JP2704032B2 - Method for manufacturing compound semiconductor single crystal - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for producing a single crystal by a sealed vertical Bridgman method, and in particular, to produce a large, high-quality compound semiconductor single crystal. It is about the method.

[Prior Art] As an industrial production method of a compound semiconductor single crystal such as GaAs, a horizontal Bridgman method (HB method), a liquid sealing pulling method (LEC method) and the like are known. The diameter of the single crystal obtained by these methods is about 50 to 75 mm by the HB method, and 75 to 100 by the LEC method.
mm.

In recent years, from the viewpoint of improving yield and productivity, device manufacturers have increasingly demanded a large diameter wafer, and development of a manufacturing technique therefor is urgently required. However, in the industrial production method as described above, there is a limit to further increasing the diameter of the single crystal, and it has been difficult to produce a single crystal having a diameter larger than that described above. That is, in the HB method, a quartz glass outer tube used as a container needs to have a large diameter. As a result, thermal deformation of the outer tube becomes remarkable and stable industrial production cannot be performed. In addition, in the LEC method, the mechanical strength of the compound semiconductor single crystal is lower than that of the silicon-based semiconductor, so if the crystal diameter increases and the weight of the pulled crystal increases, the seed crystal breaks during the pulling. It is said that increasing the diameter is difficult.

On the other hand, a vertical Bridgman method is also known as a method for producing a single crystal. According to this method, it is said that single crystallization of the compound semiconductor itself is difficult, and it has not been employed as an industrial production method until now. However, since it has the advantage of being able to grow crystals under a low temperature gradient, it is recently being reviewed as a method for producing high-quality crystals with few defects,
It has been improved in various ways. As a single crystal production method improved from the vertical Bridgman method, for example, Japanese Patent Publication No. 58-5007
No. 57 and Japanese Patent Application Laid-Open No. 64-52693 have been proposed.

FIG. 2 is a schematic explanatory view for explaining the basic principle of the vertical Bridgman method, in which 1 is a heat-resistant crucible, 2 is a heater, 3 is a raw material melt, 4 is a crystal in the growth process (grown crystal), 5 indicates a seed crystal and 6 indicates a cone. In this method, by lowering the crucible 1 while forming a temperature gradient by external heating, the raw material melt 3 is crystallized and a single crystal is grown on the seed crystal 5.

[Problems to be Solved by the Invention] In the vertical Bridgman method, as shown in FIG. 2, since the entire weight of the crystal 4 can be held by the heat-resistant crucible 1, the crystal weight increases as described in the pulling method. Can be said to be few. However, in this method, after seeding (seed), the probability that twins are generated from the wall of the crucible 1 in the process of expanding the crystal diameter of the crystal 4 through the cone portion 6 is increased, and the crystal diameter is increased. In such a case, there is an inconvenience that the tendency becomes more remarkable.

For this reason, a technique for making the diameter of the seed crystal 5 equal to the diameter of the grown crystal 4 and preventing twins from being generated from the cone portion 6 is also known. However, such a method has a disadvantage that seeding becomes difficult due to a small allowable temperature limit of the seed crystal 5. That is, in the case of seeding, extremely accurate temperature control is required, and if one step is wrong, the entire seed crystal 5 may be melted.
Such a situation is likely to be avoided by increasing the thickness of the seed crystal 4, but this requires a large-sized seed crystal, which raises a new inconvenience of increasing the cost. Also, as the diameter of the crystal increases, it becomes more difficult to effectively dissipate heat from the center of the growing crystal, the growth rate of the crystal differs between the center and the periphery, and the shape of the solid-liquid interface changes on the crystal side (the (Lower side in Fig. 2)
In this case, there is a problem that the quality is significantly deteriorated due to the introduction of dislocations into the crystal due to the thermal stress at the interface between the solid and the liquid.

The present invention has been made under such a circumstance, and an object of the present invention is to avoid the twinning as described above and manufacture a relatively thin compound semiconductor compound single crystal by the vertical Bridgman method. An object of the present invention is to provide a method for manufacturing a high-quality large-diameter compound semiconductor single crystal with a high yield by enabling stable seeding with a bulk seed crystal.

[Means for Solving the Problems] The present invention, which has achieved the above object, refers to a method of manufacturing a compound semiconductor single crystal by the vertical Bridgman method using a sealed vessel, which is equivalent to a single crystal to be manufactured. A method for producing a compound semiconductor single crystal having a gist in that a seed crystal having a diameter is used, a recess is formed in the lower center of the seed crystal, and operation is performed while heat radiation from the recess is promoted.

[Function] The present invention is configured as described above. In short, while using a seed crystal having the same diameter as the grown crystal to avoid twinning during the initial crystal growth process, By forming a concave portion and supplying a controlled amount of a cooling medium to the concave portion and forcibly cooling it, heat radiation from the central portion of the crystal is promoted, and the crystal growth rate is set so that the solid-liquid interface shape becomes flat. And obtain a high-quality large-diameter compound semiconductor single crystal.

According to the present invention, a single crystal having a desired diameter can be produced. For example, if a crystal having a diameter of 75 mm is to be produced, a seed crystal having a diameter of 75 mm may be used. Further, the thickness of the seed crystal used can be made relatively small by the above-mentioned forced cooling effect. Although the seed crystal used in the present invention is unavoidably larger in weight than the case where a thin seed crystal as shown in FIG. 2 is used, the seed crystal in the present invention is disadvantageous in seeding. Is avoided, and the point is offset because it can withstand repeated use.

The diameter of the concave portion formed in the present invention is preferably set to be equal to or less than 1/2 of the crystal diameter. Is also cooled, and the object of the present invention is not achieved.

As for the cooling mechanism employed in the present invention, for example, as shown in FIGS. 3 (a) and 3 (b), a spiral pipe 12 is provided inside a concave portion 11 formed in the lower center of the quartz glass container 10 (see FIG. 3). The other reference numerals are the same as those in FIG. 2), and a configuration in which a cooling medium such as cold gas or cold water is supplied into the pipe 12 is typically exemplified. For example, as shown in FIG. 4, it is also possible to employ a double-walled jacket type heat exchange passage 14 formed in the container 10 by glasswork as shown in FIG. Also pipeline
In FIG. 12, as shown in FIG. 3, it is advantageous to provide two independent systems (or more) in terms of delicate temperature control in the initial stage of growth, but the diameter of the grown crystal and the set temperature The design may be appropriately changed according to the above. In carrying out the present invention, the control of the furnace temperature and the supply amount of the cooling medium may be set by performing a simulation experiment corresponding to the apparatus configuration (see Examples described later).

Although FIG. 3 shows the configuration in which the raw material is directly charged into the quartz glass container, the crystal growth container used in the present invention is not limited to the configuration shown in FIG. Similarly, a crucible 15 made of pyrolytic boron nitride (PBN) is loaded into a quartz glass container 10, and a polycrystalline GaAs raw material 16 (before melting is shown in the figure) is loaded into the crucible 15. Various configurations can also be adopted. In FIG. 4, reference numeral 15a denotes a crucible lid (made of PBN). With such a configuration, mixing of silicon from the quartz glass container 10 into the crystal can be avoided, and high-purity semi-insulating GaAs suitable for high-speed ICs can be manufactured.

Hereinafter, the present invention will be described in more detail with reference to Examples.
The following examples are not intended to limit the present invention, and any change in design based on the above and following points is included in the technical scope of the present invention.

Embodiment FIG. 1 is a schematic explanatory view showing an example of an apparatus configuration for carrying out the present invention, in which 20 is a crystal growth vessel, 21 is a heating power source, 17 is a heater, and 18a to 18d are thermoelectric devices. Pair type thermometer, 19a, 19b
Denotes a heat exchanger, 20a and 20b denote mass flow meters, 25 denotes a controller, 26 denotes a temperature controller, 27 denotes a thermocouple for temperature measurement, and 28 denotes a personal computer.

First, an analysis procedure for controlling the flow rate of the cooling medium will be described.

The present inventors have grown a GaAs single crystal having a diameter of 100 mm in the configuration shown in FIG. 1 and determined the relationship between the temperature distribution in the growth vessel 20 and the cooling gas flow rate by heat flow analysis using the finite element method. Was. Examples of the results are shown in FIGS. 5 (a) to 5 (d).

Next, conditions for flattening the shape of the solid-liquid interface indicated by the isotherm at the melting point of 1238 ° C. of GaAs were determined over the entire crystal growth process. As one example, the cooling gas flow rate required for flattening the solid-liquid interface with the temperature profile A shown in FIG.
Shown in the figure. In the analysis, the boundary conditions were optimized with reference to the actual temperature measurement data in the crucible.

As a result of the analysis, simply controlling the furnace temperature without flowing cooling gas could not prevent the shape of the solid-liquid interface from becoming concave on the crystal side, but forced cooling using cooling gas In this case, it was confirmed that the control range of the interface shape could be significantly increased. If the diameter of the cooling recess formed in the center of the lower part of the crystal is too large, it becomes inappropriate for the purpose of having a cooling effect in the center of the crystal, and the interface shape is controlled at a stage where the grown crystal length is relatively short. It has been found that the effect is weakened and it becomes impossible to avoid the shape of the solid-liquid interface being concave toward the crystal. According to experiments performed by the present inventors, in the case of crystal growth with a diameter of 100 mm, in order to grow the entire crystal having a length of 20 cm while keeping the solid-liquid interface shape flat, the diameter of the concave portion is 1/2 of the crystal diameter. It has been found that the following is preferable. The minimum value of the diameter of the concave portion also differs depending on the type of the cooling unit, and is not necessarily limited, and may be within a range that does not substantially reduce the cooling effect. Therefore, finally, over the entire range of crystal growth, the combination of the temperature setting of the vessel and the flow rate of the cooling gas for crystal growth while flattening the solid-liquid interface shape should be determined to determine the optimum growth conditions. I just need.

Based on the above analysis results, a cooling gas control program was created, and a GaAs single crystal was actually manufactured according to the program.

100mm diameter, 15mm thick GaAs manufactured by LEC method.
Ultrasonic machining on a circular surface of single crystal bulk material with a diameter of 10
A hole with a hole of 10 mm in depth and 10 mm in depth was used as a seed crystal, and together with a polycrystalline raw material of GaAs and Si as a dopant (a concentration of 10 ¹⁸ / cm ³ ) were placed in the quartz container shown in FIG. Vacuum sealed. At this time, in order to prevent a reaction between the vessel during crystal growth and GaAs, it is preferable to clean and clean the inside of the growth vessel together with the filling material before vacuum encapsulation.
After setting the growth vessel in a vertical Bridgman furnace, the temperature was raised according to the usual crystal growth method, and the seed crystal was heated at the upper end face 3 mm.
Melted back at After that, by controlling the temperature of the furnace, the solid-liquid interface was moved at a rate of 3 mm per hour under a temperature gradient of 10 ° C./mm. The extensive crystallization has ended.

In the obtained GaAs crystal, no twinning was observed throughout, and the wafer 20 manufactured by cutting and polishing was used.
90% of the samples had a dislocation density of 700 / cm ² or less as an in-plane average value, were extremely low in crystal defects, and had uniformity in the ingot. It was of high quality.

Comparative Example A GaAs single crystal was grown in the same manner as in the above example except that forced cooling with a cooling gas was not performed, and its quality was examined.

As a result, the dislocation density at the initial stage of crystal growth was 1300 / cm ² in the in-plane average value, which was slightly higher than that in the example, but as the growth lengthened, the dislocation density gradually increased. Increased at 5 cm and 10 cm from the seed crystal, respectively.
It was 3300 / cm ² and 17700 / cm ² , and the deterioration of quality was conspicuous. Further, in the subsequent portions, subgrains having different crystal orientations were generated inside the crystal, and the region gradually widened as the crystal was grown, and the entire crystal was polycrystallized.

[Effects of the Invention] As described above, according to the present invention, a relatively large compound semiconductor having a diameter of 75 mm or more is employed by adopting a structure in which forced cooling is performed from the lower part of the seed crystal to promote heat radiation from the central part of the crystal. It has become possible to manufacture a single crystal with a high yield with few defects.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an example of an apparatus configuration for carrying out the present invention, FIG. 2 is a schematic explanatory view for explaining the basic principle of the vertical Bridgman method, and FIG. 3 is quartz employed in the present invention. FIG. 4 is a schematic explanatory view showing a configuration example of a glass container, FIG. 4 is a schematic explanatory view showing a state in which a PBN crucible is loaded in a quartz glass container, and FIGS. 5 (a) to (d) are temperature distributions in the growth container. FIG. 6 is a graph showing an example of a relationship between the cooling gas flow rate and the cooling gas flow rate. FIG. 6 is a graph showing a cooling gas flow rate area required for flattening the solid-liquid interface. 1 crucible, 2,17 heater 3 raw material melt 4 crystal (grown crystal) 5 seed crystal 6 cone part 20 crystal growth container 21 heating Power supply

Claims (1)

(57) [Claims] In producing a compound semiconductor single crystal by a vertical Bridgman method using a sealed vessel, a seed crystal having a diameter equal to that of the single crystal to be produced is used, and a seed crystal is formed at a lower center of the seed crystal. A method for producing a compound semiconductor single crystal, characterized in that a concave portion is formed, and operation is performed while promoting heat radiation from the concave portion.