JPH0329035B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method and apparatus for manufacturing semiconductor single crystals such as Si, Ge, GaAs, GaP, etc.

Methods for producing semiconductor single crystals can be roughly divided into the pulling method and the boat method. The pulling method is a method of growing a single crystal by immersing a seed crystal in a raw material melt in a crucible and pulling it up while rotating.
On the other hand, in the boat method, the raw material melt is placed in a boat made of materials such as quartz, PBN, or Si ₃ N ₄ , and the seed crystal is gradually solidified to grow a single crystal. It's a method.

The solid-liquid interface gradually moves inside the boat,
Depending on how the temperature distribution is given, it is divided into horizontal Bridgeman method (HB method), gradient-freeze method (GF method), etc.

In the GF method, the heater and reaction tube are not moved relative to each other. Gradually reduce the power of the heater to lower the temperature distribution. Since the temperature distribution has a gradient in the longitudinal direction, if the entire temperature distribution is lowered equally, the solid-liquid interface will move from the end of the boat where the seed crystal is located to the opposite end.

[Prior Art] The conventional GF method has the disadvantage that it is difficult to control the actual movement of the solid-liquid interface. The temperature distribution within the raw material melt and crystal inside the boat must be estimated based on the output of the heater and the temperature measured by the thermocouple. However, since the output of the heater changes and the reaction tube, boat, and raw material melt have a considerably large heat capacity, the heater output and the temperature of the raw material melt do not necessarily maintain a direct proportional relationship.

Furthermore, since the thermocouple measures the temperature between the heater and the reaction tube, it is not possible to directly determine the exact temperature of the melt or crystals in the boat.

JP-A-58-156599 (published on September 17, 1982) proposes a crystal growth apparatus that uses the GF method to keep the moving speed of the solid-liquid interface constant. This includes a high temperature furnace divided horizontally into four parts and a low temperature furnace divided into two parts. Four fixed thermocouples are attached to the high temperature furnace to measure the temperature just outside the four-part heater.

Another thermocouple is provided that can be moved horizontally between the reaction tube and the heater. The temperature of this thermocouple is kept constant. For GaAs, this temperature Tm is the melting point
The temperature should be 1238℃.

This thermocouple is sent along the length of the boat at a constant speed, and the power of the heater is adjusted so that the temperature of this thermocouple remains at Tm.

In this way, since the point where the moving thermocouple is located corresponds to the solid-liquid interface, the solid-liquid interface can be moved at a constant speed.

This device is said to have the advantage of making it easier to grasp the solid-liquid interface and controlling the movement of the solid-liquid interface more accurately.
It does not correctly indicate the temperature of the raw material melt or solid in the reaction tube. Therefore, even if the temperature of the moving thermocouple is maintained at Tm, the solid-liquid interface position and the moving thermocouple position often do not correspond. The solid-liquid interface may exist at a point isolated from the thermocouple, or this difference may change as the crystal grows. This is because the temperature measurement point is between the boat and the heater, and as the crystal grows, the amount of heat released from the solidification part changes, and the temperature gradient in the crystal changes in the horizontal and circumferential directions. A significant difference arises.

As described above, the most common method is to measure temperature using a thermocouple, but since the thermocouple is always located outside the reaction tube, it has the disadvantage that the position of the solid-liquid interface cannot be precisely controlled.

[Object of the Invention] An object of the present invention is to visually recognize the position of the solid-liquid interface and the shape of the solid-liquid interface and to predetermine them in the growth process of a semiconductor single crystal by the GF method, which is one of the boat methods. The present invention provides a method for accurately controlling the position and shape of the object, and a manufacturing apparatus that implements this method.

[Structure] The present invention relates to a method and apparatus for manufacturing a semiconductor single crystal using the GF method, which is one of the boat methods. While moving at a predetermined speed, the heater is adjusted according to the advance or delay of the solid-liquid interface relative to the speed of the imaging section, which is the standard for the crystallization progress speed. The temperature is controlled so that crystal growth progresses at a constant rate.

The configuration of the present invention will be explained below with reference to the drawings.

FIG. 1 shows, in a schematic cross-sectional view, an apparatus for carrying out the method of the invention. The heaters 1a to 1g are a group of independently controllable heaters arranged along the length of the reaction tube 2 held in the horizontal direction. Among these, heaters 1a to 1e are cylindrical high temperature heaters,
These are resistors such as Kanthal wires formed into cylindrical shapes. For example, heaters 1b and 1c located around the solid-liquid surface, as shown in FIG.
The viewing window 12 is formed by dividing into upper, lower, left, right, etc., and communicating inward from the upper surface side, so that the temperature can be adjusted independently. 1b' and 1c'.

The heaters 1f and 1g are also single cylindrical heaters, and are for low temperatures.

The horizontally long reaction tube 2 is placed inside the heaters 1a to 1g, and a boat 3 made of, for example, quartz is placed on the high temperature side of the reaction tube 2, and a seed is placed at the end of the boat 3 on the low temperature side. Crystal 4 is placed.

As shown in the figure, inside the boat 3, there is a raw material melt 13.
and the solidification part 14 coexist. The boundary is the solid-liquid interface 6. The solid-liquid interface 6 is an isothermal surface of the melting point of the semiconductor.

At the end of the reaction tube 2 on the low temperature side, a solid 5 of group V element is placed.
is placed. This is an example for the growth of a - group chemical semiconductor single crystal. For example, GaAs,
These include GaP, InSb, InSb, InAs, and InP. V
Group elements have high dissociation pressure and are easily released from solidified parts and melts. For this purpose, a group V element is introduced into the reaction tube 2 to maintain its vapor pressure appropriately.

The low temperature section heaters 1f and 1g maintain the temperature of the V group element constant and maintain the vapor pressure at a desired value. V
Group elements include P, As, Sb, etc.

In reality, in order to suppress convection between a portion of the boat 3 and a portion of the group V element, a partition wall is often provided in the middle. A small hole is made in the partition wall for the V group gas to pass through.

The viewing window 12 is provided at a position such that the solid-liquid interface 6 exists directly below it.

A photographing section of a TV camera 7 for observing the solid-liquid interface 6 is arranged above the viewing window 12.

An image of the solid-liquid interface 6 observed by the TV camera 7 is processed by an image processing device 8. The position and shape of the solid-liquid interface 6 in the viewing window 12 are data-processed by the image processing device 8, and compared with normal data based on past performance accumulated in the computer 9. Control 10.

Move at a speed based on past performance that yields crystals with the desired crystal defect density and impurity distribution.
Under normal conditions, the solid-liquid interface 6 exists at a certain position of the TV camera 7. The driving device 11 is configured to send the imaging section of the TV camera 7 at a predetermined crystal growth rate obtained from past results.

Suppose that the solid-liquid interface 6 is shifted to the right (lower temperature side) from its normal position on the image. This is because the power of the heater is too high. Correct the misalignment by reducing the power of the heater.

Suppose that the solid-liquid interface 6 is shifted to the left (toward the high temperature side) from its normal position. This means that the heater power is too low. This deviation can be corrected by increasing the heater power.

Since this is a visual observation using a TV camera, the left and right tilt of the solid-liquid interface can also be seen.

If the isothermal surface is vertical, the solid-liquid interface is also vertical. However, because the degree of heat dissipation is different between the top and bottom surfaces of the boat, the solid-liquid interface is often not vertical but inclined. Because convection and radiation are active on the top of the boat, it is slightly cooler than the bottom.
Therefore, the solidified portion 14 forms an inclined surface that protrudes toward the melt 13.

In addition to this vertical tilt of the solid-liquid interface,
There is also a lateral slope. A lateral inclination appears on the liquid level of the boat and the surface of the solidified part. This may be a convex or concave curved surface when viewed from the solidified portion, or may be tilted from side to side.

Since the observation is done with a TV camera, only the solid-liquid interface exposed on the surface can be seen. However, depending on the exposed shape of the surface of the solid-liquid interface, not only the horizontal inclination and curvature, but also the vertical inclination can often be estimated to some extent. By combining this with observation data from other sensors, we can more accurately determine the slope of the solid-liquid interface.

Since the power of the upper, lower, left, and right heaters of the multi-divided heaters 1b' and 1c' can be controlled independently, the inclination of the solid-liquid interface can be adjusted. There is not only a forward inclination of the solid-liquid interface, but also a left and right inclination.
Such an inclination can also be corrected by using multi-segment heaters 1b' and 1c'. The computer 9 calculates such adjustment operations and adjusts the heater output through the temperature controller 10.

The multi-divided heaters 1b' and 1c' must be divided into at least two parts. This is to independently and freely control the solid-liquid interface 6. However, as long as it is divided into two or more, it may be divided into three, four, five, etc. The greater the number of divisions, the more delicate temperature control becomes possible.

In the example shown in FIG. 1, as already explained, the group V element 5 is placed at the end of the reaction tube 2. This is necessary in the case of growth of -group compound semiconductors. Group V elements are volatile and have a high vapor pressure near the melting point of the compound, so that group V elements are likely to escape from the surfaces of the solidified and melted parts. For this reason, it is necessary to apply a constant vapor pressure of the group V gas.

However, in the case of growing semiconductors such as Si and Ge,
This is unnecessary.

Instead of the TV camera 7, an imaging section of an image fiber imaging device may be provided in the viewing window.

[Operation] An image near the solid-liquid interface is taken with the TV camera 7 through the viewing window. In this way, we know the position, shape, and slope of the solid-liquid interface.

Compare predetermined shapes, positions, and inclinations, and make sure that the predetermined positions, shapes, etc. are achieved.
Adjust heater output.

By this, (1) the TV moves the solid-liquid interface position at a predetermined speed;
It can always be held in a fixed position relative to the camera.
In other words, the crystal growth rate can be maintained constant.
As a result, the occurrence of crystal defects caused by fluctuations in growth rate can be suppressed.

(2) The solid-liquid interface can be maintained in the desired shape (generally flat is desirable).

As a result, crystal defects caused by strain at the interface can be suppressed.

[Example] Using the above-described apparatus of the present invention and the method of the present invention,
GaAs single crystal growth was carried out.

The following materials were charged into the quartz boat.

Ga: 1300g Si: 246mg A seed crystal was placed on the shelf at the right end of the quartz boat. This was placed at the left end of the reaction tube 2 made of quartz. 1418g of As was put into the other end. Reaction tube 2 was evacuated and sealed. Place the reaction tube in an electric furnace.

The heater was energized to melt the material in the boat 3 and form a raw material melt. The melt 13 in the boat 3 and the seed crystal 4 are connected. Thereafter, the temperature of the heater group (electric furnace) was lowered, and the TV camera 7 was moved from right to left in the figure at a constant speed of 3 to 15 mm/H.

An image of the vicinity of the solid-liquid interface was taken with the TV camera 7 through the viewing window 12, and by processing this image, the position, shape, and inclination of the solid-liquid interface were confirmed. The heater was fed back so that the solid-liquid interface was at a constant position relative to the TV camera 7.

With this, the width is 65 mm, the length is 380 mm, and the weight is 2700 mm.
We were able to obtain a GaAs single crystal of g.

This single crystal was cut diagonally into (100) wafers, etched with a KOH solution, and the etch pit density was counted to determine the etch pit density EPD. As a result, over the entire length of the ingot,
The EPD was found to be less than 1000/cm ² .

It was a single crystal with few crystal defects and low dislocation density.

[Effects] (1) It is one of the boat methods. Conventionally, in the GF method, the growth state was monitored only by temperature, so the position, speed of movement, shape, inclination, etc. of the solid-liquid interface were not always known, but the present invention Since the liquid interface is visually observed, detailed information such as the position, movement, speed, shape, and tilt of the solid-liquid interface can be obtained.

(2) The present invention can maintain a constant crystal growth rate and suppress crystal defects that occur due to fluctuations in the growth rate, thereby improving yield and quality.

(3) The present invention can maintain the solid-liquid interface in a flat shape. Therefore, crystal defects caused by interface distortion are reduced, yield is increased,
Quality improves. It has the following effects.

[Brief explanation of drawings]

FIG. 1 shows an apparatus for implementing the invention. Second
The figure is an explanatory diagram of a heater used in a part of the apparatus shown in FIG. 1a, 1b, 1c, 1d, 1e, 1f, 1g...
... Divided heater, 2 ... Reaction tube, 3 ... Boat, 4 ... Seed crystal, 5 ... Group V element, 6 ... Solid-liquid interface, 7 ... TV camera, 8 ... Image processing device,
9... Computer, 10... Temperature controller, 11
... Drive device, 12 ... Viewing window, 13 ... Raw material melt, 14 ... Solidification section.

Claims (1)

[Claims] 1. Put semiconductor raw materials in a boat, place a seed crystal on a shelf at the end of the boat, put it into a reaction tube, and if necessary, place a seed crystal on the opposite side of the boat in the reaction tube. A volatile solid is placed in the reactor tube, the reaction tube is sealed, and the semiconductor raw material is melted by placing it in a group of horizontally arranged heaters whose power can be controlled independently, and the temperature of the heater group is lowered. In the method for manufacturing a semiconductor single crystal in which a single crystal is grown in a boat following the seed crystal, an imaging unit of a TV camera or an image fiber is placed in a viewing window of a heater located at the top of the boat or inside the heater. and moving at a predetermined speed, observing a solid-liquid interface between the crystal and the melt, and controlling the output of the heater group so that the position and shape of the solid-liquid interface are set to a predetermined value. A method for manufacturing semiconductor single crystals. 2. A method for producing a semiconductor single crystal according to claim 1, characterized in that the heater arranged around the solid-liquid interface is divided into multiple parts, such as vertically, horizontally, etc., and whose temperature can be adjusted independently. . 3 A cylindrical heater group arranged horizontally and capable of independently controlling power, a temperature controller for adjusting the output of the heater group, a semiconductor raw material, and a seed crystal formed so that it can be placed on a shelf at the end. A TV camera that observes the solid-liquid interface inside the boat from between the boat, a horizontally long reaction tube that can be sealed with the boat placed inside, and a heater located at the top of the boat with the boat placed inside the reaction tube. , or an image fiber imaging device, a driving device having a function of moving an image part of the TV camera or the image fiber imaging device at a predetermined speed, and processing and fixing image information from the TV camera or the image fiber imaging device. An image processing device for determining the position, shape, etc. of the liquid interface is compared with the position, shape, etc. of the solid-liquid interface obtained by the image processing device, and the temperature controller is adjusted so as to approach a predetermined solid-liquid interface. A semiconductor single crystal manufacturing device characterized by comprising a controlling computer. 4. An apparatus for manufacturing a semiconductor single crystal according to claim 3, characterized in that the heater around the solid-liquid interface is divided into multiple parts, such as vertically, horizontally, etc., and is configured with heaters that can independently control the temperature.