Patent Application
20110297965
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-127507, filed on Jun. 3, 2010; the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a light-emitting device and a method for manufacturing the same.
The applications of light-emitting devices have expanded to lighting apparatuses, back-light sources for image-displaying apparatuses, displaying apparatuses and the like.
In recent years, light-emitting devices smaller in size have been demanded. In a manufacturing method proposed to enhance mass productivity, a semiconductor layer including a light-emitting layer is formed on a substrate by crystal growth, then the substrate is removed from the semiconductor layer by laser-light irradiation, and then the resultant semiconductor layer is divided into multiple devices.
However, further lowering of the contact resistance between the semiconductor layer and the electrode portion provided on the semiconductor layer is demanded.
In general, according to one embodiment, a light-emitting device includes a semiconductor layer, a first electrode portion and a second electrode portion, a first insulating film, and a metal layer. The semiconductor layer includes a first main surface, a second main surface on an opposite side to the first main surface, a third main surface connecting the first main surface and the second main surface, and a light-emitting layer. The first electrode portion and the second electrode portion are provided on the second main surface of the semiconductor layer. The first insulating film covers the second main surface of the semiconductor layer and the third main surface of the semiconductor layer. The metal layer is stacked on at least the second electrode portion of the first and the second electrode portions, and the metal layer extends until reaching a part of the first insulating film. The part is continuously extended from the first insulating film which covers the third main surface.
Some embodiments will be described below with reference to the drawings.
The drawings are only schematic or conceptual ones. The relationship between the thickness and the width of each portion, the size ratio between of portions, or the like are not necessarily the same as those in the actual ones. In addition, a portion may be shown with different dimensions or different size ratios between the drawings.
In addition, in the description and the drawings, the same element as that described with reference to a preceding drawing are assigned the same reference numerals, and the detailed description thereof is omitted herein.
A light-emitting device 110 according to this embodiment includes: a semiconductor layer 5 that includes a first main surface 5a, a second main surface 5b which is on the opposite side to the first main surface 5a, a third main surface 5c which connects the first main surface 5a and the second main surface 5b, and a light-emitting layer; a first electrode portion 14 and a second electrode portion 15 both of which are provided on the second main surface 5b of the semiconductor layer 5; a first insulating film 13 which covers both the second main surface 5b and the third main surface 5c of the semiconductor layer 5; and a metal layer 40(B) which is stacked at least on the second electrode portion 15 of the first and the second electrode portions 14 and 15 and which extends until reaching the extension of the first insulating film 13(13c) that covers the third main surface 5c close to the metal layer 40(B).
The semiconductor layer 5 includes a light-emitting layer, and is formed by using a substrate as a supporting body. Then, after formation the semiconductor layer, the substrate is removed by irradiation with laser light (laser lift off). The third main surface 5c of the semiconductor layer 5 is a surface which connects the first main surface 5a to the second main surface 5b. There is a case where the third main surface 5c is provided perpendicularly to the first main surface 5a or the second main surface 5b. There is also a case where the third main surface 5c is provided obliquely to the first main surface 5a or the second main surface 5b. Both of these cases are included in this embodiment.
The first insulating film 13c that covers the third main surface 5c transmit the laser light. Accordingly, the thickness t of the first insulating film 13c (thickness along the direction perpendicular to the third main surface 5c) is equal to or larger than the wavelength of the laser light.
The laser light to be used is, for example, light of ArF laser (wavelength: 193 nm), light of KrF laser (wavelength: 248 nm), light of XeCl laser (wavelength: 308 nm), or light of XeF laser (wavelength: 353 nm). The first insulating film 13c is formed to have the thickness t equal to or larger than the wavelength of the laser light used.
In the light-emitting device 110 illustrated in
The metal layer 40(A) of the metal layer 40 corresponds to the first electrode portion 14. The metal layer 40(A) is provided to extend to reach the extension, along the third main surface 5c, of the first insulating film 13c(A) covering the third main surface 5c close to the metal layer 40(A).
The metal layer 40(B) of the metal layer 40 corresponds to the second electrode portion 15. The metal layer 40(B) is provided to extend to reach the extension, along the third main surface 5c, of the first insulating film 13c(B) covering the third main surface 5c close to the metal layer 40(B).
A part of the first insulating film 13c(A) and 13c(B) is continuously extended from the first insulating film 13c(A) and 13c(B), which cover the third main surface 5c.
According to the light-emitting device 110 like this, the laser light irradiated at the laser lift off passes through the first insulating film 13c that covers the third main surface 5c, and thus the metal layer 40 is irradiated with the laser light. The metal layer 40 irradiated with the laser light is heated by energy of the laser light. The first electrode portion 14 and the second electrode portion 15 are heated by heating the metal layer 40. Furthermore, portions of the semiconductor layer 5 that are in contact with the first electrode portion 14 and the second electrode portion 15 are heated. The heating reduces the bulk resistance of the semiconductor layer 5, and the contact resistance between the semiconductor layer 5 and each of the first electrode portion 14 and the second electrode portion 15.
The metal layer 40 is made of a material that is melted by the irradiation with the laser light that has passed through the first insulating film 13c. In other word, the material to be used has a lower fluence threshold for melting than the fluence of the laser light to be irradiated. Note that the fluence is the energy amount per unit area of the laser light.
For example, Ikeda et al., “Excimer Laser Ablation Process of Different Metals,” Report for 41st Meeting of Nagoya Laser Technopole, 23 Feb. 2001, provides the fluence thresholds for various metal materials, which are shown in
Therefore, if, for example, laser light with a fluence of 1.0 J/cm2 is used, the metal to be used contains one of the metals with a fluence threshold not higher than the 1.0 J/cm2 (e.g., Mg, Al, Ti, Fe, Ni, Cu, Zn, Zr, and Ag). Of these metals, for example, Al and Ti are preferable in view of the manufacturing.
The metal layer 40 is in contact with the surface of each of the first electrode portion 14 and the second electrode portion 15. For example, the metal layer 40 is in direct contact with the surface of each of the first electrode portion 14 and the second electrode portion 15. Alternatively, the metal layer 40 may be in contact with the surfaces of the first electrode portion 14 and the second electrode portion 15 via an intermediate layer (not illustrated). All that is necessary is that the heat is conducted from the metal layer 40 to the first electrode portion 14 and the second electrode portion 15.
Further, the metal layer 40 is in contact with the first insulating film 13c at the extended portion. In other word, in the metal layer 40(A) provided corresponding to the first electrode portion 14, the extended portion is in contact with the first insulating film 13c(A) covering the third main surface 5c on the first electrode portion 14 side.
Moreover, in the metal layer 40(B) provided corresponding to the second electrode portion 15, the extended portion is in contact with the first insulating film 13c(B) covering the third main surface 5c on the first electrode portion 15 side.
Note that the metal layer 40 may be in contact with the first insulating film 13c via an intermediate layer (not illustrated). All that is necessary is that the metal layer 40 is irradiated with the laser light that has passed through the first insulating film 13c.
The light-emitting device 110 according to this embodiment is formed collectively in a wafer configuration. The semiconductor layer 5 includes a first semiconductor layer 11 and a second semiconductor layer 12. The first semiconductor layer 11 is, for example, an n-type GaN layer, and serves as a lateral pathway for a current. Note that a conductivity type of the first semiconductor layer is not necessarily the n-type, but may be p-type as well.
The light-emitting device 110 emits the light mainly from a first main surface 11a of the first semiconductor layer 11 (the first main surface 5c of the semiconductor layer 5). The second semiconductor layer 12 is provided on a second main surface 11b of the first semiconductor layer 11. The second main surface 11b is located on the opposite side to the first main surface 11a.
The second semiconductor layer 12 has a stacked structure of multiple semiconductor layers including a light-emitting layer (active layer). An example of the structure is shown in
An n-type GaN layer 31 is provided on the second main surface 11b of the first semiconductor layer 11. A light-emitting layer 33 is provided on the GaN layer 31. The light-emitting layer 33 has a multiple quantum well structure containing InGaN, for example. A p-type GaN layer 34 is provided on the light-emitting layer 33.
As shown in
The bottom surface of the recessed portion is the second main surface 11b of the first semiconductor layer 11. An n-side electrode is provided as the first electrode portion 14 on the second main surface 11b of the recessed portion.
A p-side electrode is provided as the second electrode portion 15 on the surface of the second semiconductor layer 12 opposite to the surface in contact with the first semiconductor layer 11.
The second main surface 11b of the first semiconductor layer 11 is covered with the first insulating film 13 made, for example, of silicon oxide. The first insulating film 13 is made of a material with larger band-gap energy than the energy of the laser light irradiated to remove the substrate after the semiconductor layer 5 is formed on the substrate. The first electrode portion 14 and the second electrode portion 15 are exposed from the first insulating film 13. The first electrode portion 14 and the second electrode portion 15 are insulated from each other by the first insulating film 13, and thus form electrodes electrically independent of each other. The first insulating film 13 also covers the side surfaces of the projected portion including the second semiconductor layer 12.
The metal layer 40 is provided so as to cover each of the first electrode portion 14 and the second electrode portion 15. A second insulating film 16 is provided on the second main surface 11b side so as to cover the first insulating film 13, a part of the metal layer 40(A), and a part of the metal layer 40(B).
The second insulating film 16 and the semiconductor layer 5 are made of materials each with smaller band-gap energy than the energy of the laser light irradiated to remove the substrate after the semiconductor layer 5 is provided on the substrate.
Alternatively, the second insulating film 16 and the semiconductor layer 5 are made of materials that absorb the laser light.
The second insulating film 16 is made, for example, of silicon oxide, silicon nitride, or a resin such as polyimide.
The surface of the second insulating film 16 on the opposite side to the first semiconductor layer 11 and the second semiconductor layer 12 is flattened, and an n-side interconnection as a first interconnection 17 and a p-side interconnection as a second interconnection 18 are provided on the flattened surface.
The first interconnection 17 is also provided in an opening 16a that is formed in the second insulating film 16 until reaching the metal layer 40(A). The first interconnection 17 is electrically connected to the metal layer 40(A) and the first electrode portion 14. Note that an intermediate film (not illustrated) may be provided between the first interconnection 17 and the metal layer 40(A). The second interconnection 18 is also provided in an opening 16b that is formed in the second insulating film 16 until reaching the metal layer 40(B). The second interconnection 18 is electrically connected to the metal layer 40(B) and the second electrode portion 15. Note that an intermediate film (not illustrated) may be provided between the second interconnection 18 and the metal layer 40(B).
All of the first electrode portion 14, the second electrode portion 15, the first interconnection 17, and the second interconnection 18 are provided at the second main surface 11b side of the first semiconductor layer 11, and form an interconnect layer for supplying an electric current to the light-emitting layer.
An n-side metal pillar is provided on a surface of the first interconnection 17 opposite to the first electrode portion 14 as a first metal pillar 19. A p-side metal pillar is provided on a surface of the second interconnection 18 opposite to the second electrode portion 15 as a second metal pillar 20. The surrounding area of the first metal pillar 19, the surrounding area of the second metal pillar 20, the first interconnection 17, and the second interconnection 18 are covered with a resin (third insulating film) 26.
The first semiconductor layer 11 is electrically connected to the first metal pillar 19 via the first electrode portion 14 and the first interconnection 17. The second semiconductor layer 12 is electrically connected to the second metal pillar 20 via the second electrode portion 15 and the second interconnection 18. External terminals 25 such as, for example, solder balls or metal bumps are provided on the lower-end surfaces of the first metal pillar 19 and the second metal pillar 20 exposed from the resin 26, and the light-emitting device 110 is electrically connected to the external circuit through the external terminals 25.
The thickness of the first metal pillar 19 (the thickness in the vertical direction of
According to the structure of this embodiment, even if the semiconductor layer 5 is thin, a mechanical strength can be secured by making the first metal pillar 19, the second metal pillar 20, and the resin 26 thicker. In addition, when the light-emitting device 110 is mounted on a circuit board or the like, the stress applied to the semiconductor layer 5 through the external terminals 25 can be absorbed by the first metal pillar 19 and the second metal pillar 20. Accordingly, the stress applied to the semiconductor layer 5 can be reduced. The resin 26 to reinforce the first metal pillar 19 and the second metal pillar 20 is preferably made of a resin whose coefficient of thermal expansion is equal to, or close to, that of the circuit board or the like. For example, an epoxy resin, a silicone resin, or a fluorine resin is used as the resin 26. In addition, the resin 26 is colored in black, for example. The resin 26 thus prevents the internal light from leaking out and prevents unnecessary external light from entering.
Each of the first interconnection 17, the second interconnection 18, the first metal pillar 19, and the second metal pillar 20 is made, for example, of copper, gold, nickel, or silver. Of these materials, copper is preferable because of its favorable thermal conductivity, its high electromigration resistance, and its excellent adherence to the insulating films.
A phosphor layer 27 is provided on the light-emitting surface of the light-emitting device 110 when necessary. For example, if the light-emitting layer emits blue light and the blue light is emitted from the light-emitting device 110 as it is, no such phosphor layer 27 is necessary. In contrast, if the light-emitting device 110 emits white light or the like, that is, light of a wavelength different from that of the light emitted by the light-emitting layer, the phosphor layer 27 is provided which contains phosphors absorbing the wavelength of the light emitted by the light-emitting layer and thus converting the wavelength of the light emitted by the light-emitting layer into the wavelength of the light to be emitted from the light-emitting device 110.
The light-emitting surface of the light-emitting device 110 may be provided with a lens (not illustrated) when necessary. Lenses of various shapes, such as convex lenses, concave lenses, or aspheric lenses, may be used. How many lenses to provide and where to provide the lenses may be determined appropriately.
In the light-emitting device 110 according to this embodiment, the metal layer 40 is heated by the laser light irradiated at the laser lift off, so that the bulk resistance of the semiconductor layer 5 as well as the contact resistance between the semiconductor layer 5 and each of the first and the second electrode portions 14 and 15 can be reduced. Consequently, the efficiency of the light-emitting device 110 can be enhanced.
As shown in
In step S110, a semiconductor layer 5 including a light-emitting layer (active layer) is formed on a first main surface of a substrate.
In step S120, a first insulating film 13 is formed to cover at least the top surface (second main surface 5b) of and the side surface (third main surface 5c) of the semiconductor layer 5 that has been formed on the substrate.
In step S130, a first electrode portion 14 and a second electrode portion 15 are formed so as to be electrically continuous to the semiconductor layer 5.
In step S140, a metal layer 40 is formed at least on the second electrode portion 15 of the first and the second electrode portions 14 and 15, and the metal layer 40 extends to reach the extensions of the first insulating film 13c that cover the side surface (third main surface 5c) close to the metal layer.
In step S150, a second insulating film 16 is formed to cover the first insulating film 13.
In step S160, a second main surface of the substrate, which is on the opposite side to the first main surface, is irradiated with laser light, and the substrate is removed from the semiconductor layer 5.
In this embodiment, the band-gap energy of the first insulating film 13 is larger than the energy of the laser light. In the manufacturing method like this, the laser light irradiated at the laser lift off to remove the substrate from the semiconductor layer 5 heats the metal layer 40 so as to reduce the bulk resistance of the semiconductor layer 5 as well as the contact resistance between the semiconductor layer 5 and each of the first and the second electrode portions 14 and 15.
Subsequently, a specific method for manufacturing a light-emitting device will be described with reference to
Firstly, as shown in
Subsequently, a part of the second semiconductor layer 12 and a part of the first semiconductor layer 11 are selectively removed by, for example, reactive ion etching (RIE) method using resist (not illustrated). Consequently, as shown in
A groove 8 is formed so as to pierce the semiconductor layer 5 and reach the substrate 10. The groove 8 sub-divides the semiconductor layer 5 into multiple sections on the substrate 10. For example, as shown in
Subsequently, as shown in
In this embodiment, when the first insulating film 13 is formed, the thickness t (the thickness measured in the direction perpendicular to the third main surface 5c) of the first insulating film 13c covering the side surface (third main surface 5c) of the semiconductor layer 5 is equal to or larger than the wavelength of the laser light to be used to remove the substrate 10.
The laser light to be used is, for example, light of ArF laser (wavelength: 193 nm), light of KrF laser (wavelength: 248 nm), light of XeCl laser (wavelength: 308 nm), or light of XeF laser (wavelength: 353 nm). The first insulating film 13 is formed to have the thickness t equal to or larger than the wavelength of the laser light described above.
Subsequently, openings are selectively formed in the first insulating film 13. As shown in
In addition, along with the formation of the openings in the first insulating film 13, the first insulating film 13 formed in the bottom portion of the groove 8 is removed. The first insulating film 13 is selectively removed by etching with a hydrofluoric acid solution. The first insulating film 13 in the bottom portion of the groove 8 is removed until the first main surface 10a of the substrate 10 is exposed.
Subsequently, as shown in
Subsequently, as shown in
After the formation of the second insulating film 16, both an opening 16a that reaches the first electrode portion 14 and an opening 16b that reaches the second electrode portion 15 are formed in the second insulating film 16 as shown in
Subsequently, seed metal (not illustrated) is formed on the top surface of the second insulating film 16 as well as on the inner wall (the side and bottom surface) of each of the opening 16a and the opening 16b, then resist for plating (not illustrated) is formed, and, after that, a Cu plating process is performed with the seed metal used as the current pathway. The seed meal contains Cu, for example.
Consequently, as shown in
Subsequently, after the resist for plating that has been used in the plating of the first interconnection 17 and the second interconnection 18 is removed using a chemical solution, other resist for plating for forming metal pillars is formed, and a process of electrolytic plating is performed with the seed metal used mentioned above as a current pathway. Consequently, as shown in
After that, the resist for forming metal pillars is removed using a chemical solution, and then exposed portions of the seed metal are removed. Consequently, the electric connection between the first interconnection 17 and the second interconnection 18 through the seed metal is cut off.
Subsequently, as shown in
Subsequently, as shown in
Laser light LSR to be used is light of ArF laser (wavelength: 193 nm); light of KrF laser (wavelength: 248 nm); light of XeCl laser (wavelength: 308 nm); or light of XeF laser (wavelength: 353 nm).
The laser light LSR is irradiated the semiconductor layer 5 from the second main surface 10b (the opposite side to the first main surface 10a) of the substrate 10 toward the semiconductor layer 5. The laser light LSR passes through the substrate 10, and reaches a lower surface (the second main surface 5c) of the semiconductor layer 5. The second insulating film 16 (irrespective of silicon nitride or a resin) and the semiconductor layer 5 absorb the laser light LSR. Alternatively, the band-gap energy of the second insulating film 16 and the band-gap energy of the semiconductor layer 5 are made smaller than the energy of the laser light LSR. Consequently, the laser light LSR that has passed through the substrate 10 is absorbed by the semiconductor layer 5 and the second insulating film 16. In the meanwhile, at the interface of the substrate 10 and semiconductor layer 5, the absorption of the laser light LSR causes the GaN component in the semiconductor layer 5 to be thermally decomposed in a manner shown in the following reaction formula.
GaN→Ga+(½)N2↑
Consequently, as shown in
In this embodiment, the portion of the first insulating film 13 that is in contact with the substrate 10 is removed in advance (see
In addition, the band-gap energy of the first insulating film 13 is larger than the energy of the laser light LSR. Accordingly, the laser light LSR irradiated at the laser lit off enters the first insulating film 13c that cover the side surface (third main surface 5c) of the semiconductor layer 5, and then reaches the metal layer 40.
As has been described earlier, the band-gap energy of the first insulating film 13 is larger than the energy of the laser light LSR. In addition, the first insulating film 13c is formed so that its thickness t may be larger than the wavelength of the laser light LSR. Accordingly, the laser light LSR enters the end surfaces of lower surface (second main surface 5b) side of the first insulating film 13c covering the side surface 5c of the semiconductor layer 5. Then, the laser light LSR passes through the inside of the first insulating film 13c.
The laser light LSR that has passed through the first insulating film 13c is irradiated the metal layer 40(B) extending until reaching the extension, along the side surface (third main surface 5c), of the first insulating film 13c. The metal layer 40(B) is heated by the irradiation with the laser light LSR. The heat melts the metal layer 40(B), and heats both the first electrode portion 15 and the interface between the first electrode portion 15 and the second semiconductor layer 12. The heated first electrode portion 15 and the heated second semiconductor layer 12 are activated to reduce the bulk resistance of the second semiconductor layer 12 and the contact resistance between the second semiconductor layer 12 and the first electrode portion 15.
A part of the first insulating film 13c(B) is in contact with the second semiconductor layer 12, the second electrode portion 15 and the metal layer 40(B). The edge of the first insulating film 13c(B) is interposed between the metal layer 40(B) and the second semiconductor layer 12 and in contact with the second electrode portion 15.
A part of the first insulating film 13c(A) is in contact with the first electrode portion 14 and the metal layer 40(A). The edge of 13c(A) is interposed between the metal layer 40(A) and the first semiconductor layer 11 and in contact with the first electrode portion 14.
After that, as shown in
Since the use of this manufacturing method allows the light-emitting device 110 to be built at the wafer level, CSP (Chip Size Package) of the light-emitting device 110, whose size is as small as the size of the bare chip, can be provided easily. In addition, after building at the wafer level, the light-emitting devices 110 may be completed by dicing into individuals. The cutting method to be used is, for example, the mechanical machining using a diamond blade or the like, the cutting by laser irradiation, or the cutting by high-pressured water.
According to the method for manufacturing the light-emitting device 110, the laser light irradiated at the laser lift off heats the metal layer 40 simultaneously with the laser lift off, so that the bulk resistance of the semiconductor layer 5 as well as the contact resistance between the semiconductor layer 5 and each of the first and the second electrode portions 14 and 15 can be reduced.
Subsequently, a light-emitting device according to a third embodiment will be described.
As shown in
In other words, the metal layer 40 is stacked on the second electrode portion 15, and provided to extend until reaching the extension, along the third main surface 5c, of the first insulating film 13c(B) covering the third main surface 5c close to the second electrode portion 15. On the other hand, the first interconnection 17 is formed directly on the surface of the first electrode portion 14.
In the light-emitting device 120 like this, the laser light irradiated at the laser lift off passes through the first insulating film 13c that cover the third main surface 5c. The metal layer 40 is then irradiated with the laser light and is heated by the energy of the laser light. The heating of the metal layer 40 in turn heats the second electrode portion 15. In addition, the contact portion of the second semiconductor layer 12 with the second electrode portion 15 is heated. The heating reduces the bulk resistance of the second semiconductor layer 12 and the contact resistance between the second semiconductor layer 12 and the second electrode portion 15.
The second semiconductor layer 12 includes, for example, a p-type GaN layer. The p-type GaN layer is doped with Mg, for example. The heating of the metal layer 40 heats the second semiconductor layer 12, and activates the doped Mg. Accordingly, reduction in the bulk resistance of the second semiconductor layer 12 as well as reduction in the contact resistance between the second semiconductor layer 12 and the second electrode portion 15 can be accomplished.
According to the embodiments thus far described, in the light-emitting devices 110 and 120 employing the laser lift off, the irradiation with the laser light at the laser lift off heats the metal layer 40, and thus the bulk resistance of the semiconductor layer 5 as well as the contact resistance of the electrode portions that are electrically continuous to the semiconductor layer 5 can be reduced simultaneously with the laser lift off. Thus provided are the light-emitting devices 110 and 120 with high efficiency.
Hereinabove, some embodiments have been described with reference to specific examples. The above-described embodiments are not limited thereto. For example, from the aforementioned embodiments and variations, those skilled in the art may make different modes of embodiments by providing any additional constituent element or by omitting any constituent element, based on modified design, or by appropriately combining characteristic features in the above embodiments. These different modes of embodiments are also included in the scope of the invention as long as the modes retain the gist of the invention. In addition, those skilled in the art may make various kinds of changes in design concerning the substrate, the semiconductor layers, the electrodes, the interconnections, the metal pillars, the insulating films, the material of the resin, the size, the shape, the layout, and the like. Those thus changed are also included in the scope of the invention unless the changes depart from the gist of the invention.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-127507 | Jun 2010 | JP | national |
