CN113638038A

CN113638038A - Single crystal furnace with low oxygen impurity content

Info

Publication number: CN113638038A
Application number: CN202111028089.9A
Authority: CN
Inventors: 丁俊岭; 徐志辉; 李宇卿; 肖原; 陈齐平
Original assignee: East China Jiaotong University
Current assignee: East China Jiaotong University
Priority date: 2021-09-02
Filing date: 2021-09-02
Publication date: 2021-11-12
Anticipated expiration: 2041-09-02
Also published as: CN113638038B

Abstract

The invention discloses a single crystal furnace for reducing oxygen impurities in the furnace, and mainly relates to a guide cylinder for preserving heat and guiding airflow. The guide shell consists of a central heat-insulating structure and a supporting structure. The distance from the bottom of the guide shell to the melt is gradually reduced from inside to outside, and meanwhile, the radial cross-sectional area of a channel formed by the bottom of the guide shell and the melt is kept unchanged. The design of the guide cylinder in the invention is beneficial to removing the silicon monoxide impurity gas at the free liquid level of the melt in the single crystal furnace, effectively reducing the oxygen impurities in the single crystal furnace and finally obtaining the high-quality semiconductor single crystal.

Description

Single crystal furnace with low oxygen impurity content

Technical Field

The invention belongs to the field of a monocrystalline silicon growth device by a Czochralski method, and particularly relates to a furnace body design scheme for reducing the content of oxygen impurities in a monocrystalline furnace.

Background

The czochralski method is the mainstream method for producing large-size single crystal silicon. Impurities are inevitably introduced during the preparation of single crystal silicon, wherein oxygen oxides have a significant influence on the quality of single crystal silicon. The oxygen impurities are present in the silicon crystal primarily as oxygen precipitates. Excessive oxygen precipitate size can induce secondary defects such as dislocation, stacking fault and the like in a silicon wafer body, thereby causing silicon wafer slippage and warping and weakening the electrical and mechanical properties of the silicon wafer. Meanwhile, the integrity of the thin gate oxide in the discharge area of the microelectronic device can be reduced, leakage current and even short circuit are easily caused, and the semiconductor device is caused to fail. Oxygen impurities in the silicon melt come from the melting of a high-temperature quartz crucible, wherein a small part of the oxygen impurities enter the silicon crystal through fractional condensation at a solid-liquid interface, and most of the oxygen impurities are evaporated in the form of silicon monoxide (SiO) gas at a free liquid level of the melt and are carried away by high-purity argon flowing through the free liquid level of the melt.

The distance between the bottom of the guide shell and the melt in the existing Czochralski method single crystal furnace device is gradually increased from inside to outside, so that the radial cross-sectional area of a channel formed by the bottom of the guide shell and the melt is gradually increased from inside to outside. When the high-purity argon gas flows through the free liquid surface of the melt, the flow speed is gradually reduced, so that the capability of taking away the SiO gas is greatly reduced.

Disclosure of Invention

The invention aims to provide a furnace body design scheme beneficial to reducing oxygen impurities in a single crystal furnace, so as to solve the problem of insufficient oxygen impurity removal capability caused by the design of a guide cylinder in the traditional single crystal furnace.

In order to achieve the purpose, the invention adopts the following technical scheme.

A single crystal furnace with low oxygen impurity content comprises a furnace body and a heat preservation cylinder, wherein a guide cylinder is arranged close to the heat preservation cylinder; a quartz crucible is arranged below the guide cylinder, a melt is contained in the quartz crucible, and a crystal is positioned right above the center of the melt; when the furnace works, the distance between the bottom of the guide shell and the melt is gradually reduced from inside to outside, and high-purity inert gas is introduced from the top of the furnace wall and sequentially flows through the crystal, the guide shell, the melt, the quartz crucible and the heat-preserving cylinder.

A further development of the invention is that the radial cross-sectional area of the channel formed by the bottom of the guide shell and the melt remains constant.

The invention is further improved in that the guide shell is composed of a heat insulation material and a support material.

The invention is further improved in that the minimum distance between the guide shell and the crystal is 10-40 mm.

The invention is further improved in that the minimum distance between the guide shell and the melt is 10-30 mm.

The invention is further improved in that the taper of the inner cylinder of the guide shell is 30-60 degrees.

The invention is further improved in that the heat insulation material of the guide shell is made of carbon-carbon double-core material.

The invention is further improved in that the support material of the guide shell is made of any one of molybdenum, tungsten-molybdenum alloy, titanium alloy or graphite.

The present invention has the following advantageous technical effects.

The invention provides a design scheme of a guide cylinder in a Czochralski silicon furnace, which ensures that the distance between the bottom of the guide cylinder and a melt is gradually reduced from inside to outside, and meanwhile, the radial cross-sectional area of a channel formed by the bottom of the guide cylinder and the melt is kept unchanged, so that the capability of removing oxygen impurities at the free liquid level of the melt in the single crystal furnace is improved, and the problem of insufficient oxygen impurity removal capability caused by the gradual increase of the distance between the bottom of the guide cylinder and the melt in the traditional single crystal furnace from inside to outside is effectively solved.

Drawings

FIG. 1 is a schematic view of a single crystal furnace according to the present invention.

Fig. 2 is a partial schematic view of a draft tube.

Fig. 3 is a three-dimensional cross-sectional view of the draft tube.

FIG. 4 is a graph showing the distribution of SiO impurities above the free liquid level of the melt when the design of the present invention is used.

FIG. 5 shows the distribution of SiO impurities above the free surface of the melt using conventional draft tube designs.

In the figure: 1-furnace body; 2-a heat preservation cylinder; 3-crystals; 4-a guide cylinder; 5-quartz crucible; 6-melting; 7-high purity inert gas; 8-a heat preservation structure; 9-support structure.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings.

As shown in figures 1-4, the invention relates to a czochralski silicon furnace with low oxygen impurity content, which mainly relates to a guide cylinder 4 for heat preservation and air flow guiding. The draft tube 4 is composed of a central heat insulation structure 8 and a support structure 9. The heat preservation structure 8 is made of carbon composite material. The supporting structure 9 is made of any one of molybdenum, tungsten-molybdenum alloy, titanium alloy or graphite. The guide shell 4 is positioned above the melt 6 and outside the crystal 3 and is arranged next to the heat preservation shell 2. In the process of crystal growth, high-purity argon 7 is introduced from the top of the furnace wall 1 and sequentially flows through the crystal 3, the guide cylinder 4, the melt 6, the crucible 5 and the heat-preserving cylinder 2. In order to improve the capability of carrying impurity gases by the high-purity argon 7, the product of the distance between the lower edge of the guide cylinder 4 and the free liquid level of the melt 6 and the radial distance of the guide cylinder is kept constant, and the minimum distance between the guide cylinder 4 and the melt 6 is 10-30 mm. In addition, the taper of the inner cylinder of the guide cylinder (4) is 30-60 degrees, and the minimum distance between the guide cylinder and the crystal (3) is 10-40 mm.

In order to illustrate the feasibility and effectiveness of the scheme, the monocrystalline silicon growth furnace adopting the traditional guide cylinder design and the Czochralski method designed by the guide cylinder is adopted to carry out global oxygen impurity transport simulation, and the beneficial effects of the design are researched. As shown in fig. 4 and 5, the simulation target was a 12-inch single-crystal silicon growth furnace. Comparing fig. 4 and fig. 5, it can be found that, compared with the traditional draft tube design scheme, the concentration of the SiO impurities above the free liquid level of the melt is lower by adopting the design of the invention, which is more beneficial to the volatilization of the oxygen impurities in the melt area and reduces the content of the oxygen impurities in the melt.

The reaction apparatus of the present invention is not limited to the illustrated examples, and various modifications such as changing the transition shape of the bottom of the draft tube are possible. All modifications which can be derived or suggested directly from the disclosure of the present invention by a person skilled in the art are to be considered within the scope of the present invention.

Claims

1. A single crystal furnace with low oxygen impurity content is characterized in that a furnace wall (1) and a heat preservation cylinder (2) are sequentially arranged from inside to outside, and a guide cylinder (4) is arranged close to the heat preservation cylinder (2); a crucible (5) is arranged below the guide cylinder (4), a melt (6) is contained in the crucible, and the crystal (3) is positioned right above the center of the melt (6); during operation, the distance between the bottom of the guide shell (4) and the melt (6) is gradually reduced from inside to outside, and high-purity inert gas (7) is introduced from the top of the furnace wall (1) and sequentially flows through the crystal (3), the guide shell (4), the melt (6), the crucible (5) and the heat-preserving cylinder (2).

2. A low oxygen impurity content single crystal furnace as claimed in claim 1, wherein the radial cross-sectional area of the channel formed by the bottom of the draft tube (4) and the melt (6) is kept constant.

3. A single crystal furnace in accordance with claim 1, characterized by that, the draft tube (4) is composed of a heat insulating structure (8) and a supporting structure (9).

4. A single crystal furnace in low oxygen impurity content according to claim 1, characterized in that the minimum distance between the draft tube (4) and the crystal (3) is 10-40 mm.

5. A single crystal furnace in accordance with claim 1, characterized in that the minimum distance between the draft tube (4) and the melt (6) is 10-30 mm.

6. A single crystal furnace with low oxygen impurity content according to claim 1, characterized in that the draft tube (4) has an inner tube taper of 30 ° to 60 °.

7. A single crystal furnace in accordance with claim 3, characterized by that, the heat-insulating structure (8) is made of carbon-carbon composite material.

8. A single crystal furnace with low oxygen impurity content according to claim 3, characterized in that the supporting structure (9) is made of any one of molybdenum, tungsten-molybdenum alloy, titanium alloy or graphite.