JPH02199100A - Production of inp single crystal - Google Patents

Abstract

PURPOSE:To suppress variation of thermal conductivity of B2O3 and reduce frequency of twin production by preliminarily adding a specified amount of In2O3 and P2O5 to B2O3 as a sealing liquid in growth of InP single crystal using LEC method. CONSTITUTION:InP 7 as the raw material and B2O3 8 as a sealing liquid are put into a crucible 6 and fused by heating the crucible 6 using a heater 4 while applying a high pressure using an inert gas so that the sealing liquid 8 may cover the raw fused liquid of InP 7. Gather is then carried out by dipping an InP seed crystal 9 into the raw fused liquid of InP 7 while rotating the InP seed crystal 9 and the seed crystal 9 is pulled up to grow an InP single crystal 10. In the above-mentioned method, 0.06-0.08mol% In2O3 and 0.01-0.8mol% P2O5 are preliminarily added to B2O3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to the liquid-enclosed Czochralski method.
d Encapsulated Czochralsk
i) relates to an improvement in a method for manufacturing an InP single crystal.

The liquid-sealed Czochralski method is used to pull a GaAs single crystal, which is a ■-V compound semiconductor.

This is an attempt to prevent the volatilization of group (1) elements by covering the raw material melt with a B2O3 melt and applying high pressure with an inert gas.

InP is an m-v group compound, but it has some things in common with GaAs, and some things that are different from it.

A common problem with Group III-V compounds is that the dissociation pressure at the melting point of the Group (I) element is high, making it difficult to form stoichiometric single crystals.

However, even though they are from the same V family. The dissociation pressure is higher in the order of P, As, and Sb. In particular, compounds containing P have a high dissociation pressure of P, so dissociation of P is a serious problem.

As already mentioned, the liquid-enclosed Czochralski method (LEC) is a method of covering the raw material melt with B2O3 to prevent the volatilization of group (2).

A single crystal is pulled by melting the raw material in a crucible, rotating the seed crystal attached to the upper shaft, immersing it in the raw material melt, seeding, and gradually pulling up the seed crystal.

The LEC method is used to grow GaAs single crystals, and
There is a sufficient track record for aAs.

(a) Prior art InP has the same crystal system as GaAs and has similar electrical properties, but there are some differences because P is more active than As.

The LEC method using B2O3 as a liquid encapsulant can be used to grow InP single crystals, but in this case, twin
) is likely to occur.

When twins occur, the crystal must be lowered, immersed in the raw material melt, melted again, and the seeding process must begin again. When twins occur in this way, the crystal growth must be restarted from the beginning.

If twins occur frequently, it becomes almost impossible to pull a single crystal. When pulling InP, twinning occurs frequently. The occurrence of twins is the biggest problem in growing InP single crystals by the LEC method.

(1) B2O3, which is a B2O3 liquid sealant containing P20s, Al2O3, and Ga2O3, is added with an oxide P2
There is one that proposes adding O5, Al2O3, Ga2O3, etc. (Japanese Patent Publication No. 18635, 1983).

This is because B2O3 softens slowly and decreases viscosity slowly.
Before this material has sufficient fluidity, As is converted from GaAs raw material.
This is to solve the problem that the

B2O3 is a glass-like substance that begins to soften at about 450°C and becomes a fluid at 600°C. Before becoming a fluid and covering the surface of GaAs, the As is heated and escapes.

Therefore, the Special Public Interest Publication No. 60-18635 (S 60.5.1
1) is B2O3 with Al2O3, Ga2O3, P2
Attempts are being made to lower the softening point and increase fluidity by adding O5 and the like. With these additions, at temperatures below 600° C., B2O3 gains sufficient fluidity to coat the surface of the raw material.

This solves the problem in the temperature range of 450°C to 600°C. Adding impurities generally tends to lower the melting point. These impurities are added to lower the softening point of B2O3.

In order to lower the softening point, a considerable amount of impurities must be added.

For example, it says to use B2O3 to which 0.5 mol% of Ga2O3, 1.5% of A720 and 3.5 mol% of P2O5 are added.

This targets the pull-up of GaAs. A polycrystalline GaAs raw material and B2O3 are placed in a crucible and heated with a heater. As the temperature rises, B2O3 is quickly liquefied to prevent As from being removed. The purpose is to grow stoichiometric single crystals.

2) Problems to be Solved by the Invention When growing an InP single crystal by the LEC method, the biggest problem is the frequent occurrence of twin crystals. The occurrence of twin crystals reduces productivity. This is different from the case of GaAl9.

So why do twins occur so easily? That's what it means.

Possible causes of twin crystal formation include (1) the presence of foreign matter such as scum at the solid-liquid interface, (2) temperature fluctuations near the solid-liquid interface, and (3) fluctuations in the pulling speed.

The most important of these factors is temperature fluctuation near the solid-liquid interface.

The reason why this occurs is that (t) Change in thermal conductivity of B2O3 (1j) Non-uniform temperature gradient in the raw material melt (110 Misalignment of coaxiality between the seed crystal and the crucible, etc.) may be the cause.

The solid-liquid interface is the interface between the solid single crystal and the raw material melt (
This is the surface in contact with InP).

It is approximately the same height as the surface of the raw material melt. The raw material melt is below the solid-liquid interface.

On the other hand, B2O3 is a liquid sealant that covers the raw material melt from above. Therefore, B2O3 is above the solid-liquid interface.

Since the solid-liquid interface is sandwiched between B2O3 and crystals from above and the melt from below, the temperature is controlled by these.

First, regarding (1), there is a high-pressure inert gas above B2O3, which causes active convection.

Because of the high pressure, the gas density is high and heat transfer through convection is also strong.

Wouldn't the thermal conductivity of B2O3 change? The inventor may be the first to notice this.

If the thermal conductivity of B2O3 changes during crystal growth, the temperature at the solid-liquid interface should also change.

The change in thermal conductivity of B2O3 must also be taken into account.

Let us discuss (11). The raw materials put into the crucible are
Receives heat from the heater from the side circumference and below. Therefore, the raw material melt generally has a high temperature at the bottom and a low temperature at the top. Also,
The side periphery, which is closer to the crucible, is hotter than the center. Therefore, a temperature gradient exists in the raw material melt. The direction and magnitude of the temperature gradient vary depending on the position in the raw material melt.

A downward temperature gradient also occurs near the solid-liquid interface. If the temperature gradient is large, it is easy to obtain heat from the melt, and if it is small, it is difficult to obtain heat.

The solid-liquid interface is the surface where the lower surface of the crystal comes into contact with the raw material melt. The temperature is the same within this plane. With different temperature gradients,
The degree of heat reception and heat radiation differs. As a result, irregularities occur on the solid-liquid interface, which is an isothermal surface. For this reason, twins are more likely to occur.

(110 means that the main axis of the single crystal and the center of the crucible are different from each other, so when the single crystal rotates, it rotates eccentrically, causing temperature fluctuations. Attach a seed crystal and place a crucible at the upper end of the lower axis.The center lines of the upper and lower axes are the same.Although the axes are aligned in this way, the seed crystal and the single crystal that grew following it may be eccentric with respect to the upper axis.

Of these possible causes, the inventor has determined that (i) 8
Isn't the issue of thermal conductivity of 203 important? I thought.

00 Purpose When pulling InP single crystal by LEC method, B2O
It is an object of the present invention to provide a method that reduces the frequency of occurrence of twins by suppressing fluctuations in the thermal conductivity of No. 3.

ψ) Process of the Invention The change in thermal conductivity of B2O3 is, of course, most pronounced between <450 DEG C. and 600 DEG C., as it changes from solid to liquid. However, the present invention does not deal with such a temperature range. Although the above-mentioned Japanese Patent Publication No. 18635/1988 dealt with this temperature range, this is not the case with the present invention.

The present invention aims to prevent the occurrence of twin crystals. Twins occur due to some trigger (ζ) after crystal growth begins.

Naturally, the temperature of the raw material melt and B2O3 is high. The temperature of B2O3 is, for example, about 850°C to 950°C.

At such temperatures, B2O3 is a stable liquid and
One would think that no change in physical properties would occur.

However, this is not the case.

B2O3 is in contact with the raw material InP. Don't forget this. When solid LnP melts,
The melt and B2O3 come into contact. Then, although gradually,
In and P are dissolved in B2O3. For this reason, B2
The thermal conductivity of O3 changes. There is a possibility like this.

Therefore, the present inventor placed InP polycrystal and 8
203 solid was heated in a crystal pulling apparatus while applying high pressure of inert gas, and both the B2O3 and InP polycrystals were melted. Then, we decided to measure the contents of In and P in B2O3 after the InP was melted. This was investigated by 102 emission spectrometry.

FIG. 1 is a graph showing the results. The horizontal axis is InP
(time color) after the raw material has melted. The left axis of the vertical axis is B
The In content (wt%) in 2O3 is shown. This is represented by a white circle. The In content in B2O3 becomes 0.2wt96 after 10 hours. Q becomes 5wt% after 30 hours. After 50 hours, it became 1,9wt96. In other words,
As time elapses from melting of the raw material, the content of In in B2O3 increases almost in proportion to this.

The vertical axis indicates the content of P in B2O3. This is represented by an open triangle. The P content in B2O3 is 1
After 0 hours, it became about 0.01wt96. After 30 hours, it decreased to about 0.035 wt%. Approximately 0.04 after 50 hours
It became 6wt%.

In other words, it can be seen that P in B2O3 also increases with elapsed time.

What should be noted here is that the dissolution of In and P in B2O3 is significantly different from normal dissolution phenomena.

When a solute dissolves in a normal solvent, the time required for dissolution is extremely short. If the two solutions are in contact,
Dissolution is instantaneous and saturation occurs immediately.

The shortest time is on the order of seconds, and the longest time is on the order of minutes. There is something called saturation concentration, and once saturation is reached, the concentration will not increase any higher.

However, the dissolution of In%P into B2O3 is different from this. Dissolution cannot be called dissolution in a strict sense. Therefore, In content and P content are written.

Diffusion of In-9F into B2O3 is extremely slow.

The amount of diffusion remains directly proportional even after several tens of hours. This shows that it is far from saturated. In and P diffuse into B2O3 (at an extremely slow rate, so they do not reach saturation easily. This is because B2O3 is a solvent and InJPP is a solute, and the solute dissolves in the solvent. That means no.

In this way, for a long time, In and P were added to B2O3.
It turns out that it is spreading.

From this alone, it is not possible to tell what kind of change occurred in the thermal conductivity of B2O3.

Therefore, the present inventor conducted another experiment.

When the seeding state (seeding state) is constant, how does the heater setting temperature change with the elapsed time from melting of the raw material? That's what it means. A thermocouple is in contact with the center of the bottom of the crucible to measure the temperature of the bottom of the crucible. Seeding means soaking the seed crystal in the raw material melt and making it blend with the melt. Making this constant means keeping the temperature measured by the thermocouple in contact with the bottom of the crucible during seeding constant.

In order to keep this constant, the power of the heater is controlled. Changing the power of the heater changes the set temperature of the heater.

Let h be the elapsed time from melting of the raw material. The set temperature of the heater changes over time.

FIG. 2 is a graph showing the results of this measurement.

Initially, the heater set temperature is about 1080°C.

After 20 hours, the heater set temperature becomes 1075°C.

This means that the power of the heater has been reduced. 2
After 3 hours, the heater set temperature drops to 1067°C. After 24 hours, the temperature further decreases to 1059°C. From then on, the temperature was approximately 1059° C. until 52 hours had passed, and it can be said that the temperature remained almost constant.

That is, after 20 to 25 hours have elapsed, the heater set temperature decreases rapidly. In other words, less heater power is required to obtain the same seeding conditions.

So what exactly happens between 20 and 25 hours? This is the problem.

Although the time elapsed from the melting of the raw material, in the experiments shown in FIGS. 1 and 2, the InP single crystal was not actually pulled. Therefore, the amount of raw material melt does not change with time. The amount of melt remains unchanged. It is unlikely that the thermal properties of the melt will change.

Therefore, what changes with time is the In in B2O3.
content, P content, etc.

The same seeding conditions mean that the temperature at the bottom of the crucible is the same. The fact that the temperature at the bottom of the crucible remains the same even though the heater power has decreased means that heat radiation has decreased. Why does heat radiation decrease?
Since B2O3 is in contact with the convection current of inert gas, heat is intensely removed there. Reduced heat radiation means %B2O3
This simply means that the thermal conductivity of

In other words, the thermal conductivity of B2O3 decreased as the content of In%P increased.

In fact, it would be nice if the thermal conductivity of B2O3 could be measured as a function of the In1P content, but this is not possible.

According to ζ in FIG. 2, there are two cases: a case where the heater set temperature is around 1080°C and a case where it is around 1060°C. 20:00 to 25 hours is
This is the transition period between these two cases. Therefore, at a relatively early stage when the heater setting temperature is around 1080°C,
2O3 is called the I phase, and the latter stage 8203 where the heater set temperature is around 1060° C. is called the ■ phase.

This means that the transition from phase (1) to phase (2) occurs in 20 to 25 hours.

Referring to Figure 1, the ■ phase has an In content of 0 to 0.
, 4wt%, which corresponds to a P content of about 0 to 0.02Wt96.

Phase (2) corresponds to an In content of o,svrt% or more and a P content of 0.025wt% or more.

At the time of the transition from the ■ phase to the ■ phase, the thermal conductivity of B2O3 suddenly changes. Although the change in the In1P content is slight, it is thought that there is a certain threshold, and when this threshold is exceeded, a phase transition occurs.

If the transition from ■ phase to ■ phase does not occur, B2
There should be no sudden change in the thermal conductivity of O3.

In other words, in order to eliminate the change in thermal conductivity of B2O3, it is sufficient to prohibit the transition from the ■ phase to the ■ phase. To achieve this, it is necessary to avoid the ■ phase from the beginning. It is sufficient if it is in the ■ phase from the beginning.

In other words, B2O3 has In2O3 and P2O5 from the beginning.
It is sufficient to add In and P in the form of .

How much In and P should be added?
In should be at least 0.2 wt%, preferably at least O, swt%. P is o, oiwt% or more, preferably 0
．． 025 wt% or more is sufficient, which means tζ.

In and P may be added to 8203 in the form of simple substances, but in order to avoid contamination by impurities, each may be added to 8203 in the form of an oxide I.
It is desirable to add it to B2O3 in the form of n2O3, P2O5. Expressing the same thing with mo1% of oxide, I n
203 ≧ O, Q6 mol% P2O5 ≧ 0.0
1fflO196 Therefore, p':, becomes.

However, if the amount of these oxides is too large, In2O3
, P2O5 crystallizes, B2O3 becomes partially cloudy, and B
The temperature distribution in 2O3 becomes unstable.

When B2O3 becomes cloudy, the solid-liquid interface cannot be seen from above, making it difficult to pull it up.

Therefore, In2O3 added to B2O3 is 0.08 m
The upper limit of ol 96, P2O, is o, smoz%.

In the end, B2O3 used in the present invention has the following formula: 0.06 mo1%≦In2O3 content≦0.08 mo
l 960.01mo1%≦P2O5 content≦0.8
This means mol%. Herein lies the feature of the present invention.

The method of the present invention will be explained once again using FIG.

FIG. 3 is a schematic diagram of the well-known LEC method.

A furnace body 1, which is a pressure vessel, is filled with an inert gas. The upper shaft 2 and the lower shaft 3 are rotatable shafts that can be moved up and down. A susceptor 5 and a crucible 6 are attached to the upper end of the lower shaft 3.

A heater 4 is provided around the susceptor 5 and generates heat by carbon resistance heating.

The crucible 6 contains an InP raw material melt 7 and a liquid sealant 8 covering it.

An InP seed crystal 9 is attached to the lower end of the upper shaft 2 and immersed in the InP raw material melt 7 for seeding. After seeding, the InP single crystal is pulled up by pulling up the seed crystal 9 while rotating.

The object here is not limited to non-doped nP. It may also be doped with impurities such as Fe, Sn%S, and Zn. These impurities are the InP raw material melt 7
shall be included in the

A liquid sealant 8 which is B2O3 is placed over the InP raw material melt 7.
is covered. Inside the furnace body 1 is an inert gas, for example N2.
, Ar, E gas is maintained at a high pressure of several tens of atm.

Since the inert gas applies strong pressure to the liquid sealant 8, P
dissipation can be effectively prevented.

Add 0.06 to 0.08 mol to this liquid sealant 8 in advance.
% of 1n203 and 0.01-0.8 mo196 of P
The key point of the present invention is to add 2O5.

(E) Function Since In1P is added in advance to B2O3, which is a liquid sealant, when B2O3 is softened, it is in the ■ phase from the beginning. After reaching a higher temperature than this, the InP raw material melts. From the InP that has become a melt, In and P are B2O3
It gradually diffuses into the inside, but since it is originally in the ■ phase, no transition from the ■ phase to the ■ phase occurs.

The fact that this transition does not occur means that no dramatic change in the thermal conductivity of B2O3 (Figure 2) occurs.

The fact that the thermal conductivity of B2O3 does not change means that the temperature of the solid-liquid interface S is stable.

Since the temperature near the solid-liquid interface S is stabilized, twins are less likely to occur.

ρ) Example A. When additive-free B2O3 is used as a liquid sealant.

B, 0.07 mol 96 In2O3 in B2O3
and 0.03m0J% of P2O5 is added as a liquid sealant.

Non-doped InP single crystals were grown 10 times using the above two liquid encapsulants. All other growth conditions are the same except for the liquid encapsulant. The same pulling equipment is used, and the same amounts of raw materials are used. The same applies to changes in temperature and pressure. This is to investigate differences in crystal growth based on differences in liquid sealants.

When using additive-free B2O3 of A, 40 out of 10 lots
A twin appeared in Tsuto. The probability is 40%.

When B2O3 according to the present invention was used as B, twins occurred in 20 out of 10 lots. The probability is 2096.

In this example, the probability of twin occurrence is halved from 4096 in the conventional case to 2096 according to the present invention.

Since the same LEC lifting device is used, there is no difference in mechanical precision. Furthermore, since raw materials synthesized using the same manufacturing method are used, the amount of foreign substances is the same.

Therefore, this decrease in the probability of twinning occurs because the temperature change near the solid-liquid interface caused by the dissolution of In and P in B2O3 during growth is due to the fact that In2O
3. It can be considered that this result was suppressed by adding P2O5.

←) Effects of the present invention, In2O3 and P2O are added to B2O3 in advance.
5, the thermal conductivity of B2O3 is stabilized, and the generation of twins, which is the biggest problem when producing InP single crystals by the LEC method, can be suppressed.

Furthermore, since the thermal conductivity of B2O3 is stabilized, variations in heater temperature settings during sowing are reduced, and reproducibility between lots can be improved.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the results of investigating the amount of In and P dissolved into B2O3 after melting the raw materials by ICP emission spectrometry. The horizontal axis represents the elapsed time from the melting of the InP raw material. The left vertical axis is wt96
In content shown as. The right vertical axis shows the P content in wt96. FIG. 2 is a graph showing the change over time in the heater setting temperature when the seed crystal is kept immersed in the surface of the raw material melt. FIG. 3 is a schematic cross-sectional view of a known LEC device. 1... Furnace Body 2... Upper Shaft 3... Lower Shaft 4... Heater 5... Seven Buttons 6... ... Crucible 7 ... Raw material melt 8 ... Liquid sealant 9 ... Seed crystal 10 ... Single crystal inventor Shigeru Kawahara

Claims (1)

[Claims] In a crucible, InP raw material and liquid sealant B_2O_
3 and apply high pressure with inert gas, heat the crucible with a heater, and add B_2O_3, which is a liquid sealant.
and InP raw material are melted, the liquid sealant covers the InP raw material melt, and the InP is melted while rotating the InP seed crystal.
In an InP single crystal production method in which a single crystal is grown by soaking in a raw material melt and seeding and pulling up the seed crystal, 0
．． 06 mol% to 0.08 mol% of In_2O_3 and 0.01 mol% to 0.8 mol% of P_2O_5 are added to B_2O_3 in advance.
P single crystal manufacturing method.