Patent Document

FIELD OF THE INVENTION 
   The present invention relates to semiconductor chips, and more specifically, to the semiconductor chips having crack stop regions that reduce crack propagation from chip edges/corners. 
   BACKGROUND OF THE INVENTION 
   In a conventional semiconductor chip, cracks are likely to occur at chip edges/corners and propagate to the center of the chip. Therefore, there is a need for a structure (and method of forming the same), that reduce crack propagation from chip edges/corners to the center of the chip. 
   SUMMARY OF THE INVENTION 
   The present invention provides a semiconductor chip, comprising (a) a semiconductor substrate; (b) a transistor on the semiconductor substrate; (c) N interconnect layers on top of the semiconductor substrate and the transistor, wherein N is a positive integer, and wherein the transistor is electrically coupled to the N interconnect layers; (d) a first dielectric layer on top of the N interconnect layers; (e) P crack stop regions on top of the first dielectric layer, wherein P is a positive integer; (f) a second dielectric layer on top of the first dielectric layer, wherein the first dielectric layer is sandwiched between the second dielectric layer and the N interconnect layers, and wherein each crack stop region of the P crack stop regions is completely surrounded by the first dielectric layer and the second dielectric layer; and (g) an underfill layer on top of the second dielectric layer, wherein the second dielectric layer is sandwiched between the first dielectric layer and the underfill layer. 
   The present invention provides a structure (and method of forming the same), that reduce crack propagation from chip edges/corners to the center of the chip. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A-1H  (cross-section views) illustrate a fabrication process for forming a semiconductor chip, in accordance with embodiments of the present invention. 
       FIGS. 2A-2G  (cross-section views) illustrate a fabrication process for forming a semiconductor chip, in accordance with embodiments of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1A-1H  (cross-section views) illustrate a fabrication process for forming a semiconductor chip  100 , in accordance with embodiments of the present invention. More specifically, with reference to  FIG. 1A , the fabrication process starts with the semiconductor structure  100 . The semiconductor structure  100  comprises a semiconductor substrate  11  and transistors (only source/drain regions  11   a ,  11   b , and  11   c  of the transistors are shown for simplicity) on the semiconductor substrate  11 . The semiconductor structure  100  further comprises a BPSG (Boro-Phospho-Silicate Glass) layer  12  and contact regions  12   a ,  12   b , and  12   c  in the BPSG layer  12 . The contact regions  12   a ,  12   b , and  12   c  can comprise tungsten and are electrically coupled to the source/drain regions  11   a ,  11   b , and  11   c , respectively. 
   The semiconductor structure  100  further comprises (i) an interconnect layer  13  including (a) a dielectric layer  13 ′, and (b) metal lines  13   a ,  13   b , and  13   c  in the dielectric layer  13 ′, (ii) a nitride layer  13   d  on top of the interconnect layer  13 , and (iii) a top interconnect layer  14  including (a) a dielectric layer  110 , (b) metal lines  14   a ,  14   b , and  112   a  in the dielectric layer  110 , and (c) metal vias  14   c ,  14   d ,  14   e ,  14   f , and  112   b  in the dielectric layer  110 . The metal lines  13   a ,  13   b ,  13   c ,  14   a ,  14   b , and  112   a  and metal vias  14   c ,  14   d ,  14   e ,  14   f , and  112   b  can comprise copper (Cu). The metal lines  14   a ,  14   b , and  112   a  are electrically coupled to the source/drain regions  11   a ,  11   b , and  11   c , respectively. The semiconductor structure  100  of  FIG. 1A  can be formed using conventional processes. For simplicity, in the figures hereafter, only a portion  100 ′ of the structure  100  of  FIG. 1A  is shown. The others portions of the structure  100  of  FIG. 1A  go through the same fabrication processes. 
   Next, with reference to  FIG. 1B , in one embodiment, a dielectric layer  120  (comprising silicon nitride in one embodiment) is formed on top of the structure  100  of  FIG. 1A . In one embodiment, the nitride layer  120  can be formed by CVD (Chemical Vapor Deposition) of silicon nitride on top of the interconnect layer  14 . 
   Next, with reference to  FIG. 1C , in one embodiment, a hole  122  is created in the nitride layer  120  such that a top surface  114  of the Cu line  112   a  is exposed to the surrounding ambient through the hole  122 . The hole  122  can be formed using lithographic and etching processes. 
   Next, with reference to  FIG. 1D , in one embodiment, a pad  130  (comprising aluminum (Al) in one embodiment), and crack stop regions  130   a ,  130   b ,  130   c ,  130   d , and  130   e  (comprising Al in one embodiment) are formed on top of the structure  100  of  FIG. 1C  such that the Al pad  130  (i) fills the hole  122 , and (ii) is electrically coupled to the Cu line  112   a . The Al crack stop regions  130   a ,  130   b ,  130   c ,  130   d , and  130   e  are formed on top of the nitride layer  120 . The Al pad  130 , and the Al crack stop regions  130   a ,  130   b ,  130   c ,  130   d , and  130   e  can be formed by (a) forming an Al layer (not shown) on the entire structure  100  of  FIG. 1C  including in the hole  122 , and then (b) directionally and selectively etching back the Al layer stopping at the nitride layer  120 . The directional and selective etching in step (b) may be performed using traditional lithographic and etching processes such that what remains of the Al layer after the etching are the Al pad  130 , and the Al crack stop regions  130   a ,  130   b ,  130   c ,  130   d , and  130   e.    
   Next, with reference to  FIG. 1E , in one embodiment, a photosensitive polyimide (PSPI) layer  140  is formed on top of the entire structure  100  of  FIG. 1D , and then, a hole  142  is created in the PSPI layer  140  such that a top surface  132  of the Al pad  130  is exposed to the surrounding ambient via the hole  142 . More specifically, the PSPI layer  140  is formed by (i) spin-applying a solvent-soluble polyimide on the entire structure  100  of  FIG. 1D , and then (ii) curing the deposited solvent-soluble polyimide at a high temperature resulting in the PSPI layer  140 . It should be noted that polyimide is a photosensitive polymer. 
   The hole  142  is formed in the PSPI layer  140  by using a conventional lithographic process. Moreover, the lithographic process is performed such that the Al crack stop regions  130   d , and  130   e  are exposed to the surrounding ambient. It should be noted that the Al crack stop regions  130   a ,  130   b , and  130   c  are completely surrounded by the nitride layer  120  and the PSPI layer  140 . 
   Next, with reference to  FIG. 1F , in one embodiment, a bump limiting metallurgy (BLM) region  150  and a solder bump  160  are formed in the hole  142  and on top of the Al pad  130  by using a conventional method. The solder bump  160  and the BLM region  150  are electrically coupled to the source/drain region  11   c  of  FIG. 1A  through the Al pad  130 , the metal line  112   a , the metal via  112   b , the metal line  13   c , and the contact region  12   c . The BLM region  150  comprises multiple layers of barrier metals, whereas the solder bump  160  can comprise a mixture of lead (Pb), silver (Ag), copper (Cu), and tin (Sn). The structure  100  comprises a chip region  118  and a dicing channel region  116 , which are separated by a dashed line as shown in  FIG. 1F . 
   Next, in one embodiment, a chip dicing process is performed wherein a blade (not shown) can be used to cut through the dicing channel region  116 , resulting in the separated semiconductor chip  100  in FIG.  1 F′ (top-down view). It should be noted that  FIG. 1F  is a cross-section view of FIG.  1 F′ along a line  1 F- 1 F. FIG.  1 F′ shows a top-down view of the semiconductor chip  100  after it is cut from the structure  100  of  FIG. 1F , in accordance with embodiments of the present invention. It should be noted that only solder bumps  160  and the Al crack stop regions  130   a ,  130   b ,  130   c ,  130   d , and  130   e  are shown in FIG.  1 F′ for simplicity. The solder bumps  160  are simultaneously formed in a manner similar to a manner of the solder bump  160  ( FIG. 1F ). 
   In one embodiment, the Al crack stop regions  130   a ,  130   b , and  130   c  are at four corners of the semiconductor chip  100 , whereas the Al crack stop regions  130   d  and  130   e  each form a closed loop on the perimeter the chip  100  (as shown in FIG.  1 F′). In an alternative embodiment, the Al crack stop regions  130   a ,  130   b , and  130   c  each form a closed loop on the perimeter the chip  100 . In an alternative embodiment, all Al crack stop regions are formed as multiple separate features. 
   After the semiconductor chip  100  is formed using the fabrication process described above in  FIGS. 1A-1F , a flip chip assembly process is performed. More specifically, with reference to  FIG. 1G , in one embodiment, the chip  100  (in FIG.  1 F′) is flipped upside down and aligned to a laminate substrate  180 . Then, the solder bumps  160  of the chip  100  are bonded directly, simultaneously, and one-to-one to pads  170  of the laminate substrate  180  at a high temperature and then cooled down. For simplicity, in  FIG. 1G , the semiconductor chip  100  is not flipped upside down. 
   Next, in one embodiment, space  182  between the chip  100  and the laminate substrate  180  is filled with an underfill material resulting in an underfill layer  190  in  FIG. 1H . The underfill material can be epoxy. It should be noted that the Al crack stop regions  130   d  and  130   e  are completely surrounded by the nitride layer  120  and the underfill layer  190 . 
   With reference to  FIG. 1H , due to the difference in the coefficients of thermal expansion (CTE) of the chip  100 , the laminate substrate  180  and the underfill layer  190 , cracks may occur at the fours corners and an interfacing surface  192  of the underfill layer  190  and the nitride layer  120  of the chip  100 . Such cracks can propagate from the fours corners of the chip  100  through the Al crack stop regions  130   e ,  130   d ,  130   c ,  130   b , and  130   a  into the center of the chip  100 . The presence of the Al crack stop regions  130   e ,  130   d ,  130   c ,  130   b , and  130   a  makes it more difficult for these cracks to propagate from the fours corners into the center of the chip  100 . 
     FIGS. 2A-2G  (cross-section views) illustrate a fabrication process for forming a semiconductor chip  200 , in accordance with embodiments of the present invention. More specifically, the fabrication process starts out with the structure  200  of  FIG. 2A . In one embodiment, the structure  200  of  FIG. 2A  is similar to the structure  100  of  FIG. 1B . It should be noted that similar regions of the structure  200  of  FIG. 2A  and the structure  100  of  FIG. 1A  have the same reference numerals, except for the first digit, which is used to indicate the figure number. For instance, a nitride layer  120  ( FIG. 2A ) and the nitride layer  120  ( FIG. 1A ) are similar. 
   Next, with reference to  FIG. 2B , in one embodiment, a hole  222   a  and trenches  222   b  and  222   c  are created in the nitride layer  220  such that a top surface  214  of a Cu line  212   a  is exposed to the surrounding ambient through the hole  222   a . The hole  222   a  and the trenches  222   b  and  222   c  can be formed using lithographic and etching processes. Next, the trenches  222   b  and  222   c  can be dug deeper into a dielectric layer  210  by etching the dielectric layer  210  with the nitride layer  220  as a blocking mask. The trenches  222   b  and  222   c  each form a closed loop on the perimeter the chip  200 . In an alternative embodiment, the trenches are formed as multiple separate features. 
   Next, with reference to  FIG. 2C , in one embodiment, a pad  230 , and crack stop regions  230   a ,  230   b ,  230   c ,  230   d , and  230   e  are formed on top of the structure  200  of  FIG. 2B  such that (i) the pad  230  fills the hole  222   a , (ii) the pad  230  is electrically coupled to the Cu line  212   a , and (iii) the trenches  222   b  and  222   c  remain exposed to the surrounding ambient. The pad  230  and the crack stop regions  230   a ,  230   b ,  230   c ,  230   d , and  230   e  can comprise Al and can be formed by using traditional lithographic and etching processes. 
   Next, with reference to  FIG. 2D , in one embodiment, a PSPI layer  240  is formed on top of the structure  200  of  FIG. 2C , and then, a hole  242  is created in the PSPI layer  240  such that a top surface  232  of the Al pad  230  is exposed to the surrounding ambient via the hole  242 . More specifically, the PSPI layer  240  is formed by (i) spin-applying a solvent-soluble polyimide on the entire structure  200  of  FIG. 2C , and then (ii) curing the deposited solvent-soluble polyimide at a high temperature resulting in the PSPI layer  240 . It should be noted that polyimide is a photosensitive polymer. 
   The hole  242  is formed in the PSPI layer  240  by using a conventional lithographic process. Moreover, the lithographic process is performed such that the trenches  222   b  and  222   c , and the Al crack stop regions  230   d , and  230   e  are exposed to the surrounding ambient. It should be noted that the Al crack stop regions  230   a ,  230   b , and  230   c  are completely surrounded by the nitride layer  220  and the PSPI layer  240 . 
   Next, with reference to  FIG. 2E , in one embodiment, a BLM region  250  and a solder bump  260  are formed in the hole  242  and on top of the Al pad  230  by using a conventional method. The solder bump  260  and the BLM region  250  are electrically coupled to the Al pad  230 . The BLM region  250  can comprise multiple layers of barrier metals, whereas the solder bump  260  can comprise a mixture of Pb, Ag, Cu and Sn. The structure  200  comprises a chip region  218  and a dicing channel region  216 , which are separated by a dashed line as shown in  FIG. 2E . 
   Next, in one embodiment, a chip dicing process is performed wherein a blade (not shown) can be used to cut through the dicing channel region  216 , resulting in the separated semiconductor chip  200  in FIG.  2 E′ (top-down view). It should be noted that  FIG. 2E  is a cross-section view of FIG.  2 E′ along a line  2 E- 2 E. FIG.  2 E′ shows a top-down view of the semiconductor chip  200  after it is cut from the structure  200  of  FIG. 2E , in accordance with embodiments of the present invention. It should be noted that only solder bumps  260  and the Al crack stop regions  230   a ,  230   b ,  230   c ,  230   d , and  230   e  are shown in FIG.  2 E′ for simplicity. The solder bumps  260  are simultaneously formed in a manner similar to a manner of the solder bump  260  ( FIG. 2E ). 
   In one embodiment, the Al crack stop regions  230   a ,  230   b , and  230   c  are at four corners of the semiconductor chip  200 , whereas the Al crack stop regions  230   d  and  230   e  each form a closed loop on the perimeter the chip  200  (as shown in FIG.  2 E′). In an alternative embodiment, the Al crack stop regions  230   a ,  230   b , and  230   c  each form a closed loop on the perimeter the chip  200 . In an alternative embodiment, all Al crack stop regions are formed as multiple separate features. 
   After the semiconductor chip  200  is formed using the fabrication process described above in  FIGS. 2A-2E , a flip chip process is performed. More specifically, with reference to  FIG. 2F , in one embodiment, the chip  200  (in FIG.  2 E′) is flipped upside down and aligned to a laminate substrate  280 . Then, the solder bumps  260  of the chip  200  are bonded directly, simultaneously, and one-to-one to pads  270  of the laminate substrate  280  at a high temperature and then cooled down. For simplicity, in  FIG. 2F , the semiconductor chip  200  is not flipped upside down. 
   Next, in one embodiment, space  282  between the chip  200  and a laminate substrate  280  is filled with an underfill material resulting in an underfill layer  290  in  FIG. 2G . It should be noted that the trenches  222   b  and  222   c  are also filled with the underfill material. The underfill material can be epoxy. It should be noted that the Al crack stop regions  230   d  and  230   e  are completely surrounded by the nitride layer  220  and the underfill layer  290 . 
   With reference to  FIG. 2G , due to the difference in the CTE of the chip  200 , the laminate substrate  280  and the laminate substrate  280 , cracks may occur at the fours corners and an interfacing surface  292  of the underfill layer  290  and the nitride layer  220  of the chip  200 . Such cracks can propagate from the fours corners of the chip  200  through the Al crack stop regions  230   e ,  230   d ,  230   c ,  230   b , and  230   a  into the center of the chip  200 . The presence of the Al crack stop regions  230   e ,  230   d ,  230   c ,  230   b , and  230   a  and the filled trenches  222   b  and  222   c  makes it more difficult for these cracks to propagate from the fours corners into the center of the chip  200 . 
   While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.

Technology Category: h