Selective Silicon Nitride Etch with Hot Diluted HF- an Alternative to Orthophosphoric Acid

Orthophosphoric acid is the worldwide standard chemical to quickly and selectively etch thick silicon nitride films towards silicon oxide. Along the semiconductors node evolution, new demands have arisen to etch few nanometers thick SiN films, with much better defectivity than H3PO4. Several alternatives have been developed during the past few years. Among them, a hot very diluted HF process was developed in the early 2000's. This paper deals with several applications where significant benefits are demonstrated compared with H3PO4: first a Stress Proximity Technic successfully adopted into production mode, secondly a SiN films patterning thanks to a softmask. Although this process benefits from high selectivity, low cost of ownership, good defectivity, its within wafer uniformity still remains poor due to the actual hardware.