Abstract:
A fuse structure for a semiconductor device on a substrate includes a fuse having an electrically conductive fuse line of a standard fuse length formed in an electrically conductive layer disposed over the substrate, and a pair of electrically conductive, inwardly bent interconnects formed in a first plurality of electrically conductive layers disposed over the substrate, below the electrically conductive layer in which the fuse line is formed. The inwardly bent interconnects couple the fuse line to a circuit area of the substrate disposed under the fuse line. The fuse structure may further include a protective guard ring formed around the fuse. The guard ring includes a second plurality of electrically conductive interconnects.

Description:
FIELD OF THE INVENTION 
   This invention relates to integrated circuits and semiconductors devices and, more particularly, to a laser fuse structure that provides a savings in chip area, the saved chip area being useable for routing circuits. 
   BACKGROUND OF THE INVENTION 
   Laser fuses can be used to rewire memory and logic circuits. For example, in dynamic or static memory chips, defective memory cells may be replaced by blowing fuses associated with the defective cells, and activating a spare row or column of cells. This circuit rewiring using fusible links allows considerable enhanced yields and reduces the production costs. Also, logic circuits may also be repaired or reconfigured by blowing fuses. For example, it is common to initially fabricate a generic logic chip having a large number of interconnected logic gates. Then, in a final processing step, the chip is customized to perform a desired logic function by disconnecting the unnecessary logic elements by blowing the fuses that connect them to the desired circuitry. Still other applications of laser-blown fuses are possible. 
   Although deep sub-micron technology is advancing such that transistors and interconnects are continuing to shrink in size, the size of laser fuses is becoming limited by the resolution of the laser machine. Historically, the laser fuse design rules have shrunk less compared to those of transistors and interconnects. Hence, the chip area occupied by laser fuse continues to increase as deep sub-micron technology advances. 
   Conventional fuse structures include a fuse window, a laser fuse disposed below the fuse window, and a protective guard ring formed around the fuse. The fuse area is typically defined by the area within the guard ring. Unfortunately in such conventional fuse designs, no circuits can be placed directly beneath the fuse area because the guard ring and laser fuse occupy this chip area. 
   Accordingly, a fuse structure is needed that saves chip area under the laser fuse area which can be used for routing circuits. 
   SUMMARY OF THE INVENTION 
   According to an aspect of the invention, a fuse structure for a semiconductor device on a substrate. The fuse structure includes a fuse including an electrically conductive fuse line of a standard fuse length formed in an electrically conductive layer disposed over the substrate, and a pair of electrically conductive, inwardly bent interconnects formed in a first plurality of electrically conductive layers disposed over the substrate, below the electrically conductive layer in which the fuse line is formed. The inwardly bent interconnects couple the fuse line to a circuit area of the substrate disposed under the fuse line. 
   The fuse structure may further include a protective guard ring formed around the fuse. The guard ring includes a second plurality of electrically conductive interconnects. 
   According to another aspect of the invention, a method of making a fuse structure for a semiconductor device on a substrate having a circuit area. The method includes forming a pair of electrically conductive, inwardly bent fuse interconnects having first and second ends, in a plurality of electrically conductive layers disposed over the substrate, and forming an electrically conductive fuse line of a standard fuse length in an electrically conductive layer disposed above the plurality of electrically conductive layers. The first ends of the fuse interconnects are electrically coupled to the circuit area, and the fuse line is electrically coupled to the second ends of the fuse interconnects. 
   The method may further include the step of forming a second plurality of electrically conductive interconnects around the fuse. The second plurality of electrically conductive interconnects define a protective guard ring. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a top plan view of a laser fuse structure according to a first embodiment of the present invention. 
       FIG. 2  is a sectional view through line  1 — 1  of the laser fuse structure of FIG.  1 . 
       FIG. 3  is a sectional view of a laser fuse structure according to a second embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention is a laser fuse structure for integrated circuits and semiconductor devices. The laser fuse structure minimizes chip area in a manner that allows circuit routing under the laser fuse. 
     FIGS. 1 and 2  depict a laser fuse structure  120  according to a first embodiment of the present invention. The laser fuse structure  120  is disposed over a chip or substrate  100  and may be generally formed from metal lines and metal interconnects in a plurality of metal layers Mn, Mn-1, Mn-2, Mn-3, Mn-4, and Mn-5 that extend through insulating dielectric layers  110 - 115  (FIG.  2 ). The metal lines and interconnects are typically used for global routings. The laser fuse structure  120  includes a fuse window  130 , a laser fuse  140  disposed below the fuse window  130 , and a protective guard ring  150  formed around the fuse  140  (FIG.  1 ). 
   As shown in  FIG. 2 , the fuse window  130  may extend through a portion of top insulating dielectric layer  116  such that a thin portion of the layer  116  remains above the fuse  140 . The fuse window  130  may be conventionally formed to meet standard laser repair specifications. 
   The laser fuse  140  may be formed of a standard fuse length in top metal layer Mn by metal line  141 . The metal line  141  has connected at its ends by a pair of inwardly bent metal interconnects  142 . The metal interconnects  142  may be in metal layers Mn through Mn-5, which extend down through insulating dielectric layers  115 - 110 . The metal interconnects  142  couple the fuse metal line  141  to circuits and metal circuit routings formed in underlying circuits areas  101  and  102  of the substrate  100 . The metal fuse line  141  and its metal interconnects  142  substantially form a novel T- or funnel-shape structure that uses significantly less chip or substrate area underneath the fuse  140 , than that normally used by conventional laser fuse structures, while still allowing for a standard fuse length SFL. The area underneath the fuse  140  not used by the fuse interconnects  142  of the present invention, can now be used for circuits and circuit routing as depicted by the circuit areas  101  and  102 , which extend at least partially under the fuse  140 . 
   The metal fuse interconnects  142  may be constructed from metal lines  143   a  through  143   e  which are formed respectively in metal layers Mn-1 through Mn-5, and metal filled vias  144   a  through  144   f  which are formed respectively in metal layers Mn through Mn-5 and connect the metal lines  143   a  through  143   e . The metal lines  143   c  through  143   e  in metal layers Mn-3 through Mn-5 have a reduced line spacing LS r  which is less than the standard fuse length. The metal lines  143   b  in metal layer Mn-2 are laterally extended in the direction of arrows  145  to provide a conventional line spacing of LS, which meets the standard fuse length. The metal lines  143   a  in metal layer Mn-1 are conventionally spaced to line spacing LS to meet the standard fuse length. 
   The guard ring  150  may be constructed from metal interconnects  151  in metal layers Mn through Mn-4, and through dielectric layers  115  through  111 . As shown in  FIG. 1 , the interconnects  151  form a ring like structure around the fuse  140  which in the shown embodiment may be rectangular. 
   Referring again to  FIG. 2 , the interconnects  151  forming ends walls  150   e  of the guard ring  150  are bent inwardly in a manner that may substantially mimic the fuse interconnects  142 . The guard ring interconnects  151  may be formed from metal lines  152   a  through  152   e , which are formed respectively in metal layers Mn through Mn-4, and metal filled vias  153   a  through  153   e  which are formed respectively in metal layers Mn through Mn-4. Thus, the guard ring interconnects  151  substantially form a novel T- or funnel-shape structure. The metal lines  152   e  in metal layer Mn-4 have a reduced guard line spacing GLS T . The portions of the metal lines  152   d  in metal layer Mn-3, which form the end walls  153   e  of the guard ring  150 , are laterally extended in the direction of arrows  154  to provide a conventional guard line spacing of GLS. The metal lines  152   a  through  152   c  formed respectively in metal layers Mn through Mn-2 are conventionally spaced to the guard line spacing GLS. The interconnects forming the side walls of the guard ring  150  may also be formed in a funnel-shape. 
     FIG. 3  is a sectional view of a laser fuse structure  220  according to a second embodiment of the present invention. The laser fuse structure  220  of the second embodiment is generally the same as the first embodiment, except that the laser fuse is formed in one of the metal layers below the top metal layer Mn. More specifically, the laser fuse structure  220  is disposed over a chip or substrate  200  and may be generally formed from metal lines and metal interconnects in a plurality of metal layers Mn, Mn-1, Mn-2, Mn-3, Mn-4, Mn-5, and Mn-6 that extend through insulating dielectric layers  210 - 216 . 
   The fuse window  230  may extend through portions of the top two insulating dielectric layers  217 , and  216  such that a thin portion of the second layer  216  remains above the fuse  240 . The laser fuse  240  may be formed of a standard fuse length in the second metal layer Mn-I by metal line  241 . The metal line  241  has connected at its ends a pair of inwardly bent metal interconnects  242  that together substantially form a novel T- or funnel-shape structure as in the first embodiment. The metal interconnects  242  may be in metal layers Mn-1 through Mn-6, which extend through insulating dielectric layers  215 - 210 . The metal interconnects  242  couple the fuse metal line  241  to circuits and metal circuit routings formed in circuits areas  201  and  202  of the substrate  200 . 
   The metal fuse interconnects  242  in the second embodiment of the invention may be constructed from metal lines  243   a  through  243   e  which are formed respectively in metal layers Mn-2 through Mn-6, and metal filled connecting vias  244   a  through  244   f  which are formed respectively in metal layers Mn-I through Mn-6. The metal lines  243   c  through  243   e  in metal layers Mn-4 through Mn-6 have a reduced line spacing LS r  which is less than the standard fuse length. The metal lines  243   b  in metal layer Mn-3 are laterally extended in the direction of arrows  245  to provide a conventional line spacing of LS, which meets the standard fuse length. The metal lines  243   a  in metal layer Mn-2 are conventionally spaced to line spacing LS to meet the standard fuse length. 
   The guard ring  250  may be constructed from metal interconnects  251  in metal layers Mn through Mn-5, and through dielectric layers  216  through  211 . As in the first embodiment, the interconnects  251  forming ends walls of the guard ring  250  of the second embodiment are bent inwardly in a manner that may substantially mimic the fuse interconnects  242 . The guard ring interconnects  251  may be formed from metal lines  252   a  through  252   f  which are formed respectively in metal layers Mn through Mn-5, and metal filled connecting vias  253   a  through  253   f  which are formed respectively in metal layers Mn through Mn-5. Thus, the guard ring interconnects  251  substantially form a novel funnel-shape structure. The metal lines  252   f  in metal layer Mn-5 have a reduced guard line spacing GLS T . The end wall portions of the metal lines  252   f  in metal layer Mn-5 are laterally extended in the direction of arrows  254  to provide a conventional guard line spacing of GLS. The metal lines  252   a  through  252   d  formed respectively in metal layers Mn through Mn-3 are conventionally spaced to the guard line spacing GLS. 
   One of ordinary skill in the art will appreciate that the laser fuse and the guard ring of the fuse structure of the present invention may each be formed from metal lines and metal interconnects in any number of metal layers. In addition, the metal interconnects may extend through any number of insulating dielectric layers. 
   The laser fuse structure of present invention can be fabricated using conventional integrated circuit and semiconductor fabrication methods, which are very well known to persons skilled in the art. The fuse, interconnects and guard ring can be formed of polysilicon or metals including without limitation aluminum, tungsten, titanium nitride, suicides, copper and metal alloys. 
   While the foregoing invention has been described with reference to the above embodiments, various modifications and changes can be made without departing from the spirit of the invention. Accordingly, all such modifications and changes are considered to be within the scope of the appended claims.