Wafer substrate with adhesion improved area, wafer substrate with protective film layer, and method for manufacturing wafer substrate with adhesion improved area

Abstract

To provide wafers, etc. with protective film layers that prevent solution penetration with improved adhesion of the protective film layer to wafer substrates with various surface treatments.SOLUTION: The objective is achieved by employment of a wafer substrate, etc. with an adhesion improved area 3 of a protective film layer which is a wafer substrate 1a used with the protective film layer on the surface to inhibit solution penetration and has the adhesion improved area 3 of the protective film layer along the periphery of wafer substrates with various surface treatments.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a wafer substrate having an adhesion improving region for a protective film, a wafer substrate with a protective film layer, and a method for manufacturing a wafer substrate. [Background technology]

[0002] Wafers have traditionally been an essential material in the manufacture of semiconductors, and the resulting electronic elements and components are widely used in a wide range of electronic and electrical products in the fields of automobiles, digital home appliances, and communications equipment.

[0003] For example, in the case of power semiconductors, an electrode is provided on the surface of a wafer substrate, and a metal film is formed on the entire back surface of the wafer substrate. This back metal film is formed by a method such as deposition or plating. When plating the electrodes on the surface of the wafer substrate, a protective film such as a protective film is generally attached to the entire back surface of the wafer substrate to protect the metal film on the back surface of the wafer substrate from solutions such as plating solution and cleaning solution. However, the adhesive used in the protective film generally has low adhesion to the metal film, and the solution seeps into the protective film and the wafer substrate from the outer peripheral edge of the wafer substrate around the wafer substrate. When the solution seeps in during the plating process, the metal film dissolves and the plating precipitates, causing a decrease in product yield. In addition, the precipitated plating may detach, causing contamination of the solution and the wafer, and the plating solution may be deteriorated due to elution from the film. Furthermore, if a resist is formed on the protective surface, the resist may peel off.

[0004] To solve these problems, Patent Document 1 employs a manufacturing method for a semiconductor device in which a curable resin is applied to one side of a semiconductor substrate, a film is attached, and then the curable resin is cured to prevent erosion by the plating solution and enable plating to be performed on the other side of the semiconductor substrate.

[0005] Furthermore, Patent Document 2 employs a manufacturing method for a semiconductor device in which a protective film is attached to the back surface of the wafer and also to the side surfaces, thereby enabling stable attachment and peeling of the protective film to areas where a plating layer is not to be formed, and preventing abnormal precipitation of the plating layer. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2010-182807 A [Patent Document 2] JP 2016-152317 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the inventions disclosed in the above-mentioned Patent Documents 1 and 2, in addition to the film for protecting the main surface of the wafer, in order to prevent the intrusion of the solution, in Patent Document 1, a curable resin is used to fix the film, and in Patent Document 2, a protective tape is also applied to the outer periphery. This causes problems in that a device for applying and peeling the curable resin, or a dedicated device for applying and peeling the protective tape, is required, and the cost of the protective film used increases. In addition, a certain amount of pressure must be applied using a roller to apply the protective tape, and it is considered that it may be difficult to deal with the risk of damage when the wafer is thinned.

[0008] Therefore, the present invention aims to provide a wafer substrate with a protective film layer that can improve the adhesion of the protective film layer of a wafer substrate that has been subjected to various surface treatments without using the protective tape described above, and that can prevent the intrusion of chemical solutions even without a protective tape. [Means for solving the problem]

[0009] Means for Solving the Problems The present inventors have conducted intensive research to solve the above problems and have come up with the following invention.

[0010] Wafer substrate with adhesion-improving region according to the present application: The wafer substrate with adhesion-improving region according to the present application is a wafer substrate provided with a protective film layer on the surface to prevent solution penetration, and is surface-treated by vapor deposition, sputtering, plating, etc., to form the outermost surface into a metal film made of a precious metal such as gold or silver, which is then laminated with titanium, chromium, copper, or alloys thereof. The wafer substrate is characterized by having an adhesion-improving region of the protective film layer that enhances the adhesion of the protective film layer parallel to the outer peripheral edge of the wafer substrate that has been subjected to various surface treatments.

[0011] In the wafer substrate having an adhesion improvement region according to the present application, the adhesion improvement region is preferably a region that is free of at least the precious metal components gold, silver, platinum, and palladium among the inorganic components used in the surface treatment.

[0012] In the wafer substrate having an adhesion improving region according to the present application, it is more preferable that the adhesion improving region is free of inorganic components used in the surface treatment and exposes the wafer surface.

[0013] In a wafer substrate having an adhesion improving region according to the present application, it is preferable that the adhesion improving region arranged parallel to the outer periphery of a planar wafer substrate is a band-shaped region having a width of 0.2 mm or more and 3 mm or less parallel to the outer periphery of the wafer substrate.

[0014] In a wafer substrate having an adhesion improving region according to the present application, the adhesion improving region arranged parallel to the outer peripheral edge of the wafer substrate having a band-shaped protrusion portion having a protruding shape along the outer periphery is preferably a band-shaped region having a width of 0.2 mm or more and W1 mm ​​or less from the outer peripheral edge of the wafer substrate, when the width of the band-shaped protrusion portion is W1 mm.

[0015] Wafer substrate with protective film layer according to the present application: The wafer substrate with protective film layer according to the present application is characterized in that a protective film layer is provided on the surface of a wafer substrate having the above-mentioned adhesion-improving region, thereby improving the inhibitory effect against solution penetration.

[0016] The method for manufacturing a wafer substrate having an adhesion-improving region according to the present application: The method for manufacturing a wafer substrate having an adhesion-improving region according to the present application is a method for manufacturing a wafer substrate having the adhesion-improving region described above, and is characterized in that the surface of a wafer substrate that has been subjected to various surface treatments is physically polished or cut parallel to the outer peripheral edge thereof to form an adhesion-improving region by peeling off some or all of the metal layers that make up the surface treatment layer, which is a metal film made of a precious metal such as gold or silver and has an outermost surface that is laminated with titanium, chromium, copper and alloys thereof, by methods such as vapor deposition, sputtering, plating, etc.

[0017] In the method for manufacturing a wafer substrate having an adhesion-improving region according to the present application, when the adhesion-improving region is provided on the outer periphery of a planar wafer substrate, it is preferable to physically polish or cut a surface portion having a width of 0.2 mm or more and 3 mm or less parallel to the outer periphery edge of the wafer substrate to form a band-shaped region.

[0018] In the method for manufacturing a wafer substrate having an adhesion-improving region, related to the present application, when the adhesion-improving region is provided on the outer periphery of a wafer substrate having a band-shaped protrusion portion having a raised shape along the outer periphery, when the width of the band-shaped protrusion portion is W1mm, it is preferable to physically polish or cut a surface portion having a width of 0.2 mm to W1 mm ​​parallel to the outer peripheral edge of the wafer substrate to form a band-shaped region.

[0019] In the method for manufacturing a wafer substrate having an adhesion improving region according to the present application, the polishing depth during the polishing process is preferably 20 nm to 10 μm. Effect of the Invention

[0020] According to the present invention, by providing an adhesion improving region of the protective film layer that improves the adhesion of the protective film layer parallel to the outer peripheral edge of the wafer substrate that has been subjected to various surface treatments, it is possible to effectively prevent the penetration of chemicals between the back surface of the wafer and the protective film. In addition, the adhesion improving region provided parallel to the outer peripheral edge of the wafer substrate can be easily formed by polishing or cutting, existing equipment can be used for film attachment and film peeling, and excessive capital investment is not required, making it possible to provide high-quality wafer products at low cost. By adopting the invention of the present application, it is no longer necessary to attach a protective tape to the peripheral portion as was previously used, and excessive capital investment and increases in material costs can be suppressed. [Brief description of the drawings]

[0021] [Figure 1] 1A to 1C are three views illustrating a planar wafer substrate with an adhesion improving region. [Diagram 2] 1A to 1C are three views showing a wafer substrate with an adhesion improving region, the wafer substrate having a band-shaped protrusion portion having a protruding shape along the outer periphery. [Diagram 3] FIG. 1 is an image diagram of a processing device for polishing a surface treatment layer on the outer peripheral edge of a wafer to form an adhesion improvement region. [Figure 4] This is a schematic diagram showing a state in which no solution intrusion occurs between the protective film and the wafer substrate when an adhesion improving region is provided (Example), and a state in which solution intrusion occurs between the protective film and the wafer substrate when an adhesion improving region is not provided (Comparative Example). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Hereinafter, a wafer substrate having an adhesion improving region, a wafer substrate with a protective film, and a method for manufacturing the wafer substrate having an adhesion improving region according to the present invention will be described. The wafer substrate is a substrate made of a compound semiconductor such as silicon or silicon carbide.

[0023] 1. Embodiments of a wafer substrate having an adhesion improving region The wafer substrate with an adhesion-improving region according to the present application is used with a protective film layer provided on the surface to prevent solution penetration. Generally, when a wafer substrate is used, various surface treatments are applied to the surface. Inorganic components such as gold, silver, and nickel are widely used in a multi-layered state for this surface treatment. Therefore, the protective film to be attached to the wafer substrate is attached via the surface treatment layer. In this state, the adhesiveness of the protective film is insufficient. Therefore, an adhesiveness-improving region of the protective film layer that enhances the adhesiveness of the protective film layer is provided parallel to the outer peripheral edge of the wafer substrate.

[0024] The adhesion improving region is a region in which surface treatment components that inhibit the adhesion of the protective film layer have been removed, parallel to the outer peripheral edge of the wafer substrate on which the surface treatment layer is formed. The adhesion improving region is desirably provided based on the following technical concept.

[0025] The adhesion improving region of the wafer substrate having the adhesion improving region is preferably a region that is free of at least precious metal components such as gold, silver, platinum, palladium, etc., which are inorganic components used in the surface treatment, because precious metal components are the most destabilizing factor in the adhesion of the protective film.

[0026] In the case where the adhesion of the protective film at the outer peripheral edge of the wafer is still insufficient even if the adhesion improving region from which the precious metal components have been removed is provided as described above, it is more preferable that the adhesion improving region completely removes the inorganic components used in the surface treatment in the outer peripheral region of the wafer substrate to expose the wafer surface in the outer peripheral region. This is because completely removing the components used in the surface treatment layer reliably ensures that the protective film adheres to the wafer substrate and reliably prevents the intrusion of the solution.

[0027] In the wafer substrate having this adhesion improving region, the adhesion improving region provided on the outer periphery of the planar wafer substrate is preferably a strip-shaped region having a width of 0.2 mm to 3 mm (hereinafter simply referred to as "adhesion width") parallel to the outer periphery edge of the wafer substrate. If the adhesion width is less than 0.2 mm, the adhesion of the protective film becomes unstable and it becomes impossible to completely prevent the intrusion of the solution. On the other hand, even if the adhesion width exceeds 3 mm, the improving effect of the protective film does not increase, which is not preferable.

[0028] Fig. 1 shows a three-sided view of a planar wafer substrate 1a with an adhesion improving region. It can be seen from Fig. 1 that the silicon wafer substrate 2 is provided with an adhesion improving region 4 of the protective film layer that improves the adhesion of the protective film layer 3, parallel to the outer periphery of the silicon wafer substrate 2. The three-sided view shown in Fig. 1 omits the illustration of the surface treatment layer, which has a thickness of several tens of nm to several μm.

[0029] Furthermore, when the wafer substrate having the adhesion improving region is a wafer substrate having a band-shaped protrusion portion in a raised shape along the outer periphery (meaning a so-called "TAIKO" shape), the adhesion improving region is provided as follows. When the width of the protruding band-shaped protrusion portion is W1 mm, it is preferable that the adhesion improving region is a band-shaped region having a contact width of 0.2 mm or more and W1 mm ​​or less parallel to the outer periphery edge of the wafer substrate. If the contact width is less than 0.2 mm, the adhesion of the protective film becomes unstable and it becomes impossible to completely prevent the intrusion of the solution, which is undesirable. On the other hand, if the contact width exceeds the width W1 mm ​​of the band-shaped protrusion portion in a raised shape along the outer periphery of the wafer substrate, the adhesion of the protective film to the wafer substrate becomes unstable, which is undesirable.

[0030] Figure 2 shows a three-sided view of a wafer substrate 1b with an adhesion improving region in the case of a wafer substrate 1b having a band-shaped protrusion portion that is raised along the outer periphery (meaning a so-called "TAIKO" shape). It can be seen from Figure 2 that the wafer substrate 2 has an adhesion improving region 4 of the protective film layer that improves the adhesion of the protective film layer 3, parallel to the outer periphery edge. The three-sided view shown in Figure 2 omits the depiction of the surface treatment layer, which has a thickness of several tens of nm to several μm.

[0031] Form of the wafer substrate with a protective film layer: The wafer substrate with a protective film layer according to the present application is characterized in that a protective film layer is provided on the surface of the wafer substrate having the above-mentioned adhesion improving region, thereby preventing the penetration of a solution between the wafer substrate and the protective film. In this case, the protective film can be bonded to the wafer substrate by any of the known methods such as roller bonding and vacuum bonding.

[0032] Form of the method for manufacturing a wafer substrate having an adhesion-improving region: The method for manufacturing a wafer substrate having an adhesion-improving region according to the present application is the method for manufacturing a wafer substrate having an adhesion-improving region described above. Therefore, as can be understood from the above, a wafer substrate having an adhesion-improving region that prevents the penetration of a solution between the wafer substrate and the protective film is manufactured by controlling the surface treatment components present on the wafer substrate surface.

[0033] Considering the viewpoint of removing the surface treatment layer provided on the wafer surface, various methods are conceivable. (1) Plating resist is placed or a jig is used to cover the area to be the adhesion improvement area, so that the surface treatment layer is not partially provided to prevent plating from being deposited. (2) After surface treatment, the surface treatment layer is removed by wet etching only in the outer peripheral edge area of ​​the wafer substrate. (3) After surface treatment, the surface treatment layer is removed by dry etching using argon ions or the like only in the outer peripheral edge area of ​​the wafer substrate. The above are conceivable. However, all of these methods require excessive capital investment and reduce work efficiency.

[0034] Therefore, the present invention provides a method for forming an adhesion-improved region by polishing or cutting the surface along the outer periphery of a wafer substrate that has been subjected to various surface treatments, thereby peeling off some or all of the metal layer that constitutes the surface treatment layer on the outer periphery of the wafer surface. FIG. 3 shows an image of a processing device for forming an adhesion-improving region by physically polishing or cutting the surface treatment layer on the outer peripheral edge of a wafer substrate.

[0035] In the case of a planar wafer substrate 1a with an adhesion improving region formed using such an apparatus, the adhesion improving region 4 for improving the adhesion of the protective film layer 3 provided on the outer periphery is formed by physically polishing or cutting a strip-shaped region having an adhesion width of 0.2 mm to 3 mm parallel to the outer periphery edge of the wafer substrate 2. The reason for determining the adhesion width is the same as described above.

[0036] In the case of a wafer substrate 1b having an adhesion improving region, and in the case of a wafer substrate 2 having a band-shaped protrusion portion in a protruding shape along the outer periphery, when the width of the band-shaped protrusion portion in a protruding state is W1 mm, it is preferable to physically form a band-shaped region having an adhesion width of 0.2 mm to W1 mm ​​parallel to the outer periphery edge of the wafer substrate 2 by polishing or cutting to form the adhesion improving region 3 of the protective film layer. The reason for determining the adhesion width is the same as described above.

[0037] In the manufacturing method of the wafer substrate having the adhesion improvement region according to the present application, the polishing or cutting depth when performing the polishing or cutting process is not limited in any particular way, as long as it can remove the surface treatment components that inhibit the adhesion of the protective film. However, practically speaking, it is preferably 20 nm to 10 μm. If the polishing or cutting depth is less than 20 nm, metal components that inhibit the adhesion of the protective film will remain, which is not preferable. Even if the polishing or cutting depth is more than 10 μm, the wafer surface will be exposed and the adhesion of the protective film will not be further improved.

[0038] In addition, the wafer substrate having the adhesion-improving region according to the present application can be used in various methods for protecting the rear surface of a wafer, such as a protection method using a protective tape with a single-sided adhesion layer, or a method of protecting a wafer with a glass wafer using double-sided tape.

[0039] The embodiment of the present invention described above is one aspect of the present invention, and can be modified as appropriate without departing from the spirit of the present invention. The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples. EXAMPLES

[0040] An 8-inch silicon wafer substrate with a surface treatment layer formed thereon was prepared. The surface treatment layer in this case was a multi-layer plating layer of titanium / nickel / gold (with gold as the outermost layer) formed by sputtering. This was attached to the polishing device shown in Figure 3, and the outer peripheral edge was polished to remove only the outermost gold layer, yielding a silicon wafer substrate with an adhesion improvement region.

[0041] A protective film was attached to the back surface of this silicon wafer substrate with an adhesion improving region by two different methods (roller attachment method and vacuum attachment method) to obtain a silicon wafer substrate with a protective film. A solution penetration test was then conducted on this silicon wafer substrate with a protective film. The test process is shown in Table 1. The results are also shown in Table 2 so that they can be compared with the comparative examples.

[0042] [Table 1] EXAMPLES

[0043] An 8-inch silicon wafer substrate with a surface treatment layer formed thereon was prepared as in Example 1. The surface treatment layer in this case was a multi-layer plating layer of titanium / nickel / gold (with gold as the outermost layer) formed by sputtering. This was attached to the polishing device shown in FIG. 3, and the outer peripheral edge was polished to completely remove the surface treatment layer, thereby obtaining a silicon wafer substrate with an adhesion improving region.

[0044] A protective film was attached to the back surface of this silicon wafer substrate with an adhesion improving region by two different methods (roller attachment method and vacuum attachment method) to obtain a silicon wafer substrate with a protective film. A solution penetration test was then conducted on this silicon wafer substrate with a protective film. The test process is shown in Table 1. The results are also shown in Table 2 so that they can be compared with the comparative examples. EXAMPLES

[0045] An 8-inch diameter silicon wafer substrate was prepared, which had a raised band-shaped protrusion along the outer periphery on which a surface treatment layer had been formed. The surface treatment layer in this case was a multi-layer plating layer of titanium / nickel / gold (with the outermost layer being gold) formed by sputtering. This was attached to the polishing device shown in Figure 3, and the outer peripheral edge was polished to remove only the outermost gold layer, yielding a silicon wafer substrate with a raised band-shaped protrusion with an adhesion improving region.

[0046] A protective film was attached to the back surface of this silicon wafer substrate with an adhesion improving region by two different methods (roller attachment method and vacuum attachment method) to obtain a silicon wafer substrate with a protective film. A solution penetration test was then conducted on this silicon wafer substrate with a protective film. The test process is shown in Table 1. The results are also shown in Table 2 so that they can be compared with the comparative examples. EXAMPLES

[0047] A silicon wafer substrate with a surface treatment layer formed thereon was prepared, which had a band-shaped protrusion in a raised shape along the outer periphery with a diameter of 8 inches. The surface treatment layer in this case was a multi-layer plating layer of titanium / nickel / gold (with gold as the outermost layer) formed by sputtering. This was attached to the polishing device shown in Figure 3, and the outer periphery edge was polished to completely remove the surface treatment layer, yielding a silicon wafer substrate with a band-shaped protrusion in a raised shape with an adhesion improving region.

[0048] A protective film was attached to the back surface of this silicon wafer substrate with an adhesion improving region by two different methods (roller attachment method and vacuum attachment method) to obtain a silicon wafer substrate with a protective film. A solution penetration test was then conducted on this silicon wafer substrate with a protective film. The test process is shown in Table 1. The results are also shown in Table 2 so that they can be compared with the comparative example. Comparative Example

[0049] In this comparative example, an 8-inch silicon wafer substrate with a surface treatment layer formed thereon was prepared, similar to that in Example 1. In this case, the surface treatment layer was a multi-layer plating layer of titanium / nickel / gold (with gold as the outermost layer) formed by sputtering, and a silicon wafer substrate was obtained in which the surface treatment layer remained without forming an adhesion improving region.

[0050] A protective film was attached to the back surface of this silicon wafer substrate by two methods (roller attachment method and vacuum attachment method) to obtain a silicon wafer substrate with a protective film. A solution penetration test was then conducted on this silicon wafer substrate with a protective film. The test process is shown in Table 1. The results are also shown in Table 2 for comparison with the examples.

[0051] 〔evaluation〕 The results of comparing Examples 1 to 4 with the Comparative Example are shown below. The evaluation results are summarized in Table 2.

[0052] [Table 2]

[0053] From Table 2, it can be seen that in the cases of Examples 1 to 4, which are provided with an adhesion improvement region, no solution infiltration occurs between the protective film and the silicon wafer substrate. In contrast, in the case of the comparative example, it can be seen that solution infiltration occurs between the protective film and the silicon wafer substrate. It is believed that there is no difference due to differences in the bonding method of the protective film.

[0054] Furthermore, from the number of damaged locations on the wafer shown in Table 2 and the schematic diagram in Fig. 4, it can be seen that in the cases of Examples 1 to 4, which are provided with an adhesion improvement region, no solution intrusion occurs between the protective film and the silicon wafer substrate. In contrast, in the case of the comparative example, it can be clearly seen that solution intrusion occurs between the protective film and the silicon wafer substrate, causing significant defects. [Industrial Applicability]

[0055] By using the present invention, it becomes possible to provide high-quality wafer products at low cost. As a result, it becomes possible to provide products using wafers such as high-quality power semiconductors at a reasonable price. In addition, the manufacturing method adopted in the present application has the advantage of not requiring excessive capital investment. [Explanation of symbols]

[0056] 1a, 1b Wafer substrate with adhesion improving region 2. Semiconductor elements 3. Adhesion improvement area 4 Belt Rotary Polisher

Claims

1. A wafer substrate having a protective film layer on its surface for preventing solution penetration, A wafer substrate having an adhesion improving region, characterized in that the wafer substrate has an adhesion improving region of a protective film layer that improves the adhesion of the protective film layer parallel to the outer periphery of the wafer substrate that has been subjected to various surface treatments.

2. 2. The wafer substrate having an adhesion improvement region according to claim 1, wherein the adhesion improvement region is a region free of at least precious metal components, such as gold, silver, platinum, and palladium, among inorganic components used in the surface treatment.

3. 2. The wafer substrate having an adhesion improving region according to claim 1, wherein the adhesion improving region is free of inorganic components used in surface treatment and the wafer surface is exposed.

4. 2. A wafer substrate having an adhesion improving region as described in claim 1, wherein the adhesion improving region provided on the outer periphery of a planar wafer substrate is a strip-shaped region having a width of 0.2 mm or more and 3 mm or less parallel to the outer periphery of the wafer substrate.

5. A wafer substrate having an adhesion improvement region as described in claim 1, wherein the adhesion improvement region provided on the outer periphery of a wafer substrate having a band-shaped protrusion portion having a raised shape along the outer periphery is a band-shaped region having a width of 0.2 mm or more and W1 mm ​​or less parallel to the outer periphery of the wafer substrate, when the width of the band-shaped protrusion portion is W1 mm.

6. A wafer substrate with a protective film layer, characterized in that a protective film layer is provided on the surface of a wafer substrate having an adhesion improvement region according to any one of claims 1 to 5, thereby improving the inhibitory effect against solution penetration.

7. A method for producing a wafer substrate having an adhesion improvement region according to any one of claims 1 to 5, comprising: A method for manufacturing a wafer with an adhesion-improved region, characterized in that the surface of a wafer that has been subjected to various surface treatments is cut or polished parallel to the outer periphery to peel off some or all of the metal layer that constitutes the surface treatment layer near the outer periphery of the wafer surface, thereby forming an adhesion-improved region.

8. A method for manufacturing a wafer having an adhesion improvement region as described in claim 7, wherein when the adhesion improvement region is provided on the outer periphery of a planar wafer substrate, a strip-shaped region having a width of 0.2 mm or more and 3 mm or less is cut or polished parallel to the outer periphery of the wafer substrate.

9. 8. A method for manufacturing a wafer having an adhesion improving region as described in claim 7, wherein when the adhesion improving region is provided on the outer periphery of a wafer substrate having a band-shaped protrusion portion having a protruding shape along the outer periphery, when the width of the band-shaped protrusion portion is W1 mm, a band-shaped region having a width of 0.2 mm or more and W1 mm ​​or less is cut or polished parallel to the outer periphery of the wafer substrate to form the band-shaped region.

10. 10. The method for manufacturing a wafer having an adhesion improving region according to claim 7, wherein a cutting depth when performing the cutting or polishing process is 20 nm to 10 μm.

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