JPH0132653B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat treatment apparatus for volatile compound semiconductors such as GaAs substrates.

High-frequency shot key barrier field effect transistors, GaAs logic integrated circuits, Hall elements, etc.
The use of ion implantation techniques has become essential in creating devices made of GaAs.
However, the ion implantation technology, which is characterized by in-wafer uniformity and good wafer-to-wafer reproducibility, has not yet achieved its purpose with respect to GaAs, which is a - group compound semiconductor. This is due to the instability of the crystal itself of the GaAs substrate and further to the instability of the heat treatment after ion implantation. In other words, in -group compound semiconductors such as GaAs, group atoms such as As, which are the constituent elements, evaporate very easily, so if the substrate is exposed to the high temperature during heat treatment, the crystals will decompose from the surface side. occurs, and the group atoms evaporate. However, heat treatment after ion implantation requires a high temperature of at least 800°C for GaAs, so it cannot be done as is.
As evaporation occurs, in-plane uniformity and reproducibility deteriorate significantly.

For this reason, conventionally, when heat-treating the GaAs substrate after ion implantation at high temperatures (over 800°C),
By growing a protective film such as SiO ₂ or Si ₃ N ₄ on the substrate surface, As or Ga can be removed from GaAs at high temperatures.
There was a need to prevent external spread. However, even in this method, some of the protective films act as a barrier to the diffusion of As but are not effective against Ga, or vice versa. Ta. Even if it were possible to form a suitable protective film, such as a Si ₃ N ₄ film using the plasma positioning method, there would be a problem with the in-plane non-uniformity of the protective film, and this non-uniformity would directly affect the ion-implanted layer. This appears as non-uniformity after heat treatment. Furthermore, even if a protective film with relatively good in-plane non-uniformity is obtained, it is not easy to maintain the expensive growth equipment completely and always stably supply a protective film of the same quality.

In order to overcome these drawbacks, the present applicant has already proposed an improved method of heat treating a substrate after ion implantation without forming a protective film in Japanese Patent Application No. 11605/1983. According to the method of this prior application,
The GaAs substrate is heat-treated in an atmosphere with an As vapor partial pressure higher than the decomposition pressure of As, effectively preventing the evaporation of As from the substrate crystal. In this case, thermal decomposition of arsine (AsH ₃ ) is used to obtain the partial pressure of As. However, since arsine is a highly toxic gas, it is desirable from the standpoint of safety to avoid its use if possible.

Furthermore, in order to form a PN junction on a GaAs substrate in light emitting diodes, junction field effect transistors, double heterostructure semiconductor lasers, etc., thermal diffusion of impurities, ion implantation of impurities, etc. are generally used due to the simplicity of the process. There is. In the case of the ion implantation method, as described above, high temperature heat treatment is required to recover the damaged region after the ion implantation, so the ion implantation method is inappropriate when it is desired to form an extremely shallow junction. In order to compensate for this point, a simple and stable thermal diffusion method of impurities is desired.

However, although the so-called sealed tube method is employed for the heat treatment after ion implantation and the thermal diffusion of impurities described above, this method also has many troublesome points and is not practical. In the sealed tube method, metallic arsenic, which releases a large amount of As vapor, is used to suppress the evaporation of As from the GaAs substrate.
The GaAs substrate is sealed together with the GaAs substrate in a quartz ampoule, but in addition to the hassle of sealing the quartz ampoule, special care must be taken to prevent residual impurities and As atoms from adhering to the GaAs substrate during cooling after completion of diffusion. It is required.

The present invention has been made to correct the above-mentioned defects, and includes an outer tube whose one end is closed and the other end is open; an inner tube insertable into the tube; a compound semiconductor (e.g. GaAs) having a volatile element (e.g. As) formed between the one end of the outer tube and the one end of the inner tube inserted into the outer tube; ) and a substance (e.g., metallic arsenic) that releases vapor of the volatile element; and a non-reactive gas (e.g., H ₂ , N ₂ , Ar as a carrier gas) surrounding the outer tube. ), a non-reactive gas supply means (for example, a heating furnace), and an inner circumferential surface of the outer tube and an outer circumferential surface of the inner tube inserted into the outer tube. a path communicating between the storage chamber and the outside of the outer tube in order to bring the vapor pressure of the volatile element and the pressure of the non-reactive gas surrounding the outer tube into an equilibrium state; The present invention relates to a heat treatment apparatus for a compound semiconductor containing a volatile element, which is equipped with heating means (for example, a heating furnace) for heating the compound semiconductor and the substance in a room. With this configuration, it is possible to easily and safely provide a heat treatment apparatus with good uniformity and reproducibility at low cost.

Hereinafter, the present invention will be explained in detail with reference to examples.

First, the configuration of the heat treatment apparatus used in this example will be explained with reference to FIGS. 1 and 2. This device is used in a hydrogen stream based on an open tube method, which is completely different from the conventional sealed tube method. It has an inner tube 2 made of, for example, quartz, which can be inserted into the tube and has one end open. In this case, it is extremely important that a narrow cylindrical path 3 is formed between the outer tube 1 and the inner tube 2 in the state shown in FIG. 1 when the tube is inserted into the outer tube 1. Further, on the closed end side of the inner tube 2, a stepped sample stand 4 and a lower metal arsenic reservoir 5 are integrally provided, and the inner tube 2 is placed inside the outer tube 1 together with these sample stands and the metal arsenic reservoir. is configured to be fully inserted into the After this complete insertion, a sample chamber 6 is formed by the closed end outer surface of the inner tube 2 and the closed end inner surface of the outer tube 1, but this sample chamber is communicated with the outside only through the above-mentioned narrow path 3. It has become a thing. Note that the inner tube 2 itself is taken in and out by an appropriate means, but this operation is performed using an arcuate inner tube conduit 7 provided extending from the open end side of the outer tube 1.
The process is facilitated by

The processing apparatus 8 thus constructed is set in a heating furnace 9 having heating means arranged around it, and heated to a predetermined temperature while flowing hydrogen gas into the heating furnace 9. For example, GaAs after ion implantation is placed on the sample stage 4.
A substrate is placed, metal arsenic is placed in the metal arsenic reservoir 5, and the inner tube 2 is inserted into the outer tube 1. Metallic arsenic releases As vapor into the sample chamber 6 when heated;
A portion of the As vapor is transferred from the sample chamber 6 to the external atmospheric pressure (1
H 2 is released through the path 3 so that the pressure becomes equal to the atmospheric pressure (atmospheric pressure) and is in equilibrium, and H ₂ instead enters the sample chamber 6 from the outside. However, after this pressure equilibrium (steady state), the As vapor in the sample chamber 6 moves only by diffusion in the path 3, and this movement speed is extremely slow.

Therefore, at the initial stage of processing, the sample chamber 6
Since the excess As vapor inside the sample chamber can be released until the pressure reaches equilibrium, there is no precipitation (adhesion) of As atoms inside the sample chamber as seen in the conventional closed tube method. Furthermore, after the pressure is balanced, the As vapor in the sample chamber 6 simply diffuses due to the concentration difference, so during heat treatment (annealing), the As vapor can be efficiently confined within the sample chamber 6. 6
The As concentration within is sufficient. On the contrary,
When using metallic arsenic in the conventional open tube method, unless a heating furnace with two temperature ranges is used, the added metallic arsenic will instantly scatter due to the high vapor pressure of As at the heat treatment temperature of the ion-implanted GaAs. However, in this embodiment, such a situation could be prevented by the existence of the narrow path 3.

As described above, by using the processing apparatus according to this embodiment, it is possible to efficiently confine As vapor in the sample chamber 6 at a high concentration during heat treatment. It is possible to effectively anneal a GaAs substrate into which ions have been implanted. That is, in the sample chamber 6
Since the As partial pressure is sufficient (higher than the As decomposition pressure of the GaAs substrate), release of As due to thermal decomposition of the GaAs substrate can be suppressed, and in-plane uniformity and reproducibility can be significantly improved. Furthermore, since the method is an open tube method, there are no problems associated with the sealed tube method, such as the troubles and adhesion of As atoms.

These excellent effects can be obtained only by communicating the inside and outside of the sample chamber 6 through the narrow path 3 with low gas flow rate, so the effects are enormous despite the simple configuration. Also, processing device 1
0 is configured so that the inner tube 2 can be put in and taken out,
The operation can be performed by simply putting in and taking out the inner tube 2 each time, and the workability is extremely improved compared to the trouble of sealing the tube in the sealing method.

In the above case, an ion-implanted GaAs substrate was used as the GaAs substrate to be processed, but the present invention can be applied not only to annealing after ion implantation but also to thermal diffusion treatment of impurities. In this case, metal arsenic and a diffusion source may be placed in the metal arsenic reservoir 5, and the vapors of As and impurity elements may be efficiently contained in the sample chamber 6 in the same manner as described above. Therefore, predetermined impurities can be thermally diffused while suppressing release of As from the GaAs substrate. Although the impurity element alone may be used as the diffusion source, it is convenient to use a compound with a group element. Alternatively, a compound of an impurity element and a group element can be arranged together with the group element. In addition to GaAs, there are other types of substrates as well.
Other groups such as InAs can also be processed.

Further, although the As vapor in the sample chamber 6 may be supplied by metallic arsenic as described above, an arsenic compound can also be used. In short, it is sufficient to arrange As or an As compound such that the As partial pressure within the sample chamber 6 becomes approximately 1 atm (actually, 1 atm or more) during processing.

Furthermore, the configuration of the processing device is not limited to the above-mentioned one, and for example, the inner tube 2 is fixed in the outer tube 1 without being able to be taken in and out, and an opening for loading and unloading samples, etc. is provided in the outer tube 1 at the sample chamber 6. It's okay. In this case, the inner tube 2 may not be used, and a thin tube corresponding to the above-mentioned path 3 may be provided in the container constituting the sample chamber 6, and the inside and outside of the container may be communicated through this thin tube.

Next, a specific example of this embodiment will be explained.

Example 1 Using the apparatus shown in FIGS. 1 and 2 (both the inner and outer tubes were made of quartz), an ion-implanted GaAs substrate was annealed. Metallic arsenic in the sample chamber was added at such a rate as to give an As vapor pressure of at most 1 atm at the heat treatment temperature. The volume of the sample chamber is 12.6cc
Therefore, for example, if heat treatment was to be carried out at 850°C, it would be sufficient to add 41 mg of metallic arsenic.
During the heat treatment, As vapor gradually dispersed to the outside due to diffusion, but since the vapor pressure of As required during actual heat treatment is extremely low at around 4 × 10 ^-3 atm, the vapor pressure will decrease during the 15 to 20 minutes of heat treatment. The As vapor pressure was maintained in the sample chamber much higher than the above. This means that
This was clear from a comparison with heat treatment using arsine in an As atmosphere. The vapor pressure of As in the sample chamber is thought to decrease exponentially with the heat treatment time, and its value is approximately expressed by the following equation.

P(t) = P _p exp (-D・A/LV・t) …(1) However, P(t): Pressure inside the sample chamber 6 after t seconds P _p : Sample when steady state is reached Pressure A in chamber 6: Cross-sectional area L of path 3: Length V of path 3: Volume D of sample chamber 6: Diffusion constant of gas The diffusion constant of As atoms (gas) in hydrogen gas at 850°C is 2 Figure ³ shows the results of calculating the residual As pressure in the sample chamber assuming that the As pressure at the time when the steady state is reached is 1 atm, taking into account the shape effect of the processing equipment shown in the figure. It was shown to. In this figure, the As pressure is expressed on a log scale, and the annealing time is plotted on the horizontal axis. According to this, in order to prevent the release of As from the substrate by maintaining the surrounding As vapor pressure higher than the decomposition pressure of GaAs in the ion-implanted substrate (a value slightly lower than 10 ^-3 atmospheres),
It is found that it is better to keep the annealing time within 15 minutes. In reality, the annealing time at 850° C. may be 2 to 3 minutes, and the annealing can be sufficiently completed within this processing time. Furthermore, from the above equation (1), if the size of the gas flow path 3 and the volume of the sample chamber 6, that is, A/LV, are made as small as possible, the added metal arsenic can be used as effectively as possible.

By the method of this example, Si ions are
A semi-insulating GaAs substrate implanted with 10 ¹² ions/ ^cm2 was heated to 850°C.
As a result of heat treatment for 15 minutes, the activation rate of the implanted donor atoms was approximately 100%. In addition, the effects of thermal transformation of the substrate and other properties are equivalent to or better than those of conventional heat treatment with a protective film, and when heat treated in an arsenic atmosphere using arsine according to the method of the previous application described above, (no protective film). In FIG. 4, the carrier concentration of the surface N-type layer after heat treatment is plotted as a function of depth. In the figure, curve a indicates that the applicant
Based on the method for processing semiconductor substrates related to the patent application filed on October 1st, the above GaAs substrates are processed into other -
This is data when heat treatment was performed while contacting a group compound semiconductor substrate (no ion implantation). In this case, if the As decomposition pressure of the opposing substrates is increased,
Release of As from the substrate to be processed can be effectively prevented. Curve b is data obtained in the case of processing according to this example (however, the amount of metal arsenic added was 0.1 g) and the case of processing according to the previously described method using arsine. From FIG. 4, it can be seen that when treated according to this example, the carrier concentration due to thermal transformation is comparable to that when arsine is used, and is significantly lower than when the - group compound semiconductor substrates are placed in contact. .

Example 2 In Example 1, a path with poor gas conductivity was formed by utilizing the difference in the pipe diameters of two types of cylindrical bodies (i.e., outer pipe and inner pipe) with slightly different diameters, but in this example, In equation (1) described in Example 1, the path length L was increased. In this improved version, the cross-sectional area A of the passage was reduced, and in this example, a tapered rubbing method between the inner and outer tubes, a tapered drop-lid method, etc. were adopted.

Example 3 In Example 1, both the inner and outer tubes were made of quartz, but Example 1
In Example 2, the processing apparatus was constructed of a material other than quartz, such as graphite, boron nitride, alumina, etc., which can withstand sufficiently high temperatures and has few impurities.

Example 4 Using the equipment shown in Figures 1 and 2, GaAs
Zn was thermally diffused onto the substrate. As in Example 1, metallic arsenic was added in an amount that would give an As vapor pressure of at most 1 atm at the diffusion temperature. Since the volume of the sample chamber is 12.6 cc, for example, if diffusion is to be performed at 700°C, 47
It was sufficient to add mg of metal arsenic. During impurity diffusion, As atoms in the sample chamber gradually scatter to the outside due to the diffusion phenomenon, but because they form a narrow path with very poor gas conductivity for gas phase diffusion,
As pressure can be maintained sufficiently high, and
In order to suppress the evaporation of As, an As vapor pressure of 1×10 ^-3 atmosphere or less in the sample chamber was sufficient. Therefore, during diffusion for 30 to 60 minutes, the As vapor pressure in the sample chamber could be maintained at a sufficiently high value to suppress As evaporation from the GaAs substrate.

Generally, the As vapor pressure and Zn vapor pressure in the sample chamber are approximately expressed by the equations (1) described in Example 1, respectively.
Considering the diffusion constant of As atoms (gas) in hydrogen gas at 700℃ to be about 1 to 2 cm ² /sec, and considering the shape effect of the processing equipment shown in the figure, calculate the As pressure when a steady state is reached. Remaining in the sample chamber as 1 atm
The results of calculating the As pressure are shown in Figure 5 (pressure is on a log scale). On the other hand, the vapor pressure of Zn at 700℃ is about 0.66 atm, and the amount of loss per second is about 1.5 μg in terms of mass, so in order to perform thermal diffusion under a constant Zn vapor pressure, requires the addition of at least 3.4 mg of zinc metal for a diffusion time of 30 minutes. FIG. 5 also shows the change in Zn vapor pressure in the sample chamber when the diffusion constant of Zn atoms (gas) in the gas phase is 1 to 2 cm ² /sec. According to Figure 5, even with a diffusion time of 30 minutes, the
It can be seen that Zn diffusion can be carried out effectively while maintaining the As pressure high enough to substantially suppress the evaporation of As from the GaAs substrate. In addition, the amount of As and Zn added is smaller than that in the conventional open-tube diffusion method, and since it is only necessary to add as much as the amount consumed, there may be no residual impurities or other substances on the sample surface after cooling.
It was also possible to avoid the situation where As compounds etc. were attached.

When diffusion was carried out at 700°C for 30 minutes under the conditions of this example, a P-type layer with a junction depth of ~12 μm could be formed by diffusion on a substrate of n = 3 × 10 ¹⁶ cm ^-3 , and its surface concentration was approximately 1. ×10 ²⁰ cm ^-3 and the sheet resistance was approximately 25Ω/cm ² .

Example 5 In Example 4, metallic zinc was used together with metallic arsenic, but in this example zinc arsenide (ZnAs) was used, from which As and Zn vapors were simultaneously supplied. Further, as N-type dopants, arsenic sulfide (As ₂ S ₃ ), arsenic selenide (As ₂ Se ₃ ), arsenic telluride (As ₂ Te ₃ ), etc. were used. Further, a combination of gallium sulfide (Ga ₂ S ₃ ), gallium selenide (Ga ₂ Se ₃ ), gallium telluride (Ga ₂ Te ₃ ), etc. and metal arsenic may also be used.

The characteristics of the heat treatment apparatus according to the present invention illustrated above are summarized as follows.

(1) The expensive protective film growth equipment required for conventional heat treatment with a protective film is not required, and the number of device manufacturing steps can be reduced accordingly, simplifying the process.

(2) Heat treatment can be performed in a volatile element gas atmosphere without using dangerous volatile element hydrides such as arsine, using a simple configuration rather than special equipment. The characteristics of the ion-implanted region after heat treatment are almost the same as in the case of using a hydride of a volatile element.

(3) Unlike the conventional sealing tube method, it is easy to work with and can be processed without damaging the surface of the substrate.
In particular, the device is suitable not only for annealing a substrate into which ions have been implanted, but also for thermally diffusing impurities. The adhesion of impurities, volatile elements, and their compounds to the surface of the substrate after cooling, which was unavoidable in the conventional sealing method, can be avoided by adding the necessary minimum amount of raw materials.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which Fig. 1 is a cross-sectional view of the processing device, Fig. 2 is a perspective view of the outer tube and inner tube separated, and Fig. 3 is the inside view of the sample chamber depending on the annealing time. Figure 4 is a graph showing a comparison of the distribution of carrier concentration in the depth direction after heat treatment. Figure 5 is a graph showing changes in As pressure and Zn pressure in the sample chamber depending on diffusion time. It is a graph. In addition, in the symbols used in the drawings, 1...
...Outer tube, 2...Inner tube, 3...Narrow path, 4...Sample stand, 5...Metal arsenic reservoir, 6...Sample chamber.

Claims (1)

[Claims] 1. An outer tube whose one end is closed and the other end is open; an inner tube whose at least one end is closed and which can be inserted into the outer tube from the other end of the outer tube; a storage chamber formed between the one end of the inner tube inserted into the outer tube and for accommodating a compound semiconductor having a volatile element and a substance that releases vapor of the volatile element; a non-reactive gas supply means for supplying a non-reactive gas so as to surround the housing chamber; and an inner circumferential surface of the outer tube and an outer circumferential surface of the inner tube inserted into the outer tube. a path that communicates the storage chamber with the outside of the outer tube in order to bring the vapor pressure of the volatile element and the pressure of the non-reactive gas surrounding the outer tube into an equilibrium state; A heat treatment apparatus for a compound semiconductor having a volatile element, comprising heating means for heating the compound semiconductor and the substance in a storage chamber.