Manufacturing issues of electrostatic chuck

Abstract: Electrostatic chucks use electrostatic force to hold wafers on their surface and are mainly used in vacuum processes such as plasma etching. We will briefly describe the difficulties in the manufacturing process from the perspectives of Raw material selection, various sintering process, temperature control, etc.

Ⅰ. What is an electrostatic chuck?

The electrostatic chuck is a clamping tool for transferring and transporting wafers. It is a device that utilizes the principle of electrostatic adsorption to adsorb wafers to be processed on its surface and can control the temperature of the wafer surface by back-blowing gas.

Ⅱ. Product characteristics of electrostatic chuck

The electrostatic chucking avoids irreparable damage to wafers caused by pressure, collision and other mechanical reasons during the use of traditional mechanical chucks, reduces particle contamination, increases the effective processing area of wafers, overcomes the defects of vacuum chucks that can not be used in low-pressure environments, and ensures the thermal uniformity of the surface of wafers. The core characteristics of the electrostatic chuck include high-precision adsorption, excellent temperature control, plasma resistance, fast response, high reliability, so that it has replaced the traditional mechanical chuck and vacuum chuck to become a semiconductor equipment is very important in the general-purpose parts.

Ⅲ. Technical indicators：

3.1 ESC type

3.2 Working conditions

3.3 ESC Performance

Ⅳ. Manufacturing difficulties of electrostatic chuck

1. Raw material selection: Electrostatic chucks have very high requirements for the materials used. For example, ceramic materials need to have high purity, excellent insulating properties and strength in order to maintain stable performance in harsh environments such as high temperatures and strong corrosive environments. Electrode materials, on the other hand, need good electrical conductivity to ensure effective electric field distribution and sufficient adsorption.

✔Substrate layer material: generally the substrate layer choose ceramic material as its manufacturing material, usually choose alumina or aluminum nitride. Aluminum nitride ceramic is a new type of material generally favored by the industry, it only has excellent comprehensive mechanical properties, at the same time has a very high thermal conductivity, so high-end electrostatic chuck to choose aluminum nitride as the base layer. At present, both the cost and technical difficulties, the preparation of high-purity aluminum nitride powder is much higher than alumina.

✔Electrode layer materials: electrode layer materials, conductive silver paste due to excellent room temperature conductivity, hardness, adhesion and bending resistance is more commonly used.

✔Adsorption layer materials: adsorption layer as the most important functional structure layer in the electrostatic chuck, the choice of materials has a great impact on its functionality, according to the analysis of the principle of electrostatic chuck, the adsorption layer material body resistivity needs to be controlled in the 108 ~ 109Ω-cm in order to meet the functional requirements.

At the same time, the adsorption layer needs to meet the high thermal conductivity, high abrasion resistance, good electrical properties and match the coefficient of thermal expansion with the silicon chip. Therefore, the main material of the adsorption layer is aluminum nitride ceramics, and through the doping of the resistance to make its body resistivity to meet the functional requirements.

2. Sintering: After determining the overall structure of the three-layer aluminum nitride ceramic electrostaticchuck, there are two different manufacturing methods.

✔Integral sintering: Integral sintering of the electrostatic chuck, where the three layers are sintered together. The advantage is that it can reduce the process steps and make the three-layer structure combined more secure; but the disadvantage is that the sintering process is difficult to improve, because the three layers were sintered using different materials sintering process conditions are very different, if you want to sinter at the same time there is a very high degree of difficulty.

✔Layered sintering: Layered sintering of electrostatic chucks, after which the layers are encapsulated and connected to ensure the functionality of each layer. The advantage is that each layer is processed separately, so that the processing conditions of each layer is not restricted by other layers, can ensure the quality of the processing of each layer, but the disadvantage lies in the increase in the number of process steps, the need to process each layer after the increase in the encapsulation and connection process and to ensure that the connection does not affect the performance of each layer.

3. Temperature control: semiconductor process temperature control of the wafer is critical, Ceramic electrostatic chucks need to accurately control the temperature of the wafer by heating or cooling. This requires electrostatic chucks with efficient temperature control capabilities, including zoned temperature control technology to meet the temperature requirements of different process segments.

Ceramic Electrostatic chuck mainly through the back-blowing gas and the internal cooling waterway for temperature control of the wafer, by adjusting the pressure of the back-blowing gas can improve the wafer's heat dissipation efficiency and thus effectively reduce the wafer temperature, while the pressure of the back-blowing gas will lead to the wafer is up, resulting in the process can not be carried out, at this time it is necessary to electrostatic chuck using the electrostatic adsorption mechanism will be fixed to the wafer on the surface, so the magnitude of the electrostatic force of adsorption Therefore, the size of the electrostatic force indirectly affects the temperature control of the wafer.

The size of electrostatic adsorption force needs to be controlled within a certain range, too small will lead to poor adsorption of the wafer easily blown up by the back gas, too large will lead to deformation of the wafer, destroying the structure of the wafer at the same time affecting the desorption.