Current EUV lithography pushes photoresist thickness reduction to sub-30 nm in order to meet resolution targets and mitigate pattern collapse. In order to maintain the etch budgets in hard mask open, the adhesion layer in between resist and hard mask has to scale accordingly. We have reported a grafted polymer brush adhesion layer used in an ultrathin EUV patterning stack and demonstrated sub-36 nm pitch features with significant improvement over existing adhesion promotion techniques . This paper provides further understanding of this class of materials from a fundamental point of view. We first propose a hypothesis of the adhesion mechanism, and probe key factors that could affect adhesion performance. The grafting kinetics study of polymer brush that contains different functional groups to the substrate shows grafting chemistry, time, and temperature are key factors that affect the printing performance. We then conduct a systematic study to understand printing capability at various pitches for different silicon-based substrates. By comparing the process window, we gain comprehensive understanding of the printing limits and failing modes with this approach. We provide a comparative study of a grafted adhesion layer vs. a conventional spin on BARC type material, including defectivity. Pattern transfer to hard mask with varied etch chemistry is conducted to understand the performance of polymer brush during etch.
Initial readiness of extreme ultraviolet (EUV) patterning has been demonstrated at the 7-nm device node with the focus now shifting to driving the “effective” k1 factor and enabling the second generation of EUV patterning. In current EUV lithography, photoresist thicknesses <30 nm are required to meet resolution targets and mitigate pattern collapse. Etch budgets necessitate the reduction of underlayer thickness as well. Typical spin-on underlayers show high defectivity when reducing thickness to match thinner resist. Inorganic deposited underlayers are lower in defectivity and can potentially enable ultrathin EUV patterning stacks. However, poor resist-inorganic underlayer adhesion severely limits their use. Existing adhesion promotion techniques are found to be either ineffective or negatively affect the etch budget. Using a grafted polymer brush adhesion layer, we demonstrate an ultrathin EUV patterning stack comprised of inorganic underlayer, polymer brush, and resist. We show printing of sub-36-nm pitch features with a good lithography process window and low defectivity on various inorganic substrates, with significant improvement over existing adhesion promotion techniques. We systematically study the effect of brush composition, molecular weight, and deposition time/temperature to optimize grafting and adhesion. We also show process feasibility and extendibility through pattern transfer from the resist into typical back end stacks.
Extreme ultraviolet (EUV) lithography has been recognized as a promising candidate for the manufacturing of semiconductor devices as LS and CH pattern for 7nm node and beyond. EUV lithography is ready for high volume manufacturing stage. For the high volume manufacturing of semiconductor devices, significant improvement of sensitivity and line edge roughness (LWR) and Local CD Uniformity (LCDU) is required for EUV resist. It is well-known that the key challenge for EUV resist is the simultaneous requirement of ultrahigh resolution (R), low line edge roughness (L) and high sensitivity (S). Especially high sensitivity and good roughness is important for EUV lithography high volume manufacturing.
We are trying to improve sensitivity and LWR/LCDU from many directions. From material side, we found that both sensitivity and LWR/LCDU are simultaneously improved by controlling acid diffusion length and efficiency of acid generation using novel resin and PAG. And optimizing EUV integration is one of the good solution to improve sensitivity and LWR/LCDU. We are challenging to develop new multi-layer materials to improve sensitivity and LWR/LCDU. Our new multi-layer materials are designed for best performance in EUV lithography system. From process side, we found that sensitivity was substantially improved maintaining LWR applying novel type of chemical amplified resist (CAR) and process. EUV lithography evaluation results obtained for new CAR EUV interference lithography. And also metal containing resist is one possibility to break through sensitivity and LWR trade off. In this paper, we will report the recent progress of sensitivity and LWR/LCDU improvement of JSR novel EUV resist and process.
In this study, the integrity and the benefits of the DSA shrink process were verified through a via-chain test structure, which was fabricated by either DSA or baseline litho/etch process for via layer formation while metal layer processes remain the same. The nearest distance between the vias in this test structure is below 60nm, therefore, the following process components were included: 1) lamella-forming BCP for forming self-aligned via (SAV), 2) EUV printed guiding pattern, and 3) PS-philic sidewall. The local CDU (LCDU) of minor axis was improved by 30% after DSA shrink process. We compared two DSA Via shrink processes and a DSA_Control process, in which guiding patterns (GP) were directly transferred to the bottom OPL without DSA shrink. The DSA_Control apparently resulted in larger CD, thus, showed much higher open current and shorted the dense via chains. The non-optimized DSA shrink process showed much broader current distribution than the improved DSA shrink process, which we attributed to distortion and dislocation of the vias and ineffective SAV. Furthermore, preliminary defectivity study of our latest DSA process showed that the primary defect mode is likely to be etch-related. The challenges, strategies applied to improve local CD uniformity and electrical current distribution, and potential adjustments were also discussed.
The progress of three potential DSA applications, i.e. fin formation, via shrink, and pillars, were reviewed in this paper. For fin application, in addition to pattern quality, other important considerations such as customization and design flexibility were discussed. An electrical viachain study verified the DSA rectification effect on CD distribution by showing a tighter current distribution compared to that derived from the guiding pattern direct transfer without using DSA. Finally, a structural demonstration of pillar formation highlights the importance of pattern transfer in retaining both the CD and local CDU improvement from DSA. The learning from these three case studies can provide perspectives that may not have been considered thoroughly in the past. By including more important elements during DSA process development, the DSA maturity can be further advanced and move DSA closer to HVM adoption.
Initial readiness of EUV patterning has been demonstrated at the 7-nm device node with the focus now shifting to driving the 'effective' k1 factor and enabling the second generation of EUV patterning. In current EUV lithography, photoresist thicknesses <30 nm are required to meet resolution targets and mitigate pattern collapse. Etch budgets necessitate the reduction of underlayer thickness as well. Typical spin-on underlayers show high defectivity when reducing thickness to match thinner resist. Inorganic deposited underlayers are lower in defectivity and can potentially enable ultrathin EUV patterning stacks. However, poor resist-inorganic underlayer adhesion severely limits their use. Existing adhesion promotion techniques are found to be either ineffective or negatively affect the etch budget. Here, using a grafted polymer brush adhesion layer we demonstrate an ultrathin EUV patterning stack comprised of inorganic underlayer, polymer brush and resist. We show printing of sub-36 nm pitch features with good lithography process window and low defectivity on various inorganic substrates, with significant improvement over existing adhesion promotion techniques. We systematically study the effect of brush composition, molecular weight and deposition time/temperature to optimize grafting and adhesion. We also show process feasibility and extendibility through pattern transfer from the resist into typical back end stacks.
Initial readiness of EUV (extreme ultraviolet) patterning was demonstrated in 2016 with IBM Alliance's 7nm device technology. The focus has now shifted to driving the 'effective' k1 factor and enabling the second generation of EUV patterning. With the substantial cost of EUV exposure there is significant interest in extending the capability to do single exposure patterning with EUV. To enable this, emphasis must be placed on the aspect ratios, adhesion, defectivity reduction, etch selectivity, and imaging control of the whole patterning process. Innovations in resist materials and processes must be included to realize the full entitlement of EUV lithography at 0.33NA. In addition, enhancements in the patterning process to enable good defectivity, lithographic process window, and post etch pattern fidelity are also required. Through this work, the fundamental material challenges in driving down the effective k1 factor will be highlighted.
Directed self-assembly (DSA) of block copolymers (BCPs) has become a promising patterning technique for 7nm node hole shrink process due to its material-controlled CD uniformity and process simplicity. For such application, cylinder-forming BCP system has been extensively investigated compared to its counterpart, lamella-forming system, mainly because cylindrical BCPs will form multiple vias in non-circular guiding patterns (GPs), which is considered to be closer to technological needs.[2-5] This technological need to generate multiple DSA domains in a bar-shape GP originated from the resolution limit of lithography, i.e. those vias placed too close to each other will merge and short the circuit. In practice, multiple patterning and self-aligned via (SAV) processes have been implemented in semiconductor manufacturing to address this resolution issue. The former approach separates one pattern layer with unresolvable dense features into several layers with resolvable features, while the latter approach simply utilizes the superposition of via bars and the pre-defined metal trench patterns in a thin hard mask layer to resolve individual vias, as illustrated in Fig 1 (upper). With proper design, using DSA to generate via bars with the SAV process could provide another approach to address the resolution issue.
In recent years major advancements have been made in the directed self-assembly (DSA) of block copolymers (BCP). DSA is now widely regarded as a leading complementary patterning technique for future node integrated circuit (IC) device manufacturing and is considered for the 7 nm node. One of the most straightforward approaches for implementation of DSA is via patterning by graphoepitaxy. In this approach, the guiding pattern dictates the location and pitch of the resulting hole structures while the material properties of the BCP control the feature size and uniformity. Tight pitches need to be available for a successful implementation of DSA for future node via patterning which requires DSA in small guiding pattern CDs. Here, we show strategies how to enable the desired CD shrink in these small guiding pattern vias by utilizing high χ block copolymers and/or controlling the surface properties of the template, i.e. sidewall and bottom affinity to the blocks.