Field-effect passivation by charge injection into SiNx using a novel low-cost plasma charging method

摘要

Al2O3 film with SiNx capping layer is widely used for rear side passivation of p-type PERC cells and passivation of p+ emitter in n-PERT cells because of very effective field-induced passivation by high density of negative charge in Al2O3 (5e12~1e13cm-2). This paper reports on a promising field-effect passivation by charge injection in SiO2/SiNx stack using a novel low-cost plasma charging method which can replace plasma ALD Al2O3. In addition, this tool injects either positive or negative charge in a controlled manner. It is demonstrated that emitter saturation current density(Joe) of a SiO2/SiNx passivated boron emitter decreases from ~80fA/cm2 to ~50fA/cm2 after -7.9e12cm-2 negative charge injection, which is equivalent to the Al2O3/SiNx passivated boron emitter. In addition, a 0.4% increase in absolute efficiency was observed after the injection of 1e13cm-2 negative charge in the SiO2/SiNx passivated boron emitter. Sentaurus device modeling was performed to estimate the impact of field-effect passivation by extracting Joe values as a function of injected charge in SiO2/SiNx passivated boron and phosphorus emitters. It was found that charge injection is more effective for boron emitters. And the field-effect passivation quality saturated after ~1e13cm-2 charge in both types of emitters. We expect negative and positive charging on both sides of the cell structure will further enhance field-effect passivation and achieve even higher cell efficiency.