Four technical routes for the core process of TOPCON battery

There are many technical routes in the core process of TOPCON battery. The preparation process of TOPCON battery includes cleaning and flocking, front boron diffusion, etching borosilicate glass (BSG) and back knot, oxide passivation contact preparation, front alumina / silicon nitride deposition, back silicon nitride deposition, screen printing, sintering and testing. Among them, oxide passivation contact preparation is a process added by TOPCON on the basis of perc, and it is also the core process of TOPCON. At present, there are mainly four technical routes:

(1) LPCVD intrinsic + phosphorus diffusion. Use LPCVD equipment to grow silicon oxide layer and deposit polysilicon, and then use diffusion furnace to mix phosphorus into polysilicon to make PN junction, form passive contact structure, and then etch.

(2) LPCVD ion implantation. The passive contact structure is prepared by LPCVD equipment, and then the distribution of phosphorus in polysilicon is accurately controlled by ion implanter to realize doping, followed by annealing, and finally etching.

(3) PECVD in situ doping. The tunneling oxide layer was prepared by PECVD equipment and the polysilicon was doped in situ.

(4) PVD in situ doping. Using PVD equipment, the material is deposited on the substrate surface by sputtering under vacuum.

LPCVD is the most mature. PECVD and PVD can solve the problem of wrapping plating, but their advantages and disadvantages are different. At present, the LPCVD process is relatively mature. The principle is to decompose gaseous compounds under low pressure and high temperature, and then deposit them on the surface of the substrate to form the required film. The process control is simple and easy, the uniformity of film formation is good, and the density is high, but the film formation rate is slow, high temperature is required, and the deposition of quartz pieces is relatively serious. However, the widespread phenomenon of wrapping plating needs to be solved by introducing additional etching equipment, which further increases the process complexity. Unlike LPCVD, which uses thermal energy to activate, PECVD uses microwave, radio frequency and other gases containing film atoms to form local plasma, and deposits the required film on the substrate surface with the high activity of plasma gas. Its advantage is that the film-forming rate is very fast and the winding plating is very small, but the uniformity of the passive film is difficult to control, and there may be bubbles, resulting in poor passivation effect. PVD is different from CVD in that it adopts physical deposition, there is no wrapping phenomenon, and the film-forming rate is fast. However, the current process is relatively immature, the required equipment is expensive, the amount of target material is large, the uniformity of square resistance is poor, and the quality of the generated battery is unstable.