Laser ablative microvia formation has been widely accepted as an effective manufacturing method for interconnect via formation. Current conventional nanosecond laser microvia formation has reached its limit in terms of minimum via diameter and machining quality. Femtosecond laser has been investigated intensively for its superior machining quality and capability of producing much smaller features. However, the traditional femtosecond laser has very low power and is thus unable to meet the throughput requirement. In this paper we report ablative microvia formation using femtosecond lasers at megahertz repetition rates. Laser ablation was demonstrated for the first time for sub-10 µm interconnection via drilling at a throughput of 10 000 vias per second. A systematic study of the influence of a high repetition rate in femtosecond laser micromachining of silicon was carried out. The experiments were performed using an Yb-doped fibre amplified/oscillator laser with 1030 nm wavelength in an air environment. The effects of a high repetition rate on microvia formation were observed at ∼300 fs for silicon substrates. Laser parameters along with threshold energy, via diameter, ablation depth, ablation rate and via quality were studied in detail to accentuate the need of femtosecond lasers for forming sub-10 µm diameter microvias. The experimental results show that femtosecond laser pulses with high repetition rates show unequivocally the advantages of short-pulse laser ablation for high-precision applications in micrometre-scale dimensions.

Articles you may be interested inThe origins of pressure-induced phase transformations during the surface texturing of silicon using femtosecond laser irradiation J. Appl. Phys. 112, 083518 (2012); 10.1063/1.4759140 The role of asymmetric excitation in self-organized nanostructure formation upon femtosecond laser ablation AIP Conf. Proc. 1464, 428 (2012); 10.1063/1.4739897 Laser-induced damage threshold of silicon in millisecond, nanosecond, and picosecond regimes Absence of amorphous phase in high power femtosecond laser-ablated silicon Appl. Phys. Lett. 94, 011111 (2009); 10.1063/1.3052693Removal of small particles on silicon wafer by laser-induced airborne plasma shock waves This paper reports an experimental study of the vapor plume and shockwave propagation generated during femtosecond laser ablation. An Yb-doped fiber amplified/oscillator laser with 1030 nm wavelength and pulse repetition rate up to 26 MHz was used to ablate a blank silicon substrate in an ambient air environment. The interaction of internal and external shockwaves with the sample surface was found to cause raised spherical rims around the central ablation regime within the crater. Rims formed by primary and secondary shockwaves can be clearly observed. Analysis of the rim formation is studied in detail.

Fundamentals of mega hertz femtosecond laser ablation and its application in interconnection via drilling

Fundamentals of mega hertz femtosecond laser ablation and its application in interconnection via drilling