Synthetic quartz glass substrate with antireflection film, window material, cover for optical element package, optical element package, and light irradiation device

Abstract

The present invention relates to a synthetic quartz glass substrate with an antireflection film, a window material, a cap for optical element packaging, optical element packaging, and a light irradiation device. The synthetic quartz glass substrate with an antireflection film includes: a synthetic quartz glass substrate; and an antireflection film formed on a main surface of the synthetic quartz glass substrate, wherein a contact angle of the main surface of the synthetic quartz glass substrate determined by a static drop method of JIS R 3257:1999 is within 5 degrees, and the antireflection film includes a first layer containing Al2O3, a second layer containing HfO2, and a third layer containing MgF2 or SiO2, which are sequentially stacked on the main surface of the synthetic quartz glass substrate.

Description

[0001] Cross-references to related applications

[0002] Pursuant to 35 USC §119(a), this non-provisional application claims priority to patent application number 2020-047579 filed in Japan on March 18, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a synthetic quartz glass substrate with an anti-reflective film, a window material, a cover for encapsulating optical elements, an optical element encapsulation, and a light irradiation device. Background Technology

[0004] UV-LEDs, capable of emitting light in the deep ultraviolet region, have attracted attention. LEDs can extract any wavelength, and LEDs suitable for various applications have been developed. For example, wavelengths of 265-285 nm (in the UVC region) are known to be effective for sterilization, and UV-LEDs emitting light at this wavelength have been developed for sterilization purposes. However, increasing the output of LED chips is not easy, and methods other than increasing chip output are needed to improve light extraction efficiency.

[0005] As a method to improve light extraction efficiency, one approach is to use optical elements in a wired package without sealing them with a window material to prevent light reflection loss caused by the window material. However, considering that many components are typically used in the atmosphere, optical elements are generally sealed using a window material. In particular, it is desirable to use UV-LEDs for water sterilization, and for electrical components used in near-humid environments, the hermetic sealing with a window material is essential. Therefore, from the viewpoint of high transmittance for light in the ultraviolet region and long-term stability, synthetic quartz glass is primarily chosen as the window material.

[0006] For example, Patent Document 1 reports a method in which, when manufacturing a deep ultraviolet light-emitting device, a window material with an anti-reflective film formed of a thin film having a specific film thickness is used while sealing a carrier on which the element is disposed during the manufacturing process.

[0007] In addition, Patent Document 2 reports a method to improve light extraction efficiency by forming a glass material, which is used as a window material, into a lens shape to improve light distribution characteristics.

[0008] Citation List

[0009] Patent Document 1: JP-A2018-109657

[0010] Patent Document 2: WO2019 / 039440 Summary of the Invention

[0011] However, Patent Document 1 does not explicitly describe the state of the substrate before forming the antireflective film, and there are concerns that during the formation of the antireflective film in which thin films are stacked, the transmittance will fluctuate between the substrates because a uniform film cannot be obtained at the interface between the substrate and the first layer. Furthermore, in the case of forming the antireflective film with the above configuration, it is believed that high transmittance cannot be achieved at wavelengths of 260 nm or 300 nm, and the applicable wavelength range is narrow.

[0012] Furthermore, Patent Document 2 reports a method for cutting quartz glass from a base material to form a shape. However, cutting quartz glass sheets independently and with the same precision is very difficult and uneconomical. In addition, in the method of forming by sintering powder, contamination by metallic impurities caused by forming materials such as molds during sintering is unavoidable, and it is speculated that the obtained material will not have long-term reliability for use in applications where it is continuously irradiated with short-wavelength light, such as in the deep ultraviolet region.

[0013] In view of the above, the present invention was made, and the object of the present invention is to provide a synthetic quartz glass substrate with an anti-reflective film, a window material, a cover for optical element packaging, an optical element packaging, and a light irradiation device. The synthetic quartz glass substrate is used stably over a long period of time as a window material for optical element packaging or light irradiation devices for optical elements used in short wavelength, especially in the deep ultraviolet region, and does not change over time in a wide wavelength range, and can obtain high transmittance.

[0014] As a result of research efforts to achieve the above objectives, the inventors discovered that by forming an antireflective film composed of three specific thin films on a synthetic quartz glass substrate having a predetermined contact angle, it is possible to obtain a synthetic quartz glass substrate with an antireflective film that has excellent transmittance over a wide wavelength range, particularly in the ultraviolet region, thereby completing the present invention.

[0015] Therefore, the present invention provides the following synthetic quartz glass substrate with anti-reflective film, window material, cover for optical element packaging, optical element packaging and light irradiation device.

[0016] [1] A synthetic quartz glass substrate with an anti-reflective film, comprising: a synthetic quartz glass substrate; and an anti-reflective film formed on the main surface of the synthetic quartz glass substrate, wherein the contact angle of the main surface of the synthetic quartz glass substrate, as measured by the sessile drop method of JIS R3257:1999, is within 5 degrees; the anti-reflective film comprises a first layer containing Al2O3, a second layer containing HfO2, and a third layer containing MgF2 or SiO2, sequentially stacked on the main surface of the synthetic quartz glass substrate.

[0017] [2] The synthetic quartz glass substrate with an anti-reflective film as described in [1], wherein

[0018] The optical film thicknesses of the first to third layers mentioned above are respectively within the following ranges:

[0019] 0.20λ≤n1d1≤0.30λ;

[0020] 0.45λ≤n²d²≤0.55λ; and

[0021] 0.20λ≤n³d³≤0.30λ,

[0022] Where n is the refractive index, d is the physical film thickness, n1d1 to n3d3 are the optical film thicknesses of the first to third layers, respectively, and λ is the center wavelength of light transmitted through the synthetic quartz glass substrate with the anti-reflective film and is selected from the range of 255 to 300 nm.

[0023] [3] The synthetic quartz glass substrate with anti-reflective coating as described in [1] or [2], wherein, in the height histogram obtained by measuring any 1μm×1μm area on the main surface of the synthetic quartz glass substrate using an atomic force microscope, when the median height is defined as D50 and the height of 0.1% of the highest height is defined as D99.9, the relationship D99.9-D50<5nm is satisfied.

[0024] [4] A window material made of any one of [1] to [3] of a synthetic quartz glass substrate with an anti-reflective coating.

[0025] [5] A cover for packaging optical elements, having an adhesive layer on the outer periphery of the main surface of the window material as described in [4].

[0026] [6] The cover for packaging optical elements as described in [5], wherein the adhesive layer is formed by a resin-based adhesive or a metal-based adhesive.

[0027] [7] An optical element package includes: a box-shaped housing member; an optical element for wavelengths of 255 to 300 nm housed in the housing member; and an optical element package cover covering an opening of the housing member, wherein the optical element package cover as described in [5] or [6] is engaged to the opening of the housing member.

[0028] [8] An optical element package as described in [7], wherein the optical element is a light-emitting element or a light-receiving element.

[0029] [9] An optical element package as described in [8], wherein the optical element is a light-emitting element.

[0030]

[10] A light irradiation device includes: a housing having a light-emitting port; and at least one light source housed in the housing, wherein the light source is an optical element package as described in [9].

[0031]

[11] The light irradiation device as described in

[10] further includes a window material covering the light-emitting port.

[0032]

[12] The light irradiation device as described in

[11] , wherein the window material is the window material as described in [4].

[0033] Beneficial effects of the invention

[0034] According to the present invention, when a synthetic quartz glass substrate with an anti-reflective coating is used as a window material for an optical element package having optical elements for short wavelengths, particularly deep ultraviolet regions, the substrate is stable over a long period of time, does not change over a wide wavelength range, and can achieve high transmittance.

[0035] Furthermore, since the synthetic quartz glass substrate with anti-reflective film of the present invention can reduce light reflection loss, it is expected to improve the light extraction efficiency of light emitted from the LED, even for light-emitting elements such as UV-LEDs with weak output. Attached Figure Description

[0036] Figure 1 A cross-sectional view showing an example of a synthetic quartz glass substrate with an anti-reflective coating according to the present invention; and

[0037] Figure 2 A cross-sectional view showing an example of a surface-mount optical element package using a synthetic quartz glass substrate with an anti-reflective coating according to the present invention as a window material. Detailed Implementation

[0038] The present invention will now be described in detail.

[0039] Synthetic quartz glass substrate with anti-reflective coating

[0040] Figure 1 An example of the cross-sectional structure of the synthetic quartz glass substrate with an anti-reflective film according to the present invention is shown. The synthetic quartz glass substrate 1 with an anti-reflective film shown here has an anti-reflective film 140 formed on one or both main surfaces of the synthetic quartz glass substrate 100 by sequentially stacking a first layer 110 containing Al2O3, a second layer 120 containing HfO2, and a third layer 130 containing MgF2 or SiO2. The synthetic quartz glass substrate 1 with the anti-reflective film having this structure can improve light transmittance, particularly light transmittance at wavelengths of 255 to 300 nm.

[0041] Synthetic quartz glass is a very stable material. However, for example, when synthetic quartz glass is irradiated with light of wavelengths of 255 to 300 nm while its surface is contaminated with organic matter, the organic matter is decomposed or its structure changes, and the transmittance of the substrate may decrease. Similarly, when organic matter is present at the interface between the surface of the synthetic quartz glass substrate 100 and the thin film constituting the antireflective film 140, the organic matter decomposes or its structure changes due to short-wavelength light, and the transmittance of the substrate may decrease. For this reason, it is preferable to form the antireflective film in a state where only the silanol groups of the synthetic quartz glass are exposed on the surface of the substrate 100, that is, in a state where the surface of the synthetic quartz glass substrate 100 is hydrophilic. From this point of view, when forming the antireflective film, the synthetic quartz glass substrate 100 is required to have a contact angle of 5 degrees or less, preferably 3 degrees or less, on its main surface as measured by the static drop method according to Japanese Industrial Standard JIS R 3257:1999. The present invention uses a synthetic quartz glass substrate 100, thereby enabling the obtaining of a synthetic quartz glass substrate 1 with an anti-reflective film that has a light transmittance that does not decrease even when continuously irradiated with light having a wavelength of, for example, 255 to 300 nm.

[0042] A synthetic quartz glass substrate 100 is obtained by forming, annealing, slicing, chamfering, wrapping, polishing for mirror finishing of the substrate surface, and cleaning of a synthetic quartz glass ingot. Here, known methods can be used as the method for polishing the synthetic quartz glass substrate, and the method is not particularly limited. In this invention, both sides can be finished simultaneously by double-sided polishing, or each side can be finished by single-sided polishing.

[0043] As a cleaning method, known methods can be used, and the method is not particularly limited. In this invention, for example, in DIP cleaning, precision cleaning is employed, such as cleaning including an acid or alkali cleaning step, a rinsing step, and a vapor drying step using isopropanol. Furthermore, cleaning including an acid or alkali cleaning step, a rinsing step, and a spin drying step can be performed in single-wafer spin cleaning.

[0044] Examples of acids suitable for acid cleaning include nitric acid, sulfuric acid, fluorinated nitric acid, piranha solution, and hydrochloric acid peroxide (SC-2 solution). Examples of alkalis suitable for alkaline cleaning include sodium hydroxide, potassium hydroxide, ammonia, and ammonia peroxide (SC-1 solution). By immersing the synthetic quartz glass substrate in these acids or alkalis, hydrophobic components present on the substrate surface can be removed. In this way, the inherently hydrophilic surface of the synthetic quartz glass substrate can be exposed, and the contact angle can be adjusted to the range specified in this invention.

[0045] By using isopropanol for vapor drying in a subsequent drying process, the synthetic quartz glass substrate 100 can be kept in a dry state while maintaining the substrate surface in a hydrophilic condition. In this way, a synthetic quartz glass substrate 100 with a surface suitable for forming the antireflective film 140 can be obtained.

[0046] It should be noted that even if the cleaned synthetic quartz glass substrate 100 is stored in a box that causes less venting, it is preferable to perform the cleaning process within 60 minutes, or more preferably within 30 minutes, before the anti-reflective film formation process, because an organic film gradually forms on the substrate surface.

[0047] As described above, the polishing method for synthetic quartz glass substrates can use double-sided polishing for finishing, or single-sided polishing can be applied to both sides for finishing. However, it is important thereafter to perform cleaning that can adequately remove the abrasive used in the polishing process, and to control the surface so that foreign matter does not re-adhere to the surface after cleaning. For example, when cerium oxide-based abrasives or zirconia-based abrasives are used for finishing polishing, it is preferable to use a cleaning solution in which the abrasive can be completely dissolved, such as SC-1 cleaning solution. Furthermore, from cleaning to the formation of the antireflective film, it is preferable to process the substrate in a clean environment, such as a cleaning chamber, so that foreign matter does not adhere to the substrate surface. By keeping the substrate in a clean environment, the possibility of problems such as residual abrasive and foreign matter adhering to the surface of synthetic quartz glass after cleaning can be reduced. When an antireflective film is formed on the substrate surface on which abrasive or foreign matter is present, sometimes the abrasive or foreign matter becomes a step that makes the film easy to peel off, or the desired reflective properties cannot be obtained. In addition, after the formation of the antireflective film, sometimes when the substrate is used in the light irradiation device described later, the foreign matter decomposes due to photoreaction and generates gas. In this situation, voids are created beneath the antireflective film, which promotes film peeling and deterioration of reflective properties.

[0048] Regarding the method for observing residual abrasive and foreign matter adhesion, even if contaminants are not visible by visual inspection, the presence or absence of residual abrasive or foreign matter adhesion can be confirmed by observing any 1μm × 1μm area using an atomic force microscope. In this case, in the height histogram obtained by measuring any 1μm × 1μm area on the main surface of the synthetic quartz glass using an atomic force microscope, when the median height is defined as D50 and the height 0.1% of the highest height is defined as D99.9, if there is residual abrasive or foreign matter adhesion, the adhesion area becomes higher, and the value of D99.9-D50 becomes larger. In this way, residual abrasive and foreign matter on the substrate that may cause problems after film formation can be detected. For this reason, D99.9-D50 < 5nm is preferred for defining a surface with less residual abrasive and foreign matter. When the height 0.05% of the highest height is defined as D99.95, a surface with D99.95-D50 < 5nm is desirable, and more preferably D99.95-D50 < 3nm is preferred. It should be noted that the following approach could also be considered: defining the maximum value of Rmax or the height histogram as D100 with similar parameters and comparing it with the median. However, since D100 is affected by noise that does not affect the atomic force microscope, peeling of the antireflective coating, and small amounts of foreign matter, it is not suitable to use D100 as a definition. Therefore, this invention uses statistically reliable parameters D99.9 and D99.95.

[0049] The raw materials used in vapor-deposited materials can cause point defects, linear defects, planar defects, and volumetric defects, which are considered defects in antireflective films, as shown in Japanese Industrial Standard JIS B 7080-1:2015 or ISO 9211-1:2010. However, defects can also be caused by surface foreign matter on the surface of the synthetic quartz glass substrate formed as described above. In this invention, since the synthetic quartz glass substrate 100 has a surface whose height histogram is controlled by measurements using atomic force microscopy, the probability of problems such as film peeling or swelling (one type of volumetric defect) can be significantly reduced. Furthermore, even during long-term use, it is desirable to eliminate hazardous factors caused by defects, which contributes to the formation of a physically stable film.

[0050] The synthetic quartz glass substrate 100 can be plate-shaped, spherical with an uneven shape, or non-spherical with an uneven shape. From the viewpoints of economy and ease of operation, a plate-shaped substrate is preferred for easy sealing of the housing in which the optical elements are disposed.

[0051] On the other hand, in order to efficiently extract light emitted from optical elements, spherical or non-spherical surfaces can be selected, such as simple plano-convex lens shapes, plano-concave lens shapes, or convex meniscus lens shapes with concave-convex shapes designed based on optical calculations.

[0052] The thickness of the synthetic quartz glass substrate 100 can be appropriately selected by taking into account the attenuation of the wavelength of light from the light-emitting element and the pressure (air pressure or water pressure) difference with the outside of the window material (i.e., the outside of the optical element package). When used for sealing the optical element package, i.e., as a synthetic quartz glass cover, the thickness is preferably 0.1 mm or more, more preferably 0.2 mm or more, and the upper limit of the thickness is preferably 5 mm or less, more preferably 4 mm or less. On the other hand, when used for sealing a light irradiation device, the thickness is preferably 1 mm or more, more preferably 2 mm or more, and the upper limit of the thickness is preferably 50 mm or less, more preferably 45 mm or less.

[0053] Next, the antireflective coating 140 will be described.

[0054] The antireflective film 140 has a first layer 110 containing Al2O3, a second layer 120 containing HfO2, and a third layer 130 containing MgF2 or SiO2, which are sequentially stacked on the entire main surface of the synthetic quartz glass substrate 100, starting from the side of the synthetic quartz glass substrate 100.

[0055] The first layer 110 is a thin film formed directly on the synthetic quartz glass substrate 100. The synthetic quartz glass substrate 100 has a refractive index of 1.4, and the antireflective film 140 is designed to consist of three thin films. Therefore, as a condition, the refractive index of the first layer 110 is required to be greater than the refractive index of the synthetic quartz glass substrate and less than the refractive index of the second layer. Furthermore, for the first layer 110, a material with high adhesion to the synthetic quartz glass substrate 100 and which hardly becomes an inhomogeneous film during film formation is selected. Moreover, since the synthetic quartz glass substrate 1 with antireflective film of the present invention is intended for use particularly at wavelengths of 255 to 300 nm, a material that absorbs light in this wavelength range is not preferred. From the above viewpoint, Al2O3 (refractive index: 1.62) can be considered as a candidate for a thin film selected from commonly available materials, and in the present invention, a thin film containing Al2O3 is selected as the first layer 110. It should also be noted that SiO2 (refractive index: 1.42) is also considered as a material that satisfies the conditions described above. However, considering that the synthetic quartz glass substrate 100 is an amorphous SiO2 with extremely high purity, it is not suitable to form the same type of SiO2 film as the first layer 110.

[0056] The second layer 120 is an intermediate layer of the antireflective film 140. Antireflective films with single or double-layer structures typically have a narrow wavelength range capable of exhibiting high transmittance and usually have a high transmittance region divided into two parts (W type), making them difficult to use practically. In particular, this trend is significant in the deep ultraviolet wavelength region. In view of the above, by forming the second layer 120 as a mitigating layer, it is possible to form an antireflective film 140 that stably exhibits high transmittance throughout the entire wavelength range when used in the 255 to 300 nm wavelength range. In this case, since a thin film containing Al2O3 with a relatively low refractive index was selected in the first layer 110, it is desirable that the second layer 120 be formed of a material with a high refractive index. Furthermore, since a material that absorbs light in the 255 to 300 nm wavelength range cannot be selected, it is desirable to select a thin film containing HfO2 (refractive index: 2.20) as the second layer 120. It should be noted that a thin film containing ZrO2 can also be considered as a candidate as a film with high refractive index and UV resistance. However, ZrO2 is prone to becoming a heterogeneous film, raising concerns such as difficulty in controlling film formation conditions and poor adhesion with the first layer 110 or the third layer 130.

[0057] The third layer 130 is the outermost layer of the antireflective film 140. For the outermost layer, a thin film with properties that reduce reflectivity is selected. That is, it is required to be made of a material with a low refractive index. Since the substrate on which the antireflective film 140 is formed is a synthetic quartz glass substrate 100 with a low refractive index, the refractive index of the third layer 130 as the outermost layer is preferably close to the refractive index of synthetic silicon dioxide. Furthermore, when the substrate is used in the wavelength range of 255 to 300 nm, since it is not possible to select a material that absorbs light in this wavelength range, it is desirable to select a thin film containing MgF2 (refractive index: 1.41) or SiO2 as the third layer 130.

[0058] When a MgF2-containing thin film is selected as the third layer 130, even if the optical film thickness deviates from the design target value by approximately ±0.1λ, the film is sufficient to function as the low-refractive-index material required for the outermost layer due to the fact that MgF2 is a material with stable low refractive index properties, and because the second layer 120 in the antireflective film 140 of the present invention is designed to reduce the deviation in optical path length. It should be noted that MgF2 is a fluoride and has high hygroscopicity. For example, when left in air for a long time, MgF2 absorbs moisture from the air, and as a result, the adhesion between the second layer 120 and the third layer 130 deteriorates, and partial detachment may occur. In this case, the air layer enters the location where detachment occurs, and sometimes the designed transmittance cannot be obtained. Therefore, the synthetic quartz glass substrate 1 with an antireflective film obtained by forming a MgF2-containing thin film on the outermost layer is expected to be used in environments where humidity countermeasures are implemented, such as inert gas environments or dry air environments.

[0059] When a SiO2-containing thin film is chosen as the third layer 130, although SiO2 has a slightly higher reflectivity than MgF2, there are no major problems if the optical film thickness is controlled within ±0.05λ relative to the design target value. Furthermore, since SiO2 is an oxide, its film density is higher than that of MgF2, which is a fluoride, and water molecules are less likely to penetrate the film, thus improving environmental dependence related to film resistance, such as moisture resistance. Therefore, for example, when using a substrate in a humid environment, such as in a water sterilization module application proposed for use with deep ultraviolet LEDs, it is desirable to choose a SiO2-containing thin film as the final layer.

[0060] The antireflective film 140 has the above-mentioned three-layer thin film structure, and by controlling the optical film thickness of each layer, the transmittance for light with wavelengths of 255 to 300 nm can be improved, for example.

[0061] Another method involves designing high-transmittance films by stacking multiple layers with extremely thin film thicknesses; these films are often referred to as equivalent films. However, sometimes it is necessary to control the physical film thickness to within a few nanometers, and there is a risk of film formation failure if thin films are stacked using methods such as vacuum phase deposition.

[0062] Here, considering the reflection at the upper and lower interfaces of the thin film, light entering the thin film undergoes repeated free-end or fixed-end reflection at the interfaces. In the thin film (refractive index n), the wavelength λ0 of light is λ0 / n, and if the optical thickness nd of the thin film is nd = 0.25 × λ0, then theoretically the phase of the light is aligned. Accordingly, antireflective films can be designed by setting the optical thickness of the thin film to an integer multiple of 0.25 × λ.

[0063] On the other hand, from the viewpoint of monitoring accuracy during the formation of the antireflective film 140, i.e., film thickness control, the optical film thickness of each layer is preferably 0.75λ or less. If the optical film thickness is thicker than 0.75λ, problems such as temperature inhomogeneity are likely to occur during film formation, and there is a concern that the film may become uneven. Furthermore, since some high-purity and high-cost target materials are required to form the film constituting the antireflective layer, the closer the optical film thickness of each layer is to 0.25λ, the more economical it is.

[0064] Since the antireflective coating 140 has a three-layer structure, from the perspective of economy and film formation time, n1d1≈n2d2≈n3d3≈0.25λ is the optimal solution. Here, n represents the refractive index, d represents the physical film thickness, and n1d1 to n3d3 represent the optical film thicknesses of the first layer 110 to the third layer 130, respectively. λ represents the center wavelength of light transmitted through the synthetic quartz glass substrate with the antireflective coating and is selected from the range of 255 to 300 nm.

[0065] Here, the characteristic matrix of the monolayer thin film is represented by the following equation (1):

[0066]

[0067] Where i is the imaginary unit (i 2 =-1), n ​​is the same as above.

[0068] Then, the characteristic matrix of the three-layer thin film is represented by the following equation (2):

[0069]

[0070] Where n1 to n3 represent the refractive indices of the first to third layers, respectively, and i is the same as above.

[0071] When using synthetic fused silica as a substrate, and designing the characteristic matrix M by setting the optical film thickness of each layer to 0.25λ, a thin film with a refractive index n2 of 1.19 is required for the second layer 120. However, since there is no material capable of forming a thin film with a refractive index close to this, it is impossible to obtain an antireflective film exhibiting high transmittance in the wavelength range of 255 to 300 nm under the above conditions.

[0072] Based on the above results, considering a film design that does not affect the refractive index of the second layer 120 as an improvement measure, for the characteristic matrix M of the three-layer thin film, only the part related to the second layer 120 is designed as an identity matrix, that is, n2d2=0.5λ, so the reflectivity is not affected. At this time, the characteristic matrix M is represented by the following equation (3):

[0073]

[0074] Where n1, n3, and i are the same as above.

[0075] In this invention, considering the transmittance of the antireflective film, the material constituting the second layer 120 preferably has a higher refractive index than the materials of the first layer 110 and the third layer 130.

[0076] With this design, considering the phase difference at the thin film interface, the reflectivity R of the antireflective film 140 is determined by the refractive index values ​​of the first layer 110 and the third layer 130. When calculating the characteristic matrix of the thin film under the ideal condition where the reflectivity R = 0, it is only necessary to find a thin film that satisfies the condition expressed by the following equation (4):

[0077]

[0078] Where n0 represents the refractive index of the environment in which the antireflective coating is placed, and n m The refractive index of the substrate is represented by n1 and n3, which are the same as those described above.

[0079] To clarify, in this invention, since it is assumed that light passes through the synthetic quartz substrate 1 with the anti-reflective coating and then escapes into the atmosphere, the air refractive index of 1.00 can be set as n0. When synthetic quartz glass is used as the substrate, the given refractive index n... m =1.4. If a thin film containing SiO2 or MgF2 is formed as a thin film with the property of reducing the reflectivity on the third layer 130, given n3≈1.42, n1≈1.69 is obtained, and a thin film containing Al2O3 can be used, which has a refractive index of about 1.62 and is stable.

[0080] Furthermore, considering the following facts: even assuming an ideal state of reflectivity R=0 during film deposition, the light transmittance varies depending on the uniformity of the film and the flatness of the interface, and controlling the physical thickness of the film at the nanometer scale is difficult; depending on the film deposition conditions, the optical film thickness of each of the above layers is preferably designed within the range of ±0.05λ, more preferably within the range of ±0.03λ, relative to the central optical film thickness expressed by the following formula:

[0081] n1d1=n3d3=0.25λ

[0082] n2d2=0.50λ

[0083] Among them, n, d, n1d1 to n3d3 and λ are the same as above.

[0084] The thin films designed as described above can be formed using conventional methods. For example, films can be formed using physical vapor deposition (such as vacuum vapor deposition, RF sputtering, or ion plating) or chemical vapor deposition. From the viewpoint of film formation accuracy, vacuum vapor deposition is preferred, and electron beam deposition is even more preferred.

[0085] A synthetic quartz glass substrate 1 with an anti-reflective film can be obtained by forming thin films, from the first layer 110 to the third layer 130, on the main surface of the synthetic quartz glass substrate 100 using the film-forming method described above. At this time, as... Figure 1 As shown, the anti-reflective film 140 can be formed on at least one side of the main surface of the synthetic quartz glass substrate 100. However, depending on the application, usage environment, etc., the anti-reflective film 140 can be formed on both sides of the main surface of the synthetic quartz glass substrate 100 (not shown).

[0086] As can be seen from the above, the preferred range of optical film thicknesses for the first to third layers of the antireflective film 140 in the synthetic quartz glass substrate 1 with antireflective film is:

[0087] 0.20λ≤n1d1≤0.30λ

[0088] 0.45λ≤n²d²≤0.55λ

[0089] 0.20λ≤n3d3≤0.30λ

[0090] Where n, d, n1d1 to n3d3 and λ are the same as above,

[0091] A more preferred range is:

[0092] 0.22λ≤n1d1≤0.28λ

[0093] 0.47λ≤n²d²≤0.53λ

[0094] 0.22λ≤n3d3≤0.28λ

[0095] Among them, n, d, n1d1 to n3d3 and λ are the same as above.

[0096] The synthetic quartz glass substrate 1 with an anti-reflective coating of the present invention is particularly suitable for use when transmitting light with a wavelength of 255 to 300 nm. For example, in the case of UV-LEDs intended for long-term use, it can stably improve light extraction efficiency over a long period of time.

[0097] Window materials

[0098] The synthetic quartz glass substrate 1 with an anti-reflective coating can preferably be used as a window material (optical element packaging cover) for covering the opening of the housing member of an optical element package, or as a window material for covering the light-emitting port of the housing of a light-emitting device. In particular, the synthetic quartz glass substrate 1 with an anti-reflective coating can be more preferably used as a window material for covering the opening of the housing member, in which an optical element for 255 to 300 nm is housed and the surface facing the element is open.

[0099] Cover for optical component packaging

[0100] On the surface of the window material, for example on the outer periphery of the main surface of the window material, i.e. the part of the window material that contacts the receiving member, the cover for encapsulating the optical element has an adhesive layer of adhesive.

[0101] There are no particular restrictions on the adhesive used, but resin-based or metal-based adhesives are preferred.

[0102] Resin-based adhesives are formed from resin-based pastes containing adhesive resins, and the adhesive resins have a network structure that can form a three-dimensional structure. Therefore, resin-based adhesives can adhere to synthetic quartz glass substrates, as well as to many materials such as ceramics and metal plates.

[0103] Examples of resin-based adhesives include UV-curable adhesives and silicone-based adhesives. Specific examples of resin-based adhesives include TB3114 (manufactured by ThreeBond Holdings Co., Ltd.) and KER-3000-M2 (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0104] On the other hand, examples of metal-based adhesives include those containing one or more elements selected from gold, silver, copper, palladium, tin, bismuth, and tellurium. The metal element can be in a bulk state within the adhesive or in the form of nanoparticles covered by a protective agent. Furthermore, metals comprising solder powder with solder properties can also be used.

[0105] The metal constituting the metal-based adhesive is preferably one or more metals selected from gold, silver, and copper, an alloy containing the metal, or a mixture of the metal and another metal. In the case of alloys or mixtures, the metal selected from gold, silver, and copper preferably constitutes more than 80% by weight of the total metal nanoparticles.

[0106] From a practical standpoint, the average primary particle size (average primary particle size) D of metal nanoparticles... 50The (volume average median particle size) is preferably 20 nm or more, more preferably 30 nm or more, and the upper limit of the average particle size is preferably 90 nm or less, more preferably 80 nm or less. The value measured by dynamic light scattering method can be applied to this particle size.

[0107] As solder powder, commercially available products containing the aforementioned metals can be used, with specific examples including Au-Sn solder and Sn-Bi solder.

[0108] As a method for coating adhesives, known methods can be applied, and specific examples of such methods include dispenser coating, screen printing, and inkjet printing.

[0109] Optical component packaging

[0110] The optical element package of the present invention includes: a box-shaped receiving member (package carrier); an optical element for a wavelength of 255 to 300 nm housed in the receiving member; and an optical element packaging cover covering the opening of the receiving member. The optical element packaging cover is engaged with the opening of the receiving member.

[0111] Figure 2 An example of the optical element packaging of the present invention is shown. In Figure 2 In the optical element package 2, for example, the optical element 250 is arranged at the center of the bottom of a container member (package carrier) 240 formed into a square box shape. An optical element package cover 230, having an adhesive layer 220 on the outer periphery of the main surface of a window material 210 made of synthetic quartz glass with an anti-reflective film, covers the upper opening of the package carrier 240. The window material 210 is then bonded to the upper surface (frame portion) of the package carrier 240 with the adhesive layer 220 between them. This will be explained further. Figure 2 The reflector 260 is shown. Furthermore, the encapsulation carrier 240 may have a recess (not shown) at the bottom as a receiving portion for the optical element 250.

[0112] As the encapsulation carrier 240, known components can be used to house the optical element 250 within the optical element package 2. For example, components formed from inorganic materials (such as metals and ceramics) and organic materials (such as rubber, elastomers, and resins) can be used. It should be noted that when the optical element is a light-emitting element (described later), its luminous efficiency may decrease when the optical element reaches a high temperature due to heat generated by the element. In this case, the encapsulation carrier 240 is preferably made of alumina-based ceramic or aluminum nitride-based ceramic, which has excellent heat dissipation properties, or it can be an encapsulation carrier formed by using a metal plating layer such as gold or copper as a heat dissipation material. Furthermore, the size of the encapsulation carrier 240 is appropriately selected based on the application of the optical element, the size of the optical element to be housed, the size of the window material, etc.

[0113] The optical element 250 disposed inside the encapsulation carrier 240 can be a light-emitting element or a light-receiving element. The optical element encapsulation 2 of the present invention is particularly preferred for optical elements capable of emitting or receiving light with wavelengths below 300 nm. Specific examples of optical elements include light-emitting elements having a center emission wavelength of 255 to 300 nm, light-receiving elements having a peak sensitivity wavelength of 255 to 300 nm, etc.

[0114] Examples of light-emitting elements include UV-LEDs (center wavelength 260 to 300 nm) using aluminum gallium nitride (AlGaN), ArF excimer lasers (wavelength 193 nm), KrF excimer lasers (wavelength 248 nm), and YAG FHG (fourth high frequency) lasers (wavelength 266 nm).

[0115] Examples of light-receiving elements include photodiodes.

[0116] Within the area enclosed by the encapsulation carrier 240 and the window material 210, an optical element 250, leads (not shown) for electrical conduction between the optical element 250 and the optical element package 2, and other components (such as a reflector 260 for improving light extraction efficiency) can be disposed. To prevent deterioration of the optical element 250, the interior of the optical element package 2 is preferably in a vacuum state or filled with inactive gases (such as nitrogen and argon).

[0117] The optical element package of the present invention can be manufactured by joining the optical element package cover of the present invention with a receiving member (package carrier) in which the optical element is housed. At this time, depending on the type of adhesive constituting the adhesive layer of the optical element package cover, the joining between the package carrier and the optical element package cover is performed by appropriate means such as heating or pressurizing.

[0118] Light irradiation device

[0119] The light irradiation device of the present invention includes a housing having a light-emitting port and at least one light source housed in the housing, wherein the light source is an optical element package including a light-emitting element as an optical element.

[0120] The shape of the housing is not particularly limited, as long as it has space to accommodate the light source and a light-emitting port capable of emitting light from the light source. Specific examples of shapes include cylindrical, hollow approximately cylindrical, prismatic, and hollow approximately prismatic. Considering that the housing is also exposed to ultraviolet light, a metallic material such as SUS, which is not easily degraded by ultraviolet light, is preferred as the material forming the housing.

[0121] As a light source, the optical element package of the present invention described above is used. Specific examples of the light source include a UV-LED surface-mount package (UV-LED SMD PKG) sealed with a cover for an optical element package using a synthetic quartz glass substrate with an anti-reflective coating according to the present invention. The UV-LED SMD PKG has a wide range of sizes, such as 3.5 mm square and 6.0 mm square. The UV-LED SMD PKG incorporated into a housing as a module is appropriately selected according to the application. Furthermore, the size of the synthetic quartz glass cover with the anti-reflective coating also follows the size of the UV-LED SMD PKG.

[0122] Only one light source needs to be installed in the housing, and the number of light sources can be appropriately set according to the application and purpose of the light-emitting device. Furthermore, there are no particular restrictions on the arrangement of the light sources, and they can be appropriately set according to the application and purpose. For example, when the light source is used in a resin curing device that requires simultaneous light irradiation over a large area, the light source is arranged in a planar shape facing the light-emitting port. Additionally, in applications requiring pressure resistance (such as water sterilization), for example, in a cylindrical housing made of SUS, the UV-LED SMD PKG is positioned facing the window material that serves as the sealing glass.

[0123] The light irradiation device may further include a window material covering the light-emitting port. The window material can be used without particular limitation, as long as it allows light emitted from an optical element package, such as a synthetic quartz glass substrate, to pass through. In the light irradiation device of the present invention, by sealing the optical element package with such a window material, the influence of the external environment on the optical element arranged in the UV-LED SMD PKG can be further reduced. From the viewpoint of improving the extraction efficiency of short-wavelength light emitted from the light-emitting element, it is preferable to use the synthetic quartz glass substrate with an anti-reflective film as described above as the window material. The synthetic quartz glass substrate with an anti-reflective film may have an anti-reflective film formed on one or both sides. However, in applications where fluid is expected to come into direct contact with the surface of the synthetic quartz glass substrate (such as water sterilization applications), the anti-reflective film may peel off due to friction with the fluid. Therefore, from the viewpoint of abrasion resistance, it is preferable to design the anti-reflective film to be formed only on the surface on the light source side. Furthermore, the window material of the light irradiation device can be bonded with an adhesive or fixed by fastening with a flange or the like.

[0124] To explain, in the case of a light irradiation device that uses highly directional light, such as UV-LED, a diffuser plate made of synthetic quartz glass can be inserted between the UV-LED SMD PKG and the window material attached to the light-emitting port to prevent the light from being projected unevenly onto the object to be irradiated.

[0125] Example

[0126] The present invention will now be described in detail with reference to embodiments and comparative examples. However, the present invention is not limited to the embodiments described below.

[0127] (1) Fabrication of glass substrate with anti-reflective coating

[0128] Example 1

[0129] After wrapping a 4-inch diameter synthetic quartz glass wafer substrate with a planetary double-sided polisher, a mirror finish was achieved using cerium oxide-based abrasive (MIREK E-10 manufactured by Mitsui Mining & Smelting Co., Ltd.) in a planetary double-sided polisher, resulting in a 0.5 mm thick, double-sided mirror-finished synthetic quartz glass wafer substrate. The obtained synthetic quartz glass wafer substrate was then subjected to SC-1 cleaning, rinsing, and vapor drying with isopropanol to clean the substrate surface.

[0130] According to the static drop method of Japanese Industrial Standard JIS R 3257:1999, the contact angle on the main surface of the synthetic quartz glass wafer substrate was measured by dropping water droplets onto the substrate, with both sides having a contact angle of 3.8 degrees. Furthermore, at a measurement point near the center of the main surface of the synthetic quartz glass wafer substrate, a 1 μm × 1 μm area was measured using atomic force microscopy at a resolution of 256 pixels square, and the height histogram distribution was analyzed. When the median height was defined as D50 and the height 0.1% of the highest value was defined as D99.9, the value of D99.9 - D50 was 1.3 nm, and no residual abrasive or foreign matter adhesion was observed.

[0131] Using a synthetic quartz glass wafer substrate as the substrate, thin films, from the first to the third layer, are sequentially formed from the substrate side using vacuum phase deposition. Antireflective films are formed on both sides of the main surface of the substrate. Table 1 shows the composition and optical thickness of each thin film.

[0132] The transmittance of the synthetic quartz glass substrate with antireflective coating under perpendicular incidence was measured using a spectrophotometer (Cary4000 manufactured by Agilent Technologies). Table 2 shows the initial transmittance at each wavelength (λ).

[0133] A synthetic quartz glass substrate with an anti-reflective coating was placed in a constant temperature and humidity environment of 85°C–85%RH for 2400 hours, while being irradiated with 285nm light emitted from a 30-mW UVC-LED, and then the transmittance was measured again. This transmittance was the same as that in the initial state. Furthermore, no problems such as separation in the anti-reflective coating were observed.

[0134] Example 2

[0135] Except for altering the composition and optical film thickness of each layer as shown in Table 1, a synthetic quartz glass substrate with an antireflective coating was manufactured in the same manner as in Example 1, and the transmittance was measured. Table 2 shows the initial transmittance at each wavelength.

[0136] A synthetic quartz glass substrate with an anti-reflective coating was placed in a constant temperature and humidity environment of 60°C–90% RH for 2400 hours, while being irradiated with 265nm light emitted from a 30-mW UVC-LED, and then the transmittance was measured again. This transmittance was the same as that in the initial state. Furthermore, no problems such as separation in the anti-reflective coating were observed.

[0137] Example 3

[0138] Except for altering the composition and optical film thickness of each layer as shown in Table 1, and forming the antireflective film only on one side of the main surface of the substrate, a synthetic quartz glass substrate with an antireflective film was manufactured in the same manner as in Example 1, and the transmittance was measured. Table 2 shows the initial transmittance at each wavelength.

[0139] A synthetic quartz glass substrate with an anti-reflective coating was placed in a constant temperature and humidity environment of 85°C–85%RH for 2400 hours, while being irradiated with 285nm light emitted from a 30-mW UVC-LED, and then the transmittance was measured again. This transmittance was the same as that in the initial state. Furthermore, no problems such as separation in the anti-reflective coating were observed.

[0140] Example 4

[0141] After polishing, the synthetic quartz glass wafer substrate, polished in the same manner as in Example 1, was rinsed with ultrapure water and then vapor-dried with isopropanol. When evaluating the surface condition of the substrate, the contact angle on both sides was 4.1 degrees, and the D99.9-D50 value was 6.3 nm.

[0142] Using a synthetic quartz glass wafer substrate as the substrate, an antireflective film with the same structure as in Example 1 was formed by vacuum phase deposition. Table 2 shows the initial transmittance at each wavelength.

[0143] Synthetic quartz glass substrates with antireflective coatings were placed in a constant temperature and humidity environment of 85°C–85%RH for 2400 hours, while being irradiated with 285nm light emitted from a 30-mW UVC-LED, and then the transmittance was measured again. Although the transmittance decreased by approximately 1% to 1.5% compared to the initial transmittance, there were no serious problems with the transmittance. Furthermore, when the antireflective coating was observed using an optical microscope, occasional voids with diameters of approximately 10 to 100 μm were found.

[0144] Comparative Example 1

[0145] The transmittance due to vertical incidence on a 0.5 mm thick synthetic quartz glass wafer substrate was measured using a spectrophotometer (Cary4000 manufactured by Agilent Technologies). This synthetic quartz glass wafer substrate was identical to that in Example 1 except that no anti-reflective coating was formed. Table 2 shows the initial transmittance at each wavelength.

[0146] Comparative Example 2

[0147] The synthetic quartz glass substrate, polished and cleaned in the same manner as in Example 1, was placed in a grooved acrylic resin housing for accommodating wafers with a diameter of 4 inches and stored for 72 hours. When evaluating the surface condition of the substrate, the contact angle on both sides was 43 degrees, and the D99.9-D50 value was 3.3 nm.

[0148] Using a synthetic quartz glass wafer substrate as the substrate, an antireflective film with the same structure as in Example 1 was formed by vacuum phase deposition. Table 2 shows the initial transmittance at each wavelength.

[0149] When observing the cross-section of the anti-reflective film on a synthetic quartz glass substrate with an anti-reflective coating using SEM, it was confirmed that separation occurred at the interface between the substrate and the first layer, indicating that the film's adhesion was imperfect.

[0150] Comparative Example 3

[0151] The synthetic quartz glass substrate, polished and cleaned in the same manner as in Example 1, was placed in a grooved acrylic resin housing for accommodating wafers with a diameter of 4 inches and stored for 24 hours. When evaluating the surface condition of the substrate, the contact angle on both sides was 11 degrees, and the D99.9-D50 value was 2.9 nm.

[0152] Using a synthetic quartz glass wafer substrate as the substrate, an antireflective film with the same structure as in Example 1 was formed by vacuum phase deposition. Table 2 shows the initial transmittance at each wavelength.

[0153] When observing the cross-section of the anti-reflective film on a synthetic quartz glass substrate with an anti-reflective coating using SEM, it was confirmed that separation occurred at the interface between the substrate and the first layer, indicating that the film's adhesion was imperfect.

[0154] Table 1

[0155]

[0156] Table 2

[0157]

[0158] (2) Fabrication of a cover for encapsulating optical components made of a glass substrate with an anti-reflective coating.

[0159] Example 5

[0160] On the outer periphery of the main surface of the synthetic quartz glass substrate with antireflective film prepared in Example 1, a coating of 33 wt% of a primary particle size D with an average primary particle size of 72 nm was applied using a distributor. 50A metal-based adhesive, composed of silver nanoparticles and 67 wt% Sn-Bi solder powder (ST-5 manufactured by Mitsui Mining & Smelting Co., Ltd.), was used to form an adhesive layer with a linewidth of 0.3 mm. Subsequently, a synthetic quartz glass wafer substrate was diced and cut into 3.4 mm squares along the outer periphery of the adhesive layer to obtain a cover for optical element packaging comprising a window material of synthetic quartz glass and an adhesive layer formed by the metal-based adhesive.

[0161] Example 6

[0162] By screen printing, an organosilicon resin adhesive (KER-3000-M2 manufactured by Shin-Etsu Chemical Co., Ltd.) was applied to the outer periphery of the main surface of the synthetic quartz glass substrate with an anti-reflective film prepared in Example 1, resulting in a line width of 0.5 mm, thus forming an adhesive layer. Subsequently, along the outer periphery of the adhesive layer, the synthetic quartz glass wafer substrate was diced and cut into 3.5 mm squares to obtain an optical element encapsulation cover comprising a window material of synthetic quartz glass and an adhesive layer formed by a metal-based adhesive.

[0163] (3) Fabrication of optical element encapsulation using glass substrates with anti-reflective coatings as window materials

[0164] Example 7

[0165] A UV-LED SMD PKG was fabricated by sealing a 285nm 30-mW UV-LED on a 3.5mm square surface mount device (SMD PKG) carrier based on aluminum nitride with an optical element packaging cap prepared in Example 5. Note that the surface of the junction between the SMD PKG carrier and the synthetic quartz glass cap with an anti-reflective coating is gold-plated.

[0166] Regarding the fabricated optical component package, no leakage was confirmed by the gross leak test as specified in the US military standard MIL-STD-883 Method 1014. Furthermore, in the fine leak test specified in that standard, the helium leakage rate was 5.8 × 10⁻⁶. -8 atm / cc sec. Furthermore, when the LED in the SMD package was opened and the transmittance due to vertical incidence at 285nm was measured, the transmittance was 98.4%.

[0167] Example 8

[0168] Using the optical element package cover of Example 6, the optical element package was fabricated by bonding it to the SMD PKG in the same manner as in Example 7. When the LED in the SMD package was opened and the transmittance due to vertical incidence at 265 nm was measured, the transmittance was 98.4%.

[0169] (4) Fabrication of the light irradiation device

[0170] Example 9

[0171] On the bottom surface of a cylindrical housing made of SUS with bottom and side walls, 16 optical elements (arranged in a four-by-four configuration) fabricated in Example 6 are packaged and arranged in a planar shape. A synthetic quartz glass substrate with an anti-reflective film, fabricated in Example 1, is mounted as a window material on the upper opening of the housing (light-emitting port: the surface facing the light emitted from the UVC-LED), such that the surface on which the anti-reflective film is formed is on the light source side. The window material is fixed to the housing by clamping it in the middle with a flange made of SUS. The transmittance of the light emitted from the UVC-LED mounted inside the housing is 97.5%.

[0172] Based on the above results, the synthetic quartz glass substrate with an anti-reflective coating of the present invention exhibits high transmittance in the wavelength region of 255 to 300 nm. Furthermore, there are no problems in reliability assessments under constant temperature and humidity conditions. Therefore, the synthetic quartz glass substrate with an anti-reflective coating of the present invention can be preferably used in many fields requiring high transmittance or low reflectance.

Claims

1. A synthetic quartz glass substrate with an anti-reflective coating, comprising: Synthetic quartz glass substrate; and An anti-reflective film is formed on the main surface of the synthetic quartz glass substrate, wherein... The contact angle of the main surface of the aforementioned synthetic quartz glass substrate, measured by the static drop method according to JIS R 3257:1999, is within 5 degrees, and The aforementioned anti-reflective film comprises a first layer containing Al2O3, a second layer containing HfO2, and a third layer containing MgF2 or SiO2, sequentially stacked on the main surface of the aforementioned synthetic quartz glass substrate. In the height histogram obtained by measuring any 1μm×1μm region on the main surface of the above-mentioned synthetic quartz glass substrate using atomic force microscopy, when the median height is defined as D50 and the height 0.1% of the highest height is defined as D99.9, the relationship D99.9-D50<5nm is satisfied.

2. The synthetic quartz glass substrate with an anti-reflective film according to claim 1, wherein, The optical film thicknesses of the first to third layers mentioned above are respectively within the following ranges: 0.20 min n1d1 0.30 minutes; 0.45l n2d2 0.55l; and 0.20 min n3d3 0.30l, Where n is the refractive index, d is the physical film thickness, n1d1 to n3d3 are the optical film thicknesses of the first to third layers, respectively, and λ is the center wavelength of light transmitted through the synthetic quartz glass substrate with the anti-reflective film and is selected from the range of 255 to 300 nm.

3. Window material, which is made of a synthetic quartz glass substrate with an anti-reflective film as described in claim 1 or 2.

4. A cover for encapsulating optical components, having an adhesive layer on the outer periphery of the main surface of the window material according to claim 3.

5. The cover for packaging optical components according to claim 4, wherein, The aforementioned adhesive layer is formed by a resin-based adhesive or a metal-based adhesive.

6. Optical component packaging, including: Box-shaped housing component; Optical elements for wavelengths from 255 to 300 nm are housed in the aforementioned housing component; and An optical element encapsulation cover that covers the opening of the aforementioned receiving component, wherein, The cover for encapsulating the optical element according to claim 4 or 5 is joined to the opening of the aforementioned receiving member.

7. The optical element package according to claim 6, wherein, The aforementioned optical elements are light-emitting elements or light-receiving elements.

8. The optical element package according to claim 7, wherein, The aforementioned optical elements are light-emitting elements.

9. A light irradiation device, comprising: A housing with a light-emitting port; and At least one light source is housed within the aforementioned housing, wherein The light source described above is an optical element package according to claim 8.

10. The light irradiation device according to claim 9 further includes a window material covering the light-emitting port.

11. The light irradiation device according to claim 10, wherein, The aforementioned window material is the window material according to claim 3.

Images