Process for forming deposited film and process for preparing semiconductor device

Abstract: A deposited film formation method comprises the steps of: (a) feeding a gas of an organometallic compound containing molybdenum atom and hydrogen gas onto a substrate having an electron donative surface; and (b) maintaining the temperature of the electron donative surface within the range of the decomposition temperature of the organometallic compound or lower and 800 °C or lower to form a molybdenum film on the electron donative surface.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a method for forming deposited film and a method for forming a semiconductor device. Particularly, it pertains to a method for forming an Mo deposited film preferably applied to wiring of a semiconductor circuit device, etc. and a semiconductor device using deposited Mo film. Related Background Art In the prior art, in semiconductor electronic devices or integrated circuits, aluminium (Al) or Al-Si etc. have been used primarily for electrodes and wiring. Here, Al is inexpensive and has high electroconductivity, and dense oxidized film can be formed on the surface. Accordingly, it has many advantages since its inner portion can be protected and stabilised, and adhesion to Si is good. However, on the other hand, with higher integration, the self-alignment technique, in which mask matching between the gate electrode and the diffusion layer, etc. is unnecessary, is indispensable. No metal having a low melting point such as Al can be used. In the MOS LSI of the prior art, as gate electrode wiring capable of self-alignment, a polycrystalline Si doped with an impurity at high concentration has been widely employed. However, with the progress of further higher integration, there ensues the problem that electrical resistance of fine polycrystalline Si wiring, etc. becomes higher. This is vital to high speed actuation of the device. Accordingly, it has been required to have a high melting metal which is lower in volume resistivity than polycrystalline Si and yet is capable of self-alignment basically, even when Al can be employed, Si and the wiring Al react with each other during heat treatment at the contact electrode portion with the Si layer, whereby wire breaking or increased resistance of wiring are caused to occur. For this reason, a metal having higher melting point and lower electrical resistance has been employed as the electrode wiring material, and as the barrier metal which prevents the reaction between Si and Al at the contact portion. Particularly, Mo is attracting attention for its sufficiently high melting point (2620 °C) and low electrical resistance (4.9 µΩ · cm). Deposition methods such as electron beam deposition and sputtering have been employed for Mo film used in Mo electrodes wiring, etc. With finer dimensional formation by increased integration degree, the surface of LSI, etc. is subject to excessive unevenness due to oxidation, diffusion, thin film deposition, and etching, etc. For example, electrodes or wiring metal must be deposited on the surface with a stepped difference, or deposited in a via-hole which is small in diameter and deep. In 4 Mbit or 16 Mbit DRAM (dynamic RAM), etc., the aspect ratio (via hole depth/via hole diameter) of via-hole in which a wiring metal is to be deposited is 1.0 or more, and the via-hole diameter itself also becomes 1 µm or less. Therefore, for a via-hole with large aspect ratio, a technique which can deposit wiring metal is required. Particularly, for performing sure connection to the device under insulating film such as SiO₂, etc., rather than film formation, a metal is required to be deposited so as to embed only the via-hole of the device. In such case, a method of depositing a wiring metal only on Si or metal surface and not on an insulating film such as SiO₂, etc. is required. It is difficult to achieve such a selective deposition and growth by electronic beam deposition and sputter processes used in the past. The sputter process is a physical deposition method performed by scattering the particles sputtered in vacuum. Therefore, the film thickness becomes very thin at the step portion and insulating film side wall, and breaking of wire may be caused in an extreme case. Further, unevenness of film thickness and the breaking of wire cause remarkable degradation of the reliability of LSI. On the other hand, there has been developed a bias sputtering method in which a bias is applied on a substrate and deposition is performed so as to embed Al, Al alloy or Mo silicide only in the via-hole by utilizing sputter etching action and deposition action on the substrate surface. However, since a bias voltage of some 100 V or higher is applied on the substrate, deleterious influence occurs because of charged particle damage such as change in threshold of MOS-FET, etc. Also, because of presence of both etching action and deposition action, there is a problem that the deposition speed cannot be In order to solve the problems as described above, various types of CVD (Chemical Vapor Deposition) methods have been proposed. In these methods, chemical reaction of a starting gas in some form is utilized. In plasma CVD or optical CVD, decomposition of the starting gas occurs in gas phase, and the active species formed there further react on the substrate to give rise to film formation. In these CVD methods, surface coverage on unevenness on the substrate surface is good since the reaction occurs in a gaseous phase. However, carbon atoms contained in the starting gas molecule are incorporated into the film. Also, particularly in plasma CVD, the problem has remained that there is damage by charged particles (so called plasma damage) as in the case of the sputtering method. The thermal CVD method, in which the film grows through the surface reaction primarily on the substrate surface, is good in surface coverage on unevenness such as stepped portion of the surface, etc. Also, it can be expected that deposition within via-holes will readily occur. Further, wire breaking at the stepped portion can be avoided. For this reason, various studies have been made of the thermal CVD method as the method for forming Mo film. For example, there are hydrogen reduction method of MoCl₅ and Si reduction method of MoF₆ according to normal pressure CVD or reduced pressure CVD as introduced in Chapter 4 of Handotai Kenkyu (Semiconductor Research) Vol. 20 (Kogyo Chosakai, 1983). However, in the hydrogen reduction method of MoCl₅, a plurality of molybdenum halide such as MoCl₃ and others other than Mo may be sometimes formed at the portion other than the substrate surface heated within the film forming device. Therefore, it is difficult to control film formation. Also, although film formation may be possible, no selective deposition can be seen. On the other hand, for example, in EP-A-147913 or USP 3,785,862, there is shown a method of forming Mo film using MoF₆ gas, hydrogen gas and an inert gas. Whereas, in the Si reduction method of MoF₆, MoF₆ reacts in the presence of Si to precipitate Mo, whereby Si is etched. Therefore, there is a possibility that the electronic circuit on Si wafer may be damaged. Also, SiO₂ is etched. However, for this reason, in the Si reduction method of MoF₆, deposition occurs primarily on Si substrate, rather than on SiO₂ but it is clearly stated in USP 3,785,862 that Mo film is also deposited on Si0₂. This suggests that selective deposition of Mo is not so complete. In addition, as described above, both Si and Si0₂ are subjected to etching, and under such state there is a possibility that problems may be involved practically concerning surface flatness and mixing of impurity, etc. As another method, there is an example of normal pressure CVD method of Mo(CO)₆ as described in Thin Solid Films, Vol. 63 (1979), p. 169. In this method, Mo film can be deposited on the substrate at normal pressure with Ar as the carrier gas. However, in this method, there may be sometimes incorporated a considerably large amount of oxygen and carbon in MO film as impurities, and for this reason, there is a possibility that electrical resistance of the deposited film may be increased. Also, according to this method, selective deposition can be done only with difficulty. Other known deposition methods are mentioned below. WO 86/06755 describes a selective deposition method for depositing tungsten or molybdenum on a patterned substrate. Deposition is conducted in a cold wall reaction chamber at a substrate temperature above 100°C. and the substrate is isolated from impinging radiation. In the examples described tungsten hexafluoride is reduced in an hydrogen atmosphere. It is suggested that Mo(CO)₆, MoF₆ or MoCl₅ may be used for deposition of molybdenum but no specific details are given. The method is said to be applicable to a wide variety of conductor and semiconductor surfaces, e.g. metals, alloyed metals such as platinum, molybdenum, titanium, tungsten, tantalum, aluminium metals and mixtures thereof, also transition metal silicides. Thin Solid Films, vol. 147, No. 2, March 1987, pp 193-202 "Plasma-enhanced chemical vapour deposition of molybdenum", N.J. Jarro et al, describes deposition of molybdenum films from Ar-Mo(CO)₆ gas mixtures and H₂-Mo(CO₆) gas mixtures. In the case of the former mixture the deposited films contained large quantities of carbon and oxygen before and after annealing. In the latter case the films also contained carbon, but oxygen in the form of hydroxide was removed by annealing. As described above, the deposition methods of Mo film of the prior art have many and various problems requiring solution such as coverage of the stepped difference of the LSI surface is poor, the Si surface of LSI is unnecessarily etched, damage is given to Si0₂, deposition reaction can be controlled only with difficulty, and a large amount of impurities are mixed into Mo film. SUMMARY OF THE INVENTION A deposited film formation method in accordance with the present invention is set out in claim 1 of the claims appended. A preferred method for forming the deposited film of the present invention will be described below. The Mo film obtained by this deposited film formation method contains little impurity such as carbon, etc. Also, the substrate is free from damage and the method is good in controllability. A low resistance, dense Mo film can be selectively deposited on the substrate. A method for preparing a semiconductor device in accordance with the present invention is set out in claim 10 of the claims appended. By this preparation method, an excellent semiconductor device having a low resistance, dense and flat Mo film at the wiring portion and the electrode portion can be provided. In the present invention, as the starting gases for deposited film formation, an organic Mo compound and H₂ gases are employed. By subliming Mo(CH₃)₆ as the organic Mo compound, which is solid at room temperature and carrying it in a carrier gas such as H₂, Ar, etc. to a heated substrate, Mo film is deposited upon reaction with hydrogen gas which also is supplied. The detailed mechanism of the reaction has not been clarified, but it may be considered that Mo(CH₃)₆, etc. reacts with H₂ gas on an electron donative substrate surface such as heated metal or semiconductor to form Mo. Since this reaction can proceed only with difficulty at the place where the substrate surface is not electron donative, it may be considered that deposition of the film occurs only with difficulty on an electron non-donative surface. Here, the electron donative characteristic is described below. An electron donative material refers to one having free electrons existing or free electrons intentionally formed in the substrate, for example, a material having a surface on which the chemical reaction is promoted through give-and-take of electrons with the starting gas molecules attached on the substrate surface. For example, generally metals and semiconductors correspond to such material. Those having very thin oxidized film on the metal or semiconductor surface are also included. For, with such very thin oxidised film, the chemical reaction can occur between the substrate and the attached starting molecules. Specifically, there may be included semiconductors such as single crystalline silicon, polycrystalline silicon, amorphous silicon, etc., binary system or ternary system or quaternary system III-V compound semiconductors comprising combinations of Ga, In, Al as the group III element and P, As, N as the group V element, or II-VI compound semiconducters, or metals themselves such as tungsten, molybdenum, tantalum,aluminium , titanium, copper, etc., or silicides of the above metals such as tungsten silicide, molybdenum silicide, tantalum silicide, aluminum silicide, titanium silicide, etc., further metals containing either one of the constituent of the above metals such as aluminium silicon, aluminium titanium, aluminium copper, aluminium tantalum, aluminium silicon copper, aluminium silicon titanium, aluminium palladium, titanium nitride, etc. In contrast, the materials for forming the surface on which Mo is not deposited selectively, namely the electron non-donative materials, are conventional insulating materials, oxidized silicon formed by thermal oxidation, CVD, etc., glass or oxidized film such as BSG, PSG, BPSG, etc., thermally nitrided film, silicon nitrided film by plasma CVD, low pressure CVD, ECR-CVD method, etc. BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings: Fig. 1 shows a schematic view illustrating an example of a deposition film forming apparatus applicable to the present invention; Fig. 2 shows a schematic sectional view illustrating a process for forming a deposition film according to the present invention; Fig. 3 shows a schematic view illustrating another example of a deposition film forming apparatus applicable to the present invention; and Fig. 4 shows a schematic view illustrating a method for producing a semiconductor device according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention are explained below with reference to the drawings. The following description is given by way of example only. Fig. 1 is a schematic view showing a deposition film forming apparatus for applying the present invention. Here, 1 is a substrate for forming Mo film. The substrate 1 is mounted on a substrate holder 3 provided internally of the reaction tube 2 for forming a space for formation of a deposited film which is substantially closed as shown in Fig. 1. As the material constituting the reaction tube 2, quartz is preferable, but it may be also made of a metal. Further, it is preferable to cool the reaction tube. The substrate holder 3 is made of a metal, and is provided with a heater 4 so that the substrate mounted thereon can be heated. And, the constitution is made so that the substrate temperature can be controlled by controlling the heat generation temperature of the heater 4. The feeding system of gases is constituted as described below. 5 is a gas mixer, in which the starting gas (Mo(CH₃)₆) and the reaction gas (H₂) are mixed, and the mixture is fed into the reaction tube 2. 6 is a starting gas gasifier provided for gasification of an organic metal as the starting gas. The organic metal to be used in the present invention is solid at room temperature, and is formed into saturated vapour by sublimating the organic metal by passing a carrier gas through around the metal within the gasifier 6, which is in turn introduced into the mixer 5. At this time, the sublimation is markedly accelerated by heating the gas or organic metal itself. The evacuation system is constituted as described below. 7 is a gate valve, which is opened when performing evacuation of a large volume such as during evacuation internally of the reaction tube 2 before formation of the deposited film. 8 is a slow leak valve, which is used when performing evacuation of a small volume such as in controlling the pressure internally of the reaction tube 2 during formation of the deposited film. 9 is an evacuation unit, which is constituted of a pump for evacuation such as turbo molecular pump, etc. The conveying system of the substrate 1 is constituted as described below. 10 is a substrate conveying chamber which can house the substrate before and after formation of the deposited film, which is evacuated by opening the valve 11. 12 is an evacuation unit for evacuating the conveying chamber, which is constituted of a pump for evacuation such as turbo molecular pump, etc. The valve 13 is opened only when the substrate 1 is transferred between the reaction chamber and the conveying space. As shown in Fig. 1, in the gas formation chamber 6 for forming the starting gas, for example, the gas formation chamber 6 is maintained at room temperature or the heated solid organic Mo compound (Mo(CH₃)₆) is bubbled with H₂ or Ar (or other inert gas) as the carrier gas to form gaseous organic Mo compound, which is transported to the mixer 5. The H₂ gas as the reaction gas is transported through another route into the mixer 5. The gases are controlled in flow rates so that the respective partial pressures may become desired values. Figs. 2A to 2E are schematic views showing the state of growing an Mo film. Fig. 2A is an illustration showing schematically the cross-section of the substrate before formation of the Mo deposited film according to the present invention. 90 is the substrate comprising an electron donative material, and 91 a thin film comprising an electron non-donative material. When the starting gas (Mo(CH₃)₆) and a gas mixture containing H₂ as the reaction gas are fed onto the heated substrate within a range from the decomposition temperature to 800°C, Mo is precipitated on the substrate 90 other than the thin film 91 comprising the electron non-donative material, whereby a continuous film of Mo is formed as shown in Fig. 2B. When deposition of Mo is continued via the state of Fig. 2C, the Mo film grows to the level of the uppermost portion of the thin film 91 as shown in Fig. 2D. As the result of analysis according to Auger's electron spectroscopy or photoelectric spectroscopy, no entrainment of an impurity such as carbon or oxygen is recognised in the films produced as example, discussed below. The deposited film thus formed has a resistivity of, for example, with a film thickness of 60 nm (600Å), 8-30 µohm·cm at room temperature which is close to the bulk resistivity of Mo and lower than the resistivity of polycrystalline Si, and becomes continuous and flat film. The reflectance in the visible wavelength region is approximately 70-80%, and a thin film with excellent surface flatness can be deposited. The substrate temperature in forming deposited film should be desirably in the range between the decomposition temperature of the starting gas (Mo(CH₃)₆) or higher, and 800°C or lower, but specifically a substrate temperature of 350-550°C is desirable. A more preferable substrate temperature condition is 400°C to 500°C. The Mo film deposited under this condition contains no carbon and oxygen and is sufficiently low in electrical resistance. In the apparatus shown in Fig. 1, Mo can be deposited on only one sheet of substrate in deposition for one time. Although a deposition speed of ca. 10 nm/min (100 Å/min) can be obtained, it is still insufficient for performing deposition of a large number of sheets within a short time. As the deposition film forming apparatus for improving this point, there is the low pressure CVD apparatus which can deposit Mo by simultaneous mounting of a large number of sheets of wafer. Since the Mo deposition according to the present invention utilises the surface reaction of the heated electron donative substrate surface, for example, in the hot wall type low pressure CVD method wherein only the substrate is heated, Mo can be desirably deposited. Fig. 3 is a schematic view showing a deposited film formation apparatus to which such present invention is applicable. 57 is a substrate for forming an Mo film. 50 is an outside reaction tube made of quartz for forming a space for formation of deposited film which is substantially closed with respect to surrounding. 51 is an inside reaction tube made of quartz located for separation of the gas flow within the outside reaction tube 50, 54 a flange made of a metal for opening and closing the opening of the outside reaction tube 50, and the substrate 57 is located within the substrate holding member 56 provided internally of the inside reaction tube 51. The substrate holding member 56 should be desirably made of quartz. Also, the present apparatus can control the substrate temperature by the heater portion 59. It is constituted so that the pressure internally of the reaction tube 50 is controllable by the evacuation system bound through the gas evacuation outlet 53. The present apparatus has a first gas system, a second gas system and a mixer (all are not shown) similarly as in the apparatus shown in Fig. 1, and the starting gases are introduced into the reaction tube 50 through the starting gas introducing inlet 52. The starting gases react on the surface of the substrate 57 when passing through the inner portion of the inside reaction tube 51 as shown by the arrowhead 58 in Fig. 3 to deposit Mo on the substrate surface 57. The gases after the reaction pass through the gap portion formed by the inside reaction tube 51 and the outside reaction tube 50 and are discharged through the gas discharging outlet 53. In taking in and out the substrate, the flange 54 made of a metal is ascended and descended by an elevator (not shown) together with the substrate holding member 56 and the substrate 57 to move to a predetermined position, thereby performing attachment and detachment of the substrate. By forming a deposited film under the conditions as mentioned above by use of such apparatus, Mo film of good quality can be formed at the same time in all the wafers within the apparatus. The present invention is explained below by giving Examples. Example 1 First, the procedure for Mo film formation is as follows. By use of the apparatus shown in Fig. 1, the reaction tube 2 is internally evacuated to ca.1x10⁻⁶Pa (1x10⁻⁸ Torr) by the evacuation unit 9. However, Mo film can be also formed if the vacuum degree within the reaction tube 2 may be worse than 1x10⁻⁶Pa (1x10⁻⁸ Torr). After cleaning of substrate such as Si wafer, etc., the conveying chamber 10 was released to atmospheric pressure and Si wafer was mounted in the conveying chamber. The conveying chamber was evacuated to ca. 1x10⁻⁴Pa (1x10⁻⁶ Torr), and then the gate valve 13 was opened and the substrate was mounted on the wafer holder 3. Next, the gate valve 13 was closed, and the reaction chamber 2 was evacuated to a vacuum degree of ca. 1x10⁻⁶Pa (1x10⁻⁸ Torr). In this Example, Mo(CH₃)₆ was sublimed to feed through the first gas line. H₂ was used to the carrier gas of Mo(CH₃)₆ line. The second gas line was used for H₂. By passing H₂ through the second gas line, the pressure within the reaction tube 2 was made a predetermined value by controlling the opening of the slow leak valve 8. Then, the substrate was heated by current passage through the heater 4. After the substrate temperature has reached a predetermined temperature, Mo(CH₃)₆ partial pressure was made ca. 2.7x10⁻² Pa (2.0 x 1-⁻⁴ Torr). Next, when Mo(CH₃)₆ was introduced into the reaction tube through the Mo(CH₃)₆ line. Here the total pressure was ca. 2.7x10²Pa (2.0 Torr) within the reaction tube, and the Mo(CH₃)₆ was introduced into the reaction tube 2, Mo was deposited. After a predetermined deposition time has elapsed, feeding of Mo(CH₃)₆ was stopped. Next, heating of the heater 4 was stopped to cool the substrate. Feeding of H₂ gas was stopped, and after evacuation internally of the reaction tube, the substrate was transferred to the conveying chamber, and only the conveying chamber was made atmospheric before taking out the substrate. The outline of Mo film formation is as described above. After preparing monocrystalline Si substrates as the samples, Mo films were deposited at the respective substrate temperatures according to the same procedure as described above under the following conditions: Total pressure: 2.7x10²Pa (2.0 Torr) Mo(CH₃)₆ partial pressure : 2.7x10⁻²Pa (2.0x10⁻⁴ Torr) The Mo films deposited by varying the substrate temperature were evaluated by use of various evaluation methods, and it was found that in the temperature range of the substrate temperature from 350°C to 550°C, Mo thin films containing very little carbon impurity and having low electrical resistance were deposited with good selectivity on the substrate. Example 2 Si substrates (N type, 1 - 2 ohm.cm) were subjected to thermal oxidation at a temperature of 1000°C according to the hydrogen combustion system (H₂: 4 litres/M, 0₂: 2 litres/M). The film thickness was 700±50nm (7000 ± 500Å) and the refractive index 1.46. A photoresist was coated on the whole Si substrate, and a desired pattern was baked by an exposure machine. The pattern was such that various holes of 0.25 µm x 0.25 µm - 100 µm x 100 µm were opened. After development of the resist, with the photoresist as the mask, the subbing Si0₂ was etched by the reactive ion etching (RIE), etc. to have the substrate Si partially exposed. The samples having various sizes of Si0₂holes of 0.25 µm x 0.25 µm - 100 µm x 100 µm were prepared. The deposited film was formed on the samples thus formed similarly as in Example 1. Specifically the substrate temperature was changed to a temperature in the range 350°C to 550°C and Mo film was deposited according to the procedure as described above under the following conditions: Total pressure: 2.7x10²Pa (2.0 Torr). Mo(CH₃)₆ partial pressure: 4x10⁻²Pa (3 x 10⁻⁴ Torr) The Mo films deposited by varying the substrate temperature were evaluated, and it was found that in the temperature range of the substrate temperature from 350°C to 550°C, Mo thin films containing very little carbon impurity and having low electrical resistance were deposited with good selectivity on the substrate.

Claims: A deposited film formation method comprising the steps of: providing a substrate having a surface of metal or semiconductor material, of metal or semiconductor material having a very thin oxidised film, thereon, or of tungsten silicide, molybdenum silicide, tantalum silicide, aluminium silicide, or titanium silicide; feeding a hexamethyl molybdenum Mo(CH₃)₆ gas and hydrogen gas onto said surface of said substrate; and maintaining the temperature of said surface of said substrate within a range of temperature between the decomposition temperature of hexamethyl molybdenum and 800°C to form a molybdenum film on said surface of said substrate. A method as claimed in claim 1 wherein said surface of said substrate is of a metal selected from tungsten, molybdenum, tantalum, aluminium, titanium and copper. A method as claimed in claim 1 wherein said surface of said substrate is of a metal containing another constituent or other constituents and is selected from aluminium silicon, aluminium titanium, aluminium copper, aluminium tantalum, aluminium silicon copper, aluminium silicon titanium, aluminium palladium, and titanium nitride. A method as claimed in claim 1 wherein said surface of said substrate is of a semiconductor material selected from single-crystalline silicon, polycrystalline silicon and amorphous silicon. A method as claimed in claim 1 wherein said surface of said substrate is of a binary, ternary or quaternary system III-V compound semiconductor consisting of one or more of the group III elements Ga, In and Al and one of the group V elements P, As and N. A method as claimed in claim 1 wherein said surface of said substrate is of a II-VI compound semiconductor. A method as claimed in any preceding claim wherein said substrate has an insulator surface adjacent to said surface of said substrate and said molybdenum film is formed selectively on said surface of said substrate. A method as claimed in claim 7 wherein said insulator surface is of silicon oxide formed by thermal oxidation or by chemical vapour deposition, borosilicate glass, phosphosilicate glass, borophosphosilicate glass, or silicon nitride formed by thermal nitridisation, plasma chemical vapour deposition, low pressure chemical vapour deposition or ECR-chemical vapour deposition. A method as claimed in any preceding claim when applied to produce molybdenum film wiring on the surface of a semiconductor device. A method for producing a semiconductor device comprising the steps of: providing a semiconductor substrate having a film of insulating material on its surface; forming an opening in said film to expose an area of said surface of said semiconductor substrate; and embedding an electroconductive material in said opening to form a part of electrical wiring; said method being characterised in that: said embedding step is performed by carrying out a reaction between a hexamethyl molybdenum Mo(CH₃)₆ gas and hydrogen gas at a temperature maintained within a range of temperature between the decomposition temperature of hexamethyl molybdenum and 800°C to form a molybdenum film selectively on said area of said surface of said substrate exposed by said opening thus forming said electroconductive material part of electrical wiring. A method as claimed in any preceding claim wherein said temperature is maintained within the range 350°C. to 550°C. A method as claimed in claim 11 wherein said temperature is maintained within the range 400°C to 500°C.

Inventors: IKEDA OSAMU C O CANON KABUSHIK, MATSUMOTO SHIGEYUKI C O CANON, OHMI KAZUAKI C O CANON KABUSHI, IKEDA, OSAMU, C/O CANON KABUSHIKI KAISHA, MATSUMOTO, SHIGEYUKI, C/O CANON KABUSHIKI KAISHA, OHMI, KAZUAKI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1990
Main classification: H01L21
IPC codes: H01L21