JP7499019B2 - Light emitting device and method for manufacturing the same - Google Patents

Description

The present invention relates to a light-emitting device that includes a light-emitting element that emits ultraviolet light.

Ultraviolet light with an emission wavelength of 400 nm or less is used in a variety of fields, such as detecting counterfeit banknotes using fluorescent ink, curing resins, and sterilizing water or air. In recent years, light-emitting devices that use semiconductor light-emitting elements such as ultraviolet light-emitting diodes (hereinafter referred to as LEDs) have become widespread as light-emitting devices that irradiate ultraviolet light, replacing conventional light-emitting devices that use mercury vapor as a light source. Furthermore, as this type of light-emitting device becomes more widespread, various problems have become apparent, and solutions to these problems have been disclosed.

For example, Cited Document 1 discloses a technology for preventing the deterioration of the characteristics of light-emitting elements caused by the increase in resistance of the semiconductor layer due to hydrogen present in the package by filling the inside of the package with a sealing gas containing oxygen and sealing it.

For example, Cited Document 2 discloses a technology that prevents the deterioration of the characteristics of light-emitting elements caused by a polymerization reaction between oxygen and hydrocarbons present in the package by providing a hydrogen storage material in a hermetically sealed package.

Furthermore, for example, Cited Document 3 discloses a technology that enables reliable sealing by switching from a first gas containing oxygen to a second gas that reduces the oxygen concentration during package sealing, without inhibiting heating and melting due to oxidation of the bonding material.

JP 2007-67373 A JP 2000-133868 A JP 2018-93137 A

For semiconductor light-emitting elements, multiple light-emitting elements are manufactured from one wafer. When multiple light-emitting elements are manufactured from one wafer, the output is distributed from elements with high light-emitting output to elements with low light-emitting output for a given applied voltage. However, in light-emitting devices using light-emitting elements, the light-emitting output of the shipped light-emitting device is required to be constant. Therefore, the manufactured light-emitting elements are selected according to their light-emitting output, and only the light-emitting elements having the desired light-emitting output are used in the light-emitting device. This results in a problem of a decrease in the effective number of light-emitting elements obtained from one wafer, which leads to an increase in costs.

The present invention has been made in consideration of the above points, and aims to provide a light-emitting device and a manufacturing method thereof that has a desired light-emitting output, regardless of the difference in the light-emitting output of each of the multiple light-emitting elements obtained from one wafer.

The light emitting device according to the present invention is characterized by having a substrate, a light emitting element arranged on one surface of the substrate, having a light emitting surface that emits ultraviolet light, and having a carbon layer on the light emitting surface that contains a substance made of hydrocarbon or carbon, and a housing member made of a material that transmits the ultraviolet light and arranged opposite the light emitting surface of the light emitting element, and forming a housing space that houses and seals the light emitting element together with the substrate.

The method for manufacturing a light-emitting device according to the present invention is characterized by including the steps of: applying a volatile solder paste onto the metal wiring of a substrate having metal wiring formed on one surface; placing a light-emitting element having a light-emitting surface that emits ultraviolet light on the volatile solder paste applied to the metal wiring; heating the volatile solder paste to bond the metal wiring and the light-emitting element; placing a housing member having a light-transmitting portion that transmits ultraviolet light on one surface of the substrate to seal the light-emitting element with the housing member and the substrate and form a housing space; and passing electricity through the light-emitting element via the metal wiring to form a carbon layer containing a substance made of hydrocarbon or carbon on the light-emitting surface of the light-emitting element.

1 is a top view of a light emitting device 10 according to a first embodiment of the present invention. 1B is a cross-sectional view of the light emitting device 10 taken along line AA in FIG. 1A. 3 is a flow diagram showing a manufacturing process of the light emitting device 10 according to the first embodiment of the present invention. 3A to 3C are explanatory diagrams showing a manufacturing process of the light emitting device 10 according to the first embodiment of the present invention. 3A to 3C are explanatory diagrams showing a manufacturing process of the light emitting device 10 according to the first embodiment of the present invention. 3A to 3C are explanatory diagrams showing a manufacturing process of the light emitting device 10 according to the first embodiment of the present invention. 3A to 3C are explanatory diagrams showing a manufacturing process of the light emitting device 10 according to the first embodiment of the present invention. 3A to 3C are explanatory diagrams showing a manufacturing process of the light emitting device 10 according to the first embodiment of the present invention. 1 is a graph showing a TOF-SIMS spectrum of the light emitting surface of a light emitting element 30 after current is passed through the light emitting device 10 according to the embodiment of the present invention. 4 is a graph showing the relationship between the power-on time and the light output maintenance rate of the light-emitting device 10 according to the embodiment of the present invention. 10 is a graph showing the relationship between the power-on time and the light output maintenance rate of a light-emitting device 10 according to a modified example of the present invention. 1 is a cross-sectional view showing an example of a sealing structure of a light emitting device according to the present invention. 1 is a cross-sectional view showing an example of a sealing structure of a light emitting device according to the present invention.

The following describes in detail an embodiment of the present invention. In the following description and accompanying drawings, the same reference numerals are used to refer to substantially the same or equivalent parts.

Figure 1A shows a schematic top view of the light-emitting device 10. Figure 1B shows a cross-sectional view taken along line A-A in Figure 1A.

Note that FIG. 1A is a hypothetical top view in the absence of window member 40, and window member 40 is positioned at the position indicated by the dashed line in FIG. 1A.

The light-emitting device 10 has a substrate 20 with a concave cavity formed on one surface. The light-emitting device 10 also has a light-emitting element 30 and a protective element 31 housed in the cavity of the substrate 20. The light-emitting device 10 also has a window member 40 fixed so as to cover the cavity of the substrate 20.

The substrate 20 has a rectangular planar shape and is made of ceramics with high thermal conductivity and airtightness, such as aluminum nitride (AlN). In this embodiment, we will explain the case where AlN is used as the substrate 20.

A concave cavity having a bottom surface 23 and a side surface 24 is formed on the top surface 21, which is one surface of the substrate 20. In other words, a concave cavity having a bottom surface 23 surrounded by a frame-shaped sidewall portion 22 extending around the periphery of one surface of the substrate 20 is formed on the substrate 20.

At the center of the bottom surface 23 of the cavity, an element mounting portion 25 having a rectangular planar shape is formed, for example, by plating tungsten (W), nickel (Ni), gold (Au), etc. on a conductive layer of metal, etc.

The light-emitting element 30 is a semiconductor light-emitting element with a rectangular top surface shape, such as a light-emitting diode (LED) that emits ultraviolet light, and is mounted on the element mounting portion 25. As shown in FIG. 1B, in this embodiment, the light-emitting element 30 has a support substrate 30a and a semiconductor layer 30b that is supported by the support substrate 30a and includes a light-emitting layer. The support substrate 30a is made of, for example, a substrate such as conductive silicon (Si).

The semiconductor layer 30b is, for example, a gallium nitride (GaN)-based semiconductor layer that is composed of a p-type semiconductor layer, a light-emitting layer, and an n-type semiconductor layer in that order from the support substrate 30a side, and emits ultraviolet light with a wavelength of 410 nm or less from the light-emitting layer. In this embodiment, a case where the semiconductor layer 30b including a light-emitting layer that emits ultraviolet light with a wavelength of 365 nm is used will be described.

The light-emitting element 30 has, for example, a support substrate 30a, a semiconductor layer 30b formed on the upper surface of the support substrate 30a, a first electrode (not shown) formed on the lower surface of the support substrate 30a, and a second electrode (not shown) formed on the upper surface of the semiconductor layer 30b.

The light-emitting element 30 is bonded to an element mounting portion 25 formed in the cavity of the substrate 20 via an element bonding layer 50. A first electrode provided on the lower surface of the support substrate 30a is electrically connected to the element mounting portion 25 via the element bonding layer 50.

The element bonding layer 50 is, for example, a gold-tin alloy (AuSn alloy). The element bonding layer 50 is formed by melting a volatile solder paste made of, for example, AuSn alloy particles and a flux having a boiling point near the melting point of the AuSn alloy. The flux is, for example, made of rosins, alcohols, sugars, esters, fatty acids, oils and fats, polymerized oils, surfactants, organic acids, etc., which are carbonized by ultraviolet light in a volatilized gaseous state.

The second electrode provided on the upper surface of the light-emitting element 30 is electrically connected to the second wiring 27 by a bonding wire BW such as a gold (Au) wire.

The first and second wirings 26 and 27 are metal wirings formed on the bottom surface 23 of the cavity and the lower surface 28 of the substrate 20. The first and second wirings 26 and 27 are formed, for example, by plating a conductive layer of metal or the like with tungsten (W/Ni/Au) or the like. The first and second wirings 26 and 27 are electrically connected to the metal wiring formed on the bottom surface 23 of the cavity and the metal wiring formed on the lower surface 28 of the substrate 20 via a through electrode TH provided on the substrate 20.

The first and second wirings 26 and 27 are formed on the bottom surface 23 of the cavity so as to be spaced apart from each other and from the element mounting portion 25, for example, so as to surround the central region of the bottom surface 23, specifically the element mounting portion 25 and the light emitting element 30. The first wiring 26 is formed continuously with the element mounting portion 25 so as to be connected to the element mounting portion 25 on one side of the element mounting portion 25, and is electrically connected to the element mounting portion 25.

In addition, an alignment slit AS is formed at the connection between the first wiring 26 and the element mounting portion 25, extending along one side of the element mounting portion 25. When the light-emitting element 30 is mounted on the element mounting portion 25, the position and orientation of the light-emitting element 30 are self-aligned by this alignment slit AS and each side of the element mounting portion 25 that is spaced apart from the wiring 26 and 27.

A ring-shaped substrate frame edge layer 29 is formed on the upper surface 21 of the side wall portion 22 of the substrate 20. The substrate frame edge layer 29 is a metal layer plated with, for example, W/Ni/Au or the like. The substrate frame edge layer 29 may extend to the side surface 24 within the cavity of the substrate 20.

The protective element 31 is, for example, a reverse voltage protection element such as a Zener diode. The protective element 31 operates to keep the voltage supplied to the light-emitting element 30 constant. The protective element 31 is, for example, mounted on the first wiring 26 and the second wiring 27, and is bonded to the electrodes formed on both ends of the element and the first and second wirings 26 and 27 by volatile solder paste. The protective element 31 is bonded to the bottom surface 23 of the cavity, and the first and second wirings 26 and 27 may be connected by wire bonding.

The window member 40 serving as the housing member is made of a translucent material that transmits the ultraviolet light emitted by the light-emitting element 30. The window member 40 is, for example, quartz glass or borosilicate glass.

The window member 40 is held by the substrate 20 so as to cover the cavity of the substrate 20. In addition, a ring-shaped window frame edge layer 41 is provided along the edge of the window member 40 on the lower surface of the window member 40 that faces the upper surface 21 of the substrate 20. The window frame edge layer 41 is a metal layer made of, for example, chromium (Cr)/nickel (Ni)/gold (Au).

The substrate 20 and the window member 40 are joined via a window joining layer 60. The window joining layer 60 is made of, for example, an annular AuSn alloy sheet that does not contain flux. The AuSn alloy sheet is melted and eutectic-joined with the substrate frame edge layer 29 and the window frame edge layer 41 to form a storage space HS that hermetically seals the inside of the cavity of the substrate 20.

In other words, a concave cavity is formed on the upper surface 21 of the substrate 20, and the cavity and the window member 40 form the storage space HS. The substrate 20 and the window member 40 are joined together by a metal layer that does not contain organic matter, and the storage space HS is sealed in an airtight manner.

The housing space HS is filled with a sealing gas that is not altered by ultraviolet light, for example, nitrogen (N ₂ ) gas filled at 1 atmosphere.

In addition, as a carbon layer, a carbon film 70 that is not altered by ultraviolet light and absorbs a part of the ultraviolet light is formed on the light-emitting surface of the light-emitting element 30. The carbon film 70 is, for example, a film containing a substance made of carbon or a hydrocarbon whose main component is carbon. Specifically, it is, for example, a layer of an inorganic carbon film containing graphite, amorphous carbon, or diamond-like carbon (DLC). In inorganic carbon such as graphite, amorphous carbon, and DLC, the carbon at the terminal or near the lattice defect is stabilized by, for example, bonding with hydrogen to dangling bonds or other dangling bonds.

The carbon film 70 is formed when flux residue contained in the volatile solder paste that is the element bonding layer 50 is re-volatilized within the storage space HS, carbonized by the ultraviolet light emitted by the light-emitting element 30, and deposited on the light-emitting surface of the light-emitting element 30.

In other words, the light emitting device 10 of Example 1 includes a substrate 20, a light emitting element 30 that is disposed on the bottom surface 23 of the cavity of the substrate 20, has a light emitting surface that emits ultraviolet light, and has a carbon film 70 containing a substance made of hydrocarbon or carbon on the light emitting surface, and a window member 40 that is made of a material that transmits ultraviolet light, is disposed opposite the light emitting surface of the light emitting element 30, and forms a storage space HS that, together with the substrate 20, stores and seals the light emitting element 30.

The carbon film 70 attenuates the ultraviolet light emitted from the light-emitting surface of the light-emitting element 30. In other words, for example, by controlling the film thickness of the carbon film 70, it is possible to adjust the optical output of the ultraviolet light emitted from the light-emitting element 30 to which a specified current is supplied.

In addition, in this embodiment, the light emitting device 10, the substrate 20, the cavity of the substrate 20, the element mounting portion 25, or the light emitting element 30 have a rectangular (square in this embodiment) top surface shape when viewed from a direction perpendicular to the mounting surface of the light emitting device 10. However, the above-mentioned respective top surface shapes are not limited to rectangular, and may be various shapes such as circular, elliptical, and rectangular.

Figure 2 is a flow diagram showing the manufacturing process of the light emitting device 10 of this embodiment. Figures 3A-3E are cross-sectional views of the light emitting device 10 showing each step in Figure 2. The manufacturing method of the light emitting device 10 described above will be explained with reference to Figures 2 and 3A-3E.

First, as a mounting substrate, an AlN-based substrate 20 is prepared, which includes a cavity formed in a concave shape on one of the surfaces, the top surface 21, first and second wirings 26 and 27 formed on the bottom surface 23 of the cavity and the bottom surface 28 of the substrate 20, a through electrode TH that penetrates from the bottom surface 23 of the cavity to the surface on the bottom surface 28 side of the substrate 20 to connect the metal wiring, and a ring-shaped substrate frame edge layer 29 formed on the top surface 21 of the side wall portion 22 of the substrate 20.

2 and 3A, a volatile solder paste, which is a raw material of the element bonding layer 50, is applied onto the element mounting portion 25 of the first wiring 26 (step S11). When applying the volatile solder paste onto the element mounting portion 25, it is preferable to apply it using a dispenser filled with the volatile solder paste.

Next, as shown in FIG. 3B, the light-emitting element 30 is placed on the element mounting portion 25 on which the volatile solder paste has been applied (step S12). Specifically, the light-emitting element 30 is placed so that the first electrode (not shown) provided on the lower surface of the light-emitting element 30 is in contact with the volatile solder paste.

The substrate 20 in this state is heated to, for example, 300° C. in a nitrogen atmosphere to melt the AuSn alloy particles in the volatile solder paste, and the first wiring 26 and the light emitting element 30 are fixed by the element bonding layer 50 (step S13). At this time, the first wiring 26 and the light emitting element 30 are eutectic bonded and electrically connected by the AuSn alloy. The fixed position and orientation of the light emitting element 30 are self-aligned by the AuSn alloy melted on the element mounting portion 25 of the first wiring 26, the alignment slit AS formed in the first wiring 26, and each side of the element mounting portion 25 that is separated from the wirings 26 and 27.

When the volatile solder paste is heated and melted, most of the flux contained in the volatile solder paste volatilizes.

Next, as shown in FIG. 3C, the substrate 20 on which the light-emitting element 30 is mounted is set in a wire bonding device, and the second electrode (not shown) formed on the upper surface of the light-emitting element 30 is connected to the second wiring 27 with a bonding wire BW such as an Au wire (step S14). Note that the order of connecting the Au wire can be either the second electrode of the light-emitting element 30 or the second wiring 27 first. This electrically connects the second electrode of the light-emitting element 30 to the second wiring 27.

Next, the wire-bonded substrate 20 is heated , for example, at 330° C. for 20 seconds in an air atmosphere to volatilize the flux remaining in the element bonding layer 50 (step S15). The lower limit of the temperature at which the remaining flux is volatilized is preferably equal to or higher than the melting temperature of the AuSn alloy particles at which the remaining flux is volatilized (300° C. in this embodiment). The upper limit of the temperature at which the remaining flux is volatilized is preferably equal to or lower than the temperature at which the element characteristics of the semiconductor layer 30b of the light-emitting element 30 deteriorate (for example, 330° C.).

Then, the substrate 20 from which the residual flux has been volatilized is irradiated with, for example, excimer light to clean the flux residue adhering to the surfaces of the substrate 20 and the light-emitting element 30 (step S16). In this embodiment, the surfaces of the substrate 20 and the light-emitting element 30 were cleaned by irradiating with excimer light having an emission wavelength of 172 nm for 10 minutes at an output of 2000 mJ/cm2. Note that cleaning of the surfaces of the substrate 20 and the light-emitting element 30 is not limited to cleaning with excimer light. For example, other cleaning methods may be used, such as plasma cleaning, cleaning with ozone gas, or cleaning with a solvent, as long as they can remove the organic flux residue adhering to the surfaces of the substrate 20 and the light-emitting element 30.

Next, the substrate 20 from which the flux residue has been cleaned is placed in a predetermined atmosphere (nitrogen gas at atmospheric pressure in this embodiment) and the window bonding layer 60, which is a ring-shaped AuSn sheet, is placed on the substrate frame edge layer 29. Furthermore, the window member 40 on which the window frame edge layer 41 has already been formed is placed on the window bonding layer 60 with the surface of the window frame edge layer 41 facing the substrate 20. In other words, the window bonding layer 60 and the window member 40 are placed in a position such that the substrate frame edge layer 29 of the substrate 20, the window bonding layer 60, and the window frame edge layer 41 overlap.

In this state, the window member 40 is pressed against the substrate 20 to make it adhere closely to the substrate 20. Then, while the window member 40 is pressed, it is heated , for example, to 300° C. to melt the window bonding layer 60 and bond the substrate 20 and the window member 40 (step S17). At this time, as shown in FIG. 3D, the substrate frame edge layer 29 and the window frame edge layer 41 of the substrate 20 are eutectic bonded by the AuSn alloy of the window bonding layer 60, and a hermetically sealed storage space HS is formed.

Next, a predetermined current is supplied to the light-emitting element 30 via the first and second wirings 26 and 27 of the hermetically sealed substrate 20 to age the light-emitting element 30 and form a carbon film 70 on the light-emitting surface of the light-emitting element 30 as shown in FIG. 3E (step S18).

The light-emitting element 30 generates heat by itself when driven to emit light during aging. The self-heating of the light-emitting element 30 causes the flux remaining in the element bonding layer 50 to re-evaporate into the housing space HS. The re-evaporated flux is exposed to ultraviolet light emitted by the light-emitting element 30 near the light-emitting surface and is carbonized. The carbonized flux is deposited on the light-emitting surface of the light-emitting element 30 as a carbon film 70, the main component of which is carbon.

In step S18, the light emitting device 10 may be heated while being supplied with current.

The carbon film 70 is selectively deposited on the light-emitting surface of the light-emitting element 30 as the re-volatilized flux is carbonized only near or on the light-emitting surface of the light-emitting element 30, where ultraviolet light is emitted at a high optical output density. The carbon film such as graphite described above is conductive, but is selectively deposited on the light-emitting surface of the light-emitting element 30 for the above-mentioned reasons, so that no defects such as short circuits occur between the first and second electrodes of the light-emitting element 30 or between the first and second wirings 26 and 27 of the substrate 20.

The above steps are used to manufacture the light emitting device 10 of this embodiment.

As Example 2, a light emitting device 10 was manufactured without performing the flux volatilization process (step S15) and the excimer light cleaning process (step S16) in the manufacturing flow of FIG. 2. In Example 2, the light emitting device 10 was manufactured using the same manufacturing process as Example 1 except for the above.

In Example 3, the flux volatilization process (step S15) and the excimer light cleaning process (step S16) in the manufacturing flow of FIG. 2 were not performed, and the gas atmosphere during window member bonding (step S17) was filled with nitrogen gas and then reduced to 1.0 kPa with a vacuum pump to produce a light emitting device 10. Other manufacturing steps in Example 3 were the same as those in Example 1 to produce the light emitting device 10.

In Example 4, the flux volatilization process (step S15) and the excimer light cleaning process (step S16) in the manufacturing flow of FIG. 2 were not performed, and in addition, the gas atmosphere during window member bonding (step S17) was a mixed gas of oxygen gas and nitrogen gas (oxygen gas 20 volume %, nitrogen 80 volume %) at atmospheric pressure, to manufacture a light emitting device 10. Other manufacturing processes in Example 4 were the same as those in Example 1 to manufacture the light emitting device 10.

In Example 5, the flux volatilization process (step S15) and the excimer light cleaning process (step S16) in the manufacturing flow of FIG. 2 were not performed, and in addition, the gas atmosphere during window member bonding (step S17) was a mixed gas of oxygen gas and nitrogen gas (1 vol% oxygen gas, 99 vol% nitrogen) at atmospheric pressure, to manufacture a light emitting device 10. Other manufacturing steps in Example 5 were the same as those in Example 1 to manufacture the light emitting device 10.

In other words, the manufacturing method of the light emitting device 10 of Examples 1 to 5 includes the steps of applying a volatile solder paste onto the first wiring 26 of the substrate 20, in which the metal wirings 26 and 27 are formed on the bottom surface 23 of the cavity; placing a light emitting element 30 having a light emitting surface that emits ultraviolet light on the volatile solder paste applied to the first wiring 26; heating the volatile solder paste to bond the first wiring 26 and the light emitting element 30; placing a window member 40 having a light transmitting portion that transmits ultraviolet light on the upper surface 21 of the substrate 20, sealing the light emitting element 30 with the window member 40 and the substrate 20 and forming a storage space HS; and passing a current through the light emitting element 30 via the first and second wirings 26 and 27 to form a carbon film 70 containing a substance made of hydrocarbon or carbon on the light emitting surface of the light emitting element 30.

In addition, the manufacturing method of the light-emitting device 10 of Examples 1 to 5 further includes a process of volatilizing the flux remaining in the volatile solder paste after the volatile solder paste is heated , and a process of cleaning the flux residue adhering to the surfaces of the substrate 20 and the light-emitting element 30 with excimer light.

Note that, although nitrogen gas is used as the sealing gas in Examples 1 to 3 and as the gas to be mixed with oxygen gas in Examples 4 and 5, this gas is not limited to nitrogen gas. The sealing gas and the gas to be mixed with oxygen gas may be, for example, an inert gas such as argon (Ar), xenon (Xe), or krypton (Kr) gas. In addition, one or more types of nitrogen, argon, xenon, or krypton gas may be mixed and used.

In addition, in the light emitting device 10 described in Examples 1 to 5, the sealing gas is filled at atmospheric pressure or reduced pressure, but a sealing gas with an increased sealing pressure may also be used.

[evaluation]
Table 1 shows the evaluation of continuous lighting of the light emitting devices 10 of Examples 1 to 5 described above.

To evaluate Examples 1 to 5, we checked the deposition of the carbon film 70 on the light-emitting device 10 after continuous lighting, checked the electrical characteristics, and checked the light output maintenance rate relative to the initial light output.

The deposition of the carbon film 70 was confirmed, for example, by using the naked eye and an optical microscope to confirm whether the carbon film 70 had been deposited on the light-emitting surface of the light-emitting element 30 after continuous lighting. The deposition of the carbon film 70 was determined by checking the discoloration of the light-emitting surface of the light-emitting element 30.

The electrical characteristics were confirmed by checking the voltage-current characteristics (VI characteristics), forward leakage voltage (Vf), and reverse leakage voltage (Vr) of the light-emitting device 10 after continuous lighting. By checking the VI characteristics, it was determined whether the resistivity of the semiconductor layer 30b of the light-emitting element 30 had changed. In addition, by checking Vf and Vr, it was determined whether the conductive carbon film 70 had abnormally accumulated between the first and second electrodes of the light-emitting element 30 or between the first and second wirings 26 and 27 of the substrate 20.

The light output maintenance rate is the rate of change in the light output of the light emitting device 10 after 100 hours of continuous lighting, relative to the light output of the light emitting device 10 at the start of lighting.

In the light emitting device 10 of Example 1, no discoloration was observed on the light emitting surface of the light emitting element 30 after continuous lighting. In addition, no abnormal values were observed in the V-I characteristics, Vf, and Vr. In addition, the light output maintenance rate was 90.9%, and output attenuation of about 10% was confirmed from the light output at the start of lighting.

After continuous lighting, the light emitting device 10 of Example 2 showed gray to black discoloration on the light emitting surface of the light emitting element 30, and deposition of the carbon film 70 was confirmed. Furthermore, no abnormal values were observed in the V-I characteristics, Vf, and Vr. Furthermore, the light output maintenance rate was 58.7%, and it was confirmed that the output had attenuated by approximately 40% from the light output at the start of lighting.

After continuous lighting, the light emitting device 10 of Example 3 showed black discoloration on the light emitting surface of the light emitting element 30, and deposition of the carbon film 70 was confirmed. Furthermore, no abnormal values were observed in the V-I characteristics, Vf, and Vr. Furthermore, the light output maintenance rate was 9.7%, and it was confirmed that the output had attenuated by approximately 90% from the light output at the start of lighting.

In the light-emitting device 10 of Example 4, no discoloration was observed on the light-emitting surface of the light-emitting element 30 after continuous lighting. In addition, no abnormal values were observed in the V-I characteristics, Vf, and Vr. In addition, the light output maintenance rate was 96.4%, and almost no attenuation was observed from the light output at the start of lighting, which was within the normal aging range of the light-emitting element 30.

After continuous lighting, the light emitting device 10 of Example 5 showed gray to black discoloration on the light emitting surface of the light emitting element 30, and deposition of the carbon film 70 was confirmed. Furthermore, no abnormal values were observed in the V-I characteristics, Vf, and Vr. Furthermore, the light output maintenance rate was 54.0%, and it was confirmed that the output had attenuated by about half from the light output at the start of lighting.

From the results of Examples 1 and 2, it was confirmed that in the light-emitting element 30 in which the storage space HS is filled with nitrogen gas, the light output is attenuated by about 10% to about 40% depending on whether or not the flux volatilization process and the excimer light cleaning process (steps S15 and 16 in FIG. 2) are performed. In other words, by adjusting the processing temperature and processing time of the volatilization process and the processing conditions and processing time of the excimer light cleaning process, it is possible to adjust the light output of the light-emitting element 30 by about 10% to about 40% from the initial light output.

From the results of Examples 2 and 3, it was confirmed that in a light-emitting device 10 in which the flux volatilization process and the excimer cleaning process were not performed, the light output was attenuated by about 40% to about 90% by reducing the pressure of the nitrogen gas sealing gas. In other words, by adjusting the pressure of the nitrogen gas atmosphere during the window member bonding process (step S17 in FIG. 2), it is possible to adjust the light output of the light-emitting element 30 by about 40% to about 90% of the initial light output.

From the results of Examples 4 and 5, it was confirmed that in a light-emitting device 10 that does not undergo the flux volatilization process and excimer cleaning process, by varying the oxygen concentration of the mixed gas of nitrogen gas and oxygen gas, which is the sealing gas, from 1% by volume to 20% by volume, the light output is attenuated by approximately half the light output in the aging range. In other words, by adjusting the oxygen concentration of the sealing gas during the window member bonding process, it is possible to adjust the light output of the light-emitting element 30 by approximately half the initial light output.

Next, referring to FIG. 4, we will explain the deposits that have accumulated on the light-emitting surface of the light-emitting element 30.

Figure 4 is a spectrum diagram showing the measurement results of time-of-flight secondary ion mass spectrometry (TOF-SIMS) on the light-emitting surface of the light-emitting element 30 in Example 4, in which the light output maintenance rate was almost not attenuated, and Example 5, in which the light output maintenance rate was reduced to about half. The upper spectrum in Figure 4 shows the measurement results in Example 4, and the lower spectrum in Figure 4 shows the measurement results in Example 5.

The horizontal axis (m/z) of Figure 4 indicates the mass-to-charge ratio of the secondary ions, and the vertical axis (Intensity) indicates the detection intensity. The spectra on the left, center, and right of Figure 4 are extracted and illustrated in the vicinity of the mass-to-charge ratio of the secondary ions of the detected peaks.

In the measurement results of Example 4, in which almost no deposition of carbon film 70 or attenuation of light output maintenance rate was observed, a peak derived from silicon oxide (SiO ₂ ) was detected. The SiO ₂ detected on the surface of the light-emitting element 30 in Example 4 is due to the protective film (not shown) that covers the semiconductor layer 30b of the light-emitting element 30. Furthermore, in Example 4, no peak derived from carbon was detected, indicating that no deposition of carbon film 70 occurred.

In the measurement results of Example 5, in which deposition of carbon film 70 and attenuation of light output maintenance rate were observed, a peak derived from carbon (C ₂ ) was detected, which indicates that deposition of carbon film 70 occurred in Example 5. In addition, from the detected peak, the deposited film was identified as graphite, amorphous carbon, or DLC.

In other words, in Examples 1 to 3 and 5, where discoloration and deposits were observed on the light-emitting surface of the light-emitting element 30 after step S18 of the manufacturing process, this indicates that the flux re-volatilized in the storage space HS during the light-emitting element aging and carbon film formation process (step S18 in FIG. 2) was carbonized by the ultraviolet light emitted by the light-emitting element 30 and deposited as a carbon film 70 mainly composed of carbon on the light-emitting surface of the light-emitting element 30.

Figure 5 is a graph showing the change over time in the power supply time and light output when the light-emitting devices 10 of Examples 1 to 5 are continuously lit.

In Examples 1 to 3 and 4, there are two regions where the light output attenuates steeply from the start of power application, and then gradually attenuates.

The region where the light output decays sharply indicates that a carbon film 70 has been deposited on the light-emitting surface of the light-emitting element 30. The region where the light output decays gently indicates that the semiconductor layer 30b of the light-emitting element 30 has been aged.

In the region where the light output is rapidly attenuated, the flux remaining in the element bonding layer 50 within the housing space HS is re-volatilized, carbonized by the ultraviolet light of the light-emitting element 30, and deposited as a carbon film 70 on the light-emitting surface of the light-emitting element 30. As the carbon film 70 accumulates on the light-emitting surface of the light-emitting element 30, the ultraviolet light emitted from the light-emitting surface is blocked by the carbon film 70, causing the light output to rapidly attenuate.

As shown in FIG. 5, the steep attenuation of the light output due to the deposition of the carbon film 70 disappears after about 30 hours of current flow, and then the light output transitions to a gradual attenuation due to aging of the light-emitting element 30. The amount of attenuation of the light output due to the carbon film 70 is derived from the amount of flux remaining in the element bonding layer 50.

That is, in Example 1, in which the volatilization process and the excimer light cleaning process were performed, the amount of residual flux was small, so the amount of deposition of the carbon film 70 was also small, and the amount of attenuation of the light output was also small.

In addition, in Example 2, in which the volatilization process and the excimer light cleaning process were not performed, the amount of residual flux was large, so the amount of deposition of the carbon film 70 was large, and the amount of attenuation of the light output was also large.

In addition, in Example 3, in which the volatilization process and the excimer light cleaning process were not performed and the storage space was reduced in pressure, the residual flux was easily re-volatilized from the element bonding layer 50 due to the reduced pressure, resulting in a very large amount of carbon film 70 deposition and extremely large attenuation of the light output.

In Example 4, no steep attenuation of the light output was observed. This is because the mixing of 20% by volume of oxygen gas into the sealing gas has the effect of preventing the deposition of the carbon film 70.

In addition, as in Example 5, when the oxygen gas is changed to a 1% by volume mixture, a carbon film 70 is deposited and the light output is attenuated.

According to the present invention, as in Examples 1 to 3, by using nitrogen gas as the sealing gas and adjusting the residual flux volatilization treatment conditions, excimer light cleaning conditions, and sealing gas pressure, it is possible to obtain a light emitting device 10 that has an arbitrary light output relative to the initial light output after the light emitting element aging and carbon film formation processes.

In addition, according to the present invention, even when the sealing gas is a mixture of nitrogen gas and oxygen gas as in Examples 4 and 5, it is possible to obtain a light emitting device 10 having an arbitrary light output relative to the initial light output after the light emitting element aging and carbon film formation process by adjusting the oxygen gas concentration and sealing gas pressure.

This makes it possible to manufacture a light emitting device 10 having a desired light output even when the light emitting element has an output equal to or greater than the desired light output. It also makes it possible to increase the effective number of light emitting elements obtained from one wafer, thereby reducing the cost of the light emitting device 10 that emits ultraviolet light.

The initial light output of the light-emitting element 30 is confirmed by a probe test after manufacturing multiple light-emitting elements on a wafer. At this time, the multiple light-emitting elements are selected into several light outputs according to the light output possessed by each light-emitting element, and the amount of attenuation from the initial light output to the desired light output is determined. The selected light-emitting elements are manufactured under the process conditions, sealing gas type, and sealing gas pressure conditions of the flux volatilization process and the excimer light cleaning process.

This makes it possible to manufacture a light emitting device 10 with the desired light output even when multiple light emitting elements have different light outputs.

In the above-mentioned Examples 1 to 5, a light-emitting device 10 using a light-emitting element 30 that emits ultraviolet light with an emission wavelength of 365 nm has been described. However, the emission wavelength of the ultraviolet light emitted by the light-emitting element 30 is not limited to this.

As a modified example, the following describes a light-emitting device 10 that uses a light-emitting element 30 that emits deep ultraviolet light with an emission wavelength of 275 nm.

As a first modification, a flux volatilization process and an excimer light cleaning process were performed, and a light-emitting device 10 was manufactured using atmospheric nitrogen gas as the sealing gas. The first modification uses the same manufacturing materials and method as the first embodiment, except that a light-emitting element 30 that emits deep ultraviolet light was used as the light-emitting element 30.

As a second modification, a light-emitting device 10 was manufactured without performing the flux volatilization process and the excimer light cleaning process. The second modification uses the same manufacturing materials and method as the second embodiment, except that a light-emitting element 30 that emits deep ultraviolet light is used as the light-emitting element 30.

As a third modification, the flux volatilization process and the excimer light cleaning process were not performed, and a light-emitting device 10 was manufactured using a mixture of atmospheric oxygen gas and nitrogen gas (oxygen gas 20 volume %, nitrogen 80 volume %) as the sealing gas. The third modification uses the same manufacturing materials and method as the fourth embodiment, except that a light-emitting element 30 that emits deep ultraviolet light is used as the light-emitting element 30.

The aging time of the light-emitting element 30 that emits deep ultraviolet light in this modified example is 240 hours.

Table 2 shows the evaluation of continuous lighting of the light-emitting devices 10 of the above-mentioned variations 1 to 3.

The light output maintenance rate of this modified example is the rate of change in the light output of the light-emitting device 10 after 240 hours of continuous lighting.

In the light emitting device 10 of variant 1, no discoloration was observed on the light emitting surface of the light emitting element 30 after continuous lighting. In addition, no abnormal values were observed in the V-I characteristics, Vf, and Vr. In addition, the light output maintenance rate was 76.0%, and output attenuation was confirmed from the light output at the start of lighting.

After continuous lighting, the light-emitting device 10 of variant 2 showed a gray to black discoloration on the light-emitting surface of the light-emitting element 30, and deposition of a carbon film 70 was confirmed. Furthermore, no abnormal values were observed in the V-I characteristics, Vf, and Vr. The light output maintenance rate was 51.9%, and it was confirmed that the output had attenuated by about half from the light output at the start of lighting.

In the light-emitting device 10 of the third modified example, no discoloration was observed on the light-emitting surface of the light-emitting element 30 after 100 hours of continuous lighting. Furthermore, no abnormal values were observed in the V-I characteristics, Vf, and Vr. Furthermore, the light output maintenance rate was 79.8%, and it was confirmed that the output had attenuated by approximately 20% from the light output at the start of lighting. However, this light output maintenance rate is within the normal aging range of the light-emitting element 30 that emits deep ultraviolet light and is used in this modified example.

Figure 6 is a graph showing the change over time in the power supply time and light output when the light-emitting devices 10 of variants 1 to 3 are continuously lit.

First, in the third modification, as in the fourth embodiment, no deposition of carbon film 70 was observed on the light-emitting surface of the light-emitting element 30. In other words, in the third modification, the attenuation of the light output observed up to about 120 hours of current flow is due to aging of the light-emitting element 30.

Although variant 1 shows the same behavior as variant 3, the attenuation of the light output maintenance rate is slightly larger. This is because variant 1 has undergone volatilization processing and excimer light cleaning processing, so the amount of residual flux contained in the element bonding layer 50 is small. Therefore, in variant 1, the amount of deposition of the carbon film 70 is also small, and the attenuation of the light output is also small.

In the second modification, the amount of residual flux contained in the element bonding layer 50 is large because the volatilization process and the excimer light cleaning process are not performed. Therefore, in the second modification, the amount of deposition of the carbon film 70 is also large, and the amount of attenuation of the light output is also large.

According to Modifications 1 to 3, even in a light-emitting device 10 using a light-emitting element 30 that emits deep ultraviolet light, it is possible to obtain the same effects as in Examples 1 to 5 by adjusting the sealing gas type, the residual flux volatilization processing conditions, the excimer light cleaning conditions, and the sealing gas pressure.

In other words, even in a light-emitting device 10 using a light-emitting element 30 that emits deep ultraviolet light, by depositing a carbon film 70 during the aging and carbon film formation process (step S18 in FIG. 2), it is possible to obtain a light-emitting device 10 that has an arbitrary light output relative to the initial light output.

In Examples 1 to 5 and Modifications 1 to 3, a light emitting device 10 has been described in which a substrate 20 having a cavity and a flat window member 40 are combined to form a storage space HS, but the configuration of the light emitting device 10 is not limited to this.

7A and 7B are cross-sectional views showing examples of other sealing structures of the light-emitting device 10. The same components as those in the light-emitting device 10 described above are given the same reference numerals and will not be described.

Figure 7A is a cross-sectional view of a light-emitting device 10A that is composed of a flat substrate 20a, a frame body 80 arranged to surround the periphery of the light-emitting element 30, and a window member 40a held by the frame body 80 so as to cover the light-emitting element 30.

The frame 80 serving as the side wall member is made of a material such as Kovar (an iron (Fe)-nickel (Ni)-cobalt (Co) alloy).

The upper surface of the frame body 80 (the surface opposite to the surface facing the substrate 20a, no reference number) has a joint (no reference number) where the window member 40a is joined so as to be inserted into the frame body 80. The frame body 80 and the window member 40a are prepared in advance as a window member with a frame body, for example, by airtightly fusing the window member 40a, which is glass, to the joint of the frame body 80 at 900°C.

The window member with the frame is eutectic-bonded to the substrate frame edge layer 29 by the window bonding layer 60 in the window member bonding process (step S17 in FIG. 2).

In other words, the light emitting device 10A in FIG. 7A has a plate-shaped substrate 20, and a frame-shaped frame body 80 is arranged on one surface of the substrate 20, and is spaced apart from the light emitting element 30 and the first and second wirings 26 and 27 and surrounds the light emitting element 30 and the first and second wirings 26 and 27, and the storage space HS is formed by the substrate 20, the frame body 80, and the window member 40a.

By configuring the light emitting device 10A as shown in FIG. 7A, it is possible to adopt a flat substrate 20a. As a result, in the element bonding process (step S13 in FIG. 2) and the flux volatilization process (step S15 in FIG. 2), the flux volatilized from the element bonding layer 50 does not remain in the cavity of the substrate 20 as in the light emitting device 10, and it is possible to make it difficult for the flux residue to adhere to the side surface 24 of the cavity. In addition, since the substrate 20a is flat, it is possible to improve the cleaning properties of the flux residue in the excimer light cleaning process (step S16 in FIG. 2). Therefore, in the light emitting device 10A, it is easy to control the amount of residual flux in the storage space HS in the light emitting element aging and carbon film formation process (step S18 in FIG. 2), and it is possible to more precisely control the film thickness of the carbon film 70.

Figure 7B is a cross-sectional view of a light-emitting device 10B that is composed of a flat substrate 20a and a window member 40b that has a cavity structure on its underside.

The light emitting device 10B has a similar configuration to the light emitting device 10, except that the substrate 20a is flat and the window member 40b has a cavity structure.

The window member 40b has a cavity on the surface facing the substrate 20a. The cavity of the window member 40b is formed, for example, by etching a thick glass plate with hydrogen fluoride (HF) or the like. The window member 40b is also formed, for example, by pressure welding a flat glass plate and a frame-shaped glass plate.

In other words, in the light emitting device 10B of FIG. 7B, a recess is formed on the surface of the window member 40 that faces the substrate 20, and the substrate 20 and the recess of the window member 40 form the storage space HS.

By configuring the light emitting device 10B as shown in FIG. 7B, it becomes possible to easily clean the flux residue and control the thickness of the carbon film 70, similar to the light emitting device 10A.

In addition, the light emitting device 10B can have an airtight joint at a single location between the substrate 20a and the window member 40b. Therefore, the light emitting device 10B can improve the airtightness of the storage space HS, and can prevent moisture from entering the storage space HS, thereby preventing a decrease in reliability.

In addition, the present invention has been described with reference to an example of a light-emitting element 30 including a support substrate 30a, a semiconductor layer 30b formed on the upper surface of the support substrate 30a, a first electrode formed on the lower surface of the support substrate 30a, and a second electrode formed on the upper surface of the semiconductor layer 30b, but the configuration of the light-emitting element 30 is not limited to this.

For example, the light-emitting element 30 may have a growth substrate used for crystal growth of the semiconductor layer 30b. In this case, for example, the light-emitting element 30 has a growth substrate, a semiconductor layer 30b grown on the growth substrate, and a first electrode and a second electrode formed on the semiconductor layer 30b. In this case, the light-emitting element 30 has a growth substrate bonded to the bottom surface 23 of the cavity of the substrate 20. The first and second electrodes are connected to first and second wirings 26 and 27 provided on the bottom surface 23 of the cavity of the substrate 20 via bonding wires.

As another configuration of the light-emitting element 30, the light-emitting element 30 may have a configuration including a light-transmitting support substrate 30a or growth substrate, a semiconductor layer 30b disposed on the underside of the support substrate 30a or 30b, and a first electrode and a second electrode formed on the underside of the semiconductor layer 30b. In this case, the first and second electrodes are connected to the first and second wirings 26 and 27 via the element bonding layer 50 (also called flip-chip mounting).

In the configuration of the light-emitting element 30, the top surface of the light-emitting element 30, that is, the surface opposite the bottom surface 23 of the cavity of the substrate 20 in the light-emitting element 30, may function as a light extraction surface.

In addition, the various numerical values, dimensions, materials, etc. in the above-mentioned embodiments are merely examples and can be selected appropriately depending on the application and the light emitting device to be manufactured.

REFERENCE SIGNS LIST 10 Light emitting device 20 Substrate 25 Element mounting portion 26 First wiring 27 Second wiring 29 Substrate frame edge layer 30 Light emitting element 40 Window member 41 Window frame edge layer 50 Element bonding layer 60 Window bonding layer 70 Carbon film 80 Frame body

Claims (11)

A substrate;
a light emitting element disposed on one surface of the substrate, the light emitting element having a light emitting surface for emitting ultraviolet light, the light emitting surface having a carbon layer containing a substance made of hydrocarbon or carbon;
a housing member made of a material that transmits the ultraviolet light, disposed opposite the light output surface of the light emitting element, and forming a housing space that houses and seals the light emitting element together with the substrate,
A light emitting device, characterized in that the light output of the ultraviolet light from the light emitting device is reduced by having the carbon layer. A substrate having metal wiring formed on one surface thereof;
a light emitting element disposed on the first surface of the substrate, the light emitting element having a light emitting surface for emitting ultraviolet light, the light emitting surface having a carbon layer containing a substance made of hydrocarbon or carbon;
a housing member made of a material that transmits the ultraviolet light, disposed opposite the light output surface of the light emitting element, and forming a housing space that houses and seals the light emitting element together with the substrate,
the light emitting element is bonded to the metal wiring using a volatile solder paste containing an organic flux;
The light emitting device, wherein the carbon layer is formed by carbonizing the flux contained in the volatile solder paste. The light-emitting device according to claim 1 or 2, characterized in that the carbon layer contains any one of graphite, amorphous carbon, and diamond-like carbon. The light-emitting device according to any one of claims 1 to 3, characterized in that the storage space is filled with nitrogen gas. The light-emitting device according to any one of claims 1 to 3, characterized in that the storage space is filled with argon, xenon or krypton gas. The light-emitting device according to any one of claims 1 to 5, characterized in that the substrate and the housing member are joined by a metal layer, thereby sealing the housing space in an airtight manner. The light-emitting device according to any one of claims 1 to 6, characterized in that a recess is formed on the first surface of the substrate, and the storage space is formed by the recess and the storage member. The light-emitting device according to any one of claims 1 to 6, characterized in that a recess is formed on the surface of the housing member that faces the first surface of the substrate, and the housing space is formed by the substrate and the recess of the housing member. The light-emitting device according to any one of claims 1 to 6, characterized in that the substrate is plate-shaped, metal wiring to which the light-emitting element is joined is formed on the first surface of the substrate, a frame-shaped sidewall member is disposed so as to be spaced apart from the light-emitting element and the metal wiring and to surround the light-emitting element and the metal wiring, and the storage space is formed by the substrate, the sidewall member, and the storage member. applying a volatile solder paste onto a metal wiring of a substrate having a first surface on which the metal wiring is formed;
a step of placing a light emitting element having a light emitting surface that emits ultraviolet light on the volatile solder paste applied on the metal wiring;
heating the volatile solder paste to bond the metal wiring and the light emitting element;
a step of placing a container having a light transmitting portion that transmits the ultraviolet light on the first surface of the substrate, and sealing the light emitting element and forming a container space by the container and the substrate;
a step of applying a current to the light emitting element via the metal wiring to form a carbon layer containing a substance made of hydrocarbon or carbon on the light emitting surface of the light emitting element;
A method for manufacturing a light emitting device, comprising: The method for manufacturing the light emitting device includes a step of volatilizing flux remaining in the volatile solder paste after the volatile solder paste is heated;
a step of cleaning the flux residue adhering to the surfaces of the substrate and the light emitting element with excimer light;
The method for manufacturing a light emitting device according to claim 10, further comprising:

Images