LED chip preparation method and LED chip

Abstract

The invention provides an LED chip preparation method and an LED chip, and the method comprises the steps: carrying out the MSA etching of a GaN epitaxial layer, specifically, the MSA etching is divided into two times of etching: firstly introducing Cl2 to etch the GaN epitaxial layer until a part of an N-type GaN layer is exposed, and then introducing SiCl4 gas to carry out the etching; the etched wafer is put into a BOE solution to be soaked, and then cleaning is carried out; patterning the photoresist of the cleaned wafer through a yellow light process, and exposing an area, which needs to be evaporated with metal, on the wafer; placing the wafer after the yellow light process in an oxygen plasma cleaning machine, and removing residual glue on the surface of the wafer after development; according to the method, the wafer with the adhesive residue removed is fully cleaned with deionized water, then a metal electrode is evaporated on the area, where metal needs to be evaporated, of the wafer, an N electrode metal layer is obtained, and through the technology, the contact resistance of the metal electrode and the N-type GaN layer can be further reduced, and meanwhile the light emitting brightness of an LED chip is improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for preparing an LED chip and an LED chip. Background Art

[0002] As an efficient and energy-saving light source, LED (Lighting Emitting Diode) has a unique advantage in reducing chip voltage. Compared with traditional incandescent lamps and halogen lamps, the operating voltage of GaN-based LED chips is generally around 3V. This allows the LED drive circuit to adopt a simpler and more efficient design, thereby significantly reducing the power consumption of the overall system.

[0003] In recent years, with the continuous advancement of LED manufacturing technology, the operating voltage of LED chips has also shown a trend of gradually decreasing. The main difficulty in reducing the voltage of LED chips is how to effectively reduce the contact resistance between metal electrodes and P-type and N-type GaN. Previously, metals such as Cr, Ti, and Ni have been proven to effectively reduce the contact resistance with GaN, and are therefore usually used as adhesion layer metals. Summary of the invention

[0004] Based on this, the purpose of the present invention is to provide a method for preparing an LED chip and an LED chip, aiming to further reduce the contact resistance between the metal electrode and the N-type GaN layer while improving the luminous brightness of the LED chip.

[0005] According to an embodiment of the present invention, a method for preparing an LED chip includes:

[0006] Providing a GaN epitaxial layer, the GaN epitaxial layer comprising an N-type GaN layer, a multi-quantum well layer and a P-type GaN layer deposited in sequence;

[0007] Performing MSA etching on the GaN epitaxial layer, wherein the MSA etching is divided into two etching steps, firstly, introducing Cl2 to etch the GaN epitaxial layer until a portion of the N-type GaN layer is exposed, and then introducing SiCl4 gas to etch again;

[0008] Soak the etched wafer in BOE solution and then clean it;

[0009] The cleaned wafer is patterned with photoresist through a yellow light process to expose the area on the wafer where metal needs to be evaporated;

[0010] Place the wafer after the yellow light process in an oxygen plasma cleaning machine to remove the residual glue on the surface of the wafer after development;

[0011] The wafer after the residual glue is thoroughly cleaned with deionized water is then evaporated on the area of ​​the wafer where metal is required to be evaporated to obtain an N-electrode metal layer.

[0012] Furthermore, in the step of introducing Cl2 to etch the GaN epitaxial layer until a portion of the N-type GaN layer is exposed, the flow rate of the introduced Cl2 is 60sccm~200sccm, the upper power of the ICP machine etching is 300W~800W, the lower power is 100W~300W, the etching pressure is 3mtorr~10mtorr, and the etching time is 200s~600s.

[0013] Furthermore, in the step of introducing Cl2 to etch the GaN epitaxial layer until a portion of the N-type GaN layer is exposed, the etching depth is 800nm ​​to 2000nm.

[0014] Furthermore, in the step of introducing SiCl4 gas and then etching, the flow rate of the SiCl4 gas is 70sccm~150sccm, the upper power of the ICP machine etching is 200W~600W, the lower power is 70W~200W, 3mtorr~10mtorr, and the etching time is 60s~300s.

[0015] Furthermore, the N-type GaN layer is etched to a depth of 100 nm to 300 nm.

[0016] Furthermore, in the step of immersing the etched wafer in a BOE solution and then cleaning it, the concentration of the BOE solution is 5% to 20%, and the immersion time is 30s to 180s.

[0017] Furthermore, the mass ratio of HF to NH4F in the BOE solution is 1:10-30.

[0018] Furthermore, in the step of using deionized water to fully clean the wafer after removing residual glue, and then evaporating a metal electrode in the area on the wafer where metal is required to be evaporated to obtain an N-electrode metal layer, the cleaned wafer is subjected to metal evaporation within 2 hours.

[0019] Furthermore, the thickness of the GaN epitaxial layer is 3 μm to 7 μm.

[0020] An LED chip according to an embodiment of the present invention is prepared according to the above-mentioned LED chip preparation method.

[0021] The beneficial effects of the present invention are:

[0022] The GaN epitaxial layer is subjected to MSA etching. Specifically, the MSA etching is divided into two etching steps. First, Cl2 is introduced to etch the GaN epitaxial layer until part of the N-type GaN layer is exposed, and then SiCl4 gas is introduced for further etching; the etched wafer is immersed in a BOE solution and then cleaned; the cleaned wafer is patterned with photoresist through a yellow light process to expose the area on the wafer where metal needs to be evaporated; the wafer after the yellow light process is placed in an oxygen plasma cleaning machine to remove residual glue on the surface of the wafer after development; the wafer after the residual glue is fully cleaned with deionized water to remove it, and then a metal electrode is evaporated in the area on the wafer where metal needs to be evaporated to obtain an N-electrode metal layer. The above process can further reduce the contact resistance between the metal electrode and the N-type GaN layer while improving the luminous brightness of the LED chip. DETAILED DESCRIPTION

[0023] The present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0024] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0026] An embodiment of the present invention provides a method for preparing an LED chip, and the method for preparing an LED chip specifically comprises the following steps:

[0027] S100: providing a substrate;

[0028] The substrate may be a sapphire substrate, wherein a mixed solution of deionized water, ammonia water and hydrogen peroxide is used to perform ultrasonic cleaning on the sapphire substrate to remove organic matter and particulate matter on the surface.

[0029] S200: depositing a GaN epitaxial layer, a current blocking layer, an ITO current spreading layer, a metal electrode layer and a passivation protection layer in sequence on the substrate along the epitaxial growth direction;

[0030] The GaN epitaxial layer includes a Si-doped N-type GaN layer, a multi-quantum well layer and a Mg-doped P-type GaN layer which are deposited in sequence, and the thickness of the GaN epitaxial layer is 3 μm to 7 μm.

[0031] S300: peeling off the substrate;

[0032] Specifically, S200 includes:

[0033] S201: growing a 1 μm thick gallium nitride buffer layer, a 4 μm thick N-type GaN layer, and three periods of active layers on a sapphire substrate in sequence by MOCVD (Metal-organic Chemical Vapor Deposition) technology, wherein the thickness of a single quantum well layer is 3 nm, the thickness of a single quantum barrier layer is 12 nm, the quantum well layer is an InGaN layer, and the quantum barrier layer is a GaN layer, then growing a 20 nm thick P-type AlGaN layer and a P-type GaN layer to obtain a GaN epitaxial wafer, which is then cleaned with an organic solution;

[0034] S202: depositing an ITO current spreading layer on the GaN epitaxial wafer by magnetron sputtering technology, making a pattern on the ITO current spreading layer by photolithography technology, etching the ITO current spreading layer in a specific area by wet etching using a photoresist as a mask, and then performing MSA etching on the GaN epitaxial layer. The MSA etching is divided into two etching steps. First, Cl2 is introduced to etch the GaN epitaxial layer until a portion of the N-type GaN layer is exposed, and then SiCl4 gas is introduced to etch again;

[0035] It should be noted that in the step of introducing Cl2 to etch the GaN epitaxial layer, the flow rate of the introduced Cl2 is 60sccm to 200sccm, the upper power of the ICP machine etching is 300W to 800W, that is, the plasma source power is 300W to 800W, the lower power is 100W to 300W, that is, the bias power is 100W to 300W, the etching pressure is 3mtorr to 10mtorr, the etching time is 200s to 600s, and the final etching depth is 800nm ​​to 2000nm;

[0036] Furthermore, in the step of introducing SiCl4 gas and then etching, the flow rate of the SiCl4 gas is 70sccm~150sccm, the upper power of the ICP machine etching is 200W~600W, the lower power is 70W~200W, 3mtorr~10mtorr, the etching time is 60s~300s, and the final N-type GaN layer is etched to a depth of 100nm~300nm. It should be noted that the purpose of treating the surface of the N-type GaN layer after Cl2 etching with SiCl4 gas is that after SiCl4 etching, not only the surface of the N-type GaN layer can be repaired, but also nitrogen vacancies can be formed in the N-type GaN layer, thereby producing an electronic doping effect.

[0037] S203: Soaking the etched wafer in a BOE solution and then cleaning it;

[0038] The concentration of the BOE solution is 5% to 20%, and the immersion time is 30s to 180s. Specifically, the mass ratio of HF to NH4F in the BOE solution is 1:10 to 30. It should be noted that there are two main effects of using BOE to treat the epitaxial surface after SiCl4 etching: 1. SiCl4 is easily liquefied on the wafer surface or mutually dissolved with the photoresist after treatment, resulting in residual phenomenon, and BOE can react with Si element to remove SiCl4 or the photoresist mutually dissolved with SiCl4. In the subsequent degumming process, the residual BOE solution will also be cleaned; 2. A large number of nitrogen vacancies will be formed on the surface of the N-type GaN layer after treatment. When the wafer contacts the air, a high-resistance oxide will be quickly formed, and the BOE solution can effectively remove this oxide layer to form a stable low-ohmic contact N-type GaN layer surface.

[0039] S204: Patterning the photoresist on the cleaned wafer through a yellow light process to expose the area on the wafer where metal needs to be evaporated;

[0040] S205: placing the wafer after the yellow light process in an oxygen plasma cleaning machine to remove residual glue on the surface of the wafer after development;

[0041] S206: The wafer after removing residual adhesive is thoroughly cleaned with deionized water, and then metal electrodes are evaporated in the areas on the wafer where metal is required to be evaporated to obtain an N-electrode metal layer. In this embodiment, the cleaned wafer is subjected to metal evaporation within 2 hours.

[0042] Finally, a passivation protective layer is deposited on the entire wafer, and holes are opened at the corresponding positions of the passivation protective layer. Multilayer metal films (such as Ti / Al / Ni / Au) are deposited at the openings by electron beam evaporation or sputtering equipment to form an N-electrode metal layer and a P-electrode metal layer.

[0043] In this embodiment, trimethylaluminum (TMAl), trimethylindium (TMIn), trimethylgallium or triethylgallium (TMGa or TEGa) are used as precursors of Group III sources, ammonia (NH3) and antimonide (SbH3) are used as precursors of Group V sources, silane (SiH4) and bismuth magnesium (Cp2Mg) are used as precursors of N-type dopants and P-type dopants, respectively, and nitrogen and hydrogen are used as carrier gases.

[0044] The present invention will be further described below with specific embodiments:

[0045] Example 1

[0046] Embodiment 1 of the present invention provides a method for preparing an LED chip, which specifically includes the following steps:

[0047] (1) providing a substrate;

[0048] The substrate is a sapphire substrate, and a mixed solution of deionized water, ammonia water and hydrogen peroxide is used to perform ultrasonic cleaning on the sapphire substrate to remove organic matter and particulate matter on the surface.

[0049] (2) depositing a GaN epitaxial layer, a current blocking layer, an ITO current spreading layer, a metal electrode layer and a passivation protection layer in sequence on the substrate along the epitaxial growth direction;

[0050] The GaN epitaxial layer includes a Si-doped N-type GaN layer, a multi-quantum well layer and a Mg-doped P-type GaN layer which are deposited in sequence, and the thickness of the GaN epitaxial layer is 3 μm.

[0051] (3) peeling off the substrate;

[0052] Specifically, the steps of sequentially depositing a GaN epitaxial layer, a current blocking layer, an ITO current spreading layer, a metal electrode layer and a passivation protection layer on a substrate along an epitaxial growth direction include:

[0053] Step 1: Using MOCVD (Metal-organic Chemical Vapor Deposition) technology, a 1 μm thick gallium nitride buffer layer, a 4 μm thick N-type GaN layer, and three periods of active layers are grown on a sapphire substrate in sequence, wherein the thickness of a single quantum well layer is 3 nm, the thickness of a single quantum barrier layer is 12 nm, the quantum well layer is an InGaN layer, and the quantum barrier layer is a GaN layer. Then, a 20 nm thick P-type AlGaN layer and a P-type GaN layer are grown to obtain a GaN epitaxial wafer, which is then cleaned with an organic solution;

[0054] Step 2: Deposit an ITO current spreading layer on the GaN epitaxial wafer using magnetron sputtering technology, make a pattern on the ITO current spreading layer using photolithography technology, etch the ITO current spreading layer in a specific area by wet etching using a photoresist as a mask, and then perform MSA etching on the GaN epitaxial layer. The MSA etching is divided into two etching steps. First, Cl2 is introduced to etch the GaN epitaxial layer until part of the N-type GaN layer is exposed, and then SiCl4 gas is introduced to etch again;

[0055] It should be noted that in the step of introducing Cl2 to etch the GaN epitaxial layer, the flow rate of the introduced Cl2 is 140 sccm, the upper power of the ICP machine etching is 300 W, the lower power is 120 W, the etching pressure is 5 mtorr, and the etching time is 540 s;

[0056] Furthermore, in the step of introducing SiCl4 gas for etching, the flow rate of the SiCl4 gas is 100 sccm, the upper power of the ICP machine etching is 400 W, the lower power is 200 W, the etching pressure is 10 mtorr, and the etching time is 150 s.

[0057] Step 3: Soak the etched wafer in BOE solution and then clean it;

[0058] The concentration of the BOE solution is 10%, the immersion time is 60 seconds, and the samples are fully washed in deionized water after immersion.

[0059] Step 4: Pattern the photoresist on the cleaned wafer through a yellow light process to expose the area on the wafer where metal needs to be evaporated;

[0060] Step 5: Place the wafer after the yellow light process in an oxygen plasma cleaning machine to remove the residual glue on the surface of the wafer after development;

[0061] Step 6: Use deionized water to thoroughly clean the wafer after removing the residual glue, and then evaporate the metal electrode in the area on the wafer where the metal needs to be evaporated to obtain an N-electrode metal layer. In this embodiment, the cleaned wafer is subjected to metal evaporation within 2 hours.

[0062] Furthermore, a passivation protective layer is deposited on the entire wafer, and holes are opened at positions corresponding to the passivation protective layer. A multilayer metal film is deposited at the openings by electron beam evaporation or sputtering equipment to form an N-electrode metal layer and a P-electrode metal layer. Specifically, the N-electrode metal layer is a multilayer metal film composed of Al, Ti, Ni, Pt, Ti, and Pt, with thicknesses of 120nm, 100nm, 120nm, 100nm, 100nm, and 100nm, respectively.

[0063] In this embodiment, trimethylaluminum (TMAl), trimethylindium (TMIn), trimethylgallium or triethylgallium (TMGa or TEGa) are used as precursors of Group III sources, ammonia (NH3) and antimonide (SbH3) are used as precursors of Group V sources, silane (SiH4) and bismuth magnesium (Cp2Mg) are used as precursors of N-type dopants and P-type dopants, respectively, and nitrogen and hydrogen are used as carrier gases.

[0064] Example 2

[0065] Embodiment 2 of the present invention also provides a method for preparing an LED chip. The difference from Embodiment 1 is that the N-electrode metal layer is a multilayer metal film composed of Cr, Al, Ti, Ni, Pt, Ti, and Pt, and the thicknesses are 5nm, 120nm, 100nm, 120nm, 100nm, 100nm, and 100nm, respectively.

[0066] Example 3

[0067] Embodiment 3 of the present invention also provides a method for preparing an LED chip, which differs from Embodiment 1 in that, in the step of introducing Cl2 to etch the GaN epitaxial layer until a portion of the N-type GaN layer is exposed, the upper etching power of the ICP machine is 800W and the lower etching power is 300W.

[0068] Example 4

[0069] Embodiment 4 of the present invention also provides a method for preparing an LED chip, which differs from Embodiment 1 in that, in the step of introducing Cl2 to etch the GaN epitaxial layer until a portion of the N-type GaN layer is exposed, the etching time is 400s.

[0070] Example 5

[0071] Embodiment 5 of the present invention also provides a method for preparing an LED chip, which differs from Embodiment 1 in that, in the step of introducing Cl2 to etch the GaN epitaxial layer until a portion of the N-type GaN layer is exposed, the etching time is 600s.

[0072] Example 6

[0073] Embodiment 6 of the present invention also provides a method for preparing an LED chip, which differs from Embodiment 1 in that, in the step of introducing SiCl4 gas and then etching, the upper power of the ICP machine for etching is 200W and the lower power is 70W.

[0074] Example 7

[0075] Embodiment 7 of the present invention also provides a method for preparing an LED chip, which differs from Embodiment 1 in that, in the step of introducing SiCl4 gas and then etching, the upper etching power of the ICP machine is 400W and the lower etching power is 70W.

[0076] Example 8

[0077] Embodiment 8 of the present invention also provides a method for preparing an LED chip, which differs from Embodiment 1 in that, in the step of introducing SiCl4 gas and then etching, the etching time is 60 seconds.

[0078] Example 9

[0079] Embodiment 9 of the present invention also provides a method for preparing an LED chip, which differs from Embodiment 1 in that, in the step of introducing SiCl4 gas and then performing etching, the etching time is 300s.

[0080] Comparative Example 1

[0081] Comparative Example 1 also provides a method for preparing an LED chip, which differs from Example 1 of the present invention in that no SiCl4 etching is performed and no BOE solution immersion treatment is performed.

[0082] Comparative Example 2

[0083] Comparative Example 2 also provides a method for preparing an LED chip, which differs from Example 2 of the present invention in that no SiCl4 etching is performed and no BOE solution immersion treatment is performed.

[0084] The LED chips in Examples 1 to 9, and Comparative Examples 1 and 2 were tested under the same conditions (tested on a 48mil*48mil flip chip, with a test current of 320mA). The luminous efficiency was calculated by dividing the optical power of the chip by the electrical power. The specific results are as follows:

[0085] Implementation Voltage (V) Luminous efficiency (%) Example 1 2.85 60.3 Example 2 2.78 59.6 Example 3 2.84 60.1 Example 4 2.86 59.5 Example 5 2.85 60.2 Example 6 2.86 59.8 Example 7 2.86 59.8 Example 8 2.86 59.9 Example 9 2.85 59.6 Comparative Example 1 3.62 48.3 Comparative Example 2 2.87 57.7

[0086] It can be seen from the table that the voltage of the LED chips prepared in the embodiments of the present invention is reduced to varying degrees compared with the comparative examples, that is, the contact resistance between the N-type GaN layer and the metal Al is reduced. At the same time, the brightness is improved to varying degrees. Among them, the voltage of the LED chip prepared in Example 1 of the present invention is the smallest and the luminous brightness is the strongest.

[0087] In summary, the LED chip preparation method and LED chip in the embodiment of the present invention perform MSA etching on the GaN epitaxial layer. Specifically, the MSA etching is divided into two etchings. First, Cl2 is introduced to etch the GaN epitaxial layer until a portion of the N-type GaN layer is exposed, and then SiCl4 gas is introduced for further etching; the etched wafer is immersed in a BOE solution and then cleaned; the cleaned wafer is patterned with photoresist through a yellow light process to expose the area on the wafer where metal needs to be evaporated; the wafer after the yellow light process is placed in an oxygen plasma cleaning machine to remove residual glue on the surface of the wafer after development; the wafer after the residual glue is fully cleaned with deionized water to remove it, and then a metal electrode is evaporated in the area on the wafer where metal needs to be evaporated to obtain an N-electrode metal layer. The above process can further reduce the contact resistance between the metal electrode and the N-type GaN layer while improving the luminous brightness of the LED chip.

[0088] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing an LED chip, characterized in that: The method comprises: Providing a GaN epitaxial layer, the GaN epitaxial layer comprising an N-type GaN layer, a multi-quantum well layer and a P-type GaN layer deposited in sequence; Performing MSA etching on the GaN epitaxial layer, wherein the MSA etching is divided into two etching steps, firstly, introducing Cl2 to etch the GaN epitaxial layer until a portion of the N-type GaN layer is exposed, and then introducing SiCl4 gas to etch again; Soak the etched wafer in BOE solution and then clean it; The cleaned wafer is patterned with photoresist through a yellow light process to expose the area on the wafer where metal needs to be evaporated; Place the wafer after the yellow light process in an oxygen plasma cleaning machine to remove the residual glue on the surface of the wafer after development; The wafer after the residual glue is thoroughly cleaned with deionized water is then evaporated on the area of ​​the wafer where metal is required to be evaporated to obtain an N-electrode metal layer.

2. The method for preparing an LED chip according to claim 1, characterized in that: In the step of introducing Cl2 to etch the GaN epitaxial layer until a portion of the N-type GaN layer is exposed, the flow rate of the introduced Cl2 is 60sccm~200sccm, the upper power of the ICP machine etching is 300W~800W, the lower power is 100W~300W, the etching pressure is 3mtorr~10mtorr, and the etching time is 200s~600s.

3. The method for preparing an LED chip according to claim 2, characterized in that: In the step of introducing Cl2 to etch the GaN epitaxial layer until a portion of the N-type GaN layer is exposed, the etching depth is 800nm ​​to 2000nm.

4. The method for preparing an LED chip according to claim 3, characterized in that: In the step of introducing SiCl4 gas and then etching, the flow rate of the SiCl4 gas is 70sccm~150sccm, the upper power of the ICP machine etching is 200W~600W, the lower power is 70W~200W, 3mtorr~10mtorr, and the etching time is 60s~300s.

5. The method for preparing an LED chip according to claim 4, characterized in that: The N-type GaN layer is etched to a depth of 100 nm to 300 nm.

6. The method for preparing an LED chip according to claim 5, characterized in that: In the step of soaking the etched wafer in a BOE solution and then cleaning, the concentration of the BOE solution is 5% to 20%, and the soaking time is 30s to 180s.

7. The method for preparing an LED chip according to claim 6, characterized in that: The mass ratio of HF to NH4F in the BOE solution is 1:10-30.

8. The method for preparing an LED chip according to claim 7, characterized in that: In the step of using deionized water to fully clean the wafer after removing the residual glue, and then evaporating a metal electrode in the area on the wafer where metal is required to be evaporated to obtain an N-electrode metal layer, the cleaned wafer is subjected to metal evaporation within 2 hours.

9. The method for preparing an LED chip according to claim 8, characterized in that: The thickness of the GaN epitaxial layer is 3 μm to 7 μm.

10. An LED chip, characterized in that: The LED chip is prepared according to the method for preparing the LED chip according to any one of claims 1 to 9.