Desmear treatment method and optical treatment device

Abstract

The present invention provides a method with which it is possible to effectively perform a desmear treatment.　This desmear treatment method includes: irradiating a substrate that has a hole and a smear in the hole with vacuum ultraviolet light so that the contact angle with water of the substrate is 40-70 degrees; supplying a swelling liquid for swelling the smear to the substrate that has been irradiated with the vacuum ultraviolet light; and supplying a removal liquid for removing the smear from the substrate to the substrate in which the smear has been swollen.

Description

Desmearing method and optical treatment device

[0001] The present invention relates to a desmearing method and an optical treatment device used in the desmearing method.

[0002] Conventionally, printed wiring boards mounted on electronic devices and the like have a multilayer wiring structure formed, for example, by a semi-additive process. The multilayer wiring structure is formed by alternately stacking insulating layers and wiring layers. The multilayer wiring structure is manufactured, for example, by forming a wiring layer on an insulating layer by electroless plating and electrolytic copper plating, and then forming an insulating layer to cover the formed wiring layer. In the printed wiring board manufactured in this manner, holes (vias) penetrating the insulating layer are provided as necessary, and wiring patterns of different wiring layers are electrically connected through the vias.

[0003] When such holes are formed in a substrate, smear, which is a residue of resin or the like, may accumulate in the hole. The smear present in the hole may cause poor adhesion of copper plating to the hole and poor electrical connection between the wiring layer and the copper plating. Therefore, a desmearing process for removing smear is widely performed in the manufacturing process of printed wiring boards. One known desmearing method is a wet desmearing process in which a chemical solution such as a permanganic acid solution is supplied to the surface of the substrate to dissolve and remove the smear in the chemical solution.

[0004] Improvements have been made to wet desmear treatments in the past. For example, Patent Document 1 describes a method in which, before removing smears in holes with a permanganic acid aqueous solution, the substrate surface is irradiated with ultraviolet light (vacuum ultraviolet light) having a wavelength of 200 nm or less to increase the wettability of the substrate surface (reduce the water contact angle), thereby effectively removing smears.

[0005] Japanese Patent Application Laid-Open No. 2001-15923

[0006] As a result of intensive research by the present inventors, it has been found that the desmearing method described in Patent Document 1 has the following problems. In the desmearing method described in Patent Document 1, a substrate with a water contact angle of 90 degrees is irradiated with vacuum ultraviolet light until the water contact angle becomes 10 degrees or less (see paragraph 0017 of the same document). However, the present inventors noticed that irradiating a substrate with vacuum ultraviolet light until the water contact angle becomes 10 degrees or less significantly roughens the surface of the manufactured printed wiring board. When the substrate surface becomes rough, conductor loss increases due to the skin effect in high-frequency transmission. The skin effect is a phenomenon in which current propagates unevenly near the surface of a conductor when the current frequency is high. The depth to which current propagates is called the skin depth. If the surface roughness (i.e., minute irregularities) on the substrate is greater than the skin depth, the current flows along the irregularities, resulting in a longer current path, delaying the electrical signal and increasing electrical resistance, leading to power loss.

[0007] Reducing the cumulative dose of vacuum ultraviolet light during desmearing can reduce surface roughness of the manufactured printed wiring board. However, reducing the cumulative dose of vacuum ultraviolet light does not sufficiently reduce the water contact angle. As a result, the smear is not sufficiently dissolved by the subsequent permanganic acid aqueous solution, and the smear cannot be sufficiently removed. Alternatively, if an attempt is made to sufficiently remove the smear under such circumstances, the treatment time or number of treatments with the permanganic acid aqueous solution will increase, which may result in increased surface roughness of the manufactured printed wiring board, which is counterproductive. In addition, production efficiency will decrease and the environmental load will increase.

[0008] An object of the present invention is to provide a method for solving the above-mentioned contradictory problems and for effectively performing desmearing, and an optical treatment device to be used for the method.

[0009] A desmear treatment method of the present invention includes: irradiating a substrate having holes and smears in the holes with vacuum ultraviolet light so that the substrate has a water contact angle of 40 to 70 degrees; supplying a swelling liquid to the substrate irradiated with the vacuum ultraviolet light, which causes the smears to swell; and supplying a removal liquid to the substrate in which the smears have been swollen, which removes the smears from the substrate.

[0010] The substrate is a resin substrate, and the surface of the substrate is hydrophobic. Vacuum ultraviolet light hydrophilizes the substrate surface. While the water contact angle of an untreated substrate surface is 80 degrees or more, the desmearing method irradiates the substrate surface with vacuum ultraviolet light to make the water contact angle of the substrate surface 40 to 70 degrees. This method means that irradiation with vacuum ultraviolet light is not continued until the water contact angle of the substrate surface becomes less than 40 degrees. As will be described in detail later, this makes it possible to suppress damage to the substrate, specifically surface roughness, that occurs after the supply of a remover solution due to an increase in the integrated light amount of vacuum ultraviolet light.

[0011] Generally, a large water contact angle makes it difficult for a removing liquid (hereinafter, sometimes simply referred to as a "removing liquid") for removing smears to penetrate into the pores. A substrate with a water contact angle of 40 degrees or greater has a tendency for the removing liquid to penetrate into the pores less easily than a substrate with a water contact angle of less than 40 degrees, resulting in poorer smear removal capability. However, in the desmearing method, a swelling liquid (hereinafter, sometimes simply referred to as a "swelling liquid") that swells the smear in the pores is supplied before supplying the removing liquid. This allows for sufficient smear removal even on substrates with a water contact angle of 40 degrees or greater. While methods for compensating for poor smear removal capability include extending the supply time or increasing the number of times the removing liquid is supplied, the use of a swelling liquid can maintain or improve smear removal capability without increasing the supply time or number of times the removing liquid is supplied. This improves productivity and contributes to reducing the amount of removing liquid used, thereby reducing the environmental impact and costs.

[0012] In this specification, supplying a swelling liquid or a removal liquid to a substrate refers to any action that can bring the swelling liquid or the removal liquid into contact with the substrate, and includes not only a method of discharging or spraying the swelling liquid or the removal liquid toward the substrate, but also a method of immersing the substrate in a container containing the swelling liquid or the removal liquid.

[0013] The vacuum ultraviolet light irradiation may be performed in an air environment (an environment containing approximately 21 vol% oxygen) or in an environment containing 1 to 20 vol% oxygen, which is lower in oxygen concentration than air. The vacuum ultraviolet light irradiation is preferably performed in an environment containing at least 1 vol% oxygen. As will be described in detail later, atomic oxygen and hydroxyl radicals are necessary to reduce the water contact angle, and oxygen molecules and water molecules in the environment serve as sources of atomic oxygen and hydroxyl radicals. However, because vacuum ultraviolet light is easily absorbed by oxygen molecules and water molecules, when irradiating with vacuum ultraviolet light in an air environment, it is preferable to position the light source as close as possible to the substrate. Furthermore, irradiating with vacuum ultraviolet light in an environment containing 1 to 20 vol% oxygen, which is lower in oxygen concentration than air, can suppress light absorption while supplying the atomic oxygen source.

[0014] The vacuum ultraviolet light may be used to reduce the water contact angle of the substrate surface by 20 degrees or more. By reducing the water contact angle of the substrate surface by 20 degrees or more using vacuum ultraviolet light, the hydrophilicity of the substrate surface is promoted, making it easier for the swelling liquid to penetrate into the pores.

[0015] The diameter of the holes may be 70 μm or less. As the hole diameter becomes smaller, the amount of smear removal becomes more susceptible to the influence of the water contact angle. However, when the hole diameter is small, for example, when the hole diameter is 70 μm or less, irradiating the substrate surface with vacuum ultraviolet light to reduce the water contact angle can more effectively allow the swelling liquid to penetrate into the holes. In this specification, the "hole diameter" refers to the inner diameter (the distance between the opposing inner wall surfaces of the hole) at the top surface position of the hole. Note that the shape of the hole is not necessarily a perfect circle when viewed from above, and in such cases, the "diameter" refers to the maximum value of the inner diameter measured at different angles when viewed from above.

[0016] The remover may be an aqueous solution of permanganic acid.

[0017] The swelling liquid may be an alkaline aqueous solution.

[0018] The light treatment device used in the light irradiation step of the desmear treatment method is a light treatment device that irradiates a substrate having holes and smears in the holes with vacuum ultraviolet light, and the light treatment device includes: a light treatment space separated from the surroundings; a light source that irradiates the substrate with the vacuum ultraviolet light; and a control unit that controls the light source to irradiate the substrate with the vacuum ultraviolet light so that the water contact angle of the substrate is in the range of 40 to 70 degrees. The term "light treatment space separated from the surroundings" means that the light treatment space in which the substrate is irradiated with vacuum ultraviolet light is separated from the surrounding atmosphere in which the light treatment device is placed. "Separated" means that the light treatment space is at least partially isolated from the surrounding atmosphere, and does not necessarily have to be completely isolated from the surrounding atmosphere. Of course, the light treatment space may be completely isolated (sealed) from the surrounding atmosphere.

[0019] It is possible to provide a method for effectively performing desmearing and a light treatment device used in the method.

[0020] [Correction based on Rule 91 02.07.2024] A flowchart showing an example of a desmearing method. An enlarged cross-sectional view of a substrate. A diagram showing a light irradiation step. A diagram showing a swelling step. A diagram showing a smear removal step. A diagram showing how the surface of a substrate is made hydrophilic. A diagram showing how the surface of a substrate is made hydrophilic. A diagram showing an example of a light treatment device. A graph showing the relationship between the integrated light amount of vacuum ultraviolet light and the water contact angle of a substrate. A graph showing the relationship between the integrated light amount of vacuum ultraviolet light and the surface roughness of a substrate. A graph showing the relationship between the integrated light amount of vacuum ultraviolet light and the surface roughness of a substrate. A graph showing the relationship between the water contact angle and the C / Cu ratio for samples with different integrated light amounts.

[0021] The embodiments of the present invention will be described with reference to the drawings. The drawings disclosed in this specification are schematic, except for graphs and flow charts. In other words, the dimensional ratios in the drawings do not necessarily correspond to the actual dimensional ratios, and the dimensional ratios between the drawings do not necessarily correspond to the actual dimensional ratios or the number of each component shown in the drawings.

[0022] [Desmear Treatment Method] Fig. 1 is a flowchart showing an example of a desmear treatment method. As shown in Fig. 1, the desmear treatment method includes three steps (S10, S20, S30). The first step is a light irradiation step S10 in which vacuum ultraviolet light is irradiated onto the surface of a substrate 10. The second step is a swelling step S20 in which a swelling liquid is supplied to the substrate 10 after the irradiation with vacuum ultraviolet light L1. The third step is a smear removal step S30 in which a removing liquid 12 is supplied to the substrate 10 after the supply of the swelling liquid.

[0023] FIG. 2 is an enlarged cross-sectional view of the substrate 10. The substrate 10 of this embodiment is a resin substrate. The substrate 10 includes a copper clad laminate (CCL) 9, with a first dielectric layer 1 laminated on one side and a second dielectric layer 2 laminated on the other side. The copper clad laminate 9 includes a prepreg 3, with copper-containing layers 4 formed on both sides. The prepreg 3 is formed, for example, by impregnating a resin with a reinforcing material such as glass fiber. The prepreg 3 functions as an electrical insulating layer, and the copper-containing layer 4 functions as a wiring layer (conductor layer). The first dielectric layer 1 and the second dielectric layer 2 are primarily composed of resin. The resin used for these dielectric layers (1, 2) or the prepreg 3 can be, for example, an epoxy resin. The dielectric layers (1, 2) can be made of glass epoxy film (e.g., ABF-GX-T31 manufactured by Ajinomoto Fine-Techno Co., Inc.). The CCL can be made of, for example, MCL-800 manufactured by Hitachi Chemical Co., Ltd. The substrate 10, which is a resin substrate containing CCL, can be used as a multilayer printed wiring board.

[0024] The substrate 10 has a hole 5 in the second dielectric layer 2. The hole 5 penetrates the second dielectric layer 2 in the thickness direction of the substrate 10. The hole 5 is used, for example, as a via that electrically connects conductor layers spaced apart in the stacking direction. The via functions, for example, as a blind via or a through-hole via in the manufactured printed wiring board. A hole may also be formed in the first dielectric layer 1. As shown in FIG. 2 , the hole 5 may have a tapered shape in which the diameter decreases from the surface to the bottom. Alternatively, the hole may be shaped so that the inner wall of the hole is perpendicular to the substrate surface.

[0025] The holes 5 are formed by laser processing, drilling, or the like. When laser processing or drilling is performed, smear 7, which is a residue (shavings), is generated, and the smear 7 accumulates in the holes 5. If the smear 7 remains in the holes 5, there is a risk of poor conductivity of the conductor embedded in the holes 5. Therefore, a desmearing process is required to remove the smear 7. In this embodiment, the holes 5 are formed using a laser processing machine. The laser processing machine used is a UV+CO laser processing machine manufactured by Via Mechanics. ２ The laser processing machine is LUC-2K21. In this specification, unless otherwise specified, the hole 5 is a CO ２ The holes 5 are machined with a laser and have a diameter of 70 μm.

[0026] 3A, 3B, and 3C are diagrams showing cross sections of the substrate 10 corresponding to three steps (S10, S20, and S30) constituting the desmear treatment method. Each step constituting the desmear treatment method will be described with reference to FIGS. 3A, 3B, and 3C.

[0027] 3A shows the light irradiation step S10 in which vacuum ultraviolet light L1 is irradiated onto the surface S1 of the substrate 10. The surface S1 of the substrate 10 is the surface of the second dielectric layer 2. The surface of the second dielectric layer 2 is hydrophobic. When the surface S1 exhibits hydrophobicity, the swelling liquid tends to be less likely to penetrate into the holes 5. As will be described in detail later, this tendency is particularly pronounced when the diameter of the holes 5 is small. Therefore, the entire surface S1 is irradiated with vacuum ultraviolet light L1 to make the surface S1 hydrophilic.

[0028] The vacuum ultraviolet light L1 acts on the moisture and oxygen in the light processing space to convert them into highly reactive atomic oxygen (O( １ D)) and hydroxyl radical (.OH). O( １ The chemical reactions leading to the production of H) and OH are shown in the following reaction formulas (1) to (5). ２ O → ・OH+H ...(1) hν+O ２ → O ( １ D) + O( ３ P) ...(2) O( １ D) + H ２ O → 2(・OH) ...(3) O(３ P) + O ２ +M → O ３ +M...(4) hν+O ３ +M →O( １ D) + O( ３ P) ... (5) The hν appearing in formulas (1), (2), and (5) represents the energy of the vacuum ultraviolet light L1. First, OH and O( １ Then, the reactions shown in formulas (3) and (4) produce OH and O ３ is generated. ３ is expressed as O( １ D). Note that M used in formulas (4) and (5) represents a third body. O( ３ P) is the atomic oxygen in the ground state, O( ３ P). If water vapor is not contained in the light treatment space, the reactions shown in formulas (1) and (3) do not occur.

[0029] 4A and 4B are diagrams showing how the surface of the substrate 10 is made hydrophilic. As shown in FIG. 4A, when the substrate 10 is irradiated with vacuum ultraviolet light, the molecular bonds of the organic material are broken, hydrogen atoms are extracted from the organic material molecules, and the molecular structure of the surface of the substrate 10 changes. At the same time, the highly reactive atomic oxygen O( １ D) bonds with molecules on the surface of the substrate 10 to generate highly polar carbonyl groups, hydroxyl groups, carboxyl groups, etc. As a result, the surface of the substrate 10 is modified to be hydrophilic. The state after hydrophilization is shown in FIG. 4B. As described in the previous paragraph, if -OH is generated from water vapor in the light treatment space, -OH also contributes to the hydrophilization of the surface of the substrate 10.

[0030] [Light Treatment Device] A light treatment device that irradiates the surface S1 of the substrate 10 with vacuum ultraviolet light L1 will be described. FIG. 5 shows one embodiment of the light treatment device. The light treatment device 100 has a processing chamber 30, a light source 32, and a control unit 35 that controls the light source 32. The control unit 35 controls the on / off of the light source 32. The control details will be described later. A conveyor belt 31 on which the substrate 10 is placed passes through the processing chamber 30. The conveyor belt 31 is moved by rollers (not shown). The rollers are driven to rotate by a motor M controlled by the control unit 35. The processing chamber 30 forms a light treatment space that is partitioned from the surroundings of the light treatment device 100. The processing chamber 30 has an opening through which the conveyor belt 31 and the substrate 10 enter and exit, and is therefore not a space that is sealed from the surroundings.

[0031] In this embodiment, the light source 32 that emits vacuum ultraviolet light L1 is a dielectric barrier discharge lamp that emits light with a dominant wavelength of 172 nm and is filled with xenon gas. In this specification, the term "dominant wavelength" refers to the wavelength with the highest radiation energy intensity in the radiation spectrum. However, light sources that can be used as the light source 32 are not limited to light sources that emit light with a dominant wavelength of 172 nm. Any light source having an emission spectrum that exhibits emission intensity in at least the range of 10 to 205 nm may be used. A light source having an emission spectrum that exhibits emission intensity in a range beyond 205 nm may also be used. The light source 32 may also be a dielectric barrier discharge lamp that is filled with a gas other than xenon gas. Furthermore, the light source 32 may also be another discharge lamp. The light source 32 may also be a light source other than a discharge lamp, such as a solid-state light source such as an LED.

[0032] The processing chamber 30 has a gas supply port 33 and a gas exhaust port 34. The gas supply port 33 is connected to a first gas supply source 37 and a second gas supply source 38 via a flow control valve 36. The flow control valve 36 is controlled by a control unit 35. The gas exhaust port 34 is connected to an ozone decomposer (not shown) via a flow control valve (not shown). The first gas supply source 37 is a supply source of an inert gas. Nitrogen gas may be used as the inert gas. The second gas supply source 38 is CDA (clean dry air). However, by using the flow control valve 36, gas G1 with a desired oxygen concentration can be supplied into the processing chamber 30 from the gas supply port 33. Of course, the flow control valve 36 may set the flow rate of the first gas supply source 37 to zero and supply only CDA from the second gas supply source. Furthermore, the gas supplied from the second gas supply source 38 may contain water vapor. The gas supply port 33 and the gas exhaust port 34 are not necessarily essential components of the light irradiation device. If the gas supply port 33 is not provided, for example, oxygen molecules and water vapor contained in the air outside the processing chamber 30 that enters the processing chamber 30 may be used as raw materials for hydrophilization.

[0033] The vacuum ultraviolet light L1 generates atomic oxygen from oxygen molecules in the processing chamber 30, so oxygen must be present in the processing chamber 30. The oxygen concentration in the processing chamber is preferably 1 vol% or higher. The oxygen concentration in the processing chamber 30 may be approximately 21 vol% (more than 20 vol% and less than 22 vol%), which is the same as the oxygen concentration in the atmosphere. Narrowing the gap between the light source 32 and the substrate 10 reduces the amount of vacuum ultraviolet light L1 absorbed by the gas in the processing chamber 30, allowing the vacuum ultraviolet light L1 to reach the substrate 10.

[0034] The conveyor belt 31 is not essential. If the substrate 10 itself is in the form of a sheet or film, the substrate 10 itself may be transported by rollers. Furthermore, instead of the conveyor belt 31, the substrate 10 may be transported to a table in the processing chamber 30 by a transport arm or the like. When the substrate 10 is transported to a table in the processing chamber 30 by a transport arm or the like, the processing chamber 30 may have an opening / closing door. That is, the opening / closing door is opened when the substrate 10 is transported into or out of the processing chamber 30, and is closed during the photoprocessing. The inside of the processing chamber 30 may be a space sealed from the surroundings of the photoprocessing device 100.

[0035] The distance between the substrate 10 and the light source 32 may be 2 mm or more and 30 mm or less, and preferably 4 mm or more and 10 mm or less. The distance between the substrate 10 and the light source 32 may be set depending on the oxygen concentration in the processing chamber 30. If the distance between the substrate 10 and the light source 32 is too long, the vacuum ultraviolet light L1 is absorbed by oxygen remaining in the processing chamber 30, reducing the amount of vacuum ultraviolet light L1 that reaches the surface of the substrate 10 and reducing the illuminance. The illuminance on the substrate 10 may be changed by moving the light source 32 closer to or farther away from the substrate 10. A reflector or reflective layer may be disposed on the inner wall of the processing chamber 30.

[0036] In FIG. 5, the light source 32 is positioned inside the processing chamber 30, but the light source 32 may also be positioned outside the processing chamber 30 so that the light from the light source 32 passes through the processing chamber 30 and reaches the substrate 10 inside the processing chamber 30.

[0037] 3B shows a swelling step in which a swelling liquid 11 is supplied to the substrate 10, the surface of which has been irradiated with vacuum ultraviolet light L1 and has a reduced water contact angle, to swell the smear 7. The swelling liquid 11 penetrates the holes 5 and infiltrates the smear 7 present in the holes 5. The smear 7 is mainly composed of resin. Swelling refers to the swelling liquid 11 infiltrating the smear 7 and causing the smear 7 to expand upon absorption of the swelling liquid 11. Most of the resin constituting the smear 7 does not dissolve in the swelling liquid 11, but does expand upon absorption of the swelling liquid 11. However, some of the resin (especially low-molecular-weight resin) may dissolve in the swelling liquid 11 and be removed. As will be described in detail later, swelling the smear 7 with the swelling liquid 11 improves the ability of the removal liquid to remove the smear 7.

[0038] If the water contact angle on the surface of the substrate 10 is large, the swelling liquid 11 does not easily penetrate into the pores 5. However, if the water contact angle on the surface of the substrate 10 is small, the swelling liquid 11 easily penetrates into the pores 5. Because the water contact angle of the substrate 10 is reduced to 40 to 70 degrees, the swelling liquid 11 easily penetrates into the pores 5. An alkaline aqueous solution can be used as the swelling liquid 11. After swelling the smear 7, it is preferable to remove the swelling liquid 11 from the top of the substrate 10 and wash the substrate 10 with water one or more times. Removing the swelling liquid 11 from the top of the substrate 10 and washing the substrate 10 with water one or more times after removing the swelling liquid 11 are included in the swelling step.

[0039] 3C shows a smear removal step performed after the swelling step. In the smear removal step, a remover 12 is supplied to the substrate 10 after the liquid treatment with the swelling liquid 11. As the remover 12, for example, permanganic acid (KMnO ４ As another example of the remover 12, an aqueous solution of concentrated sulfuric acid or chromic acid can be used. The remover 12 has the function of oxidizing and decomposing the smear 7.

[0040] After supplying the remover 12 to the substrate 10, the remover 12 is removed from the substrate 10. Thereafter, the substrate 10 is washed with water one or more times. Prior to the washing with water, the substrate 10 may be subjected to a neutralization treatment. Removing the remover 12 from the substrate 10, washing the substrate 10 with water one or more times after removing the remover 12, and subjecting the substrate 10 to a neutralization treatment are included in the smear removal step.

[0041] [Integrated Light Amount and Water Contact Angle] FIG. 6 shows the integrated light amount (J / cm ) of the vacuum ultraviolet light L1 irradiated onto the substrate 10. ２ 6 is a graph showing the relationship between the water contact angle and the irradiance of the vacuum ultraviolet light L1 on the surface of the substrate 10. The integrated light amount is the product of the illuminance and the irradiation time of the vacuum ultraviolet light L1 on the surface of the substrate 10. Looking at FIG. 6, it can be seen that the integrated light amount is 0 J / cm ２ 6, the water contact angle is 82 degrees (deg.). This indicates that the water contact angle on the surface of the substrate 10 before light irradiation is 82 degrees. Furthermore, it can be seen from FIG. 6 that the water contact angle on the surface of the substrate 10 decreases when irradiated with vacuum ultraviolet light L1.

[0042] 6, as the integrated light amount of the vacuum ultraviolet light L1 increases, the water contact angle of the substrate 10 decreases rapidly. The water contact angle decreases rapidly when the integrated light amount is 0.6 J / cm ２ (line P1 in the figure), and continues until the water contact angle reaches 40 degrees. When the water contact angle falls below 40 degrees, the rate of decrease in the water contact angle relative to the integrated light amount becomes gentle. When the water contact angle is reduced to 30 degrees, the water contact angle hardly decreases even if the integrated light amount is increased. From the perspective of reducing the water contact angle, as shown in FIG. 6, the upper limit of the integrated light amount of the vacuum ultraviolet light L1 is set to 3.0 J / cm ２ It turns out that setting it to is effective.

[0043] The graph shown in Fig. 6 was obtained by preparing the substrate 10 shown in Fig. 2 and repeatedly irradiating it with vacuum ultraviolet light L1 and measuring the water contact angle. An SVSA3 series manufactured by Ushio Inc. was used as the device for irradiating vacuum ultraviolet light L1, and a UEM343W-172ST manufactured by Ushio Inc. was used as the light source 32. A UIT-250 manufactured by Ushio Inc. was used as the main body of the illuminometer for calculating the integrated light amount, and a VUV-S172 was used as the light receiver for the illuminometer.

[0044] In this specification, the water contact angle was measured by the following method. A sessile drop method was employed, in which a water droplet was placed on the substrate 10 and the contact angle of the water droplet was measured. The water droplet deposited on the substrate 10 was imaged from the side of the substrate 10 using an imaging element, and the angle between the surface of the substrate 10 and the water droplet was determined by image analysis. The water droplet was deposited at three locations on the surface of the same substrate 10, and the average value of the measured angles was calculated, and this average value was defined as the final water contact angle. Other measurement conditions for the water contact angle were in accordance with Japanese Industrial Standards JIS R 3257:1999 "Test method for wettability of substrate glass surfaces."

[0045] The integrated light amount of vacuum ultraviolet light that will result in a water contact angle of 40 to 70 degrees on the substrate is determined as follows: A substrate made of the same material as the substrate 10 to be subjected to the desmear treatment and a light source that generates vacuum ultraviolet light to be used in the desmear treatment are prepared in advance, and the prepared substrate is irradiated with vacuum ultraviolet light in an air environment, and the relationship between the integrated light amount and the water contact angle is measured. The water contact angle is measured by the above-mentioned method. Then, based on the relationship between the measured water contact angle and the integrated light amount of vacuum ultraviolet light, the range of integrated light amount that will result in a water contact angle of 40 to 70 degrees is determined.

[0046] It is preferable to set the integrated light amount of the vacuum ultraviolet light irradiation so that the water contact angle of the substrate is reduced by 20 degrees or more compared to the water contact angle before the vacuum ultraviolet light irradiation. For example, if the water contact angle before the vacuum ultraviolet light irradiation is 82 degrees, it is preferable to irradiate the substrate with vacuum ultraviolet light so that the water contact angle is 62 degrees or less (however, the lower limit is 40 degrees).

[0047] [Cumulative Light Amount and Surface Roughness] FIGS. 7A and 7B show the results for the cumulative light amount of 0 to 3.0 J / cm ２ 1 is a graph showing the relationship between the integrated light amount of vacuum ultraviolet light L1 and the surface roughness of the substrate 10 in the range of 0 to 3.0 J / cm 2 . ２ The range of is a range in which the water contact angle can be effectively reduced. FIG. 7A shows the results of measuring the surface roughness of the substrate 10 after irradiating the substrate 10 with light and without performing the swelling process and smear removal process. FIG. 7B shows the results of measuring the surface roughness of the substrate 10 after irradiating the substrate 10 with light and performing the swelling process and smear removal process. The surface roughness measurement result is expressed as surface roughness Sa, i.e., arithmetic mean roughness. Specifically, surface roughness Sa is the arithmetic mean of the absolute values ​​of the differences in height from the average height of measurement points in a certain reference area, and can be obtained using a roughness meter. In this embodiment, an SPM-9600 manufactured by Shimadzu Corporation was used as the roughness meter.

[0048] The swelling process performed on the substrate 10 used in the measurement of Fig. 7B was performed by immersing the substrate 10 for 5 minutes in a container containing an alkaline aqueous swelling solution (OPC-1080 Conditioner manufactured by Okuno Chemical Industries Co., Ltd.) at 60°C. After immersion in the swelling solution, the substrate 10 was washed with water at 60°C and then with water at room temperature.

[0049] The smear removal process performed on the substrate 10 used for the measurement in FIG. 7B was performed by immersing the substrate 10 for 10 minutes in a container containing a removal solution ("OPC1200 Epoetch" manufactured by Okuno Chemical Industries Co., Ltd.) at 80° C. The removal solution was a permanganate (KMnO ４ ), which has the effect of oxidatively decomposing the smear 7. After immersion in the remover, the substrate 10 was washed with water at 60° C., washed with water at room temperature, neutralized, and then washed with water after the neutralization, in that order.

[0050] In FIG. 7A, the integrated light amount is 0 J / cm ２ 7A shows that the surface roughness Sa of the substrate 10 before light irradiation. It was found that the surface of the substrate 10 does not become significantly roughened by simply irradiating the substrate 10 with vacuum ultraviolet light L1, even if the integrated light amount increases.

[0051] On the other hand, looking at Figure 7B, it was found that the difference in the integrated light amount affects the difference in surface roughness after the swelling process and the smear removal process. Note that the plots in Figure 7B differ only in the integrated light amount, and the processing conditions for the swelling process and the smear removal process are the same. From Figure 7B, it was found that the surface roughness Sa after the light irradiation removal process increases as the integrated light amount increases. Furthermore, it was found that there is a correlation between the integrated light amount and the surface roughness Sa after the light irradiation removal process. From Figure 7B, the surface roughness Sa of the unirradiated substrate 10 is 33 nm. And, when the integrated light amount is 0.6 J / cm ２ If the surface roughness Sa is less than the P1 line in the figure, the surface roughness Sa can be suppressed to approximately 50 nm. Therefore, from the viewpoint of suppressing the surface roughness Sa, the integrated light amount is 0.6 J / cm ２ It was found that there was no particular problem if the integrated light amount was up to 0.6 J / cm ２If the thickness exceeds 1000 nm, the problem of the surface roughness Sa becoming worse becomes increasingly serious.

[0052] Consider both the relationship between the integrated light dose and the surface roughness shown in Fig. 7B and the relationship between the integrated light dose and the water contact angle shown in Fig. 6. The integrated light dose of vacuum ultraviolet light is set to 0.6 J / cm ２ It was found that by setting the upper limit at the P1 line in FIGS. 6 and 7B, the water contact angle can be effectively reduced and the surface roughness Sa can be kept at approximately 50 nm or less. In other words, by irradiating the substrate with vacuum ultraviolet light L1 to such an extent that the water contact angle does not fall below 40 degrees, the water contact angle can be effectively reduced and problems caused by an increase in surface roughness Sa can be avoided. Considering that the water contact angle of the untreated substrate 10 is 80 degrees or more, it is preferable to irradiate the substrate 10 with vacuum ultraviolet light L1 so that the water contact angle falls within the range of 40 to 70 degrees. The integrated light intensity of the vacuum ultraviolet light is 0.1 J / cm ２ ~0.6 J / cm ２ is preferred.

[0053] In the optical treatment device 100, data (in any data format, such as a data table or function) on the amount of decrease in the water contact angle, the transport speed for achieving a predetermined integrated light amount, and the light amount for one transport is obtained in advance. Then, the control unit 35 reads the data obtained in advance and controls the transport speed of the transport belt 31 and the power of the light source 32 so that the water contact angle of the substrate 10 falls within the range of 40 to 70 degrees.

[0054] [Water Contact Angle and Smear Removal Amount] Whether or not the smear 7 has actually been removed can be inspected using an EDX (energy dispersive X-ray) analyzer. The smear 7 remaining in the holes 5 of the substrate 10 after the desmearing process contains a large amount of carbon (C). Meanwhile, a wiring layer, i.e., Cu, exists below the layer in which the holes 5 are formed. Because the EDX analysis depth is as deep as several tens of micrometers, Cu on the back surface of the Cu below the holes 5 is also detected. Therefore, by calculating the ratio of the peak corresponding to C to the peak corresponding to Cu from the EDX spectrum obtained by EDX analysis of the bottom of the holes 5, the ratio of the amount of carbon (C) present in the holes 5 to the amount of copper (Cu) present in the holes 5 (hereinafter sometimes referred to as the "C / Cu ratio") can be calculated. Considering that the amount of Cu detected does not change even when the carbon remaining in the holes 5 is removed, it can be determined that a large C / Cu ratio indicates that a large amount of smear 7 remains, and that a small C / Cu ratio indicates that little smear 7 remains.

[0055] 8 is a graph showing the relationship between the water contact angle and the C / Cu ratio obtained by EDX analysis for samples a to g of the substrate 10 with different cumulative light doses. Graph a plots the water contact angle of sample a not irradiated with vacuum ultraviolet light L1 and the C / Cu ratio of sample a after the swelling step and smear removal step. Graphs b to g plot the water contact angle of samples b to g after irradiation with vacuum ultraviolet light L1 and the C / Cu ratio after the subsequent swelling step and smear removal step. The cumulative light doses for samples a to g are as follows. The processing conditions for the swelling step and smear removal step for samples a to g are all the same. Sample a: 0 J / cm ２ (Unirradiated) Sample b: 0.1 J / cm ２ Sample c: 0.3 J / cm ２ Sample d: 0.5 J / cm ２ Sample e: 1.0 J / cm ２ Sample f: 2.0 J / cm ２ Sample g: 3.0 J / cm ２

[0056] As shown in FIG. 8, samples b to d have a radiation intensity of 0.1 to 0.5 J / cm ２By irradiating the sample with vacuum ultraviolet light L1, the water contact angle can be set within the range of 70 to 40 degrees. As a result, samples b to d have a smaller C / Cu ratio than sample a. This shows that the amount of smear 7 remaining in the hole 5 after the desmear treatment is reduced compared to the amount of smear 7 when not irradiated with vacuum ultraviolet light L1. Samples e to g have a C / Cu ratio of 1.0 to 3.0 J / cm ２ However, as shown in FIG. 7B, when the substrate 10 was irradiated with 1.0 to 3.0 J / cm ２ If an integrated light amount of 100 nm is applied, the surface roughness Sa will be greater than 60 nm.

[0057] Although the C / Cu ratios of samples b to d are lower than those of samples e to g, they are close to those of samples e to g, confirming that a sufficient smear removal effect can be obtained. Even in sample g, where the smear 7 has been almost completely removed and almost no smear remains, the C / Cu ratio does not become 0. Considering the reason for this, it is thought that, as mentioned above, the EDX analysis depth is deep, at several tens of micrometers. In other words, it is thought that this is because signals from not only the smear 7 but also the carbon (C) component inside or on the back surface of the substrate 10 are detected.

[0058] [Swelling Treatment and Smear Removal Amount] Table 1 shows the EDX analysis results of four samples x to z each having a different treatment history.

[0059] Sample x is an untreated substrate that was not subjected to light irradiation and the supply of swelling liquid and removal liquid. Sample y is a substrate that was subjected to the smear removal process after the light irradiation process. Sample z is a substrate that was subjected to the swelling process and smear removal process after the light irradiation process. As shown in Table 1, it was found that the amount of smear removal increased by adding the swelling process.

[0060] [Light Irradiation Treatment and Hole Diameter] The light irradiation treatment is performed to facilitate the penetration of the swelling liquid and the removal liquid into the holes 5. However, the degree of penetration into the holes 5 is also affected by differences in the size of the holes 5. Therefore, a plurality of substrates having holes with diameters of 70 μm, 85 μm, and 100 μm were prepared, and the substrates of the first group were subjected to the light irradiation treatment and the desmear treatment, while the substrates of the second group were subjected to the desmear treatment without the light irradiation treatment. After the treatments, the C / Cu ratio of the substrates of each group was measured.

[0061] As a result of the measurements, the C / Cu ratio after the desmear treatment did not change for holes with a diameter of 85 μm and 100 μm, regardless of whether light irradiation was performed or not. In other words, it is believed that the holes in the substrate were large enough that the swelling liquid was able to penetrate into the holes sufficiently even without light irradiation. This indicates that the large hole diameter means that the contribution of the hydrophilic effect of the light irradiation treatment to the desmear treatment is small. In contrast, for substrates with holes with a diameter of 70 μm, light irradiation caused a small change in the C / Cu ratio. In other words, it is believed that light irradiation made it easier for the swelling liquid to penetrate into the holes, allowing more smears to be removed. This shows that the light irradiation treatment enhances the penetration effect of the swelling liquid.

[0062] An example of a smear removal method and an embodiment of an optical treatment device have been described above, but the present invention is not limited to the above-described method and embodiment, and various changes and improvements can be made to the above-described method and embodiment without departing from the spirit and scope of the present invention.

[0063] REFERENCE SIGNS LIST 1: First dielectric layer 2: Second dielectric layer 3: Prepreg 4: Conductive layer 5: Hole 7: Smear 9: Copper-clad laminate 10: Substrate 11: Swelling liquid 12: Smear removal liquid 30: Treatment chamber 31: Conveyor belt 32: Light source 33: Gas supply port 34: Gas exhaust port 35: Control unit 36: Flow rate adjustment valve 37: First gas supply source 38: Second gas supply source 100: Light treatment device L1: Vacuum ultraviolet light S1: Surface S10: Light irradiation process S20: Swelling process S30: Smear removal process

Claims

1. A desmear treatment method comprising: irradiating a substrate having holes and smears in the holes with vacuum ultraviolet light so that the substrate has a water contact angle of 40 to 70 degrees; supplying a swelling liquid for swelling the smear to the substrate irradiated with the vacuum ultraviolet light; and supplying a removal liquid for removing the smear from the substrate to the substrate with the smear swollen.

2. The desmearing method according to claim 1, wherein the irradiation with vacuum ultraviolet light is carried out in an air environment.

3. The desmear method according to claim 1 or 2, wherein the vacuum ultraviolet light reduces the water contact angle of the substrate surface by 20 degrees or more.

4. A desmear processing method as described in claim 1 or 2, characterized in that the diameter of the holes is 70 μm or less.

5. The desmear method according to claim 1 or 2, wherein the remover is an aqueous solution of permanganic acid.

6. The desmear method according to claim 1 or 2, wherein the swelling liquid is an alkaline aqueous solution.

7. A light treatment device that irradiates vacuum ultraviolet light onto a substrate having holes and smears in the holes, the light treatment device comprising: a light treatment space partitioned off from the surroundings; a light source that irradiates the substrate with the vacuum ultraviolet light; and a control unit that controls the light source to irradiate the vacuum ultraviolet light so that the water contact angle of the substrate falls within the range of 40 to 70 degrees.

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