Christopher J. Jones

Variable depth skin heating with lasers

Laser based devices with ability to heat sub-surface zones at certain depths within skin have several potential applications. Methods to achieve such heating at different depths have been explored in this work. Monte Carlo modeling and heat transfer calculations were performed to calculate fluence distribution, temperature distribution, and thermal damage for various laser wavelengths in the range of 1,200-1,800 nm with various pulse durations. The treatment consisted of laser irradiation combined with contact cooling. Cooling leads to preservation of the top layer leading to a zone of thermally damaged tissue under the top layer. The results indicated that the thickness and mean depth of the thermally damaged sub-surface zone can be controlled by choice of laser wavelength and cooling and irradiation times. Thermally damaged zone was deeper with lower absorbing wavelengths and/or with longer pulse durations. Histological evaluation of ex vivo pig skin immediately after treatment was done to determine thermal damage band depth and thickness for various wavelengths and pulse durations. Histological evaluation supported the modeling results. Thus, variable depth heating can be achieved through selection of the wavelength and/or laser pulse duration. With a chosen wavelength device, a variable depth heating device can be constructed by varying the cooling and laser irradiation durations.

Process window limiting hot spot monitoring for high-volume manufacturing

As process window margins for cutting edge DUV lithography continue to shrink, the impact of systematic patterning defects on final yield increases. Finding process window limiting hot spot patterns and monitoring them in high volume manufacturing (HVM) is increasingly challenging with conventional methods, as the size of critical defects can be below the resolution of traditional HVM inspection tools. We utilize a previously presented computational method of finding hot spot patterns by full chip simulation and use this to guide high resolution review tools by predicting the state of the hot spots on all fields of production wafers. In experiments with a 10nm node Metal LELELE vehicle we show a 60% capture rate of after-etch defects down to 3nm in size, at specific hot spot locations. By using the lithographic focus and dose correction knobs we can reduce the number of patterning defects for this test case by ~60%.

The use of computational inspection to identify process window limiting hotspots and predict sub-15nm defects with high capture rate

As critical dimensions for advanced two dimensional (2D) DUV patterning continue to shrink, the exact process window becomes increasingly difficult to determine. The defect size criteria shrink with the patterning critical dimensions and are well below the resolution of current optical inspection tools. As a result, it is more challenging for traditional bright field inspection tools to accurately discover the hotspots that define the process window. In this study, we use a novel computational inspection method to identify the depth-of-focus limiting features of a 10 nm node mask with 2D metal structures (single exposure) and compare the results to those obtained with a traditional process windows qualification (PWQ) method based on utilizing a focus modulated wafer and bright field inspection (BFI) to detect hotspot defects. The method is extended to litho-etch litho-etch (LELE) on a different test vehicle to show that overlay related bridging hotspots also can be identified.