High-speed flattening of crystallized glass substrates by dressed-photon–phonon etching

Dressed-photon–phonon (DPP) etching is a non-contact flattening technology that realizes ultra-flat surfaces and has been reported to achieve an arithmetic mean surface roughness, R_a, on the order of 0.1 nm in various materials, such as fused silica, plastic films, and GaN crystal. In this study, we successfully flattened the surface of a crystallized glass substrate in several seconds using laser light with a higher power density than that used in previous studies. The target substrate had an initial appearance similar to frosted glass, with an R_a of 92.5 nm. We performed DPP etching under a Cl₂ atmosphere using a CW laser with a wavelength of 532 nm, a power of 8 W, and a spot diameter of 0.2 mm. After 1 s of processing, we obtained a flat surface with an R_a of 5.00 nm. This surface roughness equaled or surpassed that of a substrate flattened by conventional chemical mechanical polishing, with an R_a of 5.77 nm. Through the detailed analysis of atomic force microscopic images, we found the DPP etching resulted in the smaller standard deviation of the height difference than CMP in the smaller lateral size than 50 nm.