The unique combination of laser characteristics used, visible wavelength, high beam quality, low pulse energy, very high repetition rate, short pulse width and high average power, enables the machining of precision, sub-millimetre, high aspect ratio features in silicon.
The images above show the excellent circularity, clean sharp edges, small heat affected zone and low recast layer that is typical of machining using an Oxford Lasers system.
Green light is strongly absorbed by silicon – in 1µm, 66% of the incident power at 511nm will be absorbed. In contrast, only 1% of the power of a 1064 nm Nd:YAG will be absorbed in the same thickness.
The high peak power used is also a critical parameter. This is in the order of 50kW to 500kW and results in very efficient material vaporisation, with negligible thermal shock and consequent cracking.
In combination with the wavelength and high peak power, the high pulse repetition frequency used, typically 2kHz to 20kHz, produces a very high drilling speed.