(Invited) Supercritical Drying: A Sustainable Solution to Pattern Collapse of High-Aspect-Ratio and Low-Mechanical-Strength Device Structures

Abstract

Collapse of nanostructures with high aspect ratio and/or low mechanical strength during drying step in wet process has become a critical issue in semiconductor industry. Even current workable drying practices are facing steeply rising challenges from rapid device scaling advancements. The objective of this work, following evaluation of multiple advanced drying technique, is to develop a sustainable non-stiction drying solution incorporating supercritical fluids. Leaning-free performance has been consistently demonstrated with our supercritical drying sequence on 2x NAND STI (trench aspect ratio ~20) and low-k trench structures, where pattern collapses were observed under conventional solvent-assisted drying or even with advanced self-assembled monolayer approach. Release of sporadic stiction and complete recovery from global pattern leaning were both achieved with our integrated supercritical drying process. Particle performance < 50 adders @0.09μm in average was attained with background particles subtracted. Metallic contamination analysis with TXRF showed all metal components interested were below detection limit.

Review of Semiconductor Flash Memory Devices for Material and Process Issues

“…These thin walls are prone to deformation or leaning toward each other during the subsequent wet-etching process. [91] To overcome this issue, trench etching is now performed across several rows of channel holes, as shown in Figure 7b, which essentially form the word plane (WP), not WL. This modification in the cell layout can also make the wall-like patterns thicker and secure enough, ensuring the structural integrity of the cell patterns during the entire fabrication process.…”

“…These thin walls are prone to deformation or leaning toward each other during the subsequent wet‐etching process. [ 91 ]…”

Liquid-Cell Transmission Electron Microscopy Observation of Two-Step Collapse Dynamics of Silicon Nanopillars on Evaporation of Propan-2-ol: Implications for Semiconductor Integration Density

“…To solve this problem, new drying techniques to prevent collapse have been developed, such as the addition of an auxiliary substrate, 6 the use of a liquid with a low surface tension to control the wettability of the substrate, 7,8 the reduction of capillary forces by electromagnetic-wave irradiation, 9 or the elimination of capillary forces by drying without the involvement of a liquid phase through sublimation or supercriticality. 10,11 However, no effective solution has yet been established, and this problem might be one factor that makes it impossible to maintain Moore's law.…”

“…One such problem is the collapse of nanostructures due to capillary interactions during evaporation of cleaning solutions, a process that is exacerbated by increasing miniaturization of semiconductor devices and consequent weakening of nanostructures. − The collapse of nanostructures destroys their expected functions, so countermeasures are essential. To solve this problem, new drying techniques to prevent collapse have been developed, such as the addition of an auxiliary substrate, the use of a liquid with a low surface tension to control the wettability of the substrate, , the reduction of capillary forces by electromagnetic-wave irradiation, or the elimination of capillary forces by drying without the involvement of a liquid phase through sublimation or supercriticality. , However, no effective solution has yet been established, and this problem might be one factor that makes it impossible to maintain Moore’s law.…”

In situ dry cleaning of Si wafer using OF2/NH3 remote plasma with low global warming potential

“…In addition, the pattern leaning can be occurred, and where the nanoscale patterns are collapsed due to the capillary phenomenon. Therefore, due to the cleaning limit of the wet cleaning method, dry cleaning methods are required for the sub-20 nm semiconductor devices [7,8].…”