10.sup.-3 Torr. The discharge characteristics obtained are substantially similar to those shown in FIG. 7.

While the power between 200 and 600 W was applied to the cylindrical A1 targets 17 and 30, the A1 films were grown over the surfaces of the substrates at room temperature at a deposition rate between 600-1800 .ANG./min in a stable and efficient manner for a long period of time even when the substrate holder was not heated. As shown in FIG. 11, the