PROCEEDINGS ARTICLE | July 1, 1991
Proc. SPIE. 1463, Optical/Laser Microlithography IV
KEYWORDS: Optical lithography, Deep ultraviolet, Etching, Metals, Silicon, Reflectivity, Aluminum, Technetium, Semiconducting wafers, Standards development
Shipley XP-89131 is a wet developable negative tone DUV resist, capable of resolving features down to 0.3 micrometers when used in conjunction with the ASM- L PAS 5000/70 stepper (NA equals 0.42). Practical implementation of this material at the limit, however, is marred by several problems, notably, poor C.D. (critical dimension) control over steps, inadequate adhesion and the formation of various types of residue between features. The authors have endeavored to find means by which these effects may be reduced. Methods investigated for tackling the residue problem have included the use of metal ion free and metal ion containing developers, a comparison of puddle, immersion and spray develop processes, changes in the percentage overdevelopment employed, as well as the effect of developer temperature. Additional work has been directed towards examining the effect of post-exposure baking time. The high transparency of such resists, coupled to the high reflectivity of substrates at 248 nm, gives rise to severe C.D. control problems over topography. We examine the effectiveness and tradeoffs of two alternative approaches potentially capable of effecting an improvement. Spin coatable DUV ARC materials have been found to significantly improve C.D. control over polysilicon and aluminum topography, although the more retrograde profiles observed, in conjunction with optical proximity effects, can impose other limitations. Several beneficial side effects have been noted, however, including improved adhesion on aluminum substrates, a wider exposure window and easier stripping of the resist following dry etching. Potential yield reducing factors such as the presence of resist residues or bridges between features, are also significantly reduced during the dry development of the ARC. The alternative method of employing dyed resists has also been evaluated using both Shipley XP-90166 and XP-90174 resists. While the latter version does offer some improvements over the undyed XP-89131 material, it is not as effective as the ARC approach in controlling C.D.s over topography. It is apparent too that the resolution limit of such materials has been blunted. Finally the focus and exposure latitude has been determined for features printed on silicon, both with and without ARC. In a similar way the focus/exposure window has been determined for etched contacts.
