In-situ, portable monitoring methods for photolithography characterization

The effective characterization of the Photolithographic performance needs inline information of the fully-assembled tools during production, and this requires in-situ monitors to track tool and process information over time. To avoid the costly integration of complex sensors into the processing equipment, in-situ, yet portable monitoring methods are desirable. In this thesis, we pursue the concept of in-situ, portable monitoring methods, and more specifically, we introduce two such novel monitors, a Probe Pattern Grating Defocus Monitor (PPGDM) and an on-wafer Integrated Aerial Image Sensor (IAIS). These monitors can be deployed non-invasively at the reticle and the wafer stages in order to characterize lithographic performance.;The first objective of this thesis is to develop an in-situ, portable monitor to characterize the defocus effect in photolithography by utilizing 90° phase shifted periodic grating in conjunction with scatterometry metrology. The monitor achieves its high sensitivity to defocus by placing transparent lines spaced at the strong focus spillover distance from the centerline of a 90° phase-shifted probe that functions as an interferometer detector.;Theoretical simulations show an aerial image defocus sensitivity of 0.83CF/RU at σ=0.1. This defocus error is translated into the probe line photoresist trench depth after exposure and development. The relationship between defocus and trench depth is largely linear. Following that, printing experiments and scatterometry calibration confirm this linearity, and demonstrate a high sensitivity of around 1 nm defocus/nm trench depth. An excellent correlation between the measured defocus and the scanner programmed defocus is achieved in the experiment. These experimental results show that the PPG monitor is likely the most sensitive defocus monitor currently available.;The second objective of this thesis is to explore an in-situ, portable monitor to measure the aerial image in photolithography directly and in real time. The Integrated Aerial Image Sensor (IAIS) concept we explored utilizes an electronic aerial image detector integrated into the surface of a tetherless wafer. The detector includes an aperture mask that is integrated on top of a CCD array. The aperture mask features a series of "moving" aperture groups which sample the aerial image to form a low spatial frequency interference pattern. This low spatial frequency image can be captured by the CCD array with an effective spatial resolution of only a few nanometers. Simulations show that an aperture width of 35nm± 15nm and thickness of 80nm±20nm in amorphous silicon is nearly optimal for the 65nm node, and that fabrication precision is relatively not critical.;A proof-of-concept prototype was designed and tested in the i-line GCA6200 stepper in the Berkeley Microlab, but securing and aligning this tethered assembly onto the wafer chuck proved to be a big challenge. It is clear that the proper vehicle for testing the IAIS concept will require a completely wireless, self-contained platform, which has the form factor of a regular silicon wafer.;Functioning as a recording tool, IAIS is able to detect aerial image features, such as intensity, contrast, slope, and feature size, as verified by first-principle simulations. Because of the structure of the design, IAIS is also a natural polarizer. A set of rotated IAIS gratings with 90°, 45° and 135° could be integrated into the same aperture mask to investigate the linear polarization components and ratios with a single exposure. Finally, combining the purpose-designed reticle, such as PPG, with the on-wafer IAIS and a suitable aperture mask, will bring forth a new family of in-situ, portable sensors that will dramatically improve the state of the art in lithography characterization. (Abstract shortened by UMI.).