JPS61158896A - Method for producing compound semiconductor single crystal and apparatus therefor - Google Patents

Abstract

PURPOSE:To obtain a compound semiconductor single crystal having uniform impurity concentration, by adding the materials of the matrix compound separately and continuously to the molten raw material in the production of impurity-doped compound semi-conductor single crystal by liquid-encapsulated pulling up process. CONSTITUTION:A crucible 6 is placed in a pressure vessel 1, and a molten raw material 7 containing the raw material compound and impurity is put into the crucible 6 and covered with an encapsulant 10. A single crystal 8 can be grown by dipping a crystal 9 in the molten raw material 7, and pulling up the crystal. In the above process, a group V element vapor is introduced into the crucible 6 through a small hole opened at the bottom of the crucible 6, and a molten liquid of a group III element 15 is charged to the crucible from above to synthesize the raw material compound. A single crystal 8 having uniform impurity concentration can be produced by pulling up the single crystal 8 while controlling the feeding rate of the molten liquid of the group III element 15 in a manner to keep the impurity concentration in the molten raw material 7 to a constant level.

Description

DETAILED DESCRIPTION OF THE INVENTION (7) Technical Field The present invention relates to a method and apparatus for manufacturing a l-V group compound semiconductor single crystal with uniform impurity concentration.

The m-v group compound semiconductors include GaAs, GaP,
Ink.

There are various combinations such as GaSb and InSb.

In some cases, single crystals are manufactured without doping with impurities, but
Impurities are sometimes doped to obtain specific properties.

Examples, t, Ha, Si, S, Zn11n, Sb, B, Al.

Doping with impurities such as Sn is often done.

Impurities include those called neutral impurities, and those called p-type and n-type impurities. P-type and n-type impurities are
This is to convert the compound semiconductor into a p-type semiconductor or an n-type semiconductor. Neutral impurities refer to elements of group Ⅰ or group V that are not parent compound elements. It is often doped to reduce dislocation density.

For GaAs, the corresponding impurities are:

N-type impurity...Si, S, Snn equivalent type impurity...Neutral impurity such as Zn...B SA#, In,
The types of these impurities are also known for other compounds such as P and Sb.

(a) Prior art and its problems Methods for growing compound semiconductors can be roughly divided into the liquid confinement Czochralski method (referred to as the LEC method) and the horizontal Bridgman method (abbreviated as the HB method). Although there are other laboratory attempts, only the above two methods are of industrial significance.

In the LEG method, a seed crystal is immersed in a raw material melt covered with a liquid capsule, and a single crystal is grown by pulling the seed crystal out of the raw material melt while rotating the seed crystal relative to the raw material melt.

In the HB method, a quartz boat is filled with raw polycrystals, a seed crystal is placed at one end of the boat, and the seed crystal is sealed in a quartz tube. This is a method of forming a single crystal by lowering the temperature of the melt from the seed crystal side while applying a partial pressure of group V elements that is in equilibrium with the raw material melt.

When doping with impurities, the impurity element or a compound containing the impurity element is added to the raw material melt in advance.

Impurities are not uniform over the entire length of the single crystal.

As a result, the electrical properties of the single crystal vary and many defects appear.

At the solid-liquid interface, the ratio of the impurity concentration S on the solid side to the impurity concentration m on the liquid side is called the segregation coefficient and is expressed by k. dis
It is called tribution coef'f'1cient or sagreption coef'f'1cient.

If this is 1, the impurity concentration during single crystal growth is constant, so a single crystal with a constant impurity concentration can be manufactured.

However, the segregation coefficient is generally not 1. The segregation coefficient is often smaller than 1.

The solidification rate g is defined as the crystal weight divided by the initial raw material melt weight. When the solidification rate is g, the impurity concentration S on the solid side near the solid-liquid interface is given by -1 S = kmo (1 g) (1). mo is the initial concentration in the melt.

When k is less than 1, the concentration S diverges as g approaches 1. In other words, the impurity concentration becomes abnormally high in the back portion. Precipitation due to impurities occurs, twin crystals occur, and it no longer becomes a high-quality single crystal.

There are no impurities with k equal to 1.

When k is larger than 1, the impurity concentration becomes dilute in the back portion, making it impossible to obtain desired characteristics.

The segregation coefficient is a value defined by the parent compound and impurities, but it also changes depending on the pressure.

Although it depends on the concentration, in most cases the pressure is kept constant and crystal growth occurs within a range where the concentration dependence is not very large.

Therefore, the segregation coefficient can be regarded as a constant.

In many cases, the segregation coefficient is less than 1.

For example, when GaAs is used as a host compound, impurities having a segregation coefficient of less than 1 include Si, S, Zn, In, and sb. On the other hand, impurities with a segregation coefficient greater than 1 are A
There are only a few, such as l.

When the segregation coefficient is smaller than 1, the impurity concentration increases in the back portion in both the LEC method and the HB method.

(1) Purpose: When manufacturing a compound semiconductor single crystal doped with impurities,
It is an object of the present invention to provide an LEC device and an LEC method that can produce a single crystal with a uniform impurity concentration.

If the impurity concentration does not vary, the electrical characteristics (carrier concentration, electron mobility) and dislocation density should also be uniform.

If the properties are uniform, most single crystals can be used. In other words, the yield is improved.

In the present invention, in order to suppress the concentration of impurities with a segregation coefficient smaller than 1 from becoming abnormally high, the base compound material is continuously replenished to the raw material melt to keep the impurity concentration constant. Make it.

Group V elements, which have a high vapor pressure, are fed into the melt as vapor from below the crucible, and Group I elements, which have a low melting point, are dropped into the melt from above the crucible.

A partition wall is floated in the melt to prevent the falling of the group (III) droplets from disturbing the interface between the single crystal and the melt (solid-liquid interface).

In this way, group (I) and group V elements are replenished into the raw material melt at a constant rate. If the amount of supply of these raw materials is dQ, the amount of replenishment when the single crystal is pulled up by dS may be as follows: dQ=(1-k)dS (2).

This will be explained below with reference to the drawings.

FIG. 1 is an overall cross-sectional view of the compound semiconductor single crystal manufacturing apparatus of the present invention. FIG. 2 is an enlarged sectional view of only the vicinity of the crucible.

The high-pressure container 1 is a sealable container, and is capable of applying a pressure of several tens of atm using N2 gas or inert gas. Peepholes etc. are not shown.

An upper shaft 2 and a lower shaft 3 are provided so as to be rotatable and movable.

A seed crystal 9 is attached to the lower end of the upper shaft 2.

In normal cases, a susceptor 5 and a crucible 6 are provided at the upper end of the lower shaft 3.
However, in the present invention, a lower storage chamber 18 for storing the group V raw material 22 is newly interposed between the susceptor 5 and the lower shaft 3.

The lower storage 18 has blind walls on the sides and the lower bottom, but a pore 21 is bored through the susceptor 5 and the crucible 6 on the upper surface. The pore 21 may be provided at the center of the bottom of the crucible, but if it is provided around the bottom of the crucible, the disturbance of the melt will be reduced.

A raw material melt 7 is contained in the crucible 6 .

This is a melt of group III-V compounds such as GaAs, GaSb, and InP, and contains impurities.

A heater 4 for heating the melt is provided around the susceptor 5 . Furthermore, there is a heat insulating cylinder on the outside, but its illustration is omitted.

There is a liquid sealant 10 on top of the raw material melt 7, and a high pressure is applied to this by N2 gas or an inert gas 17. This is to prevent group V elements from volatilizing from the raw material melt 7.

When the seed crystal 9 is immersed in the raw material melt 7 and pulled up while rotating, a single crystal 8 grows.

A cylindrical partition wall 11 is floating in the raw material melt 7 and the sealant 10, and separates the sealant 10 into inside and outside. Raw material melt 7
It is also divided into inside and outside, but it is connected at the bottom. Therefore, the levels of the melt 7 inside and outside are approximately equal. Sealant 1
The heights of 0 are also almost the same.

In the upper part of the high-pressure vessel 1, group II melt (GζIn, etc.)
There is an upper storage 13 that accommodates. Since these metals are low melting point metals, they receive heat from the melt heating heater 4 and turn into a melt state.

The upper storage 13 has at its lower bottom an opening that continues to the end of the pipe 12 and a shutter 14 that opens and closes the opening. pipe 1
The lower end 16 of 2 is open to the space outside the partition wall 11 inside the crucible 6, and the group Ⅰ melt 15 passes through the shutter 14, flows through the pipe 12, and flows out from the lower end 16 into the group Ⅰ liquid. It is replenished into the raw material melt 7 in the form of drops 25.

On the other hand, the V group raw material 22 is stored in the lower storage 18 in a solid state. A special heater 19 to heat this
are provided around the lower storage 18.

The lower storage 18 is shown having a smaller diameter than the susceptor 5. However, it is also possible to make the lower storage chamber 18 larger so that the pores 21 are bored at the periphery of the bottom of the crucible 6. In this way, the V raw gas is less likely to disturb the raw material melt 7.

(3) Function As the single crystal is pulled, a raw material melt equal to (1-k) times the pulling weight is replenished. The pulled weight S or its time differential dS/dt can be measured with a strain gauge or the like provided on the upper shaft 2.

Group V element 22 is heated by heater 19 and maintained at a constant temperature. At a vapor pressure corresponding to this, (1) the raw gas enters the raw material melt 7 through the pores 21; The pore 21 is
■Thin diameter holes that allow raw gas to pass through but prevent melt from falling.

The amount of group V element gas flowing into the raw material melt is determined by the amount of group (II) element supplied into the melt.

The Group 1 melt 15 is dripped into the crucible from the upper storage 13. This reacts immediately with the raw gas. V raw gas has a constant vapor pressure. Since the raw gas is heated by the heater 9, there is no shortage of raw gas.

When the Group (1) melt 15 is insufficient, the (1) raw gas cannot be combined, so it rises as it is, passes through the sealant 10, and escapes to the outside of the crucible.

There is no possibility that the Group molten liquid exists in the crucible unreacted. Therefore, the supply amount dQ/dt of the ■-■ compound raw material can be accurately controlled by the supply amount dU/dt of the group ■ melt.

Let A be the atomic weight of the group Ⅰ element, and B be the atomic weight of the group Ⅰ element.

Between dU and dQ The following relational expression always holds true.

Further, there is a relationship expressed by equation (2) between the raw material supply dQ and the crystal pulling amount ds. Therefore, the supply amount dU/dt of the group II melt is dU(1-k)AdS.

The supply amount dU/dt of the group (1) melt 15 can be controlled by changing the opening/closing ratio of the shutter 14. Also, shutter 14
may be replaced with a more accurate flow control valve.

Since dS/dt can be detected by a measuring device attached to the upper shaft, dU/dt is calculated and the flow rate of the shack is adjusted to match it.

(Force) Example A Si-doped GaAs single crystal was pulled using the apparatus shown in FIG.

Crucible PBN 6-inch diameter partition A weight made of a suitable material is placed on top of the BN coating on carbon so that it floats in the GaAs melt.

Tilt the crucible as shown in Figure 3. I have added a reply 20 so that there is no problem.

The charge amount is 7 tons 7' GaAs polycrystalline 4000 gSi in the crucible.
(Impurities) 0.1428 g As in the lower storage 1200 g Ga in the upper storage 1000 g.

The Si mino stage concentration in the melt was 85.7 ppm (wt
). This is the concentration to make the concentration in the crystal 5 wtppm.

The pulling conditions are: pulling speed: 8nr/H, upper shaft rotation speed: 6 rpm, lower shaft rotation speed: t2 rpm.

The impurity concentration was (5 wtppm in the crystal).Diameter of single crystal: 2 inches.Dropped Ga Sakaki solution ffi: -0.56 g/m1nAsTemperature: 617°C.The single crystal was pulled for about 24 hours, and 2 kg of single crystal was obtained.

The Si concentration of this GaAs single crystal was measured in the longitudinal direction. FIG. 4 shows the distribution of Si concentration measurements in the longitudinal direction. , the horizontal axis represents the length from the front part of the crystal in terms of the weight from the front part.

According to the invention, the impurity concentration is 5 wtppm over the entire length of the single crystal. In the case of conventional glue and EC method, 2k
When the g crystal is raised, it becomes close to 9 wtppm in the back. Even if 2 kg of single crystal is pulled from 4 kg of raw material, the impurity concentration will increase in this way.

(1) Effect When pulling a compound semiconductor single crystal using an LEC device, even if doped with an impurity whose segregation coefficient is less than 1, the impurity concentration can be kept uniform throughout the crystal.

Group (2) elements and group V elements are supplied separately, and the amount of raw material supplied corresponding to the single crystal pulling rate is controlled by the amount of group (2) elements supplied. Rather than replenishing polycrystalline compounds,
■There is no shortage of group elements. A constant supply of stoichiometric compound melt is provided.

Impurities with a segregation coefficient of less than 1 precipitate at the tail of a single crystal or cause twin crystals, but the present invention can overcome such difficulties.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of the compound semiconductor single crystal manufacturing apparatus of the present invention. FIG. 2 is an enlarged longitudinal cross-sectional view of the vicinity of the crucible of the apparatus shown in FIG. FIG. 3 is a perspective view showing an example of a partition wall. FIG. 4 is a graph showing the results of measuring how the Si concentration changes in the longitudinal direction of the single crystal when the single crystal is pulled by the conventional method and the method of the present invention. 1 ・・・・・・・・・ High pressure container 2
・・・・・・・・・ Upper axis 3 ・・・・・・
...... Lower shaft 4 ...... Heater 5 for heating melt liquid ......
Bo7 ・・・・・・・・・ Raw material melt 8 ・・・・・・・・・ Single crystal 9 ・
・・・・・・・・・ Seed crystal 10 ・・・・・・
・・・ Sealant 11 ・・・・・・・・・
Partition wall 12... Pipe 13... Upper storage 14... Shutter 15... ■ Group melt 16 ...... Lower end of pipe 11 ...
... Inert gas 18 ... ... Lower storage 19 ... ... ... H -
Ta 20... Rib 21... Pore 22... Group V raw material 25... Group V liquid Drop Inventor Ryo Hisashi Kawasaki Figure 3 @ 4 Figure U1 upper crystal! f-(iif

Claims (2)

[Claims] (1) The raw material melt 7 containing the compound semiconductor raw material compounds and impurities contained in the crucible 6 and heated by the melt heating heater 4 is covered with a sealant 10 and placed in an inert container 1. A single crystal 8 is produced from the raw material melt 7 by applying high pressure to the sealant 10 by filling it with gas 17, and by immersing the seed crystal 9 in the raw material melt 7 from above and pulling it up. In the method for manufacturing a compound semiconductor single crystal, a pore 21 is bored at the bottom of the crucible 6, a group V element gas is introduced into the crucible 6 through the pore 21, and a cylindrical partition wall 11 is formed in the crucible 6. The Group III melt 15 is introduced into the crucible 6 and outside the partition wall 11 from above the crucible 6 to synthesize the raw material compound, and the Group III melt is poured so that the impurity concentration in the raw material melt 7 is constant. A method for manufacturing a compound semiconductor single crystal, characterized by pulling the single crystal while adjusting the amount of replenishment. (2) a high-pressure vessel 1; an upper shaft 2 which is provided so as to be rotatable up and down through the high-pressure vessel 1 and to which the seed crystal 9 is attached at its lower end; and a lower shaft 3 which is provided so as to be rotatable up and down through the high-pressure vessel 1;
A lower storage 18 provided on the lower shaft 3 to accommodate group V elements, and a lower storage 18 fixed on the lower storage 18.
A susceptor 5 having a pore 21 at the bottom that communicates with the group V gas and passes only group V gas, a crucible 6, a heater 4 for heating the melt provided around the susceptor 5, and a floating single crystal in the melt of the crucible. A partition wall 11 provided to surround the crucible 6 and an upper storage 13 provided above the crucible 6 and containing the melt 15 of the group III element.
, a pipe 12 that guides the group III melt 15 in the upper storage 13 to the lower side of the partition wall 11 inside the crucible 6, and a flow rate adjustment mechanism that adjusts the flow rate of the melt in the pipe 12. A compound semiconductor single crystal manufacturing device characterized by: