Abstract:
Structures and methods for forming the same. A semiconductor chip includes a semiconductor substrate and a transistor on the semiconductor substrate. The chip further includes N interconnect layers on top of the semiconductor substrate and being electrically coupled to the transistor, N being a positive integer. The chip further includes a first dielectric layer on top of the N interconnect layers, and a second dielectric layer on top of the first dielectric layer. The second dielectric layer is in direct physical contact with each interconnect layer of the N interconnect layers. The chip further includes an underfill layer on top of the second dielectric layer. The second dielectric layer is sandwiched between the first dielectric layer and the underfill layer. The chip further includes a laminate substrate on top of the underfill layer. The underfill layer is sandwiched between the second dielectric layer and the laminate substrate.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to semiconductor chips, and more specifically, to semiconductor chips in which underfill layers are not likely to create cracks. 
       BACKGROUND OF THE INVENTION 
       [0002]    In a conventional semiconductor chip, underfill layers that fill the space between the laminate substrate and the semiconductor chip, can create cracks in the chip. Therefore, there is a need for a structure (and method of forming the same), in which underfill layers are not likely to create cracks in the semiconductor chip. 
       SUMMARY OF THE INVENTION 
       [0003]    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) a second dielectric layer on top of the first dielectric layer, wherein the second dielectric layer is in direct physical contact with each interconnect layer of the N interconnect layers; (f) 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; and (g) a laminate substrate on top of the underfill layer, wherein the underfill layer is sandwiched between the second dielectric layer and the laminate substrate. 
         [0004]    The present invention provides a structure (and method of forming the same), in which underfill layers are not likely to create cracks in the semiconductor chip. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIGS. 1A-1N  (cross-section views) illustrate a fabrication process for forming a semiconductor chip, in accordance with embodiments of the present invention. 
           [0006]      FIGS. 2A-2D  (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 
       [0007]      FIGS. 1A-1N  (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 of the semiconductor structure  100  starts with a semiconductor (silicon, germanium, etc.) substrate  110 . 
         [0008]    Next, in one embodiment, transistors (only a source/drain region  111  of one of the transistors is shown for simplicity) and a STI (Shallow Trench Isolation) region  112  are formed on the semiconductor substrate  110  by using conventional methods. The STI region  112  comprises a dielectric material such as silicon dioxide. 
         [0009]    Next, with reference to  FIG. 1B , in one embodiment, a BPSG (Boro-Phospho-Silicate Glass) layer  113  is formed on top of the entire structure  100  of  FIG. 1A . The BPSG layer  113  can be formed by CVD (Chemical Vapor Deposition) of BPSG material on top of the entire structure  100  of  FIG. 1A , followed by a CMP (Chemical Mechanical Polishing) step. 
         [0010]    Next, in one embodiment, contact regions  114   a,    114   b,    114   c,  and  114   d  are formed in the BPSG layer  113  by using a conventional method. The contact region  114   a  is electrically coupled to the source/drain region  111 , whereas the contact regions  114   b,    114   c,  and  114   d  are in direct physical contact with the STI region  112 . The contact regions  114   a,    114   b,    114   c,  and  114   d  can comprise tungsten. There is a thin metal (e.g., Titanium (Ti)) liner layer (not shown) on side walls and a bottom wall of the contact region  114   a.    
         [0011]    Next, with reference to  FIG. 1C , in one embodiment, an interconnect layer  120  is formed on top of the structure  100  of  FIG. 1B  by using a conventional method. The interconnect layer  120  includes (i) a dielectric layer  121 , and (ii) metal lines  122   a,    122   b,  and  122   c  in the dielectric layer  121 . The metal line  122   a  is electrically coupled to the contact region  114   a,  whereas the metal lines  122   b,    122   c  are in direct physical contact with the contact regions  114   b  and  114   c  and the contact region  114   d,  respectively. The metal lines  122   a,    122   b,  and  122   c  can comprise copper. In an alternative embodiment, there are thin metal (e.g., tantalum nitride) liner layers (not shown) on side walls and bottom walls of the metal lines  122   a,    122   b,  and  122   c.    
         [0012]    Next, with reference to  FIG. 1D , in one embodiment, a nitride layer  123  is formed on top of the structure  100  of  FIG. 1C . The nitride layer  123  can be formed by CVD of silicon nitride on top of the interconnect layer  120 . 
         [0013]    Next, with reference to  FIG. 1E , in one embodiment, an interconnect layer  130  is formed on top of the nitride layer  123  by using a conventional method. The interconnect layer  130  includes (i) a dielectric layer  131  on top of the nitride layer  123 , (ii) metal vias  132   a,    132   b,    132   c,  and  132   d  embedded in the dielectric layer  131 , and (iii) metal lines  133   a,    133   b,  and  133   c  electrically coupled to the metal via  132   a,  the metal vias  132   b  and  132   c,  and the metal via  132   d,  respectively. The metal via  132   a  is electrically coupled to the metal line  122   a,  whereas the metal vias  132   b  and  132   c  and the metal via  132   d  are in direct physical contact with the metal lines  122   b  and  122   c,  respectively. The metal vias  132   a,    132   b,    132   c,  and  132   d  and metal lines  133   a,    133   b,  and  133   c  can comprise copper. In an alternative embodiment, there are thin metal (e.g., tantalum nitride) liner layers (not shown) on side walls and bottom walls of the metal vias  132   a,    132   b,    132   c,  and  132   d  and metal lines  133   a,    133   b,  and  133   c.    
         [0014]    Next, with reference to  FIG. 1F , in one embodiment, a dielectric layer  140  (comprising nitride in one embodiment) is formed on top of the structure  100  of  FIG. 1E . The nitride layer  140  can be formed by CVD of silicon nitride on top of the interconnect layer  130 . The structure  100  comprises a chip region  117  and a dicing channel region  118 , which are separated by a dashed line as shown in  FIG. 1F . 
         [0015]    Next, in one embodiment, the structure  100  is diced (by a laser beam (not shown) in one embodiment) at the dicing channel region  118  until a portion of the semiconductor substrate  110  is removed, resulting in a dicing trench  116  ( FIG. 1G ). 
         [0016]    Next, with reference to  FIG. 1H , in one embodiment, a hole  142   a  and trenches  142   b  and  142   c  are created in the nitride layer  140  by etching the nitride layer  140  until top surfaces  134   a,    134   b,  and  134   c  of the metal lines  133   a,    133   b,  and  133   c,  respectively, are exposed to the surrounding ambient. The step of etching the nitride layer  140  to form the hole  142   a  and trenches  142   b  and  142   c  can involve photo-lithography and then dry etching. 
         [0017]    Next, with reference to  FIG. 11 , in one embodiment, pads  150   a,    150   b,  and  150   c  (comprising aluminum (Al) in one embodiment) are formed on top of the structure  100  of  FIG. 1H  such that (i) the Al pads  150   a,    150   b,  and  150   c  fill the hole  142   a  and trenches  142   b  and  142   c,  respectively, and (ii) the Al pad  150   a  is electrically coupled to the metal line  133   a.  The Al pads  150   a,    150   b,  and  150   c  can be formed by (a) forming a conformal Al layer (not shown) on the entire structure  100  of  FIG. 1H  including in the hole  142   a  and trenches  142   b  and  142   c  and on side walls and bottom wall of the dicing trench  116 , and then (b) directionally and selectively etching back the Al layer stopping at the nitride layer  140 . 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 pads  150   a,    150   b,  and  150   c.    
         [0018]    In one embodiment, the side wall of the dicing trench  116  is slanted (85-89 degrees), and the etching of the Al layer in step (b) above has a small isotropic component (10-50 nm). As a result, the etching of the Al layer in step (b) above can completely remove Al from the side walls and bottom wall of the dicing trench  116 . 
         [0019]    The Al pad  150   b,  the metal lines  133   b  and  122   b,  the vias  132   b  and  132   c,  and the contact regions  114   b  and  114   c  can be collectively referred to as an edge seal region  114   b + 114   c + 122   b + 132   b + 132   c + 133   b + 150   b.  The Al pad  150   c,  the metal lines  133   c  and  122   c,  the via  132   c,  and the contact region  114   d  can be collectively referred to as a crack stop region  114   d + 122   c + 132   d + 133   c + 150   c.  The edge seal region  114   b + 114   c + 122   b + 132   b + 132   c + 133   b + 150   b  and the crack stop region  114   d + 122   c + 132   d + 133   c + 150   c  each form a closed loop on a perimeter of the semiconductor chip  100  and prevent cracks from propagating from the edge of semiconductor chip  100  into the center of semiconductor chip  100 . 
         [0020]    Next, with reference to  FIG. 1J , in one embodiment, a photosensitive polyimide (PSPI) layer  160  is formed on top of the entire structure  100  of  FIG. 11 . More specifically, the PSPI layer  160  is formed by spin-applying a solvent-soluble polyimide on the entire structure  100  of  FIG. 11  including in the dicing trench  116 . 
         [0021]    Next, in one embodiment, a hole  161  is created in the PSPI layer  160  such that a top surface  151  of the Al pad  150   a  is exposed to the surrounding ambient via the hole  161 . More specifically, the hole  161  is formed in the PSPI layer  160  by using a conventional lithographic process. It should be noted that polyimide is a photosensitive polymer. After forming the hole  161 , the PSPI layer  160  is cured at a high temperature (between 150 C and 400 C) to remove the solvent and to cross-link the polymer. 
         [0022]    Next, with reference to  FIG. 1K , in one embodiment, a bump limiting metallurgy (BLM) region  170  and a solder bump  171  are formed in the hole  161  and on top of the Al pad  150   a  by using a conventional method. The solder bump  171  and the BLM region  170  are electrically coupled to the Al pad  150   a.  The BLM region  170  can comprise multiple layers of titanium-tungsten (TiW), copper (Cu), chrome (Cr), and gold (Au), whereas the solder bump  171  can comprise a mixture of silver (Ag) and tin (Sn). 
         [0023]    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  118 , resulting in the separated semiconductor chip  100  in  FIG. 1L . It is should be noted that the PSPI layer  160  is still on a side wall  115 . 
         [0024]    Next, with reference to  FIG. 1M , in one embodiment, the chip  100  (in  FIG. 1L ) is aligned to a laminate substrate  180 . Then, the solder bump  171  is bonded directly to a pad  181  of the laminate substrate  180  at a high temperature (above the melting point of the solder) and then cooled down. 
         [0025]    Next, in one embodiment, space  182  between the PSPI layer  160  and the laminate substrate  180  is filled with an underfill material (e.g., epoxy with silicon dioxide filler) resulting in an underfill layer  190  in  FIG. 1N . 
         [0026]    It should be noted that the material of the PSPI layer  160  (polyimide) is flexible, therefore, cracks are not likely to occur at the side wall  115  (the interfacing surface between the PSPI layer  160  and the interconnect layers  120  and  130  in  FIG. 1N ). 
         [0027]      FIGS. 2A-2D  (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. 1E . It should be noted that similar regions of the structure  200  of  FIG. 2A  and the structure  100  of  FIG. 1E  have the same reference numerals, except for the first digit, which is used to indicate the figure number. For instance, an interconnect layer  230  ( FIG. 2A ) and the interconnect layer  130  ( FIG. 1E ) are similar. 
         [0028]    Next, in one embodiment, the structure  200  is diced (by a laser beam (not shown) in one embodiment) at the dicing channel region  218  until a portion of the semiconductor substrate  210  is removed, resulting in a dicing trench  216  ( FIG. 2B ). 
         [0029]    Next, with reference to  FIG. 2C , in one embodiment, a dielectric layer  240  (comprising nitride in one embodiment) is formed on top of the entire structure  200  of  FIG. 2B . The nitride layer  240  can be formed by CVD of silicon nitride on top of the entire structure  200  of  FIG. 2B . It should be noted that the nitride layer  240  is on side walls and a bottom wall of the dicing trench  216 . 
         [0030]    Next, with reference to  FIG. 2D , in a manner similar to what is described in  FIGS. 1H-1N , pads  250   a,    250   b,  and  250   c,  a PSPI layer  260 , a BLM region  270 , a solder bump  271 , a laminate substrate  280 , and an underfill layer  290  are formed. 
         [0031]    It should be noted that the coefficients of thermal extension (CTE) of the nitride layer  240  and the interconnect layers  220  and  230  are not large, and that these layers are thin. Therefore, cracks are not likely to occur at a side wall  215  (the interfacing surface between the nitride layer  240  and the interconnect layers  220  and  230  in  FIG. 2D ). 
         [0032]    In the embodiments above, the semiconductor chip has two interconnect layers. In general, it can have any number of interconnect layers (e.g.,  10 ,  12 , etc.). 
         [0033]    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.