Optimization strategy for high-quality laser milling of silicon

• Roughness of laser milled silicon is controlled by spot overlapping and fluence. • Optimal ratio of spot centers interspace to spot radius is below 0.3. • Optimal fluence of 1 J/cm 2 should be achieved preferably by laser spot enlargement. Laser milling of silicon by IR picosecond pulses (λ = 1030 nm) has been investigated with a special emphasis on influence of laser fluence, spot size and spot overlapping on the surface roughening and ablation productivity. The detailed recipe for optimization of the silicon milling process has been formulated: reduction of the maximum laser fluence down to about ∼1 J/cm 2 by means of corresponding laser spot enlargement, while the ratio of the laser spot displacement to the spot radius is maintained below the level of 0.3. Fulfillment of these conditions provides minimal possible surface roughness at moderate reduction of the ablation productivity. The silicon ablation process under multi-spot irradiation was numerically simulated to specify which of two factors plays a decisive role in the surface roughening at different processing conditions: spatial non-uniformity of laser exposure or ablation-induced surface instabilities.