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.
Solvents and workplace safety
All resists we offer as well as a large number of process chemicals contain organic solvents. When handling these products, provisions of the Ordinance on Hazardou s Substances are to be complied with. The safety data sheets of our products are intended to provide required data and handling recommendations for the user to take effective measures for health protection, workplace safety and environmental protection.
The most important criterion for the rating and classification as hazardous substance is the flashpoint. The flashpoint is the lowest temperature at which under previousl y described experimental conditions at normal pressure a substance may give rise to an ignitable air-gas mixture formed above this substance.
The ignition temperature is the minimum temperature to which a substance has to be heated to spontaneously ignite in the presence of air without any external source of ignition, i.e. a flame or a spark, solely as the result of being heated. The ignition temperature does not correlate with the boiling point or the flash point of a flammable substance. The ignition temperature is a measure for the sensitivity to oxidation of a substance and exceeds for most organic solvents a temperature of 200°C.
The flammable range is the concentration at which combustible gases, mist or vapours will form a flammable mixture with air. The flammable range is defined by the explosion limits, i.e. the lower and upper limit concentration at which a mixture can be ignited by heating.
Selected properties of solvents:
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When handling organic solvents, the respective working place limit strictly has to be observed which is defined according to the German Ordinance on Hazardous Substances as the the li mit of the time-weighted average concentration of a substance in the air within the breathing zone of a worker in relation to a specified reference period. This value indicates the concentration of a substance up to which no acute or chronic harmful effects on the workers’ health in general are to be expected.