Mar. 20, 2008  12  US 2008/0067077 Al  elimination of surface level difference and the surface  roughness of the processed surface.  [0127]  For comparison, electrolytic polishing was carried  out in the same manner using the same electrolytic liquid  (pH 3) but not containing ammonium polyacrylate. As a  result, the processing rate, the elimination of surface level  difference and the surface roughness of the processed sur› face were all found to be poor. In particular, etch pits having  a diameter of several  µm  and a depth of several hundred nm  were formed in the processed surface. It is believed from the  results of this comparative test that the water-soluble poly› meric compound, ammonium polyacrylate, enhances the  effect of the corrosion inhibitor and, in addition, facilitates  mechanical polishing.  G. Effect of Starting Copper (Conductive Material) Com› ponent  [0128]  Using the electrolytic polishing apparatus shown in  FIGS.  2  and  3,  the influence of the presence or absence of  copper ( conductive material), as a starting component, in an  electrolytic liquid on the polishing rate and a surface rough› ness of a processed surface was determined. A substrate  (workpiece) sample, which was used in this experiment, is  a copper blanket wafer. In this experiment were used elec› trolytic liquids which had been prepared by adding copper  ( conductive material) in various amounts to a base liquid  having a pH of3 and comprising: IM malonic acid and 1 .4M  methanesulfonic acid; 0.3% of benzotriazole; 0.6% of  ammoniumpolyacrylate (molecular weight: 10,000); 0.7%  of methanol; 0.05% of an anionic surfactant (formaldehyde  condensate of ~-naphthalenesulfonic acid); and 0.5% of  abrasive particles. Electrolytic polishing was carried out  under the same conditions as described above under the  heading "effect of abrasive particles".  [0129]  FIG.  4  shows copper-concentration dependency of  the surface roughness (Rmax) of the processed surface, and  FIG.  5  shows copper-concentration dependency of the pol› ishing rate. As can be seen from FIG.  4,  the surface  roughness decreases with an increase in the concentration of  copper in the electrolytic liquid, and the use of the electro› lytic liquid having a copper concentration of not less than  0.005% provides the surface roughness of the polished  surface which is less than  ‰  of the surface roughness  obtained by the use of the electrolytic liquid containing no  copper as a starting component. As can be seen from FIG.  5,  the use of the electrolytic liquid having a copper concen› tration of not less than 0.01 % provides the polishing rate  which is more than 2.5 times the polishing rate attained by  the use of the electrolytic liquid containing no copper as a  starting component.  [0130]  A description will now be made of a process for  removing an unnecessary portion of a film of interconnect  material formed on a barrier film in a substrate as a polishing  object, thereby exposing the barrier film.  [0131]  The process comprises the steps of: a first step of  polishing a conductive material (i) lying over interconnect  portions at a lower polishing rate than that of the other  conductive material (ii) lying outside the interconnect por› tions so that the conductive material (i) becomes raised with  respect to the conductive material (ii); and a second step of  polishing the conductive material (ii) until the barrier film  becomes exposed while polishing the raised conductive  material (i). In the two-step process, an electrolytic liquid  (hereinafter referred to as second electrolytic liquid) is used  throughout the process.  [0132]  FIG.  6  is a vertical sectional front view of an  electrolytic polishing apparatus for carrying out this process.  In FIG.  6,  the same or equivalent members as the electrolytic  polishing apparatus shown in FIGS.  2  and  3  are given the  same reference numerals, and a duplicate description thereof  will be omitted.  [0133]  Above a polishing table  50  is disposed an electro› lytic liquid supply nozzle  60  for supplying an electrolytic  liquid (second electrolytic liquid) for the present barrier  layer-exposing process to the upper surface of the polishing  table  50  during polishing. The electrolytic liquid supply  nozzle  60  is connected to an electrolytic liquid supply line  64  which extends from an electrolytic liquid storage tank  62  for temporary storage of the second electrolytic liquid, and  which is provided with a not-shown electrolytic liquid  supply means, such as a tube pump, a diaphragm pump or a  bellows pump. Above the polishing table  50  is also disposed  a pure water supply nozzle  66  for supplying rinsing or  cleaning pure water to the upper surface of the polishing  table  50  after polishing.  [0134]  In this embodiment, an additive component(s) of  the second electrolytic liquid which easily precipitates or  decomposes is stored in a separate storage container  68  from  the electrolytic liquid storage tank  62,  and is added to the  second electrolytic liquid stored in the electrolytic storage  tank  62  to adjust the liquid into a predetermined condition  before supplying the liquid from the electrolytic liquid  supply nozzle  60  to the upper surface of the polishing table  50.  In some cases, however, it is possible not to provide the  storage tank  68  and to directly supply the second electrolytic  liquid, which has been prepared and stored in the electrolytic  liquid storage tank  62,  from the electrolytic liquid supply  nozzle  60  to the upper surface of the polishing table  50.  [0135]  A film thickness detection sensor  74,  e.g., com› prised of an eddy current sensor, for detecting a film  thickness of a (remaining) surface conductive material, such  as copper  34,  of a substrate W is embedded in the polishing  table  50  with the upper surface of the sensor exposed on the  surface of the processing electrode  56.  An output signal from  the film thickness detection sensor  74  is inputted into a  control section  76  via a not-shown slip ring, and a power  source  72,  a table drive section  78  for rotating the polishing  table  50,  a holder drive section  80  for rotating and vertically  moving a substrate holder  52,  etc. are controlled by an  output signal from the control section  78.  [0136]  The film thickness detection sensor  74  also detects  an end point of polishing by sensing of the film thickness of  conductive material, and outputs a signal to terminate pol› ishing. In terminating polishing, it is preferred to first stop  the application of a voltage and then stop the supply of the  second electrolytic liquid in order not to impair the polishing  performance.  [0137]  A description will now be made of the second  electrolytic liquid for use in the present barrier layer-expos› ing process carried out by the electrolytic polishing appa› ratus shown in FIG.  6.  [0138]  The second electrolytic liquid contains (1) at least  one organic acid or its salt, (2) at lest one strong acid having 