Processing of glass

Conventional laser milling strategy struggles to achieve high aspect ratio geometries, as ablation debris accumulates within the ablation area, preventing further material removal and resulting in saturation of ablated depth. Alternatively, in the bottom-up milling technique, the laser beam is focused at the bottom of a sample. This method allows all ablation products to be removed through the backside of the sample, enabling the formation of high aspect ratio geometries in glass.

Bessel beam scribing is the most efficient laser-based, kerf-less method for scribing glass. This technique introduces intra-volume voids, followed by mechanical or thermal separation, resulting in smooth sidewall roughness and as it requres only a single laser pass, high scribing speeds can be achieved.

Processing glass substrates thinner than 0.5 mm presents significant challenges due to their fragility and susceptibility to cracking under excessive thermal loads. Femtosecond lasers are ideal for processing thin glass substrates because their ultra-short pulse duration minimizes thermal accumulation, resulting in superior quality.

Femtosecond laser induced selective etching is a two-step process where focused femtosecond laser pulses modify the material structure, followed by chemical etching that selectively removes the laser-modified regions. This technique enables precise taper-free 3D microfabrication in transparent materials, achieving superior surface roughness in the range of hundreds of nanometers and the capability to operate at wafer-level scales.

Formation of high aspect holes in glass substrates is becoming an increasingly important topic, especially in semiconductor field. With the help of femtosecond lasers it is possible to form low degree taper and high aspect ratio TGVs in glass with high quality – low chipping, absence of cracking and smooth hole inner wall.