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Novel Method of Attaining High Etch Selectivity Using Intrinsic Polysilicon

IP.com Disclosure Number: IPCOM000061856D
Original Publication Date: 1986-Sep-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Polavarapu, MS: AUTHOR [+2]

Abstract

A process has been developed which will allow the use of present polysilicon RIE (reactive ion etch) processes for the fabrication of smaller devices with thinner gate electrodes. Referring to Fig. 1, a silicon substrate 10 having a gate silicon dioxide layer 12 has an intrinsic polysilicon layer 14 deposited thereon. This intrinsic polysilicon layer 14 is then coated with a hard masking material 16, which can be silicon dioxide, UV-hardened photoresist, multilayer resist, aluminum, etc. This hard masking material 16 is then patterned using conventional lithographic techniques to define the gate structure. Arsenic, or a similar N+ dopant, is then implanted in the intrinsic polysilicon layer 14 throughout its depth, as seen in Fig. 2.

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Novel Method of Attaining High Etch Selectivity Using Intrinsic Polysilicon

A process has been developed which will allow the use of present polysilicon RIE (reactive ion etch) processes for the fabrication of smaller devices with thinner gate electrodes. Referring to Fig. 1, a silicon substrate 10 having a gate silicon dioxide layer 12 has an intrinsic polysilicon layer 14 deposited thereon. This intrinsic polysilicon layer 14 is then coated with a hard masking material 16, which can be silicon dioxide, UV-hardened photoresist, multilayer resist, aluminum, etc. This hard masking material 16 is then patterned using conventional lithographic techniques to define the gate structure. Arsenic, or a similar N+ dopant, is then implanted in the intrinsic polysilicon layer 14 throughout its depth, as seen in Fig. 2. The hard masking material 16 prevents the dopant from penetrating in the area of the gate electrode 20. The concentration of the N+ dopant is selected such that the peak concentration resides in the bulk of the polysilicon layer 14, while the lightly doped tail of the gaussian implant distribution resides slightly below the silicon surface 22. This lightly doped region serves to replace the source-drain extension implant as conventionally practiced. The polysilicon layer 14 is RIE etched using process conditions which provide an N+ polysilicon:silicon dioxide etch rate ratio greater than 30:1 and vertical sidewalls, resulting in a structure as seen in Fig. 3....