Deep ultraviolet surface inspection with photoemission enhancement

The potential utility of surface inspection with deep ultraviolet (DUV) light has been explored from a theoretical and experimental standpoint, with the construction of a high-vacuum DUV scatterometer and photoemission measurement system. DUV based inspection has the possibility of extending surface inspection technology to meet the needs of the semiconductor industry into the era of 70 nm critical dimensions in three major respects, the enhanced light scattering cross-section from small defects and structures at shorter wavelengths, the material-sensitive properties of photoemission, and the photoemission voltage contrast effect. Experimental results in the 140 nm to 240 nm wavelength range roughly confirm theoretical predictions of the scattering cross-section in the DUV and also reinforce the idea that photoemission techniques could constitute important new inspection modes. Clear evidence of photoemission voltage contrast is also shown, and absolutely calibrated measurements of photoemission yield indicate that signal levels are sufficient to allow the use of photoemission in high-speed inspection with laser sources. Issues surrounding DUV and vacuum inspection technology are analyzed, and approaches to solving related problems, such as vacuum actuator heating and mirror fouling by carbon deposition, are discussed.