A new process removes only the top atomic layer of chip materials, helping manufacturers build smaller transistors while reducing damage during production.
Researchers in the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) have developed a method to remove only the top atomic layer of a material used in next-generation transistors while protecting the layers underneath. The approach uses oxygen or fluorine treatment before plasma processing to lower the energy needed to remove surface atoms.
The work focuses on molybdenum disulfide, a transition metal dichalcogenide (TMD) that is only three atoms thick. It is being studied as a possible material to extend transistor scaling beyond silicon. Even small damage to its lower layers can change how the device works, so precise control is important.
In conventional plasma processing, energetic ions strike the surface and remove atoms. The key challenge is removing only the top sulfur layer without affecting the molybdenum layer below. On untreated molybdenum disulfide, about 30 electron volts of energy is needed to remove a sulfur atom, which is close to the range where deeper damage can begin.
Computer simulations show that surface pretreatment changes this balance. Oxygen coating lowers the removal energy to about 14 electron volts, while fluorine reduces it further to about 10 electron volts. This creates a wider gap between safe removal and damaging impact, making the process more controllable because plasma ions naturally vary in energy.
The effect comes from chemistry working with ion impact. When ions hit an oxygen-coated surface, sulfur reacts with oxygen to form sulfur dioxide gas, which leaves the surface on its own. Fluorine produces similar reactions by forming sulfur–fluorine compounds. These intermediate products reduce the need to directly break atomic bonds.
Researchers said the method works by forming easier-to-remove chemical species rather than directly breaking bonds.
The team is now studying how much damage still occurs during processing and whether the same approach can be applied to related materials, such as replacing molybdenum with tungsten or sulfur with selenium.
