Measurement of particle flux at the intermediate focus of a DPP source

The advancement of extreme ultraviolet lithography (EUVL) is shifting focus from the source to steps later in the lithographic process. Given the critical nature of preventing damage to the projection optics, source manufacturers must create clean EUV photons at the intermediate focus (IF). The same reflective surfaces that are capable of reflecting photons are also capable of reflecting potentially damaging ion and neutral debris. The Center for Plasma Material Interactions (CPMI) at the University of Illinois at ChampaignUrbana, in conjunction with SEMATECH, is developing a detector capable of measuring this debris at the intermediate focus of the source. At CPMI, we built a prototype portable, modified electrostatic spherical sector analyzer (ESA) device incorporating a neutral detector; investigated its capabilities for measuring energetic neutrals; and report results in this paper. This detector at the IF will contain a quartz crystal microbalance (QCM), Si witness plate for ex situ analysis, a set of microchannel plates (MCPs) with corresponding ion-diverting apparatus, Faraday cup as well as triple Langmuir probe. These detectors will be capable of quantifying total particle flux, neutral particle flux, and charged particle flux. To verify the capabilities of the detector, CPMI constructed a mock collector optic, which was placed inside the experimental chamber attached to CPMI's XTS 13-35 EUV source. This mock-up simulates the reflection of debris created by discharge-produced plasma (DPP), although it will not be capable of reflecting the EUV light. Recent results on the neutral, charged particle flux, and the carbon and oxygen contamination on a Si witness plate out of the line of sight of the Z-pinch are reported in this paper.