Film deposition method and apparatus

Abstract: A deposited film formation method which forms an aluminum film by use of the plasma CVD method, wherein a substrate having an electron donative surface (A) and a non electron donative surface (B) is arranged in a space for deposited film formation having a portion which is increased in cross-sectional area toward said substrate is arranged, and a gas of trimethylaluminum and hydrogen gas are introduced into said space for deposited film formation to deposit an aluminum film selectively on said electron donative surface (A). A deposited film formation method which forms an aluminum film by use of the plasma CVD method, comprising: (a) the step of arranging a substrate having an electron donative surface (A) and a non-electron donative surface (B) in a space for deposited film formation equipped with a reverse flow preventive means into plasma, and (b) the step of introducing a gas of trimethylaluminum and hydrogen gas said space for deposited film formation, said aluminum film being selectively formed on said electron donative surface (A).

Description: This invention relates to a deposited film formation method, particularly to a formation method of Al or Al-Si deposited film which can be preferably applied to wiring of a semiconductor integrated circuit device, etc. In the prior art, in electronic devices or integrated circuits using semiconductors, for electrodes and wiring,aluminium (Al) or Al-Si, etc. have been primarily used. Here, Al has many advantages such that it is inexpensive and high in electroconductivity, that it can be also internally chemically protected because a dense oxidized film can be formed on the surface, and that it has good adhesion to Si, etc. Whereas, the integration degree of the integrated circuit such as LSI, etc. is increased, and fine formation of wiring and multi-layer wiring, etc. have been particularly required in recent years. For this reason, there is an increasing severe demand not found up to date for Al or Al-Si wiring of the prior art. With finer dimensional formation by increased integration degree of the integrated circuit, the surface of LSI, etc. is subject to excessive unevenness due to oxidation, diffusion, thin film deposition, etching, etc. Whereas, electrodes or wiring metal must be deposited on the surface with a stepped difference, or deposited in a via-hole which is fine in diameter and deep. In 4 Mbit or 16 Mbit DRAM (dynamic RAM), etc., the aspect ratio (via-hole depth/via-hole diameter) of via-hole in which a metal such as, Al-Si, etc. is deposited is 1.0 or more, and the via-hole diameter itself also becomes 1 µm or less. Therefore, even for a via-hole with large aspect ratio, a technique which can surely deposit a metal such as Al, Al-Si, etc. is required. Particularly, for performing sure electrical connection to the device under insulating film such as SiO₂, etc., rather than film formation, Al or Al-Si is required to be deposited so as to embed only the via-hole of the device. For such purpose, a method of depositing Al or Al-Si on Si or metal surface and not depositing it on an insulating film such as SiO₂, etc. is required. Such selective deposition or selective growth cannot be realized by the sputtering method which has been used in the prior art. Since the sputtering method is a physical deposition method based on flying of the particles sputtered from the target in vacuum, the film thickness et the stepped portion or the side wall of insulating film is liable to become extremely thin, leading even to wire breaking in an extreme case. And, nonuniformity of the film thickness and wire breaking will markedly lower reliability and yield of LSI. Accordingly, there has been developed the bias sputtering method in which a bias is applied to a substrate and deposition is performed so as to embed Al or Al-Si only in the via-hole by utilizing the sputter etching action and the deposition action on the substrate surface. However, since a bias voltage of some 100V or higher is applied to the substrate, deleterious influence on the device may sometimes occur because of charged particle damaging such as change in threshold value of MOS-FET, etc. Also, because of coexistence of both etching action and deposition, there is the problem that the deposition rate cannot be essentially improved. In order to solve the problems as described above, various types of CVD (Chemical Vapor Deposition) methods have been proposed. In these methods, chemical reaction of the starting gas is utilized in some form. In plasma CVD or optical CVD, decomposition of the starting gas occurs in gas phase, and the active species formed there further reacts on the substrate to form a film. In these CVD methods, surface coverage over unevenness on the substrate surface is good. However, since an organometallic compound having alkyl group bonded to Al atom is generally used as the starting gas, there is the problem that the carbon atoms contained in the starting gas molecule are incorporated into the film. Also, particularly in plasma CVD, the problem remained that damage by charged particles (so called plasma damage) may occur in some time as in the case of the sputtering method. In contrast, the thermal CVD method has good coverage over unevenness such as stepped difference of the surface, because the film grows according to the surface reaction on the surface of substrate. Also, deposition within via-hole can be expected to readily occur. Further, due to good coverage, wire breaking at the stepped difference can be also avoided. For example, as the method for forming Al film by the thermal CVD, there may be employed the method in which an organic aluminum is transported onto a heated substrate and the gas molecules are pyrolyzed on the substrate to form a film. For example, in an example seen in Journal of Electrochemical Society, Vol. 131, p. 2175 (1984), by use of triisobutyl aluminum (i-C₄H₉)₃Al (TIBA) as organic aluminum gas, film formation is effected at a film formation temperature of 260 °C and a reaction tube pressure of 7x10 Pa (0.5 torr) to form a film of 3.4 µΩ.cm. However, when TIBA is employed, no continuous film can be obtained unless such pre-treatments as flowing of TiCl₄ before film formation, activation of the substrate surface, formation of nucleus, etc. are applied. Also, including the case by use of TiCl₄, generally there is involved the problem that surface selectivity is inferior when TIBA is employed. Japanese Laid-open Patent Application No.Sho-63-33569 describes a method of forming a film by using no TiCl₄, but using in place thereof organic aluminium and heating it in the vicinity of the substrate. According to this method, Al can be deposited selectively only on the metal or semiconductor surface from which the naturally oxidized film has been removed. However, in this case, it is clearly described that the step of removing the naturally oxidized film on the substrate surface is necessary before introduction of TIBA. Also, it is described that, since TIBA can be used alone, no carrier gas is required to be used, but Ar gas may be also used as the carrier gas. However, the reaction of TIBA with another gas (e.g. H₂) is not contemplated at all, and there is no description of use of H₂ as the carrier gas. Also in addition to TIBA, trimethyl aluminum (TMA) and triethyl aluminum (TEA) are mentioned, but there is no specific description of other organometallic compounds. This is because, since the chemical properties of the organometallic compounds generally vary greatly if the organic substituent attached to the metal element varies little, it is necessary to investigate individually to determine what organometallic compound should be used. In this method, not only there is the inconvenience that the naturally oxidized film must be removed, but also there is the problem that surface smoothness cannot be obtained. In the pre-text of the 2nd Symposium of Electrochemical Society, Branch of Japan (July 7, 1989), on page 75, there is a desoription of film formation of Al according to the double wall CVD method. In this method, TIBA is used and the device is designed so that the gas temperature can be made higher than the substrate temperature. This method may be also regarded as a modification of the above-mentioned Japanese Laid-open Patent Application No. Sho-63-33569. Also in this method, Al can be selectively grown only on a metal or semiconductor, but not only the difference between the gas temperature and the substrate surface temperature can be controlled with difficulty, but also there is the problem that the bomb and the pipeline must be heated. Moreover, according to this method, there are involved such problems that no uniform continuous film can be formed, that the flatness of the film is poor, that selectivity of Al selective growth cannot be maintained for so long time, etc., unless the film is made thick to some extent. Also, since TIBA has small vapour pressure at room temperature as 1x10 Pa (0.1 torr), it has the problem that it can be transported in a large amount with difficulty. For this reason, it has been practiced to heat the bomb for organometallic compound to 45 to 50°C, but there is the problem that not only the vessel for organometallic compound, but also the pipeline to the reaction vessel must be also heated. Trimethyl aluminum (TMA) has a vapor pressure of approximately 1.3x10³ Pa (10 torr) at room temperature, and it is possible to transport TMA to a reaction vessel efficiently by flowing a gas such as H₂, etc. into the TMA starting material solution. J. Electrochem. Soc. 135 (2) (1988) 455 discloses that deposition of Al is possible by use of TMA according to the plasma CVD method or the magnetron plasma CVD method. However, in the magnetron CVD method, since even C-H bond of alkyl group is decomposed, there is the great problem that several % to several 10 % of carbon atoms are incorporated in the deposited film. Also, there is the problem of occurrence of charged particle damaging by plasma. Since the magnetron plasma CVD method is based on decomposition of TMA in the gas phase, it can be deposited on the substrate surface, whether it may be Si or SiO₂, whereby selective Al deposition is essentially impossible. According to Japanese Patent Application No. Sho-60-211149, when TMA is used, Al deposition without incorporation of carbon is possible according to the reaction with heat or heat and UV-ray irradiation by use of excited and decomposed molecules, by exciting and decomposing TMA molecules with plasma in the gas phase apart from the wafer. Similarly, Extended Abs. of 20th Solid State Devices and Materials (1988) p.573 by the present inventors, there is shown deposition of an Al film without incorporation of carbon at a deposition rate of 1.0 to 2.0 nm (10 to 20 Å)/min. on Si or a thermally oxidized SiO₂ wafer heated to 260 °C to 350 °C by use of TMA and by exciting TMA with an H₂ atmosphere high frequency (73.56 MHz) plasma. According to the method shown in Japanese Patent Application No. Sho-60-211149 and Extended Abstract of 20th Solid State Devices and Materials (1988) p. 573, although deposition example of Al thin film is shown, there is no reference to the method of depositing Al selectively only on the Si exposed portion on the Si wafer subjected to patterning of SiO₂. In Extended Abstract of 20th Solid State Devices and Materials (1988) p. 573, it is shown that Al is deposited at the similar extent of deposition rate on the thermally oxidized SiO₂ wafer and Si wafer. As described above, in the technical field of which higher integration has been desired in recent years, for providing a semiconductor which is made highly integrated and higher in performance, there is much need for improvement. The present invention has been accomplished in view of the technical problems described above, and to provide a deposited film formation method capable of forming an Al or Al-Si film having good quality as conductor with good controllability at a desired position. The method in accordance with the present invention is defined in claim 1 of the claims appended hereto. In this method reverse flow of gases into the plasma may be prevented by causing the product gases to flow through a tube of increasing cross-section and/or alternatively by directing the product gases at an angle which is inclined to the normal to the substrate surface. In the apparatus [defined in claim 6], which is in accordance with the present invention, a reaction tube is provided having an increasing cross-section and/or a substrate holder is provided arranged to hold the substrate in a position inclined to the flow of product gases. In the accompanying drawings: Fig. 1 is a schematic view showing a deposited film formation device as an example of the present invention; Fig. 2 is a schematic view showing a comparative example to the device; and Fig. 3 is a schematic view showing the principal portion of a deposited film formation device as another example of the present invention. To assist in an understanding of the present invention, preferred embodiments will be detailed hereinbelow. The following description is given by way of example only. First, Al deposition by use of trimethylaluminium (TMA) is outlined. TMA is represented by the following formula: TMA : Al(CH₃)₃ TMA has been said to have a dimer structure as shown below at room temperature: TMA, as an organometallic compound, is a material widely used in the field of chemical engineering as a catalyst material. Generally speaking, the organometallic decomposition reaction depends greatly on the kind of the metal atom, the kind of the alkyl group bonded to the metal atom and the excitation and decomposition means, and therefore excitation and decomposition reaction must be clarified for each individual material. As to TMA, as the reaction concerning the chemical vapour phase deposition method, the following points have been clarified. Pyrolysis in the gas phase is a radical decomposition in which the Al-CH₃ bond is cleaved, and forms CH₄ at a low temperature of 150 °C or lower through a reaction with atmospheric hydrogen, finally forming Al. However, at a higher temperature of 300 °C or higher, even if hydrogen may exist in the atmosphere, CH₃ group will withdraw H from TMA, whereby finally an Al-C compound is formed. In the region limited in power density to some extent in light or high frequency (13.56 MHz) plasma under H₂ atmosphere, C₂H₆ is formed through coupling of the bridging CH₃ between two Al's. According to the magnetron plasma CVD method employing TMA, Al deposition has been attempted, but several to several ten % of carbon atoms will be incorporated in the deposited film, and also the resistivity of the deposited film becomes very large as 5- to 20-fold of the bulk value. Incorporation of carbon occurs because TMA is excessively decomposed. Besides, since the plasma or magnetron plasma CVD method is based on the reaction in gas phase, no selective growth or selective deposition can be rendered possible in principle. By controlling the high frequency power to be applied, in the high frequency discharging H₂ plasma, TMA molecules will be excited and decomposed to and stable C₂H₆. The state under which excitation and decomposition occur to Al(CH₃)₂ and stable molecular species is called the selective excitation state. When the excited molecular species such as Al(CH₃)₂, etc. selectively excited are transported onto a heated Si wafer, an Al film without incorporation of carbon is deposited. However, the gas stream is jumped against the wafer, whereby the excited molecular species cannot be transported to the wafer with good efficiency, or the molecules such as C₂H₆ which should be ordinarily discharged and CH₄ formed after Al deposition reaction will flow reversely into the plasma. As a result, the selective excitation may be considered to be broken to cause unnecessary reaction for Al deposition reaction to occur, and therefore the deposition rate is small and even no selectivity depending on the kind of the substrate may be sometimes effected. In the present invention, selective excitation and decomposition of TMA in the H₂ atmosphere is the same as in the prior art, but the excited molecular species formed in plasma are permitted to be transferred onto a wafer without occurrence of reverse flow caused by convection or eddy within the space for formation of deposited film (reaction tube), to have Al deposited on the wafer. Because the excited molecular species are transferred efficiently onto the wafer and no unnecessary reaction occurs, not only flatness is high and Al of high quality is deposited, but also selectivity of deposition depending on the choice of substrate is effected. Referring now to the drawings, preferred embodiments of the present invention are described. In the present invention, the CVD method is employed in order to deposit an Al or Al-Si film of good quality as the electroconductive deposited film selectively on a substrate. More specifically, by use of trimethyl aluminium (TMA): chemical formula: Al(CH₃)₃ which is an organometallic compound as the starting gas containing at least one atom which is the constituent of the deposited film and optionally a gas containing Si atom as the starting gases, and also by use of H₂ as the reactive gas, an Al or Al-Si film is formed selectively on a substrate by gas phase growth by these mixed gases. The substrate to which the present invention is applicable has a first substrate surface material for forming the surface on which Al or Al-Si is to be deposited, and a second substrate surface material for forming the surface on which no Al or Al-Si is deposited. And, as the first substrate surface material, a material having electron donative characteristic is employed. The electron donative characteristic is described in detail below. An electron donative material is one having free electrons existing in the substrate or having intentionally free electrons formed therein and, for example, may be a material having a surface where the chemical reaction is promoted by exchange of electrons with the starting gas molecules adsorbed on the substrate surface. For example, generally metals and semiconductors correspond to this. Those having thin oxide films on metal or semiconductor surfaces are also included. This is because the chemical reaction occurs by exchange of electrons between the substrate and the adsorbed starting material molecules. Specifically, there may be included semiconductors such as single crystalline silicon, polycrystalline silicon, amorphous silicon, the binary system, ternary system or quarternary system III-V group compound semiconductors comprising combinations of Ga, In, Al as the group III element and P, As, N as the group V element, metals, alloys and silicides thereof such as tungsten, molybdenum, tantalum, tungsten silicide, titanium silicide, aluminum, aluminumsilicon, titaniumaluminum, titanium nitride, copper, aluminumsiliconcopper, aluminumpalladium, titanium, molybdenum silicide, tantalum silicide, etc. In contrast, as the material for forming the surface on which Al or Al-Si is not selectively deposited, namely the non-electron donative material, silicon oxide by thermal oxidation, CVD, etc., glass such as BSG, PSG, BPSG, etc. or oxide film, silicon nitride film by thermal CVD, plasma CVD, low pressure CVD, ECR-CVD, etc. On the substrate with such a constitution, Al or Al-Si is deposited according to the following reaction in the reaction system of the starting gas and H₂: First, Al(CH₃)₂ is formed in gas phase in a high frequency discharging plasma according to the following reaction: Al₂(CH₃)₆ → 2Al(CH₃)₂ + C₂H₆ Al(CH₃)₂ is transported onto a wafer, and Al is deposited according to the subsequent reaction. Also, deposition of Al-Si alloy by addition of Si₂H₆, etc. is effected by decomposition of Si₂H₆ reaching the substrate surface by the surface chemical reaction to be incorporated in the deposited film. Fig. 1 is a schematic view showing a deposited film formation device to which the present invention is applicable. In this example, the reverse flow preventive means is accomplished by determining adequately the shape of the reaction tube constituting the space for deposited film formation. That is, in this example, the reaction tube is made to have a shape with the cross-sectional area of the portion of the plasma generation region 32 being enlarged, for example, a horn shape (conical shape or pyramidal shape). 1 is a silicon wafer, which is set in the reaction tube 2 made of quartz having a horn shaped portion in Al deposition. A metal electrode 3 for high frequency plasma generation is mounted externally of the quartz reaction tube 2. For the metal electrode, the known three electrode system is employed, having an excitation electrode surrounded on both sides with earth electrodes. Between the excitation electrode and the earth electrodes, discharging occurs. Depending on presence or absence of the wafer holder, the shape of the plasma generation region will not be substantially changed. By use of the three electrode system, the plasma generation region 32 can be confined in the vicinity of the electrode. The plasma generation region is the portion shown by the dots. For plasma generation, a high frequency power source 4 with an oscillation frequency of approximately 13.56 MHz is employed. Since the electrical field is concentrated on the metal electrode by the three electrode structure, there occurs substantially no charged particle damage onto the substrate. In the example in Fig. 1, by making the reaction tube shape a horn shape as shown in Fig. 1, the flux of the gas is transported without convection or eddy. In the viscous flow region where the pressure is from atmospheric pressure to approximately several 10³ Pa (10 torr), there is the method of removing convection, etc. of the gas within the reaction tube by making the reaction tube shape horn shape, but in the device in Fig. 1, it is used in the medium flow region where the pressure is 7x10 to 2.0x10²Pa (0.5 to 1.5 Torr). The optimum value of the opening flare angle of horn depends on the pressure, but within the pressure range from 7x10 to 2.0x10² Pa (0.5 to 1.5 torr), it may be 10 to 20°. H₂ gas is followed from the pipeline 14 into the vessel 13 for organometallic compound to gasify the organometallic compound TMA, and the organometallic compound is led into the reaction vessel 2. From the pipeline 15, hydrogen for dilution and Si₂H₆ gas are flowed. The roles of the valves 27 and 28 are as described below. In purging thoroughly internally of the pipelines 14 and 15, with the valve 28 being closed and the valve 27 opened, pipelines 14 and 15 are purged. In leading the starting gas into the reaction tube, the valve 28 is opened and the valve 27 closed. The needle valve 29 is used for making the pressure on the inlet side of the TMA bomb approximately atmospheric. The opening of the needle valve 29 is controlled while watching the indication value of the pressure gauge 18. The organometallic compound such as TMA, etc., when H₂ is present, will be decomposed with formation of CH₄ by the reaction of CH₃ groups with H₂ according to the catalytic reaction in gas phase and on the stainless steel pipeline surface, etc. Particularly, before film formation, if the stainless steel pipeline portion through which TMA flows is treated with a baking treatment to liberate adsorbed moisture on the stainless steel surface, the stainless steel surface will be activated and thereafter TMA molecules will be more readily adsorbed thereon, whereby decomposition of TMA molecules through the catalyst reaction on the stainless steel surface can proceed with ease. Therefore, if the stainless steel pipeline from the TMA vessel to the reaction tube is unnecessarily long, TMA molecules will be decomposed in the course to the reaction tube, and particularly if pure TMA molecules do not reach the reaction tube at the initial stage of film formation, it is difficult to form an Al film with excellent flatness. Accordingly, it is desirable to arrange the TMA bomb immediately near the reaction tube. Also, the region encircled with the chained dot line around the TMA bomb should be desirably made integrated. As shown in Examples, by use of the organometallic compound vessel equipped with a by-pass valve, and an integrated structural pipeline around bomb by the present inventors, the time of maintaining selectivity is elongated. In the device shown in Fig. 1, when TMA is introduced into the reaction tube 2 under the state where plasma is generated, Al or Al-Si is selectively deposited on the electron donative substrate. Deposition of Al will vary depending on the atmospheric gas, the reaction tube pressure, the substrate temperature. For the atmospheric gas, H₂ is used. The reaction mode of the decomposition reaction of organometallic compound generally differs depending on the kind of the metal atom, the kind and the number of the alkyl group bonded to the metal atom, but when Al is deposited from TMA, hydrogen gas (H₂) is required as the reaction gas. When there is enough hydrogen, an inert gas such as Ar, etc. may be mixed therein. The reaction tube pressure for deposition of Al is desirably 7x10 to 2.0x10² Pa (0.5 to 1.5 torr). The plasma application power is very sensitive, and in the case of the present device, at a power density of 0.02 W/cm³, no Al will be deposited at a substrate temperature range from 180 to 350 °C. On the other hand, at a power density of 0.18 W/cm³ or higher, C will be incorporated into the deposited film, and therefore the power density should be desirably 0.03 to 0.06 W/cm³. The power density is a value of the power required for plasma generation divided by the plasma generation volume. When the plasma power density is 0.03 to 0.06 W/cm³, Al will be selectively deposited only on the electron donative surface at a substrate temperature range from 180 to 350 °C. When deposition is effected under constant deposition conditions of the whole pressure, the plasma power, TMA transportation amount, etc. other than the substrate temperature, Al will be deposited at a deposition rate according to the surface controlling process along the Arrhenius plot in the range from 180 to 350 °C. The Al or Al-Si film deposited selectively is found to be an Al film of high quality which is continuous and flat and also has a resistivity substantially equal to the bulk value of 2.7 µΩ·cm, even if it may be a film of 40 nm (400 Å) or less. Accordingly, even by the heat treatment of 450 °C for one hour, there is no generation of hillock, and also there is generation at the contact portion with Si. TMA has a great vapour pressure of 1.3x10³ Pa (10 torr) at room temperature, and can be easily transported in larger amount as compared with TIBE (having vapour pressure at room temperature of 1x10 Pa (0.1 torr)) of which selective CVD has been attempted in the prior art, and therefore easily deposited on a large number sheets of wafer, whereby the selective Al CVD method can be applied easily to the ultra-LSI process. In contrast, with the constitution as shown in Fig. 2 equipped with no eddy preventive means as in the present example, namely the constitution by use of the reaction tube 2' having a portion of straight tubular shape and a wafer arranged vertically to the axis line, the gas stream will be jumped up at the wafer 1, whereby the excited molecular species cannot be efficiently transported to the wafer, or the deposition rate is as small as 1.0 to 2.0nm (10 to 20 Å)/min.,probably because the molecules such as C₂H₆ which should be normally discharged or CH₄ formed after Al deposition reaction flow reversely within the reaction tube 2' to break the selective excited state to give rise to unnecessary reactions for Al deposition reaction, and also no selectivity depending on the choice of substrate has appeared. Example 1 The Al deposition procedure is as described below. By means of the device shown in Fig. 1, the reaction tube 2 is internally evacuated to ca.10⁻⁶Pa (10⁻⁸ Torr) by an evacuation equipment 12. However, Al can be deposited even if the vacuum degree in the reaction tube 2 may be worse than 1x10⁻⁶ Pa (1 x 10⁻⁸ Torr). After washing of the Si wafer, the conveying chamber 9 is opened to atmospheric pressure and the Si wafer is mounted in the conveying chamber 9. The conveying chamber 9 is evacuated to ca. 1x10⁻⁴Pa (1x10⁻⁶ Torr) by use of an evacuation equipment 10, and then the gate valve 8 is opened and the wafer is mounted on the wafer holder 7. In this Example, hydrogen gas is flowed through the pipelines 14 and 15. With the valve 28 being closed and the valve 27 opened, the pipelines are internally sufficiently purged. Also, prior to Al deposition, for purging internally the TMA bomb, with the valve 26 being closed, the valve 24 and the valve 25 opened, the TMA bomb is internally purged. In purging the TMA bomb, the valve 27 is opened to effect evacuation together with hydrogen carrier gas. After purging, introduction of carrier gas into the TMA bomb is once stopped. Hydrogen gas is flowed through the pipelines 14 and 15 into the reaction tube, and the pressure in the reaction tube 2 is adjusted to a predetermined value by controlling the opening of the slow leak valve 11. A typical pressure in this Example is 9x10Pa (0.7 Torr). Then, the wafer is heated by current passage through the heater 6. After the wafer temperature has reached a predetermined temperature, a predetermined power is applied from the plasma generation power source 4 to generate a plasma within the reaction tube 2. The generation frequency of the plasma is 13.56 MHz. After generation of the plasma, hydrogen gas from the pipeline 14 is introduced into the TMA vessel to initiate transportation of TMA. Simultaneously with initiation of transportation of TMA, Al is deposited. After elapse of a predetermined deposition time, transportation of TMA is stopped, and also generation of the plasma is stopped. Current passage to the heater 6 is stopped and the wafer cooled. Feeding of hydrogen gas into the reaction tube 2 is stopped, and after evacuation internally of the reaction tube 2, the wafer is conveyed to the conveying chamber, and only the conveying chamber is opened to the atmosphere to take out the wafer. The outline of the Al deposition procedure is as described above. For the vessel of organometallic compound used in this Example, one provided with two valves 24 for inflow of the carrier gas and a valve 25 for outflow is employed. In the following, the sample preparation in this Example is to be described. An Si substrate (N type 1 - 2Ω·cm) is thermally oxidized at a temperature of 1000 °C according to the hydrogen combustion system (H₂: 4 liter/M, O₂: 2 liter/M). The film thickness is 700.0 to 50.0 nm (7000Å) ± 500Å), and the refractive index 1.46. On the whole Si substrate surface is coated a photoresist, followed by printing of a desired pattern by an exposure machine. The pattern is such that various pores of 0.25 µm x 0.25 µm - 100 µm x 100 µm are opened. The photoresist is developed and then etched with reactive ion etching (RIE), etc. to etch the subbing SiO₂, thereby having partially the substrate Si exposed. Thus, samples having pores of SiO₂ with various sizes of 0.25 µm x 0.25 µm - 100 µm x 100 µm are prepared. The substrate temperature is set at 10 levels, and the plasma power source at 6 levels, and for the respective 60 combinations of them, deposition is carried out each for 10 sheets of samples according to the procedure as described above. The deposition conditions are as follows: Total pressure: 9x10 Pa (0.7 Torr) TMA partial pressure: 2.0x10⁻² Pa (1.5x10⁻⁴ Torr) The evaluation results of Al films deposited are shown in Table 1. At a substrate temperature of 170 °C or lower, or at a plasma power of 0.02 W/cm³ or lower, no deposition occurs on both Si and SiO₂ even by deposition for 2 hours. During plasma power application of 0.18 W/cm³, deposition of the film occurs, but there is incorporation of carbon therein. At a substrate temperature of 370 °C or higher, the deposition rate is extremely reduced, whereby carbon is incorporated into the deposited film. Shortly speaking, Al is deposited under the conditions of a substrate temperature of 180 °C - 350 °C and a plasma power of 0.03 - 0.06 W/cm³. The Al films deposited are all found to have a film thickness of 40nm (400 Å), being continuous and flat, and resistivities similar to the bulk as 2.7 - 3.0 µΩ·cm. And even if at the film thichness of 1 µm, the resistivity was 2.7 to 3.0 µΩ·cm. By Auger's analysis, photoelectron spectrophotometry, no incorporation of C is detected. However, at a substrate temperature of 300 °C or higher, with a film thickness of 100 nm (1000 Å) or higher, reflectance is slightly lowered and flatness lowered. Al deposition under the conditions of a substrate temperature of 180 °C - 350 °C and a plasma power of 0.03 - 0.06 W/cm³, occurs only at the Si exposed portion, without deposition on SiO₂ (selectivity of deposition is maintained for 1 hour). When the plasma power is made constant at 0.03, 0.045, 0.06 W/cm³, respectively, the deposition rate D.R. when the substrate temperature is 180 - 350 °C is represented by: D.R. = Do exp(-E/kT) Do = constant value E = activation energy k = Boltzmann's constant T = substrate temperature. The activation energy E is a value of 1 - 2 eV. Example 2 According to the same procedure as in Example 1, Al was deposited under the following conditions. The deposition conditions were made a reaction tube pressure of 9x10 Pa (0.7 Torr), a substrate temperature of 270 °C , a plasma generation power density of 0.045 W/cm³, with the TMA partial pressure being varied from 7x10⁻⁴ to 2.0x10⁻¹ Pa (5x10⁻⁶ to 1.5x10⁻³ Torr). The deposition rate was varied from 1.0 to 400.0 nm (10 to 4000 Å/min.) in proportion to TMA partial pressure. Regardless of TMA pressure, Al was deposited only on the exposed surface of Si similarly as in Example 1. Example 3 According to the same procedure as in Example 1, Al deposition was carried out under the following conditions. The deposition conditions were made a substrate temperature of 270 °C, a plasma generation power density of 0.045 W/cm³, a TMA partial pressure of 2.0x10⁻² Pa (1.5x10⁻⁴ Torr), with the reaction tube pressure being varied from 1x10 to 4x10² Pa (0.1 to 3 Torr). When the reaction tube pressure was ca. 7x10 to 2.0x10²Pa (0.5 to 1.5 Torr), Al was deposited only on the Si exposed portion similarly as in Example 1 at a deposition rate of ca. 20.0 to 40.0 Pa (200 to 400Å)/min. At a reaction tube pressure of ca. 4x10Pa (0.3 Torr) or less, no deposition occurred on both the Si exposed portion and the SiO₂ portion even by deposition for 2 hours. At a pressure of ca. 2.0x10²Pa (1.5 Torr), deposition occurred only on the Si exposed portion, but the deposition rate was reduced to 10.0 to 20.0 nm (100 to 200 Å)/min. Example 4 According to the same procedure as in Example 1, Al films were formed on the substrates with the constitutions as described below (Samples 5-1 to 5-179). Preparation of Sample 5-1 On a single crystalline silicon as the first substrate surface material which was electron donative, a thermally oxidized SiO₂ film as the second substrate surface material which was non-electron donative was formed, followed by patterning according to the photolithographic steps as shown in Example 1, to have the single crystalline silicon surface partially exposed. The film thickness of the thermally oxidized SiO₂ film was found to be 700.0 nm (7000 Å), and the size of the exposed portion, namely the opening of the single crystalline silicon 3 µm x 3 µm. Thus, Sample 5-1 was prepared. (hereinafter such sample is represented as "thermally oxidized SiO₂ (hereinafter abbreviated as T-SiO₂)/single crystalline silicon"). Preparation of Samples 5-2 to 5-179 Sample 5-2 was an oxidized film formed by normal pressure CVD (hereinafter abbreviated as SiO₂)/single crystalline silicon; Sample 5-3 was a boron doped oxidized film formed by normal pressure CVD (hereinafter abbreviated as BSG)/single crystalline silicon; Sample 5-4 was a phosphorus doped oxidized film formed by normal pressure CVD (hereinafter abbreviated as PSG)/single crystalline silicon; Sample 5-5 was a phosphorus and boron doped oxidized film formed by normal pressure CVD (hereinafter abbreviated as BSPG)/single crystalline silicon; Sample 5-6 was a nitrified film formed by plasma CVD (hereinafter abbreviated as P-S:N)/single crystalline silicon; Sample 5-7 was a thermally nitrified film (hereinafter abbreviated as T-S:N)/single silicon; Sample 5-8 was a nitrified film formed by low pressure DCVD (hereinafter abbreviated as LP-S:N)/single crystalline silicon; Sample 5-9 was a nitrified film formed by ECR device (hereinafter abbreviated as ECR-SiN)/single crystalline silicon. Further, according to combinations of the first substrate surface material which was electron donative and the second substrate surface material which was non-electron donative, Samples 5-11 - 5-179 shown in Table 2 were prepared. As the first substrate surface material were employed single crystalline silicon (single crystalline Si), polycrystalline silicon (polycrystalline Si), amorphous silicon (amorphous Si), tungsten (W), molybdenum (Mo), tantalum (Ta), tungsten silicide (WSi), titanium silicide (TiSi), aluminium (Al), aluminiumsilicon (Al-Si), titaniumaluminium (Al-Ti), titanium nitride (Ti-N), copper (Cu), aluminiumsiliconcopper (Al-Si-Cu), aluminiumpalladium (Al-Pd), titanium (Ti), molybdenum silicide (Mo-Si), tantalum silicide (Ta-Si). By use of these samples and Al₂O₃ substrate, SiO₂ glass, Al was deposited under deposition conditions: Reaction tube pressure : 9x10 Pa (0.7 Torr) TMA partial pressure: 2.0x10⁻²Pa (1.5x10⁻⁴ Torr) Plasma generation power density: 0.045 W/cm³ Deposition time: 20 minutes. The film forming conditions are a reaction tube pressure of 4x10 Pa (0.3 Torr), a DMAH partial pressure of 4.0x10⁻³ Pa (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 Samples 5-1 to 5-179, deposition of Al film occurred only on the first substrate surface which was electron donative to embed completely the opening with a depth of 800.0 nm (7000 Å). The film quality of Al film exhibited the same properties as one deposited under the same conditions as shown in Example 1, having both good resistivity and reflectance. On the other hand, no Al film was deposited at all on the second substrate surface which was non-electron donating. Also, on Al₂O₃ substrate and SiO₂ glass substrate which was non-electron donative, no Al film was deposited at all. Example 5 On an Si wafer having a part of Si exposed by patterning of an SiO₂ film Al was deposited under the following conditions. The Si wafer was prepared according to the same procedure as in Example 1. First, after deposition of Al under the deposition conditions (1), Al was subsequently deposited under the deposition conditions (2). The deposition conditions (1) were as follows: reaction tube temperature: 9x10 Pa (0.7 Torr) TMA partial pressure: 2.0x10⁻²Pa (1.5x10⁻⁴ Torr) plasma generation power density: 0.045 W/cm³ substrate temperature: 220 °C or 250 °C The deposition conditions when the substrate temperature was 220 °C were called the deposition conditions (1a), and those when the substrate temperature 250 °C the deposition conditions (2a). The deposition conditions (2) were as follows: reaction tube temperature:9x10Pa (0.7 Torr) TMA partial pressure: 2.0x10⁻² Pa (1.5x10⁻⁴ Torr) or 2.0x10⁻¹ Pa (1.5 x 10⁻³ Torr) plasma generation power density: 0.045 W/cm³ substrate temperature: 300 °C or 350 °C The deposition conditions when the TMA partial pressure was 2.0x10⁻² Pa (1.5x10⁻⁴ Torr), the substrate temperature 300 °C were called the deposition conditions (2a), those when the TMA partial pressure 2.0x10⁻² Pa (1.5x10⁻⁴ Torr) and the substrate temperature 350°C, the deposition conditions (2b), those when the TMA partial pressure 2.0x10⁻¹Pa (1.5 x 10⁻³ Torr) and the substrate temperature 300 °C, the deposition conditions (2c), and those when the TMA partial pressure 2.0x10⁻¹ Pa (1.5x10⁻³ Torr) and the substrate temperature 350 °C, the deposition conditions (2d). According to the eight combinations of the deposition conditions (1a), (1b) and the deposition condition of (2d), Al films were deposited to 700.0 nm (7000 Å). In all the conditions, Al was deposited only on the Si exposed portion. All the samples had resistivities similar to the bulk as 2.7 to 3.0 µΩ·cm. In Example, when the deposition temperature was 300 °C or higher, the reflectance was deteriorated, but in this Example when deposition was effected subsequently to the deposition conditions (1a) or (1b), the reflectance was good as 85 to 95 %, with surface flatness being also very good. Also, when deposition was effected under the deposition conditions (2d), the deposition rate was very great as ca. 0.7 to 1.0 µm/min. Example 6 Deposition was carried out according to the same procedure as in Example 1 under the following conditions: reaction tube pressure:9x10 Pa (0.7 Torr) TMA partial pressure 2.0x10⁻²Pa (1.5 x 10⁻⁴ Torr) plasma generation power density: 0.045 W/cm³ substrate temperature: 270 °C In transporting TMA to the reaction tube, H₂ gas containing Si₂H₆ was transported into the reaction tube from the pipeline (2) 15 in Fig. 1. Deposition was carried out by varying Si₂H₆ partial pressure from 2.0x10⁻⁴ to 2.0x10⁻³Pa (1.5x10⁻⁶ to 1.5x10⁻⁵ Torr). An Al-Si film containing Si having the same properties as Al under the same substrate temperature, the TMA partial pressure, the plasma generation power as in Example 1 could be deposited only on the exposed portion of Si. The Si amount in the deposited film was proportional to the Si₂H₆ pressure, and varied from 0.25 % to 2.5 % under the above conditions. Example 7 The organometallic vessel used in Example 1 is provided with only the inflow valve 24 and the outflow valve 25 of the carrier gas. By use of the organometallic vessel equipped with a bypass valve according to the present inventors, and also by use of the device in Fig. 1 with the distance from the carrier gas valve 25 mounted on the organometallic vessel to the connector 33 at the upper portion of the reactor being made approximately 50 cm or less, the same experiment as in Example 1 was carried out. The same Al film as in Table 1 was deposited only on the Si exposed surface. Further, in Example 1, the time when selectivity was maintained was approximately one hour, but in this Example, the time when selectivity was maintained was elongated to about 2 hours. That is, due to the reduced dead zone in the pipelines, alkanes or TMA molecules decomposed not completely were reduced, whereby the ideal reaction could be maintained for a long time. The constitution of the reverse flow presention meens for ensuring the selective excitation state can be determined suitably without being limited to the above Examples. For example, as shown in Fig. 3, even if the reaction tube may have a straight tube shape similarly as in Fig. 1, by provision of a holder 7′ which is arranged with the wafer 1 being slanted, a flow having components slanted relative to the axis line can be obtained, whereby reverse flow into the plasma caused by generation of convection or eddy will occur with difficulty and good selective deposition state can be obtained. Of course. the combination of the slanted arrangement of the substrate as shown in Fig. 3 and the horn shape in Fig. 1 was also extremely good.

Claims: A method of selective film deposition for deposition of aluminium Al film, optionally aluminium silicide Al-Si film, onto a substrate, which method comprises: introducing trimethyl aluminium starting gas, hydrogen gas, and optionally disilane, into a reaction tube and generating a high frequency plasma at a pressure of between 7x10 and 2.0x10² Pa (0.5 and 1.5 Torr) and at a plasma power density in the range 0.03 to 0.06 W/cm³, which plasma is confined within a zone of said reaction tube spaced from said substrate; causing the product gases thereof to flow towards said substrate, which substrate has an electron donative surface portion and is at an elevated temperature of 180 to 350°C, while substantially preventing reverse flow of said product gases back into said confined plasma, thereby to deposit aluminium film, optionally aluminium silicide film, selectively on said electron donative surface portion of said substrate. A method as claimed in claim 1 wherein said product gases flow towards said substrate through a portion of said reaction tube which is of expanding cross-section area, by which means reverse flow is substantially prevented. A method as claimed in either of claims 1 or 2 wherein said product gases are caused to flow towards said substrate at an angle to the normal to the surface thereof, by which means reverse flow is substantially prevented. A method as claimed in any one of the preceding claims wherein said electron donative surface portion of said substrate is of one of the following materials: single crystalline silicon, polycrystalline silicon, amorphous silicon, tungsten, molybdenum, tantalum, tungsten silicide, titanium silicide, aluminium, aluminium silicon, titanium aluminium, titanium nitride, copper, aluminium silicon copper, aluminium palladium, titanium, molybdenum silicide, tantalum silicide. A method as claimed in any one of the preceding claims wherein said substrate has a non-electron donative surface portion which is of one of the following materials: SiO₂, Al₂O₃, SiN, silicon oxide doped with boron or phosphorus. An apparatus for performing the method of claim 1, which apparatus comprises: a reaction tube (2;2'); mounting means (7;7') for mounting a substrate (1) in said reaction tube (2;2'); gas supply means (34) for supplying trimethyl aluminium starting gas, hydrogen gas, and optionally disilane, to said reaction tube; gas evacuation means (12,11) for evacuating gases from said reaction tube (2;2'), and which is cooperative with said gas supply means (34) for maintaining pressure in said reaction tube (2;2') in the range 7x10 to 2.0x10² Pa (0.5 to 1.5 Torr); energising means (3,4) co-operative with said reaction tube (2;2'), for generating a high frequency plasma in a confined zone (32) of said reaction tube (2;2'), which zone (32) shall be spaced from the substrate (1) when mounted on said mounting means (7;7'), which energising means (3,4) is operable to produce plasma at a power density in the range 0.03 to 0.06 W/cm³; and heating means (6) for heating the substrate (1) to an elevated temperature of 180 to 350°C; which apparatus is characterised in that: said reaction tube (2) is of flared construction, the cross section increasing in the direction of said mounting means (7;7') and/or said mounting means (7') is arranged for holding said substrate (1) at an angle at which the normal to the surface of the substrate (1) is inclined to the axis of flow; thereby substantially preventing the reverse flow of product gases back into said zone (32) where said plasma is confined. Apparatus as claimed in claim 6 wherein said reaction tube (2) is horn-shaped, being either conical or pyramidal, the flare angle thereof being 10 to 20°.

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: C23C16, H01L21