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The growing conflicts in international trade have pushed some advanced technologies and processes which are not familiar to the general public and rarely seen in the middle and upper reaches of the industry to the forefront of the wind and waves.

Such as lithography, lithography machine, and the protagonist of this article photoresist.

But these advanced fields, which are now commonly described as "stuck in the neck", are often known only by name, and no one asks for details-what on earth are they? What is it like upstream and downstream? How big is the market? Why did you get stuck in the neck? Why didn't anyone spend a lot of money and make great efforts to develop it in the past?

This article will focus on the photoresist which has attracted much attention because of the chip in the past two years, and analyze the basic situation of this industry for readers, as well as the main difficulties faced by domestic substitution at present.

What kind of industry is photoresist? Photoresist, also known as "photoresist", is the carrier of lithography imaging. Photochemical reaction can be used to convert the diffracted and filtered light information in the lithography system into chemical energy, so as to transfer the fine pattern from the mask to the substrate to be processed. It is widely used in the fabrication of micro-pattern circuits in optoelectronic information industry, and it is the key material of micro-machining technology.

In a word, photoresist is the most important consumable material in lithography process, its performance determines the precision and yield of finished products, and lithography process is the key process of precision electronic components manufacturing, which makes photoresist play a vital role in the whole electronic components processing industry.

It should be emphasized that although photoresist and chip have been repeatedly mentioned by the media in recent years, it has never been only used in semiconductor production, and even in the three mainstream application areas (semiconductor, PCB, LCD), the market scale of semiconductor photoresist is the smallest. Limited by space, this article will focus on the most concerned and typical "stuck neck" area-semiconductor photoresist, other uses will only be a rough introduction, will not be carried out in detail.

From the perspective of the overall industry chain, the upstream of photoresist is all kinds of special chemicals, which belongs to the fine chemical industry; the downstream is all kinds of electronic components manufacturing industry.

From the perspective of production raw materials, the upstream of photoresist is all kinds of special chemicals, which belong to fine chemical industry, including photoinitiators (photosensitizers, photoacidifiers), solvents, film-forming resins and additives (auxiliaries, monomers, etc.).

In terms of dosage, the solvent (mainly propylene glycol methyl ether acetate, referred to as PMA) is the largest material, with a content of up to 90%, but it is not prominent in cost and does not play a key role; as the core part of photochemical reaction, the dosage of photoinitiator is only about 1%-6%; the amount of resin in different photoresist products varies greatly [2].

In terms of cost, in the field of semiconductor photoresist, the more advanced the process, the higher the resin cost: take KrF (krypton fluoride) photoresist as an example, the resin cost is about 75%, the photosensitive agent is about 23%, and the solvent is about 2% [3].

The classification of photoresist is diversified, generally speaking, it follows three major classification methods:

According to the different chemical reaction principle and development principle, it can be divided into positive photoresist and negative photoresist.

According to the different chemical structure of raw materials, they can be divided into photopolymerization type, photodecomposition type, photocrosslinking type and large chemical side type.

According to different downstream applications, it can be divided into PCB photoresist, panel (LCD) photoresist, semiconductor photoresist and other photoresist.

The classification of positive photoresist and negative photoresist is mainly based on the chemical reaction with the developer after illumination, and the corresponding relationship between the resulting pattern and the mask pattern.

The exposure of the positive photoresist is partially dissolved in the developer, and the area illuminated during the etching process will be removed by plasma gas etching, leaving a pattern that is not illuminated by light in the exposure process, which is the same as that on the mask.

Negative photoresist is opposite to positive photoresist, its exposed part does not dissolve in the developer, the unilluminated area will be removed, and the pattern formed during development is opposite to that of the mask.

The production process of positive gum and negative glue is basically the same, but there are differences in properties. From the point of view of development, negative glue was first used in lithography process, and has the advantage of more corrosion resistance. However, due to the easy deformation and expansion during development, the negative glue has poor performance in the most critical resolution and can not be used in the production of advanced processes [4].

Photopolymerization, photolysis, photocrosslinking and chemical amplification this classification is based on the chemical structure of photosensitive resins in raw materials. Among them, photopolymerization and photodecomposition are mainly used in positive photoresist, while photocrosslinking is a typical negative photoresist. Chemical magnification is the most advanced type at present, which is widely used in advanced process [4].

PCB photoresist, LCD photoresist and semiconductor photoresist are classified according to the application field of photoresist, and it is also one of the most well-known standards.

Of the three main photoresist, PCB (printed circuit board, Printed circuit board) photoresist is the lowest and has the highest localization rate, accounting for 3% and 5% of the manufacturing cost of PCB. Can be divided into dry film photoresist, wet film photoresist and photoimaging soldering ink [2].

Relying on China's advantages in labor and resources, since the 21st century, the PCB industry has begun to transfer to China. Domestic manufacturers have mastered the core technology of producing key materials upstream of PCB, and have strong competitiveness in production capacity and cost. According to the data, the global PCB output value in 2019 is about US $63.7 billion. China's PCB market reached US $32.94 billion, accounting for more than 50% of the global market share, and is the largest PCB producer [2].

Data source: Cinda Securities [2], fruit shell hard science and technology lithography is also the core process of LCD panel manufacturing, so LCD photoresist, that is, panel (Liquid Crystal Display) photoresist is also the core consumables of the industry. Color filter is the key device for LCD to realize color display, accounting for 14% / 16% of panel cost, and its production cost directly affects the price and competitiveness of LCD products. Color photoresist and black photoresist are the core materials for the preparation of color filter, and color photoresist and black photoresist account for about 27% of the overall cost [5].

However, similar to semiconductor photoresist, the domestic production rate of panel photoresist in China is also not high, and the production capacity is mainly concentrated in the relatively low-end touchscreen photoresist field. Higher value-added color and black photoresist, the current market is monopolized by Japanese and Korean manufacturers. Taking the color photoresist with the greatest demand as an example, Japanese, Korean and Taiwan enterprises such as Tokyo Yinghua, LG Chemical, Toyo Ink, Sumitomo Chemical, Mitsubishi Chemical, Chi Mei and other Japanese, South Korean and Chinese Taiwan companies occupy more than 90% of the market share, and China's independent supply capacity is also not strong [2].

Data source: Cinda Securities [2], fruit shell hard science and technology mapping in the semiconductor field, the lithography process is the most core and important processing link, and its cost is about 30% of the entire chip manufacturing process. Time-consuming accounts for about 40% / 50% of the entire chip process. As the core medium of this process, the quality and performance of semiconductor photoresist are the key factors that affect the chip performance, yield and reliability, and have a vital impact on the overall lithography process.

With the requirements of the market for miniaturization and functional diversification of semiconductor products, semiconductor photoresist continues to improve the limit resolution by shortening the exposure wavelength, so as to adapt to the developing lithography process.

According to the exposure wavelength, semiconductor photoresist can be further divided into ordinary wide photoresist, g line (436nm), I line (365nm), KrF (248nm), ArF (193nm), and the most advanced EUV (

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