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Method for Preparing Void-Free Metal Silicide Films

IP.com Disclosure Number: IPCOM000040447D
Original Publication Date: 1987-Nov-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

Campbell, DR: AUTHOR [+3]

Abstract

Transition metal silicide films, such as TaSi2 and WSi2 (also CoSi2, MoSi2, NbSi2, TiSi2), are typically deposited at a silicon metal atomic ratio of 2 or larger. An excess of silicon is usually considered beneficial for subsequent oxidation. Upon crystallization, such films develop a high density of through-the-thickness voids with diameters that can approach the film thickness. These voids may lower the stress in the film but are otherwise undesirable since they make the film permeable to such things as acids, aluminum metal, and photoresist. Furthermore, films with a high void density can be expected to oxidize unevenly and to develop irregular features upon reactive ion etching. Voids can be eliminated by depositing the films metal rich, that is, with a Si/metal ratio (x-value) of less than 2.0.

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Method for Preparing Void-Free Metal Silicide Films

Transition metal silicide films, such as TaSi2 and WSi2 (also CoSi2, MoSi2, NbSi2, TiSi2), are typically deposited at a silicon metal atomic ratio of 2 or larger. An excess of silicon is usually considered beneficial for subsequent oxidation. Upon crystallization, such films develop a high density of through-the-thickness voids with diameters that can approach the film thickness. These voids may lower the stress in the film but are otherwise undesirable since they make the film permeable to such things as acids, aluminum metal, and photoresist. Furthermore, films with a high void density can be expected to oxidize unevenly and to develop irregular features upon reactive ion etching. Voids can be eliminated by depositing the films metal rich, that is, with a Si/metal ratio (x- value) of less than 2.0. These films need to be reacted with a source layer of silicon, such as polysilicon or amorphous silicon before the disilicide phase can form. In view of the necessity of drawing silicon from another layer into the metal-rich film, a clean interface between these two layers is essential. This can be accomplished by chemical and/or sputter cleaning techniques. The reaction of a metal-rich layer with a silicon layer is different, in the sense that x never exceeds 2.0, from reactions occuring when excess silicon is co-deposited with the metal (x > 2), such that the formation of large, through-the-thickness voids does not occur. Figs. 1 and 2 are schematic drawings that depict co-sputtered films with as-deposited Si/Ta ratios of < 2 and > 2, re...