Single Wafer Selective Silicon Nitride Removal with Phosphoric Acid and Steam

A single wafer silicon nitride (SiN) selective etch process with an etch rate greater than 80A/min of low-pressure chemical vapor deposited (LPCVD) SiN has been developed. Previous work with a similar single wafer system utilized a mixture of sulfuric acid, phosphoric acid and steam to achieve a high SiN etch rate [1]. The process in this work relies on phosphoric acid and steam for a high SiN etch rate. In both of these applications, addition of steam doubles the SiN etch rate. The single wafer system utilizes a closed chamber design with integrated spray bar to uniformly dispense hot phosphoric acid and steam onto the wafer surface achieving within wafer non-uniformities of less than 3%. Rinsing and drying of the phosphoric acid from the wafer surface occurs in the same chamber (dry in/dry out) providing a stable, haze free wafer. Figure 1 contains a schematic of the phosphoric acid delivery and single wafer system.