Patent Publication Number: US-2010117082-A1

Title: Semiconductor device capable of compensating for electrical characteristic variation of transistor array

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims under 35 U.S.C. §119 priority to and the benefit of Korean Patent Application No. 10-2008-0112367 filed on Nov. 12, 2008, in the Korean Intellectual Property Office, the entire content of which is incorporated by reference herein. 
     BACKGROUND 
     1. Technical Field 
     The present inventive concept relates to semiconductor devices, and more particularly, to semiconductor devices capable of compensating for a variation in an electrical characteristic according to a position of a transistor. 
     2. Discussion of Related Art 
     In a semiconductor device, such as an image sensor, a display driver, or a memory device, including a plurality of transistor pairs or a transistor array, the transistors need to have the same electrical characteristics (e.g., a source-drain current characteristic or a threshold voltage characteristic) to prevent the semiconductor device from malfunctioning. However, the transistors may have different electrical characteristics according to their positions in a substrate. 
     For instance, the electrical characteristics of a transistor may be varied by well proximity effects (WPE). For example, WPE can occur during a CMOS manufacturing process where atoms scatter laterally from an edge of a photoresist mask and become embedded in a silicon surface near edges of wells needed for latch-up protection and suppression of lateral punch-through. Such a structure can cause MOSFET electrical characteristics to vary with the distance of the transistor from the well-edge. 
     Also, the electrical characteristics of a transistor may be varied by shallow trench isolation (STI). For example, STI effects can occur because during a semiconductor device fabrication process, before transistors are formed a pattern of trenches may be etched in the silicon, with one or more dielectric materials filling the trenches and providing an STI region which may affect electrical current leakage between adjacent semiconductor device components. 
     SUMMARY 
     An exemplary embodiment of the present inventive concept provides a semiconductor device capable of compensating for an electrical characteristic variation. 
     According to an exemplary embodiment of the present inventive concept a semiconductor device includes: a well region, and a transistor array spaced from the well region. The transistor array includes a plurality of substantially similar transistors, at least one transistor more distal from the well region having an adjusted structure as compared to a transistor more proximal to the well region such that the plurality of the substantially similar transistors have substantially the same electrical characteristics. 
     The adjusted structure may include at least one amongst: a gate width adjustment, a gate length adjustment, a contact size adjustment, the number of contacts adjustment, a distance adjustment between a gate and a contact, a metal length adjustment, a metal width adjustment, and a diffusion length adjustment. 
     The electrical characteristics may be at least one amongst: current flowing between a gate and a drain of each transistor, and gate threshold voltage of the transistor. 
     The electrical characteristics may be varied based upon at least one of well proximity effect and shallow trench isolation. 
     When one of the plurality of substantially similar transistors has less source-drain current than other transistors among the plurality of substantially similar transistors, a length of the transistor may be decreased or a width of the transistor may be increased. 
     The plurality of substantially similar transistors may include a first group transistors a first distance away from the well region and a second group transistors a second distance away from the well region, the second distance being different from the first distance. 
     The structure of the transistor more distal from the well region may be adjusted by analyzing the electrical characteristics of the transistor more distal from the well region and the transistor more proximal to the well region to determine whether a structural change is needed to provide a change in the electrical characteristics to the transistor more distal from the well region based upon a result of the analyzing, and upon determining that a structural change is needed, making the structural change. 
     The structure of the transistor more distal from the well region may be further adjusted by, upon determining that an electrical characteristic variation is not compensated for, repeat analyzing the electrical characteristics to determine whether a structural change is needed to provide a change in the electrical characteristics of the transistor more distal from the well region based upon a result of the analyzing, and upon determining that a structural change is needed, making the structural change. 
     According to an exemplary embodiment of the present inventive concept semiconductor device includes a first transistor and a second transistor. A structure of the first transistor is adjusted differently from a structure of the second transistor such that the first transistor and the second transistor have substantially the same electrical characteristics in view of the first transistor and the second transistor being affected by at least one of a well proximity effect and a shallow trench isolation effect. 
     The structure of the first transistor and the structure of the second transistor may be adjusted based upon distance between a neighboring well and a corresponding transistor. 
     The structure of the first transistor and the structure of the second transistor are adjusted based upon number of adjacent transistors and distances from the adjacent transistors. 
     The structure of the first transistor and the structure of the second transistor are adjusted by analyzing the electrical characteristics of the first transistor and the second transistor to determine whether a structural change is needed to provide a change in the electrical characteristics among the first transistor and the second transistor based upon a result of the analyzing, and upon determining that a structural change is needed, making the structural change. 
     The structure of the first transistor and the second transistor may be further adjusted by, upon determining that an electrical characteristic variation is not compensated for, repeat analyzing the electrical characteristics of the first transistor and the second transistor to determine whether a structural change is needed to provide a change in the electrical characteristics among the first transistor and the second transistor based upon a result of the analyzing, and upon determining that a structural change is needed, making the structural change. 
     According to an exemplary embodiment of the present inventive concept semiconductor device includes a plurality of transistors in a row. Each of the transistors in the row have a plurality of contacts. At least one transistor at end of the row has more contacts than the other transistors in the row. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present inventive concept will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a plan view of a semiconductor device according to an exemplary embodiment of the present inventive concept; 
         FIG. 2  illustrates transistors in a transistor array illustrated in  FIG. 1  according to an exemplary embodiment of the present inventive concept; 
         FIG. 3  illustrates transistors in the transistor array illustrated in  FIG. 1  according to an exemplary embodiment of the present inventive concept; and 
         FIG. 4  is a flowchart of a method of compensating for an electrical characteristic variation of a transistor array according to an exemplary embodiment of the present inventive concept. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present inventive concept now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like numbers refer to like elements throughout. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. 
       FIG. 1  is a plan view of a semiconductor device  10  according to an exemplary embodiment of the present inventive concept.  FIG. 2  illustrates transistors in the transistor array  15  illustrated in  FIG. 1 . Referring to  FIGS. 1 and 2 , the semiconductor device  10 , which may be implemented in an image sensor, a display driver, or a memory device, includes an N-well region  12  and the transistor array  15 . The N-well region  12  is formed in a P-type substrate by implanting N-type impurities into the P-type substrate. The N-well region  12  may be formed above a deep N-well region. Although it is not illustrated in  FIG. 1 , P-type (PMOS) transistors may be formed in the N-well region  12 . 
     The transistor array  15  is spaced from the N-well region  12  and includes a plurality of transistors (e.g., transistors T 1 , T 3 , T 5 , T 7 ). The plurality of transistors T 1 , T 3 , T 5 , T 7  may be N-type (NMOS) transistors. The transistors T 1 , T 3 , T 5 , T 7  may be cells that store data. The electrical characteristics of each of the transistors T 1 , T 3 , T 5 , T 7  included in the transistor array  15  may be varied by WPE or STI. The affected electrical characteristics may include at least one from amongst: current flowing between a gate and a drain of a transistor, and gate threshold voltage of the transistor. 
     For instance, when transistors in a first group  14  (hereinafter, referred to as first group transistors) are a first distance away from the N-well region  12  and transistors in a second group  16  (hereinafter, referred to as second group transistors) are a second distance away from the N-well region  12 , the second distance being greater than the first distance, are implemented by devices having substantially the same structure, the electrical characteristics of the first group transistors may be different from the electrical characteristics of the second group transistors due to the different distances away from the N-well region  12 , resulting in WPE. In addition, although each of the first group transistors have substantially the same structure, transistors TA, TB located at both ends of the first group  14  may have a different electrical characteristics than the other transistors in the first group  14  since the transistors TA, TB each has only one adjacent transistor, resulting in an STI effect. The impact of the WPE and/or STI effect on a transistor may be different depending on a type of the transistor or fabrication processes thereof. As for the WPE, the distance from a well predominately affects the characteristics of a transistor. As for the STI effect, the numbers of adjacent transistors and the distances from the adjacent transistors affect the characteristics of a transistor. Of course, the WPE and STI effect can be cumulative for transistors in locations affected by both WPE and STI. 
     One attempt to prevent the WPE and/or the STI effect, involves a configuration such that transistors have the same surroundings using a dummy transistor or a chip may be designed large. Even in this case, however, it is still difficult to maintain the characteristics of all transistors the same and an increase in a chip size may incur an increase in manufacturing cost. 
     According to an exemplary embodiment of the present inventive concept, one or more of the exemplary transistors T 1 , T 3 , T 5 , T 7  may be adjusted such that all of the transistors T 1 , T 3 , T 5 , T 7  have the same electrical characteristic. Here, the adjustment may be at least one amongst: gate width (i.e., a width of a gate), gate length (i.e., a length of the gate), contact size, the number of contacts, distance between the gate and a contact, metal length (i.e., a length of a metal), a metal width (i.e., a width of the metal), and diffusion length of a transistor. 
     For instance, when a transistor T 5 , among the transistors T 1 , T 3 , T 5 , T 7  has less source-drain current than the other transistors T 1 , T 3 , T 7 , a length W 5  of the transistor T 5  may be decreased or a width L 5  thereof may be increased. On the other hand, when transistor T 5  has greater source-drain current than the other transistors T 1 , T 3 , T 7 , the length W 5  of the transistor T 5  may be increased or the width L 5  thereof may be decreased. Similar adjustments can also be made to dimensions L 1 , W 1  of transistor T 1 , to dimensions L 3 , W 3  of transistor T 3  and to dimensions L 7 , W 7  of transistor T 7  as needed to fine tune their electrical characteristics. 
       FIG. 3  illustrates transistors in the transistor array  15  illustrated in  FIG. 1  according to an exemplary embodiment of the present inventive concept. Referring to  FIGS. 1 and 3 , the transistors TA, TB at both ends of the first group  14 , may have more contacts than the other transistors of the first group  14  such that the transistors TA, TB have the same electrical characteristics as the other transistors in the first group  14 , thereby preventing the STI effect. In addition, when the transistors TA, TB allow greater current to flow than the other transistors in the first group  14 , the contact size of the transistors TA, TB may be reduced to match the current flow electrical characteristic with that of the other transistors in first group  14 . 
     A semiconductor device according to an exemplary embodiment of the present inventive concept may include a transistor array and a neighboring P-well region. In such an exemplary embodiment, N-type (NMOS) transistors may be formed in the P-well region. The transistor array is spaced from the P-well region and includes a first transistor and a second transistor. The structure of the first transistor would be adjusted differently from that for the second transistor to enable the first and second transistors to have the same electrical characteristics, in view of at least one of a WPE and an STI effect. For example, the structure for the first and second transistors is adjusted according to the distance between a neighboring well and a corresponding transistor. 
       FIG. 4  is a flowchart of a method of compensating for electrical characteristics variations of a transistor array according to an exemplary embodiment of the present inventive concept. Referring to  FIGS. 1 ,  2 , and  4 , a testing apparatus or simulation apparatus (not shown) analyzes the electrical characteristics of each of the transistors T 1 , T 3 , T 5 , T 7  included in the transistor array  15  in operation S 10 . The operation S 10  may be performed using simulation tool or by testing DUT (device under test). The DUT may be a semiconductor device manufactured or selected for testing. 
     In operation S 20 , a design of a transistor (e.g., a transistor determined to need a structural change to provide a change in the electrical characteristic) among the transistors T 1 , T 3 , T 5 , T 7  may be changed based upon a result of the analysis of the operation S 10 . Here, the design may be at least one amongst: gate width, gate length, contact size, number of contacts, distance between a gate and a contact, metal length, metal width, and diffusion length of a transistor. The testing apparatus may analyze a surrounding layout and predict an electrical characteristic variation through simulation or measure the electrical characteristic variation in a chip made for a test. 
     The testing apparatus determines whether the transistor having a changed design has the same electrical characteristics as the other transistors, that is, whether the electrical characteristic variation of the transistor having the changed design is compensated for, after the changed design is applied in operation S 30 . When it is determined that an electrical characteristic variation is not compensated for, the testing apparatus repeats operation S 20  in conclusionary step S 32 . When it is determined that the electrical characteristic variation is compensated for, the testing apparatus confirms the change of design in conclusionary step S 35 . 
     According to an exemplary embodiment of the present inventive concept, an electrical characteristic variation of a transistor array is compensated for in a semiconductor device. 
     While the present inventive concept has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in forms and details may be made therein without departing from the spirit and scope of the present inventive concept as defined by the following claims.