Process for forming deposited film by use of alkyl aluminum hydride

Abstract: A process for forming an Al film of good quality according to the CVD method utilizing the reaction between alkyl aluminum hydride and hydrogen, which is an excellent deposited film formation process also capable of selective deposition of Al.

Description: The present invention relates to a method for depositing a film composed wholly or mainly of aluminium in an electron donative surface of a substrate. The resulting Al film may be used to form electrodes or wiring of a semiconductor integrated circuit device. Aluminium has been used primarily as wiring of semiconductor electronic devices or integrated circuits. It has the advantages that it is inexpensive, of high electroconductivity, forms on its surface a dense oxide film that gives chemical protection to its interior, and adheres well to Si. In the prior art sputtering methods such as magnetron sputtering has been used to form Al or Al alloy film for electrodes and wiring. However, the film produced at a step on side wall of an insulating film is extremely low in thickness because sputtering is a physical deposition method based on particles flying through a vacuum. Non-uniformity of film thickness or breaks in wiring can significantly reduce the reliability of a LSI device. As the complexity of integrated circuits increases and the resulting surface features become more fine the demands made on the Al wiring also increase since the surface of the LSI may be significantly uneven as a result of oxidation, diffusion, thin film deposition or etching. For example, it may be necessary to deposit electrodes or wiring metal onto a surface having a step or into a deep, fine diameter via hole. In 4 Mbit or 16 Mbit DRAM's (dynamic RAMs) it is necessary to deposit metal composed mainly of Al such as Al, Al-Si into via holes having an aspect ratio (depth/diameter) of 1.0 or above, and the diameter of the via holes may be 1 µ m or less. There is therefore a need for a deposition technique which is applicable to via holes having such dimensions or aspect ratio. To establish reliable connections to devices located under SiO₂ or other insulating films, it may be necessary to deposit Al selectively into a via hole. A selective deposition method is therefore needed which can deposit Al only on a surface of Si or a metal and not on an insulating film such as SiO₂. This selectivity is not available using sputtering which as previously stated is a physical deposition method, so that the aluminium film produced at steps or side wall regions of the insulating film becomes extremely thin, leading in an extreme case to wire breakage. An improved sputtering method has been developed in which a bias is applied to the substrate and deposition is performed so that there is both a deposition action on the substrate surface and a sputter etching action and Al or Al alloy becomes embedded in via holes only. However, a bias voltage of 100V or above is applied to the substrate, which can cause the device to be damaged by charged particles resulting in e.g. a threshold charge of MOS-FETs. Furthermore, deposition is slow because the method employs both a deposition action and an etching action. In order to overcome the above problems, various types of chemical vapour deposition (CVD) have been proposed in which chemical reaction of a starting gas is involved. In plasma or optical CVD, the starting gas is decomposed in the gas phase to form there an active species which further reacts on the substrate to form a film. Because of the gas phase reaction, good surface coverage can be obtained even on an uneven substrate. However, carbon atoms present in the molecules of starting gas become incorporated into the film. Also, particularly in plasma CVD, the same problem is present as is encountered in the sputtering method, namely damage by charged particles or so-called plasma damage. The thermal CVD method in which film growth mainly results from a reaction at the substrate surface gives good film coverage of unevenness or steps at the substrate surface and ready deposition within via holes. Furthermore, wire breakage at stepped regions can be avoided, and for these reasons the formation of Al by CVD has been studied. In general, the thermal CVD formation of Al film involves dispersing an organic aluminium compound in carrier gas and transporting it to a heated substrate where it pyrolyses to form a film. In an example in Journal of Electrochemical Society, Vol. 131, p. 2175 (1984) the organic aluminium gas used as triisobutyl aluminium [(i-C₄H₉)₃Al or TIBA], and the film forming reaction is carried out at 260°C and a reaction tube pressure of 65Pa (0.5 Torr) to form a film of resistivity 3.4 µohm.cm. JP-A-63-33569 discloses a film forming method using instead of TiCl₄ an organic aluminium compound such as TIBA and heating it in the vicinity of the substrate. This method enables Al to be deposited selectively only on metallic or semiconductor surfaces from which the naturally oxidised film has been removed. It is clearly stated that a step of removing the naturally oxidised film on the substrate surface is required before the TIBA is introduced. The method can be carried out without carrier gas so that TIBA can be used alone, but argon gas can be used as the carrier gas. There is no disclosure of reacting TIBA with another gas such as H₂, and there is no disclosure of using H₂ as a carrier gas. Trimethyl aluminium (TMA) and triethyl aluminium (TEA) are disclosed, but there is no specific description of other organometallic compounds. Small variations in the organic substituent attached to the metallic element may give rise to great variations in the chemical properties of the organometallic compound, and it is necessary to carry out detailed experiments on individual compounds to determine what organometallic compounds should be used. The above described CVD method has a number of disadvantages. The natural oxidised film has to be removed and a smooth surface cannot be produced. There is the further limitation that heating of the gas is required and that this has to be done in the vicinity of the substrate. It has to be determined by experiment at what proximity to the substrate heating has to be carried out, so that there is the further problem that the position of the heater cannot be chosen freely. The formation of Al according to the double wall CVD method, which may be regarded as a modification of that disclosed in JP-A-63-33569, is disclosed in the pre-text of the 2nd Symposium of the Electrochemical Society, Japanese Branch, 7 July 1989 at page 75. In this method TIBA is used, the device is designed so that the temperature of the TIBA gas can exceed the substrate temperature, and Al can be grown selectively on a metal or semiconductor. However, it is difficult to control the difference between the gas temperature and the substrate surface temperature, and there is the drawback that the bomb and the pipeline must be heated. The further problems arise that a continuous uniform film is not formed, that the flatness of the film is poor, and unless a film of appreciable thickness is grown, the selectivity of the aluminium growth cannot be maintained. In summary, the above described methods are not good at producing selective aluminium growth and even where it is obtained there are problems concerning the flatness resistance and purity of the aluminium film formed. The above methods also suffer from the problem that they are complicated and difficult to control. The invention provides a method for the deposition of a film composed wholly or mainly of aluminium and having the features set out in claim 1. Embodiments of the above method can be used to produce a deposited Al film (hereinafter defined to include pure Al and metal composed mainly of Al) of good quality and with good selectivity or controllability at an intended position. The resulting Al film has a broad range of possible uses and its formation does not require a complicated and expensive film formation device. Embodiments of the process can be used to make film having excellent surface characteristics, electrical characteristics and purity. Embodiments of the invention will now be described by way of example with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view for illustration of a suitable deposited film forming device in practising the deposited film forming process according to the process of the present invention. Fig. 2 is a schematic view for illustration of another suitable deposited film forming device in practising the deposited film forming process according to the present invention. Figs. 3A - 3E are schematic sectional views for illustration of the deposited film forming process according to one embodiment of the present invention. Fig. 4 is a chart showing the X-ray diffraction pattern of the Si (111) substrate having the Al film obtained according to the deposited film forming process of the present invention. Figs. 5A and 5B are charts showing the X-ray diffraction pattern of the Al film on the Si (111) substrate obtained according to the deposited film forming process of the present invention. Fig. 6 is a chart showing the X-ray diffraction pattern on the Si (100) substrate having the Al film obtained according to the deposited film forming process of the present invention. Fig. 7 is a schematic view for illustration of the scanning µ-RHEED method. Fig. 8 is a schematic view for illustration of the scanning µ-RHEED method. Fig. 9 is a chart showing another example of the X-ray diffraction pattern of the substrate having the Al film obtained according to the selective deposited film forming process of the present invention. Figs. 10A - 10C are schematic views showing ar example of the scanning secondary electron image and the scanning µ-RHEED image of the substrate having the Al film obtained according to the selective deposited film forming process of the present invention. Fig. 11 is a chart showing another example of the X-ray diffraction pattern of the substrate having the Al film obtained by the selective deposited film forming process of the present invention. Figs. 12A - 12C are schematic views of another example of the scanning secondary electron image and the scanning µ-RHEED image of the substrate having the Al film obtained according to the selective deposited film forming process of the present invention. Figs. 13A - 13D are illustrations for explaining the mechanism of Al deposition according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments according to the present invention are described in detail below, but the present invention is not limited by these embodiments, and it may have a constitution which accomplishes the object of the present invention. One preferred embodiment of the present invention is a process for forming a deposited film comprising the steps of: (a) providing a substrate having an electron donative surface (A) in a space for formation of the deposited film; (b) introducing a gas of an alkyl aluminum hydride and hydrogen gas into the space for formation of the deposited film; and (c) maintaining the temperature of the electron donative surface (A) within the range of from the decomposition temperature of the alkyl aluminum hydride to 450 °C to form an aluminum film on the electron donative surface (A). Further, another preferred embodiment of the present invention is a process for forming a deposited film comprising the steps of: (a) providing a substrate having an electron donative surface (A) and a electron non-donative surface (B) in a space for formation of the deposited film; (b) introducing a gas of an alkyl aluminum hydride and hydrogen gas into the space for formation of the deposited film; and (c) maintaining the temperature of the electron donative surface (A) within the range of from the decomposition temperature of the alkyl aluminum hydride to 450 °C to form an aluminum film selectively on the electron donative surface (A). In the following, prior to detailed description, first, the process for forming a deposited film by use of an organic metal is outlined. The decomposition reaction of an organic metal, and hence the thin film deposition reaction will vary greatly depending on the kind of the metal atom, the kind of the alkyl bonded to the metal atom, the means of causing the decomposition reaction to occur, the atmospheric gas, etc. For example, in the case of M-R₃ (M: the group III metal, R: alkyl group), trimethyl gallium: in thermal decomposition undergoes radical cleavage wherein Ga-CH₃ bond is cleaved, while triethyl gallium: in thermal decomposition is decomposed through β-elimination into: and C₂H₄. On the other hand, triethyl aluminum attached with the same ethyl group: in thermal decomposition undergoes radical decomposition in which Al-C₂H₅ is cleaved. However,tri-iso-butyl aluminum having iC₄H₉ bonded therein: is subject to β-elimination. Trimethyl aluminum (TMA) comprising CH₃ groups and Al has a dimer structure at room temperature: and thermal decomposition is radical decomposition in which Al-CH₃ group is cleaved, and at a temperature of 150 °C or lower, it reacts with atmospheric H₂ to form CH₄, and forms finally Al. However, at a high temperature of 300 °C or higher, even if H₂ may be present in the atmosphere, CH₃ group will withdraw H from the TMA molecule, until finally Al-C compound is formed. Also, in the case of TMA, in light or a certain region controlled in electric power in H₂ atmosphere high frequency (ca. 13.56 MHz) plasma, C₂H₆ will be formed by the bridging CH₃ between two Al's. In essence, since even an organic metal comprising CH₃ group which the simplest alkyl group, C2H5 group or iC4H9 group and Al or Ga has a reaction mode depending on the kind of the alkyl group, the kind of the metal atom, the excitation decomposition means, for deposition of a metal atom from an organic metal on a desired substrate, the decomposition reaction must be strictly controlled. For example, when Al is to be deposited from triisobutyl aluminum: in the low pressure CVD method comprising mainly thermal reaction, unevenness of µm order is formed on the surface, whereby the surface morphology is inferior. Also, hillock generation by heat treatment, Si surface roughening through Si diffusion at the interface between Al and Si occur, and also migration resistance is inferior, whereby it can be utilized for ultra-LSI process with difficulty. For this reason, a method for controlling precisely both the gas temperature and the substrate temperature has been attempted. However, the device is complicated, and the method is of the sheet treatment type in which deposition can be effected only on one wafer by one deposition process. Besides, since the deposition speed is 500 Å/min. (10Å ≙1nm) at the highest, the throughput necessary for bulk production cannot be realized. Similarly, when TMA is employed, Al deposition has been attempted by use of plasma or light, the device also becomes complicated due to use of plasma or light, and also because of the sheet type device, there remains room for improvement for sufficient improvement of throughput. Dimethyl aluminum hydride (DMAH) as the alkyl aluminum hydride to be utilized in the present invention is a substance known as alkyl metal, but it could not be estimated at all what Al thin film could be deposited depending on what reaction mode, unless deposited films are formed under all the conditions. For example, in an example of deposition Al by optical CVD from DMAH, the surface morphology is inferior, and the resistivity value was greater than the bulk value (2.7 µohm·cm) as several µohm to 10 µohm·cm, thus being inferior in film quality. Now, referring to the drawings, preferred embodiments of the present invention are described in more detail. In the present invention, for depositing selectively an Al film of good quality as the electroconductive deposition film on a substrate, the CVD method is used. More specifically, by use of dimethyl aluminum hydride (DMAH): as alkyl aluminum hydride which is an organic metal or monomethyl aluminum hydride (MMAH₂): as alkyl aluminum hydride as the starting gas containing at least one atom which becomes the constituent of the deposited film, and H₂ as the reaction gas, an Al film is formed by gas phase growth with a gas mixture of these on a substrate. As the substrate applicable in the present invention, a material having an electron donative surface may be employed. The electron donative material is described in detail below. The 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 thin film, the chemical reaction can occur between the substrate and the attached starting molecules. Specifically, there may be included semiconductors such as monocrystalline 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-IV compound semiconducters, or metals themselves such as tungsten, molybdenum, tantalum, aluminum, 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 aluminum silicon, aluminum titanium, aluminum copper, aluminum tantalum, aluminum silicon copper, aluminum silicon titanium, aluminum palladium, titanium nitride, etc. On the substrate with such constitution, Al is deposited only through simple thermal reaction in the reaction system of the starting gas and H₂. For example, the thermal reaction in the reaction system between DMAH and H₂ may be basically considered as follows: DMAH assumes a dimer structure at room temperature. Also, with MMAH₂, a high quality Al film could be formed by thermal reaction as shown below in Examples. Since MMAH₂ has low vapor pressure as 1,33-13Pa(0.01 to 0.1 Torr) at room temperature, a large amount of the starting material can be transported with difficulty, and the upper limit value of the deposition speed is several hundred Å/min. in the present embodiment, and preferably, it is most desirable to use DMAH of which vapor pressure is 1 Torr at room temperature. In another embodiment of the present invention, the CVD method is used for selective deposition of a good Al film as the electroconductive deposition film on the substrate. More specifically, as described above, by use of dimethyl aluminum hydride (DMAH) or monomethyl aluminum hydride (MMAH₂) and H₂ as the reaction gas, an Al film is selectively formed on the substrate by gas phase growth with a gas mixture of these. The substrate applicable in the present invention has a first substrate surface material for formation of the surface on which Al is deposited, and a second substrate surface material on which no Al is deposited. And, as the first substrate surface material, a material having the electron donative surface is used. In contrast, as the material for forming the surface on which Al is not deposited selectively, namely the material for forming the electron non-donative surface, 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. Fig. 1 is a schematic view showing a preferable deposition film forming device for applying the present invention. Here, 1 is a substrate for forming an Al 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 to Fig. 1. As the material constituting the reaction tube 2, quartz is preferable, but it may be also made of a metal. In this case, 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 and the reaction gas are mixed, and the mixture is fed into the reaciton 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 liquid at room temperature, and is formed into saturated vapor by passing a carrier gas through the liquid of the organic metal within the gasifier 6, which is in turn introduced into the mixer 5. The evacuation 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 starting gas gasifier 6 which is the gas formation chamber for forming the starting gas, the liquid DMAH maintained at room temperature is bubbled with H₂ or Ar (or other inert gas) as the carrier gas to form gaseous DMAH, 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. In the case of forming a film by this device, the starting gas may be of course MMAH₂, but DMAH with a vapor pressure enough to become 133Pa(1 Torr) at room temperature is the most preferred. Also, DMAH and MMAH₂ may be used in a mixture. The deposited film formed at a substrate temperature of 160 °C to 450 °C by use of such starting gas and reaction gas, with a thickness of for example 400 Å, has a resistivity at room temperature of 2.7 - 3.0 µohm·cm which is substantially equal to Al bulk resistivity, and is a continuous and flat film. At this time, the pressure during film formation can be chosen within the range from 0.13 Pa to 101 KPa (10⁻³ Torr to 760 Torr). Also, even when the film thickness may be 1 µm, its resistivity is ca. 2.7 - 3.0 µohm·cm, and a sufficiently dense film can be formed also with a relatively thicker film. Also, the reflectance in the visible light wavelength region is approximately 80 %, whereby a thin film excellent in surface flatness can be deposited. The substrate temperature is desirably the decomposition temperature of the starting gas containing Al or higher, and 450 °C or lower as described above, but specifically the substrate temperature of 200 to 450 °C is more desirable, and when deposition is carried out under this condition, by making the DMAH partial pressure 0.013-0.13 Pa (10⁻⁴ to 10⁻³ Torr), the deposition speed becomes very great as 100 Å/min. to 800 Å/min., whereby sufficient great deposition speed corresponding to the cost as the Al deposition technique for ultra-LSI can be obtained. A more preferable substrate temperature condition is 270 °C to 350 °C, and the Al film deposited under this condition is also strongly orientatable and, even when subjected to the heat treatment at 450 °C for 1 hour, the Al film on the Si monocrystalline or Si polycrystalline substrate becomes a good Al film without generation of hillock, spike as seen in the film forming method of the prior art. Also, such Al film is excellent in electro-migration resistance. In the device shown in Fig. 1, Al can be deposited on only one sheet of substrate in deposition for one time. Although a deposition speed of ca. 800 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 device for improving this point, there is the low pressure CVD device which can deposit Al by simultaneous mounting of a large number of sheets of wafer. Since the Al film formation according to the present embodiment utilizes the surface reaction on the electron donative substrate surface, in the hot wall type low pressure CVD method wherein only the substrate is heated, Al can be deposited on the substrate by use of DMAH and H₂. The reaction tube pressure may be 6.65 Pa-101 KPa(0.05 to 760 Torr), desirably 13-106 Pa (0.1 to 0.8 Torr), the substrate temperature 160 °C to 450 °C, desirably 200 °C to 400 °C, the DMAH partial pressure 1 x 10⁻⁵-fold to 1.3 x 10⁻³-fold of the pressure in the reaction tube, and under such conditions, Al can be well deposited on the electron donative substrate. Fig. 2 is a schematic illustration showing a deposited film forming device to which such present invention is applicable. 57 is a substrate for formation of Al film. 50 is an outside reaction tube made of quartz for forming a space for formation of deposited film substantially closed to the surrounding, 51 an innerside reaction tube made of quartz located for separating the flow of gas within the outside reaction tube 50, 54 a flange made of a metal for opening and closing of the opening of the outside reaction tube 50, and the substrate 57 is located within the substrate holding member 56 provided internally of the innerside reaction tube 51. The substrate holding member 56 should be preferably made of quartz. Also, in the present device, the substrate temperature can be controlled by the heater portion 59. The pressure internally of the reaction tube 50 is constituted so as to be controllable by the evacuation system connected through the gas evacuation outlet 53. The gas feeding system is constituted to have a first gas system, a second gas system and a mixer (none are shown) similarly as the device shown by the symbols 5 and 6 in Fig. 1, and the starting gas and the reaction gas are introduced into the reaction tube 50 through the starting gas inlet 52. These gases react on the surface of the substrate 57 during passage internally of the innerside reaction tube 51 as shown by the arrowhead 58 in Fig. 2 to deposit Al on the substrate surface. The gases after the reaction pass through the gap formed between the innerside reaction tube 51 and the outside reaction tube 50, and evacuated through the gas evacuation outlet 53. In taking out and in the substrate, the flange 54 made of a metal is permitted to fall by an elevator (not shown) together with the substrate holding member 56 and the substrate 57 to be moved to a predetermined position where the substrate is mounted and detached. By forming a deposited film under the conditions as described above by use of such device, Al films of good quality can be formed in all the wafers within the device. As described above, the film obtained according to the Al film formation process based on the embodiment of the present invention is dense with little content of impurity such as carbon, etc. and resistivity which is similar to bulk, and also has high surface smoothness, and therefore remarkable effects as described below can be obtained. (1) Reduction of hillock Hillock is occurrence of concavities on the Al surface due to partial migration of Al when inner stress during film formation is released in the heat treatment step. Also, similar phenomenon occurs by local migration by current passage. The Al film formed by the present invention has little inner stress and is under the state of monocrystal or approximate to that. For this reason, in the heat treatment at 450 °C for one hour, as contrasted to formation of 10⁴ - 10⁶/cm² of hillocks in the Al film of the prior art, the hillock number could be greatly improved as 0 to 10/cm². Thus, due to substantial absence of Al surface concavity, the resist film thickness and the interlayer insulating film can be made thin to be advantageous for making it finer and more flat. (2) Improvement of electro-migration resistance Electro-migration is the phenomenon that the wiring atoms move by passage of a current of high density. By this phenomenon, voids are generated and grown along the grain boundary, whereby as accompanied with reduction of the cross-sectional area, the wiring generates heat to be broken. Migration resistance is generally evaluated by average wiring life. The wiring formed by the sputtering method or the CVD method of the prior art has obtained an average wiring life of 1 x 10² to 10³ hours (in the case of a wiring cross-sectional area of 1 µm²) under the current passage test conditions of 250 °C, 1 x 10⁶ A/cm². In contrast, the Al film obtained by the Al film formation method based on the embodiment of the present invention could obtain an average wiring life of 10³ to 10⁴ hours with a wiring having a cross-sectional area of 1 µm². Hence, according to the present invention, for example, when the wiring width is 0.8 µm, a wiring layer thickness of 0.3 µm can sufficiently stand practical application. That is, since the wiring layer thickness can be made thinner, unevenness on the semiconductor surface after arrangement of wiring can be suppressed minimum, and also high reliability in passing ordinary current can be obtained. Also, this is possible by a very simple process. (3) Improvement of surface smoothness (patterning characteristic improvement of wiring) In the prior art, roughness of the surface of a metal thin film had inconvenience in the alignment step for the mask and the substrate in the patterning step and in the etching step. That is, there is unevenness extending to several µm on the surface of Al film according to the prior art method, whereby the surface morphology is poor, and therefore had the following disadvantages. 1) Alignment signals cause diffused reflection to occur at the surface, whereby noise level becomes higher and inherent alignment signals cannot be discriminated. 2) For covering large surface unevenness, the resist film thickness must be taken large, which is opposite to fine formation. 3) If the surface morphology is poor, halation due to the resist internal reflection will occur locally, whereby resist remaining occurs. 4) If the surface morphology is poor, the side wall becomes notched in the wiring etching step according to its unevenness. According to the present invention, the surface morphology of Al film to be formed is markedly improved to cancell all the drawbacks described above. (4) Improvement of resistance in contact hole and through hole and of contact resistance In the prior art method, if the size of the contact hole becomes finer as 1 µm x 1 µm or less, Si in the wiring is precipitated on the substrate of the contact hole during heat treatment in the wiring step to cover thereover, whereby resistance between the wiring and the element becomes markedly larger. According to the embodiment of the present invention, since a dense film is formed according to the surface reaction, Al has been confirmed to have a resistivity of 2.7 - 3.3 µohm cm. Also, the contact resistivity can attain 1 x 10⁻⁶ ohm·cm² at an area of 0.6 µm x 0.6 µm when the Si portion has an impurity of 10²⁰ cm⁻³. That is, according to the present invention, a good contact with the substrate can be obtained. In other words, in the patterning step, at the line width of the resolving power limit of the exposure machine, the alignment precision 3σ=0.15 µm can be accomplished, whereby wiring having smooth side plane is rendered possible without causing halation to occur. (5) It becomes possible to make heat treatment during wiring step lower or abolish the heat treatment step. As described in detail above, by applying the present invention to the wiring formation method of a semiconductor integrated circuit, the yield can be improved, and reduction of cost can be promoted to great extent as compared with Al wiring of the prior art. Figs. 3A - 3E show how the Al film according to the present invention is selectively grown. Fig. 3A is an illustration showing schematically the cross-section of the substrate before formation of the Al 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. In the case of using DMAH as the starting gas, when a gas mixture containing H₂ as the reaction gas is fed onto the substrate 1 heated within a temperature range from the decomposition temperature of DMAH to 450 °C, Al is precipitated on the substrate 90, whereby a continuous film of Al is formed as shown in Fig. 3B. Here, the pressure within the reaction tube 2 should be desirably 0.13 Pa-101 KPa(10⁻³ to 760 Torr), and the DMAH partial pressure preferably 1.5 x 10⁻⁵ to 1.3 x 10⁻³-fold of the pressure within the above reaction tube. When deposition of Al is continued under the above conditions, via the state of Fig. 3C, the Al film grows to the level of the uppermost portion of the thin film 91 as shown in Fig. 3D. Further, when grown under the same conditions, as shown in Fig. 3E, the Al film can grow to 5000 Å substantially without growth in the lateral direction. This is the most characteristic point of the deposited film obtained by the present invention, and it will be understood how a film of good quality can be formed under good selectivity. 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 recognized in this film. The deposited film thus formed has a resistivity of, for example, with a film thickness of 400 Å, 2.7 - 3.0 µohm·cm at room temperature which is substantially equal to the bulk resistivity of Al, and becomes continuous and flat film. Also, even with a film thickness of 1 µm, its resistance at room temperature is approximately 2.7 - 3.0 µohm·cm and a sufficiently dense film is formed with a relatively thicker film. The reflectance in the visible wavelength region is approximately 80 %, and a thin film with excellent surface flatness can be deposited. The substrate temperature in performing such selective deposition should be desirably the decomposition temperature of the starting gas containing Al or higher and 450 °C or lower as mentioned above, but specifically a substrate temperature of 200 to 450 °C is desirable, and when deposition is performed under such condition, the deposition speed is sufficiently great as 100 Å/min. to 800 Å/min. when DMAH partial pressure is 0.013-0.13 Pa (10⁻⁴ to 10⁻³ Torr). Thus a sufficiently great deposition speed can be obtained as the Al deposition technique for ultra-LSI. A more preferable substrate temperature condition is 270 °C to 350 °C, and the Al film deposited under this condition is also strongly orientatable and, even when subjected to the heat treatment at 450 °C for 1 hour, the Al film on the Si monocrystalline or Si polycrystalline substrate becomes a good Al film without generation of hillock, spike. Also, such Al film is excellent in electro-migration resistance. Similarly in the case of selective deposition, in the device shown in Fig. 1, Al can be deposited on only one sheet of substrate in deposition for one time. Although a deposition speed of ca. 800 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 device for improving this point, there is the low pressure CVD device which can deposit Al by simultaneous mounting of a large number of sheets of wafer. Since the Al film formation according to the present embodiment utilizes the surface reaction of the electron donative substrate surface, in the hot wall type low pressure CVD method wherein only the substrate is heated, Al can be deposited on the substrate by use of DMAH and H₂. The reaction tube pressure may be 6,65 Pa to 101 KPa(0.05 to 760 Torr), desirably 13.3-106Pa (0.1 to 0.8 Torr), the substrate temperature 160 °C to 450 °C, desirably 200 °C to 400 °C, the DMAH partial pressure 1 x 10⁻⁵-fold to 1.3 x 10⁻³-fold of the pressure in the reaction tube, and under such conditions, Al can be selectively deposited on only the electron donative substrate. The deposited film forming device to which such present invention is applicable is the same as in Fig. 2 as described above, and therefore its detailed description is omitted here. By forming a deposited film under the conditions as described above by use of such device, Al films of good quality can be formed selectively and simultaneously in all the wafers within the device. As described above, the film obtained according to the Al film selective formation process based on the embodiment of the present invention is dense with very little content of impurity such as carbon, etc. and resistivity which is similar to bulk, and also has high surface smoothness, and therefore remarkable effects as described below can be obtained. (1) Reduction of hillock The Al film formed according to the present invention has little internal stress and is under the state of monocrystal or approximate to that. For this reason, in the heat treatment at 450 °C for one hour, as contrasted to formation of 10⁴ - 10⁶/cm² of hillrocks in the Al film of the prior art, the hillrock number could be greatly improved as 0 to 10/cm². (2) Improvement of electro-migration resistance The wiring formed by the method of the prior art has obtained an average wiring life of 1 x 10² to 10³ hours (in the case of a wiring cross-sectional area of 1 µm²) under the current passage test conditions of 250 °C, 1 x 10⁶ A/cm². In contrast, the Al film obtained by the Al film selective formation method based on the embodiment of the present invention could obtain an average wiring life of 10³ to 10⁴ hours with a wiring having a cross-sectional area of 1 µm². (3) Reduction of alloy pit in contact portion The Al selectively formed according to the present invention can suppress generation of alloy pit at the contact portion with the substrate crystal even by the heat treatment during wiring step, and also a wiring with good contact characteristic can be obtained. That is, even when the junction is made shallow to the extent of 0.1 µm, the junction will not be destroyed with only the Al material. (4) Improvement of surface smoothness (patterning characteristic improvement of wiring) According to the present invention, the surface morphology of the Al film to be formed can be improved epoch-makingly, whereby all of the problems of the prior art can be improved. That is, in the patterning step, at the line width of the resolving power limit of the exposure machine, the alignment precision 3σ=0.15 µm can be accomplished, whereby wiring having smooth side plane is rendered possible without causing halation to occur. (5) Improvement of resistance in contact hole and through hole and contact resistance According to the present invention, since a dense film is selectively formed by the surface reaction even when the opening may be 1 µm x 1 µm or less, it has been confirmed that the Al completely filled within the contact hole and through hole each has a resistivity of 2.7 - 3.3 µohm·cm. Also, the contact resistivity can attain 1 x 10⁻⁶ ohm·cm² in the case where the Si portion has an impurity of 10²⁰cm⁻³ in a hole of 0.6 µm x 0.6 µm. That is, according to the present invention, the wiring material can be completely embedded only in the minute opening, and also good contact with the substrate can be obtained. Therefore, the present invention can contribute greatly to improvement of resistance within hole and contact resistance which have been the greatest problems in the fine process of 1 µm or less. (6) It is possible to make the heat treatment temperature during wiring step lower or to omit the heat treatment step. As described in detail above, by applying the present invention to the wiring formation method of a semiconductor integrated circuit, particularly embedding of contact hole or through hole, the yield can be improved, and reduction of cost can be promoted to great extent as compared with Al wiring of the prior art. In the accompanying Examples, pressure in Torr can be converted to Pascals using the relationship 1 Torr = 133 Pa. Example 1 First, the procedure for Al film formation is as follows. By use of the device shown in Fig. 1, the reaction tube 2 is internally evacuated to ca. 1 x 10⁻⁸ Torr by the evacuation unit 9. However, Al film can be also formed if the vacuum degree within the reaction tube 2 may be higher than 1 x 10⁻⁸ Torr. After washing of Si wafer, the conveying chamber 10 is released to atmospheric pressure and Si wafer is mounted in the conveying chamber. The conveying chamber is evacuated to ca. 1 x 10⁻⁶ Torr, and then the gate valve 13 is opened and the wafer is mounted on the wafer holder 3. After mounting of the wafer on the wafer holder 3, the gate valve 13 is closed, and the reaction chamber 2 is evacuated to a vacuum degree of ca. 1 x 10⁻⁸ Torr. In this Example, DMAH is fed through the first gas line. As the carrier gas of DMAH line H₂ which is the same as the reaction gas is employed. The second gas line is used for H₂. By passing H₂ through the second gas line, the pressure within the reaction tube 2 is made a predetermined value by controlling the opening of the slow leak valve 8. A typical pressure in this Example is made approximately 1.5 Torr. Then, the wafer is heated by current passage through the heater 4. After the wafer temperature has reached a predetermined temperature, DMAH is introduced into the reaction tube through the DMAH line. The whole pressure is ca. 1.5 Torr, and the DMAH partial pressure is made ca. 1.5 x 10⁻⁴ Torr. When DMAH is introduced into the reaction tube 2, Al is deposited. After a predetermined deposition time has elapsed, feeding of DMAH is stopped. Next, heating of the heater 4 is stopped to cool the wafer. Feeding of H₂ gas is stopped, and after evacuation internally of the reaction tube, the wafer is transferred to the conveying chamber, and only the conveying chamber is made atmospheric pressure before taking out the wafer. The outline of Al film formation is as described above. Experimental example 1 Next, preparation of samples according to this Example 1 is described. 130 Sheets of samples of monocrystalline Si substrates (N type, 1 - 2 ohm·cm) were prepared, the substrate temperatures were set at 13 levels, and Al films were deposited at the respective temperatures each for 10 sheets according to the procedure as described above under the following conditions: whole pressure: 1.5 Torr DMAH partial pressure: 1.5 x 10⁻⁴ Torr. The Al films deposited by varying the substrate temperature at 13 levels were evaluated by use of various evaluation methods. The results are shown in Table 1. Shortly speaking, Al films of very good quality were obtained at a temperature range of 160 °C to 450 °C, more preferably 200 °C to 400 °C, optimally 270 °C to 350 °C. Example 2 First, the procedure of Al film formation is as follows. By the evacuation unit 9, the reaction tube 2 is evacuated internally to ca. 1 x 10⁻⁸ Torr. Al film can be formed even if the vacuum degree in the reaction tube 2 may be higher than 1 x 10⁻⁸ Torr. After washing of the Si wafer, the conveying chamber 10 is released to atmospheric pressure and the Si wafer is mounted in the conveying chamber. The conveying chamber is evacuated to ca. 1 x 10⁻⁶ Torr, then the gate valve 13 is opened and the wafer is mounted on the wafer holder 3. After mounting of the wafer holder 3, the gate valve 13 is closed, and the reaction chamber 2 is evacuated to a vacuum degree of ca. 1 x 10⁻⁸ Torr. In this Example, the first gas line is used for DMAH. As the carrier gas for the DMAH line, Ar is employed. The second gas line is used for H₂. By passing H₂ through the second gas line, the pressure within the reaction tube 2 is made a predetermined value by controlling the opening of the slow leak valve 8. A typical pressure in this Example is made approximately 1.5 Torr. Then, the wafer is heated by current passage through the heater 4. After the wafer temperature has reached a predetermined temperature, DMAH is introduced into the reaction tube through the DMAH line. The whole pressure is ca. 1.5 Torr, and the DMAH partial pressure is made ca. 1.5 x 10⁻⁴ Torr. When DMAH is introduced into the reaction tube 2, Al is deposited. After a predetermined deposition time has elapsed, feeding of DMAH is stopped. Next, heating of the heater 4 is stopped to cool the wafer. Feeding of H₂ gas is stopped, and after evacuation internally of the reaction tube, the wafer is transferred to the conveying chamber, and only the conveying chamber is made atmospheric pressure before taking out the wafer. The outline of Al film formation is as described above. Experimental example 2 Al films were formed according to the method of Example 2. For the films obtained, concerning resistivity, carbon content, average wiring life, deposition speed, hillock density, generation of spike and reflectance, the same results as in Example 1 were obtained. Example 3 This Example 3 performs deposition according to the same procedure by use of MMAH₂ as the starting gas by setting the conditions as follows: whole pressure: 1.5 Torr MMAH₂ partial pressure: 5 x 10⁻⁴ Torr. Experimental example 3 According to the method of the above Example 3, films were formed by varying the substrate temperature within a temperature range from 160 °C to 400 °C. As the result, Al thin films excellent in flatness, denseness containing no carbon impurity were deposited similarly as in Experimental example 1. Example 4 This Example 4 is film formation according to the low pressure CVD method. Experimental example 4 A monocrystalline silicon substrate was placed in the low pressure CVD device shown in Fig. 2, and Al film was formed within the same badge. The film formation conditions were made a reaction tube pressure of 0.3 Torr, a DMAH partial pressure of 3.0 x 10⁻⁵ Torr, a substrate temperature of 300 °C, and a film formation time of 10 minutes. As the result of film formation under such conditions, an Al film of 7000 Å was deposited. The film quality was very good, exhibiting the same properties as one prepared at a substrate temperature of 300 °C shown in Experimental example 1. Experimental example 5 Samples having Al films formed according to the same method as in Example 1 were prepared. When crystallinity of the Al film deposited on the Si wafer of the respective samples, namely under the same film forming conditions as in Example 1 by use of the X-ray diffraction method and the reflective electron beam diffraction method, it was found to be a monocrystalline Al. First, the evaluation methods are described. When the crystal direction of the Si substrate is (111) plane, from X-ray diffraction, as shown in Fig. 4, only the diffraction peak showing Al (100) was observed concerning Al. In reflective high speed electron beam diffraction by use of an acceleration voltage of 80 kV or 100 kV, as shown in Fig. 5, a monocrystal spot showing Al (100) was observed. Fig. 5A is a diffraction pattern when electron beam is permitted to enter Al (100) in the [001] direction, Fig. 5B a diffraction pattern when electron beam is permitted to enter Al (100) in the direction of [011]. Thus, the Al film on the Si (111) substrate was found to be a monocrystal having (100) plane. Within the substrate temperature range in Table 1, particularly those deposited at a range from 250 °C to 330 °C were found to have Al films deposited which were stably monocrystalline. Also, the Al films deposited on the Si (111) substrate with the substrate surface having off-angles differing by 1°, 2°, 3°, 4°, 5° from the Si (111) plane were also found to have Al (100) monocrystals deposited stably, particularly under the temperature conditions of the substrate temperature ranging from 250 °C to 330 °C, similarly as in the case when deposited on the Si (111) substrate as described above. When the crystal direction of the Si substrate is (100) plane, from X-ray diffraction, as shown in Fig. 6, only the diffraction peak showing Al (111) was observed concerning Al. In reflective high speed electron beam diffraction by use of an acceleration voltage of 80 kV or 100 kV, a monocrystal spot showing Al (111) was observed. Thus, the Al film on the Si (100) substrate was found to be a monocrystal having (111) plane. Within the substrate temperature range in Table 1, particularly those deposited at a range from 250 °C to 330 °C were found to have Al films deposited which were stably monocrystalline. Also, the Al films deposited on the Si (100) substrate with the substrate surface having off-angles differing by 1°, 2°, 3°, 4°, 5° from the Si (100) plane were also found to have Al (111) monocrystals deposited stably, particularly under the temperature conditions of the substrate temperature ranging from 250 °C to 330 °C, similarly as in the case when deposited on the Si (111) substrate as described above. Experimental example 6 Crystallinities of the Al films formed according to the method of Example 2 were evaluated. Similarly as in the case of Example 5, particularly within the range of the substrate temperature from 250 °C to 330 °C, Al (100) monocrystal was formed on the Si (111) substrate, and Al (111) monocrystal on the Si (100) substrate. Experimental example 7 Al films were formed on Si substrate according to the method of Example 3. As the result of evaluation of crystallinities of the Al films by the X-ray diffraction method and the reflective high speed electron beam diffraction method, the following results were obtained. When the crystal direction of the Si substrate surface is (111) plane, from X-ray diffraction, as shown in Fig. 4, only the diffraction peak showing Al (100) was observed concerning Al. In reflective high speed electron beam diffraction by use of an acceleration voltage of 80 kV or 100 kV, as shown in Fig. 5, a monocrystal spot showing Al (100) was observed. Thus, the Al film on the Si (111) substrate was found to be a monocrystal having (100) plane. Also, the Al films deposited on the Si (111) substrate with the substrate surface having off-angles differing by 1°, 2°, 3°, 4°, 5° from the Si (111) plane were also found to have Al (100) monocrystals deposited, similarly as in the case when deposited on the Si (111) substrate as described above. When the crystal direction of the Si substrate is (100) plane, from X-ray diffraction, as shown in Fig. 6, only the diffraction peak showing Al (111) was observed concerning Al. In reflective high speed electron beam diffraction by use of an acceleration voltage of 80 kV or 100 kV, a monocrystal spot showing Al (111) was observed. Thus, the Al film on the Si (100) substrate was found to be a monocrystal having (111) plane. Also, the Al films deposited on the Si (100) substrate with the substrate surface having off-angles differing by 1°, 2°, 3°, 4°, 5° from the Si (100) plane were also found to have Al (111) monocrystals deposited, similarly as in the case when deposited on the Si (111) substrate as described above. The Examples 5 to 8 and the Experimental examples 8 to 15 are examples when forming Al films selectively. Example 5 First, the procedure of Al film formation according to this Example is as follows. By use of the device shown in Fig. 1, the reaction tube 2 is internally evacuated to ca. 1 x 10⁻⁸ Torr by the evacuation unit 9. However, Al film can be also formed even if the vacuum degree within the reaction tube 2 may be higher than 1 x 10⁻⁸ Torr. After washing of the Si wafer treated so as to effect selective deposition, the conveying chamber 10 is released to atmospheric pressure and the Si wafer is mounted in the conveying chamber. The conveying chamber is evacuated to ca. 1 x 10⁻⁶ Torr, then the gate valve 13 is opened and the wafer is mounted on the wafer holder 3. After mounting of the wafer on the wafer holder 3, the gate valve 13 is closed, and the reaction chamber 2 is evacuated to a vacuum degree of ca. 1 x 10⁻⁸ Torr. In this Example, DMAH is fed through the first gas line. As the carrier gas of DMAH line, H₂ is employed. The second gas line is used for H₂. By passing H₂ through the second gas line, the pressure within the reaction tube 2 is made a predetermined value by controlling the opening of the slow leak valve 8. A typical pressure in this Example is made approximately 1.5 Torr. Then, the wafer is heated by current passage through the heater 4. After the wafer temperature has reached a predetermined temperature, DMAH is introduced into the reaction tube through the DMAH line. The whole pressure is ca. 1.5 Torr, and the DMAH partial pressure is made ca. 1.5 x 10⁻⁴ Torr. When DMAH is introduced into the reaction tube 2, Al is deposited. After a predetermined deposition time has elapsed, feeding of DMAH is stopped. Next, heating of the heater 4 is stopped to cool the wafer. Feeding of H₂ gas is stopped, and after evacuation internally of the reaction tube, the wafer is transferred to the conveying chamber, and only the conveying chamber is made atmospheric pressure before taking out the wafer. The outline of Al film formation is as described above. Experimental example 8 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 liters/M, O₂ : 2 liters/M). The film thickness was 7000 Å + 500 Å, and the reflactive 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 photoresist, with the photoresist as the mask, the subbing SiO₂ was etched by the reactive ion etching (RIE), etc. to have the substrate Si partially exposed. Thus, 130 sheets of samples having various sizes of SiO₂ holes of 0.25 µm x 0.25 µm - 100 µm x 100 µm were prepared, the substrate temperature was set at 13 levels, and for the samples each of 10 sheets at the respective temperatures, Al films were selectively deposited following the procedure as described above under the following conditions: whole pressure: 1.5 Torr DMAH partial pressure: 1.5 x 10⁻⁴ Torr. The Al films deposited by varying the substrate temperature at 13 levels were evaluated by use of various evaluation methods. The results are shown in Table 2. In the above samples, no Al was deposited on SiO₂ at a temperature range from 160 °C to 450 °C, and Al was deposited only on the portion with opening of SiO₂ to have Si exposed. Also, when deposition was carried out in the above temperature range continuously for 2 hours, similar selective depositability was maintained. Example 6 First, the procedure of Al film formation is as follows. By the evacuation unit 9, the reaction tube 2 is evacuated internally to ca. 1 x 10⁻⁸ Torr. Al film can be formed even if the vacuum degree in the reaction tube 2 may be higher than 1 x 10⁻⁸ Torr. After washing of the Si wafer, the conveying chamber 10 is released to atmospheric pressure and the Si wafer is mounted in the conveying chamber. The conveying chamber is evacuated to ca. 1 x 10⁻⁶ Torr, then the gate valve 13 is opened and the wafer is mounted on the wafer holder 3. After mounting of the wafer on the wafer holder 3, the gate valve 13 is closed and the reaction chamber 2 is evacuated to a vacuum degree of ca. 1 x 10⁻⁸ Torr. In this Example, the first gas line is used for DMAH. As the carrier gas for the DMAH line, Ar is employed. The second gas line is used for H₂. By passing H₂ through the second gas line, the pressure within the reaction tube 2 is made a predetermined value by controlling the opening of the slow leak valve 8. A typical pressure in this Example is made approximately 1.5 Torr. Then, the wafer is heated by current passage through the heater 4. After the wafer temperature has reached a predetermined temperature, DMAH is introduced into the reaction tube through the DMAH line. The whole pressure is ca. 1.5 Torr, and the DMAH partial pressure is made ca. 1.5 x 10⁻⁴ Torr. When DMAH is introduced into the reaction tube 2, Al is deposited. After a predetermined deposition time has elapsed, feeding of DMAH is stopped. Next, heating of the heater 4 is stopped to cool the wafer. Feeding of H₂ gas is stopped, and after evacuation internally of the reaction tube, the wafer is transferred to the conveying chamber, and only the conveying chamber is made atmospheric pressure before taking out the wafer. The outline of Al film formation is as described above. Experimental example 9 Al films were formed according to the method of Example 6. For the films obtained, concerning resistivity, carbon content, average wiring life, deposition speed, hillock density, generation of spike and reflectance, the same results as in Experimental example 8 were obtained. Also, selective depositability with substrate was the same as in Experimental example 8. Example 7 This Example is selective deposition of Al according to the low pressure CVD method. Experimental example 10 By means of the low pressure CVD device shown in Fig. 2, Al films were formed on the substrates with the constitutions as described below (Samples 5-1 - 5-179) Preparation of Sample 5-1 On a monocrystalline silicon as the electron donative first substrate surface material, a thermally oxidized SiO₂ film as the electron non-donative second substrate surface material was formed, and patterning was effected according to the photolithographic steps as shown in Example 1 to have the monocrystalline surface partially exposed. The film thickness of the thermally oxidized SiO₂ film was found to be 7000 Å, with the size of the exposed portion of the monocrystalline silicon, namely opening being 3 µm x 3 µm. Thus, Sample 5-1 was prepared. (Hereinafter, such sample is expressed as "thermally oxidized SiO₂ (hereinafter abbreviated as T-SiO2)/monocrystalline silicon"). Preparation of Samples 5-2 - 5-179 Sample 5-2 is an oxidized film formed by normal pressure CVD (hereinafter abbreviated as SiO₂)/monocrystalline silicon. Sample 5-3 is a boron doped oxidized film formed by normal pressure CVD (hereinafter abbreviated as BSG)/monocrystalline silicon. Sample 5-4 is a phosphorus doped oxidized film formed by normal pressure CVD (hereinafter abbreviated as PSG)/monocrystalline silicon. Sample 5-5 is a phosphorus and boron doped oxidized film formed by normal pressure CVD (hereinafter abbreviated as BSPG)/monocrystalline silicon. Sample 5-6 is a nitrided film formed by plasma CVD (hereinafter abbreviated as P-S:N)/monocrystalline silicon. Sample 5-7 is a thermally nitrided film (hereinafter abbreviated as T-S:N)/monocrystalline silicon. Sample 5-8 is a nitrided film formed by low pressure CVD (hereinafter abbreviated as LP-S:N)/monocrystalline silicon. Sample 5-9 is a nitrided film formed by ECR device (hereinafter abbreviated as ECR-SiN)/monocrystalline silicon. Further, by combinations of the electron donative first substrate surface materials and the electron non-donative second substrate surface materials, Samples 5-11 - 5-179 shown in Table 3 were prepared. As the first substrate surface material, monocrystalline silicon (monocrystalline Si), polycrystalline silicon (polycrystalline Si), amorphous silicon (amorphous Si), tungsten (W), molybdenum (Mo), tantalum (Ta), tungsten silicide (WSi), titanium silicide (TiSi), aluminum (Al), aluminum silicon (Al-Si), titanium aluminum (Al-Ti), titanium nitride (TiN), copper (Cu), aluminum silicon copper (Al-Si-Cu), aluminum palladium (Al-Pd), titanium (Ti), molybdenum silicide (Mo-Si), tantalum silicide (Ta-Si) were employed. These samples and Al₂O₃ substrates, SiO₂ glass substrates were placed in the low pressure CVD device shown in Fig. 2, and Al films were formed within the same badge. The film forming conditions were a reaction tube pressure of 0.3 Torr, a DMAH partial pressure of 3.0 x 10⁻⁵ Torr, a substrate temperature of 300 °C and a film formation time of 10 minutes. As the result of film formation under such conditions, concerning all the samples applied with patterning from Sample 5-1 to 5-179, deposition of Al film occurred only on the electron donative first substrate surface film to embed completely the opening with the depth of 7000 Å. The film quality of the Al film was found to be very good, exhibiting the same properties as one prepared at a substrate temperature of 300 °C shown in Experimental example 8. On the other hand, on the second substrate surface which is electron non-donative, no Al film was deposited at all, whereby complete selectivity was obtained. On both the Al₂O₃ substrate and the SiO₂ glass substrate which are electron non-donative, no Al film was deposited at all. Experimental example 11 By use of the low pressure CVD device shown in Fig. 2, Al film was formed on the substrate with the constitution as described below. On a thermally oxidized film as the electron non-donative second substrate surface material, a polycrystalline Si as the electron donative first substrate surface material was formed, patterning was effected according to the photolithographic steps as shown in Example 1 to have the thermally oxidized film surface partially exposed. The film thickness of the polycrystalline silicon at this time was 2000 Å, with the size of the thermally oxidized film exposed portion, namely opening being 3 µm x 3 µm. Such sample is called 6-1. By combinations of the electron non-donative second substrate surface materials (T-SiO₂, CVD-SiO₂ , BSG, PSG, BPSG, P-SiN, T-SiN, LP-SiN, ECR-S:N) and the electron-donative first substrate surface materials (polycrystalline Si, amorphous Si, Al, W, Mo, Ta, WSi, TiSi, TaSi, Al-Si, Al-Ti, TiN, Cu, Al-Si-Cu, Al-Pd, Ti, Mo-Si), Samples of 6-1 - 6-169 shown in Table 3 were prepared. These samples were placed in the low CVD device shown in Fig. 2, and Al film was formed within the same badge. The film forming conditions were a reaction tube pressure of 0.3 Torr, a DMAH partial pressure of 3.0 x 10⁻⁵ Torr, a substrate temperature of 300 °C and a film forming time of 10 minutes. As the result of film formation under such conditions, in all the samples from 6-1 to 6-169, no Al film was deposited at all at the opening having the electron non-donative second substrate exposed, but Al of about 7000 Å was deposited only on the electron donative first substrate, whereby complete selectivity was obtained. The film quality of the Al film deposited was found to be very good, exhibiting the same properties as one prepared at a substrate temperature of 300 °C in Experimental example 1. Example 8 This Example is the method of depositing selectively Al by use of MMAH₂. Experimental example 12 When deposition was carried out according to the same procedure as shown in Example 1 by use of MMAH₂ as the starting gas and setting the conditions as follows: whole pressure: 1.5 Torr MMAH₂ partial pressure: 5 x 10⁻⁴ Torr, in the temperature range of the substrate temperature from 160 °C to 400 °C, an Al thin film containing no carbon impurity and having excellent flatness, denseness and selectivity with the substrate surface materials was deposited similarly as in Example 1. Experimental example 13 According to the same method as in Example 5, a sample having an Al film formed thereon was prepared. The crystallinity of the Al film selectively deposited on Si at the same substrate temperature as in Table 1 was evaluated by the X-ray diffraction method and the scanning µ-RHEED microscope. The scanning µ-RHEED microscope is the method disclosed in Extended Abstracts of the 21th Conference on Solid State Devices and Materials (1989) p.217 and Japanese Journal of Applied Physics vol. 28, No. 11 (1989), L2075. According to the RHEED (Reflection High Energy Electron Diffraction) method of prior art, electron beam was permitted to be incident on the sample surface at a shallow angle of 2 - 3°, and the crystallinity of the sample surface was evaluated from the diffraction pattern formed by the diffracted electron beam. However, since the electron beam diameter is large as 100 µm to several hundred µm, only average information on the sample surface could be obtained. In the µ-RHEED microscope, an electron beam diffraction pattern from a specific fine region on the sample surface can be observed by narrowing the electron beam diameter of 0.1 µm. Also, by scanning the electron beam two-dimensionally on the sample surface, by use of any desired diffraction spot intensity change on the diffraction pattern as the image signal, two dimensional image (scanning µ-RHEED image) on the sample surface can be obtained. At this time by observation of the scanning µ-RHEED image by use of different diffraction spots A and C on the diffraction pattern as shown in Fig. 7, even if the lattice planes in parallel to the sample surface may be aligned in (100), the crystal grain boundaries rotating within the plane can be visualized as distinguished from each other. Here, the diffraction spot A is a diffraction spot on the line (line 1) where the plane in which the diffraction pattern occurs and the sagittal plane formed by the incident electron beam are crossed at right angle, while the diffraction spot C is a diffraction spot not on the line 1. As shown in Fig. 8, when the lattice plane in parallel to the sample surface is, for example, (100), but crystal grains x and y are rotating mutually within the plane, in the scanning µ-RHEED image by use of the diffraction spot A, both crystal grains x and y are displayed as the region with strong intensity. On the other hand, in the scanning u-RHEED image by use of the diffraction spot C, only the crystal grain x is displayed as the region with strong intensity. Therefore, by observation of the scanning µ-RHEED image by use of the diffraction spots A and C as shown in Fig. 7, it can be discriminated whether the crystal in the region observed is a polycrystal including interplanar rotation or a monocrystal. In Extended Abstracts of the 21th Conference on Solid State Devices and Materials (1989) p.217 and Japanese Journal of Applied Physics vol. 28, No. 11 (1989) L2075, concerning Cu thin film, it has been clarified that, for example, even if the lattice plane in parallel to the sample surface may be {100}, there exists a crystal grain including interplanar rotation in the {100} crystal grains. First, the Al film deposited selectively on the Si exposed surface at the substrate temperature in Table 1 was evaluated. When the crystal direction on the Si substrate surface is (111) plane, from X-ray diffraction, concerning Al, as shown in Fig. 9, only the diffraction peak showing Al (100) could be observed. Next, crystallinity of the Al film deposited selectively was evaluated by use of a scanning µ-RHEED microscope. As shown in Fig. 10, after the region where Al had been selectively deposited was specified by the scanning secondary electron image showing the surface form (Fig. 10A), by use of the diffraction spot 200 (corresponding to the diffraction spot A in Fig. 7) and the diffraction spot 620 (corresponding to the diffraction spot C in Fig. 7) on the diffraction pattern occurring when the electron beam was permitted on the Al (100) plane from the [001] direction, the scanning µ-RHEED image (Fig. 10B) and Fig. 10C) was observed. As shown schematically in Fig. 10B and Fig. 10C, there is no change in lightness and darkness on the Al film selectively deposited, and the Al selectively deposited was confirmed to be an Al (100) monocrystal. On the other hand, when the Si exposed plane is not linear but like via-hole, irrespectively of the via-hole diameter, the Al selectively deposited was found to be similarly Al (100) monocrystal. Those at substrate temperatures ranging from 250 °C to 330 °C were selectively deposited stably, and the Al obtained was found to become monocrystal. Also, Al films deposited selectively on the Si (111) substrate with the Si (111) plane being at off-angles by 1°, 2°, 3°, 4°, 5° from the Si substrate were also found to deposit Al (100) monocrystals under the temperature conditions of the substrate temperature ranging from 250 °C to 330 °C similarly as deposited on the Si (111) substrate as described above.. When the crystal direction of the Si substrate surface is the (100) plane, from X-ray diffraction, concerning Al, as shown in Fig. 11, only the diffraction peak showing Al (111) could be observed Fig. 12 shows the scanning secondary electron image (Fig. 12A) and the scanning µ-RHEED image (Figs. 12B and 12C) when Al was selectively deposited on only the Si exposed surface on a substrate having Si (100) exposed in a line by patterning of SiO₂ in a line. For the scanning µ-RHEED image, the 333 diffraction spots (Fig. 12B) and 531 diffraction spots (Fig. 12C) were employed. The Al film selectively deposited was confirmed to be an Al (111) monocrystal. Those at substrate temperatures ranging from 250 °C to 330 °C were found to be selectively deposited stably, and the Al films obtained became monocrystals. Also, Al films deposited selectively on the Si (100) substrate with the Si (100) plane being at off-angles by 1°, 2°, 3°, 4°, 5° from the Si substrate surface were also found to deposit Al (111) monocrystals under the temperature conditions of the substrate temperature ranging from 250 °C to 330 °C similarly as deposited on the Si (111) substrate as described above. Experimental example 14 Crystallinity of the Al film deposited selectively according to the same method as shown in Example 6 was evaluated. Similarly as in Experimental example 8, at substrate temperatures ranging from 250 °C to 330 °C, Al (100) monocrystals on the Si (111) substrate and Al (111) monocrystals on Si (100) substrate were obtained stably. Experimental example 15 Crystallinity of the Al film deposited selectively according to the same method as shown in Example 7 was evaluated. From the scanning µ-RHEED microscope observation according to the same observation method as described in Experimental example 13, when the first substrate material is Si (111), in either case when the second substrate material is T-SiO₂, SiO₂, BSG, PSG, BPSG, P-SiN, T-SiN, LP-SiN or ECR-SiN, the Al selectively deposited on Si was found to be Al (100). When the first substrate material is Si (100), in either case when the substrate material is T-SiO₂, SiO₂, BSG, PSG, BPSG, P-SiN, T-SiN, LP-SiN or ECR-SiN, the Al film selectively deposited was found to be Al (111). When the first material is TiN, in either case when the second substrate material is T-SiO₂, SiO₂, BSG, PSG, BPSG, P-SiN, T-SiN, LP-SiN or ECR-SiN, the Al film selectively deposited on TiN was found to be oriented in Al (111) from X-ray diffraction, and from reflective high speed electron beam diffraction pattern of the prior art by use of an electron beam of an acceleration voltage of 80 kV or 100 kV, diffraction spots concerned with Al (111) were strongly observed. Comparative experiment An Al film was formed on a monocrystalline silicon under the following conditions. By passing Ar in place of H₂, Al was deposited by pyrolysis of DMAH. The total pressure at this time was made 1.5 Torr, the DMAH partial pressure 1.5 x 10⁻ ⁴ Torr, and the substrate temperature of 270 - 350 °C. When the Al film thus formed was evaluated, about 2 % of carbon was found to be contained at the minimum. Resistivity became greater by 2-fold or more than the case when hydrogen was employed. As to reflectance, it was lowered to about 1/3 to 1/9 relative the case when hydrogen was employed. Similarly, wiring life was shorter by 1 to 2 cipher, generation probability of hillock became greater by 2 cipher or more, and a large number of spikes were found to be generated. As to the deposition speed, it was lowered to 1/2 to 1/4. As described above, Al deposited only by decomposition of DMAH without use of H₂ is inferior in film quality, and was unsatisfactory as the Al film for a semiconductor device. Separately, without use of H₂, DMAH was decomposed by the optical CVD method to deposit Al. As the result, same improvement such as no containment of carbon, and the like was observed from the Al film prepared as compared with the case when no light was employed, but other characteristics were not improved so much, and the Al film was still unsatisfactory as the Al film for a semiconductor device. As described above, the mechanism of Al deposition according to the present invention may be presently hypothesized as follows. When DMAH reaches the electron donative substrate, namely the substrate having electrons under the state on which hydrogen atoms are attached (Fig. 13A) with the methyl groups directed toward the substrate side, one electron of the substrate cut one bond of Al and methyl group (Figs. 13B, 13C). The reaction scheme at this time is as follows: (CH₃)₂AlH + 2H + 2e → 2CH₄ ↑ + Al-H Further, similar reactions will proceed for the hydrogen atoms remaining on deposited Al having free electrons (Fig. 13D). Here, when hydrogen atoms are deficient, hydrogen molecules constituting the reaction gas are decomposed on the substrate to suppy hydrogen atoms. On the other hand, since there is no electron on the electron non-donative surface, the above-mentioned reaction will not proceed and no Al deposited. Figs. 13A - 13D are illustrations for better understanding of the reacion mechanism, and the numbers of H, e and Al shown in Figs. 13A - 13D are not necessarily coincident. As described above, according to the present invention, a low resistivity, dense and flat Al film could be deposited on a substrate. Also, depending on the kind of the substrate, deposition can be effected selectively.

Claims: A method for the deposition of a film composed wholly or mainly of aluminium on an electron donative surface of a substrate, the method comprising: (a) arranging the substrate in a film formation space of a reaction chamber which is evacuated for the formation of deposited film; (b) introducing into said space an alkyl aluminium hydride in gaseous form and gaseous hydrogen; and (c) maintaining the surface of the substrate at a temperature at which the alkyl aluminium hydride decomposes but not more than 450°C, so that the film composed wholly or mainly of aluminium is formed by chemical vapour deposition on the electron donative surface. The method of claim 1, wherein the substrate is a metal. The method of claim 1, wherein the substrate is a semiconductor. The method of claim 1, wherein the substrate is a silicide. The method of claim 1, wherein the substrate is of monocrystalline silicon, polycrystalline silicon, amorphous silicon, a III-V compound semiconductor, a II-VI compound semiconductor, AlSi, AlTi, AlCu, AlTa, Al-Si-Cu, Al-Si-Ti, Al-Pd or Ti₃N₄. The method of any preceding claim, wherein the aluminium film is monocrystalline. The method of claim 1, wherein the substrate is of silicon and has a (100) plane crystal orientation, and there is formed on the (100) plane surface of the substrate monocrystalline aluminium having a (111) plane crystal orientation. The method of any preceding claim, wherein the alkyl aluminium hydride is monomethyl aluminium hydride or dimethyl aluminium hydride or a mixture thereof. The method of any preceding claim, wherein the surface of the substrate is maintained at 270 to 350°C. The method of any preceding claim, wherein selective formation of Al is carried out by hot wall low pressure CVD in which the substrate is heated. A method according to any preceding claim, wherein the surface of the substrate has electron donative regions and electron non-donative regions. The method of claim 11, wherein the electron non-donative regions are of silicon oxide, glass or silicon nitride. The method of claim 11 or 12, wherein the substrate has a covering of electron non-donative material formed with contact-holes through which electron donative material is exposed, and the Al is selectively deposited in the contact-holes. The method of claim 13, wherein the size of the contact hole is 1µm x 1µm or less. The method according to any one of claims 1 to 8, wherein the surface of the substrate is maintained at 160°C - 450°C. The method according to any one of claims 1 to 8, wherein the surface of the substrate is maintained at 200°C to 400°C. The method according to any one of claims 1 to 8, wherein the internal pressure of the reaction chamber is within the range of 0.13 Pa - 101 kPa (10⁻³ Torr to 760 Torr). The method according to claim 17, wherein the partial pressure of the alkyl aluminium hydride is within the range of 0.013 Pa - 0.13 Pa (10⁻⁴ Torr to 10⁻³ Torr).

Inventors: MASU KAZUYA, MIKOSHIBA NOBUO, TSUBOUCHI KAZUO, MASU, KAZUYA, MIKOSHIBA, NOBUO, TSUBOUCHI, KAZUO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1990
Main classification: C23C16
IPC codes: H01L21, C23C16