4. What is the optimal pre-treatment of substrates for photoresists?
If new and clean substrates (wafers) are used, a bake at approximately 200 °C for several minutes (2~3 minutes, hot plate) is sufficient for drying, but the substrates have to be processed quickly afterwards. A temporary storage in a desiccator is highly recommended in order to prevent rehydration.
Pre-used wafers or wafers which are contaminated with organic agents require previous cleaning steps, e.g. in easy cases cleaning in acetone, followed by isopropanol or ethanol treatment and subsequent bake (→ Section 1). This procedure improves the adhesion features of the resist. On no account only acetone should be used, since the evaporative heat loss during the bake a condensation of air humidity on the wafer.