In the manufacturing process of chips (integrated circuits), from production to packaging of the final device, every link is inseparable from electronic properties. For example, steps such as photolithography, etching, and ion implantation all require the use of high-quality electron gases.
What is electronic specialty gas? How does it play a role in chip production? How is the development of domestic electronic specialties? This article will outline these topics around electronic specialty gas.
In the industry, products that are gaseous at room temperature and pressure are collectively called industrial gas products. As the basic raw material, industrial gases have a wide range of application fields, including industries relating to people’s livelihood, such as integrated circuits, LCD panels, LED, optical fiber communications, photovoltaics, high-end equipment manufacturing, metallurgy, chemical industry, machinery, and other traditional industries.
Industrial gases have three links: the upper, middle, and lower reaches of the industrial chain. Among them, the upstream link is mainly raw materials (air, industrial waste gas, basic chemical raw materials) and equipment (gas separation and purification equipment, and pressure vessel equipment). The midstream link is the preparation of industrial gases (including bulk gases and special gases), and the downstream link is for terminal application fields.
Industrial gases can also be divided into bulk gases and specialty gases. Among them, bulk gases can be divided into electronic bulk gases (used for environmental gas, protective gas, and carrier) and non-electronic bulk gases (used for metallurgy, chemical industry, and mechanical processing). While special gases mainly include electronic special gases and medical gases, laser gas, food gas and other non-electronic specialty gases.
The demand for electronic specialty gas mainly comes from the fields of integrated circuits and display panels. According to the CSSC Special Gas prospectus, in the global electronic special gas consumption structure, integrated circuits, display panels, photovoltaics and semiconductor lighting account for 71%, 18%, 3% and 8% respectively.
In the field of integrated circuits, electronic specialty gases are mainly used in cleaning, epitaxial deposition, oxidation film formation, photolithography, etching, doping and many other processes in front-end wafer manufacturing. It is used in almost every link during the production process. It has an important impact on product performance, yield, integration, and other aspects. According to data from Guanyan Tianxia, electronic special gases account for 36% of etching gases in the integrated circuit field, 34% of doping gases, and 30% of epitaxial deposition, photolithography, and other gases. At the same time, according to SEMI (International Semiconductor Industry Association) data, among wafer manufacturing materials, silicon wafers account for the largest cost, reaching 35%. In addition, electronic special gas is the second largest consumable, accounting for 13%.
So, what are the commonly used electronic properties? The following will introduce the practical uses of electronic specialty gases in the etching, doping and epitaxial deposition of integrated circuit manufacturing processes.
1.Etching
Etching is the process of selectively removing unwanted material from the surface of a silicon wafer using chemical and physical methods. The purpose of etching is to correctly replicate the mask pattern on the glued silicon wafer. Etching methods are divided into wet chemical etching and dry chemical etching. Dry chemical etching uses ions or free radicals in the plasma generated by low-voltage discharge to chemically react with the material, with its main medium as gas. Silicon etching gases mainly refer to fluorine-based gases, including CF4, SF6, C2F6, NF3, as well as chlorine-based (Cl2) and bromine-based (Br2, HBr) gases.
2.Doping
When semiconductor devices and integrated circuits are manufactured, certain impurities are doped into semiconductor materials to make the materials have the required conductivity type and certain resistivity to create resistors, PN junctions and buried layers. Gases used in the doping process are called doping gas, mainly including arsine, phosphine, phosphorus trifluoride, phosphorus pentafluoride, arsenic trifluoride, arsenic pentafluoride, boron trifluoride and diborane. Usually, the doping source and carrier gas (such as argon and nitrogen) are mixed in the source cabinet. The mixed gas flow is continuously injected into the diffusion furnace, surrounding the wafer. The dopant is deposited on the surface of the wafer, and then reacts with the silicon to generate doping. The metal then migrates into the silicon.
3.Epitaxial deposition
Epitaxial deposition is coating a thin film on the substrate wafer as a buffer layer to prevent harmful impurities from entering the silicon substrate. Commonly used methods include chemical vapor deposition (CVD) and physical vapor deposition (PVD). Chemical vapor deposition uses a large amount of electron gas. It is a process technology in which reactive substances react chemically under gaseous conditions to generate solid substances that are deposited on the surface of a heated solid substrate, thereby producing solid materials.
In the semiconductor industry, chemical vapor deposition is used to grow one or more layers of material on a carefully selected substrate. The gas used to grow one or more layers of material is called an epitaxial gas. Commonly used silicon epitaxial gases include SiH2Cl2, SiCl4 and SiCl4. Epitaxy mainly includes epitaxial silicon deposition, silicon oxide film deposition, silicon nitride film deposition and amorphous silicon film deposition. Epitaxy is a process in which single crystal materials are deposited and grown on the surface of a substrate.
Currently, China’s industrial gas industry’s supply system for high-end semiconductor products is incomplete. With overseas gas monopolies dominating the international market and controlling the qualification certification of high-end products, the development of China’s special gas industry cannot quickly accelerate through market regulation alone. The main problems faced are:
First, there is an oligopoly market structure, causing competitive disadvantages to domestic companies. The industrial gas industry in developed Western countries started early and thus has first-mover advantages. The global electronic specialty gas market has formed an oligopoly pattern. Relevant data show (Source: The Paper) that overseas oligarchs accounted for 86% of China’s electronic specialty gas market share in 2020, while the market share of domestic electronic special gas companies was only 14%. Low market share limits the production scale of domestic enterprises, making it difficult to reduce marginal costs while limiting market competitiveness and profit scale.
Second, there are low economic benefits of producing raw materials, thus companies are unmotivated. Take neon gas as an example. The production of pure neon gas generally uses steelmaking waste gas as raw material. Although there are many steel companies in China that have already mastered this technology, the primary market for high-purity neon production has not yet been formed. This is because neon gas is subject to steel production, thus the output is unstable. In addition, the storage and transportation costs of gas products are high. When the market demand is unstable and not strong, steel companies are faced with a greater risk of loss.
Third, the cooperation between downstream enterprises and overseas suppliers is sticky. The purity and cleanliness of electronic specialty gas affects the quality of related electrical components. If there is a problem with the gas quality, the entire production line will be scrapped. To avoid trial and error costs in production and operation practice, electronic specialty gas manufacturers and products must pass the audit to obtain qualifications, which takes about 2-3 years. Due to the high time cost and opportunity cost of changing suppliers, the cooperative relationship between upstream and downstream enterprises is not easily terminated, making it even more difficult for domestic electronic specialties to develop the market.
Fourth, overseas lithography machine oligarchs control the qualification certification of equipment manufacturers, making it more difficult for domestic gas companies to obtain certifications. Japan’s Nikon, Canon and the Netherlands’ ASML have a global semiconductor lithography machine market share of more than 90%, and ASML has a monopoly on the most high-end ultraviolet lithography machine market. If semiconductor manufacturers use ASML’s products, they must choose gas products from companies certified by ASML. Only ASML will be responsible for the quality of the semiconductor products they manufacture. If domestic gas companies want to enter the high-end semiconductor industry, they must seek this certification, which has become a problem in the industry chain.
To ensure the stable supply of electronic specialty gases, the localization rate of electronic specialty gas products must be improved, and the of the electronic special gas industry should be improved.
In recent years, China has successively issued several ministries. The electronic specialty gas industry support policy includes special gases in the new material industry. In July 2022, the Ministry of Industry and Information Technology, the Ministry of Science and Technology, and the Ministry of Natural Resources jointly issued the “14th Five-Year Plan for the Development of Raw Materials Industry”, which focuses on key application areas such as integrated circuits, information communications, and energy industries to conquer special coatings and photoresists, and key materials such as industrial gases, catalysis, optical functions, and hydrogen storage materials. In the context of national policies that continue to favor the development of the electronic specialty gas industry, China’s electronic specialty gas industry will have bright projections.
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