CN103367544A - Method for diffusing polycrystalline silicon battery emitter with gettering function - Google Patents

Abstract

The invention discloses a method for diffusing the emitter of a polycrystalline silicon battery with gettering effect, which is characterized in that a layer of silicon dioxide film is coated on the suede surface of the silicon wafer before the diffusion, and the diffusion is double-sided diffusion and includes two steps. Source diffusion and two-step gettering. The invention improves the diffusion process and improves the minority carrier life of the silicon chip, thereby improving the electrical performance of the battery chip. It is especially suitable for the preparation of the silicon wafer battery emitter in the A area.

Description

A kind of method of diffusion with polycrystal silicon cell emitter of gettering effect

Technical field

The invention belongs to the crystal silicon solar energy battery technical field, particularly relate to a kind of method of diffusion with polycrystal silicon cell emitter of gettering effect.

Background technology

At present, the ingot casting polycrystalline silicon material has been substituted pulling of silicon single crystal and has become topmost solar cell material, and the ingot casting polysilicon that obtains by directional solidification processes has that crystalline orientation is consistent, the equal first-class characteristics of coarse grains.The efficiency of solar cell that use for laboratory high-quality casting polycrystalline silicon is prepared surpasses 20%, indicates the development prospect that it is good.Although polycrystal silicon cell has numerous advantages such as cost, but inside exists high density dislocation and impurity to have influence on consumingly its electric property, there is certain difference in the diverse location Crystal impurity content of ingot casting simultaneously, thereby prepared cell photoelectric conversion efficiency is lower than monocrystalline silicon battery.The efficient of polycrystal silicon cell generally hangs down about 1% than monocrystalline silicon in the industrial production at present.But also Just because of this, the performance of polysilicon also has very large room for promotion.Yet existing market is more and more higher for the transformation efficiency requirement of polycrystal silicon cell, so that more outstanding to the requirement of ingot casting polycrystalline crystal mass.

Because the ingot casting polycrystalline exists a large amount of high density grain boundary defects and impurity defect in growth course, battery performance is produced harmful effect.The zone on especially close crucible limit, its impurity and defect concentration are higher, although when the silicon ingot evolution, can remove a part, but or can there be the subregion, usually these foreign atoms itself or by interacting with crystal defect, can become the complex centre of minority carrier, greatly reduce minority carrier lifetime, and then affect the conversion efficiency of battery.Take 25 silicon ingots of evolution of present standard as example (Fig. 1), be positioned at the A district in crucible corner, because the zone of contact crucible is larger, thereby introduce more impurity, have a strong impact on the efficient of battery.A district silico briquette has occupied 16% zone of whole ingot casting, and its silicon chip efficient has a significant impact whole silicon ingot efficient.

The current battery end is the same for the processing mode of A, B, C district silicon chip, does not do special processing for the A district, adopts same battery process, thus cause A district silicon chip efficient much lower than B, C district, from causing the impact on whole silicon ingot efficient.So urgent need will solve A district silico briquette quality problems at present, come Si wafer quality is improved by battery process optimization, improve battery conversion efficiency.

Normally used gettering process has the following disadvantages: a. at high temperature (greater than the 900 ℃) time oversize, destroyed the structure of silicon chip, easily cause fragment; B. sheet resistance is restive, the requirement of inadaptable batch production.

Summary of the invention

The purpose of this invention is to provide a kind of method of diffusion with polycrystal silicon cell emitter of gettering effect, by improving diffusion technology, improve the silicon chip minority carrier life time, thereby improve the electrical property of cell piece.Be specially adapted to the preparation of A district silicon chip battery emitter.

The technical scheme that technical solution problem of the present invention is taked is, a kind of method of diffusion with polycrystal silicon cell emitter of gettering effect, it is characterized in that, at silicon wafer wool making face plating layer of silicon dioxide film, be diffused as Double side diffusion and comprised two active diffusions of step and two step getterings before the diffusion.

As a kind of preferred, the thickness of described silicon dioxide film is 5-20nm.

As a kind of preferred, in described two active diffusions of step and the two step getterings, the oxygen content of the active diffusion of the active diffusion ratio first step of second step is high by 50%, and first step gettering is than low 100 ℃ of second step gettering temperature.

As further preferred, the step of described two active diffusions of step and two step getterings is as follows:

⑴ for the first time active diffusion: constant source diffusion, the pre-deposited of PN junction; Use liquid POCl ₃, 800 ~ 850 ℃ of temperature, time 5 ~ 20min, in percent by volume, large N ₂Ratio 70% ~ 90%, oxygen proportion 1% ~ 20%, little N2 ratio 5% ~ 15%;

⑵ for the first time gettering: by high temperature the impurity in the silicon is dissolved, become the impurity of gap attitude; Obstructed phosphorus, 900 ~ 950 ℃ of temperature, time 20 ~ 60min, in percent by volume, large N ₂Ratio 80% ~ 90%, oxygen proportion 1% ~ 20%;

⑶ for the second time active diffusion: the constant source diffusion, at silicon chip surface growth one deck phosphorosilicate glass; Use liquid POCl ₃, 900 ~ 950 ℃ of temperature, time 5 ~ 20min, in percent by volume, large N ₂Ratio 60% ~ 90%, oxygen proportion 1% ~ 20%, little N2 ratio 5% ~ 15%;

⑷ for the second time gettering: by reducing temperature, change the impurity segregation coefficient, make impurity enter into phosphorosilicate glass; Obstructed phosphorus, 800 ~ 850 ℃ of temperature, time 20 ~ 60min, in percent by volume, large N ₂Ratio 80% ~ 90%, oxygen proportion 1% ~ 20%.

After described diffusion was finished, the sheet resistance of making herbs into wool face was 60 ~ 80 Ω/, back side sheet resistance 30 ~ 50 Ω/.

A kind of new polysilicon solar cell diffusion technology of the present invention, plate the layer of silicon dioxide film at silicon chip surface before the diffusion, and adopt the liquid phosphorus source, Double side diffusion, reach the performance of the cell piece that improves the leftover pieces silicon wafer to manufacture by twice TongYuan and twice gettering, and effectively control the purpose of emitter phosphorus diffusion profile.

Remarkable advantage of the present invention is: the minority carrier life time that ⑴ effectively improves cell piece improves electrical property; ⑵ control easily the curve of sheet resistance and phosphorus diffusion; ⑶ major impurity is controlled in the phosphorosilicate glass, can remove easily in the PSG operation, is fit to large-scale industrial needs.

Description of drawings

Fig. 1 silicon ingot butt administrative division map.

Fig. 2 diffusion technology temperature profile.

Embodiment

156 polysilicon chips after the making herbs into wool, at its making herbs into wool face plating layer of silicon dioxide film, the thickness of film is in the 5-20nm scope; Double side diffusion in tubular diffusion furnace carries out first the active diffusion first time, 800 ℃ of temperature, time 8min, large N ₂Ratio 80%, oxygen proportion 10%, little N ₂Ratio 10%; Carry out again the gettering first time, obstructed phosphorus, 950 ℃ of temperature, time 40min, large N ₂Ratio 90%, oxygen proportion 10%; Then carry out the active diffusion second time, 900 ℃ of temperature, time 8min, in percent by volume, large N ₂Ratio 70%, oxygen proportion 20%, little N ₂Ratio 10%; Carry out at last the gettering second time, obstructed phosphorus, temperature 800, time 40min, large N ₂Ratio 80%, oxygen proportion 20%.The diffusion technology temperature curve as shown in Figure 2.After tested, after diffusion was finished, all in 60 ~ 80 Ω/ scope, back side sheet resistance was all in 30 ~ 50 Ω/ scope for battery slice etching face sheet resistance.

Claims (5)

1. the method for diffusion with polycrystal silicon cell emitter of gettering effect is characterized in that, at silicon wafer wool making face plating layer of silicon dioxide film, is diffused as Double side diffusion and has comprised two active diffusions of step and two step getterings before the diffusion.

2. the method for diffusion of preparation polycrystal silicon cell emitter according to claim 1 is characterized in that, the thickness of described silicon dioxide film is 5-20nm.

3. the method for diffusion of preparation polycrystal silicon cell emitter according to claim 1, it is characterized in that, in described two active diffusions of step and the two step getterings, the oxygen content of the active diffusion of the active diffusion ratio first step of second step is high by 50%, and first step gettering is than low 100 ℃ of second step gettering temperature.

4. according to claim 1 or the method for diffusion of 3 described preparation polycrystal silicon cell emitters, it is characterized in that the step of described two active diffusions of step and two step getterings is as follows:

⑴ for the first time active diffusion: constant source diffusion, the pre-deposited of PN junction; Use liquid POCl ₃, 800 ~ 850 ℃ of temperature, time 5 ~ 20min, in percent by volume, large N ₂Ratio 70% ~ 90%, oxygen proportion 1% ~ 20%, little N2 ratio 5% ~ 15%;

⑵ for the first time gettering: by high temperature the impurity in the silicon is dissolved, become the impurity of gap attitude; Obstructed phosphorus, 900 ~ 950 ℃ of temperature, time 20 ~ 60min, in percent by volume, large N ₂Ratio 80% ~ 90%, oxygen proportion 1% ~ 20%;

⑶ for the second time active diffusion: the constant source diffusion, at silicon chip surface growth one deck phosphorosilicate glass; Use liquid POCl ₃, 900 ~ 950 ℃ of temperature, time 5 ~ 20min, in percent by volume, large N ₂Ratio 60% ~ 90%, oxygen proportion 1% ~ 20%, little N2 ratio 5% ~ 15%;

⑷ for the second time gettering: by reducing temperature, change the impurity segregation coefficient, make impurity enter into phosphorosilicate glass; Obstructed phosphorus, 800 ~ 850 ℃ of temperature, time 20 ~ 60min, in percent by volume, large N ₂Ratio 80% ~ 90%, oxygen proportion 1% ~ 20%.

5. according to claim 1, the method for diffusion of 3 or 4 described preparation polycrystal silicon cell emitters, it is characterized in that after described diffusion was finished, the sheet resistance of making herbs into wool face was 60 ~ 80 Ω/, back side sheet resistance 30 ~ 50 Ω/.