JP5554052B2 - Polishing composition and polishing method - Google Patents

Description

  The present invention relates to a polishing composition capable of efficiently polishing even a hard material to be polished and a polishing method using the same.

Until now, silicon (Si) single crystals have often been used for electronic device substrates, but recently single crystals such as silicon carbide (SiC) and gallium nitride (GaN), which are excellent in various properties, are being used. is there.
However, single crystal substrates such as SiC and GaN are very hard and difficult to process. For this reason, it is not easy to efficiently polish these substrates while maintaining high accuracy, and research has been conducted to improve the polishing properties. For example, a method for efficiently polishing an ultra-hard substrate is proposed in the following patent documents.

JP 2007-311586 A JP 2008-68390 A

However, the contents disclosed in the above-mentioned patent documents all relate to a finish polishing method for a hard single crystal plate such as silicon carbide (SiC), which includes chemical components or chemicals in a polishing liquid (polishing slurry). It has characteristics in chemical polishing such as characteristics.
Unlike the prior art, the present invention provides a polishing composition capable of efficiently performing at least mechanical polishing even on a hard material to be polished, and polishing using the polishing composition. It aims to provide a method.

  As a result of extensive research and trial and error, the present inventor conducted polishing by adding metal compound particles containing nitrogen (N) to diamond particles frequently used for polishing hard materials to be polished. Thus, it has been newly found that polishing performance much higher than that of the prior art can be obtained while suppressing the amount of expensive diamond particles used. The present inventor has completed the present invention described below by developing this result.

<< Polishing composition >>
(1) The polishing composition of the present invention is a polishing composition comprising abrasive grains and a dispersion liquid in which the abrasive grains are dispersed, and is used for polishing a material to be polished. becomes a main particle, seen including a sub particles of a metal compound containing N, the sub-particles, silicon (Si), aluminum (Al), oxygen (O), and it is sialon particles consisting of nitrogen (N) It is characterized by.

(2) The abrasive grains constituting the polishing composition of the present invention are not only primary particles composed of diamond (hereinafter referred to as “diamond particles” as appropriate), but also secondary particles composed of metal compounds containing N (hereinafter referred to as “compounds” as appropriate). Particle ")). When a material to be polished is polished using a polishing slurry (or suspension or polishing liquid) in which the abrasive grains are dispersed in a dispersion liquid, even a material to be polished made of a very hard difficult-to-process material is efficient. Polishing becomes possible. In particular, as compared with the conventional polishing composition in which the abrasive grains are only diamond particles and the polishing composition in which the mixed particles obtained by adding other oxide particles to the diamond particles are used as abrasive grains. Thus, it has been found that when the polishing composition of the present invention is used, a remarkably high polishing property (polishing rate) can be obtained while suppressing the amount of diamond particles used.

(3) However, the reason why excellent polishing properties can be obtained by the polishing composition of the present invention is not necessarily clear. The current situation is considered as follows.
That is, the secondary particles made of a metal compound containing N are not only high strength and high rigidity, but also are pulverized using a ball mill or the like in order to adjust to an optimum particle size as abrasive particles. Many of them have a sharp grain shape.
For this reason, the secondary particles encapsulated in the polishing pad used for polishing are restrained from rolling in the polishing pad and easily stay in the polishing pad. Then, the diamond particles (main particles) surrounded by such sub-particles are also inhibited from rolling in the polishing pad by the sub-particles, and eventually stay in the polishing pad for a longer time than before.

  Such a mechanism is considered to increase the density of diamond particles contained in the polishing pad during the polishing operation and improve the polishing performance. Therefore, if the polishing composition of the present invention is used, the efficiency of polishing work can be greatly improved, and the amount of expensive diamond particles used can be suppressed while achieving the same or better polishing performance as before. Thus, the cost of the polishing operation can be reduced.

(4) By the way, the composition and structure of the secondary particles according to the present invention are not particularly limited as long as they exhibit the above-described effects. However, it is preferable that such subparticles are sialon particles composed of sialon which is a kind of metal compound composed of silicon (Si), aluminum (Al), oxygen (O) and N.
Sialon particles are very hard, high strength or high rigidity among ceramic particles, and are suitable for the abrasive grains according to the present invention. Such sialon particles naturally have excellent properties close to diamond particles, even if they do not reach diamond particles, and exhibit excellent polishing properties as described above by cooperating with or synergistic with diamond particles. I think that.

  In addition, the coexistence of such sialon particles makes it possible to significantly reduce the amount of expensive diamond particles used while ensuring a polishing performance equivalent to or higher than that of conventional sialon particles. Of course, sialon particles are much cheaper than diamond particles and are available. Thus, according to the polishing composition of the present invention, it is possible to easily achieve a remarkable improvement in polishing properties and a significant reduction in cost.

(5) Furthermore, when the sialon particles constituting the secondary particles are made of an inorganic metal compound represented by Si ₅ AlON ₇ , the specific gravity between the main particles made of diamond and the secondary particles is close (specifically, Sialon: 3.2 / Diamond: 3.6). For this reason, the centrifugal force acting on each particle during the polishing operation becomes close, and the distribution of both particles coexisting in the polishing pad is easily made uniform. Accordingly, the main particles and sub-particles are likely to be included and retained in the polishing pad almost uniformly, so that the improvement of the polishability by the cooperation of the main particles and sub-particles as described above is stably exhibited. It is thought that it became.

<Polishing method>
The present invention is understood not only as a polishing composition as described above but also as a polishing method using the same. That is, the present invention provides a slurry supply step of supplying a polishing slurry, in which abrasive grains are dispersed in a dispersion, onto a polishing pad, and sliding between the polishing pad supplied with the polishing slurry and a material to be polished. A polishing method comprising polishing a material, and the polishing slurry is composed of the above-described polishing composition of the present invention.

<Others>
(1) “Abrasiveness” as used herein can be evaluated by, for example, a polishing rate. The polishing rate is represented by the polishing amount per unit time. The amount of polishing may be a change in mass, or may be a change in the size of the polished surface if the cross section has a constant cross section. For example, in the case of primary polishing (rough polishing) of a SiC single crystal plate, the polishing rate is preferably 11 μm / hr or more (hr: time), 12 μm / hr or more, or 14 μm / hr or more.

(2) “x to y” in the present specification includes the lower limit value x and the upper limit value y unless otherwise specified. Moreover, the various lower limit value or upper limit value described in this specification can be arbitrarily combined to constitute a range such as “ab”. Furthermore, any numerical value included in the range described in the present specification can be used as an upper limit value or a lower limit value for setting the numerical value range.

It is the schematic which shows an example of the grinding | polishing apparatus which can implement the grinding | polishing method of this invention.

K polishing apparatus P polishing pad W wafer (material to be polished)
10 Surface plate 20 Head 30 Conditioner

  The present invention will be described in more detail with reference to embodiments of the invention. In addition, the content demonstrated by this specification including the following embodiment is suitably applied not only to the polishing composition of this invention but the grinding | polishing method using the same. One or two or more configurations arbitrarily selected from the configurations shown below can be added to the configuration of the present invention described above. Note that which embodiment is the best depends on the target, required performance, and the like.

《Abrasive grains》
The abrasive grains according to the polishing composition of the present invention are mainly composed of main particles and sub-particles.
(1) Main Particle The main particle according to the present invention is a particle mainly responsible for polishing the material to be polished, and is a particle having a higher polishability of the material to be polished than sub-particles. The main particles according to the present invention are mainly composed of diamond particles, but need not be only diamond particles, and may contain other hard particles (other than secondary particles) effective for polishing the material to be polished.

The particle size and blending amount of the main particles are not particularly limited, and can be appropriately selected according to the type and characteristics of the material to be polished, the required polishing properties, and the like. In the case of the polishing composition of the present invention, by containing the secondary particles, sufficient polishing properties can be ensured even if the content of the main particles is reduced. Therefore, the main particles are 0.1 to 20%, 0.5 to 10%, and further 0.8 to 5% when the polishing composition is 100% by mass (hereinafter simply referred to as “%”). If it exists, it is suitable because it is possible to achieve both abrasiveness and economical efficiency. If the number of main particles is too small, efficient polishing becomes difficult, and if it is too large, the polishing composition becomes expensive.
Further, the average particle diameter (D) of the main particles is preferably about 0.5 to 10 μm, 1 to 5 μm, and more preferably about 2 to 4 μm in view of improving the polishing properties. If the average particle size is too small, the polishing efficiency is lowered, and if it is too large, uniform polishing becomes difficult and large scratches can be generated. The average particle size referred to in the present specification is an integrated value 50 of the particle size distribution automatically measured by dispersing the particles in a dispersion medium using a laser diffraction / scattering particle size distribution measuring device and performing flow cell measurement. % Particle size (median diameter).

(2) Sub-particles The sub-particles according to the present invention are particles that assist polishing with main particles. Of course, the secondary particles may be particles that themselves are responsible for polishing the material to be polished, but are particles having a lower polishing property of the material to be polished than the main particles. The sub-particle according to the present invention is a particle mainly composed of a metal compound containing N. However, the sub-particle need not be composed only of particles composed of a metal compound containing N, and is effective for polishing a material to be polished. Other hard particles (other than the main particles) may be contained. The composition of the metal compound is not limited, but examples of such a metal compound include zirconium nitride, silicon nitride, and aluminum nitride. As described above, it is particularly preferable that the secondary particles are sialon particles.

The particle size and blending amount of the secondary particles are not particularly limited, and can be appropriately selected according to the type and characteristics of the material to be polished, the required polishing properties, and the like. The secondary particles according to the present invention only need to be contained in the polishing composition within the range of assisting at least the polishing of the material to be polished by the main particles and further improving the polishing properties in cooperation with the main particles. Therefore, the sub-particles are preferably 0.5 to 30%, 1 to 20%, and further 5 to 15% when the entire polishing composition is 100% by mass. Polishing efficiency can be reduced even if the number of main particles is too small or too large. Since the secondary particles are cheaper than the main particles, even if the secondary particle content is increased, the cost is not significantly increased.
The average particle diameter (d) of the secondary particles is preferably about 0.01 to 3 μm, 0.05 to 2 μm, and more preferably about 0.1 to 1 μm, since the polishing property can be improved. If the average particle size is too small, efficient polishing becomes difficult, and if it is too large, uniform polishing becomes difficult and scratches become large, which is not preferable.

(3) The abrasive grains according to the present invention are mainly composed of such main particles and sub-particles. However, when viewed as a whole abrasive grain in which both particles are mixed, the sub-particles (m) with respect to the main particles (M) ) Mass ratio (m / M) is preferably 1 to 99, 1 to 90, and more preferably 1 to 18. If this mass ratio is too small, it is uneconomical, and if it is too large, improvement in polishing properties cannot be expected. Furthermore, when the polishing composition is 100%, it is preferable that the concentration of the abrasive grains consisting of the sum of the main particles and the sub-particles is 1 to 20%, further 5 to 15%. If the abrasive grain concentration is too low, improvement in polishing properties cannot be expected, and if it is too high, it is uneconomical.

  The average particle size ratio (d / D) of the secondary particles to the main particles is preferably 0.05 to 0.5, and more preferably 0.1 to 0.3. When the average particle size ratio becomes excessive (approaching 1), the particle size difference between the main particles and the sub-particles is reduced, and the contact relationship between the sub-particles and the material to be polished becomes the contact relationship between the main particles and the material to be polished. Get closer. For this reason, the abrasiveness by the main particles is relatively hindered by the secondary particles, and improvement in the abrasiveness due to the cooperation or synergy between the primary particles and the secondary particles can hardly be expected. If the average particle size ratio is too small, the particle size of the main particles becomes relatively large, resulting in the formation of large scratches on the polishing surface of the material to be polished, or the effect of the secondary particles retaining the main particles in the polishing pad is weak Therefore, it is difficult to efficiently perform good polishing.

<Dispersion>
The dispersion uniformly disperses the above abrasive grains, whereby a polishing slurry that is a suspension is obtained. The type or pH of the dispersion is not limited, but water can be used for primary polishing (rough polishing) or the like. However, in order to suppress contamination of the material to be polished, it is preferable to remove impure ions and use ion exchange water. Furthermore, the dispersion according to the present invention is at least one selected from an acidic substance, an alkaline substance, an oxidizing agent, an oxide dissolving agent, an abrasive dispersing agent, a chelating agent, a saccharide, and the like, depending on the material to be polished and the polishing stage. A mixed solution containing an appropriate amount of these additives may also be used.

<Polishing method>
The polishing method of the present invention mainly comprises a slurry supply step and a polishing step.
(1) Slurry supply process A slurry supply process is a process of supplying the polishing composition (polishing slurry) mentioned above on a polishing pad. This step may be a step of dripping the polishing slurry onto the polishing pad, a step of spraying the polishing slurry onto the polishing pad, or a step of immersing the polishing pad in the polishing slurry.

(2) Polishing Step The polishing step is a step of forming a polishing surface while sliding the material to be polished on the polishing pad supplied with the polishing slurry and enclosing the abrasive grains. The pressure to press the polishing material onto the polishing pad, the relative speed (relative rotation speed) between the polishing pad and the polishing material, the type of polishing material, the composition of the polishing slurry, the accuracy required for the polishing surface, the task The time is adjusted appropriately.

(3) Polishing Apparatus Such a polishing method of the present invention can be performed by, for example, a polishing apparatus K as outlined in FIG.
The polishing apparatus K includes a disk-shaped surface plate 10, a head 20 that is provided above the surface plate 10 and holds a disk-shaped wafer W that is a material to be polished via a holding material, and a surface plate 10. It is mainly composed of a movable disk-shaped conditioner 30 that conspicuously the surface of the polishing pad P that is detachably fixed thereon, and a dropping nozzle 40 that supplies polishing slurry (or polishing liquid) L.

  Here, the surface plate 10 and the head 20 are each driven by a motor and can rotate around a vertical axis. These rotation directions can be changed. For example, the rotation direction is the direction indicated by the arrow in FIG. The conditioner 30 is pivotally supported at the tip of the rod 31 and can reciprocate on the polishing pad P while rotating.

  When the polishing apparatus K is operated, the polishing pad P impregnated with the dropped polishing slurry L rotates together with the surface plate 10. On the rotating polishing pad P, the wafer W pressed by the head 20 slides while rotating. Thus, the polishing surface of the wafer W is gradually polished by the abrasive grains included in the polishing pad P. Note that the condition of the polishing pad P is constantly adjusted by the reciprocating motion of the conditioner 30 on the polishing pad P, so that the polishing quality such as planarity, uniformity and scratch free of the polishing surface of the wafer W is achieved.

<Material to be polished>
The type and shape of the material to be polished are not particularly limited. For example, when the material to be polished is an electronic device material (wafer), the material to be polished may be a silicon single crystal, or may be a single crystal such as harder silicon carbide (SiC) or gallium nitride (GaN).

The present invention will be described more specifically with reference to examples.
<< Preparation of polishing slurry >>
(1) Abrasive grains As abrasive grains, diamond particles (main particles), sialon particles (sub-particles) that are inorganic metal compounds represented by Si ₅ AlON ₇ , and silica that is inorganic oxides represented by SiO ₂ Particles were prepared. All of the particles are commercially available, and the average particle size of each particle is as follows: diamond particles: 3.5 μm (Tomei Diamond Co., Ltd.), sialon particles: 0.5 μm (Keisei Co., Ltd.), silica particles: It was 0.5 μm.

(2) Mixing / Dispersing Abrasive grains prepared by variously blending these particles as shown in Table 1 were mixed and dispersed in ion-exchanged water (dispersion) to obtain a polishing slurry. This mixing / dispersing was performed using a homomixer and ultrasonic waves.

<Measurement of polishing rate>
Using the above-mentioned various polishing slurries, primary polishing (rough polishing) of a wafer (diameter 2 inches, 6H type wafer) made of a silicon carbide (SiC) single crystal plate was performed. Specifically, a polishing pad (Nippon Engis Co., Ltd.) made of the above-mentioned various polishing slurries at a rate of 50 cc / min using a single-side polishing apparatus (manufactured by MT Corporation, BC-15). 410) (slurry supplying step), and the wafer was slid while being pressed on this polishing pad (polishing step). At this time, the surface pressure between the polishing pad containing the polishing slurry and the wafer to be polished was about 41 kPa (6 psi), and the rotation speed of the polishing pad was 60 times / minute (rpm). . This polishing was performed for 10 minutes.
In each case, the change in the mass of the wafer before and after polishing was measured, and the change in the mass was converted into a decrease in the thickness of the wafer (having a constant cross-sectional area) to determine the polishing rate (μm / hr). The results are also shown in Table 1.

<Evaluation of abrasiveness>
(1) First, the sample No. shown in Table 1 was used. C1 and sample No. As is clear from comparison with C3, it can be seen that the polishing rate is improved by increasing the content ratio (or mass%) of the diamond particles as the main particles. However, even if the number of expensive diamond particles is increased 10 times, the polishing rate is only increased by about 1.5 times.
Sample No. C1 and sample No. As apparent from comparison with C2, the polishing rate could be improved while reducing the blending of the diamond particles by mixing the silica particles as the secondary particles with the diamond particles as the main particles. However, the increase in the polishing rate in this case is about 1.18 times at most, and the improvement range of the polishing property is very small, which is not as much as when diamond particles are increased.

  Furthermore, sample no. As apparent from C4, when the abrasive grains in the polishing slurry consist only of sialon particles harder than the silica particles (that is, when the main particles do not include diamond particles), the polishing rate was very low. The polishing rate in this case is the sample No. 1 consisting only of diamond particles with a content ratio of 1/10. It did not reach C1. From this, it was found that the main particles composed of diamond particles are mainly responsible for polishing hard wafers and are essential for improving the polishing properties.

(2) With respect to such a tendency to polish, sample No. 1 in which the abrasive grains consist of diamond particles and sialon particles. In the case of No. 1, the content ratio of the expensive diamond particles is Sample No. In spite of the same small amount as C1, the relatively inexpensive sialon particles are present in the polishing slurry, so that the polishing rate is remarkably improved. Specifically, Sample No. The polishing rate of sample No. 1 with the same diamond particle content ratio. It was about twice the polishing rate of C1. Moreover, this sample No. The polishing rate of sample No. 1 in which the content ratio of diamond particles is 10 times. It was much larger than the polishing rate of C3.
From the above, even if it is a very hard SiC wafer, by using a polishing slurry composed of abrasive grains in which diamond particles (main particles) and sialon particles (sub-particles) are combined, it is much better than before. It has become clear that polishing can be performed efficiently and at low cost.
Incidentally, the sample No. 1 exhibiting such excellent characteristics. The polishing slurry of No. 1 had a mass ratio of sialon particles as sub-particles to diamond particles as main particles of 9, and the abrasive concentration (main particle concentration + sub-particle concentration) with respect to the entire polishing slurry was 10% by mass. . The average particle diameter (D) of the diamond particles as the main particles is 3.5 μm, the average particle diameter (d) of the sialon particles as the secondary particles is 0.5 μm, and the average particle diameter ratio (d / D) was about 0.14. Therefore, this sample No. Any one of the polishing slurries is within the range of the polishing composition of the present invention.

Claims (9)

A polishing composition comprising abrasive grains and a dispersion liquid for dispersing the abrasive grains, and used for polishing a material to be polished,
The abrasive grains, seen including a main particles of diamond, and a secondary particle comprising a metal compound or found containing nitrogen (N),
The polishing composition, wherein the sub-particles are sialon particles composed of silicon (Si), aluminum (Al), oxygen (O), and nitrogen (N) . The polishing composition according to claim 1, wherein a mass ratio (m / M) of the sub-particles (m) to the main particles (M) is 1 to 99. 3. The polishing according to claim 1, wherein when the whole is 100 mass% (hereinafter simply referred to as “%”), the abrasive concentration comprising the sum of the main particles and the sub-particles is 1 to 20%. Composition. The average particle size (D) of the main particles is 0.5 to 10 µm, and the average particle size (d) of the sub-particles is 0.01 to 3 µm. Composition. The average particle size ratio of the secondary particles to the primary particles (d / D), the polishing composition according to any one of claims 1 to 4, which is 0.05 to 0.5. The sialon _particles, the polishing composition according to claim 1 comprising an inorganic metal compound represented by Si 5 AlON _7. The polishing composition according to any one of claims 1 to 6, wherein the dispersion liquid comprises water or a mixed liquid of water and an additive. The polishing composition according to any one of claims 1 to 7, wherein the material to be polished is made of a single crystal of silicon carbide (SiC) or gallium nitride (GaN). A slurry supply step of supplying a polishing slurry in which abrasive grains are dispersed in a dispersion liquid onto a polishing pad;
A polishing step of polishing the material to be polished by sliding between the polishing pad supplied with the polishing slurry and the material to be polished;
A polishing method comprising:
The abrasive slurry polishing method characterized by comprising the polishing composition according to any one of claims 1-8.

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