Method for drilling micro-holes with a laser beam

A method for drilling micro-holes in a multi-layer substrate including a first metal layer and at least one second metal layer, and including a dielectric layer arranged between two metal layers, comprising:

• irradiating, with an energy beam of a solid-state laser having a repetition frequency of at least 10 kHz, a wavelength of less than 1100 nm and a pulse length of less than 50 ns, the irradiation being carried out in two operations including,
• ablating, in the first operation, the first metal layer and a part of the underlying dielectric layer, and,
• ablating, in the second operation, the dielectric layer cleanly down to the second metal layer, wherein, in the first operation, the laser beam is set to a repetition frequency of at least 15 kHz, focused onto the first metal layer and moved with a first circumferential velocity in a circle corresponding to the diameter of the desired hole, in such a number of passes until at least the first metal layer is cut through, the metal layer being fully removed in the hole region, and in the second operation, the laser beam is set to a repetition rate at most equal to that in the first operation, directed out of focus onto the dielectric layer exposed in the hole and moved, with a circumferential velocity which is higher than the first, in at least one concentric circle inside the desired hole diameter, in such a number of passes until the dielectric layer is ablated in the hole region, the defocusing and the second velocity being set such that the effective energy density in the second operation lies below the threshold for ablation of the second metal layer.