A “chuck” is a tool that is used widely around the world and is a tool for holding work objects or cutting tools in place. For example, typical examples of a chuck include tools that clamp a work in place like a vice or a drill chuck that fixes drill bits for cutting onto a processing machine. An electrostatic chuck is a tool that achieves adsorption through Coulomb force generated between the work (object for machining) and electrodes to which a voltage has been applied. An electrostatic chuck is the same as a vice or a drill chuck in the sense that it is used to hold an object in a fixed position. However, an electrostatic chuck applies adsorption force evenly over a wide area of the work object, providing the optimal features required when you want to fix the position of a delicate and fragile object that cannot be handled by a vice or drill chuck.
The two operating principles of electrostatic chuck
There are two types of adsorption methods for electrostatic chucks: the Coulomb force type, which uses an insulating material as the dielectric, and the Johnsen-Rahbeck force type, which flows a minute current across the small gap between the work and the dielectric to cause charge polarization, resulting in attractive force .
Comparison of chucks based on other operating principles
Adsorption by an electrostatic chuck is based on an electrical force applied evenly over the entire adsorption surface. This provides the benefit of making it difficult to apply physical stress to the work.
As a result, electrostatic chucks are being used in production sites manufacturing advanced electronics as an adsorption-based fixing method for thin, delicate work (semiconductor wafers, glass, metal foil, film).
By comparison, mechanical chucks and vacuum chucks widely used in manufacturing plants are widely used in applications such as work movement where delicacy is not required. These types of chucks are selected based on the work characteristics.
Mechanical chucks use a machine to fix work in place so the work is subjected to physical stress, which can result in breakage or warping.
Vacuum chucks fix work in place by creating a vacuum environment. As a result, work cannot be maintained evenly in some cases or can leave adsorption marks on the work, meaning this method can be difficult to apply depending on the work properties.
Adsorption principles of Tsukuba Seiko electrostatic chucks
Voltage is applied to the electrostatic chuck’s internal electrodes optimized over many years of R&D to concentrate an electric field around the interface of the work adsorption surface. This electric field separates the positive and negative ions inside the work to drive the positive ions near the negative electrodes and drive the negative ions near the positive electrodes.
Adsorption results from a strong Coulomb force generated between the positive ions and the negative electrodes and between the negative ions and the positive electrodes. No electrical load is applied to the work and the work is not subject to electrostatic damage because this process only polarizes ions that were already present.
Three characteristics of Tsukuba Seiko electrostatic chucks
Characteristic 1: Broad applicability
Adsorption possible for glass, film, paper, ultra-thin wafers, etc.
Optimizing the electrodes makes this method applicable to all types of work. That means that this method can be used for materials that cannot be handled using existing electrostatic chucks, including glass and other insulation materials or the ultra-thin wafers and other semiconductor materials. Adsorption is also possible on work made of porous materials regardless of size.
Perforated, porous material
Characteristic 2: Strong adsorption
Strong absorption enables stable transport
Optimizing the electrodes enables the generation of uniform suction force along the adsorption surface. This enables use on work that is fragile, easily cracked, wrinkled, or warped, work that cannot be handled by conventional vacuum chucks and mechanical chucks, semiconductor materials like ultra-thin wafers, and insulation materials that cannot be handled using existing electrostatic chucks. As this method only polarizes the contact interface, there is no concern of destroying electronic circuits formed in the work.
Characteristic 3: Products that maintain adsorption without a power supply unit
Maintains adsorption without power supply unit, enabling integration into existing production lines
Typical electrostatic chucks require permanent connections to a power supply unit to maintain adsorption. However, the Tsukuba Seiko electrostatic chuck, Supporter, can maintain adsorption even after the power supply unit is disconnected.
Once the power supply unit is used to create an electric field, this force is maintained semi-permanently. To remove the work from the Supporter, you can separate the work at any time by reconnecting the power supply unit and disengaging the electric field.
Strengths and weaknesses of electrostatic chucks
Adsorption of thin, fragile, or porous work
For thin, brittle, or porous work, it can be difficult to adsorb and fix the position using conventional chucks such as mechanical clamps or vacuum chucks. This is because these methods can result in cracked or scratched work, leave suction marks, cause wrinkles or warpage, or porous material cannot be adsorbed due to air leakage. Since electrostatic chuck generates a uniform adsorption force on the entire work surface, there are no issues resulting from the non-uniform force of a conventional chuck. Also, warping that occurs in thin work such as semiconductor wafers can be corrected through uniform adsorption, so it is possible to continue machining in a flattened state.
Wet work and thick, curved work
Holding work in place using electrostatic adsorption is difficult when the work is wet or the work is thick and warped.
Main target markets for our electrostatic chucks
1: Automotive power semiconductor market
There is demand for EVs and other battery-operated vehicles to extend their single-charge range to match that of gasoline vehicles.
This is drawing industry attention to the critical issue of minimizing energy loss in the IGBT and MOSFET power semiconductors to constrain EV battery consumption.
Integrating our Supporter into power semiconductor production lines enables the production of ultra-thin semiconductors, which will achieve the production of high-performance IBGT and MOSFET with low energy loss.
2: 5G communications, IoT-related markets
The conditions required for 5G communication and IoT include ultra-high-speed communication, ultra-multi-terminal connection, ultra-low latency, etc.
Fulfilling these parameters will require breaking through the barriers of production technology with new communication devices such as gallium arsenide (GaAs), gallium nitride (GaN) devices, and silicon, silicon germanium (SiGe) devices.
Our Supporter is attracting attention as a future handling tool that can safely and securely adsorb and hold all types of thin materials regardless of differences in the materials.
3: Display-related markets
In the display market, the advent of OLED has driven power savings and OLED displays have become the centerpiece of the display market, particularly on mobile products.
Recent years have seen the need for further power savings due to the miniaturization and thinning of on-board products in smartphones and smart watches. As a result, mini and micro-LEDs are viewed as next-generation displays.
We will apply our cumulative technology to contribute to dynamic steps in the display market by addressing the need for thinner base materials and the formation of low-cost, high-quality thin films for various displays.
Tsukuba Seiko Profile
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