JPS62230694A - Production of gaas single crystal - Google Patents

Abstract

PURPOSE:To obtain a GaAs single crystal, suitable as substrates for ultrahigh-speed and ultrahigh-density IC and having a low carbon concentration and high uniformity in the growth direction in high yield with high reproducibility, by repeatedly bubbling a raw material melt by a specific method and pulling up a crystal from the raw material melt by a liquid- encapsulated high-pressure pulling up process. CONSTITUTION:A crucible 12 is placed in a crucible receiver 16 in a high-pressure vessel 11 and a heater 13 for heating the crucible 12 is installed in a furnace member consisting of an AlN crucible wall 19, AlN heat shield 20 and AlN top plate. Raw materials Ga and As and encapsulating agent of B2O3 with <=200ppm moisture content are put in the crucible 12 and Ar gas is introduced from a gas cylinder 24 and pressure. The raw materials are then heated with the heater 13 to give a raw material melt 19 and encapsulating agent layer 15. A valve 23 is then opened to reduce the pressure in the vessel 11 below the pulling up pressure to carry out bubbling and the interior of the vessel 11 is repressured. The above- mentioned operation is repeated several times and the crucible 12 is rotated periodically in the forward and reverse directions through a motor 17 and controller 18 at the same time of the number of revolutions is increased and decreased to stir the melt 14 and the sealing agent 15. A seed crystal 25 is pulled from the melt 15 to grow the titled single crystal.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides G
The present invention relates to a method of manufacturing an aAs single crystal, and more particularly to a method of manufacturing a GaAs single crystal that produces a single crystal with a low carbon concentration and high uniformity of carbon concentration at a high yield.

(Prior Art) GaAs single crystals have electron mobility several times higher than that of Sl at room temperature, and therefore have recently been widely used as substrates for ultrahigh-speed ICs. IC substrates are required to be semi-insulating and have uniform electrical properties, and undoped semi-insulating GaAs single crystals directly synthesized using PBN crucibles are gaining popularity due to their high purity and high mobility. being developed.

This directly synthesized undoped crystal exhibits semi-insulating properties because residual shallow donors (mainly silicon) are compensated by residual shallow acceptors (mainly carbon), and excess shallow acceptors are further compensated by deep donors (E L 2). Carbon is an important impurity that controls the electrical properties of crystals. Crystallization with high carbon concentration A s-g
Although the resistivity of row becomes high, the surface resistance after heat treatment becomes low, and in extreme cases, it becomes 106[ΩcI!] for P type. ]
Thereafter, the resistance decreases and so-called thermal transformation occurs. Also, MES
It is known that the threshold voltage of an FET changes depending on the carbon concentration (A ppl, P hys,
45 (1984) 459).

Therefore, in order to produce ultra-high-speed, ultra-high-density ICs with good yield, it is essential that the carbon concentration be controlled to a certain predetermined value and that there be no variation between wafers or between lots. However, it is known that the segregation coefficient of carbon in GaAs is larger than 1, and the effective segregation coefficient Kef'f'
is said to be 1.44 (J, Cryst,
71 (1985) 240).

That is, the carbon concentration in the crystal is generally defined by the following formula.

NC-No -Kef'f' (1-g) ""r
f″″l Here, No is the initial carbon concentration in the melt, and g is the solidification rate. - As an example, the calculation result of the above formula when Keff'-1,44 is shown in FIG. From this, the carbon concentration (Nc/No) will be 1.4 to 0.7 between g-0.1 and 0.8, which is normally used as a wafer, and a difference of about twice will inevitably occur. become. This not only limits the rate at which wafers with a predetermined carbon concentration can be obtained from a single crystal, but also has the drawback of complicating the wafer manufacturing process, such as having to sort wafers by carbon concentration. Ta. For this reason, the GaAs single crystal produced by the conventional LEC method does not have sufficient uniformity as a substrate for ultra-high-speed, ultra-high-density ICs, and the carbon concentration cannot be controlled.
In addition, it has been difficult to provide uniform substrates from wafer to wafer and from lot to lot in large quantities and at low cost.

By the way, it is known that the carbon concentration in the crystal is affected by the amount of water in B2O3, which is the sealant, and that the higher the amount of water, the lower the carbon concentration (A ppl p
Hys, Lett; 44 (1984) 7
(see 4).

This is thought to be because oxygen dissociated by water decomposition combines with carbon in the melt to form carbon monoxide, which is discharged into the gas phase. However, the higher the water content, the more likely B2O3 becomes cloudy, the more frequently twins and polycrystals occur, and the single crystallization rate decreases. Furthermore, even if the carbon concentration decreases, the carbon concentration is still controlled by the segregation phenomenon, resulting in problems such as concentration differences in the growth direction. It is impossible to produce crystals with a uniform carbon concentration and a uniform carbon concentration in the growth direction with a high yield.

There is also a method in which the raw material melt under high pressure is placed under a pressure lower than the pulling pressure to generate bubbles from the melt and then pulled (JP-A-58-187500 and JP-A-5
9-83999). This method is called bubbling, and it is known that impurities in the melt are more actively removed and the purity of the melt is improved. As a result, St mainly decreases, even when using HB method polycrystal as the raw material.
Semi-insulating GaA without doping with impurities such as chromium
There is an advantage that s single crystal can be obtained. This means that Si is B2O
It is thought that this is because 3 is reduced to become SiO, which is discharged into the gas phase. Furthermore, it is thought that the reaction between the moisture in B2O3 and carbon is also promoted. However, since the carbon concentration in the crystal is affected not only by the residual carbon in the raw materials but also by the carbon mixed in from the furnace components, B2O, which has a low moisture content,
When No. 3 was used, no significant decrease in carbon concentration was observed.

In addition, as a method for preventing the contamination of carbon from furnace members, there is a method of replacing the carbon members with sintered aluminum nitride furnace members (see Japanese Patent Laid-Open No. 80-228492). However, with this method, even if the carbon concentration is reduced, there is still a concentration difference in the growth direction, and it is not possible to produce crystals with a high yield with a low carbon concentration and a uniform carbon concentration in the growth direction, which is necessary for IC substrates. There wasn't.

(Problems to be Solved by the Invention) As described above, with the conventional method, GaAs single crystals with low carbon concentration and uniform carbon concentration in the growth direction, which are necessary for ultra-high-speed, ultra-high-density IC substrates, can be produced with good yield. It was difficult to do so.

The present invention has been made in consideration of the above circumstances, and its purpose is to obtain a GaAs single crystal with low carbon concentration and high uniformity of carbon concentration in the growth direction with good reproducibility and high yield. An object of the present invention is to provide a method for manufacturing a GaAs single crystal.

[Structure of the Invention] (Means for Solving the Problems) The gist of the present invention is to use aluminum nitride as a furnace member and to bubble the raw material melt multiple times.

The inventors of the present invention believe that AI! Using a pulling device using N furnace parts, we conducted various investigations on the water content and bubbling conditions in B2O3 as a sealant, the carbon concentration of crystals, and the uniformity of carbon concentration in the growth direction. In addition, we have newly discovered conditions under which crystals with uniform carbon concentration in the growth direction can be obtained. That is, when crystal growth was performed after repeating bubbling several times using B203 with a low water content, there was a tendency for the difference in carbon concentration in the growth direction to decrease as shown in FIG. Here, A in the figure is a conventional method without bubbling, and the carbon concentration is high and the concentration difference in the growth direction is large.

B is an example of one bubbling, and although both the carbon concentration and the concentration difference in the growth direction are smaller than A, it cannot be said to be sufficient as an IC substrate. C is an example of bubbling twice, and the carbon concentration is 1. OX 1016 [cII-3] or less, and the concentration difference in the growth direction is also extremely small, providing sufficient characteristics as an IC substrate. D is an example of bubbling three or more times, and has substantially the same characteristics as C.

In addition, when the melt and B2O3 are stirred by periodically increasing/decreasing and reversing the crucible rotation speed and rotation direction at the same time as bubbling, as shown in E (bubbling 2 times) and F (bubbling 3 or more times) in Figure 4, Furthermore, it was found that the difference in carbon concentration was reduced, and crystals with clearly improved uniformity and low carbon concentration were obtained.

The present invention focuses on such points, and includes a crucible filled with a raw material melt and a sealant that covers the surface thereof, a heating element arranged around the crucible to heat the crucible, and a heating element arranged around the crucible to heat the crucible. A GaAs single crystal is pulled from the raw material melt in the crucible by the LEC method using a pulling device comprising a heat shield placed in the crucible, and a high-pressure container housing the crucible, the heating element, and the heat shield. In the method for producing a GaAs single crystal, aluminum nitride is used as the material of the heat shield, and the pressure in the container is lowered to a pressure lower than the pulling pressure with respect to the raw material melt melted under high pressure. In this method, after bubbling is performed at least twice, the pressure inside the container is set to a pulling pressure to pull the GaAs single crystal.

(Function) According to the above method, by using A or i7N as the furnace member, it is possible to prevent the incorporation of carbon from the furnace member, and by bubbling the raw material melt two or more times. , the carbon concentration and the difference in carbon concentration in the growth direction can be made sufficiently small to values that can be used as an IC substrate. Therefore, the reproducibility of the specific resistance after A s-grown and heat treatment, and the FET threshold voltage between wafers and between lots is improved, making it possible to improve the reproducibility of device characteristics and the device manufacturing yield. .

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic diagram showing a single crystal manufacturing apparatus used in a method according to an embodiment of the present invention. In the figure, 11 is a high pressure vessel, 12
13 is a heater, 14 is a raw material melt, 15 is B2O3 as a sealant, 16 is a crucible holder, 17 is a crucible rotation motor, 18 is a crucible rotation controller, 19 is A
NoN Crucible All, 20 is ANoN Heat Shield, 2
1 is an A, l'N top plate, 22 is a gas inlet valve, 23 is a gas outlet valve, 24 is a gas cylinder, and 25 is a seed crystal.

Pulling device main body and A, ll'N furnace parts 19.20°2
The configuration of 1 itself is well known. After putting the raw material and sealant into a crucible 12 housed in a high-pressure container 11 and applying pressure, the raw material melt 14 and B2O are heated by a heater 13.
3 sealant layer 15 is obtained.

Here, B2O3 is one with low water content (dry B
203) is used. Next, in order to produce a single crystal with a low carbon concentration and a uniform concentration in the growth direction, the following operation is performed.

After opening the gas outlet valve 23 to make the pressure in the high pressure vessel 10 lower than the pulling pressure, the gas outlet valve 23 is closed and left for a while to perform so-called bubbling. after that,
The gas introduction valve 22 is opened, the pressure is again increased to a level higher than the pulling pressure, and bubbling is repeated several times. At the same time, crucible 1
6 is periodically rotated forward and backward by a crucible rotation motor 17 to stir the melt 14 and B20315. The rotation is controlled by a crucible rotation controller 18. Thereafter, the seed crystal 25 is brought into contact with the melt 14 and pulled up to grow a single crystal.

Next, a method for producing a GaAs single crystal using the above-mentioned apparatus will be described in more detail.

Inner diameter 150 [8F PBN crucible 12a and As
A total of ~3 [KSF] and B203 as a sealant (water content ~10,100 pp) and ~ [100 [g] were placed in a high-pressure container 11, and a GaAs melt 14 was obtained by a direct synthesis method.Next, Open the gas outlet valve 23 and remove the high pressure container 1.
The pressure inside 1 was lowered to ~3 [atm] and left for ~30 minutes. After pressurizing the inside of the container 11 again to ~50 [atm], bubbling was repeated five times. At the same time, the crucible 12 was rotated forward and backward at a cycle of 1 minute from 0 to 20 [rp11] as shown in FIG. After that, wait for the temperature to stabilize and sow the seeds.The diameter ~ gofml, the weight ~2.5
[Kg] <100>GaAs single crystal was obtained.

The obtained single crystal was cut into wafers, and the carbon concentration was measured at three points, the tip, the center, and the end.
As shown in F in the figure, 2.9 to 2.4×1015[Ol
"3], which was approximately uniform from the tip to the end, and the carbon concentration was also low. The specific resistance of each wafer was 3 to 2 x 10' [Ωc-I!] from the tip to the end, and after heat treatment (8
The specific resistance after (50℃, 15 minutes, As atmosphere) is also ~2X10
7 [011 or more, there was no thermal alteration and it was uniform.

2. Apply silicon to the above wafer at 150 [K e V].
5X 1012[α-2] ion implantation, D-MES
An FET was created and its threshold voltage was measured. The average threshold voltage of 300 FETs arranged in the radial direction of the wafer is 'c' at the positions corresponding to the tip, center and end.
tL4:irL -3,51[V], -3,51
[V], -3,56[V], and the difference is 50
[It was within mV1.]

In the same way, when 10 crystals were produced in succession, no polycrystals or twins were observed, and the same carbon concentration and electrical properties as above were obtained, with good reproducibility between lots. It turned out that there was enough.

Furthermore, when single crystals were created by varying the water content of B2O3 to ~200 ppm and the number of bubbling cycles from 2 to 4 times, a uniform carbon concentration in the growth direction was obtained in all cases. Thereby, single crystal production can be performed by selecting various conditions depending on the purpose.

As described above, according to the method of this embodiment, a single crystal with a low carbon concentration and high uniformity in the growth direction can be obtained with good reproducibility, thereby improving the controllability of the threshold voltage of MESFET from wafer to wafer and from lot to lot. .

Therefore, by using it as a substrate for ultra-high-speed IC,
There are effects such as a significant improvement in device manufacturing yield. Furthermore, since B2O3 with a low water content is used, polycrystals and twin crystals are hardly observed, GaAs single crystals can be obtained with good reproducibility and high yield, and manufacturing costs can be reduced. Furthermore, it has the advantage that it can be easily implemented without significantly modifying the conventional lifting device.

It should be noted that the present invention is not limited to the method of the embodiment described above, and can be implemented with various modifications without departing from the gist thereof. For example, the number of times of bubbling can be changed as appropriate within the range of two or more times. Furthermore, B20
The water content of No. 3 may be within the range of 200 [ppm] and may be adjusted as appropriate. In addition, it is not necessarily necessary to increase or decrease the rotational speed of the crucible or reverse the rotational direction during bubbling.
It may be omitted depending on conditions such as the carbon concentration required for the GaAs single crystal to be manufactured and the concentration difference in the growth direction.

[Effects of the Invention] As detailed above, according to the present invention, as a furnace member A)
By bubbling the raw material melt at least twice using N, it is possible to produce a GaAs single crystal with low carbon concentration and high uniformity of carbon concentration in the growth direction with good reproducibility and high yield. Therefore, it is possible to provide an excellent GaAs substrate as a substrate for ultra-high-speed ICs, and its usefulness in the field of semiconductor manufacturing is tremendous.

[Brief explanation of drawings]

Figure 1 is a schematic configuration diagram showing a single crystal manufacturing apparatus used in an embodiment method of the present invention, Figure 2 is a schematic diagram showing changes in the rotation direction and rotation speed of the crucible, and Figures 3 and 4 are Each figure is for explaining the present invention in detail, and FIG. 3 is a characteristic diagram showing changes in carbon concentration with respect to solidification rate according to the conventional method.
FIG. 4 is a characteristic diagram showing the change in carbon concentration with respect to the position in the crystal growth direction. 11... High pressure container, 12... Crucible, 13... Heater, 14... Melt, 15... B2O3, 16...
・Crucible holder, 17... Crucible rotation motor, 18...
・Crucible rotation controller, 19...Aj7N crucible oar, 20...Ai heat shield, 21...
A, 17N) Tube plate, 22... Gas introduction valve, 23... Gas outlet valve, 24... Gas cylinder. Applicant's agent Patent attorney Takehiko Suzue Level 1 (x 10' 3) - JJJ (No/No) -

Claims (3)

[Claims] (1) A crucible filled with a raw material melt and a sealant that covers the surface of the crucible, a heating element placed around the crucible to heat the crucible, and a heat shield placed around the heating element. , a method for producing a GaAs single crystal by pulling and producing a GaAs single crystal from the raw material melt in the crucible by the LEC method using a pulling device comprising a crucible, a heating element, and a high-pressure container containing a heat shield. , using aluminum nitride as the material of the heat shield, and bubbling the raw material melt melted under high pressure at least twice to lower the pressure in the container to a pressure lower than the pulling pressure. , wherein the GaAs single crystal is pulled by setting the pressure in the container to a pulling pressure.
A method for producing an As single crystal. (2) During the bubbling, the number of rotations of the crucible is periodically increased or decreased, or the direction of rotation of the crucible is reversed.
A method for producing an As single crystal. (3) The sealant has a water content of 200 [ppm].
] The method for producing a GaAs single crystal according to claim 1, characterized in that the following B_2O_3 is used.