METHOD OF MANUFACTURING SEMICONDUCTOR LIGHT EMITTING DEVICE

A method of manufacturing a semiconductor light emitting device may include: forming a buffer layer on a substrate; forming a protective layer on the buffer layer; performing heat treatment on a stacked structure of the substrate, the buffer layer, and the protective layer; removing the protective layer; and forming a light emitting structure on the buffer layer.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims benefit of priority to Korean Patent Application No. 10-2017-0181752 filed on Dec. 28, 2017 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

Example embodiments of the present inventive concepts relate to a method of manufacturing a semiconductor light emitting device and/or a semiconductor light emitting device.

2. Description of Related Art

Semiconductor light emitting devices may emit light using the principle of the recombination of electrons and holes when an electric current is applied thereto, and have been widely used as light sources due to various advantages thereof such as low power consumption, high brightness, and ease of miniaturization. Further, after the development of nitride-based semiconductor light emitting devices, the utilization range thereof has been further enlarged, and such nitride-based semiconductor light emitting devices have been employed in backlight units, household lighting devices, lighting apparatuses for vehicles, and the like. Ultraviolet semiconductor light emitting devices may be used for various purposes, such as for sterilizing and disinfecting devices, UV curing devices and the like.

SUMMARY

An aspect of example embodiments of the present inventive concepts is to provide a method of manufacturing a semiconductor light emitting device having improved optical characteristics.

According to an example embodiment of the present inventive concepts, a method of manufacturing a semiconductor light emitting device includes: forming a buffer layer on a substrate; forming a protective layer on the buffer layer; performing a heat treatment on a stacked structure of the substrate, the buffer layer, and the protective layer; removing the protective layer after the heat treatment; and forming a light emitting structure on the buffer layer after removing the protective layer.

According to an example embodiment of the present inventive concepts, a method of manufacturing a semiconductor light emitting device includes: forming a buffer layer having a composition of AlxGa1-xN on a substrate, where 0<x≤1; forming a protective layer on the buffer layer such that the protective layer is formed of an dielectric material; performing a heat treatment on the buffer layer after forming the protective layer; and removing the protective layer.

According to an example embodiment of the present inventive concepts, a method of manufacturing a semiconductor light emitting device includes: forming a buffer layer on a substrate; forming a protective layer on the buffer layer such that the protective layer is formed of a material different from a material of the buffer layer; and performing heat treatment on the buffer layer after forming the protective layer.

DETAILED DESCRIPTION

Hereinafter, example embodiments of the present inventive concepts will be described with reference to the accompanying drawings.

FIG. 1is a flowchart schematically illustrating a method of manufacturing a semiconductor light emitting device according to example embodiments.

FIG. 2atoFIG. 2fare cross-sectional views schematically illustrating main processes of the method of manufacturing a semiconductor light emitting device according to example embodiments.

Referring toFIG. 1andFIG. 2a, in operation S110, a buffer layer110may be formed on a substrate101.

The substrate101may be a substrate for semiconductor growth, and may be a hetero-substrate for a nitride-based semiconductor layer to be grown thereon. For example, the substrate101may be sapphire and in this case, the substrate101is stable at high temperatures and may facilitate growth of a nitride film on an upper portion thereof. In addition to such matter, SiC, MgAl2O4, MgO, LiAlO2, LiGaO2, GaN and the like may be used for the substrate101.

The buffer layer110is a layer for improving crystallinity of semiconductor layers formed thereon. The buffer layer110may be formed to reduce crystal defects of the semiconductor layers due to a difference in lattice constants between the substrate101and the semiconductor layers. The buffer layer110may be formed of, for example, an aluminum gallium nitride (AlxGa1-xN, 0<x≤1) grown without doping. For example, when an ultraviolet (UV) semiconductor light emitting device is manufactured, the buffer layer110may be MN having relatively high band gap energy.

The buffer layer110may be formed on the substrate101by a metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HYPE), molecular beam epitaxy (MBE), or physical vapor deposition (PVD) process. According to example embodiments, prior to the forming of the buffer layer110, an internal temperature of a chamber where said process is performed may be raised to a desired (or, alternatively, a predetermined) temperature to allow for desorption of contaminants on the substrate101.

The buffer layer110may be formed to have a first thickness T1, and the first thickness T1may range from several tens of nanometers to several thousands of nanometers, for example, from 10 nm to 3000 nm. The first thickness T1may be selected depending on a material of the substrate101, a thickness and composition of a light emitting structure formed on an upper portion of the buffer layer110, and the like. In the process, the buffer layer110may be amorphous or polycrystalline and may be formed of an epitaxial layer according to a deposition method.

Referring toFIG. 1andFIG. 2b, in operation S120, a protective layer120may be formed on the buffer layer110.

The protective layer120may be a layer for protecting the buffer layer110during a subsequent heat treatment process. The protective layer120may be formed of a material different from that of the buffer layer110or may have a composition different from that of the buffer layer110. The protective layer120may be formed of, for example, a dielectric material. In this case, the protective layer120may contain, for example, a silicon oxide (SiO2), a silicon nitride (SiNx), an aluminum oxide (Al2O3), a tantalum oxide (Ta2O3), a titanium oxide (TiO2), an yttrium oxide (Y2O3), a zirconium oxide (ZrO2), a hafnium oxide (HfO2), a lanthanum oxide (La2O3), or combinations of these oxides.

The protective layer120may be formed by a physical vapor deposition (PVD), chemical vapor deposition (CVD), or atomic layer deposition (ALD) process.

The protective layer120may be formed to have a second thickness T2, and the second thickness T2may range from several angstroms to several hundreds of nanometers, for example, from 5 Å to 1000 Å. When the second thickness T2is smaller than the above range, protective functions for the buffer layer110may not be sufficiently performed. When the second thickness T2is greater than the above range, process efficiency may be lowered. The second thickness T2may be smaller than the first thickness T1of the buffer layer110, but is not limited thereto, and may be selected depending on heat treatment temperature and time and the like.

Referring toFIG. 1andFIG. 2c, in operation S130, a heat treatment process may be performed after the protective layer120is formed.

The heat treatment process is a process for performing a heat treatment on the buffer layer110covered with the protective layer120. The heat treatment process may be performed to reduce a defect such as dislocation, in the buffer layer110, thereby improving crystallinity. The heat treatment process may be performed on a stacked structure in which the buffer layer110and the protective layer120are formed on the substrate101. The heat treatment process may be performed at a temperature of about 1500° C. to 1800° C. for about 1 hour to 3 hours. The temperature and duration of the heat treatment process may be determined in consideration of temperature and duration at which defects in the buffer layer110may be sufficiently reduced. Further, the heat treatment process may be performed within a temperature range in which the stacked structure is not decomposed.

In example embodiments, an upper surface of the buffer layer110may be protected by the protective layer120during the heat treatment process, and, thus example embodiments may be able to reduce (or, alternatively, prevent) the decomposition of the buffer layer110from the upper surface thereof. In the heat treatment process, the buffer layer110may be protected from particles or foreign substances adsorbed on a surface thereof. Therefore, when the protective layer120is formed and the buffer layer110is subjected to heat treatment, particularly, upper surface morphology of the buffer layer110may be improved. This will be described in more detail below with reference toFIGS. 3aand3b.

Referring toFIG. 1andFIG. 2d, in operation S140, after the heat treatment process is completed, the protective layer120may be removed.

The protective layer120may be selectively removed from the buffer layer110by a dry or wet etching process. An etchant used in the etching process may be selected depending on a material of the protective layer120and may be selected as a material that does not affect the surface of the buffer layer110.

After the protective layer120is removed, an upper surface110AS of the buffer layer110covered by the protective layer120may be exposed. The upper surface110AS of the buffer layer110may have smooth surface morphology.

Referring toFIG. 1andFIG. 2e, in operation S150, a light emitting structure130may be formed on the buffer layer110.

The light emitting structure130may include a first conductive-type semiconductor layer132, an active layer134, and a second conductive-type semiconductor layer136sequentially formed on the buffer layer110. After the light emitting structure130is formed, the active layer134, the second conductivity-type semiconductor layer136, and the first conductivity-type semiconductor layer132are partially removed, as shown inFIG. 2e, such that a portion of the first conductivity-type semiconductor layer132may be exposed.

The first and second conductivity-type semiconductor layers132and136may be formed of semiconductors doped with n-type impurities and p-type impurities, respectively, but are not limited thereto. The first and second conductivity-type semiconductor layers132and136are formed of a nitride semiconductor, for example, a material having a composition of AlxInyGa1-x-yN (0≤x≤1, 0≤y≤1, 0≤x+y≤1), and each of the layers may be a single layer, but may have a plurality of layers having different characteristics in terms of a doping concentration, a composition, and the like. However, in addition to the nitride semiconductor, AlInGaP or AlInGaAs-based semiconductors may be used for the first and second conductivity-type semiconductor layers132and136.

The active layer134is disposed between the first and second conductivity-type semiconductor layers132and136and may emit light having a desired (or, alternatively, a predetermined) energy through the recombination of electrons and holes. The active layer134may be a layer formed of a single material, but may be a single quantum well (SQW) structure or multiple quantum well (MQW) structure in which a quantum well layer and a quantum barrier layer formed by controlling the magnitude of band gap energy while changing the composition of AlxInyGa1-x-yN (0≤x≤1, 0≤y≤1, 0≤x+y≤1) are alternately stacked. For example, a structure of AlGaN/AlGaN, AlGaN/AlN, InGaN/GaN, InGaN/InGaN, InGaN/AlGaN, InGaN/InAlGaN, or GaN/InGaN may be used. In particular, when the active layer134emits UV-C (200 to 280 nm wavelength) ultraviolet light, the quantum well layer and the quantum barrier layer may be formed of AlxGa1-xN (0.4≤x≤1) having a high Al composition of 40% or more.

Referring toFIG. 1andFIG. 2f, in operation S160, first and second electrodes150and160may be formed on the light emitting structure130.

The first and second electrodes150and160may be disposed on and electrically connected to the first and second conductive type semiconductor layers132and136, respectively. The first and second electrodes150and160may be formed of a single layer or multilayer structure of a conductive material.

For example, the first and second electrodes150and160may contain a material such as aurum (Au), silver (Ag), copper (Cu), zinc (Zn), aluminum (Al), indium (In), titanium (Ti), silicon (Si), germanium (Ge), tin (Sn), magnesium (Mg), tantalum (Ta), chrome (Cr), tungsten (W), ruthenium (Ru), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), or the like, or at least one of alloys of these materials. In example embodiments, at least one of the first and second electrodes150and160may be a transparent electrode, for example, an ITO (Indium tin Oxide), an AZO (Aluminum Zinc Oxide), an ITO (Indium Zinc Oxide), a zinc oxide (ZnO), GZO (ZnO:Ga), an indium oxide (In2O3), a tin oxide (SnO2), a cadmium oxide (CdO), a cadmium tin oxide (CdSnO4), or a gallium oxide (Ga2O3).

Positions and shapes of the first and second electrodes150and160shown inFIG. 2fare merely examples, and may be variously changed according to embodiments. In example embodiments, an ohmic electrode layer may be further disposed on the second conductivity-type semiconductor layer136, and the ohmic electrode layer may include, for example, p-GaN containing a high concentration p-type impurity. Alternatively, the ohmic electrode layer may be formed of a metal material or a transparent conductive oxide.

By the process, finally, a semiconductor light emitting device100may be manufactured. In the semiconductor light emitting device100, since the buffer layer110is formed to have a surface such as a mirror surface, with improved crystallinity, through the processes described above, the semiconductor layers constituting the light emitting structure130formed on the buffer layer110may be formed of films having excellent crystallinity. Therefore, the semiconductor light emitting device100may have high output characteristics and improved reliability.

In some example embodiments, the method may further include incorporating the semiconductor light emitting device into an apparatus.

In some example embodiments, the apparatus may be a purifier. For example, the apparatus may be a purifier that is configured to sterilize a substance (e.g., water) using the ultraviolet rays from the semiconductor light emitting device100. The purifier according to example embodiments may be higher in intensity of ultraviolet rays and purifying ability due to the high output characteristics achieved by the improved buffer layer110.

In other example embodiments, the apparatus may be a sterilizing device. The sterilizing device according to example embodiments may promote healing and prevent suppuration due to infection and infectious bacteria by preventing the propagation of infectious bacteria using ultraviolet rays from the semiconductor light emitting device100. The sterilizing device according to example embodiments may be higher in intensity of ultraviolet rays and sterilizing ability due to the high output characteristics achieved by the improved buffer layer110.

In still other example embodiments, the apparatus may be a curing device. The curing device according to example embodiments may cure a UV sensitive material, such as an ink, adhesive or coating. The curing device according to example embodiments may be higher in intensity of ultraviolet rays and curing ability due to the high output characteristics achieved by the improved buffer layer110.

FIG. 3AandFIG. 3Bare optical micrographs for illustrating characteristics of a semiconductor light emitting device according to example embodiments.

Referring toFIG. 3AandFIG. 3B, there are provided as images showing surfaces of buffer layers after the heat treatment operation (S130) in a comparative example and example embodiments, the images being captured by optical microscopy.

FIG. 3Ashows the surface of the buffer layer when a heat treatment was performed without the process of forming the protective layer of operation S120for the Comparative Example. That is, it is an image of a case in which a heat treatment was performed without the protective layer.FIG. 3Bshows the surface of the buffer layer when the protective layer was formed and then, the heat treatment process was performed and the protective layer was removed, as in the processes described above with reference toFIG. 1toFIG. 2d.

As illustrated inFIG. 3A, in the case of the comparative example, it may be confirmed that the surface of the buffer layer was partially decomposed and detached, whereby a state of the surface was not smooth and roughness thereof was significantly large. On the other hand, as shown inFIG. 3B, in example embodiments, a foreign substance was not present and a smooth surface was exhibited. Therefore, it can be understood that when heat treatment is performed on the buffer layer after the protective layer is formed, the surface state of the buffer layer is improved, and crystal quality of the semiconductor layers forming the light emitting structure formed on the buffer layer may be improved.

FIGS. 4 and 5are schematic cross-sectional views of semiconductor light emitting devices according to example embodiments.

Referring toFIG. 4, a semiconductor light emitting device100amay include a substrate101a, and a buffer layer110, a first conductivity-type semiconductor layer132, an active layer134, and a second conductivity-type semiconductor layer136that are disposed on the substrate101a. The semiconductor light emitting device100amay further include the first and second electrodes150and160as electrode structures.

Unlike the embodiment ofFIG. 2f, the semiconductor light emitting device100amay have a structure in which uneven portions P are formed on an upper surface of the substrate101a, that is, a growth surface of the semiconductor layers forming the light emitting structure130. Due to the uneven portions P, crystallinity and light emission efficiency of the semiconductor layers constituting the light emitting structure130may be further improved, and light extraction efficiency may be improved.

The semiconductor light emitting device100amay be manufactured by the manufacturing method described above with reference toFIG. 1toFIG. 2f. Thus, the buffer layer110may have high crystallinity and may have a smooth upper surface110AS.

Referring toFIG. 5, in a semiconductor light emitting device100b, a buffer layer110amay be formed of first and second buffer layers112and114, unlike the example embodiment ofFIG. 2f.

The semiconductor light emitting device100amay be manufactured by the manufacturing method described above with reference toFIG. 1toFIG. 2f. Specifically, the semiconductor light emitting device100bmay be manufactured by, after forming the protective layer120on an upper portion of the first and second buffer layers112and114, performing a heat treatment thereon and then, removing the protective layer120, during the formation of the respective first and second buffer layers112and114. Thus, the first and second buffer layers112and114may have high crystallinity and may have smooth upper surfaces112AS and114AS. In the example embodiments, the formation of the protective layer120and heat treatment processes may be applied to the formation of only one of the first and second buffer layers112and114. For example, the protective layer120may be formed and thermally treated only when the second buffer layer114in direct-contact with the light-emitting structure130is formed. This can be determined according to the purpose of forming the first and second buffer layers112and114, materials thereof, and the like.

The buffer layer110ais formed to have a structure including the first and second buffer layers112and114, thereby further improving film quality of the light emitting structure130formed thereon. For example, by further forming the second buffer layer114, the progress of defects such as dislocations in the first buffer layer112may be interrupted. The second buffer layer114may have a composition different from that of the first buffer layer112. For example, the second buffer layer114may have a composition between those of the first buffer layer112and the first conductivity-type semiconductor layer132, and for example, the second buffer layer114may have a higher content of aluminum (Al) than the first buffer layer112.

In example embodiments, a superlattice layer may be further disposed between the buffer layer110aand the light emitting structure130. The superlattice layer may be a layer in which a plurality of layers having different levels of band gap energy are alternately, repeatedly stacked, and may include n-type impurities. The superlattice layer forms a two-dimensional electron gas layer at an interface thereof due to discontinuity of energy bands caused by the plurality of layers. Thus, a tunneling phenomenon occurs through the two-dimensional electron gas layer when a voltage is applied, such that cladding effects of the first conductivity-type semiconductor layer132disposed above the superlattice layer may be improved, and high carrier mobility may be ensured to improve current diffusion effects. In addition thereto, the semiconductor light emitting device100bmay further include various compositions and numbers of cladding layers.

FIG. 6is a schematic cross-sectional view of a semiconductor light emitting device according to example embodiments.

Referring toFIG. 6, a semiconductor light emitting device100cmay include a light emitting structure130ahaving a shape different from that of the embodiment shown inFIG. 2f, and structures of the first and second electrodes150aand160amay be different from those of the example embodiment shown inFIG. 2f. The semiconductor light emitting device100cmay further include an insulating part170. The semiconductor light emitting element100cmay be manufactured by employing the manufacturing method described above with reference toFIG. 1toFIG. 2f. Thus, the buffer layer110may have high crystallinity and may have a smooth upper surface110AS.

The first electrode150amay include a connection electrode part155in the form of a conductive via that is connected to the first conductivity-type semiconductor layer132aby penetrating through the second conductivity-type semiconductor layer136aand the active layer134a, and a first electrode pad158connected to the connection electrode part155. The connection electrode part155may be surrounded by the insulating part170and electrically separated from the active layer134aand the second conductivity-type semiconductor layer136a. The number, shape and pitch of the connection electrode unit155, or the contact area of the connection electrode unit155with the first conductivity-type semiconductor layer132amay be appropriately designed so as to lower contact resistance. The second electrode160amay include an ohmic-contact layer165and a second electrode pad168on the second conductivity-type semiconductor layer136a.

The connection electrode part155and the ohmic-contact layer165may have a single layer or multilayer structure of a conductive material having ohmic characteristics with the first and second conductivity-type semiconductor layers132aand136a, respectively. For example, the connection electrode part155and the ohmic-contact layer165may be formed of at least one of Ag, Al, Ni, Cr and a transparent conductive oxide (TCO).

The first and second electrode pads158and168may be connected to the connection electrode part155and the ohmic-contact layer165, respectively, to function as external terminals of the semiconductor light emitting device100c. For example, the first and second electrode pads158and168may contain Au, Ag, Al, Ti, W, Cu, Sn, Ni, Pt, Cr, NiSn, TiW, AuSn, or eutectic metals thereof. The first and second electrodes150aand160amay be arranged in the same direction, and may be mounted on a lead frame or the like, in flip chip form.

The first and second electrodes150aand160amay be electrically separated from each other by the insulating part170. The insulating part170may be formed of an insulating material, and a material having low light absorptivity may be used. For example, for the insulating part170, a silicon oxide or silicon nitride such as SiO2, SiOxNy, SixNyor the like may be used. In one embodiment, the insulating part170may be formed as a light reflecting structure in which light reflective fillers are dispersed in a light-transmitting material. Alternatively, the insulating part170may be a multilayer reflective structure in which a plurality of insulating layers having different refractive indices are alternately stacked.

As set forth above, a method of manufacturing a semiconductor light emitting device having improved optical characteristics by covering the protective layer and performing heat treatment on the buffer layer can be provided.

Various and advantageous advantages and effects of example embodiments of the present inventive concepts are not limited to the above descriptions, and can be more easily understood in describing example embodiments of the present inventive concepts.