Glass etching with gaseous hydrogen fluoride: Rapid management of surface nano‐roughness

Abstract

Surface roughness of glass is desired to be arbitrary controlled because it affects a variety of properties such as tactile impression, optical properties, and contact chargeability. While the surface modification is currently achieved by wet etching of the glasses with hydrofluoric acid, there is still room for improvement because the wet etching cannot be simultaneously applied during flat glass production. We recently developed novel etching scheme, which uses gaseous hydrogen fluoride (HF) under high temperature. Because the flat glasses are kept hot during the production, our procedure can be introduced to the flat glass production process. Here, we demonstrate that surface nano-roughness (1-20 nm of arithmetic mean roughness) of silicate glasses can be rapidly and reproducibly controlled by our method with changing the reaction temperature. It was found that the reaction with gaseous HF heterogeneously left metal fluorides on the glasses and that the fluorides partially masked the further reaction. High reaction temperature led the fluoride particles larger, resulting in rougher surface after removing the fluoride layer. It took only a few seconds for this reaction.

The role of silanol groups on the reaction of SiO2 and anhydrous hydrogen fluoride gas

“…Vacuum heating was performed in the same chamber for HF gas etching, which was described elsewhere. 17 Briefly, the substrates were placed in a carbon box, which was heated by an infrared lamp furnace (Advance Riko, Inc., VHC-610CP). Because almost all silanol groups are known to be annihilated at 1000 • C, 16 the heating duration was set to 10 min.…”

“…The detail of the gaseous HF etching chamber was the same as that used for vacuum heating. 17 Anhydrous HF gas diluted with N 2 was introduced to the carbon box through a vitreous silica tube. A mass flow controller (MFC:HORIBA SEC 8440F) was used to control HF concentration to be 5% with a total flow speed of 5 SLM.…”

“…1,16 Recently, we have developed gaseous HF etching of glasses at high temperature (typically 400-650 • C). 17 The reaction at high temperatures should improve the reaction rate. Because the reaction temperature in dry-process is not limited as the solution process (<100 • C), the etching rate can be in principle arbitrarily raised.…”

“…In fact, very recently we demonstrated rapid reactions between gaseous HF and various glasses (soda-lime-, alumino-, and borosilicates) under high temperatures. 17 The reactions with such cation-containing glasses afforded nanoroughness on the reacted surface because the cation fluorides left on the surface acted as a heterogeneous mask. The magnitude of the roughness was controllable depending on the reaction temperature, and hence it would be useful for, for example, adjusting tactile impressions of flat glasses.…”

“…The remaining issue is the reaction rate (50–150 nm/min), 13–15 which is as slow as or only slightly faster than that of the wet‐process (10–100 nm/min) 1,16 . Recently, we have developed gaseous HF etching of glasses at high temperature (typically 400–650°C) 17 . The reaction at high temperatures should improve the reaction rate.…”