JPH0645517B2 - Method for producing compound semiconductor single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Technical Field The present invention relates to a three temperature horizontal Britzmann method (three temper).
The present invention relates to a method for producing a III-V compound semiconductor single crystal by means of ature horizontal Bridgman.

The three temperature HB method is a single crystal growth method using a boat.
In a furnace having three different heating heater sections, a high temperature heating section, an intermediate temperature heating section, and a low temperature heating section, the temperature distribution is moved horizontally with respect to the boat by moving the furnace to grow a single crystal.

(A) Prior art For the growth of compound semiconductor single crystals such as GaAs, see
Many innovations have been made such as 51-18471, JP-A-51-18472, and JP-A-52-117300.

Japanese Patent Application Laid-Open Nos. 51-18471 and 18472 use a three-temperature horizontal Britzmann method for G
A single crystal of aAs is manufactured.
The intermediate temperature heating part is set to 1080 to 1220 ° C, and the low temperature heating part is set to 605 to 620 ° C. The temperature gradient between the high temperature heating part and the intermediate temperature heating part is 2 to 10 ° C./cm, and the growth rate is 2 to 10 mm / H.

Japanese Unexamined Patent Publication No. 56-100200 also relates to a three-temperature horizontal Britzmann method for GaAs, but the temperature gradient from the melting point (1238 ° C.) to 1180 ° C. to 1200 ° C. is 2 to 5 ° C./cm, 1180 ° C. to 1200 ° C. It is proposed to control the temperature gradient to 2 ° C / cm or less.

These are improvements related to the three-temperature horizontal Britzmann method, but also improvements in the method for producing a compound semiconductor single crystal by the gradient freeze method (GF). The gradient freeze method is a method in which the power of the heater is gradually reduced without moving the heater, thereby causing crystal solidification while maintaining a temperature gradient. Create a temperature profile with a constant temperature gradient (linear), but with a temperature gradient of 1
In the case of a boat longer than 40 cm at ℃ / cm, the difference between the highest temperature part and the lowest temperature part becomes 40 ℃ or more.

Therefore, JP-A-58-176193 discloses that the temperature gradient is 0.5 ° C / cm to ° C / cm above and below the melting point, the low temperature side of the boat is within 15 ° C of the melting point during growth, and the high temperature side and the low temperature side are low. Claims that the temperature difference with the side should be within 20 ° C.

In the manufacturing method of compound semiconductor single crystal, the melting point is 20 ° C
If the temperature gradient in the area within the range is 0.5 to 1 ° C./cm, the melt causes a compositional supercooling phenomenon, and the solid-liquid interface cannot be stably controlled. Therefore, it is difficult to obtain a long single crystal.

In the temperature range lower than 20 ℃ just below the melting point, 0.5 ℃
It is necessary to maintain a gradual temperature gradient of ~ 2 ° C / cm.
If this is not the case, heat dissipation at the interface will not be sufficient, and heat shrinkage will tend to cause crystal defects. Therefore, a single crystal cannot be manufactured with a high yield.

Also, after solidification is completed, the temperature is lowered at an arbitrary rate, the container is taken out, and the single crystal is taken out to room temperature.
Large thermal shrinkage may cause distortion and increase crystal defects.

The cooling process must also be appropriate. The above mentioned prior art does not mention cooling at all.

(C) Objective It is an object of the present invention to enable production of a large compound semiconductor single crystal having a low dislocation density and a uniform size by the three-temperature horizontal Britzmann method (3T-HB).

In particular, the present invention makes it possible to produce a good-quality single crystal by setting the cooling process of the single crystal to a suitable condition.

(D) Structure of the Invention In order to achieve such an object, the present invention has
The temperature gradient is 1 to 4 ° C / cm in the range of 20 ° C or less, and the temperature gradient is 0 to 2 ° C / cm in the range of 20 ° C or less, and the minimum temperature of the boat is 90 ° C or less from the melting point until the growth is completed. The growth of the whole crystal is controlled at 2 to 20 ° C./H until the high temperature portion reaches the temperature T _y that is 0.7 to 0.8 times the melting point while maintaining the temperature gradient after the growth, From T _y to a temperature T _z corresponding to ⅓ of the melting point, the temperature is lowered at a rate of 2 to 300 ° C./H, and the single crystal is taken out to room temperature when the high temperature portion becomes T _z or less. .

First, some temperature constants are defined.

A temperature 20 ° C. lower than the melting point T _m is T _q , and a temperature 90 ° C. lower than the melting point T _m is T _p . 0.7 to 0.8 of melting point in degrees Celsius
The temperature doubled is T _y . The temperature ⅓ of the melting point is T _z .

T _q = T _m −20 (1) T _p = T _m −90 (2) T _y = 0.7T _{m to} 0.8 T _m (3) T _z = T _m / 3 (4) Consider the position coordinate x in the longitudinal direction of the single crystal, which is the origin. The length of the crystal in the boat is approximately equal to the boat length L ₁ .

The growth and cooling processes defined by the present invention will be described in more detail.

I Under growth conditions T _q ≦ T ≦ T _m , the temperature gradient G ₁ is G ₁ = 1 to 4 ° C./cm. When T <T _q , the temperature gradient G ₂ is G ₂ = 0 to 2 ° C./cm. And Furthermore, for all positions in the boat, T (x ₁ t) ≧ T _p (5) during the growth process. If it is less than 1 ° C./cm in G ₁ , supercooling will occur near the solid-liquid interface. If it is higher than 4 ° C / cm, the dislocation density increases.

G ₂ is the temperature gradient of the solidified portion. It seems that 0 ° C / cm is sufficient, but it may be 2 ° C / cm or less. 2 ° C /
Above cm, the dislocation density of the grown single crystal increases.

The condition (5) is that the temperature of all points in the boat during the growth process is
It is within 90 ° C of the melting point. This is a condition that is imposed regardless of the length of the boat. This is also a condition for reducing the temperature distribution and making the temperature uniform in the single crystal.

II Cooling conditions After solidification is completed, the entire crystal is cooled uniformly while maintaining the temperature distribution formed in the single crystal.

The rate of temperature decrease S is until the temperature of the high temperature part (T, anyway) reaches T _y . And The rate of temperature decrease shall be the same in all parts of the crystal, and the relative temperature relationship shall not change.

In other words, uniform cooling in the cooling process Always satisfy the condition.

The rate of temperature decrease S is therefore a function of time only, regardless of the position in the single crystal. The range of the cooling rate S is defined in two stages. In the latter half of T _{y to} T _z , it becomes wider.

That is, S = 2 to 300 ° C./H (7) from T _y to T _z . When the temperature is lowered to T _z or lower, the heater heating the single crystal is turned off to naturally lower the temperature, and the temperature is brought to room temperature.

In terms of the quality of the single crystal, it is better that the cooling rate is smaller.

However, industrially, it is better that the cooling rate is faster. This is because the shorter the cooling time, the lower the manufacturing cost of the single crystal.

The cooling rate is determined by combining quality and cost requirements. 20 ° C / H or less up to T _y, 300 ° C / H up to T _z
One of the features of the present invention is that the temperature lowering rate is determined by imposing a limit of H or less.

It will be described with reference to the drawings. FIG. 1 is a diagram showing the structure of a crystal growth furnace of the three-temperature horizontal Britzmann method and the temperature distribution of the method of the present invention.

1, 2 and 3 are electric furnaces. This is divided into a high temperature heating unit 1, an intermediate temperature heating unit 2 and a low temperature heating unit 3, and the power can be controlled independently. By appropriately controlling the powers of the heaters 1, 2, and 3 of the electric furnace, T ₁ , T ₂ , and T ₃ are generated in the furnace.
The temperature distribution can be realized.

A high-purity quartz container 4 is provided horizontally in the furnace. In this, a boat 5 made of high-purity quartz is placed.

A raw material melt 6 of a compound semiconductor is accommodated in the boat 5. A shelf is provided at one end of the boat 5, and a seed crystal 7 having an appropriate crystal orientation is placed there.

A group V element 9 is placed on the opposite side of the position where the quartz boat 5 is located. This is for controlling the vapor pressure of the group V element in the quartz container 4. Group V elements are P, As, Sb and the like. The distributions of the temperature profiles T ₁ , T ₂ , and T ₃ are III-
Although the same shape is obtained in the growth of the group V compound, the melting point and the dissociation pressure of the group V element are different depending on the kind of the compound, so that the temperature value is different.

In the following, the growth of GaAs will be described as an example. In this case, V
Since the group element is As, it will be written as excess As9.

In the case of GaAs, T ₁ = 1245 ° C. to 1270 ° C. T ₂ = 1100 ° C. to 1220 ° C. T ₃ = 600 ° C. to 620 ° C.

In the middle of the quartz container 4, a partition 10 having a hole 8 is provided. The pores 8 allow vapor of As to pass through. As a result, the vapor pressure of As near the boat 5 and the melt 6 is controlled by the excess As 9. However, the pores 8 do not pass gallium oxide or silicon oxide.

Melting point T _m (1238 ° C. is between the high temperature portion T ₁ and the intermediate temperature portion T _{2. Since} there is a portion for solidifying the melt between T ₁ and T ₂ , there must be a certain temperature gradient. . T ₂
It is better that the temperature gradient of is gentle.

The temperature 20 ° C. below the melting point T _m is defined as T _q , but T _{m to} T _q
The temperature gradient G _{1 in the above} is G ₁ = 1 to 4 ° C./cm. The temperature gradient G ₂ of T _q or less is G ₂ = 0 to 2 ° C./cm.

Further, the length _{L 2} of the intermediate temperature heating portion _{T 2} are longer than the boat length _{L 1.}

Initially, since the boat 5 is at the high temperature T ₁ , all the raw materials in the boat are melted and become a melt. Heaters A, B,
C is moved to the left with respect to the quartz container 4 at a speed of 1 to 10 mm / H. Then, since the temperature of the seed crystal becomes lower than the melting point from the vicinity of the seed crystal, the seed crystal continues to be solidified. The solid and the melt coexist. The boundary is called a solid-liquid interface. The solid-liquid interface moves to the left as the heater moves. The solidified part is a single crystal. It is at intermediate temperature T ₂ .

. Solidification is complete when the rear end of the boat crosses the melting point T _m . At this time, the entire solidified portion is at the intermediate temperature T ₂ due to the intermediate temperature heating unit 2.

Moreover, while solidification is taking place, the already solidified part of the boat must be above the temperature T _p below 90 ° C. below its melting point. In other words, if it is GaAs, it must be higher than 1148 ℃.

Next, the cooling process will be described.

This is to lower the temperature while maintaining the relative temperature gradient of the temperature distributions T ₁ and T ₂ .

T ₃ should also maintain a relative relationship, but since the temperature difference between T ₂ and T ₃ is about 600 ° C at the beginning, when T ₁ and T ₂ decrease in temperature, T ₃ will move relative to this. It becomes impossible to keep the same temperature difference. However, this is insignificant.

Since the temperature relationship is fixed at T ₁ and T ₂ , if the temperature at any one point is specified, the temperatures at all other points are determined.

Therefore, since the temperature of the high temperature heating part T ₁ is uniform, this is written as T and the temperature is expressed by T.

So until T becomes about _{90 ℃ (0.7T m ~0.8T m)} 2~
The temperature is lowered at 20 ℃ / H, and T becomes 900 ℃ or less, 400 ℃
Until the temperature reaches 2 to 300 ° C./H.

The temperature profile in the middle of FIG. 1 is about 900 ° C.

The temperature profile in the lower part of FIG. 1 shows a state in which T is lowered to about 400 ° C.

The high temperature, intermediate temperature and low temperature distributions are indicated by T ₄ , T ₅ and T ₆ . The relationship between T ₄ and T ₅ is equal to the relationship between T ₁ and T ₂ .

At this time, T ₄ is about 400 ° C. or lower.

T ₆ is about 100~200 ℃.

As described above, in the present invention, the temperature T is T _m
Through T _y At a _{2~20 ℃ / H, T y ~T} z to below S = 2
~ 300 ° C / H. However, S does not have to be constant in each region.

FIG. 2 is a graph showing the relationship between the temperature T and the cooling rate S. The horizontal axis represents the temperature decrease rate S, and the vertical axis represents the temperature T of the high temperature portion.

The above condition defined by the present invention is that there is a correspondence between the temperature and the cooling rate of the region framed by the diagonal lines in FIG.

All that is required is to go through this area and lower the temperature. Various temperature reduction modes are possible.

The polygonal line a gives a simple example of the cooling rate. This is T _m ~ T
_{In y} , S takes a constant value between 2 and 20 ° C / H, and T _y ~
It has a constant value between 2 and 300 ° C./H in T _z .

However, it does not mean that it must be a constant value in each area. The broken line b gradually increases the temperature decrease rate S from T _{m to} T _y , and keeps S constant from T _{y to} T _z .

In the polygonal line c, in the region from T _{y to} T _z , the temperature-falling temperature is first increased and is set to a constant value in the middle.

In addition, At a region of T _y through T _z, it may be to increase the cooling rate in two steps.

In addition, as shown in chain line d, it may be kept constant cooling rate up to T _m through T _z. This is the simplest cooling mode.

(E) Effect The solid-liquid interface is stable during growth, and uniform high cooling is performed during cooling, so that the thermal stress generated in the crystal after solidification can be minimized.

This is effective in suppressing the generation and proliferation of dislocations.

The present invention is therefore capable of producing large compound semiconductor single crystals with low dislocation density.

(F) Example I 3,500 g of Si-doped GaAs polycrystal was charged in a quartz boat having a semicircular cross section, an inner diameter of 65 mm and a total length of 500 mm. The seed crystal was placed on the seed shelf. The growth direction is the <111> As direction.

The quartz boat was placed in the container shown in Figure 1, placed in a temperature of the electric furnace of T _1, by energizing the electric furnace, T _1,
A temperature distribution of T ₂ and T ₃ was formed. 12 from melting point 1238 ℃
The temperature gradient up to 18 ℃ is 2 ℃ / cm, 1218 ℃ to 11
The temperature gradient up to 48 ° C (90 ° C below the melting point) was 1.0 ° C / cm.

Such an electric furnace was relatively moved to the left at a speed of 5.0 mm / H to grow a Si-doped GaAs single crystal.

The growth time of the single crystal was 120 hours. After this, T ₁ ,
The entire temperature distribution of T ₂ was lowered at a rate of 20 ° C./H. It took 45 hours to cool down. At this time,
The temperature distribution is T ₄ and T ₅ . The temperature of T ₃ was lowered at a rate of 10 ° C./H to reach T ₆ .

Then, the temperature was brought to room temperature and the solidified product was taken out. 70% of the total
Was single crystallized.

(a) At a position 120 mm from the seed crystal position, a carrier concentration of 1.5 × 10 ¹⁸ / cm ³ Etchpit density 5.7 × 10 ² / cm ² (b) At a position 450 mm from the seed crystal position, a carrier density of 5.0 × 10 ¹⁸ / Cm ³ Etch-pit density was 1.0 × 10 ² / cm ² .

(G) Example II A Zn-doped GaAs polycrystal was charged at 4,000 gr in a quartz boat having a semicircular cross section, an inner diameter of 63 mm, and a total length of 600 mm.

A single crystal was grown with the same temperature distribution and the same growth rate as in Example I. Growth was completed in 145 hours.

After solidification, the temperatures of T ₁ and T ₂ were lowered at 15 ° C./H, and after 60 hours, they were set to the temperatures of T ₄ and T ₅ shown in FIG. During this time,
The temperature of T ₃ was lowered at a rate of 8 ° C./H to reach the temperature of T ₆ .

75% of the total amount of charge was single crystallized.

(a) Carrier concentration 1.0 × 10 ¹⁹ / cm ³ Etchpit density 5 × 10 ² / cm ² at a position 90 mm from the seed crystal (b) Carrier concentration 2.3 × 10 ¹⁹ / cm ³ Etchpit density 14 at a position 400 mm from the seed crystal 14 It was × 10 ² / cm ² . It turns out that it is a good quality single crystal.

[Brief description of drawings]

FIG. 1 is a diagram showing an electric furnace of a three-temperature horizontal Britzmann method for carrying out the present invention, and a temperature distribution formed by the electric furnace. FIG. 2 is a temperature / cooling rate relationship diagram of the cooling process of the present invention. 1 ... High temperature heating part 2 ... Intermediate temperature heating part 3 ... Low temperature heating part 4 ... High-purity quartz container 5 ... High-purity quartz boat 6 ... Melt 7 ... Seed crystal 8 ... Pore 9 ... … Excess As 10 …… Partition wall

Claims (1)

[Claims] 1. A boat having a space partitioned by partition walls having pores, containing a raw material melt of a III-V compound semiconductor and a seed crystal, and a group V element placed in each space and sealed. A method for growing a single crystal by placing a quartz container in an electric furnace having a high-temperature heating unit, an intermediate-temperature heating unit, and a low-temperature heating unit in the horizontal direction and moving the heater of the furnace with respect to the quartz container At the melting point T _m of the compound semiconductor,
In the range up to the temperature T _{q of} 20 ° C. below the melting point, a temperature gradient of 1 to
4 ° C. / cm to, 0 to 2 ° C. The temperature gradient below the _{T q} / cm
And the entire boat is within 90 ° C. below the melting point T _m during the growth of the single crystal.
While maintaining the temperature gradient of the intermediate temperature heating unit, 2 to 20 ° C. from the melting point T _m to a temperature T _y is 0.7 to 0.8 times the melting point T _m
/ Was lowered at a H cooling rate of from the temperature _{T y} is 0.7 to 0.8 times the melting point _{T m} until below the temperature _{T z} is 1/3 of the melting point of _{the T m} at a cooling rate of 2 to 300 ° C. / H Cool down and after this
A method for producing a compound semiconductor single crystal, which comprises extracting the single crystal to room temperature.