Polishing slurry and polishing method

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

[Technical field]

[0001] The present invention relates to a polishing slurry and a polishing method. [Background technology]

[0002] 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 the polishing body are moved relative to each other under a predetermined surface pressure to polish the Si wafer (Patent Document 1). An example of this polishing slurry is disclosed in Patent Document 2. This polishing slurry contains a processing liquid and a countless number of abrasive particles dispersed in the processing liquid.

[0003] In a typical polishing slurry, each abrasive particle is a granular primary particle of silica, alumina, etc. 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 abrasive particle. The processing liquid is composed of a dispersion medium such as water and an additive. When the polishing slurry is used in a chemical mechanical polishing (CMP) method, an oxidizing agent such as ferric nitrate or hydrogen peroxide solution is also used as an additive. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-209987 A [Patent Document 2] JP 2001-40335 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional polishing slurries, it is difficult to achieve both high polishing rate and small surface roughness of the polished object after polishing. That is, if large grain size polishing particles are used to obtain high polishing rate, the surface roughness of the polished object after polishing becomes large. In addition, in this case, damage such as scratches and processing-induced alteration layer is likely to occur on the polished object after polishing. On the other hand, if small grain size polishing particles are used to reduce the surface roughness of the polished object after polishing, the polishing rate is too low, and processing takes a long time.

[0006] The present invention has been made in consideration of the above-mentioned conventional situation, and the problem to be solved is to provide a polishing slurry that can easily achieve both high polishing rate and small surface roughness of the polished object after polishing.The problem to be solved is to provide a polishing method that can easily achieve both high polishing rate and small surface roughness of the polished object after polishing. [Means for solving the problem]

[0007] The inventors have intensively studied the reason why it is difficult to achieve both a high polishing rate and a small surface roughness of the polished object after polishing in conventional polishing slurries. The inventors first studied the polishing mechanism of the polished object by the polishing slurry. It is considered that the polishing of the polished object proceeds by a reaction force acting from the polished object to each abrasive particle during the relative movement between the polished object and each abrasive particle, and each abrasive particle countering each reaction force. Abrasive particles with a large particle size strongly counter the reaction force, that is, are highly aggressive to the polished object, 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 after polishing tends to increase, and the polished object tends to cause scratches, etc. On the other hand, abrasive particles with a small particle size are difficult to counter the reaction force, that is, are less aggressive to the polished object, and can only achieve a low polishing rate. On the other hand, when abrasive particles with a small particle size are used, the surface roughness of the polished object after polishing can be reduced.

[0008] The reason why it is difficult to achieve both a high polishing rate and a small surface roughness of the polished object after polishing in conventional polishing slurries is that each polishing particle is a granular primary particle, and each of the polishing particles is difficult to break and polishes the polished object by its surface. Therefore, it is aimed at each polishing particle having secondary particles. The secondary particles are composed of countless primary particles and a binder that bonds each primary particle. It is considered that it is particularly preferable for the primary particles to be flat. When a test is carried out to polish an object using the polishing slurry obtained in this way, it is demonstrated that both a high polishing rate and a small surface roughness of the polished object after polishing can be achieved. Based on these findings, the present invention has been completed.

[0009] The polishing slurry of the present invention has a processing liquid and a countless number of abrasive particles dispersed in the processing liquid, and is used for polishing an object to be polished, Each of the abrasive particles has secondary particles composed of a countless number of flat primary particles and a binder that bonds the primary particles together, The processing fluid dissolves the binder. Without Each of the secondary particles has a BET specific surface area of ​​1.49 m 2 / g or more, 2.10m 2 / g or less and a bulk density of 0.70 g / cm 3 More than 0.95g / cm 3 Is less than or equal to It is characterized by:

[0010] In the polishing slurry of the present invention, it is presumed that the secondary particles having a large particle diameter, which are formed by bonding each primary particle, can resist a larger reaction force than the reaction force that the primary particle resists, that is, they can exhibit moderate aggressiveness, and can achieve a high polishing rate. At this time, since each primary particle is flat, the edge of each primary particle becomes a cutting edge. Also, since each primary particle is flat, it breaks under a large reaction force and does not strongly resist the reaction force. Therefore, it is presumed that the cutting edge acts frequently due to the bonding of primary particles while reducing the local pressure acting on the point of action, and thus exhibits good polishing properties.

[0011] When a large reaction force that the secondary particles cannot resist acts on the secondary particles, the bonds are broken and primary particles are generated. Since the processing liquid does not dissolve the binder, the secondary particles cannot be broken apart by forces other than the reaction force. This makes it possible to reduce the surface roughness of the polished object after polishing. In addition, the polished object is less likely to develop scratches.

[0012] Therefore, the polishing slurry of the present invention can achieve both a high polishing rate and small surface roughness on the polished object after polishing.

[0013] The polishing method of the present invention is a polishing method for polishing an object to be polished by interposing an abrasive slurry between the object to be polished and a polishing body and relatively moving the object to be polished and the polishing body under a predetermined surface pressure, comprising: The polishing slurry includes a processing liquid and a countless number of abrasive particles dispersed in the processing liquid, Each of the abrasive particles has secondary particles composed of a countless number of flat primary particles and a binder that bonds the primary particles together, The processing fluid dissolves the binder. Without Each of the secondary particles has a BET specific surface area of ​​1.49 m 2 / g or more, 2.10m 2 / g or less and a bulk density of 0.70 g / cm 3 More than 0.95g / cm 3 Is less than or equal to It is characterized by:

[0014] The polishing method of the present invention uses the polishing slurry of the present invention, and therefore can achieve both a high polishing rate and small surface roughness on the polished object after polishing. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a SEM photograph of the abrasive particles used in Example 3 at 1000 times magnification. [Diagram 2] FIG. 2 is an enlarged schematic view of the abrasive particles used in Examples 1 to 4. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The processing liquid may include a dispersion medium and an additive depending on the object to be polished. The dispersion medium may include water, oil, alcohol, etc. The additive may include a dispersant, a surfactant, an oxidizing agent, a chlorinating agent, etc.

[0017] The abrasive particles according to the present invention have secondary particles. The secondary particles are composed of primary particles and a binder that bonds the primary particles. The primary particles may be inorganic, organic, or a hybrid of inorganic and organic components. As inorganic materials, silica, alumina, silicon carbide, zirconia, ceria, CBN, diamond, glass, etc. may be adopted. As organic materials, methacrylic resin, phenolic resin, urea resin, melamine resin, polystyrene, polyacetal, polycarbonate, acrylic, etc. may be adopted. As hybrids of inorganic and organic components, particles in which these inorganic and organic components are arbitrarily bonded may be adopted. The abrasive particles according to the present invention may be only secondary particles, or may contain primary particles.

[0018] The primary particles according to the present invention are flat-shaped. As the flat-shaped primary particles, plate-shaped crystal grains of alumina or the like can be used. Also, glass solidified into a thin plate shape and pulverized can be used.

[0019] The processing fluid is selected so as not to dissolve the binder. When the processing fluid is water-based, oil-based, or alcohol-based, the binder may be a glass material containing silicon dioxide, a metal, or the like. When the processing fluid is water-based, the binder may be a resin, or the like. The inventors have confirmed the effectiveness of the processing fluid when the processing fluid is water, the primary particles are plate-like crystal grains of alumina, and the binder is a glass material containing silicon dioxide.

[0020] According to the inventors' test results, each secondary particle has a BET specific surface area of ​​1.49 m 2 / g or more, 2.10m 2 / g or less and a bulk density of 0.70 g / cm 3 More than 0.95g / cm 3 In this case, the polishing rate is sufficiently high and the surface roughness of the polished object after polishing is sufficiently small.

[0021] According to the results of tests conducted by the inventors, when the object to be polished is a Si wafer, the polishing slurry can be used for lapping the object to be polished.

[0022] "test" The following machining fluids and abrasive particles were prepared. (processing fluid) Dispersion medium: water (abrasive particles) Example 1: Secondary particles (binding material is glass containing silicon dioxide, BET specific surface area is 1.49 m 2 / g, bulk density is 0.76g / cm 3 ) Example 2: Secondary particles (binding material is glass containing silicon dioxide, BET specific surface area is 1.64 m 2 / g, bulk density is 0.95g / cm 3 ) Example 3: Secondary particles (binding material is glass containing silicon dioxide, BET specific surface area is 1.84 m 2 / g, bulk density is 0.70g / cm 3 ) Example 4: Secondary particles (binding material is glass containing silicon dioxide, BET specific surface area is 2.10 m 2 / g, bulk density is 0.79g / cm 3 ) Comparative Example 1: Primary particles (average particle size 30 μm, BET specific surface area 0.22 m 2 / g, bulk density is 1.76g / cm 3 ) Comparative Example 2: Primary particles (average particle size 3 μm, BET specific surface area 1.82 m 2 / g, bulk density is 1.30g / cm 3 ) Comparative Example 3: Secondary particles (binding material is glass containing silicon dioxide, BET specific surface area is 1.19 m 2 / g, bulk density is 0.50g / cm 3 ) The primary particles constituting the secondary particles in Examples 1 to 4 and Comparative Example 3 are plate-like crystal grains of alumina, while the primary particles in Comparative Examples 1 and 2 are granular crystal grains of alumina. The BET specific surface area and bulk density of each abrasive particle are shown in Table 1.

[0023] [Table 1]

[0024] A SEM photograph of the abrasive particles used in Example 3 at 1000 times magnification is shown in Fig. 1. Moreover, an enlarged schematic diagram of the abrasive particles used in Examples 1 to 4 and Comparative Example 3 is shown in Fig. 2. As shown in Fig. 2, the abrasive particles 1 used in Examples 1 to 4 and Comparative Example 3 are secondary particles in which numerous plate-like primary particles 3 are bonded together. These secondary particles are composed of primary particles 3 and binder 5 that bonds each primary particle 3. The binder 5 is vitreous and does not dissolve in water.

[0025] 10% by mass of abrasive particles were mixed into water as a processing liquid to prepare polishing slurries for Examples 1 to 4 and Comparative Examples 1 to 3.

[0026] Using the polishing slurries of Examples 1 to 4 and Comparative Examples 1 to 3, S was processed under the following processing test conditions. iU The wafer was polished, and the polishing rate (μm / min) and surface roughness (Sa) (nm) were examined.

[0027] <Test conditions> Testing machine: Wafer polishing machine (Engis EJW-380) Workpiece (object to be polished): S iBe Wafer (4 inch) Processing pressure: 20kPa Platen / Workpiece Rotation Speed: 60 / 60 rpm Lapping machine dimensions: diameter 30cm Amount of polishing slurry supplied: 10mL / min Polishing body fixed to the platen: Polyurethane pad Processing time: 30 minutes

[0028] 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 △, and less than 0.2 μm / min as ×. The surface roughness was evaluated using a white light interference microscope (Sa of 200 μm square field of view) as ◯ for 65 nm or less, △ for over 65 nm and 110 nm or more, and × for over 110. In addition, the dispersion state of the abrasive particles in the polishing slurry during processing was visually judged. If each abrasive particle settled and formed a mass, it was evaluated as ×, and if each abrasive particle was dispersed without settling, it was evaluated as ◯. The results are shown in Table 2.

[0029] [Table 2]

[0030] From Table 2, it can be seen that the polishing slurries of Examples 1 to 4 can achieve both a high polishing rate and small surface roughness on 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 small surface roughness on the polished Si wafer. 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, 2.10m 2 / g or less and a bulk density of 0.70 g / cm 3 More than 0.95g / cm 3 Since the BET specific surface area and bulk density are within these ranges, it can be seen that the polishing rate is sufficiently high and the surface roughness of the polished object is sufficiently small after polishing. In particular, according to the polishing slurries of Examples 3 and 4, the polishing rate is sufficiently high and the surface roughness of the polished Si wafer is sufficiently small after polishing.

[0031] In addition, it is found that in the polishing slurries of Examples 1 to 4, the polishing particles are dispersed in the processing liquid for a long period of time and are less likely to settle, compared to the polishing slurries of Comparative Examples 1 and 2. Therefore, the polishing slurries of Examples 1 to 4 do not require the addition of an excessive amount of dispersant, making it easier to process the polishing slurry after polishing, realizing lower manufacturing costs, and also reducing the environmental load.

[0032] In the above, the present invention has been described based on Examples 1 to 4. However, the present invention is not limited to the above Examples 1 to 4, and it goes without saying that the present invention can be modified and applied as appropriate without departing from the spirit of the present invention. [Industrial Applicability]

[0033] The present invention can be used in a manufacturing method and an apparatus for manufacturing a semiconductor device. [Explanation of symbols]

[0034] 1...Abrasive particles 3…Primary particles 5…Binding material

Claims

1. A polishing slurry for polishing a workpiece, comprising a processing liquid and a countless number of abrasive particles dispersed in the processing liquid, Each of the abrasive particles has secondary particles composed of a countless number of flat primary particles and a binder that bonds the primary particles together, The working fluid does not dissolve the binder, 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.

2. The working fluid is water; the primary particles are plate-like crystal grains of alumina, 2. The polishing slurry according to claim 1, wherein the binder is a vitreous material containing silicon dioxide.

3. The object to be polished is a silicon wafer, 3. The polishing slurry according to claim 1, which is used for lapping the object to be polished.

4. A polishing method for polishing an object to be polished by interposing an abrasive slurry between the object to be polished and a polishing body and relatively moving the object to be polished and the polishing body under a predetermined surface pressure, comprising: The polishing slurry includes a processing liquid and a countless number of abrasive particles dispersed in the processing liquid, Each of the abrasive particles has secondary particles composed of a countless number of flat primary particles and a binder that bonds the primary particles together, The working fluid does not dissolve the binder, A polishing method, wherein 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.

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