Adhesion properties of a structural etch stop material for use in multilayer electronic wiring structures
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Willi Volksen, James L. Hedrick, and Jeff Labadie IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose, California 95120 (Received 10 August 1994; accepted 12 December 1994)
A thermally stable copolymer of a polyimide and a dianiline terminated polydimethylsiloxane has been developed for use as a structural oxygen etch barrier material in high performance multilayer electronic wiring structures. We report on the preparation of the etch barrier material and on investigations of the etch stop and adhesion properties of this material. Studies on the effects of adhesion-promoting plasma treatments are supported by x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectrometry (RBS) data. Before plasma treatment, it is observed that the siloxane component segregates to the surface. After either an O2 reactive ion etch treatment or H2O plasma exposure, the unusual XPS charging effects are interpreted as a surface layer containing two distinct phases: the etched polyimide fraction and a partial overlayer of a carbon containing SiO 2 .
I. INTRODUCTION Interconnect structures based on polymeric dielectrics with imbedded thin film metal wiring have many advantages for high performance electronic packaging, such as the thin film module employed in the high end models of the IBM ES/9000 series mainframes.1*3 Some alternative schemes for fabricating such a structure have been discussed in Ref. 4. If the wiring channels of a given wiring plane inside the structure are defined using reactive ion etching (RIE) of the polyimide dielectric, then an etch stop layer is preferably used to protect underlying polyimide. Such a layer, made of a suitable oxygen etch barrier material, then allows for a reasonable amount of overetching, thus providing a manufacturable process window (see Fig. 1). It should be noted that in such a scheme the etch stop material will remain in the wiring structure. The material, therefore, should have a low dielectric constant, very good thermal stability, durability, and good adhesion properties to the polyimide above and below. Moreover, as shown in Ref. 4, good gap-filling properties of the etch stop material are very useful if the metallization of the wiring channels is done by lift-off. Such an etch stop material has recently been developed by incorporation of polydimethylsiloxane (PMDS) segments into a thermally stable, high Tg polyimide, such as pyromellitic dianhydride-oxydianiline (PMDA-ODA) (Fig. 2). In this article, we report on the etch properties under O 2 RIE conditions and on the adhesion properties of this material. In particular, since the siloxane and polyimide fractions of the copolymer are immiscible, the 1028 http://journals.cambridge.org
J. Mater. Res., Vol. 10, No. 4, Apr 1995
Downloaded: 18 Mar 2015
siloxane fraction will tend to segregate to the surface. This necessitates a surface treatment to ensure adhesion to the polyimide layer on top. The effects of such surface treatments are investigated using surface analysis techniques. II. EXPERIMEN
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