Photoresists Raw Materials
Introduction
Photoresist can change its solubility under the irradiation of ultraviolet light, electron beam and other light sources, and then become soluble or insoluble in the developer. Photoresist raw materials can be roughly divided into two categories: organic materials and organic-inorganic hybrid materials. Among them, organic photoresist materials mainly include polyacetal, polyester, polyarylsulfonate, polymers containing unsaturated double bonds and other small molecular compounds. The main components of organic-inorganic hybrid photoresist materials are metal oxygen clusters and silsesquioxane.
Organic Materials
- Acetals and esters
Acetals and esters can be decomposed under acid catalysis. After adding photoacid generators (PAGs), the degree of decomposition can be controlled by ultraviolet light so that their solubility becomes different in exposed and unexposed areas, and then images can be formed by development. These materials that can be decomposed by acid catalysis are usually used as chemically amplified photoresists. Chemically amplified photoresist is a chain reaction system with chemical amplification effect and acid catalysis. PAGs are used as catalysts or photoinitiators to generate a large number of strong acid hydrogen ions under light, and photoresist resin is catalyzed by strong acid hydrogen ions to remove protective groups or decompose into substances that are soluble in alkaline solutions. Although chemically amplified photoresist is a widely used organic system photoresist, there are still problems of low resolution and sensitivity when applied to EUV lithography.
- Aryl sulphonate
Unlike the traditional chemically amplified photoresist, this new type photoresist is a material that is directly sensitive to radiation and does not require PAGs in its formulation. Therefore, the formulation of non-chemically amplified photoresist is relatively simple, and usually only contains two components: polymer and solvent. For example, a series of polymers can be prepared by free radical polymerization using (4-(methacryloyloxy) phenyl)-dimethyl sulfonyl trifluorate as the backbone material and copolymerizing with methyl methacrylate, 4-carboxylstyrene and N-vinylcarbazole respectively. These polymers can be used as EUV photoresists to obtain images at 20 nm.
- Polymers containing unsaturated bonds
Polymers containing unsaturated double bonds can be cross-linked, and then become insoluble in the developer, so they are good negative photoresist materials. Negative photoresist usually has high sensitivity and is expected to be used in EUV photolithography. For example, in order to improve the transparency of the polymer in the EUV region, trimethylsilyl and other polar groups can be introduced into the norbornene monomer to obtain an etching resistant norbornene copolymer for EUV lithography. This polymer has good photolithographic properties at 248 nm and EUV wavelength, and can be used as the next generation photoresist material.
Organic-Inorganic Hybrid Materials
- Organometallic nanoclusters
The solution state of organometallic nanoclusters is a unique nano precursor. Under the action of EUV or X-ray photons, these organometallic nanoclusters will interact and change solubility, making it possible to become photoresists. In particular, compared with traditional polymers or emerging metal oxide nanoparticles, the size and atomic composition of nanoclusters are controllable, which is a great advantage in making high-resolution patterns.
- Silsesquioxane
Hydrogen silsesquioxane (HSQ) photoresist has high resolution performance in electron beam lithography and interference lithography, and is a potential candidate material for EUV photoresist. By adding acidic methanol functional group, HSQ photoresist system can be further improved to obtain higher resolution patterns.
Application
Lithography is the core step of chip manufacturing, and photoresist plays an important role in the process of lithography. Photoresist raw materials have been continuously used in mobile phones, computers, cameras and other electronic products, and have become a necessity in people's lives, prompting these electronic products to develop in the direction of "light, thin, short, small" and multifunction integration.
Reference
- Willson, C. Grant; DAMMEL, Ralph R.; REISER, Arnost. Photoresist materials: a historical perspective. In: Metrology, Inspection, and Process Control for Microlithography XI. SPIE, 1997. p. 38-51.