Patent Publication Number: US-2007102792-A1

Title: Multi-layer crack stop structure

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application is the continuation-in-part application of the U.S. patent application Ser. No. 11/163,982, filed on Nov. 07, 2005. All disclosures are incorporated herewith by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      This invention relates to a wafer structure, and more particularly, to a multi-layer crack stop structure formed on a wafer. The multi-layer crack stop structure is disposed surrounding the active circuit region of a die, so as to prevent the active circuit region from being damaged when the wafer is being sawn or when the die is subject to thermal cycles for testing, which significantly improves the reliability of the packaged die.  
      2. Description of the Related Art  
      Along with the continuous development of new technology, integrated circuits (IC) had been widely applied in our daily life. An IC product is typically fabricated with three processes: wafer preparation, IC formation and IC packaging. A die sawing process is performed at the beginning of an IC packaging process.  
      A wafer generally includes many horizontal and vertical scribe lines that define many dies. After the device fabrication is finished on a wafer, a diamond blade is used to saw the wafer along the scribe lines to obtain separate dies. Because many material layers having different properties are formed on a wafer, damages like chipping or peeling-off easily occur to the material layers in a die beside the scribe lines during the wafer sawing or the thermal cycles for testing a separated die. The chipping and delamination problem becomes even worse if the wafer is formed with a low-k/Cu structure thereon. Moreover, when the device dimension is scaled down, the scribe line becomes narrower so that the problem of sawing cracks penetrating into the operating metal or the active circuit region is more serious. Thus, the reliability of the packaged die is deteriorated.  
      In another prior-art wafer dividing method, laser grooving is introduced replacing the blade sawing. However, the laser grooving method also has some problems. For example, when the wafer layers include a metal layer, it is difficult to completely remove the metal layer with laser so that some debris still remains to stain the dies. In addition, a large heat effect area is formed beside the scribe line during the laser grooving, greatly impacting the reliability of the dies. Moreover, a laser grooving device is 2-3 times more expensive than a diamond blade device, making the cost of such method much higher.  
      Accordingly, a crack stop structure formed on a wafer for preventing damages in blade sawing was disclosed in U.S. Pat. No. 5,530,280. As shown in  FIG. 1 , two active circuit regions  110  and  120  are defined on a wafer  100 , and two dielectric layers  132  and  134  are formed thereon. The dielectric layer  132  has therein a metal contact  112  and two tungsten rings  142  and  152 . The dielectric layer  134  has therein a metal contact  116 , interconnect metals  114 ,  144  and  154 , and two tungsten rings  146  and  156  respectively having hollow rings  145  and  155 . Interconnect metals  118 ,  148  and  158  are formed on the dielectric layer  134 , and a scribe line  160  is defined between  148  and  158 .  
      The structure for protecting the active circuit region  110  from a crack includes the tungsten rings  142  and  146  and the interconnect metals  144  and  148 . The structure for protecting the active circuit region  120  from a crack includes the tungsten rings  152  and  156  and the interconnect metals  154  and  158 . Since different materials react differently to the same stress, the crack stop structure containing different materials cannot rapidly and effectively protect the active circuit region from a crack during the sawing operation done to the scribe line  160  or during the thermal cycles for testing the separated die.  
     SUMMARY OF THE INVENTION  
      Therefore, this invention provides a multi-layer crack stop structure, which is disposed entirely in a die, entirely in the scribe line region outside the die, or partially in the die and partially in the scribe line region.  
      When the multi-layer crack stop structure is disposed entirely in the die, it may be disposed between the die seal ring structure and the active circuit region, between the two die seal rings of a dual die seal ring structure or between the die seal ring structure and the scribe line region. In such cases, the crack stop structure may be a single ring structure or include a ring portion and four corner portions at the four corners of the die, wherein the corner portions can enhance the crack stop effect at the four corners of the die.  
      Similarly, when the multi-layer crack stop structure is disposed entirely in the scribe line region, it may be a single ring structure or include a ring portion and four corner portions in the scribe line region outside the four corners of the die, wherein the corner portions can enhance the crack stop effect at the four corners of the die.  
      When the multi-layer crack stop structure is partially in the die and partially in the scribe line region, a portion thereof in the die may be disposed as in the cases where the crack stop structure is disposed entirely in the die. In some embodiments, the crack stop structure includes four bar-like portions at or outside the four edges of the die and four corner portions outside or at, or partially outside or at, the four corners of the die.  
      In some embodiments where the crack stop effect at the four corners of the die is enhanced, the multi-layer crack stop structure include a ring portion in the die or in the scribe line region and four corner portions in, or partially in, the scribe line region outside the four corners of the die or in, or partially in, the die.  
      In some embodiments, the crack stop structure has two ring portions respectively in the die and in the scribe line region for enhancing the crack stop effect all around the die, while the two ring portions may be merged to be a single ring partially in the die and partially in the scribe line region. The crack stop structure may further have four corner portions at four corners of the die or (partially) in the scribe line region outside the four corners of the die to further enhance the crack stop effect at the four corners of the die.  
      The above variations of the multi-layer crack stop structure of this invention are all macroscopic shape variations in the dimension of a die, approximately in the order of millimeter to sub-millimeter. As for the microscopic structure approximately in the order of micrometer to deep sub-micron, the multi-layer crack stop structure may be formed by contiguously or interleavedly stacking multiple layers of hollow crack stop units in one or more linear regions. When there are multiple linear regions each with crack stop units interleavedly stacked therein, the units in the linear regions may be staggered in a cross section of the crack stop structure. Each hollow crack stop unit in a top view of the crack stop structure may have a contiguous structure or have a segmented structure having multiple segments. The contiguous (or segmented) structure may be a contiguous (or segmented) ring or a contiguous (or segmented) straight or L-shaped line, etc.  
      The above multi-layer crack stop structure of this invention can effectively avoid the damages like chipping, peeling-off and cracking to the active circuit region when the wafer is being sawn or when the die is subject to thermal cycles for testing. Hence, a better die is obtained, and the reliability of the packaged die is significantly improved.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION DRAWINGS  
       FIG. 1  illustrates a conventional multi-layer crack stop structure on a wafer.  
       FIG. 2  illustrates a wafer with dies thereon and a representative multi-layer crack stop structure on the wafer according to an embodiment of this invention.  
       FIG. 3  illustrates a cross section of a die seal ring structure and an interleaved and staggered multi-layer crack stop structure in a first embodiment of this invention.  
       FIG. 4  illustrates a cross section of a die seal ring structure and a contiguously stacked multi-layer crack stop structure in a second embodiment of this invention.  
       FIG. 5A  illustrates a top view of an interleaved and staggered multi-layer crack stop structure according to a third embodiment of this invention, and  FIG. 5B  illustrates a cross section of the same along line V-V′.  
       FIGS. 6A-6F  illustrate top views of six macroscopically different examples of the multi-layer crack stop structure of this invention, each including four bar-like portions and four corner portions.  
       FIGS. 7A-7D  illustrate top views of four further examples of the multi-layer crack stop structure of this invention, each including a ring portion and four corner portions.  
       FIGS. 8A-8B  illustrate top views of two further examples of the multi-layer crack stop structure of this invention, each at least having two ring portions respectively in the die and outside the die. 
    
    
     DESCRIPTION PREFERRED EMBODIMENTS  
      In some embodiments, the multi-layer crack stop structure is disposed entirely in the die not occupying any area of the scribe line region. Specifically, the multi-layer crack stop can be disposed between the active circuit region and the die seal ring structure, between two die seal rings of a dual die seal ring structure, or between the die seal ring structure and the scribe line region. In certain embodiments, however, the crack stop structure is disposed entirely in the scribe line region not occupying any area of the die.  
      In other embodiments, the multi-layer crack stop structure is disposed partially in the die and partially in the scribe line region, while a portion thereof in the die may be disposed between the active circuit region and the die seal ring structure, between two die seal rings of a dual die seal ring structure or between the die seal ring structure and the scribe line region. Moreover, a portion of the multi-layer crack stop structure between the die seal ring structure and the scribe line region may be merged with a portion of the same in the scribe line region to form a contiguous structure.  
      The principle of this invention is described in greater detail in reference of the accompanying drawings. However, the scope of this invention is not limited by them.  
      Referring to  FIG. 2  that illustrates a wafer with dies thereon and a representative multi-layer crack stop structure in an embodiment of this invention. The dies  210  on the wafer  200  are separated by scribe line regions  205 , so that the wafer  200  can be divided into separate dies  210  through sawing. Moreover, pad metals are often disposed at the outer periphery of the active circuit region  220  in the die  210  to form a dual die seal ring structure including two rings  230  and  240 . The corner region  235  of the die seal rings  230  and  240  suffering from a maximal stress during the sawing is generally bent to an angle like 45 degrees. It is also possible to form only one die seal ring for one die. Nevertheless, variations of the die seal ring structure in this invention are not limited to the above.  
      In the embodiment of  FIG. 2 , the multi-layer crack stop structure  212  is shaped as a ring entirely in the corresponding die  210  and, more specifically, in a region of the die  210  between the outer die seal ring  230  and the scribe line region  205 . It is also possible that the outer boundary of the crack stop structure  212  coincides with the outer boundary of the die  210  that is also the inner boundary of the scribe line region  205 . However, in other embodiments exemplified by  FIGS. 6-8 , the multi-layer crack stop structure may be disposed entirely in the scribe line region  205  or partially in the die  210  and partially in the scribe line region  205 . In addition, the multi-layer crack stop structure is not limited to have a ring shape but may include multiple bar-like portions, L-shaped portions, shorter slanted bar-like portions or block portions in the top view.  
      In a microscopic cross-sectional view, the multi-layer crack stop ring structure of this invention may be formed by contiguously or interleavedly stacking multiple layers of hollow crack stop rings in one linear region or in each of multiple linear regions, as shown in  FIGS. 3-4 . When multiple layers of hollow crack stop rings are interleavedly stacked in each of multiple linear regions, the crack stop rings in the linear regions may be staggered in a cross section of the multi-layer crack stop ring structure, as shown in  FIGS. 4 and 5 B.  
      A die seal ring structure and a multi-layer crack stop structure in a microscopic view according to a first embodiment and a second embodiment of this invention are described below in reference of  FIG. 3  and  FIG. 4 , respectively.  
       FIG. 3  illustrates a cross section of a die seal ring structure and an interleaved and staggered multi-layer crack stop structure in the first embodiment of this invention. The region  310  for forming the crack stop structure is between the die seal ring region  320  and the scribe line region  305 , but may be set at another position in alternative embodiments. The interleaved and staggered multi-layer crack stop structure is formed by interleavedly stacking multiple layers of hollow crack stop units in each of two or more linear regions and staggering the crack stop units in all linear regions in a cross section of the crack stop structure at the same time when the die seal ring is formed in the die seal ring region  320 . Therefore, the crack stop units in multiple layers may have the same material. The die seal ring is formed at the same time when the metal layers M 1 -M 9  and the via plugs VIA 1 -VIA 8  between each two layers are formed in the die seal ring region  320 , and is connected to the substrate  330  via a contact  331  at its bottom. Then, an aluminum (Al) layer  350  and a passivation layer  360  are sequentially formed on the resulting structure.  
      The overlaid part between each two adjacent crack stop units  312  is an important feature of the interleaved and staggered crack stop structure of the first embodiment. For example, in the stack of adjacent crack stop units  312 B,  312 A and  312 C, when viewed from the direction  318 , the overlaid parts  316 A and  316 B are interleavedly disposed. During the sawing process, the overlaid parts can be rapidly cut off by the mechanical stress due to the sawing, so that chipping is avoided resulting in a better protection.  
      In the above interleaved and staggered multi-layer crack stop structure, each crack stop unit  312  has a void  314  therein. In an embodiment, the voids  314  of the hollow units  312  are overlaid with each other as view from the direction  318 . For example, in the stack of adjacent crack stop units  312 B,  312 A and  312 C, the void  314 A is overlaid with the void  314 B and the void  314 C, respectively, as viewed from the direction  318 . Thus, the interleaved and staggered multi-layer crack stop structure is more effective in preventing clipping to provide a better protection.  
       FIG. 4  illustrates a cross section of a die seal ring structure and a contiguously stacked multi-layer crack stop structure in the second embodiment of this invention. The region  410  for forming the crack stop structure is between the die seal ring region  420  and the scribe line region  405 , but may be set at another location in alternative embodiments. The multi-layer crack stop structure is formed by contiguously stacking multiple layers of hollow crack stop units  412  at the same time when the die seal ring is formed in the region  420 , so that the crack stop units  412  in multiple layers may have the same material.  
      The die seal ring is formed at the same time when the multiple metal layers and via plugs between each two layers are interleavedly formed in the die seal ring region  420 , and is connected to the substrate  430  via a contact  431  at its bottom. Then, an Al layer  450  and a passivation layer  460  are sequentially formed on the resulting structure. On the other hand, any two adjacent crack stop units are formed contiguously, as illustrated by the stacked structure of the crack stop units  412 B,  421 A and  412 C. During the sawing process, the multi-layer crack stop ring structure can be rapidly cut off by the mechanical stress because of the voids  414  in the crack stop units  412 , so that chipping is avoided and a better protection is provided.  
       FIG. 5A  illustrates a top view of an interleaved and staggered multi-layer crack stop structure according to a third embodiment of this invention, and  FIG. 5B  illustrates a cross section of the same along line V-V′.  
      Referring to  FIGS. 5A-5B , the interleaved and staggered multi-layer crack stop structure  510  includes multiple separate linear stacks  511  of crack stop units, rather than multiple connected linear stacks as shown in  FIG. 3 . Each linear stack  511  includes an interleaved stack of hollow crack stop units  512  in multiple dielectric layers  520 , wherein each crack stop unit  512  has a void  514  therein. As shown in  FIG. 5B , the crack stop units  512  in one linear stack  511  may be interleavedly stacked such that every two adjacent dielectric layers  520  has one crack stop unit  512  therein and the crack stop unit  512  is disposed through the upper one of the two adjacent dielectric layers  520  and into but not through the lower one.  
      Meanwhile, the crack stop units  512  in the multiple linear stacks  511  are staggered in a cross section of the crack stop structure  510 . For example, when a crack stop unit  512  in a linear stack  511  a is formed through a dielectric layer and into but not through the underlying one, one adjacent crack stop unit  512  in one adjacent linear stack  511   b  is disposed through an overlying dielectric layer and into but not through the dielectric layer, and the other adjacent crack stop unit  512  in the linear stack  511   b  is disposed through the underlying dielectric layer and into but not through the further underlying one. The two adjacent crack stop units  512  in the other adjacent linear stack  511   c  are likely disposed.  
      In addition, each crack stop unit  312 ,  412  or  512  as mentioned above may include a metal layer with a void therein, and may be formed by forming a narrow trench in one or two dielectric layers and then filling in a metal with poor step coverage for forming a void in the metal layer. Moreover, in a microscopic top view, each crack stop unit  312  or  512  in an interleaved and staggered multi-layer crack stop structure may have a contiguous structure like a contiguous ring or a contiguous straight or L-shaped line, etc., or have a segmented structure like a segmented ring or a segmented straight or L-shaped line, etc., that includes multiple separate segments  515 .  
      When each crack stop unit  312  or  512  is a contiguous or segmented ring, straight line or L-shaped line in a microscopic top view, a ring portion, a (slanted) bar-like portion or a L-shaped portion of the multi-layer crack stop structure as illustrated in  FIGS. 6-8  in a macroscopic top view can be formed by interleavedly stacking and staggering the crack stop units  312  or  512  in the cross-sectional view to form multiple linear stacks of crack stop units. The segments  515  in multiple linear stacks  511  are preferably also staggered in the top view, as shown in  FIG. 5A , so as to completely protect the active circuit region. For example, in the y-direction of  FIG. 5A , a segment  515   a  in a linear stack  511   a  is positioned between two segments  515   b  of one layer higher or one layer lower than the segment  515   a  in one adjacent linear stack  515   b  and between two segments  515   c  of one layer higher or one layer lower than the segment  515   a  in the other adjacent linear stack  515   c.    
       FIGS. 6A-6F  illustrate six macroscopically different examples of the multi-layer crack stop structure of this invention, each including four bar-like portions at/outside the four edges of the die and four corner portions (partially) outside/at four corners of the die.  
      Referring to  FIG. 6A , the scribe region, the die and the active circuit region are respectively labeled with  605 ,  610  and  620 , and the die seal ring structure  630  in the die  610  may be a dual die seal ring structure including two rings  632  and  634 . The multi-layer crack stop structure  640  includes four bar-like portions  642  at the four edges of the die  610  and four L-shaped portions  644  in the scribe line region  605  outside the four corners of the die  610 . An L-shaped portion  644  is preferably overlaid with each adjacent bar-like portion  642  at the x- or y-direction by a certain length, so that a crack generated in the scribe line region  605  can be effectively stopped outside the active circuit region  620 .  
      The four bar-like portions  642  in the die  610  may alternatively be formed between the two die seal rings  632  and  634  of the dual die seal ring structure  630  or between the active circuit region  620  and the die seal ring structure  630 , as shown in  FIGS. 6B-6C . Moreover, the L-shaped portions  644  in the scribe line region  605  may be replaced by four shorter slanted bar-like portions each having an orientation different from that of any of the four bar-like portions  642 . The four slanted bar-like portions  644  may be disposed entirely or partially in the scribe line region  605 , or mostly in the scribe line region  605  and slightly overlapping with the region of the die  610 , as shown in  FIG. 6D .  
      Analogously, the multi-layer crack stop structure  640  may alternatively include four L-shaped portions  642  at the four corners of the die  610  and four bar-like portions  644  in the scribe line region  605  outside the four edges of the die  610 , as shown in  FIG. 6E . The four L-shaped portions  642  may similarly be replaced by four shorter slanted bar-like portions entirely or partially in the die  610 , or mostly in the die  610  and slightly overlapping with the scribe line region  605 , as shown in  FIG. 6F .  
       FIGS. 7A-7D  illustrate four further macroscopically different examples of the multi-layer crack stop structure of this invention, each including a ring portion in the die or the scribe line region and four corner portions for enforcing the crack stop effect at the four corners of the die. Referring to  FIG. 7A , the multi-layer crack stop structure  640  has a ring portion  642  entirely in the die region  610  and four L-shaped portions  644  in the scribe line region  605  outside the four corners of the die  610 . The L-shaped portions  644  may be replaced by four shorter slanted bar-like portions, or be replaced by four block portions  646  that are entirely or partially in the die  610 , as shown in  FIG. 7B . Each block portion  646  may have any shape other than the illustrated one, and may alternatively be disposed entirely in the scribe line region  605 . It is noted that a block portion  646  may include a larger number of linear stacks of crack stop units than the ring portion  642   a  to be wider than the latter.  
      On the contrary, the multi-layer crack stop structure  640  in  FIG. 7C  includes four L-shaped portions  642  at the four corners of the die  610  and a ring portion  644  entirely in the scribe line region  605 . The four L-shaped portions  642  may also be replaced by four shorter slanted bar-like portions entirely or partially in the die  610 , or be replaced by four block portions  648  entirely or partially in the scribe line region  605 , as shown in  FIG. 7D . Each block portion  648  may have any shape other than the illustrated one, and may alternatively be disposed entirely in the die region  610  apart from the ring portion  644   a.    
      It is also noted that though the above ring, bar-like or L-shaped portion is disposed either entirely in the die  610  or entirely in the scribe line region  605 , it may alternatively be disposed partially in the die  610  and partially in the scribe line region  605 , while the positions of the other portions of the crack stop structure can be adjusted accordingly.  
       FIGS. 8A-8B  illustrate two more macroscopically different examples of the multi- layer crack stop structure, each at least including two ring portions respectively in and outside the die to enhance the crack stop effect all around the active circuit region. In  FIG. 8A , the crack stop structure  640  has two ring portions  642  and  644  only respectively in and outside the die  610 . The two ring portions  642  and  644  may be merged to form a single ring that is partially in the die  610  and partially in the scribe line region  605 .  
      Moreover, the multi-layer crack stop structure  640  may further include four block portions  648  entirely or partially in the scribe line region  605  outside the four corners of the die  610 , as shown in  FIG. 8B , to further enhance the crack stop effect at the four corners of the die  610 . Each block portion  646  may have any shape other than the illustrated one, and may alternatively be disposed entirely in the die  610 .  
      In summary, a multi-layer crack stop structure disposed entirely in a die, entirely in the scribe line region around the die or partially in the die and partially in the scribe line region is provided by this invention. The multi-layer crack stop structure can effectively prevent certain damages like chipping, delamination, or peeling-off from occurring to the active circuit region during wafer sawing or thermal cycles for testing, so that a better single die is obtained and the reliability of the packaged die is significantly improved.  
      It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.