LED chip preparation method and LED chip
By performing ICP etching and acidic solution treatment on the surface of the N-type GaN layer, combined with Al metal evaporation technology, the problem of high contact resistance between Al electrode and N-type GaN is solved, and the LED chip voltage reduction and brightness improvement effect is achieved.
Patent Information
- Application Number
- CN202411509162.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-28
- Publication Date
- 2025-02-07
AI Technical Summary
How to reduce the contact resistance of the Al electrode with N-type GaN while avoiding the generation of additional auxiliary products, solves the problems of excessive LED chip voltage and reduced brightness.
By ICP etching on the surface of the N-type GaN layer, it is divided into two etchings. First, argon gas is passed through for rapid etching, and then a mixture of argon and oxygen is passed through for etching. Then, the The wafer is soaked in an acidic solution and washed; finally, Al metal deposition is carried out to deposit the N-electrode metal layer.
The contact resistance of the N-type GaN layer and metal Al is significantly reduced, the voltage of the LED chip is reduced, and the brightness of the LED chip is increased without additional auxiliary products.
Smart Images
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Abstract
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 (Light 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 gradual reduction. The main difficulty in reducing the voltage of LED chips is how to effectively reduce the contact resistance between the metal electrode 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. However, metals such as Cr, Ti, and Ni have strong absorption of visible light, which will cause the brightness of the LED chip to decrease. Metal Al has a high reflectivity for visible light, so it was once considered for use as an adhesion layer metal. However, the ohmic contact between Al and N-type GaN is far inferior to that of metals such as Cr, Ti, and Ni, and direct use will cause the LED chip voltage to be too high. How to reduce the contact resistance between the Al electrode and N-type GaN without producing other byproducts is currently a major problem. 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 reduce the contact resistance between the Al electrode and the N-type GaN without generating additional by-products.
[0005] According to an embodiment of the present invention, a method for preparing an LED chip includes:
[0006] The surface of the N-type GaN layer is processed. Specifically, the wafer with the N-type GaN layer exposed after the yellow light process is subjected to ICP etching. The ICP etching is divided into two etching steps. First, argon gas is introduced for rapid etching, and then a mixed gas of argon and oxygen is introduced for further etching.
[0007] Soak the etched wafer in an acid solution and then clean it;
[0008] The cleaned wafer is subjected to Al metal evaporation to deposit an N-electrode metal layer.
[0009] Furthermore, the step of treating the surface of the N-type GaN layer includes:
[0010] providing a substrate;
[0011] Depositing a GaN epitaxial layer, a current blocking layer, and an ITO current spreading layer in sequence on the substrate;
[0012] The GaN epitaxial layer includes an N-type GaN layer, a multi-quantum well layer and a P-type GaN layer which are deposited in sequence.
[0013] Furthermore, in the step of introducing argon gas for rapid etching, the flow rate of the introduced argon gas is 20 sccm to 100 sccm, the ICP etching upper power is 400W to 1200W, the lower power is 300W to 600W, the etching pressure is 3mtorr to 15mtorr, and the etching time is 20s to 60s.
[0014] Furthermore, in the step of introducing a mixed gas of argon and oxygen for etching, the flow rate of the introduced argon is 2sccm~10sccm, the flow rate of the oxygen is 20sccm~80sccm, the ICP etching upper power is 400W~800W, the lower power is 200W~400W, the etching pressure is 3mtorr~10mtorr, and the etching time is 20s~60s.
[0015] Furthermore, in the step of immersing the etched wafer in an acidic solution and then cleaning it, the concentration of the acidic solution is 2% to 8%, and the immersion time is 20s to 120s.
[0016] Furthermore, the acidic solution is a hydrochloric acid solution or a BOE solution.
[0017] Furthermore, in the step of subjecting the cleaned wafer to Al metal evaporation to deposit the N-electrode metal layer, the cleaned wafer is subjected to metal evaporation within 4 hours.
[0018] Furthermore, the thickness of the GaN epitaxial layer is 3 μm to 7 μm.
[0019] An LED chip according to an embodiment of the present invention is prepared according to the above-mentioned LED chip preparation method.
[0020] The beneficial effects of the present invention are:
[0021] The surface of the N-type GaN layer is treated. Specifically, the wafer with the N-type GaN layer exposed after the yellow light process is subjected to ICP etching. The ICP etching is divided into two etching steps. First, argon gas is introduced for rapid etching, and then a mixed gas of argon and oxygen is introduced for further etching. The etched wafer is immersed in an acidic solution and then cleaned. The cleaned wafer is subjected to Al metal evaporation to deposit an N-electrode metal layer. The surface of the N-type GaN layer is treated with argon and oxygen, so that the contact resistance between the N-type GaN layer and the metal Al can be significantly reduced without generating additional byproducts. In addition, the process can not only reduce the voltage of the LED chip, but also improve the brightness of the LED chip. DETAILED DESCRIPTION
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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:
[0026] S100: providing a substrate;
[0027] 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.
[0028] 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;
[0029] 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.
[0030] S300: peeling off the substrate;
[0031] Specifically, S200 includes:
[0032] 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;
[0033] 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, then etching an MSA step by using an MSA yellow light process, and finally etching the epitaxial layer to the N-type GaN layer by using an N metal electrode yellow light process to expose a portion of the N-type GaN layer;
[0034] The surface of the N-type GaN layer is processed. Specifically, the wafer with the N-type GaN layer exposed after the yellow light process is subjected to ICP (Inductively Coupled Plasma) etching in an ICP machine. The ICP etching is divided into two etching steps. First, argon gas is introduced for rapid etching, and then a mixed gas of argon and oxygen is introduced for further etching.
[0035] It should be noted that, in the step of introducing argon gas for rapid etching, the flow rate of the introduced argon gas is 20sccm~100sccm, the ICP etching upper power is 400W~1200W, that is, the plasma source power is 400W~1200W, the lower power is 300W~600W, that is, the bias power is 300W~600W, the etching pressure is 3mtorr~15mtorr, and the etching time is 20s~60s. In this step, increasing the etching kinetic energy and speed of argon gas as much as possible in a short time is one of the core keys of the entire process. Large etching kinetic energy and speed are conducive to etching deep pit structures and a large number of N vacancies on the surface of the N-type GaN layer, providing suitable conditions for subsequent oxygen atom injection. However, the etching time of argon in this step should not be too long, otherwise it will cause epitaxial damage and the chip voltage will increase. In addition, argon has poor etching selectivity for different materials. Therefore, compared with CF4, Cl2 and other gases, it can better and indiscriminately remove oxides and particles on the surface of the N-type GaN layer.
[0036] Furthermore, in the step of introducing a mixed gas of argon and oxygen for etching, the flow rate of the introduced argon is 2sccm~10sccm, the flow rate of the oxygen is 20sccm~80sccm, the upper power of ICP etching is 400W~800W, the lower power is 200W~400W, the etching pressure is 3mtorr~10mtorr, and the etching time is 20s~60s. It should be noted that the upper and lower powers set by the ICP machine should not be too large or too small. Excessive power will cause epitaxial damage and increase the chip voltage; too small power will lead to insufficient oxygen injection, and the contact resistance on the surface of the Al and N-type GaN layers cannot be effectively reduced. It can be understood that the role of oxygen is to form GaO on the surface of the N-type GaN layer. x 、GaO x N 1-x and other compounds, and the closer to the surface, the greater the GaO x The greater the proportion of the content, the effect of adding a small amount of argon is to destroy the surface to form GaO x compounds, thereby increasing the etching depth of oxygen, which is conducive to the formation of GaO at a deeper position on the surface of the N-type GaN layer. x N 1-x , among which, GaO x N 1-x It is a highly conductive compound that can effectively reduce the contact resistance with the Al electrode.
[0037] S203: Soaking the etched wafer in an acid solution and then cleaning it;
[0038] The concentration of the acid solution is 2% to 8%, the immersion time is 20s to 120s, the acid solution is a hydrochloric acid solution or a BOE solution, and after immersion, the wafer is placed in deionized water for thorough cleaning. It should be noted that the hydrochloric acid or BOE solution is used to immerse the wafer after the above-mentioned gas treatment after etching, which can effectively remove the high-resistance GaO remaining on the surface of the N-type GaN layer. x compound, exposing the GaO underneath x N 1-x , thereby reducing the contact resistance between the N-type GaN layer surface and the Al metal, and reducing the LED chip voltage.
[0039] S204: performing Al metal evaporation on the cleaned wafer to deposit an N-electrode metal layer.
[0040] Specifically, the cleaned wafer is subjected to metal evaporation within 4 hours to prevent the surface of the N-type GaN layer from being exposed to air for too long, which may easily cause oxide to re-form on the surface and cause voltage increase.
[0041] Furthermore, a passivation protective layer is deposited on the entire wafer, and holes are opened at positions corresponding to 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.
[0042] 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.
[0043] The present invention will be further described below with specific embodiments:
[0044] Example 1
[0045] Embodiment 1 of the present invention provides a method for preparing an LED chip, which specifically includes the following steps:
[0046] (1) providing a substrate;
[0047] 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.
[0048] (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;
[0049] 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.
[0050] (3) peeling off the substrate;
[0051] 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:
[0052] 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;
[0053] 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 photoresist as a mask, then use the MSA yellow light process to etch out the MSA step, and finally use the N metal electrode yellow light process to etch the epitaxial layer to the N-type GaN layer to expose part of the N-type GaN layer;
[0054] The surface of the N-type GaN layer is processed. Specifically, the wafer with the N-type GaN layer exposed after the yellow light process is subjected to ICP (Inductively Coupled Plasma) etching in an ICP machine. The ICP etching is divided into two etching steps. First, argon gas is introduced for rapid etching, and then a mixed gas of argon and oxygen is introduced for further etching.
[0055] It should be noted that in the step of introducing argon gas for rapid etching, the flow rate of the introduced argon gas is 70 sccm, the upper power of ICP etching is 800 W, the lower power is 400 W, the etching pressure is 10 mtorr, and the etching time is 30 s;
[0056] Furthermore, in the step of introducing a mixed gas of argon and oxygen for etching, the flow rate of the introduced argon is 5 sccm, the flow rate of the oxygen is 50 sccm, the ICP etching upper power is 600 W, the lower power is 300 W, the etching pressure is 10 mtorr, and the etching time is 30 s.
[0057] S203: Soaking the etched wafer in an acid solution and then cleaning it;
[0058] The concentration of the acidic solution is 5%, the immersion time is 30 seconds, the acidic solution is BOE solution, and after immersion, the solution is placed in deionized water for thorough cleaning.
[0059] S204: performing Al metal evaporation on the cleaned wafer to deposit an N-electrode metal layer.
[0060] Specifically, the cleaned wafer is subjected to metal evaporation within 4 hours to prevent the surface of the N-type GaN layer from being exposed to air for too long, which may easily cause oxide to re-form on the surface and cause voltage increase.
[0061] 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, Pt, and Ti, with thicknesses of 120nm, 100nm, 120nm, 100nm, 100nm, 100nm, and 5nm, respectively.
[0062] 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.
[0063] Example 2
[0064] Embodiment 2 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 a mixed gas of argon and oxygen and then etching, the upper power of ICP etching is 400W and the lower power is 200W.
[0065] Example 3
[0066] 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 a mixed gas of argon and oxygen and then etching, the upper power of ICP etching is 800W and the lower power is 400W.
[0067] Example 4
[0068] 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 a mixed gas of argon and oxygen and then performing etching, the etching time is 60 seconds.
[0069] Example 5
[0070] 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 argon gas for rapid etching, the upper power of ICP etching is 1200W and the lower power is 600W.
[0071] Example 6
[0072] 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 argon gas for rapid etching, the etching time is 60 seconds.
[0073] Comparative Example 1
[0074] Comparative Example 1 also provides a method for preparing an LED chip, which differs from Example 1 in that, in the step of introducing argon gas for rapid etching, the etching time is 120 seconds.
[0075] Comparative Example 2
[0076] Comparative Example 2 also provides a method for preparing an LED chip, which differs from Example 1 in that, in the step of introducing a mixed gas of argon and oxygen and then etching, the upper power of ICP etching is 1000W and the lower power is 600W.
[0077] Comparative Example 3
[0078] Comparative Example 3 also provides a method for preparing an LED chip, which differs from Example 1 in that, in the step of introducing a mixed gas of argon and oxygen and then etching, the upper power of ICP etching is 300W and the lower power is 150W.
[0079] Comparative Example 4
[0080] Comparative Example 4 also provides a method for preparing an LED chip, which differs from Example 1 in that, in the step of introducing a mixed gas of argon and oxygen and then etching, the flow rate of the introduced argon is 0 sccm, the upper power of ICP etching is 300 W, and the lower power is 150 W.
[0081] Comparative Example 5
[0082] Comparative Example 5 also provides a method for preparing an LED chip. The difference from Example 1 of the present invention is that oxygen plasma is used to remove the residual glue on the surface of the wafer after development of the wafer with the N-type GaN layer exposed after the yellow light process, and then the wafer is cleaned with an acidic solution, and then the wafer is quickly placed in a metal evaporation machine to deposit the N-electrode metal layer.
[0083] Comparative Example 6
[0084] Comparative Example 6 also provides a method for preparing an LED chip. The difference from Comparative Example 1 is that the N-electrode metal layer is a multilayer metal film composed of Cr, Al, Ti, Ni, Pt, Ti, Pt, and Ti, with thicknesses of 5nm, 120nm, 100nm, 120nm, 100nm, 100nm, 100nm, and 5nm, respectively.
[0085] The LED chips in Examples 1 to 6 and Comparative Examples 1 to 6 were tested under the same conditions (tested on a 48mil*48mil flip chip with a test current of 320mA), and the specific results are as follows:
[0086]
[0087]
[0088] 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, and at the same time, the brightness is improved to varying degrees, among which the voltage of the LED chip prepared in Example 1 of the present invention is the smallest and the luminous brightness is the strongest. In addition, when the etching time increases and the upper and lower powers of the ICP etching increase, the voltage of the LED chip increases and the luminous brightness decreases.
[0089] In summary, the flip-chip LED chip and the preparation method thereof in the embodiment of the present invention process the surface of the N-type GaN layer. Specifically, the wafer with the N-type GaN layer exposed after the yellow light process is subjected to ICP etching, and the ICP etching is divided into two etching steps. First, argon gas is introduced for rapid etching, and then a mixed gas of argon and oxygen is introduced for further etching; the etched wafer is immersed in an acidic solution and then cleaned; the cleaned wafer is subjected to Al metal evaporation to deposit an N-electrode metal layer, wherein the surface of the N-type GaN layer is treated with argon and oxygen, so that the contact resistance between the N-type GaN layer and the metal Al can be significantly reduced without generating additional by-products. In addition, this process can not only reduce the voltage of the LED chip, but also improve the brightness of the LED chip.
[0090] 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: The surface of the N-type GaN layer is processed. Specifically, the wafer with the N-type GaN layer exposed after the yellow light process is subjected to ICP etching. The ICP etching is divided into two etching steps. First, argon gas is introduced for rapid etching, and then a mixed gas of argon and oxygen is introduced for further etching. Soak the etched wafer in an acid solution and then clean it; The cleaned wafer is subjected to Al metal evaporation to deposit an N-electrode metal layer.
2. The method for preparing an LED chip according to claim 1, characterized in that: The step of processing the surface of the N-type GaN layer includes: providing a substrate; Depositing a GaN epitaxial layer, a current blocking layer, and an ITO current spreading layer in sequence on the substrate; The GaN epitaxial layer includes an N-type GaN layer, a multi-quantum well layer and a P-type GaN layer which are deposited in sequence.
3. The method for preparing an LED chip according to claim 1 or 2, characterized in that: In the step of introducing argon gas for rapid etching, the flow rate of the introduced argon gas is 20 sccm to 100 sccm, the ICP etching upper power is 400W to 1200W, the lower power is 300W to 600W, the etching pressure is 3mtorr to 15mtorr, and the etching time is 20s to 60s.
4. The method for preparing an LED chip according to claim 1 or 2, characterized in that: In the step of introducing a mixed gas of argon and oxygen and then etching, the flow rate of the introduced argon is 2sccm~10sccm, the flow rate of the oxygen is 20sccm~80sccm, the ICP etching upper power is 400W~800W, the lower power is 200W~400W, the etching pressure is 3mtorr~10mtorr, and the etching time is 20s~60s.
5. The method for preparing an LED chip according to claim 1 or 2, characterized in that: In the step of soaking the etched wafer in an acidic solution and then cleaning it, the concentration of the acidic solution is 2% to 8%, and the soaking time is 20s to 120s.
6. The method for preparing an LED chip according to claim 5, characterized in that: The acidic solution is a hydrochloric acid solution or a BOE solution.
7. The method for preparing an LED chip according to claim 1 or 2, characterized in that: In the step of subjecting the cleaned wafer to Al metal evaporation and depositing the N-electrode metal layer, the cleaned wafer is subjected to metal evaporation within 4 hours.
8. The method for preparing an LED chip according to claim 2, characterized in that: The thickness of the GaN epitaxial layer is 3 μm to 7 μm.
9. 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 8.