A silicon wafer polishing by a chemical mechanical polishing (CMP) ensures a high-accuracy flattening by a multistage-polishing having three or four stages. A primary polishing performed in a first stage and a secondary polishing performed in a second stages aim mainly to flatten the surface of the silicon wafer and, therefore, require a high polishing rate.
In the primary polishing and some of the secondary polishing, the polishing composition slurry is generally used cyclically and repeatedly. However, the repeated use of slurry leads to the decrease of pH and polishing properties of slurry. In particular, the polishing rate is decreased remarkably. Thus, it is necessary that a slurry which is degraded in properties to a certain degree is replaced with new slurry, which causes a problem such as interruption of processes for the replacement and increase in costs.
In order to prevent the decrease of the polishing properties such as a polishing rate without the replacing operations, it is effective to occasionally add an inorganic alkali solution such as potassium hydroxide or sodium hydroxide or add new slurry itself, to the circulating slurry.
In addition, polishing solution for a semiconductor wafer disclosed in Japanese Unexamined Patent Publication JP-A 2002-252189 is used when performing the polishing with a polishing tool in which abrasive grains are fixed. Moreover, as the polishing solution, a mixture of sodium hydroxide or potassium hydroxide with sodium carbonate or potassium carbonate is used.
By adding the inorganic alkali solution such as potassium hydroxide or sodium hydroxide or by adding new slurry itself, it is possible to prevent the decrease of an average polishing rate after performing the polishing more than once. However, there is a problem that the polishing rate varies widely before and after the addition of them.
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