Substrate polishing device for superconducting wire and method for manufacturing superconducting wire using the same

Abstract

The present invention relates to a substrate polishing device for superconducting wire, and includes an unwinding unit that provides a substrate, a polishing unit that polishes the substrate provided from the unwinding unit, a cleaning unit that cleans the substrate after polishing in the polishing unit, and a winding unit around which the substrate cleaned in the cleaning unit is wound, characterized in that the substrate provided from the unwinding unit is provided with protective layers formed on both sides, and the polishing unit polishes the rear surface of the substrate.

Description

[Technical Field]

[0001] The present invention relates to a substrate polishing apparatus for superconducting wire rods and a method for manufacturing superconducting wire rods using the same, and more particularly to a substrate polishing apparatus for superconducting wire rods that can polish thinner superconducting wire rods so as to improve the performance of the superconducting wire rods, and a method for manufacturing superconducting wire rods using the same. [Background technology]

[0002] Superconductors allow electrical current to flow without loss of power. For example, superconductors have the property that their resistance becomes zero below their critical temperature. Because of these properties, superconductors are the subject of active research and development for commercialization in power equipment such as cables, transformers, generators, current limiters, nuclear fusion devices, and motors, as well as medical / biological applications such as magnetic resonance imaging (MRI) and nuclear magnetic resonance (NMR).

[0003] In particular, high temperature superconductor (HTS) materials, which are oxide superconductors, provide a means for carrying large amounts of electrical current with extremely low losses at liquid nitrogen temperatures (77K).

[0004] Superconducting wire is manufactured by forming a buffer layer composed of Al2O3, Y2O3, MgO, and LaMnO3 on a metal substrate made of Hastelloy or STS material, then forming a superconducting film, ReBaCuO layer, and then forming Ag to surround the entire surface of the wire. Finally, Cu is plated to complete the wire manufacturing process.

[0005] The thickness of commonly used Hastelloy and STS substrates is 50 or 60 μm, and the superconducting wire material occupies most of the volume.

[0006] The magnetic flux density of an electromagnet is proportional to the number of turns N in the coil and the current I flowing through the coil. Therefore, if the thickness of the superconducting wire substrate is reduced, the number of turns in the superconducting coil can be increased, making it possible to create an electromagnet with an even higher magnetic flux density.

[0007] Therefore, research and development efforts are being made to develop thinner superconducting wires.

[0008] The background art of the present invention is disclosed in Korean Patent Publication No. 10-0985122, entitled "System and Method for Surface Polishing of Metal Tape." Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been devised to solve the above-mentioned problems, and an object of the present invention is to provide a substrate polishing apparatus for superconducting wire, which can polish the substrate after manufacturing a superconducting wire to manufacture a thinner superconducting wire, and a method for manufacturing a superconducting wire using the same. [Means for solving the problem]

[0010] The superconducting wire substrate polishing apparatus according to the present invention includes an unwinding unit that provides a substrate, a polishing unit that polishes the substrate provided from the unwinding unit, a cleaning unit that cleans the substrate after polishing in the polishing unit, and a winding unit around which the substrate cleaned in the cleaning unit is wound, wherein the substrate provided from the unwinding unit has protective layers formed on both sides, and the polishing unit polishes the rear surface of the substrate.

[0011] The polishing unit includes a polishing tank containing a deformation prevention agent for preventing deformation of the substrate, a plurality of polishing guide rollers for guiding the substrate in the polishing tank, and a polishing roller for polishing the rear surface of the substrate guided by the polishing guide rollers.

[0012] The deformation inhibitor is characterized in that it is an inert liquid gas.

[0013] The polishing guide roller formed at the rear end of the polishing guide rollers is characterized by being a heating roller.

[0014] The polishing unit includes a cooling roller that contacts the front surface of the substrate to prevent deformation of the substrate, and a polishing roller that is disposed below the cooling roller and polishes the rear surface of the substrate.

[0015] The polishing roller is characterized in that it is a crown roller.

[0016] The cleaning unit includes a cleaning tank containing a cleaning agent and a plurality of cleaning guide rollers for guiding the substrate into the cleaning tank, and a cleaning guide roller formed at a rear end of the cleaning guide rollers is a heating roller.

[0017] The cleaning unit includes a polishing correction unit that measures the thickness of the substrate and corrects the polishing roller, and the polishing correction unit includes a thickness measurement unit that measures the thickness of the substrate passing through the cleaning unit, and a control unit that corrects the degree of polishing by the polishing roller according to the value measured by the thickness measurement unit.

[0018] The method for manufacturing a superconducting wire using a substrate polishing apparatus for a superconducting wire according to the present invention is characterized by including a buffer layer forming step of forming a buffer layer on a substrate, a superconducting layer forming step of forming a superconducting layer on the buffer layer, a first protective layer forming step of forming protective layers on both sides of the substrate to protect the superconducting layer, a thickness reducing step of reducing the thickness of the substrate on which the protective layers have been formed, a second protective layer forming step of forming protective layers on the side surfaces of the substrate, and a stabilizing layer forming step of forming a stabilizing layer on the peripheral surface of the substrate.

[0019] The thickness reducing step includes a backside polishing step of polishing the backside of the substrate to reduce the thickness of the substrate provided with protective layers formed on both sides thereof; a first removal step of removing dust generated on the substrate due to polishing; a cleaning step of cleaning the substrate after the first removal step; a second removal step of removing dust from the substrate; and a thickness correction step of measuring the thickness of the substrate after the second removal step and correcting the degree of polishing in the backside polishing step.

[0020] The second removing step is characterized in that dry nitrogen is sprayed onto the substrate after the cleaning step, thereby coating the surface of the substrate with nitrogen. [Effects of the Invention]

[0021] As described above, the superconducting wire substrate polishing apparatus and the superconducting wire manufacturing method using the same according to the present invention can polish the substrate after manufacturing the superconducting wire to manufacture a thinner superconducting wire, thereby producing a superconducting wire with excellent properties in terms of passing a large current, generating a strong magnetic field, etc.

[0022] In the present invention, in order to prevent deformation or denaturation due to heat generated during the polishing process, an inert liquid gas is used as a deformation prevention agent and as a cleaning agent. This not only prevents deformation or denaturation of the substrate, but also eliminates the use of moisture, thereby protecting the superconductor, which is sensitive to moisture, and preventing moisture adsorption.

[0023] After cleaning, the air knife removes foreign matter from the substrate, spraying dry nitrogen onto the surface of the substrate, coating the surface with nitrogen, thereby protecting the substrate from moisture and preventing corrosion.

[0024] In the present invention, since the polishing roller is a crown roller, it is possible to prevent the edge polishing rate from being high due to stress during polishing, and to achieve a uniform polishing rate on the front surface of the substrate.

[0025] The present invention has an effect of providing a superconducting wire having excellent performance since the thickness of the final substrate after polishing can be continuously measured and corrected by the polishing correction unit. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a diagram for explaining the structure of a superconducting wire according to the present invention.

[0027] [Figure 2]1 is a schematic diagram for explaining a polishing apparatus for a superconducting wire according to the present invention;

[0028] [Figure 3] FIG. 10 is a schematic diagram for explaining a modified example of the polishing apparatus for superconducting wire according to the present invention.

[0029] [Figure 4] 1 is a diagram illustrating a polishing roller of a polishing apparatus for polishing a superconducting wire according to the present invention.

[0030] [Figure 5] 1 is a flowchart illustrating a method for manufacturing a superconducting wire according to the present invention.

[0031] [Figure 6] 3 is a flowchart illustrating a thickness reducing step of a method for manufacturing a superconducting wire according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, preferred embodiments of a superconducting wire polishing apparatus and a method for manufacturing a superconducting wire using the same according to the present invention will be described with reference to the accompanying drawings. In this process, the thickness of wires and the size of components shown in the drawings may be exaggerated for clarity and convenience.

[0033] The terms described below are defined in consideration of their functions in the present invention, and may vary depending on the intentions or practices of users or operators. Therefore, the definitions of such terms should be based on the overall content of this specification.

[0034] Figure 1 is a drawing for explaining the structure of the superconducting wire of the present invention, Figure 2 is a schematic diagram for explaining the polishing apparatus for superconducting wire of the present invention, Figure 3 is a schematic diagram for explaining a modified example of the polishing apparatus for superconducting wire of the present invention, Figure 4 is a drawing for explaining the polishing roller of the polishing apparatus for superconducting wire of the present invention, Figure 5 is a flowchart for explaining the manufacturing method for superconducting wire of the present invention, and Figure 6 is a flowchart for explaining the thickness reduction step of the manufacturing method for superconducting wire of the present invention.

[0035] 1 to 4, a substrate polishing apparatus 100 for a superconducting wire according to one embodiment of the present invention comprises an unwinding section 110, a polishing section 120, a cleaning section 130, and a winding section 160.

[0036] The unwinding section 110 provides the substrate 12 , and the substrate 12 to be polished is wound on a feeding reel. The substrate 12 is sequentially drawn out from the unwinding section 110 and provided to the polishing section 120 .

[0037] The take-up unit 160 is a continuous supply reel that provides the substrate 12 at a constant speed, and by adjusting the tension in conjunction with the take-up unit 160, which will be described later, the substrate 12 can be prevented from sagging or stretching.

[0038] The transport speed of the substrate 12 can vary depending on a number of factors, such as the polishing thickness, the polishing rate, and the like.

[0039] At this time, the substrate 12 provided at the unwinding unit 110 is provided with protective layers 17 formed on both sides. More specifically, referring to Fig. 1, the substrate 12 is provided with a buffer layer 14 and a superconducting layer 16 formed thereon, and protective layers 17 formed with Ag to surround the entire surface and only on both sides of the substrate 12. In other words, the substrate is provided at the unwinding unit 110 in a manufactured state as the superconducting wire 10.

[0040] The polishing unit 120 polishes the substrate 12 provided from the unwinding unit 110, and is composed of a polishing tank 122 containing a deformation prevention agent 123 for preventing deformation of the substrate 12, a plurality of polishing guide rollers 124 for guiding the substrate 12 into the polishing tank 122, and a polishing roller 126 for polishing the rear surface of the substrate 12 guided by the polishing guide rollers 124.

[0041] The deformation prevention agent 123 contained in the polishing tank 122 is made of non-flammable liquid gas. More specifically, the non-flammable liquid gas is made of liquid nitrogen (LN2) or liquid helium (LHe). Because polishing is performed in non-flammable liquid gas, deformation and denaturation due to heat can be prevented, and scattering of particles generated during polishing can also be prevented.

[0042] In this embodiment, by using a non-flammable liquid gas as a coolant, it is possible to protect the superconductor, which is vulnerable to moisture, and prevent moisture absorption, thereby improving adhesion of the film during the coating process.

[0043] The polishing guide rollers 124 are made up of first and second polishing guide rollers 124a and 124b that guide the substrate 12 into the polishing tank 122, and third and fourth polishing guide rollers 124c and 124d that guide the substrate 12 to the outside of the polishing tank 122. The polishing guide roller 124 formed at the rear end of the polishing guide rollers 124 is made up of a heating roller. That is, the fourth polishing guide roller 124d is made up of a heating roller and prevents moisture from being adsorbed on the surface of the substrate 12 pulled out of the polishing tank 122.

[0044] The polishing unit 120 performs polishing in a polishing chamber 128 formed under vacuum to prevent scattering of particles from the polished substrate 12 and adsorption of moisture on the surface.

[0045] The polishing roller 126 is provided below between the second polishing guide roller 124b and the third polishing guide roller 124c to polish the rear surface of the substrate 12, thereby making the thickness of the substrate 12 thinner.

[0046] As shown in FIG. 3, the polishing unit 220 is composed of a cooling roller 222 that contacts the front surface of the substrate 12 to prevent deformation of the substrate 12, and a polishing roller 224 that is disposed below the cooling roller 222 and polishes the rear surface of the substrate 12.

[0047] That is, the cooling roller 222 comes into contact with the superconducting vapor deposition surface to cool the heat generated when the rear surface of the substrate 12 is polished by the polishing roller 224, thereby preventing deformation or degeneration. The polishing roller 224 may also be cooled as needed.

[0048] The polishing rollers 126, 224 are crown rollers as shown in Figure 4. This is because if the polishing rollers 126, 224 are parallel rolls with a circular cross section, the polishing rate at the edge of the substrate 12 will be higher than at the center due to stress during polishing. To compensate for this, it is preferable to use crown rollers with a larger diameter at the center and a smaller diameter toward the edge of the roll.

[0049] The cleaning unit 130 cleans the substrate 12 that has been polished in the polishing unit 120, and is composed of a cleaning tank 132 containing a cleaning agent 133 and a plurality of cleaning guide rollers 134 that guide the substrate 12 into the cleaning tank 132.

[0050] The cleaning guide rollers 134 are made up of first, second, and third cleaning guide rollers 134a, 134b, and 134c that guide the substrate 12 into and out of the cleaning bath 132. The cleaning guide roller 134 formed at the rear end of the cleaning guide rollers 134 is made up of a heating roller. That is, the third cleaning guide roller 134c is made up of a heating roller and prevents moisture from being adsorbed on the surface of the substrate 12 pulled out of the cleaning bath 132.

[0051] The cleaning agent 133 contained in the cleaning tank 132 is the same inert liquid gas as the deformation prevention agent 123, such as liquid nitrogen (LN2), liquid helium (LHe), anhydrous ethanol, ethylene, etc. The cleaning unit 130 is cleaned in a cleaning chamber 138 formed under vacuum to prevent moisture from being adsorbed on the surface of the substrate 12 after cleaning.

[0052] The third cleaning guide roller 134c, which is a heating roller, is heated to room temperature to prevent absorption of moisture when exposed to the atmosphere.

[0053] Dust removal units 140 are provided before and after the cleaning unit 130. The dust removal unit 140 includes a first dust removal unit 142 that removes dust from the substrate 12 polished in the polishing unit 120, and a second dust removal unit 144 that finally removes dust from the substrate 12 cleaned in the cleaning unit 130 and nitrogen, which is a liquid.

[0054] The first dust removal unit 142 comprises a dust collection and suction unit 142a that collects and sucks dust from the polished substrate 12 and an air knife 142b that sprays high-pressure dry nitrogen, and the second dust removal unit 144 comprises an air knife 144a that sprays dust from the cleaned substrate 12 and liquid nitrogen into high-pressure dry nitrogen.

[0055] In particular, moisture may be generated on the substrate 12 while it is cleaned in the vacuum chamber 138 formed under vacuum and then exposed to the atmosphere and moved to the next process. However, dried nitrogen is sprayed from the second dust removal unit 144, so that the surface of the substrate 12 is coated with nitrogen, thereby protecting the substrate 12 from moisture.

[0056] The superconducting wire polishing apparatus 100 according to this embodiment includes a polishing correction unit 150 that measures the thickness of the substrate 12 and corrects the polishing roller 126 .

[0057] The polishing correction unit 150 is composed of a thickness measuring unit 154 that measures the thickness of the substrate 12 that has passed through the cleaning unit 130 and a control unit 154 that corrects the degree of polishing by the polishing roller 126 based on the value measured by the thickness measuring unit 154.

[0058] Since the degree of polishing of the substrate 12 can be immediately corrected by the polishing correction unit 150, the superconducting wire 10 can be provided with a thickness desired by the user.

[0059] The substrate 12, which has been polished and cleaned to reduce its thickness, is provided to the winding unit 160. The winding unit 160 comprises a winding grill around which the substrate 12 is wound.

[0060] A method for manufacturing a superconducting wire using a substrate polishing apparatus for a superconducting wire according to an embodiment of the present invention will now be described.

[0061] A method for manufacturing a superconducting wire using a polishing apparatus 100 for a substrate 12 of a superconducting wire according to one embodiment of the present invention includes a buffer layer forming step (S100), a superconducting layer forming step (S200), a first protective layer forming step (S300), a thickness reducing step (S400), a second protective layer forming step (S600), and a stabilizing layer forming step (S700).

[0062] First, a rolled substrate 12 is provided (S110), and an electropolishing process is performed to planarize the substrate 12 (S120).

[0063] Thereafter, a buffer layer 14 is formed on the front surface of the substrate 12 (S130). The buffer layer 14 is formed as follows.

[0064] The buffer layer 14 is formed by treating the surface using the electrolytic polishing process (S120) and then depositing an Al2O3 diffusion barrier layer on the metal substrate 12 made of Hastelloy or STS material, depositing a Y2O3 seed layer on top, and sequentially depositing MgO and LaMnO3 layers (S130).

[0065] The superconducting layer 16 is formed on the buffer layer 14 (S200). The superconducting layer 16 is formed by depositing a ReBaCuO layer, which is a superconducting film.

[0066] After the buffer layer 14 and the superconducting layer 16 are formed on the front surface of the substrate 12, a first protective layer 17 is formed (S300). The first protective layer 17 is formed by depositing Ag on both sides of the substrate 12 to protect the ReBaCuO superconducting metal oxide containing rare earth elements.

[0067] Thereafter, a thickness reducing step (S400) is performed. In the thickness reducing step (S400), the thickness of the substrate 12 is reduced with the protective layer 17 formed thereon. In this embodiment, the superconducting wire 10 is manufactured with the buffer layer 14, the superconducting layer 16, and the first protective layer 17 formed on the substrate 12, and then polished to reduce the thickness of the superconducting wire, thereby providing excellent characteristics in terms of passing a large current and generating a strong magnetic field.

[0068] When the deposition process of the buffer layer 14 and the superconducting layer 16 is carried out using a substrate that has been thinly rolled to a thickness of 30 μm or less, there is a problem that it is difficult to control the tension due to the structure of the process equipment. However, in this embodiment, the rear surface of the substrate 12 is polished after the superconducting wire 10 has already been manufactured, so this problem can be solved and a superconducting wire 10 with a thin thickness can be provided.

[0069] The thickness reducing step (S400) includes a backside polishing step (S410), a first removal step (S420), a cleaning step (S430), a second removal step (S440), and a thickness correction step (S450).

[0070] The rear surface of the substrate 12 is polished to reduce the thickness of the substrate 12 provided with the protective layer 17 formed on both sides. At this time, the substrate 12 is introduced through polishing guide rollers 124 into a polishing tank 122 containing an inert liquid gas (liquid nitrogen: LN2) or liquid helium: LHe) as a deformation prevention agent 123, and the rear surface is polished by polishing rollers 126 in the polishing tank 122, thereby reducing the thickness of the substrate 12 without deformation or modification (S410). At this time, the polishing guide roller 124 located at the rear end of the polishing guide rollers 124 is formed as a heating roller to prevent moisture absorption due to external exposure.

[0071] The rear polishing step (S410) may be performed using a cooling roller 222 and a polishing roller 224 arranged side by side at the top and bottom as shown in Figure 3. If necessary, the polishing roller 224 may also be cooled to prevent deformation or deterioration of the substrate 12 due to heat generated during polishing.

[0072] Thereafter, dust generated during polishing of the substrate 12 whose rear surface has been polished is removed by the first dust removal unit 142 (S420). The first dust removal unit 142 is composed of a dust collection and suction unit 142a and an air knife 142b, and collects and sucks dust from the substrate 12 and removes it by spraying high-pressure dry nitrogen.

[0073] After the first removing step (S420), a cleaning step (S430) is performed to clean the substrate 12. The cleaning step (S430) is performed by guiding the substrate 12 through a cleaning bath 132 containing a cleaning agent 133 using a plurality of cleaning guide rollers 134. The cleaning unit 130 is preferably cleaned in a cleaning chamber 138 in a vacuum to prevent moisture from being adsorbed onto the surface of the substrate 12, and a third cleaning guide roller 134c formed at the rear end of the cleaning guide rollers 134 is formed as a heating roller to prevent moisture from being adsorbed onto the substrate 12 when it is exposed to the atmosphere.

[0074] After the cleaning is completed, the substrate 12 is finally subjected to a second removal step (S440) to remove dust and liquid nitrogen. In the second removal step (S440), the dust is removed by high-pressure dry nitrogen from a second dust removal unit 144 formed by an air knife 144a.

[0075] The second removal step (S440) sprays dry nitrogen onto the substrate 12 that has been cleaned (S430) so that the surface of the substrate 12 is coated with nitrogen, thereby protecting the substrate 12 from moisture.

[0076] After the second removing step (S440), a thickness correcting step (S450) is performed to measure the thickness of the substrate 12 and correct the degree of polishing in the backside polishing step (S410).

[0077] In the thickness correction step (S450), the thickness of the substrate 12 that has passed through the second dust removal unit 144 is measured by the thickness measurement unit 154, and the degree of polishing by the polishing roller 126 is corrected by the control unit 154 based on the value measured by the thickness measurement unit 154. In this way, the thickness of the final substrate 12 that has completed the backside polishing can be continuously measured and corrected, thereby providing a superconducting wire 10 with excellent performance.

[0078] Thereafter, a slitting step (S500) is performed to cut the substrate 12 at regular intervals. In the slitting step (S500), the substrate 12 is cut at regular intervals using a slitter to form unit substrates 12. The cut substrates 12 are then subjected to a second protective layer forming step (S600) to form protective layers 17 made of Ag coating on the sides of the substrates 12. A stabilizing layer forming step (S700) is performed to form a stabilizing layer 18 on the entire peripheral surface of the substrate 12 using Cu electroplating, thereby completing the superconducting wire 10.

[0079] As described above, according to the present invention, after manufacturing a superconducting wire, the substrate can be polished to manufacture a thinner superconducting wire, thereby providing a superconducting wire with excellent properties in terms of passing a large current and generating a strong magnetic field.

[0080] While the present invention has been described with reference to the embodiments illustrated in the drawings, this is by way of example only, and those skilled in the art will recognize that various modifications and equivalent alternative embodiments are possible.

[0081] Therefore, the true technical scope of protection of the present invention should be determined by the following claims.

Claims

1. an unwinder for providing the substrate; a polishing unit that polishes the substrate provided from the unwinding unit; a cleaning unit that cleans the substrate after polishing in the polishing unit; a winding section around which the substrate cleaned in the cleaning section is wound; The substrate provided at the unwinding section is provided with protective layers formed on both sides thereof, 10. A polishing apparatus for a superconducting wire, wherein the polishing unit polishes the rear surface of the substrate.

2. the polishing unit includes a polishing tank containing a deformation prevention agent for preventing deformation of the substrate; a plurality of polishing guide rollers for guiding the substrate into the polishing tank; and 2. The superconducting wire polishing apparatus according to claim 1, further comprising a polishing roller for polishing a rear surface of the substrate guided by the polishing guide roller.

3. 3. The apparatus for polishing a superconducting wire according to claim 2, wherein the deformation preventing agent is an inert liquid gas.

4. 3. The polishing apparatus for a superconducting wire according to claim 2, wherein the polishing guide roller formed at the rear end of the polishing guide rollers is a heating roller.

5. the polishing unit includes a cooling roller in contact with the front surface of the substrate to prevent deformation of the substrate; and 2. The apparatus for polishing a superconducting wire according to claim 1, further comprising a polishing roller disposed below the cooling roller for polishing the rear surface of the substrate.

6. 3. The polishing apparatus for a superconducting wire according to claim 2, wherein the polishing roller is a crown roller.

7. The cleaning unit is a cleaning tank containing a cleaning agent; and a plurality of cleaning guide rollers for guiding the substrate into the cleaning tank; 2. The apparatus for polishing a superconducting wire according to claim 1, wherein the guide roller formed at the rear end of the cleaning guide roller is a heating roller.

8. a polishing correction unit that measures the thickness of the substrate and corrects the polishing roller; the polishing correction unit is a thickness measurement unit that measures the thickness of the substrate that has passed through the cleaning unit; 3. The polishing apparatus for a superconducting wire according to claim 2, further comprising a control unit that corrects the degree of polishing by said polishing roller in accordance with the value measured by said thickness measuring unit.

9. a buffer layer forming step of forming a buffer layer on the substrate; a superconducting layer forming step of forming a superconducting layer on the buffer layer; a first protective layer forming step of forming protective layers on both sides of the substrate to protect the superconducting layer; a thickness reducing step of reducing the thickness of the substrate on which the protective layer is formed; forming a second protective layer on the side surface of the substrate; and A method for manufacturing a superconducting wire, comprising the step of forming a stabilizing layer on a peripheral surface of the substrate.

10. the thickness reducing step includes polishing a rear surface of the substrate so as to reduce the thickness of the substrate provided with protective layers formed on both surfaces; a first removing step of removing foreign particles generated by polishing the substrate; a cleaning step of cleaning the substrate after the first removing step; a second removal step of removing foreign matter from the substrate; and 10. The method of claim 9, further comprising a thickness correction step of measuring the thickness of the substrate after the second removing step and correcting the degree of polishing in the back-surface polishing step.

11. 11. The method of claim 10, wherein the second removing step involves spraying dried nitrogen onto the substrate after the cleaning step, thereby coating the surface of the substrate with nitrogen.

Images