Process optimization of 200 nm wide trenches in SiO2 using a chemically amplified acid catalyzed e-beam resist

Abstract

In this article we present a novel acid catalyzed chemically amplified resist and the associated silicon-dioxide etch process that was developed using that resist. The 200 nm wide and 250 nm deep trenches in the silicon dioxide are part of a multilevel fully planar metallization scheme, where copper lines are fully imbedded in the interlevel dielectric. Conventional resist materials are not sensitive enough to be used in high-throughput production and in many cases their selectivity versus silicon dioxide reactive ion etching is low. Resist materials based on acid catalyzed chemical amplification show very desirable properties with respect to their sensitivity, flexibility in design, and resolution capability. The resolution capability extends down to 200 nm for 290 nm thick resist presented in this report. Moreover, as such resists meet the requirements of deep UV, x-ray, and e-beam exposure tools, it is expected that they will replace the ‘‘standard’’ novolac resists in many applications. A process window for silicon dioxide etching using a single layer resist based on poly(4-hydroxy styrene-co-4-acetoxymethyl styrene) has been developed. Lithographic sensitivity, resolution, contrast as well as etching characteristics of this resist were evaluated. The resist demonstrated a sensitivity of 2–2.5 μC/cm2 for 50 keV e-beam exposure by the JEOL 5DIIU system. A contrast value of 5.1 was obtained using a postexposure bake of 130 °C for 2 min. The resist selectivity with respect to thermal oxide in CHF3 plasma reactive ion etching (RIE) was about 1–3. Using this resist and CHF3 RIE we were able to etch 0.25 μm deep and 0.2 μm wide trenches with vertical sidewalls in SiO2. These results showed that the resist system is very feasible for future single layer resist e-beam pattern definition, and it also has a very promising prospects for deep UV and x-ray lithographies.