In situ Photoluminescence Study of Plasma Effects on Passivation of Crystalline Silicon Coated with Aluminum Oxide

A degradation of crystalline silicon surface passivation provided by aluminum oxide (Al₂O₃) is generally observed after plasma processes, e.g., deposition of amorphous silicon nitride. To minimize such detrimental effect, a better understanding of the interaction between plasma species and the Al₂O₃ layer is required. Using in situ photoluminescence, the passivation quality of as-deposited and annealed crystalline silicon wafers coated with Al₂O₃ grown by atomic layer deposition is characterized in real time during argon-hydrogen plasma exposure. The photoluminescence intensity of as-deposited samples instantly steps up after the plasma ignition, and then it gradually decreases as a function of plasma exposure time. However, only degradation of photoluminescence signal can be found if the samples are annealed prior to the plasma treatment. The interaction between vacuum UV light from plasma and different types of chemical bonds in the Al₂O₃ layer is proposed to explain the obtained results. Understanding the mechanisms and root cause leading to different behavior between as-deposited and annealed samples under plasma exposure is a first step toward redesigning the process flow for better surface passivation.