Specific Process Knowledge/Thin film deposition/Furnace LPCVD PolySilicon

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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 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 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
Substrates	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)