Journal of Vacuum Science & Technology B, Vol.20, No.2, 596-603, 2002
High-resolution in situ electron beam patterning using Ti(OC3H7)(4) as a negative-type resist
Our previous studies on the electron beam resist properties of inorganic titanium isopropoxide films condensed on semiconductor surfaces addressed mainly the electron sensitivity of this negative-type resist, i.e., the contrast curve behavior. In order to determine its resolution capabilities, we have used scanning electron microscopy to analyze the pixel sizes and shapes that result after exposing condensed titanium isopropoxide films of various thicknesses (from as low as the 10's of Angstrom range to as high as 10 000 Angstrom) to a scanning electron beam for different times. We have found that resolution is strongly dependent on initial film thickness and electron beam exposure. While occurring at the lowest electron exposure, the smallest, well-defined pixels were observed with films on the order of 100 Angstrom; thinner films (in the 10's of Angstrom range) resulted in pixels with poor definition. For films with sufficient thickness, dual pixel behavior was observed above a critical electron exposure, in which a narrow pixel with height approximating the initial film thickness would appear at the center of a thin, a broader area pixel that was observed for all exposures. Moreover, the broad area pixel's height was relatively insensitive to initial thickness and exposure. By qualitative comparison with standard electron-resist scattering models in the literature, we argue that the thin, a broad area pixel is an artifact of the backscattered electron component generated from the interaction of the electron beam with the substrate, whereas the narrow and thick central pixel that appears after sufficiently high exposures, is representative of the forward-scattered electron distribution of the incident beam within the resist film.