How to evaluate the quality of photoresist?

A photoresist mainly considers the following characteristics: resolution, contrast, sensitivity, viscosity, adhesion, corrosion resistance, thermal stability, purity.....etc.

Resolution 

Refers to the smallest feature size that the photoresist can produce. We often say that 7nm, 28nm refers to the feature size. The reduction of technical nodes requires the photoresist to have higher resolution. Low resolution photoresist is unable to make a chip with a very small line width.

Contrast

It shows the slope and steepness of the photoresist sidewall. The higher contrast degree means that the edge of the lithographic pattern is sharper, the lines are clearer, and the steepness is closer to 90°.

Sensitivity

Refers to the minimum exposure dose required to form an acceptable pattern, expressed as millijoules per square centimeter (mJ/cm²). Highly sensitive photoresist require lower exposure energy and correspondingly shorter exposure times. In large-scale production, it can greatly save time and reduce process costs.

Viscosity

Viscosity is a physical property that measures the fluidity of photoresist and directly affects the uniformity and thickness of the uniform. The unit is cp. High viscosity photoresist can be even thicker.

Adhesion 

Refers to the adhesion of the photoresist to the wafer. Good adhesion, the photoresist will not fall off on the wafer.

Corrosion resistance

Refers to the ability of the photoresist to chemical attack during etching. For example, in etching, ion implantation and other processes, the corrosion resistance of the photoresist should be considered. The corrosion resistance is not good, and it is easy to fall off or pattern offset and deformation, affecting the process results.

Thermal stability

The ability of photoresist to maintain its physical and chemical properties unchanged during high-temperature processing. In many processes, the temperature of the wafer will rise, and if the thermal stability is not good, it is easy to deform the photoresist.

Purity 

Refers to the impurity content of the photoresist. The higher the resolution of the photoresist, the higher the purity required, even up to the ppb level.

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