JPH06302532A - Method for heat treating compound semiconductor single crystal wafer and wafer support used therefor - Google Patents

Abstract

(57) [Summary] [Object] To provide a heat treatment method for a compound semiconductor single crystal wafer capable of performing heat treatment without causing crystal defects, and a wafer support used therefor. [Structure] A flat plate-shaped support plate 12 that contacts the back surface of the wafer 20 is provided on the wafer holder 10, and the support plate 12 is formed of pyrolytic boron nitride, graphite, molybdenum, tungsten, tantalum, or silicon. In the case of a horizontal furnace, the holder 10 was formed so that the support plate 12 was inclined 10 degrees from the vertical when installed. In the case of a vertical furnace, the holder 30 should be installed so that the support plate 32 is inclined 10 degrees from the horizontal.
Was formed. [Effect] The compressive stress due to the weight of the wafer is dispersed, and the thermal stress due to the temperature difference in the wafer is reduced, so that the occurrence of crystal defects is prevented and the manufacturing yield is improved. Furthermore, residual stress is reduced, and variations in electrical characteristics can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for a compound semiconductor single crystal wafer such as GaAs and a wafer support used therefor, and particularly to a heat treatment method and a wafer support useful when applied to a wafer support structure during heat treatment. Regarding

[0002]

2. Description of the Related Art In a semi-insulating compound semiconductor single crystal wafer such as GaAs used as a substrate for high-frequency devices and high-speed ICs, in order to improve the in-plane uniformity of characteristics such as resistivity, impurities of impurities are used. In order to perform diffusion and activation, heat treatment may be performed, and various heat treatment methods and treatment conditions have been proposed. Generally, in heat treatment, a support tool called a so-called wafer holder is used to support a horizontal furnace with a plurality of wafers standing upright, and in a vertical furnace with a plurality of wafers lying down. Are being processed at the same time. Conventionally, the holder is
As shown in the wafer holders 50 and 55 shown in FIG. 6 or FIG. 7, a plurality of wafer holders are provided in order to keep the temperature of the entire wafer at a uniform temperature by minimizing the hindrance to the uniformization of the atmosphere in the furnace due to radiant heat and convection. Quartz rod members 51, 5 in the shape of rods
Many are composed of 6 frames. And
Grooves into which the edges of the wafers 60 and 65 are inserted are formed in the rod members 51 and 56, respectively, and the outer peripheral portions of the wafers 60 and 65 are inserted into the grooves to support four or three points on the outer peripheral portions. It was.

[0003]

However, when the present inventor heat-treats a GaAs single crystal wafer having a diameter of 4 inches at a high temperature of 900 ° C. or higher for a long time using the above-mentioned wafer holder 50, the result shown in FIG. As shown, the wafer 60
That is, a minute slip line (slip line) crystal defect group 61 is generated at a contact position with the wafer holder 50, that is, a position corresponding to the groove, and the wafer is not suitable for manufacturing an electronic device or the like. I found that. Even when the above-mentioned wafer holder 55 was used, a defect group 66 similar to that of the wafer 60 occurred like the wafer 65 shown in FIG. Such defects were also found in the wafers having a diameter of 2 inches or 3 inches after the heat treatment.

The present invention has been made to solve the above problems, and provides a heat treatment method for a compound semiconductor single crystal wafer which can be heat treated without causing crystal defects, and a wafer support used therefor. The purpose is to

[0005]

In order to achieve the above object, in the heat treatment method for a compound semiconductor single crystal wafer according to the present invention, the thermal conductivity of the compound semiconductor is equal to or higher than that of the compound semiconductor. The back surface of the wafer is uniformly supported by a supporting plate that has a strain force applied to the wafer and is equal to or less than the critical shear stress of the compound semiconductor at the heat treatment temperature so that the back surface of the wafer is supported uniformly. I did it.

Further, as a wafer support used in the heat treatment method for a compound semiconductor single crystal wafer according to the present invention,
A wafer support having the following structure is proposed. That is, a support plate made of a flat plate having a shape similar to or larger than that of a wafer to be heat-treated, a support portion for installing the support plate at a predetermined tilt angle with respect to the horizontal or vertical direction, And a receiving portion that abuts the outer peripheral portion of the wafer on the low side. The low side of the tilted support plate usually means that the wafer support is installed according to its intended use, that is, the wafer support is installed so that the force due to the wafer load is applied to the tilted support plate. In this state, when the wafer moves while sliding on the surface of the inclined support plate due to gravity, it means the moving side (direction).
Further, the inclination angle of the support plate determines the load of the wafer according to the surface state (roughness) of the back surface of the wafer and the surface of the support plate that contacts the wafer, and further according to the size (thickness and area) of the wafer. It is chosen to be dispersible in the support plate. Specifically, a wafer holder (wafer holder) is provided with a plurality of flat plate-shaped parallel support plates that come into contact with the back surface of the wafer, and the support plates are pyrolytic boron nitride, graphite, molybdenum, tungsten, tantalum, or silicon. Formed by.
In the case of a holder for a horizontal furnace, the support plate is formed with a slight inclination (for example, about several degrees to 10 degrees) from the vertical. In this case, it is preferable that the oriental flat (hereinafter simply referred to as "flat") portion of the wafer be a bottom plate of the holder (a supporting portion capable of installing the holder in the furnace with the supporting plate inclined) and an outer peripheral portion of the wafer. The wafer may be placed so as to come into contact with the receiving part to be brought into contact. In the case of a holder for a vertical furnace, the support plate is formed with a slight inclination (for example, about several degrees to 10 degrees) from the horizontal. Desirably, a side plate of a holder provided on the lower side of the inclined support plate (a support part capable of installing the holder in the furnace in a state where the support plate is inclined and a receiving part for abutting the outer peripheral part of the wafer).
Then, the wafer may be installed so that the flat portion of the wafer is brought into contact with the wafer.

[0007]

According to the above means, the back surface of the wafer is brought into contact with the supporting plate capable of dispersing the load of the wafer so that the strain force applied to the outer peripheral portion and the back surface of the wafer becomes equal to or less than the critical shear stress. Since the conventional holder is used, the mechanical compressive stress due to the weight of the wafer, which is concentrated at the three or four points where the holder is in contact with the conventional holder, is dispersed, and the occurrence of crystal defects is prevented. In particular, when the wafer is set upright, the effect of dispersing the wafer weight by the support plate is reduced, so it is advisable to bring the flat portion into contact with the bottom plate of the holder, and thereby distribute the wafer weight over the support plate and the flat portion. Can be made. Even when the wafer is laid down, a compressive stress is applied to the outer peripheral portion of the wafer that comes into contact with the holder because the support plate is inclined, so by bringing the flat portion into contact with the side plate (receiving portion) of the holder,
The compressive stress can be dispersed. When the support plate is formed of pyrolytic boron nitride, graphite, molybdenum, tungsten, tantalum, or silicon,
The above materials are chemically stable at heat treatment temperatures,
It also has sufficient mechanical strength, and the thermal conductivity of the support plate is similar to or greater than the thermal conductivity of the wafer. The temperature difference that may occur in the wafer can be relaxed, and the generation of crystal defects due to the thermal stress that can occur in the wafer can be prevented. In addition, if the wafer holder to be used has the above structure, the shape of the supporting plate is a flat plate having a shape similar to or larger than that of the wafer, so that the area in contact with the back surface of the wafer can be made sufficiently wide and the weight of the wafer itself can be increased. It becomes easy to disperse. At the same time, since the back surface of the wafer is in contact with a sufficiently large area, heat can be effectively conducted between the wafer and the support plate, and the above-mentioned temperature difference can be effectively mitigated. If the inclination angle of the support plate greatly exceeds 10 °, the wafer holder has a function of vertically arranging the wafer in the case of a horizontal furnace or laying the wafer substantially horizontally in the case of a vertical furnace. The characteristics will be impaired. Further, when the wafer is erected, if the inclination angle of the supporting plate is set to zero, the mechanical compressive stress due to the weight of the wafer itself cannot be dispersed by the supporting plate. On the other hand, when the wafer is laid almost horizontally, tilting it at least several degrees
It becomes easy to arrange the wafer so that the flat portion contacts the side plate or the bottom plate of the holder. Further, by bringing the flat portion into contact with the bottom plate or the side plate of the wafer holder, it is possible to prevent the substantially circular wafer from rotating and displacing, and the desired wafer arrangement, that is, the entire back surface of the wafer and the supporting plate are in contact with each other. Can be kept in contact arrangement.

[0008]

EXAMPLES The features of the present invention will be clarified below with reference to Examples and Comparative Examples. An example of a wafer holder for a horizontal furnace used for carrying out the present invention is shown in FIG. 1 and described. As shown in FIG.
Is a state in which the support plate 12 is erected on the flat plate-like bottom plate 11 in a state of being tilted by several degrees to 10 degrees (here, 5 degrees) with respect to the vertical direction. PBN (pyrolytic boron nitride) having the same shape as
It was formed of a flat plate. The bottom plate 11 is a support part for mounting the holder 10 in the furnace so that the support plate 12 is inclined with respect to the vertical as described above, and also the wafer 20
It also serves as a receiving portion for uniformly abutting the flat portion of. The bottom plate 11 is made of, for example, pBN or quartz. In the case of pBN, the bottom plate 11 and the support plate 12 are, for example, integrally molded, and when the support plate 12 is made of a different material such as quartz, the bottom plate 11 is made.
The support plate 12 is inserted into a slit (not shown) provided in the above, and the two are joined.

FIG. 2 shows an example of a wafer holder for a vertical furnace used for carrying out the present invention. As shown in the figure, the wafer holder 30 comprises a flat side plate 31 and a flat support plate 32, and the support plate 32 is lowered from the side plate 31 by several degrees to 10 degrees with respect to the horizontal. Formed at an angle. Then, for example, the support plate 32 is formed of graphite in the same shape as the wafer 40 (shown by the chain double-dashed line), and is brought into contact with the entire back surface of the wafer 40. Here, the side plate 31 is a receiving portion for contacting the outer peripheral portion of the wafer 40 (a flat portion is preferable although not particularly limited). Further, at the lower end of the side plate 31, there is provided a support portion 33 for installing the holder 30 so that the support plate 32 is inclined with respect to the horizontal as described above. The side plate 31, the support plate 32, and the support portion 33 are integrally molded or connected by a slit or the like like the bottom plate 11 and the support plate 12 in the holder 10 described above.

(Example 1) 650 μ from a GaAs single crystal grown by the LEC (Liquid Sealed Czochralski) method.
After cutting to a thickness of m, sodium hydroxide (NaO
A wafer 20 having a diameter of 2 inches, the surface of which was removed by about 30 μm with an H) type etchant, was set up in a state of standing on the wafer holder 10 of FIG. At this time, the flat portion in the <110> direction formed on the wafer 20 was brought into uniform contact with the bottom plate 11 of the wafer holder 10.

Then, as shown in FIG. 3, they were vacuum-sealed in a quartz ampoule 25 and heat-treated at 1100 ° C. for 5 hours. After the treatment, the wafer 20 was naturally cooled to room temperature, and the surface of the wafer 20 taken out from the ampoule 25 was removed by lapping and a sulfuric acid-based etchant to a depth of about 60 μm to obtain a mirror surface state. Further, after the surface thereof was subjected to etching treatment with a potassium hydroxide (KOH) melt at 400 ° C., pits generated corresponding to defects such as dislocations were observed to examine the presence or absence of defects. In this case, no pit was confirmed on the wafer 20, and it was found that crystal defects did not occur during the heat treatment.

In order to prevent thermal decomposition of the wafer 20,
Needless to say, the arsenic pressure in the ampoule 25 is set to be excessive. Further, the length of the flat portion was set to 18 mm, and the weight ratio of the wafer to the area of the end face of the flat portion was suppressed to 500 g / cm ² or less. This value was sufficiently smaller than the critical shear stress at 1100 ° C. of GaAs to which impurities were not added. In FIG. 3, reference numerals 26 and 27 denote a furnace core tube and an electric furnace, respectively.

(Embodiment 2) In a vertical furnace as shown in FIG. 4, a wafer 40 manufactured in the same manner as in Embodiment 1 is laid on a wafer holder 30 shown in FIG. Then, the presence or absence of pits was observed. In this case, pits were not confirmed on the wafer 40 regardless of whether or not the flat portion was brought into contact with the side plate 31, and it was found that crystal defects did not occur during the heat treatment. In FIG. 4, reference numerals 45, 46, and 47 respectively denote a quartz ampoule, a furnace core tube, and an electric furnace.

(Embodiment 3) A GaAs wafer having a diameter of 4 inches is erected on the wafer holder 10 shown in FIG. 1 and heat-treated at 1100 ° C. for 5 hours in the horizontal furnace shown in FIG. The presence or absence of pits was observed. In this example, the support plate 12 was made of pBN laminated material or graphite having excellent thermal conductivity, and was tilted about 10 degrees with respect to the vertical. In any case, no pits were confirmed on the wafer,
It was found that during the heat treatment, a slip line, that is, a crystal defect generated due to a thermal stress that can occur in the wafer due to a temperature difference was not generated. In addition, GaAs single crystal (L
Cut out with a thickness of 800 μm from (grown by EC method),
A wafer whose surface was removed by about 30 μm was used. The rate of temperature increase was 12 ° C./min on average from room temperature to 1000 ° C., and then 4 ° C./min on average until the temperature stabilized at 1100 ° C.

(Embodiment 4) A GaAs wafer having a diameter of 4 inches is laid on the wafer holder 30 shown in FIG. 2 and heat-treated in the vertical furnace shown in FIG. did. The support plate 32 was made of pBN laminated material or graphite. In each case, no pits were confirmed on the wafer, indicating that slip lines did not occur during the heat treatment.

(Comparative Example) The support plate 32 of the wafer holder 30 shown in FIG. 2 was made of quartz having a small thermal conductivity, and heat treatment was performed in the same manner as in Example 4 above. As a result, as shown in FIG. The pits were confirmed, and it was found that a large number of slip lines were formed during the heat treatment from the outer periphery of the wafer to the central portion. Occurrence of a slip line may be similarly observed even when the temperature raising / lowering rate is relatively slow at about 5 ° C./minute.

According to the first and second embodiments described above, the weight of the wafer is dispersed on the support plates 12 and 32, and in addition, when the wafer is erected, the flat portion is brought into contact with the bottom plate 11 of the holder 10. By further dispersing the wafer weight, it was possible to prevent the occurrence of crystal defects during heat treatment. Further, according to the third and fourth embodiments, the support plates 12, 3
Since No. 2 has excellent thermal conductivity, it is possible to reduce the temperature difference that can occur in the wafer, and thus suppress the generation of thermal stress and prevent the generation of crystal defects during heat treatment.

The materials of the supporting plates 12 and 32 are not limited to those described in the above embodiment, but they have high thermal conductivity, are hard to be oxidized, and are chemically stable to form a compound with a group V element. Any material may be used, and examples thereof include refractory metals such as molybdenum, tungsten, and tantalum, and high-purity silicon. In the case of silicon, a thermal oxide film (SiO ₂ ) is formed on its surface in advance. Even if the supporting plate made of these materials is used, the same effects as those of the above-described first to fourth embodiments can be obtained. In addition to GaAs, other III-V
Needless to say, the present invention can be applied to the heat treatment of the group-II or II-VI group compound semiconductor single crystal wafer by appropriately determining the material of the supporting plate according to the material (composition) of the wafer. Absent.

[0019]

By carrying out the heat treatment using the wafer support according to the present invention, not only the mechanical compressive stress due to the weight of the wafer itself can be dispersed without concentrating in a narrow region, but also the temperature inside the wafer can be dispersed. The thermal stress due to the difference can be reduced, and the occurrence of crystal defects during the heat treatment can be prevented. Therefore, the manufacturing yield of the single crystal wafer is improved, and its economic effect is extremely large. Further, by applying the present invention to the manufacture of a GaAs single crystal wafer having a large diameter of 4 inches or more, for example, residual stress due to mechanical stress or thermal stress can be reduced, and variation in electrical characteristics can be improved. You can Further, it is particularly effective in the case of two-step annealing in which the temperature is changed during the heat treatment.

[Brief description of drawings]

FIG. 1 is a view showing an example of a wafer holder for a horizontal furnace used in a heat treatment method according to the present invention.

FIG. 2 is a diagram showing an example of a wafer holder for a vertical furnace used in the heat treatment method according to the present invention.

FIG. 3 is a schematic view showing a state in which the wafer holder of FIG. 1 is installed in a horizontal furnace.

FIG. 4 is a schematic view showing a state where the wafer holder of FIG. 2 is installed in a vertical furnace.

FIG. 5 is a schematic diagram showing a surface state of a wafer after heat treatment in a comparative example, showing a state in which a slip line due to thermal stress is generated.

FIG. 6 is a schematic view of a wafer supported by a conventional wafer holder.

FIG. 7 is a schematic view of a wafer supported by a conventional wafer holder.

FIG. 8 is a schematic diagram showing a surface state of a wafer heat-treated using the wafer holder shown in FIG. 6, showing a state in which crystal defects are generated.

9 is a schematic diagram showing a surface state of a wafer that has been heat-treated using the wafer holder shown in FIG. 7, and shows a state where crystal defects are generated.

[Explanation of symbols]

 11 Bottom plate (supporting part, receiving part) 12,32 Supporting plate 33 Supporting part 20,40 Wafer 31 Side plate (receiving part)

Claims (3)

[Claims] 1. The thermal conductivity of the compound semiconductor is the same as or higher than that of the compound semiconductor, and the strain force applied to the wafer is set to be equal to or lower than the critical shear stress of the compound semiconductor at the heat treatment temperature. A heat treatment method for a compound semiconductor single crystal wafer, wherein a heat treatment is performed by uniformly supporting the back surface of the wafer on a support plate capable of dispersing the load of the wafer. 2. A wafer support used in the heat treatment method according to claim 1, wherein the support plate is a flat plate having a shape similar to or larger than a wafer, and the support plate is horizontal or vertical. A compound semiconductor single crystal wafer, comprising: a support part that is installed at a predetermined tilt angle and a receiving part that abuts the outer peripheral part of the wafer on the lower side of the tilted support plate. Wafer support used in the heat treatment method of. 3. The heat treatment method for a compound semiconductor single crystal wafer according to claim 2, wherein the support plate is formed of pyrolytic boron nitride, graphite, molybdenum, tungsten, tantalum, or silicon. Wafer support.