Abstract:
A linear image sensor integrated circuit has a semiconductor substrate having a pixel region and a scribe region adjacent to the pixel region. A diffusion layer is disposed in the pixel region of the semiconductor substrate. A PN junction is formed between the semiconductor substrate and the diffusion layer for receiving light. A passivation film covers the PN junction and is disposed over a surface of the semiconductor substrate except for a portion of the surface thereof in the scribe region.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a linear image sensor IC suitable for a facsimile machine, an image scanner, or the like for reading and transmitting image information, and to a semiconductor device having the linear image sensor IC. 
     2. Description of the Related Art 
     In an image sensor, a PN junction is used as a photoelectric conversion device. FIG. 3 is a sectional view illustrating a pixel portion of a conventional image sensor. A PN junction between an N type silicon substrate  1  and a pixel P type diffusion layer  2  is used as a photoelectric conversion device. Light enters a pixel region  10  and impinges on silicon lattice to generate minority carriers. The minority carriers move in the N type silicon substrate  1  and reach the pixel P type diffusion layer  2  to be photoelectrically converted. 
     By absorbing minority carriers generated in the silicon substrate  1  except the pixel region  10  with a guard ring  8  which is a P type diffusion layer formed so as to surround the pixel region  10 , only light which enters the pixel region  10  can be sensed. When the pixel region  10  is adjacent to an edge of a chip, the minority carriers coming from that direction is ignorable and thus, the guard ring  8  can be omitted with regard to that direction. Further a scribe region  11  has an isolation  3  on the substrate  1  and a passivation  4  on the isolation  3 . A wire  5  is disposed on the isolation  3  and is connected to the pixel P type diffusion layer  2  and the passivation  4 . 
     However, an image sensor structured as above has a problem in that its characteristics when the sensor is on a wafer are different from those when it becomes a finished product. This is due to difference in the amount of the minority carriers in the respective pixel areas caused by special structures such as an alignment mark on scribe regions or structures of peripheral circuits for adjacent chips. 
     SUMMARY OF THE INVENTION 
     In order to solve the above problem, according to an aspect of the present invention, a linear image sensor IC is structured as in the following. A linear image sensor IC having no guard ring PN junction between a PN junction for receiving light and an adjacent scribe region is structured such that a silicon substrate surface retaining a silicon substrate impurity concentration appears in the scribe region. Alternatively, a linear image sensor IC is structured such that the scribe region forms a PN junction of a silicon substrate impurity concentration, the PN junction being given no electric potential. 
     According to another aspect of the present invention, a semiconductor wafer having a linear image sensor IC arranged on a surface thereof, the linear image sensor IC having a PN junction for receiving light and a guard ring spaced from the PN junction, further comprises a scribe region adjacent to the linear image sensor IC on a side opposite to a side of the guard ring, the scribe region having a surface impurity concentration equal to a substrate impurity concentration of the semiconductor wafer. Further, a PN junction of a substrate impurity concentration of the semiconductor wafer is arranged in the scribe region. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a sectional view of a pixel region and a scribe region of an image sensor according to a first embodiment of the present invention; 
     FIG. 2 is a sectional view of a pixel region and a scribe region of an image sensor according to a second embodiment of the present invention; and 
     FIG. 3 is a sectional view of a pixel region and a scribe region of a conventional image sensor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is now described with reference to the drawings. 
     FIG. 1 is a sectional view of a pixel region and a scribe region of an image sensor according to a first embodiment of the present invention. A PN junction formed between an N type silicon substrate  1  and a pixel P type diffusion layer  2  in the N type silicon substrate  1  carriers out photoelectric conversion. No guard ring  8  exists between the PN junction and a scribe region  11 . The scribe region  11  is adjacent to a pixel region  10  through the N type silicon substrate  1  only. The N type silicon substrate  1  as it is appears on a surface of the scribe region  11 . The guard ring  8  is formed in the surface of the substrate  1 , separate from the diffusion layer  2  in the direction against the scribe region  11 . There is also an isolation film  3  (hereinafter referred to as “isolation”), a wire  5  on the isolation  3  and connected to diffusion layer  2 , and passivation film  4  (hereinafter referred to as “passivation”) disposed on the isolation  3 . 
     The impurity concentration of the surface is the same as that in the silicon substrate  1 . Surface roughness to some extent is observed on the surface because the silicon substrate is etched during contact etching, metal etching, and passivation etching. 
     The concentration on the surface of the scribe region is the same as that in the substrate. Therefore, it becomes easier for minority carriers in the substrate to reach the surface of the scribe region. Further, since the surface is exposed as it is to the atmosphere, recombination at the surface occurs more remarkably, and thus, the minority carriers disappear more easily. Excess minority carriers generated in the scribe region  11  and in adjacent chips move to the surface in the scribe region  11  and disappear due to the recombination of the surface, and thus, do not flow in the pixel region  10 . Even in a finished product, by dicing along the scribe region  11 , the surface thereof is formed into the silicon substrate exposed to the atmosphere with the impurity concentration almost same as that in the silicon substrate. As a result, there is almost no difference between the characteristics of the image sensor when the sensor is on a wafer and those when the sensor becomes a finished product, and thus, characteristic inspection of a finished product can be carried out when the image sensor is still on a wafer. 
     FIG. 2 is a sectional view of a pixel region and a scribe region of an image snesor according to a second embodiment of the present invention. A PN junction formed between an N type silicon substrate  1  and a pixel P type diffusion layer  2  in the N type silicon substrate  1  carriers out photoelectric conversion. No guard ring  8  exists between the PN junction and a scribe region  11 . The scribe region  11  is adjacent to a pixel region  10  through the N type silicon substrate  1  only. The guard ring  8  is formed in the surface of the substrate  1 , separate from the diffusion layer  2  in the direction against the scribe region  11 . There is also an isolation  3 , a wire  5  on the isolation  3  and connected to diffusion layer  2 , and a passivation  4  on the isolation  3 . A scribe P type diffusion layer  6  is formed over the whole surface of the scribe region. A PN junction is formed between the scribe P type diffusion layer  6  and the N type silicon substrate  1 . No direct electric potential is given to the scribe P type diffusion layer  6 , and its electric potential is through the N type silicon substrate  1 . 
     Minority carriers in the substrate in the scribe region  11  easily reach the PN junction, and thus, are easily absorbed in the scribe P type diffusion layer  6 . Excess minority carriers generated in the scribe region  11  and in adjacent chips are absorbed in the PN junction surface in the scribe region, and thus, do not flow in the pixel region  10 . Therefore, there is almost no difference between the characteristics of the image sensor when it is on a wafer and those when it becomes a finished product, and thus, characteristic inspection of a finished product can be carried out when the image sensor is still on a wafer. In such a structure, the effect can be obtained only by forming a P type diffusion layer under any surface structure without limitation on the surface of the scribe region  11  of Embodiment  1 , and thus, the present embodiment is particularly useful when, for example, structures such as alignment marks  7   a , 7   b  on the scribe region  11  are required to be planarized. 
     No electric potential is given to the scribe P type diffusion layer  6  for the purpose of suppressing unstable leak which may be caused by the PN junction on a diced surface. The scribe P type diffusion layer  6  can be formed as a P well diffusion layer or a P type channel stop layer in a typical CMOS manufacturing process without increasing the number of manufacturing steps. 
     Further, the structures of Embodiments 1 and 2 may be used together, i.e., the structure of Embodiment 1 may be used in a scribe region with no particular structure arranged therein, while the structure of Embodiment 2 may be used in a scribe region with an alignment mark or the like arranged therein. 
     As described in the above, according to the present invention, a CMOS linear image sensor which has small difference between characteristics inspected when it is on a wafer and those when it becomes a finished product, which does not require a guard ring, and the chip size of which is small can be provided.