Reexamination Certificate
2001-11-28
2003-09-09
Marcheschi, Michael (Department: 1755)
C051S307000, C423S263000
Reexamination Certificate
active
06615499
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for producing cerium oxide, a cerium oxide abrasive, a method for polishing a substrate using the same, and a method for manufacturing a semiconductor device, and more specifically relates to a method for producing cerium oxide particles with high productivity and yield, a cerium oxide abrasive that can provide high speed polishing without causing scratches irrespective of the film properties, a method for polishing a substrate using the same, and a method for manufacturing a semiconductor device having high reliability with high productivity and yield.
BACKGROUND ART
In a manufacturing process of a semiconductor device, as a chemical-mechanical polishing method for smoothing an inorganic insulating layer such as an SiO
2
insulating layer, which is formed by a plasma CVD method, or low-pressure CVD method, a CMP method has been conventionally used. As an abrasive used for the CMP method, a colloidal silica series abrasive or slurry using silica particles, cerium oxide particles or the like as the abrasive grain is used.
The colloidal silica series abrasive is produced by grain-growing silica particles by a process of pyrolyzing silicic acid tetrachloride or the like and pH adjusting the silica particles with an alkaline solution containing no alkali metal such as ammonia, etc. However, such an abrasive has a technical problem that the polishing speed on an inorganic insulating film is not sufficient and higher polishing speed is required for practical use.
On the other hand, as a glass-surface abrasive for a photomask, a cerium oxide abrasive has been used. Cerium oxide particles have lower hardness than silica particles or alumina particles, therefore it tends to cause few scratches on the surface to be polished and thereby it is useful in finishing mirror polishing. Further, as the cerium,oxide has been known as a strong oxidant, it has chemically active properties. Thus, by utilizing these advantages of the cerium oxide, the application of it to a chemical-mechanical abrasive for the insulating film is useful.
However, when a cerium oxide abrasive is applied to inorganic insulating film polishing as it is to polish a glass surface for a photomask, a problem arises that it causes scratches to a degree that can be visually noticed on the insulating film surface as the diameter of the primary grain is large. Further, there is another problem that some types of a cerium oxide abrasive greatly change its polishing speed depending on the film properties of a surface to be polished.
An object of the present invention is to provide a method of easily producing cerium oxide that can polish a surface to be polished such as an SiO
2
insulating film, etc., at high speed and good yield without causing scratches.
Another object of the present invention is to provide a cerium oxide abrasive having cerium oxide as an essential component that can polish a surface to be polished such as an SiO
2
insulating film, etc., at high speed irrespective of the film properties without causing scratches.
Yet another object of the present invention is to provide a method for polishing a substrate that can polish a surface to be polished such as an insulating film, etc., at high speed irrespective of film properties without causing scratches.
Still further object of the present invention is to provide a method for manufacturing a semiconductor device in which a semiconductor device having excellent reliability can be manufactured with high productivity and yield.
DISCLOSURE OF THE INVENTION
The present invention relates to a method for producing cerium oxide comprising rapid heating of cerium salts to a calcining temperature to calcine them.
Further, the present invention relates to the method for producing cerium oxide in which the temperature rise rate of raising to the calcining temperature is set to 20 to 200° C./min.
Further, the present invention relates to the method for producing cerium oxide in which the calcining is performed by a rotary kiln.
Further, the present invention relates to the method for producing cerium oxide in which the calcining temperature is set to 600 to 1,000° C. and the calcining time is set to 30 minutes to 2 hours.
Further, the present invention relates to a cerium oxide abrasive containing the cerium oxide produced by the above-mentioned method for producing cerium oxide and pure water.
The present invention also relates to an abrasive containing a slurry in which cerium oxide particles having an intensity ratio of the area of a primary peak appearing at 27 to 30° to that of a secondary peak appearing at 32 to 35° (primary peak/secondary peak) of 3.20 or more in a powder X-ray diffraction chart are dispersed into a medium.
Further, the present invention relates to an abrasive containing slurry in which abrasive grains having pores are dispersed into a medium.
Further, the present invention relates to an abrasive containing slurry in which cerium oxide particles having a bulk density of 6.5 g/cm
3
or less are dispersed into a medium.
Further, the present invention relates to a method for polishing a substrate comprising polishing a predetermined substrate using the above-mentioned abrasive.
Further, the present invention relates to a method for manufacturing a semiconductor device comprising the step of polishing a semiconductor chip on which a silica film is formed with the above-mentioned abrasive.
BEST MODE FOR CARRYING OUT THE INVENTION
The cerium salts to be used in the present invention may include cerium carbonate, cerium sulfate, cerium oxalate and the like. These cerium salts may be hydrates. From the viewpoint of producing a cerium oxide easily with good yield, which is an essential component of a cerium oxide abrasive that can polish a surface to be polished such as an SiO
2
insulating film, etc., at high speed without causing scratches, cerium carbonate is preferably used and cerium carbonate hydrate is more preferably used as the cerium salts.
It is preferred that these cerium salts be in the form of powder in terms of workability.
In the method for producing cerium oxide of the present invention, it is necessary to rapidly heat cerium salts to raise the temperature to a calcining temperature and calcine them.
When gradual heating of the cerium salts is conducted to raise the temperature to a calcining temperature and they are calcined, the obtained cerium oxide does not have desired performance, and a cerium oxide abrasive using such cerium oxide is likely to cause scratches on the surface to be polished and high speed polishing becomes difficult.
Here, the temperature rise rate of raising the temperature of cerium salts to a calcining temperature is preferably set to 20 to 200° C./min, and more preferably to 40 to 200° C./min.
Further, while the calcining process may be performed in a batch furnace, it may be preferably performed by a rotary kiln.
Further, the calcining temperature is preferably set to 600 to 1,000° C.
Further, the calcining time is preferably set to 30 minutes to 2 hours.
The rotary kiln is an already known furnace, and a type of the rotary kiln is not limited. There may be mentioned, for example, a material in which a refractory lined cylindrical kiln is provided such that the axis of the kiln is inclined relative to the horizontal line, both ends of the kiln are rotatably supported by the upper and lower side supporting members respectively, and the rotary kiln is rotatably driven through a driving apparatus such as a motor and a gear attached to the output shaft of the driving apparatus with a ring-shaped gear mounted on the periphery of the kiln.
In case of using a rotary kiln, a preferred embodiment is as follows. The temperature in the rotary kiln duct is defined as 600 to 1,000° C. and the rotary kiln is previously heated to the temperature. Then cerium carbonate hydrate is charged into the kiln duct at a predetermined weight per hour, and the rotary kiln is rapidly heated at a temperature rise rate of 20 to 200° C./min. At that time, the filling rate of cerium carbonat
Ashizawa Toranosuke
Hirai Keizou
Matsuzawa Jun
Ootsuki Yuuto
Sugimoto Atsushi
Hitachi Chemical Co. Ltd.
Marcheschi Michael
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