Experimental and numerical investigation of the thermomechanical response of reticles during the optical lithography process

Optical lithography is the primary commercial method for manufacturing integrated circuit (IC) chips in 2003, but it may be replaced by other technologies due to its physical limitations on the minimum feature size. Currently, optical technology is able to produce ICs with 90 nm minimum feature size. The demand for faster ICs continuously drives down the feature size on these microchips. To extend the optical lithography technology to produce chips with feature sizes of 65 nm or 45 nm, all mask (reticle) related distortions must be minimized. The reticle expansion due to thermal loading caused by the exposing illumination causes a considerable distortion to the mask.; Building correct numerical models to simulate the thermomechanical response during the optical lithography process is the main objective of this research. Three dimensional finite element (FE) models were developed to predict the thermal response and the corresponding structural response of the reticle during the exposure process. Experimental model verifications of the thermal FE models were performed with three sets of experiments. The experimental model verification program was initiated with a simple experiment, and the complexity was increased step-by-step for the proceeding experiments. For each experiment, the light source was calibrated to estimate the heat flux delivered and the heat loss coefficient for each configuration. FE models were developed to replicate each experiment. The comparison between the experimental and the numerical results showed a good agreement.; As a conclusion of this work, it has been shown that the thermal FE models developed to simulate the thermal response of the reticles during the optical lithography exposure process are credible. Therefore the FE models were used for predicting the thermomechanical distortion of the optical reticles during exposure for current and future technologies in close collaboration with the IC industry members.