Ultrasonic monitoring of photoresist processing

Abstract

A high frequency ultrasonic technique has been developed to monitor photoresist processing in situ during semiconductor manufacturing. Photoresist pre-exposure bake and development have been monitored using the sensor, and the post-exposure bake has been studied as well. The in situ glass transition temperature (Tg ) was determined during the prebake for I-line films down to O.6im as well as for chemically-amplified DUV resists of similar thicknesses. Using classical reflection theory, photoresist properties such as the density, thickness, and acoustic velocity were determined during processing. This in situ parameter inversion method can be used to determine process endpoint if the optimal density, velocity, and thickness are predetermined. The Tg for post-exposure bake of Iline resists is expected to be the Tg of the novolac resin alone, without solvent present. Measurements using the described sensor have confirmed that the resin Tg during postbake is 1 18CC, the value of Tg provided by Shipley. This provides a measurement of postbake as well as a confirmation that the sensor is measuring Tg accurately. The development process was also monitored using this sensor. Results prove the usefulness of this sensor for in situ measurement of resist thickness changes during development. This was verified for different exposure doses and for resist coated on a wafer with circuit topography.

High-responsivity thermoelectric infrared detectors with stand-alone sub-micrometer polysilicon wires

“…This oxide layer is deposited by a plasma enhanced chemical vapor deposition (PECVD) system and patterned/etched using a positive resist (Shipley 1827) in an inductively coupled plasma (ICP) etcher to form small oxide islands on the wafer. Before etching the oxide, the patterned resist is baked at 150 °C, above its glass transition temperature (T g ~ 120 °C [34]), for 15 min to reflow and to get sloped sidewalls. The sloped sidewall of the resist will be transferred to the oxide layer during ICP etching of the oxide layer (the actual slope of the sidewall will also depend on the resist to oxide etch rate ratio in the etching process).…”

On Control of Resist Film Uniformity in the Microlithography Process

“…For positive-tone resist such as DNQ/novolac resists, subjecting the resist to temperatures above 100 °C can have the same effect as exposure, namely decomposition of the DNQ photoactive compound which may degrade feature size and uniformity (Morton, et al 1999). Hence, the bake temperature has to be constrained during softbake.…”

In-Situ Monitoring of Photoresist Thickness Contour

“…To study the bake mechanism, Paniez et al [3] used in-situ ellipsomtery while Fadda et al [4] used contact angle measurements to monitor the resist thickness. Morton et al [5] used in-situ ultrasonic sensors to monitor the change in resist properties to determine whether the resist has been sufficiently cured, thereby determining the endpoint of the softbake process. In related work, Lee et al [7] used in-situ multiwavelength reflection spectrometer to measure the resist thickness versus bake time and then real time feedback control applied to improve thickness uniformity.…”