Surface Modification Method

Abstract

To provide a surface modification method for imparting adhesion to the surface of a base material with controllability higher than a conventional method without substantially providing unevenness on the surface of a base material.SOLUTION: A surface modification method includes: a step (a) of preparing a base material having an insulating resin material; and a step (b) of irradiating the surface of the base material with ultraviolet light of a wavelength of 200 nm or less in the atmosphere having an oxygen concentration of 0.01-10 vol.%, and modifying a treatment object region containing the surface of the base material into a microporous layer having a gap of a nm order.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to a method for modifying the surface condition of a substrate, and more particularly to a surface modification method using light. [Background technology]

[0002] A wiring board having a wiring pattern formed on the surface of an insulating resin material is known. Conventionally, this wiring board is obtained by forming an electroless plating layer called a seed layer on the base resin, and then forming an electrolytic copper plating layer on top of that. Another known method for producing a wiring board is to use an adhesive to bond copper foil to one or both sides of an insulating resin material.

[0003] To obtain stable electrical properties, the resin and seed layer must adhere firmly to each other. A conventional method for improving adhesion is to roughen the surface of the resin to create irregularities, and then form a seed layer on the surface of the resin with the irregularities. The anchor effect resulting from the presence of the irregularities firmly fixes the resin and seed layer together.

[0004] Incidentally, the 5G communications system, which has been under development in recent years, will utilize extremely high-frequency electrical signals. Such high-frequency currents flow only on the surface of the conductor, with difficulty flowing through the center due to a phenomenon known as the skin effect. If the surface of the conductor is uneven, the signal transmission path will become longer, resulting in increased transmission loss. Therefore, wiring boards, especially those intended to handle high-frequency signals, are required to minimize the unevenness of the conductor surface.

[0005] Patent Document 1 below describes a method of irradiating a resin material with ultraviolet rays in an oxygen atmosphere to finely roughen the resin material with ultraviolet rays and ozone. This method is said to be able to roughen the resin material more finely than a method using a desmear treatment, which is known as a conventional roughening method. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-091840 Summary of the Invention [Problem to be solved by the invention]

[0007] However, as a result of investigations by the present inventors, it was found that the method of Patent Document 1 easily weakens the substrate made of a resin material. In other words, the method of Patent Document 1 requires extremely precise control to modify the surface without weakening the substrate, which poses practical problems. Furthermore, in light of the above investigations, it is believed that similar problems will arise when bonding and joining copper foil using an adhesive.

[0008] An object of the present invention is to provide a surface modification method that can impart adhesion to the surface of a substrate without substantially creating irregularities on the surface of the substrate and with a method that is more controllable than conventional methods. [Means for solving the problem]

[0009] The surface modification method according to the present invention is characterized by comprising the steps of: (a) preparing a substrate made of an insulating resin material; and (b) irradiating the surface of the substrate with ultraviolet light having a wavelength of 200 nm or less in an atmosphere having an oxygen concentration of 0.01% by volume to 10% by volume, thereby modifying a treatment target area including the surface of the substrate into a microporous layer containing voids of nanometer order size.

[0010] The present inventors speculate as follows about the reason why the substrate is likely to become brittle by the method described in Patent Document 1.

[0011] It was previously thought that when a resin substrate is irradiated with ultraviolet light, the contact angle on the substrate surface decreases monotonically with the amount of ultraviolet light irradiated, as shown schematically in Figure 1. A smaller contact angle means that when another layer is adhered to the surface of the substrate, the adhesive strength between the two increases. Therefore, it was thought that adhesive strength increases monotonically with the amount of ultraviolet light irradiated, as shown schematically in Figure 2.

[0012] In other words, it was thought that stable adhesion of another layer to the surface of a substrate could be achieved by irradiating the substrate with ultraviolet light at an irradiation dose greater than the point where the curve showing the change in contact angle shows an inflection point, i.e., an irradiation dose equal to or greater than Q1 in Figure 1.

[0013] However, through intensive research by the present inventors, when the relationship between the dose of ultraviolet light and the adhesive strength was measured while irradiating the substrate with ultraviolet light in an air atmosphere, it was confirmed that as the dose of irradiation was increased, the adhesive strength reached a peak value and then showed a tendency to decrease, as shown in Figure 3. Figure 3 is a graph that schematically shows the relationship, newly confirmed by the present inventors, between the dose of ultraviolet light irradiated onto the substrate and the adhesive strength between the substrate surface and another layer.

[0014] In other words, the results of Figure 3 show that in order to impart high adhesive strength to the surface of the substrate, it is necessary to adjust the amount of ultraviolet radiation to fall within a limited range of radiation amounts (Qr1).

[0015] Figure 4 shows graphs of the relationship between the UV irradiation time and the contact angle of the substrate surface, and the relationship between the irradiation time and the adhesive strength, measured by actually irradiating the surface of a substrate with UV light at a predetermined intensity in an atmospheric environment. In Figure 4, the horizontal axis represents the UV irradiation time, the left vertical axis represents the adhesive strength, and the right vertical axis represents the contact angle. Figure 4 is a graph created based on the results of measurements specifically performed using the following method.

[0016] A polyimide resin (Kapton 100EN-C, manufactured by Toray DuPont Co., Ltd.) was prepared as a substrate sample (Kapton is a registered trademark of the company). The surface of this sample was irradiated with ultraviolet light from an irradiation distance (separation distance) of 3 mm using an ultraviolet irradiation device (SVC 232 Series, manufactured by Ushio Inc., peak wavelength 172 nm).

[0017] After each sample was irradiated with ultraviolet light for different irradiation times, the contact angle of the sample surface was measured using a contact angle measuring device (manufactured by Kyowa Interface Science Co., Ltd.: DMo-501).

[0018] Next, each sample was irradiated with ultraviolet light for different irradiation times, and then the irradiated surfaces of the same samples were bonded together with an adhesive sheet (Aron Mighty AF-700, manufactured by Toagosei Co., Ltd.) interposed between them and laminated at 100°C (Aron Mighty is a registered trademark of the company). Then, a pressure of 2-3 MPa was applied while the samples were pressed at 180°C for 30 minutes. The adhesive strength of the bonded samples was measured using a method conforming to JIS K 6854-3 (Adhesives - Peel Adhesion Strength Test Method, Part 3: T-Peel). Note that in Figure 4, the adhesive strength is shown as a relative value.

[0019] The results in Figure 4 show that the graph showing the relationship between adhesive strength and irradiation time shows a tendency for adhesive strength to decrease as the irradiation time increases from the peak value. When the ultraviolet irradiance is constant, the irradiation time is proportional to the irradiation amount. In other words, Figure 3 shows the tendency in Figure 4.

[0020] The results in Figures 3 and 4 show that when UV light is irradiated onto a substrate using conventional methods, the conditions for the dose required to achieve high adhesive strength are extremely limited. In other words, high adhesive strength cannot be achieved unless the UV light dose is controlled with extremely high precision. The results in Figure 4 show that adhesive strength decreases even if the irradiation time is extended by just one to several seconds. However, although the relationship between adhesive strength and irradiation time (dose) shown in Figure 4 shows a general tendency for the range showing peak values ​​to be narrow, the actual preferred dose varies depending on the resin. As a result, UV light is irradiated onto the substrate in excess of the preferred dose, resulting in reduced adhesive strength on the substrate surface.

[0021] On the other hand, if the irradiation time is adjusted so as not to exceed the desired irradiation dose, the irradiation dose required for the adhesive strength to reach its peak value may not be reached, and in this case too, high adhesive strength cannot be imparted to the substrate.

[0022] Figure 5 is a graph showing the absorption spectra of oxygen (O2) and ozone (O3). For reference, the emission spectrum of a Xe excimer lamp is superimposed on Figure 5. In Figure 5, the horizontal axis represents wavelength, the left vertical axis represents the relative value of the light intensity of the excimer lamp, and the right vertical axis represents the absorption coefficients of oxygen (O2) and ozone (O3).

[0023] Patent Document 1 states that the wavelength of ultraviolet light is preferably 150 nm to 400 nm, more preferably 150 nm to 350 nm, and even more preferably 150 nm to 300 nm. According to the examples in Patent Document 1, an ultraviolet irradiation device (SSP-16, manufactured by Sen Special Light Sources Co., Ltd.) is used for surface treatment of resins, and the company's catalog makes clear that this light source exhibits peak values ​​of its emission spectrum at 185 nm and 254 nm. From this, it can be understood that Patent Document 1 intends to use a low-pressure mercury lamp as a light source for surface treatment of substrates.

[0024] Low-pressure mercury lamps emit ultraviolet rays with extremely short peak wavelengths at half-width near 185 nm and near 254 nm. As shown in Figure 5, ultraviolet rays near 185 nm are easily absorbed by oxygen. Therefore, when ultraviolet rays from a low-pressure mercury lamp are irradiated onto a resin substrate in an air atmosphere, part of the ultraviolet rays is absorbed by oxygen in the air, and the ground-state atomic oxygen O( 3 P) is generated. O2+ hν (185nm) → O( 3 P) + O( 3 P) ...(1)

[0025] This atomic oxygen O( 3 P) reacts with oxygen (O2) in the atmosphere to produce ozone (O3) according to the following equation (2): O( 3 P) + O2 → O3...(2)

[0026] As shown in Figure 5, ozone (O3) has the property of absorbing ultraviolet rays. When ultraviolet rays from a low-pressure mercury lamp are absorbed by ozone (O3), excited atomic oxygen O( 1 D) is produced. O3+ hν (185nm, 254nm) → O2+ O( 1 D) ...(3)

[0027] Atomic oxygen O( 1 D) is extremely reactive. Therefore, the polymer (C) of the resin that constitutes the base material m H n O k ) and cuts the molecular chain. In the following formula (4), m, m', n, n, k, and k' are all integers, with m>m', n>n', and k>k'. However, please note that formula (4) is a schematic representation of the reaction and is not an accurate chemical reaction formula. C m H n O k + O( 1 D) → H2O, CO, CO2+ C m' H n' Ok' ···(4)

[0028] Polymers that make up the resin (C m H n O k ) and the intermediate product produced in the reaction of equation (4) is O( 1 In addition to the action of D), direct exposure to ultraviolet light also partially breaks the bond.

[0029] The ultraviolet rays emitted from the low-pressure mercury lamp contain a long-wavelength component of 254 nm, which makes it easier for the ultraviolet rays to penetrate deeper into the substrate than short-wavelength components of 200 nm or less. For this reason, as shown in Figure 6, some of the ultraviolet rays L90 from the low-pressure mercury lamp 90 travels in the depth direction of the substrate 3. In other words, energy derived from the ultraviolet rays L90 is input to a region from the surface 3a of the substrate 3 to a point d90 in the depth direction.

[0030] Then, due to the above circumstances, ultraviolet L90 itself and the highly reactive O( 1 D) acts at a location sufficiently deep from the surface 3a of the base material 3. As a result, the polymer (C m H n O k As a result, molecular chains with small molecular weights overlap each other, which is thought to weaken the base material 3.

[0031] FIG. 7 is a diagram schematically illustrating the molecular chains of the polymer material that constitutes the substrate 3. As described above, ultraviolet light and mainly O( 1 D) acts, the molecular chains are cut at many points, and low molecular weight substances are generated (see Figure 8). Figure 8 is a schematic diagram showing the state in which the constituent material of the substrate 3 shown in Figure 7 has been cut and reduced to low molecular weight substances.

[0032] That is, the ultraviolet light L90 emitted from the low-pressure mercury lamp has wavelength components of 185 nm and 254 nm, which modifies the surface 3a of the base material 3, but also damages the base material 3 in the depth direction due to the long wavelength components, resulting in a decrease in the strength of the base material 3.

[0033] Therefore, the inventors investigated using a xenon (Xe) excimer lamp, which emits ultraviolet light with a small amount of wavelength components of 200 nm or more, as a light source instead of a low-pressure mercury lamp, and irradiating the substrate with ultraviolet light from the light source. However, as described above with reference to Figure 4, the amount of ultraviolet light irradiation that can impart high adhesive strength to the substrate is limited.

[0034] The present inventors considered that the reason why the amount of ultraviolet light irradiation that can impart high adhesive strength to a substrate is limited is because the reaction proceeds extremely quickly. In particular, in the case of ultraviolet light with a peak wavelength of less than 185 nm, such as that from a Xe excimer lamp (peak wavelength of about 172 nm), when part of the ultraviolet light is absorbed by oxygen in the atmosphere, excited atomic oxygen O( 1 D) is produced. O2+ hν (172nm) → O( 1 D) + O( 3 P) ...(5)

[0035] In addition, the atomic oxygen O( 3 As mentioned above, a part of the oxygen atoms in the excited state, O( 1 D) changes to

[0036] In other words, the shorter the wavelength of the ultraviolet light irradiated onto the substrate, the more the reaction occurs only on the surface of the substrate, with almost no damage to the depth direction, and the more reactive O( 1 D) is generated at a faster rate. This is thought to increase the rate at which the molecular chains of the polymer material that makes up the base material are cleaved.

[0037] To efficiently modify the surface of a substrate, it is preferable to sever only the molecular chains of the polymeric material present near the surface of the substrate and generate voids through such severing. This is because, if an adhesive or catalyst is subsequently applied to adhere another layer, the adhesive's constituent materials or compounds containing molecules or atoms that exhibit catalytic activity (hereinafter referred to as "catalytic compounds") can penetrate into the voids. However, as described above, if the reaction that severs the molecular chains of the polymeric material proceeds at a high rate, the same phenomenon occurs not only on the surface of the substrate but also in deeper regions, weakening the substrate. In other words, the limited irradiation dose that can impart high adhesive strength to the substrate, as described above with reference to Figures 3 and 4, can be said to be an irradiation dose that is sufficient to sever only the molecular chains of the polymeric material present near the surface of the substrate.

[0038] In the method according to the present invention, the atmosphere in which ultraviolet light is irradiated is set to 0.01% by volume to 10% by volume, which is an extremely low oxygen concentration compared to the atmosphere. 1 D) is generated at a slower rate, broadening the range of irradiation doses that can impart high adhesive strength to the substrate, increasing the degree of freedom in control and improving controllability. Note that "control" here refers to control carried out to realize a production process that can obtain stable adhesive strength (including plating strength).

[0039] Fig. 9 is a graph that schematically shows the relationship between the amount of ultraviolet light irradiated onto the substrate and the adhesive strength between the substrate surface and another layer when the atmosphere has a low oxygen concentration, following the example of Fig. 3. For comparison, Fig. 9 also shows a graph of the results in an air atmosphere overlaid.

[0040] The results in Figure 9 show that when the atmosphere is low in oxygen concentration, the range of ultraviolet irradiation dose (Qr2) that can impart high adhesive strength to the surface of the substrate is significantly expanded compared to the air atmosphere (Qr1). Furthermore, by irradiating the substrate with ultraviolet irradiation doses within this range (Qr2), polymer chains near the surface of the substrate are cleaved, forming voids. In other words, only the surface vicinity of the substrate is modified into a layer containing voids (microporous layer).

[0041] Figure 10 shows graphs of the relationship between the UV irradiation time and the contact angle of the substrate surface, and the relationship between the irradiation time and the adhesive strength, measured by actually irradiating the surface of the substrate with UV light at a predetermined intensity in a low-oxygen atmosphere. The graphing method is the same as in Figure 4, except for the oxygen concentration of the atmosphere. In Figure 10, the oxygen concentration of the atmosphere was set to 0.1% by volume (1000 ppm).

[0042] The results in Fig. 10 confirm that even when ultraviolet light is irradiated for several tens to hundreds of seconds longer than the irradiation time at which the adhesive strength reaches its peak, the adhesive strength does not decrease significantly compared to Fig. 4. In other words, Fig. 10 shows the tendency of Fig. 9 in a schematic manner.

[0043] FIG. 11 is a diagram, similar to FIG. 6, that schematically illustrates the progression of ultraviolet light L10 when the ultraviolet light L10 from the Xe excimer lamp 10 is irradiated onto the substrate 3. The ultraviolet light L10 from the Xe excimer lamp 10 has a peak wavelength near 172 nm. As shown in FIG. 11, the ultraviolet light L10 travels a distance d10 in the depth direction from the surface of the substrate 3. The ultraviolet light L10 from the Xe excimer lamp 10 has a shorter wavelength band than the ultraviolet light L90 emitted from the low-pressure mercury lamp. Therefore, the distance d10 is extremely shorter than the progression distance d90 (FIG. 6) when ultraviolet light L90 from the low-pressure mercury lamp 90 is irradiated. In other words, the ultraviolet light L10 acts only near the surface of the substrate 3.

[0044] By setting the atmosphere 1 irradiated with ultraviolet light L10 to a low oxygen concentration, the range of the irradiation dose of ultraviolet light L10 that can impart high adhesive strength to the surface 3a of the substrate 3 is expanded, as described above. When ultraviolet light L10 is irradiated onto the surface 3a of the substrate 3 at such an irradiation dose, only a portion of the polymer chains that make up the substrate 3 are cleaved and oligomerized. At this time, spaces (voids 4) are formed between the oligomers (see FIG. 12). FIG. 12 is a schematic diagram, following FIG. 8, illustrating how a portion of the polymer chains that make up the substrate 3 are cleaved to form voids 4.

[0045] By forming the voids 4 in the vicinity of the surface 3a of the base material 3, the constituent molecules of the adhesive or catalyst contributing compound can enter the voids 4. As a result, it is possible to impart high adhesive strength to the surface 3a of the base material 3 without roughening the surface 3a of the base material 3.

[0046] In other words, in this specification, the "microporous layer" is a layer containing voids 4 generated by cutting a portion of the polymer chains that make up the substrate 3, and these voids 4 are on the order of nm (1 nm to several nm) in size.

[0047] The presence and thickness of the microporous layer can be confirmed by adhering another layer to the surface of the substrate and then observing the cross section with a transmission electron microscope (TEM), as will be described in detail later.

[0048] In the above explanation, the case where the peak wavelength of ultraviolet light is around 172 nm was taken as an example, but the same explanation can be applied to the case where the peak wavelength is 200 nm or less. In the case of ultraviolet light with a wavelength longer than 172 nm and less than 200 nm, atomic oxygen O( 1 Although the rate of generation of D) is expected to be somewhat slower, when irradiated in an air atmosphere, the adhesive strength decreases significantly if the irradiation time is extended by several seconds, just as in the case of a wavelength of 172 nm. However, when the wavelength of ultraviolet light exceeds 200 nm, for the reasons mentioned above, the proportion of ultraviolet light that travels in the depth direction of the substrate increases little by little, making the substrate more likely to become brittle.

[0049] The region to be processed may be a region between the surface and a location 3 nm to 50 nm from the surface in a depth direction perpendicular to the surface.

[0050] After step (b), another layer may be bonded to the surface of the substrate via a catalyst. As described above, by forming a microporous layer near the surface of the substrate, the catalyst-contributing compound is incorporated into the voids within the microporous layer, achieving high adhesive strength. Because the outer diameter of the catalyst-contributing compound is approximately 3 nm, if the thickness of the treatment target area is less than 3 nm, the catalyst-contributing compound does not sufficiently penetrate into the voids, and the effect of increasing adhesive strength is limited.

[0051] Furthermore, at locations 50 nm or more in depth from the surface, the base material itself becomes weaker, resulting in a decrease in adhesive strength.

[0052] The surface modification method may further include, after the step (b), a step (c) of removing low-molecular-weight components contained in the base material.

[0053] As described above, when ultraviolet light is irradiated onto the substrate, ultraviolet light itself or atomic oxygen O( 1 D) The polymers that make up the base material are broken down. During this process, molecular chains with extremely low molecular weights compared to the resin that makes up the base material may be generated as a by-product. If a catalyst or adhesive is introduced after step (b), the catalyst or adhesive will be incorporated into these low molecular chains. However, the catalyst or adhesive incorporated into the low molecular chains will not contribute to improving the adhesive strength.

[0054] As described above, by performing step (c) of removing low-molecular-weight components contained in the substrate, much of the catalyst and adhesive introduced thereafter can be incorporated into the voids in the microporous layer. In other words, this method allows for high adhesive strength to be achieved while reducing the amount of catalyst and adhesive used.

[0055] Examples of the step (c) for removing low molecular weight components include alkaline washing, hot water washing, and drying, among which alkaline washing is particularly preferred.

[0056] That is, the step (c) may be a step of immersing the substrate after the step (b) in an alkaline solution.

[0057] The type of alkaline solution used in this step is not particularly limited, but for example, one or more types belonging to the group consisting of sodium hydroxide, lithium hydroxide, and potassium hydroxide can be suitably used.

[0058] The step (a) includes a step of placing the substrate on a transport path, The step (b) includes a step of irradiating the substrate with ultraviolet light from an ultraviolet light source in a treatment space containing the ultraviolet light source while transporting the substrate, During the step (b), nitrogen gas is introduced into the processing space, The step (b) may be completed at the latest when the substrate passes through the treatment space.

[0059] The step (a) includes a step of placing the substrate at a predetermined position in a chamber, The step (b) may include a step of sealing a space including the predetermined location in the chamber while setting the space to an atmosphere consisting of a mixed gas containing oxygen and nitrogen at a concentration of 0.01% by volume to 10% by volume, and then irradiating the substrate with ultraviolet light from an ultraviolet light source installed in the chamber. [Effects of the Invention]

[0060] According to the present invention, it is possible to impart adhesion to the surface of a substrate by a method with higher controllability than conventional methods, without providing substantial irregularities on the surface of the substrate. [Brief explanation of the drawings]

[0061] [Figure 1]1 is a graph schematically showing the conventionally assumed relationship between the amount of ultraviolet light irradiated onto a substrate and the contact angle on the substrate surface. [Figure 2] 1 is a graph schematically showing the conventionally assumed relationship between the amount of ultraviolet light irradiated onto a substrate and the adhesive strength between the surface of the substrate and another layer. [Figure 3] 1 is a graph showing a relationship, derived from the inventors' investigations, between the amount of ultraviolet light irradiated onto a substrate in an air atmosphere and the adhesive strength between the surface of the substrate and another layer. [Figure 4] 1 is a graph showing the relationship between the ultraviolet irradiation time and the contact angle of the substrate surface, and the relationship between the irradiation time and the adhesive strength, when the surface of the substrate is irradiated with ultraviolet light at a predetermined intensity in an atmospheric environment. [Figure 5] 1 is a graph showing the emission spectrum of a Xe excimer lamp and the absorption spectra of oxygen (O2) and ozone (O3) superimposed on each other. [Figure 6] 1 is a diagram schematically showing how ultraviolet light travels when it is irradiated onto a substrate from a low-pressure mercury lamp. [Figure 7] 1 is a diagram schematically illustrating molecular chains of a polymer material that constitutes a substrate. [Figure 8] 1 is a diagram schematically illustrating a state in which the molecular chains of a polymer material constituting a substrate are significantly cut and reduced in molecular weight. [Figure 9] 1 is a graph schematically showing the relationship between the amount of ultraviolet light irradiated onto a substrate and the adhesive strength between the substrate surface and another layer when the atmosphere has a low oxygen concentration. [Figure 10] 1 is a graph showing the relationship between the ultraviolet irradiation time and the contact angle of the substrate surface, and the relationship between the irradiation time and the adhesive strength, when the surface of the substrate is irradiated with ultraviolet light at a predetermined intensity in a low-oxygen atmosphere. [Figure 11] 1 is a diagram schematically showing how ultraviolet light travels when it is irradiated onto a substrate from an Xe excimer lamp. [Figure 12] 1 is a diagram schematically illustrating a state in which a part of the molecular chain of a polymer material constituting a substrate is cut to form a void. [Figure 13]1 is a cross-sectional view schematically showing an example of the configuration of a system for carrying out a surface modification method of the present invention. [Figure 14] FIG. 2 is a cross-sectional view schematically showing another example of the configuration of a system for carrying out the surface modification method of the present invention. [Figure 15] FIG. 2 is a cross-sectional view schematically showing another example of the configuration of a system for carrying out the surface modification method of the present invention. [Figure 16] 1 is a graph showing the relationship between the ultraviolet irradiation time and the peak value of adhesive strength when ultraviolet rays are irradiated on the surface of a substrate at a predetermined intensity, for each oxygen concentration in the atmosphere. [Figure 17] 10 is a graph illustrating a "ratio" that serves as an index for evaluating the level of controllability. [Figure 18] FIG. 2 is a cross-sectional view schematically showing a state in which an electroless plating layer is formed on the surface of a substrate on which a microporous layer has been formed. [Figure 19] 1 is a graph showing the results of a TEM-EDS analysis of a substrate having an electroless plated layer formed on its upper surface, the analysis proceeding in the depth direction from the interface with the electroless plated layer toward the substrate. [Figure 20] 1 is a graph showing the results of mass spectrometry of substances with lower molecular weights than the constituent material of the substrate, performed by TOF-SIMS, on a substrate irradiated with ultraviolet light and a substrate not irradiated with ultraviolet light. [Figure 21A] 1 is a graph showing the results of an MSE test performed on a substrate irradiated with ultraviolet light and a substrate that has not been irradiated with ultraviolet light. [Figure 21B] 21B is a graph showing the results of FIG. 21A with an approximation line added. [Figure 22] 1 is a graph comparing the adhesive strength of the surface of a substrate when the substrate is subjected to alkaline cleaning after being irradiated with ultraviolet light and when the substrate is not subjected to alkaline cleaning. DETAILED DESCRIPTION OF THE INVENTION

[0062] Hereinafter, embodiments of the surface modification method according to the present invention will be described with reference to the drawings as appropriate. However, the drawings are merely schematic illustrations, and the dimensional ratios in the drawings do not necessarily correspond to the actual dimensional ratios. Furthermore, the dimensional ratios between the drawings may not match each other.

[0063] In the following drawings, the same elements as those in FIG. 11 are denoted by the same reference numerals, and the description thereof will be simplified.

[0064] The surface modification method according to the present invention includes the step (a) of preparing a substrate 3 made of an insulating resin material, and the step (b) of irradiating the surface of the substrate 3 with ultraviolet light L10 having a wavelength of 200 nm or less in an atmosphere 1 having an oxygen concentration of 0.01% by volume to 10% by volume. This step (b) is a step of modifying a treatment target region (region within a depth d10) including the surface 3a of the substrate 3 into a microporous layer 4a (see FIG. 18) containing voids 4 (see FIG. 12) of nanometer order size.

[0065] The substrate 3 is not limited to any particular type as long as it is made of an insulating resin material, and examples thereof include polyimide resin, liquid crystal polymer, polystyrene, polyphenylene sulfide, polyether ether ketone, polyethylene naphthalate, cycloolefin polymer, cyclic olefin copolymer, polytetrafluoroethylene, epoxy resin, etc. The substrate 3 may be a sheet-like film or a plate-like member.

[0066] 13 is a diagram showing a schematic configuration example of a system for carrying out the surface modification method according to the present invention. This system 2 carries out surface treatment of a substrate 3 to be treated while transporting the substrate 3 along a transport path 40.

[0067] The system 2 includes a light source device 5 including a Xe excimer lamp 10. The light source device 5 is provided with an irradiation window 6, and ultraviolet light L10 from the Xe excimer lamp 10 is irradiated onto the transport path 40 side through the irradiation window 6. The irradiation window 6 may be made of any material as long as it transmits ultraviolet light L10, and may be made of synthetic quartz glass, for example. The light source device 5 may be configured such that nitrogen gas is sealed in the space in which the Xe excimer lamp 10 is installed. In the example shown in FIG. 13 , nitrogen gas is introduced from a nitrogen gas source 34 into the space in which the excimer lamp 10 is installed. In this example, an exhaust port 35 is provided, and it is assumed that nitrogen gas is constantly flowing from the nitrogen gas source 34 during processing. However, this is merely an example.

[0068] The substrate 3 placed on the transport path 40 is taken in through the carry-in opening 18 while moving in the dX direction along the transport path 40, and approaches a location facing the irradiation window 6. Thereafter, the substrate 3 is irradiated with ultraviolet light L10 through the irradiation window 6 while further moving in the dX direction, and is taken out through the carry-out opening 19.

[0069] When the substrate 3 is a plate-like body, the transport path 40 may have a structure including, for example, a plurality of transport rollers. When the substrate 3 is a sheet-like film, the transport path 40 may have a structure in which the sheet-like film is stretched between an unwinding roll and a winding roll and is wound from the unwinding roll onto the winding roll.

[0070] The light source device 5 is disposed at a position where the irradiation window 6 is close to the substrate 3 on the transport path 40 in relation to the optical axis direction of the ultraviolet light L10. Specifically, the distance between the irradiation window 6 and the substrate 3 is preferably 1 mm to 50 mm, and more preferably 2 mm to 10 mm.

[0071] In this example, the ultraviolet light source provided in the light source device 5 is described as a Xe excimer lamp 10, but as described above, the light source is not limited to the Xe excimer lamp 10 as long as it emits ultraviolet light with a peak wavelength of 200 nm or less. For example, a solid-state light source such as an LED or laser diode may also be used.

[0072] The system 2 includes a nitrogen gas source 31, an oxygen-containing gas source 32, and a gas mixer 33. The nitrogen gas source 31 is a gas source filled with nitrogen gas. The oxygen-containing gas source 32 is a gas source filled with a gas containing oxygen, and a typical example is CDA (clean dry air). The gas mixer 33 mixes the nitrogen gas from the nitrogen gas source 31 and the oxygen-containing gas from the oxygen-containing gas source 32 while adjusting the flow ratio, to generate and deliver a gas for the processing space. This gas for the processing space delivered from the gas mixer 33 constitutes the atmosphere 1 for the substrate 3. FIG. 13 illustrates a case where the flow direction of the gas for the processing space is the same as the flow direction of the substrate 3 (dX direction), but it may be reversed. That is, the processing space gas, which is composed of a mixed gas of nitrogen gas from the nitrogen gas source 31 and oxygen-containing gas from the oxygen-containing gas source 32, may be introduced against the flow of the substrate 3, in other words, from the downstream side to the upstream side of the transport direction in the transport path 40.

[0073] As described above, when the system 2 includes the nitrogen gas source 34, the nitrogen gas source 34 may be common to the nitrogen gas source 31.

[0074] An oxygen concentration detector (not shown) may be installed in the space through which the substrate 3 passes, and the gas mixer 33 may be feedback-controlled so that the oxygen concentration in the atmosphere 1 in the space is kept at a predetermined constant value. The same applies to the system 2 shown in Fig. 14, which will be described later.

[0075] The gas mixer 33 adjusts the mixing ratio so that the atmosphere 1 around the substrate 3 has a low oxygen concentration. Specifically, the oxygen concentration in the atmosphere 1 is 0.01% to 10% by volume, more preferably 0.01% to 5% by volume, and particularly preferably 0.1% to 5% by volume.

[0076] The system 2 preferably includes sub-chambers 21 and 22. The sub-chambers 21 and 22 forcibly exhaust gas leaking from the processing space through the inlet 18 or the outlet 19 to the outside.

[0077] According to this system 2, the substrate 3 is irradiated with ultraviolet light L10 while moving on the transport path 40, and the area near the surface of the substrate 3 is modified into a microporous layer 4a (see Figure 18) containing voids 4 (see Figure 12).

[0078] In the configuration of the system 2 shown in Fig. 13, the space (light source device 5) housing the Xe excimer lamp 10 and the space through which the substrate 3 passes are separated, but they may be arranged in the same space (processing space 8) as shown in Fig. 14. Fig. 14 is a diagram schematically illustrating another configuration example of a system for carrying out the surface modification method according to the present invention, following Fig. 13.

[0079] In the system 2 shown in Fig. 14, the processing space gas delivered from the gas mixer 33 is supplied into the processing space 8 via the gas supply pipe 16. In the case of the system 2 shown in Fig. 14, it is preferable to provide a gas outlet 17 for forcibly exhausting the gas in the processing space 8 to the outside. At the start of processing, the gas in the processing space 8 is once exhausted via the gas outlet 17, and then the mixed gas with a low oxygen concentration delivered from the gas mixer 33 is supplied into the processing space 8 via the gas supply pipe 16, thereby making the atmosphere 1 around the substrate 3 have a low oxygen concentration.

[0080] In this case, as shown in FIG. 14, it is preferable to provide sub-chambers 21 and 22 at two locations, one above the other, with transfer path 40 sandwiched between them.

[0081] The surface treatment of the substrate 3 does not necessarily have to be performed while the substrate 3 is being transported. That is, even in the case of the system 2 shown in Figures 13 and 14, after the substrate 3 is transported to a location where it is irradiated with ultraviolet light L10 from the Xe excimer lamp 10, the transport path 40 may be temporarily stopped and the substrate 3 may be irradiated with ultraviolet light L10.

[0082] 15, ultraviolet rays L10 may be irradiated onto the substrate 3 within a closed chamber 7. In the system 2 shown in FIG. 15, similar to the system 2 shown in FIG. 13, the space 7a housing the Xe excimer lamp 10 and the space 7b housing the substrate 3 are separated. A low-oxygen-concentration processing space gas delivered from a gas mixer 33 is supplied to the space 7b housing the substrate 3. Similarly to the configuration shown in FIG. 13, nitrogen gas is introduced from a nitrogen gas source 34 into the space 7a housing the Xe excimer lamp 10. In this case, it is also preferable to provide a gas outlet 17 for forcibly exhausting the gas within the space 7b. The nitrogen gas source 34 may be a common nitrogen gas source 31.

[0083] After the substrate 3 is irradiated with ultraviolet light L10 by the system 2 illustrated in FIGS. 13 to 15, the polymer chains constituting the substrate 3 are cleaved near the surface 3a, resulting in a modified microporous layer 4a (see FIG. 18) containing voids 4 (see FIG. 12). During this process, molecular chains with extremely low molecular weights compared to the resin constituting the substrate 3 may be generated secondarily in some locations near the surface 3a. Therefore, the substrate 3 after being irradiated with ultraviolet light L10 may be removed and subjected to an alkali cleaning treatment, a warm water cleaning treatment, a drying treatment, or the like to remove these low molecular weight components. Among these, an alkali cleaning treatment is particularly preferred.

[0084] The alkaline cleaning treatment can be performed by immersing the substrate 3 after UV irradiation in an alkaline solution such as sodium hydroxide, potassium hydroxide, or lithium hydroxide. The alkaline concentration of this alkaline solution is preferably 4% to 20%, more preferably 8% to 12%. The temperature of the alkaline solution is preferably 40°C to 80°C, and particularly preferably 60°C to 70°C. If the temperature of the alkaline solution is below 40°C, the cleaning ability will not be fully exerted, and if it exceeds 80°C, the alkaline component will easily evaporate. The immersion time of the substrate 3 in the alkaline solution is not particularly limited, but typically, if it is 10 seconds or more, it is expected to be effective in removing low-molecular-weight materials. [Example]

[0085] Specific test examples will be shown below to explain the present invention in more detail, but the present invention is not limited to the embodiments of these test examples.

[0086] (Verification 1: Oxygen concentration in the atmosphere) The relationship between the irradiation time of the ultraviolet light L10 and the adhesive strength of the base material 3 was measured using a method similar to the measurement method described above with reference to Fig. 10. That is, the verification method was as follows.

[0087] A polyimide resin (Kapton 100EN-C, manufactured by Toray DuPont Co., Ltd.) was prepared as a sample of the substrate 3. A light irradiation device (SVC 232 Series, manufactured by Ushio Inc., peak wavelength 172 nm) was used to irradiate the sample surface with ultraviolet light L10 from an irradiation distance (separation distance) of 3 mm, with the atmospheric oxygen concentration varied in seven patterns: 0.01 vol%, 0.1 vol%, 0.5 vol%, 1 vol%, 5 vol%, 10 vol%, and 21 vol%. The atmosphere with an oxygen concentration of 21 vol% corresponds to the air 100 shown in FIG. 6. The light irradiation device was equipped with a Xe excimer lamp 10.

[0088] Each sample was irradiated with ultraviolet light L10 for different irradiation times, and then the irradiated surfaces of the same samples were bonded together using an adhesive sheet (Aron Mighty AF-700, manufactured by Toagosei Co., Ltd.) and laminated at 100°C. Then, a pressure bonding process was performed at 180°C for 30 minutes while pressing at a pressure of 2 MPa to 3 MPa. The peak adhesive strength of the bonded samples obtained after bonding was measured using a method conforming to JIS K 6854-3.

[0089] FIG. 16 is a graph in which the vertical axis represents the relative value of the peak value of the adhesive strength, and the horizontal axis represents the irradiation time of ultraviolet light L10.

[0090] 16, it can be seen that the rate of decrease in adhesive strength due to an increase in irradiation time is slower when ultraviolet light L10 is irradiated onto the substrate 3 in an atmosphere with a low oxygen concentration than when ultraviolet light L10 is irradiated onto the substrate 3 in an air atmosphere. Specifically, in the air atmosphere, the adhesive strength reached its maximum value after an irradiation time of about 6 seconds, and when the irradiation time was further extended by about 6 seconds, the adhesive strength decreased to less than 50% of the peak value.

[0091] In contrast, in an atmosphere with an oxygen concentration of 10% by volume or less, even if ultraviolet light L10 is continued for an additional 20 seconds after the irradiation time at which the adhesive strength reaches its peak, the adhesive strength remains at 50% or more of the peak value. In particular, the results in Figure 16 show that the lower the oxygen concentration, the more effectively the adhesive strength decreases with increasing irradiation time.

[0092] The results in Figure 16 show that by lowering the oxygen concentration of the atmosphere from the air (21%), the allowable time for which ultraviolet light L10 can be irradiated to bring the adhesive strength close to its peak value can be extended. In other words, the higher the ratio of the allowable time to the irradiation time required to bring the adhesive strength to its peak value, the greater the degree of freedom in the irradiation time of ultraviolet light L10 to impart high adhesive strength to the substrate 3. In other words, the higher the ratio, the better the controllability when performing the modification treatment on the substrate 3. Therefore, the value of this ratio can be used to evaluate the level of controllability.

[0093] FIG. 17 is a graph illustrating the "ratio," an index used to evaluate the level of controllability. The tolerance for the degree of variation when discussing adhesive strength is generally set at 5%. Therefore, the level of controllability can be evaluated by the ratio (τ95 / tp) of the allowable time τ95 of ultraviolet light L10 that can be irradiated to bring the adhesive strength close to the peak value (i.e., 95% or more of the peak value) to the irradiation time tp required to bring the adhesive strength of the substrate 3 to its peak value. Alternatively, if the irradiation time tp required to bring the adhesive strength of the substrate 3 to its peak value is 10 seconds or longer, the controllability can be determined to be high because a deviation in the irradiation time of 10 seconds or more is acceptable.

[0094] Table 1 below shows the results of calculating the ratio (τ95 / tp) using the above method according to the oxygen concentration of the atmosphere based on the results of Figure 16, and evaluating the level of controllability of the surface treatment for the substrate 3 based on this value. In Table 1, a ratio (τ95 / tp) of 0.3 or more indicating high controllability is given an "Evaluation A," and a low controllability is given an "Evaluation C."

[0095] [Table 1]

[0096] According to Table 1, by lowering the oxygen concentration in the atmosphere below that of the air, the ratio (τ95 / tp) can be set to 0.5 or more, or the allowable time τ95 can be set to 10 seconds or more. As a result, it becomes possible to modify only the vicinity of the surface 3a of the substrate 3 without precisely controlling the irradiation time.

[0097] (Verification 2: Confirmation of the microporous layer) After irradiating the substrate 3 with ultraviolet light L10, a catalyst is applied and then an electroless plating layer is formed, thereby forming a conductive layer on the surface of the insulating substrate 3. Figure 18 is a cross-sectional view that schematically shows a state in which an electroless plating layer 50 has been formed on the surface of the substrate 3.

[0098] By irradiating the surface of the substrate 3 with ultraviolet light L10 using the method described above, the vicinity of the surface 3a of the substrate 3 is modified, and a microporous layer 4a containing voids 4 (see FIG. 12) is formed. When a catalyst is applied in this state, it is believed that the catalyst-contributing compound is captured in the voids 4 within the microporous layer 4a.

[0099] Therefore, as shown in Figure 18, when a cross section of the substrate 3 is analyzed while proceeding in the depth direction dZ from the surface 3a of the substrate 3 (the interface between the substrate 3 and the electroless plating layer 50) toward the substrate 3, if a substance derived from the catalyst can be detected inside the substrate 3, this proves that voids 4 existed near the surface 3a of the substrate 3, in other words, that a microporous layer 4a had been formed.

[0100] After irradiating the substrate 3 with ultraviolet light L10 in an atmosphere 1 with an oxygen concentration of 0.1% in the same manner as in Verification 1, an electroless plating layer 50 was formed in the following manner. However, in this verification, an epoxy resin was used as the substrate 3.

[0101] After irradiating with UV light L10, the substrate 3 was immediately immersed in conditioner solution M1 to degrease and adjust the surface potential of the substrate 3 to cationic. Next, after rinsing with water, the substrate 3 was immersed in pre-dip solution M2 to adjust the surface potential of the substrate 3 to anionic. Next, the substrate 3 was immersed in catalyst application solution M3 to apply a catalyst complex to the surface of the substrate 3. Next, after rinsing with water, the substrate 3 was immersed in activation treatment solution M4 to reduce the catalyst complex to metal. Next, after rinsing with water, the substrate 3 was immersed in electroless metal plating solution M5 to reduce the metal ions via the catalyst, forming an electroless metal coating on the surface of the substrate 3.

[0102] When the substrate 3 was immersed in each chemical solution, the substrate 3 was dipped in a chemical solution pod storing the respective chemical solution for a predetermined time (several seconds to several minutes) and then removed. The water washing treatment was performed by dipping the substrate 3 in a cleaning pod storing cleaning water (pure water) for a predetermined time (several seconds to several minutes) and then removing it.

[0103] The chemicals used were as follows: Conditioner Liquid M1: OPC-370 Condiclean ELA (Okuno Pharmaceutical Industries) Pre-dip solution M2: A mixture of OPC Pre-dip 49L (Okuno Chemical Industries Co., Ltd.) and 98% sulfuric acid Catalyst solution M3: A mixture of OPC-50 Inducer AM and OPC-50 Inducer CM (both manufactured by Okuno Chemical Industries Co., Ltd.) Activation treatment solution M4: A mixture of OPC-150 Crystal RW (manufactured by Okuno Pharmaceutical Industries) and boric acid Electroless metal plating solution M5: A mixture of ATS Addcopper IW-A, ATS Addcopper IW-M, ATS Addcopper IW-C, and electroless copper RN (all manufactured by Okuno Chemical Industries Co., Ltd.)

[0104] 19 is a graph showing the results of analyzing the interface between the substrate 3 and the electroless plated layer 50 using a TEM-EDS (JEM-2100PLUS, manufactured by JEOL Ltd.). In FIG. 19, the horizontal axis represents the travel distance (nm) in the depth direction dZ from the interface between the substrate 3 and the electroless plated layer 50. Also, in FIG. 19, the vertical axis represents the value (cps / ROI) obtained by dividing the detected count number of palladium (Pd), a substance that constitutes the catalyst, by the effective time; a larger value indicates a larger amount of Pd.

[0105] 19, it can be seen that Pd derived from the catalyst is present in a region 30 nm in the depth direction dZ toward the substrate 3 from the interface between the substrate 3 and the electroless plated layer 50. From the results in FIG. 19, it is estimated that the thickness of the microporous layer 4a formed by the voids 4 formed in the substrate 3 is within a range of 30 nm to 40 nm.

[0106] Incidentally, when the substrate 3 is irradiated with ultraviolet light L10, some of the polymer chains constituting the substrate 3 are cleaved, as described above, and low-molecular-weight substances are secondarily generated. For this reason, it is expected that substances other than the polymer material constituting the substrate 3 will be detected by mass spectrometry using TOF-SIMS on the substrate 3 after irradiation with ultraviolet light L10. Furthermore, if the ultraviolet light L10 reaches only the vicinity of the surface 3a of the substrate 3, it is expected that low-molecular-weight substances will be detected only in this region.

[0107] A liquid crystal polymer resin defined by the following formula (6) was prepared as the substrate 3, and ultraviolet light L10 was irradiated onto the substrate 3 in an atmosphere 1 with an oxygen concentration of 0.1% by volume using the same method as above. Next, mass analysis was performed using the TOF-SIMS method while sputtering the surface of the substrate 3 using an Ar gas cluster ion beam (Ar-GCIB). Both sputtering and mass analysis were performed using a TOF-SIMS5 manufactured by ION-TOF. For comparison, mass analysis was also performed on a substrate 3 made of the same material using the same method without irradiating it with ultraviolet light L10.

[0108] In mass spectrometry, the data was normalized using the spectral intensity of C6H5O, which is assumed to be obtained by cleaving a portion of the molecular chain of the liquid crystal polymer resin defined by formula (6). The results are shown in Figure 20.

[0109] [ka]

[0110] In principle, no signal derived from C6H5O is generated for a base material 3 that is not irradiated with ultraviolet light L10. On the other hand, the results in Figure 20 confirm that the intensity of the signal derived from C6H5O generated from a base material 3 irradiated with ultraviolet light L10 decreases as the depth direction increases. Furthermore, when the intensity of the signal derived from C6H5O generated from a base material 3 irradiated with ultraviolet light L10 reaches a depth position where it is approximately the same as the intensity of the signal derived from C6H5O for a base material 3 that is not irradiated with ultraviolet light L10, it is suggested that ultraviolet light L10 is no longer substantially irradiated in regions deeper than this depth position.

[0111] That is, the results of FIG. 20 suggest that the substrate 3 was modified into a microporous layer 4a over a region of about 50 nm from the surface 3a in the depth direction.

[0112] As described above, when the substrate 3 is irradiated with ultraviolet light L10, some of the polymer chains that make up the substrate 3 are cut. For this reason, it is thought that the strength of the substrate 3 near its surface will decrease compared to before it was irradiated with ultraviolet light L10. Therefore, the strength of the substrate 3 in the depth direction was evaluated by a micro-slurry-jet erosion (MSE) test.

[0113] The MSE test is an impact abrasion test using solid particles, in which a fixed amount of particles is projected onto the same location on the surface of the test piece, causing erosion wear due to the impact, and the depth of the abrasion is measured. When a graph is created by repeatedly measuring the depth and shape, if there are layers of different hardness on the substrate surface, the rate of abrasion progress will change, resulting in a graph with a different slope.

[0114] A polyimide resin (Kapton 100EN-C manufactured by Toray DuPont Co., Ltd.) similar to that used in Verification 1 was prepared as the substrate 3. This substrate 3 was irradiated with ultraviolet light L10 in an atmosphere 1 with an oxygen concentration of 0.1% by volume, using the same method as described above. Next, a slurry jet containing alumina particles was locally sprayed onto the surface of the substrate 3 using an injector, and the maximum wear depth of the local area formed by the spray was measured with a shape measuring device. The erosion rate (= maximum wear depth μm / amount of projected particles g) was calculated from the ratio of the degree of wear (depth) to the amount of projected particles in the local area. The amount of projected particles was calculated based on the slurry flow rate using a predetermined relationship for an alumina slurry containing alumina particles.

[0115] The equipment used for the verification is as follows: Injection device: Localized slurry injection abrasion device (Palmeso, MSE-A), nozzle diameter 1mm x 1mm, projection distance 4mm Shape measuring instrument: Stylus-type shape measuring instrument (Kosaka Laboratory, PU-EU1), stylus tip R=2μm, load 80μN, measurement magnification 20,000, measurement length 1mm, measurement speed 0.1mm / sec

[0116] 21A is a graph in which the vertical axis represents depth (erosion depth) and the horizontal axis represents erosion rate. In the verification, three types of substrate 3 were used: (b) a substrate 3 in which the ultraviolet ray L10 was irradiated for 25 seconds, (c) a substrate 3 in which the ultraviolet ray L10 was irradiated for 120 seconds, and (a) a substrate 3 in which the ultraviolet ray L10 was not irradiated for comparison.

[0117] From the above definition, a high erosion rate means that the abrasion depth is deep with the same amount of projected particles, and therefore the mechanical strength of the substrate 3 in the depth direction region where the slurry jet was sprayed within that time is weak. Conversely, a low erosion rate means that the abrasion depth is shallow with the same amount of projected particles, and therefore the mechanical strength of the substrate 3 in the depth direction region where the slurry jet was sprayed within that time is strong. For ease of understanding, the "strength" and "weakness" of the mechanical strength are indicated schematically in Figure 21A.

[0118] 21A, the graphs (b, c) corresponding to the substrate 3 irradiated with ultraviolet light L10 are inclined near the surface, and after progressing in the depth direction up to a certain value, they show almost the same slope as the graph (a) corresponding to the substrate 3 not irradiated with ultraviolet light L10. This result means that irradiation with ultraviolet light L10 causes a tendency for the intensity near the surface of the substrate 3 to decrease compared to deeper areas. In other words, it is suggested that irradiation with ultraviolet light L10 forms a microporous layer 4a near the surface 3a of the substrate 3.

[0119] Even when not irradiated with ultraviolet light L10, the intensity is slightly reduced in a location very close to the surface 3a, which is thought to be caused during the resin manufacturing process.

[0120] Figure 21B shows the graph of Figure 21A with approximation lines superimposed on it. Approximation line k1 is an approximation line of the test results corresponding to the original strength of the base material 3 (polyimide resin) that has not been irradiated with ultraviolet light L10. Approximation lines k2 and k3 correspond to approximation lines of the region of the graph of the results for the base material 3 that has been irradiated with ultraviolet light L10, where the slope is significantly inverted compared to approximation line k1.

[0121] By comparing the approximation line k1 with the approximation lines k2 and k3, it can be seen that the depth region indicated by the approximation lines k2 and k3 is the region where the strength of the substrate 3 has decreased due to irradiation with ultraviolet light L10, i.e., the region where the microporous layer 4a has been formed. Therefore, it can be concluded that in the substrate 3 irradiated with ultraviolet light L10 for 25 seconds, the microporous layer 4a has been formed up to the depth region at the intersection of the approximation lines k1 and k2. Similarly, it can be concluded that in the substrate 3 irradiated with ultraviolet light L10 for 120 seconds, the microporous layer 4a has been formed up to the depth region at the intersection of the approximation lines k1 and k3.

[0122] 21B, when a polyimide resin is used as the substrate 3 and ultraviolet light L10 is irradiated for 25 seconds, it is estimated that a region of the substrate 3 extending from the surface 3a to a depth of about 30 nm is modified into a microporous layer 4a. Similarly, when a polyimide resin is used as the substrate 3 and ultraviolet light L10 is irradiated for 120 seconds, it is estimated that a region of the substrate 3 extending from the surface 3a to a depth of about 50 nm is modified into a microporous layer 4a.

[0123] (Verification 3: Cleaning with alkaline solution) The effect of alkaline cleaning after treating the substrate 3 with ultraviolet light L10 was examined. The same material as in Test 1 was used as the substrate 3 sample.

[0124] The surface of the sample was irradiated with ultraviolet light L10 from a distance of 3 mm using an ultraviolet irradiation device (Ushio Inc.: SVC 232 Series, peak wavelength 172 nm) in an atmosphere with an oxygen concentration of 0.2% by volume. The peak adhesive strength was then measured using the same method as in Verification 1 without alkaline cleaning treatment, yielding Example 8, and the peak adhesive strength was measured using the same method as in Verification 1 after alkaline cleaning treatment, yielding Example 9. The results are shown in Figure 22. For comparison, Figure 22 also shows the peak adhesive strength of a sample not irradiated with ultraviolet light L10 as Comparative Example 2.

[0125] In Example 9, the alkaline cleaning treatment was carried out specifically by the following method.

[0126] After being irradiated with ultraviolet light L10, the sample (substrate 3) was immersed for 2 minutes in a NaOH aqueous solution with a molar concentration of 2.5 mol / L (10% by mass concentration) heated to 65° C. The sample was then removed and immersed in pure water for 1 minute to be washed.

[0127] 22, it can be seen that the adhesive strength of the substrate 3 is further increased by treating the substrate 3 with ultraviolet light L10 and then cleaning it with alkali. In the case of the sample of Example 8, which was not cleaned with alkali, the adhesive molecules contained in the adhesive sheet bond to the low molecular chains generated secondarily by the irradiation with ultraviolet light L10. These adhesive molecules do not contribute to the adhesion that occurs during lamination. In other words, it is presumed that the adhesive strength was lower than in Example 9 because some of the introduced adhesive did not contribute to the adhesion between the substrate 3 and other layers.

[0128] In the case of Example 9, the substrate 3 is treated with ultraviolet light L10, and then alkaline cleaning is performed, whereby the surface of the substrate 3 from which the low molecular chains have been removed is bonded via an adhesive sheet. As a result, most of the introduced adhesive can be captured in the voids 4 (see FIG. 12) in the microporous layer 4a (see FIG. 18) created by the treatment with ultraviolet light L10. This is thought to be why the adhesive strength is even higher than in Example 8.

[0129] From this perspective, it is believed that the effect of further increasing the adhesive strength can be similarly obtained by removing the low molecular weight material by a method other than alkaline cleaning after ultraviolet treatment. [Explanation of symbols]

[0130] 1: Atmosphere 2: System 3: Base material 3a: Surface of the substrate 4 :Void 4a: Microporous layer 5:Light source device 6: Irradiation window 7: Chamber 7a: Space inside the chamber 7b: Space inside the chamber 8: Processing space 10: Xe excimer lamp 16: Gas supply pipe 17: Gas outlet 18: Loading entrance 19:Export exit 21: Sub-chamber 22: Sub-chamber 31: Nitrogen gas source 32: Oxygen-containing gas source 33: Gas mixer 34: Nitrogen gas source 35: Exhaust port 40: Transport path 50: Electroless plating layer 90: Low pressure mercury lamp 100: Atmosphere L10: Ultraviolet light L90: Ultraviolet light

Claims

1. A step (a) of preparing a substrate made of an insulating resin material; a step (b) of irradiating the surface of the substrate with ultraviolet light having a wavelength of 200 nm or less in an atmosphere having an oxygen concentration of 0.01% by volume to 10% by volume, thereby modifying a treatment target region including the surface of the substrate into a microporous layer containing pores of nanometer order size; (d) applying a catalyst or adhesive to introduce the catalyst or adhesive into the voids in the microporous layer; A surface modification method, characterized in that the treatment target area is an area between the surface and a point 3 nm to 50 nm from the surface in a depth direction perpendicular to the surface.

2. 2. The surface modification method according to claim 1, further comprising, after the step (b), a step (c) of removing low-molecular-weight components contained in the substrate and having a lower molecular weight than the resin material constituting the substrate.

3. 3. The surface modification method according to claim 2, wherein the step (c) is a step of immersing the substrate after the step (b) in an alkaline solution.

4. The step (a) includes a step of placing the substrate on a transport path, The step (b) includes a step of irradiating the substrate with ultraviolet light from an ultraviolet light source in a treatment space containing the ultraviolet light source while transporting the substrate, During the execution of the step (b), nitrogen gas is introduced into the processing space, 3. The surface modification method according to claim 1, wherein the step (b) is completed at the latest when the substrate has passed through the treatment space.

5. The step (a) includes a step of placing the substrate at a predetermined position in a chamber, The step (b) includes a step of closing a space including the predetermined location in the chamber in an atmosphere containing a mixed gas containing oxygen and nitrogen at a concentration of 0.01% by volume to 10% by volume, and then irradiating the substrate with ultraviolet rays from an ultraviolet light source installed in the chamber. The surface modification method according to claim 1 or 2, characterized in that it includes a step of irradiating the substrate with ultraviolet rays from an ultraviolet light source installed in the chamber.

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