Abstract:
A semiconductor device ( 100 ) is provided in which an element region ( 3 ) for elements for which accuracy is particularly required and which should be prevented from receiving stress from a package among elements constituting the semiconductor device ( 100 ) is surrounded by a buffer region ( 8 ) for relaxing the stress, suppressing an influence of tensile or compressive stress generated during a packaging process to thereby reduce characteristic changes before and after the packaging process.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a semiconductor device capable of suppressing characteristic changes caused during a packaging process of the semiconductor device. 
         [0003]    2. Description of the Related Art 
         [0004]    Semiconductor devices formed on a wafer are cut and divided into chips through a dicing process to be assembled into packages. During a packaging process through sealing by resin and heat treatment, stress is applied to the semiconductor chip from the package, causing a warp in the semiconductor device whose characteristics are measured after the package assembling of the semiconductor device. Due to the warp, the measured characteristics of the semiconductor device may deviate from electrical characteristics of the semiconductor device measured on the wafer. As to a method for relaxing the stress, there has been proposed so far a method including forming a trench in a scribe region to thereby relax the stress in a wafer form, as disclosed in JP 2003-332270 A. 
         [0005]    In such a method as described above, however, the effect for stress relaxation is obtained only in a wafer form, and it has been a problem that the stress relaxation cannot be expected in a chip form after the dicing process. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the present invention to provide a semiconductor device which is capable of relaxing stress on a semiconductor chip caused during a packaging process, and has small characteristic changes before and after the packaging process. 
         [0007]    In order to solve the above-mentioned problem, the present invention employs the following means. 
         [0008]    According to the present invention, there is provided a semiconductor device which includes: an element region which is prevented from receiving stress and which is formed on a semiconductor substrate; a buffer region provided around the element region which is prevented from receiving the stress; and a semiconductor element formation region which is provided around the buffer region. 
         [0009]    The semiconductor device is provided in which the element region which is prevented from receiving the stress is arranged substantially at a center of the semiconductor substrate. 
         [0010]    The semiconductor device is provided in which: the buffer region includes a trench and one of a filler embedded into the trench and a hollow surrounded by the trench; and the trench has a depth larger than a depth of the element region which is prevented from receiving the stress, and larger than a depth of the semiconductor element formation region. 
         [0011]    The semiconductor device is provided in which the filler includes a material having a Young&#39;s modulus lower than a Young&#39;s modulus of the semiconductor substrate. 
         [0012]    A difference between the characteristics of the semiconductor device formed on a wafer and the characteristics of the semiconductor device assembled in a package is caused by the following reason. A resin used for sealing the semiconductor chip in the packaging process undergoes thermal expansion or thermal contraction during subsequent heat treatment, whereby tensile stress or compressive stress is applied to the semiconductor chip, adding additional resistance such as piezoresistance to elements. According to the present invention, the buffer region is formed around elements for which accuracy is particularly required for the circuit, whereby the buffer region absorbs the stress from the package, permitting suppression of the characteristic changes of the semiconductor device before and after the packaging process. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]    In the accompanying drawings: 
           [0014]      FIG. 1  is a plan view illustrating a semiconductor device according to a first embodiment of the present invention; 
           [0015]      FIG. 2  is a cross-sectional view illustrating the semiconductor device taken along a line A-A of  FIG. 1 ; 
           [0016]      FIG. 3  is a plan view illustrating a semiconductor device according to a second embodiment of the present invention; 
           [0017]      FIG. 4  is a cross-sectional view illustrating a semiconductor device according to a third embodiment of the present invention; 
           [0018]      FIG. 5  is a cross-sectional view illustrating a semiconductor device according to a fourth embodiment of the present invention in a case where a width of a trench is set to be 10 to 30 μm; and 
           [0019]      FIG. 6  is a cross-sectional view illustrating the semiconductor device according to the fourth embodiment of the present invention in a case where the width of the trench is set to be 30 to 100 μm. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    Referring to the attached drawings, preferred modes for embodying the present invention are described below. 
       First Embodiment 
       [0021]      FIG. 1  is a plan view illustrating a semiconductor device  100  according to a first embodiment of the present invention. In  FIG. 1 , the semiconductor device  100  includes: a semiconductor element formation region  1  to which stress induces little effect in terms of characteristics; a scribe region  2 ; an element region  3  for which accuracy is particularly required and which is preferably prevented from receiving the stress during a packaging process; and a buffer region  8  for relaxing the stress. For example, a current mirror circuit is a circuit in which currents flowing through two current paths act to be equal to each other by utilizes the fact that the same amount of current flows in each of the paired P-channel MOS transistors. Such paired transistors as described above are required to have characteristics little different from each other, and therefore are desirably formed within the above-mentioned element region  3  which is preferably prevented from receiving the stress. 
         [0022]    According to the first embodiment of the present invention, arrangement is made into two divided regions so that elements which are prone to change their characteristics by stress are arranged within the element region  3  which is preferably prevented from receiving the stress, and elements which hardly change their characteristics by stress are arranged within the semiconductor. element formation region  1 . In addition, the element region  3  which is preferably prevented from receiving the stress is arranged at the center of a chip, the buffer region  8  is formed around the element region  3 , and the semiconductor element formation region  1  is further provided around the buffer region  8 . The reason for this arrangement is because, when the element region  3  which is preferably prevented from receiving the stress is arranged at the center of the chip, the influence of stress less affects the element region  3  than a case where the element region  3  is arranged in a periphery of the semiconductor device  100 . 
         [0023]      FIG. 2  is a cross-sectional view illustrating the semiconductor device  100  taken along a line A-A of  FIG. 1 . The element region  3  which is preferably prevented from receiving the stress and the semiconductor element formation region  1  are formed on a surface of a semiconductor substrate  10 . The buffer region  8  is provided between the element region  3  and the semiconductor element formation region  1 . The buffer region  8  includes a trench  5  which is dug from the surface of the semiconductor substrate  10  into an inside thereof, and a filler  4  filling the trench  5  or a hollow  9  corresponding to a space inside the trench  5 . The filler  4  having a low Young&#39;s modulus occupies the trench  5 . A Young&#39;s modulus of silicon is approximately 110 GPa. The material to be embedded into the trench  5  is desired to have a Young&#39;s modulus lower than that of silicon. Thus, elastic materials such as polyimide, epoxy resin, rubber, and silicon resin are appropriate for the material. It should be noted that polyimide, epoxy resin, and rubber have Young&#39;s moduli of 3 to 5 GPa, 2.6 to 3 GPa, and 0.01 to 0.1 GPa, respectively. 
         [0024]    In addition, a depth of the trench  5  is desirably larger than element formation depths of the semiconductor element formation region  1  and the element region  3  which is preferably prevented from receiving the stress. There may be employed a structure in which the trench  5  extends through the semiconductor substrate  10 , and the element region  3  which is preferably prevented from receiving the stress and the surrounding semiconductor element formation region  1  are bonded to each other via the filler  4  embedded inside the trench  5 . It should be noted that a film formed on an uppermost surface of the semiconductor device  100  is a protective film  6 , and the protective film  6  is desirably made of an elastic material similarly to the case of the filler  4 . Elements formed within the element region  3  which is preferably prevented from receiving the stress and elements formed within the surrounding semiconductor element formation region  1  are electrically connected to each other through an interconnection (not shown). The interconnection is arranged so as to lie across a surface of the filler  4  embedded inside the trench  5 . In the case where the trench  5  is not embedded with the filler  4  but has a space as the hollow  9 , those elements can also be electrically connected to each other by forming an interconnection on a rear surface of the protective film  6 . 
         [0025]    With the above-mentioned structure, stress to be applied to the semiconductor device from a sealing resin which is covered in the packaging process is absorbed through a distortion in the buffer region  8 . As a result, the semiconductor device is suppressed from being warped due to the stress. Therefore, it becomes possible to suppress the characteristic changes in the elements arranged within the element region  3  which is preferably prevented from receiving the stress. 
       Second Embodiment 
       [0026]      FIG. 3  is a plan view illustrating a semiconductor device  100  according to a second embodiment of the present invention. The semiconductor device  100  includes: a semiconductor element formation region  1  for elements which cause no problem even under stress; a scribe region  2 ; an element region  3  for elements for which accuracy is particularly required and which is preferably prevented from receiving the stress during a packaging process; a buffer region  8  for relaxing the stress; and a support region  7 . 
         [0027]    In the second embodiment, similarly to the first embodiment, the element region  3  which is preferably prevented from receiving the stress is also arranged at a center of the semiconductor device  100 , and is also isolated from the surrounding semiconductor element formation region  1  by the buffer region  8 . However, the support region  7  is provided for connecting the element region  3  which is preferably prevented from receiving the stress and the semiconductor element formation region  1  for elements which cause no problem even under the stress. The buffer region  8  is not provided in the support region  7 . In the case where the element region  3  which is preferably prevented from receiving the stress is surrounded all around by the buffer region  8 , an interconnection for electrically connecting the element region  3  which is preferably prevented from receiving the stress and the semiconductor element formation region  1  for elements which cause no problem even under the stress is formed so as to lie across the buffer region  8 . In this state, when the semiconductor device  100  receives so large stress that the trench  5  expands or contracts largely, there is fear that the interconnection formed on the buffer region  8  cannot bear the expansion or contraction to be disconnected. However, in the second embodiment, the support region  7  is provided, and the interconnection for connecting both of the element region  3  and the semiconductor element formation region  1  lies on the support region  7 . Therefore, the interconnection is not affected by the expansion or contraction caused by the stress. The structure of the second embodiment has higher reliability than that of the first embodiment.  FIG. 3  illustrates an example in which only one support region  7  is provided, but a structure may be employed in which a plurality of the support regions  7  is provided. 
       Third Embodiment 
       [0028]      FIG. 4  is a cross-sectional view illustrating a semiconductor device  100  according to a third embodiment of the present invention.  FIG. 4  is different from  FIG. 2 . in that the filler  4  is left on the surface of the semiconductor substrate  10 . In this case, the semiconductor device  100  includes the support region  7 , and an interconnection (not shown) is provided on the support region  7 . As is apparent from this embodiment, the filler  4  may be embedded into the trench  5  at the formation of the protective film  6 . 
       Fourth Embodiment 
       [0029]      FIG. 5  is a cross-sectional view illustrating a semiconductor device  100  according to a fourth embodiment of the present invention. In a case where a width of the trench  5  is set to be approximately 10 to 30 μm, the trench  5  does not need to be completely filled with the filler  4 . The remaining space in the trench  5  may be filled with the protective film  6 . Alternatively, in a case where the width of the trench  5  is set to be 30 to 100 μm, such a structure as illustrated in  FIG. 6  may be employed in which an inner wall surface of the trench  5  is protected by the filler  4  and the protective film  6 , and the hollow  9  having a cylindrical shape is provided inside the resultant trench  5 .