Resist Requirements

Photoresist thickness is a major factor that determines the resolution limits and quality of patterns defined by ENFOL. The optimum resist thickness of 60 nm is required to ensure that the exposure is performed in the evanescent near field of the mask. For thinner resist layers, pattern transfer using RIE becomes difficult and for thicker resist layers the resolution degrades due to diffraction. Fig. 17.5(a) shows a partially resolved pattern exposed for 70 s into a 125 nm thick resist layer. The equivalent exposure into a 60 nm resist layer is shown in Fig. 17.5(b). Similar resolution degradation is observed if the mask and substrate are not held in conformable contact. These results illustrate the need to have significant exposure from the evanescent field close to the aperture plane of the mask in order to attain sub-wavelength features.

Fig. 17.5.(a) Partially resolved pattern formed by ENFOL exposure into 125 nm thick resist, (b) Pattern clearly resolved, obtained by exposing resist with the optimum thickness of 60 nm. Subtractive pattern transfer has been used to transfer the pattern in (a) and (b) into the silicon substrate to a depth of 100 nm

Fig. 17.5.(a) Partially resolved pattern formed by ENFOL exposure into 125 nm thick resist, (b) Pattern clearly resolved, obtained by exposing resist with the optimum thickness of 60 nm. Subtractive pattern transfer has been used to transfer the pattern in (a) and (b) into the silicon substrate to a depth of 100 nm

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