At IBM, one of the focus items for EUV patterning development is to enable the fullest extent of scaling to a second EUV node while maintaining single-exposure levels. The challenge for the next node of EUV patterning has been with attaining acceptable defectivity levels that can enable electrical yield at pitches 32nm and below. For single-expose EUV, the primary detractors to sub-32nm pitch yield are typically microbridging and line break defects, which have different root causes but can exist in the same dose range. Since the etch strategies for mitigating one of these defect types will result in exacerbating the other, the burden to improve defectivity cannot be placed solely on the pattern transfer process. Resist scumming, which is the root cause of microbriging, can be modulated through interactions with the resist-hardmask interface. The lack of acid at the substrate interface causes resist scumming, and therefore increasing the acidity at the resist hardmask interface can be expected to mitigate post-litho microbridge defects. As the number of EUV photons are significantly less compared to DUV exposures due to the high energy contained in each photon, an extra acid boost can also help to address the stochastics failures that dominate EUV patterning. This paper will demonstrate the concept of modulating the resist-hardmask interaction through surface activation layers, and show the subsequent effects on patterning process window and microbridging defectivity toward yield at pitches <32nm.
Dissolution of ultrathin exposed EUV photoresist can deviate from the bulk regime due to the modulating influence of the adjacent top and bottom interfaces, which can eventually dominate the behavior of the entire film. Furthermore, use of TMAH 0.26N as aqueous developer for CARs has remained the industry standard without thorough investigation of other possible aqueous bases and concentrations. In this work, we provide a detailed description of the interfacial dissolution behavior of model ultrathin EUV resists in a variety of tetraalkylammonium-based developers, using a representative open source polymer platform. Dissolution kinetics measured using QCM (quartz crystal microbalance) with and without added PAG highlight the convolution of vertical distribution of resist additives with their dissolution inhibition effect throughout the resist film. Results for the local dissolution at the resist-substrate interface using interrupted development and AFM measurements are provided and explained in terms of confinement effects (polymer chain mobility, vacid diffusion) and polymer-substrate interactions. This work can serve as initial guidance to understand the attainable interfacial dissolution modulation afforded by a rational developer selection and a matching EUV resist design.