Experimental validation of rigorous, 3D profile models for negative-tone develop resists

Abstract

The extension of 193nm immersion lithography to the 14nm node and beyond directly encounters a significant reduction in image quality. One of the consequences is that the resist profile varies noticeably, impacting the already limited process window. Resist top-loss, top-rounding, T-top and footing all play significant roles in the subsequent etch process. Therefore, a reliable rigorous model with the capability to correctly predict resist 3D (R3D) profiles is acquiring higher importance. In this paper, we will present a calibrated rigorous model of a negative-tone develop resist. Resist profiles can be well simulated through focus and dose, and cases that match well to the experimental wafer data are validated. Such a model can not only provide early investigation of insights into process limitation and optimization, but can also complement existing OPC models to become R3D-aware in process development.

Metal1 patterning study for random-logic applications with 193i, using calibrated OPC for litho and etch

“…between different structures or through PW) can affect the actual litho-etch bias, as also reported in Reference [11]. In our investigation, we did conclude that the limiter #1 tip-to-line structure is hypothetically R3D sensitive (see section 4.1).…”

“…R3D effects. Reference [11] looks more in detail for this particular structure and comes to the same conclusion. Following this assumption, if the resist profiles obtained with the alternative OPC solution are different from the ones obtained with the 'reference OPC', the etch process might well behave differently on both cases, leading to the observed after-etch PWs.…”

“… Resist 3D effects [11][12] (R3D): Differences in resist profiles (e.g. between different structures or through PW) can affect the actual litho-etch bias, as also reported in Reference [11].…”

“…It is clear that the change of the resist profile is quite dramatic through focus, and even more if looking at different (horizontal) planes in the resist itself. Such quantities are reported in [11], for the same 20nm Logic node test vehicle. This leads to the hypothesis that the limiter #1, associated to the tip-to-line structure, could be the consequence of the resist-profile, i.e.…”

“…For that purpose, we used a rigorous simulator (S-Litho) with a calibrated NTD resist model [11] , to simulate the PW at litho. We found that the after-litho PWs are quasi identical, see Figure 10.a.…”