Photoresist resin, also known as film-forming resin, is an inert polymer matrix. It is the core component of photoresist and constitutes the basic photoresist skeleton. Photoresist resins are often used in conjunction with photosensitive agents and play a crucial role in making photoresist photosensitive. The structures vary from different photoresist resins, which mainly determine the basic properties of the photoresist after exposure, including hardness, flexibility, adhesion, the solubility for specific solvents, optical properties, aging resistance, etching, thermal stability, etc.
Resin Types
Different types of photoresists have different resin systems. Table 1 lists several common UV photoresists with different exposure wavelengths and their corresponding film-forming resins.
| Photoresist Types | Resins |
| G/I line | Phenolic resins |
| KrF | Poly(p-hydroxystyrene) resins |
| ArF | Polymethacrylate resins |
| EUV | Poly(p-hydroxystyrene) resins |
Table 1. Photoresist types and resin systems.
- Resins for G/I-line resists
The o-diazonaphthoquinone (DNQ)-phenolic resin system of positive photoresist was developed in the middle of the 20th century, using phenolic resin as the film-forming resin. This kind of photoresist has good clarity, good dry etching resistance, and good heat resistance, so the DNQ-phenolic resin system is still the most widely used photoresist system in the electronics manufacturing industry currently. At present, the vast majority of G/I line resists are based on Novolac-DNQ systems, whose main components are phenolic resin and DNQ [1].
- Resins for KrF resists
Phenolic resin is difficult to meet the sensitivity requirements of high-precision circuits, so it is no longer used in photoresists of 248 nm and below. Most film-forming resins used in deep ultraviolet photoresists are concentrated in p-hydroxystyrene and its derivatives, methylbenzene selenate, and maleic anhydride. Poly(p-hydroxystyrene) and its derivatives are commonly used in KrF resists because of the large number of benzene rings in their molecular structure and their high etching resistance.
- Resins for ArF resists
For ArF resists with shorter exposure wavelengths, the light transmission performance of the film-forming resin becomes the main problem. Isobutyl methacrylate polymers are preferred due to their high transparency at 193 nm. The material is, however, not resistant to etching. The discovery that polymers with multiple alicyclic structures exhibit good etching resistance led methacrylates with multiple alicyclic side chains to be widely used as resins in ArF resists.
- Resins for EUV resists
The wavelength of the light source used in EUV resist is the shortest, at 13.5 nm. Since almost all optical materials absorb at this wavelength, the focus on film-forming resins gradually changes from light transmission to high resolution, roughness of the edges, and high photospeed. The mainstream EUV resist systems include poly(p-hydroxystyrene) copolymers, and polycarbonate derivatives.
