CN103943719B - A kind of method that adopts pre-oxygen in conjunction with the alternating temperature diffusion way of low temperature-high temperature-low temperature, phosphorus doping density to be controlled - Google Patents

Abstract

The invention discloses a kind of method that adopts pre-oxygen in conjunction with the alternating temperature diffusion way of low temperature-high temperature-low temperature, phosphorus doping density to be controlled, the method comprises pre-oxidation and low temperature-high temperature-low temperature three step alternating temperature diffusion processes, this technique is by being optimized thermograde, can accurately control phosphorus doping density gradient, obtain good PN junction and sheet resistance uniformity, improve the conversion efficiency of solar cell.

Description

A method of controlling phosphorus doping concentration by using pre-oxidation combined with low temperature-high temperature-low temperature variable temperature diffusion method

technical field

The invention belongs to the technical field of solar cells, and in particular relates to a method for controlling phosphorus doping concentration by adopting a pre-oxygenation combined with a low temperature-high temperature-low temperature variable temperature diffusion method.

Background technique

At present, phosphorus diffusion process is usually used to prepare PN junction in traditional solar cell manufacturing. The performance of PN junction directly affects the conversion efficiency of the cell, and the pros and cons of the diffusion process play a key role. With the continuous improvement of the conversion efficiency of polycrystalline silicon cells, shallow junctions with high square resistance have become the main development direction, and the diffusion process has also developed from a single-step constant temperature diffusion to a three-step variable temperature diffusion. High diffusion square resistance can reduce the surface recombination rate, improve the effective minority carrier life and the short-wave response of the battery, but at the same time it will also lead to poor square resistance uniformity, local PN junction burn-through leakage, and high control accuracy requirements for equipment , and the three-step variable temperature diffusion process can effectively improve the uniformity of square resistance and improve the stability of the process.

However, the common three-step variable temperature diffusion process only simply splits the single-step diffusion process, and the temperature gradient setting method is a single temperature rise, as shown in Figure 1-2. Improvement, but the characteristics of the PN junction have not been essentially optimized, and it is impossible to obtain a significant improvement in battery conversion efficiency.

Contents of the invention

The technical problem to be solved by the present invention is to provide a variable temperature diffusion process, which can precisely control the phosphorus doping concentration gradient by optimizing the temperature gradient, obtain good PN junction and square resistance uniformity, and improve the conversion efficiency of solar cells .

The technical problem to be solved by the present invention is achieved through the following technical solutions: a method for controlling the phosphorus doping concentration by adopting pre-oxidation combined with low temperature-high temperature-low temperature variable temperature diffusion mode, comprising the following steps:

(1) Into the boat, pre-oxidize the textured silicon wafer at 700-800°C with oxygen and large nitrogen, and the oxidation time is 3-10 minutes;

(2) Adjust the temperature to 700-800°C, feed small nitrogen, large nitrogen and oxygen carrying phosphorus sources for deposition, diffusion and pushing, and the time is 10-30 minutes;

(3) Raise the temperature to 800~860℃, feed small nitrogen, large nitrogen and oxygen carrying phosphorus source to deposit, diffuse and push the junction, and the time is 10~20min;

(4) Cool down to 700~800°C, feed small nitrogen, large nitrogen and oxygen carrying phosphorus source for deposition, diffusion and push junction, the time is 5~15min;

(5) Carry out cooling and get out of the boat.

In each of the above steps:

The flow rate of oxygen in step (1) of the present invention is 1800-2200 sccm/min, and the flow rate of large nitrogen is 13000-20000 sccm/min.

The flow rate of small nitrogen in step (2) of the present invention is 600-1000 sccm/min, the flow rate of large nitrogen is 13000-20000 sccm/min, and the flow rate of oxygen is 200-500 sccm/min.

The flow rate of small nitrogen in step (3) of the present invention is 700-1200 sccm/min, the flow rate of large nitrogen is 13000-20000 sccm/min, and the flow rate of oxygen is 200-500 sccm/min.

The flow rate of small nitrogen in step (4) of the present invention is 700-1200 sccm/min, the flow rate of large nitrogen is 13000-20000 sccm/min, and the flow rate of oxygen is 200-500 sccm/min.

The pre-oxidation treatment of the present invention is mainly to form an oxide layer on the surface of the silicon chip, which can improve the uniformity of phosphorus impurity diffusion, and can effectively control the surface diffusion concentration as a mask layer.

Due to the high density of structural defects such as grain boundaries, dislocations, micro-defects and a large number of metal impurities in the casting process of polysilicon, these metal impurities will become deep energy levels to form recombination centers, thereby affecting the conversion efficiency of the battery. However, the present invention can achieve a good gettering effect by setting variable temperature, that is, rapidly and effectively dissolving metal precipitates or metal complexes at high temperatures, and the subsequent cooling process greatly increases the segregation of impurity atoms in the gettering region, making The impurity atoms have sufficient time to move to the surface of the silicon wafer, thereby significantly improving the performance of the silicon material. At the same time, the cooling setting can reduce the damage to the silicon wafer during the long-term high-temperature process and form new recombination centers.

Compared with the prior art, the present invention has the following advantages: the present invention can precisely control the phosphorus doping concentration gradient through pre-oxygenation combined with a three-step variable temperature diffusion process, obtain good PN junction characteristics and square resistance uniformity, and improve solar cell conversion efficiency.

Description of drawings

Figure 1 is a schematic diagram of the temperature gradient of a conventional solar cell single-step constant temperature diffusion process;

Fig. 2 is a schematic diagram of the temperature gradient of a three-step variable temperature diffusion process for a conventional solar cell;

Fig. 3 is a schematic diagram of the temperature gradient of the solar cell three-step variable temperature diffusion process of the present invention;

The temperature platform indicated by ①②③ in the figure indicates the phosphorus source deposition push-in step in the diffusion process, and does not include other auxiliary process steps such as heating and cooling;

Fig. 4 is a schematic diagram of comparing the ECV curves of the diffusion process of the present invention and the conventional three-step diffusion process, wherein the dotted line is the ECV curve of the diffusion process of the present invention, and the solid line is the ECV curve of the conventional three-step diffusion process.

detailed description

The present invention is described below in conjunction with the examples, it should be pointed out that the embodiments are only used to further illustrate the present invention, and do not represent the protection scope of the present invention, and other people's non-essential modifications and adjustments made according to the prompts of the present invention are still Belong to the protection scope of the present invention.

Example 1

As shown in Figure 3, taking polysilicon wafers as an example:

(1) Put the textured silicon wafer into the boat, and at a low temperature of 750°C, feed 2000 sccm/min oxygen and 15000 sccm/min nitrogen for pre-oxidation, and the oxidation time is 7 minutes;

(2) The temperature is controlled at 750°C, and 800 sccm/min of small nitrogen carrying phosphorus source, 15000 sccm/min of large nitrogen and 200 sccm/min of oxygen are fed for deposition and diffusion push junction for 20 minutes;

(3) Raise the temperature to 825°C, feed 900 sccm/min of small nitrogen carrying phosphorus source, 15000 sccm/min of large nitrogen and 300 sccm/min of oxygen for deposition, diffusion and pushing, and the time is 15 minutes;

(4) Cool down to 765°C, feed 900 sccm/min of small nitrogen carrying phosphorus source, 15000 sccm/min of large nitrogen and 300 sccm/min of oxygen for deposition, diffusion and push junction, and the time is 7 minutes;

(5) Carry out cooling and get out of the boat.

Using the variable temperature process in this embodiment, the ECV curve change can be realized by precisely controlling the phosphorus doping concentration gradient (as shown in Figure 4). The ECV curve obtained in this embodiment has low surface concentration, shallow junction, high effective doping The characteristics of impurity concentration, so it has good PN junction characteristics. At the same time, by adopting the technical solution in this embodiment, good square resistance uniformity can also be obtained. Through the four-probe test of 25 points of square resistance, it is found that the conventional three-step diffusion process (see Figure 2) has a std of about 4-5 , while adopting the variable temperature technology in this embodiment can realize std at about 3-4. The PN junction characteristics and square resistance uniformity are substantially improved, and the conversion efficiency of solar cells will be improved accordingly. The electrical performance comparison data and process square resistance test values are shown in Table 1 and Table 2.

Table 1 Comparison of electrical performance indicators of solar cells prepared by the process of this example and the conventional three-step diffusion process

Table 2 Comparison of various performance indicators of solar cells prepared by the process of this example and the conventional three-step diffusion process

Example 2

As shown in Figure 3, taking polysilicon wafers as an example:

(1) Put the textured silicon wafer into the boat, and at a low temperature of 750°C, feed 2000 sccm/min oxygen and 15000 sccm/min nitrogen for pre-oxidation, and the oxidation time is 7 minutes;

(2) The temperature is controlled at 770°C, and 750 sccm/min of small nitrogen carrying phosphorus source, 15000 sccm/min of large nitrogen and 200 sccm/min of oxygen are fed for deposition and diffusion push junction for 20 minutes;

(3) Raise the temperature to 830°C, feed 800 sccm/min of small nitrogen carrying phosphorus source, 15000 sccm/min of large nitrogen and 300 sccm/min of oxygen for deposition, diffusion and push junction, and the time is 15 minutes;

(4) Cool down to 790°C, feed 800 sccm/min of small nitrogen carrying phosphorus source, 15000 sccm/min of large nitrogen and 300 sccm/min of oxygen for deposition, diffusion and push junction, and the time is 7 minutes;

(5) Carry out cooling and get out of the boat.

Example 3

As shown in Figure 3, taking polysilicon wafers as an example:

(1) Put the textured silicon wafer into the boat, and at a low temperature of 750°C, feed 2000 sccm/min oxygen and 15000 sccm/min nitrogen for pre-oxidation, and the oxidation time is 7 minutes;

(2) Under the condition of temperature control at 750°C, 700 sccm/min of small nitrogen carrying phosphorus source, 16000 sccm/min of large nitrogen and 200 sccm/min of oxygen are fed for deposition and diffusion pushing for 25 minutes;

(3) Raise the temperature to 825°C, feed 800 sccm/min of small nitrogen carrying phosphorus source, 16000 sccm/min of large nitrogen and 300 sccm/min of oxygen for deposition and diffusion push junction, and the time is 17 minutes;

(4) Cool down to 765°C, feed 800 sccm/min of small nitrogen carrying phosphorus source, 16000 sccm/min of large nitrogen and 300 sccm/min of oxygen for deposition, diffusion and push junction, and the time is 9 minutes;

(5) Carry out cooling and get out of the boat.

Claims (1)

1. a method that adopts pre-oxygen in conjunction with the alternating temperature diffusion way of low temperature-high temperature-low temperature, phosphorus doping density to be controlled, is characterized in that containing following steps:

(1) enter boat, the silicon chip after making herbs into wool, under 700 ~ 800 DEG C of conditions, is passed into oxygen and carries out pre-oxidation with large nitrogen, oxidization time is 3 ~ 10min;

(2) regulating temperature is 700 ~ 800 DEG C, passes into carry the little nitrogen in phosphorus source, large nitrogen and oxygen and deposit, spread knot, and the time is 10 ~ 30min;

(3) be warming up to 800 ~ 860 DEG C, pass into and carry the little nitrogen in phosphorus source, large nitrogen and oxygen and deposit, spread knot, the time is 10 ~ 20min;

(4) be cooled to 700 ~ 800 DEG C, pass into and carry the little nitrogen in phosphorus source, large nitrogen and oxygen and deposit, spread knot, the time is 5 ~ 15min;

(5) lower the temperature and boat;

In step (1), the flow of oxygen is 1800 ~ 2200sccm/min, and the flow of large nitrogen is 13000 ~ 20000sccm/min;

The flow of the medium and small nitrogen of step (2) is 600 ~ 1000sccm/min, and the flow of large nitrogen is 13000 ~ 20000sccm/min, and the flow of oxygen is 200 ~ 500sccm/min;

The flow of the medium and small nitrogen of step (3) is 700 ~ 1200sccm/min, and the flow of large nitrogen is 13000 ~ 20000sccm/min, and the flow of oxygen is 200 ~ 500sccm/min;

The flow of the medium and small nitrogen of step (4) is 700 ~ 1200sccm/min, and the flow of large nitrogen is 13000 ~ 20000sccm/min, and the flow of oxygen is 200 ~ 500sccm/min.