Method and apparatus for via drilling and selective material removal using an ultrafast pulse laser

A laser machining apparatus for via drilling and selective material removal in a semiconductor wafer or workpiece having an ultrafast laser pulse emitted directly from an ultrafast laser oscillator, comprising:

• an emitter configured to emit a pulsed laser beam from a diode pumped or CW laser pumped solid state ultrafast laser oscillator without amplification in addition to the amplification provided by the ultrafast laser oscillator;
• a controller configured to control the laser pulse, to minimize the cumulative heating effect and to improve the machining quality;
• a varying unit configured to vary the diameter of the laser beam along at least one axis;
• a scanner configured to scan the laser beam in two axes;
• and
• a focus unit configured to focus the pulsed laser beam onto the work piece or semiconductor wafer;
• wherein a via is drilled or material is selectively removed from the work piece or semiconductor wafer;
• wherein a one axis or two axis galvanometer scanner or a piezo scanner scans the laser beam across the work piece or semiconductor wafer;
• wherein the piezo scanner avoids pillow shaped field distortion at the image field due to common pivot points;
• wherein the ultrafast laser oscillator includes a fiber oscillator amplifier of a repetition rate greater than 1 MHZ.

A laser machining apparatus for via drilling and selective material removal in a semiconductor wafer or workpiece having an ultrafast laser pulse emitted directly from an ultrafast laser oscillator, comprising:

• an emitter configured to emit a pulsed laser beam from a diode pumped or CW laser pumped solid state ultrafast laser oscillator without amplification in addition to the amplification provided by the ultrafast laser oscillator;
• a controller configured to control the laser pulse, to minimize the cumulative heating effect and to improve the machining quality;
• a varying unit configured to vary the diameter of the laser beam along at least one axis;
• a scanner configured to scan the laser beam along two axes;
• and
• a focus unit configured to focus the pulsed laser beam on to the work piece or semiconductor wafer;
• wherein a via is drilled or material is selectively removed from the work piece or semiconductor wafer;
• which further comprises a beam shaper to change the shape of the beam profile at the focused spot size;
• wherein the beam shaper includes a monoclinic double tungstate MDT element based on the phenomenon of internal conical reflection;
• wherein the beam shaping is obtained by the combination of a quarter wave plate and the MDT element;
• wherein the resultant beam profile depends on the diameter and wavelength on the incoming laser beam and the length of the MDT element;
• wherein a flat top beam profile can be generated at the focal plane;
• wherein the aspect ratio of the via holes can be increased;
• wherein flat bottom via holes can be generated;
• wherein the efficiency of beam shaping is high due to the transitive efficiency of the MDT material and minimal optical elements involved;
• and
• wherein the machining efficiency and quality of machining is improved due to beam Shaping;
• wherein the ultrafast laser oscillator includes a fiber oscillator amplifier of a repetition rate greater than 1 MHZ.

An apparatus for ablating a feature smaller then the focused spot size of the pulsed laser beam from an ultrafast laser oscillator of a pulse repetition rate greater than 1 MHZ comprising:

• an emitter configured to emit a pulsed laser beam from a solid state ultrfast laser oscillator without any amplification in addition to the amplification provided by the ultrafast laser oscillator;
• a controller configured to control the laser threshold fluence slightly above the ablation threshold of the material;
• a control unit configured to control the number of pulses and the duration between the pulses for minimizing or eliminating the cumulative heating effect, using a pulse modulator having an acousto optic device or an electro optic device;
• wherein a spatial machining resolution of less than one-twentieth of a cross-sectional diameter of the pulsed laser beam in a focused state at the surface of the work piece is obtained;
• wherein the ultrafast laser oscillator includes a fiber oscillator amplifier of a repetition rate greater than 1 MHZ.