Metal polishing liquid and method for polishing film to be polished

Disclosed is a metal polishing liquid which enables a CMP with a high Cu polishing rate, while resolving the problems such as (a) polishing scratches caused by solid particles, (b) deterioration in planarity such as dishing and erosion, (c) complication of the cleaning step for removing polishing particles remaining on the substrate surface after polishing, and (d) increase in cost due to the initial cost of the solid abrasive grain itself and the cost of wastewater treatment. Also disclosed is a method for polishing a film to be polished using such a metal polishing liquid. Specifically disclosed is a metal polishing liquid containing a metal oxidizing agent, a metal oxide dissolving agent, a metal anticorrosive agent, and a water-soluble polymer having a weight average molecular weight of not less than 8,000 and containing an anionic functional group. The metal polishing liquid has a pH of not less than 1 but not more than 3. Also disclosed is a method for polishing a film to be polished, wherein a substrat