Resist formulation effects on contrast and top-loss as measured by 3D-SEM metrology

We have implemented 3D-SEM metrology to measure resist height as a function of dose for negative e-beam resists. Converting the resist height to a dissolution rate produces a new way to determine resist contrast. We have used this method to demonstrate improved aspect ratios for a low contrsat resist compared to a high contrast resist. We have also found that increasing the cross-linker concentration causes an increase in the resist dissolution rate and contrast. We have measured this change in contrast using the 3D-SEM technique for three resists systems with varying cross-linker concentration. We have plotted the dissolution rate as a function of e-beam exposure intensity, and used this information to model how contrast effects the final resist profile. Both the model and the experimental data suggest that the higher contrast resist gives a straighter side-wall angle with a negligible effect on the final CD.