3.4.3 Simulation Examples

Here we present some results of the application of the methods described previously. We start with a medium size layout and a conventional imaging system: Figure 3.13-(i) depicts the aerial image of mask METAL2 of the layout in Figure 3.2. The simulated imaging system uses a lens with a numerical aperture NA of 0.55, a wavelength of 365nm (I-line) and the focus error is $1\mu m$. The resulting binary mask is shown in Figure 3.13-(ii). The simulation time for this relatively large example is only five minutes onn a DEC-600 workstation.

In the second example phase-shift masks are used. Figure 3.14 shows simulation results of one layout with nested elbows and minimum feature size of 0.4$\mu$m. We compare conventional binary masks (left) with alternating phase-shifting masks (right). The simulation parameters are: Numerical aperture of $\mathit{NA}=0.60$, a wavelength of also 365nm (I-line), and a focus error of $0.9\mu m$. Figure 3.14-bottom demonstrates the superior performance of phase-shifting masks.

Figure 3.13: Lithography simulation of the layout in Figure 3.2 (layer METAL2): (i) -  Aerial image; (ii) - Resulting binary image.

Figure 3.14: Simulation of nested elbows: (i) Conventional mask; (ii) Phase-shift mask. Top: Layout; Bottom: Binary mask after applying threshold.