JPH07172971A - Apparatus for pulling up semiconductor single crystal - Google Patents

Abstract

PURPOSE:To prolong the time for passing a single crystal through a high- temperature range of >=1200 deg.C and to quickly pass through a temperature range of about 900-500 deg.C in the production of a single crystal using a semiconductor single crystal pull-up apparatus provided with a radiation screen. CONSTITUTION:The radiation screen 1 to be used in this pull-up apparatus is composed of an upper screen 2 having a three-layer structure consisting of a heat-insulation material 2a made of graphite or ceramic fiber and outer members 2b and 2c made of graphite and covering the heat-insulation material 2a and a lower screen 3 having a single layer structure and composed of graphite, quartz or fine ceramic material. The radiation heat emitting from a molten liquid 4, etc., passes through the lower screen 3 and heat the lower part of a single crystal 6 to prolong the time for passing through the above high- temperature range. The single crystal 6 in the part surrounded by the upper screen 2 is shielded from the above radiation heat and, accordingly, relatively quickly cooled to pass the temperature range of 90-500 deg.C in a short time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor single crystal pulling apparatus having a radiation screen which surrounds a pulling single crystal and is installed so that its lower end is close to the melt surface.

[0002]

2. Description of the Related Art A high-purity silicon single crystal is mainly used for a substrate of a semiconductor element. As one of the methods for producing this silicon single crystal, a cylindrical single crystal is prepared from a raw material melt in a crucible. Czochralski method of pulling up (hereinafter C
There is a Z method). In the CZ method, a crucible installed in a chamber of a semiconductor single crystal pulling apparatus is filled with a polycrystal as a raw material, the raw material is heated and melted by a heater provided on the outer periphery of the crucible, and then a seed crystal attached to a seed chuck. Is immersed in a melt, and the seed chuck is pulled up while the seed chuck and the crucible are rotated in the same direction or opposite directions to grow a single crystal.

In the above single crystal pulling apparatus, a radiation screen is installed around the single crystal pulling region as a means for increasing the pulling speed of the single crystal and preventing contamination by impurities to improve dislocation-free single crystal. It is known. FIG. 3 is a sectional view schematically showing a part of a semiconductor single crystal pulling apparatus having a radiation screen. The radiation screen 1 is a heat shield surrounding the single crystal pulling region, and is generally a conical tube having a lower end opening diameter smaller than an upper end opening diameter. The radiant screen 1 blocks the radiant heat applied to the single crystal 6 from the melt 4, the quartz crucible 5 and the like to accelerate the cooling of the single crystal 6, speed up the single crystal pulling speed and prevent the generation of crystal defects. Further, an inert gas introduced from above the chamber 7 is guided around the single crystal 6 to form a gas flow from the central portion of the quartz crucible 5 to the exhaust hole provided at the bottom of the chamber 7 through the peripheral portion. As a result, silicon oxide generated from the melt 4 or metal vapor generated from the graphite crucible 8,
It has the function of eliminating the gas that inhibits single crystallization.
In addition, 9 is a heater and 10 is a heat insulation cylinder.

[0004]

Since the cooling of the single crystal is promoted by providing the radiation screen, it is said that the frequency of occurrence of crystal defects is 900 ° C to 500 ° C.
The temperature range before and after can be passed in a short time, and the rate of single crystallization is improved by efficiently discharging silicon oxide and the like. However, 900 ° C to 50
Simply passing the temperature region around 0 ° C in a short time does not always provide a stable and high-quality wafer even after the device process. That is, since the conventional single crystal pulling apparatus having a radiation screen passes through all temperature regions in a short time, the single crystal is pulled to a high temperature region of 1200 ° C. or higher necessary for obtaining a wafer having a good oxide film withstand voltage. Cannot be retained for a long time. Also,
When the radiation screen is abolished and the pulling rate of the single crystal is reduced, the withstand voltage performance of the oxide film is improved, but the single crystallization rate is lowered and the defective rate of the device is increased due to the generation of OSF or dislocation loops. The production efficiency of crystals also decreases.

When pulling the single crystal, if the distance between the lower end of the radiant screen and the melt surface is made wider than before,
The lower end portion of the single crystal during pulling is not affected by the shielding effect of the radiation screen and is less likely to be cooled. Therefore, 120
The passage time in the high temperature region of 0 ° C. or higher becomes long, and the temperature region around 900 ° C. to 500 ° C., which receives the shielding effect of the radiation screen, can pass in a short time. However, in order to efficiently discharge silicon oxide and the like, to control the oxygen concentration in the single crystal with high accuracy, and to maintain the productivity of the single crystal, the distance between the lower end of the radiation screen and the melt surface is set. You must keep it as usual. The present invention has been made by paying attention to the above-mentioned problems of the prior art.
Provided is a semiconductor single crystal pulling apparatus provided with a radiation screen which can quickly pass through a temperature range of about 500 ° C. and can efficiently discharge silicon oxide and the like by an inert gas flow. Is intended.

[0006]

In order to achieve the above object, a semiconductor single crystal pulling apparatus according to the present invention comprises a crucible for melting a raw material of a semiconductor single crystal and a raw material in a crucible surrounding the crucible. A semiconductor single crystal puller provided with a heater for heating and a pulling mechanism for pulling a single crystal by immersing a seed crystal in a melted raw material, and a radiation screen consisting of a conical heat insulating cylinder surrounding a pulling region provided near the melt In the device, the heat insulation performance of the upper and lower parts of the radiation screen is changed at arbitrary positions, and in such a structure, the heat insulation performance of the lower part of the radiation screen is lower than the heat insulation performance of the upper part of the radiation screen. Is characterized by.

[0007]

According to the above structure, the heat insulation performance of the radiation screen surrounding the pulling region of the single crystal is different between the upper portion and the lower portion, and the heat insulation performance of the lower portion of the radiation screen is lower than that of the upper portion, so that the radiation screen is surrounded by the lower portion of the radiation screen. Part,
That is, in the portion immediately above the solid-liquid interface, the radiant heat from the melt, the quartz crucible, etc. passes through the lower portion of the radiant screen and reaches the single crystal. Therefore, the single crystal is heated and the transit time in the high temperature region becomes long. The single crystal grows, is pulled up, and the part surrounded by the upper part of the radiant screen with high heat insulation performance is cooled in the same manner as in the conventional method, so that the temperature is 900 ° C.
It can quickly pass through the temperature range around 0 ° C. Further, by keeping the distance between the lower end of the radiant screen and the melt surface as usual, it is possible to efficiently discharge silicon oxide and the like by the inert gas flow.

[0008]

Embodiments of the semiconductor single crystal pulling apparatus according to the present invention will be described below with reference to the drawings. Figure 1
Is a schematic cross-sectional view of the radiant screen and its surroundings. The radiant screen 1 is divided into an upper screen 2 and a lower screen 3 having different heat insulating properties. The upper screen 2 has a three-layer structure and includes a heat insulating material 2a made of graphite or ceramic fibers and outer members 2b and 2c made of graphite.
It has been encapsulated in. The upper screen 2 is a conical cylinder whose lower end opening is smaller than its upper end opening, and has an annular flange at its upper end. Further, a hooking portion for attaching the lower screen 3 is provided at the lower end of the upper screen 2. The lower screen 3 has a single-layer structure and is made of graphite, quartz, or fine ceramics, and a flange provided on the upper end is hooked on the lower end of the upper screen 2. 4 is a melt, 5 is a quartz crucible, and 6 is a single crystal being pulled.

Since the lower screen 3 has a one-layer structure,
It does not have the function of completely shielding the radiant heat from the melt 4 and the quartz crucible 5 unlike the conventional radiant screen. Therefore, the radiant heat from the melt 4 directly passes through the lower screen 3 or after being reflected by the inner surface of the quartz crucible 5 and then passes through the lower screen 3 to reach the lower portion of the single crystal 6 being pulled, The lower part of the crystal 6 is heated. When a conventional radiant screen is used, the lower part of the single crystal 6 is cooled by passing through a high temperature region of 1200 ° C. or higher in a short time because radiant heat is blocked. However, in the case of the present embodiment, the radiation screen is heated conversely, so that the passage time in the high temperature region is prolonged. On the other hand, since the upper screen 2 has sufficient heat insulation performance as in the conventional case, it can exhibit a rapid cooling function in the middle and low temperature regions. Therefore, when the single crystal 6 is pulled up from the lower screen 3 and surrounded by the upper screen 2, it is cooled relatively rapidly and can pass through a temperature range of about 900 ° C to 500 ° C in a short time. it can.

The distance between the lower end of the lower screen 3 and the surface of the melt 4 is maintained in the conventional size range, and the lower screen 3 exerts the rectifying effect of the inert gas. An inert gas such as argon introduced from the upper portion of the single crystal pulling apparatus flows down along the outer periphery of the single crystal 6, and then passes through the gap between the lower end of the lower screen 3 and the melt 4 to pass through the quartz crucible 5. After ascending along the inner surface, it is discharged from an exhaust hole provided at the bottom of the single crystal pulling apparatus.

FIG. 2 shows the non-defective product rate related to the breakdown voltage of the oxide film after the device process, obtained by the product obtained by using the single crystal pulling apparatus according to this embodiment and the conventional single crystal pulling apparatus equipped with a radiation screen. It is the figure compared with the product. The non-defective rate of the oxide film breakdown voltage as used herein means the ratio of the number of elements in which a large number of elements are formed on a silicon wafer and the dielectric breakdown voltage of the oxide film is 8 MV / cm or more. As is clear from the figure, the non-defective rate of the product according to the present embodiment is more than 1.5 times that of the conventional product.

Although the upper screen and the lower screen are divided in this embodiment, the present invention is not limited to this, and the upper screen having a three-layer structure and the lower screen having a one-layer structure may be integrally formed. In addition, by changing the thickness and material of the lower screen, it becomes possible to give an arbitrary heat history to the single crystal. Needless to say, the oxide film breakdown voltage characteristics are improved by eliminating the lower screen.

[0013]

As described above, according to the present invention, in a semiconductor single crystal pulling apparatus provided with a radiation screen as a means for increasing the single crystal pulling rate and improving dislocation-free single crystal, the radiation screen By making the heat insulation performance different between the upper part and the lower part and making the heat insulation performance of the lower part of the radiant screen lower than that of the upper part, the part surrounded by the lower part of the radiant screen receives radiant heat. As a result, 120
It is possible to extend the passage time in the high temperature region of 0 ° C. or higher, and it is possible to obtain a wafer having a good oxide film breakdown voltage after the device process. Further, since the single crystal surrounded by the upper part of the radiation screen is cooled in the same manner as in the conventional case,
The temperature range around 00 ° C can be passed quickly, and the generation of crystal defects is as small as that of the conventional one. By keeping the installation height of the radiation screen as usual, discharge of silicon oxide etc. by the inert gas flow can be performed. Can be performed efficiently. Furthermore, the present invention can be used to change the thickness or the material of the lower screen to give an arbitrary heat history to the single crystal, and the single crystal corresponding to various quality standards can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a radiation screen and its periphery.

FIG. 2 is a diagram comparing a non-defective product rate related to an oxide film breakdown voltage after a device process between a product according to this embodiment and a conventional product.

FIG. 3 is a schematic partial cross-sectional view of a semiconductor single crystal pulling apparatus including a radiation screen according to a conventional technique.

[Explanation of symbols]

 1 Radiation Screen 2 Upper Screen 2a Heat Insulating Materials 2b, 2c Outer Member 3 Lower Screen 4 Melt 5 Quartz Crucible 6 Single Crystal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuhiro Iida 2612 Shinomiya, Hiratsuka-shi, Kanagawa Komatsu Electronics Co., Ltd.

Claims (2)

[Claims] 1. A crucible for melting a raw material of a semiconductor single crystal, a heater for heating the raw material in a crucible around the crucible, and a pulling mechanism for dipping a seed crystal in the molten raw material to pull up the single crystal. In a semiconductor single crystal pulling apparatus provided with a radiation screen consisting of a conical heat insulating tube surrounding a pulling region above the vicinity of the melt, the heat insulating performance of the upper part and the lower part of the radiation screen may be changed at any position. Characteristic semiconductor single crystal pulling apparatus. 2. The apparatus for pulling a semiconductor single crystal according to claim 1, wherein the heat insulating performance of the lower portion of the radiation screen is lower than that of the upper portion of the radiation screen.