A METHOD FOR THE REPAIR OF HYDROCHLORIC ACID DAM OPTICAL COMPONENTS OF THE GCA STEPPER LENSES
Original Publication Date: 2000-Mar-01
Included in the Prior Art Database: 2003-Jun-18
Problem to be Addressed In current technology, the final optical component in a lithographic tool is coated with an anti-reflection coating in order to maximize the amount of transmitted light. In quartz or glass optical components, the coating is typically a single layer of MgF2 due to the optical match between it and either glass or quartz. This coating is initially depos- ited at elevated temperature to improve the film properties. However, in cases where the outgassing of agents such as HCI occur during the exposure of the photoresist, the MgF2 film will be etched resulting in degradation of lens performance and with repeated use complete loss of the optical exposure tool. Disclosure We describe a process whereby a bi-layer film system of A1203 and SiO2, can be deposited onto the surface of the lens with the thickness of each layer tuned to provide the desired anti- reflection properties. In addition to the anti-reflecting properties, the bi-layer is impervious to hydrochloric acid (HCI) attack which can be released from photoresists during photolithographic processing. The films are deposited at room temperature, thus the coating process is compatible with lens arrangements which are sensitive to temperatures above room temperature, for example, when a lens to be repaired is epoxied or potted into a metallic, plastic, or ceramic fixture. As degradation does not occur uniformly over the surface of the lens, complete removal of the initial MgF2 coating must be performed. This is accomplished by immersion of the lens surface to be repaired into a solution containing 10% HCI in de-ionized water for approxi- mately 2 minutes. This results in the complete removal of the MgF2 layer with the underlying glass or quartz lens remaining untouched. As such no polishing or grinding of the lens is required after the chemical strip.