Shadowing effect modeling and compensation for EUV lithography

Abstract

Extreme ultraviolet (EUV) lithography is one of the leading technologies for 16nm and smaller node device patterning. One patterning issue intrinsic to EUV lithography is the shadowing effect due to oblique illumination at the mask and mask absorber thickness. This effect can cause CD errors up to a few nanometers, consequently needs to be accounted for in OPC modeling and compensated accordingly in mask synthesis. Because of the dependence on the reticle field coordinates, shadowing effect is very different from the traditional optical and resist effects. It poses challenges to modeling, compensation, and verification that were not encountered in tradition optical lithography mask synthesis.In this paper, we present a systematic approach for shadowing effect modeling and model-based shadowing compensation. Edge based shadowing effect calculation with reticle and scan information is presented. Model calibration and mask synthesis flows are described. Numerical experiments are performed to demonstrate the effectiveness of the approach.

EUV and e-beam manufacturability

“…For the flare effect, OPC corrects the CD of a layout pattern according to the flare value the pattern receives [35,41]. For the shadowing effect, OPC modifies each layout pattern according to the pattern shape and the pattern location [26,33]. However, these two effects should be simultaneously considered since they might conflict with each other, reducing OPC efforts.…”

“…It can be observed that horizontal 1-D equal L/S patterns of 30 nm pitch (P30H) suffer from rather high contrast loss compared to P60H. To compensate the shadowing effect in advanced process nodes, therefore, recent studies mainly focus on developing model-based OPC techniques [26,28,33]. Different shadowing models and lithography simulators adopted in these model-based OPC flows present a trade-off between runtime efficiency and correction effectiveness.…”

“…Consequently, the oblique illumination and absorber thickness result in shadows around patterns represented by the absorber shapes, making patterns wider during an exposure process [33]. As illustrated in Figure 4, as the incident ray is perpendicular to the pattern edge, the shadow width is computed by h tan φ, where φ is the incident angle with respect to the z-axis, as shown in Figure 4(a).…”

Gradient-based inverse extreme ultraviolet lithography

“…[6]. Figure 2(a) illustrates the sketch of the mask shadowing effect, where the outer and inner contours represent the target on the wafer scale and the print image due to the shadowing effect.…”

“…Both the absorber thickness, which is large compared to the wavelength, and the oblique incidence contribute to a pronounced shadowing and other mask topography effects [5]. The mask shadowing effect is orientation-dependent relying on the mask topography, which induces a directional CD bias and shift on the order of several nanometers [5,6]. In contrast with a 22-nm or smaller half-pitch, the mask shadowing effect is too pronounced to be ignored and must be compensated.…”