Specific Process Knowledge/Thin film deposition/Furnace LPCVD PolySilicon

LPCVD (Low Pressure Chemical Vapor Deposition) PolySilicon

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. In 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 (6" polySi furnace) or 30 wafers (4" polySi furnace). The polySi has a good step coverage, and especially for standard polySi the film thickness is very uniform over the wafers.

The reactive gas is silane (SiH₄). The dopant for boron doped polySi is BCl₃ (6" polySi furnace) or B₂H₆ (4" polySi furnace), and for phosphorous doped polySi the dopant is PH₃. For standard polysilion the deposition takes place at a temperature of 620 ^oC and a pressure of 200-250 mTorr. For amorphous polysilicon the deposition temperatures and thus the deposition rate are lower, and for boron and phosphorous doped polySi the deposition temperature is 600 ^oC - 620 ^oC depending on whether you use the 6" or the 4" polySi furnace. For phousphorous doped polySi the deposition rate is approximately ten times lower than for boron doped polySi. More process information about the process parameters can be found in the table below.

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

Process Knowledge

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

Overview of the performance of the LPCVD polysilicon processes and some process related parameters

Purpose	Deposition of LPCVD polysilicon	6" furnace: Standard polySi Amorphous polySi Boron doped polySi (BCl $_{3}$ dopant) 4" furnace: Standard polySi Amorphous polySi Boron doped polySi (B $_{2}$ H $_{6}$ dopant) Phosphorus doped polySi
Performance	Film thickness	6" furnace: Standard polySi: 0-2000 nm Amorphous polySi: 0-1000 nm Boron doped polySi: 0-1000 nm 4" furnace: Standard polySi: 0-2000 nm Amorphous polySi: 0-2000 nm Boron doped polySi: 0-2000 nm Phosphorus doped polySi: 0-1000 nm Thicker layers have to be deposited over more runs
	Step coverage	Good
	Film quality	Deposition on both sides of the substrate Good uniformity over the wafer
Process parameter range	Process Temperature	6" furnace: Standard polySi: 620 ^oC Amorphous polySi: 560-580 ^oC Boron doped polySi: 600-620 ^oC 4" furnace: Standard polySi: 620 ^oC Amorphous polySi: 560-580 ^oC Boron doped polySi: 620 ^oC Phosphorus doped polySi: 620 ^oC The process temperature vary over the furnace tube
	Process pressure	6" furnace: 150-220 mTorr 4" furnace: 250 mTorr The process pressure depends on the actual process
	Gas flows	6" furnace: SiH $_{4}$ : 50-70 sccm BCl $_{1}$ : 1 sccm 4" furnace: SiH $_{4}$ : 80 sccm B $_{2}$ H $_{6}$ : 7 sccm PH $_{1}$ : 7 sccm The silane (SiH $_{4}$ ) flow depends on the actual process
Substrates	Batch size	6" furnace: 1-25 4" wafers or 6" wafers per run 4" furnace: 1-30 4" wafers per run Deposition on both sides of the substrate
Substrates	Substrate materials allowed	Silicon wafers (only clean 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)