Laser Induced Desorption Time of Flight Mass Spectrometer Analysis of Adsorbed Contaminants on Vacuum Ultraviolet Lithography Optic Materials

Adsorbed surface contaminants on optical elements absorb light energy in an optical lithography system and, if left unclean, will result in reduced wafer yield. In order to nondestructively analyze the surface adsorbate of different CaF2 samples, a laser induced desorption-Time of Flight Mass Spectrometer (LID-TOFMS) technique was developed. The main object of this technique is to investigate the surface composition of adsorbed contaminants as a function of position on the sample. An Er:YAG laser at 2.94 μm was used as the light source to induce desorption. Electron impact ionization was used to obtain ionization of desorbed molecules. The detection of ionized species was accomplished by TOFMS operated in Angular Reflectron (AREF) mode to obtain better resolution.

The data reported here can be used in semiconductor industries either to modify conventional processing or to design a new efficient laser cleaning process for optical elements.