JPH0616493A - Method for growing gallium arsenide single crystal - Google Patents

Abstract

PURPOSE:To obtain the gallium arsenide single crystal which is low in oxygen content and high in purity. CONSTITUTION:Gallium (Ga) and arsenic (As) are charged respectively into a crucible 7 and an arsenic vessel 16 and a pump 4a is operated to evacuate the inside of an outer vessel 4 to a vacuum. Heaters 10a, 10b are operated to raise the temp. in the respective parts of the hermetic vessel 1 up to 200 to 600 deg.C. This temp. is maintained until the arsenic oxide in the arsenic vessel 16 and a vapor pressure control section 11 and the gallium oxide on the surface of the gallium raw material in the crucible 7 are removed to the outside of the hermetic vessel 1. A pushing up shaft 17 is then risen to press the seal 5 of the hermetic vessel 1 and to hermetically seal the hermetic vessel 1; thereafter, the single crystal is grown by the method similar to the conventional methods.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of gallium arsenide single crystals used for substrates for ICs and semiconductor lasers, and in particular, gallium arsenide single crystals enabling the growth of high purity crystals with a low oxygen content. About how to grow.

[0002]

2. Description of the Related Art A vapor pressure control pulling method has been known as one of the methods for growing a gallium arsenide single crystal (hereinafter referred to as a single crystal). The outline of the production of a single crystal by the vapor pressure controlled pulling method will be described with reference to FIG.

FIG. 2 shows a production state of a single crystal by a vapor pressure control pulling apparatus. Reference numeral 4 is a pump 4a
An outer container capable of being evacuated by means of the above, and a sealed container 1 composed of an upper container 2 and a lower container 3 which are vertically separable by a seal portion 5 is provided in the outer container 4. A lower rotary shaft 8 is installed inside the sealed container 1 so as to be rotatable about its axis, and the susceptor 6 is mounted on the lower rotary shaft 8.
The crucible 7 made of pBN is supported via. Furthermore,
An upper rotary shaft 12 is installed above the crucible 7 coaxially with the susceptor 8 so as to be rotatable and vertically movable. on the other hand,
Reference numeral 11 is a vapor pressure control unit, and heaters 10a, 10b and 11a are installed outside the upper container 2 and the lower container 3 and around the vapor pressure control unit 11, respectively.

Reference numeral 13 is an observation window for observing the inside of the sealed container 1, and reference numeral 14 is an upper rotary shaft 12 and an upper container 2, a lower rotary shaft 8 and a lower container 3, and a seal portion 5.
Is B ₂ O ₃ that seals each. Reference numeral 16 is an arsenic container installed at the bottom of the sealed container 1.

A melt Y of gallium arsenide is placed in the crucible 7. The heating is performed by the heaters 10a and 10b, and the single crystal T is obtained by gradually pulling up the upper rotary shaft 12. In this case, the atmosphere gas to be pulled up is a gas mainly containing arsenic vapor, and the pressure thereof is the vapor pressure control unit 11.
It is kept constant by the control of the heater 11a.

[0006]

In the vapor pressure controlled pulling method, oxygen is taken into the crystal through the following route. First, when controlling the vapor pressure, it is necessary to condense a certain amount or more of arsenic until the end of crystal growth.
After the growth operation is completed, a considerable amount of arsenic remains in the vapor pressure control unit 11. This arsenic condensed phase is exposed to the atmosphere during preparation for the next growth operation, and the surface is oxidized. Arsenic oxide is also charged on the surface of arsenic, which is charged as a raw material every time.
Exist, though slightly.

These arsenic oxides are sublimed by heating at the beginning of the synthesis operation to become a component of the atmospheric gas, and are taken into the melt Y when the melt Y is synthesized. Also, the sealed container 1
The inner wall surface of the will absorb water while exposed to the atmosphere,
This moisture decomposes at a high temperature during growth to become an oxygen source. Moreover, the remaining oxygen content not taken into the melt Y returns to the vapor pressure control unit 11 again and is fixed at the stage when the growth operation is completed. Therefore, when the growth operation is repeated, the amount of oxygen fixed in the vapor pressure control unit 11 gradually increases.

Further, gallium, which is another raw material component, is a liquid at room temperature, and its surface is oxidized when it is charged as a raw material, so that it can be an oxygen source like arsenic oxide. It is known that this gallium oxide (Ga ₂ O) begins to sublime at around 500 ° C (Gmelins Handbuch der
Anorganischen Chemie, 36, P166, Verlag Chemie Berin1
936).

These oxygens have at least two lattice positions in the gallium arsenide crystal (J. Schneide
r Other Applied Physics Letters 54,10,1989). One of them is a pair of arsenic vacancy-oxygen (VAs-O), which is electrically active and has a deep defect level. The other one is that oxygen enters between the bonds of gallium and arsenic and takes an interstitial position, and in this case, it becomes electrically inactive.

Further, as the oxygen in the gallium arsenide crystal, one named ELO level, which forms an energy level extremely close to the EL2 level, is known (J.
Lagowski et al Applied Physics Letters 44,336,198
Four). This ELO level exists in the crystal at a concentration equal to or higher than the EL2 level (10 ¹⁶ cm ⁻³ level).

As described above, the oxygen taken into gallium arsenide forms at least two kinds of deep defect levels. Therefore, in order to make a single crystal into a semi-insulating material used for ICs, it is necessary to change it. An extra acceptor impurity (carbon) is required to compensate. That is, the crystal becomes so impure that it is disadvantageous in terms of device characteristics. Further, it is considered that the presence of ELO located near the center of the forbidden band acts as a center of generation or recombination of carriers and deteriorates characteristics such as reverse breakdown voltage resistance of the device, and is important in the carrier compensation relation. Under the circumstances, due to the high diffusion coefficient of oxygen, the characteristics become unstable during the heat treatment in the device process, and nonuniformity of the characteristics correlated with the dislocation cells occurs. Therefore, there is a need for a method of growing a high-purity crystal that can reduce the oxygen content in the crystal and achieve semi-insulating properties even at low carbon concentrations.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and includes an outer container that can be evacuated, an openable and closable sealed container disposed in the outer container, and a sealed container that can be opened and closed. A crucible rotatably arranged around its own axis, a pulling mechanism for immersing a seed crystal in a raw material melt contained in the crucible to pull up a single crystal, and vapor pressure control in communication with the sealed container Section, and using a pulling device comprising a plurality of heaters surrounding the sealed container and heating the sealed container, the gallium held in the crucible and the arsenic raw material placed under the sealed container are heated by the heater. After synthesizing a raw material melt of gallium arsenide in the crucible and condensing a part of the arsenic raw material in the vapor pressure control unit, arsenic gas filled in the sealed container is obtained. In the growth method of a gallium arsenide single crystal which performs the raising of the gallium arsenide single crystal while controlling the pressure, the sealed container while evacuating the entire puller while opening the sealed container 200 to 600
After the temperature is maintained at 0 ° C., the sealed container is sealed again to synthesize the raw material melt.

[0013]

In the method for growing a gallium arsenide single crystal of the present invention, prior to each raw material synthesis, the sealed container is kept at 200 to 600 ° C. while the whole of the pulling device is evacuated while the sealed container is opened. After that, by inserting a step of sealing the hermetically sealed container, the arsenic raw material in the hermetically sealed container and the oxide formed on the surface of arsenic and gallium remaining in the vapor pressure control unit are mixed prior to the synthesis of the raw material melt. , Previously removed outside the sealed container.

[0014]

Embodiments of the present invention will now be described in more detail with reference to the drawings. 1 and 2 each show an example of a single crystal pulling apparatus according to the present invention.
2 shows the state before the raw material synthesis, and FIG. 2 shows the state during the single crystal pulling.

Here, the structure of the single crystal pulling apparatus according to the present invention is completely the same as that of the conventional single crystal pulling apparatus. That is, reference numeral 1 is the seal portion 5.
It is a hermetically sealed container divided into an upper container 2 and a lower container 3 via a container, and the hermetically sealed container 1 is further housed in an outer container 4 which can be evacuated by a pump 4a. Heaters 10a and 10b are installed around the sealed container 1, and heaters 11a are installed around the vapor pressure control unit 11 to provide a predetermined temperature distribution, that is, a region corresponding to the crucible 7. The maximum temperature is reached and the vapor pressure control unit 1
The sealed container 1 is heated so that the lowest and uniform temperature is 1.

Reference numeral 12 is an upper rotary shaft arranged so as to penetrate the top plate portion of the sealed container 1, and a seed crystal S is fixed to the lower end thereof. Further, reference numeral 8 is a lower rotary shaft arranged so as to penetrate the bottom of the sealed container 1, and a susceptor 6 holding a crucible 7 is installed at the upper end thereof. Further, reference numeral 14
Is B for sealing the upper rotary shaft 12 and the upper container 2, the lower rotary shaft 8 and the lower container 3, and the seal portion 5, respectively.
₂ O ₃ , reference numeral 16 is an arsenic container into which raw material arsenic is charged, reference numeral 1
Reference numeral 7 denotes a push-up shaft that is fixed to the lower end of the lower container 3 and covers the lower rotary shaft 8 so as to be vertically movable so as to be coaxial with the lower rotary shaft 8.

Here, in the crucible 7 and the arsenic container 16, gallium Ga and arsenic As, which are the raw materials for the single crystal, are placed. In addition, arsenic As has condensed in the vapor pressure control unit 11 due to the growth operation up to the previous time.

When a single crystal is produced using the above apparatus,
First, gallium Ga and arsenic As are charged in the crucible 7 and the arsenic container 16 respectively, and the pump 4a is operated to evacuate the inside of the outer container 4 while the sealed container 1 is opened as shown in FIG. , Heater 10
Operate a and 10b to increase the temperature of each part of the sealed container 1 to 200
C. to 600.degree. C., and kept as it is for a predetermined time (until oxygen is removed from the arsenic oxide in the sealed container 1 and the vapor pressure controller 11 to the outside of the sealed container 1). Here, the temperature of each part of the sealed container 1 is set to 200 ° C. to 600 ° C. When the temperature of each part of the sealed container 1 is 200 ° C. or lower, the sublimation of oxygen from the arsenic oxide is insufficient, and This is because the sublimation of gallium oxide formed on Ga occurs at 500 ° C. or higher.

In this case, in order to completely remove gallium oxide, it is desirable to set the temperature of each part of the sealed container 1 to 500 ° C. or higher. However, if the temperature of all parts of the sealed container 1 is raised, arsenic As itself will be generated. Since the vapor pressure of H 2 increases and the amount of arsenic As scattered off increases, the temperature of each part of the sealed container 1 is set to 500 ° C. or lower. In addition, only gallium Ga in the crucible 7 is set to 500 to 600 ° C.
Even if it is below 0 ℃, due to the flow of molecules by vacuum exhaust,
The removal of gallium oxide can be expected, and the scattering loss of arsenic does not have to be increased.

Next, the push-up shaft 17 is raised, the seal 5 of the hermetic container 1 is pressed to hermetically seal the hermetic container 1, and the heaters 10a and 10b are operated to change the temperature of gallium Ga to the melting point of gallium arsenide (1238 ° C.). In addition to the above heating, the arsenic As is heated to increase the arsenic partial pressure, and the melt Y of gallium arsenide is synthesized in the crucible 7.

After the synthesis of the melt Y is almost completed, the composition of the melt Y is made uniform by allowing the heater 11a to control the temperature of the vapor pressure control unit 11 and leaving it for a predetermined time. Further, after lowering the upper rotating shaft 8 and immersing the seed crystal S in the melt Y, as shown in FIG. 2, while pulling up the seed crystal S while adjusting the outputs of the heaters 10a, 10b, 11a, Single crystal T
Grows while expanding its diameter. When the single crystal T has grown to a predetermined length, the pulling temperature is slightly accelerated, the tail portion is formed, the position of the crucible 7 is lowered, and the lower end portion of the single crystal T is separated from the remaining melt Y. Furthermore, the heaters 10a, 10b,
The output of 11a is gradually reduced to gradually cool the single crystal T and the growth operation is completed.

As a result, it becomes possible to grow a high-purity semi-insulating crystal having a low oxygen content. Note that this method can be similarly applied to a vertical Bridgman device that repeatedly uses the sealed container 1 and has a vapor pressure control unit 11, or a VGF method.

[0023]

[Experimental Examples] Experimental effects will be described below with reference to experimental examples. First, 4.6 kg of arsenic As was added to the sealed container 1
Into the crucible 7 was placed 4 kg of gallium Ga while being placed in the arsenic raw material container 16 arranged at the bottom of the.
At this time, arsenic As remains condensed in the vapor pressure control unit 11 due to the growth operation up to the previous time.

To obtain gallium arsenide from 4 kg of gallium Ga, stoichiometrically, 4298 g of arsenic A is used.
s is required. Therefore, in the case of this experimental example, about 300 g
The excess content of arsenic As is the amount existing in the sealed container 1 as a gas, or the amount of scattering loss, and the amount of condensation in the vapor pressure control unit 11. The arsenic As supplement amount is determined from the arsenic remaining amount calculated from the arsenic As scattering amount in the previous growth. A small amount of Si impurity was added to the crucible 7 in order to make the single crystal T have a carrier concentration of about 10 ¹⁶ cm ^−3, which is necessary for measuring the transient response of the junction capacitance.

Next, the outer container 4 is evacuated while the seal portion 5 of the hermetic container 1 is opened, and the heater 1
The temperature of each part of the hermetically sealed container was raised to 500 to 600 ° C near the crucible and to 200 to 500 ° C in the other parts by 0a and 10b, and the temperature was maintained for about 30 minutes. Then, the hermetically sealed container 1 is sealed, and then the temperature of gallium Ga is raised to the melting point of gallium arsenide or higher and arsenic
As the temperature was raised, the melt Y of gallium arsenide was synthesized in the crucible 7. The subsequent pull-up growth is the same as the conventional one.

A single crystal T having a diameter of about 4 inches thus grown, an equivalent crystal pulled by the conventional vapor pressure raising method excluding the process of the present application and a typical single crystal obtained by the LEC method Table 1 shows the measured and compared contents of the above two levels in which oxygen is involved after the respective predetermined heat treatments. Here, as the crystal growth method, Comparative Example 1 is a conventional vapor pressure raising method, and Comparative Example 2 is a LEC method.

[0027]

[Table 1] (Note) Heat treatment 1) Rapid growth after crystal growth. 2) Gradually cool after crystal growth. And outside the furnace, 950 ℃, 20hr
After heat treatment, slowly cool.

It can be seen from Table 1 that all levels are reduced to the same level as or higher than that of the LEC crystal by incorporating the process of the present invention.
Moreover, the uniformity of the obtained single crystal T was sufficiently good without impairing the characteristics of the vapor pressure control method.

The scattered loss of arsenic As after the pulling growth is about 70 to 80 g, and the increased loss is practically no problem compared to the scattered loss of 50 to 70 g in the conventional method without the process of the present invention. It was small enough.

[0030]

As described above, according to the present invention,
Arsenic oxide in the hermetically sealed container is inserted by inserting a step of hermetically sealing the hermetically sealed container after the hermetically sealed container is kept at 200 to 600 ° C. while the whole of the pulling device is evacuated in an opened state. And gallium oxide are removed from the sealed container in advance prior to the synthesis of the raw material melt. As a result, a gallium arsenide single crystal having a low oxygen content and high purity can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a state before starting crystal growth of a compound semiconductor single crystal pulling apparatus according to the present invention.

FIG. 2 is a vertical cross-sectional view showing a situation during crystal growth in the compound semiconductor single crystal pulling apparatus according to the present invention.

[Explanation of symbols]

1 Sealed Container 2 Upper Container 3 Lower Container 4 Outer Container 4a Pump 5 Sealing Part 6 Susceptor 7 Crucible 8 Lower Rotating Shaft 10a, 10b, 11a Heater 11 Vapor Pressure Control Unit 12 Upper Rotating Shaft 13 Observation Window 14 B ₂ O ₃ 16 Arsenic Container 17 Push-up axis S Seed crystal T Single crystal Y Melt Ga Gallium As Arsenic

Claims (1)

[Claims] 1. An outer container that can be evacuated, an openable and closable sealed container disposed in the outer container, a crucible that is rotatably disposed in the sealed container about its own axis, and the crucible. A pulling mechanism for immersing the seed crystal in the raw material melt contained in the pulling mechanism to pull up a single crystal, a vapor pressure control unit in communication with the hermetic container, and a plurality of heating the hermetic container surrounding the hermetic container. Using a pulling device equipped with a heater, the gallium held in the crucible and the arsenic raw material placed under the sealed container are heated by the heater to synthesize a raw material melt of gallium arsenide in the crucible, and then the arsenic By condensing a part of the raw material in the vapor pressure control unit, the pressure of the arsenic gas filled in the sealed container is controlled to pull up the gallium arsenide single crystal. In the method for growing a muarsenic single crystal, after holding the sealed container at 200 to 600 ° C. while evacuating the inside of the outer container with the sealed container opened,
A method for growing a gallium arsenide single crystal, characterized in that the sealed container is sealed again to synthesize the raw material melt.