Specific Process Knowledge/Thin film deposition/Furnace LPCVD Nitride

LPCVD (Low Pressure Chemical Vapor Deposition) Silicon Nitride

At Danchip there are two LPCVD nitride furnaces for deposition of silicon nitride: A new furnace (installed in 2008) for deposition of stoichiometric nitride on 4" or 6" wafers and a older furnace (installed in 1993) for deposition of stoichiometric nitride and low stress nitride on 4" wafers. Please, be aware that it is not allowed to deposit low stress nitride in the new nitride furnace (to avoid problems with particles). In LabManager the two furnaces are named "Furnace: LPCVD nitride (6")" and "Furnace LPCVD nitride", respectively. Both furnaces are Tempress horizontal furnaces.

The LPCVD silicon nitride deposition is a batch process, meaning that you can run a batch of up to 25-35 wafers at a time. The deposition takes place at temperatures of 780-835 degrees Celsius and at pressures of 200-230 mTorr. The reactive gases are ammonia (NH₃) and dichlorsilane (SiH₂Cl₂). The LPCVD nitride has a good step coverage, and the film thickness is very uniform over the wafers. On the old nitride furnace we have two standard silicon nitride processes: One for deposition of stoichiometric nitride (Si₃N₄) and one for deposition of low stress nitride (SNR). On the new nitride furnace we have two standard recipes for deposition of stoichiometric nitride: One for 4" wafers and one for 6" wafers.

To get information on how to operate the furnace please read the user manuals which are uploaded to LabManager on the machine page.

Process Knowledge

Please take a look at the process side for deposition of Silicon Nitride using LPCVD: Deposition of Silicon Nitride using LPCVD

Overview of the performance of LPCVD Silicon Nitride and some process related parameters

Purpose	Deposition of silicon nitride	Stoichiometry: Si₃N₄ SRN (old nitride furnace, only 4" wafers) Si₃N₄: Stoichiometric nitride SRN: Silicon rich nitride (low stress nitride)
Performance	Film thickness	Si₃N₄: ~50Å - ~3000Å SRN: ~50Å - ~10000Å Thick layers have to be deposited over more runs
	Step coverage	Good
	Film quality	Deposition on both sides of the substrate Dense film Few defects
	Nitride thickness uniformity	New nitride furnace: Uniformity within wafer: ~ 3 % Wafer-to-wafer uniformity: ~ 3 % Run-to-run uniformity: ~ 3 % Old nitride furnace: Uniformity within wafer: <1.3 % Wafer-to-wafer uniformity: <4% Run-to-run uniformity:
Process parameter range	Process Temperature	780-835 ^oC The process temperature depends on the actual process
	Process pressure	80-230 mTorr The process pressure depends on the actual process
	Gas flows	Dichlorsilane (SiH $_{2}$ Cl $_{2}$ ): 10-120 sccm Ammonia (NH $_{3}$ ): 10-75 sccm The gas flows depend on the actual process
Substrates	Batch size	New nitride furnace: 1-25 4" or 6" wafers per run Old nitride furnace: 1-35 4" wafer per run The number of wafers depends on the size of the quartz boat
Substrates	Substrate material allowed	Silicon wafers (new wafers from a new box or RCA cleaned wafers) with layers of silicon oxide or silicon (oxy)nitride (RCA cleaned) from furnaces in stack A or B in cleanroom 2 Quartz wafers (RCA cleaned)