From Phys Org:

A precise, chemical-free method for etching nanoscale features on silicon wafers has been developed by a team from Penn State and Southwest Jiaotong University and Tsinghua University in China.

In standard lithography, a photosensitive film is deposited on a  wafer and a pattern called a mask is used to expose certain portions of the film. Then, chemicals—such as a potassium hydroxide solution—etch patterns into the silicon. Further steps are required to smooth out the roughened surface.

The Penn State and Southwest Jiaotong University researchers developed an entirely different, – and mask-free, one-step process. They lightly rubbed a rounded silica tip of an instrument called a  across a silicon substrate—the material base typically used to make electronic devices. When exposed to the water vapor in air, the top layer of silicon forms bonds with the tip of the scanning probe, and a single layer of atoms slides off as the probe moves across the silicon. Because the atoms below do not take part in the chemical reaction, they are completely undamaged.

Read more at: A simple method etches patterns at the atomic scale reposted by Silicon Valley Microelectronics.