Chemical-mechanical polishing

[2] The process uses an abrasive and corrosive chemical slurry (commonly a colloid) in conjunction with a polishing pad and retaining ring, typically of a greater diameter than the wafer.

The pad and wafer are pressed together by a dynamic polishing head and held in place by a plastic retaining ring.

For example, CMP can bring the entire surface within the depth of field of a photolithography system, or selectively remove material based on its position.

Typical CMP tools, such as the ones seen on the right, consist of rotating an extremely flat plate which is covered by a pad.

Generally, these pads are made from porous polymeric materials with a pore size between 30 and 50 μm, and because they are consumed in the process, they must be regularly reconditioned.

In addition to aluminum and copper, CMP processes have been developed for polishing tungsten, silicon dioxide, and (recently) carbon nanotubes.

In addition, it was discovered that the CMP process has several potential defects including stress cracking, delaminating at weak interfaces, and corrosive attacks from slurry chemicals.

If the oxide layer has not been sufficiently thinned and/or the desired degree of planarity has not been achieved during this process, then (theoretically) the wafer can be repolished, but in a practical sense this is unattractive in production and is to be avoided if at all possible.

Moreover, STI has a higher degree of planarity making it essential in photolithographic applications, depth of focus budget by decreasing minimum line width.

To planarize shallow trenches, a common method should be used such as the combination of resist etching-back (REB) and chemical mechanical polishing (CMP).