Light emitting device

A light emitting device includes: a first light emitting element mounting unit including: a first substrate; a first light emitting element on a first surface of the first substrate; and a first substrate holder which includes a first column, and a first protrusion which extends from the first column toward the first light emitting element and bonded to the first surface of the first substrate; and a second light emitting element mounting unit including: a second substrate; a second light emitting element mounted on a first surface of the second substrate; and a second substrate holder which includes: a second column, and a second protrusion which extends from the second column toward the second light emitting element and bonded to the first surface of the second substrate. The second light emitting element mounting unit is stacked on the first light emitting element mounting unit.

This application claims priority from Japanese Patent Application Nos. 2011-286756, filed on Dec. 27, 2011 and 2012-257836, filed on Nov. 26, 2012, the entire contents of which are herein incorporated by reference.

BACKGROUND

1. Technical Field

Embodiments described herein relates to a light emitting device having a plurality of light emitting elements.

2. Related Art

In recent years, a light emitting device has become known in which a plurality of light emitting elements held by a holding member are stacked so as to emit a plurality of light beams. As such a light emitting element, for example, a semiconductor laser diode has been used, and as such a holding member, for example, a copper-tungsten (CuW) substrate has been used. Since such a light emitting device has a structure in which copper-tungsten (CuW) substrates that are holding members and light emitting elements are alternately stacked, the thickness of the copper-tungsten (CuW) substrates becomes a factor for the pitch of the light emitting elements (see e.g., JP-A-2001-339122 and JP-A-2009-524223).

However, since such a copper-tungsten (CuW) substrate is difficult to make thinner, and the thickness accuracy becomes poor when the substrate is thinned, it has been difficult to stack light emitting elements with a narrow or high pitch accurately.

SUMMARY OF THE INVENTION

Exemplary embodiments of the present invention address the above disadvantages and other disadvantages not described above. However, the present invention is not required to overcome the disadvantages described above, and thus, an exemplary embodiment of the present invention may not overcome any disadvantages described above.

It is one of illustrative aspects of the present invention to provide a light emitting device in which light emitting elements can be stacked with a narrow or high pitch accurately.

According to one or more illustrative aspects of the present invention, there is provided a light emitting device. The light emitting device comprises a first light emitting element mounting unit comprising: a first substrate made of a conductive material and comprising a first surface and a second surface opposite to the first surface; a first light emitting element configured to emit light and mounted on the first surface of the first substrate; and a first substrate holder which supports the first substrate and comprises: a first column which faces a side surface of the first substrate and extends in a thickness direction of the first light emitting element and the first substrate; and a first protrusion which extends from the first column toward the first light emitting element and which is bonded to the first surface of the first substrate; a second light emitting element mounting unit comprising: a second substrate made of a conductive material and comprising a first surface and a second surface opposite to the first surface; a second light emitting element configured to emit light and mounted on the first surface of the second substrate; and a second substrate holder which supports the second substrate and comprises: a second column which faces a side surface of the second substrate and extends in a thickness direction of the second light emitting element and the second substrate; and a second protrusion which extends from the second column toward the second light emitting element and which is bonded to the first surface of the second substrate. The second light emitting element mounting unit is stacked on the first light emitting element mounting unit such that the second column of the second substrate holder is bonded to the first column of the first substrate holder and the first light emitting element is bonded to the second surface of the second substrate via a first bonding material.

According to one or more illustrative aspects of the present invention, there is provided a light emitting device. The light emitting device comprises: a first substrate made of a conductive material and comprising a first surface and a second surface opposite to the first surface; a first light emitting element configured to emit light and mounted on the first surface of the first substrate; a second substrate made of a conductive material and comprising a first surface and a second surface opposite to the first surface; a second light emitting element configured to emit light and mounted on the first surface of the second substrate; a substrate holder which supports the first and second substrates and made of a plate-like member, the substrate holder comprising: a first through hole, wherein the first substrate is inserted into the first through hole and bonded to an inner wall of the first through hole; and a second through hole, wherein the second substrate is inserted into the second through hole and bonded to an inner wall of the second through hole. The first light emitting element is bonded to the second surface of the second substrate via a bonding material.

According to one or more illustrative aspects of the present invention, there is provided a light emitting device. The light emitting device comprises: a first substrate made of a conductive material and comprising a first surface and a second surface opposite to the first surface; a first light emitting element configured to emit light and mounted on the first surface of the first substrate; a second substrate made of a conductive material and comprising a first surface and a second surface opposite to the first surface; a second light emitting element configured to emit light and mounted on the first surface of the second substrate; a substrate holder which supports the first and second substrates and made of a plate-like member, the substrate holder comprising: a first groove, wherein the first substrate is inserted into the first groove and bonded to an inner wall of the first groove; and a second groove, wherein the second substrate is inserted into the second groove and bonded to an inner wall of the second groove. The first light emitting element is bonded to the second surface of the second substrate via a first bonding material.

Other aspects and advantages of the present invention will be apparent from the following description, the drawings and the claims.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. In all the drawings for the explanation of the embodiments, the members having the same functions are represented by the same reference numerals, and repeated description thereof will be omitted.

First Embodiment

First, the structure of a light emitting device according to a first embodiment will be described.FIGS. 1A and 1Bare diagrams illustrating the light emitting device according to the first embodiment.FIG. 1Ais a perspective view andFIG. 1Bis a cross-sectional perspective view showing a part ofFIG. 1A.FIG. 2is a front view illustrating a portion A ofFIG. 1in an enlarged manner (a side from which emission light L is emitted is set to be the front side).FIG. 2is a front view, however for the sake of convenience, there is a portion that undergoes hunting corresponding toFIG. 4(cross-sectional view) to be described later (the same is applied also toFIGS. 16 and 21to be described below).

InFIGS. 1A,1B and2, a light emitting device10has been disposed so as to emit emission light L of a light emitting element80in the horizontal direction, but the direction in which the light emitting device10emits is not limited thereto. For example, the light emitting device10may be disposed so as to emit the emission light L of the light emitting element80in the vertical direction, or the light emitting device10may be disposed so as to emit the emission light L of the light emitting element80in an oblique direction. The emission direction of the emission light L is set as a Z direction inFIG. 1and the like.

Referring toFIGS. 1A,1B and2, the light emitting device10broadly includes a plurality of light emitting element mounting units20and bonding materials30. The plurality of light emitting element mounting units20are provided and each of the light emitting element mounting units20is stacked on top of each other via the bonding material30. As a material of the bonding material30, for example, a conductive material such as gold-tin solder, indium solder, silver paste, or the like can be used. The thickness of the bonding material30can be, for example, about 5 μm. In the present embodiment, three light emitting element mounting units20are stacked on top of each other, but two or four or more units may be stacked.

The light emitting element mounting unit20includes a substrate holder40, a substrate50, an adhesive material60and a bonding material70, and the light emitting element80. The light emitting element mounting unit20is configured to hold the conductive substrate50(in which the light emitting element80is provided in one surface) using the substrate holder40that is made of silicon, and a plurality of the light emitting element mounting units20are stacked on top of each other at a predetermined pitch.

The substrate holder40is disposed on the outside of a side face of the substrate50. The substrate holder40includes a column41and a protrusion42formed integrally with the column41. The column41is formed to extend in the thickness direction of the substrate50and the light emitting element80. The protrusion42is formed to extend from one side face of the column41which faces the substrate50as shown inFIGS. 1A,1B and2in a plane direction (X direction) of the substrate50.

The substrate holder40in the present embodiment is formed in a hook shape in both side faces of the substrate50when viewed in the cross-sectional direction. The bottom face42tof the protrusion42is bonded to a portion including the outer edge portion of one face of the substrate50via the adhesive material60. Further, the protrusion42is formed integrally with one side face of the column41.

The substrate holders40are bonded to each other via an insulating film43. Especially, the upper surface of the column41of one of the substrate holders40is bonded to the lower surface of the column41of the other substrate holder40via the insulating film43. Instead of the insulating film43, the substrate holders may be bonded to each other via an adhesive material.

The insulating film43is, for example, a silicon dioxide film (SiO2). The thickness of the insulating film43can be, for example, about 1 μm. Note that, if the protrusion42and the substrate50can be reliably insulated by using an insulating material as the adhesive material60, the insulating film43may not be formed.

The substrate holder40is formed like a “U” shape when viewed from the top. The protrusion42protrudes toward, for example, the inner side of the “U” shape from one end side of the column41. When the substrate holder40is formed like a “U” shape, the column41is disposed on the outside of both side faces of the substrate50. Further, the protrusion42has outer circumferential portions42rand42qthat face each other, and a center portion42vthat extends in the plane direction of the substrate50to connect the outer circumferential portions42rand42q.

The column41and the protrusion42are formed of the same material in an integrated manner. The height H of the column41defines the pitch of the light emitting element mounting portion20(in other words, the pitch of the light emitting element80). Note that, in the present embodiment, an inner side face42sof the protrusion42(the inner portion of the letter U) is set to be an inclined face, but is not limited to the inclined surface.

The substrate50is a conductive substrate on which the light emitting element80is to be mounted. The reason for using a conductive substrate as the substrate50is that, when current is made to flow in series in each light emitting element80, the substrate50serves as a part of the current route, as described below. As the substrate50, for example, a copper-tungsten (CuW) substrate can be used. The thickness of the substrate50can be, for example, about 100 to 400 μm. The copper-tungsten (CuW) substrate is favorable in that the thermal expansion coefficient thereof matches that of the light emitting element80when the light emitting element80to be mounted is a semiconductor laser diode. The thermal expansion coefficient of the copper-tungsten (CuW) substrate is about 6.5 to 8.5 ppm/° C.

The substrate50has one face and the other face opposite to the one face. On the one face of the substrate50, the light emitting element80is mounted, and the bottom face42tof the protrusion42of the substrate holder40is bonded to the one face of the substrate50. The other face of the substrate50is bonded to a second face (a face of an N-type semiconductor layer82inFIGS. 1A and 2) of another light emitting element80of another adjacent light emitting element mounting portion20via the bonding material30.

The substrate50has a light emitting element mounting region50ain which the light emitting element mounting portion20is formed and a protruding portion50bthat is a region protruding from the light emitting element mounting portion20and extending from the light emitting element mounting region50a. The protruding portion50bextends in the opposite direction to the emission light L (the Z direction inFIG. 1B).

The outer circumferential portion of the one face of the substrate50(the portion facing the outer circumferential portions42rand42qof the protrusion42) and the center portion (the portion facing the center portion42vof the protrusion42) are bonded to the bottom face42tof the protrusion42of the substrate holder40via the adhesive material60. As a material of the adhesive material60, for example, a photosensitive adhesive agent can be used. The thickness of the adhesive material60can be set to, for example, about 5 μm. The photosensitive adhesive agent is favorable in that the agent can be applied with high positional accuracy by using photolithography.

The light emitting element80is a semiconductor laser diode, wherein light is emitted from the end surface of the light emitting element80. The light emitting element80has a structure in which, for example, a P-type semiconductor layer (a first semiconductor layer)81and an N-type semiconductor layer (a second semiconductor layer)82are connected to each other by PN junction. As the semiconductor laser diode, for example, an AlGaAs laser can be used. The light emitting element80is configured to emit the emission light L in the arrow direction ofFIG. 1with a predetermined operational current.

A first face of the light emitting element80is mounted in one end side on the one face of the substrate50via the bonding material70. For example, one face of the P-type semiconductor layer81is mounted in one end side on the one face of the substrate50via the bonding material70. Further, a second face of the light emitting element80opposite to the first face is bonded to the other face of another substrate50of another light emitting element mounting portion20via the bonding material30.

The thickness of the light emitting element80can be, for example, about 100 μm. As a material of the bonding material70, for example, a conductive material such as gold-tin solder, indium solder, silver paste can be used. The thickness of the bonding material70can be, for example, about 5 μm.

FIG. 3is a perspective view illustrating a light emitting device according to a first embodiment of the invention.FIG. 4is a cross-sectional view taken along line A-A ofFIG. 3. The light emitting device shown inFIGS. 3 and 4has a structure in which a face opposite to the light emitting face of each substrate50of the light emitting device10is bonded onto one face of a wiring substrate100via a bonding material110.

That is, an end face of the protruding portion50bthat protrudes from the substrate holder40of the substrate50is bonded to the one face of the wiring substrate100via the bonding material110while each substrate50stands on the one face of the wiring substrate100. Each light emitting element80has a light emitting face that is parallel to the one face of the wiring substrate100, and can emit the emission light L toward the opposite side of the one face of the wiring substrate100.

As the wiring substrate100, a ceramic substrate can be used. As a material of the ceramic substrate, for example, aluminum nitride (AlN), beryllium oxide (BeO) can be used. Further, as the wiring substrate100, other existing substrates such as an organic substrate can be appropriately used. Heat generated from each light emitting element80is transmitted to the wiring substrate100via each substrate50, and then is radiated from the wiring substrate100. As the bonding material110, for example, indium solder can be used.

Further, each lens120is disposed on the optical path of each beam of the emission light L of each light emitting element80. As the lens120, for example, a cylindrical lens can be used. It is necessary for the lens120to be disposed on the optical path of the emission light L of each light emitting element80with high accuracy. The lens120can be disposed on the substrate holder40with high accuracy by, for example, disposing a lens holder (not shown) made of silicon on the light emitting end face of the substrate holder40. On the light emitting end face of the substrate holder40, a groove or a protruding portion for holding the lens120may also be formed in advance by etching.

In the light emitting device10, each of the light emitting elements80are connected to each other in series. That is, current I is made to flow in series from the outermost substrate50in one side to the outermost light emitting element80in the other side via input and output terminals (not shown), and then each of the light emitting elements80simultaneously emits the emission light L.

In this way, if predetermined operational current is made to flow in each of the light emitting elements80of the light emitting device10, the light emitting elements80emit light, respectively. Then, the emission light L of each of the light emitting elements80is condensed at a predetermined position via each of the lenses120, and heat generated from each of the light emitting elements80is transmitted to the wiring substrate100via each of the substrates50and is radiated from the wiring substrate100.

Next, a manufacturing method of the light emitting device according to the first embodiment will be now described.FIGS. 5A to 14are diagrams illustrating the manufacturing method of the light emitting device according to the first embodiment. Particularly,FIGS. 5A to 11Care diagrams illustrating a manufacturing process of the substrate holder40according to the first embodiment. For example, regions on which a plurality of substrate holder40are to be formed are provided on one silicon substrate410, and a plurality of substrate holders40are manufactured by dicing process. InFIGS. 5A to 11C, the regions on which the plurality of substrate holder40are to be formed are not shown for the sake of convenience of description.

First of all, in the process shown inFIGS. 5A and 5B, the silicon substrate410is prepared, and an insulating film430is formed on the surface of the silicon substrate410. As the insulating film430, an SiO2film can be formed by performing thermal oxidation using a wet thermal oxidation method. A temperature around the surface of the silicon substrate410is set to be, for example, 1000° C. or higher. The thickness of the insulating film430can be, for example, about 1 μm. As the insulating film430, a film of, for example, silicon oxide (SiO2), silicon nitride (SiN), polyimide (PI) may be formed by a CVD (Chemical Vapor Deposition) method.

In addition, on a first face of the silicon substrate410of which the surface is formed with the insulating film430, a resist layer500is formed which has “U” shape in a plan view and has an opening portion500xcorresponding to a region where the insulating film430is removed. For example, the resist layer500is formed within the range of a predetermined width from the sides (except one side) of the first face of the silicon substrate410in a plan view. For example, the resist layer500is formed by coating the first face of the silicon substrate410with a photosensitive resin, and then the opening portion500xcan be formed by photolithography.

Next, in the process shown inFIG. 6, the insulating film430exposed through the opening portion500xshown inFIGS. 5A and 5Bis removed by wet etching, and then the resist layer500is removed. As an etching solution for removing the insulating film430, for example, an alkaline solution such as KOH (potassium hydroxide), TMAH (tetramethylammonium hydroxide) can be used. Hereinafter, the insulating film430of which a portion has been removed is referred to as an insulating film430A.

Next, in the process shown inFIG. 7, a groove410xis formed by removing a portion of the silicon substrate410on which the insulating film430A has not been formed by using wet etching. In the process of the wet etching, the insulating film430A is used as a mask. The inner faces of the groove410xbecome inclined faces (a tapered shape). In the process, for example, the same etching solution as in the process shown inFIG. 6can be used.

Next, in the process shown inFIGS. 8A and 8B, a second face of the silicon substrate410(the face in which the groove410xis not formed) is ground using a backside grinder so as to remove the insulating film430A that covers the second face of the silicon substrate. Alternatively, the silicon substrate410is made to be thin, if necessary, together with the removal of the insulating film430A that covers the opposite face thereof.

Next, in the process shown inFIGS. 9A and 9B, a resist layer510having an opening portion510xis formed on the second face of the silicon substrate410in order to form the column41and the protrusion42. For example, in a plan view, the resist layer510is formed with the range of a predetermined width from facing sides among the sides of the first face of the silicon substrate410. The resist layer510is formed by, for example, coating a photosensitive resin on the second face of the silicon substrate410, and then the opening portion510xcan be formed by photolithography.FIGS. 9A to 11Care depicted upside down from the state ofFIG. 1, and the like.

Next, in the process shown inFIGS. 10A and 10B, the silicon substrate410that is exposed through the opening portion510xis removed to the grove410xby dry etching. Accordingly, the silicon substrate410is formed in “U” shape, when viewed from the top. As the dry etching, for example, reactive ion etching (DRIE: Deep Reactive Ion Etching) using SF6(sulfur hexafluoride), or the like is favorably used.

Next, in the process shown inFIGS. 11A to 11C, the peripheral portion of the insulating film430A formed in “U” shape as shown inFIG. 10is cut by, for example, dicing. Accordingly, the substrate holder40is formed to have the column41, the protrusion42including the outer circumferential portions42rand42qand the center portion42v, and the insulation film43, which are formed of silicon.

Next, in the process shown inFIG. 12, at one end side of one face of the substrate50formed of a copper-tungsten (CuW), the light emitting element80that is a semiconductor laser diode is mounted via the bonding material70. The thickness of the substrate50can be, for example, about 100 to 400 μm. As a material of the bonding material70, for example, a conductive material such as gold-tin solder, indium solder, silver paste, or the like, can be used. The thickness of the bonding material70can be, for example, about 5 μm.

Subsequently, the adhesive material60is formed on the substrate50to correspond to the region where the substrate50is bonded to the substrate holder40. The adhesive material60is formed by applying, for example, a photosensitive adhesive agent to the substrate50and patterning the photosensitive adhesive agent through photolithography. The thickness of the adhesive material60can be set to, for example, about 5 μm. In the present embodiment, three structures shown inFIG. 12are prepared.

Next, in the process shown inFIGS. 13A and 13B, via the adhesive material60, the portion including the outer circumferential portion of one face of the substrate50is brought into contact with the bottom face42tof the protrusion42of the substrate holder40prepared in the process shown inFIG. 11. Then, the adhesive material60is hardened by heating, so that the portion including the outer circumferential portion of the one face of the substrate50is bonded to the bottom face42tof the protrusion42via the adhesive material60. In the present embodiment, three structures shown inFIG. 13are prepared.

Next, in the process shown inFIG. 14, the three structures shown inFIG. 13are stacked via the bonding materials30. Then, the upper face of the column41of one substrate holder40is bonded to the bottom face of the column41of another substrate holder40via the insulating film43while the bonding material30is heated. After that, the bonding material30is hardened. Accordingly, the light emitting device10is completed.

As such, in the first embodiment, the plurality of the light emitting element mounting units20on which the light emitting elements80are mounted are stacked on top of each other in the light emitting device10. However, the pitch of the light emitting elements80is determined by the height H of the column41of the substrate holder40that is made of silicon. Since silicon can be processed with extremely high accuracy through the photolithography such as etching, the light emitting elements80can be stacked with high pitch accuracy.

Further, since the thickness of the substrate50on which the light emitting elements80are mounted does not contribute to the pitch of the light emitting elements80, the thickness is not important even if the substrate is made to be thin and then the thickness accuracy is degraded. In other words, by reducing the thickness of the substrate50, the light emitting elements80can be stacked on top of one another with a narrow or high pitch accurately. Unevenness in the thickness of the substrate50is relaxed by the bonding material30.

In the present embodiment, the light emitting elements80can be stacked at, for example, a pitch of 200 μm, and unevenness in the pitch can be suppressed to about ±5 μm. Meanwhile, in a prior-art light emitting device, it is very hard to stack light emitting elements at a pitch of 400 μm or less, and unevenness of the pitch is about ±10 μm.

FIG. 15is a perspective view illustrating a light emitting device according to a first modified example of the first embodiment.FIG. 16is a front view illustrating the portion A ofFIG. 15in an enlarged manner. Referring toFIGS. 15 and 16, the light emitting device10A is different from the light emitting device10(seeFIGS. 1A,1B and2) in that the substrate holder40is replaced by a substrate holder40A (the protrusion42is replaced by a protrusion42A).

In the first embodiment, the inner side face42s(the inner side portion in the “U” shape) of the substrate holder42is set to an inclined face, but the inner side face42scan be set as a vertical face as in the protrusion42A of the light emitting device10A shown inFIG. 16.

In order to set the inner side face42sof the protrusion42A as a vertical face, the same processes to those ofFIGS. 5A,5B and6of the first embodiment are performed, and then, the process shown inFIG. 17is performed instead of the process shown inFIGS. 8A and 8B(the wet etching process). In the process shown inFIG. 17, a resist layer520having an opening portion520xis formed on one face of the silicon substrate410. The resist layer520can be formed in, for example, the same manner as that of the resist layer510. Then, the portion of the silicon substrate410that is exposed through the opening portion520xis removed by dry etching so as to form a groove410y. An inner side face of the groove410yis set to a vertical face.

After that, the same processes as those ofFIGS. 9A to 10Bof the first embodiment are performed, and then, in the process shown inFIG. 18, the peripheral portion where the insulating film430A of the outer side face of the “U” shape of the structure shown inFIG. 10is formed is cut by, for example, dicing. Accordingly, the substrate holder40A having the column41, the protrusion42A including the outer circumferential portions42rand42qand the center portion42v, and the insulation film43is formed of silicon.

In this way, the same effect as that of the first embodiment is exhibited even if the inner side face42sof the protrusion42A is set to a vertical face.

FIGS. 19A and 19Bare perspective views illustrating a light emitting device according to a second modified example of the first embodiment. Referring toFIGS. 19A and 19B, the light emitting device10B is different from the light emitting device10(seeFIGS. 1A,1B and2) in that the substrate holder40is replaced by the substrate holder40B (the column41is replaced by a column41B and the protrusion42is replaced by a protrusion42B).

In the first embodiment, the substrate holder40is formed in “U” shape, but in the second modified example of the first embodiment, the substrate holder40B of the light emitting element mounting unit20has a shape in which “U” shaped center portion42vof the substrate holder40is removed. In other words, the substrate holder40B including the column41B and the protrusion42B is disposed on each side of the substrate50such that the column41B on one side of the substrate50faces the column41B on the other side of the substrate50via the substrate50.

When the substrate holder40B is prepared, for example, the resist layer500is formed within the range of a predetermined width from the side facing each other among the sides of one face of the silicon substrate410in a plan view in the process shown inFIGS. 5A and 5Bof the first embodiment. Then, in the process shown inFIG. 6of the first embodiment, the insulating film430that is exposed though the opening portion500xis removed by wet etching. Then, the resist layer500is removed so as to form the insulating film430A. The insulating film430A is formed within the range of a predetermined width from the side facing each other among the sides of the one face of the silicon substrate410. After that, the same processes as those ofFIGS. 7 to 11Cof the first embodiment may be performed using the insulating film430A as a mask.

In this manner, the same effect as that of the first embodiment is exhibited even when the pair of the substrate holders40B of which the plane shapes are rectangles are disposed on both sides of the substrate50. In the same manner as in the first modified example of the first embodiment, the inner side face of the protrusion42B may set to be a vertical face.

Second Embodiment

In a second embodiment, an example will be described in which a plurality of conductive substrates each mounting a light emitting element thereon are stacked on top of one another at a predetermined pitch and are held by one substrate holder. Especially, in this embodiment, the respective conductive substrates are stacked at the same pitch. In the second embodiment, description of the same constituent parts as those in the above-described embodiment will be omitted herein.

FIG. 20is a perspective view illustrating a light emitting device according to the second embodiment.FIG. 21is a front view illustrating the portion A ofFIG. 20in an enlarged manner. Referring toFIGS. 20 and 21, the light emitting device10C is different from the light emitting device10(seeFIGS. 1A,1B and2) in that the substrate holder40is replaced by the substrate holder40C.

In the first embodiment, the substrate holder40is provided in the direction parallel to the substrate50, but in the second embodiment, the substrate holder40C is provided in the direction vertical to the substrate50.

The substrate holder40C is a plate-like member made of silicon and has a plurality of through holes42xformed in an elongated shape (slit shape) that are arranged at a predetermined pitch (the same pitch) in the direction in which the substrates50are stacked on top of one another. The through hole42xis formed to allow the substrate50to pass through the through hole42x. Each of the substrates50is inserted through a corresponding one of the through holes42x, and is bonded to the inner wall face of the corresponding through hole42xvia the adhesive material60. Especially, each of the substrate50might be bonded to the upper surface (one surface) of the inner wall face of the corresponding through hole42z.

Each of the substrates50and the substrate holder40C needs to be electrically insulated from each other. As shown inFIG. 21, for example, on the surface of the substrate holder40C including the inner wall faces of each of the through holes42x, an insulating film of SiO2may be formed. Alternatively, a ceramic that is an insulating material may be used as the substrate holder40C instead of silicon. When a ceramic is used as the substrate holder40C, the through holes42xcan be formed using, for example, an ultrasonic machining method.

The heat-radiating property can be enhanced by using a ceramic material having a thermal conductivity closer to that of the substrate50that is a copper-tungsten (CuW) substrate, as a material of the substrate holder40C. The thermal conductivity of the copper-tungsten (CuW) substrate is about 160 W/m·K, the thermal conductivity of silicon (Si) is about 149 W/m·K, and the thermal conductivity of a silicon oxide (SiO2) film is about 10 W/m·K or lower. Further, the thermal conductivity of an aluminum nitride (AlN) that is a ceramic material is about 150 W/m·K.

Therefore, by using, for example, the aluminum nitride (AlN) as the material of the substrate holder40C, the heat-radiating property can be enhanced as compared with the case where silicon (Si) is used as the material of the substrate holder40C and a silicon oxide (SiO2) film is formed on the surface thereof.

In this manner, the same effect as that of the first embodiment can be obtained even when the substrate holder40C is used in which the plurality of through holes42xof an elongated shape (slit shape) are arranged at a predetermined pitch in the direction in which the substrates50are stacked on top of one another.

Third Embodiment

A third embodiment is another example in which plural conductive substrates each mounted with a light emitting element on one surface are held by one substrate holder and stacked at a prescribed pitch. In the third embodiment, descriptions of constituent parts having the same ones in the above-described embodiments will be omitted.

FIG. 22is a perspective view of a light emitting device10D according to the third embodiment.FIG. 23is a sectional view of part B shown inFIG. 22, and shows a cross section which is parallel with the YZ plane. An insulating film43shown inFIG. 23is omitted inFIG. 22.

As shown inFIGS. 22 and 23, the light emitting device10D is different from the light emitting device10(seeFIGS. 1A and 1BandFIG. 2) in that the substrate holder40is replaced by a substrate holder40D.

The substrate holder40D is made of silicon. A prescribed surface (light-emission-side surface) of the substrate holder40D is formed with a plurality of elongated (slit shape) grooves42yin such a manner that they are arranged at a prescribed pitch in the stacking direction of substrates50. Each groove42yhas openings in the two respective side surfaces, perpendicular to the prescribed surface (light-emission-side surface), of the substrate holder40D. The insulating film (made SiO2or the like) is formed on the surfaces of the substrate holder40D including the inner wall surfaces of the grooves42y.

A first metal layer75is formed on the inner wall surfaces of the grooves42yvia the insulating film43. As shown inFIG. 23, the first metal layer75may consist of a metal layer75awhich is formed on the inner wall surfaces of the grooves42yvia the insulating film43, a metal layer75bwhich covers the metal layer75a, and a metal layer75cwhich covers the metal layer75b.

The metal layer75amay be made of a metal material that provides high adhesion to silicon, such as titanium (Ti) or tungsten (W). The thickness of the metal layer75amay be set at about 0.05 μm. The metal layer75bmay be made of a metal material such as nickel (Ni). The thickness of the metal layer75bmay be set at about 3 μm.

The metal layer75cmay be made of a solder material such as tin (Sn), tin-silver (Sn—Ag), or tin-gold (Sn—Au). The thickness of the metal layer75cmay be set at about 10 μm. The metal layer75bhas a function of preventing the solder material of the metal layer75cfrom diffusing into the metal layer75a.

Each groove42yhas such a size as to allow insertion of a substrate50, and portions (not mounted with light emitting elements80) of the substrates50are inserted in the grooves42y, respectively. When the substrates50are inserted into the respective grooves42yand the solder material of the metal layer75cis melted and then solidified, electrical continuity is established between the first metal layer75and the conductive substrates50and the portions (not mounted with light emitting elements80) of the substrates50are bonded to the inner walls of the grooves42y.

A second metal layer76and a third metal layer77are formed on one end portion and the other end portion (i.e., two portions outside, in the Y direction, the area where the grooves42yare arranged) of the prescribed surface of the substrate holder40D, respectively. The second metal layer76is in physical and electrical contact with the end face of that part of the first metal layer75which is formed in the groove42ythat is closest to the one end portion of the prescribed surface. The third metal layer77is in physical and electrical contact with the end face of that part of the first metal layer75which is formed in the groove42ythat is closest to the other end portion of the prescribed surface.

The plural light emitting elements80are connected in series between the second metal layer76and the third metal layer77via the portions of the first metal layer75formed in the grooves42yand the substrates50. The second metal layer76and the third metal layer77may be made of gold (Au). Alternatively, each of the second metal layer76and the third metal layer77may have the same layered structure as the first metal layer75and be formed so as to be integral with the first metal layer75.

As described above, the light emitting elements80are connected to each other in series via the portions of the first metal layer75and the substrates50. Therefore, the light emitting elements80can emit light at the same time by supplying a current from an input terminal to an output terminal, the input terminal being one of the second metal layer76and the third metal layer77and the output terminal being the other.

Although in this embodiment the width (in the X direction) of the substrates50is the same as that of the light emitting elements80, as in the first embodiment the width (in the X direction) of the substrates50may be set greater than that of the light emitting elements80.

As shown inFIG. 24, a structure may be employed in which the back surface (opposite to the prescribed surface) of the substrate holder40D is bonded to one surface of a wiring board100via a bonding material110. The bonding material110may be an indium solder or an insulating adhesive such as an epoxy resin or a silicone resin.

As shown inFIG. 24, the second metal layer76and the third metal layer77which are formed on the one portion and the other portion of the prescribed surface of the substrate holder40D are electrically connected to traces (not shown) on the wiring board100by metal wires150(copper wires, gold wires, or the like) such as bonding wires, respectively. However, the metal wire150which electrically connects the third metal layer77to the traces (not shown) on the wiring board100is not shown inFIG. 24. As in the example ofFIG. 3, lenses120may be disposed on the optical paths of light beams emitted from the light emitting elements80, respectively.

For example, the light emitting device10D is manufactured in the following manner. First, as shown inFIG. 25A, in the same manner as shown inFIG. 9, a resist layer530is formed on the prescribed surface (inFIG. 25, the top surface) of a silicon substrate so as to have openings530xwhich expose portions where grooves42yare to be formed. The portions, exposed by the openings530x, of the silicon substrate are removed by dry etching, whereby a substrate holder40D is provided with grooves42yeach corresponding to one of the openings530xformed on the prescribed surface. For example, DRIE (deep reactive ion etching) using SF6(sulfur hexafluoride) is a suitable dry etching method.

Then, in the step shown inFIG. 25B, in the same manner as in the step shown inFIGS. 5A and 5B, an insulating film43is formed on the surfaces of the substrate holder40D including the inner wall surfaces of the grooves42y.

Then, as shown inFIG. 25C, a first metal layer75is formed on the inner wall surfaces of the grooves42yvia the insulating film43. More specifically, metal layers75a,75b, and75c(not shown inFIG. 25C) are formed sequentially on the portions, formed on the inner wall surfaces of the grooves42y, of the insulating film43by sputtering, evaporation, plating, or the like. The materials of the metal layers75a,75b, and75care the same as described above.

Then, in the step shown inFIG. 25D, a second metal layer76and a third metal layer77are formed on the one side portion and the other side portion (i.e., two portions outside, in the Y direction, the area where the grooves42yare arranged) of the prescribed surface of the substrate holder40D, respectively. The second metal layer76and the third metal layer77may be formed on the one side portion and the other side portion of the prescribed surface of the substrate holder40D by electroless gold (Au) plating. Alternatively, the second metal layer76and the third metal layer77may be formed integrally with the first metal layer75in the step shown inFIG. 25Cso as to form a single layer together.

Then, in the same manner as in the step shown inFIG. 12, plural (in the example ofFIG. 22, four) members are prepared in each of which a light emitting element80is mounted on one end portion of one surface of a substrate50via a bonding material70and a bonding material30is formed on the light emitting element80. One substrate50which is not mounted with a light emitting element80is also prepared. These substrates50are inserted into the respective grooves42yand bonded to the inner walls of the grooves42yby the metal layer75c, and each light emitting element80is bonded to the adjacent substrate50by the bonding material30. Thus, a light emitting device10D is completed.

An alternative step is as follows. Each of four light emitting elements80is bonded to adjacent one of four substrates50via the bonding material30. The light emitting element80that is not sandwiched between the respective substrates50is bonded, by the bonding material30, to the substrate50which is not mounted with a light emitting element80. Then, the substrates50are inserted into the respective grooves42ysimultaneously and bonded to the inner walls of the grooves42yby the metal layer75c.

As mentioned in the second embodiment, the substrate holder40D may be made of ceramic instead of silicon. In this case, the grooves42ycan be formed by dicing, for example. Since ceramic is an insulating material, it is not necessary to form the insulating film43.

The same advantages obtained by the first embodiment can be also obtained by using the above-described substrate holder40D in which the plurality of elongated (slit-shape) grooves42yare arranged at the prescribed pitch in the stacking direction of the substrates50.

In the example ofFIG. 24, heat generated by each light emitting element is transmitted to the wiring board100via the associated substrates50and the substrate holder40D and dissipated through the wiring board100. Since each substrate50is in contact with the entire inner wall surfaces of the corresponding groove42y, heat can be transmitted efficiently from each substrate50to the substrate holder40D. As a result, the heat dissipation efficiency of the light emitting device10D as a whole can be increased.

The same effect as that of the respective embodiments can be obtained even when a substrate holder made of, for example, ceramic or glass instead of silicon is used. Ceramic or glass can be processed using a micro-blaster or laser beams.

In the third embodiment, both sides of the respective grooves42yare opened, but the embodiment is not limited thereto. For example, the respective grooves42ymight be formed such that an opening is formed only in substrate insertion side of the substrate holder40D while no opening is formed in both sides of the substrate holder40D.