A new conformal dry-etch technique for submicrometer structuresa)

A new microlithographic pattern transfer technique that does not require resist development has been studied. The technique involves the diffusion of gaseous HF and water vapor through the exposed resist and the selective etching of the underlying SiO2. Etching is found to proceed only when the resist is in contact with the SiO2 underneath. The ratio of the etch rate of SiO2 beneath exposed and unexposed resist can be essentially infinity and this very high selectivity was used for etching high resolution SiO2 patterns without development. Variations of etch rate with substrate temperature (100° to 250°C), exposure dose (0−54 J/cm2 for UV, and 0−3.2 mC/cm2 for e-beam at 20 keV) HF vapor flow and resist thickness (1600 to 4000 Å) are presented. This new microlithographic etch process for patterning SiO2 does not require resist development and therefore reduces the three key steps in microlithography—exposure, development, and etching to two. As a result it eliminates the problems introduced during the development stage such as pinholes and loss of pattern fidelity. The process is capable of resolution down to at least 0.7 μm linewidths in silicon dioxide and in principle can be applied to other materials with volatile reaction products.