Improved validation and optimization of physics-based NTD compact modeling flows

Due to the semiconductor industry's ever-increasing need for finer resolution and improved critical dimension (CD) control, negative tone development (NTD) photoresists (resists) have been adopted for several advanced applications in lithographic patterning. NTD resists enable brightfield imaging by using an organic solvent developer to penetrate and remove the unexposed regions of the resist [1]. For certain critical patterning layers, such as metal trenches and vias, NTD resists provide better resist imaging quality compared to the previous positive tone development (PTD) resist process. However, there are several additional engineering difficulties which must be addressed for an NTD resist process. Specifically, NTD resists have low contrast organic solvent development and in an NTD process the material remaining on the wafer substrate is the exposed resist which has been substantially transformed both chemically and mechanically. Therefore, the remaining exposed resist shows significantly more complex physical behavior than the remaining resist in a PTD process. These behaviors require substantial improvement in OPC (compact) model physical modeling accuracy in order to match wafer data and trends [2,3]. Additionally, these more complex resist behaviors place further requirements on the physical validation of OPC modeling inference. In this paper, we present results of our work to understand and improve the optimization and physical validation of physics-based NTD compact modeling flows by utilizing new methods for analysis and automation. We utilize a compact model flow containing physics-based resist model forms for chemically amplified resist (CAR) exposure, CAR reaction-diffusion, resist top-loss due to exposure with post-exposure bake (PEB), low contrast organic solvent development of resist, and mechanical deformation effects in multiple process steps. We present this flow and benefits obtained from automating different validation tests including the usefulness of employing rigorous lithography simulation NTD results early in the compact modeling work to improve overall model quality.