Si + SiNx Wafers
Silicon Nitride Coating
Fields of Application for Silicon Nitride
In the field of tool-making, stoichiometric trisilicon tetranitride (Si3N4) with its very high mechanical and thermal stability is used for tools such as roller bearings used under harsh conditions.
For semiconductor devices, the chemical, electrical and optical properties of amorphous hydrogenated silicon nitride (SiNx) make this material well-suited for different applications, such as for
- Passivation or insulating layers in integrated circuits
- masking or etch stop material in wet and plasma etching processes due to its high chemical stability
- masking material in silicon oxidation processes due to the very low oxygen diffusion coefficient in SiNx
- anti-reflective coating in photovoltaics due to its adjustable refractive index
- PECVD and LPCVD Silicon Nitride
SiNx layers realized by the plasma enhanced chemical vapour deposition (PECVD) technique from SiH4 and NH3 typically – depending on the deposition temperature and gas composition – contain 5 - 20 atom% hydrogen which saturates dangling bonds and thus chemically and mechanically stabilizes the SiNx lattice.
SiNx layers realized by the low pressure chemical vapour deposition (LPCVD) technique typically shows a lower H-content and higher stability against HF.
SiNx can be etched via photoresist masks either with buffered or unbuffered HF or (selectively to SiO2) with concentrated phosphoric acid. The HF etch rate of SiNx depends on the SiNx deposition temperature and its refractive index. A hydrogen-rich SiNx film deposited at 100°C with a refractive index of n = 1.9 shows an etch rate of several 100 nm/min in buffered HF (12.5 % HF). The etch rate drops to less than 10 nm/min for SiNx films deposited at 400°C with a refractive index of n = 2.