Compound semiconductor substrate and method of manufacturing the same

Abstract: According to this invention, there is provided a compound semiconductor substrate (16) including, on a compound semiconductor base (12) containing a high-concentration impurity, a high-resistance single-crystal layer (14) consisting of the same compound semiconductor as the compound semiconductor constituting the base. Active elements are formed in the high-resistance single-crystal layer (14).

Description: The present invention relates to a method of manufacturing a compound semiconductor device. GaAs is known well as a type of a compound semiconductor. When the GaAs is made to have a resistivity of 10⁶ Ω·cm or more, it has semi-insulating characteristics. When active elements are formed in a semi-insulating GaAs substrate, they are not advantageously required to be electrically isolated from each other using a field insulating film. In order to obtain this advantage, a semi-insulating GaAs single-crystal is conventionally made using a single-crystal manufacturing technique such as an LEC method, and the single-crystal is sliced to manufacture semi-insulating GaAs substrates. Since the semi-insulating GaAs single-crystal is constituted by bonding two types of atoms, a shearing stress acting inside the Gas single-crystal is stronger than that of a silicon single-crystal, and a dislocation density in the GaAs single-crystal is disadvantageously increased. The following documents all show some of the features of the present invention. Applied Physics Letters, Vol. 37, No.8, October 1980, New York US, pages 734-737; S. A. Barnett et al.: "Growth of high-quality epitaxial GaAs films by sputter deposition"; Derwent Publications Ltd., London, GB, database WPI Accession No.79-134188, week 7907 & JP-A-54 004 567 (Nippon Electric KK) 13 January 1979; Applied Physics Letters, Vol. 42, No.1, January 1983, New York US, pages 66-68; JCM Hwang et al.: "Growth of high-purity GaAs layers by molecular beam epitaxy"; Applied Physics Letter, vol. 42, No.2, January 1983, New York US, pages 178-180; H Temkin et at.: "Un-doped, semi-insulating GaAs layers grown by molecular beam epitaxy"; Patent Abstracts of Japan, Vol. 10, No.258 (E-434) 04 September 1986, & JP-A-61 085 814 (NEC Corp) 01 May 1986; Materials Letters, Vol. 5, No.4, March 1987, Amsterdam NL, pages 129-133; S. Ozawa et al: "In-doped GaAs substrate assessment for thin film applications". Nevertheless none of the documents suggest forming a semi-insulating epitaxial layer and manufacturing compound semiconductor devices in the layer, on a doped single-crystal substrate. The present invention has been made in consideration of the above problem, and has as its object to provide a method of manufacturing a compound semiconductor device with a substrate having a low dislocation density. The above object can be achieved by the following arrangement. According to the present invention there is provided a method of manufacturing a compound semiconductor device as set out in claim 1. Since a high concentration impurity is contained in the compound semiconductor base, a dislocation density can be decreased. When the same semiconductor as that of the compound semiconductor base is epitaxially grown on the compound semiconductor base having a low dislocation density, a high-resistance single-crystal layer having a low dislocation density, i.e., a single-crystal layer having semi-insulating characteristics can be formed. When the high-resistance single-crystal layer is formed in a portion where an active element is to be formed, a compound semiconductor substrate having a low dislocation density and even advantageously having a high-resistance, i.e., semi-insulating characteristics can be obtained. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a graph showing a relationship between an impurity concentration and a dislocation density; Figs. 2A to 2E are perspective views showing a compound semiconductor substrate according to the embodiment of the present invention in the order of manufacturing steps; Fig. 3 is a partially enlarged sectional view showing the compound semiconductor substrate in Fig. 2E; and Fig. 4 is a sectional view showing a condition wherein an active element is formed in the compound semiconductor substrate in Fig. 3. An embodiment of the present invention will be described below with reference to the accompanying drawings. As a method of relieving a shearing stress, a phenomenon wherein an impurity is doped in a single-crystal to decrease a dislocation density in the single-crystal is known. A curve I in Fig. 1 indicates a decrease in dislocation density when an impurity is doped in GaAs after a crystal is grown. The decrease in dislocation density typically occurs when an n-type impurity is doped. As is indicated by the curve I in Fig. 1, a doping concentration of the impurity at a time when the dislocation density is rapidly decreased is 5 × 10¹⁷ cm⁻³ or more. This phenomenon is not limited to the GaAs, and it occurs in a compound semiconductor such as GaP or InP consisting of two elements. Silicon or carbon is used as an n-type impurity, and selenium, magnesium or the like is used as a p-type impurity. When the n- or p-type impurity is used, a doping concentration is set to be 5 × 10¹⁷ cm⁻³ or more to obtain a compound semiconductor single-crystal having a low dislocation density. The present invention is made on the basis of the above phenomenon, n-type GaAs in which a single-crystal, e.g., a silicon element, having a density of 5 × 10¹⁷ cm-³ or more is doped as an impurity is grown by an LEC method or an HB method, thereby forming an n-type GaAs single-crystal 10 having a low dislocation density (Fig. 2A). The single-crystal 10 is cut (Fig. 2B). The cut single-crystal 10 is sliced to obtain an n-type GaAs base 12 (Fig. 2C). The base 12 sliced as described above is prospectively used as a substrate for epitaxial growth. Mirror polishing is performed on the surface of the base 12, and the base 12 is washed by a chemical treatment to clean its mirror surface (Fig. 2D). A high-resistance GaAs single-crystal layer 14 having a resistivity of 10⁶ Ω·cm is epitaxially grown on the surface of the base 12 (Fig. 2E). In order to form the single-crystal layer 14 having a resistivity of 10⁶ Ω·cm or more, an amount of impurity contained in GaAs is decreased, or the GaAs is undoped. The high-resistance GaAs single-crystal layer 14 is prospectively used as a portion where an active element is to be formed. A compound semiconductor substrate 16 according to the present invention is finished by the above method. A dislocation density of a single-crystal layer which is epitaxially grown is generally lower than that of a substrate on which the single-crystal layer is grown. In the GaAs substrate 16 with the above arrangement, the dislocation density of the n-type GaAs base 12 is decreased by doping an impurity, and the dislocation density of the GaAs single-crystal layer 14 grown on the base 12 is further decreased. At present, in a GaAs substrate consisting of an undoped GaAs single-crystal, a dislocation density is about 50,000 cm⁻² at a portion where an active element is to be formed. In the GaAs substrate 16 according to the present invention, the dislocation density of the GaAs single-crystal layer 14 where an active element is to be formed can be set to be 100 cm⁻² or less. Fig. 3 is a partially enlarged sectional view showing the GaAs substrate 16 shown in Fig. 2E, and Fig. 4 is a sectional view showing a condition wherein an active element is formed on the GaAs substrate 16. As shown in Fig. 3, the GaAs single-crystal layer 14 which is undoped to have a high-resistance is stacked on the n-type GaAs base 12 by epitaxial growth. The high-resistance GaAs single-crystal layer 14 is a layer where an active element 18 is prospectively formed, and an active region 20 prospectively serving as a source, a drain, and a channel of the active element 18 is formed on the single-crystal layer 14. Since the high-resistance GaAs single-crystal layer 14 is formed to have a resistivity of 10⁶ Ω·cm or more, a field insulating film for isolating the active elements 18 from each other need not be formed (the high-resistance GaAs single-crystal layer 14 has semi-insulating characteristics). In addition, since the high-resistance GaAs single-crystal layer 14 is epitaxially grown on the n-type GaAs base 12 having a low dislocation density, the dislocation density of the single-crystal layer 14 is also low. The active elements 18 formed on the GaAs single-crystal layer 14 having a low dislocation density have excellent characteristics, and variations in characteristics of all the active elements 18 can be decreased. Since the variations in characteristics of the active elements 18 can be decreased, in all cases wherein an IC/LSI is formed and wherein an individual semiconductor device is formed, the performance of the IC/LSI and the individual semiconductor device can be improved, and a yield of the products can be improved. In the compound semiconductor substrate 16 according to the present invention, a thickness t of the high-resistance GaAs single-crystal layer 14 is required to be a minimum thickness required for forming the active region 20. For example, at present, when the thickness t of the high-resistance GaAs single-crystal layer 14 is set to be about 500 nm or more, it can sufficiently cope with formation of the active region 20. When the high-resistance GaAs single-crystal layer 14 is epitaxially grown, a method of growing a crystal at an atomic layer level such as MBE, MOCVD, or MOMBE is preferably used from the viewpoint of improvements of a film quality and controllability of the film thickness t . This embodiment has been described in the combination of the GaAs base 12 containing a high-concentration impurity and the GaAs single-crystal layer 14 which is undoped to have a high resistance. However, the same effect as described above can be obtained with the following combinations. 1) GaP is used as the base 12, and GaP is used as the single-crystal layer 14. 2) InP is used as the base 12, and InP is used as the single-crystal layer 14. In the above combinations, as in the above embodiment, the base 12 contains an impurity to have a low dislocation density. The single-crystal layer 14 stacked thereon is undoped to have a high resistance so as to have semi-insulating characteristics. As an impurity having an effect of decreasing the dislocation density of the base 12, carbon, selenium, magnesium, or the like is used in addition to silicon. When any of these impurities is doped not only in a GaAs single-crystal but also in a GaP or InP single-crystal, the dislocation density of the single-crystal can be decreased.

Claims: A method of manufacturing a compound semiconductor device, including a compound semiconductor substrate (16), comprising the step of epitaxially growing the same compound semiconductor as a compound semiconductor base (12) to form a semi-insulating epitaxial single-crystal layer (14) of sufficiently high resistance to give semi-insulating characteristics for electrical isolation of active elements (18) on the substrate, the layer being formed on a major surface of said compound semiconductor base containing an impurity of sufficiently high concentration to give significantly decreased dislocation density; and forming active elements in said semi-insulating epitaxial layer, said semi-insulating epitaxial layer being used as an element-isolating region for isolating said active elements from each other. A method according to claim 1, characterised in that a concentration of an impurity of said compound semiconductor base is not less than 5 x 10¹⁷ cm⁻³. A method according to claim 1, characterised in that a resistivity of said high-resistance single-crystal layer is not less than 10⁶ Ω·cm. A method according to claim 1, characterised in that said high-resistance single-crystal layer is an undoped layer. A method according to claim 1, characterised in that said high-resistance single-crystal layer has a thickness of not less than 500 nm. A method according to claim 1, characterised in that said impurity is an element selected from the group consisting of silicon, selenium, and magnesium. A method according to claim 1, characterised in that said compound semiconductor comprises an element from Group III, IV or V. A method according to claim 7, characterised in that said compound semiconductor is selected from the group consisting of GaAs, GaP, and InP. A method according to claim 1, characterised in that the step of epitaxially growing the same compound semiconductor as said compound semiconductor base comprises the step of performing one method selected from the group consisting of MBE, MOCVD and MOMBE.

Inventors: IWASAKI HIROSHI, IWASAKI, HIROSHI, IWASAKI, HIROSHI, C/O INTELLECTUAL PROPERTY DIV.
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1991
Main classification: C30B29
IPC codes: H01L21, H01L27, H01L29