JP2023141786A - Polishing slurry and polishing method - Google Patents

Abstract

To provide a polishing slurry that can easily achieve both a high polishing rate and a small surface roughness on an object to be polished after polishing.SOLUTION: A polishing slurry of the present invention includes a working liquid and countless polishing particles 1 dispersed in the working liquid. Each polishing particle 1 has secondary particles consisting of countless primary particles 3 having a flat plate shape and a binding material 5 that binds each primary particle 3. The working liquid does not dissolve the binder.SELECTED DRAWING: Figure 2

Description

The present invention relates to a polishing slurry and a polishing method.

For example, when lapping a Si wafer as an object to be polished, a polishing slurry is interposed between the Si wafer and a polishing pad, and the Si wafer and polishing body are moved relative to each other under a predetermined surface pressure. A Si wafer is polished (Patent Document 1). An example of this polishing slurry is disclosed in Patent Document 2. This polishing slurry includes a machining liquid and countless abrasive particles dispersed in the machining liquid.

In a typical polishing slurry, each polishing particle is a granular primary particle of silica, alumina, or the like. When polishing a Si wafer by lapping, since the Mohs hardness of the Si wafer is 7, alumina or silicon carbide, which has a Mohs hardness of 9, is generally used as each polishing particle. The processing liquid consists of a dispersion medium such as water and additives. When the polishing slurry is used in a chemical mechanical polishing (CMP) method, oxidizing agents such as ferric nitrate and hydrogen peroxide are also used as additives.

JP2016-209987A Japanese Patent Application Publication No. 2001-40335

However, with conventional polishing slurries, it is difficult to achieve both a high polishing rate and a small surface roughness of the polished object after polishing. That is, if abrasive particles with a large particle size are employed in order to obtain a high polishing rate, the surface roughness of the polished object will increase after polishing. Furthermore, in this case, damage such as scratches and damaged layers is likely to occur on the polished object after polishing. On the other hand, if abrasive particles with a small particle size are used to reduce the surface roughness of the object to be polished after polishing, the polishing rate will be too low and processing will take a long time.

The present invention has been made in view of the above-mentioned conventional situation, and the problem to be solved is to provide a polishing slurry that can easily achieve both a high polishing rate and a small surface roughness of the polished object after polishing. It is said that Another object of the present invention is to provide a polishing method that can easily achieve both a high polishing rate and a small surface roughness of the object to be polished after polishing.

The inventors have conducted extensive studies on the reason why it is difficult to achieve both a high polishing rate and a small surface roughness of the polished object in conventional polishing slurries. The inventors first studied the mechanism of polishing an object to be polished using a polishing slurry. It is believed that polishing of the object to be polished progresses by a reaction force acting on each abrasive particle from the object to be polished during relative movement between the object to be polished and each abrasive particle, and each abrasive particle resisting each reaction force. It will be done. Abrasive particles with a large particle size strongly resist reaction force, that is, are highly aggressive toward the object to be polished, and can achieve a high polishing rate. On the other hand, when abrasive particles with a large particle size are used, the surface roughness of the polished object tends to increase after polishing, and the polished object tends to be prone to scratches and the like. On the other hand, abrasive particles with a small particle size have difficulty resisting reaction force, that is, have low aggressiveness toward the object to be polished, and can only achieve a low polishing rate. On the other hand, if abrasive particles with a small particle size are used, the surface roughness of the polished object can be reduced.

The reason why it is difficult for conventional polishing slurries to achieve both a high polishing rate and a small surface roughness of the polished object after polishing is that each abrasive particle is a granular primary particle, and each hard-to-break abrasive particle is The idea was to polish the object by its surface. Therefore, we aimed for each abrasive particle to have secondary particles. The secondary particles consist of countless primary particles and a binder that binds each primary particle. In particular, it was considered preferable that the primary particles have a tabular shape. A test was conducted to polish an object using the polishing slurry obtained in this way, and it was demonstrated that both a high polishing rate and a small surface roughness of the object after polishing could be achieved. Based on these findings, the present invention was completed.

The polishing slurry of the present invention includes a machining liquid and countless abrasive particles dispersed in the machining liquid, and is a polishing slurry for polishing an object to be polished.
Each of the abrasive particles has secondary particles consisting of countless plate-shaped primary particles and a binder that binds each of the primary particles,
The processing liquid is characterized in that it does not dissolve the binder.

In the polishing slurry of the present invention, the secondary particles having a large particle size in which each primary particle is combined resist a reaction force larger than the reaction force opposed by the primary particles, that is, exhibit moderate aggressiveness, and have a high polishing rate. It is assumed that this can be achieved. At this time, since each primary particle has a tabular shape, the edge of each primary particle becomes a cutting edge. Furthermore, since each primary particle has a tabular shape, it will crack under a large reaction force and will not strongly resist the reaction force. Therefore, it is presumed that while the local pressure acting on the point of application is reduced, the cutting edge acts more frequently due to the bonding of the primary particles, and good polishing performance is exhibited.

When a large reaction force, which the secondary particles cannot resist, acts on the secondary particles, the bonds are broken and primary particles are generated. Since the machining fluid does not dissolve the binder, the secondary particles are not loosened by forces other than reaction force. Therefore, the surface roughness of the polished object after polishing can be reduced. In addition, the object to be polished is less likely to be scratched.

Therefore, according to the polishing slurry of the present invention, it is possible to achieve both a high polishing rate and a small surface roughness of the polished object after polishing.

In the polishing method of the present invention, a polishing slurry is interposed between the workpiece to be polished and the polishing body, and the workpiece to be polished and the polishing body are relatively moved under a predetermined surface pressure. In the polishing method of polishing
The polishing slurry includes a machining liquid and countless abrasive particles dispersed in the machining liquid,
Each of the abrasive particles has secondary particles consisting of countless plate-shaped primary particles and a binder that binds each of the primary particles,
The processing liquid is characterized in that it does not dissolve the binder.

Since the polishing method of the present invention uses the polishing slurry of the present invention, it is possible to achieve both a high polishing rate and a small surface roughness of the object to be polished after polishing.

FIG. 1 is a SEM photograph of the abrasive particles used in Example 3, magnified 1000 times. FIG. 2 is an enlarged schematic diagram of the abrasive particles used in Examples 1 to 4.

As the processing fluid, a dispersion medium and additives can be used depending on the object to be polished. As the dispersion medium, in addition to water, oil, alcohol, etc. can be used. As additives, dispersants, surfactants, oxidizing agents, chlorinating agents, etc. can be employed.

The abrasive particles according to the present invention have secondary particles. The secondary particles consist of primary particles and a binder that binds each primary particle. The primary particles may be inorganic, organic, or a hybrid of inorganic and organic components. As the inorganic material, silica, alumina, silicon carbide, zirconia, ceria, CBN, diamond, glass, etc. can be used. As the organic substance, methacrylic resin, phenol resin, urea resin, melamine resin, polystyrene, polyacetal, polycarbonate, acrylic, etc. can be employed. As a hybrid of an inorganic component and an organic component, particles in which these inorganic components and organic components are optionally combined can be used. The abrasive particles according to the present invention may be only secondary particles or may include primary particles.

The primary particles according to the present invention have a tabular shape. As the plate-shaped primary particles, plate-shaped crystal grains of alumina or the like can be used. Further, it is also possible to use a material obtained by pulverizing glass that has been solidified into a thin plate.

The processing fluid is selected so as not to dissolve the binder. When the processing fluid is aqueous, oily, or alcoholic, a glassy substance containing silicon dioxide, metal, or the like can be used as the binder. When the processing fluid is aqueous, a resin or the like may be used as the binder. The inventors have confirmed the effect when the processing fluid is water, the primary particles are alumina plate-shaped crystal grains, and the binder is glassy containing silicon dioxide.

According to the inventors' test results, each secondary particle has a BET specific surface area of 1.49 m ² /g or more and 2.10 m ² /g or less, and a bulk density of 0.70 g/cm ³ or more. , 0.95 g/cm ³ or less. In this case, the polishing rate is sufficiently high and the surface roughness of the polished object after polishing is sufficiently small.

According to the test results of the inventors, when the object to be polished is a Si wafer, it is practical to use the polishing slurry for lapping the object to be polished.

"test"
The following machining liquid and abrasive particles were prepared.
(processing fluid)
Dispersion medium: water (abrasive particles)
Example 1: Secondary particles (binder is glassy containing silicon dioxide, BET specific surface area is 1.49 m ² /g, bulk density is 0.76 g/cm ³ )
Example 2: Secondary particles (binder is glassy containing silicon dioxide, BET specific surface area is 1.64 m ² /g, bulk density is 0.95 g/cm ³ )
Example 3: Secondary particles (binder is glassy containing silicon dioxide, BET specific surface area is 1.84 m ² /g, bulk density is 0.70 g/cm ³ )
Example 4: Secondary particles (binder is glassy containing silicon dioxide, BET specific surface area is 2.10 m ² /g, bulk density is 0.79 g/cm ³ )
Comparative Example 1: Primary particles (average particle size 30 μm, BET specific surface area 0.22 m ² /g, bulk density 1.76 g/cm ³ )
Comparative Example 2: Primary particles (average particle size 3 μm, BET specific surface area 1.82 m ² /g, bulk density 1.30 g/cm ³ )
Comparative Example 3: Secondary particles (binder is glassy containing silicon dioxide, BET specific surface area is 1.19 m ² /g, bulk density is 0.50 g/cm ³ )
The primary particles constituting the secondary particles of Examples 1 to 4 and Comparative Example 3 are plate-shaped crystal grains of alumina, and the primary particles of Comparative Examples 1 and 2 are granular crystal grains of alumina. Table 1 shows the BET specific surface area and bulk density of each abrasive particle.

A SEM photograph of the abrasive particles used in Example 3 at a magnification of 1000 times is shown in FIG. Further, an enlarged schematic diagram of the abrasive particles used in Examples 1 to 4 and Comparative Example 3 is shown in FIG. As shown in FIG. 2, the abrasive particles 1 used in Examples 1 to 4 and Comparative Example 3 are secondary particles in which countless plate-shaped primary particles 3 are combined. The secondary particles are composed of primary particles 3 and a binder 5 that binds each primary particle 3 together. The binding material 5 is vitreous and does not dissolve in water.

Polishing slurries of Examples 1 to 4 and Comparative Examples 1 to 3 were prepared by mixing 10% by mass of abrasive particles with water as a processing fluid.

Using the polishing slurries of Examples 1 to 4 and Comparative Examples 1 to 3, SiC wafers were polished under the following processing test conditions, and the polishing rate (μm/min) and surface roughness (Sa) (nm) were examined. Ta.

<Test conditions>
Testing machine: Wafer polishing equipment (Engis EJW-380)
Workpiece (object to be polished): SiC bare wafer (4 inches)
Processing pressure: 20kPa
Surface plate/work rotation speed: 60/60 rpm
Lap board dimensions: 30cm in diameter
Supply amount of polishing slurry: 10 mL/min Polishing body fixed on surface plate: Polyurethane pad Processing time: 30 minutes

The polishing rate was evaluated as 0.3 μm/min or more as ○, 0.2 μm/min or more and less than 0.3 μm/min as Δ, and less than 0.2 μm/min as ×. The surface roughness was evaluated using a white interference microscope (Sa with a 200 μm square field of view) when 65 nm or less was rated as ○, when it was more than 65 nm and 110 nm or more, it was Δ, and when it was more than 110 was evaluated as ×. In addition, the dispersion state of the abrasive particles in the abrasive slurry during processing was visually determined. If each abrasive particle settled and became a lump, it was evaluated as ×, and if each abrasive particle was dispersed without settling, it was evaluated as ○. The results are shown in Table 2.

Table 2 shows that the polishing slurries of Examples 1 to 4 can achieve both a high polishing rate and a small surface roughness of the polished Si wafer. In other words, by polishing a Si wafer using the polishing slurries of Examples 1 to 4, it is easy to achieve both a high polishing rate and a small surface roughness of the Si wafer after polishing. The abrasive particles in the polishing slurries of Examples 1 to 4 have a BET specific surface area of 1.49 m ² /g or more and 2.10 m ² /g or less, and a bulk density of 0.70 g/cm ³ or more and 0. Since it is .95 g/cm ³ or less, it can be seen that if the BET specific surface area and bulk density are within these ranges, the polishing rate is sufficiently high and the surface roughness of the polished object after polishing is sufficiently small. In particular, according to the polishing slurries of Examples 3 and 4, the polishing rate was sufficiently high and the surface roughness of the Si wafer after polishing was sufficiently small.

Furthermore, in the polishing slurries of Examples 1 to 4, compared to the polishing slurries of Comparative Examples 1 and 2, the abrasive particles were dispersed in the processing fluid for a long period of time, and it was found that the abrasive particles were less likely to settle. Therefore, in the polishing slurries of Examples 1 to 4, there is no need to add an excessive amount of dispersant, making it easier to process the polishing slurry after polishing, reducing manufacturing costs and reducing environmental impact. Is possible.

In the above, the present invention has been explained based on Examples 1 to 4, but the present invention is not limited to Examples 1 to 4, and can be applied with appropriate changes without departing from the spirit thereof. Needless to say.

INDUSTRIAL APPLICATION This invention can be utilized for the manufacturing method of a semiconductor device, a manufacturing apparatus, etc.

1... Abrasive particles 3... Primary particles 5... Binding material

Claims (5)

A polishing slurry for polishing an object to be polished, which includes a machining fluid and countless abrasive particles dispersed in the machining fluid,
Each of the abrasive particles has secondary particles consisting of countless plate-shaped primary particles and a binder that binds each of the primary particles,
A polishing slurry characterized in that the processing liquid does not dissolve the binder. the processing fluid is water;
The primary particles are plate-shaped crystal grains of alumina,
The polishing slurry according to claim 1, wherein the binder is vitreous containing silicon dioxide. Each of the secondary particles has a BET specific surface area of 1.49 m ² /g or more and 2.10 m ² /g or less, and a bulk density of 0.70 g/cm ³ or more and 0.95 g/cm ³ or less. The polishing slurry according to claim 1 or 2. The object to be polished is a Si wafer,
The polishing slurry according to any one of claims 1 to 3, which is used for lapping the object to be polished. A polishing method for polishing the object to be polished by interposing a polishing slurry between the object to be polished and the polishing body and relatively moving the object to be polished and the polishing body under a predetermined surface pressure,
The polishing slurry includes a machining liquid and countless abrasive particles dispersed in the machining liquid,
Each of the abrasive particles has secondary particles consisting of countless plate-shaped primary particles and a binder that binds each of the primary particles,
A polishing method characterized in that the processing liquid does not dissolve the binder.

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