Mar. 20, 2008  13  US 2008/0067077 Al  a sulfonic acid group, (3) a corrosion inhibitor, (4) a water› soluble polymeric compound, (5) a pH adjustor, (6) abrasive  particles and (7) a surfactant. The second electrolytic liquid  may also contain, as a starting component, (8) the same  conductive material as the polishing object, e.g., copper.  [0139]  The pH of the second electrolytic liquid for the  present process is preferably adjusted to 3 to 6, more  preferably 3 to 4.5. An interaction between a polishing  object (conductive material), such as copper, in an oxidized  state and a corrosion inhibitor, a water-soluble polymeric  compound and an organic acid differs depending on the pH  of the electrolytic liquid, producing a difference in the  quality of a protective film which is formed on the surface  of the conductive material, such as copper, during polishing.  For example, when a polymeric compound is involved in the  formation of a complex between copper and a corrosion  inhibitor, such as BTA (benzotriazole ), the protecting effect  of BTA is low and the resistance to electrolytic etching is  poor at around neutral pH of the electrolytic liquid. On the  other hand, a dense strong protective film can be formed  when the pH of the second electrolytic liquid is adjusted to  3  to 4.5.  [0140]  As with the above-described electrolytic liquid, the  organic acid contained in the second electrolytic liquid for  the present process needs to form a soluble complex with a  metal (conductive material), such as copper, as a polishing  object. In particular, the organic compound needs to make a  coordinate bond with a metal, such as copper, to form a  complex which is soluble in the aqueous solution. At least  the organic acid itself must be water-soluble. As with the  above-described electrolytic liquid, the organic acid prefer› ably has at least one carboxyl group (-COOH) in the  molecule, or also has at least one hydroxyl group (-OH)  together with a carboxyl group(s) in the molecule. The same  specific organic acids as mentioned above can be used also  for the second electrolytic liquid.  [0141]  Of such usable organic acids, malonic acid, suc› cinic acid, citric acid, glycolic acid, lactic acid and gluconic  acid are particularly preferred.  [0142]  The corrosion inhibitor contained in the second  electrolytic liquid preferably is a nitrogen-containing het› erocyclic compound and may be one which is known to form  a compound with a metal, such as copper, to be processed,  and form a protective film on the metal surface, thereby  preventing corrosion of the metal. Such a corrosion inhibitor  has the effect of preventing excessive etching, thus prevent› ing dishing.  [0143]  Benzotriazole (BTA), which is well known as a  corrosion inhibitor for copper, or its derivatives can be  preferably used as a corrosion inhibitor in the second  electrolytic liquid. Examples of the derivatives include  5-methyl-lH-benzotriazole (tolyltriazole ), 1-hydroxybenzo› triazole,  4-hydroxybenzotriazole,  5-chlorobenzotriazole,  benzotriazole-5-carboxylic acid, and 5-nitrobenzotriazole.  From the viewpoint of effectively inhibiting corrosion of a  processing surface and, in addition, obtaining a glossy  processed surface with little surface roughening, it is pre› ferred to use benzotriazole or 5-methyl-lH-benzotriazole.  [0144]  Examples of other usable corrosion inhibitors, hav› ing the effect of preventing excessive polishing and thereby  preventing dishing after forming a protective film on the  surfaces of recessed portions of a polishing object, such as  copper, and clearing off a conductive material, such as  copper, between interconnect portions, may include indole;  diazole, triazole or tetrazole derivatives such as 2-ethylimi› dazole, benzimidazole, 2-mercaptobenzimidazole, 3-amino- 1,2,4-triazole,  3-amino-5-methyl-4H-1,2,4-triazole,  and  5-amino-lH-tetrazole; thiazole derivatives such as 2-mer› captobenzothiazole,  sodium  2-mercaptobenzothiazole,  2-methylbenzothiazole, (2-benzothiazolylthio )acetic acid,  3-(2-benzothiazoly lthio )propionic acid, 2-mercapto-2-thia› zolin, 2-mercaptobenzoxazole, 2-5-dimercapto-l ,3,4-thia› diazole  (bismuthiol),  5-methyl-1,3,4-thiadiazole-2-thiol,  and 5-amino-1,3,4-thiadiazole-2-thiol; pyridine; phenazine;  acridine;  l-hydroxypyridine-2-thione;  2-aminopyridine;  2-aminopyrimidine; trithiocyanuric acid; 2-dibutylamino-4,  6-dimercapto-s-triazine;  2-anilino-4,6-dimercapto-s-triaz› ine; 6-aminopurine; 6-thioguanine; thiourea; salicylic acid  and its derivatives such as salicylaldehyde and salicylalde› hyde oxime; and hydroxyquinolines such as 8-quinolinol  and 2-methyl-8-quinolinol (2-methyl-8-hydroxyquinoline ).  These compounds may be used either singly or as a mixture  of two or more.  [0145]  These compounds can form a stronger protective  film on the surfaces of recessed portions of a polishing  object, such as copper, by their adsorption onto the surface  of copper or copper oxide or by the formation of a chelate  complex or a polymeric complex with copper or copper  oxide.  [0146]  The water-soluble polymeric compound contained  in the second electrolytic liquid for the present process,  together with the corrosion inhibitor, forms a uniform pro› tective film, which effectively prevents excessive etching  and flattens a metal surface, such as copper. The viscosity of  the electrolytic liquid containing the water-soluble poly› meric compound is high in the vicinity of a metal surface  (processing surface), such as copper. A viscous film is  formed on recessed portions of fine irregularities present in  the metal surface, and the fine irregularities are polished and  removed, providing a glossy surface.  [0147]  Examples of preferable polymeric compounds hav› ing the above effect are those compounds as exemplified  above with reference to the above-described electrolytic  liquid, such as polyacrylic acid and its salts. Preferable  molecular weight and concentration of the present water› soluble polymeric compound are also the same as described  above.  [0148]  When electrolytic polishing is carried out using an  electrolytic liquid containing a corrosion inhibitor but not  containing a water-soluble polymeric compound, a protec› tive film, which is strong but not uniform, is formed on a  processing surface.  If polishing is continued, variation in the  processing rate of the processing surface, surface roughen› ing of the processing surface, the formation of pits in the  processing surface, etc. are likely to occur. Such drawbacks  can be prevented and uniform polishing becomes possible  by adding a water-soluble polymeric compound to the  electrolytic liquid. Thus, a water-soluble polymeric com› pound has the effect of adjusting the strength of a protective  film formed by a corrosion inhibitor and making the pro› tective film uniform. Polishing may therefore be carried out  in such a manner that in an initial polishing period, an  electrolytic liquid containing a water-soluble polymeric 