In terms of principle, what are the differences in application between alumina vacuum chuck and electrostatic chuck?
In the precise and complex field of semiconductor manufacturing, every link is related to the final quality of the product. For instance, the fixation and handling of seemingly basic workpieces are actually crucial links in ensuring the smooth progress of production and meeting product quality standards. When performing high-precision processes such as photolithography and etching, if the workpiece moves even slightly, it is highly likely to lead to the scrapping of the entire chip, and the large amount of manpower, material resources and time invested in the early stage will be wasted.
At present, alumina vacuum chuck and alumina electrostatic chuck, as the mainstream adsorption technologies in the semiconductor manufacturing field, have the advantages of high strength, excellent wear resistance, long service life, and good chemical stability. They can respectively achieve wafer fixation and transfer through pressure difference and electrostatic field. However, due to different principles, the applicable scenarios vary significantly.
Alumina vacuum chuck
Vacuum wafer chuck is the use of a vacuum adsorption principle of fixed workpiece bearing platform, its transfer part of the vacuum is usually alumina porous ceramic plate, porous ceramic plate assembly on the base of sink holes in its surrounding bonded seal with the base, the base for the density of precision ceramic or metal material processing and into. When negative pressure is applied during operation, the chuck is connected to the vacuum pump through the porous structure inside the ceramic plate to extract air, creating a vacuum area far lower than the external atmospheric pressure beneath the wafer. Under the effect of this powerful pressure difference, the wafer is firmly adhered to the surface of the chuck. Generally speaking, the higher the vacuum degree beneath the wafer, the tighter the adhesion between the chuck and the workpiece will be, and the stronger the adsorption force will be.
As a key component for vacuum transmission in chuck, the pores of alumina porous ceramics are often extremely fine, with a porosity of 30% to 50%, and the pore size requirement is at the micrometer or even nanometer level. This ensures that when the workpiece surface adheres to the vacuum chuck, it will not be scratched or dented due to negative pressure and other adverse factors. Meanwhile, when alumina vacuum chuck are applied in the photolithography process of electronic components, to avoid interference caused by the reflection of stray light by the chucks, it is often required that the color of the alumina porous ceramic plate be black.
Due to the relatively simple structure of the alumina vacuum chuck, its manufacturing and maintenance costs are low, and the adjustment of the adsorption force is also relatively simple. This can be achieved by adjusting the working state of the vacuum pump or the distance between the chuck, which can ensure the absolute stable fixation of the wafer during the processing. However, when wafers undergo processes such as chemical vapor deposition that require operation in a vacuum or low-pressure environment, vacuum chuck that rely on pressure differences cannot meet the working requirements, thus limiting their application scope. In addition, when the wafer is adsorbed on the surface of the vacuum chuck, it will deform due to air pressure. After processing, the wafer will rebound, causing the cut surface to be wavy and the surface flatness to decrease, which affects the processing accuracy. Therefore, alumina vacuum chuck are often used to fix or transport some flat and well-sealed components, such as metal plates, plastic sheets...etc., and in the semiconductor manufacturing process, they are often applied in low-level processes.
Alumina electrostatic chuck
Electrostatic chuck (ESC) to the "sandwich" layered structure, the main body from the table to include the dielectric absorption layer, the metal electrode layer and the base layer of a support role, in addition internal studded with electrodes columns, gas channel, bonding materials and other auxiliary structures, can be heat transfer through gas circulating, stable to control the temperature of the wafer. Unlike vacuum chuck, the working principle of alumina electrostatic chuck is based on the effect of an electrostatic field. During operation, a direct current voltage is applied between the dielectric layer and the electrode to polarize the dielectric, thereby generating charges on the surface of the dielectric layer that are opposite in polarity to those on the surface of the wafer, which adsorbs the workpiece onto the chuck.
According to whether the dielectric adsorption layer is doped dielectric, alumina ceramic electrostatic chuck can be classified into Coulomb type and Jions hot back (JR) type. Among them, the Coulomb type uses high-impedance pure ceramic materials as dielectrics, while the Jions hot back (JR) type uses ceramic materials doped with substances such as titanium oxide as dielectrics. Therefore, compared with the Coulomb type, the JR type will not only generate polarized charges, There is still a large portion of free charge that can be adsorbed at a relatively low voltage. However, during the desorption stage, due to the presence of free charge on the surface of JR type chucks, in addition to turning off the high-voltage DC power supply, it is usually necessary to use a reverse static voltage to forcibly eliminate the residual charge before the chip can be desorbed. To a certain extent, this increases the difficulty and complexity of control.
At present, in addition to alumina, ceramic electrostatic chuck can also use aluminum nitride, which has even better comprehensive performance, as the dielectric material. However, to achieve stable adsorption of workpieces, electrostatic chuck have extremely high requirements for surface flatness, smoothness, and micron-level concave-convex structures. The precision of the concave-convex structure needs to reach the micron-level. This leads to certain technical barriers in the material ratio, sintering and surface treatment during the production process. The production process is extremely complex and time-consuming. Moreover, the technical route of aluminum nitride as a dielectric material is even more complicated. As a result, the advantages of aluminum nitride ceramics over alumina have not yet been reflected in electrostatic chuck. At present, the electrostatic chuck still mainly use alumina ceramics as the main manufacturing material.
Summary
In semiconductor manufacturing, precision machining, and other fields, the wafer and the substrate stable clamping is the core of the process precision of protection. Alumina vacuum suction cups have been widely used in some industrial fields with relatively low precision requirements, such as metal processing and low-level semiconductor manufacturing processes, due to their simple structure and low manufacturing cost. However, with the high-end development of the manufacturing industry, the existing alumina vacuum suction cups are gradually unable to meet the demands in some aspects, such as in the advanced processes of semiconductor manufacturing that require a vacuum environment, like ion implantation and CVD. In contrast, alumina electrostatic suction cups, with their uniform adsorption force and good vacuum matching performance, can well meet the usage requirements.
Fountyl Technologies Pte Ltd., is focusing with 20 years of the semiconductor industry experience of advanced ceramic parts manufacturing in Singapore, main product is pin chuck(chuck pin) which made of various kinds of ceramic materials(alumina,zirconia,silicon carbide, silicon nitride, aluminum nitride and porous ceramics),fully independent control of ceramic material sintering, precision processing, testing, and precision cleaning, with guaranteed delivery time. products are exported to the United States, Europe and Southeast Asia , more than 20 countries and regions.
