Sapphire Selective Laser Etching Dependence on Radiation Wavelength and Etchant

Sapphire is a transparent, high-hardness material with mechanical stability and optical transparency into the UV range. Its use in microfabrication is limited by brittleness. Selective laser etching (SLE) is a method for microprocessing brittle materials. However, traditional SLE etchants like hydrofluoric acid are ineffective for sapphire. This gap motivated the search for alternative etchants and wavelengths. Prior research has shown that femtosecond lasers can modify crystalline materials. Yet, the effect of different wavelengths on sapphire remained unclear. No prior work had resolved the optimal etchant for sapphire SLE. This uncertainty drove the investigation into femtosecond laser-induced SLE. The study aimed to compare wavelengths and etchants for sapphire processing.

The goal was to evaluate the effectiveness of different laser wavelengths and etchants for sapphire microprocessing. The problem is that sapphire’s brittleness complicates 3D fabrication. The motivation is to find a reliable SLE method for sapphire. The authors focused on C-cut sapphire and femtosecond laser irradiation. They tested wavelengths of 1030 nm, 515 nm, and 343 nm. The study compared the impact of various etchants on material modification. The aim was to identify a suitable etchant and wavelength combination. This work addresses the challenge of etching crystalline sapphire effectively.

The researchers used femtosecond laser pulses to modify C-cut sapphire. They tested three wavelengths: 1030 nm, 515 nm, and 343 nm. After laser treatment, the material was exposed to different etchants. The etchants included hydrofluoric acid, sodium hydroxide, potassium hydroxide, and a mixture of sulphuric and phosphoric acids. The study compared the etching efficiency of each solution. Material changes were analyzed after each processing step. The team evaluated structural modifications using optical and scanning electron microscopy. The experimental setup allowed for controlled irradiation and etching conditions.

The study found that traditional SLE etchants failed to etch sapphire effectively. Hydrofluoric acid and potassium hydroxide showed minimal etching. A mixture of 78% sulphuric and 22% phosphoric acid at 270 °C etched sapphire successfully. The etching depth varied with laser wavelength. At 343 nm, the etching was most pronounced. The material’s surface morphology changed after laser irradiation. The etched regions showed structural modifications visible under microscopy. The combination of 343 nm laser and the sulphuric-phosphoric acid mixture produced the best results.

The authors concluded that sapphire SLE requires alternative etchants and wavelengths. Regular SLE etchants like hydrofluoric acid are ineffective for sapphire. A sulphuric-phosphoric acid mixture at 270 °C is a viable alternative. The 343 nm wavelength produced the most effective material modification. The study demonstrated that femtosecond lasers can alter sapphire’s structure. The results suggest that wavelength choice influences etching efficiency. The findings provide a perspective for sapphire structure formation. The authors propose that this method could advance microfabrication of sapphire components.