Sunit S. Dixit

Reduced photoresist scumming tendencies through the optimization of photoresist formulation parameters

Abstract This paper describes research on the subject of resist scumming induced by TMAH development. Variations in the resist formulations were made according to a statistical design. The factors investigated were resin molecular weight and polydispersity (PD), sensitizer functionalization, resin to sensitizer loading, and solvent effects. Resin molecular weight and sensitizer functional-ization were found to be critically important to reduce scumming.

Enhanced photoresist focus latitude through the use of statistical design experimentation in photoresist formulation optimization

Abstract This paper describes a statistical design experiment that was used to evaluate the effect of changes in a photoresist formulation on the photo-microlithographic performance characteristics. The variations in formulation construction investigated are resin molecular weight, resin concentration, and sensitizer content. A model that indicates optimum depth- of-focus, exposure latitude, linearity, and swing curve response is obtained for the test formulations when resin molecular weight is maximized, resin concentration is minimized, and sensitizer content is maximized.

Photoresist formulation optimization through the use of statistical design of experimentation

This paper describes the use of statistical design experimentation to improve the photoresist performance properties of Dynachems Nova 2070. A full factorial design was employed to investigate the effects of changes in the weight percent of both the minor resin and sensitizer in the total solids and of changes in the major resins molecular weight on the after-hardbake wall profiles. The effect of the formulation changes on lithographic properties such as process latitude and resolution has also been measured. Scanning electron micrographs (SEMs) were generated to measure wall profile, thermal, and lithographic properties. A SEM measurement technique was then developed to quantify resist thermal stability. From these measurements models were generated to show the effects of the various formulation changes and to make predictions with respect to optimum formulations. Graphs of profile tendencies as a function of formulation changes and hardbake temperature and response surfaces generated from the various models are presented to help illustrate the optimization trends. With respect to lithographic performance, the experimental and model data indicate that the optimum resist formulation within the tested experimental matrix has the following make-up: high major resin molecular weight, low minor resin content, and high sensitizer content. With respect to thermal stability, the data suggests that the optimum resist formulation is the following: high major resin molecular weight, high minor resin content, and low to medium sensitizer content. The lithographic property optimum formula was retested to optimize its performance as a function of process changes according to a quadratic statistical design. Comparative process latitude graphs contrasting the optimum formula to alternative formulas under their respective optimized process conditions are also presented. These studies are collectively analyzed to indicate the direction that future resist formulation changes could be made to further optimize resist performance.

Dynalith® Resists For Mid-Uv Applications: Formulation Optimization For Gaas Related Processing

Recent advances in optical lithography driven by the use of mid-UV radiation (365/313 nm) require resists optimized to operate effectively at these wavelengths. New positive resist formulations have been developed to meet this need. DYNALITH resists X-1608 and X-1605 display enhanced sensitivity toward mid-UV exposure. Comparison data vs. standard and deep UV resists are presented. A variety of exposure modes, including projection and contact, have been investigated. DYNALITH Positive Resist X-1608 is based on a novolac and 2,1,4 quinone diazides which are optimized for resist performance. This new resist la.s sensitivity which is improved over standard resists in mid-UV exposures. Sensitivity of 30-70 mJ/cm is demonstrated at 313 nm and 365 nm. X-1608 mid-UV resist demonstrates submicron imaging capability with high contrast and wide process windows. DYNALITH Positive Resist X-1605 is based on a novolac and the more standard 2,1,5 quinone diazide. This resist formulation provides an overhung or reentrant sidewall profile with the use of standard processing steps. The absence of the necessity of a chlorobenzene soak coupled with the appearance of sidewall profiles as displayed indicates the X-1605 resist to have application for metal lift off processing. The suitability of consistent resist sidewall profiles for metal lift off provides an application for X-1605 resist in GaAs lithography. A control of the degree of curvature and overhang displayed by the resist profiles relative to formulation is described. Process stability of soft bake and exposure is presented for DYNALITH X-1608 on mid-UV projection aligners. Dry etch data relating resists X-1608 and X-1605 to standard resists is presented. Statistical process control (SPC) is an important control method as production requirements shrink to the one micron regime. The use of process control (X) and range charts (R) generated for coating DYNALITH X-1608 resist is presented. SEM photos characterizing the resists and certain process latitudes are presented. Analytical techniques, such as GPC and C13 NMR, assisted the characterization of structure/performance relationships.