JP2012529170A - Light emitting semiconductor device and manufacturing method - Google Patents

Abstract

The light-emitting semiconductor device (1) of the present invention is made of a nitride of a group III metal, and includes an n-type semiconductor layer (2), a p-type semiconductor layer (3), and an active region between the n-type semiconductor layer and the p-type semiconductor layer. And (4). The layer structure further includes a reflective contact structure (6) having a contact surface (5) defined by any one of the n-type semiconductor layer and the p-type semiconductor layer and attached to the contact surface. In accordance with the present invention, the reflective contact structure (6) has a polycrystalline structure, a first transparent conductive oxide (TCO) contact layer (13) deposited on the contact surface (5) of the layer structure, A second transparent conductive oxide (TCO) contact layer (14) having a crystalline structure and a metal reflective layer (15) attached to the second TCO layer.
[Selection] Figure 1

Description

  The present invention relates generally to light emitting semiconductor structures comprised of nitrides of Group III metals. More particularly, the present invention relates to a reflective contact used in, for example, vertical light emitting diodes (LEDs) and a method for manufacturing the same.

  The role of light emitting semiconductor devices such as LEDs in different fields of daily life is increasing day by day. For example, there are numerous applications in telecommunications, lighting and display technology.

  From a materials perspective, one dramatically expanding area of today's LED technology is based on nitrides of Group III metals such as gallium nitride GaN, aluminum gallium nitride AlGaN, indium gallium nitride and their alloys. These materials are known as particularly suitable candidates for high brightness LEDs, for example for lighting applications.

  In the intensive development of more effective LED structures, the leading technological trend in recent years has been directed to vertical LED shapes, replacing previous laterally spreading structures. Previously, the two electrodes that form the electrical connection between the n-type and p-type layers of the component were formed on the same side of the LED chip laterally separated from each other. This configuration caused some limitations on the operation of the device. A vertical LED configuration with contact electrodes on the opposite side of the chip can provide essential advantages for device thermal management as well as current uniformity and light extraction efficiency.

  The simplified general principle of manufacturing vertical LEDs can be described, for example, as shown below. First, a layer structure including an n-type semiconductor layer, an active region, and a p-type semiconductor layer is formed on, for example, a sapphire growth substrate. A reflective contact layer is then formed on top of the structure to provide electrical connection to the p-type semiconductor layer and function as a mirror that reflects incident light generated from the back of the active region. A reflective thick metal layer is then deposited on the reflective contact layer to form the p-side contact electrode of the chip. This thick metal layer also functions as a support structure for the finished LED chip. Next, the growth support is removed, and the surface of the n-type layer originally grown on the growth substrate is exposed. Finally, another thick layer is formed on this exposed surface to form the n-side contact electrode.

  One important point in the vertical LED structure is the reflective contact structure. In addition to the desired high reflectivity and low electrical resistance, the reflective metal layer itself should also remain stable during the component life cycle, while in fact the metal layer that forms the p-side electrode. It should provide good adhesion between the device layers that operate at high speeds. For example, conventional solutions include a composite of different metals such as one or more layers of aluminum or gold deposited directly on a p-type semiconductor layer, or an intermediate adhesion layer initially formed on the semiconductor surface. . In the former case, the adhesive strength and long-term durability of the structure are usually insufficient. For example, an intermediate adhesive layer that includes nickel can promote adhesion. On the other hand, light loss through light absorption in the adhesive layer increases.

  An object of the present invention is to provide a novel light-emitting semiconductor device having excellent mechanical, optical and electrical characteristics.

  The light-emitting semiconductor device and the method for manufacturing a light-emitting semiconductor of the present invention are characterized by what is described in claims 1 and 8, respectively.

  The light emitting semiconductor device according to the present invention is made of a group III metal nitride. One preferred material is a different variation of gallium nitride, such as gallium nitride GaN and indium gallium nitride InGaN and aluminum gallium nitride AlGaN. Consisting of said material means that at least an essential part of the device in use contains at least some of said material. Of course, the device may also include materials that do not meet the above definition at different locations. As a main part, the device includes a layer structure including an n-type semiconductor layer, a p-type semiconductor layer, and an active region between the n-type semiconductor layer and the p-type semiconductor layer. The details of the layer structure may vary within the known technical scope and are not the essence of the present invention. The layer structure includes a contact surface defined by one of the n-type semiconductor layer and the p-type semiconductor layer, and a reflective contact structure attached to the contact surface. The reflective contact structure provides electrical contact to the semiconductor layer defining the contact surface and functions as a mirror that reflects incident light from the active region.

  According to the present invention, the reflective contact structure has a polycrystalline structure, a first transparent conductive oxide (TCO) contact layer deposited on a contact surface of the layer structure, and a second having an amorphous structure. A transparent conductive oxide (TCO) contact layer and a metal reflective layer deposited on the second TCO layer.

  The structure of the reflective metal contact using a two-layer intermediate TCO structure between the metal reflective layer and the contact surface offers significant advantages over prior art solutions. Each of the two TCO layers has a specific purpose. The polycrystalline metal structure of the first TCO layer provides high light transmission and low electrical resistance. On the other hand, the second TCO layer having an amorphous structure enables strong adhesion to the metal reflective layer.

  In addition to different crystal structures, the exact chemical composition of the two layers can be optimized separately for these different purposes. In order to obtain all the advantages of this opportunity, in a preferred embodiment of the invention, the chemical composition of the first TCO layer is such that the layer structure has strong adhesion to the contact surface, good transparency and the first Selected to promote high electrical conductivity of one TCO contact layer, and the chemical composition of the second TCO contact layer promotes strong adhesion of the metal reflective layer to the second TCO contact layer Selected as That is, the properties of the two TCO layers in this embodiment are optimized separately for these different purposes.

  The second TCO contact layer can be in direct contact with the first TCO contact layer. However, it is possible to have several intermediate layers between the two TCO contact layers.

  The layer defining the contact surface preferably comprises p-type indium gallium nitride InGaN. For that portion, the first TCO contact layer preferably comprises indium tin oxide that allows the presence of indium to provide excellent adhesion of the Group III metal to the metal. The first TCO contact layer is 30-500 nm in order to effectively spread current across the reflective contact structure and ensure a good intrinsic contact resistance that has little impact on the overall series resistance through the LED chip. Preferably, the thickness is 100 to 150 nm. If the thickness is too thin, the electrical properties of the layer will be insufficient. On the other hand, if this layer is too thick, the disadvantage of unnecessarily absorbing light generated in the active region increases.

  In a preferred embodiment of the present invention, the second TCO contact layer comprises zinc aluminum oxide (AZO), and the metal reflective layer comprises aluminum deposited on the second TCO contact layer, A strong adhesion between the second TCO contact layer and the metal reflective layer is ensured. Of course, these are just examples of possible materials. For example, another preferred material for the metal reflective layer is silver.

  The thickness of the second contact layer is limited due to the low light transmittance and electrical conductivity compared to polycrystalline TCO. On the other hand, if the thickness is too thin, the electrical conductivity is further reduced, or the adhesion to the upper metallic reflective layer is also reduced. A preferred range for the thickness is 0.2-20 nm, more preferably 1-3 nm.

  The metal reflective layer may be, for example, 20-1000 nm thick to ensure that light does not enter through the metal reflective layer and thereby maximize the reflectivity of the reflective contact structure. Furthermore, it is preferable that the thickness is at least 200 nm.

  In order to protect the metallic reflective layer from oxidation during further device processing, for example, an antioxidant layer formed of gold and having a thickness of 1-20 nm, preferably 5-10 nm, deposited on the metal reflective mirror surface Can exist.

  A method for manufacturing a light emitting semiconductor device made of a nitride of a Group III metal according to the present invention includes an n-type semiconductor layer, a p-type semiconductor layer, and an active region between the n-type semiconductor layer and the p-type semiconductor layer. Including a step of fabricating a structure, wherein the layered structure has a contact surface defined by one of the n-type semiconductor layer and the p-type semiconductor layer. The layer structure can be produced, for example, by conventional vapor phase epitaxial processes that are commonly used and known in the production of LEDs. Therefore, detailed description of the manufacturing process is omitted. The method further includes forming a reflective contact structure on the contact surface.

  According to the present invention, the step of forming the reflective contact structure has a polycrystalline structure, the step of forming a first transparent conductive oxide contact layer on the contact surface of the layer structure, and the amorphous structure Forming a second transparent conductive oxide (TCO) contact layer; and forming a metal reflective layer on the second TCO layer.

  The TCO contact layer can be deposited, for example, by sputtering. The deposited TCO is amorphous. Thus, the first TCO contact layer needs to be annealed to change the phase, such as crystallizing an originally amorphous layer. A suitable temperature range for annealing depends, for example, on the exact material composition, for example 150-300 ° C. The second TCO contact layer is deposited directly on several intermediate layers deposited directly on the first TCO contact layer or previously deposited on the first TCO contact layer.

  Preferably, in the method of the present invention, the chemical composition of the first TCO contact layer is such that the layer structure has strong adhesion to the contact surface, good transparency and high electrical conductivity of the first TCO contact layer. Selected to promote rate, and the chemical composition of the second TCO contact layer is selected to promote strong adhesion of the metal reflective layer to the second TCO contact layer. That is, in this embodiment, the characteristics of the two TCO layers are optimized separately according to their different functions. In practice, how to select the composition of the material is such that the properties depend on the material of the semiconductor structure. However, this is a habitual technique for those skilled in the art.

  The layer defining the contact surface preferably includes p-type indium gallium nitride InGaN. One preferred material for the first TCO contact layer comprises indium tin oxide.

  The first TCO contact layer is preferably formed with a thickness of 30-500 nm, preferably 100-150 nm.

  In a preferred embodiment, the second TCO contact layer includes aluminum zinc oxide, and the step of forming the metal reflective layer includes depositing aluminum on the second TCO contact layer.

  The second TCO contact layer is preferably formed with a thickness of 0.2-20 nm, and more preferably with a thickness of 1-3 nm. The metal reflective layer is preferably produced with a thickness of 20-1000 nm, but is preferably produced with a thickness of at least 200 nm.

  In addition to the manufacturing processes described above with respect to the main concepts of the present invention, the overall manufacturing process of the structure that provides electrical contact to the contact surface defining the semiconductor layer also includes depositing many additional layers. sell. First, in order to protect the metal reflective layer from oxidation during the next processing step, an oxidation resistant layer made of, for example, gold and having a thickness of 1-20 nm, preferably 5-10 nm is formed on the surface of the metal reflective layer. Can be deposited. Next, in order to promote adhesion of the next layer to the reflective contact structure, for example, an adhesive layer of titanium is deposited on the oxidation resistant layer. The diffusion barrier layer can then be deposited to protect the metal reflective layer from possible aggressive metal diffusion of the bonding pad that ultimately defines the surface electrode of the component. Finally, a thicker solderable layer can be deposited, for example, by galvanic deposition. Examples of suitable solderable metals include Au, Au / In alloys, and Cu. Of course, in addition to the deposition process described above, the manufacturing process can also include different patterning processes, eg, by lithography, to achieve the desired device shape.

  On the other hand, as a whole manufacturing process of the light emitting device, for example, in the case of a vertical light emitting diode LED, many additional processes may be required. Examples of these are, for example, a step of removing the growth substrate by chemical etching and a step of forming an electrical contact structure on the opposite side of the semiconductor device exposed in this way.

  The manufacturing method according to the present invention is suitable for mass production of cost-effective light-emitting devices in which several tens of wafers can be processed simultaneously.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.
FIG. 1 shows a schematic diagram of a vertical LED according to the present invention. 2a-2f show the manufacturing method according to the present invention. Corresponding layers are denoted by the same reference numerals in the figures. The drawings are different from the actual dimensions.

  The vertical LED chip of FIG. 1 includes an electron emitter layer 2 made of n-doped GaN, a hole emitter layer 3 made of p-doped InGaN, and an active region 4 that generates light between these two layers. Based on heterostructure. Below the hole emitter is a reflective contact layer 6. The underlying layer is an oxidation resistant layer 7 that prevents oxidation of the reflective contact layer during the manufacturing process after depositing the reflective contact layer. The oxidation resistant layer is made of Au and has a thickness of about 5 nm. The adhesive layer 8 formed of Ti is under the oxidation resistant layer and forms strong adhesion with the upper and lower layers of the adhesive layer 8. The lowermost layer of the chip of FIG. 1 is a lower metal layer 9, which is formed of, for example, Ni, by a diffusion barrier layer 10 that protects the upper device layer from diffusion of metal atoms in the lower metal layer. Separated from the rest of the semiconductor device. The lower metal layer functions as a p-side electrode that provides one of the two electrical connections required to electrically connect an external power source to the LED chip. The lower metal layer also provides an effective path for exhausting excess heat to the outside of the chip. On the other hand, the lower metal layer also functions as a protection and mechanical support for the structure of the chip. Through the lower metal layer, the chip can be bonded to an electrically conductive and thermally conductive pad such as a circuit board by, for example, soldering. The lower metal layer may be formed of, for example, Au, Au alloy, Cu, or other solderable metal and has a thickness in the range of 2-200 μm.

  The surface of the upper n-doped GaN layer 2 of the chip of FIG. 1 is constructed to have a non-planar surface topology. The rough surface reduces the total internal reflection of light 11 from the active layer 4 at the device surface, thereby facilitating light extraction from the chip. On top of this uneven surface is a reticulated upper metal layer 12 that forms the other contact electrodes of the chip.

  As shown in FIG. 1, the reflective contact structure 6 of the present embodiment includes three sub-layers. The next layer of the hole emitter layer is a first transparent conductive oxide (TCO) layer 13 formed of polycrystalline indium tin oxide and having a thickness in the range of 100-150. The layer below the first transparent conductive oxide layer 13 is a second transparent conductive oxide layer 14 made of amorphous aluminum zinc oxide and having a thickness in the range of 1-3 nm. The bottom sub-layer deposited on the second transparent conductive oxide layer is made of aluminum and has a thickness of at least 200 nm.

  The reflective contact structure 6 as a whole has two main purposes. First, the reflective contact structure 6 provides an electrical connection from the lower metal layer 9 to the hole emitter layer 3. Second, it functions as a mirror that reflects downward light 16 from behind the active region 4, thereby redirecting the light 16 in a direction that may leak out of the chip. Considered in more detail, each sublayer has its own purpose as part of the reflective contact layer. Of course, the metal mirror layer 15 is a factor in the actual reflective performance of the reflective contact structure. The thickness of the mirror layer is selected to ensure that light cannot substantially penetrate from the mirror layer to the next layer having high absorbency. The main purpose of the TCO layer is to provide a strong bond between the mirror layer 15 and the hole emitter layer 3. The first transparent conductive oxide layer 13 formed of indium tin oxide provides a strong adhesion of the reflective contact layer to the hole emitter layer 3 containing indium. Its polycrystalline structure provides good light transmission and minimizes the effect of the layer on the optical performance of the device. The polycrystalline structure of the layers also provides a relatively thick layer thickness with high electrical conductivity, and sufficient current spreading across the reflective contact structure, and good specific contact resistance to the hole emitter layer 3 Secure. Instead, the second transparent conductive oxide layer 14 of amorphous aluminum zinc oxide provides a strong bond between the first TCO layer 13 and the mirror layer 15 made of aluminum. Due to the low light transmission and low electrical conductivity of the amorphous material structure, the layer thickness is limited to a value substantially lower than the first TCO.

  As shown in FIG. 2 a, the exemplary manufacturing method begins by growing a semiconductor heterostructure including an insulating substrate wafer 17, an active region 4 sandwiched between an electron emitter layer 2 and a hole emitter layer 3. To do. Next, the mask metal 18 is deposited on the heterostructure and patterned by photolithography according to the desired chip size and shape. The heterostructure is then etched by reactive ion etching through the openings in the mask metal layer to form a separate mesa layer stack 19 as shown in FIG. 2b. The mask metal is removed after etching. The first transparent conductive oxide layer 13 is deposited on the wafer by sputtering, for example, and patterned by photolithography to remove the outer layer of mesas, and then the wafer is annealed to form a TCO polycrystalline structure. . Next, the other TCO layer 14, the reflective metal layer 15 and the metal oxidation resistant layer 7 of amorphous structure are deposited on top of each other and patterned by photolithography to remove the deposited material outside the mesa. To do.

  A dielectric passivation layer 20 is deposited and patterned by photolithography to protect the mesa sidewalls from materials deposited during subsequent processing steps. The passivation layer also reduces leakage current from the sidewall. The trenches between the mesas can be protected by depositing resist 21 and hard baking. The situation at this stage of the process is shown in FIG. The adhesion layer 8 and the diffusion barrier layer 10 are both made of metal, and are deposited and patterned on top of the mesa. After this, a thick metal layer 9 is deposited on the top of the wafer by electroplating. As shown in FIG. 2d, the metal is deposited as a continuous film across the wafer. As shown in FIG. 2 e, this metal layer forms a support structure that allows the next step, ie removal of the basic growth substrate 17, and a mesa layer structure is located on the thick metal layer 9.

  After removing the basic growth substrate, the exposed surface of the electron emitter layer 2 has irregularities. The n-side electrode of the chip is formed as a metal net on the uneven electron emitter surface. Finally, the mesa is separated into a single LED chip as shown in FIG. 2f.

  As an alternative to the above process, the process of removing the heterostructure and forming a separated mesa layer stack process may be performed as the last process after the n-side electrode formation.

  It is also important to note that, in general, the embodiments described above with reference to the drawings are merely some preferred embodiments and do not exclude all possible ways in which the invention can be implemented. is there. In particular, for all materials, the layer thicknesses and treatments used in the different manufacturing processes can be freely varied within the scope of the invention as defined in the claims.

Claims (14)

A light-emitting semiconductor device (1) made of a group III metal nitride, wherein the light-emitting semiconductor device includes an n-type semiconductor layer (2), a p-type semiconductor layer (3), the n-type semiconductor layer, and the p And an active region (4) between the type semiconductor layers, the layer structure having a contact surface (5) defined by one of the n-type semiconductor layer and the p-type semiconductor layer. The layer structure further includes a reflective contact structure (6) attached to the contact surface, the reflective contact structure (6)
A first transparent conductive oxide (TCO) contact layer (13) having a polycrystalline structure and attached to the contact surface (5) of the layer structure;
A second transparent conductive oxide (TCO) contact layer (14) having an amorphous structure;
A semiconductor device (1), comprising a metal reflective layer (15) attached to the second TCO layer.   The chemical composition of the first TCO contact layer (13) promotes strong adhesion of the layer structure to the contact surface (5), good transparency and high electrical conductivity of the first TCO contact layer. And the chemical composition of the second TCO contact layer (14) is selected to promote strong adhesion of the metal reflective layer (15) to the second TCO contact layer. The semiconductor device (1) according to claim 1, characterized in that:   The semiconductor device (1) according to claim 1 or 2, wherein the p-type semiconductor layer (3) defining the contact surface contains p-type InGaN.   The semiconductor device (1) according to any one of claims 1 to 3, wherein the first TCO contact layer (13) comprises indium tin oxide.   The semiconductor device (1) according to any one of claims 1 to 4, characterized in that the first TCO contact layer (13) has a thickness of 30-500 nm, preferably 100-150 nm.   The second TCO contact layer (14) comprises zinc aluminum oxide and the metal reflective layer (15) comprises aluminum deposited on the second TCO contact layer. 5. The semiconductor device (1) according to claim 5.   7. The semiconductor device (1) according to claim 1, wherein the second TCO contact layer (14) has a thickness of 0.2-20 nm, preferably 1-3 nm. ). A method for manufacturing a light-emitting semiconductor device (1) made of a nitride of a group III metal, comprising an n-type semiconductor layer (2), a p-type semiconductor layer (3), the n-type semiconductor layer, and the p-type semiconductor layer And a contact surface (5) defined by any one of the n-type semiconductor layer and the p-type semiconductor layer. And the step of forming a reflective contact structure (6) on the contact surface, and the step of forming the reflective contact structure (6) on the contact surface,
-Forming a first transparent conductive oxide (TCO) contact layer (13) on the contact surface (5) of said layer structure having a polycrystalline structure;
-Forming a second transparent conductive oxide (TCO) contact layer (14) having an amorphous structure;
-Forming a metal reflective layer (15) on the second TCO layer.   The chemical composition of the first TCO contact layer (13) promotes strong adhesion of the layer structure to the contact surface (5), good transparency and high electrical conductivity of the first TCO contact layer. And the chemical composition of the second TCO contact layer (14) is selected to promote strong adhesion of the metal reflective layer (15) to the second TCO contact layer. The manufacturing method of Claim 8 characterized by these.   10. The manufacturing method according to claim 8, wherein the p-type semiconductor layer (3) defining the contact surface (5) contains p-type InGaN.   The method according to any one of claims 8 to 10, wherein the first TCO contact layer (13) comprises indium tin oxide.   The method according to any one of claims 8 to 11, characterized in that the first TCO contact layer (13) is produced with a thickness of 30-500 nm, preferably 100-150 nm.   The second TCO contact layer (14) includes aluminum zinc oxide, and the step of forming the metal reflective layer (15) includes a step of depositing aluminum on the second TCO contact layer. The manufacturing method according to any one of claims 8 to 12.   14. A method according to any one of claims 8 to 13, characterized in that the second TCO contact layer (14) is produced with a thickness of 0.2-20 nm, preferably 1-3 nm. .

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