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Separation of Oxidation And Diffusion Steps in Symmetric Transistor Manufacture

IP.com Disclosure Number: IPCOM000100752D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 1 page(s) / 34K

Publishing Venue

IBM

Related People

Chu, SFS: AUTHOR [+3]

Abstract

This method minimizes diffusion and stress which may occur when the base polysilicon (polysi) of symmetric transistors is oxidized. The method provides for depositing the undoped polysi and then oxidizing the surface at high temperature to avoid any outdiffusion. Boron is then implanted through the oxide, followed by a second heat cycle to firm the extrinsic/intrinsic base link-up.

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Separation of Oxidation And Diffusion Steps in Symmetric Transistor Manufacture

       This method minimizes diffusion and stress which may
occur when the base polysilicon (polysi) of symmetric transistors is
oxidized.  The method provides for depositing the undoped polysi and
then oxidizing the surface at high temperature to avoid any
outdiffusion.  Boron is then implanted through the oxide, followed by
a second heat cycle to firm the extrinsic/intrinsic base link-up.

      In the conventional processing of symmetric transistors the
extrinsic base is formed by the high pressure oxidation of the doped
polysi.  If this is done at a high temperature, it is difficult to
control the base outdiffusion and excessive boron may be diffused
into the single crystal region.  If it is done at low temperatures,
the crystal is subject to stress and related defects.

      The new technique decouples the oxidation step and the
diffusion step to make them independent of each other. Instead of
depositing boron into the polysi prior to oxidation, it is proposed
to first deposit an undoped intrinsic polysi layer followed by
polishing.  The top layer of polysi is oxidized at high temperatures
to reduce any stress-induced defect in the epi.  An ion implant of
boron is made into the polysi layer through the oxide layer, followed
by an annealing step which will diffuse the boron to obtain an
optimal linkup of the extrinsic/intrinsic bases.