Recently, the research team of Deng Hui, assistant professor of the Department of Mechanical and Energy Engineering of Southern University of Science and Technology, published a titled "An efficient approach for atomic-scale polishing of single-crystal silicon via plasma-based" in the International Journal of Machine Tools and Manufacture, a top journal in the field of mechanical manufacturing. The latest research results of "atom-selective etching" and was selected as the cover. This paper proposes for the first time a high-efficiency manufacturing method for the atomic-level surface of a single crystal silicon wafer based on the plasma-induced atomic selective etching effect. 

Monocrystalline silicon is currently the most versatile semiconductor material. With the further reduction of chip manufacturing processes, more advanced chip manufacturing processes have higher and higher requirements for wafer flatness and surface roughness. When the process node reaches 3nm or less, the requirements for the surface quality of the wafer in the photolithography process tend to be atomic. Traditional mechanical polishing or chemical mechanical polishing (CMP) processes are based on plastic deformation to achieve material removal. On the one hand, the material removal principle of the traditional process determines that it cannot obtain a non-damaged surface. On the other hand, the tool scale of the traditional process determines It cannot obtain a regular surface atomic arrangement. Therefore, for the atomic-level surface requirements of high-end chip manufacturing, there is an urgent need to develop new ultra-precision surface manufacturing technologies that can achieve perfect atomic arrangement.

Based on the above requirements, Deng Hui’s team proposed an ultra-precision polishing method (Plasma-based Atom-Selective Etching, PASE) based on the plasma-induced atomic selective etching effect. The principle is shown in Figure 1. The rough monocrystalline silicon surface can be regarded as composed of silicon atoms with different numbers of dangling bonds. In the PASE process, the silicon atoms with 3 dangling bonds have the highest etching priority, followed by silicon atoms with 2 dangling bonds, and finally It is a silicon atom with a dangling bond. This difference in etching priority can be adjusted by changing the parameters of the ion body. Once the higher priority silicon atoms are etched away, the sub-layer silicon atoms will be exposed, causing the bonding state of the surface to change continuously. Figure 1(b) demonstrates the process of polishing a rough area into a smooth surface by the PASE process. After multiple selections, the final surface can be regarded as an equipotential surface in which all atoms are regularly arranged, that is, all atoms are uniformly etched. Therefore, the PASE process can obtain an atomic-level ultra-smooth surface. 

Based on the above principles, the researchers optimized various process parameters such as plasma power and gas ratio. For a 2-inch single crystal silicon wafer (100), the material removal rate of the PASE process exceeds 0.7μm/min, and the surface Sa roughness can be effectively reduced from 195nm to less than 1nm within 5 minutes, achieving an atomic-level surface with high efficiency Manufactured and polished single crystal silicon wafers were also confirmed by TEM observation that there is no sub-surface damage (Figure 2). At the same time, Deng Hui's team also applied this polishing technology to single crystal silicon wafers with (110) and (111) crystal planes, and achieved good polishing results. This proves that PASE is a universal single crystal silicon polishing method, and has nothing to do with the crystal orientation of the silicon wafer.

The plasma induced atom selective etching technology proposed by this research has no mechanical stress, which effectively avoids the surface and sub-surface damage caused by mechanical effects such as shearing and extrusion in the traditional polishing process. Non-destructive, atomic-level surface manufacturing. At the same time, this technology is very efficient, and does not need to consume expensive polishing liquids and polishing pads that require harmless treatment. Compared with the traditional CMP method, it has a huge advantage. Since this technology can polish single crystal silicon wafers in all crystal orientations, it has great application potential in wafer processing in the electronic and electrical fields. In addition, this method is theoretically expected to achieve a large-scale smooth surface at the level of a single atomic layer, which provides new possibilities for cutting-edge fields such as the manufacture of quantum chips.

Source: The content comes from "Southern University of Science and Technology", thank you.