A Practical Approach To Submicron Lithography

Abstract

This paper will describe the characterization and optimization of a high resolution image reversal process using dissolution rate data and the development simulation computer program, PROSIM, and compare the results with experimental data. AZ®5214 E photoresist was chosen for its simplicity of processing in negative tone and the potential to print submicron lines and spaces with good latitude using a 0.35 NA I-line stepper. This resist is unique in the sense that the image reversal process is thermally induced after exposure and requires no pre- or post-exposure chemical treatment. Without the post-exposure bake this resist is positive working, and in either tone is developed with standard aqueous alkali developers. The key variables in the optimization are the temperature of post-exposure bake, the concentration of developer, type of developer, and the time of development. The driving force in the optimization was to achieve a high resolution process with good contrast and process latitude. Development rate data and the development simulation computer program, PROSIM, were used to assist in determining the process conditions with the best contrast and broadest process latitude. Using a process which included a flood exposure after the post-exposure bake it is possible to use a 110°C to 120°C post-exposure bake and developer concentration of 0.21N TMAH. Such a process produced the best resolution with excellent side wall profiles and wider process latitude, but with some sacrifice of photospeed. Also the effect of defocus was examined near the limits of resolution and superior latitude to a comparable positive tone system was found. Thin film interference effects were examined for their impact on linewidth control and process consistency and image reversal was found to suppress linewidth variation as compared to conventional positive tone resists. The AZ 5214 E in image reversal is sensitive over a broad spectrum of exposure energy. Data for image reversed patterns produced from g-line steppers and from a 248 nm excimer laser will be presented.