The main function of the mask plate is to transfer the designed circuit pattern to the substrate or wafer of the downstream product through exposure. As the benchmark and blueprint for lithographic reproduction, mask plates are the key to connecting industrial design and process manufacturing. The accuracy and quality level of the mask plate will directly affect the excellent rate of the final downstream product. The function of the mask plate is similar to the "negative" of the traditional camera, and the image (circuit graphics) is copied by means of transparent and non-transparent, so as to achieve mass production.
In semiconductor manufacturing, the mask plate forms gate, source drain, doping window, electrode contact hole and other structures on the surface of semiconductor wafer through multiple exposure process. In the flat panel display manufacturing, the designed TFT array and color filter pattern are exposed and transferred to the glass substrate according to the sequence of film layer structure of the thin film transistor by using the exposure masking effect of the mask plate, and the display device with multiple film layers is finally formed.
Second, the structure and material of the mask plate
The mask plate is mainly composed of substrate, shading layer and protective film.
Substrate: Mask plate substrate is a photosensitive blank plate for making fine photomask graphics. Common substrate materials are quartz glass and soda glass. Quartz glass has high optical transmittance, low thermal expansion rate, high flatness and wear resistance, mainly used in high-precision mask plate. The optical properties of soda glass are slightly inferior to quartz glass, and it is mainly used for medium and low precision mask plates.
Shielding layer: Shielding layer is mainly divided into hard shielding layer and latex shielding layer. The hard shading layer is usually formed by chromium plating on the substrate, has high mechanical strength and durability, and can form fine patterns. Latex shading layer is mainly used in PCB and touch control scenes.
Protective film: Protective film (Pellicle) refers to a mask plate protective film with light resistance and high light transmittance, used to protect the mask plate from dust, stains and other pollution.
Mask plate manufacturing process is complex, many steps. The mask plate is manufactured based on the original design pattern, processed by a computer-aided system, and supplemented with optical proximity effect compensation. The corrected design pattern is transplanted to a quartz substrate with good light transmission performance by laser or electron beam exposure. Finally, the mask plate is etched and inspected.
Mask version is widely used downstream, mainly including IC manufacturing, IC packaging, flat display and printed circuit board industries. The mask version is closely related to the development trend of mainstream consumer electronics (mobile phones, tablets, wearable devices), laptop computers, vehicle electronics, network communications, household appliances, LED lighting, Internet of Things, medical electronics and other products in the downstream terminal industry.
Fourth, the classification and technology of mask plate
Mask plate according to the use of classification can be divided into chromium plate, dry plate, liquid relief plate and film. Among them, chromium plate has the highest precision and better durability, and is widely used in flat panel display, IC, printed circuit board and fine electronic components industry; Dry plate, liquid relief plate and film are mainly used in low and medium precision LCD industry, PCB and IC carrier board and other industries.
According to the different light sources used in the lithography process, common mask plates are roughly divided into binary mask plates, phase-shifted mask plates and EUV mask plates.
Binary mask plate: Photomask plate composed of two parts of light transmission and light transmission, is the earliest and most used type of mask plate, is widely used in 365nm (I-wire) to 193nm immersion lithography.
Phase shift mask version: A mask product with a phase shift layer whose thickness is proportional to 1/2 light wave length is arranged at the adjacent light transmission gap. The phase-shift mask technology enables the exposure light passing through the phase-shift layer to produce a light phase difference of 180 degrees from other transmitted light, improving the resolution and focus depth of the wafer exposure, and ultimately improving the photomask with higher reproduction characteristics.
EUV Mask plate: A novel mask plate used during EUV lithography. Because EUV has a short wavelength and is easily absorbed by all materials, a refracting element like a lens cannot be used, but instead reflects the beam through a multilayer (ML) structure according to Bragg's Law. EUV mask plate is often used in 7nm, 5nm and other advanced processes.
Fifth, the mask version of the market and technology development trend
The mask plate industry will develop in the direction of high precision and large size in the future. The development of the mask plate industry is mainly affected by the development of the downstream chip industry, flat panel display industry, touch industry and circuit board industry. With the development of the semiconductor chip manufacturing process to the direction of refinement, this puts forward higher requirements for the mask plate with which it is matched, and the line seam accuracy is becoming higher and higher.
In terms of semiconductors, the current mainstream domestic advanced manufacturing process is 28nm process, the mainstream overseas is 14nm, Samsung has mass produced 7nm process wafers, and TSMC has mass produced 5nm process. In the future, the manufacturing process of integrated circuits will be further refined and developed toward a 5nm-3nm process.
Mask version product size will continue to trend to large size in the future. In the field of flat panel display, China's mainland TFT-LCD has occupied an absolute advantage, and the proportion of OLED in the world has rapidly increased. The demand for mask version soil is increasing, and the market space is steadily improving.
Six, mask plate industry challenges and opportunities
The main challenges facing the mask plate industry include technical barriers, high costs and market competition. Due to the lithographic mask plate industry has certain technical barriers, the global lithographic mask plate is mainly professional manufacturers. The most important raw material for the mask plate is the mask substrate, of which the cost of high-purity quartz glass is higher and the number of suppliers is small.
However, there are also huge opportunities in the mask industry. With the rapid development of the downstream industry, especially the continued growth of the semiconductor and flat panel display industries, the market demand for mask plates will continue to increase. At the same time, with the continuous progress of technology, the accuracy and performance of the mask version will be further improved, bringing new growth points to the industry.
Seven, mask version of the potential alternative technology
Currently, masked plates dominate microelectronics manufacturing, but potential alternative technologies such as mask-free technology are also evolving. Because the maskless technology can only meet the needs of graphics transfer in industries with relatively low precision requirements (such as PCB), and its production efficiency is low, it cannot meet the needs of industries with high graphics transfer accuracy requirements and production efficiency requirements. Therefore, the technology change of the mask plate industry is still slow at this stage, and there is no risk of rapid iteration of technology.
Viii. Summary
As a graphics transfer master in the process of microelectronics manufacturing, mask plate plays a crucial role in the manufacturing process of flat panel display, semiconductor, touch control, circuit board and other industries. The accuracy and quality level of the mask plate directly affect the excellent rate of the final downstream product. With the rapid development of the downstream industry and the continuous progress of technology, the mask industry will usher in more opportunities and challenges. In the future, the mask version will develop in the direction of high precision and large size, providing more high-quality and efficient graphics transfer solutions for the microelectronics manufacturing industry.
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