KEYWORDS: Optical lithography, Metals, Etching, Transistors, Atomic layer deposition, Silica, Inspection, Electrodes, Transmission electron microscopy, System on a chip
The surrounding-gate-transistor (SGT) is a vertical gate-all-around device with a new design to exploit natural area gain for further scaling the SRAM size beyond N5 node. One of the benefits in SGT is it can fully decouple the dependency of the gate length (Lg) and the source/drain (S/D) contact size from the contact gate pitch (CGP) scaling, which is seen as a hard limit for the conventional scaling. To fully realize the benefit of area gain and Lg scaling independent from lithography, the patterning challenges of 3D vertical device structure must be resolved. In this paper, we report the MOL patterning challenges in SGT device fabrication, such as Metal recess process, Bottom Contact formation (VBG), Cross point formation (XC), Top electrode (TE) patterning.
Buried power rail (BPR), a novel integration approach for further device scaling, brings in new patterning needs and requirements, the most importantly, the challenging middle-of-line (MOL) patterning process steps. In this paper, some of the critical plasma dry etch development processing results for the FinFET device flow with BPR integrated are presented. Mainly, the study was focused on plasma dry etch development of high aspect ratio Via contact to BPR metal (VBPR) and Trench contact etch (M0A) to the source/drain (S/D) device region. We demonstrate the short-free M0A (no attack on the neighboring gates) contact etch to the S/D, with the high etch selectivity values obtained in case of the dielectric SiO2 trench etch to the thin Si3N4 liner (deposited over epitaxial S/D), and subsequently the high selectivity values during SiN liner etch to the underlying S/D (SiN liner etch results in 0nm epitaxial film loss). Patterning of high aspect ratio (HAR) Via consisting of the multi-stack, SiO2/SiN/SiO2/SiN dielectric, landing on the bottom BPR metal was achieved, with the target critical dimension (CD) required to avoid shorting to the adjacent gates. Additionally, we report our learnings on how choice of buried power metal (W, Ru and Mo) impacts the etch requirements, i.e., the etch challenges associated by using Ru and Mo as a replacement for standardly used W metal.
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