Metal film forming method

Abstract: A metal film forming method comprises steps of: forming a non-monocrystalline metal film principally composed of aluminum, in contact, at least in a part thereof, with a monocrystalline metal principally composed of aluminum; and heating the non-monocrystalline metal film to convert at least a part thereof into monocrystalline state.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method for forming a thin metal film, and more particularly to a method for forming a thin metal film principally composed of aluminum, adapted for use in wirings for example for semiconductor devices. Related Background Art In the electronic semiconductor devices or integrated circuits, the electrodes and wirings have principally be composed of pure aluminum or a metal principally composed of aluminum, such as Al-Si. Aluminum has various advantages, such as low cost, high electrical conductivity, formation of a dense surfacial oxide film capable of chemically protecting the interior, and good adhesion to silicon. Recent advancements in the level of integration in the ultra large-scale integrated circuits (ULSI) are requiring finer geometry and multi-layered structures in the wirings. For this reason there is being required a deposition method for aluminum film, excellent in step coverage, in order to avoid breakage of wirings at a stepped portion. Also required is a deposition method capable of deposition into via holes such as small contact holes or through-holes with satisfactory step coverage, or selective deposition in such via holes. The wirings have to be highly reliable, excellent in resistances to electromigration and stress migration. In the conventional large-scale integrated circuits (LSI), the deterioration in step coverage at the stepped portions has been prevented by formation of a tapered portion at a step, but the step can no longer be tapered but has become vertical with the miniaturization of geometry. Since sputtering is based on linear particle movement in vacuum, the film thickness at the vertical step becomes inevitably smaller than in other places so that satisfactory step coverage cannot be maintained. Also via holes cannot be filled in completely but generate gaps therein, so that satisfactory contact cannot be expected. On the other hand, deposition of Al or Al-Si can be deposited by chemical vapor deposition (CVD) in which aluminum-containing gas is transported into a space including a substrate and a desired deposition film is formed by absorption and reaction of a raw material gas on the substrate surface. Such CVD method has a feature of satisfactory step coverage at the stepped portion, because it utilizes the absorption and reaction of the raw material gas on the substrate surface. Selective deposition is also possible, depending on the specy of the substrate surface. The CVD method generally employs an organometallic material, such as trimethylaluminum (TMA; (CH 3 ) 6 Al 2 ), triisobutylaluminum (TIBA; (iC 4 H 9 ) 3 Al), or dimethylaluminum hydride (DMAH; (CH 3 ) 2 HAl) as the raw material gas. As is already known, the Al film obtained by the CVD method is superior in step coverage to that obtained by sputtering. Also the CVD method is capable of selective deposition on the exposed Si area on a Si substrate bearing SiO 2 thereon. The CVD method utilizing DMAH and hydrogen (Tsubouchi et al., Nikkei Microdevices, June 1, 1990; p.96 - 102; or 1990 Symposium on VLSI Technology, June 1990, Honolulu, USA, pages 5-6) is capable of selective growth of Al or Al-Si solely on a conductive substrate such as Si or a metal, and the aluminum selective deposited on Si substrate becomes monocrystalline. The aluminum area selectively grown on Si, being monocrystalline, is free from errosion or spike generation or deterioration in contact resistance at the Si interface in the thermal treatment. Also after aluminum is selectively deposited in the via hole, it can be deposited over the entire area of the substrate, so that such via hole can be completely planarized by deposition of Al or Al-Si. Consequently satisfactory wirings can be formed, without breakage in the steps, contacts or via holes in the miniaturized ULSI. Electromigration (EM) is a wiring breakage which occurs when the wiring is continuously given a current, and such breakage is considered to occur at the crystal grain boundary of Al wiring. Also stress migration (SM) is a wiring breakage by a stress in the aluminum wiring, induced by an insulation film such as SiO or SiN provided on said wiring. Al or Al-Si is generally polycrystalline in crystallographic sense. Polycrystals are composed of monocrystalline grains. Each monocrystalline area is called crystal grain, and the interface of grains is called grain boundary. In general, in ULSI's, the size of crystal grain is generally in the order of a micron. The electromigration and the stress migration are major causes deteriorating the reliability of the wirings of Al or Al-Si, and improvement in the resistance to such migration phenomena is an essential condition for improving the reliability of the metal wirings in ULSI's. Although investigations are being made for improving the resistance to electromigration and stress migration by adding a small amount of Cu or Ti to Al or Al-Si, or by using non-aluminum metal such as W, Mo or Cu, no other materials than Al or Al-Si can be selected for satisfying all the requirements such as adhesion to SiO 2 , ease of bonding and ease of microworking. The digest of IEDM (international Electron Devices Meeting) held by IEEE in December 1989 reported, in pages 677 - 681, that the resistances to EM and SM were significantly improved if Al was monocrystalline. Preparing Al single crystal films on amorphous substrates is disclosed in IBM Technical Disclosure Bulletin, vol. 15, No. 11, pages 3525-3526, April 1973. Thus the wiring of Al or Al-Si, if made in monocrystalline state instead of conventional polycrystalline state, can satisfy the requirements of adhesion, ease of bonding and ease of microworking, and can also attain high reliability without breakage by electromigration or stress migration. However, in the ULSI's, the wirings with monocrystalline Al or Al-Si have not been realized as will be explained in the following. The monocrystalline thin Al films which have been reported thus far are all formed on monocrystalline Si substrates. The report on improvement in EM/SM resistances by monocrystalline Al (aforementioned 1989 IEDM digest) is also based on the measurement on an Al film formed by CVD on a Si substrate. On the other hand, the Al or Al-Si wirings in ULSI's are formed on an insulating film such as SiO 2 . On an insulating film such as SiO 2 , the Al film formed by sputtering, CVD or ICB (ion cluster beam) is polycrystals consisting of crystal grains of the order of a micron. According to Tsubouchi et al. (reference cited before), after selective deposition of monocrystalline Al (first Al) in the via hole, second Al can be deposited over the entire surface of the substrate. Though the first Al is monocrystalline, the second Al is still polycrystalline, consisting of crystal grains of the order of a micron. SUMMARY OF THE INVENTION The present invention, attained in consideration of the foregoing, is based on a new finding of the present inventors, that an A1 film present on an insulating member such as SiO 2 can also be made monocrystalline by a heat treatment if monocrystalline Al is present in a lower layer. In the field of semiconductor devices in which a higher level of integration and a higher speed have been seeked for by size reduction in circuit geometry as explained above, there is still room for improvement in the reliability of such semiconductor devices which have already been improved in the level of integration and in functions. In accordance with claim 1 of the present invention there is provided a metal film forming method for a semiconductor device, which is defined in the appended claims. The present invention can convert a non-monocrystalline thin metal film, formed in contact with a monocrystalline metal, into monocrystalline state by heating said metal film, utilizing said monocrystalline metal as a seed crystal. The film is converted into amorphous or microcrystalline state (naturally a state of microcrystals mixed in amorphous substance is also acceptable) prior to heating. Such monocrystalline thin film can be used as a wiring layer in a semiconductor device, thereby improving the migration resistance. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A to 1C are schematic cross-sectional views showing a method of single crystal formation of the present invention, and a wiring forming method utilizing the same; Figs. 2A, 2B and 2C are schematic plan views showing monocrystalline Al seed patterns applicable to the present invention; Fig. 3 is a schematic view of a scanning µ-RHEED microscope; Fig. 4 is a schematic view of an instantaneous heating apparatus (RTA); Figs. 5A and 5B are schematic views showing the shape of specimen applicable to the present invention, and a laser beam irradiating method; Figs. 6A and 6B are schematic views showing the shape of specimen applicable to the present invention, and a laser beam irradiating method; Figs. 7A and 7B are schematic views showing the shape of specimen applicable to the present invention, and a laser beam irradiating method; Fig. 8 is a schematic view showing a heating method with a linear heater; Fig. 9 is a schematic view showing a heating method with a lamp; Fig. 10 is a schematic view showing a heating method with a high frequency; Fig. 11 is a schematic view showing a heating method with an electron beam; Fig. 12 is a schematic view showing the principle of a scanning p-RHEED; Fig. 13 is a schematic view showing the principle of observation with a scanning µ-RHEED microscope; Figs. 14A and 14B are views showing electron beam diffraction patterns; Figs. 15A to 17C are views showing examples of scanning µ-RHEED images indicating the crystal grain boundaries of an Al film deposited on the entire surface of a specimen, wherein: Figs. 15A, 16A and 17A indicate images prior to heating; Figs. 15B, 16B and 17B indicate images after heating (diffraction spot 111); and Figs. 15C, 16C and 17C indicate images after heating (diffraction spot 202); and Figs. 18 and 19 are schematic perspective views of a specimen prior to single crystal formation. DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention an ion implantation, followed by a heat treatment, is applied to an Al film, containing monocrystalline Al and non-monocrystalline A1 in mutual contact in at least a part thereof, thereby converting the non-monocrystalline Al into monocrystalline state. The monocrystalline Al used as the seed crystal is formed by aluminum deposition on monocrystalline silicon by a CVD method utilizing dimethylaluminum hydride (Al(CH 3 ) 2 H), monomethylaluminum hydride (Al(CH 3 )H 2 ) or triisobutylaluminum (Al(iC 4 H 9 ) 3 ) as the raw material gas. On the other hand, the non-monocrystalline A1 may be formed by a method for forming polycrystalline Al by depositing Al by the CVD method utilizing the above-mentioned gas onto a surface of a material other than monocrystalline Al, a method of forming polycrystalline Al by sputtering, or a method of forming polycrystalline Al by a CVD method utilizing trimethylaluminum (Al(CH 3 ) 3 ) or diethylaluminum chloride (Al(C 2 H 5 ) 2 Cl). The monocrystalline Al seed must be so provided that at least a part thereof is in contact with the non-monocrystalline Al to be converted into monocrystalline state. For example the seeds and the insulation film may be arranged in a grating pattern, or the seeds may be deposited in via hole patterns formed in the insulation film, or the seeds and the insulation films may constitute a line-and-space pattern. In another embodiment of the present invention, monocrystalline Al formed in an aperture (via hole) in an insulation film is used as the seed crystal, and the non-monocrystalline Al in other parts is converted into monocrystalline state by ion implantation followed by heating. Such method allows to obtain a flat Al film without a recess formation in the Al film on the via hole. The monocrystalline Al used as the seed is formed by a CVD method utilizing alkylaluminum hydride and hydrogen (said method hereinafter called Al-CVD method). This CVD method is capable of selective Al deposition on an electron-donating surface, such as of monocrystalline silicon. Said alkylaluminum hydride can be dimethylaluminum hydride (Al(CH 3 ) 2 H) or monomethylaluminum hydride (AlCH 3 H 2 ). The non-monocrystalline Al, prior to ion implantation and conversion to monocrystalline state, can be formed by ordinary sputtering or CVD. The raw material gas for such CVD method can be trimethyl aluminum (Al(CH 3 ) 3 ), triisobutyl aluminum (Al(iC 4 H 9 ) 3 ), or diethylaluminum chloride (Al(C 2 H 5 ) 2 Cl). Such method allows to obtain wirings adapted for use in semiconductor devices. Now the present invention will be clarified in greater detail by embodiments thereof shown in the attached drawings. Fig. 1 gives schematic cross-sectional views showing the single crystal forming method of the present invention, applied to formation of wirings. In Fig. 1A, there are shown a substrate 1 composed for example of monocrystalline Si; an insulation film 2 composed for example of silicon oxide; a monocrystalline Al 3 serving as a seed; and an Al layer 4 to be converted into monocrystalline state by the method to be explained later. At first the insulation film 2 is formed on the substrate 1. Then a via hole is formed for example by reactive ion etching, thereby exposing a part of the surface of the substrate 1. Said insulation film can be composed, for example, of a silicon oxide film, a silicon nitride film or a silicon oxinitride film such as NSG, PSG, BSG or BPSG. These films can be formed by thermal oxidation, CVD or sputtering already known. Then monocrystalline Al (first Al) 3 is formed in the via hole. In this operation, the above-explained Al-CVD method may be employed to form monocrystalline Al selectively in said via hole. The substrate surface temperature in this operation is in a range at least equal to the decomposition temperature of alkylaluminum hydride but not exceeding 450°C, more preferably from 260° to 440°C, and most preferably from 270° to 350°C. Thus formed monocrystalline Al has satisfactory interface with the underlying Si, and also has satisfactory surface properties. After the formation of monocrystalline Al 3 in the via hole, non-monocrystalline Al (second Al) 4 is formed on the monocrystalline Al 3 and on the insulation film 2. In this case there can be employed already known deposition methods other than said Al-CVD method. If the Al-CVD method is to be employed, the insulation film 2, constituting an electron non-donating surface, is subjected to a surface modifying step such as supply of ions or electrons by plasma, plasma damage or ion implantation to obtain a practically electron-donating surface. The non-monocrystalline Al can be formed also on the insulation film by the introduction of such surface modifying step (Fig. 1A). Subsequently ion implantation and heat treatment to be explained later is conducted to convert the non-monocrystalline Al into a monocrystalline state. Said treatment may be conducted at this point, or after the formation of an insulation film 5. Also said treatment may be conducted after the non-monocrystalline Al, to be converted into monocrystalline state, is patterned into the form of desired wirings, or prior to said patterning. The insulation film 5 is formed after the patterning of Al 4, as shown in Fig. 1B. Said insulation film 5 may be formed, like the insulation film 2, by CVD or sputtering. The wirings consisting of monocrystalline Al can be obtained in this manner. In case of forming multi-layered wirings, the above-explained procedure is repeated to obtain a two-layered wiring structure of monocrystalline Al as shown in Fig. 1C. A three or four-layered wiring structure can also be obtained by repeating said procedure further. In Fig. 1C, there are shown an interlayer insulation film 5, selectively deposited monocrystalline Al 6, Al 7 in converted monocrystalline state, and a protective insulation film 8. In the foregoing description, the metal principally composed of Al is limited to pure aluminum, but it is also possible to convert Al containing Si in a small amount, for example 1 %, namely Al-Si, to monocrystalline state. In such case, the monocrystalline Al-Si seed can be formed, in the aforementioned Al-CVD method, by introducing Si-containing gas such as SiH 4 or Si 2 H 6 together with alkylaluminum hydride gas and hydrogen gas. Fig. 2 shows examples of arrangement of monocrystalline Al seeds. In an example shown in Fig. 2A, apertures of a lateral length of L1 are formed in a checkered pattern in an insulation film 11, formed for example on a Si surface, and monocrystalline Al is selectively deposited in said apertures. An unrepresented non-monocrystalline A1 film is formed on the insulation film 11 and on the monocrystalline Al in the apertures 12, and is converted into monocrystalline state by heating, utilizing the monocrystalline Al as the seeds. In an example shown in Fig. 2B, apertures of a lateral length L2 are formed as via hole pattern with an interval L3, and, in an example in Fig. 2C, a line-and-space pattern is formed by insulators 11 of a width L5 and apertures 12 of a width L4. In either case the monocrystalline Al is deposited selectively in the apertures, and an unrepresented non-monocrystalline Al film is formed, covering the monocrystalline Al and the insulator. Upon heating, the non-monocrystalline Al film is converted into monocrystalline state, utilizing the monocrystalline Al as the seeds. In the following there will be explained the method for converting Al or Al-Si into monocrystalline state. The basic procedure consists of preparing a specimen of a cross section as shown in Fig. 1A or 1B, and subjecting said specimen to ion implantation followed by heating. Observations were made with X-ray diffraction, conventional RHEED and scanning µ-RHEED microscope, before and after the heating. The transition of the second Al from the polycrystalline state to the monocrystalline state by heating is ascribed to the rearrangement of Al atoms, based on the increased flowability thereof. It is already known that a semiconductor containing a covalent bonding such as Si or GaAs present on a thin insulation film can be converted into monocrystalline state by heating. It is also known that an Al or Al-Si film, present on an insulation film, can be grown into polycrystals consisting of crystal grains of several microns by a heat treatment of 450°C, but the present invention is based on a finding that Al or Al-Si present on an insulator can be converted into monocrystalline state over an area in excess of 10 µm if a monocrystalline Al area is present under such Al or Al-Si film. Heating of the specimen can be achieved, for example, by heating in an electric oven with an atmosphere of H 2 , N 2 or Ar or a mixture thereof, heating in vacuum, heating with a rapid thermal annealer (RTA), heating with a laser, heating with a linear heater such as a carbon heater, high frequency heating, lamp heating or electron beam heating. In a LSI in general, a pure Al film or an Al-Si film formed on Si reacts, when heated, with Si thereby causing erosion of the Si substrate or a leak in the Si pn junction present below the Al or Al-Si film. For this reason, the heating treatment should preferably be conducted at a temperature as low as possible. However, in order that Al or Al-Si can be transformed into monocrystalline state, the Al atoms have to become flowable by thermal energy. Consequently the heating method is preferably such as to heat the Al or Al-Si alone but not the Si substrate present thereunder. Heating in vacuum can be achieved, in a scanning µ-RHEED microscope shown in Fig. 3, by a heater positioned behind the substrate. In case of heat treatment in vacuum, there is preferably employed high vacuum of ca. 1x 10 -6 Torr or lower, in order to suppress the oxidation of Al surface. In Fig. 3 there are shown an electron gun 20; an electron beam 21; a diffracted electron beam 22; a fluorescent plate 23; optical fibers 24, 24', 24"; photomultipliers 25, 25', 25"; diffraction spot intensity signals 26, 26', 26" converted into electrical signals; a scanning signal 27; a cathode ray tube (CRT) 28; a secondary electron signal 29; a secondary electron detector 30; a specimen 31; a vacuum chamber 34; and a vacuum system 35. A specimen as shown in Fig. 1A is placed in the vacuum chamber 34, and is heated from the back by a heater 32. The temperature of the specimen is measured from the back thereof by a thermocouple 33. The heating may also be conducted by a lamp or a laser instead of the heater. The vacuum chamber 34 is evacuated by the vacuum system 35, to a level of 5 x 10 -10 Torr (133 Pa = 1 Torr) prior to heating, and to a level of 5 x 10 -9 - 5 x 10 -8 Torr during the heating. Though a higher vacuum level is preferable, the conversion to monocrystalline state by heating is still possible even at a higher pressure than stated above. In the following there will be explained a rapid thermal annealer (RTA) which can be employed in the present invention. The RTA can heat solely the wafer surface within a short period, thereby minimizing the reaction of Al or Al-Si with the Si substrate. Fig. 4 shows an example of the RTA. A substrate 200 is supported by fingers 205 of a quartz substrate support 201. A quartz tube 202 may have a circular or square cross section, or may be replaced by a metal tube, such as a stainless steel tube, equipped with a quartz window. A linear lamp 203, of which light is reflected by a reflector 204 and irradiates the specimen 200 whose Al deposition face is directed to said lamp, may be composed of a halogen lamp, tungsten lamp, a Xe lamp or a Xe-Hg lamp. In the present example there is employed a halogen lamp of a higher heating speed. At the heating, the interior of the quartz reaction tube is maintained at a low pressure or at atmospheric pressure. The internal atmosphere can be H 2 , N 2 or Ar, or a mixture thereof. The H 2 atmosphere is most preferred because highly pure gas, low in contents of moisture and oxygen, is available. The substrate temperature was measured at the surface thereof, by means of a radiation thermometer utilizing PbS as a detector. In the following there will be explained laser heating applicable to the present invention. Laser heating can also heat the substrate surface only, and has an advantage of providing a wider monocrystalline area than with the RTA. The laser employable for this purpose can be an argon ion laser (hereinafter represented as Ar laser), a krypton ion laser (hereinafter represented as Kr laser), a He-Ne laser, a CO 2 laser, a YAG laser, an excimer laser such as ArF, KrF, XeF or XeCl laser with an output of several to twenty watts. The oscillation frequency can be continuous oscillation or pulsed oscillation of ca. 10 - 100 Hz. The laser heating is featured by a fact that the monocrystalline area can be enlarged by scanning of the specimen with the laser beam. Such enlargement of the monocrystalline area by laser scanning will be explained in the following. There is employed a specimen on which the first Al 62 is formed with a width L10 on the semiconductor substrate 61, while the second Al 63 is formed over the entire surface of said substrate, as shown in Figs. 5A, 5B, 6A, 6B, 7A or 7B. On said second Al 63, there may be formed an insulation film 65 over the entire surface as shown in Fig. 5B or 6B. Otherwise an insulation film 66 may be formed in stripes, as shown in Figs. 7A and 7B, substantially perpendicularly to the lines of the first Al 62. Said specimen is scanned with a laser beam 67 in reciprocating manner as indicated by a line 68 in Fig. 5A, 5B or 7A, or in one direction as indicated by a line 69 in Fig. 6A, 6B or 7B. In case of Fig. 5A, 5B or 7A, the laser beam is obtained from a continuously oscillated Ar laser or a pulse oscillated XeCl excimer laser and is focused to about 20 - 100 µm. In case of Fig. 6A, 6B or 7B, a laser beam of a circular cross section is converted into a parallel beam 71 by an optical system 70 employing a cylindrical lens. The scanning direction of such laser beam or parallel laser beam is substantially perpendicular to the line of the first Al 62, as shown in Fig. 5A, 5B, 6A, 6B, 7A or 7B. In a specimen as shown in Fig. 6A, in which a thermally oxidized SiO 2 layer of a thickness of ca. 7000 Å (10 Å = 1 nm) is formed on the Si substrate, with a line width L10 of ca. 10 µm for the first Al 62 and with a thickness of ca. 5000 Å for the second Al 63, the beam from an Ar laser is converted into a parallel beam 71 and the specimen is scanned in one direction 69 with a speed of ca. 1 cm/sec. The rear face of the specimen is not heated. The Ar laser has an output of ca. 20 - 50 W, with a power density of ca. 50 - 200 Kw/cm 2 on the specimen. The atmosphere of laser heating is H 2 gas of 1 atmosphere. The substrate temperature is measured at the position of irradiation, with a radiation thermometer employing a PbS detector. In the following there will be explained heating with a linear heater, applicable to the present invention. Fig. 8 illustrates the method of heating with a linear heater. The substrate 82 to be heated is placed on a substrate support 81, made of carbon. On said substrate 82 there is positioned a linear heater 83, which is also of carbon and energized by a power source 84. The substrate support 81 is also heated by a heater (not shown) provided at the bottom side of said support. The linear heater 83 moves in a direction 85. The atmosphere at heating may assume any pressure from vacuum to atmospheric pressure, and is preferably composed of H 2 , N 2 Ar or a mixture thereof in order to prevent the oxidation of Al surface. Single crystal formation is possible also in vacuum, but the structure of the apparatus is simpler when the atmospheric pressure is employed. The transformation of the second Al to monocrystalline state takes place immediately below the linear heater. The substrate temperature is measured with a radiation thermometer employing a PbS detector. The feature of heating with such linear heater lies, as in the laser heating, in a fact that the area of monocrystalline transformation can be expanded by scanning the heated area. In the following there will be explained lamp heating, applicable to the present invention. Fig. 9 illustrates the heating method with a lamp, wherein a substrate 92 to be heated is placed on a substrate support 91, made of carbon. A lamp 93 can be a mercury lamp, a Hg-Xe lamp, a Xe lamp or a Xe flash lamp, and preferably has a linear structure. The light from the lamp 93 is condensed by a reflector 94 so as to form a line on the substrate surface. The substrate support 91 is also heated by a heater (not shown) provided on the bottom side thereof. The heated area 95 moves on the substrate in a direction 96, by the movement of the lamp. The atmosphere at heating may assume any pressure from atmospheric pressure to vacuum, and is preferably composed of H 2 , N 2 , Ar or a mixture thereof, in order to prevent oxidation of the Al surface. The single crystal formation is possible also in vacuum, but the atmospheric pressure allows to employ a simpler structure of the apparatus. The transformation of the second Al to monocrystalline state takes place in the heated linear area 95. The substrate temperature is measured by a radiation thermometer employing a PbS detector. In the following there will be explained heating with high frequency, applicable in the present invention. Fig. 10 illustrates the heating method by high frequency heating. A substrate 103 to be heated is placed on a substrate support 101, made of carbon. Quartz plates 102 are provided with a gap therebetween. The substrate support bearing the substrate thereon as shown in Fig. 10 is heated by a high frequency coil (not shown) positioned therearound. Since the quartz plates 102 are not heated by the high frequency, a part 104 of the substrate is heated to a highest temperature. By a wafer movement in a direction 105, the high temperature area 104 moves on the wafer. The atmosphere at heating may assume any pressure from atmospheric pressure to vacuum, and is preferably composed of H 2 , N 2 , Ar or a mixture thereof, in order to prevent oxidation of the Al surface. The single crystal formation is also possible in vacuum, but the atmospheric pressure allows to simplify the structure of the apparatus. In the following embodiment, the pressure of the atmosphere is atmospheric pressure. The transformation of the second Al to monocrystalline state takes place in the linear heated area 104 The substrate temperature is measured with a radiation thermometer employing a PbS detector. In the following there will be explained heating with an electron beam, applicable to the present invention. Fig. 11 illustrates the heating method with an electron beam. An electron beam 113 from a filament 112 is focused in the form of a line on a substrate 111 to be heated, by means of a condensing coil 115, a scanning coil and deflecting plates 115'. Thus, on the substrate, a linear portion 114 is heated to a high temperature. With a wafer movement in a direction 116, the heated area 114 also moves on the wafer. The atmosphere of heating is preferably high vacuum in order to prevent oxidation of the Al surface. The transformation of Al to monocrystalline state takes place at a presure of ca. 10 -6 Torr or lower. The moving speed of the substrate is ca. 0.5 - 10 cm/min. The substrate surface temperature in the heated area is measured with a radiation thermometer employing a PbS detector. In the following there will be explained the method of observation of a monocrystalline area with a scanning µ-RHEED microscope shown in Fig. 3. The scanning µ-RHEED microscope is disclosed in Extended Abstracts of the 21st Conference on Solid State Devices and Materials (1989) p.217 and Japanese Journal of Applied Physics Vol. 28, No. 11(1989) L2075. The conventional RHEED (reflection high energy electron diffraction) method is to irradiate the specimen surface with an electron beam at a shallow angle of 2 - 3° and to evaluate the crystallinity of the specimen surface from the diffraction pattern generated by the diffracted electron beam, but can only provide averaged information of the specimen surface, because the diameter of the electron beam is as large as 100 to several hundred µm. In the scanning µ-RHEED microscope shown in Fig. 3, the diameter of the electron beam from the electron gun 20 is reduced to 0.1 µm, and the electron beam diffraction pattern from a specified small area on the specimen surface can be observed on the fluorescent plate 23. It is also possible to two-dimensionally scan the specimen surface with the electron beam 21, to guide the diffracted electron beam 22 to the fluorescent plate 23, to utilize the intensity change of an arbitrary diffraction spot on the diffraction pattern as image signals 26, 26', 26", and to obtain a two-dimensional image (scanning µ-RHEED image) of the specimen surface by the diffraction spot intensity change on the CRT 28. In this method, observation of a scanning µ-RHEED image employing different diffraction spots A, C on the diffraction pattern as shown in Fig. 12 allows to separately display the crystal grains in which the lattice planes are parallel to the specimen surface, for example to a plane (100) but are rotated in said plane. Said diffraction spot A is on a line ℓ on which a plane of the diffraction spots and a sagittal plane of the incident electron beam perpendicularly cross, while the diffraction spot C is not on said line ℓ. For example, as shown in Fig. 13, if a lattice plane (100) parallel to the specimen surface has mutual rotation in crystal grains x, y in said plane, the scanning µ-RHEED image utilizing the diffraction spot A shows both the crystal grains x, y as high intensity areas, but the image utilizing the spot C shows only the crystal grain x as the high intensity area. Consequently observation of the scanning µ-RHEED image utilizing the diffraction spots A and C as shown in Fig. 12 allows to identify whether the crystal in the observed area is polycrystalline including in-plane rotation or monocrystalline. The preferred embodiment of the present invention utilizes monocrystalline Al formed in a via hole which is formed in an insulation film as a seed crystal, and converts non-monocrystalline Al in other areas into monocrystalline state by heating. It is preferable, after formation of monocrystalline Al by selective deposition of Al in the via hole, to non-selectively deposit Al also on the insulation film, and, after ion implantation, to apply heat treatment thereby converting Al on the insulation film into monocrystalline state. Such method allows to obtain a flat Al film, without formation of a recess in the Al film on the via hole. The non-monocrystalline Al film is once converted into amorphous or microcrystalline state, and is then transformed into monocrystalline state by heating, employing the monocrystalline Al as a seed crystal. According to the present invention, the non-monocrystalline Al film, formed as explained above, is subjected to the implantation of H + , Ar + , Si + or Al + ions by a known ion implanting method. Although other ions may also be employed, the above-mentioned four ions are preferably employed in order not to deteriorate the reliability of the Al or Al-Si wirings for ULSI, and Al + or H + ions are most preferable. Said H + , Al + , Ar + or Si + ions are preferably implanted with an acceleration voltage of ca. 50 kV or higher and with a dose of ca. 1 x 10 15 cm -2 or higher. Thus the second Al can be converted into amorphous or microcrystalline state, even when said second Al has a thickness of ca. 5000 Å. The ion implantation transforms Al, which is polycrystalline when deposited, into amorphous state. Since the Al atoms can more easily flow in the amorphous state than in the polycrystalline state, the transformation to monocrystalline state is achieved at a lower temperature than in the heat treatment at the polycrystalline state. It is already known that a semiconductor having covalent bonds such as Si or GaAs on an insulating film is transformed into monocrystalline state by heat treatment. For example in a method called single phase epitaxy (SPE), silicon deposited on a monocrystalline Si substrate is converted into amorphous state by ion implantation, and is then converted to monocrystalline state by heat treatment for example in an electric oven. The present invention is based on a finding that even a metal film such as of Al present on an insulating film, after conversion into amorphous or microcrystalline state by ion implantation, can be transformed into monocrystalline state at a relatively low temperature. It is already known that an Al or Al-Si film on an insulating film can be grown into a polycrystalline film consisting of crystal grains of several microns by heat treatment of ca. 450°C. However transformation to the monocrystalline state by heat treatment has been impossible because the method of Al deposition for obtaining the structure shown in Fig. 1A has not been known, and also because the selectively deposited Al (first Al in Fig. 1A) has not been monocrystalline. The present invention has enabled, for the first time, to transform an Al film (second Al in Fig. 1A) on an insulating film into monocrystalline state by heat treatment after ion implantation, if selectively grown monocrystalline Al (first Al in Fig. 1A) is present thereunder. The semiconductor substrate is most preferably a Si substrate, but it may also be composed of GaAs, InP or Ge. The cross sectional structure of the specimen after formation of Al of Al-Si is as shown in Fig. 1A. In the following embodiments, the transformation to monocrystalline state is realized even if the second Al becomes thinner or thicker on the first Al. Also an insulation film 5 may be present on the second Al film as shown in Fig. 1B. Said insulation film 5 may be composed of SiO 2 obtained by normal pressure CVD, phosphor-doped oxide film (PSG), boron-doped oxide film (BSG), phosphor- and boron-doped oxide film (BPSG), silicon nitride film (SiN) obtained by low pressure CVD, or silicon nitride film obtained by ECR. The method of heat treatment for monocrystalline transformation is same as explained in the foregoing. In the following there will be explained examples of monocrystalline transformation of Al, including a step of conversion to amorphous or microcrystalline state. Specimens were prepared with monocrystalline seed patterns as explained before, namely a checkered pattern as shown in Fig. 2A with L1 within a range of 0.5 - 20 µm, or a via hole pattern as shown in Fig. 2B with L3 of 20 µm or less, or a line-and-space pattern with L5 of 20 µm, and also with non-monocrystalline Al on such monocrystalline seed pattern. Said specimens, when evaluated by X-ray diffraction, showed only a peak of Al(111). Also observation with the conventional RHEED apparatus with an electron beam diameter of 100 µm to 1 mm provided a circular electron beam diffraction pattern as shown in Fig. 14A. Thus the Al deposited over the entire surface was identified as polycrystals with an orientation (111). Such X-ray diffraction and conventional RHEED observation proved the polycrystalline state, but were unable to identify the size of the crystal grains. Observation with a scanning µ-RHEED microscope with an electron beam diameter reduced to 0.1 µm provided a spot pattern shown in Fig. 14B though the intensity was weak. Also Fig. 15A shows the result of observation of the scanning µ-RHEED image, utilizing the spot intensity variation on the diffraction pattern, wherein hatched areas indicate areas with a high diffraction spot intensity, while a white area indicates an area of weak intensity. The size of the hatched areas suggests that the size of the crystal grains is in the order of several to ten microns. Said specimen was implanted for example with Al + ions with an acceleration voltage of 50 kV and with a dose of 1 x 10 16 /cm 2 . Said ion implantation caused transformation of the second Al into amorphous or microcrystalline state. Said transformation was confirmed in the following manner. The X-ray diffraction showed a diffraction peak of Al(111) in the deposited state, but, after ion implantation, no longer showed diffraction peak for aluminum. Also observation of the electron beam diffraction pattern by the conventional RHEED apparatus did not show circular nor spot pattern but so-called hallow pattern, indicating that the Al or Al-Si film was transformed by the ion implantation into a state which is not monocrystalline nor polycrystalline but amorphous or microcrystalline. After the same specimen was heated in the scanning p-RHEED microscope for 15 minutes at 250°C, it was subjected to observation of the electron beam diffraction pattern and the scanning µ-RHEED image. The electron beam diffraction pattern showed spots of higher intensity than those before heating, as shown in Fig. 14B. The spots in Fig. 14B were identified as a diffraction pattern generated when the electron beam is introduced from a direction [101] into the Al(111) plane. Figs. 15B and 15C indicate the results of observation of the scanning µ-RHEED image, utilizing the intensity of a spot A (111 diffracted spot) and a spot C (202 diffracted spot) on the diffraction pattern in Fig. 14B. In any position on the specimen surface, the spots A, C were both strong, suggesting that all the observed area has turned into monocrystalline state. It was therefore confirmed that an Al film even existing on SiO 2 could be transformed into monocrystalline state by heat treatment, if monocrystalline Al was present under said Al film. The specimen after heat treatment, when evaluated by X-ray diffraction, showed only a peak of Al(111), and observation with the conventional RHEED apparatus provided a spot pattern indicating monocrystalline state as shown in Fig. 14B. As will be explained in the following examples, monocrystalline Al can be formed on a substrate surface of any material. Also there can be obtained A1 wirings with preferred characteristics for use in semiconductor devices, such as surface properties, antimigration resistance, adhesion to the underlying silicon etc. [Example G1] The specimens used in the measurement, having a cross-sectional structure as shown in Fig. 1A, were prepared in the following manner. A Si wafer was subjected to thermal oxidation at 1000°C by hydrogen combustion (H 2 : 4 1/min., O 2 : 2 l/min.). The surface orientation of Si wafer was (100) or (111). The entire wafer was coated with photoresist and was exposed to a desired pattern by an exposure apparatus. After the photoresist was developed, reactive ion etching was conducted, utilizing the photoresist as a mask, to etch the underlying SiO 2 , thereby locally exposing the Si surface. Then an Al film was deposited by a low pressure CVD method, employing dimethylaluminum hydride and hydrogen, with a deposition temperature of ca. 270°C and a pressure of ca. 1.5 Torr in the reactor tube. At first selective A1 deposition (first A1) was conducted solely on the exposed Si surface, then a surface modifying step was conducted by generating plasma in the low pressure CVD apparatus when the Al film thickness became equal to the SiO 2 film thickness, and Al (second Al) was deposited on the entire surface. Following SiO 2 patterns and Al film thicknesses were employed on the specimens. The SiO 2 film thickness was varied in 5 levels of 1000, 2500, 500, 7500 and 10000Å. The checkered pattern shown in Fig. 2A was used on the Si wafer, with size L1 varied in 8 levels of 0.25, 0.5, 1, 2, 3, 5, 10 and 20 pm. Thickness of the A1 film deposited on the entire surface (second A1 film 4 in Fig. 1) was varied in 3 levels of 100, 2500 and 5000 Å. By taking combinations of the above-mentioned four conditions, namely substrate surface orientation, SiO 2 film thickness, checkered pattern size L1 and second Al film thickness, there were prepared 2 x 5 x 8 x 3 = 240 specimens. In the X-ray diffraction conducted after the deposition of the first and second Al films, all the specimens showed only an Al(111) peak, regardless of the SiO 2 film thickness, size of the checkered pattern or second Al film thickness. Also in the observation of the electron beam diffraction pattern by the conventional RHEED apparatus with an electron beam diameter of 100 µm - 1 mm, all the specimens showed ring-shaped patterns as shown in Fig. 14A. It was therefore confirmed that the Al deposited over the entire surface was polycrystals with an orientation (111). Also observation of the electron beam diffraction pattern in the scanning µ-RHEED microscope with an electron beam reduced to a diameter of 0.1 µm provided a spot pattern as shown in Fig. 14B, though the intensity was weak. Also the scanning µ-RHEED image utilizing the diffracted spot intensity of the diffraction pattern provided an image as shown in Fig. 15A, wherein hatched areas indicate areas of high diffraction spot intensity, indicating polycrystalline state consisting of crystal grains of several to ten microns. In such specimens, the second Al was subjected to Al + implantation by known ion implanting method, with an acceleration voltage of 50 kV and a dose of 5 x 10 15 cm -2 or 1 x 10 16 cm -2 . Said ion implantation caused transformation of the second Al into amorphous or microcrystalline state, and said transformation was confirmed in the following manner. X-ray diffraction in the deposited state showed an Al(111) diffracted peak, but did no longer show the peak relating to Al after ion implantation. Also the electron beam diffraction in the conventional RHEED apparatus showed so-called hallow pattern which is neigher ring-shaped nor spot-shaped pattern. Thus, as a result of ion implantation, the Al or Al-Si film was transformed into a state which is not monocrystalline nor ordinary polycrystalline but amorphous or microcrystalline. The iron implanted specimens were heated treated in an electric over, at temperatures of 9 levels of 200°, 250°, 300°, 350°, 400°, 450°, 550° and 600°C, for about 3 hours, in hydrogen gas atmospheric pressure. After the heat treatment in the above-mentioned conditions, the specimens were subjected to the observation of electron beam diffracted pattern and scanning µ-RHEED image in the scanning µ-RHEED microscope. All the specimens treated at 250°C or higher showed spot patterns as shown in Fig. 14B, with higher intensities than before the heat treatment, regardless of the Si wafer surface orientation, SiO 2 film thickness, size of the checkered pattern or second Al film thickness. The diffraction pattern in Fig. 14B was identified, from the position of the diffracted spots, as being generated by the electron beam introduced from a direction [101] into the Al(111) plane. The scanning µ-RHEED images, obtained utilizing the intensities of a diffracted spot A (111 diffracted spot) and a spot C (202 diffracted spot) on the diffraction pattern in Fig. 14B were similar to those shown in Figs. 15B and 15C, wherein areas of high diffraction spot intensity are hatched. The Al film deposited in the area of checkered pattern provided high intensities both for the spots A and C, indicating the transformation to monocrystalline state by heat treatment. In observation of the electron beam diffraction pattern in the conventional RHEED apparatus, all the specimens after heat treatment showed spot patterns indicating monocrystalline state, as shown in Fig. 14B. Thus the second Al film, which had been polycrystals when deposited by the LP-CVD method, was transformed into monocrystalline state by heat treatment, after transformation into amorphous state by ion implantation. At the substrate surface temperature of 600°C, the measurement of element distribution, by Auger electron spectroscopy or secondary ion mass spectroscopy, indicated diffusion of Si and Al at the interface of the insulation film on the substrate surface and the second Al film. [Example G2] In the example G1, Al + ions were implanted into the second Al film. In this example Si + ions were implanted in the same specimens and procedures as in said example G1. Si + ion implantation was conducted with an acceleration voltage of 80 kV and a dose of 5 x 10 15 cm -2 or 1 x 10 16 cm -2 . There were obtained results similar to those in the example G1. The second Al was transformed by ion implantation into amorphous or microcrystalline state, and then to monocrystalline state at the heat treating temperature of 250°C or higher. [Example G3] In contrast to Al + ion implantation to the second Al in the example G1, the present example conducted implantation of H + ions in the same specimens and procedure as in the example G1. H + ion implantation was conducted with an acceleration voltage of 20 kV and a dose of 5 x 10 16 cm -2 or 1 x 10 17 cm -2 . There were obtained results similar to those in the example G1. The second Al was transformed by ion implantation into amorphous or microcrystalline state, and then to monocrystalline state at the heat treating temperature of 250°C or higher. [Example G4] In contrast to Al + ion implantation to the second Al in the example G1, the present example conducted implantation of Ar + ions in the same specimens and procedure as in the example G1. Ar + ion implantation was conducted with an acceleration voltage of 80 kV, and a dose of 5 x 10 16 cm -2 or 5 x 10 16 cm -2 . There were obtained similar results to those in the example G1. The second Al was transformed by ion implantation into amorphous or microcrystalline state, and then to monocrystalline state at the heat treating temperature of 250°C or higher. [Example G5] Specimens with a cross-sectional structure shown in Fig. 1A were prepared in the same manner as in the example G1, and were subjected to ion implantation and heat treatment. Different from the example G1, the via hole pattern shown in Fig. 2B was formed on the Si wafer, with size L2 varied in 5 levels of 0.25, 0.5, 1, 2 and 5 µm and size L3 varied in 5 levels of 1, 2, 5, 10 and 20 µm. Thus there were prepared 25 different via hole patterns, taking combinations of said L2 and L3. The thicknesses of the SiO 2 film and the Al film deposited on the entire wafer (second Al 4 in Fig. 1) were same as in the example G1. The specimens prepared as explained above were subjected to A1 + ion implantation in the same manner as in the example G1, then to heat treatment in the electric oven and subsequently observed. The A1 + ion implanting conditions and the heat treating conditions were same as in the example G1. Based on X-ray diffraction, electron beam diffraction pattern obtained in the conventional RHEED apparatus, and electron beam diffraction pattern and scanning µ-RHEED image obtained by the scanning µ-RHEED microscope as in the example G1, the second Al in the deposited state by the LP-CVD method was identified, in any speciment, as polycrystals with an orientation (111), consisting of crystal grains of several to ten microns. After the Al + ion implantation, it was confirmed, as in the example G1, that all the specimens were converted into amorphous or microcrystalline state. Then the heat treatment in the electric oven was conducted in the same conditions as in the example G1, and the electron beam diffraction pattern and the scanning µ-RHEED image were observed in the scanning µ-RHEED microscope. The scanning µ-RHEED images indicated, as in the example G1, that all the specimens treated at 250°C or higher were transformed into monocrystalline state, regardless of the surface orientation of the Si wafer, size of the checkered pattern or second Al film thickness. Also as in the example G1, the measurement of element distribution in the direction of depth, by Auger electron spectroscopy or secondary ion mass spectroscopy, indicated diffusion of Si and Al at the interface between the insulation film on the substrate surface and the second Al film when the substrate surface temperature was 600°C or higher. [Example G6] In contrast to Al + ion implantation into the second Al in the example G5, the present example conducted Si + ion implantation with the same specimens and procedure as in the example G5. The Si + ion implanting conditions were same as those in the example G2. There were obtained similar results as those in the example G5, wherein the second Al was transformed by ion implantation into amorphous or microcrystalline state, and into monocrystalline state at the heat treating temperature of 250°C or higher. [Example G7] In contrast to the example G5 employming Al + ion implantation into the second Al, the present example conducted H + ion implantation with the same specimens and procedure as in the example G5. The H + ion implanting conditions were same as those in the example G3. There were obtained similar results as those in the example G5, wherein the second Al was transformed by ion implantation into amorphous or microcrystalline state, and into monocrystalline state at the heat treating temperature of 250°C or higher. [Example G8] In contrast to the example G5 employing Al + ion implantation into the second Al, the present example conducted Ar + ion implantation with the same specimens and procedure as in the example G5. The Ar + ion implanting conditions were same as those in the example G4. There were obtained similar results as those in the example G1, wherein the second Al was transformed by ion implantation into amorphous or microcrystalline state, and into monocrystalline state at the heat treating temperature of 250°C or higher. [Example G9] Specimens of a cross-sectional structure as shown in Fig. 1A were prepared in the same manner as in the example G1, and were subjected to ion implantation and heat treatment. Different from the example G1, the line-and-space pattern shown in Fig. 2C was formed on the Si wafer, with the size L4 varied in 5 levels of 0.25, 0.5, 1, 2 and 5 µm and size L5 in 5 levels of 1, 2, 5, 10 and 20 µm. Thus 25 different line-and-space patterns were prepared by taking the combinations of L4 and L5. The thicknesses of the SiO 2 film and the Al deposited on the entire surface (second Al 4 in Fig. 1) were same as in the example G1. The specimens prepared as explained above were subjected to Al + ion implantation in the same manner as in the example G1, then to heat treatment in the electric oven and were observed. The Al + ion implanting conditions and heat treating conditions were same as those in the example G1. Based on X-ray diffraction, electron beam diffraction pattern obtained in the convetional RHEED apparatus, and electron beam diffraction pattern and scanning µ-RHEED image obtained by the scanning µ-RHEED microscope, the Al deposited on the entire surface (second Al) in any specimen was identified, as in the example G1, as polycrystals with an orientation (111), consisting of crystal grains of several to ten microns. It was also confirmed, as in the example G1, that all the specimens were transformed into amorphous or microcrystalline state by Al + ion implantation. Then heat treatment with the electric oven was conducted in the same manner as in the example G1, and the electron beam diffraction pattern and the scanning µ-RHEED image were observed in the scanning µ-RHEED microscope. The scanning µ-RHEED image indicated, as in the example G1, that all the specimens treated at 250°C or higher were transformed to monocrystalline state regardless of the Si wafer surface orientation, SiO 2 film thickness, size of the checkered pattern or second Al film thickness. Also as in the example G1, the measurement of element distribution in the direction of depth, by Auger electron spectroscopy or secondary ion mass spectroscopy, indicated diffusion of Si and Al at the interface between the insulation film on the substrate surface and the second Al film, when the substrate surface temperature was 600°C or higher. [Example G10] In contrast to the example G9 employing Al + ion implantation into the second Al, the present example conducted Si + ion implantation with the same specimens and procedure as in the example G9. The Si + ion implanting conditions were same as those in the example G3. There were obtained similar results to those in the example G9, wherein the second Al was transformed into amorphous or microcrystalline state by ion implantation, and to monocrystalline state by heat treatment at 250°C or higher. [Example G11] In contrast to the example G9 employing Al + ion implantation into the second Al, the present example conducted H + ion implantation with the same specimens and procedure as in the example G9. The H + ion implanting conditions were same as those in the example G3. There were obtained similar results to those in the example G9, wherein the second Al was transformed into amorphous or microcrystalline state by ion implantation, and to monocrystalline state by heat treatment at 250°C or higher. [Example G12] In contrast to the example G9 employing Al + ion implantation into the second Al, the present example conducted Ar + ion implantation with the same specimens and procedure as in the example G9. The Ar + ion implanting conditions were same as in the example G4. There were obtained similar results to those in the example G9, wherein the second Al was transformed into amorphous or microcrystalline state by ion implantation, and to monocrystalline state by heat treatment at 250°C or higher. [Example G13) In the examples G1 - G12, the second Al was formed on the entire surface of the speciment, as shown in cross section in Fig. 1A. In the present example, an insulation film was formed on the second Al of the specimens of the examples G1 - G12, as shown in Fig. 1B, and ion implantation and heat treatment with the electric oven were conducted in the same manner as in the examples G1 - G12. In this example, after the deposition of the first and second Al films, there were conducted the ion implantation and then the heat treatment in the electric oven. The conditions of ion implantation and heat treatment were same as in the examples G1 - G12. The insulation film on the second Al film was composed of a SiO 2 film obtained by normal pressure CVD (hereinafter expressed as CVD-SiO 2 ), a boron-doped oxide film obtained by normal pressure CVD (BSG), a phosphor-doped oxide film obtained by normal pressure CVD (PSG), a boron- and phosphor-doped oxide film obtained by normal pressure CVD (BPSG), a nitride film obtained by plasma CVD (P-SiN), or a nitride film obtained by ECR apparatus (ECR-SiN). Said insulation film on the second Al will hereinafter be called the second insulation film. The thickness of the second insulation film was selected as 1000, 2000, 5000 or 10000Å. The heat treating temperature was same as in the examples G1 - G12. After the heat treatment, the second insulation film was removed by etching, and the electron beam diffraction pattern and the scanning µ-RHEED image were observed, as in the examples G1 - G12, in the scanning µ-RHEED microscope. There were obtained similar results to those in the examples G1 - G12, indicating that the second Al was transformed into monocrystalline state when the substrate temperature was 250°C or higher. Also as in the examples G1 - G12, the measurement of element distribution in the direction of depth, by Auger electron spectroscopy or secondary ion mass spectroscopy, indicated diffusion of Si and Al at the interface between the insulation film on the substrate surface and the second Al film, when the substrate surface temperature was 600°C or higher. [Example G14] In the examples G1 - G12, the second Al film was formed on the entire surface of the specimen, as shown in cross section in Fig. 1A. In the present example, an insulation film was formed on the second Al as shown in Fig. 1B, and ion implantation and heat treatment with the electric over were conducted in the same manner as in the examples G1 - G12. In contrast to the example G13 in which conducted in succession were the ion implantation, the deposition of the second insulation film and the heat treatment with the electric over, the present example conducted in succession the deposition of the first and second Al films, the deposition of the second insulation film, the ion implantation and the heat treatment with the electric oven. The conditions of ion implantation and heat treatment were same as in the examples G1 - G12. The insulation film on the second Al was composed of CVD-SiO 2 , BSG, PSG, BPSG, P-SiN or ECR-SiN, with a thickness of 500 or 1000 Å. The heat treating temperature was same as in the examples G1 - G12. After the heat treatment, the second insulation film was removed by etching, and the electron beam diffraction pattern and the scanning µ-RHEED image were observed, as in the examples G1 - G12, by the scanning µ-RHEED microscope. There were obtained similar results to those in the examples G1 - G12, and the second Al was transformed to monocrystalline state when the substrate temperature was 250°C or higher. Also as in the examples G1 - G12, the measurement of element distribution in the direction of depth, by Auger electron spectroscopy or secondary ion mass spectroscopy, indicated diffusion of Si and Al at the interface between the insulation film on the substrate surface and the second Al film, when the substrate surface temperature was 600°C or higher. [Example G15] In the examples G1 - G14, the first insulation film formed on the Si substrate, as shown in Fig. 1A, was composed of SiO 2 formed by thermal oxidation. In the present example, the insulation film on the Si substrate was composed of CVD-SiO 2 , BSG, PSG, BPSG, P-SiN, T-SiN, LP-SiN or ECR-SiN, with a thickness of 1000, 2500, 5000, 7500 or 10000 Å. The thicknesses of the first and second Al films, and the ion implanting conditions were same as those in the examples G1 - G14. As in the examples G1 - G14, the second Al film was transformed into monocrystalline state when the substrate temperature was 250°C or higher. Also as in the examples G1 - G14, the measurement of element distribution in the direction of depth, by Auger electron spectroscopy or secondary ion mass spectroscopy, indicated diffusion of Si and Al at the interface between the insulation film on the substrate surface and the second Al film, when the substrate surface temperature was 600°C or higher. [Example G16] There was measured the area of monocrystalline transformation of the second Al film. The structure and cross section of the specimens are as shown in Fig. 18 and Fig. 1A. The insulation film on the Si substrate was provided with a gap of a width L10, in which monocrystalline Al (first Al) was formed. Said width was varied in 6 levels of 0.5, 1, 2, 5, 10 and 20 µm. The surface orientation of the Si wafer was selected as (100) or (111). The insulation film was composed of SiO 2 formed by thermal oxidation, with a thickness varied in 5 levels of 1000, 2500, 5000, 7500 and 10000 Å. The thickness of the Al deposited on the entire surface (second Al film 4 in Fig. 1, or second Al film 63 in Fig. 18) was varied in 3 levels of 1000, 2500 and 5000 Å. By taking combinations of the above-mentioned four parameters, namely the Si substrate surface orientation, SiO 2 film thickness, width L10 of the gap in first Al and second Al film thickness, there were prepared 2 x 5 x 6 x 3 = 180 different specimens. Based on X-ray diffraction, electron beam diffraction pattern obtained by the conventional RHEED apparatus, and electron beam diffraction pattern and scanning µ-RHEED image obtained by the scanning µ-RHEED microscope, the second Al was identified, as in the example G1, as polycrystals consisting of crystal grains of several to ten microns. Al + ions were implanted under the same conditions as those in the example G1, whereby the second Al was transformed into amorphous or microcrystalline state. Thereafter heat treatment in the electric oven was conducted in the same conditions as in the example G1. After the heat treatment, the electron beam diffraction pattern and the scanning µ-RHEED image were observed in the scanning µ-RHEED microscope. The electron beam diffraction provided, as in the example G1, a spot pattern as shown in Fig. 14B, with a higher intensity than before the heat treatment. The scanning µ-RHEED images obtained utilizing the 111 and 202 diffracted spots were similar to those shown in Figs. 17B and 17C. Fig. 17A shows the pattern on the Si substrate, wherein the direction of first Al (line direction) is parallel to the y-direction in Fig. 17A. The length of the transformed monocrystalline area can be determined by measuring L8 in Fig. 17C. Though L8 is illustrated in the order of 10 - 20 µm in Fig. 17C, it was in fact about 1 cm when the substrate temperature was 250°C or higher. Stated differently, the second Al on SiO 2 was transformed into monocrystalline state over a length of 1 cm, utilizing monocrystalline first Al as the seed. Also as in the examples G1 - G12, the measurement of element distribution in the direction of depth, by Auger electron spectroscopy or secondary ion mass spectroscopy, indicated diffusion of Si and Al at the interface between the insulation film on the substrate surface and the second Al film, when the substrate surface temperature was 600°C or higher. [Example G17] In contrast to the example G16 employing Al + ion implantation into the second Al, the present example conducted Si + ion implantation with the same specimens and procedure as in the example G16. The Si + ion implanting conditions were same as those in the example G2. There were obtained similar results to those in the example G16, wherein the second Al was transformed into amorphous or microcrystalline state by ion implantation, and further to monocrystalline state by heat treatment at 250°C or higher. [Example G18] In contrast to the example G16 employing Al + ion implantation to the second Al, the present example conducted H + ion implantation with the same specimens and procedure as in the example G16. The H + ion implanting conditions were same as those in the example G3. There were obtained similar results to those in the example G16, wherein the second Al was transformed into amorphous or microcrystalline state by ion implantation, and further to monocrystalline state by heat treatment at 250°C or higher. [Example G19] In contrast to the example G16 employing Al + ion implantation to the second Al, the present example conducted Ar + ion implantation with same specimens and procedure as in the example G1. The Ar + ion implanting conditions were same as those in the example G4. There were obtained similar results to those in the example G16, wherein the second Al was transformed into amorphous or microcrystalline state by ion implantation, and further to monocrystalline state by heat treatment at 250°C or higher. [Example G20] In the examples G16 - G19, the second Al was formed on the entire surface of the specimen, as shown in Fig. 18. In the present example, an insulation film was formed on the second Al film as shown in Fig. 19 and ion implantation and heat treatment with the electric oven were conducted in the same manner as in the examples G16 - G19. In the present example, the deposition of the first and second Al films was followed by ion implantation and then heat treatment in the electric oven. The conditions of said ion implantation and heat treatment were same as in said examples G16 - G19. The insulation film (second insulation film) on the second Al film was composed of CVD-SiO 2 , BSG, PSG, BPSG, P-SiN or ECR-SiN, with a thickness of 1000, 2000, 5000 or 10000 Å. The heat treating temperature was same as in the examples G16 - G19. After the heat treatment, the second insulation film was removed by etching, and the electron beam diffraction pattern and the scanning µ-RHEED image were observed in the scanning µ-RHEED microscope, as in the examples G16 - G19. There were obtained similar results to those in said examples, wherein the second Al was transformed into monocrystalline state with heat treatment at 250°C or higher. Also as in the examples G16 - G19, the measurement of element distribution in the direction of depth, by Auger electron spectroscopy or secondary ion mass spectroscopy, indicated diffusion of Si and Al at the interface between the insulation film on the substrate surface and the second Al film, when the substrate surface temperature was 600°C or higher. [Example G21] In the examples G16 - G19, the second Al was formed on the entire surface of the specimen as shown in cross section in Fig. 1A. In the present example, an insulation film was formed on the second Al in-the specimens of the examples G1 - G12, and ion implantation and heat treatment with the electric oven were conducted in the same manner as in the examples G16 - G19. In contrast to the example G20 in which ion implantation, deposition of the second insulation film and heat treatment in the electric oven are conducted in succession, the present example conducted, after the deposition of the first and second Al films, the deposition of the second insulation film, ion implantation and heat treatment by the electric oven. The conditions of ion implantation and heat treatment were same as in the examples G16 - G19. The insulation film on the second Al was composed of CVD-SiO 2 , BSG, PSG, BPSG, P-SiN or ECR-SiN, with a thickness of 500 or 1000 Å. The heat treating temperature was same as in the examples G16 - G19. After the heat treatment, the second insulation film was removed by etching, and the electron beam diffraction pattern and the scanning µ-RHEED were observed, as in the examples G16 - G19, in the scanning µ-RHEED microscope. There were obtained similar results to those in the examples G16 - G19, wherein the second Al was transformed into monocrystalline state when the substrate temperature was 250°C or higher. Also as in the examples G16 - G19, the measurement of element distribution in the direction of depth, by Auger electron spectroscopy or secondary ion mass spectroscopy indicated diffusion of Si and Al at the interface between the insulation film on the substrate surface and the second Al film, when the substrate surface temperature was 600°C or higher. [Example G22] In the examples G16 - G21, the first insulation film formed on the Si substrate of the structure shown in Fig. 18 or 19 was composed of SiO 2 obtained by thermal oxidation. In the present example, the insulation film on the Si substrate was composed of CVD-SiO 2 , BSG, PSG, BPSG, P-SiN, T-Sin, LP-SiN, or ECR-SiN, with a thickness varied in 5 levels of 1000, 2500, 5000, 7500 and 10000 Å. The thicknesses of the second Al film and of the second insulation film, and the ion implanting conditions, were same as those in the examples G16 - G21. As in said examples, the second Al was transformed into monocrystalline state when the substrate temperature was 250°C or higher. Also as in said examples, the measurement of element distribution in the direction of depth, by Auger electron spectroscopy or secondary ion mass spectroscopy, indicated diffusion of Si and Al at the interface between the insulation film on the substrate surface and the second Al film, when the substrate surface temperature was 600°C or higher. [Example G23] In the examples G1 - G22, the first and second Al films were both composed of pure aluminum formed by a LP-CVD method employing DMAH (dimethylaluminum hydride) and hydrogen. In the present example, pure aluminum was replaced by Al-Si, deposited by the addition of Si 2 H 6 in LP-CVD in addition to DMAH and hydrogen. The Si content in the first and second Al-Si films was selected as 0.2, 0.5 or 1.0%. The heat treatment was conducted in the same manner as in the examples G1 - G22, except that Al was replaced by Al-Si. There were obtained similar results to those in said examples G1 - G22. [Example G24] In the examples G1 - G22, the first and second Al films were both formed by the LP-CVD method employing DMAH and hydrogen. In order to convert the second Al film into monocrystalline state by heat treatment, the first Al has to be monocrystalline. The LP-CVD method has the advantage of being capable of depositing the first and second Al films in succession in the same apparatus, but the second Al film need not be formed by CVD as long as it is polycrystalline or amorphous. The present example employed the same specimens and heat treating conditions as those in the examples G1 - G22, but the second Al film alone was formed by sputtering. Based on X-ray diffraction, electron beam diffraction pattern obtained by the conventional RHEED apparatus, and electron beam diffraction pattern and scanning µ-RHEED image obtained by the scanning µ-RHEED microscope, the second Al film in the deposited state was identified as polycrystals consisting of crystal grains of 1 µm or smaller. By ion implantation and heat treatment in the same conditions as in the examples G1 - G22, there were obtained similar results to those in said examples, wherein the second Al was transformed into monocrystalline state when the substrate temperature was 250°C or higher. However the transformed monocrystalline area L3, measured in the same manner as in the examples G16 - G22, was about 0.8 cm, which was shorter than 1.0 cm obtained when the second Al film was formed by CVD. Also as in the examples G1 - G22, the measurement of element distribution in the direction of depth, by Auger electron spectroscopy or secondary ion mass spectroscopy indicated diffusion of Si and Al at the interface between the insulation film on the substrate surface and the second Al film, when the substrate surface temperature was 600°C or higher. [Example G25] There were employed same specimen structure and heating conditions as those in the examples G1 - G22, but the first Al film was composed of Al-Si formed by LP-CVD employing DMAH, hydrogen and Si 2 H 6 , while the second Al film was composed of pure aluminum formed by LP-CVD employing DMAH and hydrogen. The Si content in the first Al-Si film was selected as 0.2, 0.5 or 1.0 %. There were obtained similar results to those in the examples G1 - G22. [Example G26] There were employed same specimen structure and heating conditions as in the examples G1 - G22, but the first Al film was composed of Al-Si formed by LP-CVD employing DMAH, hydrogen and Si 2 H 6 , while the second Al film was composed of Al-Si formed by sputtering. The Si content in the first Al-Si film was selected as 0.2, 0.5 or 1.0 %. There were obtained similar results to those in the examples G1 -G22. However the transformed monocrystalline area L8, measured as in the examples G16 - G22, was 0.8 cm, which was shorter than 1.0 cm when the second Al was formed by CVD. As detailedly explained in the foregoing, the present invention can achieve transformation into monocrystalline state by a heat treatment, even in an Al film present on SiO 2 , if said SiO 2 is so patterned to expose a Si surface and monocrystalline Al is present on thus exposed Si surface. Said monocrystalline transformation can be achieved with heat treatment of a low temperature. Said transformed monocrystalline Al can be utilized in wirings and can improve the resistances to migration phenomena.

Claims: A metal film forming method for a semiconductor device, comprising steps of: forming an insulation film (2) on a principal surface of a semiconductor substrate (1); forming an aperture in said insulation film (2) thereby exposing the surface of said semiconductor substrate (1); depositing a monocrystalline metal (3) composed of aluminum, selectively in said aperture, by a CVD method employing alkylaluminum hydride gas and hydrogen gas, so that a surface of said monocrystalline metal (3) is at the same level as the surface level of said insulation film (2); forming a metal film (4) principally composed of aluminum on said monocrystalline metal (3) and on said insulation film (2); converting said metal film by ion implantation to an amorphous state, a micro-crystalline state, or an amorphous state with microcrystalline inclusions; and heating said metal film (4) to 250°C or higher to convert at least a part thereof to monocrystalline state, utilising said monocrystalline metal (3) as a seed crystal. A method according to claim 1, wherein said heating is conducted after a second insulation film (5) is formed on said metal film (4). A method according to claim 2, wherein said metal film (4) is heated by resistance heating. A method according to claim 2, wherein said metal film (4) is heated by radiation. A method according to claim 2, wherein said metal film (4) is heated by laser beam. A method according to claim 2, wherein said metal film (4) is heated by electron beam. A method according to claim 2, wherein said metal film (4) is heated by induction. A method according to any preceding claim in which said metal film includes Si.

Inventors: MASU KAZUYA, TSUBOUCHI KAZUO, MASU, KAZUYA, TSUBOUCHI, KAZUO
Applicants: TSUBOCHI KAZUO, TSUBOUCHI, KAZUO
Application year: 1991
Main classification: H01L21
IPC codes: H01L23, H01L21