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Sputtered Tungsten/Aluminum System for Subsequent CVD Tungsten Via Stud

IP.com Disclosure Number: IPCOM000038388D
Original Publication Date: 1987-Jan-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Cronin, JE: AUTHOR

Abstract

This article relates to the formation of a patterned composite metal structure which interposes a film of sputtered tungsten between an aluminum layer and a chemical vapor deposited (CVD) tungsten contact stud to eliminate a contact resistance problem and provide the added benefit of using the interposed film as an etch mask. Tungsten hexafluoride (WF6) is used as the source gas for CVD tungsten (W) when fabricating metal via studs for semiconductor circuits. The metal fluorides formed when studs are fabricated on a surface of aluminum (Al) or titanium (Ti) are non-volatile at the temperatures of deposition. The compounds formed, AlF3 and TiF3, respectively, increase the contact resistance since these compounds are poor conductors.

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Sputtered Tungsten/Aluminum System for Subsequent CVD Tungsten Via Stud

This article relates to the formation of a patterned composite metal structure which interposes a film of sputtered tungsten between an aluminum layer and a chemical vapor deposited (CVD) tungsten contact stud to eliminate a contact resistance problem and provide the added benefit of using the interposed film as an etch mask. Tungsten hexafluoride (WF6) is used as the source gas for CVD tungsten (W) when fabricating metal via studs for semiconductor circuits. The metal fluorides formed when studs are fabricated on a surface of aluminum (Al) or titanium (Ti) are non-volatile at the temperatures of deposition. The compounds formed, AlF3 and TiF3, respectively, increase the contact resistance since these compounds are poor conductors. A typical reaction is: WF6 + H2 + Al yields W + HF (gas) + AlF3 (solid) A non-volatile metalic fluoride, i.e., AlF3 solid, left at the Al/W interface, forms a high resistance barrier which increases the contact resistance of the stud and introduces reliability concerns.

Low contact resistance studs are formed by depositing AlCu on a boron phosphorus silicon glass (BPSG) insulator to the thickness required, followed by a thin film of sputtered W as shown in Fig. 1. Since W is an etch stop for Al, it can be used as a mask as well as an interposed material. A thin resist is used to pattern the thin W film. Once the W is etched, a second etch step is used to etch the A...