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POLYSILICON DOPING BELOW PHOSPHOROUS SOLID SOLUBILITY

IP.com Disclosure Number: IPCOM000007230D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2002-Mar-06
Document File: 1 page(s) / 75K

Publishing Venue

Motorola

Related People

Randy Kent: AUTHOR [+2]

Abstract

This paper describes a new polysilicon doping process. The equipment is a standard atmospheric thermal diffusion furnace. The dopant source is liq- uid phosphorous oxytrichloride. Polysilicon resistiv- ity uniformity improves because the deposition and drive steps are processed at different temperatures.

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MOlOROLA Technical Developments Volume 22 June 1994

POLYSILICON DOPING BELOW PHOSPHOROUS SQLID SOLUBILITY

by Randy Kent and John Franka

was compared to a POCl, process with different dep- osition and drive temperatures. The "two-step" proc- ess employed a deposition temperature below solid solubility. All process parameters including drive tem- perature, gas flows and ramp rates were identical. Results show the "two-step" process demonstrated an overall improvement of 54% in sheet resistivity uniformity The primary improvement was in across- the-furnace load sheet resistivity. A secondary ben- efit was better uniformity across-the-wafer.

OVERVIEW

  This paper describes a new polysilicon doping process. The equipment is a standard atmospheric thermal diffusion furnace. The dopant source is liq- uid phosphorous oxytrichloride. Polysilicon resistiv- ity uniformity improves because the deposition and drive steps are processed at different temperatures. HISTORY

  Traditionally, polysilicon doping processes deposit a layer of phosphorous glass, then drive the phos- phorous into the under-lying polysilicon at a single temperature. That process is severely limited by phos- phorous depletion which causes poor resistivity uni- formity, Depletion is more pronounced in lightly doped polysilicon layers, This effect becomes impor- tant as the smaller geometry of new product demands better transistor-to-transistor isolation.

SIMS Analysis: "Two-Step" verses Single Temperature Pro&wing

  Monitors analyzed ~for phosphorous concentra- tion variation throughout the polysilicon layer, using Secondary Ion Mass Spectrography, sho...