Correct dilution of resists (see “Dilution of resists”)
Resists are mainly composed of solvents. The majority of photoresists and the negative-tone e-beam resists utilize PGMEA (PMA) as main solvent. This solvent is consequently also the most commonly used thinner and offered by us as AR 300-12. PGMEA is often also used for the removal of edge beads (see Removal or minimizing of edge beads during coating).
We strongly recommend using only the recommended thinner for the dilution of resists. The solid content can of course also be reduced with other solvents. The solubility features of acetone, isopropanol, dioxane, butyl acetate and others would lead to a complete dissolution of all solid components, but the coating behavior of the resist would often change dramatically and high surface quality could only be obtained in exceptional cases.
For PMMA e-beam lithography, different solvents like chlorobenzene, anisole and ethyl lactate are used. Each of these solvents is also available as thinner: chlorobenzene as AR 600-01, anisole as AR 600-02 and ethyl lactate as AR 600-09. A further solvent of PMMA copolymers is methoxy propanol which is offered as AR 600-07.
For the various spray resists, special conditions apply. The resist solvent is composed of fast-drying and film-forming components. The solvent composition for spray resists was optimized with great effort. Already minor changes of the solvent composition cause vastly different coating features. For this reason, exclusively the original thinner should be used here. With the exception of the thinner-mixtures of spray resists, all other (pure) thinners may be used far beyond the expiration date. These thinners contain no components which are subjected to changes.
Overview Process Chemicals- Thinner