Method of cutting interconnection pattern with laser and apparatus thereof

#The present invention relates to laser cutting of interconnecting material. More particularly, the present invention pertains to a method of and an apparatus for cutting an interconnection pattern with a laser which enables laser cutting to be carried out to change interconnection of a semiconductor device or a large-scale interconnection substrate without damaging the vicinity of a cut portion.

#The techniques of cutting an LSI interconnection pattern with a laser, which are the redundancy techniques, have been described in IEEE Journal of Solid-State Circuits, vol, SC-16, No. 5, Oct. 1981, from page 506 to 513. Cutting of Al interconnection in an LSI has been described in Annals of the CIRP Vol. 28/1, 1979, from page 113 to 116.

#In the above-described conventional techniques, the effective range of the laser power with which cutting can be performed without giving damage is narrow, and deviation of the laser beam from the interconnection to be cut easily occurs, generating damage.

#FIG. 1 shows an embodiment of a laser processing apparatus according to the present invention;

#FIGS. 2A to 2C show a projection pattern generated when the apparatus of FIG. 1 is applied to the redundant operation of defective bits of a semiconductor memory IC as well as the results of cutting of an interconnection pattern;

#FIGS. 3A and 3B are respectively plan and cross-sectional views of links used in the redundant operation of defective bits of the semiconductor memory IC;

#An embodiment of the present invention will now be described with reference to FIG. 1.

#A laser beam 2 emitted from a pico-second laser 1 ("LASERS" published by University Science Books and written by Anthony E. Siegman, pp. 1041-1131), which outputs a laser beam having a pulse width of 1 ns or less (which is 100 to 300 ps) and several mjouls, is refracted by a reflection mirror 3 by 90 degrees, and is then led to a transmission type liquid crystal mask 4. A light 5 which has passed through a light-transmission pattern of the liquid crystal mask 4 passes through a half mirror 6 for observation and a projection lens 7, and is then projected to the surface of a workpiece 8, such as a semiconductor device or a large-scale multi-layer substrate, as a liquid crystal pattern to illuminate it. The workpiece 8 is placed on an XY table 9, which is automatically operated by a table control power source 10. The liquid crystal mask 4 is illuminated by a projection pattern illuminating lamp 11, and the workpiece 8 is illuminated by an object illuminating lamp 12 through a half mirror 13. Behind the half mirror 13 is disposed an imaging device 14 which may be a camera tube or a solid state imaging device. The imaging device 14 provides an image of the portion of the workpiece 8 to be processed. The obtained image enters an image determining device 15 which pattern recognizes the portion of the image to be illuminated with a laser beam, which displays on a TV monitor 18 both an image 16 obtained by the pattern recognition and an area 17 to be illuminated with a laser beam, and which sends to a liquid crystal pattern controller 19 the signal representing the area 17 to generate the transmission pattern of the liquid crystal mask 4 corresponding to the area 17 to be illuminated with the laser beam in such a manner that the transmission pattern is accurately aligned with a desired portion of the interconnection pattern (link) on the semiconductor device or the large-scale multi-layer substrate 8. Once it is confirmed by the imaging device 14 and the image determining device 15 that the liquid crystal mask pattern indicates the area to be illuminated with the laser beam and that the pattern is accurately projected onto the desired portion of the interconnection pattern by the projected pattern illumination lamp, a laser illumination signal is sent from the image determining device 15 to a laser power source controller 20 which controls the laser. Thus, only the required portion of the workpiece is illuminated with a laser beam accurately.

#The image determining device 15 is connected to a processed position inputting device 21 which supplies information representing a plurality of positions to be illuminated with the laser beam to the image determining device 15. Consequently, a plurality of portions can be processed with a laser in one operation, and the speed for the redundancy process of the defective LSI memory bits can thus be increased greatly.