WO2011160293A1 - Efficient heat shield for silicon single crystal furnace - Google Patents

Abstract

An efficient heat shield for silicon single crystal furnace is disclosed, which comprises an outer layer (1) of the heat shield, an inner layer (2) of the heat shield, a thermoelectric battery module (4), a cool source module (5) and heat insulating materials (3). The thermoelectric battery module (4), at the other side of which the cool source module (5) is located, is provided attaching to the inner layer (2) of the heat shield. The space between the cool source module (5) and the outer layer (1) is filled with the heat insulating materials (3). During the pulling of single crystal, the surface temperature of the inner layer (2), as a hot source of the thermoelectric battery module (4), is generally above 500℃, and the cool source module (5) is used as cool source of the thermoelectric battery module (4). The heat is conducted from the high temperature zone to the low temperature zone so that exhausted heat can be reused after being partly converted into electrical power by the thermoelectric battery module (4). Meanwhile, the surface temperature at the inner side of the heat shield is decreased under the action of the cool source module (5), thereby contributing to the increase of longitudinal temperature gradient within the crystal and then to the increase of crystal growth speed.

Description

 Crystal furnace high efficiency heat screen

 The invention relates to the technical field of photoelectric conversion material manufacturing equipment, in particular to a silicon single crystal furnace high efficiency heat screen.

Background technique

 The Czochralski method is a CZ straight-drawing single crystal method. The polycrystalline silicon contained in the quartz crucible is melted by resistance heating and maintained at a temperature slightly higher than the melting point of silicon. Under the protection of an inert gas, the crystal is introduced and placed. Shoulder, shoulder, equal diameter growth, finishing, crystal removal, etc., complete the growth of silicon single crystal. Due to the higher melting point of silicon (1420 ° C), a large amount of electrical energy is required in the process of pulling a single crystal. Therefore, from the consideration of reducing energy consumption and arranging the gas flow field in the single crystal furnace, the single crystal thermal field has basically introduced a heat shield device. Compared to the open thermal field, energy consumption is greatly reduced and the life of the thermal field components is improved. At the same time, due to the introduction of the heat shield device, the longitudinal temperature gradient of the crystal is increased, the pulling speed is increased to some extent, the productivity is increased, and the cycle is shortened.

 However, the conventional heat shield device is generally an inner and outer composite device, the outer layer is made of graphite or carbon/carbon composite material, and the inner layer is made of heat insulating material. The average speed of the average is 0. 6~0. 9mm/min, the average speed is 0. 6~0. 9mm/min.

 d T , 3 Τ ,

 V λ λ

 P Δ H d η d η

 The above formula is the theoretical value of the crystal growth rate. It can be seen from the above formula that the larger the longitudinal temperature gradient of the crystal, the larger the crystal growth rate is 3⁄4^. Due to the limitation of the maximum longitudinal temperature gradient that the heat shield can provide, the space for the rise in speed is very limited.

In the prior art, the publications CN101575731A and CN1782141A both provide a water jacket device for increasing the longitudinal temperature gradient, but this solution excessively occupies the space inside the furnace chamber and affects the furnace chamber. The distribution of the gas flow also adversely affects the detection of the shape of the single crystal rod. A method of reducing the temperature of the inner surface of a heat shield by adding a cooler to the heat shield is disclosed in U.S. Patent No. 2,001,304,302, issued to A. However, in this way, the high temperature and high grade thermal energy of the surface of the ingot are wasted. Did not achieve the purpose of resource reuse.

Summary of the invention

 The technical problem to be solved by the present invention is: The conventional heat shield is improved to realize the reuse of the high-temperature heat energy emitted from the surface of the ingot and to increase the pulling speed of the single crystal production.

 The technical solution adopted by the present invention to solve the technical problem is: a high-efficiency heat screen of a silicon single crystal furnace, comprising an outer layer of a heat shield and an inner layer of a heat shield, filling a space between the outer layer of the heat shield and the inner layer of the heat shield Insulation material, a temperature difference battery module and a cold end module are arranged between the outer layer of the heat shield and the inner layer of the heat shield, and the cold end module is closely attached to the outer layer of the temperature difference battery module.

 The temperature difference battery module is in close contact with the inner layer of the heat shield.

 The cold end module is a coiled or tubular heat exchanger that uses liquid or gas as a coolant.

 The coolant of the cold junction module is water or argon.

 The cone angle of the thermoelectric cell module and the cold junction module is the same as or less than 5 degrees from the cone angle of the inner layer of the heat shield.

 The height of the thermoelectric module and the cold junction module account for 20% and 80% of the total height of the thermal screen, and the thickness of the cold junction module is 10 30.

The distance between the lower edge of the cold junction module and the lower edge of the heat shield is 2 (T300m _m

The invention has the beneficial effects that the inner layer of the heat shield and the cold end module constitute the high temperature and low temperature ends of the temperature difference battery module, so that electric energy can be output. At the same time, due to the lower temperature of the cold junction module, the surface temperature of the inner layer of the heat shield is lowered by heat conduction, the radiation heat exchange between the inner layer of the crystal rod and the heat shield is enhanced, and the longitudinal temperature gradient in the crystal rod is increased. By controlling the temperature of the cold junction module, the growth rate of the crystal can be indirectly promoted. Under the premise of not affecting the crystal quality, the crystal pulling speed can be greatly improved, the production efficiency is improved, and the production efficiency is lowered. Cost.

 The analysis of the thermal field shows that the longitudinal temperature gradient of the single crystal silicon rod near the crystalline interface portion plays a leading role in the increase of the pulling rate. The farther away from the crystallization interface, the less obvious the effect on the pulling rate. Compared with the prior art, the present invention is directed to a key part that affects the pulling rate, and provides a solution that can realize waste heat utilization and increase the longitudinal temperature gradient of the ingot and increase the pulling speed. It does not occupy the cavity space, does not affect the flow of gas in the cavity, and does not affect the appearance detection of the single crystal rod and the capture of the diameter control signal.

BRIEF DESCRIPTION OF THE DRAWINGS - Figure 1 Schematic diagram of the structure of the present invention

 Figure 2 The present invention causes a change in the longitudinal temperature gradient in the ingot

 In the figure: 1. The outer layer of the heat shield; 2. The inner layer of the heat shield; 3. The thermal insulation material; 4. The temperature difference battery module; 5. The cold end module; 6. The heat shield support plate; 7. The coolant pipe; 8. The temperature difference Battery cable.

detailed description

As shown in FIG. 1, a high-efficiency heat shield of a silicon single crystal furnace of the present invention comprises a heat shield outer layer 1, a heat shield inner layer 2, a heat insulating material 3, a temperature difference battery module 4, a cold end module 5, and a coolant pipe 7 , Temperature difference battery cable 8. The temperature difference battery module 4 is disposed adjacent to the inner layer 2 of the heat shield, and the cold end module 5 is disposed after the temperature difference battery module 4, and the space between the cold end module 5 and the outer layer 1 of the heat shield is filled with the heat insulating material 3. In the process of pulling the single crystal, the surface temperature of the inner layer 2 of the heat shield is usually above 500 ° C. As the hot end of the temperature difference battery module 4, the cold end module 5 serves as the cold end of the temperature difference battery module 4, and the high temperature region conducts heat to the low temperature region. The partial heat is converted into electric energy by the temperature difference battery module 4, and the purpose of reusing waste heat is achieved. At the same time, under the action of the cold junction module 5, the surface temperature of the inner layer 2 of the heat shield is also lowered, thereby contributing to enhancing the longitudinal temperature gradient inside the crystal and increasing the growth rate of the crystal. The material of the heat shield inner layer 2 and the heat shield outer layer 1 may be any one of isostatic graphite, carbon/carbon composite material or metal molybdenum. The cold end module 5 is a coil type or tubular heat exchanger which uses a liquid or a gas as a coolant, and has a truncated cone shape in cross section. The cold end module 5 is internally provided with a coolant passage. In order to maintain the temperature required for the cold junction of the battery module 4. The cold end module 5 has a thickness of 10 to 30 Å. The temperature difference battery module 4 and the cold end module 5 have the same taper angle as the inner layer 2 of the heat shield, and the height is 20% to 80% of the total height of the heat shield.

 In actual operation, the present invention is placed on the heat shield support plate 6 to form a closed thermal field. The flow rate of the coolant is adjusted by detecting the coolant outlet temperature and the set draw speed. The temperature of the outer surface of the inner layer 2 of the heat shield is indirectly controlled to control the longitudinal temperature gradient of the crystal to match the set pull speed value.

 The following is a comparison of the simulation analysis of two single crystal thermal fields using a conventional thermal screen and the thermal screen of the present invention:

 Comparison 1: Comparison of longitudinal temperature gradients in the crystal.

 The invention is applied in a single crystal furnace. After model analysis, when the wall temperature of the cold junction module is 60 °C, the longitudinal temperature in the crystal is compared from the crystal interface to the height of the crystal 500 如图 as shown in Fig. 2. As can be seen from the figure, after applying the present invention, the longitudinal temperature gradient in the crystal rises from the original 3500 K/m to 6000 K/m, which is nearly doubled. If the coolant flow rate is increased and the wall temperature of the cold junction module is lowered, the longitudinal temperature gradient in the crystal will be lower and the crystal pulling speed will be higher.

 Comparison 2: Crystal growth interface and crystallization interface V/G ratio

The defects in the Czochralski crystal are basically formed during crystal growth and cooling, and are related to the growth rate and temperature gradient of the crystal interface. It is generally considered that the closer the V/G of the crystal interface is to the critical value, the better the crystal quality is. 00134cnT2/min. k。 The value of the critical value is generally considered to be 0. 00134cnT2/min. k. 0015 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ~0. 00295. The 002~0. 003. The range of the value of the V/G ratio of the crystallization interface is 0. 002~0. 003. It can be seen that, after applying the invention, after the crystal pulling speed is increased by 120%, the V/G value of the crystal interface does not increase but decreases. That is, after application of the present invention greatly improve the pulling rate, the quality of the crystal ₄₁ no adverse to violence.

Claims

 1. A high-efficiency heat shield for a silicon single crystal furnace, comprising a heat shield outer layer (1) and a heat shield inner layer (2), in a space between the heat shield outer layer (1) and the heat shield inner layer (2) Filling the heat insulating material (3), characterized in that: a temperature difference battery module (4) and a cold end module (5) are arranged between the outer layer of the heat shield (1) and the inner layer of the heat shield (2), and the cold end module (5) Adhere to the outer layer of the thermoelectric battery module (4).  2. The high efficiency heat shield of a silicon single crystal furnace according to claim 1, wherein: the temperature difference battery module (4) is in close contact with the inner layer of the heat shield (2).  3. The high efficiency heat shield of a silicon single crystal furnace according to claim 1, wherein: the cold end module (5) is a coil type or a tube type heat exchanger which uses a liquid or a gas as a coolant.  4. The high efficiency heat shield of a silicon single crystal furnace according to claim 3, wherein: the coolant of the cold end module (5) is water or argon.  5. The high efficiency heat shield of a silicon single crystal furnace according to claim 1, characterized in that: the cone angle of the temperature difference battery module (4) and the cold end module (5) and the cone of the inner layer of the heat shield (2) The angles are the same or the deviation does not exceed 5 degrees.  6. The high efficiency heat shield of a silicon single crystal furnace according to claim 1, wherein: the height difference between the temperature difference battery module (4) and the cold end module (5) accounts for 20% and 80% of the total height of the heat shield. The cold end module (5) has a thickness of 10 30 7. The high efficiency heat shield of a silicon single crystal furnace according to claim 1, wherein: the lower edge of the cold end module (5) is 2 (T300 _{m m} ) from the lower edge of the heat shield.