In-situ diagnostics of PECVD AlOx deposition by optical emission spectroscopy

Plasma enhanced chemical vapor deposition (PECVD) is ubiquitously used in the crystalline silicon photovoltaics industry to deposit surface passivation and anti-reflection coatings. Aluminum oxide deposited by PECVD is becoming an increasingly common rear surface passivation layer, due to the growing market share of solar cells with partial rear contacts, such as the passivated emitter and rear solar cell. In this study, we use in-situ monitoring to investigate the correlation between the PECVD plasma properties and the resulting aluminum oxide film properties. Although no linear correlation between the density of the constituent radicals (aluminum, oxygen, and hydrogen) in the plasma and the surface passivation quality was observed, we did identify optimum processing conditions for a high quality surface passivation layer using in-situ plasma monitoring. This study also highlights the limited knowledge that currently exists within the photovoltaic community regarding plasma characterization and its impact on device performance.