Portable conformable mask

Deep-UV resists are used in two principal modes as surface resist in single layer mode, or as the thick planarizing layer in portable conformable mask (PCM) bilayer mode. In the single layer mode, the use of deep-UV resists provides improved resolution, while in the PCM mode, a deep-UV resist is used in combination with a conventional resist to make use of the wavelength selectivity of the two types of resists. The PCM process (Figure 5.47) first exposes and develops the conventional novolac-based thin top resist using a 436 nm masked exposure. A second full exposure is then made in the deep-UV, which is... 

FIGURE 5.47 Schematic of portable conformable mask (PCM) bilayer process. (PR, photoresist dUV, deep-UV). 

Fig. 7 a and b. Portable Conformable mask. A substrate with step is covered (planarized) with a deep LTV-sensitive resist (e.g. PMMA) and a top layer which consists of a normal positive photoresist. After imagewise irradiation through a mask (a), the top layer is developed (b) and blanket exposed to deep UV. This results in a sharp image (see text)... 

In toth cases, as well as with the two-layer portable conformable mask (ii, 12) and other two-layer processes (i-5) there is concern about intermixing of the layers it is not easy to devise solvent tems that are adequate for the respective polymers that also do not result in some interpentration of the two layers, with resultant scum or other deleterious effects on resist development. To circumvent this, a barrier layer of a water-soluble polymer sudi as PVA is often used in between. We used s approach in our early development work on PIE (7), and discovered as a consequence some unexpected effects on pofymer morphology that may reveal fundamentally interesting features of interfadal layers. 

---