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Improved Dopant-Gas Injector Design for Doped Poly Low Pressure CVD

IP.com Disclosure Number: IPCOM000122992D
Original Publication Date: 1998-Mar-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 54K

Publishing Venue

IBM

Related People

Buchet, C: AUTHOR [+4]

Abstract

Achieving a good Within-Wafer (WIW) uniformity of the sheet resistance (Rs) of "in situ" doped polysilicon layers is always a challenge for process engineers in a conventional high batch size mass production environment. Hereinbelow, there is described an improved dopant-gas injector design, used for "In-Situ" boron-doped polysilicon in a conventional vertical LPCVD tube reactor such as the reactor referenced, VTR 7000, manufactured by the Silicon Valley Group (SVG). As a result, we could improve the WIW Rs uniformity by a factor of 1.8 without significant drawbacks like additional costs, long term stability or degradation of Wafer-to-Wafer (W2W) uniformity.

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Improved Dopant-Gas Injector Design for Doped Poly Low Pressure CVD

      Achieving a good Within-Wafer (WIW) uniformity of the sheet
resistance (Rs) of "in situ" doped polysilicon layers is always a
challenge for process engineers in a conventional high batch size
mass production environment.  Hereinbelow, there is described an
improved dopant-gas injector design, used for "In-Situ" boron-doped
polysilicon in a conventional vertical LPCVD tube reactor such as the
reactor referenced, VTR 7000, manufactured by the Silicon Valley
Group (SVG).  As a result, we could improve the WIW Rs uniformity by
a factor of 1.8 without significant drawbacks like additional costs,
long term stability or degradation of Wafer-to-Wafer (W2W)
uniformity.

In a typical LPCVD furnace, silane (SiH4) is injected mainly at the
top of the reactor and the reactant flows in an annular space along a
batch of typically 100 wafers, evenly spaced by a pitch of ppr.  0.2
inch.  Gas transfer between the wafers (i.e. approximately 0.2 inch.
Gas transfer between the wafers (i.e. lateral to the wafer surface)
takes place by diffusion.  If the main process parameters are
properly adjusted, the diffusion rate is fast compared to the SiH4
pyrolysis rate on the wafer surface.  Finally, this results in a
thickness uniformity of typically less than 2%.  Decreasing of the
deposition rate along the flow due to gas depletion (W2W uniformity)
can easily be compensated by an appropriate temperature tilt along
the...