Laser processing method
A laser processing method includes a laser light emitting step of emitting a pulsed laser light along a line from a back surface of a target having a functional element layer on side of a front surface. The laser light emitting step includes: a first step of irradiating the functional element layer with a first pulsed laser light along the line, to form a weakened region in the functional element layer along the line; and a second step of emitting a second pulsed laser light into the target to follow the first pulsed laser light along the line, to form a crack reaching the front surface along the line in the target. The first pulsed laser light has a pulse width that is shorter than a pulse width of the second pulsed laser light.
1 . A laser processing method comprising a laser light emitting step of emitting a pulsed laser light along a line from a back surface of a target comprising a substrate, wherein
the laser light emitting step includes:
a first step of irradiating a functional element layer of the substrate that is made of a different material from the rest of the substrate and defines a front surface of the substrate with a first pulsed laser light along the line in a first focusing position located proximal to the front surface, to form a weakened material region in the functional element layer along the line by embrittling the material without removing the material; and
a second step of emitting a second pulsed laser light into the substrate of the target to follow the first pulsed laser light along the line in a second focusing position located between the first focusing position and the back surface, wherein
(i) the emitted second pulsed laser light causes formation of a crack that begins in a first intermediate portion of the substrate located at a depth between the front surface and the back surface of the substrate as defined by the second focusing position,
(ii) the crack extends in a first direction to reach the front surface and also extends in a second direction different from the first direction to reach a second intermediate portion of the substrate located between the first intermediate portion and the back surface along the line in the target, and
(iii) the crack only extends between the front surface and the second intermediate portion of the substrate leaving the substrate intact from the second intermediate portion to the back surface as a result of the second step of emitting the second pulsed laser light into the substrate, and
the first pulsed laser light has a pulse width that is shorter than a pulse width of the second pulsed laser light.
2 . The laser processing method according to claim 1 , wherein a pulse pitch of the first pulsed laser light is shorter than a pulse pitch of the second pulsed laser light.
3 . The laser processing method according to claim 1 , wherein the functional element layer includes at least one of a protective film, a low dielectric constant film, and a metal layer.
4 . The laser processing method according to claim 1 , wherein in the first step, a focusing position of the first pulsed laser light is a position that is separated from the functional element layer on an opposite side of an incident side of the pulsed laser light, a position in the target, or a position in the functional element layer.
5 . The laser processing method according to claim 1 , wherein a protective tape or a protective substrate is attached to the front surface of the substrate.
6 . The laser processing method according to claim 1 , wherein
in the first step, a first laser processing head moves along the line while emitting the first pulsed laser light, and
in the second step, a second laser processing head moves along the line to follow the first laser processing head while emitting the second pulsed laser light.