JPH0568439B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Technical field This invention relates to the three-temperature Bridgeman method.
The present invention relates to a method for manufacturing a compound semiconductor single crystal by a temperature horizontal Bridgman. The three-temperature Bridgeman method is a boat-based crystal growth method in which single crystal growth is performed in a furnace having three different heating sections: a high-temperature heating section, an intermediate-temperature heating section, and a low-temperature heating section. (a) Prior art Regarding the growth of single crystals of GaAs,
18471, JP-A-51-18472, JP-A-52-117300, etc., many innovations have been made. JP-A-51-18471 and 18472 disclose high-temperature heating parts,
1245℃~1270℃, intermediate temperature heating section 1080℃~
The temperature is set at 1220°C, and the low temperature heating section is set at 605°C to 620°C. Then, the temperature gradient between the high-temperature heating section and the intermediate-temperature heating section was set at 2 to 10°C/cm, and the growth rate was set at 2 to 10 mm/cm.
It is set as H. JP-A-56-100200 discloses that from the melting point (1238℃),
Temperature gradient from 1180℃ to 1200℃ at 2 to 5℃/cm,
It is proposed that the temperature gradient below 1180°C to 1200°C be controlled to 2°C/cm or less. These are three-temperature horizontal Bridgeman methods, but improvements have also been made to methods for producing compound semiconductor single crystals using gradient freezing methods. Tokukai Akira
No. 58-176193 has a temperature gradient of 0.5 above and below the melting point.
It is proposed that the temperature should be between ℃/cm and 2℃/cm. Also, during crystal growth, the cold side of the boat should be within 15°C of the melting point, and the temperature difference between the hot side and the cold side of the boat should be within 20°C. In the conventional manufacturing method of compound semiconductor single crystal, the temperature gradient within 20℃ from the melting point is set at 0.5 to 2℃/
cm, a compositional overcooling phenomenon occurs and the solid-liquid interface cannot be stably controlled. For this reason, long single crystals cannot be easily obtained. It is also necessary to maintain a gentle temperature gradient of 0.5 to 2°C/cm below the melting point of 20°C. Otherwise, heat dissipation at the interface will not be sufficient and crystal defects will likely occur due to thermal contraction. For this reason, single crystals cannot be manufactured with high yield. Furthermore, passing through a point of temperature equal to the melting point,
Even if the material is successfully formed into a single crystal, if it is cooled at an arbitrary cooling rate, large thermal stress will occur and crystal defects will increase. Therefore, it is impossible to obtain a large single crystal with a low dislocation density. (c) Purpose The purpose of the present invention is to enable the production of a uniform large compound semiconductor single crystal with a low dislocation density by the three-temperature HB method. In particular, the present invention makes it possible to produce a good single crystal by setting the cooling process of the single crystal to suitable conditions. (d) Structure of the invention In order to achieve such an object, the present invention:
Temperature gradient 1 to 4 within 20℃ of melting point
°C/cm, temperature gradient 0 to 2 in the range below 20 °C
℃/cm, a single crystal is grown using the three-temperature horizontal Bridgeman method, and after the growth is completed, the overall temperature is lowered to the lowest temperature in the boat to maintain a uniform temperature inside the single crystal, and then the overall temperature is While maintaining temperature uniformity, the temperature is lowered at a rate of 2℃/H to 20℃/H up to a temperature Ty, which is 0.7 to 0.8 times the melting point, and at a rate of 2 to 300℃ from Ty to a temperature Tz, which is 1/3 of the melting point. The temperature was lowered at a rate of °C/H, and when the temperature of the single crystal fell below Tz, the single crystal was taken out to room temperature. Let Tm be the melting point of a compound semiconductor. 20 from this
℃ lower temperature is Tq. Hereinafter, temperatures will be expressed in degrees Celsius. Ty is 0.7 to 0.8 of Tm, which is the temperature in degrees Celsius. The same goes for Tz. In the case of GaAs, Tm = 1238℃, so Tq =
1218°C, Ty = 867°C to 990°C, Tz = 412°C. In the case of InP, Tm = 1070℃, so Tq = 1050
°C, Ty = 749 °C to 856 °C, Tz = 350 °C. The temperature at a certain position x inside the boat at a certain time t is T, and the spatial temperature gradient G is written as T(x, t) and G(x, t) as a function of x and t. I can do it. The temperature gradient G is also given by x and t, but here the range of G is defined by the temperature T. The method of the present invention defines single crystal growth conditions and cooling conditions, and the main novelty lies in the cooling conditions. Next, conditions for growth and cooling will be explained in order. Growth conditions The temperature gradient of the crystallized portion and the crystal solidified portion is defined as follows. When Tq≦T≦Tm, G=1 to 4℃/cm (1) When T<Tq, G=0 to 2℃/cm (2). In (1), not keeping the temperature below 1℃/cm is because
This is because supercooling is likely to occur. If it is greater than 4°C/cm, the dislocation density will increase, so it is better to be less than this. The above-mentioned Japanese Patent Application Laid-Open No. 56-100200 proposes a value of G of 2 to 5° C./cm in a similar range. Therefore, the temperature range of 1 to 2°C/cm has been proposed for the first time in the present invention. Also, below Tq, G = 0℃/cm,
The present inventor discovered that the vicinity of G=0° C./cm is particularly good. After solidification is completed After solidification into a single crystal, the temperature of the entire single crystal is
Match the minimum speed (temperature near the seed crystal) Tx. In other words, by eliminating the temperature gradient G, the temperature T(x)
is set to a constant value Tx. In the entire single crystal, G = 0 (3) T(x) = Tx (constant) (4) Tx is the temperature of the lowest temperature region in the single crystal after solidification is completed, or somewhat lower than this It's temperature. In the conventional method, G≠0 even after the solidification was completed, but in the present invention, G=0. After that, the temperature of the single crystal is uniform and has no distribution. Therefore, instead of T(x), it is sometimes simply written as T. Cooling conditions: The speed of temperature drop is changed from Ty to temperature Ty, which is 0.7 to 0.8 of the melting point, and from Ty to temperature Tz, which is 1/3 of the melting point. In other words, it is 2 to 20℃/H until Ty, and
Tz is 2 to 300°C/H. When the temperature drops below Tz, it should be taken out to room temperature. That is, while maintaining the condition of G=0, Tx≧T≧Ty, and the temperature decreasing rate S is set to S=2 to 20° C./H (5). Further, when Ty>T>Tz, S=2~300℃/H (6) When Tz>T, the single crystal is taken out to room temperature. This will be explained using drawings. FIG. 1 shows a schematic configuration of a crystal growth furnace using the three-temperature horizontal Bridgeman method and the temperature distribution before crystal growth. A is a high temperature heating section, B is an intermediate temperature heating section, and C is a low temperature heating section. These are resistance heaters such as carbon. Each is a group of multiple controllable heaters. A high-purity quartz container 1 is placed horizontally within a group of heaters. A high-purity quartz boat 2 is a quartz container 1
placed near one end of the The boat 2 contains a raw material melt 3. There is a shelf at the inner end of the boat 2, on which a seed crystal 4 is placed. At the other end of the quartz container 1 there is excess As 6 for controlling the vapor pressure of As. There is a partition wall 7 in the middle of the quartz container 1, in which a pore 5 is bored. The pores 5 are dimensioned to allow only As vapor to pass through, but not Ga or Si oxides. By controlling the heaters A, B, and C, the temperature inside the quartz container can be set arbitrarily. In the method of the present invention, the temperature ranges T ₁ , T ₂ , and T ₃ are realized by the high temperature heating section A, the intermediate temperature heating section B, and the low temperature heating section C. During crystal growth, T ₁ = 1240-1270°C T ₂ = 1100-1220°C T ₃ = 600-630°C. Tm is the melting point of GaAs (1238°C), which is between T ₁ and T ₂ . The temperature gradient G ₁ in this vicinity is G ₁ =1 to 4°C/cm 2 . More precisely, this gradient is taken between 1238°C and 1218°C. Initially, the boat 2 is located at the high temperature heating section A, and the temperature T ₁ is uniform throughout, which is higher than the melting point, so the raw material in the boat 2 is in a molten state. Since the solid-liquid interface is formed between T ₁ and T ₂ , the temperature gradient G ₁ must be relatively large. However, the gentler the T ₂ , the better. The temperature gradient G ₂ here is G ₂ =0 to 2°C/cm. This is from Tq (1218℃) to Tx. The length L ₂ of the intermediate temperature zone (T ₂ ) is longer than the overall length L ₁ of the boat. L ₁ <L ₂ (8). To perform crystal growth, heaters A, B, and C are moved to the left in this figure. The moving speed Q is Q=2 to 8 mm/H (9). The temperature profile will remain approximately the same. As the temperature decreases from the side of the seed crystal 4 of the boat 2, a single crystal having the same crystal orientation as the seed crystal 4 solidifies. The boundary between the melt and the crystallized portion, that is, the solid-liquid interface, moves to the left. In this way, the crystal grows at a speed equal to Q. When the rear end of boat 2 crosses Tm to the right, crystallization is complete. The temperature profile at this time is
As shown in the figure, there are regions T ₁ , T ₂ , and T ₃ . However, the boat has entered the intermediate temperature region _T2 . In order for this to happen, the condition of equation (8) is necessary. The temperature at the front end of the boat is the lowest. Let this temperature be Tx. Tx=min {T(x, t ₂ )} (10) (0≦x≦L ₁ ). x is a coordinate defined from the starting end (also referred to as front side or seed side) of the crystal on the side of the seed crystal toward the terminal end. t ₂ is the time when growth is completed. Stop moving heaters A, B, and C. Let Q=0. Next, the temperature of the parts such as T ₁ and T ₂ where T>Tx is lowered so that they all become equal to Tx. In other words, T(x)=Tx (11) G(x)=0 (12). This point is one of its characteristics. Tx is slightly less than Tm minus G ₂ L ₁ , so the length of the boat L ₁ and the temperature gradient G ₂
It depends. The temperature in the crystal becomes constant. Therefore, there is no difference in expansion and swelling due to temperature differences. The boat is L ₁
Since there is only a length of , it is sufficient that only this part has a constant temperature, and only the part T ₂ in Fig. 1 needs to be aligned with Tx, but in this case, T ₁ is also made equal to Tx. This is because T ₁ does not need to be higher than Tx. However, _T3 does not go to the trouble of raising its temperature, so it remains at a low temperature and cannot match Tx. The temperature graph at the top of FIG. 2 shows this state. Next, the cooling process begins. In the present invention, cooling is performed in two stages. While keeping the temperature inside the boat uniform, the overall temperature T is lowered. G(x)=0 (13) T(x, t)=T(t) (14) Uniform cooling is performed, but the cooling rate is defined in two stages. From Ty to Tz, S = 2 to 20°C/H, and from Ty to Tz, S = 2 to 300°C/H. Ty is, as already mentioned, 867 for GaAs
°C to 990 °C, and Tz is 412 °C. For example, if Ty is 900℃, up to 900℃ is 2
The temperature decreases at a rate of ~20°C/H, and from 900°C to 412°C or less, the temperature decreases at a rate of 2 to 300°C/H. The temperature graph in the middle of FIG. 2 shows the distribution of T=Ty. Here, change the cooling rate. The temperature graph at the bottom of FIG. 2 shows the distribution of T≦Tz. Now take it out to room temperature. The temperature in the low-temperature section has also fallen, reaching _T5 . As explained above, for Tx ~ Ty, S = 2 ~ 20
C/H, and S=2 to 300 C/H from Ty to Tz, but S does not have to be constant in each region. FIG. 3 is a graph showing the relationship between temperature and cooling rate. The horizontal axis is the cooling rate, and the vertical axis is the temperature. The above-mentioned condition defined by the present invention is that the temperature and the rate of temperature decrease exist in the area bounded by diagonal lines in FIG. All that is required is that the temperature decreases through this region. The broken line a gives the simplest example of the temperature decreasing rate. This means that the temperature drop rate is 2 to 20℃/H from Tx to Ty.
Take a constant value between 2 and 300 in Ty to Tz.
It takes a constant value between °C/H. However, it does not necessarily have to be a constant value in each region, and there may be a case like the broken line b. In this region, the temperature decreasing rate is gradually increased in the region from Tx to Ty, and is kept constant in the region from Ty to Tz. In the polygonal line c, in the region from Ty to Tz, the temperature decreasing rate is increased at first, and then kept at a certain constant value in the middle. In addition, the temperature decreasing rate may be increased in two stages in the region from Ty to Tz. Ty is the point where the range of cooling rate changes,
There is a range of 0.7 to 0.8 Tm. Alternatively, the temperature may be lowered at a constant rate from Tx to Tz, as shown by a straight line (dash-dotted line) d. The slower the cooling rate, the easier it is to obtain high-quality crystals. However, if the cooling rate is slow, it takes a long time to cool the crystals, which increases the cost of the product. The cooling rate should be determined depending on the balance between crystal quality and cost. However, below Ty, the temperature must not fall above 300°C/H. From the point of view of quality only, Ty
It is better to have a lower temperature drop rate even at ~Tz. However, when it is desired to shorten the cooling time, a mode such as the straight line d is not suitable. What is meant by FIG. 3 is that when it is desired to increase the temperature decreasing rate S in order to shorten the cooling time, the temperature decreasing rate S may be increased with a limit of 300° C./H between Ty and Tz. (E) Effects When a chemical semiconductor single crystal is grown according to the present invention, the following effects can be obtained. (1) During the growth process, in the range below the melting point Tm to 20℃, the temperature gradient is 1 to 4℃/cm, so the single crystal can be grown while maintaining a stable interface without compositional supercooling. can grow. (2) Also in the intermediate temperature region T ₂ , the temperature gradient G ₂ is
The rate is extremely moderate, ranging from 0 to 2°C/cm. Under high temperature conditions, the solidified portion does not undergo distortion due to rapid thermal contraction. (3) Therefore, if the cross-sectional area of the crystal is 10 cm ² or more and the length is
Even objects larger than 350 mm can be easily made into single crystals. (4) After solidification is completed, adjust the temperature of the single crystal to Tx,
Place under uniform temperature. This results in annealing of the crystal, which has the effect of reducing defects that have occurred so far. Furthermore, since the temperature of the crystal is made uniform, there is no difference in expansion due to temperature differences. For this reason,
Prevent new defects from occurring. (5) Because the temperature decreases while maintaining a uniform temperature state,
No difference in heat shrinkage occurs. Therefore, almost no thermal stress is generated, and the generation and proliferation of dislocations are suppressed. Even when producing a large crystal with a cross-sectional area of 10 cm ² or more and a length of 350 mm or more, it is possible to produce a crystal with a low dislocation density throughout. (6) At the beginning of temperature drop (until Ty), set it to 2 to 20℃/H,
Since Ty to Tz is set at 2 to 300°C/H, there is no occurrence of thermal stress due to the temperature drop rate being too fast. (F) Example 4100 gr of Zn-doped GaAs polycrystal was charged into a quartz port having a semicircular cross section, an inner diameter of 63 mm, and a total length of 550 mm. The growth direction was the <111>As direction. Such seed crystals were placed on the boat's seed shelf. The quartz boat was placed in a quartz container, excess As was also added, and the container was sealed. A temperature distribution as shown in FIG. 1 was formed using electric furnaces A, B, and C. The melting point Tm and the temperature Tq (1218
℃) was set to _2.1 ℃/cm. Below Tq, the temperature gradient G ₂ was set to 0.5°C/cm. Electric furnaces A, B, and C were moved to the left at a speed of 3.2 mm/H relative to the container. _T1 , _T2 , _T3 ,
The GaAs melt was solidified while maintaining G ₁ and G ₂ . The whole solidified in 160 hours. The movement of the electric furnace was stopped. Temperature at seed crystal location
Since Tx was 1195°C, the temperatures of T ₁ and T ₂ were lowered to bring the overall temperature to 1195°C. In this state, 16
Holds time. Next, the single crystal was cooled to 350°C at a rate of 18°C/H while keeping the temperature of the single crystal uniform. Of the material grown in this way, 71% of the total charge amount was single crystallized. (a) At a position 100 mm from the tip of the single crystal, the carrier concentration is 1.0×10 ¹⁹ /cm ³ Dislocation density is 3.2×10 ² /cm ² (b) At a position 200 mm from the tip of the single crystal, the carrier concentration is 1.6×10 ¹⁹ /cm ³ Dislocation density 11.0×10 ² /cm ³ (c) At a position 400 mm from the tip of the single crystal, carrier concentration 2.7×10 ¹⁹ /cm ³ Dislocation density 15.8×10 ² /cm ² (G) Comparative example (G ≠0) Examples of changing cooling conditions will be shown and compared. A quartz boat with a semicircular cross section, inner diameter of 63 mm, and total length of 500 mm was charged with 3750 g of Zn-doped GaAs polycrystal. It was solidified under the same temperature conditions as in the example. After this
Temperature T ₁ , T ₂ without matching T ₁ , T ₂ to Tx
temperature of 2/3 of the melting point (825
℃). The temperature decreasing rate is 100°C/H.
After this time, it was taken out to room temperature. 79% of the total charge amount was single crystallized. However, the dislocation density was high. (d) At a position of 100 mm from the seed crystal, the carrier concentration is 1.1×10 ¹⁹ /cm ³ dislocation density 47.2×10 ² /cm ² (e) At a position of 400 mm from the seed crystal, the carrier concentration is 3.0×10 ¹⁹ /cm ³ dislocation Density: 71.1×10 ² /cm ² Because there is no uniform cooling or annealing process, the dislocation density is high. The single crystal obtained by the method of the present invention has a significantly lower dislocation density. (H) Comparative Example (Value of G ₁ ) The comparative example showed an example in which the temperature gradient G was not set to 0 after solidification. Here, in order to confirm the optimal range of G ₁ during growth, an example and two comparative examples that differ only in the temperature gradient G ₁ during growth will be described. When G ₁ was smaller than 1°C/cm, polycrystals tended to form instead of single crystals. This is probably because supercooling is likely to occur. G ₁ = 4.8℃/cm, other conditions (G ₂ = 0.5℃/
cm S = 18°C/H) were the same, and single crystals were grown. The EPD and carrier concentration at 100mm and 400mm from the seed crystal are as follows: 100mm from the seed crystal Dislocation density 17.5×10 ² cm ^-2 Carrier concentration 1.1×10 ¹⁹ cm ^-3 400mm from the seed crystal Dislocation density 28.3×10 ² cm ^-2 The carrier concentration was 2.9×10 ¹⁹ cm ^-3 . It can be seen that the dislocation density is considerably higher than in the previous example. (ke) Comparative example (value of G ₂ ) In order to find out the optimal range of _the value of G ₂ ,
= 0.5°C/cm), GaAs single crystals were grown under the same conditions except for _G2 . The values of G ₂ are 0°C/cm, 0.5°C/cm (previous example), 2°C/cm, 3°C/cm. In Table 1, 100
The dislocation densities at the positions mm and 400 mm (from the seed crystal) are shown, and Table 2 shows the measured values of the carrier concentration at the same positions. The smaller G ₂ is, the lower the dislocation density is, but if G ₂ is 3℃/
If it exceeds cm, the dislocation density becomes too large. However, the carrier concentration hardly depends on _G2 . This can be seen from Table 2.

【table】

[Table] (J) Comparative example (Temperature cooling rate from Tx to Ty) For Tx to Ty, the temperature cooling rate is 2 to 20°C/H, but if Ty = 900°C for GaAs, 2°C/H or less,
The cases of 18°C/H (Example) and 25°C/H were compared. A temperature of 2° C./H or less is not industrially practical because it takes too long to cool down. For example, if Tx~Ty is 300℃, it will take more than 150H. The case of 18°C/H was described above. The results for the case of 25°C/H will be described. (i) Dislocation density at 100mm from the seed crystal: 19.2×10 ² cm ^-2 carrier concentration 1.2×10 ¹⁹ cm ^-3 (ii) Dislocation density at 400mm from the seed crystal: 63.1×10 ² cm ^-2 carrier concentration 3.2 It was ×10 ¹⁹ cm ^-3 . The dislocation density is 4 to 6 times higher than that when S=18°C/H. (Sa) Comparative example (temperature fall rate from Ty to Tz) In the present invention, S = 2 to 300°C/H is adopted,
Experiments were conducted for cases in which only the cooling rate was different, and the dislocation density and carrier concentration were compared. If the temperature is 2° C./H or less, it takes too long to cool down and is not suitable for industrial use. 18℃/H (Example), 250
Table 3 shows the experimental results for ℃/H and 400℃/H.
It is shown in Table 4.

【table】

[Table] As shown above, the higher the cooling rate, the higher the dislocation density. When S=400°C/H, it is more than twice as much as when S=250°C/H. The carrier concentration remains almost unchanged.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic diagram of a single crystal growth apparatus using the three-temperature horizontal Bridgeman method in association with temperature distribution (temperature distribution before crystal growth). FIG. 2 is a diagram showing the temperature distribution at the end of crystal growth and the temperature distribution at the end of the uniform cooling process in the same apparatus. Figure 3 is a temperature/cooling rate graph. A...High temperature heating section, B...Intermediate temperature heating section, C
...Low temperature heating section, 1...High purity quartz container, 2...
Quartz boat, 3... Raw material melt, 4... Seed crystal, 5
... Pore, 6... Excess As, 7... Partition wall.

Claims (1)

[Claims] 1. A boat having a space partitioned by a partition wall having pores and containing a raw material melt and a seed crystal for a -group compound semiconductor, and a horizontal quartz container with a group element placed in each space are placed horizontally. In a method for producing a single crystal, the single crystal is placed in an electric furnace having a high-temperature heating section, an intermediate-temperature heating section, and a low-temperature heating section, and the single crystal is grown while moving the furnace heater relative to the quartz container. In the range from the melting point Tm of the compound semiconductor to the temperature Tq 20℃ below the melting point, the temperature gradient is 1 to 4℃/cm.
Below Tq, a single crystal is grown while maintaining a temperature gradient of 0 to 2°C/cm, and after the growth is completed, the temperature is increased to the lowest temperature in the crystal near the seed crystal, or to a certain temperature Tx slightly lower than the lowest temperature. Lower the temperature of the high-temperature heating section and the intermediate-temperature heating section to obtain a uniform temperature distribution, and maintain the temperature gradient of the entire section that was higher than the seed crystal at 0℃/cm for a certain period of time until the high temperature gradient reaches 0℃/cm. While maintaining the condition of
The temperature is lowered to a temperature Ty that is ~0.8 times that temperature Ty.
The single crystal is characterized in that the temperature T is uniformly lowered at a rate of 2 to 300°C/H until the temperature Tz corresponding to 1/3 of the melting point Tm is lowered, and when the temperature drops below Tz, the single crystal is taken out to room temperature. A method for manufacturing a compound semiconductor single crystal.