Abstract:
The uniformity of a plasma distribution having a tendency to peak toward the axis of a processing chamber is improved by positioning a hollow body on the chamber axis with an open end facing the processing space. The hollow body controls the distribution of the plasma away from the center and allows plasma at the center. The geometry of the hollow body can be optimized to render the plasma uniform for given conditions. In combined deposition and etch processes, such as simultaneous and sequential etch and iPVD processes, the hollow body provides for a uniform plasma for etching while allowing deposition parameters to be optimized for deposition.

Description:
[0001]     This invention relates to the control of plasma etch process uniformity in an ionized physical vapor deposition (iPVD) processing of semiconductor wafers, and, in general, to metallization plasma processing in semiconductor technology. This invention more particularly relates to processes that combine iPVD and etch processing.  
       BACKGROUND OF THE INVENTION  
       [0002]     Ionized PVD has been utilized in semiconductor processing for metallization and interconnects and shows promise for extending processing to submicron technology. In the metallization of high aspect ratio (HAR) via holes and trenches on semiconductor wafers, barrier layers and seed layers must provide good sidewall and bottom coverage across the wafer. Ionized PVD is used for barrier and seed layer metallization in advanced IC wafers. Ionized PVD provides good sidewall and bottom coverage in via and trench structures. However, the ionized deposition requirements become more critical as the geometries shrink and as the via dimensions are further reduced below 0.15 micrometers. In such applications, it is highly desirable to have an ionized PVD process where bottom coverage and sidewall coverage are well balanced and overhang is minimized.  
         [0003]     The Metallization process may use an ionized physical vapor deposition (iPVD) apparatus having the features described in U.S. Pat. Nos. 6,080,287, 6,132,564, 6,197,165, 6,287,435 and 6,719,886 which patents are hereby expressly incorporated by reference herein. The processing apparatus described in these patents are particularly well suited for sequential or simultaneous deposition and etching. The sequential deposition and etching process can be applied to a substrate in the same process chamber without breaking vacuum or moving the wafer from chamber to chamber. Sequential deposition and etching processes are described in U.S. Pat. No. 6,755,945, hereby expressly incorporated by reference herein. The configuration of the apparatus allows rapid change from ionized PVD deposition mode to etching mode or from etching mode to ionized PVD deposition mode. The configuration of the apparatus also allows for simultaneous optimization of ionized PVD process control parameters during deposition mode and etching process control parameters during etching mode. The consequence of these advantages is a high throughput of wafers with superior via metallization and subsequent electroplated fill operation.  
         [0004]     Notwithstanding the advantages of ionized PVD, there are still some constraints to using iPVD at the maximum of its performance. For example, existing hardware does not allow for simultaneous optimizing of the uniformity in both deposition and etching over a wide process window, specifically a wide pressure range. An annular target provides excellent flat field deposition uniformity, but geometrically is limited to the use of large area inductively coupled plasmas (ICP) to generate large size low-pressure plasma for uniform etch processes. An axially situated ICP source is optimal to ionize metal vapor sputtered from the target and fill features in the center of the wafer, but such a source generates an axially peaked high-density plasma profile that does not provide uniform etch in a sequential deposition-etch process or no net deposition process (NND).  
         [0005]     The etch portion of a combined deposition-etch process occurs at increased bias at the wafer so deposited metal, typically TaN/Ta for adhesion and barrier properties or Cu for a seed layer, is removed from the flat field areas, namely the horizontal surfaces like the top and bottom planes of a feature, but remains deposited at the sidewalls of the features. The process requires fully identical non-uniformity distributions of the etch and deposition processes, or highly uniform processes.  
       SUMMARY OF THE INVENTION  
       [0006]     An objective of the present invention is to generate and adjust plasma so as to contribute to the uniform plasma processing in simultaneous and sequential processes that combine deposition and etching. One particular objective of the invention is to provide uniform plasma processing for high aspect ratio feature coverage by ionized PVD, particularly for large diameter wafers, for example, 300 millimeter (mm) wafers.  
         [0007]     The present invention provides for the production of a plasma by a large electrode, a ring-shape antenna in the preferred embodiment, and for the adjusting of the plasma density profile by use of an axially positioned device having hollow-body geometry. The device is provided in the vacuum space of the plasma source into which the energy is coupled. The device geometry, including its dimensions and shape, and its placement in the chamber may be optimized for the particular chamber geometry and process pressure range.  
         [0008]     These and other objects and advantages of the present invention will be more readily apparent from the following detailed description of illustrated embodiments of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a sectional view of an iPVD system for use with the present invention.  
         [0010]      FIG. 2  are graphs of plasma density showing the radial dependence of the ion density with and without the plasma adjusting device of the present invention.  
         [0011]      FIG. 3  is a cross-sectional view of one embodiment in an iPVD chamber of the type shown in  FIG. 1  with a plasma adjusting device according to principles of the present invention.  
         [0012]      FIGS. 3A and 3B  are perspective and cross-sectional views, respectively, of the hollow body of the embodiment of  FIG. 3 .  
         [0013]      FIG. 4  are normalized forms of the graphs of  FIG. 2 .  
         [0014]      FIG. 5  is a graph showing uniformity of the ion density as a function of the height of the plasma adjusting device two radii R=40 mm and R=70 mm.  
         [0015]      FIGS. 6A-6C  are two dimensional plots of lines of equal ion density in an iPVD chamber in which:  
         [0016]      FIG. 6A  shows the peaked plasma in a baseline chamber with a central ICP source as in  FIG. 1 ;  
         [0017]      FIG. 6B  shows a chamber such as in  FIG. 1 , but with an enlarged diameter ICP source without a plasma adjusting device and ring-shaped plasma source according to the present invention; and  
         [0018]      FIG. 6C  shows a chamber similar to  FIG. 3  with a plasma adjusting device provided according to principles of the present invention.  
         [0019]     FIGS.  7 A-B are elevational views, respectively, of conical and spherical plasma adjusting devices according to other embodiments of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0020]     Embodiments of the present invention are described in the context of the apparatus  10  of  FIG. 1 , even though applicable to other types of systems. The apparatus has features similar to those described in U.S. Pat. Nos. 6,080,287, 6,287,435 and 6,719,886 referred to above.  
         [0021]     A typical iPVD system  10 , as illustrated in  FIG. 1 , may include a vacuum chamber  11 , an ICP source  12 , a metal source  13 , and wafer holder  14  on which is supported a wafer  15  for processing, with a processing space  16  through which the sources  12  and  13  and the wafer  15  interact. Energy is coupled from the plasma source  12  into the processing space  16  to form a plasma  17 . In iPVD, metal is sputtered from the metal source  13  into the plasma  17  in the space  16 , where it is ionized for deposition onto the wafer  15 . When the plasma source  12  is an ICP source, RF energy is inductively coupled into the plasma  17 .  
         [0022]     While plasma processing systems are designed with maximum care and computer simulation, in many cases only a real process performed with a real plasma will reveal the impact of some hardware components of a processing chamber and their interaction with the plasma. Typically, this impact concerns the uniformity of the processing at the wafer. For example, non-uniformity in processing can be generated when changing processing conditions, for example, by interaction of a static magnetic field from a metal source, from inductively coupled plasma (ICP) antenna geometry, and from the simultaneous combination of different plasma processes within the chamber.  
         [0023]     Existing iPVD systems, such as those described in U.S. Pat. Nos. 6,080,287, 6,287,435 and 6,719,886, for example, have an on-axis ICP source which produces a strongly peaked plasma density. Such a plasma can provide excellent ionization of the metal sputtered from a target and the subsequent transport of the sputtered metal to a wafer.  
         [0024]     Such an iPVD system  10  exhibits a plasma density profile  21  that is peaked at the center, as illustrated in  FIG. 2 . The profile  21  represents zero table bias on the substrate holder  14 , where a table bias of 800 watts results in a similarly shaped but less peaked profile  22 . Flattening of the plasma profile can be achieved by reduction of the chamber height, to produce a profile such as the profile  23 . However, more significant reduction of chamber height would require radical changes in overall iPVD hardware. The plasma distribution typically does not markedly affect deposition uniformity with iPVD when performed in thermalized metal plasmas and at higher pressure, above 30-50 mTorr. But when performing an etch process at a lower pressure, etch state uniformity can be affected. Etch processes might be typically performed at pressures in the 1 to 10 mTorr range, for example.  
         [0025]     In accordance with certain principles of the present invention, to solve etch rate uniformity problems with minimal impact on the deposition process, an iPVD system  50  is provided in which the center ICP source  12  of  FIG. 1  is replaced by a ring-like source  30 . The ring-shaped source  30  surrounds a concentric hollow body device  40 , which is placed in position below deposition shield  60  inside of a dielectric portion of the chamber wall such as a dielectric window  41  behind which is positioned the antenna of the ring-shaped source  30 .  FIGS. 2 and 4  are comparative illustrations of density profiles, showing a transition from a center-peaked to a dished ion density profile with increasing radial or axial dimensions of the hollow body plasma adjusting device  40 . The graphs of  FIG. 4  are normalized forms of the curves of  FIG. 2  and also include curves  24  that show the lateral and vertical dimensions of the hollow device  40  have an effect on the plasma density profile.  FIG. 4  shows plasma density profiles for various dimensions of the hollow device. Extended surfaces of the hollow device  40  affects recombination of the plasma by impeding ionization in the bulk plasma in the central area of the processing space  16  within the chamber  11 . The plasma density profile changes from the domed shape illustrated by curves  21 - 23  in  FIG. 4  to a more dish shape as illustrated by curves  24  in  FIG. 4 . Dependence of the shape and dimensions of the device  40  affect the distribution of the plasma, as illustrated at different radii in  FIG. 5 . One example of an embodiment is shown in  FIGS. 3A and 3B . Accordingly, while some improvement in plasma uniformity can be gained by reduced chamber height, substantial uniformity improvement can be achieved utilizing a hollow plasma shaping device  40 .  
         [0026]     More specifically, in the embodiment illustrated in  FIG. 3 , processing system  50  has a top portion  53  that includes the top ring-like ICP source  52 , which includes the ring-shaped antenna  30 , and the RF biased substrate holder  14  at the bottom of a chamber  51  connected through a matching network (not shown) to RF generator (not shown). A process space  55  is enclosed by the vacuum chamber  51  and includes a metal source  56 . The ring-shaped plasma source  30  includes an inductive antenna  57 , which is separated from the processing space  55  by a TEFLON spacer  58  and a dielectric window  41  in the wall of the chamber  51 , which is protected by a deposition shield  60  having radial slots (not shown). The hollow device  40  is positioned below, or toward the processing space  50  from, the deposition shield  60 .  
         [0027]     One example of the device  40  is shown in  FIGS. 3A and 3B . It consists of a hollow cylindrical shape made of aluminum or other metal that is compatible with the process. Other materials, for example stainless-steel, Cu, or Ta, can be used. Alternatively, the device  40  can be made of SiC, alumina, or other dielectric material. Material thickness for the cylindrical embodiment of the device  40  that is shown in  FIGS. 3A and 3B  is 5 mm, but other thicknesses may be acceptable or preferred, depending on chamber and process parameters. For other practical reasons such as maximum temperature, thermal conductivity, rigidity, particle elimination, etc., thicknesses in the range of from 2 mm to 10 mm may be found appropriate, with surface texture or some other processed surface provided, as may be typically required for internal surfaces in sputtering systems known to persons skilled in this field. The dimensions of the plasma adjusting device  40  depend on actual chamber size and chamber aspect ratio. Typical dimensions of the plasma adjusting device  40  of the cylindrical type for a 300 mm wafer processing tool include a radius in the range of from 40 mm to 150 mm, preferably from 40 mm to 100 mm, and a height of from 10 mm to 150 mm, preferably from 10 mm to 80 mm, and more preferably of from 30 to 50 mm.  
         [0028]     A typical geometrical shape for the device  40  is that of a hollow body in cylindrical form or of frusto-conical geometry having a bottom radius larger than the upper radius, as for example the device  30   a  illustrated in  FIG. 7   a . A hemispherical shape having a cross-section that is parabolic or of some other convex shape or combination of shapes is also useful. An example is the device  30   b  illustrated in  FIG. 7B .  
         [0029]     In applicant&#39;s U.S. patent application Ser. No. 10/854,607, filed May 26, 2004, hereby expressly incorporated by reference herein, a buffer device is disclosed which provides a complementary effect on the radial distribution of metal atoms and ions inside a processing chamber. With the present invention, devices are provided having shapes for buffering performance by improving plasma uniformity and radial plasma density control.  
         [0030]     Although only certain exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.