Specific Process Knowledge/Thin film deposition/Furnace LPCVD Nitride

LPCVD (Low Pressure Chemical Vapor Deposition) Silicon Nitride

6" LPCVD nitride furnace (new nitride furnace) positioned in cleanroom 14

LPCVD nitride furnace (old nitride furnace) positioned in cleanroom 2

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 an older furnace (installed in 1995) for deposition of stoichiometric nitride and silicon rich (i.e. low stress) nitride on 4" wafers. In LabManager the two furnaces are named "Furnace: LPCVD nitride (6")" and "Furnace: LPCVD nitride", respectively. Please be aware that it is not allowed to deposit silicon rich nitride in the new nitride furnace to avoid problems with particles. Both furnaces are Tempress horizontal furnaces.

The LPCVD silicon nitride deposition is a batch process, meaning nitride can be deposited on a batch of up to 17 wafers (in the old nitride furnace) or 25 wafers (in the new nitride furnace) at a time. The deposition takes place at temperatures of 780-845 degrees Celsius and at pressure of 120-200 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 there are at moment only a standard recipe for deposition of silicon rich nitride (SRN) on 4" wafers. On the new nitride furnace there are two standard recipes for deposition of stoichiometric nitride (Si₃N₄), one for 4" wafers and one for 6" wafers.

To get information on how to operate the furnaces please read the user manuals which are uploaded to LabManager on the machine page or consult the Furnace group at Danchip (furnace@danchip.dtu.dk).

Process Knowledge

Please take a look at the process side to get more information about deposition of silicon nitride using an LPCVD furnace: 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 (only new nitride furnace at the moment) SRN (only old nitride furnace, only 4" wafers) Si3N4: Stoichiometric nitride SRN: Silicon rich nitride (low stress nitride)
Performance	Film thickness	Si3N4: ~50Å - ~1400Å SRN: ~50Å - ~2800Å Thicker 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 (Si3N4): Uniformity within wafer: <3 % Wafer-to-wafer uniformity: <3 % Run-to-run uniformity: <3 % Old nitride furnace (SRN): Uniformity within wafer: <4 % Wafer-to-wafer uniformity: <4% Run-to-run uniformity: <3 %
Process parameter range	Process Temperature	780-845 oC The process temperature depends on the actual process and vary over the furnace tube
	Process pressure	120-200 mTorr The process pressure depends on the actual process
	Gas flows	Dichlorsilane (SiH$_{2}$Cl$_{2}$): 30-80 sccm Ammonia (NH$_{3}$): 20-120 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: 1-17 4" wafers per run
	Substrate material allowed	Silicon wafers (new wafers 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 Pure quartz (fused silica) wafers (RCA cleaned)