Laser processing method
Laser lights L 1 to L 3 are relatively moved along a line to cut 5 , while repeating a converging step of simultaneously converging the laser lights L 1 to L 3 at converging positions P 1 to P 3 separated from each other along the line 5 . This forms a plurality of modified spots S along the line 5 and causes the plurality of modified spots S to form a modified region 7 . The converging positions P 1 to P 3 in the repeated converging steps are kept from being superposed on each other, while at least one of converging positions P 21 to P 23 in the converging step in a later stage is located between converging positions P 11 to P 13 in the converging step in an earlier stage.
1. A laser processing method for converging a plurality of laser lights at an object to be processed to form a modified region in the object along a line to cut, the method comprising:
a converging step of simultaneously converging a plurality of laser lights at a plurality of converging positions separated from each other along the line to cut; and
a forming step of relatively moving the plurality of laser lights along the line to cut while repeating the converging step to generate one or more repeated converging steps, to form a plurality of modified spots along the line to cut and cause the plurality of modified spots to form the modified region;
an irradiating step on the line to cut, comprising:
(i) causing the plurality of modified spots to be formed simultaneously by an (n)th laser light irradiation;
(ii) simultaneously causing, by an (n+1)th laser light irradiation, one modified spot to be formed in a region between a pair of modified spots that are formed simultaneously by the (n)th laser light irradiation, and a modified spot to be formed at a position outside an outermost modified spot among the plurality of modified spots that are formed simultaneously by the (n)th laser light irradiation;
(iii) increasing (n) by one to repeat the process of (ii);
wherein the plurality of converging positions in the one or more repeated converging steps are kept from being superposed on each other; and
wherein at least one of the plurality of converging positions along the line to cut in a later stage is located between at least two of the plurality of converging positions along the line to cut in an earlier stage that immediately precedes the later stage.
2. A laser processing method according to claim 1 , wherein the plurality of modified spots are formed equidistantly along the line to cut.
3. A laser processing method according to claim 2 , wherein the plurality of converging positions in the converging step span an interval H, the interval H being a length given by a product of a separation interval for each of the plurality of modified spots and a predetermined number other than an integral multiple of a divisor of a number N of the plurality of converging positions, wherein the divisor is not unity.
4. A laser processing method according to claim 2 , wherein, in the forming step, the plurality of laser lights are relatively moved from outside to inside or from inside to outside of the object in a direction along the line to cut while repeating the converging step.
5. A laser processing method according to claim 3 , wherein, in the forming step, the plurality of laser lights are relatively moved from outside to inside or from inside to outside of the object in a direction along the line to cut while repeating the converging step.
6. A laser processing method according to claim 1 , wherein the plurality of laser lights are simultaneously converged to be separated from each other and kept from being superposed on each other on at least one of a front face and a rear face of the object, and
wherein an energy density in the front face or rear face is less than a predetermined intensity which deteriorates the object.