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Method of Forming Doped Polycrystalline Silicon Pattern With Desired Sidewall Profile

IP.com Disclosure Number: IPCOM000047063D
Original Publication Date: 1983-Sep-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Chanclou, R: AUTHOR [+2]

Abstract

Doped polycrystalline silicon (polysilicon) is widely used in the semiconductor industry, and more particularly for FET products, as a field plate, the gate electrode and/or the interconnection lines. In these applications, the tapered edge of the doped polysilicon pattern is desired to improve the edge coverage of the overlying material which may be either a passivating layer or a metal land. When polysilicon is N-type doped with phosphorous atoms in an open-tube diffusion process with POCl3, a layer of phosphosilicate glass (PSG) is formed atop its surface. In standard silicon processing, this undesired layer of PSG is removed, the doped polysilicon is covered by a photoresist layer which is selectively etched by a known photolithographic process. Unfortunately, the sidewall profile is negatively tapered.

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Method of Forming Doped Polycrystalline Silicon Pattern With Desired Sidewall Profile

Doped polycrystalline silicon (polysilicon) is widely used in the semiconductor industry, and more particularly for FET products, as a field plate, the gate electrode and/or the interconnection lines. In these applications, the tapered edge of the doped polysilicon pattern is desired to improve the edge coverage of the overlying material which may be either a passivating layer or a metal land. When polysilicon is N-type doped with phosphorous atoms in an open-tube diffusion process with POCl3, a layer of phosphosilicate glass (PSG) is formed atop its surface. In standard silicon processing, this undesired layer of PSG is removed, the doped polysilicon is covered by a photoresist layer which is selectively etched by a known photolithographic process. Unfortunately, the sidewall profile is negatively tapered. That is to say, there is a nonnegligible undercut at the base of the polysilicon layer, which, in turn, results in discontinuities in the overlying material at the edge. The following method allows the achievement of a polysilicon pattern with a positively tapered edge. The method will be illustrated with relation to the formation of the gate electrode of a MOSFET. Fig. 1 shows a silicon single crystal substrate 10 covered by a thin dielectric layer 11 and a layer of polysilicon 12. When the polysilicon layer 12 is doped with POCl3, a thin layer of PSG 13 forms atop its surfa...