JP3702775B2 - Abrasive grain classification method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to abrasive grain classification technology, and more particularly to a method and apparatus for classifying abrasive grains mixed in a polishing agent or the like of a silicon wafer.
[0002]
[Prior art]
In the manufacturing process of a silicon wafer, abrasives are contained in the slurry and abrasive for wire saw. For example, SiC abrasive grains and SiO ₂ abrasive grains. The abrasive grains give a grinding action to the silicon wafer in slicing, polishing and the like.
And the management of the particle size is important for the abrasive grains used in such slicing and polishing. This is because the polishing accuracy and slicing accuracy can be increased by using abrasive grains having a uniform particle size distribution. The distribution of the grain size of the abrasive grains greatly affects the flatness of the silicon wafer surface.
Conventionally, the classification of the abrasive grains is performed by primary to tertiary water sieve classification. In water sieving classification, water volume, water pressure, and water temperature are controlled and classified.
Specifically, primary water sieving classification, secondary water sieving classification, tertiary water sieving classification, filtration, drying, sieving (giving vibration), and inspection are performed in this order.
[0003]
[Problems to be solved by the invention]
However, in such a wet classification method, the abrasive grains are hardened, and there is a limit to reducing the distribution width of the abrasive grains as the abrasive grains become finer. Also, the yield is very bad. This is because if the particle size is small, it will float in the air, making it difficult to capture by gravity.
[0004]
Therefore, as a result of extensive research, the inventor applied static charges to each abrasive grain by blowing dry nitrogen gas onto the abrasive grains dried in the sieving machine, and the particle diameter was selected by this charge. Thus, the present invention has been completed by focusing on the fact that the accuracy of the abrasive grain size distribution can be improved and the yield is improved.
[0005]
OBJECT OF THE INVENTION
An object of the present invention is to provide a classification technique capable of managing the particle size distribution of fine abrasive grains with high accuracy.
Another object of the present invention is to provide an abrasive classification technique with a high yield in classification.
[0006]
[Means for Solving the Problems]
According to the first aspect of the present invention, a dry nitrogen gas is blown onto a predetermined amount of dry abrasive grains to give each abrasive grain a charge due to static electricity and move in one direction. Is a method for classifying abrasive grains by classifying each abrasive grain by accelerating it in an electric field and passing a magnetic field through the moving abrasive grains .
Examples of the abrasive grains include SiC abrasive grains and diamond abrasive grains.
[0007]
For example, it is assumed that predetermined kinetic energy is applied to each abrasive grain by spraying dry nitrogen gas or the like at a predetermined flow rate.
[0008]
According to a second aspect of the present invention, when the abrasive grains pass through the magnetic field, a plurality of pockets are charged to a conductivity type opposite to the charge of the abrasive grains, and the movement direction of each abrasive grain is changed by Lorentz force. In addition, the abrasive grain classification method according to claim 1 , wherein the moving abrasive grains are separated and captured in each pocket by making the curvature of the movement locus different depending on the mass of each abrasive grain .
For example, dry nitrogen gas or the like is sprayed at a predetermined flow rate, and each charged abrasive grain is accelerated by an electric field to give a predetermined kinetic energy.
[0009]
According to a third aspect of the present invention, there is provided means for causing each abrasive grain to be charged by static electricity by blowing dry nitrogen gas onto a predetermined amount of dried abrasive grain, and for moving in one direction. A means for accelerating each charged abrasive grain with an electric field and a means for classifying each abrasive grain size by passing a magnetic field through the moving abrasive grains. It is a classification device.
[0010]
[0011]
According to a fourth aspect of the present invention, the classifying means charges the plurality of pockets to a conductivity type opposite to the charge of the abrasive grains when the abrasive grains pass through the magnetic field, and uses each Lorentz force to The abrasive grains according to claim 3, wherein the abrasive grains that have moved are separated and captured in each pocket by changing the direction of movement of the grains and changing the curvature of the locus of movement depending on the mass of each abrasive grain. This is a classification device.
[0012]
[Action]
According to this invention, an electric charge is added to each abrasive grain, and further kinetic energy is added. By passing an electric field or a magnetic field through the abrasive grains moved in one direction, the abrasive grains can be classified according to the kinetic energy and the Lorentz force from the magnetic field. This is because the larger the grain size, the larger the mass and the different reach distance due to inertia.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, an abrasive grain supply unit 12 is disposed at one end of a bowl-shaped casing 11, and an abrasive capturing unit 14 is disposed at the other end. The supply unit 12 and the capture unit 14 are separated by a predetermined distance.
A fixed amount of dry nitrogen gas is flowed to a predetermined amount of abrasive grains (fine silica) supplied by the supply unit 12 to stir the abrasive grains, and each abrasive grain is fixed by static electricity due to friction. Apply charge.
The accelerating unit 13 includes an anode 15 on one end side and a cathode 16 on the other end side separated from the anode 15 by a predetermined distance. In this acceleration part 13, the said abrasive grain is accelerated. Reference numeral 17 denotes the power source.
Further, a nitrogen gas blow-out port 18 is provided at one end portion so as to open toward the other end side. Nitrogen gas is blown into the accelerating portion 13 of the casing 11 at a predetermined flow rate from the blowout port 18 and is discharged from the outlet 19 on the other end side.
The capture unit 14 provided at the other end is configured to apply an electric field (or magnetic field) to each abrasive grain when the charged abrasive grains are caused to flow by nitrogen gas. Capture it in two. That is, the capturing pockets 20A, 20B, 20C,... Are arranged side by side along the direction of movement of the abrasive grains. In these pockets 20A, 20B..., Abrasive grains are captured and stored according to the particle diameter.
[0014]
In this classifying apparatus, a predetermined amount of abrasive grains is charged into the supply unit 12. Electric charges are applied by blowing nitrogen gas in the supply unit 12. The charged abrasive grains are transferred from the blow-out port 18 to the accelerating unit 13 where the abrasive grains are accelerated in a certain direction (toward the other end side). Each abrasive grain has a predetermined kinetic energy depending on its grain size, that is, mass.
The charged abrasive grains are accelerated by the acceleration unit 13 and fly toward the other end.
These abrasive grains are sucked and captured in the capturing unit 14. That is, in the capture unit (magnetic field application unit) 14, the pockets 20A, 20B,... Are charged to have a conductivity type opposite to that of the abrasive grains (a magnetic field is formed), whereby the pockets 20A, 20B,. · Sucks abrasive grains. The movement direction of the abrasive grains is changed by the Lorentz force, and the curvature of the movement trajectory varies depending on the mass of each abrasive grain, so that the abrasive grains that have flew are separated into the pockets 20A, 20B. Be captured.
[0015]
【The invention's effect】
According to this invention, it is possible to classify abrasive grains with high accuracy. At the same time, the yield in classifying abrasive grains can be increased. As a result of this classification, the distribution width of the abrasive grains can be kept small. As a result, the finished thickness, processing accuracy, processing allowance, and processing time of a workpiece (for example, a silicon wafer) in processing using the abrasive grains are stabilized. be able to. In addition, the work-affected layer can be made uniform.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a schematic configuration of an abrasive grain classification device according to an embodiment of the present invention.
[Explanation of symbols]
12 supply section,
13 Accelerator,
14 Capture part,
18 Gas outlet.

Claims (4)

By spraying dry nitrogen gas to a predetermined amount of dry abrasive grains, each abrasive grain is charged with static electricity and moved in one direction,
Accelerate with an electric field for each charged abrasive grain moving in this one direction,
A method for classifying abrasive grains by classifying each abrasive grain size by passing a magnetic field through the moving abrasive grains . When the abrasive grains pass through the magnetic field, a plurality of pockets are charged to a conductivity type opposite to the charge of the abrasive grains, the direction of movement of each abrasive grain is changed by Lorentz force, and the difference in mass of each abrasive grain The method of classifying abrasive grains according to claim 1, wherein the abrasive grains that have moved are separated and captured in each pocket by varying the curvature of the locus of movement . A means for causing each abrasive grain to be charged by static electricity by blowing dry nitrogen gas onto a predetermined amount of dried abrasive grain, and means for moving in one direction,
Means for accelerating in an electric field for each charged abrasive grain moving in this one direction;
A means for classifying abrasive grains, including means for classifying each abrasive grain size by passing a magnetic field through the moving abrasive grains . The classifying means charges the plurality of pockets in a conductivity type opposite to the charge of the abrasive grains when the abrasive grains pass through the magnetic field, changes the movement direction of each abrasive grain by Lorentz force, The apparatus for classifying abrasive grains according to claim 3, wherein the abrasive grains that have moved are separated and captured in each pocket by making the curvature of the movement locus different depending on the mass of the abrasive grains .

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