Abstract:
A method for forming a contact hole in a semiconductor device and related computer-readable storage medium are provided, the method and program steps of the medium including measuring a percentage of oxygen in an etching chamber, and controlling the percentage of oxygen in the etching chamber to enlarge a temporary inner diameter near a top of the contact hole.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present disclosure generally relates to metal contact etch patterning in semiconductor integrated circuits. More particularly, the present disclosure relates to metal contact etch patterning with a transition step using closed-loop feedback. 
         [0002]    In metal contact (CA) etch patterning, the process window is quite narrow in sub-45 nm devices, for example. A typical goal is to achieve a final critical dimension (FCD) that is as small as possible without incurring an open-failure, such that an overlay margin can be extended. Earlier approaches to the etch process generally had to shrink the critical dimension (CD) over a 20 nm bias. Thus, polymerizing gas chemistry has been applied to the etch process. Prior approaches attempted to pre-select a gas flow rate to achieve such a CD. Unfortunately, the smaller the CD using this approach, the higher the risk of open-failures. 
       SUMMARY OF THE INVENTION 
       [0003]    These and other issues are addressed by methods for contact patterning with transition etch feedback. Exemplary embodiments are provided. 
         [0004]    An exemplary embodiment method for forming a contact hole in a semiconductor device includes measuring a percentage of oxygen in an etching chamber, and controlling the percentage of oxygen in the etching chamber to enlarge a temporary inner diameter near a top of the contact hole. 
         [0005]    Other exemplary embodiments further include methods wherein the enlarged temporary inner diameter near the top of the contact hole increases a flow of etchant to a bottom of the contact hole; methods wherein the enlarged temporary inner diameter near the top of the contact hole is less than a developed critical dimension (DCD); methods wherein the enlarged temporary inner diameter near the top of the contact hole is less than a final critical dimension (FCD); methods further comprising determining an optimal flow of etchant to a bottom of the contact hole, wherein the percentage of oxygen is controlled to optimize the flow of etchant to the bottom of the contact hole; methods further comprising comparing the temporary inner diameter near the top of the contact hole with a developed critical dimension (DCD), wherein the percentage of oxygen is controlled to increase the dimension near the top of the contact hole without reaching the DCD; methods wherein the contact hole is one of a plurality of contact holes, and the percentage of oxygen is controlled to substantially equalize the temporary inner diameters near the tops of each of the plurality of contact holes, respectively; methods wherein enlarging the top of the contact hole reduces a residue restriction near the top of the contact hole. 
         [0006]    Additional exemplary embodiments further include methods wherein enlarging the top of the contact hole reduces a polymer or polymer-like restriction near the top of the contact hole; methods further comprising comparing a polymer-restricted dimension near the top of the contact hole with a developed critical dimension (DCD), wherein the percentage of oxygen is controlled to reduce without eliminating the polymer restriction; methods wherein the contact hole is one of a plurality of contact holes, and the percentage of oxygen is controlled to substantially equalize polymer restrictions in each of the plurality of contact holes, respectively; methods wherein controlling the percentage of oxygen takes place in a transition step after a first oxide etch and before a second oxide etch; methods wherein controlling the percentage of oxygen comprises controlling the ratio of carbon-fluoride (C4F6) gas to oxygen (O2) gas; methods further comprising controlling a process time for each of a plurality of flow rates through the enlarging temporary inner diameter near the top of the contact hole. 
         [0007]    Still other exemplary embodiments further include methods wherein the oxygen percentage and process time are control variables optimized to obtain a desired final critical dimension (FCD) at the bottom of the contact hole; methods wherein a resulting critical dimension at the top of the contact hole is no greater than a developed critical dimension (DCD) at the top of the contact hole; methods wherein a declination angle between a resulting critical dimension at the top of the contact hole and a final critical dimension (FCD) at the bottom of the contact hole is no less than 88 degrees; methods wherein a final critical dimension (FCD) at a bottom of the contact hole is large enough to substantially prevent open circuit failures. 
         [0008]    Still additional exemplary embodiments further include methods wherein the semiconductor device is a 45 nm device and the final critical dimension (FCD) at a bottom of the contact hole is at least 50 nm; methods further comprising controlling a process time for each of a plurality of flow rates through the enlarging temporary inner diameter near the top of the contact hole, wherein the oxygen percentage and process time are control variables optimized to obtain a desired final critical dimension (FCD) at the bottom of the contact hole, and wherein the oxygen percentage and process time control variables are further optimized to obtain a desired resulting critical dimension at the top of the contact hole; methods wherein a resulting critical dimension at the top of the contact hole is small enough to prevent short circuit failures; and methods wherein the semiconductor device is a 45 nm device and a resulting critical dimension at the top of the contact hole is less than 65 nm. 
         [0009]    Exemplary computer-readable storage medium embodiments include program steps comprising measuring a percentage of oxygen in an etching chamber, and controlling the percentage of oxygen in the etching chamber to enlarge a temporary inner diameter near a top of the contact hole. 
         [0010]    The present disclosure will be further understood from the following description of exemplary embodiments, which is to be read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present disclosure provides methods and apparatus for contact patterning with transition etch feedback in accordance with the following exemplary figures, in which: 
           [0012]      FIG. 1  shows a schematic side view of a sub-45 nm semiconductor integrated circuit; 
           [0013]      FIG. 2  shows a schematic bottom view of the sub-45 nm device of  FIG. 1 , taken from a reference line at about the midsections of the metal contacts; 
           [0014]      FIG. 3  shows a plot of yield versus critical dimension (CD) for sub-45 nm devices without transition etch feedback; 
           [0015]      FIG. 4  shows a schematic top view of a sub-45 nm device, including contact holes with polymer bridging; 
           [0016]      FIG. 5  shows a schematic side view of the sub-45 nm device of  FIG. 4 ; 
           [0017]      FIG. 6  shows a schematic side view of a contact hole of  FIG. 5 ; 
           [0018]      FIG. 7  shows a process flowchart for metal contact patterning; 
           [0019]      FIG. 8  shows a process flowchart for metal contact patterning with an oxygen (O2) flash; 
           [0020]      FIG. 9  shows a process flowchart for variable ratio feedback control in accordance with a preferred embodiment of the present disclosure; 
           [0021]      FIG. 10  shows a schematic side view of a contact hole during the transition feedback step of  FIG. 9  in accordance with a preferred embodiment of the present disclosure; 
           [0022]      FIG. 11  shows schematic top views of a sub-45 nm device in accordance with a preferred embodiment of the present disclosure; 
           [0023]      FIG. 12  shows a plot of critical dimension versus a reciprocal ratio of oxygen percentages for sub-45 nm devices in accordance with a preferred embodiment of the present disclosure; and 
           [0024]      FIG. 13  shows a comparative plot for old versus new conditions on the rate of ion etch (RIE) or etch rate in accordance with a preferred embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0025]    A method is provided for forming semiconductor integrated circuits with metal contact (CA) etch patterning. Exemplary embodiments provide a metal contact etch patterning method with a transition etch step for sub-45 nm logic devices. 
         [0026]    A polymer build-up near the top of a contact hole affects flow during subsequent etching and deposition processes, and thereby affects the final contact; but the polymer build-up itself is only temporary. Embodiments of the present disclosure may control the oxygen (O2) ratio to increase a critical dimension (CD) at the bottom of the contact. More O2 opens the top of the contact hole so that more etchant reaches the bottom to increase the CD and prevent open failures. In a preferred operating range where some polymer is removed and some remains, less O2 yields a smaller bottom CD, while more O2 yields a larger bottom CD. This is because, all else being equal, more O2 eats away more of the polymer at the top of the contact hole. An exemplary process controls the percentage of C4F6 to O2 to maximize the bottom CD and prevent open failures without causing short failures. This process controls the bottom CD more precisely than was possible without controlling the percentage of oxygen. 
         [0027]    As shown in  FIG. 1 , a sub-45 nm device, shown here in a side view, is indicated generally by the reference numeral  100 . The device  100  includes first, second and third metal contacts  110 ,  112  and  114 , respectively. The first metal contact  110  has a top critical dimension (CD) of 67.5 nm and a bottom CD of 53.6 nm. A second metal contact  112  has a top CD of 54.6 nm and a bottom CD of zero. That is, the second metal contact  112  has an open failure. A third metal contact  114  has a top CD of 52.6 nm, which is smaller than the top CD of the second metal contact, but has a workable bottom CD of 26.3 nm. 
         [0028]    Turning to  FIG. 2 , the sub-45 nm device of  FIG. 1 , shown here in a bottom view through about the midsections of the metal contacts, is indicated generally by the reference numeral  200 . The device  200  includes first through fifth metal contacts,  110 ,  112 ,  114 ,  116  and  118 , respectively. Here, the contacts  110 ,  114 ,  116  and  118  are robust, but the second contact  112  is already too restricted. 
         [0029]    Turning now to  FIG. 3 , a plot of yield versus CD without transition etch feedback is indicated generally by the reference numeral  300 . Here, a region  310  has a relatively small CD, but a high incidence of open-circuit failures. A region  312  has a medium CD, and a lower number of failures within its approximate margin. A region  314  has a relatively large CD, but a high incidence of short-circuit failures. 
         [0030]    Random open failures typically occur in the metal contact pattern because the process window is so narrow in sub-45 nm devices. It is desirable to achieve a final critical dimension (FCD) that is as small as possible without incurring open failures, particularly so that an overlay margin can be extended. General etch processes have had to shrink the CD over about a 20 nm bias. Thus, polymerizing gas chemistry is generally applied to etch processes. A lot of time and effort is typically devoted to pre-selecting the most desirable gas flow rate to reduce failures for a given integrated circuit design. Unfortunately, the smaller the CD, the higher the risk of random open failures due to polymer bridging. 
         [0031]    As shown in  FIG. 4 , a sub-45 nm device, shown here in a top view, is indicated generally by the reference numeral  400 . The device  400  includes a plurality of etched contact holes  410 , including contact holes  412  through  420  that show signs of polymer bridging. 
         [0032]    Turning to  FIG. 5 , the sub-45 nm device  400  of  FIG. 4 , shown here in a side view, is indicated generally by the reference numeral  500 . Here, the partially bridged contact hole  412  of  FIG. 4  is indicated by the reference numeral  512 . A ring of polymer-like material  520  partially restricts the top opening of the contact hole  512 . 
         [0033]    Turning now to  FIG. 6 , the contact hole  512  of  FIG. 5 , shown her in a side view, is indicated generally by the reference numeral  600 . Here, the contact hole  600  exhibits a polymer build-up  620 , which significantly reduces the internal diameter near the top of the hole. 
         [0034]    During the main or oxide etch, a polymer or polymer-like by-product generally builds up on a top edge area of the contact holes. Thus, there is typically a bridging in the top corner area by a polymer-like material that builds up during the main etch. Such bridging significantly contributes to the open-circuit failures of the resulting metal contact patterns, although such failures are generally known as “random open failures”. 
         [0035]    In particular, whenever an attempt is made to shrink the mask layer CD, such random open failures may occur. The root cause can originate from a TLR etch, but generally gets worse during the main etch. The overhang-like build-up of polymer has the disadvantage that it restricts the flow of etchant from the top to the bottom of the contact hole. Thus, sufficient etchant may not get through to the bottom, and this results in an open failure for the resulting metal contact. In the present disclosure, the build-up of polymer is controlled in a transition step to achieve shrinkage gain and substantially avoid open failures due to bridging. 
         [0036]    As shown in  FIG. 7 , a process flowchart for metal contact patterning is indicated generally by the reference numeral  700 . Here, a function block  710  performs a Si-ARC etch, and passes control to a function block  712 . The function block  712  performs an ODL etch, and passes control to a function block  714 . The function block  714 , in turn, performs a Si-ARC removal, and passes control to a function block  716 . The function block  716  performs a main or oxide etch, and passes control to a function block  718 . The function block  718  performs an ashing step, and passes control to a function block  720 . The function block  720 , in turn, performs a SiN etch. 
         [0037]    The process  700  relies on the tri-layer etch, particularly blocks  710  and  712 , as the key to controlling CD. While this is a reasonable approach, defining a smaller bottom CD for the tri-layer hardly avoids the risk of open failures during the main etch  716 . 
         [0038]    Turning to  FIG. 8 , a process flowchart for metal contact patterning with an oxygen (O2) flash, which entirely removes the polymer build-up, is indicated generally by the reference numeral  800 . Here, a function block  810  performs a Si-ARC etch, and passes control to a function block  812 . The function block  812  performs an ODL etch, and passes control to a function block  814 . The function block  814 , in turn, performs a Si-ARC removal, and passes control to a function block  816 . The function block  816  performs a first main or oxide etch, and passes control to a function block  818 . The function bock  818  performs an O2-only flash, and passes control to a function block  820 . The function block  820 , in turn, performs a second main or oxide etch, and passes control to a function block  822 . The function block  822  performs an ashing step, and passes control to a function block  824 . The function block  824  performs a SiN etch. 
         [0039]    Turning to  FIG. 9 , a process flowchart for variable ratio feedback control, which uses closed-loop feedback to control CD, is indicated generally by the reference numeral  900 . Here, a function block  910  performs a Si-ARC etch, and passes control to a function block  912 . The function block  912  performs an ODL etch, and passes control to a function block  914 . The function block  914 , in turn, performs a Si-ARC removal, and passes control to a function block  916 . The function block  916  performs a first main or oxide etch, and passes control to a function block  918 . The function bock  918  performs a transition step, and passes control to a function block  920 . The function block  920 , in turn, performs a second main or oxide etch, and passes control to a function block  922 . The function block  922  performs an ashing step, and passes control to a function block  924 . The function block  924  performs a SiN etch. 
         [0040]    Here, the transition step  918  uses closed-loop feedback to control a variable ratio of O2 to C4F6 or similar gas, and further controls process time. Thus, the transition step implements a feedback loop for automatic process control (APC) of CD. 
         [0041]    As shown in  FIG. 10 , a contact hole during the transition feedback step  918  of  FIG. 9  is indicated generally by the reference numeral  1000 . The contact hole has a top FCD target of b, a reduced actual top diameter of b−2Y, where Y is the width of the remaining polymer, an ILD height of h, a bottom FCD target of a, and a slope of about h/c=2h/(b−a). The top FCD target b may also be expressed as b= 2 *{h/tan(α)}+a, where α is the requested profile angle. In an exemplary application, the parameter values might be a=50 nm, a=88°, h=420 nm, c=15.04 nm, and top CD b=80.01 nm. 
         [0042]    Turning to  FIG. 11 , a sub-45 nm device, shown here in top views, is indicated generally by the reference numeral  1100 . The device is shown before the transition step  918  of  FIG. 9  as reference numeral  1110 , and after the transition step  918  of  FIG. 9  as reference numeral  1120 . Before the transition step, the device  1110  includes a plurality of contact holes, including contact holes  1112  and  1114  that show signs of polymer bridging. After the transition step, the device  1120  includes a plurality of optimized contact holes, including optimized contact holes  1122  and  1124  that have had some of the polymer residue removed. 
         [0043]    Here, the remaining polymer layer Y=f(x,t) at one edge is a function of x and t, where x is the ratio of C4F6 to O2 gases, and t is the process time. Here, when the remaining polymer for both edges, 2Y= 2 f(x,t), is between about 60 nm and about 80 nm, open-circuit failures are too prevalent. When 2Y=2f(x,t) is between about 0 nm and about 30 nm, short-circuit failures are too prevalent. When 2Y=2f(x,t) is between about 30 nm and about 60 nm, an optimized yield may be realized by significantly reducing failures in this moderate region. 
         [0044]    Turning now to  FIG. 12 , a plot of CD versus a reciprocal ratio of oxygen percentages for sub-45 nm devices is indicated generally by the reference numeral  1200 . The plot shows a control variable for gas ratio on the horizontal axis, and an output variable for CD on the vertical axis. The plot includes an illustrative top view of a device resulting from a 40% ratio of C4F6 to C4F6 plus O2, indicated by the reference numeral  1240 . The device  1240  exhibits a top CD of 53.4 nm. The plot includes an illustrative top view of a device resulting from a 26% ratio of C4F6 to C4F6 plus O2, indicated by the reference numeral  1226 . The device  1226  exhibits a top CD of 63.5 nm. In this exemplary application, a regulated gas ratio of about 33% was found to optimize the process yield or POR by reducing open-circuit failures without increasing short-circuit failures. 
         [0045]    As shown in  FIG. 13 , a comparative plot for old versus new conditions on the rate of ion etch (RIE) or etch rate is indicated generally by the reference numeral  1300 . Results were analyzed using an ES32 inspection tool. The new RIE conditions are achievable by the transition step  918  of  FIG. 9 . 
         [0046]    Using the old conditions, a process batch having a final critical dimension (FCD) of 70 nm had an open yield of 67%. That is, only 67% lacked open failures. One batch having a developed CD (DCD) of 81 nm led to an FCD of 74 nm and an open yield of 81%, while another batch having a DCD of 81 nm led to an FCD of 74 nm and an open yield of 77%. 
         [0047]    Using the new RIE conditions with closed-loop transition step, a process batch having a DCD of 79 nm led to an FCD of 62 nm with an open yield of 94%. A process batch having a DCD of 83 nm led to an FCD of 64 nm with an open yield of 98%; and a process batch having a DCD of 81 nm led to an FCD of 63 nm with an open yield of 99%. 
         [0048]    In addition, alternate embodiments are contemplated. For example, an SRAM process embodiment of the present disclosure has produced SRAM with significantly improved yields. Although FCD was decreased by more than 13%, which would normally reduce yield by a significant amount, open yield was actually improved by as much as 30%. 
         [0049]    Random open contact failures can result from aggressive polymer generation during an ILD oxide etch with carbon-fluoride gas chemistry, for example. The present disclosure teaches that such polymers and/or like materials may be moderately reduced at some etch time frame so that sufficient etchant will be able to pass through the top of the contact hole to reach the bottom of the contact hole and avoid open failures. The new transition step, which can control or regulate the C4F6:O2 ratio and process time using closed-loop feedback, can significantly reduce open failures and increase yield. By adjusting the C4F6:O2 gas ratio, for example, the CD bias can be more finely controlled. This process may be applied to any applicable automatic process control (APC) feedback loop, and shall not be construed as being limited to 45 nm devices, for example. 
         [0050]    Although illustrative embodiments have been described herein with reference to the accompanying drawings, it is to be understood that the present disclosure is not limited to those precise embodiments, and that various other changes and modifications may be effected therein by those of ordinary skill in the pertinent art without departing from the scope or spirit of the present disclosure. All such changes and modifications are intended to be included within the scope of the present disclosure as set forth in the appended claims.