This review highlights the progress and challenges in chip atomic layer polishing. Chips are fundamental to the modern information society. According to Moore's Law, the chip feature size is shrinking and approaching the physical limit. At the same time, advanced packaging technologies such as hybrid bonding continuously evolve. These create pressing needs to develop atomic layer polishing, a technique that enables extremely precise material removal at the atomic layer level, to achieve surfaces with atomic-level precision for demanding processes such as photolithography and bonding. Currently, chemical mechanical polishing (CMP) is the only key technology in chip manufacturing capable of simultaneously achieving local and global planarization of the wafer surface, with the potential to realize atomic layer polishing. This review provides a systematic summary of the mechanisms and processes of CMP for chip substrate surfaces and interconnect heterogeneous surfaces.
Significant progress has been made in the controlled removal with a single atomic layer precision at the microscopic level and in the CMP with surface roughness close to the theoretical limit at the macroscopic level for the monocrystalline silicon substrate. These advances highlight the extreme precision processing capability of CMP for the wafer surface. Furthermore, ongoing developments in multi-field assisted CMP and energy particle beam polishing hold promise for enabling atomic layer polishing for new substrates like GaN, SiC and diamond. In the case of interconnect heterogeneous surfaces, two material removal modes in CMP are summarized from a tribological perspective based on the interactions between the abrasive and material surfaces: mechanical plowing and chemical bonding. Copper, cobalt, and nickel are mainly removed through the mechanical plowing mode, while tantalum, ruthenium, and titanium are mainly removed through chemical bonding. According to this foundation, control principles and methods for achieving equivalent removal of heterogeneous surfaces are proposed based on different material removal modes. In the mechanical plowing material removal mode, corrosion and its impact on the mechanical strength of the material surface can be adjusted through the modulation of the effects of oxidation, complexation, and corrosion inhibition, as well as their synergistic effects. This approach allows for controlling the material removal rate (MRR). In the chemical bonding material removal mode, the number of reactive sites and their influence on interfacial chemical bonds can be regulated through the adjustment of pH, oxidation, and ionic strength, along with their synergistic effects, thus controlling the MRR. According to these control principles, a systematic summary of the planarization processes for interconnect heterogeneous surfaces, such as copper/tantalum, copper/cobalt, and copper/ruthenium, is provided. Finally, based on existing research progress, it is proposed to leverage the synergistic effects of mechanical, chemical, and electrical/optical/plasma/energy beams to confine chemical reactions and mechanical-chemical reactions to the surface atomic layer, to achieve atomic layer polishing. Specifically, for the mechanical plowing material removal mode, the focus is on designing the molecular structures of chemical additives to precisely modulate the effects of oxidation, complexation, and corrosion inhibition. This approach confines the corrosion behavior to the outermost atomic layer while controlling the mechanical action of the abrasive to enable precise, controllable atomic layer removal. For the chemical bonding material removal mode, the investigation focuses on confining chemical bonding reactions to the outermost atomic layer, weakening back bonds, and simultaneously controlling the mechanical action of the abrasive to disrupt chemical bonds between the outermost and sub-surface atoms, thus achieving controlled atomic layer removal.
This review highlights the growing demand for atomic-level manufacturing of high-end chips and the development of atomic layer polishing. It provides a systematic summary of the mechanisms, progress, and challenges in atomic layer polishing, with the aim of offering critical theoretical and technical support for the atomic-level manufacturing of advanced chips. The findings from this research have potential applications in key areas such as high-end optical components and superlubricity devices.
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