Chemical Mechanical Polishing - CMP

What is Chemical Mechanical Polishing?

Chemical Mechanical Polishing, more commonly known as CMP Polishing is the final removal step in the manufacture of silicon wafers. To achieve high surface flatness of silicon wafers, this process is performed through two parallel actions as its name suggests:

Mechanical action (polishing pad and retaining ring) helped with a chemical substance (abrasive and corrosive) named slurry (commonly a colloid). 

Chemical Mechanical Polishing - CMP for silicon wafer

A slurry is a thin and viscous fluid mixture composed of a pulverized solid and a liquid.

The pad and the wafers are pressed together (according to a precise and controlled pressure) by a dynamic polishing head. This head is rotated with different axes of rotation. This process enables the elimination of any irregular area in order to get a silicon wafer completely flat and planar. It is necessary to follow this procedure to succeed a Roughness down to the Angstrom and a Total Thickness Variation (TTV) as low as possible.  

This process achieves super-flat silicon wafers, mirrored surface with an extra low roughness.

 

Two steps are used for silicon wafers: “Pre-polishing” (stock removal) and “Final Polishing”

The “Pre-polishing” process generates the required geometrical properties of the wafer. Then, two polishing process are available:

During SSP (Single Side Polishing)

  • Only one side is polished, the second one presents an etched surface named “backside”.

During DSP (Double Side Polishing)

  • Two sides are polished. This process is suitable for highest flatness.
  • The “Final Polishing” process generates the final roughness of the wafer.
  • With the standard process the RMS (Root Mean Square) is closed to 5 Å.
  • On demand, we perform a specific “final Polishing” process to reach a RMS less than 3 Å.

technical data

Total thickness variation (ttv) on Double side polished

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  • TTV 4’’ wafers with a thickness > 400μm => TTV < 2μm
  • TTV 6’’ wafers with a thickness > 500 μm => TTV < 3 μm

roughness

Roughness

  • Average surface Roughness (Ra) < 3 Å (AFM measurement) (25 x 25 μm)

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