Method for filtering polishing additive-containing liquid, polishing additive-containing liquid, polishing composition, method for producing polishing composition, and filter
Provided is a method for filtering an additive-containing liquid that can achieve a polishing composition exhibiting excellent defect reducing capability while maintaining a practical filter life. The method for filtering a polishing additive-containing liquid provided by the present invention includes the step of: filtering the polishing additive-containing liquid with a filter that satisfies the following conditions (1) and (2). (1) The average pore diameter P measured by a palm porometer is 0.15 μm or less. (2) The pore diameter gradient (S in /S out ), which is the ratio of the inlet-side average pore diameter (S in ) to the outlet-side average pore diameter (S out ), both diameters being measured through observation with an SEM, is 3 or less.
1 . A method for filtering a liquid containing a polishing additive, the method comprising the step of:
filtering the liquid with a filter, wherein the filter has the following properties:
an average pore diameter P, measured by a palm porometer, of 0.15 μm or less; and
a pore diameter gradient (S in /S out ) of 1.11 or greater and 3 or less, wherein the pore diameter gradient is a ratio of an inlet-side average pore diameter (S in ) to an outlet-side average pore diameter (S out ), the diameters being measured through observation with an SEM;
wherein:
the liquid is a filtrate subjected to at least one pre-filtration; and
a removal rating of a first-step filtration in the pre-filtration is from 0.05 μm to 0.25 μm.
2 . The method according to claim 1 , wherein the polishing additive contains a water-soluble polymer.
3 . The method according to claim 2 , wherein the water-based polymer contains a cellulose derivative.
4 . The method according to claim 2 , wherein the liquid contains water, and at least part of the water-soluble polymer is dissolved in the water.
5 . The method according to claim 1 , wherein the liquid contains substantially no abrasive.
6 . The method of claim 1 , wherein the pore diameter gradient (S in /S out ) is 1.74 or greater and 3 or less.
7 . A polishing additive-containing liquid that has been filtered by the method according to claim 1 .
8 . A polishing composition comprising:
a polishing additive contained in a polishing additive-containing liquid that has been filtered with a filter, wherein the filter has the following properties:
an average pore diameter P, measured by a palm porometer, of 0.15 μm or less; and
a pore diameter gradient (S in /S out ) of 1.11 or greater and 3 or less, wherein the pore diameter gradient is a ratio of an inlet-side average pore diameter (S in ) to an outlet-side average pore diameter (S out ), the diameters being measured through observation with an SEM;
wherein:
the polishing additive-containing liquid is obtained by filtering a liquid that has been subjected to at least one pre-filtration; and
a removal rating of a first-step filtration in the pre-filtration is from 0.05 μm to 0.25 μm.
9 . The polishing composition of claim 8 , wherein the pore diameter gradient (S in /S out ) is 1.74 or greater and 3 or less.
10 . A method for producing a polishing composition, the method comprising the steps of:
filtering a liquid comprising a polishing additive with a filter to obtain a polishing additive-containing liquid; and
mixing the obtained polishing additive-containing liquid with a liquid containing abrasive to prepare a polishing composition,
wherein the filter has the following properties:
an average pore diameter P, measured by a palm porometer, of 0.15 μm or less; and
a pore diameter gradient (S in /S out ) of 1.11 or greater and 3 or less, wherein the pore diameter gradient is a ratio of an inlet-side average pore diameter (S in ) to an outlet-side average pore diameter (S out ), the diameters being measured through observation with an SEM;
wherein:
the liquid is a filtrate subjected to at least one pre-filtration; and
a removal rating of a first-step filtration in the pre-filtration is from 0.05 μm to 0.25 μm.
11 . The method of claim 10 , wherein the pore diameter gradient (S in /S out ) is 1.74 or greater and 3 or less.
12 . A filter used for filtering a liquid containing a polishing additive, the filter having the following properties:
an average pore diameter P, measured by a palm porometer, of 0.15 μm or less; and
a pore diameter gradient (S in /S out ) of 1.11 or greater and 3 or less, wherein the pore diameter gradient is a ratio of an inlet-side average pore diameter (S in ) to an outlet-side average pore diameter (S out ), the diameters being measured through observation with an SEM; and
wherein the filter is a pleated filter.
13 . The filter of claim 12 , wherein the pore diameter gradient (S in /S out ) is 1.74 or greater and 3 or less.
14 . A filter used for filtering a liquid containing a polishing additive, the filter having the following properties:
an average pore diameter P, measured by a palm porometer, of 0.15 μm or less; and
a pore diameter gradient (S in /S out ) of 3 or less, wherein the pore diameter gradient is a ratio of an inlet-side average pore diameter (S in ) to an outlet-side average pore diameter (S out ), the diameters being measured through observation with an SEM; and
wherein:
the filter is a pleated filter; and
the filter comprises polyethersulfone or polysulfone.