A large variety of applications include a wet-chemical etching step which very often involves highly alkaline etching baths. While for example negative resists of the CAR44 series can easily be stabilised by a subsequent flood exposure and hard bake against alkaline conditions, is a simple hard bake of positive resists not sufficient to obtain the desired effect since in this case no stabilising crosslinking takes place. A stabilisation can however be achieved by blocking the reactive alkali-soluble groups in the resist layer. The example of AR-P 3210 demonstrated convincingly that (already developed) resist structures can sufficiently be stabilised against alkaline solutions by a subsequent silylation with HMDS. Initially it was necessary to activate the patterned resist layer by flood exposure. Due to the intense exposure, the photosensitive component (DNQ) is at first converted into indene carboxylic acid. At temperatures in a range between 110 °C – 120 °C, HMDS (gas phase) silylates both the OH-groups of the novolac as well as the indene carboxylic acid quantitatively to a poorly alkali-soluble compound, but structures will nevertheless still not withstand a silicon etch (40 % KOH at 85 °C).
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