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Process for Producing an Isolation Technique With a Reduced Bird's Beak

IP.com Disclosure Number: IPCOM000060448D
Original Publication Date: 1986-Apr-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 37K

Publishing Venue

IBM

Related People

Polavarapu, M: AUTHOR [+3]

Abstract

Typical VLSI processes utilize local oxidation techniques to define the isolation regions separating the active devices. A problem which results from these processes is the encroachment of the "bird's beak" on the active area of the chip, thereby compromising circuit density. This problem is reduced by the following sequence of process steps. Referring to Fig. 1, a pad SiO2 layer 10 and pad nitride (Si3N4) layer 12 are deposited upon silicon substrate 14. The pad nitride 12 is photolithographically defined and selectively etched to the pad SiO2 layer 10 using known reactive ion etch (RIE) techniques. Feasible gas mixtures include CH2F2 and CH3F. A conformal layer of polysilicon is next deposited over the pad nitride 12 and pad SiO2 10.

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Process for Producing an Isolation Technique With a Reduced Bird's Beak

Typical VLSI processes utilize local oxidation techniques to define the isolation regions separating the active devices. A problem which results from these processes is the encroachment of the "bird's beak" on the active area of the chip, thereby compromising circuit density. This problem is reduced by the following sequence of process steps. Referring to Fig. 1, a pad SiO2 layer 10 and pad nitride (Si3N4) layer 12 are deposited upon silicon substrate 14. The pad nitride 12 is photolithographically defined and selectively etched to the pad SiO2 layer 10 using known reactive ion etch (RIE) techniques. Feasible gas mixtures include CH2F2 and CH3F. A conformal layer of polysilicon is next deposited over the pad nitride 12 and pad SiO2 10. The thickness of the layer can be adjusted to effectively control the length of the bird's beak. This conformal polysilicon layer is anisotropically etched using the following RIE conditions: Power Density - 1.24 watts per cm2 Pressure - 80 mtorr % NH3 in CCl2F2 - 30.0% This process has a high selectivity to both SiO2 and Si3N4 . The end result is polysilicon spacers 16, as shown in Fig. 2. The field ion implantation is performed, as known in the art, followed by the growth of the field oxide 18, as seen in Fig. 3.

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