Abrading – Abrading process – Glass or stone abrading
Reexamination Certificate
2000-09-08
2002-02-05
Eley, Timothy V. (Department: 3723)
Abrading
Abrading process
Glass or stone abrading
C051S309000
Reexamination Certificate
active
06343976
ABSTRACT:
TECHNICAL FIELD
This invention relates to an abrasive, a method of polishing a target member, and a process for producing a semiconductor device.
BACKGROUND ART
Conventionally, in the steps of fabricating semiconductor devices, studies are commonly made on colloidal silica type abrasives used as chemical mechanical abrasives for smoothing inorganic insulating film layers such as SiO
2
insulating films formed by processes such as plasma-assisted CVD (chemical vapor deposition) and low-pressure CVD. The colloidal silica type abrasives are produced by growing silica particles into grains by a method of, e.g., thermal decomposition of tetrachlorosilicic acid, and making pH adjustment with an alkali solution containing no alkali metal, such as ammonia. Such abrasives, however, can not provide any sufficient rate of polishing for the polishing of inorganic insulating films, and have a technical problem of low polishing rate for their practical utilization.
Meanwhile, cerium oxide abrasives are used as glass surface abrasives for photomasks. Cerium oxide particles are useful for finish mirror-polishing because they have a lower hardness than silica particles and alumina particles and hence may hardly scratch polished surfaces. Also, cerium oxide, which is known as a strong oxidant, has chemically active nature. Making the most of this advantage, its application in chemical mechanical abrasives for the insulating films is useful. However, when such cerium oxide abrasives for glass surface abrasives for photomasks are used in the polishing of inorganic insulating films as they are, they have so large a primary particle diameter as to scratch, on polishing, the insulating film surface to a visually observable extent.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an abrasive that can polish polishing target surfaces of SiO
2
insulating films or the like at a high rate without scratching the surface, a method polishing a target member, and a process for producing a semiconductor device.
The present invention provides an abrasive comprising a slurry comprising a medium and dispersed therein cerium oxide particles constituted of at least two crystallites and having crystal grain boundaries.
The cerium oxide particles having crystal grain boundaries may preferably have diameter with a middle value of from 60 nm to 1,500 nm, more preferably from 100 nm to 1,200 nm, and most preferably from 300 nm to 1,000 nm. The crystallites may preferably have diameter with a middle value of from 5 nm to 250 nm, and more preferably from 5 nm to 150 nm. Preferably usable are particles wherein the cerium oxide particles having crystal grain boundaries have diameter with a middle value of from 300 nm to 1,000 nm and the crystallites have diameter with a middle value of from 10 nm to 50 nm. Also preferably usable are particles wherein the cerium oxide particles having crystal grain boundaries have diameter with a middle value of from 300 nm to 1,000 nm and the crystallites have diameter with a middle value of from 50 nm to 200 nm. The cerium oxide particles having crystal grain boundaries may preferably have a maximum diameter not larger than 3,000 nm, and the crystallites may preferably have a maximum diameter not larger than 600 nm. Those in which the crystallites have a diameter of from 10 nm to 600 nm are preferred.
The present invention also provides an abrasive comprising a slurry comprising a medium and dispersed therein abrasive grains having pores. As the abrasive grains, cerium oxide particles may preferably be used.
The pore may preferably be in a porosity of from 10% to 30% as determined from the ratio of a density measured with a pycnometer to a theoretical density determined by X-ray Rietveld analysis. The pores may also preferably have a pore volume of from 0.02 cm
3
/g to 0.05 cm
3
/g as measured by the B.J.H. (Barret, Joyner and Halende) method.
The present invention still also provides an abrasive comprising a slurry comprising a medium and dispersed therein cerium oxide particles having a bulk density not higher than 6.5 g/cm
3
. Those having a bulk density of from 5.0 g/cm
3
to 5.9 g/cm
3
are preferred.
As the medium, water may preferably be used. The slurry may contain a dispersant. The dispersant may preferably be at least one selected from a water-soluble organic polymer, a water-soluble anionic surface-active agent, a water-soluble nonionic surface-active agent and a water-soluble amine. Ammonium polyacrylate may preferably be used.
The present invention further provides an abrasive comprising cerium oxide particles constituted of at least two crystallites and having crystal grain boundaries; cerium oxide particles with a diameter not smaller than 1 &mgr;m occupying at least 0.1% by weight of the total weight of the cerium oxide particles, and the cerium oxide particles having crystal grain boundaries being capable of polishing a target member while collapsing at the time of polishing.
The present invention still further provides an abrasive comprising cerium oxide particles constituted of at least two crystallites and having crystal grain boundaries; the cerium oxide particles having crystal grain boundaries being capable of polishing a target member while forming new surfaces not coming into contact with any medium at the time of polishing.
The present invention still further provides an abrasive comprising cerium oxide particles constituted of at least two crystallites and having crystal grain boundaries, wherein;
(1) the content of cerium oxide particles having a particle diameter not smaller than 0.5 &mgr;m after polishing, measured by centrifugal sedimentation after a target member has been polished, is in a ratio of not more than 0.8 with respect to the content of cerium oxide particles having a particle diameter not smaller than 0.5 &mgr;m before polishing, measured likewise by centrifugal sedimentation;
(2) cerium oxide particle diameter at D99% by volume after polishing, measured by laser diffraction after a target member has been polished, is in a ratio of from 0.4 to 0.9 with respect to cerium oxide particle diameter at D99% by volume before polishing, measured likewise by laser diffraction; and
(3) cerium oxide particle diameter at D90% by volume after polishing, measured by laser diffraction after a target member has been polished, is in a ratio of from 0.7 to 0.95 with respect to cerium oxide particle diameter at D90% by volume before polishing, measured likewise by laser diffraction.
The method of polishing a target member according to the present invention comprises polishing a target member by the use of the abrasive described above. The target member may preferably have a strength higher than the grain boundary breaking strength of the cerium oxide particles. The target member may be a semiconductor chip on which a silica film has been formed.
The process for producing a semiconductor device according to the present invention comprises the step of polishing a semiconductor chip on which a silica film has been formed, by the use of the abrasive described above.
BEST MODE FOR PRACTICING THE INVENTION
Cerium oxide is commonly obtained by firing a cerium compound such as carbonate, sulfate or oxalate. SiO
2
insulating films formed by TEOS(tetraethoxysilane)-CVD can be polished at a higher rate as the cerium oxide has larger particle diameter and can have less crystal strain, i.e., has better crystallizability, but tend to be scratched on polishing. Accordingly, the cerium oxide particles used in the present invention are prepared without making them highly crystallizable so much. Also, since they are used in polishing for semiconductor chips, alkali metals and halogens may preferably be kept in a content of 1 ppm or less.
The abrasive of the present invention has so high a purity as to contain 1 ppm or less each of Na, K, Si, Mg, Ca, Zr, Ti, Ni, Cr and Fe and 10 ppm or less of Al.
In the present invention, the cerium oxide particles may be prepared by firing. However, in order to prepare particles not causative of polish scratches, low-
Ashizawa Toranosuke
Kurata Yasushi
Matsuzawa Jun
Ootuki Yuuto
Tanno Kiyohito
Eley Timothy V.
Hitachi Chemical Company Ltd.
Nguyen Dung Van
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