Abstract:
The present invention provides an integrated circuit including N1 NAND flash array segments with N2 local bit lines, N1 intra array multiplexers and N2/2 global bit lines. Further, the present invention provides a method of producing an integrated circuit including N1 NAND flash array segments with N2 local bit lines, N1 intra array multiplexers and N2/2 global bit lines.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a method of forming an integrated circuit with NAND flash array segments and intra array multiplexers and to a corresponding integrated circuit with NAND flash array segments and intra array multiplexers. 
         [0003]    2. Related Art 
         [0004]    A flash memory is a non-volatile computer memory that can be electrically erased and reprogrammed. E.g. each flash memory may store information in an array of floating-gate transistors, often called cells. One example for a flash memory is a NAND memory which uses tunnel injection for writing and tunnel release for erasing. 
         [0005]    As manufactures increase the density of data storage in flash devices, the size of an individual memory cell is shrinking. Also, the distance between two adjacent memory cells decreases. Therefore, it is a challenge to provide a high cell density as well as a sufficient stability of its components. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0006]    The invention can be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. 
           [0007]      FIG. 1   a  illustrates a schematic plain view of an embodiment of an integrated circuit and  FIG. 1   b  shows a schematic cross section of the integrated circuit; 
           [0008]      FIG. 2  shows a flow chart of a first embodiment of the method of forming an integrated circuit; 
           [0009]      FIG. 3  illustrates a schematic plain view of an embodiment of a brute force double patterning process of forming active areas; 
           [0010]      FIG. 4  illustrates a schematic plain view of an embodiment of a brute force double patterning process of forming contacts; 
           [0011]      FIGS. 5   a  and  5   b  illustrate schematic plain views of embodiments of a pitchfrag double patterning process of forming active areas; 
           [0012]      FIGS. 6   a  and  6   b  illustrate schematic plain views of further embodiments of a pitchfrag double patterning process of forming active areas using a trim mask; and 
           [0013]      FIGS. 7   a  and  7   b  illustrate alternative layouts with a joint of a source line and an inhibit voltage supply; and 
           [0014]      FIG. 8  shows a flow chart of a second embodiment of the method of forming an integrated circuit. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration one or more specific implementations in which the invention may be practiced. It is to be understood that other implementations may be utilized and structural changes may be made without departing from the scope of this invention. 
         [0016]      FIG. 1   a  illustrates a schematic plain view of an embodiment of an integrated circuit  10  and  FIG. 1   b  shows a schematic cross section of the integrated circuit  10 . 
         [0017]    The integrated circuit  10  includes a number N1 of NAND flash array segments  20  and N1 intra array multiplexers  31 ,  32 , each NAND flash array segment  20  is surrounded by a first and a second half  31 ,  32  of the corresponding multiplexer. Reference sign  31  designates the first half or left half of the corresponding multiplexer and reference sign  32  designates the second half or right half of the corresponding multiplexer. 
         [0018]    Each NAND flash array segment  20  has a number N2 of rows or active areas  41 - 43 . Further, the active areas  51 - 56  of the intra array multiplexers  31 ,  32  may be formed by double patterning and may have a 3F width W 1  and a 1F pitch P 1 . Each row  41 - 43  or active area of the corresponding NAND flash array segment  20  has a local bit line  61 - 64  connected. The rows  41 - 43  may be formed by double patterning and may have a 1F width W 2  and a 1F pitch P 2  to each other. 
         [0019]    The integrated circuit  10  has global bit lines  71 - 73  and local bit lines  61 - 64 . At least one global bit line  71 - 73  is connected to at least two local bit line  61 - 64 . Preferably, a respective global bit line  71 - 73  may be connected to at least two associated or neighbouring local bit lines  61 - 64 . 
         [0020]    Preferably, the integrated circuit  10  further includes a number N4 of global bit lines, in particular with N4=½N2, the i th  global bit line  71 - 73  is able to be connected to the (2i−1) th  local bit line  61 ,  63  and the (2i) th  local bit line  62 ,  64 , iε[1, . . . , N4], the global bit lines  71 - 73  are formed by double patterning and have a 2F width W 3  and a 2F pitch P 3  to each other. 
         [0021]    That NAND flash array segment  20  forms a NAND flash array. In contrast to conventional NAND flash array segments, the total number of bit lines connected to the periphery of the NAND flash array is decreased, because not every row of the corresponding segment is coupled by a bit line connected to said periphery. In contrast, only the global bit lines  71 - 73  may be connected to the periphery, said global bit lines multiplexed to the local bit lines  61 - 64  coupling a respective row or string. Said multiplexing within said integrated circuit  10  or NAND flash array is provided by means of said N1 intra array multiplexers. The phrase intra within intra array multiplexer indicates that the intra array multiplexers are incorporated or integrated within the integrated circuit  10 . 
         [0022]    That NAND flash array may have 32 to 128 word lines or rows forming a string or NAND string. Said string has a respective select transistor at its beginning and at its end. On the one end, said string is connected to source, and on the other end it is connected to bit lines. Said string structure recurs and, therefore, forms a NAND flash array segment  20 . After a predefined number of said strings, e.g. several hundreds or thousands, there is arranged an intra array multiplexer. 
         [0023]    Further, each row  41 - 43  can have a number N3 of NAND strings  81 ,  82 , wherein the corresponding local bit line  61 - 64  of the respective rows  41 - 43  is connected to the number N3 of NAND strings  81 ,  82 . To increase the legibility of  FIGS. 1   a  and  1   b  not all elements shown are comprised with reference signs. 
         [0024]    Further, the first half  31  of the intra array multiplexer can have a first and a second transistor  91 ,  92  for activating the (2i−1) th  local bit line  41 ,  43 , respectively. The first transistor  91  is able to connect the i th  global bit line  71  with the (2i−1) th  local bit line  41 , respectively. E.g. the first transistor  91  is able to connect the first global bit line  71  with the first local bit line  41 . 
         [0025]    Further, the second transistor  92  can be able to connect the i th  global bit line  71  with an inhibit voltage  101 , respectively. E.g. the second transistor  92  is able to connect the first global bit line  71  with the inhibit voltage supply  101 . 
         [0026]    The second half  32  of the multiplexer can have a third and a fourth transistor  93 ,  94  for activating the (2i) th  local bit line  42 ,  44 , respectively. In particular, the third transistor  93  is able to connect the (2i) th  local bit line  62  to an inhibit voltage supply  102 , respectively. E.g. the third transistor  93  can be able to connect the second local bit line  42  with the inhibit voltage supply  102 . 
         [0027]    Furthermore, the fourth transistor  94  may be able to connect the i th  global bit line  91  with the (2i) th  local bit line  62 , respectively. E.g. the fourth transistor  94  can be able to connect the first global bit line  71  with the second local bit line  62 . 
         [0028]    The global bit lines  71 - 73  can be arranged over all N1 flash array segments  20 , wherein the local bit lines  61 - 63  are arranged over the corresponding NAND flash array segment  20 . 
         [0029]    The first half  31  of the intra array multiplexer can have N4 global bit line contacts  111 - 113 , wherein the i th  global bit line contact  111  can connect the i th  global bit line  71  with the first transistor  91 , respectively E.g. the first global bit line contact  111  can connect the first global bit line  71  with the first transistor  91 . 
         [0030]    The first half  31  of the intra array multiplexer can have N4 local bit line contacts  114 - 116 , wherein the i th  local bit line contact  114  can connect the (2i−1) th  local bit line  61  with the first transistor  91 , respectively. E.g. the first local bit line contact  114  can connect the first local bit line  61  with the first transistor  91 . 
         [0031]    Further, the second half  32  of the intra array multiplexer can have N4 global bit line contacts  121 - 123 , wherein the j th  global bit line contact  121 , jε[1, . . . , N4], can connect the i th  global bit line  71  with the fourth transistor  94 , respectively. E.g. the first global bit line contact  121  can connect the first global bit line  71  with the fourth transistor  94 . 
         [0032]    Furthermore, the second half  32  of the intra array multiplexer can have a number N4 of local bit line contacts  124 - 126 , wherein the i th  local bit line contact  124  can connect the (2i) th  local bit line  62  with the fourth transistor  93 , respectively. E.g. the first local bit line contact  124  can connect the second local bit line  62  with the fourth transistor  93 . 
         [0033]    Also, contacts  133  can be provided over each NAND string  81 ,  82  for connecting a corresponding bit line (not shown) with the underlying active area  41 . 
         [0034]    A NAND flash array segment  20  comprises a source line  129 , a ground select transistor  130 , a number of word lines  131  and a bit line select transistor  132 . Without loss of generality, this is shown in  FIG. 1   b  for the first row of the integrated circuit. 
         [0035]      FIG. 2  shows a flow chart of an embodiment of a method of forming an integrated circuit  10 . In the following, the method of forming an integrated circuit is explained with reference to the block diagram of  FIG. 2  referring to the schematic plain view of  FIG. 1   a  and the schematic cross section of  FIG. 1   b.    
         [0036]    The embodiment of the method of forming an integrated circuit  10  has the method steps S 1 -S 4  as shown in  FIG. 2 : 
       Step S 1 : 
       [0037]    Active areas  41 - 43  for a number N1 of NAND flash segments  20  are formed by double patterning respectively a double patterning process, wherein each NAND flash segment  20  has a number N2 of rows  41 - 43  with a 1F width W 2  and a 1F pitch P 2  to each other. 
       Step S 2 : 
       [0038]    Active areas  51 - 56  for a number N1 of intra array multiplexers  31 ,  32  are formed by double patterning respectively a double patterning process, wherein the active areas  51 - 56  have a 3F width W 1  and a 1F pitch P 1  to each other 
       Step S 3 : 
       [0039]    A local bit line  61 - 63  is formed over each row  41 - 43  respectively, each local bit line having a 1F width W 2  and a 1F pitch P 2  to each other. 
       Step S 4 : 
       [0040]    A number N4 of global bit lines  71 - 73 , 
         [0000]    
       
         
           
             
               
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         [0000]    is formed with a 2F width W 3  and a 2F pitch P 3  to each other by double patterning respectively a double patterning process such that a i th  global bit line  71 - 73  is able to be connected to a (2i−1) th  local bit line  61 ,  63  and a (2i) th  local bit line, iε[1, . . . , N4]. E.g. the first global bit line  71  is able to be connected to the first local bit line  61  and the second local bit line  62 . Further, the second global bit line  72  can be able to be connected to the third local bit line  63  and the fourth local bit line  64 . 
         [0041]    Further to method steps S 1 -S 4 , the method of forming an integrated circuit  10  can have the following embodiments: 
         [0042]    Each NAND flash array segment  20  can be surrounded by the first and second halves  31 ,  32  of the corresponding intra array multiplexer. Further, a number N3 of NAND strings  81 ,  82  can be formed within each row  41 - 43 , wherein the formed N3 NAND strings  81 ,  82  can be connected with the corresponding local bit lines  61 - 61 . E.g. the first NAND string  81  and the second NAND string  82  within the first row  41  can be connected to the first local bit line  61 . 
         [0043]    Further, the first half  31  of the intra array multiplexer can be provided with a first and a second transistor  91 ,  92  for activating the (2i−1) th  local bit line  41 ,  43 , respectively. In this regard, the first transistor  91  can be formed to be able to connect the i th  global bit line  71  with the (2i−1) th  local bit line  41 , respectively. E.g. the transistor  91  can be able to connect the first global bit line  71  with the first local bit line  41 . 
         [0044]    The second transistor  92  can be formed to be able to connect the (2i−1) th  global bit line  71  with an inhibit voltage supply  101 , respectively. E.g. the second transistor  92  is formed to be able to connect the first global bit line  71  with the inhibit voltage supply  101 . 
         [0045]    The second half  32  of the intra array multiplexer can be provided with a third and a fourth transistor  93 ,  94  for activating the (2i) th  local bit line  42 ,  44 , respectively the even-numbered local bit line  42 ,  44 , respectively. In this regard, the third transistor  93  can be formed to be able to connect the (2i) th  local bit line  62  with an inhibit voltage supply  102 , respectively. E.g. the third transistor  93  can be formed to be able to connect the second local bit line  62  with the inhibit voltage supply  102 . 
         [0046]    Further, the fourth transistor  94  can be formed to be able to connect the i th  global bit line  71  with the (2i) th  local bit line  62 , respectively. E.g. the fourth transistor  94  can be formed to connect the first global bit line  71  with the second local bit line  62 . 
         [0047]    The global bit lines  71 - 73  can be arranged over all N1 NAND flash array segments  20 , wherein the local bit lines  61 - 63  can be arranged over only the corresponding NAND flash array segments. E.g. the first local bit line  61  is arranged only over the corresponding NAND flash array segment  20 . Further, the integrated circuit  10  can be formed as a memory device for a memory circuit. 
         [0048]    Further, the active areas  41 - 43  for the N1 NAND flash segments  20  and the active areas  51 - 56  for the N1 intra array multiplexers  31 ,  32  can be formed with one double patterning process at the same time or simultaneously. 
         [0049]    Also, the first half  31  of the intra array multiplexer can be provided with N4 global bit line contacts  111 - 113 , wherein the i th  global bit line contact  111  can connect the i th  global bit line  71  with the first transistor  91 , respectively. E.g. the first global bit line contact  111  can connect the first global bit line  71  with the first transistor  91 . 
         [0050]    Further, the first half  31  of the intra array multiplexer can be provided with N4 local bit line contacts  114 - 116 , wherein the i th  local bit line contact  114  can connect the (2i−1) th  local bit line with the first transistor  91 , respectively. That means that the N4 local bit line contacts  114 - 116  can connect the odd-numbered (by means of parameter i) bit lines  61 ,  63 . E.g. the first local bit line contact  114  can connect the first local bit line  61  with the first transistor  91 . 
         [0051]    Further, the second half  32  of the intra array multiplexer can be provided with a number N4 of global bit line contacts  121 - 123 , the j th  global bit line contact, jε[1, . . . , N4], can connect the i th  global bit line  71  with the fourth transistor  94 , respectively. E.g. the first global bit line contact  121  can connect the first global bit line  71  with the fourth transistor  94 . 
         [0052]    Further, the second half  32  of the intra array multiplexer can be provided with a number N4 of local bit line contacts  124 - 126 , wherein the i th  local bit line contact  124  can connect the (2i) th  local bit line  62  with the fourth transistor  94 , respectively. E.g. the first local bit line contact  124  can connect the second local bit line  62  with the fourth transistor  94 . 
         [0053]    Furthermore, the first half  31  of the intra array multiplexer can be provided with N4 local bit line contacts  114 - 116 , the i th  bit line contact  114  can connect the (2i−1) th  local bit line  61  with the first transistor  91 , the second half  32  of the intra array multiplexer can be provided with N4 local bit line contacts  124 - 126 , the i th  local bit line contact  124  can connect the (2i) th  local bit line  62  with the fourth transistor  94 , wherein the local bit line contacts  114 - 116 ;  124 - 126  are structured as stackered CB chain by lithography or by double patterning. 
         [0054]    Further, the N4 global bit line contacts  111 - 113  at the first half  31  of the intra array multiplexer and the N4 global bit line contacts  121 - 123  at the second half  32  of the intra array multiplexer can be formed by a double patterning process, wherein the global bit line contacts  111 - 113 ;  121 - 123  can be landed on a contact  127 ,  128  processed within a local bit line  114 - 116 ;  124 - 126  structuring processor on the respective local bit line  61 - 64 . 
         [0055]      FIG. 3  illustrates a schematic plain view of an embodiment of the brute force double patterning process of forming active areas  51 - 56  of a first half  31  of an intra array multiplexer and active areas  41 - 49  of an NAND array segment  20 . In a first sub-step of the brute force double patterning process, the active areas  51 ,  53 ,  58  and  41 ,  43 ,  45 ,  47 ,  49  can be formed simultaneously. In a second sub-step of the brute force double patterning process, the active areas  52 ,  57  and  42 ,  44 ,  46  and  48  can be formed simultaneously. 
         [0056]      FIG. 4  illustrates a schematic plain view of an embodiment of the brute force double patterning process of forming contacts  201 - 208  for connecting a corresponding bit line (not shown) with the underlying active area  41 - 48  and local bit line contacts  301 ,  303 ,  305 ,  307  of the active areas  54 ,  55 ,  56 ,  59  of the second half  32  of the intra array multiplexer. 
         [0057]    In a first sub-step of the brute force double patterning process, the contacts with an odd number, namely  201 ,  203 ,  205 ,  207 ,  301 ,  303 ,  305  and  307 , are formed simultaneously. 
         [0058]    In a second sub-step, the contacts with an even number, namely  202 ,  204 ,  206  and  208 , are formed simultaneously. 
         [0059]    The sequence of the first and second sub-steps of the brute force double patterning process as described with reference to  FIGS. 3 and 4  can be changed. 
         [0060]      FIGS. 5   a  and  5   b  show schematic plain views of embodiments of a pitchfrag double patterning process of forming active areas  51 - 55  of the first half  31  of an intra array multiplexer and active areas  41 - 49  of a NAND flash array segment  20 . 
         [0061]    Before processing the pitchfrag double patterning, an active area  400  is provided which forms the basis for the intra array multiplexers  31 ,  32  and the NAND flash array  27 . 
         [0062]    Without loss of generality, the  FIGS. 5   a  and  5   b  show only the first half  31  of one intra array multiplexer and one NAND flash array segment  20 . 
         [0063]    After providing the active area  400 , carrier layers  401  used as a spacer for building an isolation area for the active areas are processed. Subsequently to the processing of the carrier layers  401 , spacer layers  402  are processed on the respective carrier layers  401 . By means of the spacer layers  402  isolation areas between neighbouring active areas of the first half  31  of the intra array multiplexer and the NAND flash array segment  20  can be processed. 
         [0064]    Alternatively for dividing the first half  31  of the intra array multiplexer and the NAND flash array segment  20  as depicted in  FIG. 5   a , a trim mask  403  as shown in  FIG. 5   b  can be used. The trim mask may be a hard mask. 
         [0065]    In an analogous way, the  FIGS. 6   a  and  6   b  show schematic plain view of embodiments of a pitchfrag double patterning process of forming contacts  501 - 516 . 
         [0066]    Further,  FIGS. 6   a  and  6   b  show the use of a CB mask  600  for defining the length of the contacts  501 - 516 . 
         [0067]    As an alternative to the embodiment of  FIG. 5   a , the  FIGS. 7   a  and  7   b  show alternative layouts for an integrated circuit as shown in  FIGS. 1   a  and  1   b  with a joint of source line  129  and inhibit voltage supply  101  processed by a pitchfrag double patterning process. 
         [0068]      FIG. 8  shows a flow chart of a second embodiment of a method of forming an integrated circuit  10 . In the following, the method of forming an integrated circuit is explained with reference to the block diagram of  FIG. 8  referring to the schematic plain view of  FIG. 1   a  and the schematic cross section of  FIG. 1   b.    
         [0069]    The embodiment of the method of forming an integrated circuit  10  has the method steps T 1 -T 4  as shown in  FIG. 8 : 
       Step T 1 : 
       [0070]    Active areas  41 - 43  for a number N1 of NAND flash segments  20  are formed, wherein each NAND flash segment  20  has a number N2 of rows  41 - 43  with a 1F width W 2  and a 1F pitch P 2  to each other. 
       Step T 2 : 
       [0071]    Active areas  51 - 56  for a number N1 of intra array multiplexers  31 ,  32  are formed, wherein the active areas  51 - 56  have width W 1  greater than 2F and a pitch P 1  to each other smaller than 2F. 
       Step T 3 : 
       [0072]    A local bit line  61 - 63  is formed over each row  41 - 43  respectively, each local bit line having a 1F width W 2  and a 1F pitch P 2  to each other. 
       Step T 4 : 
       [0073]    A number N4 of global bit lines  71 - 73 , 
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         [0000]    is formed with a 2F width W 3  and a 2F pitch P 3  to each other such that a i th  global bit line  71 - 73  is able to be connected to a (2i−1) th  local bit line  61 ,  63  and a (2i) th  local bit line, iε[1, . . . , N4]. E.g. the first global bit line  71  is able to be connected to the first local bit line  61  and the second local bit line  62 . Further, the second global bit line  72  can be able to be connected to the third local bit line  63  and the fourth local bit line  64 .