Specific Process Knowledge/Thin film deposition/Furnace LPCVD PolySilicon

LPCVD (Low Pressure Chemical Vapor Deposition) PolySilicon

A4 Furnace PolySilicon (situated in cleanroom 2

Danchip has two furnaces for deposition of LPCVD polysilicon: A new 6" furnace (installed in 2011) for deposition of standard polySi, amorphous polySi and boron doped polySi on 4" or 6" wafers and an older 4" furnace (installed in 1995) for deposition of standard polySi, amorphous polySi, boron- and phosphorous doped polySi on 4" wafers. I LabManager the two furnaces are named "Furnace: LPCVD Poly-Si" and "Furnace: LPCVD Poly-Silicon 6inch", respectively. Both furnaces are Tempress horizontal furnaces.

The LPCVD polysilicon deposition is a batch process, where polySi is deposited on a batch of 25 or 50 wafers (the 6" polySi furnace) or 30 wafers (the 4" polySi furnace). For standard polysilion the deposition takes place at a temperature of 620 degrees Celsius and a pressure of xxx MTorr. For amorphous polysilicon the deposition temperatures and thus the deposition rate is lower, and for boron and phosphorous doped polySi the depostion temperature and depends on whether you use the new or the old polySi furnace. For phousphorous doped polySi the deposition rate is approximately ten times lower than for boron doped polySi. The reactive gas is silane (SiH4). The dopant for boron doped polySi is BCl3 (the 6" polySi furnace) or B2H6 (the 4" polySi furnace), and for phosphorous doped polySi the dopant is PH3.

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).

At the moment there is one furnace for PolySilicon depositions at Danchip. The furnace is a Tempress horizontal furnace. The process is a batch process meaning you can run a batch of 25 wafers at a time. The deposition takes place at temperatures of 800-835 degrees Celsius. The reactive gases are Ammonia and dichlorsilane. 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 of low stress nitride (SNR). To get information on how to operate the furnace please read the manual which is uploaded to LabManager.

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 SRN: Silicon Rich Nitride
Performance	Film thickness	Si3N4:~50Å - ~3000Å SRN: ~50Å - ~10000Å
	Step coverage	Good
	Film quality	Dense film Few defects
Process parameter range	Process Temperature	800-835 oC
	Process pressure	80-230 mTorr
	Gas flows	SiH$_{2}$Cl$_{2}$:10-100 sccm NH$_{3}$:10-75 sccm
Substrates	Batch size	1-25 4" wafer per run Deposition on both sides of the substrate
	Substrate material allowed	Silicon wafers (new from the box or RCA cleaned) with layers of silicon oxide or silicon (oxy)nitride (RCA cleaned) Quartz wafers (RCA cleaned)