JP2010030847A - Production method of semiconductor single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method of a semiconductor single crystal, by which a high-quality semiconductor single crystal can be obtained with high reproducibility, having small variance in the impurity concentration in the growing direction of the crystal. <P>SOLUTION: The production method of a semiconductor single crystal comprises housing a semiconductor melt 5 with addition of an impurity in a crucible 6 and gradually solidifying the melt upward from the seed crystal 10 side while rotating the crucible 6 in a state where the semiconductor melt 5 is brought into contact with a seed crystal 10 which is placed in a seed crystal placement part formed at the bottom of the crucible 6, wherein the rotation speed of the crucible 6 is gradually decreased with proceeding of the crystal growth. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor single crystal using a semiconductor melt as a raw material, and more particularly to a method for manufacturing a semiconductor single crystal for uniformly controlling the impurity concentration along the crystal growth direction.

  Up to now, as a method for producing a III-V compound semiconductor crystal or the like, the semiconductor melt is accommodated in a container such as a crucible, and the seed crystal is in contact with one end of the semiconductor melt from the seed crystal side to the other end. Many crystal growth techniques for growing a single crystal by gradually solidifying it have been developed and put into practical use.

  For example, as a so-called vertical growth method in which a semiconductor melt is accommodated in a vertical crucible, a seed crystal is arranged at the lower end thereof, and the crystal is grown from below to above, vertical bridgman (Vertical Bridgman: VB) method, vertical gradient freeze (VGF) method, vertical zone melt solidification (VZM) method and the like are known.

  Non-patent document 1 describes in detail the VB method and the VGF method. Also, Patent Documents 1 to 4 and the like describe the applied technology.

For example, Patent Document 1 includes a container for storing a semiconductor melt as a raw material, a temperature gradient furnace disposed around the container, and means for moving the temperature gradient furnace relative to the container. Describes a single crystal production apparatus using a BN (Boron Nitride) container containing B ₂ O ₃ in the wall of the container.

In addition, according to the single crystal manufacturing apparatus described in Patent Document 3, B ₂ O ₃ gradually oozes out from the wall surface of the BN container during use, and the wall surface of the crucible is covered with the B ₂ O ₃ film. The generation of crystal nuclei caused by the contact between the semiconductor melt and the irregular wall surface of the crucible surface can be prevented.

Japanese Patent No. 2558515 Japanese Patent No. 2664085 Japanese Patent No. 2850581 Japanese Patent No. 3391503 T. Hikawa “Advanced Electronics I-4 Bulk Crystal Growth Technology” Baifukan, May 1994, p. 222-241

  However, the above-described conventional technology for manufacturing a compound semiconductor crystal has a problem that the impurity concentration largely changes along the crystal growth direction inside the crystal due to the segregation effect of the doped impurities.

  The variation in impurity concentration results in variation in electrical characteristics of the crystal substrate, which ultimately leads to variation in the characteristics of devices manufactured using the crystal substrate. In addition, excessive condensation of impurities due to segregation may cause polycrystal generation during crystal growth.

  Accordingly, an object of the present invention is to provide a method for producing a semiconductor single crystal that solves the above-described problems and that can obtain a high-quality semiconductor single crystal with good reproducibility with little variation in impurity concentration in the crystal growth direction. There is to do.

  The present invention has been devised to achieve the above object, and the invention of claim 1 contains a semiconductor melt to which an impurity as a dopant is added in a crucible, and the semiconductor melt is contained in the crucible. Production of a semiconductor single crystal that gradually solidifies the semiconductor melt from the seed crystal side upward while rotating the crucible while in contact with the seed crystal arranged in the seed crystal arrangement part formed at the bottom The method is a method for producing a semiconductor single crystal in which the rotational speed of the crucible is gradually decreased with the progress of crystal growth.

  The invention according to claim 2 is the method for producing a semiconductor single crystal according to claim 1, wherein the rotation speed of the crucible is gradually decreased and the crystal growth speed is gradually decreased as the crystal growth proceeds.

  According to a third aspect of the present invention, the diameter of the crucible is 160 mm and the length is 300 mm, and the rotational speed of the crucible is changed from 20 rpm at the start of growth to 1 rpm at the end of the growth, with 0.25 rpm as the crystal growth proceeds. 3. The method for producing a semiconductor single crystal according to claim 1, wherein the semiconductor single crystal is gradually slowed at a rate of / h.

  According to the present invention, it is possible to suppress a change in the doped impurity concentration with respect to the growth direction of the single crystal, and as a result, a crystal substrate with uniform electrical characteristics can be manufactured with a high yield.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of the invention will be described with reference to the accompanying drawings.

  As a result of various studies to solve the problem of uneven impurity concentration along the crystal growth direction described above, the present inventor has focused on the fact that the effective segregation coefficient of impurities is a function of the growth boundary layer thickness, A method has been devised in which the growth boundary layer thickness of the crystal is gradually or gradually changed during the growth in accordance with the equilibrium segregation coefficient of the impurity to be doped.

The concentration C _s of impurities taken into the crystal is expressed by the following formula (1).

_{C s = k e C 0 (} 1-g) ke-1 ··· (1)
Here, k _e is the effective segregation coefficient, C ₀ is the impurity concentration of the initial semiconductor melt, g is the solidification ratio of the crystal (the value representing the ratio of the weight of the crystals solidified initial semiconductor melt weight) .

Further, the effective segregation coefficient k _e is expressed by the following equation (2).

_{k e = k 0 / (k} 0 + (1-k 0) · exp (-R · d / D)) ··· (2)
Here, k ₀ is the equilibrium segregation coefficient, R is the crystal growth rate, D is the diffusion coefficient of impurities in the semiconductor melt, and d is the thickness of the growth boundary layer in the semiconductor melt near the interface.

As can be seen from equation (2), the effective segregation coefficient k _e impurities, crystal growth rate R and has a function of growth boundary layer thickness d, as the crystal growth rate R is low, also the growth boundary layer thickness d the thinner the effective segregation coefficient k _e closer to the equilibrium segregation coefficient k _0. The faster the crystal growth rate R Conversely, also the effective segregation coefficient k _e thicker the growth boundary layer thickness d approaches 1.

Further, as can be seen from the equation (1), the impurities taken into the crystal are expressed as a function of the solidification rate g of the crystal. When k _e > 1, the impurity concentration decreases as the solidification rate g increases. On the other hand, when k _e <1, the impurity concentration increases as the solidification rate g increases.

To eliminate the influence of segregation of impurities, but the effective segregation coefficient k _e better the closer to 1, actually finite crystal growth rate R is forced to take the growth boundary layer thickness d can not but more, k _e is It takes a value between 1 and the equilibrium segregation coefficient k ₀ .

  Here, the present inventor believes that the crystal growth rate R and the growth boundary layer thickness d should not always remain constant during crystal growth, and alleviates impurity segregation. From the viewpoint, the crystal growth rate R and the growth boundary layer thickness d during crystal growth were examined.

  In the initial stage of crystal growth, the volume of the crystal is small, and conversely, the volume of the semiconductor melt is large. At this time, the temperature gradient in the crystal tends to increase, and crystal defects tend to occur. Also, temperature fluctuations are likely to occur due to convection of the semiconductor melt, and the heat flow that dissipates heat through the crystal is difficult to stabilize.

  For this reason, it is necessary to keep the crystal growth rate R stable and suppress strain applied to the crystal. Moreover, in order to suppress the temperature fluctuation of the semiconductor melt, the crystal growth is more stable when the convection is suppressed by using a method such as crucible rotation. As a result, the growth boundary layer thickness d must be increased to some extent.

  However, if the crystal growth progresses and the volume of the crystal increases and the volume of the semiconductor melt decreases, the growth becomes stable. Therefore, the crystal growth rate R at the beginning of crystal growth and the growth boundary layer are not necessarily limited. It is not necessary to keep the thickness d constant.

  Considering the impurity concentration distribution, the impurity concentration distribution in the longitudinal direction (crystal growth direction) in the crystal is better as the crystal region with less dissociation from the initial growth of the impurity concentration lasts longer.

However, in actuality, the impurity concentration greatly deviates from the initial concentration of growth as it goes to the rear end of the crystal due to segregation. Impurity concentration distribution in the crystal, but it not determined according to the initial impurity concentration C ₀ and the effective segregation coefficient k _e of impurities into the semiconductor melt, if it is possible to vary the effective segregation coefficient k _e during crystal growth, slightly However, it should be possible to grow a crystal region with little impurity concentration and dissociation at the beginning of growth for a long time.

For this purpose, it is better to bring the rear end of the large area of the dissociation of the impurity concentration of the initial growth by segregation possible crystal, in order that the value of the effective segregation coefficient k _e during growth, the equilibrium segregation it may be set so as to be close to the coefficient k _0.

From the above relationship, when crystal growth is performed with an impurity doped, as the effective segregation coefficient k _e approaches equilibrium segregation coefficient k ₀ as solidification rate g of the crystal increases, gradually slow the crystal growth rate R In other words, the influence of the segregation of impurities can be mitigated by gradually reducing the growth boundary layer thickness d.

  Now, a method for manufacturing a semiconductor single crystal according to an embodiment of the present invention and a crystal growth furnace used in this manufacturing method will be described.

  First, an example of a crystal growth furnace used for manufacturing a semiconductor single crystal will be described. FIG. 1 is a schematic cross-sectional view of a crystal growth furnace used in the present invention.

  The crystal growth furnace 1 includes a crucible 6 as a container for containing a raw material of a compound semiconductor crystal to be grown, a susceptor 7 as a crucible container for containing the crucible 6, a susceptor support member 8 for holding the susceptor 7, and the crucible 6. And a peripheral heater 3 as a plurality of peripheral heaters that heat the surface from the side. In the illustrated example, the outer peripheral heater 3 is composed of four outer peripheral heaters 3a, 3b, 3c, and 3d arranged vertically in the furnace.

  Further, the crystal growth furnace 1 includes a plurality of heat insulating materials 2 that prevent heat generated by the plurality of outer peripheral heaters 3 from being transmitted to the outside of the crystal growth furnace 1, an upper outer peripheral heater 3a 3b, and a lower outer peripheral heater. The heat insulating material 4 provided between the heaters 3c and 3d, these heat insulating materials 4, and the chamber 11 which covers these heat insulating materials 2 and 4 from the outside are provided.

  The crucible 6 is connected to a cylindrical straight body part, a conical cylinder-like inclined part formed by being connected to the lower end of the straight body part and gradually reducing the diameter downward, and to the inclined part. And a small-diameter portion having a bottomed cylindrical shape as a seed crystal arrangement portion that accommodates the seed crystal 10 of the compound semiconductor crystal.

  As an example, the straight body portion of the crucible 6 is a cylinder having a diameter of 160 mm and a length of 300 mm. The crucible 6 is formed from pyrolytic boron nitride (pBN). The crucible 6 can also be formed from quartz.

That is, the crucible 6 has a narrow diameter portion at the bottom and a crucible opening at the upper end of the straight body portion. The crucible 6 accommodates the seed crystal 10 in the small diameter portion and also contains a predetermined amount of the compound semiconductor crystal raw material introduced from the crucible opening and a predetermined dopant for p-type or n-type as required. To do. The compound semiconductor crystal material is a growing compound semiconductor polycrystal. The crucible 6 may further contain a liquid sealant 9 such as B ₂ O ₃ .

  The susceptor 7 is made of graphite, and holds and accommodates the crucible 6. The susceptor support member 8 is provided so that it can be moved up and down and rotated in the crystal growth furnace 1. The susceptor 7 is mounted and held on the susceptor support member 8.

  In this case, the lower part of the susceptor 7 comes into contact with the susceptor support member 8, and the susceptor 7 is mounted on the susceptor support member 8. Thereby, the crucible 6 can be rotated while keeping the temperature distribution in the crucible 6 gently and constant during crystal growth.

  A plurality of outer peripheral heaters 3 (3 a, 3 b, 3 c, 3 d) arranged along the direction from the upper part to the lower part of the crystal growth furnace 1 are predetermined inside the crystal growth furnace 1 so as to surround the periphery of the susceptor 7. Are arranged at respective heights. The set temperatures of the plurality of outer peripheral heaters 3 are set so as to decrease sequentially along the direction from the upper part to the lower part of the crystal growth furnace 1.

  As an example, the outer periphery heater 3 is formed of a resistance heater formed of a material such as graphite. Moreover, the outer periphery heater 3 can also be comprised by the heater etc. which use the heating element heated with the silicon carbide (SiC) heater, the infrared heating heater, and the RF coil as a secondary heater.

  The heat insulating material 2 is provided so as to surround the outside of the plurality of outer peripheral heaters 3. By providing the heat insulating material 2, the heat generated by the plurality of outer peripheral heaters 3 can be efficiently transferred to the crucible 6. On the other hand, the heat insulating material 4 is disposed in order to ensure a predetermined temperature difference between the upper outer peripheral heaters 3a and 3b and the lower outer peripheral heaters 3c and 3d, but the installation is not necessarily required. .

  The heat insulating material 2 is comprised from the molding material of a graphite as an example. Moreover, the heat insulating material 2 can also be comprised with an alumina material, glass wool, a firebrick, etc.

  The chamber 11 seals the crucible 6, the susceptor 7 that accommodates the crucible 6, the susceptor support member 8 that holds the susceptor 7, the plurality of outer peripheral heaters 3, the heat insulating material 2, and the heat insulating material 4. The crystal growth furnace 1 has a mechanism for setting the atmosphere in the chamber 11 to a predetermined gas atmosphere, and a gas pressure control mechanism for keeping the pressure in the chamber 11 at a constant value.

  The crystal growth furnace 1 grows a single crystal of a compound semiconductor crystal by a VGF method. That is, in the crystal growth furnace 1, the seed crystal 10 installed at the bottom of the crucible 6 is a semiconductor melt 5 in which a raw material containing a dopant contained in the crucible 6 is melted at a predetermined temperature by the heating of the outer peripheral heater 3. The temperature of the semiconductor melt 5 is lowered while keeping the lower end of the crucible 6 on the seed crystal 10 side at a lower temperature than the upper end of the crucible 6 (crucible opening side). In the crucible 6, the melted semiconductor melt 5 of the compound semiconductor material comes into contact with the seed crystal 10 of the small diameter portion to start the growth of the single crystal, and the semiconductor is directed from the seed crystal 10 side to the upper side of the crystal growth furnace 1. The melt 5 gradually solidifies and a compound semiconductor single crystal grows. As an example, the compound semiconductor crystal grown in the crystal growth furnace 1 is a single crystal of GaAs which is a III-V group compound semiconductor.

  Further, in the crystal growth furnace 1, when the compound semiconductor semiconductor melt 5 has a dissociation pressure equal to or higher than atmospheric pressure, the chamber 11 can be used as a pressure vessel. By using the chamber 11 as a pressure vessel, even when the semiconductor melt 5 of the compound semiconductor has a dissociation pressure equal to or higher than atmospheric pressure, the liquid sealant 9 is used and at the same time the pressure inside the chamber is equal to or higher than the dissociation pressure. By setting to, dissociation of the semiconductor melt 5 can be prevented and a single crystal of a compound semiconductor can be grown.

  Also, the entire crucible 6 can be enclosed in an ampoule made of quartz or the like. Then, an ampoule in which the crucible 6 is sealed can be installed at a predetermined position in the crystal growth furnace 1 to grow a compound semiconductor single crystal.

  In the crystal growth furnace 1, the set temperature of the plurality of outer peripheral heaters 3 is gradually lowered at a predetermined speed to lower the temperature in the crucible 6, and the single crystal is obtained from the semiconductor melt 5 in the crucible 6. Although it is grown, the manufacturing method of the crystal is not limited to this. For example, the single crystal may be grown by gradually lowering the susceptor support member 8 while rotating it.

  In the crystal growth furnace 1 described above, not only a GaAs single crystal but also other III-V group compound semiconductor crystals can be grown. For example, a single crystal of a compound semiconductor such as InP, InAs, GaSb, or InSb can be grown using the crystal growth furnace 1. Further, using the crystal growth furnace 1, growth of a ternary mixed crystal of a III-V compound semiconductor crystal such as AlGaAs, InGaAs or InGaP or a quaternary mixed crystal of a III-V compound semiconductor crystal such as AlGaInP is performed. Application is also possible.

  In addition, the crystal growth furnace 1 can be used to grow II-VI group compound semiconductor crystals such as ZnSe and CdTe or IV group semiconductor crystals such as Si and Ge. Furthermore, the crystal growth furnace 1 can be used to grow crystals such as metal crystals, oxide crystals, and fluoride crystals, which are crystals of materials that are not compound semiconductor crystals or semiconductor single crystals.

  Next, a method for manufacturing a semiconductor single crystal according to the present embodiment will be described.

The method for manufacturing a semiconductor single crystal according to the present embodiment uses a phenomenon in which the growth boundary layer thickness d increases by suppressing convection in the semiconductor melt 5, and a semiconductor melt to which an impurity as a dopant is added. 5 is solidified to grow a semiconductor single crystal. The crucible 6 is rotated during crystal growth to apply centrifugal force to the semiconductor melt 5 to suppress natural convection of the semiconductor melt 5 and progress of crystal growth. with the (with increasing solidification rate g of crystals), so that the effective segregation coefficient k _e approaches equilibrium segregation coefficient k _0, gradually the effect of gradually slow to be a natural convection the rotational speed of the crucible 6 In this method, the impurity concentration is made uniform along the crystal growth direction.

  For example, in the case of the above-described crucible 6 having a diameter of 160 mm, the rotational speed of the crucible 6 is gradually increased from 20 rpm at the start of growth to 1 rpm at the end of growth at a rate of 0.25 rpm / h as the crystal growth proceeds. It is good to be late.

According to the method for producing a semiconductor single crystal, the crucible 6 is rotated during crystal growth, and centrifugal force is applied to the semiconductor melt 5 to suppress the natural convection of the semiconductor melt 5 and to progress the crystal growth. with it (with increasing solidification rate g of crystals), so that the effective segregation coefficient k _e approaches equilibrium segregation coefficient k _0, to gradually slow the rotational speed of the crucible 6, with respect to the growth direction of the single crystal As a result, a change in the doped impurity concentration can be kept small, and as a result, a crystal substrate with uniform electrical characteristics can be manufactured with a high yield.

Further, in the method of manufacturing a semiconductor single crystal by solidifying the semiconductor melt 5 to which an impurity as a dopant is added to grow a semiconductor single crystal, as the crystal growth proceeds (with an increase in the solidification rate g of the crystal) in order to effective segregation coefficient k _e is to approach equilibrium segregation coefficient k _0, it is also effective to gradually slow the crystal growth rate.

  Therefore, this is combined with the above-described embodiment, that is, the method in which the crucible 6 is rotated during crystal growth, and the rotational speed of the crucible 6 is gradually decreased as the crystal growth proceeds, and a semiconductor doped with impurities. When the semiconductor single crystal is grown by solidifying the melt 5, centrifugal force is applied to the semiconductor melt 5 to suppress the natural convection of the semiconductor melt 5. As the g increases, the crucible rotation speed is slowed down, and at the same time the crystal growth rate is gradually slowed (or the temperature drop rate of the semiconductor melt 5 is gradually reduced), and the crystal growth direction The impurity concentration along the line can also be made uniform.

  In the present invention, in order to eliminate the centrifugal force applied to the semiconductor melt 5 and maximize the influence of the convection of the semiconductor melt 5, the rotation of the crucible 6 may be stopped completely. Since the axial symmetry of the temperature distribution in 5 collapses and other problems such as unstable crystal growth and disordered distribution of electrical characteristics of the crystal occur, the rotation of the crucible 6 cannot be completely stopped. Better.

  The present invention is effective when applied to a case where the crystal to be grown is a II-VI group or III-V group compound semiconductor crystal, particularly a GaAs single crystal.

  For example, when applied to crystal growth of GaAs, the impurities include Si, S, Se, Mg, Zn, Cd, In, Ge, Sn, Sb, Te, Cr, Mn, Fe, C, Al, P, and Be. Etc.

  The present invention is preferably applied to the vertical boat method (VB method, VGF method, etc.). Although it can be applied to crystal production methods such as pulling method (CZ method, LEC method) and chiroporus method, in these crystal growths, forced convection is generated in the semiconductor melt 5 due to crystal rotation. It is difficult to control the convection in the semiconductor melt 5 by the centrifugal force generated by the crucible rotation, and it is difficult to obtain the effects of the present invention.

Example 1
In Example 1, single crystal growth of GaAs doped with Si was performed by the VGF method using the crystal growth furnace 1 described above.

The crucible 6 was made of pBN having a diameter of the straight body portion of 160 mm and the length of the straight body portion of 300 mm. First, the GaAs seed crystal 10 was stored in the narrow diameter portion of the crucible 6. Subsequently, 24,000 g of a bulk GaAs polycrystal synthesized in advance was filled in the crucible 6. Next, 7.2 g of silicon as a dopant (impurity) and 400 g of B ₂ O ₃ as a liquid sealant 9 were charged in the crucible 6.

  Next, the crucible 6 was accommodated in a susceptor 7 made of graphite. Further, the susceptor 7 was mounted on the susceptor support member 8. Next, the crystal growth furnace 1 was sealed, and the inside of the crystal growth furnace 1 was replaced with nitrogen gas. Thereby, the gas atmosphere in the crystal growth furnace 1 became a nitrogen gas atmosphere.

  Subsequently, the crucible 6 started to rotate. The crucible 6 was rotated by rotating the susceptor support member 8 and the rotational speed of the crucible 6 was set to 20 rpm. Further, the crucible 6 was heated by energizing the plurality of outer peripheral heaters 3. By continuing to heat the crucible 6 for a predetermined time after the start of the heating of the crucible 6, the GaAs polycrystal in the crucible 6 was completely melted to obtain the semiconductor melt 5.

  In the process of heating the crucible 6, the volume of the atmospheric gas in the chamber expands. Therefore, the pressure in the chamber was controlled so that the pressure in the chamber did not exceed 0.5 MPa. That is, in Example 1, the gas pressure in the chamber was controlled automatically and continuously so that the pressure in the chamber was always maintained at 0.5 MPa even during crystal growth.

In the process of melting the GaAs polycrystal in the crucible 6, the B ₂ O ₃ added to the crucible 6 softened faster than the GaAs polycrystal melted. The softened B ₂ O ₃ covered the surface of the semiconductor melt 5 in a transparent water tank shape. Thereby, the volatilization of As due to the decomposition of GaAs could be suppressed.

  Subsequently, the set temperature of the plurality of outer peripheral heaters 3 was set to a temperature that decreased from the top to the bottom of the crystal growth furnace 1.

  Specifically, the set temperature of the outer peripheral heater 3a arranged at the top of the four outer heaters 3 is set to 1290 ° C., and the set temperature of the outer heater 3b arranged therebelow is set. Set to 1260 ° C. Furthermore, the set temperature of the outer peripheral heater 3c arranged under the heat insulating material 4 was set to 1150 ° C., and the set temperature of the outer peripheral heater 3d arranged in the lowest stage was set to 1050 ° C. After setting the heater temperature in this way, the temperature was maintained for 2 hours until the temperature of the semiconductor melt 5 was stabilized.

  The position of the crucible 6 relative to the positions of the plurality of outer peripheral heaters 3 was determined based on a temperature distribution measured by inserting a thermocouple into the crystal growth furnace 1 in advance. Specifically, in order to prevent the seed crystal 10 from melting and disappearing while holding the crucible 6, an isotherm of 1238 ° C. which is the melting point of GaAs is applied to the upper end portion of the seed crystal 10. The crucible 6 was placed in

  After the temperature in the crystal growth furnace 1 is stabilized, the set temperature of each of the outer peripheral heaters 3 is lowered at a rate of 0.5 K / h, and this constant temperature drop rate is maintained. It cooled until the preset temperature of the outer periphery heater 3a became 1250 degreeC. In addition, the rotational speed of the crucible 6 was started to decrease along with the start of lowering of the set temperature of each outer peripheral heater 3, and the rotational speed was gradually decreased at a rate of 0.25 rpm / h until the rotational speed reached 1 rpm.

Thereafter, while the crucible 6 is rotated at 1 rpm, the temperature drop of each outer heater 3 is stopped, and then gradually cooled over 24 hours so that the temperature of each outer heater 3 becomes 950 ° C. Then, the temperature of each outer peripheral heater 3 was decreased at a rate of −20 ° C./h until the temperature of each outer peripheral heater 3 reached 400 ° C. Subsequently, the rotation of the crucible 6 was stopped, the energization of each outer peripheral heater 3 was stopped, and the crucible 6 was cooled to room temperature. After cooling the crucible 6 to room temperature, remove the crucible 6 from the crystal growth furnace 1, was taken out grown crystals were removed B ₂ O ₃ (liquid sealant 9). As a result, it was confirmed that the grown crystal was a GaAs single crystal over the entire length.

  In the above-described process, crystal growth was performed 20 times continuously. As a result, it was possible to obtain a crystal whose entire length was a single crystal of GaAs in any crystal growth.

(Comparative Example 1)
As Comparative Example 1 for comparison with Example 1 described above, single crystal growth of GaAs doped with Si was performed by the VGF method using the same first crystal growth furnace 1 as Example 1.

  The procedure of crystal growth work in this comparative example 1 is the same as that of the above-mentioned example 1. The difference between Example 1 and Comparative Example 1 is the rotational speed of the crucible 6. In Comparative Example 1, the crucible 6 was rotated at a constant speed while maintaining the rotation speed of the crucible 6 from the start of crystal growth until the cooling of the grown crystal was completed.

  Also in Comparative Example 1, after cooling the crucible 6 to room temperature, the grown crystal in the crucible 6 was taken out and examined, and it was confirmed that it was a GaAs single crystal over the entire length.

(Comparison between Example 1 and Comparative Example 1)
In order to compare Example 1 and Comparative Example 1, one of the 20 GaAs single crystals obtained in the process of Example 1 described above was selected. Then, a portion corresponding to the straight body portion of one selected GaAs single crystal was sliced to cut out a plurality of substantially circular wafers having a (100) plane. Next, a wafer at a position corresponding to a solidification rate of every 0.1 was extracted from the cut wafer, and the silicon concentration in the central portion was measured by SIMS (Secondary Ion Mass Spectrometry).

  Similarly, one GaAs single crystal obtained in the process of Comparative Example 1 described above is selected, and a portion corresponding to the straight body portion of the GaAs single crystal is sliced to obtain a substantially circular shape having a (100) plane. A plurality of wafers having a shape were cut out, wafers at positions corresponding to solidification rates of every 0.1 were extracted from the cut out wafers, and the silicon concentration at the center was measured by SIMS.

  FIG. 2 shows the result of SIMS measurement of the distribution of the silicon concentration in the crystal longitudinal direction in the GaAs single crystals grown in Example 1 and Comparative Example 1 described above.

  In the GaAs single crystal grown in Comparative Example 1, following the normal segregation phenomenon of silicon, the distribution of the silicon concentration in the longitudinal direction of the crystal became higher as it reached the rear end of the crystal.

That is, the silicon concentration was 1.01 × 10 ¹⁸ cm ⁻³ at the solidification rate of 0.1, whereas the silicon concentration was 6.16 × 10 ¹⁸ cm ^{−3 at the} solidification rate of 0.9. The difference was 5.15 × 10 ¹⁸ cm ⁻³ .

On the other hand, in Example 1, the distribution of the silicon concentration in the longitudinal direction of the crystal is slightly slower than that in Comparative Example 1, and there is no difference in the silicon concentration at the position where the solidification rate is 0.1. When the solidification rate was 0.9, the silicon concentration was increased only to 6.01 × 10 ¹⁸ cm ⁻³ , and the difference was 5.00 × 10 ¹⁸ cm ⁻³ .

When the silicon concentration values in Example 1 and Comparative Example 1 are compared, it seems that there is not much difference, but the carrier concentration specification (allowable range) of the non-defective substrate is assumed to be (2.0 ± 1.0) × If it is 10 ¹⁸ cm ⁻³ , the yield is 68.6% in Example 1, whereas the yield is 65.7% in Comparative Example 1, which is obtained from one crystal ingot. This means that there is an opening of nearly 10 to the number of non-defective substrates. Therefore, it can be said that there is a sufficiently significant difference.

  The specification of the carrier concentration of a non-defective substrate is of a character that depends on the conditions of use of the substrate, so the range cannot be limited, and therefore the effect of the present invention is difficult to express numerically. There is no doubt that it has the effect of mitigating the influence and reducing the difference in impurity concentration distribution between the early and late stages of crystal growth.

(Example 2)
In Example 2, single crystal growth of GaAs doped with Si was performed by the VGF method using the same first crystal growth furnace 1 as in Example 1 described above.

  The procedure of the crystal growth operation in the second embodiment is basically the same as that in the first embodiment. The difference between Example 2 and Example 1 is that the crystal growth rate was changed during growth. In Example 2, after the semiconductor melt 5 was formed and the temperature in the crystal growth furnace 1 was stabilized, the set temperature of each outer peripheral heater 3 was lowered at a rate of 0.6 K / h.

  Then, after being left for 6 hours in this state, the rate of decrease in the set temperature of each of the outer peripheral heaters 3 is slowly reduced from 0.6 K / h to 0.008 K / h, and finally 0 over 50 hours. The speed was lowered to 2 K / h and left for 6 hours. As a result, the set temperature of the uppermost peripheral heater 3a was lowered to about 1265 ° C.

  Further, as in the first embodiment, the rotational speed of the crucible 6 begins to decrease in conjunction with the start of lowering of the set temperature of each outer peripheral heater 3, and is gradually increased at a rate of 0.25 rpm / h until the rotational speed reaches 1 rpm. Decreased.

  By the above operation, the crystal growth rate, that is, the moving rate of the interface between the crystal and the semiconductor melt was about 4 mm / h at the beginning of the growth, but gradually becomes slower as the heater temperature lowering rate decreases, Eventually it decreased to about 1.5 mm / h.

  Thereafter, the temperature drop of each of the outer peripheral heaters 3 is stopped, and from there, further cooling is performed over 24 hours so that the temperature of all the outer peripheral heaters 3 becomes 950 ° C., and then the temperature of each of the outer peripheral heaters 3 Until the temperature reached 400 ° C., the temperature of each outer peripheral heater 3 was decreased at a rate of −20 ° C./h. Subsequently, energization of each outer peripheral heater 3 was stopped, and the crucible 6 was cooled to room temperature.

  By observing the crystal taken out after cooling to room temperature, it was confirmed that the GaAs crystal obtained in this example was also a single crystal over the entire length. FIG. 3 shows the Si concentration in the crystal measured by the same method as in Example 1 and aligned with the result of Comparative Example 1.

In Example 2, the distribution of the silicon concentration in the longitudinal direction of the crystal is more gradual than that of Example 1, and the silicon concentration is 1.01 × 10 ¹⁸ cm ⁻ when the solidification rate is 0.1. ^Although it was ³ , the silicon concentration was increased to 5.78 × 10 ¹⁸ cm ⁻³ at the position where the solidification rate was 0.9, and the difference was 4.77 × 10 ¹⁸ cm ⁻³ .

  Thus, according to the method for producing a semiconductor single crystal of the present invention, the difference in impurity concentration between the head and tail of the grown crystal can be reduced. This reduces variations in electrical characteristics, optical characteristics, mechanical characteristics, and the like among a plurality of semiconductor substrates formed by slicing the grown crystal. In addition, the acquisition rate of non-defective substrates can be improved, raw materials can be used efficiently, and manufacturing costs can be reduced.

  In the above-described embodiment, an example in which an impurity having a segregation coefficient smaller than 1 has been described has been described. However, the present invention can also be applied when an impurity having a segregation coefficient larger than 1 is added.

It is a cross-sectional schematic diagram of the crystal growth furnace used by this invention. It is a figure which shows distribution of the crystal | crystallization longitudinal direction of a silicon concentration in the GaAs single crystal produced by this invention and the prior art. It is a figure which shows distribution of the crystal | crystallization longitudinal direction of a silicon concentration in the GaAs single crystal produced by other embodiment of this invention and the prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crystal growth furnace 2, 4 Heat insulating material 3 Peripheral heater 5 Semiconductor melt 6 Crucible 7 Susceptor 8 Susceptor support member 9 Liquid sealing agent 10 Seed crystal 11 Chamber

Claims (3)

In the crucible, a semiconductor melt to which an impurity as a dopant is added is accommodated, and the crucible is placed in contact with a seed crystal placed in a seed crystal placement portion formed at the bottom of the crucible. In the method for producing a semiconductor single crystal, in which the semiconductor melt is gradually solidified from the seed crystal side upward while rotating,
A method for producing a semiconductor single crystal, wherein the rotational speed of the crucible is gradually decreased as the crystal growth proceeds.   2. The method for producing a semiconductor single crystal according to claim 1, wherein the rotation speed of the crucible is gradually decreased and the crystal growth speed is gradually decreased as the crystal growth proceeds.   The diameter of the crucible is 160 mm and the length is 300 mm, and the rotational speed of the crucible is gradually increased from 20 rpm at the start of growth to 1 rpm at the end of growth at a rate of 0.25 rpm / h as the crystal growth proceeds. The manufacturing method of the semiconductor single crystal of Claim 1 or 2 made late.

Images