|Unexposed photoresist is sufficiently alkaline stable for most applications such as electroplating. A correct applied hardbake (> 140°C) can further increase the alkaline stability of the resist film. It has to be considered, that during electroplating the pH-value near the region of metal deposition may be far higher than measured in the bath volume. Crosslinking resists such as the aqueous alkaline developable AZ® nLOF 2000 negative resist family) generally reveal an improved alkaline stabilty. However, our resists are not suited as mask for KOH-based Si-etching under any circumstances.
In acidic solutions, the resist stability is less dependant from the pH-values, but much more from the chemical nature of the etchant: Phosphoric acid and hydrochloric attack the resist only weakly. Using HF, the resist film permeability limits the process stability. Strongly oxidizing acids such as sulphuric acid or nitric acid attack the resist comparable strong.
Non crosslinking resists are generally not stable in organic solvents. Themal crosslinking of positive tone resists (starting at 150°C) or the usage of crosslinking negative tone resists such as the AZ® nLOF 2000 negative resist increase the stability against organic solvents to a certain extent depending on the degree of crosslinking.