Introduction to Photoresist

Photoresist, also known as a photo‑sensitive resist, is a light‑sensitive liquid formulation composed of a photoinitiator, photoresist resin, monomers, solvents, and various additives. As a pattern‑transfer medium, it enables the transfer of mask‑defined features onto a substrate by exploiting differences in solubility following exposure to light. Today, photoresist is extensively employed in the fabrication of fine‑line patterns in the optoelectronics and information‑technology industries, serving as one of the critical materials in the electronics manufacturing sector.

　　Based on the wavelength of light, photoresists can be classified into ultraviolet (300–450 nm) photoresists, deep‑ultraviolet (160–280 nm) photoresists, extreme ultraviolet (EUV, 13.5 nm) photoresists, electron‑beam photoresists, ion‑beam photoresists, X‑ray photoresists, and others. Generally speaking, under identical process conditions, a shorter wavelength yields higher patterning resolution.

　　Depending on the application, photoresists can be categorized into those for printed circuit boards (PCBs), liquid crystal displays (LCDs), semiconductors, and other uses. Among these, PCB photoresist technology faces relatively lower technical barriers compared to the other two categories, whereas semiconductor photoresist represents the most advanced level of photoresist technology.

　　Classified by chemical structure, photoresists can be divided into photopolymerizable, photodecomposable, photocrosslinkable, and chemically amplified types. Photopolymerizable photoresists use vinyl‑type monomers; under illumination, free radicals are generated, which then initiate further monomer polymerization, ultimately yielding a polymeric film. Photodecomposable photoresists employ materials containing diazonaphthoquinone (DQN) compounds as the photosensitive agent; upon exposure to light, these undergo photodecomposition, enabling the formation of positive‑tone photoresists. Photocrosslinkable photoresists utilize photosensitive polymers such as poly(vinyl alcohol) laurate; under light irradiation, they form an insoluble crosslinked network that provides resistivity, resulting in negative‑tone photoresists. Following the adoption of deep ultraviolet (DUV) light sources in semiconductor integrated‑circuit lithography, chemically amplified resists (CAR) have gradually become the industry standard. In chemically amplified photoresist technology, the resin is a polyvinyl compound whose chemical functional groups confer insolubility; a photoacid generator (PAG) serves as the photoinitiator. Upon exposure, the PAG in the exposed areas generates an acid, which acts as a catalyst during the post‑exposure bake step to cleave the protecting groups on the resin, thereby rendering it soluble. Chemically amplified photoresists exhibit an exposure speed approximately ten times that of DQN‑based resists, demonstrate excellent optical sensitivity to DUV wavelengths, and offer high contrast and superior resolution.

　　Photoresist is a critical material in integrated circuit manufacturing: its quality and performance are key determinants of IC performance, yield, and reliability. Photolithography accounts for roughly 35% of the total cost of chip fabrication and consumes about 40–50% of the overall process time. Photoresist costs represent approximately 4% of the total materials expense in IC production, underscoring the market’s substantial size. According to third-party research firm Zhiyan Consulting, the global photoresist market was estimated at nearly US$9 billion in 2019, with a compound annual growth rate (CAGR) of about 5.4% since 2010. The market is expected to continue expanding at an average annual rate of 5% over the next three years, surpassing US$10 billion by 2022. The photoresist industry exhibits extremely high barriers to entry, resulting in an oligopolistic structure worldwide. For many years, the sector has been dominated by specialized firms from Japan and the United States. Today, the top five manufacturers collectively hold 87% of the global photoresist market, reflecting a highly concentrated industry landscape. Among them, Japan’s JSR, Tokyo Ohka Kogyo, Shin-Etsu Chemical, and Fujifilm Electronic Materials together account for 72% of the market share. Moreover, core technologies for high-resolution KrF and ArF semiconductor photoresists are largely controlled by Japanese and U.S. companies, with most products originating from firms such as DuPont, JSR Corporation, Shin-Etsu Chemical, Tokyo Ohka Kogyo, Fujifilm, and South Korea’s Dongjin. Overall, Japan remains the dominant hub for the photoresist industry. At present, mainland China remains heavily reliant on foreign suppliers, particularly for electronic materials like photoresist. Consequently, domestic substitution in the semiconductor materials sector is an inevitable trend.

　　Reference: New Materials Online