Core ceramic components inside the etching machine

If a chip is compared to a flat engraving work, then the photolithography machine is the brush for sketching, the etching machine is the engraving knife, and the deposited film is the material used for engraving. The precision of photolithography directly determines the size of the component etching, while the precision of etching and thin film deposition determines whether the size of photolithography can be actually processed. To transfer the chip circuit diagram from the mask to the wafer to achieve the predetermined chip function, the etching process is an important link.  In chip manufacturing, photolithography and etching are two precisely connected steps. The previous process of etching is photolithography, which develops the circuit pattern onto the wafer through photoresist. Then, the etching method is used to remove the parts of the film layer not covered by photoresist, thus completing the transfer of the pattern from the mask to the wafer and preparing for subsequent steps such as ion implantation.

The principle of etching is a process that selectively removes unnecessary materials by using chemical or physical methods. The etching process is carried out after coating, adhesive application, photolithography and development. Through etching, the unnecessary film material exposed on the wafer surface is removed, leaving the required part, and then the excess photoresist is removed. By repeating the above steps many times, a complex-structured integrated circuit can be obtained. Because it involves material removal, etching is called a "subtractive process".

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According to their working principles, the most common classifications of etching are dry etching and wet etching. The difference between the two lies in whether solvents or solutions are used for etching. Among them, the market share of dry etching exceeds 95%.

Wet etching

Immersion in a chemical solution for corrosion removal has the advantages of low cost, fast etching speed and high productivity. However, this will cause the mask and the oxide film after etching to not be fully aligned, thus making it difficult to ensure the fineness of the process line width and resulting in a decrease in yield.

Dry etching

Dry etching, also known as plasma etching, dominates in semiconductor etching.

Plasma etching machines are roughly divided into two major categories based on the differences in plasma generation and control technologies, namely capacitive coupled plasma (CCP) etching machines and inductively coupled plasma (ICP) etching machines. CCP etching machines are mainly used in the etching process of dielectric materials, while ICP etching machines are mainly used for silicon etching and metal etching, also known as conductor etching machines. The objects of dielectric etching are dielectric materials such as silicon oxide, silicon nitride and hafnium dioxide, while the objects of conductor etching include silicon materials (monocrystalline silicon, polycrystalline silicon and silicides, etc.) and metallic materials (aluminum, tungsten, etc.).

The structure of an etching machine can be divided into two major parts: the main body and the auxiliary equipment. Among them, the main body of the etching equipment includes three major modules: EFEM (front end of the equipment), TM (transmission module), and PM (process module). The accessory equipment provides guarantee and support for the above three major modules, and its layout is relatively independent of the main body of the machine.

Etching machine cavity

The corrosive plasma environment in the semiconductor manufacturing process mainly consists of plasma cleaning and plasma etching. In addition, the halogen-based plasmas used in plasma-enhanced chemical vapor deposition also have strong corrosiveness. As the minimum feature size of semiconductor devices continues to shrink, the requirements for wafer defects have become increasingly strict. To prevent contamination by metal impurities and particles, more stringent requirements have been put forward for the cavity of semiconductor equipment and the materials of the components inside the cavity. At present, ceramic materials have become the main materials for the cavities of etching machines.

The main features of the plasma etched ceramic materials in the etching machine cavity are:

• High purity and low content of metal impurities;
• Maincomponents: It has stable chemical properties, especially with halogen corrosive gas chemical reaction rate is lower;
• High density, few open pores;
• The grains are fine and the content of grain boundary phases is low;
• With excellent mechanical properties, easy to production and processing;
• Some components may have other performance requirements, such as good dielectric properties, electrical conductivity or thermal conductivity, etc.

At present, this kind of ceramic materials mainly include quartz, silicon carbide, aluminum nitride, alumina, silicon nitride, yttrium oxide, etc

Electrostatic chuck 

The uniformity of the temperature distribution on the wafer is an important factor affecting the wafer etching rate and etching uniformity. Electrostatic chucks play a key role in controlling the wafer temperature. The internal structure of an electrostatic chuck mainly includes a dielectric layer, a heating layer and a base. Both AlN and SiC can be used to make the dielectric layer of electrostatic chucks due to their high thermal conductivity. Although AlN has better plasma etching resistance than SiC in fluorine-containing plasma, the fluoride generated by the reaction between SiC and fluorine-containing plasma is volatile and can be removed through a vacuum system without causing etching contamination to the chip.

Focusing ring

The function of the focusing ring is to provide balanced plasma, which is required to have a similar electrical conductivity to the silicon wafer. In the past, the main material used was conductive silicon. However, fluorine-containing plasmons would react with silicon to form volatile silicon fluoride, which would significantly shorten its service life, requiring frequent replacement of components and reducing production efficiency. SiC has a similar electrical conductivity to single-crystal Si and better resistance to plasma etching, making it suitable as a material for focusing rings.

The material of the window sight glass on the window sight glass etching machine requires high light transmittance. Initially, quartz glass material was used, but it was prone to corrosion and became blurred. Later, it was replaced by Al2O3 material. However, with the application of fluorine-containing plasmas, the corrosion resistance of Al2O3 has gradually failed to meet the demands of mass production. This is because the Al in Al2O3 reacts with fluoride ions to form AL-F compounds, which then deposit and crystallize to form granular impurities, easily contaminating the wafers. Y2O3 transparent ceramics exhibit excellent corrosion resistance in fluorine-containing plasma, but they have poor sintering performance, high production costs, and relatively poor mechanical properties, making them difficult to process and thus limiting their practicality. YAG transparent ceramics have a high light transmittance, and their corrosion resistance to fluorine-containing plasma is similar to that of yttrium oxide. Moreover, their mechanical properties are even more outstanding, making them a relatively ideal alternative material.

As a key consumable in the plasma etching process of semiconductor materials, SiC etching rings have extremely high purity requirements. Generally, only the CVD process can be used to grow thick layers of SiC blocks, which are then precisely processed to obtain them. They are mainly used in the preparation stage of semiconductor etching processes. For a long time, the development of semiconductors and their supporting materials has been a weak link in China's manufacturing process. However, due to their high technical barriers, they have long been monopolized by the United States, Japan, Germany and other countries, and have always been one of the key materials that have been "strangled".

Insulating ring ceramic materials are excellent insulators in most cases. Especially silicon nitride ceramics have the characteristics of insulation, high-temperature resistance, corrosion resistance and long service life. Therefore, it can be fabricated into insulating rings with high insulation requirements under harsh working conditions. Compared with alumina ceramic insulating rings, silicon nitride ceramic insulating rings have higher temperature resistance, greater strength, strong thermal stability, and their service life can be extended by about ten times or more. To a large extent, they can reduce production costs and save operation time.  In the plasma cleaning process of gas nozzles, corrosive gases containing highly reactive halogen elements such as fluorine and chlorine are used. Gas nozzles are typically made of alumina ceramics and are required to have high ionic resistance, dielectric strength, and strong corrosion resistance to process gases and by-products. At the same time, they have a precise internal pore structure to precisely control the gas flow rate.

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