GB2189166A

GB2189166A - A single crystal of IIIb-Vb compound, particularly GaAs, and method for producing the same

Info

Publication number: GB2189166A
Application number: GB08609480A
Authority: GB
Inventors: Kouji Sumino; Fumikazu Yajima; Toshihiko Ibuka; Fumio Orito
Original assignee: Mitsubishi Kasei Corp; Mitsubishi Monsanto Chemical Co
Current assignee: Mitsubishi Kasei Polytec Co; Mitsubishi Kasei Corp
Priority date: 1985-02-04
Filing date: 1986-04-18
Publication date: 1987-10-21
Also published as: JPS61178497A; DE3614079A1; FR2597885A1; FR2597885B1; GB8609480D0

Abstract

A single crystal of IIIb-Vb group compound contains 1 x 10<17> SIMILAR 8 x 10<19> cm <3> of oxygen and has a dislocation density which is low and uniform in a direction perpendicular to the growth direction. An LEC method for crystal growth of a single crystal of GaAs comprises an addition of oxide at an oxygen concentration of 1 x 10<17> SIMILAR 2 x 10<21> cm <3>.

Description

SPECIFICATION A single crystal of Illb-Vb compound, particularly GaAs, and method for producing the same BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Illb-Vb group compound single crystal (hereinafter referred to as "lllb-Vb single crystal"), particularly to a gallium arsenide (GaAs) single crystal having a low dislocation density, and a production method thereof, in particular, to a liquid encapsulated Czochralski method (hereinafter referred to as the "LEC method"). The single crystal GaAs has a high electron mobility and hence is widely used for an UHF or SHF element, a high-speed switching element, and a substrate of integrated circuit (IC) ("Information Processing" 25 (1) pp 37-46 (1984) by Hideki Hasegawa).

2. Description of the Related Arts The properties required of a Illb-Vb single crystal, such as GaAs, when used as the above electronic elements and IC substrate, are a high level of purity, a high degree of crystalline perfection, and uniform electrical properties. A semi-insulative property is necessary for the IC substrate.

Dislocation, which degrades the crystalline perfection, causes malfunctions in ICs. Thus, in order to use the Illb-Vb single crystal for a substrate of highly integrated ICs and high output FETs having a large chip area, a Illb-Vb single crystal having a low dislocation density is first produced and then cut into wafers. The LEC method is used for producing a GaAs single crystal for use as the substrate of an IC or the like, since the thus-produced GaAs has a large diameter and a high level of purity needed to enhance the activation rate of ions implanted in a GaAs substrate (BULLETIN OF THE JAPAN INSTITUTE OF METALS. Vol 23 (1984), No. 7, pp 586--592).

In the LEC method, the B203 melt, which is an encapsulant, covers the surface of the melt of Illb-Vb group command. The temperature gradient across the layer of the B203 melt can amount to 100"C/cm, and hence is considered high as compared with the horizontal boat growth method. The GaAs single crystal pulled from the GaAs melt undergoes great thermal stress during passage through the layer of the B203 melt. This thermal stress is one cause of the generation of a number of dislocations in the Illb-Vb single crystal.The disclocation density, in terms of etch pit density (EPD) of the GaAs single crystals produced by the LEC method, generally ranges from approximately 104 to 105 cam~2. The dislocation distribution of GaAs single crystals produced by the LEC method, in a plane perpendicular to the pulling-up direction, is such that it is highest around the periphery, and is at its next highest level in the center of the Illb-Vb single crystals. The disclocation density, therefore, may be seen as a W shape, in which a low dislocation-density region is formed around the center and is encompassed by the outer, highest dislocation-density regions.

B. Jacob describes in "Semi-lnsulating Ill-V Materials" S. Makrnm-Ebid et al. Ed. p. 2--18 (1984) Shiva Publishing Ltd., a method for decreasing the dislocation by adding indium, which is an electrically neutral impurity, to the GaAs. According to this method, a GaAs single crystal is pulled up from the melt, to which metallic indium has been added in an amount of from 1018 to 1020 cm-3, and the disclocation density is drastically decreased by this In addition.

The present inventors investigated the dislocation density of Illb-Vb single crystals produced by the LEC method, and found a drastic reduction occurred in EPD of (100). Nevertheless, in several GaAs single crystals, etch pits arranged linearly in the t110 > direction around the periphery were discovered, and EPD occasionally exceeded 1 x 104 cm-2 in the region containing the etch pits.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a Illb-Vb single crystal which is free of locally high EPD and thus has a low EPD through the crystal.

It is another object of the present invention to improve an LEC method for the growth of a Illb-Vb group compound, thereby preventing locally high EPD in a plane perpendicular to the pulling direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Illb-Vb Single Crystal The Illb-Vb single crystal according to the present invention is characterized by containing from 1 x 1017 to 8x 1019 cm-3 of oxygen.

When the oxygen concentration of the Illb-Vb single crystal is less than 1 x 1017 cm-3, the amount of linear etch pits becomes appreciable, and thus the phenomenon of locally high EPD cannot be prevented. On the other hand, when the oxygen concentration exceeds 8 x 1019 cm-3, the crystalline properties are degraded. The compounds of Illb-Vb group are GaAs, InAs and InP.

The In concentration of the Illb-Vb single crystal is preferably from 1 x 1018 to 1 x 1020 cm-3.

At the In concentration less than 1 x 1018 cm-3, the EPD tends to increase. On the other hand, when the In concentration of the GaAs single crystal exceeds 1 x 1020 cm-3, the Illb-Vb single crystal tends to embrittle and disadvantageous precipitation and the like of In tends to occur. A more preferred In concentration is from 2x 1019 to 5x 1019 cm-3.

GaAs Single Crystal Containing Oxygen and Indium This GaAs single crystal can be produced by growing GaAs from a GaAs melt, to which from 1 x 1019 to 1 x 1021 cm-3 of In and from 1 x 1018 to 2x 1021 cm-3 of oxygen are added. The preferred added concentrations of In and oxygen are from 2 x 1020 to 5 x 1021 cm-3, and from 1 x 1018 to 3 x 1019 cm-3, respectively. The addition concentration herein indicates the number of atoms of In or oxygen added to 1 cm3 of the melt. When the addition concentrations lie outside the ranges mentioned above, the preferred In concentration and requisite oxygen concentration cannot be ensured in the GaAs single crystal.

The addition of In and oxygen to the GaAs melt is preferably carried out by using indium oxide (In203). In this case, the indium oxide is added to obtain an In concentration of from 1 x 1019 to 1 x 1021 cm-3 in the GaAs melt. Alternatively, In and oxygen may be separately added. In this case, In in the metallic form, and oxygen in the from of As (Ill) oxide (As203) and gallium oxide (Ga203) are added to the melt to obtain the requisite concentrations in the melt.

The crystal growth method used for growing the GaAs single crystal from the melt, to which In and oxygen are added, is preferably the LEC method using an encapsulant, such as B203 or the like, since a high oxygen concentration in the melt can be thus attained, contamination of the melt by a crucible and an encapsulant is slight, and productivity is high. This crystal growth method could be used in a boat growth method, such as a gradient freeze method or horizontal Bridgeman method.

During the crystal growth, impurities, such as Si, S, Cr, and the like, which determine the electrical properties, may or may not be added to the melt. The undoped, semi-insulative GaAssingle crystal which does not contain the impurities at all, is appropriate as a substrate for UHF or SHF elements and ICs.

The crystal growth direction is preferably in the < 100 > direction, since a round substrate is: thus obtained. The crystal growth direction, however, may be < 111 > .

LEC Method for Growing Single Crystal of Illb-Vb Compound The LEC method for growing a Illb-Vb single crystal using an encapsulant, according to the present invention, is characterized by adding at least one oxide selected form the group consisting of oxide of the Illb-group element and oxide of the Vb group element to the melt of the Illb- Vb group compound at an oxygen concentration of at least one oxide of from 1 x 1018 to 2x 1021, preferably from 1 x 1019 to 1 x 1021 per cm3 of the melt of the Illb-Vb group compound.

When the Illb-Vb group compound is GaAs, the oxide of the Illb element is preferably gallium oxide (Ga2O3) and the oxide of the Vb element is preferably diarsenic trioxide.

When the Illb-Vb group compound is GaP, the oxide is preferably Ga203.

When the Illb-Vb group compound is InP, the oxide is preferably yin203.

When the Illb-Vb group compound is InAs, the oxide of the Illb element is preferably In203 and the oxide of the Vb element is preferably As203.

A special LEC growth device is not required for carrying out the method according to the present invention, and a usual such device may be used. A preferable crucible is made of PBN (pyrolitic boron nitride) or is coated with PBN, since the contamination of the melt by the crucible is slight. Graphite is less preferable but may be used as the material of a crucible or vessel.

The heating is usually carried out by means of a graphite resistance-heater having a cylindrical or wine-glass shape. The temperature gradient in the LEC growth device may be adjusted, if necessary, by disposing a heat-shield made of graphite or a cylindrical heater above the crucible or vessel. The interior of LEC growth apparatus is pressurized, during the crystal growth, to a pressure of usually from 10 to 60 kg/cm2 (gauge pressure) by using an inert gas, such as argon or nitrogen. As the liquid sealant, high purity boron oxide (B203) thoroughly desiccated is ordinarily used.

When commencing the growth of a Illb-Vb single crystal, a predetermined amount of B203 and polycrystalline Illb-Vb compound are loaded in a crucible or the like. However, instead of loading the Illb-Vb compound, a metallic IlIb element and elementary Vb in an amount slightly greater than the stoichiometric amount may be loaded. In this case, the Illb-V melt is formed during heating and temperature-elevating the crucible or the like.

Subsequently, at least one of the oxide of the Illb group element, e.g., gallium oxide (Ga203), and the oxide of the Vb group element, e.g., diarsenic trioxide (As203), is loaded into the crucible or the like. The addition amount of Ga2O3 and/or As2O3 is not the analysis value but the calculation value, namely such that the number of oxygen atoms of Ga2O3 and/or As2O3 added amounts to a concentration of from 1 x 1018 to 2x 1021, preferably 3x 1019 to 3.5x 1020, per cm3 of the melt. When the oxygen concentration is less than 1 x 1018 cm-3, it is difficult to decrease the dislocation density of the obtained Illb-Vb single crystal.On the other hand, when the oxygen concentration exceeds 2 x 1021 cm-3, a Illb-Vb single crystal is difficult to obtain, and even if a Illb-Vb single crystal is obtained, crystal defects, such as dislocations, are disadvantageously increased.

Ga203 and As2O3 may be added alone or together at an optional proportion to one another.

An equal molar ratio of Ga2O3 and As2O3 is preferred, because this suppresses the generation of vacancies.

The conditions for LEC growth other than those described above are the same as usual.

The Illb-Vb single crystal produced by the method according to the present invention has a dislocation density, in terms of EPD, lower than that obtained by conventional methods, and attains an EPD of 5000 cm-2 or less. In the Illb-Vb single crystal produced by the method according to the present invention, the distribution of dislocations in a plane perpendicular to the pulling direction is uniform.

The present invention is further explained with reference to the examples and comparative examples.

In the examples and comparative examples, the LEC crystal puller used was an "MSR-6" type manufactured by the Cambridge Instruments Co., Ltd. of Britain.

EPD was measured by dipping test samples in fused potassium hydroxide at 350"C for 20 minutes and then counting the amount of etch pits, under a microscope.

The oxygen concentration of wafers was measured by using a secondary-ion mass analysis device "CAMECA 3F" type manufactured by the Thomson CFS Co., Ltd. of France.

The In concentration of the wafers was measured by using an atomic absorption analyzer "AAS-4000" type produced by the "Perkinson-Elmer" Co., Ltd. of the U.S.A.

Example 1 500 g of Ga, 550 g of As, 4.5 g of yin203 (corresponding to the In addition concentration of 1 x 1020 cm-3 and the oxygen addition concentration of 1.5x 1020 cm-3) and 150 g of B203 were contained in a crucible made of PBN (pyrolitic boron nitride) and having an inner diameter of 100 mm. The interior of the LEC crystal puller was pressurized to 65 kg/cm2 (gauge pressure) and the crucible was heated to 1400"C to form the GaAs melt. The crucible temperature was then lowered to 13500C. While the crucible and a seed crystal were rotated, the seed crystal was brought into contact with the GaAs melt and then pulled upwards to attain a growth of a GaAs single crystal in the < 100 > direction. The obtained GaAs single crystal has a weight of 650 g and diameter of 50 mm.A (100) wafer was cut from the top end of a straight body portion of the single crystal and subjected to the EPD measurement. The EPD of the wafer, except for a 6 mm wide outer peripheral part, was 900 cm 2 in average and 1100 cm-2 at greatest. No linearly arranged etch pits were detected.

The In concentration of the wafer was 9.5 x 1018 cm-3 and the oxygen concentration of the wafer was box 1017 cm-3.

Example 2 The procedure of Example 1 was repeated to produce the GaAs single crystal, except that instead of In2O3 added in the case of Example 1, 1.89 g of metallic In and 3.2 g of As2O3 (the In addition concentration was 5x 1019 and the oxygen addition concentration was 1.5x 1020 relative to cm3 of the GaAs melt) were added.

A (100) wafer was cut from the top end of a straight body portion of the single crystal and subjected to the EPD measurement. The EPD of the wafer, except for a 6 mm wide outer peripheral part, was 1200 cm-2 in average and 1500 cm-2 at greatest. No linearly arranged etch pits were detected.

The In concentration of the wafer was 5 x 1018 cm-3 and the oxygen concentration of the wafer was 6x 1017 cm-3.

Comparative Example 1 The procedure of Example 1 was repeated to produce the GaAs single crystal, except that instead of the In203 added in the case of Example 1, 3.7 g of metallic In (the In addition concentration was 9.95 x 1019 relative to cm3 of the GaAs melt) was added.

A (100) wafer was cut from the top end of a straight body portion of the single crystal and subjected to the EPD measurement. The EPD of the wafer, except for a 6 mm wide outer peripheral part, was 1000 cm-2 in average and 5000 cm-2 at greatest. Linearly arranged etch pits were detected at portions of the wafer where the EPD was greater than 1000 cm-2.

The In concentration of the wafer was 1 x 1018 cm-3 and the oxygen concentration of the wafer was 2x 1016 cm-3.

Example 3 1500 g of Ga, 1631.6 g of As, 1.5 g of Ga2O3, 1.58 9 of As2O3, and 600 g of B203 were contained in a crucible made of PBN and having an inner diameter of 150 mm. The interior of the LEC growth device was pressurized to 65 kg/cm2 (gauge pressure) and the crucible was heated to 1400 C to form the GaAs melt. The pressure was then reduced to 20 kg/cm2. While the crucible and a seed crystal were rotated at 10 rpm in an anticlockwise direction and 8 rpm in a clockwise direction, respectively, the seed crystal was brought into contact with the GaAs melt and then pulled upwards at a speed of 7 mm/h to attain a growth of a GaAs single crystal in the < 100 > direction. The obtained GaAs single crystal had a weight of 2000 g and a diameter of 80 mm.

A (100j wafer was cut from the top end of a straight body portion of the single crystal where the fraction solidified was 0.10. The fraction solidified indicates a weight ratio of the ingot portion at a side adjacent to the seed crystal and above the wafer relative to the whole ingot.

The wafer was subjected to measurement of the EPD and resistivity. Epd was uniform throughout the wafer, including its peripheral portion, and was 1500 cm-2 Neither linage (linear defects) nor defects by precipitates were detected throughout the wafer. The resistivity exhibited a tendency to decrease at an outer peripheral portion of the wafer, but was 1 x 107 Q-cm or higher throughout the major portion of the wafer.

Another I100 wafer was cut from a straight body portion of the single crystal where the fraction solidifed was 0.61 and subjected to the EPD measurement. The EPD was slightly high, but the average EPD taken from eight points across the diameter of the wafer was 2400 cm-2, and the highest EPD was 2850 cm-2.

Comparative Example 2 The same crystal growth procedure of Example 3 was repeated except that Ga2O3 and As2O3 was not added.

A wafer was cut from an upper straight body portion of the ingot where the fraction solidified was 0.12 and subjected to the EPD measurement. The average EPD taken from nine points across the diameter of the wafer was 10500 cm-2, and the minimum and highest EPDs were 6000 cm~~2 and 25000 cm-2, respectively.

Claims

1. A single crystal of Illb-Vb group compound having a low dislocation density, characterized by containing from lox 1017 to 8x 1019 cm- 3 of oxygen.

2. A single crystal of Illb-Vb group compound according to claim 1, which consists of gallium arsenide.

3. A single crystal of gallium arsenide according to claim 2, which contains from 1 x 1018 to 1 x 1020 cm 3 of indium.

4. A single crystal of Illb-Vb group compound according to claim 1, 2, or 3, wherein said single crystal is produced by single crystal growth from a melt of said Illb-Vb group compound, which contains from 1 x 1018 to 2x 1021 cm -3 of oxygen atom.

5. A single crystal of lilb-Vb group compound according to claim 4, wherein said single crystal is grown by liquid encapsulated Czochralsky method.

6. A method for producing a single crystal of a Illb-Vb group compound from a melt of the Illb-Vb group compound by a liquid encapsulated Czochralsky method, characterized in that at least one oxide selected from the group consisting of an oxide of said Illb group-element and an oxide of said Vb group-element is added to said melt at an amount of from 1 x 1017 to 2x 10 of oxygen atoms of said oxide(s) per cm3 of said melt.

7. A method according to claim 6, wherein said Illb-Vb group element GaAs and said group consists of gallium oxide and diarsenic trioxide.

8. A method according to claim 7, wherein gallium oxide and diarsenic trioxide are added at equal molar amounts.

9. A method according to claim 6, 7, or 8, wherein indium oxide is added to said melt.