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

Al
₂
O
₃
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 Al
₂
O
₃
(5e12~1e13cm
^-2
). This paper reports on a promising field-effect passivation by charge injection in SiO
₂
/SiNx stack using a novel low-cost plasma charging method which can replace plasma ALD Al
₂
O
₃
. 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 SiO
₂
/SiNx passivated boron emitter decreases from ~80fA/cm
²
to ~50fA/cm
²
after -7.9e12cm
^-2
negative charge injection, which is equivalent to the Al
₂
O
₃
/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 SiO
₂
/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 SiO
₂
/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.