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 silicon nitride can be made in an LPCVD nitride furnace. Danchip has two LPCVD nitride furnaces: A new furnace for deposition of stoichiometric nitride on 4" or on 6" wafers and an older furnace for deposition of stoichiometric nitride and low stress nitride on 4" wafers.

The LPCVD nitride deposition is a batch process, meaning that you can run a batch of 25-35 wafers at a time. The deposition takes place at temperatures of 780-850 degrees Celsius. The LPCVD silicon nitride has a good step coverage, and the film thickness is very uniform over the wafers. On the furnaces we have standard processes for deposition of stoichiometric nitride (Si₃N₄) and for deposition of 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 the thickness uniformity of the film are 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 furnace and in the clean PECVD (PECVD1). We also have a PECVD for deposition on III-V materials (PECVD2).

Deposition of silicon nitride using PECVD - or oxynitride

Comparison of LPCVD and PECVD for silicon nitride deposition

	LPCVD	PECVD
Stoichiometry	Si₃N₄ SRN (old nitride furnace, only 4" wafers) Si₃N₄: Stoichiometric nitride SRN: Silicon rich nitride (low stress nitride)	Si_xN_yH_z Si_xO_yN_zH_v Can be doped with boron, phosphorus or germanium
Film thickness	Si₃N₄: ~50 Å - ~3000 Å SRN: ~50 Å - ~10000 Å Thick nitride layers can be deposited over more runs	~40 nm - 10 µm
Process Temperature	780 ^oC - 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	1-35 4" wafers per run (old nitride furnace) 1-25 4" or 6" wafers per run (new nitride furnace) 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 materials allowed	New or RCA cleaned silicon wafers with layers of silicon oxide or silicon (oxy)nitride Quartz wafers	Silicon wafers 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 80 ^oC KOH	Expected <1 Å/min	Dependent on recipe: ~1-10 Å/min
Etch rate in BHF	Very low	Very high compared to the etch rate of LPCVD nitride