High speed drilling of thin silicon wafer by UV laser
Drilling rate of thin silicon wafer of 50µm was investigated as a function of diameter and fluence by using KrF excimer laser. The drilling rate at constant fluence increases rapidly with decreasing beam diameter below 20µm, reaching approximately up to 4µm/pulse at diameter of 7µm. Melt ejection is the predominant mechanism in drilling at beam diameters less than 30µm, and approximately 60% of laser energy remains in the silicon wafer. A simple formula giving drilling rate was derived as a function of diameter and fluence of laser beam, and agreed well with the experimental values in a wide range of diameter and fluence. Drilling rate of 7milion holes/s of 10µm in diameter for 50µm thick silicon wafer are estimated at laser power of 100W.
We present what is to our knowledge the most complete 1-D numerical analysis of the evolution and the propagation ::: dynamics of an ultrashort laser pulse in a Ti:Sapphire laser oscillator. This study confirms the dispersion ::: managed model of mode-locking, and emphasizes the role of the Kerr nonlinearity in generating mode-locked ::: spectra with a smooth and well-behaved spectral phase. A very good agreement with experimental measurements ::: of pulse energy, spectrum, and temporal width of extracavity compressed pulses is found.