GB2200576A

GB2200576A - Method of growing single crystal of compound semiconductor and apparatus therefor

Info

Publication number: GB2200576A
Application number: GB08718725A
Authority: GB
Inventors: Seikoh Yoshida; Naomi Nishibe; Toshio Kikuta; Yuzo Kashiwayanagi
Original assignee: Furukawa Electric Co Ltd
Current assignee: Furukawa Electric Co Ltd
Priority date: 1987-02-06
Filing date: 1987-08-07
Publication date: 1988-08-10
Anticipated expiration: 2007-08-07
Also published as: DE3726713A1; JPH0432800B2; JPS63195187A; GB2200576B; GB8718725D0

Description

1 1 A- a 1 2.',"-'0 0 5 7 6 Method of growing single crystal of compound

semiconductor and apparatus therefor.

FIELP OF THE INVENTION The present invention rel ates to a method of growing single crystal of compound semiconductor by the temperature -gradient f reezing method (GF method), the horizontal Bridgman method (HB method) or the like and an a-. .:),Dara-,-us therrefor. The -invention has made it possible to grow t he single crystal surely by controlling the current of heat and, at the same time, made the growth of crystal easy under high pressure as the case of growing the 0 crystal of InP Undium phosphide), in particular.

BACKGROUND OF THE INVENTION

When growing single crystal after placed a volatile eiemen at lowertemperature portion and a boat accommodated a metal element at highertempexature portion in a quartz ampule heated with electric furnaces and produced a molten liquor of compound semiconductor in said boat, a method wherein the gradient is shifted A i 2 through the adjustment of temperature inside of electric furnaces leaving the quartz ampule and the electric furnaces as they a're fixed is the GF method and a method wherein the quartz ampule or the electric furnaces is (are) shifted is the HB method. In each case, only by lowering the temperature inside of electric furnaces gradually from seedportion to molten liquor portion, it is difficult to control the current of heat in the molten liquor, in particular, the current of heat at the interface between solid and liquid resulting in most frequent polycrystallization on the way of growth.

For this reason, various improvements have been made in order to control the current of heat at molten liquor portion and to produce the single crystal with low carrier density. For example, in a method disclosed in Japanese Unexamined Patent Publication No. sho 55-62882, the growing interface is controlled freely by providing a blowing device of cooled gas above the boat and the single crystal with low carrier density is allowed to grow at a rapid growth rate.

However, only by providing the blowing device of cooled gas at the upper portion inside of electric furnace, the accurate -control of the current of heat in molten liquor is difficult. In particular, with such one that the stacking fault energy is18 erg /CM2 which amounts about one third of that of gallium arsenide and the twin crystal tents to generate in extrem, as indium phosphide, there is a problem that the-polycrystallization 1 j i 1 3 :occurs by a subtle fluctuation of heat.

Accordingly, more accurate control of the current of heat Z 1 1 is requested in order to produce the single.crystal of compound semiconductors such as indium phosphide and others, the monocrystallization thereof being difficult.

When determining the temperature distribution actually on the inner wall of electric furnace and inside of boat at the time of growing the single crystal of indium phosphide by the GF method, it is. observed in many times that the temperature A of the molten liquor of indium phosphide inside of boat is higher than the temperature B on the inner wall of electric furnace as shown in Fig.

8. At a such state of temperature, the current of heat escaping from the molten liquor of indium phosphide to the outside of boat via the wall of boat is to be existent resulting in that the crystalline nucleus tends to generate on the inner wall of boat. Thus, the polycrystallization is apt to occur and the production of single crystal is extremely difficult.

For this reason, in the invention, the temperature inside of boat was made lower than that of circumference and, by causing the current of heat from the circumference outside of boat toward inside of boat, the generation of nucleus on the inner wall of boat was suppressed to make sure the growth of single crystal possible.

Moreover, the dissociation pressure of InP at the melting point is very high showing about 27 atm. When conducting the A 4 4 growth of crystal of such compound semiconductor in the quartz ampule, it is necessary to grow the crystal at a state applied the outer pressure to the outside of quartz ampule and removed the difference between inside and outside pressures in order to prevent the destruction of quartz ampule.

In Fig. 16, one example of conventional apparatus'for the growth of crystal is shown. In the diagram, numeral 31 is a highpressure vessel into which nitrogen gas is filled up under pressure, numerals 32-and 33 are cylindrical electric furnace for lower temperature and that for higher temperature provided in series in the high-pressure vessel 31 and numeral 34 is a quartz. liner tube provided so as to pass through the electric furnace for lower temperature 32 and that for higher temperature 33. Inside of quartz liner tube 34, a quart z ampule 11 sealed, for example, red phosphorus 12 and indium 27 is provided. Indium 27 is sealed in a state placed in a boat 13. Moreover, numerals 39 and 40 are tube-end heat insulators provided at both ends of the quartz liner tube 34.

In general, the temperature of the electric furnace for lower temperatijre 32 is adjusted so as the pressure of phosphorus in. the quartz ampule 11 to become to 10 to 15 atm or so and the pressure equivalent thereto is applied to the inside of high-pressure vessel 31. Thus, taking the pressure balance, the temperature on the side of indium 27 is adjusted to 1000 to 1050 OC or so and a temperature profile A as in Fig. 17 is plotted. In this state, 1 1 1 I- the quartz ampule 11 is shifted to-the direction B shown by an arrow mark (or the electric furnaces 32 and 33 are shifted to the opposite direction) to grow the polycrystal or monocrystal of InP in the boat 13 in the case of HB method, and the temperature gradient is shifted through the adjustment of temperatute of electric furnaces in the case of GF method.

Now, with the conventional apparatus as above, it is difficult to take the pressure balance to the dissociationpressure at the temperature of molten liquor and there arises a danger to break the quartz ampule when synthesizing the compound semiconductor as InP high in the dissociation pressure at the melting point. Moreover, if raised the pressure in the high-pressure vessel, the transfer of heat by the convection becomes violent leading to that it is difficult-to stabilize the temperature distribution inside of electric furnace and the growth of crystal becomes hard. For this reason, low-temperature synthesis at a lower temperature than the-melting point is conducted conventionally making the pressure of phosphorus 10 to 15 atm or so. However, when using thia method, there are problems that the time for the growth of crystal is long, that the inclusion of indium tends to generate in crystal, and the like.

SUMMARY OF THE INVENTION

The inv ention is characterized in that, in the method of growing single crystal after placed a volatile element at lowertemperature portion and a boat accommodated a metal element at 11-1 6 higher-temperature portion in a quartz ampule heated with electric furnaces and produced a molten liquor of compound semiconductor in said boat by the temperature-gradient freezing method or the horizontal Bridgman method, a heat sink is connected thermally to the side of seed end of said boat and a cooling pipe leading to the outside of furnace is provided around the heat sink to absorb the heat inside of said'boat toward heat sink via seed and, at the same time, auxiliary heaters are provided around said heat to supply the heat, so that the single crystal is grown supplying always the heat from the circumference of boat to the molten liquor in boat in a state kept the temperature inside of said boat lower than that outside of boat.

An apparatus to be used for carrying out this method is provided with the heat sink arranged so as to contact with the end of seed of said boat, the cooling pipe which is provided outside. of said quartz ampule surrounding said heat sink and the end portion of which is led to the outside of furnace, auxiliary heaters provided outside of said quartz ampule surrounding said boat and divided into at least top and bottom and a heat-insulating plate provided between said cooling pipe and auxiliary heaters-.

The second embodiment of the invention is an apparatus in which, in the apparatus of growing the crystal of compound'semiconductor, wherein a high-pressure vessel, a gas being fidled up thereinto under pressure, cylindrical electric furnace for lower temperature and electric furnace for higher temperature provided t 1 i 7 in series in said high-pressure vessel, a quartz liner tube pro- vided passing through said electric furnace for lower temperature and that for higher temperature and auxiliary heaters provided between said quartz liner tube and said electric furnace for higher temperature are provided, and the quartz ampule sealed the raw materials at compound semiconductor, the heat sink and further the cooling pipe leading to the outside of high-pressure vessel is provided in said quartz liner tube, an inert gas, the heat transfer coefficient thereof being lower than that of nitrogen gas is used as said gas, and-an interfurnace heat insulator, a furnace-end heat insulator on lower-temperature side, a furnaceend heat insulator on higher-temperature side and an intermediate insulator are provided between said electric furnace for lowertemperature and that for higher temperature, at the outer end of, electric furnace for lower temperature,-at the outer end of electric furnace for higher temperature and between said electric furnace for lower temperature and that for higher temperature, and on the quartz liner tube,- respectively.

Further, as the third embodiment of the invention, an apparatus in which the heat sink and the cooling.pipe leading to the outside of highpressure vessel both to be sealed in the quartz ampule and the auxiliary heaters outside of quartz liner tube are taken off from the apparatus of the second embodiment aforementioned is proposed.

BRIEF DESCRIPTION OF THE DRAWINGS

9 1 1 8 Fig. 1 through Fig. 8 concern with the first embodiment of the invention. Fig. 1 is a cross section showing one example of the apparatus used for the method of growing the single crystal. Fig. 2 through Fig. 4 are cross sections on II-II line, III-III line and IV-IV line in Fig. 1, respectively. Fig. 5 is an oblique view of the auxiliary heater used in the same apparatus. Fig. 6 is an explanatory diagram showing the current of heat inside and outside of boat in the method of the invention. Fig. 7 is a graph showing the temperature distribution when carried out the temperature-gradiept freezing method according to the method of the invention. And, Fig. 8 is a graph showing the temperature distribution_by conventional temperature-gradient freezing method.

Fig. 9 is a cross section of one example of the apparatus in accordance with the second embodiment of the invention.

Fig. 10 through Fig. 17 relate to the third embodiment of the invention. Fig. 10 is a cross section of the apparatus for the growth of crystal of compound semiconductor according to one example of the invention. Fig. 11 is an explanatory diagram showing the measurement points of the temperature distribution inside of electric furnace for higher temperature. Fig. 12 is a graph showing the action-of interfurnace heat insulator. Fig. 13 is a graph showing the action of furnace-end heat insulators on the side of lower temperature and on the side of higher temperature. Fig. 14 is a graph showing the temperature distribution when provided interfurnace heat insulator and two furnace-end 1 1 g 9 9 heat insulators and not provided intermediate heat insulator. Fig. 15 is a graph showing the temperature distribution when provided interfurnace heat insulator, two furnace-end heat insulators and intermediate heat insulator. Fig. 16 is a cross section showing conventional apparatus for the growth of crystal of compound, semiconductor. And, Fig. 17 is a graph showing the temperature distribution inside of furnace in the same apparatus.

DETAILED DESCRIPTION OF THE IN'QENTION

In following, the examples of the invention will be illustrated in detail referring to the drawings. Example 1 Fig. 1 through Fig. 4 show one example of the apparatus used for the method of growing the single crystal in accordance with the first embodiment of the invention. in the diagrams, numeral 11 is the quartz ampule, the inside-thereof being made vacuum, numeral 12 is the volatile element, for example, phosphorus placed n one side thereof, and numeral 13 is the boat provided on the other side. In boat 13, the metal element, for example, indium is accommodated and, on one side thereof, seed 14 is provided. Numeral 15 is the electric furnace on the side of lower temperature which controls the vapor pressure of phosphorus inside of quartz ampule 11 and numeral 16 is the electric furnace on the side of higher temperature which heats the side'of boat with a predetermined temperature profile.

The method of the invention is same as conventional one in i a point that, after produced the molten liquor of indium phosphide in boat 13 by volatilizing phosphorus 12 and allowing it to diffuse into indium, the temperature profile inside of electric furnace on the side of higher temperature 16 is varied gradually, or the electric furnaces or the ampule are (is) shifted gradually leaving the temperature profile inside of furnaces as it is to-grow the single crystal in boat 13 from the side of seed 14.

In such method, the invention adopts a following constitution further in order to make out the current of heat from outside toward inside of boat 13.

First, in the quartz ampule 11, the heat sink 21 excellent in the thermal conductivity is provided contacting with the tip of seed shelf of boat 13 Moreover, surroundingthe heat sink 21, the cooling pipe 22 for cooling the heat sink 21 is provided outside of quartz ampule 11. The end portion of cooling pipe 22 is.led to the outside of electric furnace 16 and the inert gas for cooling is made to flow thereinto. By adjusting the flow rate of this inert gas, the quantity of heat released from the heat sink 21 is controlled. Besides, the cooling pipe 22 is provided at a fixed position in the electric furnace 16 and the quartz ampule 11 is to be provided through -the ring portion thereof.

Furthermore, the flange-like heat-insulating plate 23 is provided a little to the boat 13 of cooling pipe 22 in order not to give the outer thermal disturbance from the cooling pipe 22 to the vicinity of boat 13.

1 6i 1 11 In addition, at a position outside of quartz ampule 11 and corresponding to the circumference of boat 13, many auxiliary heaters 24 divided into axial direction and circumferential direction are provided. Individual auxiliary heater is one fixed with a heater wire 26 for high temperature such as kanthal wire, pyromax wire or the like onto approximately semicylindrical quartz material 25 in a suitable pattern as shown, for example, in Fig. 5 and the heat value of each one can be controlled in-, dependently. The reasons why the auxiliary heaters 24 are divided plurally into axial direction are because of that the homogeneity of heat in the vicinity of boat 13 is made easy to obtain which is hard to realize only by the electric furnace 16, and that the temperature distribution in the axial direction is adjusted finely. Moreover, the reason why the auxiliary heaters 24 are divided in two into top and bottom is because of that, by adjusting the heat values of top and bottom, the temperature difference between upper and lower directions inside of electric furnace 16 is eliminated. Besides, the auxiliary heaters may be divided, for example, in four into circumferential direction to make the temperature_ adjustment possible from top and bottom and right and left.

Now, in order to grow the single crystal after produced the molten liquor of indium phosphide 27 in boat 13, a state of the homogeneity of heat is made out over approximately whole length of boat 13 using electric, furnace 16, auxiliary heaters 24 and 12 heat sink 21 and thereafter the growth of crystal is initiated by means of, for example, temperature-gradient freezing method. The temperature profile is given by the electric furnace 16 as usual, but, in the state kept the temperature profile, the absorption of heat by the heat sink 21 and the cooling pipe 22 and the auxiliary heating by the auxiliary heaters are made further. As a result, the currents of heat inside and outside of boat 13 become as arrow marks.in Fig. 6. That is to say, the heat supplied from auxiliary heaters 24 enters into the inside of boat 13 from the circumference outside of boat 13 and is to flow to the heat sink 21 via the molten liquor of indium phosphide 27 and the seed 14. Accordingly, in this state, the temperature in the molten liquor 27 becomes lower than that on the wall of boat 13 and the generation of nucleus from the surface of inner wall of boat 13 is suppressed resulting in sure growth of single crystal from the seed 14.

Fig. 7 shows the temperature distribution in the process of this growth of crystal. Namely, in the whole process by the temperature-gradient freezing method, the temperature A of the molten liquor of indium, phosphide in boat 13 is lower than the temperature B on the inner wall of electriefurnace 16. To give such temperature distribution is extremely effective for the growth of single crystal.

Now, inside of the usual horizontal-type electric furnace, the temperature difference of 20 to 3CC exists between top and 1 1 1 13 bottom ( upper portion shows higher temperature). The existence of such temperature difference affects inversely for the growth of one- directional freezing. Such temperature difference can be removed by providing the auxiliary heaters divided into top and bottom in the electric furnace as in the example above and by adjusting the supply power to respective auxiliary heaters. Moreover, unless the auxiliary heaters affect the length of homogeneity of heat in the temperature- distribution in the axial direction inside of electric furnace, they have only to be provided one by one at top and bottom. When any effect is exerted on the length of homogeneity of heat, the auxiliary heaters may be divided plurally also in the axial direction and the respective heat values may be adjusted to obtain a desirable length of homogeneity of. heat.

Moreover, in the example above, the number of winding of cooling pipe around the heat sink was made one turn, but, when desired to increase in the effect of the absorption of heat further, it may be made two turns or more. However, in that case, the thickness Of heat-in'sulating plate is necessary to be made thicker in order not to-give the-outer thermal disturbance to the utmost to the growth portion of crystal.

Moreover, when the temperature gradient in the process of growth cannot be taken-sufficiently in view of the temperature distribution at lowertemperature portion in quartz ampule (zone, the volatile element being placed) in the case of growing the 14 1 X 11 crystal by the temperature-gradient freezing method, there happens that the boat is pr ovided inversly to above, that is, so as the seed shelf to occupy a position on the opposite side of volatile element. At that time, the heat sink and the cooling pipe are to be provided, of course, on the end side of the quartz ampule.

Besides, in the example described above, such case that the invention was applied mainly to the temperature-gradient freezing method was illustrated, but the invention is applicable similarly also to the horizontal bridgeman method.

Furthermore, in the example above, the growth of single crystal of indium phosphide was illustrated, but the invention is applicable also to the growth of single crystal of other compound semiconductors.

Example 2

This example shows one example of the second embodiment of the invention and is applied to the case of high pressure.

As shown in Fig. 9, in a high-pressure vessel 31, two electric furnaces 32 and 33 and a quartz liner tube 34 are placed, and heat insul-ators 39 through 44 are provided at respective positions outside of said electric furnaces 32 and 33 in order to stabilize the temperature distribution inside of electric furnaces under high pressure. Moreover, in the electric furnaces 32 and 33, the quartz ampule_11 sealed red phosphorus 12 and a boat 13 with the seed and In so as the former to occupy the position on the side of lower temperature and the latter on the side of higher 1 Z temperature is placed. On the outer circumference of said quartz ampule 11, auxiliary heaters 24 divided in six into top and bottom are provided at the position corresponding to boat 13. By means of said-auxiliary heaters 24, accurate temperature profile can be realized. Furthermore, in order to perform the stabilized releasing of heat on e-directionally from the molten liquor to the side of seed in the process for growth, a heat sink 21 excellent in the thermal conductivity is provided from the tip of seed to the direction on the side of lower temperature in said quartz ampule ll.. On the outer circumference in the vicinity of the tip of said heat sink 21 (side of lower temperature), a cooling pipe 22 for cooled gas is provided to make the release of heat vigorous from said heat sink 21 to-. ward the outside. By the flow rate at gas flowing in said cooling"pipe 22, the release of heat from the si de of heat sink can be controlled freely.

The temperature profile in the process for growth is established so that the temperature around the boat becomes always higher than the temperature inside of boat, as shown in Fig. 7.

Under such condition, the heat becomes to enter always from thecircumference-of boat to the inside of boat and to be released via tie molten liquor and via the heat sink.

In the case of such one-directional current of heat, the occurrence ofnucleus from the side wall of boat is suppressed in utmost making it possible to grow the single crystal onedirection-ally from the-side of seed.

16 As the gas to be filled up in to the high-pressure vessel, nitrogen gas has been used conventionally. The reason why an inert gas with lower heat transfer coefficient than that of nitro gen gas is used is due to that it became clear that the use of inert gas was more advantageous to stabilize the temperature distribution in_side of electric furnaces. When providing the inter furnace heat insulator, furnace-end heat insulator on the side of lower temperature, furnace-end-heat insulator on the side of higher temperature and intermediate heat insulator as described above in addition to the use of such-inert gas, the outer thermal distur bance due to convection etc4 is suppressed even under high pressure and the temperature distribution inside of electric furnaces is stabilized. The action of inert gas, in particular, argon gas and the reason for p - rovision and effect of respective heat insulators are illustrated minutely in following Example 3.

Example 3

This example is also applied to the growth of crystal under high pressure and describes an apparatus eliminated the heat sink, coolinc, pipe and auxiliary heaters from that in Example 2.

Namely, in Fig. 10,_numeral 31 is a high-pressure vessel, numerals 32 and 33 are electric furnace for lower temperature and that for higher temperature, respectively, numeral 34 is a quartz liner tube, numeral 11 is a quartz ampule, numeral 1.2 is red phosphorus, numeral 27 is indium, numeral 13 is a boat, numerals 39 and 40 are tube-end heat insulators, and numeral 36 is introductory k 1 17 p and exhaust ports of gas to be filled-up into the high-pressure vessel.

Similarly to Example 2, argon gas is filled up into the high-pressure vessel 31 under pressure, and an interfurnace heat insulator 41, a furnace-end heat insulater on the side of lower temperature 42, a furnaceend heat insulator on the side of higher temperature 43 and an intermediate heat insulator 44 are provided between electric furnace forlower temperature 32 and that for higher temperature 33, at the outer end of electric furnace for lower temperature 32, at the outer end of electric furnace for higher temperature 33 and between electric furnace for lower temperature 32 and that for higher temperature 33 and on the quartz liner tube 34, respectively.

The reason,why argon gas is used is as follows: Using nitrogen gas an d argon gas comparatively the temperature of heater 45 of electric-furnace for higher temperature 33 Tout and the surface temperature on quartz liner tube 34 inside thereof Tin were determined at respective positions of I to IV with a thermocouple as shown in Fig. 11. The results are shown in Table 1 and Table 2 (data at the posit ions of II and III are omitted).

18 j.

I_ Table 1 (Case of nitrogen gas) Temperature Pressure Position Tout Tin A T 1130 C 1050 'C 80 'C atm IV 1100 1052 48 1 'C 1061.,C 139 'C 1200 23 atm - iv 1150 1067 83 1 1200 'C 900 "C 300 C 27 atm IV 1200 950 250 AT=Tout-Tin Table 2 (Case of argon gas) Temperature Pressure Position Tout Tin A T 1 1110 Oc 1072 OC 38 C atm IV 1140 1070 70 1 1120 c 1076 C 44 'C 23 atm IV 1165 1075 90 1125 c 1071 Oc 54 Oc 27 atm IV 1175 1073 102.

t- 19 1 o 3 1 When used nitrogen gas, the temperature difference AT between the- temperature of heater Tout and the temperature on quartz liner tube (temperature inside of furnace) Tin becomes large as the pTessure of gas increases. When increasing the pressure of nitrogen gas to 27 atm, which is the dissociation pressure at the melting point of InP,_the transfer to heat due to the convection becomes violent, so that the temperature on the quartz liner tube never reaches to 1000 'C. Whereas. when used argon gas, the temperature difference LX between heater and quartz liner tube does not very so much.even if increasing the pressure of ga.s. Consequently, as the gas to be filled up into the high-pressure vessel, the use of argon gas, the heat transfer coefficient thereof being lower than that of nitrogen gas, is more advantageous from the aspect of the stability of temperature inside of electric furnace. Besides, as a gas low in the heat transfer coefficient, there is krypton gas besides of argon gas. This is also usable, but has a difficulty that the price is high.

Next, the necessity of interfurnace heat insulator 41 will be explained. When the pressure inside of high-pressure vessel 31 _is, relatively low (less than 10 atm), there is no question even without the interfurnace heat insulator 41. But, when the pressure inside of high-pressure vessel 31 exceeds 15 atm, it was made evident that the temperature between two electric furnaces was decreased lower than that in the phosphorus chamber on the side of lower temperature as shown by a solid line in Fig. 12. If causing 4 4 such lowering of temperature, it becomes difficult to control the pressure of phospho.us by the temperature in phosphorus chamber. For this reason, the interfurnace heat insulator 41 was provided between two electric furnaces 32 and 33 to prevent the lowering of temperature between furnaces and the temperature distribution as shown by a dotted line in Fig. 12 was made out. As the materials for the heat insulator, blanket, monofelt for high temperature, kaowool, quartz wool, etc. are usable. Besides, as shown in Fig. 10, sufficient preventive effect on the lowering of temperature can be obtained, even if the outer diameter of interfurnace heat insulator 41 is smaller than that of two electric furnaces 32 and 33.

Next, the necessity of furnace-end heat insulator on the side of lower temperature 42 and that on the side of higher temperature 43 will be explained. When these heat insulators 42 and 43 are not provided, it became clear from the experiments that the temperature on the side of higher temperature became not to rise due to the convection if increasing the pressure of gas. For this reason, the furnace-end heat insulator on the side of lower temperature 42 was provided at the outer end of electric furnace for. lower temperature 32 and on the quartz liner tube 34 and simultaneously the furnace-end heat insulator on the side of higher_temperature 43 was provided at the outer end of electric furnace for higher temperature 33 and on the quartz liner tube 34 to suppress the convection inside of furnaces and to make it possi- IS j, 1 1 n 21 ble to rise the temperature on the side of higher temperature to desirable temperature.

There, if providing such furnace-end heat insulators 42 and 43, there happens that the temperature on the side of lower temperature becomes higher than desirable temperature (solid line) under the influence of the temperature on the side of higher temperature as shown by a dotted line in Fig. 13. In order to avoid this, it is effective to make the heat insulation of furnace-end heat insulator on the side of lower temperature 42 lower than that of furnace-end heat insulator on the side of higher temperature 43 and an appropriate quantity of heat is released from the outer end of electric furnace for lower temperature 32. In the example in Fig. 10, the difference in the heat insulation is created by using heat insulators of same quality of material for both furnace-end heat insulators 42 and 43 and by making the thickness of furnace-end heat insulator on the side of lower temperature 42 thinner than that of furnaceend heat insulator on the sideof higher temperature 43. According to the experiment, the ratio of thickness was suitable to be around 2:5 (side of lower temperature:side of higher temperature) Finally, the necessity of intermediate heat insulator 44 is as follows: When the process for the growth of crystal is put forward by the GF method providing the interfurnace heat insulator 41 and the furnace-end heat insulators 42 and 43 aforementioned, it became clear that, as the temperature on the side 9 22 of higher temperature decreases, the temperature in the phosphorus chamber on the side of lower temperature is also lowered as shown in Fig. 14. This is because of the occurrence of heat transfer inside of furnaces. For this reason, the intermediate heat insulator 44 was provided between electric furnace for lower temperature 32 and that for higher temperature 33 and on the quartz liner tube 34, whereby the temperature on the side of lower temperature became not to vary even if allowing the temperature on the side of higher temperature to decrease as shown in Fig. 15 and independent control of temperatures on the side of lower temperature and on the side of higher temperature became possible.

As described above, in accordance with the invention, the generation of crystal nucleus on the surface of inner wall of boat is suppressed and the single crystal can be grown sure.1y when growing the sin-1-e crystal by the temperature-gradient freezing method or the horizontal Bridgman method, since, by the combination of the heat sink, cooling pipe and auxiliary heaters, the heat entering into the boat from the circumference otLtside of boat makes out a current of heat flowing into the heat sink via the molten liquor of compound semiconductor and via the seed, so that the temperatureof the molten liquor becomes lower than that on the wall of boat.

Moreover, in accordance with the invention, a stabilized temperature distribution becomes possible to be made out without Z 1 23 t the influence of pressure virtually even if the pressure of gas inside of high-pressure vessel is made high. As a result, it becomes possible to conduct the growth of crystal of compound semiconductor as InP, the dissociation pressure at the melting point thereof being very high, under high pressure by the HB method, GF method or others, and the advantage that the crystal of compound semiconductors with high quality can be prepared within a short time is secured.

1 1 4 24

Claims

What is claimed is: (1) A method of growing single crystal of compound

semiconductor, wherein, in the method of growing single crystal after placed a volatile element at lower-temperature portion and a boat accommodated a metal element at higher-temperature portion in a quartz ampule heated with electric furnaces and produced a molten liquor of compound semiconductor in said boat by the temperature-gradient freezing method-or the horizontal Bridgman method, a heat sink is connected thermally to the side of seed end of said boat and a cooling pipe leading to the outside of furnace is provided around the heat sink to absorb the heat inside of said boat toward heat sink via seed and, at the same time, auxiliary heaters are provided around said boat to supply the heat, so that the single crystal is grown supplyIng always the heat from the circumference of boat to the molten liquor in boat in a state kept the temperature inside of said boat lower than that outside of boat. (2) An apparatus of growing single crystal of compound semiconductor characterized in that, in the apparatus of growing single crystal provided with a quartz ampule, in which a volatile element is placed at one end and a boat accommodated a metal element is placed at other end, horizontally in the electric furnaces, said one end being made lower- temperature portion and said.other end being Made a higher-temperature portion, a heat sink provided at the seed end of said boat, a cooling pipe which is provided outside of said quartz ampule surrounding said heat sink and the

C 1 1 W 1 1 end portion of which is led to the outside of furnace, auxiliary heaters provided outside of said quartz ampule surrounding said boat and divided into at least top and bottom and a heat-insulating plate provided between said cooling pipe and auxiliary heaters are provided. M-The apparatus of growing single crystal of compound semiconductor characterized in that, in the apparatus of growing the crystal of compound semiconductor wherein a high-pressure vessel, a gas being filled up thereinto under pressure, cylindrical electric furnace for lower temperature and electric-furnace for higher temperature provided in series in said high-pressure vessel, a quartz liner tube provided passing-through,said electric furnace for lower temperature and that for higher temperature and auxiliary heaters provided between said quar-tz liner tube and said electric furnace for higher temperature are provided, and the quartz ampule sealed the raw materials of compound semiconductor, the heat sink and further the cooling pipe leading to the outside of high-pressure vessel is provided in said quartz liner tube, an inert gas, the heat transfer coeficient thereof being lower than that of nitrogen gas is used-as-said gas, and on interfur nace heat insulator, a furnace-end heat insulator on lower- temperature side, a furnace-end heat insulator on higher temperature side and an intermediate insulator are provided between said electric furnace for lower temperature and that for higher temperature, at the outer end of electric furnace for lower temperature, at the t 4 1 1 26 outer end of electric furnace for higher temperature and betwee said electric furnace for lower temperature and that for higher temperature and on the quartz liner tube, respectively. (4) The apparatus of growing single crystal of compound semiconductor characterized in that, in the apparatus of growing the crystal of compound semiconductor wherein a high- pressure vessel, a gas being filled up thereinto under pressure, Cylindrical electric furnace for lower temperature and electric furnace for higher temperature provided in series in said high-'pressure vessel, a quartz liner tube provided passing through said electric furnace for lower temperature and that for higher temperature are provided,-and the quartz ampule sealed the raw materials of compound semiconductor is provided in said quartz liner tube, an inert gas, the heat transfer coefficient thereof being lower than that of nitrogen gas is used as said gas, and an interfurnace heat insulator, a furnace-end heat insulator on lower-temperature side, a furnace end heat insulator on higher temperature side and an intermediate insulator are provided between said electric furnace for lower temperature and that for higher temperature, at the outer end of electric furnace for lower temperature, at the outer end of electric furnace for higher temperature and between said electric furnace for lower temperature and that for higher temperature and on the quartz liner tube, respectively. (5) The apparatus according to claim 4, wherein the heat insulation of furnace-end heat insulator on the side of lower tempera- i A 1 1 27 1 ture is made lower than that of furnace-end heat insulator on the side of higher temperature. (6) The apparatus according to Claim 4 or Claim 5, wherein the outer diameter of interfurnace heat insulator is made smaller than the outer diameter of electric furnace for lower tem peraturd and that for higher temperature. (7) The apparatus according to Claim 3, Claim 4, Claim 5 or Claim 6, wherein argon gas is used as a gas.

]Published 1988 at The Pstent. Otace. Stat,- Ho-use. 66 71 High Holbc-r;, Lo.-idon W, C 1B 4TP. Firther oopies may be ob=ied Lrom The Patent C=cc, Sales Brancr.. St WELT Cray, Orpir4wn, Kent BR5 3FLI). Printed by MuJt4plex techniques ltd. St Maxy Cray, Kent Cor.. 1/87.