WO2011156976A1

WO2011156976A1 - Method for polycrystalline silicon ingot casting

Info

Publication number: WO2011156976A1
Application number: PCT/CN2010/074107
Authority: WO
Inventors: 李毕武
Original assignee: 常州天合光能有限公司
Priority date: 2010-06-19
Filing date: 2010-06-19
Publication date: 2011-12-22

Abstract

A method for polycrystalline silicon ingot casting is disclosed, which is as follows: a. using a crystal with both density and melting point higher than that of silicon as induction seed crystal for crystal growth and impurity absorption center, b. cutting the prepared crystal into single crystal wafer, c. chemically washing the resulting single crystal wafer, d. putting the washed single crystal wafer into the bottom of quartz ceramic crucible with a graphite guard board, e. then feeding silicon material into the quartz ceramic crucible, f. putting the quartz ceramic crucible into a polycrystalline growth furnace, g. evacuating the polycrystalline growth furnace and charging argon gas as a protective gas, h. heating and melting silicon material, i. adjusting the temperature to make the molten silicon material gradually solidify from the bottom to the top, j. finally finishing the growth of polycrystalline silicon by means of high temperature annealing and cooling. A method for polycrystalline silicon ingot casting by means of induction of a crystal with certain crystal orientation is disclosed. The fluctuating range of crystal quality in different zones of the crystal ingot is greatly reduced, therefore decreasing the fluctuating range of battery efficiency and improving quality of the crystal.

Description

Polycrystalline silicon ingot casting method

Technical field

The invention relates to a method for ingot casting polycrystalline silicon, belonging to the field of solar cell ingot casting.

Background technique

At present, the production of polycrystalline silicon is made of quartz ceramic crucible as a container of polycrystalline silicon. It is controlled by double temperature zone or three temperature zone, and the directional solidification is realized by the temperature gradient above and below the ingot. The silicon nitride powder coating is used as the release agent. In the solar cell ingot industry. At present, the efficiency of the battery made of polysilicon is uneven along its growth direction, the efficiency of the head and tail of the polysilicon is low, and the efficiency of the middle region is much higher than that of the cell efficiency distribution of the single crystal silicon rod.

At present, there is no method for solving the uneven distribution of polycrystalline ingot efficiency in domestic and foreign industries.

SUMMARY OF THE INVENTION In order to overcome the above drawbacks, the technical problem to be solved by the present invention is to provide a crystal using a certain crystal orientation as an induced seed crystal and a gettering center. Thereby, the crystal quality fluctuation range of different regions of the silicon ingot is greatly reduced, the quality stability of the polycrystalline silicon ingot is achieved, and the fluctuation range of the vertical battery efficiency of the silicon ingot is reduced.

In order to overcome the defects in the prior art, the technical solution adopted by the present invention to solve the technical problems thereof is as follows: A method for ingot casting polycrystalline silicon, the preparation method is as follows: a. Preparation of raw materials: using crystals having a higher density and a higher melting point than silicon The crystal growth induces the seed crystal and the gettering center; b, the prepared crystal is cut into a single wafer; c, the cut single wafer is chemically cleaned; d, the cleaned single wafer is placed with a graphite shield The quartz ceramic crucible bottom; e, then the silicon material is loaded into the above quartz ceramic crucible; f, the quartz ceramic crucible is placed in the polycrystalline furnace; g, the polycrystalline furnace is evacuated and a protective gas argon is added; h, the silicon material is heated and melted; i, the temperature is adjusted, and the molten silicon material is gradually crystallized from the bottom to the upper portion; j. finally, the high temperature annealing, cooling, and completion of the polysilicon Growth.

Further, the crystal has a certain crystal plane or crystal orientation, and after cutting, the thickness of the single wafer is 0.5 - 15 匪; the single wafer is a flat sheet exposed by a single crystal plane, and the crystal orientation of the exposed crystal face of the single wafer It is 0001 crystal orientation.

Further, the single wafer has a square or circular cross section.

Further, the inner wall of the quartz ceramic crucible has a silicon nitride coating.

Further, the crystal is sapphire or quartz or silicon carbide.

Advantageous Effects: The present invention uses a high melting point single wafer as a long crystal induced seed crystal and a gettering center, so that the growth of polycrystalline silicon greatly improves the uniformity of crystal quality, so that the cell conversion efficiency is uniformly distributed along the growth direction of the ingot. Controlling the fluctuation range of the cell efficiency distribution of the single crystal silicon rod improves the quality of the crystal.

DRAWINGS

The invention will now be further described with reference to the drawings and embodiments.

Fig. 1 is a schematic view showing the distribution trend of the efficiency of the polycrystalline silicon along the growth direction.

Wherein: a, the density and melting point are higher than the silicon single crystal wafer induced polycrystalline silicon along the growth direction battery efficiency distribution curve;

b. Distribution curve of battery efficiency along the growth direction of ordinary polysilicon.

detailed description

A method for ingot casting polycrystalline silicon, the preparation method is as follows:

1. A crystal having a higher density and melting point than silicon, such as sapphire, quartz, etc., cut into a single wafer of a certain thickness and shape. For processing, it can be cut into square, round, etc., and then organic solvent, HF and pure. Multiple ultrasonic cleaning of water;

2. Put the cleaned single wafer into a quartz pottery with a silicon nitride coating and a graphite shield. Porcelain

3. The silicon material is then placed in a quartz ceramic crucible, and the quartz ceramic crucible is placed in a polycrystalline furnace, the polycrystalline furnace is evacuated and a protective gas argon is added, and the silicon material is heated and melted;

4. Adjusting the temperature to gradually crystallize the molten silicon material from the bottom to the upper portion;

Fifth, finally through high temperature annealing, cooling, complete the growth of polysilicon.

The core of the scheme is: using a high melting point, high density single wafer as the polycrystalline growth inducing seed and gettering center, the high melting point is to prevent the single wafer from melting in the silicon liquid, and the high density is to prevent the single wafer Upward, the quality of the single wafer must ensure low impurity content and perfect crystal form. The single wafer placed in the quartz ceramic crucible is a flat sheet exposed by a single crystal face. Polycrystalline silicon and cell sheet preparation process: The present invention uses a single wafer having a higher density and higher melting point than silicon to be placed in a quartz ceramic crucible for crystal growth induction and improved impurity distribution of the silicon ingot. Before being placed, the quartz ceramic crucible is sprayed with silicon nitride, baked, and then normally filled with silicon material and dopant. After being charged into the polycrystalline furnace, it is evacuated, leak tested, argon-filled, preheated, and The process of material, stabilization, growth, annealing and cooling completes the growth of polysilicon. After the ingot is completed, the silicon wafer is opened, the silicon ingot is tested for life, the head and tail are cut off, and the silicon ingot is cut into silicon wafers on the in-line cutting machine, and then cleaned, inspected, and packaged into a battery process. During the silicon wafer ablation process, the silicon carbide portion is individually cut off. The wafer was formed by wafer faburing, diffusion, etching, PECVD coating, screen printing and sintering, and the test was performed. Compared with the crystal ingots without crystal addition, after the crystal-inducing silicon ingot is cut into silicon sheets by silicon wafer cutting, the longitudinal distribution deviation of the battery conversion efficiency of the entire silicon ingot is significantly reduced. The cell conversion efficiency of the silicon ingot without a single wafer is longitudinally distributed at 0. 156~

0 163〜。 After the insertion of a single wafer, the cell conversion efficiency of the silicon ingot is longitudinally distributed in the interval of 0. 163~

0. 168 or so, and its average conversion efficiency is not lower than the normal silicon ingot. It can be seen that the deviation of the longitudinal conversion efficiency of the silicon ingot becomes small, and the quality of the silicon ingot is greatly improved.

The invention will be further illustrated by the examples, but the examples are not intended to One step limit. The sample used in this example is a 845 X 845 X 420 mm ³ quartz ceramic crucible with a loading of 200-450 kg of silicon; the silicon carbide single wafer used is in the form of a flake and placed in the bottom of the crucible before being fed. The flat surface of the single wafer is in contact with the silicon liquid, and the thickness of the single wafer is 0.5-15 mm, and the crystal orientation effect of the exposed crystal face of the single wafer is optimally 0001 crystal orientation. Cutting the wafer into flakes is a requirement for the normal growth of polysilicon. In order to make the flat surface of the single wafer sufficiently in contact with the silicon liquid, when the single wafer is placed in the bottom of the quartz ceramic crucible, the flat surface of the single wafer is placed face up.

We used the same crystal growth process and battery production process to finally compare the battery conversion rate trends of the produced polysilicon to demonstrate the great progress achieved by the present invention.

As shown in Fig. 1, the fluctuation range of the distribution of the curve a is significantly smaller than that of the curve b, and it can be seen that the fluctuation range of the efficiency of the polycrystalline silicon cell induced by the single wafer is significantly smaller than that of the normal silicon ingot, and the standard deviation is 0. 00105, 0 . 00345. Thus, it has been proved that the invention adopts single wafer to induce polycrystalline silicon growth, which is a good method for solving the wide fluctuation range of polycrystalline battery efficiency.

Claims

Claim

1. A method for ingot casting polycrystalline silicon, characterized in that the preparation method is as follows: a. Preparation of raw materials: crystals having a higher density and a higher melting point than silicon are used as a long crystal-inducing seed crystal and a gettering center; b a prepared crystal Cutting into a single wafer; c, chemically cleaning the cut single wafer; d placing the cleaned single wafer into the bottom of the quartz ceramic crucible with the graphite shield; e, then charging the silicon material into the quartz ceramic crucible described above f; then put the quartz ceramic crucible into the polycrystalline furnace; g, vacuum the polycrystalline furnace and add protective gas argon; h, silicon material is heated and melted; i, adjust the temperature, make the molten silicon from the bottom Gradual crystallization to the upper part; j, finally by high temperature annealing, cooling, complete polycrystalline silicon growth.

The method of ingot casting polycrystalline silicon according to claim 1, wherein: said crystal has a certain crystal plane or crystal orientation.

3. The ingot casting method of polycrystalline silicon according to claim 1, wherein: said single wafer is a flat sheet exposed by a single crystal face.

The ingot casting method of polycrystalline silicon according to claim 3, wherein the crystal orientation of the exposed crystal face of the single wafer is 0001 crystal orientation.

5 - 15 The thickness of the single wafer is 0. 5 - 15

6. The ingot casting method of polycrystalline silicon according to claim 1, wherein: said single wafer has a square or circular cross section.

The ingot casting method of polycrystalline silicon according to claim 1, wherein the inner wall of the quartz ceramic crucible has a silicon nitride coating.

The ingot casting method of polycrystalline silicon according to claim 1, wherein the crystal is sapphire or quartz or silicon carbide.