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Dissolution rate monitors (DRMs) and related techniques have been used for a number of years to study the dissolution behavior of photoresist materials in detail. Due to the relative difficulty in obtaining commercial DRM instruments, crude methods for measuring dissolution rates such as the (formula availble in paper) have been developed. In this method, the resist-coated substrate is immersed in a developer solution for a fixed development time, removed and dried, and the remaining film thickness is measured. The dissolution rate information for the resist is then calculated from the slope of the resist thickness versus development time data. This method is simple and can easily be used in a fab environment, but it suffers from a number of limitations. For example, this method is very inaccurate for resists that develop very quickly (< 20 seconds) such as many modern chemically amplified resists. Such quick development times are often crucial in exploring the full behavior of a resist. A much better method for measuring the dissolution behavior of photoresist films is to use interferometric methods such as those suggested originally by Dill and coworkers. In this work, an extremely flexible and simple instrument based on inexpensive, commercially available, PC card spectrometers will be presented that can be used quite robustly in both fab and laboratory environments for measuring the dissolution behavior of photoresist films. The hardware required in order to construct such a simple apparatus will be discussed along with various experimental configurations that are appropriate for different measurement tasks. Thin film thickness estimation using the DRM can be done using either single wavelength versus time interferometry data (plot of reflected light intensity versus development time) or the complete multiwavelength spectra obtained from a spectroscopic reflectometry system. Film thickness estimation using single wavelength data analysis is good for films that: develop completely to the substrate, do not swell during the development process, and do not develop very fast (i.e., > 100 nm/s). Hence for films that either have very long development times (typically very thick films of the order of ~ 5μm), films that have very short development times (usually with dissolution rates exceeding 100 nm/s), or films that swell during development, film thickness determination using the multiwavelength reflectance spectra is the best solution. With this motivation, a multiwavelength interferometric data analysis software (MIDAS) has been developed in this work that can robustly perform both single and multiwavelength DRM data analysis. It has been found to be very useful in analyzing thin film dissolution data with dissolution rates exceeding 400 nm/s. Another useful application has been to measure swelling in the processing of photoresists and other polymer thin films. For example, such resist swelling appears to be an issue in the case of resists or other polymers developed or cleaned using high pressure CO2. The basic approaches and algorithms used for thin film thickness/rate determination in MIDAS will be discussed. The advantages and disadvantages of this method will be compared with quartz crystal microbalance techniques as well. It will also be shown that these two methods can be coupled for demanding applications. Results from the use of the MIDAS software in various applications will be presented.
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