JPS61155293A - Preparation of compound semiconductor single crystal - Google Patents

Abstract

PURPOSE:To prepare the title single crystal having uniform concentration of impurity by melting starting polycrystal and impurity contained in an external crucible wherein a floating crucible contg. a liquid encapsulating agent is provided therein, thus, supplying a specified amt. of the impurity to the floating crucible. CONSTITUTION:Starting polycrystal 7 and impurity 8 are contained in an external crucible 2 supported by a susceptor 3 at the top end of a foot shaft 6 so as to obtain a desired concn. of the impurity. A floating crucible 1 having a small hole 17 on the bottom clogged with the starting polycrystal 9 is provided therein, and a liquid encapsulating agent 10 is contained in the floating crucible 1. The liquid encapsulating agent 10, starting polycrystal 7, and the impurity 8 are melted by supplying electric current to a heater 4. Then, the polycrystal 9 is melted and the small hole 17 is opened. Thus, the level of the melt 7' in the crucible 1, 2 are made equal. Thereafter, a seed crystal 12 fixed to a foot end of an upper shaft 11 is pulled up, and simultaneously, the impurity expressed by the formula (n/k-n)U [wherein (U) is the weight of the melt to be fed as the starting material; k is a segregation coefft. of the impurity] is fed to the crucible as a single substance or a compound from a jig 13 provided to the upper shaft 11.

Description

DETAILED DESCRIPTION OF THE INVENTION (7) Technical Field The present invention relates to a method for producing a compound semiconductor single crystal, which involves pulling up a crystal containing impurities from a melt by a liquid encapsulation method (LEC method).

Compound semiconductors include semiconductors of the ■-■ group and the It-Vl group. Single crystals can be made by the pulling method, but because the vapor pressure of group Ⅰ and group Ⅰ elements is high, the LEC method is used, in which the raw material melt is covered with a liquid capsule and high pressure is applied with an inert gas. .

Sometimes undoped single crystals are pulled, but sometimes they are doped with impurities.

Impurities include isoelectronic impurities that do not change the electrical characteristics, and impurities that change the electrical characteristics to p-type or n-type.

The types of impurities are diverse, and the purposes for which they are added are also diverse.

No matter what type of impurity is doped, it is desirable that the impurity concentration be uniform within the single crystal.

(a) Prior art and its problems Concentration of impurities is used in two senses: concentration in liquid and concentration in solid. The concentration in a liquid can be defined when it is in equilibrium. It is the weight of impurities divided by the total weight. This is one value.

Concentration in a solid cannot be expressed by a single value. This is because the concentration varies depending on the location.

The ratio of the impurity concentration S in the solid part and the impurity concentration m in the liquid part that are in contact at the solid-liquid interface is called the segregation coefficient.

This is a function of pressure, but if the pressure is constant, it is constant regardless of the solidification rate g as long as the concentration is sufficiently low.

If the segregation coefficient k is 1, the impurity concentration remains unchanged when the single crystal is pulled.

However, if k is not 1, the impurity concentration varies depending on the solidification rate g. The assimilation rate g is the initial raw material rs
'h The weight of the liquid is divided by the weight of the crystals, indicating how much of it has solidified, 0
It is a variable from 1 to 1.

The initial concentration in the melt is m. Therefore, the impurity concentration S in the crystal at the solidification rate g is expressed by: In many cases it is significantly less than 1. In this case, as the crystal pulling progresses, the impurities are concentrated and diverged as follows.

In reality, g=1 is often raised, but even then, the impurity concentration at the tail of the crystal becomes abnormally high, causing precipitation, etc., or twin crystal formation.

A method using a floating crucible has been proposed, but even this method cannot make the impurity concentration uniform.

The floating crucible method involves providing a floating crucible inside the crucible. Since the floating crucible has a lower specific gravity than the raw material melt, it can float in the middle of the melt. There are small holes in the bottom or side walls of the floating crucible through which the melt can flow. There is a single crystal in a floating crucible, and an amount of melt exactly equal to the amount lost by pulling the single crystal enters the floating crucible through a hole from the outside.

For simplicity, we will write the melt inside the floating crucible as the inner melt and the melt outside the floating crucible as the outer liquid. As the single crystal is pulled up, the external liquid decreases, but the internal melt remains unchanged. The floating crucible should float at a height where its weight and buoyancy are balanced, but since the buoyancy should be constant, the height of the floating crucible relative to the liquid level will not change unless it is tilted.

When pulling a single crystal using a floating crucible, first impurity elements are placed in the floating crucible, and only pure compound raw materials are placed in the outer crucible. In this way, when the melt is melted, the pure raw material melt enters the floating crucible and has a certain impurity concentration m. become.

On the other hand, the impurity concentration of the external liquid is set to 0. In this way, the impurity concentration within the floating crucible will change slightly, and it should be possible to pull a single crystal with a constant concentration. However, in this floating crucible method, the impurity concentration does not remain constant.

Unlike conventional products, the concentration does not increase, but on the contrary, it becomes thinner. To pull the single crystal up by a minute amount of dG,
The weight of impurities included here is km dG. Let the weight of the internal melt be U (this is constant).

The external liquid enters the crucible floating by dG. Therefore, the decrease dm in the impurity concentration of the internal melt is m dm ni -, -dG (2).

Since the impurity concentration in the internal melt decreases, the impurity concentration in the crystal also decreases.

By integrating equation (2), G m = mo6Xp (--) (8). The impurity concentration decreases from the initial concentration mo to an exponential function.

This does not mean that it is impossible to maintain a constant impurity concentration even if a floating crucible is used. It is possible to keep the impurity concentration constant. love. The limited 4fi is enough. Let n be the impurity concentration of the external liquid.

Suppose now that the crystal is pulled up by dG (weight). As already mentioned, the weight of impurities lost from the internal melt is k m d
It is G. The external fluid enters the internal melt by dG. The impurity contained in this is ndG.

The increase dm in the impurity concentration of the internal melt is Udm = ndG - kmdG (4) The boundary between the external liquid and the internal melt is a small hole bored in the bottom of the floating crucible. This hole is sufficiently small that there is flow from the external liquid to the internal melt, but not from the inside to the outside. Therefore, the impurity concentration n in the external liquid is constant. It does not depend on the amount of outer sling liquid.

Since n is constant, equation (4) can be integrated. The solution is It is.

G is the weight of the growing crystal. According to equation (5), it can be seen that the impurity concentration of the internal melt changes as the crystal grows.

However, if mo--= 0 (6) is set as the initial condition, the impurity concentration m of the internal melt will always be m regardless of the progress of crystal growth. is constant and equal to

In order to do this, it seems to be sufficient to charge the solid state raw material polycrystal and impurities into a floating crucible or an outer crucible in such a ratio that they match.

Raw material polycrystal (non-doped) is placed in W1 in the outer crucible, U in the inner crucible, impurities in kmoW in the outer crucible, and m in the inner crucible.

U charge. If this is melted as is, the impurity concentration in the outer crucible will be kmo(-n), and the impurity concentration in the inner melt will be m. Therefore, the impurity concentration of the lucid crystal should be n.

But that's not the case. When the impurity is In, Ga, etc.
Since it has a significantly lower melting point than compounds such as GaAs and InP, impurities melt first. Impurities melted inside the floating crucible may flow outward through the small holes. Then, the initial concentration (internal melt) becomes equal to the preset n
/ becomes smaller. Conversely, the initial concentration of the external liquid becomes greater than n.

For example, the melting point of In is about 156.6°C, and the melting point of In is about 156.6°C,
The melting point of is 1238°C.

Also, there is a time lag in melting the raw material polycrystal.

First, the raw material polycrystals outside the floating crucible melt. At this time, the raw material polycrystal in the floating crucible remains solid. Then,
Since the melt inside and outside is not balanced, the outside liquid enters the inside. After this, the polycrystals inside the floating crucible also melt, so a weight of melt equal to the amount that entered earlier flows out from the inside.

In this way, since the internal and external melts mix together at first, the concentration deviates from the preset concentration.

Furthermore, when using liquid capsules, e.g.
Although it melts at 600°C, it generally melts faster than the polycrystalline raw material, but it may get into small holes and obstruct the flow of the raw material melt from the outside to the inside. This is because liquid capsules are highly viscous fluids.

(1) Purpose A floating crucible is used to pull a single crystal with a uniform impurity concentration, but the initial impurity concentration of the floating crucible is n/k.
It is an object of the present invention to provide a method for containing compound polycrystals and impurities in a crucible such that the initial concentration of the outer crucible is n.

Here, n is the impurity concentration in the single crystal.

(1) Method The raw materials in the floating crucible and the outer crucible are stored as follows.

The outer crucible here is what is usually called the crucible, and is called the outer crucible to distinguish it from the floating crucible. In this invention, (1) only a liquid capsule is contained in the floating crucible.

(2) Put raw material polycrystals and impurities into the outer crucible.

The impurity concentration is the impurity concentration n in the single crystal to be pulled.
be equal to .

(3) The small hole in the floating crucible is closed with a small piece of raw material polycrystal. Since it has a high melting point, even if the liquid capsule melts, it will not melt and prevent the liquid capsule from flowing out of the floating crucible.

(4) After all the raw material polycrystals are melted, an impurity element is put into the floating crucible so that the impurity concentration becomes n/k.

In this way, raw material polycrystals, impurities, and liquid capsules are charged.

This will be explained using drawings. Figure 1 shows the state immediately after charging solid polycrystals, impurities, and liquid capsules. The diagonal lined haratin indicates that it is solid.

A floating crucible 1 contains a solid liquid capsule 10.

The susceptor 2 is supported by a lower shaft 6. There is a crucible 2 inside the susceptor 2. Here it is called the outer melting pot. Inside the outer crucible 2 and outside the floating crucible 1, raw material polycrystal 7 is charged in a solid state. Impurity 8 is also accommodated in this. Here, the amount of impurities is determined so that the concentration of impurities is equal to the concentration n in the crystal [11].

A small hole 17 at the bottom of the floating crucible 1 is plugged with raw material polycrystal 9. A heater 4 is provided around the crucible 2 to heat the melt and liquid capsule.

A moisturizing material 5 is placed around the heater 4 to prevent heat from dissipating. All of these are surrounded by a chamber (not shown). The inside of the chamber is maintained at high pressure by inert gas (N2 gas, argon gas).

Here, the original Fl polycrystal is GaAs, InP
.

InAs, GaSb, InSe, etc. (D
/doped polycrystal) CdS, CdSe, CdT
e, refers to non-doped polycrystals such as Zn5e SHg5. Impurities include In, Si, S
, Zn, Cr..., etc.

Liquid capsules have raw materials such as GaAs and InAs.
In such cases, it is set as B2O3. N for GaSb etc.
a. (JlKCI product is used as a liquid capsule.

Next, the heater 4 is energized to heat the materials in the crucible 2 and floating crucible 1.

First, impurity 8 is melted. This is because they have low melting points, such as In and Ga.

The liquid capsule is then melted. This is floating crucible 1
The liquid drips inside. However, since the raw material polycrystal plug 9 is present, the small hole 17 is closed and the liquid capsule comes out.

Hiko, if the heating is continued, the raw material polycrystal 7 in the outer crucible will melt and become raw material melt 7/. This impurity concentration is
- equal to the impurity concentration n in the crystal to be obtained.

FIG. 2 shows such a situation. Next, the raw material polycrystalline plug 9 is melted. Since the small hole 17 is opened, the raw material liquid 71 flows into the floating crucible 1 from the outside, and the floating crucible 1 descends.

The liquid capsule 10 inside the floating crucible 1 is pushed up, overflows from the periphery of the floating crucible 1, and enters the outer crucible 2. Since the liquid level of the liquid capsule 10 is horizontal, the liquid level of the raw material melt 7/ in the floating crucible 1 and the outer crucible 2 is also horizontal.
They should be equal.

FIG. 3 shows such a situation. The impurity concentration in the melt is n.

Seed crystals 12 are attached to the lower ends of the shafts 11 at □ and -.

This is used to pull the single crystal. The seed crystals 12 are connected with molybdenum wire or the like.

In addition to this, a cage-shaped jig 13 is provided on the upper shaft 11.
On this is placed an impurity or a compound containing an impurity.

For example, if the melt is GaAs and the impurity is In, it is placed in the form of InAs. The melting point of InAs is 943
°C, but at about 700 °C, As evaporates and leaves As. Separated In (melting point 156°C)
Since it is in liquid form, it falls from the basket-shaped jig 13.

As the upper axis is lowered, the impurity compound 14 is heated, becomes liquid, and falls into the mountain liquid. In this way, the impurity concentration within the floating crucible 1 is made to reach n/k.

The jig 13 is made of molybdenum, quartz, BN, PBN, or the like.

If the weight of the melt in the floating crucible is U, the amount of impurities in the state shown in FIG. 3 is nU. The weight of impurities to be added to this is (-n)U. If this many impurities are added, the impurity concentration will reach n/k.

Instead of making it into an impurity compound, a single impurity may be placed in the jig 13 and dropped into the inner door (into the liquid).If the impurity has a higher melting point, such as In, this is possible. be.

(E) Example 3 In-doped Ga LECEC product growth device for inch diameter
Pull up the rB crystal of As. The conditions are as follows.

Outer crucible (PBN) Inner diameter 15.2 [φ Charge amount GaAs /1000 gIn 8.4g Floating crucible (BN) Outer diameter 14.81φ, Inner diameter 1.2
．． 0cMφ height 4m, wall thickness 3my With SM6 weight (adjust the weight so that the depth of the internal melt is 2Qmm) Charge amount B203600g Small hole 2mm square hole with a length of 1 (7) In segregation Coefficient 0.14 The small hole is plugged with 2rm square GaAs.

The impurity concentration n in the outer crucible is 226n3 since the depth of the inner melt is 20k and 7 when the inner and outer melts communicate through the small holes. The weight of GaAs in the floating crucible is 1290 g.

The weight of In contained in this is 2.71 g.

Since the desired value of the In concentration in the floating crucible is given by n/, the In concentration in the floating crucible is n 0.0021 - = -□ = 0.015 = 1.5%k
Should be 0.14. To prevent this from happening, the weight of In that should be added to the floating crucible is (--n) U-(0,015-0,0021)X1
290 = 16.6 g. Since this is supplied as an InAs compound, the amount of InAs is 27.4.
g is necessary. Place this in a basket-shaped jig made of quartz and attach it to the upper shaft. After the inner and outer melts communicate with each other, this In is supplied to the inner melt.

In this way, inside and outside the crucible, Internal melt weight: 1290 g In concentration 1.5% External liquid weight 2785 g In concentration 0.21% We were able to create a melt of .

After this, the axial humidity gradient in B2O3 was adjusted to 40-60°0
A GaAs single crystal with a diameter of 3 inches was pulled up as a glaze. 3
kg of single crystals were obtained. The length of the straight body portion was approximately 15α.

In concentration was measured. 2150 pPm (0,215%) at the front (closer to the seed crystal) and 20 pPm at the back.
00 ppm (0.2%). It can be seen that the In concentration is almost uniform.

This was sliced into wafers and the dislocation density was measured.

The dislocation density was 2×10 3 /α 2 or less.

The yield is about 60% compared to when the inner crucible is not used.
Nijita.

(Force) Effect (1) If the impurity concentration of the external liquid is n1, the impurity concentration of the internal melt is m, and the impurity concentration in the crystal is S, then n = s
(7) m2□ (8) $ m = −(9) The following formula holds true. (9) always holds, but (8)
The feature of the present invention is that it is made as shown in the equation (7).
) holds true, and the impurity concentration S in the crystal becomes constant.

Therefore, no precipitation of impurities occurs, and no twin crystals occur.

Dislocation density and electrical resistance become uniform in the axial direction. High quality single crystals can be pulled.

(2) There is no fear that the liquid capsule will block the small holes in the floating crucible. This is because the small holes are filled with polycrystalline raw material, which has a higher melting point than the liquid capsule.

This dam allows communication between the inside and outside of the melt.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a state immediately after solid raw material polycrystals and capsules are placed in an outer crucible or a floating crucible in an apparatus for pulling single crystals by the liquid capsule method. FIG. 2 is a cross-sectional view showing the moment when the inside of the crucible is heated by a heater, the liquid capsule in the floating crucible melts, and the raw material polycrystal in the outer crucible melts as well. FIG. 3 is a sectional view showing a state in which the liquid levels of the inner and outer raw material melts and the liquid capsule become the same, and then impurities are made into droplets and replenished into the floating crucible. 1 ・・・・・・・・・ Floating crucible 2 ・・・・・・・・・ Outer crucible 3 ・・・・・・・・・ Susceptor 4 ・・・・・・・・・ Hi -
Ta 5 ...... Insulating material 6 ...... Lower shaft 7 ...
... Raw material polycrystal 71 ...... Raw material melt 8 ...
...Impurity 9 ...... Raw material polycrystalline plug 10 ...
... Liquid capsule 11 ... Upper shaft 12 ... Seed crystal

Claims (1)

[Claims] Crucible 2 supported by susceptor 3 at the upper end of lower shaft 6
A compound semiconductor raw material melt containing impurities is put into the container, and the raw material melt is covered with a liquid capsule to which high pressure is applied.
A compound semiconductor single crystal is prepared by fixing a seed crystal 12 to the lower end of the upper shaft 11 and pulling the single crystal containing impurities by immersing the seed crystal in a raw material melt heated by a heater 4 and pulling it up. In the manufacturing method, the impurity segregation coefficient is k, the desired impurity concentration in the single crystal is n, and in the outer crucible 2,
A floating crucible 1 having a small hole 17 is provided, the outer crucible 2 contains the raw material polycrystal and impurities so that the impurity concentration is n, the floating crucible 1 contains only the liquid capsule, and the small hole 17 contains the raw material polycrystal and impurities so that the impurity concentration is n. Fill it with crystals, melt the liquid capsule, raw material polycrystal, and impurities with the heater 4, and make the height of the raw material melt in the floating crucible 1 and the outer crucible 2 the same,
Letting the weight of the raw material melt in the floating crucible 1 be U, {(n/k
)-n}U is supplied into the floating crucible 1 from a jig 13 provided on the upper shaft 11, either as a single substance or as a compound.