Abstract:
A corner free structure of a nonvolatile memory is disclosed in this present invention. The key aspect of this present invention is employing a corner free structure for isolating a trench isolation device and a nonvolatile memory, and thus the reliability of the above-mentioned nonvolatile memory is improved. Furthermore, based on the definition of coupling ratio, as a result of the above-cited corner free structure, the effective channel area of the nonvolatile memory is modified, and thus the nonvolatile memory according to this present invention can achieve higher efficiency than the nonvolatile memory in the prior art. Therefore, this invention can not only improve the reliability of a nonvolatile memory, but also advance the efficiency of the nonvolatile memory.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This present invention relates to a structure of corner free, and more particularly to a corner free structure of nonvolatile memory.  
         [0003]     2. Description of the Prior Art  
         [0004]     In recent years, it is well known for employing trench isolation devices, such as shallow trench isolation (STI), to isolate the semiconductor devices. However, corners of the trench isolation devices always come with the trench isolation devices. In the prior art, due to the corners of the trench isolation devices, many unwanted issues of the semiconductor devices will occur.  
         [0005]     For instance,  FIG. 1  depicts a semiconductor structure according to the prior art. Referred to  FIG. 1 , the semiconductor structure comprises a substrate  100 , and a plurality of trench isolation device  120  in the substrate  100 . Corners  125  are usually formed between the substrate  100  and the trench isolation device  120 . In point of the nonvolatile memory  130  between two trench isolation devices  120 , it is obviously that the tunnel oxide layer  135  of the nonvolatile memory  130  is close to the corners  125 , and even the tunnel oxide layer  135  is touched with the corners  125 . Therefore, because the trench isolation devices  120  and the nonvolatile memory  130  are not complete isolated, the reliability of the nonvolatile memory  130  is decreased.  
         [0006]     Hence, it is an important object of developing a corner free structure for raising the reliability of a nonvolatile memory. Moreover, the above-mentioned corner free structure can increase the efficiency of the nonvolatile memory.  
       SUMMARY OF THE INVENTION  
       [0007]     In accordance with the present invention, a corner free structure of a nonvolatile memory is provided, wherein the corner free structure efficient isolates the nonvolatile memory and trench isolation devices, and the reliability of the nonvolatile memory is increased.  
         [0008]     It is another object of this invention to provide a corner free structure of a nonvolatile memory. According to the definition of coupling ratio, through changing the width of the tunnel oxide layer and the dielectric layer of the nonvolatile memory in this present invention, the efficiency of the above-mentioned nonvolatile memory can be improved.  
         [0009]     In accordance with the above-mentioned objects, the invention provides a corner free structure of a nonvolatile memory. The above-mentioned corner free structure of a nonvolatile memory comprises a substrate, at least one trench isolation device, and a plurality of nonvolatile memory. The trench isolation device comprises a corner free structure for complete isolating the nonvolatile memory and the trench isolation device, and thus the reliability of the nonvolatile memory is improved. Additionally, the above-mentioned corner free structure is helpful for modifying the width of the tunnel oxide layer of the nonvolatile memory. Therefore, the corner free structure according to this invention can improve the efficiency of the nonvolatile memory. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0011]      FIG. 1  is a diagram showing a semiconductor structure with trench isolation devices according to the prior art;  
         [0012]      FIG. 2  is a corner free structure according to this present invention; and  
         [0013]      FIG. 3  is a corner free structure of a nonvolatile memory according to this present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0014]     Some sample embodiments of the invention will now be described in greater detail. Nevertheless, it should be recognized that the present invention can be practiced in a wide range of other embodiments besides those explicitly described, and the scope of the present invention is expressly not limited except as specified in the accompanying claims.  
         [0015]     Then, the components of the semiconductor devices are not shown to scale. Some dimensions are exaggerated to the related components to provide a more clear description and comprehension of the present invention.  
         [0016]     One preferred embodiment of this invention is a corner free structure of a nonvolatile memory. The above-mentioned corner free structure of a nonvolatile memory comprises a substrate, and a plurality of trench isolation device. The trench isolation device comprises a first portion on the substrate, and a second portion in the substrate. The above-mentioned trench isolation structure of a nonvolatile memory further comprises a spacer at a sidewall of the first portion of the trench isolation device. The spacer is employed for covering a corner between the sidewall of the first portion of the trench isolation device.  
         [0017]     In this preferred embodiment, due to the spacer at the sidewall of the first portion of the trench isolation device, the tunnel oxide layer of a nonvolatile memory between two trench isolation device is kept from the corner of the trench isolation device, and thus the reliability of the nonvolatile memory is improved. On the other hand, the width of the nonvolatile memory is modified by the spacer of the trench isolation device. In other words, the width of the tunnel oxide layer of the nonvolatile memory is decreased, and the width of the dielectric layer of the nonvolatile memory is increased. According to the definition of coupling ratio, the above-mentioned width modification of the nonvolatile memory can improve the coupling ratio of the nonvolatile memory. Hence, the efficiency of the nonvolatile memory according to this present embodiment is better than the efficiency of the nonvolatile memory in the prior art.  
         [0018]     Another preferred embodiment of this present invention is about a corner free structure of a nonvolatile memory. Referred to  FIG. 2 , the corner free structure according with this present embodiment comprises a substrate  200 , and at least one trench isolation device  220 . The trench isolation device  220  may be shallow trench isolation (STI). The trench isolation device  220  comprises a first portion  222  on the substrate  200 , and a second portion  224  in the substrate  200 .  
         [0019]     Corners  230  are formed between the first portion  222  of the trench isolation device  220  and the substrate  200 . In the prior art, because the corner  230  is close to the tunnel oxide layer of the nonvolatile memory or touched with the tunnel oxide layer of the nonvolatile memory, the reliability of the nonvolatile memory will be decreased. Therefore, in this present embodiment, a spacer  240  is at a sidewall of the first portion  222  of the trench isolation device  220 , and covers the corner  230  between the sidewall of the first portion  222  of the trench isolation  220  and the substrate  200 . The spacer  240  is consisted of deposited silicon dioxide, deposited silicon nitride, and the like dielectric materials. The spacer  240  can be formed by the technology in the prior art. For example, the spacer  240  may be formed at the sidewall of the first portion  222  by a depositing step and an etching step. In this manner, the trench isolation device  220  and the tunnel oxide layer of the nonvolatile memory can be efficiently isolate the spacer  240 , and thus the reliability of the nonvolatile memory can be improved.  
         [0020]     Another preferred embodiment according to this invention is a corner free structure of a nonvolatile memory. As shown in  FIG. 3 , the corner free structure of a nonvolatile memory comprises a substrate  300 , a plurality of trench isolation device  320 , and a plurality of nonvolatile memory  340 , wherein each of the nonvolatile memory is between two trench isolation devices  320 . The substrate comprises silicon. The trench isolation device may be shallow trench isolation. The above-mentioned trench isolation device comprises a first portion  322  on the substrate  300 , and a second portion  324  in the substrate  300 . As the trench isolation device  220  in the above-mentioned embodiment, corner  330  is formed between the first portion  322  of the trench isolation device  320  and the substrate  300 . In order to preventing the issues in the prior art, the trench isolation device  320  also comprises a spacer  325  at the sidewall of the first portion  322  of the trench isolation device  320  for covering the corner  330  between the first portion  322  and the substrate  300 . The material of the spacer  325  may be deposited silicon dioxide, deposited silicon nitride, or other dielectric materials. The spacer  325  may be formed by ordinary technology. For instance, after depositing a dielectric material layer onto the substrate  300  and the trench isolation device  320 , and etching parts of the above-mentioned dielectric material layer, the spacer  325  is formed at the sidewall of the first portion  322  of the trench isolation device  320 . Therefore, the spacer  325  can efficiently keep the tunnel oxide layer of the nonvolatile memory  340  from touching the corner  330 . In other words, the reliability of the nonvolatile memory according to this embodiment can be improved by the spacer  325 .  
         [0021]     Referred to  FIG. 3 , a nonvolatile memory  340  is disposed between two trench isolation devices  320 . The nonvolatile memory  340  may be flash memory. The nonvolatile memory  340  comprises a tunnel oxide layer  342  on the substrate, a floating gate  344  on the tunnel oxide layer  342 , a dielectric layer  346  on the floating gate  344 , and a control gate  348  on the dielectric layer  346 . In this present embodiment, the coupling ratio may be defined as the ratio between the capacitive value of the dielectric layer  346  and the sum of the capactive value of the dielectric layer  344  and width of the tunnel oxide layer  342 , as shown in the equation 1.
 
coupling ratio= B/B+A   (equation 1)
 
         [0022]     In the equation 1, A is the capacitive value of the tunnel oxide layer  342 , and B is the capacitive value of the dielectric layer  346 . In the point of a nonvolatile memory, coupling ratio is relative to the efficiency of the nonvolatile memory. From  FIG. 3 , due to the existence of spacer  325  in this embodiment, the capacitive value A of the tunnel oxide layer  342  is decreased because the width of the tunnel oxide layer  342  is decreased. Consequently, according to the definition of coupling ratio of a nonvolatile memory, the nonvolatile memory according to this embodiment can achieve higher efficiency.  
         [0023]     According to the preferred embodiments, this invention discloses a corner free structure of a nonvolatile memory. The corner free structure of a nonvolatile memory comprises a substrate, at least a trench isolation device, and a plurality of nonvolatile memory, wherein each of the nonvolatile memory is disposed between two trench isolation devices. The above-mentioned trench isolation device comprises a first portion on the substrate, and a second portion in the substrate. The corner free structure of a nonvolatile memory further comprises a spacer at a sidewall of the first portion of the trench isolation device. The spacer is utilized for covering a corner between the substrate and the sidewall of the first portion of the trench isolation device. The trench isolation device and the tunnel oxide layer of the nonvolatile memory can be efficiently isolated by the spacer. Hence, the reliability of a nonvolatile memory can be advanced by the corner free structure according to this invention. On the other hand, as a result of the spacer according to this invention, the width of the tunnel oxide layer of the nonvolatile memory is decreased, and the width of the dielectric layer of the nonvolatile memory is increased. Therefore, based on the definition of coupling ratio, the nonvolatile memory according to this present invention can achieve higher efficiency than the nonvolatile memory in the prior art.  
         [0024]     Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various modifications may be made without departing from what is intended, but not to be limited solely by the appended claims.