JPH0717793A - Method for producing compound semiconductor single crystal - Google Patents

Abstract

(57) [Summary] [Objective] A hydrocarbon having a low reactivity with a jig made of graphite is used to stably obtain a single crystal having a uniform carbon concentration distribution without deteriorating the jig. [Structure] Crucible 2 surrounded by graphite heater 9
A GaAs melt 4 is prepared inside. Then GaAs crystal 4
When pulling up, the pure Ar gas and the mixed Ar gas mixed with a predetermined amount of methane gas are simultaneously supplied from the gas cylinders 12 and 13 into the pressure vessel 2. At this time, the gas concentration measuring device 19 and the pressure gauge 17 are used to adjust the methane gas concentration in the atmosphere in the container 4 and the pressure in the container to predetermined values by the valve 1
4 and 15 are controlled. Even after this, the carbon concentration in the crystal is kept at the same concentration and the same pressure, aiming at the target value.
In this state, the seed crystal 3 is dipped in the melt 18 to pull up the GaAs crystal 4 having a predetermined diameter and a predetermined length. During the growth, since methane gas does not contain oxygen, it does not react with the heater 9 or the like, and the methane gas concentration is accurately controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a compound semiconductor crystal in which a carbon-based gas is mixed in a furnace filled with an inert gas for growth in order to mix carbon into the crystal as an impurity. In particular, the present invention relates to a method suitable for a method for producing a GaAs single crystal by the LEC method.

[0002]

2. Description of the Related Art A compound semiconductor single crystal, for example, a GaAs single crystal, is used for a magnetoelectric conversion element, a field effect transistor (FE).
T), ICs, LSIs, etc. are used as substrates for high-speed high-frequency devices in a wide range of applications. One of the methods for producing a single crystal of a substrate material used for these elements is a liquid sealing pulling method (hereinafter referred to as LEC method).

In the LEC method, a raw material and a liquid sealant having low reactivity with raw material elements are contained in a crucible made of pBN installed in a pressure vessel constituting a furnace, and an inert gas of a predetermined pressure ( Argon (Ar) gas, etc.) is sealed. After that, it is heated by a heater located on the outer peripheral portion of the crucible, and Ga
Make As melt. Then, a seed crystal is brought into contact with the GaAs melt, the seed crystal is gradually pulled up, and the GaAs single crystal is obtained by pulling up the seed crystal while controlling it to a predetermined diameter.

In the production of a single crystal by the LEC method, a graphite material is used for a jig used for growth, such as a susceptor for supporting a crucible, a heater, a heat retaining plate, etc., so that carbon is included in the crystal. It is unavoidable that impurities are mixed in, and the carbon concentration in the crystal becomes nonuniform.
Carbon in the GaAs crystal serves as a shallow acceptor, and the electrical characteristics (semi-insulating characteristics) of the crystal change greatly depending on the concentration thereof.

The electrical characteristics required for a GaAs wafer are
The wafer varies depending on the type of device used as a substrate, and the carbon content is not necessarily low. Therefore, it is desirable that the concentration of carbon contained in the crystal be as uniform as possible with respect to the desired concentration from the front end to the rear end of the crystal. There is also a need for a method of growing such single crystals with good reproducibility.

Therefore, carbon mixed in the GaAs single crystal by the LEC method is supplied from carbon monoxide or the like in the atmosphere gas during crystal growth to control the carbon monoxide concentration in the furnace during crystal growth to a predetermined value. A proposal has been made to do so. For example, a method of growing a GaAs single crystal while substituting the gas in the pressure vessel with a pure inert gas or a mixed gas of carbon monoxide and the like (Reference 1), one method in the pressure vessel during crystal growth In order to control the carbon oxide concentration within a predetermined range, there is a method of growing a GaAs single crystal by mixing a predetermined amount of carbon dioxide and carbon monoxide with an inert gas in a pressure vessel (Reference 2).

Reference 1: The carbon and boron concentra
tion control in GaAs crystalsgrown by LEC method '
N.Sato et.al., 6th Conf. On SI III-Vmaterials, Tor
onto (1990) Document 2: Japanese Patent Laid-Open No. 1-192793

[0008]

However, in the methods according to the above-mentioned conventional documents 1 and 2 for supplying carbon from carbon monoxide or the like in the atmospheric gas, the concentration of carbon monoxide in the furnace during crystal growth is set to a predetermined value. Even when trying to control to the value of, the fluctuation of the carbon monoxide concentration could not be effectively suppressed, and stable control could not be performed.

As a result of investigating the cause of this variation, the following has been found. That is, the oxygen released from carbon monoxide is
It reacts with a graphite jig such as a heater used for growth to generate carbon monoxide. And while growing up,
The surface of the jig becomes rough and the jig deteriorates. Therefore, it has been found that as the number of times of crystal growth increases, the same growth conditions as the first time cannot be maintained, and it becomes difficult to grow a single crystal containing a desired carbon concentration distribution uniformly.

Therefore, even if the carbon concentration is made uniform by a certain number of times of crystal growth and a single crystal can be obtained over the entire length, a single crystal is obtained by another number of times of crystal growth but the carbon concentration becomes non-uniform. In addition, a phenomenon in which a polycrystal was generated in an excess portion and a single crystal could not be obtained due to the nonuniformity occurred, and the yield was not good.

Further, due to the reaction between carbon monoxide and graphite, the weight of the heater and the graphite jig near the heater are gradually reduced, and a new jig has to be replaced on the way, resulting in economical loss. It was great.

It is an object of the present invention to use a hydrocarbon gas having a low reactivity in place of a carbon monoxide gas having a high reactivity with respect to a jig without deteriorating the jig used for growth. An object of the present invention is to provide an economical method for producing a compound semiconductor single crystal, which enables stable growth of a single crystal having a small variation in carbon concentration with good reproducibility.

Another object of the present invention is to use the GEC according to the LEC method.
An object of the present invention is to provide a method for producing a compound semiconductor single crystal that can achieve the above object with an aAs single crystal.

Another object of the present invention is to provide a method for producing a compound semiconductor single crystal, which can further reduce the production cost by using an inexpensive mixed gas.

[0015]

A method for producing a compound semiconductor single crystal according to the present invention is a method for producing a compound semiconductor single crystal by cooling and solidifying a raw material melt obtained by heating a raw material in a furnace filled with an inert gas. In the method of growing a crystal, a hydrocarbon gas was introduced into the furnace, and the concentration of the hydrocarbon gas in the furnace was controlled during the crystal growth to control the carbon concentration contained in the crystal to a predetermined value. It is a thing.

Further, the LEC method is effective in the present invention. That is, while filling the atmosphere gas in the furnace consisting of the pressure vessel, the crucible is installed, the raw material and the sealant placed in the crucible are heated and melted, and the seed crystal is brought into contact with the GaAs melt obtained in the crucible. While pulling up the seed crystal, GaA
The method for producing the s single crystal is particularly effective.

In these methods for producing a compound semiconductor single crystal, a gas having a structural formula of C _n H _{2n + 2} (n is a natural number) is used as a hydrocarbon gas that fills the container with an inert gas during crystal growth. Is preferred.

[0018]

In the furnace for the LEC method, as a graphite jig used for manufacturing a single crystal, for example, a susceptor for supporting the crucible, a heater for heating the crucible, or a heat retention for maintaining the temperature of the crucible. A plate or the like is installed, and this graphite jig is easily deteriorated in the presence of oxygen.

Therefore, when a hydrocarbon gas is used as a gas to be introduced into the furnace to contain carbon as an impurity in the crystal, unlike the case where carbon monoxide is used, the hydrocarbon gas contains oxygen. Therefore, oxygen is not liberated and does not react with the graphite jig.

Therefore, like carbon monoxide gas, oxygen liberated therefrom reacts with the graphite jig used for growth to generate carbon monoxide, and as the growth is repeated,
There is no possibility of roughening the surface of the jig and degrading the jig.

Further, in order to control the concentration of carbon contained in the crystal to a predetermined value, the number of crystal growth is increased when controlling the concentration of the hydrocarbon gas introduced together with the inert gas into the furnace during the growth. However, since there is no deterioration of the jig due to the reaction with oxygen, the control can be stably performed even under the same growth conditions as the first time, and it becomes possible to grow a single crystal having a desired carbon concentration. Since the heater made of graphite and the jig near the heater do not react with the hydrocarbon gas, the weight is not reduced over a long period of time, and it is not necessary to replace it with a new jig on the way, and there is no economical loss. .

In particular, when a GaAs single crystal is manufactured by the LEC method, a GaAs single crystal having a small carbon concentration variation can be grown with good reproducibility from the front end to the rear end of the crystal, and methane gas is used. By using a hydrocarbon gas represented by the structural formula C _n H _{2n + 2} , it is possible to manufacture at a lower cost.

[0023]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an LEC for carrying out the method of the present invention.
An example of an apparatus for producing a GaAs single crystal by the method is shown.

The manufacturing apparatus (furnace) is equipped with pBN in the pressure vessel 1.
A crucible 2 made of aluminum is installed, and the crucible 2 is integrally housed and supported in the susceptor 3. GaA in crucible 2
s melt 4 is contained, and the upper surface of the GaAs melt 4 is B ₂ O.
It is covered with a liquid sealant 5 composed of ₃ . A crucible shaft 6 is attached to a lower portion of the crucible 2 so that the crucible 2 can be rotated and can be raised and lowered. On the other hand, a crystal pulling shaft 7 is provided above the crucible 2, and a seed crystal 8 is attached to the lower end of the pulling shaft 11. A heater 9 for heating is provided on the outer peripheral portion of the crucible 2 so as to surround the crucible 2. Heater 9
The outer circumference of the crucible 2 and the heater 9 are surrounded by the crucible 2
A heat insulating plate 10 for keeping the internal temperature is provided. The above-mentioned susceptor 3, heater 9 and heat insulating plate 10 are all made of graphite.

Further, various piping systems are connected to the pressure vessel 1 in order to keep the inside of the pressure vessel under a predetermined atmosphere gas and under a predetermined gas pressure. Piping system 11 shown in the lower left of the figure
Is a system for supplying an atmospheric gas, and is provided with a mixed gas cylinder 12 filled with a mixed gas in which Ar gas is mixed with a small amount of methane (CH ₄ ) gas and a pure gas cylinder 13 filled with a pure gas of Ar in parallel, By opening and closing the valves 14 and 15, it is possible to selectively or simultaneously supply the mixed gas or the pure gas into the pressure vessel 1.

In the piping system 16 shown in the upper left, the upper side is a pressure gauge 17 for measuring the pressure in the pressure vessel 1, and the lower side is the opening and closing of a valve 18 to collect the atmospheric gas in the pressure vessel 1. The gas concentration measuring device 19 measures the concentration of hydrocarbon gas in the atmosphere gas. Piping system 20 shown on the right
Is an exhaust system for discharging the gas in the pressure vessel 1 by opening and closing the valve 21.

Next, an example in which a GaAs single crystal is manufactured using the GaAs single crystal manufacturing apparatus will be described together with a comparative example.

(Embodiment 1) The mixed gas cylinder 12 contains A
A mixed gas in which 5% of methane gas was mixed in r gas was added.
First, only the valve 15 is opened and pure Ar gas is supplied from the gas cylinder 13 into the pressure vessel 1, so that the As composition becomes excessive in the pBN crucible 2 under a pressure of 20 kg / cm ^2.
20 kg of aAs melt 4 was prepared. After forming the melt, the valve 21 is used to remove bubbles in B ₂ O ₃ which is the liquid sealant 5.
To open part of the atmospheric gas inside the container 1
The internal pressure was reduced to 3 kg / cm ² and the mixture was left for 1 hour.

Then, the valve 14 was opened in addition to the valve 15, and pure Ar gas and mixed Ar gas containing methane gas were simultaneously supplied from the gas cylinders 13 and 12 into the pressure vessel 2. At this time, the valve 18 was also opened, the methane gas concentration was measured by the gas concentration measuring device 19, and the opening and closing of the valves 14 and 15 were controlled so that the methane gas concentration in the atmosphere gas in the container 4 was 1000 ppm.

After that, the carbon concentration in the crystal was set to 2.5 × 10 5.
The pressure inside the container is 20 kg / cm ² and the concentration of methane gas inside the container is 1000 ppm by controlling the opening and closing of the valves 14 and 15 while monitoring the pressure gauge 17 and the gas concentration measuring device 19 aiming at ¹⁵ / cm ^3. And the seed crystal 3 is melted.
10 GaAs crystals 4 having a diameter of 110 mm and a length of 350 mm were pulled up.

(Example 2) 20 kg under the same conditions as in Example 1
After preparing the GaAs melt 4 of Example 1, the concentration of methane gas in the pressure vessel 1 was maintained at 3000 ppm with the aim of adjusting the concentration of carbon contained in the crystal to 6.0 × 10 ¹⁵ / cm ^3. Ten crystals having the same shape as in (1) were pulled up.

Comparative Example 1 Crystals were grown using the apparatus shown in FIG. The mixed gas cylinder 12 was filled with a mixed gas in which 5% of carbon monoxide (CO) gas was mixed with Ar gas.
Under pressure of 20 kg / cm ² , 20 kg of GaAs melt 4 which makes As excessive composition is prepared in the crucible 2 made of pBN, and then valves 14 and 15 are opened / closed to form pure Ar in the container.
Gas and Ar gas containing carbon monoxide gas are simultaneously supplied to the container 2 so that the carbon monoxide gas concentration in the container is 100.
It was set to 0 ppm. Even after this, the pressure in the container is kept at 20
kg / cm ² , 1000ppm carbon monoxide gas concentration in the container
To maintain the carbon concentration in the crystal at 2.5 × 10 ¹⁵ / cm ³
Aiming at this, 10 crystals having the same shape as in Example 1 were pulled up.

(Comparative Example 2) GaA under the same conditions as in Comparative Example 1
After producing 20 kg of s melt, in the same manner as in Comparative Example 1, pure Ar gas and Ar gas containing carbon monoxide gas were supplied into the container 1 from the gas cylinders 12 and 13, and one of the inside of the container was supplied. The carbon oxide gas concentration was adjusted to 3000 ppm. Even after this, the pressure in the container was kept at 20 kg / cm ² , the carbon monoxide gas concentration in the container was kept at 3000 ppm, and the carbon concentration in the crystal was adjusted to 6.0 × 10 ¹⁵ / cm ³ Ten crystals having the same shape as in Example 1 were pulled up.

[0034]

[Table 1]

In Table 1, as a result of examining the polycrystal generation positions (in mm) of a total of 40 crystals pulled by the methods of Examples 1 and 2 and Comparative Examples 1 and 2, a single crystal was obtained. The number of crystals is shown. The crystals grown by the methods of Examples 1 and 2 are all single crystals, and it can be seen that the single crystals can be grown stably as compared with the methods of Comparative Examples 1 and 2.

FIG. 2 shows changes in the amount of change in weight of the graphite heaters used in Examples 1 and 2 and Comparative Examples 1 and 2 depending on the number of crystal growths. The weight change amount of the heater before growth is set to 0. The weight was measured after growing the crystal. The weight of the heater used in Examples 1 and 2 is the same as Comparative Example 1,
It can be seen that there is almost no decrease in weight as compared with 2. Further, the surface of the heater 9 used in the methods of Examples 1 and 2 had almost no surface roughness even after the growth of 10 crystals.
On the other hand, the surface of the heater 9 used in Comparative Examples 1 and 2 was considerably rough.

Next, one crystal was randomly selected from the single crystals grown in Examples 1 and 2, and a sample having a thickness of 5 mm was sampled from the positions of 30 mm, 180 mm, and 330 mm from the tip of each crystal. Then, both surfaces of each sample were polished to be mirror-finished. Then, the carbon concentration of each sample was measured by the infrared absorption method, and the distribution of carbon concentration in the crystal was examined. The result is shown in Figure 3.
Shown in.

Similarly, the crystals grown in Comparative Examples 1 and 2 were randomly selected one by one from the single crystals, and the crystals were grown in the same manner as the crystals grown by the method of Example. The distribution of carbon concentration was investigated. The results are shown in Fig. 4.

From FIGS. 3 and 4, it can be seen that even when methane gas is used as in the case of carbon monoxide, the variation can be controlled to be small with respect to the desired concentration.

(Other Examples) Even when a crystal is grown using ethane gas (CH ₃ CH ₃ ) gas or propane (CH ₃ CH ₂ CH ₃ ) gas instead of methane (CH ₄ ) gas, The crystals could grow stably. Further, the grown single crystal had a small variation with respect to the desired carbon concentration.

Although each of the above embodiments relates to the LEC method, in addition to this, Czochralski (CZ:
Czochralski) method, vertical gradient coagulation (VGF: Vertical gra
dient freeze) method, Vertical Bridgeman (VB: Vertical)
Bridemann) method, vertical zone melting (VZM: Vertical Zon)
e Melt) method is also effective. Even with a manufacturing apparatus in which a graphite jig is not installed in the furnace, a single crystal having a uniform carbon concentration in the growth direction can be obtained by implementing the present invention.

[0042]

【The invention's effect】

(1) According to the invention described in claim 1, since an inert gas into which a hydrocarbon gas is introduced is used as an atmosphere gas in the furnace and oxygen is not introduced into the furnace, a graphite jig used for oxygen and growth is used. The chemical reaction can be effectively prevented, and the life of the graphite jig is significantly longer than that of the conventional method in which carbon monoxide gas is introduced. Also, since the reactive gas is not generated due to the chemical reaction between the graphite jig and oxygen,
The hydrocarbon gas concentration during growth can be precisely controlled, and a single crystal having a uniform carbon concentration distribution can be stably manufactured even if the number of times of growth increases. Therefore, a compound semiconductor single crystal having more uniform electric characteristics can be produced at low cost, and the production cost of an element using these as a substrate can be reduced.

(2) According to the invention described in claim 2, L
Since the method is applied to the method for producing a GaAs single crystal by the EC method, a desired GaAs single crystal with a small variation in carbon concentration can be stably produced from the front end to the rear end of the crystal with good reproducibility.

(3) According to the invention described in claim 3, since the general and inexpensive gas whose structural formula is C _n H _{2n + 2} is used as the hydrocarbon gas, the production cost is further reduced. be able to.

[Brief description of drawings]

FIG. 1 is a G according to the LEC method for carrying out the method of the present invention.
The schematic block diagram of an aAs single crystal manufacturing apparatus.

FIG. 2 is an explanatory diagram showing changes in the amount of change in weight of a heater used when a crystal was grown by each of the methods of Examples and Comparative Examples.

FIG. 3 is an explanatory diagram comparing the carbon concentration in the growth direction of the crystal grown by this example and the crystal grown by the conventional method in order to obtain a crystal having a carbon concentration of 2.5 × 10 ¹⁵ / cm ³ .

FIG. 4 is an explanatory diagram comparing the carbon concentration in the growth direction of the crystal grown by the present invention and the crystal grown by the conventional method in order to obtain a crystal having a carbon concentration of 6.0 × 10 ¹⁵ / cm ³ .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 pressure vessel 2 pBN crucible 3 susceptor 4 GaAs crystal 5 liquid sealant 6 crucible support shaft 7 crystal pulling shaft 8 seed crystal 9 heater 10 heat retaining plate 11 piping system 12 mixed gas cylinder 13 pure valve 14 valve 15 valve 16 piping system 17 Pressure gauge 18 Valve 19 Gas concentration measuring device 20 Piping system 21 Valve

Claims (3)

[Claims] 1. A method of growing a compound semiconductor single crystal by cooling and solidifying a raw material melt obtained by heating a raw material in a furnace filled with an inert gas, wherein a hydrocarbon gas is introduced into the furnace. Then, the concentration of carbon gas contained in the crystal is controlled by controlling the concentration of hydrocarbon gas in the furnace during crystal growth. 2. A method for producing a compound semiconductor single crystal according to claim 1, wherein a furnace consisting of a pressure vessel is filled with atmospheric gas and a crucible is installed, and the raw material and the sealant placed in the crucible are charged. G melted in the crucible by heating and melting
A method for producing a compound semiconductor single crystal, which is an LEC method of producing a GaAs single crystal by pulling the seed crystal while bringing the seed crystal into contact with an aAs melt. 3. The method for producing a compound semiconductor single crystal according to claim 1, wherein the hydrocarbon gas mixed with the inert gas has a structural formula of C _n H _{2n + 2} (n is a natural number). Method for producing compound semiconductor single crystal using.