Patent Publication Number: US-2007102791-A1

Title: Structure of multi-layer crack stop ring and wafer having the same

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a wafer, and more particularly, to a wafer having a multi-layer crack stop ring structure. Specifically, the multi-layer crack stop ring structure surrounding the active circuit region is disposed between the active circuit region and the scribe line, so as to prevent the active circuit region from being damaged when sawing the wafer, which significantly improves the reliability of the packed object.  
      2. Description of the Related Art  
      Along with the continuous development of the new technology, the integrated circuits (IC) had been widely applied in our daily life. In general, the IC manufacturing process mainly includes three steps: the silicon wafer manufacturing process, the IC manufacturing process, and the IC packaging process. A die sawing process is performed as the first step of the IC packaging.  
      A silicon wafer generally comprises a plurality of horizontal scribe lines disposed parallelly with each other and a plurality of vertical scribe lines disposed vertically disposed with each other that are used to separate a plurality of dies. After the devices are completely fabricated on the wafer, then a diamond blade is used to saw the scribe line disposed along with the wafer, so as to obtain a plurality of dies. Specifically, various material layers are disposed on the wafer, during the wafer sawing operation, since the characteristic of the material layers are not the same, some damages such as chipping or peeling is occurred on the material layers on the scribe line.  
      In another conventional sawing technique, a laser grooving technique is introduced to replace the blade sawing. However, the laser grooving technique also has some problems. For example, during the wafer sawing operation, if the material layer disposed on the wafer contains a metal material, it is very hard to completely remove the metal material during the laser fusion operation. Accordingly, some debris still remains on the wafer, which stains the dies. In addition, a heat effect area is formed on the periphery of the scribe line during the laser grooving operation, and a big heat effect area will greatly impact the reliability of the dies. Moreover, the price of a general laser grooving equipment is about 2˜3 times higher than the price of the diamond blade equipment, which makes such method very expensive.  
      In addition, a method for manufacturing a crack stop structure on the device had been disclosed in U.S. Pat. No. 5,530,280. As shown in  FIG. 1 , two active circuit regions  110  and  120  are disposed on a substrate  100 , and two dielectric layers  132  and  134  are formed on the substrate  100 . Wherein, the dielectric layer  132  contains a metal contact  112  and two tungsten metal rings  142  and  152 . The dielectric layer  134  contains a metal contact  116 , three interconnect metals  114 ,  144 ,  154 , and two tungsten metal rings  146  and  156  that have the hollow rings  145  and  155 , respectively. The interconnect metals  118 ,  148 ,  158  are formed on the dielectric layer  134 , respectively. Moreover, a scribe line region  160  is disposed between the interconnect metals  148  and  158 .  
      The structure for preventing the active circuit region  110  from being impacted by the crack disclosed in the patent mentioned above comprises a tungsten metal ring  142 , an interconnect metal  144 , a tungsten metal ring  146 , and an interconnect metal  148 . In addition, the structure for preventing the active circuit region  120  from being impacted by the crack comprises a tungsten metal ring  152 , an interconnect metal  154 , a tungsten metal ring  156 , and an interconnect metal  158 . Since different material reacts differently to the same stress, the crack stop structure composed of different materials cannot rapidly and effectively prevent the active circuit region structure from being impacted by the crack during the horizontal scribe line region  160  sawing operation.  
     SUMMARY OF THE INVENTION  
      Therefore, in an embodiment of the present invention, a multi-layer crack stop ring structure is provided. Wherein, the multi-layer crack stop ring structure disposed between a die seal ring and a scribe line or disposed between a dual die seal ring does not occupy the space of the scribe line.  
      In an alternative embodiment, an interleaved multi-layer crack stop ring structure is provided.  
      The multi-layer crack stop ring structure mentioned above can effectively avoid the damages such as chipping, peeling, or cracking on the scribe line. Accordingly, a better die can be obtained from the sawing operation, which significantly improves the reliability of the packed object.  
      In order to achieve the objects mentioned above, a wafer is provided by an embodiment of the present invention, and a plurality of dies is formed on the wafer. The dies are separated from each other by a plurality of scribe lines, and each die is surrounded by a scribe line mentioned above. Each die comprises an active circuit region, a die seal ring structure that surrounds the active circuit region, and a multi-layer crack stop ring structure surrounding the active circuit region. Here, the multi-layer crack stop ring structure is formed by stacking a plurality of hollow crack stop rings.  
      In the wafer of the embodiment mentioned above, wherein the multi-layer crack stop ring structure is disposed between the die seal ring structure and the scribe line or disposed between the die seal ring structure and the active circuit region.  
      In the wafer of the embodiment mentioned above, wherein the multi-layer crack stop ring structure is formed by stacking a plurality of crack stop rings having the same material.  
      In another embodiment of the present invention, the multi-layer crack stop ring structure in the wafer of the above embodiment is formed by interleavedly stacking the crack stop rings mentioned above.  
      In the wafer of the above embodiment, wherein the die seal ring structure is formed by interleavedly stacking a plurality of metal layers and contact VIAs. In addition, each metal layer and each VIA correspond to a crack stop ring. 
    
    
     BRIEF DESCRIPTION DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention, and together with the description, serve to explain the principles of the invention.  
       FIG. 1  is a schematic diagram of a conventional crack stop structure on the device.  
       FIG. 2 a  schematic diagram of a wafer with a plurality of dies formed thereon, and the dies are individually separated by the scribe lines.  
       FIG. 3  is schematically shows a diagram illustrating an interleaved multi-layer crack stop ring structure according to an embodiment of the present invention.  
       FIG. 4  schematically shows a diagram illustrating a multi-layer crack stop ring structure having the same material according to an embodiment of the present invention. 
    
    
     DESCRIPTION PREFERRED EMBODIMENTS  
      In general, the device formed on the wafer usually comprises a plurality of material layers, and the material layers are also formed on the scribe line when the device is being fabricated. Therefore, during the wafer sawing operation, since each material layer on the scribe line has different material characteristics, some problems such as chipping or peeling easily happens on the scribe line. If the Low-k/Cu structure is going to be sawed, the problem of chipping and interlayer delamination becomes worse. When the scale of the device becomes smaller, the width of the scribe line becomes relatively smaller too, such that the problem of the crack formed in the sawing process penetrating into the operating metal or the active circuit region is more serious. Accordingly, the reliability of the packed object is deteriorated.  
      In an embodiment of the present invention, a multi-layer crack stop ring structure having the same material is provided. The multi-layer crack stop ring structure is disposed between the die seal ring and the scribe line. Specifically, the die seal ring is disposed on the periphery of the die and regarded as a protection wall on the periphery of the die to avoid the crack possibly occurred when sawing the die. In addition, the scribe line is disposed between the dies for separating each sawed die and regarded as a channel outside the protection wall of the die.  
      In another embodiment of the present invention, the multi-layer crack stop ring structure having the same material provided by the present invention is disposed between the dual die seal ring, wherein its physical layout is determined by the design requirement. The multi-layer crack stop ring structure having the same material provided by the present embodiment does not occupy the space of the scribe line. In addition, the present embodiment can effectively prevent the damage such as chipping, delamination, or peeling from happening on the scribe line when sawing the die.  
      In an alternative embodiment of the present invention, an interleaved multi-layer crack stop ring structure is provided. The multi-layer crack stop ring structure is disposed between the die seal ring and the scribe line. In another embodiment, the multi-layer crack stop ring structure is disposed between the dual die seal ring, and the physical layout is determined by the design requirement. The interleaved multi-layer crack stop ring structure having the same material provided by the present embodiment can effectively prevent the damage such as chipping, delamination, or peeling from happening on the scribe line. In addition, the interleaving parts described herein and after are interleavedly disposed between every two layers of the stack structure in the multi-layer crack stop ring. The interleaving parts can prevent the chipping generated during the sawing process from being torn from one of the layers or multiple layers for providing a better protection, and its detail is described in greater detail with referring to the accompanying drawings hereinafter.  
      In an alternative embodiment of the present invention, an interleaved multi-layer crack stop ring structure having the same material is provided for effectively preventing the damage such as chipping, delamination, or peeling from happening on the scribe line.  
      The principle of the present invention is described in greater detail with referring to the accompanying drawings. However, the scope of the present invention is not limited by it.  
      Referring to  FIG. 2 , a plurality of dies are formed on the wafer  200 , wherein the dies are individually separated by the scribe line  205 , such that the die can be formed independently after the sawing process. Although the description only describes the die  210 , other dies also have the same structure as the die  210 . In addition, the pad metals are disposed on the periphery of the active circuit region  220  inside the die  210 , so as to form the dual die seal ring structure that comprises the die seal rings  230  and  240 . The corner region  235  of the die seal rings  230  and  240  where a maximum stress occurs during the sawing process is generally bended to a certain angle of 45 degrees. Alternatively, in an embodiment of the present invention, it is also possible to use only one of the die seal rings  230  and  240 . Even though, the present invention is not limited by it. The multi-layer crack stop ring structure having the same material or the interleaved multi-layer crack stop ring structure according to the embodiment of the present invention is formed between the scribe line  205  and the dual die seal ring  230  and  240 , and it is near the scribe line edge  214 .  
      The die seal ring structure and the multi-layer crack stop ring structure according to an embodiment of the present invention are described in greater detail with referring to  FIGS. 3 and 4  hereinafter.  
       FIG. 3  schematically shows a diagram illustrating an interleaved multi-layer crack stop ring structure according to an embodiment of the present invention. The crack stop ring structure region  310  is disposed between the die seal ring region  320  and the scribe line  305 . The interleaved multi-layer crack stop ring structure is formed by stacking multiple layers of the crack stop rings, and the stack structure is formed at the same time when the die seal ring is formed on the die seal ring region  320 . Therefore, the interleaved multi-layer crack stop ring structure may have the same material. Wherein, the die seal ring is formed at the same time when the metal layers M 1 ˜M 9  and the VIAs VIA 1 ˜VIA 8  between each two layers are formed on the die seal ring region  320 . The die seal ring disposed on the substrate  330  is connected to a contact  331 . Then, an aluminum (Al) metal layer  350  is disposed thereon, and a passivation layer  360  is disposed on the aluminum (Al) metal layer  350 .  
      The overlaid parts between each two neighboring crack stop rings are referred to as the interleaved structure. For example, in the stack structure of the neighboring crack stop rings  312 B,  312 A, and  312 C, when viewing from the direction marked by the arrow  318  in the diagram, the overlaid parts  316 A and  316 B are interleavedly disposed. During the sawing process, the interleaved multi-layer crack stop ring structure can be rapidly cut off by the mechanical stress generated by it, such that the chipping is avoided and a better protection is provided.  
      In the interleaved multi-layer crack stop ring structure of the present embodiment, each crack stop ring has a hollow ring. In one embodiment, some portions of the hollow rings are overlaid in the direction marked by the arrow  318 . In other words, in the stack structure of the neighboring crack stop rings  312 B,  312 A, and  312 C, some portions of the hollow rings  314 B,  314 A, and  314 C are overlaid in the direction marked by the arrow  318 . Accordingly, it can more effectively avoid the clipping and provide a better protection.  
       FIG. 4  schematically shows a diagram illustrating a multi-layer crack stop ring structure having the same material according to an embodiment of the present invention. The crack stop ring structure region  410  is disposed between the die seal ring region  420  and the scribe line  405 . The multi-layer crack stop ring structure is formed by directly stacking multiple layers of the crack stop rings, and the stack structure is formed at the same time when the die seal ring is formed on the die seal ring region  420 . Therefore, the multi-layer crack stop ring structure may have the same material. Wherein, the die seal ring is formed at the same time when the multiple metal layers and the VIAs between each two layers are interleavedly formed on the die seal ring region  420 . The die seal ring disposed on the substrate  430  is connected to a contact  431 . Then, an aluminum (Al) metal layer  450  is disposed thereon, and a passivation layer  460  is disposed on the aluminum (Al) metal layer  450 . Each two neighboring crack stop rings are disposed interleavedly as the stack structure of the neighboring crack stop rings  412 B,  421 A, and  412 C shown in the diagram. During the sawing process, the multi-layer crack stop ring structure can be rapidly cut off by the mechanical stress generated by it, such that the chipping is avoided and a better protection is provided. In the multi-layer crack stop ring structure of the present embodiment, each crack stop ring has a hollow ring. For example, the crack stop ring  412 A has a hollow ring  414 A, which avoids the clipping more effectively and provides a better protection.  
      In summary, a multi-layer crack stop ring structure disposed between a die seal ring and a scribe line or disposed between a dual die seal ring is provided by the present invention. The multi-layer crack stop ring structure provided by the present invention does not occupy the space of the scribe line, and can effectively prevent the damages such as chipping, delamination, or peeling from happening on the scribe line when performing the sawing process, such that a better die can be provided and the reliability of the packed object can be significantly improved.  
      Although the invention has been described with reference to a particular embodiment thereof, it will be apparent to one of the ordinary skills in the art that modifications to the described embodiment may be made without departing from the spirit of the invention. Accordingly, the scope of the invention will be defined by the attached claims not by the above detailed description.