Abstract:
A method of etching a stack using a fluorine containing gas and an ammonia containing gas is provided. Generally, the stack is placed in a plasma processing chamber. A fluorine containing gas is flowed into the plasma processing chamber. An ammonia containing gas is flowed into the plasma processing chamber. A plasma is generated. The stack is then etched.  
     In addition, a device for etching stacks on a substrate is provided. The device comprises: a plasma chamber with chamber walls; a plasma confinement device for reducing plasma contact with the chamber walls; a gas source; plasma generation and energizing device; and an exhaust system for pumping plasma away. The gas source comprises a fluorine containing gas source and an ammonia containing gas source.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to the fabrication of semiconductor-based devices. More particularly, the present invention relates to improved techniques for fabricating semiconductor-based devices with low dielectric constant materials.  
           [0002]    In semiconductor-based device (e.g., integrated circuits or flat panel displays) manufacturing, dual damascene structures may be used in conjunction with copper conductor material to reduce the RC delays associated with signal propagation in aluminum based materials used in previous generation technologies. In dual damascene, instead of etching the conductor material, vias, and trenches may be etched into the dielectric material and filled with copper. The excess copper may be removed by chemical mechanical polishing (CMP) leaving copper lines connected by vias for signal transmission. To reduce the RC delays even further, low dielectric constant materials may be used. Low dielectric constant materials are here defined as materials with a dielectric constant of less than about 3.7. These low dielectric constant materials may include organo-silicate-glass (OSG) materials, such as Coral™ and Black Diamond™, or may be purely organic materials, such as SILK™ or Flare™. OSG materials may be silicon dioxide doped with organic components such as methyl groups. Etching these materials and stripping the photoresist on these materials may be significantly different and much more challenging than when conventional oxide materials are used. Oxygen containing plasmas may not be suitable for stripping resist on OSG materials, since oxygen plasmas may oxidize the organic content of low k OSG materials or may cause bowing during the etch of purely organic low k materials.  
           [0003]    To facilitate discussion, FIG. 1A is a cross-sectional view of a stack  100  on a wafer  110  used in the damascene process of the prior art. A contact  104  may be placed in a dielectric layer  108  over the wafer  110 . A barrier layer  112 , which may be of silicon nitride or silicon carbide, may be placed over the contact  104  to prevent the copper diffusion. A via level low k material layer  116  may be placed over the barrier layer  112  and dielectric layer  108 . A trench stop layer  120  may be placed over the via level low k layer  116 . A trench level low k material layer  124  may be placed over the trench stop layer  120 . A hard mask and/or an antireflective coating (ARC) layer  128  may be placed over the trench level low k material layer  124 . A patterned resist layer  132  may be placed over the hard mask and/or an antireflective coating (ARC) layer  128 . The via level low k material layer  116  and the trench level low k material layer  124  may be formed from a low dielectric constant OSG material or organic material. The trench etch stop layer  120  may be formed from silicon carbide or silicon nitride. SiON or organic anti reflective coating (BARC) may be used to form the ARC layer  128 .  
           [0004]    [0004]FIG. 1B is a cross-sectional view of the stack  100  after a via  136  and a trench  140  have been etched. To etch through the hard mask and/or an antireflective coating (ARC) layer  128 , the etch stop layer  120  and the barrier layer  112  it may be desirable to use a fluorine containing gas as a gas source for an etching plasma. To etch through the via level organic low k material layer  116  and the trench level organic low k material layer  124 , it may be desirable to use an ammonia (NH 3 ) containing gas as a gas source for an etching plasma. In addition, for organic low k materials, a fluorine source may be added to NH 3  to remove any unwanted polymeric residue from the open areas of the wafer. To etch through the via level OSG low k material layer  116  and the trench level OSG low k material layer  124 , it may be desirable to use a fluorine containing gas similar to the gas used to etch the ARC layer  128 , the etch stop layer  120  and barrier layer  112 . To strip the photo resist after via, trench, or barrier etch, it may be desirable to use NH 3  gas. After the trench and via etches of OSG materials a polymer crust  144  may be deposited over the patterned resist layer  132  and side walls of the trench  140  and via  140 . To remove a silicon containing polymer crust  144  it may be desirable to use a fluorine containing etchant gas in combination with NH3. Although it is desirable to use an etchant gas with a fluorine containing gas and an ammonia containing gas either together or in alternating steps, such attempts in the prior art resulted in the formation of particles, which may contaminate the plasma processing chamber and may increase defects in the resulting semiconductor structure. Thus such processes, which used ammonia and fluorine in the same chamber were avoided.  
           [0005]    It is desirable to provide an efficient etching with minimal particle contamination.  
         SUMMARY OF THE INVENTION  
         [0006]    To achieve the foregoing and other objectives and in accordance with the purpose of the present invention for etching a stack, generally, the stack is placed in a plasma processing chamber. A fluorine containing gas is flowed into the plasma processing chamber. An ammonia containing gas is flowed into the plasma processing chamber. A plasma is generated. The stack is then etched.  
           [0007]    In addition, the present invention provides a device for etching stacks on a substrate. The device comprises: a plasma chamber with chamber walls; a plasma confinement device for reducing plasma contact with the chamber walls; a gas source; plasma generation and energizing device; and an exhaust system for pumping plasma away. The gas source comprises a fluorine containing gas source and an ammonia containing gas source.  
           [0008]    These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:  
         [0010]    FIGS.  1 A-B are cross-sectional views of a stack on a wafer used in the damascene process of the prior art.  
         [0011]    [0011]FIG. 2 is a schematic view of a plasma processing chamber that may be used in a preferred embodiment of the invention.  
         [0012]    [0012]FIG. 3 is a flow chart of a process that uses the plasma processing chamber.  
         [0013]    FIGS.  4 A-B are cross-sectional views of a stack on a wafer used in the damascene process in a preferred embodiment of the invention.  
         [0014]    [0014]FIG. 5 is a more detailed flow chart for the step of etching the via.  
         [0015]    FIGS.  6 A-C are cross-sectional views of a stack on a wafer used in the damascene process in a preferred embodiment of the invention after a via has been etched.  
         [0016]    [0016]FIG. 7 is a more detailed flow chart for the step of etching the trench.  
         [0017]    [0017]FIG. 8 is a graph of the number of particles over 0.16 microns versus the number of wafers processed found during a test. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0018]    The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention.  
         [0019]    To facilitate discussion, FIG. 2 is a schematic view of a plasma processing chamber  200  that may be used in a preferred embodiment of the invention. The plasma processing chamber  200  comprising confinement rings  202 , an upper electrode  204 , a lower electrode  208 , a gas source  210 , and an exhaust pump  220 . The gas source  210  comprises a fluorine containing gas source  212  and an ammonia containing gas source  216 . The gas source  210  may comprise additional gas sources. Within plasma processing chamber  200 , a substrate  224  is positioned upon the lower electrode  208 . The lower electrode  208  incorporates a suitable substrate chucking mechanism (e.g., electrostatic, mechanical clamping, or the like) for holding the substrate  224 . The reactor top  228  incorporates the upper electrode  204  disposed immediately opposite the lower electrode  208 . The upper electrode  204 , lower electrode  208 , and confinement rings  202  define the confined plasma volume  240 . Gas is supplied to the confined plasma volume  240  by gas source  210  and is exhausted from the confined plasma volume  240  through the confinement rings  202  and an exhaust port by the exhaust pump  220 . A first RF source  244  is electrically connected to the upper electrode  204 . A second RF source  248  is electrically connected to the lower electrode  208 . Different combinations of connecting RF power to the electrode are possible. In case of Exelan HP both the RF sources are connected to the lower electrode and the upper electrode is grounded. Chamber walls  252  surround the confinement rings  202 , the upper electrode  204 , and the lower electrode  208 . Both the first RF source  244  and the second RF source  248  may comprise a  27  MHz power source and a 2 MHz power source. The upper electrode  204  and the lower electrode are spaced are preferably spaced apart by a distance of about 1.35 cm but may have a spacing up to 2.0 cm.  
         [0020]    [0020]FIG. 3 is a flow chart of a process that uses the plasma processing chamber  200 . A stack  400  is formed on a wafer  224  (step  304 ), as shown in FIG. 4A. A contact  404  may be placed in a dielectric layer  408  over a wafer  224 . A barrier layer  412 , which may be of silicon nitride or silicon carbide, may be placed over the contact  404  to prevent a copper or metal diffusion. A via level low k material layer  416  may be placed over the barrier layer  412 . A trench stop layer  420  may be placed over the via level low k layer  416 . In a preferred embodiment, the trench stop layer  420  may be made of silicon nitride (SiN). A trench level low k material layer  424  may be placed over the trench stop layer  420 . A hard mask and/or an antireflective coating (ARC) layer  428  may be placed over the trench level low k material layer  424 . A patterned resist layer  432  patterned for etching a via may be placed over the hard mask and/or an antireflective coating (ARC) layer  428 . The via level low k material layer  416  and the trench level low k material layer  424  may be formed from a low dielectric constant OSG material or organic material. The trench etch stop layer  420  may be formed from silicon carbide, instead of silicon nitride, and the hard mask layer may be formed from SiN. The ARC layer  428  may be formed from SiON or organic anti reflective coating. The patterned resist layer  432  may be made of a photo resist layer with the ARC layer  428  acting as an antireflective coating. The stack  400  may be placed over other layers over the wafer  224 .  
         [0021]    The wafer  224  may then be placed in the plasma processing chamber  200  (step  308 ). A via is then etched (step  312 ). Generally, to provide etching in the plasma processing chamber  200  a gas is flowed from the gas source  210 . Energy is provided by the first RF source  244  and the second RF source  248 , which energizes and ionizes the gas generating a plasma. The plasma is partially confined to the confined plasma volume  240 , where the plasma is able to etch the stack  400  on the wafer  224 . The plasma is then vented past the confinement rings  202  to the exhaust pump  220 . The confinement rings  202  reduce plasma interaction with the chamber walls  252 . FIG. 4B is a schematic view of the stack  400  with an etched via  440 . To etch the via  440  the hard mask and or ARC layer  428 , the trench level low k material layer  424 , the trench stop layer  420 , and the via level low k material layer  416  are etched.  
         [0022]    [0022]FIG. 5 is a more detailed flow chart for the step of etching the via (step  312 ) where the trench level low k material  424  and the via level low k material  416  are organic. First the via is etched through the hard mask/ARC layer  428  (step  504 ). One recipe set of parameters for etching the hard mask/ARC layer  428  is provided in Table I where sccm stands for Standard Cubic Centimeters per minute.  
                           TABLE I                                   MORE               PREFERRED   PREFERRED       PARAMETERS   BROAD RANGE   RANGE   RANGE                   PRESSURE    0-140    35-105   60-80       (mTorr)       Flow rate of Ar    80-320   120-200   150-170       (sccm)       Flow rate of C 4 F 8     1-9   3-7   5       (sccm)       Flow rate of CF 4     10-80   30-50   35-45       (sccm)       Flow rate of O 2      4-26   10-20   13-17       (sccm)       Power at 27 MHz   250-750   300-700   450-550       (Watts)       Power at 2 MHz    500-1500    750-1250    900-1100       (Watts)                  
 
         [0023]    In a preferred embodiment for etching the hard mask/ARC layer  428 : the flow rate of pressure was approximately 70 mTorr; approximately 500 Watts was provided at 27 MHz; approximately 1,000 Watts was provided at 2 MHz; the flow rate of Argon (Ar) was approximately 160 sccm; the flow rate of oxygen (O 2 ) was approximately 15 sccm; the flow rate of CF 4  was approximately 40 sccm; the flow rate of C 4 F 8  was approximately 5 sccm.  
         [0024]    Next the via level organic low k material layer  424  is etched (step  508 ). One recipe set of parameters for etching the trench level low k material layer  424  is provided in Table II.  
                           TABLE II                                   MORE               PREFERRED   PREFERRED       PARAMETERS   BROAD RANGE   RANGE   RANGE                   PRESSURE    0-300   100-200   140-160       (mTorr)       Flow rate of NH 3      500-1500    750-1250    900-1100       (sccm)       Power at 27 MHz   250-750   300-700   450-550       (Watts)       Power at 2 MHz    0-500    0-250   0       (Watts)                  
 
         [0025]    In the preferred embodiment for etching the trench level low k material layer  424 : the flow rate of pressure was approximately 150 mTorr; approximately 500 Watts was provided at 27 MHz; approximately 0 Watts was provided at 2 MHz; the flow rate of NH 3  was approximately 1,000 sccm. During the via etch of the organic low k material using NH 3  plasma, all the resist material to form the via pattern is removed. After via etch the stack is repatterned with photo resist trench pattern to form trench pattern on the wafers.  
         [0026]    Next the trench stop layer  420  is etched (step  512 ). One recipe set of parameters for etching an SiN trench stop layer  420  is provided in Table III.  
                           TABLE III                                   MORE               PREFERRED   PREFERRED       PARAMETERS   BROAD RANGE   RANGE   RANGE                   PRESSURE    0-180    60-120    80-100       (mTorr)       Flow rate of Ar    75-300   100-200   130-170       (sccm)       Flow rate of CHF 3      6-18    9-15   11-13       (sccm)       Flow rate of CF 4     10-40   15-35   20-30       (sccm)       Flow rate of O 2      5-15    7-13    9-11       (sccm)       Flow rate of N 2     15-45   20-40   25-35       (sccm)       Power at 27 MHz    300-1200   450-750   550-650       (Watts)       Power at 2 MHz    50-200    75-125    90-110       (Watts)                  
 
         [0027]    In the preferred embodiment for etching the trench stop layer  420 : the flow rate of pressure was approximately 90 mTorr; approximately 600 Watts was provided at 27 MHz; approximately 100 Watts was provided at 2 MHz; the flow rate of Argon (Ar) was approximately 150 sccm; the flow rate of oxygen (O 2 ) was approximately 10 sccm; the flow rate of CF 4  was approximately 25 sccm; the flow rate of CHF 3  was approximately 12 sccm; the flow rate of N 2  was approximately 30 sccm.  
         [0028]    Next the trench level low k material layer  424  is etched (step  516 ). One recipe set of parameters for etching the trench level low k material layer  424  is provided in Table IV.  
                           TABLE IV                                   MORE               PREFERRED   PREFERRED       PARAMETERS   BROAD RANGE   RANGE   RANGE                   PRESSURE    0-300   100-200   140-160       (mTorr)       Flow rate of NH 3      500-1500    750-1250    900-1100       (sccm)       Power at 27 MHz   250-750   300-700   450-550       (Watts)       Power at 2 MHz    0-500    0-250   0       (Watts)                  
 
         [0029]    In the preferred embodiment for etching the via level low k material layer  416 : the flow rate of pressure was approximately 150 mTorr; approximately 500 Watts was provided at 27 MHz; approximately 0 Watts was provided at 2 MHz; the flow rate of NH 3  was approximately 1,000 sccm;.  
         [0030]    While etching via  440  in the OSG low k materials to the barrier layer  412  the via etching may be stopped. A silicon containing polymer crust  444  may be deposited over the patterned resist layer  432  and the sidewalls of the via  440  as a result of the via etching. The plasma chamber  200  may be used to strip the polymer crust  444 , when etching OSG low k materials, and the patterned resist layer  432 , when etching either OSG low k materials or organic low k materials (step  316 ). A recipe for stripping the polymer crust  444  and patterned resist layer  432  may use NH 3  as a plasma source gas for stripping the photoresist. Once the polymer crust  444  and patterned resist layer  432  have been stripped, the wafer  224  may be removed from the plasma chamber  200  to allow the depositing of a new patterned resist layer  504  (step  320 ), as shown in FIG. 6A.  
         [0031]    The wafer  224  may be placed back in the plasma chamber  200  (step  324 ). A trench  604  is etched (step  328 ), as shown in FIG. 6B. FIG. 7 is a more detailed flow chart for the step of etching the trench (step  328 ) when the trench level layer  424  is an organic low k material. First, the trench is etched through the hard mask/ARC layer  428  (step  704 ). One recipe set of parameters for etching the hard mask/ARC layer  428  is provided in Table I above. In a preferred embodiment for etching the hard mask/ARC layer  428 : the flow rate of pressure was approximately 70 mTorr; approximately 500 Watts was provided at 27 MHz; approximately 1,000 Watts was provided at 2 MHz; the flow rate of Argon (Ar) was approximately 160 sccm; the flow rate of oxygen (O 2 ) was approximately 15 sccm; the flow rate of CF 4  was approximately 40 sccm; the flow rate of C 4 F 8  was approximately 5 sccm.  
         [0032]    Next the trench level organic low k material layer  424  is etched (step  708 ). One recipe set of parameters for etching the trench level organic low k material layer  424  is provided in Table II. In the preferred embodiment for etching the trench level low k material layer  424 : the flow rate of pressure was approximately 150 mTorr; approximately 500 Watts was provided at 27 MHz; approximately 0 Watts was provided at 2 MHz; the flow rate of NH 3  was approximately 1,000 sccm.  
         [0033]    Once the trench  604  has been etched to the trench stop layer  420  the trench etching may be stopped. The barrier layer  412  may then be etched (step  332 ). One recipe set of parameters for etching the barrier layer  412  is provided in Table V.  
                           TABLE V                                   MORE               PREFERRED   PREFERRED       PARAMETERS   BROAD RANGE   RANGE   RANGE                   PRESSURE   100-220   130-190   150-170       (mTorr)       Flow rate of Ar   100-500   200-400   250-350       (sccm)       Flow rate of CHF 3      5-40   10-30   15-25       (sccm)       Flow rate of N 2      40-200    60-140    80-120       (sccm)       Power at 27 MHz   300-800   500-600   400       (Watts)       Power at 2 MHz    50-400   100-300   200       (Watts)                  
 
         [0034]    In the preferred embodiment for etching the barrier layer  412 : the flow rate of pressure was approximately 158 mTorr; approximately 400 Watts was provided at 27 MHz; approximately 200 Watts was provided at 2 MHz; the flow rate of Argon (Ar) was approximately 300 sccm; the flow rate of CHF 3  was approximately 20 sccm; the flow rate of N 2  was approximately 100 sccm.  
         [0035]    A silicon containing polymer crust  608  may be deposited over the patterned resist layer  432  and the sidewalls of the via  440  and trench  604  as a result of the trench etching, as shown in FIG. 6B. The plasma chamber  200  may be used to strip the polymer crust  608  and patterned resist layer  504  (step  336 ). A recipe for stripping the polymer crust  608  and patterned resist layer  504  may use NH 3  as a plasma source gas for stripping the photoresist. Once the polymer crust  608  and patterned resist layer  504  have been stripped, the wafer  224 , as shown in FIG. 6C, may be removed from the plasma chamber  200  (step  340 ).  
         [0036]    In an Exelan HP, made by LAM Research Corporation™ of Fremont, Calif., a test was performed using the above recipes for 500 wafers. An O 2  clean was done every 60 seconds. Particles were collected periodically in 25 or 50 wafer intervals. A particle count was taken using an NH 3  recipe as described above for 10 seconds, where the particle size monitored was 0.16 to 9,000 microns with 6 mm edge exclusion. The test temperature was about 0° C. FIG. 8 is a graph of the number of particles over 0.16 microns (Particle count) versus the number of wafers processed (0-500) found during the test. It can be seen that the level of particle generation is below 30, which is normal for the chamber, indicating that the confinement rings  202 , small plasma volume  240 , and exhaust pump  220  speed help to minimize plasma contact with the walls of the chamber so that formed ammonium fluoride does not have a chance to condense onto the walls of the chamber to form a higher number of particles.  
         [0037]    In another embodiment of the invention, where the trench level low k material layer  424  and the via level low k material  416  are made of an OSG material the trench level low k material  424 , the via level low k material  416 , the ARC layer  428 , barrier layer  412 , and the trench stop layer  420  may be all etched with fluorine containing etchant gases. For stripping the patterned resist layer  432  an NH 3  stripping gas may be used. More preferably an NH 3  gas combined with a CF 4  gas may be used to strip the patterned resist layer. In such an embodiment an ammonia containing gas and a fluorine containing gas are used at the same time within the same plasma chamber and at alternating times.  
         [0038]    In other embodiments other types of plasma confinement devices, which keep plasma from the chamber walls may be used in place of the confinement rings. Other types of plasma generation and energizing systems may be used in place of the upper and lower electrodes  204 ,  208  and the first and second RF sources  244 ,  248 , which may generate and energize a plasma in a small plasma volume.  
         [0039]    Another embodiment of the invention may use a combined resist strip and barrier etch step to reduced etching damage as described in U.S. patent application Ser. No. ______ (Attorney Docket Number LAM1P158) entitled “A Combined Resist Strip And Barrier Etch Process For Dual Damascene Structures” by Rao Annapragada and Reza Sadjadi, with the same filing date, and which is incorporated by reference.  
         [0040]    Sidewalls formed by the crust may be removed during the stripping of the resist or may be removed using a separate wet stripping as described in U.S. patent application Ser. No. ______ (Attorney Docket Number LAM1P156) entitled “Method of Preventing Damage To Organo-Silicate-Glass Materials During Resist Stripping” by Rao Anapragada, with the same filing date, and which is incorporated by reference.  
         [0041]    While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and substitute equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and substitute equivalents as fall within the true spirit and scope of the present invention.