Multiple step CMP polishing

A chemical mechanical polishing method for planarizing semiconductor substrates, comprising the steps of:

• providing two concentric and coplanar rotatable platens with detachable polishing pads for supporting semiconductor substrates;
• said concentric and coplanar platens cover radial distances greater than the outside dimensions of said semiconductor substrate;
• providing a means for distributing two kinds of polishing slurries, one to each polishing pad;
• providing an annular gap between said polishing platens for preventing cross contamination from one polishing platen to the other;
• providing a differential drive arrangement for independently controlling the rotation of each of said concentric polishing platens, said differential drive arrangement includes a controllable primary drive that is coupled to rotate both concentric polishing platens, with a piggy-back secondary drive that is coupled to the inner most platen, said secondary drive is used to controllably add to or to subtract from the rotation of said inner most platen;
• providing a means for controlling an applied pressure to said substrate during polishing.