Benefits of non-polar assist liquids as alternatives to water assist in the laser machining of silicon

The use of a water assist has been shown to improve machining efficiency and feature cleanliness for the laser micro machining of features in silicon. However, the water assist has been shown to have some disadvantages, including the fact that it dissolves protective coatings on semiconductor wafers and it tends to cause blockages in the debris extract system. Protective coatings dissolve because they are typically water-based in order to facilitate their removal after machining and therefore they are not compatible with the water assist process. Blockages in the extract system are due to the deposition of silicon debris, which does not remain adequately entrained in the water flowing through the extract system. This paper describes the use of oil assist instead of water assist to solve these problems while maintaining the advantages of water assist. Unlike water, which is polar in nature, oil does not dissolve the water-based coating. Due to the properties of the oil assist, the debris does not tend to deposit on the surfaces of the extract system so blockages are avoided. Suitable oils include industrial oils like Castrol Carecut and common vegetable oils like grape seed oil or olive oil.