Method of producing a semiconductor device with Schottky junction

Abstract: A semiconductor device having a Shottky junction comprises: a first semiconductor area composed of an n-type semiconductor; a second semiconductor area composed of an n-type semiconductor of a higher resistance than in said first semiconductor area; an insulation film provided adjacent to said second semiconductor area and having an aperture therein; an electrode area provided in said aperture; and a third semiconductor area composed of a p-type semiconductor provided at the junction between said insulation film and said electrode area. The electrode area is composed of a monocrystalline metal and constitutes a Shottky junction with said second semiconductor area.

Description: The present invention relates to a process for producing a semiconductor device having a Schottky junction. In the preparation of a conventional semiconductor device with a Schottky junction, such as a Schottky barrier diode, aluminium film, constituting a Schottky barrier with a semiconductor, has been formed by sputtering or evaporation. However such conventional method has been associated with a first drawback that Al and Si constituting the Schottky barrier diode react by mutual diffusion in a thermal treatment of 400 - 500°C for forming ohmic contact after the Al film formation. Also a second drawback lies in a fact that the breakdown voltage of such diode is lower than that of a PN junction diode. In the following an additional explanation will be given on the conventional semiconductor device with a Schottky junction. So-called PNM type semiconductor device, which a modification of lateral PNP semiconductor device, is so designed to concentrate the current in a Schottky junction formed in a portion corresponding to the collector of the lateral PNP device, thereby realizing a function equivalent to that in the ordinary PNP device. Figs. 1 and 2 are band charts showing the function states of a PNM device, while Figs. 3 and 4 are band charts showing the function states of a PNP device, wherein shown are an emitter 201, 210; a base 202, 211; a collector 203, 212; and a depletion layer 204, 213 between the collector and the base. The movement of the positive holes, functioning as the principal carriers, is same in both devices. Fig. 5 illustrates a conventional PNM semiconductor device, wherein shown are semiconductor substrate 101 for example of p-type; an n + buried layer 102 constituting the collector; an n-epitaxial layer 103 constituting the actual device; an isolation area 104; a diffused emitter area 105; emitter and base electrodes 107; Schottky electrodes 118 composed for example of aluminum for constituting Schottky junctions with the epitaxial layer 103; an insulation layer 106 composed for example of SiO 2 for insulating the emitter, base electrodes 107 and the metal layers 118 from the semiconductor surface; and a diffusion layer 109 for electrical connection with the base electrode 107. Also Fig. 6 shows a conventional structure in which a Schottky junction is utilized in the drain portion, wherein shown are an n-type semiconductor substrate 111; a diffusion layer 112 constituting a source area; an isolation oxide film 113 formed for example by LOCOS (local oxidation of silicon); an insulation layer 114 composed for example of phosphor glass; a Schottky electrode 115 composed for example of Al; a gate oxide film 116; a gate electrode 117; and a source electrode 118. The conventional PNM semiconductor device shown in Fig. 5 has been associated with a drawback of an extremely low current collecting efficiency because of a planar structure of the Schottky junction. As shown in Fig. 7, the depletion layer 119 generated at the Schottky junction (collector) is concentrated in the surface area of the device and is therefore unable to efficiently collect the carriers diffusing from the emitter, so that the carriers leak to the device isolation area, leading to a lowered current gain. It is also necessary to effect control on the silicon substrate so as to realize satisfactory interface characteristics. Also as shown in Fig. 8 which is a magnified view of Fig. 7, the depletion layer 119 generates a protruding portion 119a extending along the surface of the device, thus forming a generation/recombination (G-R) area and hindering the improvement in the device characteristics. It is also conceived, in order to prevent such drawback, to form a highly doped region 120 in a position corresponding to said protruding portion 119a as shown in Fig. 9. A process of producing a Schottky junction device having a highly doped region guard ring surrounding the periphery of the Schottky junction, is described in Japanese Patent Application JP-A-02051274. Features of this disclosure which are common to the present invention are recited in the preamble of claim 1. Schottky contact metallisation is performed by depositing platinum and forming a platinum silicide junction. In consideration of the foregoing, a principal object of the present invention is to provide a method for producing a semiconductor device capable of high-speed rectifying operation. Another object of the present invention is to provide a highly reliable semiconductor device of satisfactory performance and a sufficiently high breakdown voltage with a low cost. Still another object of the present invention is to provide a semiconductor device having a metal electrode constituting a Schottky junction. The present invention, as defined by the appended claims, is characterised by a metallisation step in which a Schottky contact and another contact are produced simultaneously by filling contact holes with monocrystalline aluminium deposited selectively by chemical vapour deposition using an alkylaluminium hydride and hydrogen. In the accompanying drawings: Figs. 1 and 2 are band charts showing function states of a PNM device; Figs. 3 and 4 are band charts showing function states of a PNP device; Fig. 5 is a longitudinal partial cross-sectional view of a conventional PNP semiconductor device; Fig. 6 is a longitudinal cross-sectional view of a conventional structure in which a Schottky junction is utilised in a drain portion; Fig. 7 is a cross-sectional view showing the function of the conventional semiconductor device shown in Fig. 5; Figs. 8 and 9 are schematic views showing a depletion layer formed in conventional semiconductor devices; Fig. 10 is a schematic cross-sectional view of a Schottky barrier diode; and Figs. 11A to 11D are schematic cross-sectional views showing a method for producing the Schottky barrier diode, which method is an embodiment of the present invention. According to a preferred embodiment of the present invention, there is provided a method of producing a semiconductor device having a Schottky junction consisting of a metal electrode and a semiconductor area, wherein said metal electrode is formed by a single crystal principally composed of Al. Also foregoing objects can be attained by a method for producing a semiconductor device, in which a Schottky electrode area is formed by a chemical vapour deposition (CVD) process utilising alkylaluminium hydride gas and hydrogen. The present invention enables the preparation of a Schottky junction in a well controlled and uniform manner by controlling the reaction between Al and Si, by selectively burying monocrystalline aluminium in a constant hole, utilising the CVD process utilising alkylaluminium hydride and hydrogen, called Al-CVD process. Fig. 10 illustrates a semiconductor device having a Schottky junction, provided with: a first semiconductor area of an n-type semiconductor; a second semiconductor area of an n-type semiconductor of a higher resistance than in the first semiconductor area; an insulation film provided adjacent to the second semiconductor area and having an aperture; an electrode area formed in the area of the aperture; and a third semiconductor area of a p-type semiconductor formed at the junction of the insulation film and the electrode area; wherein said electrode area is composed of monocrystalline aluminium constituting a Schottky junction with the second semiconductor area. Fig. 10 illustrates, as an example of a semiconductor device having a Schottky junction, a Schottky barrier diode. On a p-type semiconductor substrate 301 there is formed a buried layer 302, on which an n-type layer 303 is epitaxially grown. From the principal surface of the substrate there is formed an n + layer 304 for contacting with the buried layer 302, and said n + layer is in ohmic contact with an upper cathode electrode. On the n layer 303 there are provided silicon oxide layers 305, 307, in which an aperture is formed to locally expose the n layer 303 and monocrystalline Al is formed therein to constitute a Schottky junction with said n layer 303. A p + -layer 306 is formed below and across the boundary between the anode electrode consisting of said monocrystalline Al and the silicon oxide insulation layer 305. Since the anode electrode in contact with the n-layer 303 including the junction thereof with the p + -layer 306 is formed by monocrystalline aluminium, the interface characteristics are improved to provide a satisfactory Schottky junction. Now reference is made to Figs. 11A to 11D for explaining the method of the present invention for producing a Schottky barrier diode utilizing aluminium film. At first, on a semiconductor substrate 301, there is formed an n + -layer 302 of a high impurity concentration, as a buried layer for reducing the serial resistance (Fig. 11A). Then an n-semiconductor layer 303 is epitaxially grown., The impurity concentration is such as to form a Schottky junction with aluminium and is preferably 5 x 10 16 /cm 3 or lower. Subsequently an n + -layer 304 of a high impurity concentration is formed for reducing the serial resistance, and a thin thermal oxide film 305 of 30-50 nm (300-500Å) is formed in the device forming area. Then a p + -layer 306 is formed thereon by ion implantation in order to secure the inverse voltage resistance of the Schottky barrier diode, and an interlayer insulation film 307 of a thickness of 300 - 800 nm (3000 - 8000 Å) is formed by a CVD process (Fig. 11B). Then contact holes are formed by opening the interlayer insulation film 307 and the thermal oxide film 305 in desired positions by an ordinary photolithographic process, and aluminium for forming wiring electrodes is selectively grown in said contact holes by a CVD process to be explained later. The aluminium film formation is conducted, in a reaction chamber evacuated to a pressure of 0.7 Pa (5x10 -3 Torr) or lower, by introduction of dimethylaluminium hydride (DMAH) with H 2 as carrier gas, with a total pressure of 70 Pa-10 5 Pa (0.5-760 Torr), preferably 1.3-11.0 x 10 Pa (0.1 to 0.8) Torr with a DMAH partial pressure of 1x10 -5 to 1.3 x 10 -3 times of the total pressure and with a substrate temperature of 270 - 350°C. The formed Al film 308 grows as a single crystal selectively in the contact hole, and can fill in the contact hole with flat top surface (Fig. 11C). After the contact holes are filled with aluminium, an Al film of a thickness of 400-1200 nm (4000-12000 Å) is formed by sputtering with a substrate temperature of 100 - 500°C without breaking the vacuum condition, and is subsequently patterned by a photolithographic process to form wiring electrodes 309. The use of monocrystalline Al obtained by the above-explained CVD process in the Al electrodes of the Schottky barrier diode suppresses the reaction between Al and Si of substrate, thereby providing the following advantages: 1) well-controlled Schottky characteristics; 2) reduced device-to-device fluctuation; and 3) semiconductor device of high reliability, capable of high-speed operation, can therefore be obtained with a high production yield. The Al-CVD process employed for forming the Schottky electrode provides particularly satisfactory interface characteristics, thus allowing to obtain a satisfactory Schottky junction,and facilitates the control of preparation of the device. [Description of preparation method] In the following there will be outlined the method for producing the Schottky electrode, adapted for use in the present invention. [Film forming method] In the following there will be explained a method for forming a metal film composed solely or principally of aluminium, adapted for use in the present invention, said method being called Al-CVD process. This method is suitable for filling a fine and deep aperture with an aspect ratio of 1 or larger, such as a contact hole or a through hole, with a metal material, and is characterized by a splended selectivity. The metal film formed by this method is characterized by splendid crystallinity, such as monocrystalline aluminium, and is almost free from carbon inclusion. Said metal film has excellent surface characteristics, with a resistivity as low as 0.7 to 3.4 µΩ·cm, a reflectance as high as 85 to 95 %, and a density of hillocks equal to 1 µm or larger in a range of 1 to 100 cm -2 . Also the probability of generation of alloy spikes at the interface with silicon, represented by the probability of destruction of semiconductor junction of 0.15 µm, is almost equal to zero. More specifically, said method consists of forming a deposition film by a surface reaction, on an electron-donating substrate, utilizing alkylaluminium hydride gas and hydrogen gas. An aluminium film of particularly satisfactory quality can be deposited by employing mono-methylaluminium hydride (MMAH) or dimethylaluminium hydride (DMAH) as the raw material gas and hydrogen as the reaction gas, and heating the substrate surface. At the selective deposition of aluminium, the substrate surface is preferably heated, either by direct or indirect heating, to a temperature range at least equal to the decomposition temperature of alkylaluminium hydride but lower than 450°C, more preferably within a range from 260 - 440°C. The substrate may be heated to the above-mentioned temperature range either by indirect or direct heating, but an aluminium film of satisfactory quality can be obtained with a particularly high deposition speed if the substrate is maintained within the above-mentioned temperature range by direct heating. For example, when the substrate surface temperature is maintained within the more preferred range of 260 - 440°C by direct heating, a satisfactory film can be obtained with a deposition speed of 300 - 500 nm/min (3000 - 5000 Å/min.), which is higher than the deposition speed obtainable with resistance heating. Such direct heating, in which the substrate is heated by direct energy transfer from heating means, is for example achieved by heating with lamps, such as halogen lamps or xenon lamps. The indirect heating can for example be achieved by resistance heating, utilizing a heat generating member provided in a substrate support member, provided for supporting the substrate for film formation in a film forming chamber. This method, when applied to a substrate having both an electron donating surface area and an electron non-donating surface area, forms monocrystalline aluminium with a satisfactory selectivity, solely on the electron donating surface area. The electron donating material means a material in which free electrons are present or intentionally generated, and which has a surface capable of accelerating a chemical reaction by electron transfer with molecules of the raw material gas deposited onto said surface. Metals and semiconductors generally fall into this category. Also metals and semiconductors having a thin surfacial oxide film are included in the electron donating materials of the present invention, since a chemical reaction can be induced by electron transfer between the substrate and the raw material molecules deposited thereon. Examples of the electron donating material include III-V compound semiconductors of two-, three- or multielement system obtained by combining element(s) of group III such as Ga, In, Al etc. with element(s) of group V such as P, As, N etc.; and semiconductors such as monocrystalline or amorphous silicon. On the other hand, example of the electron non-donating material, constituting a surface not inducing selective deposition of Al or Al-Si, include silicon oxide formed by thermal oxidation or by CVD; glass materials such as BSG, PSG and BPSG; oxide films; thermal nitride films; and a silicon nitride film formed by plasma CVD, low pressure CVD, or ECR-CVD. Also since said Al-CVD method is capable of film formation with excellent selectivity and with satisfactory surface characteristics of the obtained film, there may be employed non-selective film forming method in the succeeding film deposition to obtain a metal film solely or principally composed of aluminium, both on the selectively deposited aluminium film and on the SiO 2 insulation film, thereby obtaining a metal film generally usable as wirings for the semiconductor devices. Such metal film can be obtained by the combinations of non-selectively deposited Al, Al-Si, Al-Ti, Al-Cu, Al-Si-Ti or Al-Si-Cu and selectively deposited Al, Al-Si, Al-Ti, Al-Cu, Al-Si-Ti or Al-Si-Cu. Said non-selective film deposition can be achieved for example by a CVD method other than the above-explained Al-CVD method, or by sputtering. The wirings may also be formed by forming a conductive film by CVD or sputtering, patterning said film to obtain a sub layer of a form of desired wirings, and selectively depositing aluminium or a metal principally composed of aluminium on said sub layer by the Al-CVD method. Furthermore a metal may be deposited on an insulation film by the Al-CVD method. For this purpose the insulation film is subjected to a surface modification to form a substantially electron-donating surface area. In this operation a pattern of desired wirings may be drawn with a beam, whereby the film is selectively deposited only on the electron-donating area obtained by said beam drawing, and the wirings can be obtained in self-aligned manner without the patterning operation.

Claims: A method of producing a semiconductor device having a Schottky junction, which method comprises the following steps: forming an n + -type semiconductor layer (302) of a high impurity concentration on a semiconductor substrate (301); forming an n-type semiconductor layer (303) of lower impurity concentration, adapted for forming a Schottky junction with aluminium, on said n + -type semiconductor layer (302); forming an n + -type semiconductor region (304) of a high impurity concentration in said n-type semiconductor layer (303) and in contact with said n + -type semiconductor layer (302); forming a p + -type semiconductor region (306) as a guard ring in said n-type semiconductor layer (303); forming an insulation film (305, 307) having a first contact hole exposing a region of said n-type semiconductor layer (303) and part of the surrounding p + -type semiconductor guard ring region (306); and forming a Schottky metal contact (308) at the exposed region of said n-type semiconductor layer (303); which method is characterised in that: said insulating film (305, 307) is formed having therein a second contact hole exposing said n + -type semiconductor region (304); and said Schottky metal contact (308) and a contact to said n + -type semiconductor region (304) are produced simultaneously by depositing monocrystalline aluminium selectively by chemical vapour deposition using an alkyl aluminium hydride and hydrogen. A method as claimed in claim 1 wherein after the first and second contact holes are filled with monocrystalline aluminium, an aluminium film is formed by sputtering and is patterned by a photolithographic process. A method as claimed in claim 2 wherein after the chemical vapour deposition is performed, the sputtering is performed without breaking vacuum.

Inventors: KIKUCHI SHIN, NAKAMURA YOSHIO, NISHIMURA SHIGERU, KIKUCHI, SHIN, NAKAMURA, YOSHIO, NISHIMURA, SHIGERU
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: H01L29
IPC codes: H01L29, H01L21