Abstract:
A semiconductor device layout involving the following: arranging active regions of a plurality of transistors having at least more than one first and second electrodes disposed on a substrate; arranging a plurality of gates of transistors between more than one first and second electrodes of those active regions respectively by positioning at least more than one gates having predetermined width and length at a constant gap on the substrate; and arranging a plurality of dummy gates having predetermined width and length between a plurality of transistors (or between and outside transistors) at the same gap as that of the gates of transistors on the substrate, so that all the gates of transistors are arranged at a constant gap to minimize the variance of process deviations and accordingly reduce the difference of threshold voltage of transistors, thereby increasing reliability of the semiconductor device.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a layout method of a semiconductor device, and more particularly to the layout method of the semiconductor device to reduce the variance in process deviations which may occur during photo and etching processes. 
   BACKGROUND OF THE INVENTION 
   As progress is made in functions of a system to which a semiconductor device is applied, functions of high speed and high integration in the semiconductor device have become important to the semiconductor device. Accordingly, the layout method is as important as the circuit design and fabricating in response to the trend of high speed and high integration of the semiconductor device. 
   Some fabricating techniques for conventional semiconductor device, e.g., the uneven light reflection of the photo process and non-uniformity of the etching process, have brought about variances in process deviations at gates of transistors. 
   The process deviation depends upon the extent of differences in the length of the gates when measured before and after the photo process. Some process deviation is to be expected and is quite acceptable when it is uniform as among various gates. When it is not substantially uniform, i.e., if there is a great variance in the process deviation, the threshold voltage of the transistors fluctuates, thereby leading to malfunctions of the semiconductor device. In other words, the device may operate differently from what the designer intends it to. 
   Thus, great efforts have been made to minimize the variances in the process deviations which may occur in the course of manufacturing the semiconductor device. 
     FIG. 1  is a schematic diagram for explaining problems in the photo masking process, one of the manufacturing processes of a semiconductor device, comprising silicon  10 , silicon dioxide  12 , aluminum  14 , photo resist  16 , transparent glass  18 , and opaque layer  20 . 
   When the photo process is performed with the photo resist  16  being covered over the aluminum  14 , the aluminum  14  does not absorb light, instead, the aluminum reflects light as shown in FIG.  1 . Moreover, aluminum  14  is disposed in certain areas with a slant angle of θ, and thus reflects light obliquely on the slant surface, so that a photo pattern is not formed precisely as desired. 
   However, the layout method of the conventional semiconductor device is to arrange gates without a regular gap between gates. The result is that the slant angle of θ as between gates is not kept constant. As a result, the angle of reflecting light becomes different between gates, despite nearly identical photo masking and etching processes, to bring about a potentially wide variance in process deviations at the gates. 
     FIG. 2  is a schematic diagram for explaining a problem in the etching process, one of the manufacturing processes of the semiconductor device, comprising silicon  10  silicon dioxide  12  and photo resist  16 . 
   As shown in  FIG. 2 , etching of the oxide layer through open regions of photo resist  16  produces undercut of silicon dioxide  12 , as described by circles that increase in radius to the depth of silicon  10 . The greater the radius of the circle, the more deeply the photo resist  16  gets undercut. The extent to which the photo resist  16  may be undercut cannot be known until the photo resist  16  is removed. But the shape of the edge of the oxide layer pattern (as shown with dot lines in  FIG. 2 ) is a good indicator of the degree of undercut. In other words, the etching process is not uniform thereby producing undesirable process deviations. These etching process deviation also vary widely between gates having irregular gaps there between. 
   Therefore, there is a problem in the layout method of the conventional semiconductor device, in that the gates of transistors conventionally are arranged with irregular gaps. As a result, the gates reflect light differently in the photo process and do not uniformly etch the layer in the etching process, thereby increasing process variances. 
   In addition, as the layout method of neighboring circuits of the conventional semiconductor device is the same as that of the aforementioned general semiconductor device, the extent of process deviations gets bigger during photo and etching processes. 
   Especially, a sense amplifier of the semiconductor device is a circuit for amplifying and outputting a very small voltage difference of input signals, so that it is very sensitive. Therefore, it is important to correct differences of threshold voltages of transistors which make up the sense amplifier. However, as the layout method of the conventional sense amplifier is the same as that of the general semiconductor device, variances in the process deviations during the photo and etching processes increases. 
   In other words, the variance in process deviations of the etching process is added to that of the photo process, thereby increasing overall variances in the fabrication process. 
   As described above, the problems in those photo and etching processes have already been well known, so that it is necessary to minimize the variances in process deviations because the variances in process deviations caused at the gates during those processes may bring about changes in the threshold voltage of transistors. 
   SUMMARY OF THE INVENTION 
   It is an object to provide a layout method of a semiconductor device to minimize the variances in process deviations which may occur in photo and etching processes. 
   It is another object to provide a layout method of neighboring circuits of the semiconductor memory device to minimize the variances in process deviations which may occur in photo and etching processes. 
   It is also another object to provide a layout method of a sense amplifier of the semiconductor device to minimize the variances in process deviation which may occur in photo and etching processes. 
   In order to accomplish the aforementioned first object, there is provided a layout method of a semiconductor device comprising the steps of:
         arranging active regions of a plurality of transistors having at least more than one first and second electrodes disposed on a substrate;   arranging a plurality of gates of transistors between more than one first and second electrodes of those active regions respectively by positioning at least more than one gates having predetermined width and length at a constant gap on the substrate; and   arranging a plurality of dummy gates having predetermined width and length between a plurality of transistors or between and outside transistors at the same gap as that of the gates of transistors on the substrate.       

   In order to accomplish the aforementioned second object, there is provided a layout method for a neighboring circuit of the semiconductor device, the same method as that of the aforementioned semiconductor device. 
   In order to accomplish the aforementioned third object, there is provided a layout method for a sense amplifier of a semiconductor device having input transistors for data and control signals in accordance with the aforementioned layout method of a semiconductor device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram for explaining a problem in a photo process. 
       FIG. 2  is a schematic diagram for explaining a problem in an etching process. 
       FIG. 3  is a block diagram illustrating the layout of an embodiment of a conventional semiconductor memory device. 
       FIG. 4  is a circuit diagram of a conventional sense amplifier. 
       FIG. 5  illustrates the layout of sources, drains and gates of the transistors which make up the sense amplifier. 
       FIG. 6  illustrates contacts formed in the layout shown in FIG.  5 . 
       FIG. 7  illustrates metals formed at the contacts shown in FIG.  6 . 
       FIG. 8  illustrates contacts formed at the metals shown in FIG.  7 . 
       FIG. 9  illustrates metal lines formed along with the contacts shown in FIG.  8 . 
       FIG. 10  illustrates metals for applying power voltage and grounding voltage to the metal lines. 
       FIG. 11  is a diagram for illustrating the layout of the sense amplifier shown in  FIG. 4  in accordance with a layout method of an embodiment of the present invention. 
       FIG. 12  illustrates a layout method of the sense amplifier as shown in  FIG. 4  in accordance with an embodiment of the present invention. 
       FIG. 13  illustrates contacts formed in the layout shown in FIG.  12 . 
       FIG. 14  illustrates metals formed at the contacts shown in FIG.  13 . 
       FIG. 15  illustrates contacts formed at the metals shown in FIG.  14 . 
       FIG. 16  illustrates metal lines formed along with the contacts shown in FIG.  15 . 
       FIG. 17  illustrates a power voltage applying line and a grounding voltage applying line. 
       FIG. 18  is a graph illustrating variances in process deviations in accordance with the conventional layout method and the layout method of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 3  is a block diagram illustrating the layout of an embodiment of a conventional semiconductor memory device, comprising memory cell array blocks  30 - 1 ,  30 . 2  . . .  30   n , block row decoders  32 - 1 ,  32 - 2 , . . .  32 - n , a bit line pre charge circuit  34 , a block selector  36 , a column selection gate  38 , a sense amplifier/light driver  40 , a column decoder  42 , a wide zone row decoder  44 , a column address input buffer  46 , a data input/output buffer  48 , a control signal input buffer  50  and a row address input buffer  52 . 
   The layout of the prior art semiconductor memory device includes the memory cell array  30  and neighboring circuits of controlling data input/output to the memory cell array  30 . 
   However, there is a problem in the conventional layout method of neighboring circuits of the semiconductor device in that the transistor gates of the neighboring circuits have been arranged at an irregular gap in the conventional layout method of the semiconductor device, thereby increasing variances in process deviations at the transistor gates in the course of the photo and etching processes. 
   In addition, there is another problem in the conventional layout method of the semiconductor device in that the increase in variances in process deviations as such has caused the semiconductor device not to operate properly as the designer intends it to. 
   Now, the conventional layout method of the semiconductor memory device and that of the present invention will be compared and explained by using the sense amplifier among the neighboring circuits. 
     FIG. 4  is a circuit diagram for illustrating the structure of the conventional sense amplifier, comprising PMOS transistors P 1 , P 2 , P 3  and NMOS transistors N 1 , N 2 , N 3 , N 4 . Also shown in  FIG. 4  are control signal line CON input signal D, input signal DB and output signal OUT. 
     FIGS. 5 through 10  illustrate the layout of the sense amplifiers shown in  FIG. 4  in accordance with the conventional layout method. 
     FIG. 5  illustrates the layout of sources, drains and gates of the transistors which make up the sense amplifier. 
   In  FIG. 5 , the sources, drains and gates of the PMOS transistors P 1 , P 2 , P 3  are respectively denoted with P 1 S, P 2 S, P 3 S, P 1 D, P 2 D, P 3 D, and P 1 G, P 2 G, P 3 G, while the sources, drains and gates of the NMOS transistors N 1 , N 2 , N 3 , N 4  are respectively denoted with N 1 S, N 2 S, N 3 S, N 4 S, N 1 D, N 2 D, N 3 D, N 4 D and N 1 G, N 2 G, N 3 G, N 4 G. Reference numerals  60 ,  66  are bias lines while reference numerals  62 ,  64  are power lines. In addition, symbols W 1 , W 2  and L are respectively width and length of the transistors. 
   First of all, the gates of the PMOS transistors P 1 , P 2 , P 3  and those of the NMOS transistors N 1 , N 2 , N 3 , N 4  are divided from one common terminal into two and, then, separately arranged. The width W 1  of the gates of the NMOS transistors N 1 , N 2  is smaller than that W 2  of the gates of the PMOS transistors P 1 , P 2 , P 3  and those of the NMOS transistors N 3 , N 4 . On the other hand, the length L of the gates of the PMOS transistors P 1 , P 2 , P 3  is the same as that of the NMOS transistors N 1 , N 2 , N 3 , N 4 . 
   According to the conventional layout method shown in  FIG. 5 , gaps (a) between separate gates of all transistors are constant, while gaps (b, c, d) between the other gates of those transistors are inconstant. Therefore, uneven light reflection in the photo process and non-uniformity of the etching process result in increase in the variances in process deviations. 
     FIG. 6  illustrates contacts formed in the layout shown in  FIG. 5 , that is, the contacts being formed on the sources, drains, a gate common terminal, power lines, and bias lines of the PMOS transistors P 1 , P 2 , P 3  and NMOS transistors N 1 , N 2 , N 3 , N 4 . In  FIG. 6  the portions  70  marked with squares indicate where the contacts are formed. 
     FIG. 7  illustrates metals ME 1  formed at the contacts shown in  FIG. 6 , that is, the metals being formed all over the contacts  70  and power lines  60 ,  66  (not visible in FIG.  7 ). In  FIG. 7 , the portions marked with horizontally slanting lines indicate where the metals are formed. 
     FIG. 8  illustrates contacts formed at the metals shown in  FIG. 7 , and the portions  72  marked with dark squares indicate where the contacts are formed. 
     FIG. 9  illustrates metal lines formed along with the contacts shown in  FIG. 8 , and the portions ME 2  marked with vertically slanting lines are where the metals are formed. Thus, the gates, drains, sources of the transistors of the sense amplifier shown in  FIG. 4  are connected by metals. In  FIG. 9 , the metal lines  74 ,  76 ,  78 ,  80  respectively indicate control signal CON applying line, input signal D applying line, other input signal DB applying line and gate connecting line of the PMOS transistor P 1  and NMOS transistors N 1 , N 2 . 
     FIG. 10  illustrates metals ME 3  for applying power voltage and grounding voltage to the metal lines ME 2 . The striped portions, marked with dots, indicate where the metals ME 3  are formed, while the portions  82  marked with lattices indicate where VIA contacts are formed. The portions  82  and metals ME 3  are connected to apply the power voltage and grounding voltage. 
     FIG. 5  has shown the problem in the conventional layout method of the semiconductor memory device. The diagrams shown in  FIGS. 6 through 10  have briefly illustrated the layout of the sense amplifier shown in FIG.  4 . The inconstancy, or non-uniformity, of gaps on the semiconductor are described and illustrated in  FIG. 5  at a, b, and d, and are clear from the non-uniformity of feature column spacing in  FIGS. 6-10 . 
   On the other hand,  FIG. 11  illustrates a layout of a semiconductor memory device in accordance with an embodiment of the present invention. Dummy gates DG 1 , DG 2  having the same gap (a) as gates divided in the layout shown in  FIG. 5  are additionally assembled at the space among gates of the transistors which make up the sense amplifier. 
   A common line connecting the dummy gates DG 1 , DG 2  is shown in  FIG. 11 , but it can be properly divided and installed. 
   The dummy gates thus constructed do not exert any influence upon operations of the circuits of the sense amplifier, but advantageously exert a beneficial influence on the semiconductor fabrication processes. 
   After all the gates are completely disposed as previously described in  FIG. 11 , the rest of the layout of the semiconductor device can be arranged according to the conventional or any other layout method. 
   In other words, according to the layout method of the sense amplifiers of the present invention shown in  FIG. 11 , there are the gates which perform actual operations of the sense amplifier while the dummy gates are positioned between or outside those actually operating gates without making any influence on the actual operations of the sense amplifier. 
   However, the installation of the dummy gates minimizes the variances in the process deviations which may occur in the photo and etching processes for the production of the semiconductor device. 
     FIGS. 12 through 17  illustrate a layout method of the sense amplifier shown in  FIG. 4  in accordance with another embodiment of the present invention. 
   In  FIG. 12 , the sources, drains and gates of the PMOS transistors P 1 , P 2 , P 3  are respectively denoted with P 1 S, P 2 S, P 3 S, P 1 D, P 2 D, P 3 D, and P 1 G, P 2 G, P 3 G, while the sources, drains and gates of the NMOS transistors N 1 , N 2 , N 3 , N 4  are respectively denoted with N 1 S, N 2 S, N 3 S, N 4 S, N 1 D, N 2 D, N 3 D, N 4 D and N 1 G, N 2 G, N 3 G, N 4 G. Reference numerals  60 ,  66  are bias lines while reference numerals  62 ,  64  are power lines. In addition, symbols DG 1 , DG 2 , DG 3 , DG 4 , DG 5 , DG 6  respectively indicate dummy gates formed at the same gap (a) as that of the gates divided between and outside the transistors. 
   First of all, gates of the PMOS transistors P 1 , P 2 , P 3  and those of the NMOS transistors N 3 , N 4  are divided from one common terminal into four and separately arranged. As a result, the sources and drains of the transistors are respectively divided into three and two for the arrangement. 
   Symbol L indicates the length of the gates of the transistors P 1 , P 2 , P 3 , N 1 , N 2 , N 3 , N 4  and that of the dummy gates DG 1 , DG 2 , DG 3 , DG 4 , DG 5 , DG 6 . On the other hand, symbols W 2 / 2 , W 1 / 2 , W 3 , W 5 , and W 4  respectively indicate the width of the gates of the PMOS transistors P 1 , P 2 , P 3  and the NMOS transistors N 3 , N 4 , that of the gates of the NMOS transistors N 1 , N 2 , that of the dummy gates DG 5 , DG 6 , that of the dummy gates DG 1 , DG 4 , and that of the dummy gates DG 2 , DG 3 . Dummy gate widths W 3  and W 4  may be seen to vary, as shown, depending upon the placement and gate widths of PMOS transistors P 1 , P 2 , P 3  and NMOS transistors N 1 , N 2 , N 3 , N 4 . 
   As shown in  FIG. 12 , the gap (a) between the divided gates which compose a single transistor is the same as that between the various transistors. 
   There is a difference between the layouts shown in  FIGS. 5 and 12  in additional arrangement of dummy gates DG 1 , DG 2 , DG 3 , DG 4 , DG 5 , DG 6 . 
   Although one gate has been divided into four as in the aforementioned embodiment, it will be understood by those skilled in the art that a gate may be divided into more than four. 
   In the present invention, the gates are arranged at a constant gap (a) as shown in  FIG. 12  to thereby reduce the variances in process deviations. 
     FIG. 13  illustrates contacts formed in the layout shown in  FIG. 12 , that is, the contacts being formed on the sources, drains, gate common terminals and bias lines of the PMOS transistors P 1 , P 2 , P 3  and NMOS transistors N 1 , N 2 , N 3 , N 4 . In  FIG. 13  the portions  90  marked with squares indicate where the contacts are formed. 
     FIG. 14  illustrates metals ME 1  formed at the contacts shown in  FIG. 13 , that is, the metals being formed all over the contacts  90  and power lines  60 ,  66 . In  FIG. 14 , the portions ME 1  marked with horizontally slanting lines indicate where the metals are formed. 
     FIG. 15  illustrates contacts formed at the metals ME 1  shown in  FIG. 14 , and the portions  92  marked with dark squares indicate where the contacts are formed. 
     FIG. 16  illustrates metal lines formed along with the contacts shown in  FIG. 15 , and the portions ME 2  marked with vertically slanting lines are where the metals are formed. Thus, the transistors of the sense amplifier shown in  FIG. 4  are connected with metals. The metal lines  94 ,  96 ,  98 ,  100  respectively indicate a control signal CON applying line, a data D input line, another data DB input line and an output signal OUT generating line. 
   A power voltage applying line  102  and a grounding voltage applying line  104  are id illustrated in FIG.  17 . 
     FIG. 12  illustrates the layout method of the sense amplifiers in accordance with another embodiment of the present invention. However, the layout shown in  FIGS. 13 through 17  may be in a different arrangement. The drawings shown in  FIGS. 13 through 17  here are to show an actual example of the sense amplifier in accordance with the present invention. 
   It is a unique characteristic of the present invention that the dummy gates having no influence upon actual operations of transistors are arranged between and outside the gates formed for actual operations of transistors. In accordance with the invention, all of those divided gates are arranged at a constant gap, thereby minimizing the variances in process deviations that may occur in the photo and etching processes. 
   In the aforementioned embodiment, the dummy gates are arranged between and outside the gates of transistors. However, it may be also possible for the dummy gates to be arranged only between the gates of transistors. 
     FIG. 18  is a graph for illustrating variances of the process deviations in case layouts of the semiconductor device are made in accordance with the conventional method or that of the present invention. The horizontal axis shows the number of measured gates while the vertical axis shows the process deviations (that is, the length gm of the gates respectively measured). 
   After the gates of transistors of the semiconductor device are manufactured in accordance with a conventional layout method or that of the present invention, the process deviations of those seventeen gates are measured. As a result, it has been found that the gates of the transistors arranged in the layout method of the present invention shows a smaller variances in process deviations than that of the conventional layout method. The maximum, minimum and average values of process deviations and its variance are shown in the following Table. 
   
     
       
             
             
             
           
         
             
                 
             
             
                 
                 
               method of the 
             
             
               unit (μm) 
               conventional method 
               present invention 
             
             
                 
             
           
           
             
               maximum process deviation 
               0.234 μm 
               0.221 μm 
             
             
               minimum process deviation 
               0.226 μm 
               0.218 μm 
             
             
               average process deviation 
               0.233 μm 
               0.223 μm 
             
             
               variance in deviation (μm) 
               0.008 μm 
               0.003 μm 
             
             
                 
             
           
        
       
     
   
   As shown in Table, the variances in process deviations has been decreased by as much as 0.005 m when the layout method of the present invention is applied instead of the conventional layout method. 
   As shown in the aforementioned embodiment of the present invention, the layout method of the sense amplifier of the semiconductor device has been explained. Also, the layout method of the present invention may be applied to the semiconductor device or the neighboring circuits of the semiconductor memory device, thereby minimizing the variances in process deviations. 
   Furthermore, the transistors to which the data signals of the sense amplifier are input and the transistors to which the enable signals of the sense amplifier are input, that is, the PMOS transistors P 1 , P 2 , P 3  and the NMOS transistors N 1 , N 2 , N 3 , N 4  of the circuit shown in  FIG. 4 , are arranged in accordance with the layout method of the present invention, thereby m 9  reducing the variances in process deviations and difference of the threshold voltage. 
   According to the layout method of the present invention, all the gates of the transistors which compose of circuits of the semiconductor device or other neighboring circuits of the semiconductor memory device are arranged at a constant gap by additionally installing dummy gates. 
   The dummy gates are arranged to keep all those gates at a constant gap between and outside (or only between) the gates which have been already formed for actual operations, thereby minimizing the variances in process deviations which may occur in the photo and etching processes. 
   Therefore, there is an advantage in the layout method of the present invention in that the dummy gates are additionally installed to arrange the gates of the transistors composing of the neighboring circuits at a constant gap, thereby minimizing the variances in process deviations. 
   In addition, there is another advantage in the layout method of the present invention in that the variances in process deviations is minimized to reduce the difference in the threshold voltage, thereby improving reliability of the semiconductor memory device. 
   Having illustrated and described the principles of my invention in a preferred embodiment thereof, it should be readily apparent to those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. I claim all modifications coming within the spirit and scope of the accompanying claims.