KR20090088050A - Polishing method - Google Patents

Abstract

A chemical mechanical polishing method is provided to control a polishing rate of a SiC substrate by controlling a size of a particle and a mixing ratio of a second polishing particle after controlling a mixing ratio of an oxidizing agent and a first polishing particle. A polishing jig(20) is rotated by a top rotation shaft(30). A substrate(10) is attached on the polishing jig. A plate(50) is rotated by a bottom rotation shaft(60). A polishing pad(40) is attached on the plate. A first spray unit(70) is positioned on a top part of the plate, and sprays a first polishing slurry(71). A second spray unit(80) sprays a second polishing slurry(81) in which a second polishing particle is included. A mechanical defect layer is formed on a surface of a SiC single crystal substrate. After the substrate is attached on the polishing jig, a polishing pad is attached.

Description

Polishing method

TECHNICAL FIELD The present invention relates to a polishing method, and more particularly, to a chemical mechanical polishing ("CMP") method of a silicon carbide (SiC) substrate using an abrasive slurry containing an oxidizing agent and abrasive particles containing carbon. .

In general, silicon carbide single crystal is a substrate material such as gallium nitride (GaN), aluminum nitride (AlN), silicon carbide, which is used to manufacture high voltage, high power, and optoelectronic devices.

Such silicon carbide single crystals are grown by Liquid Phase Epitaxy (LPE), Sublimation (Physical Vapor Transport; PVT), Chemical Vapor Deposition (CVD), etc. Sublimation methods that can produce carbide single crystals are widely known. However, silicon carbide single crystal ingots grown through sublimation (PVT) must be thinly processed to be used as substrate materials. The mechanical defect layer having a plurality of defects is distributed on the surface of the silicon carbide single crystal substrate thus processed. Therefore, the mechanical defect layer was removed by mechanically polishing the surface of the substrate, etching the surface of the substrate, or performing a CMP process using a colloidal silica polishing liquid.

However, such a conventional mechanical polishing process, etching process or CMP process did not generate fine scratches or completely remove the mechanical defect layer on the silicon carbide single crystal substrate surface. In particular, the mechanical defect layer generated in such a process is a factor of lowering the crystallinity of the gallium nitride, aluminum nitride, silicon carbide epitaxial layer formed on the silicon carbide substrate to fabricate the device.

The present invention provides a polishing method capable of removing a mechanical defect layer present on a silicon carbide substrate surface.

The present invention provides a method of polishing a silicon carbide substrate using a first polishing slurry containing first abrasive particles and an oxidant and a second polishing slurry containing second abrasive particles containing carbon.

The present invention provides a method of polishing a silicon carbide substrate in which a defect layer is oxidized by an oxidant included in a first polishing slurry to form an oxide layer, and an oxide layer is removed by second polishing particles included in a second polishing slurry.

Polishing method according to an aspect of the present invention comprises the steps of preparing a substrate; Providing a first abrasive slurry comprising first abrasive particles and an oxidant; Providing a second abrasive slurry comprising second abrasive particles; And polishing the substrate using the first and second polishing slurries.

The substrate comprises a silicon carbide substrate.

The first abrasive particles include at least one of silica (SiO ₂ ), alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), manganese (MnO ₂ ) or zirconia (ZrO ₂ ).

The first abrasive particles are colloidal silica, and the colloidal silica has an average size of particles of 10 to 200 nm.

The oxidizing agent uses at least one of NaOCl, H ₂ O ₂ , Fe (NO ₃ ) ₃ , H ₅ lO ₆ , KlO ₃ , K ₃ Fe (CN).

The colloidal silica and the oxidant are mixed in a ratio of 7: 1 to 9: 1.

The colloidal silica is mixed at 70 to 90 vol% and the oxidant is mixed at 10 to 30 vol%.

The second abrasive particles use at least one of diamond, silicon carbide, boron carbide (B ₄ C), and the second abrasive particles have an average size of 5 to 100 nm.

The first polishing slurry is continuously sprayed, and the second polishing slurry is sprayed periodically.

The second abrasive particles are stronger in strength than the first abrasive particles.

The second abrasive particles are mixed at 1% or less with respect to the mixed amount of the first abrasive particles and the oxidant.

A substrate polishing method according to another aspect of the present invention comprises the steps of preparing a substrate; Providing an abrasive slurry comprising at least two abrasive particles and oxidants having different strengths; And polishing the substrate using the polishing slurry.

According to the present invention, silicon is obtained by using a first polishing slurry in which first abrasive particles such as colloidal silica and an oxidizing agent such as NaOCl are mixed, and a second abrasive slurry containing second abrasive particles containing carbon such as diamond particles. The carbide substrate polishing process is performed. That is, the defect layer on the surface of the silicon carbide substrate is oxidized by the oxidizing agent of the first polishing slurry to form an oxide layer, and the oxide layer is polished by the second abrasive particles of the second polishing slurry to polish the silicon carbide substrate. In addition, the degree of polishing of the silicon carbide substrate may be controlled by adjusting the mixing ratio of the first abrasive particles and the oxidant, and controlling the mixing ratio and the size of the particles of the second abrasive particles.

Therefore, it is possible to remove the mechanical defect layer of the silicon carbide substrate to improve the crystalline of the epitaxial layer formed on the silicon carbide substrate, thereby improving the characteristics of the device.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention; However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention and to those skilled in the art. It is provided for complete information.

1 is a schematic cross-sectional view of a CMP apparatus according to an embodiment of the present invention, Figure 2 is a schematic flowchart of a CMP method according to an embodiment of the present invention.

Referring to FIG. 1, a CMP apparatus according to an embodiment of the present invention includes a polishing jig 20 to which a substrate 10 is attached, a plate 50 to which a polishing pad 40 is attached, and a first polishing slurry ( First injection means 70 for injecting 71 and second injection means 80 for injecting the second polishing slurry 81 are included.

The polishing jig 20 is made of steel or ceramic material, and preferably has a flat surface. In addition, the polishing jig 20 is rotated by the upper rotary shaft 30, and at the same time the rocking movement. Then, the polishing jig 20 is pressed to be in close contact with the plate 50 by a constant pressure. The substrate 10 attached to the polishing jig 20 may include a silicon carbide substrate, and the substrate 10 is attached to the polishing jig 20 using wax.

The plate 50 rotates by the lower rotation shaft 60, and the rotation direction of the plate 50 and the rotation direction of the polishing jig 20 may be the same direction. The polishing pad 40 may be made of a resin such as polyurethane, and a plurality of minute holes may be formed in order to control the polishing rate, polishing uniformity, and the like.

The first injection means 70 is positioned above the plate 50 to inject the first polishing slurry 71. The first injection means 70 may be installed perpendicular to the plate 50.

The first polishing slurry 71 contains first abrasive particles, an oxidizing agent, and the like. As the first abrasive particles, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), manganese (MnO ₂ ), or zirconia (ZrO ₂ ) may be used. It can also be used. Here, it is preferable to use silica as a 1st abrasive particle, and it is more preferable to use colloidal silica. In addition, colloidal silica may be prepared based on potassium hydroxide (KOH), ammonia water (NH _` OH), sodium hydroxide (NaOH). Accordingly, the polishing slurry 71 has a pH of 7 to 11, and the pH of the polishing slurry 71 is preferably adjusted to 10. In addition, the colloidal silica has an average particle size of 10 to 200 nm, preferably 100 to 150 nm. If the average size of the colloidal silica particles is greater than the above range, scratches may occur when polishing the substrate 10 by the colloidal silica, and if the average size is within the above ranges, the polishing by the colloidal silica particles may not proceed. . In addition, the oxidizing agent is for oxidizing the defect layer on the surface of the substrate 10, and at least one of NaOCl, H ₂ O ₂ , Fe (NO ₃ ) ₃ , H ₅ lO ₆ , KlO ₃ , and K ₃ Fe (CN) Can be used. Here, the colloidal silica and the oxidizing agent may be mixed in a ratio of about 7: 1 to 9: 1, the colloidal silica may be mixed in the polishing slurry 71 at about 70 to 90 Vol%, and the oxidizing agent at about 10 to 30 Vol%. Preferably, the colloidal silica is mixed at 85 to 90 vol% and the oxidant is mixed at 10 to 15 vol%. When the oxidant is mixed above the mixing ratio, not only the defect layer of the substrate 10 but also the surface of the substrate 10 may be oxidized. When the oxidant is mixed below the mixing ratio, the defect layer of the substrate 10 may not be oxidized. do.

The second injection means 80 may be installed separately from the first injection means 70, and the second injection means 80 may be installed at an angle. A second abrasive slurry 81 containing second abrasive particles is injected through the second jetting means 80, the second abrasive particles having a stronger strength than the first abrasive particles, for example carbon containing diamond At least one of silicon carbide and boron carbide (B ₄ C) may be used. In addition, the average size of the second abrasive particles may be 5-100 nm. If the average size of the second abrasive particles is greater than or equal to the above range, the oxide layer may be excessively polished to cause scratches on the substrate 10. If the average size of the second abrasive particles is less than the above range, the oxide layer may not be polished. In addition, the second abrasive particles are preferably mixed at 1% or less with respect to the first abrasive particles and the oxidant as a whole. That is, if the mixing amount of the first abrasive particles and the oxidant is 100, the second abrasive particles are preferably mixed in the second polishing slurry 81 in an amount of 1 or less.

Referring to the CMP method according to an embodiment of the present invention using the CMP device as described above are as follows.

First, the substrate 10, for example, a silicon carbide substrate, is produced by thinly processing a silicon carbide single crystal ingot made by a sublimation method. There are many mechanical defect layers on the surface of the silicon carbide single crystal substrate thus processed. After attaching the silicon carbide substrate having a defect layer formed on the surface to the polishing jig 20, the silicon carbide substrate is pressed against the plate 50 to which the polishing pad 40 is attached at a predetermined pressure. Then, the first polishing slurry 71 is sprayed onto the polishing pad 40 through the first spraying means 70, and the second polishing slurry 81 is sprayed through the second spraying means 80. Spray onto 40). At this time, the upper rotary shaft 30 and the lower rotary shaft 60 are rotated to cause the polishing jig 20 and the plate 50 to rotate, and the polishing jig 20 also oscillates. Here, the first polishing slurry 71 may be continuously sprayed, and the second polishing slurry 81 may be sprayed at a predetermined amount every predetermined time. The first polishing slurry 71 is sprayed according to the area of the substrate 10, the polishing amount, and the polishing time. For example, in the case of the substrate 10 of 10 × 10 mm 2, the first polishing slurry 71 is 100 It may be sprayed in an amount of ˜300 [ml / min]. In addition, the amount of spraying is adjusted according to the area of the substrate 10, the amount of polishing, the polishing time, and the size of the second abrasive particles. In the case of spraying onto the substrate 10 having a size of 10 mm 2, the second polishing slurry 81 may be sprayed for 1 second every 2 minutes to spray a total of 3 g of the second abrasive particles for 1 hour. In addition, when the surface roughness (Roughness average Ra) does not meet the standard specifications after the polishing process, the polishing process may be repeated, in which case the polishing process may be performed by adjusting the polishing time. In addition, the degree of polishing may be adjusted by controlling the mixing ratio of the first abrasive particles and the oxidant of the first polishing slurry 71 and the mixing ratio and the particle size of the second abrasive particles of the second polishing slurry 81.

When the first polishing slurry 71 including the first abrasive particles and the oxidant and the second polishing slurry 81 including the second abrasive particles are sprayed to perform the polishing process, the first polishing slurry 71 is applied to the first polishing slurry 71. A hydroxyl group (-OH) bonded to the first abrasive particles included is bonded to SiC of the substrate 10 to form a hydroxyl group bond on the surface of the substrate 10, and an oxidant of the first polishing slurry 71 is formed on the substrate 10. It chemically reacts with the surface of) to form an oxide layer. Then, the surface of the substrate 10 bonded to the hydroxyl group or the oxide layer is formed is polished by the first and second abrasive particles. The second abrasive particles increase the polishing rate of the substrate 10 with high-strength abrasive particles, and the first abrasive particles finely polish the surface of the substrate 10 with the abrasive particles softer than the second abrasive particles. Therefore, the defect layer on the surface of the substrate 10 is removed, and this polishing process can control the surface roughness (Ra) of the substrate 10 to be 2 GPa or less. More preferably, the surface roughness of the substrate 10 can be controlled to 1 dB or less.

Hereinafter, embodiments according to the polishing process according to the present invention and comparative examples according to the conventional polishing process will be described.

Example

10 × 10 mm 2 using a first polishing slurry containing 1 L of NaOCl as an oxidant in 7 L of KOH based colloidal silica having an average particle size of 120 nm and a second polishing slurry containing diamond particles having an average particle size of 25 nm. The silicon carbide substrate was polished. At this time, the first polishing slurry was introduced in an amount of 125 [ml / min], the polishing pad was SUBA800, and the polishing jig was pressed at a pressure of 200 [g / cm 2]. The plate was rotated at a speed of 120 rpm, and the diamond particles contained in the second abrasive particles were sprayed for 1 second every 2 minutes, so that a total of 3 g was sprayed for 1 hour.

In the embodiment of the present invention, the Ra of the silicon carbide substrate was measured to be 4.738 Å before the polishing process, but was measured to 1.087 Å after the polishing process. In addition, the root mean square (RMS) was changed from 6.183 1. to 1.403 Å. The weight was changed from 99.8 mg to 99.5 mg, and the MRR (Material Removal Rate) was 0.3 [mg / min]. Atomic force microscopy (AFM) photographs of the surface of the silicon carbide substrate before and after the CMP process according to the embodiment of the present invention are shown in FIGS. 2 (a) and 2 (b), and the FE of the surface of the silicon carbide substrate after the CMP process SEM 5000 times photograph is shown in FIG. 2 (c). Prior to polishing, a string-like defect layer is present on the substrate surface as shown in FIG. 2 (a), but after polishing, the defect layer is removed on the substrate surface shown in FIGS. 2 (b) and 2 (c). .

Comparative Example 1

A 10 × 10 mm 2 silicon carbide substrate was polished using a first polishing slurry using KOH based colloidal silica having an average particle size of 120 nm. Other conditions were the same as in Example, and the polishing process was performed for 1 hour.

In the comparative example 1, Ra of the silicon carbide substrate was 4.879 GPa before the polishing process, but Ra was rather poor to 5.977 GPa after the polishing process. In addition, the root mean square (RMS) also became busy from 6.363 Å to 7.911 Å, and the weight was measured as 95.7 mg before and after grinding, so that the material removal rate (MRR) was 0 [mg / min]. Atomic force microscopy (AFM) photographs of the surface of the silicon carbide substrate before and after the CMP process according to Comparative Example 1 are shown in FIGS. 3 (a) and 3 (b), and the FE-SEM 5000 of the surface of the silicon carbide substrate after the CMP process. A pear photograph is shown in FIG. 3 (c).

In Comparative Example 1, the surface roughness of the silicon carbide substrate cannot be improved and the surface roughness becomes worse.

Comparative Example 2

A 10 x 10 mm 2 silicon carbide substrate was polished using a first polishing slurry using KOH-based colloidal silica having an average particle size of 120 nm and a second polishing slurry containing diamond particles having an average particle size of 25 nm. Other conditions were the same as in Example and Comparative Example 1, and the polishing process was performed for 1 hour.

In Comparative Example 2, the Ra of the silicon carbide substrate was 5.818 kPa before the polishing process, but was measured to be 2.190 kPa after the polishing process. In addition, the root mean square (RMS) was measured from 7.519 2. to 2.908 Å. The weight was measured before and after polishing at 97.2 mg, and the MRR (Material Removal Rate) was 0 [mg / min]. Atomic force microscopy (AFM) photographs of the surface of the silicon carbide substrate before and after the CMP process according to Comparative Example 2 are shown in FIGS. 4 (a) and 4 (b), and the FE-SEM 5000 of the surface of the silicon carbide substrate after the CMP process. A pear photograph is shown in Figure 4 (c).

In Comparative Example 2, the surface roughness of the silicon carbide substrate may be improved than in Comparative Example 1, but the surface roughness is improved less than in the embodiment according to the present invention.

The results of the above Examples and Comparative Examples are summarized in the following table.

Example Comparative Example 1 Comparative Example 2 colloidal silica (120 nm) + diamond (25 nm) + NaOCl colloidal silica (120 nm) colloidal silica (120 nm) + diamond (25 nm) Board 10 × 10㎡ Silicon Carbide Polishing pad SUBA800 Slurry Inflow 125 [ml / min] Plate rotation speed 120 [rpm] pressure 800 [g / cm 2] Polishing time One One One Ra [Å] before 4.738 4.879 5.818 after 1.087 5.977 2.190 RMS [Å] before 6.183 6.363 7.519 after 1.403 7.911 2.809 weight before 99.8 95.7 97.2 after 99.5 95.7 97.2 MRR 0.3 0 0

Meanwhile, in the above, the first polishing slurry 71 in which the colloidal silica and the oxidant are mixed is injected through the first spraying means 70, and the second abrasive particles contain the second abrasive particles through the second spraying means 80. Although the polishing slurry 81 has been described as being sprayed, the second polishing particles may be further mixed with the first polishing slurry 71 in which colloidal silica and the oxidant are mixed. That is, the polishing slurry 71 may be manufactured by mixing the first abrasive particles, the oxidizing agent, and the second abrasive particles. In this case, the CMP apparatus does not need to provide the second injection means 80.

1 is a schematic cross-sectional view of a CMP apparatus applied to the present invention.

2 is a schematic flowchart of a CMP method according to the present invention;

3 (a) to 3 (c) are AFM images and FE-SEM images of the surface of the silicon carbide substrate before and after the CMP process according to an embodiment of the present invention.

4 (a) to 4 (c) are AFM images and FE-SEM images of the surface of a silicon carbide substrate before and after performing a CMP process according to a comparative example 1 of the related art.

5 (a) to 5 (c) are AFM images and FE-SEM photographs of silicon carbide substrate surfaces before and after performing the CMP process according to the conventional Comparative Example 2.

Claims (14)

Preparing a substrate; Providing a first abrasive slurry comprising first abrasive particles and an oxidant; Providing a second abrasive slurry comprising second abrasive particles; Polishing the substrate using the first and second polishing slurries. The method of claim 1, wherein the substrate comprises a silicon carbide substrate. The method of claim 1, wherein the first abrasive particles include at least one of silica (SiO ₂ ), alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), manganese (MnO ₂ ), or zirconia (ZrO ₂ ). Polishing method. 4. The method of claim 3, wherein said first abrasive particles are colloidal silica. 5. The polishing method according to claim 4, wherein the colloidal silica has an average size of particles of 10 to 200 nm. The method of claim 1 wherein the oxidizing agent is _{NaOCl, H 2 O 2, Fe} (NO 3) 3, H 5 lO 6, KlO 3, K 3 Fe polishing method using at least one of (CN). The polishing method according to claim 4 or 6, wherein the colloidal silica and the oxidizing agent are mixed at a ratio of 7: 1 to 9: 1. 8. The polishing method according to claim 7, wherein the colloidal silica is mixed at 70 to 90 vol% and the oxidant is mixed at 10 to 30 vol%. The polishing method of claim 1, wherein the second abrasive particles use at least one of diamond, silicon carbide, and boron carbide (B ₄ C). The polishing method of claim 9, wherein the second abrasive particles have an average size of 5 to 100 nm. The polishing method of claim 1, wherein the first polishing slurry is continuously sprayed and the second polishing slurry is sprayed periodically. The polishing method according to claim 1, wherein the second abrasive particles have a stronger strength than the first abrasive particles. The polishing method according to claim 1, wherein the second abrasive particles are mixed at 1% or less with respect to the mixing amount of the first abrasive particles and the oxidizing agent. Preparing a substrate; Providing an abrasive slurry comprising at least two abrasive particles and oxidants having different strengths; And Polishing the substrate using the polishing slurry.

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