JPH04305086A - Production of single crystal of high-dissociation pressure compound semiconductor - Google Patents

Abstract

PURPOSE:To obtain the single crystal of a high-dissociation pressure compd. semiconductor which is controlled in carbon impurity concn. with high accuracy by adding >=1 kind selected from CO, CO2 and gaseous hydrocarbon at prescribed ratios to the gaseous high-dissociation pressure component in a hermetic vessel. CONSTITUTION:A crucible is disposed in the hermetic vessel which can be divided and hermetically sealed. The single crystal of the semiconductor is pulled up from the melt of the high-dissociation pressure compd. semiconductor (e.g.; GaAs) stored in the crucible while the pressure of the gaseous high- dissociation pressure component (e.g.: gaseous As) in the hermetic vessel is controlled. At least one kind selected from gaseous carbon monoxide, carbon dioxide and hydrocarbon are added at <=1.5X10<-6>mol per 1kg high-dissociation pressure compd. semiconductor raw material to the gaseous high-dissociation pressure component in the hermetic vessel. The carbon impurity concn. in the atmosphere in the hermetic vessel is increased in this way and the carbon impurity concn. in the single crystal of the high-dissociation pressure compd. semiconductor is controlled to an adequate value with good accuracy.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to gallium arsenide (GaAs) useful for semiconductor lasers or semiconductor substrates.
The present invention relates to a method for producing a high dissociation pressure compound semiconductor single crystal such as the following.

0002

[Prior Art] Conventionally, when growing a high dissociation pressure compound semiconductor single crystal (hereinafter simply referred to as a single crystal) such as GaAs or InP, high dissociation pressure components (As, P
A method of growing crystals in a high dissociation pressure component gas atmosphere that is in equilibrium with the dissociation pressure of the crystal at the crystal growth temperature (hereinafter referred to as vapor pressure control trigger), in order to prevent the scattering of (referred to as the above law) has been adopted.

FIG. 3 shows an example of a single crystal pulling apparatus used in the above vapor pressure controlled pulling method. In this single crystal pulling apparatus 1, an airtight container 4, which is composed of an upper container 2 and a lower container 3 and can be divided and sealed, is placed inside an outer container 5. Seal material 6
is interposed.

The lower container 3 is connected to a lower push-up shaft 7,
It is pressed against the upper container 2 with an appropriate stress by a stress buffering device 8. Further, a susceptor 9 is provided at the bottom 3a of the lower container 3.
A lower shaft 9a of the susceptor 9 is inserted therethrough, and a crucible 10 is placed on the susceptor 9.

On the other hand, the upper container 2 is provided with a vapor pressure control section 12 equipped with a heater 11, and in the center of the upper part of the upper container 2, a pulling shaft 13 is connected to its lower end 13a.
is inserted so as to be positioned substantially directly above the crucible 10. Further, a transparent observation window 14 made of quartz or sapphire and having a visual field substantially directly above the crucible 10 is inserted into the upper container 2 into the airtight container 4 with one end surface 14a exposed. In addition, the pulling shaft 13 and the lower shaft 9 of the susceptor 9
A shaft seal portion 16 that holds a liquid sealing material 15 made of B2O3 or the like is provided at the insertion portion a into the airtight container 4.

[0006] An upper heater 17 is provided around the upper container 2, and a lower heater 18 is provided around the lower container 3.
19 is provided, and the airtight container 4 is heated and maintained at a predetermined temperature by the upper heater 17 and lower heaters 18 and 19.

Next, using the single crystal pulling apparatus 1 described above, Ga
About the method of producing single crystals such as As and InP
This will be explained using s as an example. First, an As raw material is placed in the bottom 3a of the lower container 3, a Ga raw material is placed in the crucible 10, and a GaAs seed crystal S is placed in the lower end 13a of the pulling shaft 13, and the inside of the outer container 5 is evacuated to create a vacuum. After this, the lower push-up shaft 7 is pushed up to bring the lower container 3 into pressure contact with the upper container 2, and the inside of the airtight container 4 is sealed.

After that, the upper heater 17 and the lower heater 1
8 and 19 to heat the airtight container 4, the bottom 3a of the lower container 3 to 550 to 650°C, and the crucible 10 to GaAs.
When the temperature is maintained at a temperature higher than the melting point of 1238°C, for example about 1300°C, the vapor pressure of the As gas in the airtight container 4 increases,
The As gas and Ga in the crucible 10 react, and GaAs
A raw material melt M is synthesized. During this synthesis, an inert gas such as Ar gas is introduced into the outer container 5 to keep the final pressure at most several atmospheres, thereby maintaining a balance between the pressures inside and outside the airtight container 4.

After synthesizing the GaAs raw material melt M in this manner, the pulling shaft 13 is lowered, and the seed crystal S attached to the lower end 13a is immersed in the raw material melt M, and the seed crystal S is immersed in the raw material melt M through the observation window 14. While observing the state of crystal growth, the single crystal C is grown by pulling up while rotating the pulling shaft 13. Also, at this time, the temperature of the vapor pressure control unit 12 is maintained at the lowest constant temperature inside the airtight container 4, and the As gas is condensed there, thereby controlling the vapor pressure of the As gas inside the airtight container 4. .

In the single crystal pulling apparatus 1 described above, the airtight container 4
can be divided and reused; As the As raw material and Ga raw material are placed in different locations, the As raw material can be purified by sublimation;
It has advantages such as being able to manufacture large diameter single crystal ingots.

[0011]

[Problems to be Solved by the Invention] However, in the above-mentioned vapor pressure controlled pulling method, for example, when the As raw material is sublimated, carbon impurities contained in the As raw material are also removed at the same time. The disadvantage was that the carbon impurity concentration of the carbon impurities was too low.

[0012] The reason for this is that in the case of the LEC method in which As raw materials and Ga raw materials are placed in a crucible at the same time, carbon impurities in the raw materials enter the melt as they are, and the carbon components that are the main components of heaters and heat insulating materials are It is known that trace amounts of oxygen and moisture present in the crystal pulling apparatus, especially moisture in B2O3, can be oxidized and become a source of carbon pollution, but in the above method,
The airtight container 4 is made of a high-purity, gas-impermeable material other than carbon, and from raw material synthesis to the growth process, the raw material melt M is connected to a heater or heat insulating material placed outside the airtight container 4. This is because the incorporation of carbon impurities is extremely small due to the isolation.

[0013] In the above-mentioned LEC method, the problem of carbon pollution is extremely serious, and several methods have been proposed and disclosed for reducing and controlling it.

For example, in Japanese Patent Application Laid-Open No. 62-30700, the atmospheric gas in the device is partially released or new gas is replenished during the pulling operation to reduce the CO concentration in the device to 1000 ppm or less. is controlled. Furthermore, in Japanese Patent Application Laid-open No. 1-192793, CO and/or CO2
0.01-0.1% gas in inert gas such as Ar gas
At the same time as mixing, the water concentration in B2O3 is reduced to 100 to 50.
It is controlled at 0 ppm. Also, JP-A-2-13779
In Publication No. 2, the carbon concentration in the crystal is controlled by circulating pressurized inert gas inside the puller chamber and removing carbon impurity gas generated from inside the chamber using a purifier during the circulation. ing.

In the LEC method, the water contained in B2O3 oxidizes carbon in the raw material melt and acts as a decarbonizing agent, while at the same time oxidizing the carbon members in the furnace as an oxidizing gas to generate carbon oxide gas. It acts in the direction of carbon uptake, and also acts as a diffusion barrier layer in carbon uptake. Since these reactions proceed in the direction of reaching equilibrium, carbon incorporation into the crystal is not uniform depending on the carbon oxide gas concentration in the atmosphere and the carbon concentration in the raw material melt, and may decrease or increase as the crystal solidifies. .

The above-mentioned vapor pressure controlled pulling method differs from the LEC method in many respects, and the mechanism of carbon uptake has not been elucidated, so the above-mentioned known techniques cannot be applied to it.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a method for producing a single crystal that allows the concentration of carbon impurities in the single crystal to be controlled with high precision.

[0018]

[Means for Solving the Problems] In order to solve the above problems, the present invention employs the following single crystal manufacturing method. That is, manufacturing a single crystal by pulling a semiconductor single crystal from a high dissociation pressure compound semiconductor melt stored in a crucible in the airtight container while controlling the pressure of a high dissociation pressure component gas in an airtight container that can be divided and sealed. In the method, at least one selected from the group consisting of carbon monoxide, carbon dioxide, and hydrocarbon gas is added to the high dissociation pressure component gas in the airtight container at a rate of 1.5 x 10 - per 1 kg of the high dissociation pressure compound semiconductor raw material. It is characterized in that it is added in an amount of 6 moles or less.

[0019]

[Function] Too much carbon impurity in single crystal C such as GaAs causes thermal transformation, and conversely, too little carbon impurity makes it impossible to obtain the semi-insulating properties required for IC substrates, etc. This may cause problems such as non-uniform electrical characteristics. Both of these problems are due to the total amount of donor impurities such as Si, S, and Te in the crystal for semi-insulating properties.
This problem arises because the total amount of acceptor impurities such as C and Zn is larger, and the difference is compensated for by a deep donor level. Therefore, the carbon impurity concentration needs to be appropriately controlled depending on the donor impurity concentration.

In the method for producing a single crystal of the present invention, at least one gas selected from the group consisting of carbon monoxide, carbon dioxide, and hydrocarbon gas is added to the high dissociation pressure component gas in the airtight container.
1.5 x 10 seeds per 1 kg of high dissociation pressure compound semiconductor raw material
By adding -6 mol or less, the carbon impurity concentration in the atmosphere within the airtight container is increased, and the carbon impurity concentration in the single crystal is appropriately controlled.

The advantage of using hydrocarbon gas is that it does not decompose to produce oxygen. Oxygen is not incorporated into GaAs to form a deep level, and does not oxidize the airtight container material and shorten its life.

[0022]

EXAMPLE An example of the method for producing a single crystal according to the present invention will be described below with reference to FIG. First, 4300g of As raw material was placed in the bottom 3a of the lower container 3, and Ga was placed in the crucible 10.
Add 3850g of raw material, and then add 3850g of raw material to the lower end 1 of the
A GaAs seed crystal S was attached to 3a, and the inside of the outer container 5 was evacuated.

Next, after introducing Ar gas diluted with CO gas to 2000 ppm in an amount of 1.2 x 10-5 moles of CO in the volume of the airtight container 4, the lower push-up shaft 7 is pushed up to lower the lower container 3. was pressed against the upper container 2, and the inside of the airtight container 4 was sealed. The amount of CO gas added is calculated in terms of pressure at room temperature.
(not shown).

After that, the upper heater 17 and the lower heater 1
8 and 19, the bottom 3a of the lower container 3 is heated to 550 to 650°C, and the crucible 10 is heated to about 130°C.
When maintained at 0° C., the vapor pressure of the As gas in the airtight container 4 increases, and the As gas reacts with Ga in the crucible 10.
About 8000 g of GaAs raw material melt M was synthesized. During this synthesis, an inert gas such as Ar gas was introduced into the outer container 5 to keep the final pressure at most several atmospheres, thereby maintaining the balance between the pressures inside and outside the airtight container 4.

After synthesizing the GaAs raw material melt M, the raw material melt M is held at about 1300° C. for a predetermined time, and then the temperature is gradually lowered, and the pulling shaft 13 is lowered and attached to the lower end 13a. The seed crystal S was immersed in the raw material melt M and pulled up while rotating the pulling shaft 13 to grow a single crystal C with a diameter of 4 inches. During this time, the temperature of the vapor pressure control unit 12 is maintained at the lowest constant temperature inside the airtight container 4, for example 615° C., and the vapor pressure of the As gas inside the airtight container 4 is controlled by condensing the As gas there. did.

FIG. 1 shows the carbon concentration in the portion directly below the shoulder of the GaAs single crystal obtained in this manner, measured by the FTIR method, and plotted against the standing time until seeding. As is clear from FIG. 1, the carbon concentration shows a tendency to rapidly increase and become saturated with the standing time.

In this method, if the standing time is short, the raw material melt absorbs carbon during crystal growth, resulting in large non-uniformity in carbon concentration between the seed side and the tail side of the single crystal. However, when the carbon concentration becomes saturated by leaving it for 50 hours, the difference in carbon concentration between the seed side and the tail side falls within about 10%. Therefore, in this state, the carbon concentration (3.8×101
5cm-3), all the C in the CO gas initially introduced is G.
The carbon concentration assumed to be incorporated into aAs (4.8×
1015 cm-3). That is, it can be considered that the raw material melt after being left for a sufficiently long time decomposes and incorporates almost all of the CO.

FIG. 2 shows a similar experiment in which the number of moles sealed in an airtight CO container was changed, and after leaving it for 50 hours, a portion just below the shoulder was cut out from the GaAs single crystal obtained by crystal growth, and the carbon concentration was reduced. CO measured and sealed in an airtight container
It is plotted against the number of moles. Even if the number of moles of CO is changed, it is thought that carbon uptake will be saturated in approximately the same amount of time, but from Figure 2 it is clear that the saturated carbon concentration shows a uniform change with the number of moles of CO sealed in an airtight container. Ta.

FIG. 2 also shows a similar experiment using CO2 gas,
The results obtained for CH4 gas and C2H6 gas are also plotted, and it can be seen that almost the same dependence on carbon concentration is shown for each partial pressure. in this case,
When using a hydrocarbon gas containing two or more carbon atoms in one molecule, such as the above C2H6 gas, it is possible to reduce the number of moles of the hydrocarbon gas compared to the above CO, CO2, CH4 gas, etc. Almost the same carbon concentration can be obtained. For any gas, it is shown that almost all carbon is incorporated into the raw material melt in an equilibrium state, but this is a big difference from the LEC method using a liquid sealant.

From the above experimental results, by converting the carbon concentration required for the weight of raw material GaAs into the number of moles of CO in the airtight container 4 at room temperature, and furthermore into the partial pressure of CO,
A single crystal with precisely controlled carbon concentration can be obtained.

As explained above, according to the single crystal manufacturing method of the above embodiment, CO, CO2, C
The Ar gas diluted with H4 and C2H6 is converted to the number of moles of each gas of CO, CO2, CH4, and C2H6 in 4 volumes of an airtight container at room temperature, which is 1.5 per kg of GaAs raw material.
When only ×10−6 moles are introduced, the concentration of carbon impurities in the atmosphere inside the airtight container 4 can be increased, and the concentration of carbon impurities in the single crystal C can be controlled to an appropriate value of 4×1015 cm−3 or less. can. Therefore, it is possible to provide a method for manufacturing a single crystal in which the concentration of carbon impurities in the single crystal C can be controlled with high precision.

[0032]

As explained above, according to the method for producing a single crystal of the present invention, while controlling the pressure of the high dissociation pressure component gas in the airtight container that can be divided and sealed, the crucible in the airtight container can be controlled. In the single crystal manufacturing method of pulling a semiconductor single crystal from a high dissociation pressure compound semiconductor melt stored in at least one selected
1.5 x 10 seeds per 1 kg of high dissociation pressure compound semiconductor raw material
By adding -6 moles or less, the concentration of carbon impurities in the atmosphere within the airtight container can be increased, and the concentration of carbon impurities in the single crystal can be appropriately controlled. Therefore, it is possible to provide a method for producing a single crystal that can control the carbon impurity concentration in the single crystal with high precision.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the carbon concentration and standing time of a single crystal produced by the method for producing a single crystal of the present invention (when 1.2 × 10-5 mol of CO is introduced into an airtight container,
The GaAs raw material was 8 kg).

[Figure 2] Carbon concentration and CO, CO2, CH4, C2H6 of a single crystal produced by the single crystal production method of the present invention
FIG. 2 is a diagram showing the relationship between the number of moles in the airtight container and the number of moles in the airtight container (GaAs raw material is 8 kg).

FIG. 3 is a schematic cross-sectional view of a conventional single crystal pulling apparatus.

Claims (1)

[Claims] 1. A method for raising a semiconductor single crystal from a high dissociation pressure compound semiconductor melt stored in a crucible in the airtight container while controlling the pressure of a high dissociation pressure component gas in an airtight container that can be divided and sealed. In the method for producing a dissociation pressure compound semiconductor single crystal, at least one selected from the group consisting of carbon monoxide, carbon dioxide, and hydrocarbon gas is added to the high dissociation pressure component gas in the airtight container as a high dissociation pressure compound semiconductor raw material. 1
A method for producing a high dissociation pressure compound semiconductor single crystal, the method comprising adding 1.5×10 −6 mol or less per kg.