Micro light emitting device based on tin alloy electrode application and preparation method thereof

Abstract

The application provides a micro light emitting device based on a tin alloy electrode application and a preparation method thereof, wherein a DBR structure layer is arranged on the surface of an epitaxial stack, the DBR structure layer comprises DBR reflection layers and stress buffer layers which are sequentially stacked along the surface of the epitaxial stack, and the DBR structure layer has a first through hole and a second through hole; a first electrode is deposited in electrical connection between the first through hole and the first type semiconductor layer and extends upward to the surface of the DBR structure layer, and the first electrode comprises a tin alloy electrode; and a second electrode is deposited in electrical connection between the second through hole and the second type semiconductor layer and extends upward to the surface of the DBR structure layer, and the second electrode comprises a tin alloy electrode. The surface of the LED chip adopts a tin alloy electrode structure, realizes a tin paste-free packaging mode, avoids abnormal problems such as tin connection caused by the low printing precision of the tin paste steel mesh, and simultaneously avoids problems such as the precise control of the steel mesh in the tin paste printing.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of light-emitting diodes, in particular to a micro light-emitting device based on tin alloy electrode application and a preparation method thereof. BACKGROUND

[0002] With the continuous development of semiconductor light-emitting technology, the application of LED is changing with each passing day, especially the development of LED in display technology. At the same time, due to the need for high resolution of LED display screen, the pitch of LED chip and the size of chip are becoming smaller and smaller, such as Mini-LED and other micro light-emitting devices.

[0003] Mini-LED and other micro light-emitting devices have a size of microns, and there are usually thousands of chips and tens of thousands of solder joints on each substrate. Such a large number of solder joints, and due to the limitation of chip size and the pitch between two polarity electrodes, the electrode pad size is small, which brings great difficulty to the packaging and soldering of the chip. At the same time, in order to overcome the size limitation of discrete devices on the pitch, the integrated packaging (COB) method is usually used, which has higher requirements for stability and consistency during operation. Therefore, the stable and reliable realization of the soldering of the chip and the substrate during the packaging process is one of the most important links in the application process of Mini-LED and other micro light-emitting devices.

[0004] For LED chip soldering, the conventional methods include reflow soldering and eutectic soldering.

[0005] Among them, reflow soldering is: in the packaging process, through the tin paste fixing method, the corresponding electrode surface is Au structure, and the specific tin paste is applied to the corresponding pad position of the substrate, then the chip is fixed, and then the high temperature curing is carried out through the reflow soldering furnace according to a certain temperature curve. The selection of tin paste determines the temperature required for curing, which is usually selected between 180-260℃, the temperature is relatively low, and is basically consistent with the chip process temperature, which has little effect on the chip structure. At the same time, due to the small size of Mini-LED and other micro light-emitting devices and the solder pad, the amount and position accuracy of tin paste are extremely important. At the same time, the adaptability of the chip electrode pad to the tin paste is also very important. If the protection is insufficient, electrode corrosion and falling off are prone to occur, resulting in low yield of tin paste die bonding process and high repair cost.

[0006] Eutectic soldering is: in the packaging process, through the flux fixing method, if the AuSn electrode structure is used for the chip electrode pad, due to the eutectic temperature limitation of AuSn material itself, the temperature is usually around 320℃, which has high requirements for the stability of chip structure and auxiliary materials at high temperature.

[0007] Therefore, the present application is designed based on the tin alloy electrode application and the preparation method thereof, and the present application is produced. SUMMARY

[0008] The application aims to provide a micro light emitting device based on tin alloy electrode application and a preparation method thereof to solve the packaging welding problem of the micro light emitting device.

[0009] To achieve the above-mentioned purpose, the technical scheme adopted by the application is as follows:

[0010] A micro light emitting device based on tin alloy electrode application, comprising a substrate and a plurality of LED array units arranged on the surface of the substrate and spaced from each other by grooves, wherein the LED array unit comprises:

[0011] An epitaxial stack, comprising a first type semiconductor layer, an active region and a second type semiconductor layer stacked in sequence along a first direction, and a local area of the epitaxial stack is etched to part of the first type semiconductor layer to form a groove and a mesa; the first direction is perpendicular to the substrate and points from the substrate to the epitaxial stack;

[0012] A DBR structure layer, comprising a DBR reflection layer and a stress buffer layer stacked in sequence along the surface of the epitaxial stack, and the DBR structure layer has a first through hole and a second through hole, and the second through hole exposes part of the surface of the mesa, and the first through hole exposes part of the surface of the groove;

[0013] A first electrode, deposited in the first through hole and electrically connected with the first type semiconductor layer, and extending upward to the surface of the DBR structure layer; and the first electrode comprises a tin alloy electrode;

[0014] A second electrode, deposited in the second through hole and electrically connected with the second type semiconductor layer, and extending upward to the surface of the DBR structure layer, and the second electrode comprises a tin alloy electrode, and the second electrode is arranged away from the first electrode.

[0015] Preferably, the stress buffer layer comprises an organic silicon elastomer, used to buffer the stress extrusion of the tin alloy electrode at high temperature reflow.

[0016] Preferably, a metal filling layer is arranged in the first through hole and the second through hole, and the first electrode and the second electrode are stacked on the surface of the metal filling layer in the corresponding through hole.

[0017] Preferably, the thickness of the metal filling layer is equal to the thickness of the DBR structure layer.

[0018] Preferably, the metal filling layer comprises an isolation layer and a filling layer stacked in sequence; wherein the isolation layer comprises a Ti layer, and the filling layer comprises an Al layer.

[0019] Preferably, a transparent conductive layer is laid on the mesa, and electrode extension bars are formed on the surface of the transparent conductive layer and the bottom surface of the groove, respectively, and the metal filling layer is laminated on part of the surface of the electrode extension bars.

[0020] Preferably, the electrode extension bars are connected with the second-type semiconductor layer by embedding the transparent conductive layer through the through holes.

[0021] Preferably, the first electrode and the second electrode respectively comprise a reflective layer, a mutual solubility barrier layer, a eutectic mutual solubility layer and a tin alloy layer which are stacked in sequence.

[0022] Preferably, the mutual solubility barrier layer comprises a Ni-V alloy layer, which provides a high elastic modulus to reduce the stress between the metal layers, and has a slow wetting speed with the tin alloy layer, so that the electrode pads can still be guaranteed not to fall off after multiple reflow.

[0023] Preferably, the eutectic mutual solubility layer comprises one or more of Au, Ag, Cu, Al, Pb, Sb and Bi.

[0024] Preferably, the tin alloy layer comprises a Sn-Ag-Cu alloy layer, wherein the proportion of Sn is >90%.

[0025] Preferably, the reflective layer comprises at least one of Al and Ag.

[0026] Preferably, a metal adhesion layer is further provided on the side of the reflective layer away from the mutual solubility barrier layer.

[0027] Preferably, the metal adhesion layer comprises at least one of Ni and Cr.

[0028] Preferably, the DBR structure layer further comprises a DBR adhesion layer, which is provided on the surface of the side of the DBR reflective layer away from the stress buffer layer, and comprises at least one of Ti3O5, SiO2 and Al2O3.

[0029] Preferably, the DBR reflective layer comprises a plurality of film layers with alternating high and low refractive indexes, and the thickness of each film layer is one fourth of the wavelength of the light emitted by the micro light emitting element.

[0030] Preferably, the electrode extension bar comprises at least one of Cr, Ni, Al, Ti, Pt and Au.

[0031] The application also provides a preparation method of a micro light emitting device based on a tin alloy electrode application, characterized in that the preparation method comprises the following steps:

[0032] S01, providing a substrate;

[0033] S02, growing an epitaxial stack, the epitaxial stack comprising a first type semiconductor layer, an active layer and a second type semiconductor layer stacked in sequence on the substrate surface;

[0034] S03, exposing part of the first type semiconductor layer by etching the epitaxial stack to form a plurality of grooves and mesas, the grooves and mesas being oppositely arranged;

[0035] S04, forming a plurality of epitaxial stacks spaced apart by through trenches by deep etching the epitaxial stack to expose the substrate surface;

[0036] S05, depositing a transparent conductive layer on the mesa of each of the independent epitaxial stacks;

[0037] S06, forming electrode extension bars on the surface of the transparent conductive layer and the bottom surface of the grooves, respectively;

[0038] Or, etching the transparent conductive layer to form a through hole, and the electrode extension bar is embedded in the transparent conductive layer to form a connection with the second type semiconductor layer;

[0039] S07, forming a DBR structure layer on the surface of the epitaxial stack, the DBR structure layer comprising a DBR adhesion layer, a DBR reflection layer and a stress buffer layer stacked in sequence;

[0040] Wherein, the stress buffer layer comprises an organosilicon elastomer;

[0041] S08, forming a first through hole and a second through hole in the DBR structure layer by etching process, wherein the second through hole exposes part of the surface of the electrode extension bar located on the mesa, and the first through hole exposes part of the surface of the electrode extension bar located on the groove;

[0042] S09, depositing a metal filling layer in the first through hole and the second through hole, and the thickness of the metal filling layer is equal to the thickness of the DBR structure layer;

[0043] S10, performing photoetching on the surface of the chip by using high-temperature-resistant photoresist to form reflow grooves of electrode pads, the reflow grooves respectively exposing the metal filling layer corresponding to the first through hole and the second through hole; and manufacturing a first electrode and a second electrode in the reflow grooves, the first electrode being deposited in the reflow groove corresponding to the first through hole, and the second electrode being deposited in the reflow groove corresponding to the second through hole;

[0044] Wherein, the first electrode and the second electrode respectively comprise a tin alloy electrode;

[0045] S11, using RTA to perform multi-stage annealing reflow;

[0046] S12, removing the high-temperature resistant photoresist.

[0047] Preferably, the first electrode and the second electrode each comprise a reflective layer, a mutual solubility barrier layer, a eutectic mutual solubility layer and a tin alloy layer stacked in sequence.

[0048] The mutual solubility barrier layer comprises a Ni-V alloy layer, which provides a high elastic modulus to reduce the stress between the metal layers, and has a slow wetting speed with the tin alloy layer, so that the electrode pad can be prevented from falling off after multiple reflow processes.

[0049] Preferably, the temperature of each stage of the multi-stage annealing reflow is gradiently increased, and the temperature does not exceed 280 DEG C. After the multi-stage annealing reflow, the surface of the tin alloy electrode is smooth without unevenness, the overall height of the P / N electrode is consistent, and the thin film stress generated in the metal electrode evaporation process is gradually released. Preferably, in the step S10, the thickness of the high-temperature resistant photoresist is greater than the thickness of the first electrode and / or the second electrode, and the photoresist can resist a temperature greater than 280 DEG C.

[0050] Through the above technical solution, the micro light emitting device based on the tin alloy electrode application provided by the application is known. The DBR structure layer is arranged on the surface of the epitaxial stack, which comprises a DBR reflective layer and a stress buffer layer stacked in sequence along the surface of the epitaxial stack, and the DBR structure layer has a first through hole and a second through hole. The first electrode is deposited in electrical connection between the first through hole and the first type semiconductor layer, and extends upward to the surface of the DBR structure layer. The first electrode comprises a tin alloy electrode. The second electrode is deposited in electrical connection between the second through hole and the second type semiconductor layer, and extends upward to the surface of the DBR structure layer. The second electrode comprises a tin alloy electrode. The surface of the LED chip adopts a tin alloy electrode structure, which realizes a solder paste-free packaging method, avoids the abnormal problems such as tin connection caused by the low precision of the solder paste steel mesh printing, and avoids the problem of precise control of the steel mesh in the solder paste printing.

[0051] Further, the stress buffer layer comprises an organic silicon elastomer, which is used to buffer the stress extrusion of the tin alloy electrode at high temperature reflow, so as to improve the reliability of the push-pull force of the DBR structure layer and avoid the risk of electrode falling.

[0052] Secondly, the electrode comprises a reflective layer, a mutual solubility barrier layer, a eutectic mutual solubility layer and a tin alloy layer stacked in sequence. The tin alloy layer is directly connected with the outside as an electrode pad. The eutectic mutual solubility layer is used to provide a metal supplement layer which can be mutually soluble with the tin alloy layer. The mutual solubility barrier layer is used to block the mutual solubility of the eutectic mutual solubility layer and the tin alloy layer from flowing to the reflective layer. The reflective layer is used to reflect the light from the epitaxial stack.

[0053] Then, the mutual solubility barrier layer comprises a Ni-V alloy layer, which has a slow wetting speed with the tin alloy layer and can ensure that the electrode pad does not fall off after multiple reflow, while providing a high elastic modulus to reduce the stress between the metal layers.

[0054] Secondly, the tin alloy layer comprises a Sn-Ag-Cu alloy layer, wherein the proportion of Sn is > 90%, so that the electrode surface has a low solidification temperature and reduces damage to the epitaxial stack.

[0055] Further, the eutectic mutual solubility layer is provided as one or more of Au, Ag, Cu, Al, Pb, Sb, Bi, so that it is mutually soluble with the tin alloy layer, which can further reduce the eutectic temperature and reduce damage to the epitaxial stack.

[0056] Further, a metal filling layer is provided in the first and second through holes, and the first and second electrodes are stacked on the surface of the metal filling layer in the corresponding through hole; further, the thickness of the metal filling layer is equal to the thickness of the DBR structure layer. This can reduce the surface height difference of the two electrode pads during evaporation, so as to flatten the surface of the LED chip, facilitate pad evaporation, and improve reliability.

[0057] The application also provides a preparation method of a micro light emitting device based on a tin alloy electrode, which is simple and convenient in process and is easy to produce.

[0058] Secondly, before the first and second electrodes are made, a high-temperature resistant photoresist is used for photoetching on the surface of the chip to form a reflow groove of the electrode pad, and the reflow groove exposes the metal filling layer corresponding to the first and second through holes, respectively; then, the first and second electrodes are made in the reflow groove. In this way, solder overflow and expansion can be avoided, so that the overall pad surface is flat, facilitating solder paste-free packaging.

[0059] Meanwhile, after the first and second electrodes are made, RTA is used for multi-stage annealing and reflow, which can reduce the void rate and unevenness of the electrode pad surface and gradually release the stress generated during the metal electrode evaporation process, thereby improving the reliability of the micro light emitting device. BRIEF DESCRIPTION OF DRAWINGS

[0060] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only embodiments of the present application, and those skilled in the art can obtain other drawings according to the provided drawings without any creative effort.

[0061] Figure 1 Structure diagram of micro light emitting device based on tin alloy electrode application provided by the embodiment of the present application;

[0062] Figures 2.1 to 2.12 Structure diagram corresponding to the preparation method step of micro light emitting device based on tin alloy electrode application provided by the embodiment of the present application;

[0063] Figure 3 Temperature change diagram when RTA is used for multi-stage annealing reflow in the preparation method step S11 of micro light emitting device based on tin alloy electrode application provided by the embodiment of the present application;

[0064] Symbol explanation in the figure: 1, substrate, 2, first type semiconductor layer, 3, active region, 4, second type semiconductor layer, 5.1, groove, 5.2, mesa, 6, transparent conductive layer, 7, electrode expansion strip, 8.1, DBR adhesion layer, 8.2, DBR reflection layer, 8.3, stress buffer layer, 8.4, first through hole, 8.5, second through hole, 9, metal filling layer, 10, high-temperature-resistant photoresist, 11, first electrode, 12, second electrode. DETAILED DESCRIPTION

[0065] In order to make the content of the present application clearer, the content of the present application will be further described below in combination with the drawings. The present application is not limited to this specific embodiment. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative efforts fall within the scope of protection of the present application.

[0066] As shown in the figure, the micro light emitting device based on tin alloy electrode application includes a substrate 1 and a plurality of LED array units arranged on the surface of the substrate 1 and spaced from each other by grooves, and the LED array unit includes: Figure 1 An epitaxial stack, which includes a first type semiconductor layer 2, an active region 3 and a second type semiconductor layer 4 stacked in sequence along a first direction, and a local area of the epitaxial stack is etched to part of the first type semiconductor layer 2 to form a groove 5.1 and a mesa 5.2; the first direction is perpendicular to the substrate 1 and points from the substrate 1 to the epitaxial stack;

[0067] A DBR structure layer, which includes a DBR reflection layer 8.2 and a stress buffer layer 8.3 stacked in sequence along the surface of the epitaxial stack, and the DBR structure layer has a first through hole 8.4 and a second through hole 8.5, and the second through hole 8.5 exposes part of the surface of the mesa 5.2, and the first through hole 8.4 exposes part of the surface of the groove 5.1;

[0068]

[0069] ​The first electrode 11 is deposited on the first via 8.4 and is electrically connected to the first type semiconductor layer 2, and extends upward to the surface of the DBR structure layer; and the first electrode 11 comprises a tin alloy electrode;

[0070] The second electrode 12 is deposited on the second via 8.5 and is electrically connected to the second type semiconductor layer 4, and extends upward to the surface of the DBR structure layer, and the second electrode 12 comprises a tin alloy electrode, and the second electrode 12 is arranged away from the first electrode 11.

[0071] It should be emphasized that, in the embodiment of the present application, in order to highlight the technical point of the present application, Figure 1 Only one LED array unit in the micro light emitting device is shown, and in actual use, the surface of the substrate 1 contains thousands of LED array units, which is determined according to the specific situation, and the present application does not limit this.

[0072] It should be noted that the type of the substrate 1 is not limited in the micro light emitting element of the embodiment, for example, the substrate 1 can be but is not limited to a sapphire substrate 1, a silicon substrate 1, etc. In addition, the type of the first type semiconductor layer 2, the active region 3 and the second type semiconductor layer 4 of the epitaxial stack can also be not limited in the micro light emitting element of the embodiment, for example, the first type semiconductor layer 2 can be but is not limited to a gallium nitride layer, and correspondingly, the second type semiconductor layer 4 can be but is not limited to a gallium nitride layer.

[0073] On the basis of the above-mentioned embodiment, in an embodiment of the present application, the stress buffer layer 8.3 comprises an organic silicon elastomer, which is used to buffer the stress extrusion of the tin alloy electrode during high-temperature reflow and release the stress.

[0074] On the basis of the above-mentioned embodiment, in an embodiment of the present application, a metal filling layer 9 is arranged in the first via 8.4 and the second via 8.5, and the first electrode 11 and the second electrode 12 are laminated on the surface of the metal filling layer 9 in the corresponding via.

[0075] On the basis of the above-mentioned embodiment, in an embodiment of the present application, the thickness of the metal filling layer 9 is equal to the thickness of the DBR structure layer.

[0076] On the basis of the above-mentioned embodiment, in an embodiment of the present application, the metal filling layer 9 comprises a lamination of an isolation layer and a filling layer in sequence; wherein the isolation layer comprises a Ti layer, and the filling layer comprises an Al layer.

[0077] On the basis of the above-mentioned embodiment, in an embodiment of the present application, a transparent conductive layer 6 is arranged on the mesa 5.2, and an electrode expansion strip 7 is formed on the surface of the transparent conductive layer 6 and the bottom surface of the groove 5.1, respectively, and the metal filling layer 9 is laminated on part of the surface of the electrode expansion strip 7.

[0078] On the basis of the above-mentioned embodiments, in an embodiment of the present application, the electrode extension strip 7 is embedded into the transparent conductive layer 6 through the through hole to form a connection with the second-type semiconductor layer 4.

[0079] It is required that the number of the electrode extension strip 7 can be one or more, which is determined according to the situation, and the present application does not limit this.

[0080] It is worth mentioning that, in the above-mentioned embodiments, the material of the transparent conductive layer 6 can be ITO, which is determined according to the situation, and the present application does not limit this.

[0081] On the basis of the above-mentioned embodiments, in an embodiment of the present application, the first electrode 11 and the second electrode 12 respectively include: a reflective layer, a mutual solubility barrier layer, a eutectic mutual solubility layer, and a tin alloy layer which are stacked in sequence.

[0082] On the basis of the above-mentioned embodiments, in an embodiment of the present application, the mutual solubility barrier layer includes a Ni-V alloy layer, which provides a high elastic modulus to reduce the stress between the metal layers, and has a slow wetting speed with the tin alloy layer, so that the electrode pad can still be guaranteed not to fall off after multiple reflows, and the thickness of the Ni-V alloy layer is set according to the required reflow repair times.

[0083] On the basis of the above-mentioned embodiments, in an embodiment of the present application, the eutectic mutual solubility layer includes one or more of Au, Ag, Cu, Al, Pb, Sb, and Bi.

[0084] On the basis of the above-mentioned embodiments, in an embodiment of the present application, the tin alloy layer includes a Sn-Ag-Cu alloy layer.

[0085] On the basis of the above-mentioned embodiments, in an embodiment of the present application, the reflective layer includes at least one of Al and Ag.

[0086] On the basis of the above-mentioned embodiments, in an embodiment of the present application, a metal adhesion layer is further arranged on the side of the reflective layer away from the mutual solubility barrier layer.

[0087] On the basis of the above-mentioned embodiments, in an embodiment of the present application, the metal adhesion layer includes at least one of Ni and Cr.

[0088] On the basis of the above-mentioned embodiments, in an embodiment of the present application, the DBR structure layer further includes a DBR adhesion layer 8.1, which is arranged on the side surface of the DBR reflective layer 8.2 away from the stress buffer layer 8.3, and includes at least one of Ti3O5, SiO2, and Al2O3.

[0089] Based on the above embodiments, in one embodiment of this application, the DBR reflective layer 8.2 includes a plurality of films with alternating high and low refractive indices, and the thickness of each film is one-quarter of the wavelength of the light emitted by the micro light-emitting element.

[0090] Based on the above embodiments, in one embodiment of this application, the electrode extension strip 7 includes at least one of Cr, Ni, Al, Ti, Pt, and Au.

[0091] This invention also provides a method for fabricating a micro-light-emitting device based on tin alloy electrodes, characterized in that the fabrication method includes the following steps:

[0092] S01, such as Figure 2.1 As shown, a substrate 1 is provided;

[0093] It should be noted that the type of substrate 1 is not limited in the micro light-emitting element of this embodiment. For example, substrate 1 can be, but is not limited to, sapphire substrate 1, silicon substrate 1, etc.

[0094] S02, such as Figure 2.2 As shown, an epitaxial stack is grown, comprising a first type semiconductor layer 2, an active layer, and a second type semiconductor layer 4 sequentially stacked on the surface of a substrate 1.

[0095] It should be noted that the types of the first type semiconductor layer 2, the active region 3, and the second type semiconductor layer 4 in the epitaxial stacked micro light-emitting element in this embodiment are not limited. For example, the first type semiconductor layer 2 may be, but is not limited to, a gallium nitride layer, and correspondingly, the second type semiconductor layer 4 may be, but is not limited to, a gallium nitride layer.

[0096] S03, such as Figure 2.3 As shown, by etching the epitaxial stack, a portion of the first-type semiconductor layer 2 is exposed, thereby forming several grooves 5.1 and mesas 5.2, with the grooves 5.1 and mesas 5.2 positioned opposite each other; wherein, Figure 2.3 The diagram only illustrates the epitaxial stacked structure corresponding to a single LED array unit;

[0097] In one embodiment of this application, etching the epitaxial stack to form a plurality of grooves 5.1 and mesa 5.2 includes using an inductively coupled plasma (ICP) process, with etching gases including Cl2, Ar, and O2. However, this application does not limit this process and the specific method depends on the circumstances.

[0098] S04, such as Figure 2.4 As shown, by deep etching the epitaxial stack to the surface of the exposed substrate 1, a plurality of epitaxial stacks are formed by spacing them between each other through trenches; wherein, Figure 2.4 The diagram only illustrates the epitaxial stacked structure corresponding to a single LED array unit;

[0099] In one embodiment of the present application, deep etching is performed on the epitaxial stack to expose the surface of the substrate 1 to form a plurality of spaced epitaxial stacks; the etching gas includes Cl2, Ar and O2 by using an inductively coupled plasma (ICP) process. However, the present application is not limited thereto, and the specific process can be determined as appropriate.

[0100] S05, as shown in the figure, a transparent conductive layer 6 is deposited on the mesa 5.2 of each independent epitaxial stack; Figure 2.5

[0101] It is worth mentioning that in the above embodiment, the material of the transparent conductive layer 6 can be ITO, and the forming process can be electron beam evaporation process, sputtering evaporation process, etc. The specific process can be determined as appropriate, and the present application is not limited thereto.

[0102] S06, as shown in the figure, an electrode extension bar 7 is formed on the surface of the transparent conductive layer 6 and the bottom surface of the groove 5.1; Figure 2.6

[0103] Or, a via hole is etched on the transparent conductive layer 6, and the electrode extension bar 7 is embedded in the transparent conductive layer 6 to form a connection with the second type semiconductor layer 4;

[0104] It should be noted that the number of electrode extension bars 7 can be one or more; and the forming process can be electron beam evaporation process, etc. The specific process can be determined as appropriate, and the present application is not limited thereto.

[0105] S07, as shown in the figure, a DBR structure layer is formed on the surface of the epitaxial stack, which includes a DBR adhesion layer 8.1, a DBR reflection layer 8.2 and a stress buffer layer 8.3 which are sequentially stacked; Figure 2.7

[0106] In one embodiment of the present application, the DBR adhesion layer 8.1 is obtained by atomic layer deposition, and it includes at least one of Ti3O5, SiO2 and Al2O3, etc. The specific process can be determined as appropriate, and the present application is not limited thereto.

[0107] In one embodiment of the present application, the DBR reflection layer 8.2 includes a plurality of high and low refractive index alternating film layers, and the thickness of each film layer is one quarter of the wavelength of the light emitted by the micro light emitting element.

[0108] In one embodiment of the present application, the stress buffer layer 8.3 includes an organic silicon elastomer; preferably, such as tetramethyl-p-silphenylen-diphenylsiloxane, octamethylcyclotetrasiloxane and other polysiloxane materials, which facilitates the deformation of the metal pad and the underlying DBR reflection layer 8.2 at different thermal expansion rates during high-temperature reflow, preventing the pad and the DBR reflection layer 8.2 from delaminating due to excessive stress. ​​​

[0109] S08、as shown in the figure, the DBR structure layer is etched to form a first via hole 8.4 and a second via hole 8.5, wherein the second via hole 8.5 exposes part of the surface of the electrode extension strip 7 on the mesa 5.2, and the first via hole 8.4 exposes part of the surface of the electrode extension strip 7 on the groove 5.1; Figure 2.8

[0110] S09、as shown in the figure, a metal filling layer 9 is deposited in the first via hole 8.4 and the second via hole 8.5, and the thickness of the metal filling layer 9 is equal to the thickness of the DBR structure layer; Figure 2.9

[0111] On the basis of the above embodiment, in an embodiment of the present application, the metal filling layer 9 comprises a separation layer and a filling layer stacked in sequence; wherein the separation layer comprises a Ti layer, and the filling layer comprises an Al layer.

[0112] S10、as shown in the figure, a high-temperature-resistant photoresist 10 is used for photoetching on the surface of the chip to form a reflow groove of the electrode pad, and the reflow groove exposes the metal filling layer 9 corresponding to the first via hole 8.4 and the second via hole 8.5 respectively; and a first electrode 11 and a second electrode 12 are made in the reflow groove, wherein the first electrode 11 is deposited in the reflow groove corresponding to the first via hole 8.4, and the second electrode 12 is deposited in the reflow groove corresponding to the second via hole 8.5; Figure 2.10

[0113] On the basis of the above embodiment, in an embodiment of the present application, the thickness of the high-temperature-resistant photoresist 10 is greater than the thickness of the first electrode 11 and / or the second electrode 12, and the temperature resistance of the photoresist is greater than 280℃.

[0114] Among them, the first electrode 11 and the second electrode 12 respectively comprise a tin alloy electrode;

[0115] On the basis of the above embodiment, in an embodiment of the present application, the first electrode 11 and the second electrode 12 respectively comprise: a metal adhesion layer, a reflection layer, a mutual solubility barrier layer, a eutectic mutual solubility layer and a tin alloy layer stacked in sequence;

[0116] On the basis of the above embodiment, in an embodiment of the present application, the mutual solubility barrier layer comprises a Ni-V alloy layer, which provides a high elastic modulus to reduce the stress between the metal layers, and has a slow wetting speed with the tin alloy layer, which can still ensure that the electrode pad does not fall off after multiple reflows;

[0117] On the basis of the above embodiment, in an embodiment of the present application, the eutectic mutual solubility layer comprises one or more of Au, Ag, Cu, Al, Pb, Sb and Bi;

[0118] ​​​On the basis of the above-mentioned embodiments, in an embodiment of the present application, the tin alloy layer comprises a Sn-Ag-Cu alloy layer, wherein the proportion of Sn is > 90%;

[0119] On the basis of the above-mentioned embodiments, in an embodiment of the present application, the reflective layer comprises at least one of Al and Ag.

[0120] On the basis of the above-mentioned embodiments, in an embodiment of the present application, the metal adhesion layer comprises at least one of Ni and Cr.

[0121] S11, multi-stage annealing reflow is performed by using RTA.

[0122] On the basis of the above-mentioned embodiments, in an embodiment of the present application, the temperature of each stage of the multi-stage annealing reflow is gradiently increased, and the temperature does not exceed 280℃. After the multi-stage annealing reflow, the surface of the tin alloy electrode is smooth without unevenness, the overall height of the first and second electrodes is consistent, and the film stress generated in the metal electrode evaporation process is gradually released, finally obtaining the electrode effect as shown in Figure 2.11 .

[0123] On the basis of the above-mentioned embodiments, in an embodiment of the present application, as shown in Figure 3 , multi-stage annealing reflow is performed by using RTA, the reflow temperature interval is between 140℃-280℃, the annealing reflow temperature does not exceed 280℃, and multiple stages of reflow can be set to improve the reflow effect. This embodiment adopts four-stage reflow:

[0124] The temperature of the first stage is 150℃, and the duration is 60s;

[0125] The temperature of the second stage is 180℃, and the duration is 60s;

[0126] The temperature of the third stage is 220℃, and the duration is 60s;

[0127] The temperature of the fourth stage is 260℃, and the duration is 60s;

[0128] In this way, when the Sn-Ag-Cu alloy layer is mutually soluble with the metal eutectic layer below, it is blocked by the peripheral high-temperature photoresist 10 to avoid overflow, the molten Sn alloy can fill the uneven electrode surface to form a stable metal eutectic structure, obtain a large-pull force surface flat solder wire electrode without tin paste, and gradually release the film stress generated in the metal electrode evaporation process.

[0129] S12, as shown in Figure 2.12 , the high-temperature photoresist 10 is removed.

[0130] Via the technical solutions, the micro light emitting device based on the tin alloy electrode application is provided, the DBR structure layer is arranged on the surface of the epitaxial stack, the DBR structure layer includes the DBR reflection layer 8.2 and the stress buffer layer 8.3 which are sequentially stacked along the surface of the epitaxial stack, and the DBR structure layer has the first through hole 8.4 and the second through hole 8.5; the first electrode 11 is deposited in electrical connection between the first through hole 8.4 and the first type semiconductor layer 2, and extends upwards to the surface of the DBR structure layer; and the first electrode 11 includes the tin alloy electrode; the second electrode 12 is deposited in electrical connection between the second through hole 8.5 and the second type semiconductor layer 4, and extends upwards to the surface of the DBR structure layer, and the second electrode 12 includes the tin alloy electrode. The tin alloy electrode structure is adopted on the surface of the LED chip, the solder paste free packaging mode is realized, the abnormal problems such as tin connection caused by the low printing precision of the solder paste steel mesh are avoided, and the abnormal rate is reduced; meanwhile, the problem of the precise control of the steel mesh in the solder paste printing is avoided.

[0131] Further, the stress buffer layer 8.3 includes the organic silicon elastomer, which is used for buffering the stress extrusion of the tin alloy electrode in the high temperature reflow, so as to improve the push-pull force reliability of the DBR structure layer and avoid the risk of electrode falling.

[0132] Secondly, the electrode includes a reflection layer, a mutual solubility barrier layer, a eutectic mutual solubility layer and a tin alloy layer which are sequentially stacked; the tin alloy layer is directly connected with the outside as an electrode pad; the eutectic mutual solubility layer is used for providing a metal supplement layer which can be mutually soluble with the tin alloy layer; the mutual solubility barrier layer is used for blocking the mutual solubility of the eutectic mutual solubility layer and the tin alloy layer from flowing to the reflection layer; and the reflection layer is used for reflecting the light from the epitaxial stack.

[0133] Then, the mutual solubility barrier layer includes a Ni-V alloy layer, which provides a high elastic modulus to reduce the stress between the metal layers, and has a slow wetting speed with the tin alloy layer, so that the electrode pad can still be guaranteed not to fall off after multiple reflows, and the thickness of the Ni-V alloy layer is set according to the required reflow repair times.

[0134] Secondly, the tin alloy layer includes a Sn-Ag-Cu alloy layer, in which the proportion of Sn is > 90%, so that the electrode surface has a low solidification temperature and reduces the damage to the epitaxial stack.

[0135] Further, the eutectic mutual solubility layer is set as one or more of Au, Ag, Cu, Al, Pb, Sb and Bi, so that it is mutually soluble with the tin alloy layer, and the eutectic temperature can be further reduced and the damage to the epitaxial stack is reduced.

[0136] Furthermore, the metal filling layer 9 is arranged in the first through hole 8.4 and the second through hole 8.5, and the first electrode 11 and the second electrode 12 are laminated on the surface of the metal filling layer 9 in the corresponding through hole; further, the thickness of the metal filling layer 9 is equal to the thickness of the DBR structure layer. The surface height difference during evaporation of the two electrode pads can be reduced, the LED chip surface is planarized, the pad evaporation is facilitated, and the reliability is improved.

[0137] The application further provides a preparation method of a micro light emitting device based on a tin alloy electrode, which is simple and convenient in process and is convenient for production while realizing the beneficial effects of the micro light emitting element.

[0138] Secondly, before the first electrode 11 and the second electrode 12 are made, the reflow groove of the electrode pad is formed on the chip surface through high-temperature photoresist 10 photolithography, and the reflow groove exposes the metal filling layer 9 corresponding to the first through hole 8.4 and the second through hole 8.5, respectively; then, the first electrode 11 and the second electrode 12 are made in the reflow groove. In this way, the solder overflow and expansion can be avoided, the overall pad surface is flat, and the solder paste-free packaging is facilitated.

[0139] Meanwhile, after the first electrode 11 and the second electrode 12 are made, RTA is used for multi-stage annealing reflow, which can reduce the void rate of the electrode pad surface, thereby improving the reliability of the micro light emitting device.

[0140] Each of the embodiments in the specification is described in a progressive manner, and each embodiment focuses on the difference from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0141] It should also be noted that, in this document, the relationship terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between the entities or operations. Moreover, the terms "include", "contain" or any other variants thereof are intended to cover non-exclusive inclusion, so that the article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such article or device. Without more limitation, the element defined by the statement "including a" does not exclude the presence of another identical element in the article or device including the above element.

[0142] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and that the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Therefore, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A micro-light-emitting device based on tin alloy electrodes, comprising a substrate and a plurality of LED array units disposed on the surface of the substrate and isolated from each other by trenches, characterized in that, The LED array unit includes: An epitaxial stack includes a first type semiconductor layer, an active region, and a second type semiconductor layer stacked sequentially along a first direction, wherein a local area of ​​the epitaxial stack is etched to a portion of the first type semiconductor layer to form a groove and a mesa; the first direction is perpendicular to the substrate and extends from the substrate toward the epitaxial stack. The DBR structure layer includes a DBR reflective layer and a stress buffer layer sequentially stacked along the surface of the epitaxial stack, and the DBR structure layer has a first through hole and a second through hole, wherein the second through hole exposes a portion of the surface of the platform and the first through hole exposes a portion of the surface of the groove. A first electrode is deposited in the first via and electrically connected to the first type of semiconductor layer, and extends upward to the surface of the DBR structure layer; and the first electrode includes a tin alloy electrode. The second electrode is deposited in the second via and electrically connected to the second type of semiconductor layer, and extends upward to the surface of the DBR structure layer. The second electrode includes a tin alloy electrode, and the second electrode is disposed away from the first electrode. The stress buffer layer includes an organosilicon elastomer, which is used to buffer the stress extrusion of the tin alloy electrode during high-temperature reflow.

2. The micro-light-emitting device based on tin alloy electrodes according to claim 1, characterized in that, A metal filling layer is provided in the first through hole and the second through hole, and the first electrode and the second electrode are stacked on the surface of the metal filling layer in the corresponding through hole.

3. The micro-light-emitting device based on tin alloy electrodes according to claim 2, characterized in that, The thickness of the metal filler layer is the same as the thickness of the DBR structure layer.

4. The micro-light-emitting device based on tin alloy electrodes according to claim 3, characterized in that, The metal filler layer comprises an isolation layer and a filler layer stacked sequentially; wherein the isolation layer comprises a Ti layer and the filler layer comprises an Al layer.

5. The micro-light-emitting device based on tin alloy electrodes according to claim 2, characterized in that, A transparent conductive layer is laid on the table surface, and electrode extension strips are formed on the surface of the transparent conductive layer and the bottom surface of the groove, respectively. The metal filling layer is stacked on a portion of the surface of the electrode extension strips.

6. The micro-light-emitting device based on tin alloy electrodes according to claim 5, characterized in that, The electrode extension strip is connected to the second type of semiconductor layer by embedding it into the transparent conductive layer through a through hole.

7. The micro-light-emitting device based on tin alloy electrodes according to claim 1, characterized in that, The first electrode and the second electrode each include: a reflective layer, a mutual dissolution barrier layer, a eutectic mutual dissolution layer and a tin alloy layer stacked sequentially.

8. The micro-light-emitting device based on tin alloy electrodes according to claim 7, characterized in that, The mutual-solubility barrier layer includes a Ni-V alloy layer.

9. The micro-light-emitting device based on tin alloy electrodes according to claim 7, characterized in that, The eutectic intersoluble layer includes one or more of Au, Ag, Cu, Al, Pb, Sb, and Bi.

10. The micro-light-emitting device based on tin alloy electrodes according to claim 7, characterized in that, The tin alloy layer includes a Sn-Ag-Cu alloy layer.

11. The micro-light-emitting device based on tin alloy electrodes according to claim 7, characterized in that, A metal adhesion layer is also provided on the side of the reflective layer opposite to the intersoluble barrier layer.

12. A method for fabricating micro-light-emitting devices based on tin alloy electrodes, characterized in that, The preparation method includes the following steps: S01, Provide a substrate; S02. Growing an epitaxial stack, wherein the epitaxial stack comprises a first type semiconductor layer, an active layer, and a second type semiconductor layer sequentially stacked on the surface of the substrate; S03. By etching the epitaxial stack, a portion of the first type semiconductor layer is exposed, thereby forming a plurality of grooves and mesa, wherein the grooves and mesa are disposed opposite to each other; S04. By deeply etching the epitaxial stack to expose the substrate surface, a plurality of epitaxial stacks are formed by spacing them between each other through trenches; S05. Deposit a transparent conductive layer on the mesa of each epitaxial stack; S06. Electrode extension strips are formed on the surface of the transparent conductive layer and the bottom surface of the groove, respectively; Alternatively, a via can be formed by etching the transparent conductive layer, and the electrode extension strip can be connected to the second type semiconductor layer by embedding it into the transparent conductive layer through the via; S07. A DBR structure layer is formed on the surface of the epitaxial stack, which includes a DBR adhesive layer, a DBR reflective layer and a stress buffer layer stacked sequentially. The stress buffer layer includes an organosilicon elastomer; S08. The DBR structure layer is formed with a first through hole and a second through hole by etching process, wherein the second through hole is exposed on a part of the surface of the electrode extension strip of the mesa, and the first through hole is exposed on a part of the surface of the electrode extension strip of the groove. S09. Deposit a metal filler layer in the first through hole and the second through hole, wherein the thickness of the metal filler layer is equal to the thickness of the DBR structure layer; S10. Photolithography is performed on the chip surface using high-temperature resistant photoresist to form reflow grooves for electrode pads, wherein the reflow grooves expose the metal filling layers corresponding to the first and second through holes respectively. A first electrode and a second electrode are fabricated in the reflux groove, with the first electrode deposited in the reflux groove corresponding to the first through hole and the second electrode deposited in the reflux groove corresponding to the second through hole. Wherein, the first electrode and the second electrode each comprise a tin alloy electrode; S11. Use RTA for multi-stage annealing and reflow; S12. Remove the high-temperature resistant photoresist.

13. The method for fabricating a micro-light-emitting device based on tin alloy electrodes according to claim 12, characterized in that, The first electrode and the second electrode each comprise: a reflective layer, a mutual dissolution barrier layer, a eutectic mutual dissolution layer, and a tin alloy layer stacked sequentially; The mutual-solution barrier layer includes a Ni-V alloy layer.

14. The method for fabricating a micro-light-emitting device based on tin alloy electrodes according to claim 12, characterized in that, The temperature of each stage of the multi-stage annealing and reflow process increases in a gradient.

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