Silica-based composite fine particle dispersion and method for manufacturing same
Disclosed is a silica-based composite fine particle dispersion including a silica-based composite fine particle which comprises a mother particle containing amorphous silica as a main component with a child particle containing crystalline ceria as a main component on a surface thereof. Features of the silica-based composite fine particle include a silica to ceria mass ratio of 100:11 to 316, and when subjected to X-ray diffraction, only the crystalline phase of ceria is detected, and when subjected to X-ray diffraction for measurement, the crystalline ceria has a crystallite diameter of 10 to 25 nm.
1. A silica-based composite fine particle dispersion, child particles primarily composed of crystalline ceria being formed on surfaces of mother particles primarily composed of amorphous silica, the silica-based composite fine particle dispersion comprising silica-based composite fine particles having an average particle size of 50 to 350 nm and having characteristic features of [1] to [5]:
[1] the silica-based composite fine particles have a mass ratio between silica and ceria of 100:11 to 316;
[2] only a ceria crystal phase is detected when the silica-based composite fine particles are subjected to X-ray diffractometry;
[3] a crystallite size in the crystalline ceria, as measured by subjecting the silica-based composite fine particles to X-ray diffractometry, is 10 to 25 nm;
[4] each of the silica-based composite fine particles has a silica coating formed partly on surfaces of the child particles; and
[5] a ratio of a percentage of a number of Si atoms to a percentage of a number of Ce atoms (Si atom %/Ce atom %) as measured by EDS measurement is not less than 0.9, the EDS measurement being performed by selectively applying electron beams to a portion of the silica coating of the silica-based composite fine particles that can be observed using a transmission electron microscope,
wherein when cation colloidal titration is performed, a streaming potential curve in which a ratio (ΔPCD/V) between an amount of streaming potential change (ΔPCD) and an amount of cation colloidal titrant added at a knick (V) as expressed by formula (1) is in a range of −110.0 to −15.0 is obtained:
Δ PCD/V =( I−C )/ V formula (1)
C: streaming potential (mV) at the knick
I: streaming potential (mV) at a starting point of the streaming potential curve; and
V: amount of the cation colloidal titrant added at the knick (mL).
2. The silica-based composite fine particle dispersion according to claim 1 having a characteristic feature of [6]:
[6] in the silica-based composite fine particles, a percentage of a number of particles having a ratio between a shorter diameter and a longer diameter, as measured by an image analysis method, of not more than 0.8 is not more than 35%.
3. The silica-based composite fine particle dispersion according to claim 1 having a characteristic feature of [7]:
silicon [7] silicon atoms enter into solid solution in the crystalline ceria as a main component of the child particles.
4. The silica-based composite fine particle dispersion according to claim 3 , wherein as for cerium atoms and silicon atoms included in the child particles, a relationship of R 1 <R 2 , where R 1 is a distance between adjacent cerium and silicon atoms, and R 2 is a distance between adjacent cerium atoms, is satisfied.
5. The silica-based composite fine particle dispersion according to claim 1 , wherein impurities are contained in the silica-based composite fine particles in amounts shown in (a) and (b):
(a) Na, Ag, Al, Ca, Cr, Cu, Fe, K, Mg, Ni, Ti, Zn, and Zr are contained in amounts of not more than 100 ppm, respectively; and
(b) U, Th, Cl, NO 3 , SO 4 , and F are contained in amounts of not more than 5 ppm, respectively.
6. The silica-based composite fine particle dispersion according to claim 1 , wherein a streaming potential before titration is a negative potential at a pH value ranging from 3 to 8.
7. A polishing abrasive grain dispersion comprising the silica-based composite fine particle dispersion according to claim 1 .
8. The polishing abrasive grain dispersion according to claim 7 , wherein the polishing abrasive grain dispersion is used for flattening a semiconductor substrate having a silica film formed thereon.
9. A polishing abrasive grain dispersion comprising the silica-based composite fine particles according to claim 1 and having an ionic strength of not less than 0.007.
10. A polishing abrasive grain dispersion according to claim 9 comprising one or two ionic strength adjusters selected from the group consisting of ammonium nitrate and ammonium acetate.
11. The polishing abrasive grain dispersion according to claim 9 , wherein the polishing abrasive grain dispersion is used for flattening a semiconductor substrate having a silica film formed thereon.
12. The polishing abrasive grain dispersion according to claim 9 , wherein the polishing abrasive grain dispersion has a pH of 3 to 8, and is used for flattening a semiconductor substrate having a silica film formed thereon.
13. The polishing abrasive grain dispersion comprising the silica-based composite fine particles according to claim 1 and further comprising an acidic compound having an acid dissociation constant (pKa) of not less than 1.5.
14. The polishing abrasive grain dispersion according to claim 13 , wherein the acidic compound is contained in an amount of 0.0002 to 0.1 mass %.
15. The polishing abrasive grain dispersion according to claim 13 , wherein the acidic compound is acetic acid.
16. The polishing abrasive grain dispersion according to claim 13 , wherein the polishing abrasive grain dispersion is used for flattening a semiconductor substrate having a silica film formed thereon.
17. The polishing abrasive grain dispersion according to claim 13 , wherein the polishing abrasive grain dispersion has a pH of 3 to 8, and is used for flattening a semiconductor substrate having a silica film formed thereon.