JPH0653640B2 - Heat treatment apparatus and heat treatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat treatment technique, and particularly to a heat treatment apparatus and a heat treatment method which are effective when applied to a heat treatment of a compound semiconductor single crystal.

[Prior Art] Generally, a compound semiconductor single crystal is used as a high-speed device for an optical element such as an LED, an LD, a light-receiving element or a substrate such as an FET, and also for forming an optical element and an FET together.
It has come to be used for C etc. As a method for producing such a compound semiconductor single crystal, as in the liquid-encapsulated Czochralski method (LEC method), a method of immersing a seed crystal in a raw material melt of the crystal and pulling it up to grow a single crystal,
There are methods such as a slow cooling method (GF), a horizontal Bridgman method (HB method), and a vertical Bridgman method (VB method) in which a raw material melt of crystals is gradually solidified to grow a single crystal.

Although there are differences in the manufacturing methods of such various compound semiconductor single crystals, basically, a method of causing a temperature gradient between a grown crystal and a raw material melt to solidify the crystal from the raw material melt The solid-liquid interface where the crystal growth is performed is at the melting point, but the part where the crystal has already grown is common in that it is always exposed to a temperature lower than the melting point.
Therefore, in the method for producing the compound semiconductor single crystal,
In each case, the characteristics in the grown crystal were non-uniform. Therefore, in devices using these compound semiconductor single crystals, there are large variations in device characteristics within the wafer, and particularly in discrete high-frequency FETs, digital ICs, etc., such variations cause poor yield, The spread of compound semiconductor devices was hindered.

Conventionally, various methods have been proposed in order to improve the variations in device characteristics. For example, a method of heat-treating an ingot of a grown crystal, a block after cylindrical grinding, a wafer, etc., using an apparatus as shown in FIG.

In FIG. 5, reference numeral 1 denotes a furnace core tube made of quartz or alumina in a resistance heating furnace, and stainless steel end plates 2a and 2b are fixed to both ends of the furnace core tube 1. Object to be heat treated 3
The heat treatment container 4 for accommodating is made of a quartz ampoule, and the heat treatment object 3 is enclosed in the heat treatment container 4 evacuated to a high vacuum of, for example, 5 × 10 ⁻⁷ Torr. In some cases, a group V element such as As is also enclosed in the heat treatment container 4. The heat treatment container 4 is arranged at a predetermined position in the furnace core tube 1, and a heater 5 capable of surrounding the heat treatment container 4 is arranged outside the furnace core tube 1 so as to be movable along the axial direction of the furnace core tube 1. It is set up.

In the annealing by the heat treatment apparatus shown in FIG. 5, the object to be heat treated 3 enclosed in the heat treatment container 4 is heated to a predetermined temperature lower than the melting point of the crystal by the heater 5 and held for a predetermined time, and then the power supply to the heater is stopped. As shown by the phantom line in FIG. 5, the heater 5 was moved and cooled.

[Problems to be Solved by the Invention] However, in the above-described conventional heat treatment apparatus, since the crystal is cooled by natural heat dissipation after the heater is stopped, the cooling rate cannot be increased so much and the temperature is high. Has a high cooling rate, but becomes slower as the temperature decreases, making it difficult to cool at a constant rate. However, the present inventors have a correlation between the cooling rate in the heat treatment and the characteristics of the crystal substrate, and by controlling the cooling rate, the uniformity of the crystal characteristics is further improved, and the dislocation density (EPD) and It was found that the occurrence of slip lines due to the movement of dislocations can be reduced.

The present invention has been made in view of the above conventional problems, and can freely control the cooling rate, thereby making the crystal identification uniform, and suppressing the increase of dislocation density and the occurrence of slip lines. The purpose is to provide heat treatment technology.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a furnace core tube constituting a heat treatment apparatus with a gas inlet port at one end and a gas outlet port at the other end. A structure in which the tube and the heater on the outside of the tube are movable relative to each other, the heater is moved after heating is completed, and an inert gas is introduced into the furnace core tube so that the heat-treated object can be forcibly cooled by this gas. Is.

[Operation] According to the above-described means, the power of the heater can be adjusted after the heating is finished to cool it more slowly than the natural heat dissipation. In addition, the movement amount of the heater can be adjusted to control the speed of the natural heat dissipation. In addition to that, by flowing a gas in the furnace core tube, it is possible to cool at a speed faster than natural heat dissipation, and the cooling rate can be freely controlled regardless of the temperature in the furnace.

[Example] An example of annealing a GaAs single crystal grown by the LEC method will be described below. FIG. 1 shows an embodiment of a heat treatment apparatus to which the present invention is applied. The same parts as those of the prior art are indicated by the same reference numerals as those in FIG. 5 and their explanations are omitted.

In the heat treatment apparatus of FIG. 1, an exhaust pipe 6a is connected to one end plate 2a that covers the side surface of the furnace core tube 1, so that the inside of the furnace core tube 1 can be evacuated to a high vacuum by a vacuum pump (not shown). Has become. Further, the gas introduction pipe 6 is provided on the other end plate 2b.
b is connected, a gas cylinder 7 is connected to the starting end of the gas introduction pipe 6b, and a valve 8 provided on the way is adjusted to flow gas into the furnace core tube 1 and control its flow rate. ing.

Further, in this embodiment, two heaters 5a and 5b are arranged around the furnace core tube 1 and are configured to be movable left and right along the axial direction by motors 9a and 9b, respectively.

The heat treatment in the heat treatment apparatus configured as described above is performed as follows.

That is, first, one of the end plates 2a or 2b on the side surface of the furnace core tube 1 is removed, and the ampoule 4 in which the GaAs single crystal to be heat-treated is enclosed is installed at substantially the center of the furnace core tube 1. Next, the vacuum pump is operated to exhaust the gas from the exhaust pipe 6a to evacuate the furnace core tube 1, and then the heaters 5a and 5b are moved to the center as shown in FIG. Raise to a high temperature such as 1100 ° C. Then, after maintaining this temperature for several hours, the power supply to the heaters 5a and 5b is stopped and the heating is finished.

Then, the process shifts to cooling, but at this time, if the power supply is stopped without moving the heaters 5a and 5b,
As indicated by the symbol a in FIG. 4, the cooling can be performed at a slow rate of, for example, 3 ° C./min. The temperature sensor 10 such as a thermocouple indicates that the power supply to the heater is not completely stopped and the power is controlled to perform slower cooling, or that the temperature inside the furnace has decreased and the cooling rate has slowed. If detected, the power supply to the heater can be stopped or the heater can be moved to keep the cooling rate constant.

On the other hand, when it is desired to cool the ampoule 4 containing the object to be heat-treated at a rate faster than 3 ° C./min, for example, 20 ° C./min, the power supply to the heaters 5a and 5b is stopped after the heating is completed, and the motor 9a, 9b is driven to move the heaters 5a and 5b left and right as shown in FIG. At this time, the heater 5
The cooling rate can be controlled by appropriately adjusting the movement amounts of a and 5b. After the heating is completed, the heaters 5a and 5b can be moved to cool them at a high speed as indicated by the symbol b in FIG. 4, but this alone slows down the cooling rate as the temperature inside the furnace decreases. Therefore, the valve 8 is opened midway and an inert gas such as N ₂ gas is flown into the furnace core tube 1 to cool the ampoule 4 directly by the gas. As a result, the cooling rate can be kept constant as indicated by the symbol C in FIG. If you want to cool the ampoule at a speed faster than 20 ℃ / min, use the heater 5 after heating.
It is only necessary to move a and 5b to the left and right, open the valve 8 to flow the gas into the furnace through the gas introduction pipe 6b, and exhaust the gas through the exhaust pipe 6a with the vacuum pump.

FIG. 3 shows a second embodiment of the heat treatment apparatus according to the present invention.

In this embodiment, only one movable heater 5 is provided, and the ampoule 4 is placed in the furnace core tube 1 inside a cylindrical heat equalizing cover 11 made of a material having high thermal conductivity, and heat treatment is performed. I am trying to apply.

As a material having a high thermal conductivity forming the soaking cover 11,
For example, graphite, pBN, Si as a single material
C, Mo, etc. are suitable, and heat pipes, etc. are suitable for composite materials. On the other hand, materials having low thermal conductivity such as alumina and quartz (opaque) are not suitable. Further, the soaking cover 11 may be provided inside or outside the ampoule, but in particular, the opening portions at both ends are closed by end plates made of the same material as the tubular portion to prevent heat from flowing out in the axial direction. Is preferred.

When annealing is performed using the soaking cover 11 in this way, radiative cooling in the cooling process is prevented and cooling is solely due to heat conduction, so that the temperature distribution of the object to be heat-treated is made uniform and thermal stress is remarkably increased. Can be reduced.

In the above embodiment, the heater 5 is configured to move along the axial direction of the furnace core tube 1, but the heater may be fixed and the furnace core tube may be movable.

[Effects of the Invention] As described above, according to the present invention, a gas inlet is provided at one end and a gas outlet is provided at the other end of the furnace core tube that constitutes the heat treatment apparatus, and the furnace core tube and the heater outside thereof are provided. Is configured to be movable relative to each other, the heater is moved after the heating is completed, and an inert gas is introduced into the furnace core tube to forcibly cool the object to be heat-treated by this gas. By adjusting the power, it is possible to cool it more slowly than natural heat dissipation, as well as adjust the heater and movement amount to control the speed of natural heat dissipation, and by flowing gas in the furnace core tube. It can be cooled at a speed faster than natural heat dissipation, and the cooling rate can be controlled freely regardless of the temperature inside the furnace. If this is used to perform heat treatment of semiconductor single crystals, the crystal characteristics can be evened out. There is an effect that the unification can be achieved and an increase in dislocation density and the occurrence of slip lines can be suppressed.

Further, a heat treatment apparatus comprising a furnace core tube, a heating means arranged so as to be relatively movable along the axial direction of the furnace core tube, and a gas introducing means for flowing a gas into the furnace core tube. Use, the object to be heat-treated is housed in the furnace core tube and heated by the heating means for a predetermined time, then the heating means is moved, and the gas is introduced into the furnace core tube to force the object to be heat-treated. Since the cooling is performed in such a manner, it is possible to cool the gas at a speed faster than natural heat dissipation by flowing the gas in the furnace core tube.

Furthermore, a heat treatment apparatus comprising a furnace core tube, heating means arranged so as to be relatively movable along the axial direction of the furnace core tube, and gas introducing means for flowing gas into the furnace core tube. Using the object to be heat-treated in the furnace core tube and heating it by the heating means for a predetermined time, the heating means is moved by a predetermined amount, and the gas introduction means when the object to be heat-treated is cooled to a predetermined temperature. Since the gas flow rate is controlled so that the gas is flown into the furnace core tube to be cooled at a constant rate, the cooling rate can be controlled to be constant regardless of the temperature in the furnace, and it can be applied to the heat treatment of semiconductor single crystals. The crystal characteristics can be made uniform, and the increase of dislocation density and the occurrence of slip lines can be suppressed.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of a heat treatment apparatus according to the present invention, FIG. 2 is a partially cutaway front view showing a state of the heat treatment apparatus of the embodiment shown in FIG. 1 during cooling, and FIG. A partially broken front view showing a second embodiment of the heat treatment apparatus according to the present invention, FIG. 4 is a graph showing a temperature profile during cooling by the heat treatment apparatus of the present invention, and FIG. 5 is an example of a conventional heat treatment apparatus. It is a partially broken front view shown. 3 ... Heat treatment object, 4 ... Ampoule, 5a, 5b ... Heater, 6a ... Exhaust pipe, 6b ... Gas introduction pipe.

Claims (4)

[Claims] 1. A furnace core tube around which an object to be heat treated is stored,
A heating means is provided so as to be relatively movable along the axial direction, and a gas introduction port and a discharge port are provided on the end surface of the furnace core tube.
A heat treatment apparatus characterized in that an object to be heat-treated in a furnace core tube can be forcibly cooled by a gas. 2. The heat treatment apparatus according to claim 1, wherein the heating means is divided into two parts, each of which has a driving means, and is movable in the axial direction. 3. A furnace core tube, a heating means arranged so as to be relatively movable along the axial direction of the furnace core tube, and a gas introducing means for flowing gas into the furnace core tube. Using the heat treatment apparatus, the object to be heat treated is housed in the furnace core tube and heated by the heating means for a predetermined time, and then the heating means is moved, and the gas is introduced into the furnace core tube to flow the gas into the object to be heat treated. A heat treatment method, characterized in that it is forcibly cooled. 4. A furnace core tube, a heating means arranged so as to be relatively movable along the axial direction of the furnace core tube, and a gas introduction means for flowing a gas into the furnace core tube. Using a heat treatment apparatus, after the object to be heat-treated is housed in the furnace core tube and heated by the heating means for a predetermined time, the heating means is moved by a predetermined amount, and when the object to be heat-treated is cooled to a predetermined temperature. A heat treatment method characterized in that a gas flow is controlled by a gas introduction means so as to flow the gas into the furnace core tube so as to be cooled at a constant rate.