embodiments of the present invention are described in the context of the apparatus 10 of fig1 , 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 . a typical ipvd system 10 , as illustrated in fig1 , 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 . 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 . 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 . such an ipvd system 10 exhibits a plasma density profile 21 that is peaked at the center , as illustrated in fig2 . 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 . 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 fig1 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 . fig2 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 fig4 are normalized forms of the curves of fig2 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 . fig4 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 fig4 to a more dish shape as illustrated by curves 24 in fig4 . dependence of the shape and dimensions of the device 40 affect the distribution of the plasma , as illustrated at different radii in fig5 . one example of an embodiment is shown in fig3 a 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 . more specifically , in the embodiment illustrated in fig3 , 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 . one example of the device 40 is shown in fig3 a 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 fig3 a 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 . 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 fig7 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 fig7 b . 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 . 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 .