JPH0368000B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a heat treatment container, and more particularly to a heat treatment container used when annealing a heat treatment object made of a compound semiconductor single crystal.

[Prior art] In general, compound semiconductor single crystals are used in LEDs, LDs,
It is used as a high-speed device for optical devices such as photodetectors and substrates such as FETs, and has also come to be used in OEICs and the like in which optical devices and FETs are formed together. A method for producing such a compound semiconductor single crystal is the liquid-encapsulated Czyochralski method (LEC method).
There are methods such as immersing a seed crystal in the crystal raw material melt and pulling it up to grow a single crystal, methods such as slow cooling method (GF), horizontal Bridgeman method (HB method), vertical Bridgeman method (VB method) Another method is to gradually solidify a crystal raw material melt to grow a single crystal.

Although there are differences in the manufacturing methods of these various compound semiconductor single crystals, basically they are as follows:
A temperature gradient is created between the growing crystal and the raw material melt to solidify the crystal from the raw material melt.
The solid-liquid interface where crystal growth is occurring is at the melting point, but the part where the crystal has already grown is always exposed to a temperature lower than the melting point. Therefore, in the above method for manufacturing a compound semiconductor single crystal,
In both cases, the characteristics within the grown crystals were non-uniform. For this reason, devices using these compound semiconductor single crystals have large variations in device characteristics within the wafer, especially at high frequencies in discretes.
Variations in FETs, digital ICs, etc. have led to poor yields and have hindered the spread of compound semiconductor devices.

Conventionally, various methods have been proposed to improve variations in device characteristics. For example, GaAs
In the production of - group compound semiconductor single crystals such as, etc., the source material was doped with impurities such as In to form dislocation-free crystals, assuming that the cause of variation was due to dislocations in the growing crystal. . However, although this doping method can make the crystal dislocation-free, it only slightly reduces the variation in device characteristics, and is not satisfactory. Furthermore, as shown in FIG. 3, a method has been used in which an ingot of a grown crystal, a block after cylindrical grinding, a wafer, etc. is used as the object to be heat treated, and the object is annealed.

In FIG. 3, reference numeral 1 denotes a quartz or alumina furnace core tube in a resistance heating furnace, and stainless steel end plates 2 are fixed to both ends of the furnace core tube 1.
The heat treatment container 4 that houses the heat treatment object 3 is made of a quartz ampoule, and the heat treatment object 3 is sealed in the heat treatment container 4 which is evacuated to a high vacuum of, for example, about 5×10 ^-7 Torr. Inside the heat treatment container 4
Group elements such as As may also be similarly included. The heat treatment container 4 is arranged at a predetermined position within the furnace core tube 1, and a heater 5 that can surround the heat treatment container 4 is arranged on the outside of the furnace core tube 1 so as to be movable in the axial direction of the furnace core tube 1. ing.

To perform annealing using the heat treatment apparatus shown in FIG.
is heated by the heater 5 to a predetermined temperature lower than the melting point of the crystal and maintained for about 5 hours. Thereafter, as shown by the imaginary line in FIG. 3, the heater 5 is moved to stop heating the object 3 to be heat treated, and the object 3 is cooled at a predetermined rate.

[Problems to be Solved by the Invention] However, although the conventional annealing method described above can definitely make the crystal properties uniform, it is not necessarily sufficient, and the dislocation density (EPD) increases and There was a problem with slip lines.

That is, the heat treatment container 4 used in the conventional annealing method consists only of a quartz ampoule that vacuum-seals the object 3 to be heat treated, and even if the annealing temperature is set to any temperature lower than the melting point of the crystal, the object 3 to be heat treated will not be heated during the cooling process. Parts with different cooling rates occurred within the crystal of Product 3, causing thermal stress. In other words, in the cooling process of annealing, most of the heat of the object 3 to be heat treated is released as radiant heat, and in particular, if the heat treatment container 4 is a transparent quartz ampoule, the outside of the object 3 to be heat treated is cooled faster than the inside. This created thermal stress within the crystal, leading to an increase in EPD and the formation of slip lines.

The present invention was made in view of such conventional problems, and an object of the present invention is to provide a heat treatment container that can uniformize crystal properties and suppress increase in dislocation density and generation of slip lines. do.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a heat treatment container that stores the heat treatment object when annealing the heat treatment object made of a compound semiconductor single crystal. A shield made of a material with high thermal conductivity and surrounding the object to be heat treated was provided on the inside or outside of the ampoule enclosing the object.

In the present invention, suitable materials with high thermal conductivity for forming the shield include, for example, graphite, pBN, SiC, Mo, etc. as a single material.
For composite materials, heat pipes etc. are suitable. On the other hand, materials with low thermal conductivity such as alumina and quartz (opaque) are unsuitable. The shield may be provided either on the inside or outside of the ampoule, but in particular, it is recommended to close the openings at both ends of the shield tube with end plates made of the same material as the tube to prevent heat from escaping in the axial direction. Most preferred. Furthermore, if the shield is made of a material that easily reacts with air, such as graphite or Mo, the shield may be made of an inert gas,
It is preferable to use N ₂ gas or vacuum atmosphere.

[Function] If annealing is performed using the heat treatment container with the above configuration, the radiation cooling is prevented by the shield during the cooling process, and cooling is mainly done by heat conduction, so the temperature distribution of the object to be heat treated becomes uniform. thermal stress can be significantly reduced.

[Example] An example of annealing a GaAs single crystal grown by the LEC method will be described. FIG. 1 shows a heat treatment apparatus in this embodiment, and the same parts as in the conventional apparatus are designated by the same reference numerals as in FIG. 3, and the explanation thereof will be omitted.

In the heat treatment apparatus shown in FIG. 1, a vacuum exhaust pipe 8 is connected to the end plate 2, so that the inside of the furnace core tube 1 can be evacuated to a high vacuum.

The heat treatment container 9 includes an ampoule 4 that encloses the object 3 to be heat treated, and a shield 10 made of graphite that houses the ampoule 4 and surrounds the object 3 to be heat treated. The shield 10 includes a cylindrical shield tube portion 10a and end plates 10b that close both ends of the shield tube portion 10a.

In this example, the heat-treated object 3 was a cylindrical-ground block having a diameter of 3 inches, and this was vacuum-sealed into an ampoule 4 at 5×10 ^-7 Torr. and,
This ampoule 4 was housed in a shield 10, and the shield 10 was placed at a predetermined position within the furnace core tube 1. Next, the inside of the furnace core tube 1 was evacuated via the evacuation tube 8, and the heat-treated material 3 was heated for 5 hours at 1100° C., which is lower than the melting point of the crystal (1238° C.), using the heater 5.

After that, as shown by the imaginary line in FIG.
The heater 5 was moved to stop heating the object 3 to be heat treated, and cooling was performed at a rate of about 20° C./min.

After annealing in this manner, the heat-treated object 3 was cut at an appropriate position, and the EPD at the cut surface was measured. The measurement results are shown in FIG. In Figure 2, A, B, C, and D on the horizontal axis indicate the lot names of the crystals, and the vertical axis indicates EPD (cm
^-2 ). For comparison, annealing was performed using the conventional example shown in Figure 3 with the same conditions as the annealing temperature and other conditions as in the above example.
The EPD was measured and is also shown in Figure 2. In FIG. 2, E, F, G, and H each indicate the lot name of the crystal of the conventional example.

As can be seen from FIG. 2, the EPD after annealing (indicated by a solid line) in this example is almost the same as the EPD before annealing (indicated by a broken line), but in the case of the conventional method, the EPD obtained by annealing is is significantly increased compared to the EPD before annealing.

Further, in the case of the present example, no slip lines were observed, whereas in the case of the conventional method, slip lines were formed after annealing.

In the above embodiment, a block after cylindrical grinding was used as the object 3 to be heat treated, but the same effect could be obtained with an ingot or a wafer. In the case of a wafer, it is preferable to use a jig made of quartz or graphite to lean it up in the ampoule 4.

[Effects of the Invention] As described above, according to the heat treatment container of the present invention,
A shield made of a material with high thermal conductivity and surrounding the object to be heat-treated is provided inside or outside the ampoule that encloses the object to be heat-treated, so that radiation cooling is prevented by the shield, and cooling is mainly done by thermal conduction. As a result, the temperature distribution of the object to be heat treated is made uniform, and thermal stress is significantly reduced. Therefore, the crystal properties can be made uniform, and the increase in EPD and the occurrence of slip lines can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway front view showing a heat treatment apparatus using a heat treatment container according to an embodiment of the present invention, and FIG. 2 is a partially cutaway front view showing a heat treatment apparatus using a heat treatment container according to an embodiment of the present invention and a conventional example. A graph showing the subsequent EPD measurement results, and FIG. 3 is a partially cutaway front view showing a heat treatment apparatus using a conventional heat treatment container. 3... object to be heat treated, 4... ampoule, 9... heat treatment container, 10... shield, 10a... shield cylinder part, 10b... end plate.

Claims (1)

[Scope of Claims] 1. When annealing a compound semiconductor single crystal, in a heat treatment container that stores the object to be heat treated, a material to be heat treated made of a material with high thermal conductivity is placed on the inside or outside of an ampoule that encloses the object to be heat treated. A heat treatment container characterized by being provided with a shield that surrounds an object. 2 Materials with high thermal conductivity are graphite, pBN,
The heat treatment container according to claim 1, characterized in that it is SiC, Mo, or a heat pipe.