JP2001180918A - Method of directly synthesizing indium phosphide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of directly synthesizing indium phosphide. SOLUTION: Indium and phosphorus are directly synthesized by using at least two vessels, one of which is contained in the other, in a completely closed reacting system, while they are continuously heated up to a temperature ranging from 1,070 up to 1,250 deg.C, favorably from 1,100 to 1,200 deg.C, given a pressure ranging from 1,850 up to 2,000 bar, according to the following formula; y=kx (y is a temperature in a unit of deg.C, x is time in a unit of minute. k is a constant obtained from 5 to 20 deg.C/minute).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for directly synthesizing indium phosphide.

[0002]

BACKGROUND OF THE INVENTION Optoelectronic devices (lasers, photodetectors) and microelectronic devices (HEMTs, HBTs, and JBTs).
There is increasing interest in indium phosphide used in the manufacture of FETs.

Recently, dislocations have been increased by increasing the purity of a polycrystalline substance or a monocrystalline substance, or by controlling growth conditions (by growing phosphorus under a controlled pressure or reducing a thermal gradient). Developments have been made to reduce the density EPD (etch pit density) to less than 10 ⁴ cm ⁻² .

[0004] At present, there is particular interest in InP semi-insulating wafers. In the field of optoelectronics I
Although the use of nP substrates is predominant, semi-insulating InP is becoming increasingly important in the electronics field as a material for high-power, high-frequency devices that support transfer service systems used in telecommunications. Is expanding. Unfortunately, however, the technology is not yet sufficiently developed to allow mass production.

For the production of semi-insulating InP on an industrial scale, LEC technology involving the doping of Fe is currently used. From an industrial point of view, commonly obtained polycrystalline and pre-oriented materials are n-type semiconductors. Therefore, it is essential to use an acceptor doping agent such as iron of high purity (99.999%) metal. The amount of dopant required to obtain a semi-insulating material is directly proportional to the amount of residual impurities present. Since an InP semi-insulating wafer having a high iron concentration (high precipitate density) adversely affects the performance of the apparatus, it is necessary to use a raw material of high purity. One of the essential requirements for obtaining single crystals with high crystal quality and suitable electrical properties is to obtain high purity polycrystalline InP and controlled stoichiometry. Particular care must be taken to control the purity, stoichiometry, and production costs of starting materials and synthetic products.

[0006] Stoichiometric and ultra-high purity I
Specific conditions for manufacturing nP are as follows. The starting materials used, ie the indium and phosphorus TI
L (total impurity level) must be less than 1 ppm. The synthesis process must be carried out in an inert atmosphere (Ar, N ₂ ), in a reactive and contaminating crucible. -The reaction system must be closed or pressurized to prevent phosphorus evaporation.

[0007] The synthesis of InP is very dangerous because liquid phosphorus has a high vapor pressure and is present in a small amount in the starting red phosphorus or the yellow phosphorus produced during the synthesis is highly flammable. Process. Conventional synthetic methods for producing polycrystalline indium phosphide are:-High pressure Bridgman method (HB)-Solute diffusion method (SSD)-Phosphorus injection method.

[0008] The horizontal high pressure Bridgman method (Adamski, JA,
Synthesis of Indium Phosphide, J. Crystal Growth
(1983) 64, 1-9; Bonner KA and Temkin, H., Prepar
ation and Characterization of High Purity Bulk In
In P, J. Crystal Growth (1983) 64, 10-14), InP is synthesized using a high-pressure oven to prevent the explosion of the ampule. Indium is placed in a graphite tube, plugged with the same material, and reinforced with a quartz tube. On the outside, there is another quartz tube containing debris-like phosphorus and a quartz wool disk separating the phosphorus from a graphite container.

The quartz ampule is placed in a steel jacket and pressurized to 20 to 30 atmospheres. This system consists essentially of a three-compartment oven.

In this process, a quartz tube is moved with a coil at a speed of 6 cm / hour.

A major drawback of this method is the impurities from graphite containers. Using a crucible made of pBN (pyrolytic boron nitride) will prevent contamination of the product. However, such crucibles may cause a sticking phenomenon when the indium does not react completely and thus sticks to the walls of the container. To avoid the use of graphite containers, a balanced pressurization system was subsequently developed. In this case, the reaction is performed in a quartz vessel (boat,
And in a crucible). The synthesis of polycrystalline InP is performed in an oven with a horizontal cooling gradient placed in a high pressure autoclave.

In order to make the pressure difference between the two chambers close to zero,
The phosphorus pressure in the quartz ampoule is balanced by the pressure of the inert gas in the autoclave. The system has a transducer that senses the differential pressure and transmits it to a servo mechanism that performs the necessary pressure correction in the autoclave. During the reaction stage, the pressure in the system reaches about 30 atm.

[0013] SSD (synthetic solute diffusion) technology (Kubota, E.
And Sugii, K., Preparation of High Purity InP by
the Synthesis, Solute Diffusion Technique., J. App
l. Phys. (1981) 52, 2983-2986) is a polycrystalline InP
Is a method of growing from a solution that can be used for the production of

The red phosphorus is placed on the bottom of a quartz ampoule. A crucible containing indium is placed inside the ampoule at a certain height from the bottom of the ampoule.

Indium is distilled under vacuum for several hours using a similar synthesis oven and a suitable temperature profile,
Remove indium oxide from the surface.

Thereafter, the ampoule is evacuated and sealed at 10 ^-6 Torr.

With an average synthesis temperature of 900 ° C., a thermal gradient of molten indium of 20 ° C./cm, and a crystallization rate of 3-4 mm / day, an ingot consisting of small granular masses (2-10 mm ² ) is produced.

Although the SSD method is simple and inexpensive,
Since it takes a very long time, it cannot be used industrially.

Injection method (Farges, JP, A method for the
“In-situ” Synthesis and Growth of Indium Phosph
ide in a Czochralski Puller, J. Crystal Growth (19
82) 59, 665-668; Hyder, SB and Holloway, CJ J
r., In-situ Synthesis and Growth of Indium Phosphi
de, J. Electron. Mater. (1983) 12, 575-585)
A high pressure reactor is used. Put phosphorus in ampoule separately from indium. This phosphorus vapor is brought into contact with the molten indium through a layer of molten B ₂ O ₃ . Reaction chamber A
pressurized to 30-60 atm by using the r or _{N 2.} I
After the n and B ₂ O ₃ have melted, the crucible is moved vertically until the ends of the projections of the quartz ampule are immersed in the melted indium. The temperature of the phosphorus in the ampoule is 520-570 ° C.

According to this procedure, a polycrystalline InP in which In is slightly excessive outside the crystal and in the last crystallized portion.
1-2 kg are obtained. If the ampoule is not coated with PBN, acceptable contamination by Si may occur.

This method was initially developed with two main goals: The possibility of obtaining a method for producing phosphorus-rich InP, and the inevitable expectation that this will result in an undoped semi-insulating (SI) material. -As in the case of GaAs,
The thermal potential of synthesizing polycrystalline materials and orienting crystals in a single process and in the same reactor.

Neither of these goals has been fully achieved, and at present only a few workers (only one of which are commercially available) require this method to be synthesized, Subsequent growth appears to produce a polycrystalline product, which appears to be used to limit contamination by silicon. The polycrystalline material is then oriented (s) using conventional techniques.
(tretch) to make it monocrystalline.

An ultra-high pressure autoclave (27000 p.
s. i. ), A non-conventional direct synthesis method (HP
DS) is described in the literature [“Semi-insulating II
IV Materials ”(Edited by DC Look and JS Blakemore, Sh
iva Publishing Limited, 1984) 171-17
Savage, RO, Anthony, JE,
AuCoin, TR, Ross, RL, Harsh, W. and Cantwel
l, HE High Pressure Direct Synthesis of Bul
k Indium Phosphide].

The authors use a pressure-temperature cycle that involves venting gases (argon and phosphorus) present in the reaction environment at processing temperatures above 750 ° C. This operation is essential so that the maximum working pressure of the device is not exceeded. Therefore, this reaction system can be considered open. This method does not allow precise control of the stoichiometry and increases safety concerns, since phosphorus vapors are released during the degassing stage. Also,
A single unsealed container (crucible and suitable lid) is used.

[0025]

The present inventors have now found an improved method of the current industrial method, namely the horizontal Bridgman method. This improved method uses a completely closed reaction system, so that the maximum working pressure of the reactor is never reached, so there is no venting step.

The method of the present invention for the direct synthesis of indium phosphide starting from indium and phosphorus is intended to reduce the amount of phosphorus released into the reaction environment by replacing one vessel with another vessel. In a completely closed reaction system utilizing a reactor with at least two vessels contained therein, a temperature of up to 1070 to 1250 ° C., preferably 1100 to 12 ° C.
00 ° C. and pressure up to 1850-2000 bar, the following formula: y = kx, where y is temperature in ° C., x is time in minutes and k is 5-20 ° C./min The synthesis is performed while the temperature is constantly increased with time according to the following formula:

One of the major problems from a manufacturing perspective is that
The point is that the implementation of the synthesis process and the orientation of the single crystal need to be performed by two different devices. In fact, the high pressure created by phosphorus at a temperature close to the melting point of indium phosphide makes it impossible with ordinary equipment to react directly in the liquid state and orient the single crystal in the same reactor. Therefore, the synthesis method according to the present invention includes an inert gas (200
There is a need for a reactor that can withstand the very high pressures created by 0 bar argon or nitrogen).

In order to limit the phosphorus leaks which necessarily occur during the operation of the method, such high values of pressure and
Appropriately shaped containers are required.

The accompanying drawings show a temperature-pressure cycle in a closed system according to the invention (FIG. 1) and, by way of comparison, the above open system synthesis cycle adopted by the author Savage et al. (FIG. 2). is there.

It can be seen from the graph that our technique does not include any degassing stages, since the maximum working pressure of the device is never reached, but from the graph of FIG. It can be seen that a mixture of argon vapor and phosphorus vapor needs to be released from the degassing line to reduce the internal pressure. Eliminating the degassing operation allows for better control of the stoichiometry and reduces environmental concerns.

[0031]

The advantages of the method according to the invention are as follows. −
Possibility of obtaining an ingot large enough to be directly introduced into a 5-inch crucible used for producing a 2-inch InP single crystal. This is a considerable advantage over the Bridgman method used in industry. That is, the potential for contamination is reduced while eliminating the two steps of handling the substance. Also, the use of one or more disks of appropriate diameter made of polycrystalline material reduces the leakage of phosphorus during the heating step of the LEC growth process and thus the stoichiometric properties of the product. Is improved.
The possibility that the charge carrier concentration value can reach less than 10 ¹⁵ atm cm ^-3 ; This can be achieved by eliminating all quartz parts. In the case of the high-pressure Bridgman method, many attempts have been made in the past to replace quartz ampules with other materials to eliminate contamination by Si (this requires pre-orientation of the resulting polycrystalline material). And the difficulties that cannot be solved with available materials. This problem has been completely overcome by a method for directly producing materials containing low levels of silicon as defined in the claims of the present invention.

[0032]

EXAMPLES The following examples are given, but do not limit the scope of the present invention.

The washed at least 2 hours in Example advance aqua regia, 18 megohms the quartz crucible with rinsed lid with ultrapure water, raw materials, namely indium 6N and red phosphorus 6N, controlled atmosphere (class (Class) 100).
This crucible is placed in a graphite crucible holder, the lid is closed, and the crucible is placed in the reactor.

This system was pressurized to 50 MPa, and 1150 ° C.
(See FIG. 1).

The resulting polycrystalline InP product is treated with ethyl alcohol to remove any phosphorus residues that may be present on the surface, and then HCl-HNO
₃ (1: 1) to remove any excess indium that may be present.

[Brief description of the drawings]

FIG. 1 is a diagram showing a temperature-pressure cycle of a VHPS method.

FIG. 2 is a diagram showing a temperature-pressure cycle of the HPDS method.

Continued on the front page (72) Inventor Franco, Danieli, Italy, Italy, Via, San, Fermo, 7 / A (72) Inventor Letizia, Meregalli, Venice, Italy, Dorso, Duro, 2416

Claims (2)

[Claims] 1. A method for directly synthesizing indium phosphide starting from indium and phosphorus, wherein one vessel is placed in another vessel and a complete reactor is used using at least two vessels. Temperature up to 10 in a closed reaction system
70 to 1250 ° C and pressure up to 1850 to 2000
Bar and over time according to the following formula: y = kx where y is temperature in ° C, x is time in minutes, and k is a constant value of 5-20 ° C / min. Wherein the synthesis is carried out while constantly increasing the temperature. 2. The method according to claim 1, wherein the maximum temperature is in the range from 1100 to 1200 ° C.