Dry Etching of Chrome for Photomasks for 100nm Technology using Chemically Amplified Resist

摘要

Photo mask etching for the 100nm technology node places new requirements on dry etching processes. As the minimum-size features on the mask, such as assist bars and optical proximity correction (OPC) patterns, shrink down to 100nm, it is necessary to produce etch CD biases of below 20nm in order to reproduce minimum resist features into chrome with good pattern fidelity. In addition, vertical profiles are necessary. In previous generations of photomask technology, footing and sidewall profile slope were tolerated, since this dry etch profile was an improvement from wet etching. However, as feature sizes shrink, it is extremely important to select etch processes which do not generate a foot, because this will affect etch linearity and also limit the smallest etched feature size. Chemically amplified resist (CAR) from TOK is patterned with a 50keV MEBES~(~R) eXara~(TM) e-beam writer, allowing for patterning of small features with vertical resist profiles. This resist is developed for raster scan 50 kV e-beam systems. It has high contrast, good coating characteristics, good dry etch selectivity, and high environmental stability. Chrome etch process development has been performed using Design of Experiments to optimize parameters such as sidewall profile, etch CD bias, etch CD linearity for varying sizes of line/space patterns, etch CD linearity for varying sizes of isolated lines and spaces, loading effects, and application to contact etching. Etch processes have been developed specifically for etching small features, but these are also applicable to etching of larger feature sizes. Etch processes are capable of patterning of chrome features below 100nm with vertical sidewalk, <20nm etch bias, and similarity of profile and etch bias for lines and spaces between 100nm and >1μm. Excellent uniformity and reptoducibility are also demonstrated. SEM micrographs illustrate processes applicable to small feature etching, along with processes that are limited to large feature etching. In this paper, we will discuss CD uniformity, sidewall profile, etching bias, loading effects, and linearity and how these relate to small-feature chrome etching.