Specific Process Knowledge/Thin film deposition/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).

Deposition of Silicon Nitride using LPCVD

LPCVD nitride can be made in the LPCVD nitride furnace. It is a batch process meaning you can run a batch of 25 wafers at a time. The deposition takes place at temperatures of 800-850 degrees Celsius. The LPCVD nitride has a good step coverage and the film thickness is very uniform over the wafer. We have two standard LPCVD nitride processes: One for depositing stoichiometric nitride (Si₃N₄) and one for deposition low stress nitride (SNR).

• Deposition of Silicon Nitride using LPCVD

Deposition of Silicon Nitride using PECVD

PECVD nitride and oxynitride can be deposited in one of the PECVD systems. You can run 1-3 wafers at a time depending on which one of the PECVD's you use. The deposition takes place at 300 degrees Celcius. This can be of importance for some applications but it gives a less dense film and the stoichiometry is on the following form: Si_xN_yO_zH_v. The step coverage and thickness uniformity of the film is not as good as for the LPCVD nitride. In one of our PECVD systems (PECVD3) we allow small amounts of metal on the wafers entering the system, this is not allowed in the LPCVD and in the other PECVD (PECVD1).

• Deposition of Silicon Nitride using PECVD - or oxynitride

Comparison of LPCVD and PECVD for silicon nitride deposition

	LPCVD	PECVD
Stoichiometry	Si3N4 SRN SRN: Silicon Rich Nitride	SixNyHz SixOyNzHv Can be doped with boron, phosphorus or germanium
Film thickness	Si3N4:~50Å - ~3000Å SRN: ~50Å - ~10000Å	~40nm - 10µm
Process Temperature	800-835 oC	300 oC
Step coverage	Good	Less good
Film quality	Dense film Few defects	Less dense film Incorporation of hydrogen in the film
Batch size	1-25 4" wafer per run deposition on both sides of the substrate	1-3 4" wafers or one 6" wafer or many smaller chips per run deposition on one side of the substrate
Substrate material allowed	Silicon wafers with layers of silicon oxide or silicon (oxy)nitride Quartz wafers	Silicon with layers of silicon oxide or silicon (oxy)nitride Quartz Small amount of metal < 5% of the wafer coverage (ONLY in PECVD3!)
Etch rate in 80oC KOH	Expect <1Å/min	Dependent on recipe: ~1-10Å/min
Etch rate in BHF	Very low	Very high compared to the etch rate of LPCVD nitride