JP2017130558A - Method of manufacturing ultraviolet light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an ultraviolet light-emitting element capable of reducing a driving voltage.SOLUTION: In a method of manufacturing an ultraviolet light emitting element 10 including a laminate 20 in which an n-type AlGaN-based semiconductor layer 3, a light-emitting layer 4 and a p-type AlGaN-based semiconductor layer 5 are arranged in this order, a negative electrode 8 provided directly on a site 3aa which is not covered with the light emitting layer 4 on the surface 3a of the n-type AlGaN-based semiconductor layer 3, and a positive electrode 9 provided directly on the surface 5a of the p-type AlGaN-based semiconductor layer 5, when the p-type AlGaN-based semiconductor layer 5 is formed, an AlGaN-based semiconductor layer 6 containing at least one of Mg, Zn, Ca, Cd and Be is grown by an MOVPE method, thereafter, a first heat treatment for desorbing hydrogen in the AlGaN-based semiconductor layer 6 is performed on the AlGaN-based semiconductor layer 6, and then a second heat treatment is performed while being in contact with substance which contains no hydrogen and has reducibility.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing an ultraviolet light emitting element.

  Conventionally, in a method for manufacturing a gallium nitride-based compound semiconductor light emitting device, annealing is performed on a gallium nitride-based compound semiconductor layer containing magnesium, which is grown by vapor deposition, and then bonded to magnesium from the gallium nitride-based compound semiconductor layer containing magnesium. It is known to remove p-type hydrogen and form a p-type gallium nitride compound semiconductor layer in which the amount of hydrogen is less than that of magnesium (Patent Document 1).

JP-A-10-178212

  In the field of ultraviolet light emitting devices that require a p-type AlGaN layer with a high Al composition ratio, further reduction of the driving voltage by increasing the hole concentration is desired.

  An object of the present invention is to provide a method for manufacturing an ultraviolet light-emitting element capable of reducing the driving voltage.

  An ultraviolet light emitting device manufacturing method according to an aspect of the present invention includes an n-type AlGaN-based semiconductor layer, a light-emitting layer, and a p-type AlGaN-based semiconductor layer sequentially arranged on the surface of the n-type AlGaN-based semiconductor layer. A method for manufacturing an ultraviolet light emitting device comprising: a negative electrode provided directly on a portion not covered with the light emitting layer; and a positive electrode provided directly on the surface of the p-type AlGaN semiconductor layer. In forming the p-type AlGaN semiconductor layer, an AlGaN semiconductor layer containing at least one of Mg, Zn, Ca, Cd and Be is grown by MOVPE, and then the AlGaN semiconductor layer is grown. In contrast, the first heat treatment for desorbing hydrogen in the AlGaN-based semiconductor layer is performed, and then contacted with a reducing substance that does not contain hydrogen. Performing a heat treatment.

  The method for producing an ultraviolet light emitting element of the present invention has an effect that it is possible to reduce the driving voltage of the ultraviolet light emitting element.

1A to 1E are main process cross-sectional views illustrating a method for manufacturing an ultraviolet light emitting element according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of main processes for explaining a modification of the method for producing the ultraviolet light emitting element according to the above.

  Each drawing described in the following embodiment is a schematic diagram, and the ratio of the size and thickness of each component in the drawing does not necessarily reflect the actual dimensional ratio. In addition, the materials, numerical values, and the like described in the embodiments are merely preferable examples and are not intended to be limited thereto. Furthermore, the present invention can be appropriately modified in configuration without departing from the scope of its technical idea.

(Embodiment)
Below, before explaining the manufacturing method of the ultraviolet light emitting element 10 of this embodiment based on FIG. 1A-1E, the ultraviolet light emitting element 10 is demonstrated based on FIG. 1E.

  The ultraviolet light emitting element 10 is a rectangular parallelepiped LED chip (Light Emitting Diode Chip). The LED chip is also called an LED die (Light Emitting Diode die). Here, the planar view shape of the ultraviolet light emitting element 10 is, for example, a square shape. The “planar shape of the ultraviolet light emitting element 10” is an outer peripheral shape of the ultraviolet light emitting element 10 as viewed from one direction of the thickness direction of the ultraviolet light emitting element 10. The chip size of the ultraviolet light emitting element 10 in a plan view is, for example, 400 μm □ (400 μm × 400 μm). The planar view shape of the ultraviolet light emitting element 10 is not limited to a square shape, and may be, for example, a rectangular shape.

  The ultraviolet light emitting element 10 includes a stacked body 20 in which an n-type AlGaN semiconductor layer 3, a light emitting layer 4, and a p-type AlGaN semiconductor layer 5 are arranged in this order. Further, the ultraviolet light emitting element 10 includes a negative electrode 8 provided directly on a portion 3aa not covered with the light emitting layer 4 on the surface of the n-type AlGaN semiconductor layer 3, and a surface 5a of the p type AlGaN semiconductor layer 5. And a positive electrode 9 provided directly on.

  The ultraviolet light emitting element 10 further includes a substrate 1 that supports the laminate 20. The stacked body 20 is provided on one surface 1 a of the substrate 1. The n-type AlGaN semiconductor layer 3, the light emitting layer 4, and the p-type AlGaN semiconductor layer 5 are arranged in this order from the one surface 1a of the substrate 1. The ultraviolet light emitting element 10 preferably includes a buffer layer 2 interposed between the substrate 1 and the n-type AlGaN-based semiconductor layer 3.

  The ultraviolet light emitting element 10 has a mesa structure 11. The mesa structure 11 includes a part of the stacked body 20 including the buffer layer 2, the n-type AlGaN semiconductor layer 3, the light emitting layer 4, and the p-type AlGaN semiconductor layer 5 from the surface 20 a side of the stacked body 20. The semiconductor layer 3 is formed by etching halfway. In the ultraviolet light emitting element 10, the surface 5 a of the p-type AlGaN-based semiconductor layer 5, the surface 20 a of the stacked body 20, and the upper surface 11 a of the mesa structure 11 are configured by the same surface. In the ultraviolet light emitting element 10, a negative electrode 8 and a positive electrode 9 are disposed on one surface side in the thickness direction of the ultraviolet light emitting element 10. Here, “one surface in the thickness direction of the ultraviolet light-emitting element 10” means a portion 3aa of the n-type AlGaN semiconductor layer 3 on the light emitting layer 4 side that is not covered with the light emitting layer 4 and a p-type AlGaN system. The surface 5a of the semiconductor layer 5 is included.

In the ultraviolet light emitting element 10, an electrical insulating film (not shown) is formed across a part of the upper surface 11 a of the mesa structure 11, a side surface 11 b of the mesa structure 11, and a part of the surface 3 a of the n-type AlGaN-based semiconductor layer 3. It is preferable. As a material for the electrical insulating film, for example, SiO ₂ can be employed. The thickness of the electrical insulating film is, for example, 800 nm.

  The substrate 1 that supports the stacked body 20 is, for example, a sapphire substrate. One surface 1a (hereinafter, also referred to as “first surface 1a”) of the substrate 1 is a (0001) plane, that is, a c-plane. The first surface 1a of the substrate 1 has an off angle from the (0001) plane of 0 ° to 0.4 °. In the ultraviolet light emitting element 10, the second surface 1 b opposite to the first surface 1 a in the substrate 1 constitutes a light extraction surface that emits ultraviolet light. The thickness of the substrate 1 is, for example, 100 μm to 500 μm.

  The buffer layer 2 is a layer provided for the purpose of improving the crystallinity of the n-type AlGaN semiconductor layer 3, the light emitting layer 4, and the p-type AlGaN semiconductor layer 5. By providing the buffer layer 2, the ultraviolet light emitting element 10 can reduce the dislocation density and improve the crystallinity of the n-type AlGaN semiconductor layer 3, the light emitting layer 4, and the p-type AlGaN semiconductor layer 5. It becomes possible.

The buffer layer 2 is directly formed on one surface 1 a of the substrate 1. The buffer layer 2 is composed of, for example, an Al _x Ga _1-x N layer (0 <x ≦ 1). The thickness of the buffer layer 2 is, for example, 3 μm or more and 6 μm or less. As an example, the buffer layer 2 is an AlN layer having a thickness of 4 μm.

In the ultraviolet light emitting element 10, the n-type AlGaN-based semiconductor layer 3 is a layer for transporting electrons to the light emitting layer 4. The n-type AlGaN-based semiconductor layer 3 is composed of n-type In _x1 Al _y1 Ga _1-x1-y1 N layers (0 ≦ x1 <1, 0 <y1 <1, 0 <x1 + y1 <1). The In composition ratio x1 is, for example, 0 or more and 0.1 or less. For example, the Al composition ratio y1 is preferably 0.3 or more and less than 1, and more preferably 0.5 or more and less than 1. The n-type AlGaN semiconductor layer 3 contains Si. In other words, the n-type AlGaN semiconductor layer 3 contains Si as a donor impurity.

The n-type AlGaN-based semiconductor layer 3 also serves as an n-type contact layer for realizing good ohmic contact with the negative electrode 8. The Si concentration of the n-type AlGaN-based semiconductor layer 3 is, for example, not less than 5 × 10 ¹⁸ cm ^{−3 and not} more than 5 × 10 ¹⁹ cm ⁻³ . The thickness of the n-type AlGaN semiconductor layer 3 is, for example, not less than 1 μm and not more than 3 μm. For example, the n-type AlGaN-based semiconductor layer 3 is an n-type Al _0.60 Ga _0.40 N layer having a thickness of 2 μm. In this specification, the Si concentration is a value measured by, for example, SIMS (Secondary Ion Mass Spectroscopy).

  The light emitting layer 4 between the n-type AlGaN semiconductor layer 3 and the p-type AlGaN semiconductor layer 5 in the thickness direction of the stacked body 20 preferably has a multiple quantum well structure. In the multiple quantum well structure, a plurality of barrier layers and a plurality of well layers are alternately arranged in the thickness direction of the stacked body 20. The light emitting layer 4 is a layer that emits light (ultraviolet rays) by recombination of two types of carriers (electrons and holes) injected into the well layer.

Each of the plurality of well layers is constituted by a first In _a1 Al _b1 Ga _1-a1-b1 N layer (0 ≦ a1 <1, 0 <b1 <1, 0 <a1 + b1 <1). Each of the plurality of barrier layers includes a second In _a2 Al _b2 Ga _{1 -a2-b2} N layer (0 ≦ a2 <1, 0 <b2 <1, 0 <) having a larger Al composition ratio than the plurality of well layers. a2 + b2 <1).

  The ultraviolet light emitting element 10 is configured with a well layer of the light emitting layer 4 so as to emit ultraviolet rays in a UV-C wavelength region. The “wavelength range of UV-C” is, for example, 100 nm to 280 nm according to the classification according to the wavelength of ultraviolet rays by the International Commission on Illumination (CIE).

The light emitting layer 4 in the ultraviolet light emitting element 10 has four well layers and four barrier layers. The thickness of the well layer is, for example, not less than 0.5 nm and not more than 3 nm. The thickness of the barrier layer is, for example, 2 nm or more and 20 nm or less. The well layer is, for example, an Al _0.45 Ga _0.55 N layer having a thickness of 2 nm. As an example, the barrier layer is an Al _0.60 Ga _0.40 N layer having a thickness of 10 nm. The emission peak wavelength in the emission spectrum of the ultraviolet light emitting element 10 is about 275 nm. The “emission peak wavelength” here is the main emission peak wavelength at room temperature (27 ° C.).

In the ultraviolet light emitting element 10, the p-type AlGaN-based semiconductor layer 5 is a layer for transporting holes to the light emitting layer 4. The p-type AlGaN-based semiconductor layer 5 is composed of p-type In _x2 Al _y2 Ga _{1 -x2-y2} N layers (0 ≦ x2 <1, 0 <y2 <1, 0 <x2 + y2 <1). The In composition ratio x2 is, for example, 0 or more and 0.1 or less. For example, the Al composition ratio y2 is preferably 0.3 or more and less than 1, and more preferably 0.5 or more and less than 1. The p-type AlGaN semiconductor layer 5 contains Mg as an acceptor impurity. In this specification, the Mg concentration is a value measured by SIMS, for example. The acceptor impurity in the p-type AlGaN-based semiconductor layer 5 is not limited to Mg, and may be, for example, Zn, Ca, Cd, Be, or the like.

The p-type AlGaN-based semiconductor layer 5 also serves as a p-type contact layer for realizing good ohmic contact with the positive electrode 9. The concentration of Mg in the p-type AlGaN-based semiconductor layer 5 is, for example, 1 × 10 ¹⁹ cm ⁻³ or more and 2 × 10 ²⁰ cm ⁻³ or less. The thickness of the p-type AlGaN semiconductor layer 5 is, for example, 20 nm to 100 nm. For example, the p-type AlGaN-based semiconductor layer 5 is a p-type Al _0.70 Ga _0.30 N layer having a thickness of 50 nm and an Mg concentration of 1.5 × 10 ²⁰ cm ⁻³ . In this specification, the Mg concentration is a value measured by SIMS, for example.

  In the present specification, the composition ratio can be determined by, for example, composition analysis by the EDX method (Energy Dispersive X-ray Spectroscopy). In discussing the relative magnitude relationship of the composition ratio, the composition ratio is not limited to the EDX method, and may be a value obtained by, for example, composition analysis by Auger Electron Spectroscopy. Further, the composition ratio may be an approximate value obtained by using the Vegard's law based on the lattice constant obtained from the X-ray diffraction measurement, for example.

  The negative electrode 8 is for contact formed on the surface 3 a of the n-type AlGaN semiconductor layer 3 and not covered with the light emitting layer 4 in order to obtain ohmic contact with the n-type AlGaN semiconductor layer 3. Electrode. The negative electrode 8 is, for example, a laminated film of a first Al layer, a first Ni layer, a second Al layer, a second Ni layer, and an Au layer (hereinafter also referred to as “first laminated film”). Is formed on the portion 3aa of the n-type AlGaN-based semiconductor layer 3, and then annealed and slowly cooled. As an example, the first laminated film has the thicknesses of the first Al layer, the first Ni layer, the second Al layer, the second Ni layer, and the Au layer, which are 200 nm, 30 nm, 200 nm, 30 nm, and It is set to 200 nm. Here, the negative electrode 8 is composed of a solidified structure mainly composed of Ni and Al. The “solidified structure” means a crystal structure formed as a result of transformation of a molten metal into a solid. In other words, the “solidified structure” is a molten solidified structure formed by solidification of a molten metal containing Ni and Al. The solidified structure mainly composed of Ni and Al may contain, for example, Au and N as impurities. In the solidified structure, a plurality of Ni primary crystals in contact with the portion 3aa of the n-type AlGaN semiconductor layer 3 and an AlNi eutectic in contact with the portion 3aa of the n-type AlGaN semiconductor layer 3 are mixed. Since the AlNi eutectic has an Al composition ratio of about 96 to 97 at%, it is an Al-rich structure in which Al is richer than Ni. In the solidification structure constituting the negative electrode 8, it is presumed that a plurality of Ni primary crystals mainly contribute to the reduction of contact resistance, and the AlNi eutectic mainly contributes to the reduction of sheet resistance. The Ni primary crystal preferably contains, for example, Au and N as impurities. The reason why the Ni primary crystal contains N as an impurity is considered to be an estimated mechanism in which a part of N is extracted from the n-type AlGaN-based semiconductor layer 3 to form a solid solution when the Ni primary crystal grows. For example, the AlNi eutectic may contain Au as an impurity. The Ni primary crystal is a dendritic crystal, and the cross-sectional shape perpendicular to the thickness direction of the n-type AlGaN-based semiconductor layer 3 is preferably dendritic.

  Note that the negative electrode 8 is not limited to a configuration having Ni and Al as main components, and may have a configuration having Ti and Al as main components, for example.

  The positive electrode 9 is a contact electrode formed on the surface 5 a of the p-type AlGaN semiconductor layer 5 in order to obtain ohmic contact with the p-type AlGaN semiconductor layer 5. For example, the positive electrode 9 is formed by forming a laminated film of an Ni layer and an Au layer (hereinafter also referred to as “second laminated film”) on the surface 5 a of the p-type AlGaN-based semiconductor layer 5 and then performing an annealing process. It is formed by. For example, in the second laminated film, the thicknesses of the Ni layer and the Au layer are set to 20 nm and 150 nm, respectively.

  The ultraviolet light emitting element 10 preferably includes a first pad electrode (not shown) on the negative electrode 8. The first pad electrode is an external connection electrode. The first pad electrode is, for example, a laminated film of a Ti film and an Au film. The first pad electrode is electrically connected to the negative electrode 8. The first pad electrode preferably covers the negative electrode 8.

  The ultraviolet light emitting element 10 preferably includes a second pad electrode (not shown) on the positive electrode 9. The second pad electrode is an external connection electrode. The second pad electrode is, for example, a laminated film of a Ti film and an Au film. The second pad electrode is electrically connected to the positive electrode 9. The second pad electrode preferably covers the positive electrode 9.

  The ultraviolet light emitting element 10 is not limited to the UV-C wavelength range, and may be configured to emit ultraviolet rays in the UV-B wavelength range, for example. The “UV-B wavelength range” is, for example, 280 nm to 315 nm according to the classification by the wavelength of ultraviolet rays in the International Commission on Illumination.

  Below, the manufacturing method of the ultraviolet light emitting element 10 is demonstrated based on FIG.

  In the method for manufacturing the ultraviolet light emitting element 10, first, a wafer 100 that serves as a base for the substrate 1 of each of the plurality of ultraviolet light emitting elements 10 is prepared. The wafer 100 is, for example, a sapphire wafer.

In the method of manufacturing the ultraviolet light emitting element 10, after the wafer 100 is prepared, the wafer 100 is pretreated, and then the wafer 100 is introduced into a reaction furnace of a MOVPE (metal organic vapor phase epitaxy) apparatus. On the first surface 101, an epitaxial layer 21 that is the basis of the stacked body 20 is grown by the MOVPE method (see FIG. 1A). The epitaxial layer 21 is a multilayer epitaxial layer including the buffer layer 2, the n-type AlGaN semiconductor layer 3, the light emitting layer 4, and the AlGaN semiconductor layer 6 that is the basis of the p-type AlGaN semiconductor layer 5. The first surface 101 of the wafer 100 is a surface corresponding to the first surface 1 a of the substrate 1. In the MOVPE method, it is preferable to employ trimethylaluminum (TMAl) as the Al source gas. Trimethylgallium (TMGa) is preferably employed as the Ga source gas. Trimethylindium (TMIn) is preferably used as the In source gas. As the N source gas, NH ₃ is preferably employed. It is preferable to employ tetraethylsilane (TESi) as a source gas of Si that is an impurity imparting n-type conductivity. It is preferable to employ biscyclopentadienyl magnesium (Cp ₂ Mg) as a source gas for Mg, which is an impurity contributing to p-type conductivity. For example, H ₂ gas is preferably used as the carrier gas of each source gas. Each source gas is not particularly limited. For example, triethylgallium (TEGa) may be employed as a Ga source gas, hydrazine derivative may be employed as a N source gas, and monosilane (SiH ₄ ) may be employed as a Si source gas. The growth conditions of the epitaxial layer 21 are the substrate temperature, the V / III ratio, the supply amount of each source gas, the growth pressure, etc. for each of the buffer layer 2, the n-type AlGaN semiconductor layer 3, the light emitting layer 4 and the AlGaN semiconductor layer 6. May be set as appropriate. “Substrate temperature” means the temperature of the wafer 100. As the “substrate temperature”, for example, the temperature of a susceptor that supports the wafer 100 in the reaction furnace of the MOVPE apparatus can be substituted. “V / III ratio” means a source gas of N which is a group V element with respect to a molar supply amount [μmol / min] of a group III element source gas (Al source gas, Ga source gas, In source gas) It is a ratio with the molar supply amount [μmol / min]. The “growth pressure” is the pressure in the reaction furnace in a state where each source gas and each carrier gas are supplied into the reaction furnace of the MOVPE apparatus. As the substrate temperature, the temperature of the susceptor measured by a thermocouple can be substituted. When growing the buffer layer 2, for example, TMAl and NH ₃ are supplied into the reactor as source gases, the growth pressure is 40 kPa, and the substrate temperature is 1300 ° C. When growing the n-type AlGaN-based semiconductor layer 3, for example, TMAl, TMGa, NH ₃ and TESi are introduced into the reactor as source gases, the growth pressure is set to 20 kPa, and the substrate temperature is set to 1100 ° C. When the light emitting layer 4 is grown, for example, TMAl, TMGa, and NH ₃ are introduced into the reactor as source gases, the growth pressure is set to 20 kPa, and the substrate temperature is set to 1100 ° C. When the AlGaN-based semiconductor layer 6 is grown, for example, TMAl, TMGa, NH ₃ and Cp ₂ Mg are supplied as source gases, the growth pressure is 20 kPa, and the substrate temperature is 1100 ° C.

  In the method for manufacturing the ultraviolet light emitting element 10, after the first step of growing the epitaxial layer 21 on the first surface 101 of the wafer 100, the wafer on which the epitaxial layer 21 is grown is taken out from the MOVPE apparatus. Hereinafter, a structure including at least the wafer 100 and the epitaxial layer 21 is referred to as an epitaxial wafer 120.

  In the method for manufacturing the ultraviolet light emitting element 10, the epitaxial wafer 120 taken out from the MOVPE apparatus is introduced into the first annealing apparatus 130, and first heating for activating Mg (p-type impurities) in the AlGaN-based semiconductor layer 6 is performed. Processing is performed (see FIG. 1B). The first heat treatment is a treatment for heating the AlGaN semiconductor layer 6 in order to remove (desorb) hydrogen in the AlGaN semiconductor layer 6. “Removing hydrogen in the AlGaN-based semiconductor layer 6” is a concept including removing not only all of the hydrogen in the AlGaN-based semiconductor layer 6 but also part of the hydrogen. By performing the first heat treatment, the hole concentration of the AlGaN-based semiconductor layer 6 can be increased, and the p-type conductivity can be improved. This is presumed that by performing the first heat treatment, H bonded to Mg in the AlGaN-based semiconductor layer 6 is removed and Mg is activated. The hole concentration is, for example, a carrier concentration obtained from the result of hole measurement.

As the first annealing apparatus 130 for performing the first heat treatment, for example, a lamp annealing apparatus, an electric furnace annealing apparatus, or the like can be employed. The first heat treatment condition (first annealing condition) is, for example, an annealing temperature of 600 ° C. to 1000 ° C. and an annealing time of 10 minutes to 50 minutes. As an example of the first annealing condition, the annealing temperature is 750 ° C. and the annealing time is 10 minutes. For example, the first heat treatment is preferably performed in an inert gas atmosphere. The inert gas is preferably N ₂ gas. This makes it possible to suppress the desorption of N, which is a constituent element of the AlGaN-based semiconductor layer 6, during the first heat treatment, and the AlGaN-based semiconductor layer 6 caused by the N desorption. It is assumed that the occurrence of defects can be suppressed. In the first heat treatment, the entire epitaxial wafer 120 is heated. However, the present invention is not limited to this, and at least the AlGaN-based semiconductor layer 6 may be heated. Further, the first heat treatment is not limited to being performed in the first annealing apparatus 130, and may be performed, for example, in a reaction furnace of the MOVPE apparatus before the epitaxial wafer 120 is taken out from the MOVPE apparatus.

By the way, the inventors of the present application evaluated the impurity concentration of the AlGaN-based semiconductor layer 6 (p-type Al _0.70 Ga _0.30 N layer) by SIMS for the first sample for evaluation after the first heat treatment was completed. As a result, regarding the impurity concentration of the AlGaN-based semiconductor layer 6, the Mg concentration is 1.5 × 10 ²⁰ cm ⁻³ , the O concentration is 1.0 × 10 ¹⁸ cm ⁻³ , and the O concentration relative to the Mg concentration is The concentration ratio was 6.67%. In addition, the inventors of the present application conducted a p-type test on the second sample for evaluation performed up to the first heat treatment on the GaN layer (GaN containing Mg) grown in place of the AlGaN-based semiconductor layer 6. The impurity concentration of the GaN layer was evaluated by SIMS. As a result, regarding the impurity concentration of the p-type GaN layer, the Mg concentration is 1.5 × 10 ¹⁹ cm ⁻³ and the O concentration is less than the detection limit (less than 5.0 × 10 ¹⁶ cm ⁻³ ), The ratio of the O concentration to the Mg concentration was less than 0.03%. The inventors of the present application have one reason that the hole concentration of the AlGaN-based semiconductor layer 6 (p-type Al _0.70 Ga _0.30 N layer) is lower than that of the p-type GaN. It was thought that the concentration ratio between the Mg concentration in the _0.70 Ga _0.30 N layer) and the O concentration was large.

Accordingly, the inventors of the present invention take out the epitaxial wafer 120 from the first annealing apparatus 130 after the second step of performing the first heat treatment on the AlGaN-based semiconductor layer 6 in the method for manufacturing the ultraviolet light emitting element 10. After that, the epitaxial wafer 120 was introduced into the second annealing device 140, and the second heat treatment for desorbing O in the AlGaN-based semiconductor layer 6 was performed (see FIG. 1C). The second heat treatment is a treatment for heating the surface of the AlGaN-based semiconductor layer 6 so as to be in contact with a reducing substance that does not contain hydrogen. “Removing O in the AlGaN-based semiconductor layer 6” is a concept including removing not only all of the oxygen in the AlGaN-based semiconductor layer 6 but also part of oxygen. Thereby, in the manufacturing method of the ultraviolet light-emitting device 10, O in the AlGaN-based semiconductor layer 6 can be removed by a reduction reaction between O in the AlGaN-based semiconductor layer 6 and a reducing substance, and the second heat treatment is being performed. In addition, it is possible to suppress the incorporation of H into the AlGaN-based semiconductor layer 6. By performing the second heat treatment, the p-type AlGaN semiconductor layer 5 in which O is removed from the AlGaN semiconductor layer 6 is formed. An example of the reducing substance is a reducing gas. The reducing gas is, for example, CO gas. The reducing gas is not limited to CO gas, and may be NO (nitrogen monoxide) gas, for example. The second heat treatment is not limited to heating the AlGaN semiconductor layer 6 so that the surface of the AlGaN semiconductor layer 6 is in contact with only the reducing gas. For example, the surface of the AlGaN semiconductor layer 6 is reduced. The AlGaN-based semiconductor layer 6 may be heated so as to be in contact with a reactive gas and an inert gas (for example, N ₂ gas).

  As the second annealing apparatus 140 for performing the second heat treatment, for example, a lamp annealing apparatus, an electric furnace annealing apparatus, or the like can be employed. The conditions for the second heat treatment (second annealing conditions) are, for example, an annealing temperature of 400 ° C. to 1000 ° C. and an annealing time of 10 minutes to 50 minutes. The annealing temperature is preferably equal to or lower than the growth temperature of the AlGaN-based semiconductor layer 6 from the viewpoint of preventing decomposition of the AlGaN-based semiconductor layer 6, desorption of N, and the like. Thus, it is assumed that it is possible to suppress the occurrence of defects in the AlGaN-based semiconductor layer 6 during the second heat treatment. In the second heat treatment, the entire epitaxial wafer 120 is heated. However, the present invention is not limited to this, and at least the AlGaN-based semiconductor layer 6 may be heated. The second heat treatment is not limited to being performed in the second annealing apparatus 140, and may be performed in the first annealing apparatus 130 before the epitaxial wafer 120 is taken out from the first annealing apparatus 130, for example. Further, the second heat treatment may be performed in a reactor of the MOVPE apparatus before the epitaxial wafer 120 is taken out from the MOVPE apparatus.

  In the method for manufacturing the ultraviolet light emitting element 10, after the third step of performing the second heat treatment on the AlGaN-based semiconductor layer 6, the epitaxial wafer 120 is taken out from the second annealing apparatus 140, and then the photolithography technique and the etching are performed. The mesa structure 11 is formed using technology or the like (see FIG. 1D).

  In the method for manufacturing the ultraviolet light emitting element 10, after the fourth step of forming the mesa structure 11, an electrical insulating film (not shown) is formed. The electrical insulating film can be formed using a thin film forming technique such as a chemical vapor deposition (CVD) method, a photolithography technique, and an etching technique.

In the method for manufacturing the ultraviolet light emitting element 10, the negative electrode 8 and the positive electrode 9 are formed after the fifth step of forming the above-described electrical insulating film (see FIG. 1E). In order to form the negative electrode 8, first, a first resist layer patterned so as to expose only a region where the negative electrode 8 is to be formed is formed on the surface of the epitaxial wafer 120. Thereafter, for example, a first Al layer with a thickness of 100 nm, a first Ni layer with a thickness of 20 nm, a second Al layer with a thickness of 100 nm, a second Ni layer with a thickness of 20 nm, and a thickness of 100 nm A first laminated film in which an Au layer is laminated is formed by vapor deposition. After the first laminated film is formed, lift-off is performed to remove the first resist layer and unnecessary films on the first resist layer (the portion of the first laminated film formed on the first resist layer). Thus, the first laminated film is patterned. Thereafter, annealing is performed. The annealing process is a process for making the contact between the negative electrode 8 and the n-type AlGaN-based semiconductor layer 3 ohmic contact. The laminated structure and each thickness of the first laminated film are examples, and are not particularly limited. The annealing treatment is preferably RTA (Rapid Thermal Annealing) in an N ₂ gas atmosphere. The conditions for the RTA treatment may be, for example, an annealing temperature of 700 ° C. and an annealing time of 1 minute, but these values are merely examples and are not particularly limited. The annealing temperature is preferably a temperature at which Al is easily diffused, and more preferably 650 ° C. or more and less than 750 ° C. The annealing time may be set in the range of about 30 seconds to 3 minutes, for example. In order to form the negative electrode 8 mainly composed of Ti and Al, a laminated film of a Ti layer and an Al layer is formed, patterned, and then annealed at an annealing temperature of 800 ° C. and an annealing time of 1 minute. Just do it.

In the method for manufacturing the ultraviolet light emitting element 10, the positive electrode 9 is formed after the negative electrode 8 is formed. In order to form the positive electrode 9, first, a second resist layer is formed on the surface of the epitaxial wafer 120 so as to expose only the region where the positive electrode 9 is to be formed. After that, for example, a second laminated film of a Ni layer having a thickness of 20 nm and an Au layer having a thickness of 150 nm is formed by an electron beam evaporation method, and lift-off is performed, whereby the second resist layer and the second resist layer are formed. The unnecessary film (the portion of the second laminated film formed on the second resist layer) is removed. Thereafter, an RTA process is performed in an N ₂ gas atmosphere so that the contact between the positive electrode 9 and the p-type AlGaN-based semiconductor layer 5 is an ohmic contact. The laminated structure and each thickness of the second laminated film are examples, and are not particularly limited. The RTA treatment conditions may be, for example, an annealing temperature of 500 ° C. and an annealing time of 15 minutes, but these values are merely examples and are not particularly limited.

  In the method for manufacturing the ultraviolet light emitting element 10, after the sixth step of forming the negative electrode 8 and the positive electrode 9, the first pad electrode and the second pad electrode are lifted off using, for example, photolithography technology and thin film formation technology. Form by the method.

  In the method for manufacturing the ultraviolet light emitting element 10, an epitaxial wafer 120 on which a plurality of ultraviolet light emitting elements 10 are formed can be obtained.

  In the method for manufacturing the ultraviolet light emitting element 10, after the seventh step of forming the first pad electrode and the second pad electrode, the epitaxial wafer 120 is cut by a dicing saw or the like, thereby making one epitaxial wafer 120. Thus, a plurality of ultraviolet light emitting elements 10 can be obtained. In the method of manufacturing the ultraviolet light emitting element 10, before cutting the epitaxial wafer 120, the wafer 100 is placed on the second surface 102 side opposite to the first surface 101 so that the thickness of the wafer 100 is the desired thickness of the substrate 1. It is preferable to polish from. Thereby, the manufacturing method of the ultraviolet light emitting element 10 can improve the manufacturing yield.

  The method for manufacturing the ultraviolet light emitting element 10 according to this embodiment described above includes the stacked body 20 in which the n-type AlGaN semiconductor layer 3, the light emitting layer 4, and the p-type AlGaN semiconductor layer 5 are arranged in this order, and the n-type AlGaN semiconductor. A negative electrode 8 provided directly on a portion of the surface 3a of the layer 3 that is not covered with the light-emitting layer 4, and a positive electrode 9 provided directly on the surface 5a of the p-type AlGaN-based semiconductor layer 5 This is a method for manufacturing the ultraviolet light emitting element 10. In forming the p-type AlGaN-based semiconductor layer 5, an AlGaN-based semiconductor layer 6 containing at least one of Mg, Zn, Ca, Cd, and Be is grown by MOVPE, and then the AlGaN-based semiconductor layer 6 is grown. On the other hand, after the first heat treatment for desorbing hydrogen in the AlGaN-based semiconductor layer 6 is performed, the second heat treatment is performed so as to be in contact with a reducing substance that does not contain hydrogen. Therefore, the method for manufacturing the ultraviolet light emitting element 10 can reduce the driving voltage of the ultraviolet light emitting element 10. The method for manufacturing the ultraviolet light emitting element 10 can reduce the resistance of the p-type AlGaN semiconductor layer 5 by reducing the concentration of O in the p-type AlGaN semiconductor layer 5, thereby reducing the driving voltage of the ultraviolet light emitting element 10. It becomes possible to achieve voltage.

  In the method for manufacturing the ultraviolet light emitting element 10, the reducing substance is preferably a reducing gas. Thereby, the manufacturing method of the ultraviolet light emitting element 10 can simplify the manufacturing process.

  Here, the reducing gas is preferably CO (carbon monoxide). Thereby, the manufacturing method of the ultraviolet light emitting element 10 can desorb O in the AlGaN-based semiconductor layer 6 while suppressing the introduction of new impurities into the AlGaN-based semiconductor layer 6.

  The reducing substance may be a reducing metal. Thereby, the manufacturing method of the ultraviolet light emitting element 10 can further suppress the decomposition of the AlGaN-based semiconductor layer 6 and the desorption of N during the second heat treatment. Therefore, in the method for manufacturing the ultraviolet light emitting element 10, it is possible to further reduce the resistance of the p-type AlGaN semiconductor layer 5.

  In the method for manufacturing the ultraviolet light emitting element 10, when the reducing substance is a reducing metal, the first heat treatment described above is performed, and then the epitaxial wafer 120 is taken out from the first annealing apparatus 130 and then AlGaN is removed. A reducing metal layer 7 (see FIG. 2) is formed on the surface of the semiconductor layer 6 and then the epitaxial wafer 120 is introduced into the second annealing device 140 to desorb O in the AlGaN semiconductor layer 6. A second heat treatment is performed. As a method for forming the reducing metal layer 7, for example, a vacuum deposition method, a sputtering method, or the like may be employed.

  The reducing metal is preferably an alkali metal or an alkaline earth metal. Thereby, the manufacturing method of the ultraviolet light emitting element 10 can desorb O in the AlGaN-based semiconductor layer 6 while suppressing the introduction of new impurities into the AlGaN-based semiconductor layer 6.

  In the method for manufacturing the ultraviolet light emitting element 10, it is preferable to remove the reducing metal after the second heat treatment, and then form the positive electrode 9 on the surface 5 a of the p-type AlGaN-based semiconductor layer 5. Thereby, the manufacturing method of the ultraviolet light emitting element 10 increases the degree of freedom in selecting the material of the positive electrode 9 and further reduces the contact resistance between the p-type AlGaN-based semiconductor layer 5 and the positive electrode 9. Is possible. Thereby, the manufacturing method of the ultraviolet light emitting element 10 can further reduce the driving voltage of the ultraviolet light emitting element 10. In order to remove the reducing metal, the reducing metal layer 7 may be removed by etching.

  The substrate 1 is a single crystal substrate and is preferably a sapphire substrate. The single crystal substrate is not limited to a sapphire substrate, and may be, for example, a SiC substrate, an AlN substrate, or the like. Thereby, the ultraviolet light emitting element 10 can emit the ultraviolet light emitted from the light emitting layer 4 from the second surface 1 b of the substrate 1.

The ultraviolet light emitting element 10 may include an electron blocking layer between the light emitting layer 4 and the p-type AlGaN semiconductor layer 5. The electron blocking layer is a layer for blocking electrons from the light emitting layer 4 side in the thickness direction of the stacked body 20. In other words, among the electrons injected from the n-type AlGaN-based semiconductor layer 3 into the light-emitting layer 4, electrons that have not been recombined with holes in the light-emitting layer 4 are converted into p-type AlGaN-based semiconductor layers 5. This is a layer for suppressing the leak (overflow). The electron block layer is preferably composed of, for example, a p-type AlGaN layer, and preferably has an Al composition ratio larger than that of the p-type AlGaN-based semiconductor layer 5 and contains Mg. The electron blocking layer is, for example, a p-type Al _0.90 Ga _0.10 N layer having a thickness of 50 nm. In this case, in the method for manufacturing the ultraviolet light emitting element 10, after the light emitting layer 4 is grown by the MOVPE method, the AlGaN layer serving as the base of the electron blocking layer is grown and then the AlGaN-based semiconductor layer 6 is grown.

  The ultraviolet light emitting element 10 is not limited to an LED chip that emits ultraviolet rays, but may be, for example, an LD chip (Laser Diode Chip) that emits ultraviolet rays.

1 substrate 1a one surface 3 n-type AlGaN semiconductor layer 3a surface 3aa part 4 light emitting layer 5 p-type AlGaN semiconductor layer 5a surface 6 AlGaN semiconductor layer 8 negative electrode 9 positive electrode 10 ultraviolet light emitting element 20 laminate

Claims (6)

A laminate in which an n-type AlGaN-based semiconductor layer, a light-emitting layer, and a p-type AlGaN-based semiconductor layer are arranged in this order, and a surface of the n-type AlGaN-based semiconductor layer that is not directly covered with the light-emitting layer. A method for producing an ultraviolet light emitting device comprising a negative electrode and a positive electrode provided directly on the surface of the p-type AlGaN-based semiconductor layer,
In forming the p-type AlGaN-based semiconductor layer,
Growing an AlGaN-based semiconductor layer containing at least one of Mg, Zn, Ca, Cd, and Be by the MOVPE method,
Thereafter, a first heat treatment for desorbing hydrogen in the AlGaN-based semiconductor layer is performed on the AlGaN-based semiconductor layer, and then a second material is brought into contact with the reducing substance not containing hydrogen. Heat treatment,
A method for producing an ultraviolet light-emitting element. The reducing substance is a reducing gas.
The method for producing an ultraviolet light-emitting device according to claim 1. The reducing gas is CO gas.
The method for producing an ultraviolet light-emitting device according to claim 2. The reducing substance is a reducing metal.
The method for producing an ultraviolet light-emitting device according to claim 1. The reducing metal is an alkali metal or an alkaline earth metal,
The method for producing an ultraviolet light-emitting element according to claim 4. Removing the reducing metal after the second heat treatment;
Thereafter, the positive electrode is formed on the surface of the p-type AlGaN-based semiconductor layer.
The method for producing an ultraviolet light-emitting device according to claim 4 or 5, wherein:

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