An electrostatic chuck is a device that uses the principle of electrostatic force adsorption to fix the wafer to be processed and can control the temperature of the wafer. It has many advantages over traditional mechanical chucks and vacuum suction cups. Mechanical chucks will cause damage to the wafer due to excessive pressure and collision during use, and although the vacuum chuck causes little damage to the wafer, it cannot be used in a low-pressure environment. Therefore, electrostatic chucks gradually replace mechanical chucks and vacuum chucks, and are widely used in semiconductor integrated circuit manufacturing processes.
First, the application principle of electrostatic chuck.
The working principle of electrostatic chucks is based on the adsorption effect of electrostatic force. It usually consists of a flat electrode surface, and by applying an electric charge on the electrode surface, an electrostatic force is generated, which causes the workpiece to be adsorbed by the electrostatic force and fixed on the chuck surface. According to the different mechanical models of electrostatic chucks, they are divided into two categories: Coulomb type, J and R type.
Coulomb-type electrostatic chucks: Coulomb-type electrostatic chucks use the electrostatic interaction in Coulomb's law to adsorb the surface of the workpiece. By applying a high voltage to the inside of the suction cup, the surface of the suction cup is electrostatically charged, creating an electric field with an electric charge. When this charged suction cup is close to the surface of the workpiece, the electrostatic force causes the opposite charge on the surface of the workpiece and creates an attractive force to hold the workpiece firmly on the electrostatic chuck.
J-R electrostatic chuck: The thermodynamic back chuck uses the principle of thermodynamic back pressure to control the temperature distribution and pressure difference on the surface of the chuck, so that the back side of the silicon wafer is subjected to upward thermal pressure, so as to better fix the silicon wafer and improve its stability. This thermodynamic back pressure effect can further enhance the adsorption effect of the electrostatic chuck and help reduce the deformation and cracks caused by thermal stress on the silicon wafer. Therefore, the J-R suction cup is better than the coulombic suction cup and has a wider range of applications.
2. Screen printing process in electrostatic chuck.
The electrostatic chuck is mainly composed of a ceramic substrate, an electrostatic electrode, a mechanical thimble, a peripheral power supply, a back blowing system, and a water-cooled matrix. The process flow is shown in the figure below, and the screen printing process is mainly used in printed electrodes and HTCC.
Image source network J-R electrostatic chuck process).
HTCC, also known as high-temperature co-fired multilayer ceramics, refers to ceramics with electrical interconnection characteristics that are sintered with tungsten, molybdenum, manganese and other metals with high melting points between 1300-1600.
Image source network HTCC process).
Graphic printing in HTCC is the same printing process as electrode printing in electrostatic chucks, and hole filling printing is one process. The two processes are described below, and the process-related equipment is introduced.
1) Electrode printing.
The principle of electrode printing is that under the action of the scraper of the screen printing machine, the slurry is deposited on the substrate through the mesh of the electrode structure part on the screen plate, and the electrode is made after high-temperature sintering. The screen printing electrode is mainly made of conductive metal paste, such as gold paste, silver paste, carbon paste, etc., which can reduce the resistance and background current while conducting electricity, and the HTCC electrode printing mainly uses tungsten, molybdenum, manganese and other refractory metal materials. At present, many domestic screen printing equipment can meet the requirements of electrode printing and has reached the advanced level.
Source: Jianyu screen printing electrode printing finished product).
2) Hole filling printing.
The principle of hole filling printing is the same as that of electrodes, and the difference lies in the different processes. The raw porcelain pieces are cut and punched, and then the holes are filled using a high-precision screen printing machine to ensure the electrical interconnection of the raw porcelain pieces after stacking. The scraping pressure and screen spacing of the screen printing machine will affect the uniformity, fullness and effect of hole filling. If there is less slurry in the hole, leakage will be formed, resulting in poor circuit performance of the substrateIf there is too much slurry in the hole, there will be slurry thrown out on the front and back sides, resulting in bulges, which will seriously affect the later welding and assembly process.
Image source network: schematic diagram of the hole filling process).
Since hole filling printing is a key link in the HTCC process, high-precision screen printing equipment has been widely used. The use of appropriate high-precision screen printing equipment and perfect process technology is the premise to ensure the effect of hole filling.
Source: Jianyu Network Printing Customer Proofing Report).
The picture below shows the high-precision screen printing machine of Changsha Jianyu screen printing, which mainly has the following advantages when printing electrodes and filling holes
High alignment accuracy, CCD automatic alignment vision system is adopted, and the printed point is used as the mark point to make the position alignment between the screen and the product accurate. Equipped with X, Y, three-dimensional workbench, can be in 0Within 3 seconds, the placement deviation of the product substrate can be quickly identified and automatically visually corrected, and the printing alignment accuracy is 5um.
The printing pressure of hole filling is controllable and adjustable, and the printing system adopts a special cylinder and a precision pressure regulator adjusting device to adjust the pressure.
The hole filling printing precision is high, the ceramic platform is adopted, the air tightness is good, and the raw porcelain piece will not be damaged during adsorption, and it will not leave adsorption traces on the back.
It can meet the two processes of electrode printing and hole filling printing at the same time, although electrode printing can be realized by many equipment, but the hole filling process cannot be realized. If you buy two types of equipment, it will increase the cost of the enterprise.
The operation is simple, the printing efficiency is high, the scalability is strong, and the automatic printing production line can be quickly matched according to the production requirements.
After an in-depth analysis of the principle of electrostatic chuck, as well as the detailed description of the screen printing process in the electrostatic chuck, it can be seen that the high-precision screen printing process plays a key role in the manufacture of electrostatic chuck, and the successful application of this process undoubtedly provides strong technical support for the manufacture of electrostatic chuck. In the future, it is also expected that domestic screen printing machine manufacturers can make more technological breakthroughs in this field and promote the sustainable development of China's microelectronics manufacturing industry.