Specific Process Knowledge/Thin film deposition/Deposition of Silicon Nitride

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Deposition of silicon nitride

Deposition of silicon nitride can be done with either LPCVD (Low Pressure Chemical Vapor Deposition) or PECVD (Plasma Enhanced Chemical Vapor Deposition). Stiochiometric nitride or silicon rich (low stress) LPCVD nitride is deposited on a batch of wafers in a LPCVD nitride furnace, and PECVD nitride (or oxynitride) is deposited on a few samples at a time in a PECVD system. LPCVD nitride has a good step coverage and a very good uniformity. Using PECVD it is possible to deposit a thicker layer of nitride on different types of samples, but the nitride does not cover sidewalls very well.

Nitride deposition using LPCVD

Nitride deposition using PECVD (or oxynitride)

Comparison of LPCVD and PECVD for silicon nitride deposition

	LPCVD	PECVD
Generel description	Low Pressure Chemical Vapour Deposition (LPCVD furnace process)	Plasma Enhanced Chemical Vapour Deposition (PECVD process)
Stoichiometry	Si₃N₄ SRN (only 4" nitride furnace) Si₃N₄: Stoichiometric nitride SRN: Silicon rich (low stress) nitride	Si_xN_yH_z Si_xO_yN_zH_v Silicon nitride can be doped with boron, phosphorus or germanium
Film thickness	Si₃N₄: ~50 Å - ~1400 Å SRN: ~50 Å - ~2800 Å Thicker nitride layers can be deposited over more runs	~40 nm - 10 µm
Process temperature	780 ^oC - 845 ^oC	300 ^oC
Step coverage	Good	Less good
Film quality	Deposition on both sides og the substrate Dense film Few defects	Deposition on one side of the substrate Less dense film Incorporation of hydrogen in the film
KOH etch rate (80 ^oC)	Expected <1 Å/min	Dependent on recipe: ~1-10 Å/min
BHF etch rate	Very low	Very high compared the LPCVD nitride
Batch size	1-25 100 mm wafers 1-25 150 mm wafers (only 6" furnace) Depending on what furnace you use	Several smaller samples 1-several 50 mm wafers 1-3 100 mm wafers 1 150 mm wafer Depending on what PECVD you use
Allowed materials	Silicon Silicon oxide Silicon nitride Pure quartz (fused silica) Processed wafers have to be RCA cleaned	Silicon Silicon oxide (with boron, phosphorous and germanium) Silicon nitrides (with boron, phosphorous and germanium) Pure quartz (fused silica)