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Technique for Tapering Contact Windows

IP.com Disclosure Number: IPCOM000060496D
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

Stanasolovich, D: AUTHOR

Abstract

Current VLSI processes contain contact windows which are anisotropically etched by reactive ion etching (RIE) in relatively thick layers of phosphosilicate glass (PSG). A problem exists when the first metal interconnect, defined by lift-off, passes over the vertical-walled contact window and cracks or fissures are incurred in the metal line. This problem is resolved by the sequence of processing steps described below, which produce an optimally tapered (less than or equal to 60 degrees) contact window. In the first step, an SiO2 and a 7-11 mole % PSG film are deposited to a thickness equal to the desired final thickness plus an additional 1500 - 2000 Angstroms. A 10-minute 900 - 1000ΠC nitrogen anneal is performed to partially flow the PSG film.

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Technique for Tapering Contact Windows

Current VLSI processes contain contact windows which are anisotropically etched by reactive ion etching (RIE) in relatively thick layers of phosphosilicate glass (PSG). A problem exists when the first metal interconnect, defined by lift- off, passes over the vertical-walled contact window and cracks or fissures are incurred in the metal line. This problem is resolved by the sequence of processing steps described below, which produce an optimally tapered (less than or equal to 60 degrees) contact window. In the first step, an SiO2 and a 7-11 mole % PSG film are deposited to a thickness equal to the desired final thickness plus an additional 1500 - 2000 Angstroms. A 10-minute 900 - 1000OE C nitrogen anneal is performed to partially flow the PSG film. Next, a contact mask is defined using conventional photolithographic techniques. A 15-second buffered HF dip is then used to remove approximately 1000 Angstroms of PSG. An undercut 8 (Fig. 1) of the photoresist mask is produced by the wet etch which prevents the PSG from flowing into the contact window during the ensuing PSG anneal. Next, RIE, using 30% H2 in CF4 is used to etch the contact window until approximately 1000 Angstroms of PSG 10 and SiO2 12 remain in the contact window 14, as shown in Fig. 1. The depth of the etch is determined by time or laser interferometry. Following the RIE, a nitrogen and/or oxygen anneal is performed to taper the contact window 14, as shown in F...