The material requirement for ESC chucks
Base and cover polyimide: The ESC chucks operate in a high temperature / high corrosion environment. The basic material used comes from the polyimide family. As the name suggests, there are many options available in this family. The typical polyimide used for the flexible circuits application does not work because of the porosity and moisture permeation. Tests conducted in real life operation clearly indicated rapid destruction of the top polyimide layer. In order to achieve a reasonable life on the ESC, a special polyimide with higher moisture resistance and gas permeation characteristics was developed. This material is light yellow in color (used by some refurnish shops). Subsequent tests showed that these chucks do degrade over time and contaminate the chamber along with cross contamination on the wafers. The material we use has the best temperature and moisture resistance as well as gas permeation. It is darker in color because it is denser in nature (longer lamination cycle and higher lamination temperature can also darken the color). This material has high modulus of elasticity and it has been used successfully in thousands of ESCs
Adhesive: The adhesive layer is another critical component of the design. Typical acrylic adhesives used in polyimide flex circuits do not work very well in a chamber. It was therefore necessary to develop a special adhesive that can withstand the rigors of the process cycle over and over again. The breakdown in adhesive can cause arcing from the charged copper plane to base ESC metal. This catastrophic failure can permanently damage the chuck. We have developed this special adhesive that will be resistant to this failure mode.