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.

It is also possible to deposit silicon nitride using the Lesker sputter system. However, the process hasnot been tested yet, but the required sputter targets for nitride deposition are avaliable.

• Nitride deposition using LPCVD

• Nitride deposition using PECVD] (or oxynitride)

• Nitride deposition using Lesker sputter system

Comparison of LPCVD, PECVD and Lesker sputter system for silicon nitride deposition

	LPCVD	PECVD	Lesker sputter system
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	SixNyHz SixOyNzHv 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 (stoichiometric nitride: 0.75 nm/min)	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)