Plasma etching technology is an indispensable processing technology in the preparation process of ultra-large-scale integrated circuits.
Ceramic parts of the plasma etching equipment
Plasma etching technology is an indispensable processing technology in the preparation process of ultra-large-scale integrated circuits. With the sharp reduction in the size of semiconductor transistors and the increase in the energy of halogen plasmas, the contamination problem of wafers has become more and more prominent. For the plasma corrosion resistance of materials in the cavity of plasma etching equipment under high-density plasma conditions during wafer processing, the requirements are becoming more and more stringent. The new generation of etching technology requires more powerful and reliable materials to solve problems such as plasma corrosion, particle generation, metal contamination, and oxygen decomposition.
1. Ceramics are the key materials for plasma etching equipment components
Compared with organic materials and metal materials, ceramic materials generally have better physical and chemical corrosion resistance and higher operating temperatures. Therefore, in the semiconductor industry, ceramic materials have become the core component manufacturing materials of semiconductor wafer processing equipment. The components of plasma etching equipment using ceramic materials mainly include window mirrors, focusing rings, electrostatic chucks, nozzles, cavities, gas dispersion disks, etc.
The main characteristics of plasma etching resistant ceramic materials in the etcher chamber are: high purity, low metal impurity content; stable chemical properties of the main components, especially low chemical reaction rate with halogen corrosive gases; high density, few open pores; fine grains, low grain boundary phase content; excellent mechanical properties, easy to produce and process; some components may have other performance requirements, such as good dielectric properties, electrical conductivity or thermal conductivity, etc.
In a plasma environment, the selection of ceramic materials depends on the working environment of the core components and the quality requirements for process products, such as plasma etching resistance, electrical properties, insulation, etc.
2. Application of ceramics in the core components of plasma etching equipment
(1) Chamber
As the main source of wafer contamination, the impact of plasma etching on the chamber material of the etcher determines the wafer yield, quality, and stability of the etching process etc. High-purity alumina ceramic is a good plasma corrosion-resistant material, which can provide reliable plasma impedance as a chamber material.
However, the alumina ceramic cavity in the plasma etcher equipment is a large ceramic. The production of such large-sized and ultra-high-purity alumina ceramics has problems such as easy deformation, cracking, and difficulty in sintering to a dense state. To obtain highly dense and high-purity alumina ceramics, high requirements are placed on the purity of the powder and the preparation process.
(2) Focusing ring
The focusing ring is designed to improve the etching uniformity around the edge or periphery of the wafer, fix the wafer in place to maintain the plasma density, and prevent the side of the wafer from being contaminated. When used with an electrostatic chuck, the wafer is placed on the focusing ring and fixed in place by static charge. Since the focusing ring is in direct contact with the plasma in the vacuum reaction chamber, it is necessary to use a material that is resistant to plasma corrosion and has an electrical conductivity similar to that of a silicon wafer. The materials of the focusing ring include conductive silicon and silicon carbide.
Conductive silicon is a commonly used focusing ring material. Its electrical conductivity is almost equal to that of a silicon wafer, but its disadvantage is that it has poor etching resistance in fluorine-containing plasma. The materials of the etcher components often suffer from severe corrosion after a period of use, which seriously reduces their production efficiency. Silicon carbide has similar electrical conductivity to silicon and good resistance to ion etching, and is suitable for focus ring materials.
Usually, the focus ring is made by depositing silicon carbide generated by chemical reaction into a certain shape through vapor deposition, and then machining the silicon carbide into a certain shape according to specific use conditions to generate the focus ring.
(3) Electrostatic chuck (ESC)
During the entire etching process, the chip is adsorbed and fixed by the electrostatic chuck (ESC) in the lower electrode system, and radio frequency RF is passed into the electrostatic chuck, so that the radio frequency RF will form a DC bias on the chip. This promotes the plasma etching reaction on the chip. At the same time, the electrostatic chuck will control the temperature of the chip to promote the uniformity of chip etching. The interior of the electrostatic chuck is mainly composed of a dielectric layer, a base, and a heating layer. Aluminum oxide and aluminum nitride are often used as dielectric layer materials for electrostatic chucks because of their high thermal conductivity and low thermal expansion coefficient.
(4) Window mirror
The window mirror of the etcher has high requirements on the material transmittance and etching resistance. When the etching resistance of the window mirror is poor, the surface of the window mirror tends to become blurred. Yttrium oxide is a ceramic material that is transparent in the visible light range and has a high transmittance. It can be used as a window mirror material for plasma etching equipment. However, yttrium oxide ceramics have the disadvantages of poor sintering performance, high production cost, poor mechanical properties, and difficult processing. By adding a certain amount of aluminum oxide to yttrium oxide ceramics to form yttrium aluminum garnet (YAG) composite materials, it has excellent light transmittance and etching resistance, and has good mechanical properties, making it an ideal alternative material.
(5) Nozzle
Nozzles are used for precise gas flow rate and uniform control to evenly disperse the gas into the etching process chamber. These components require high plasma tolerance, dielectric strength, and strong corrosion resistance to process gases and by-products. Commonly used ceramic materials are aluminum nitride ceramics and aluminum oxide ceramics. At present, ceramic nozzles in the etching chamber can also be produced through ceramic 3D printing technology to improve product manufacturing efficiency and stability.