stability & storage condition
Stability and optimum storage conditions
Photoresists are light-sensitive, they react to light exposure or high temperatures and also during storage, agerelated changes occur. Resists are therefore filled in light-protected amber bottles, stored in a cool place and can only be processed under yellow light (λ > 500 nm). The date of expiry and the recommended storage temperature are indicated on the product label of each bottle. If these temperatures are maintained, resists in unopened bottles are stable until expiry date (which is in general 2 years after production), at least however for 6 month
after date of sale. Brief temperatures deviations have no influence on general product properties.
If resists are to be used later than 6 month after date of sale or to be processed within a very small process window, storage at 4 – 8 °C is recommended. Exceptions are only resists with recommended storage temperatures between 18 – 25 °C. These resists should not be stored colder.
Photoresists stored for several years are outdated and may only be used with considerable restrictions. This also applies to resists stored at too high temperatures and to highly diluted resists which age faster than normal. Possible
consequences are the formation of particles which is caused by a precipitation of the light-sensitive component. Repeated fine filtrations is however only helpful at
an early stage. The steadily declining concentration of the light-sensitive component will successively lead to lower development rates, increased dark erosion and reduced resist adhesion properties.