Etching method of GaN substrate

Abstract

The present invention discloses a method for etching a GaN substrate, comprising: forming a first mask layer on the top surface of the GaN substrate; making a patterned photoresist layer on the surface of the first mask layer; an etching step, using an etching gas to continuously etch the first mask layer and the GaN substrate to form a plurality of microstructures isolated from each other by etching grooves on the GaN substrate, wherein the microstructures have a set sidewall inclination angle; wherein the etching gas comprises a chlorine-based gas, a bromine-containing gas, and a boron-containing gas. The present invention can avoid the microgroove effect generated by dry etching of high-angle GaN microstructures.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing, and more specifically, to an etching method for a GaN substrate. Background Art

[0002] With the development of LED technology, LED has gradually moved from traditional LED lighting applications to the display field. Among the many display technologies currently available, Micro-LED display technology is considered to be a disruptive new generation of display technology due to its outstanding advantages such as excellent image quality and outstanding life stability, and has received widespread attention from academia and industry. The size of Micro-LED (1~100μm) is significantly smaller than that of traditional lighting LEDs (300μm~1mm). At the same time, in order to increase the number of chips per unit area, increase the luminous area, improve chip integration, and reduce the crosstalk effect, the mesa (high platform) and ISO (photosensitive) processes of Micro-LED light-emitting chips have higher angle requirements than traditional LEDs. Taking the Mesa electrode etching process as an example, the etching angle requirement of traditional LEDs is 30~40°, while the etching angle requirement of Micro-LEDs is increased to 60~80°.

[0003] Plasma dry etching of GaN-Mesa electrodes is a key step in the manufacturing process of Micro-LED chips. However, in the actual etching process, it was found that the use of traditional chlorine-based etching system to etch low-angle GaN-Mesa (sidewall inclination angle <40°) would not cause micro-grooving problems, such as Figure 1a As shown in the figure, for high-angle GaN-Mesa etching (sidewall inclination angle>60°), etching is very likely to form the following at the corner of the Mesa pattern (the junction of the etched sidewall and the etched bottom): Figure 1b The micro-groove structure shown in the figure. The presence of micro-grooves can easily cause current accumulation at this position of the LED chip during operation, thereby causing the chip performance to deteriorate. The known chlorine-based etching system can no longer meet the requirements of Mini / Micro-LED-Mesa high-angle etching. Summary of the invention

[0004] The purpose of the present invention is to provide a method for etching a GaN substrate, so as to avoid the micro-groove effect caused by dry etching of a high-angle GaN microstructure.

[0005] To achieve the above object, the present invention provides a GaN substrate etching method, comprising:

[0006] forming a first mask layer on a top surface of the GaN substrate;

[0007] forming a patterned photoresist layer on the surface of the first mask layer;

[0008] An etching step, wherein the first mask layer and the GaN substrate are continuously etched by an etching gas to form a plurality of microstructures isolated from each other by etching grooves on the GaN substrate, wherein the microstructures have a set sidewall inclination angle;

[0009] Wherein, the etching gas includes chlorine-based gas, bromine-containing gas and boron-containing gas.

[0010] Optionally, the chlorine-based gas includes Cl 2 , the boron-containing gas includes BCl 3 .

[0011] Optionally, the chlorine-based gas includes Cl 2 , BCl 3 At least one of the above-mentioned boron-containing gas comprises a borane-based gas.

[0012] Optionally, the etching gas further includes a nitrogen-containing gas, and the molar amounts of the boron element and the nitrogen element in the etching gas are equal.

[0013] Optionally, the nitrogen-containing gas includes NH 3 、N 2 at least one of them.

[0014] Optionally, the etching gas further includes a carbon-fluorine gas.

[0015] Optionally, the gas containing bromine elements is a gas containing hydrogen elements and bromine elements.

[0016] Optionally, the borane gas flow range is 5 to 20 sccm; the fluorocarbon gas flow range is 20 to 50 sccm; the bromine-containing gas flow range is 40 to 100 sccm; the nitrogen-containing gas flow range is 20 to 80 sccm; and the chlorine-based gas flow range is 10 to 40 sccm.

[0017] Optionally, the sum of the flow rates of the borane gas, the nitrogen-containing gas, the carbon fluorine gas and the bromine-containing gas is 60% to 80% of the total flow rate of the etching gas.

[0018] Optionally, the borane gas is B 2 H 6 , the carbon fluorine gas is CHF 3 The bromine-containing gas is HBr, and the nitrogen-containing gas is NH 3 , the chlorine-based gas is Cl 2 and BCl 3 ;

[0019] Optionally, a material of the first mask layer includes at least one of silicon oxide and silicon nitride.

[0020] The beneficial effects of the present invention are:

[0021] The etching method of the GaN substrate of the present invention adopts an etching gas including a chlorine-based gas, a bromine-containing gas and a boron-containing gas. In the etching gas system, the chlorine-based gas and the bromine-containing gas can etch the hard mask and GaN at the same time, and the boron-containing gas can correct the morphology. The etching gas can eliminate the micro-groove effect formed between the angle between the side wall of the etched groove and the bottom surface of the groove caused by the traditional dry etching method of high-angle GaN (a recognized mechanism for forming micro-grooves is that ions moving from top to bottom rebound through the side wall and collide with the bottom corner to cause bottom corner damage. Therefore, the larger the side wall angle, the more obvious the effect, that is, the more difficult it is to eliminate the micro-groove effect), thereby improving the electrical yield of the Mini / Micro-LED chip.

[0022] Furthermore, with respect to the method of using PR+hard mask to obtain a large etching angle, the method of the present invention can enable the hard mask to be opened by wet / dry method without a separate process, and only one step of etching with the GaN epitaxial layer is required to complete the patterned opening etching of the hard mask and the etching of the GaN epitaxial layer, thereby effectively reducing the process flow and avoiding the problems of chamber state instability and particle contamination caused by mixing different gases due to the separate etching of the hard mask and the GaN epitaxial layer.

[0023] The system of the present invention has other characteristics and advantages, which will be apparent from the drawings incorporated herein and the following detailed description, or will be described in detail in the drawings incorporated herein and the following detailed description, which together serve to explain the specific principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, in which like reference numerals generally represent like components.

[0025] Figure 1a and Figure 1b The sidewall morphologies of low-angle and high-angle GaN microstructures etched by conventional GaN are shown respectively.

[0026] Figure 2 A schematic diagram of GaN structural changes corresponding to each step of a conventional GaN etching method is shown.

[0027] Figure 3 A step diagram of an etching method for a GaN substrate according to Embodiment 1 of the present invention is shown.

[0028] Figure 4 A schematic diagram of GaN structural changes corresponding to each step of a GaN substrate etching method according to Embodiment 1 of the present invention is shown.

[0029] Figure 5 The sidewall morphology of a GaN microstructure obtained by an etching method of a GaN substrate according to Example 1 of the present invention is shown.

[0030] Figure 6a-6c A sidewall morphology image of a GaN microstructure obtained by an etching method of a GaN substrate according to Example 2 of the present invention is shown. DETAILED DESCRIPTION

[0031] Conventional GaN etching methods usually use Cl 2 Gas-based, BCl 3 / Ar assisted bombardment gas system (BCl 3 With the formation of BCl 2 + bombardment, but relative to Cl 2 The ability of forming Cl radicals is weaker than that of gas, so the physical bombardment effect is enhanced while the chemical etching effect is reduced) The epitaxial GaN substrate is dry-etched with a negative photoresist mask or a positive photoresist + SiO 2 / SiN x Mask form to obtain a large-angle GaN-Mesa mesa microstructure, where positive photoresist + SiO 2 / SiN x Mask structure, usually requires SiO 2 / SiN x After the mask is dry-etched using fluorine-containing gas or wet-opened using fluorine-containing etching solution, chlorine-based gas is used to dry-etch the GaN mesa.

[0032] like Figure 2 As shown, the traditional GaN etching steps are as follows:

[0033] Step 1: Provide a substrate to be etched, which includes a sapphire substrate, a U-GaN layer, an N-GaN layer, a multi-quantum well (MQWs) layer, a P-GaN layer, and a SiO 2 / SiN x layer and photoresist (PR) layer;

[0034] Step 2: Dry etching process using fluorine-based plasma to etch SiO 2 / SiN x The layer is opened and etched to form a hard mask;

[0035] Step 3: wet removal of photoresist;

[0036] Step 4: A dry etching process is used to etch the GaN epitaxial layer (composed of a U-GaN layer, an N-GaN layer, a multi-quantum well (MQWs) layer, and a P-GaN layer) using chlorine-based plasma.

[0037] For high-angle GaN-Mesa etching, this etching method uses the above-mentioned Cl-based etching system, and it is easy to form a micro-groove structure at the corner of the pattern (the junction between the side wall of the etched groove and the bottom of the groove), such as Figure 1b The existence of the micro-groove structure can easily cause charge accumulation at this position during the operation of the LED chip, resulting in a decrease in chip performance.

[0038] Moreover, for positive photoresist + SiO 2 / SiN x Mask structure, the traditional etching method is to SiO 2 / SiN x Using fluorine-based gas dry etching to open or using fluorine-containing corrosive liquid to open, using wet etching to open adds a process step. At the same time, using fluorine-based gas dry etching to open and then performing Cl-based gas dry etching will lead to the mixing of different etching gases, resulting in unstable chamber environment of dry etching equipment, which is not conducive to particle control and causes particle contamination.

[0039] The method of the present invention uses etching gases including chlorine-based gas, bromine-containing gas and boron-containing gas when etching high-angle (60-80°) GaN patterns. The bromine-containing gas and boron-containing gas provide sidewall protection and correct morphology, thereby eliminating the micro-groove effect of the bottom angle of the etched groove caused by the traditional dry etching method of the high-angle GaN structure. In addition, the use of the etching gas system can achieve the SiO 2 / SiN x The hard mask and the GaN substrate are dry-etched in one step to avoid the problems of unstable chamber state and particle contamination caused by mixing different gases. The present invention will be described in more detail with reference to the accompanying drawings. Although the preferred embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0040] Example 1

[0041] The method of this embodiment is mainly used for GaN-Mesa pattern etching of LED substrates, such as Figure 3 and Figure 4 As shown, the etching method of the GaN substrate of this embodiment includes:

[0042] S1: forming a first mask layer on the top surface of the GaN substrate;

[0043] In this embodiment, the GaN substrate includes a sapphire base, a U-GaN layer, an N-GaN layer, a multi-quantum well layer and a P-GaN layer stacked in sequence from bottom to top.

[0044] The preparation process of the GaN substrate is as follows: providing a sapphire substrate, and using an epitaxial process to sequentially epitaxially grow a U-GaN layer, an N-GaN layer, a multi-quantum well layer and a P-GaN layer on the surface of the sapphire substrate to form a GaN epitaxial layer.

[0045] In this step, a first mask layer can be formed on the P-GaN layer by epitaxy or deposition process. The material of the first mask layer includes at least one of silicon oxide and silicon nitride. In this embodiment, the material of the first mask layer is preferably SiO 2 .

[0046] S2: forming a patterned photoresist layer on the surface of the first mask layer;

[0047] In this step, a patterned photoresist layer may be formed by spin coating a photoresist on the first mask layer and patterning the photoresist through a photolithography process. Preferably, the photoresist layer is a positive photoresist pattern.

[0048] S3: an etching step, continuously etching the first mask layer and the GaN substrate using an etching gas to form a plurality of microstructures isolated from each other by etching grooves on the GaN substrate, wherein the microstructures have a set sidewall inclination angle;

[0049] The etching gas includes chlorine-based gas, bromine-containing gas and boron-containing gas.

[0050] like Figure 4 As shown, this step uses a dry etching process to etch the first mask layer and the GaN substrate simultaneously. The specific process is as follows:

[0051] First, a GaN substrate is placed in a process chamber of a plasma etching device, and then an etching gas is introduced into the process chamber. At the same time, process parameters such as chamber pressure, upper electrode radio frequency power, and lower radio frequency power are adjusted to set values ​​to excite the etching gas to generate plasma.

[0052] Then, the dielectric layer is etched with a patterned photoresist layer and an etching gas to form a patterned first mask layer;

[0053] Afterwards, the dry etching process is continued to be adopted, and the GaN epitaxial layer is etched using the first mask layer and the etching gas to form a plurality of microstructures isolated from each other by etching grooves and having a set sidewall inclination angle.

[0054] In the etching process, the opening etching of the first mask layer and the etching of the GaN epitaxial layer are one-step etching.

[0055] In this embodiment, the etching gas includes chlorine-based gas, bromine-containing gas and boron-containing gas. 2 , boron-containing gases include BCl 3 The gas containing bromine element is a gas containing hydrogen element and bromine element, which may include HBr, H 2 +Br 2 , H 2 +BBr 3 , HBrO 3 , HBrO 4 At least one of the following, preferably HBr.

[0056] In the etching gas, Cl 2 It can etch the hard mask and GaN at the same time (forming gallium chloride to volatilize and extract it), HBr gas (when etching the first mask layer, it can form SiBr4 with Si element to have an etching effect, and it can also absorb oxygen elements in the chamber and photoresist to form SiBr x O y The oligomers protect the sidewalls, and the bromide of gallium formed during GaN etching is volatilized and extracted, thus having an etching effect, and can also form Br x O y Oligomers protect the sidewalls), BCl 3 The gas can protect the sidewall and modify the sidewall morphology (reduce the free Cl radicals with chemical etching activity).

[0057] Among them, Cl 2 Mainly used for etching GaN, the reaction equation is:

[0058] Chlorine plasma formation:

[0059] Cl 2 →Cl*

[0060] GaN etching:

[0061] GaN+Cl*→GaCl 3 ↑+N 2 ↑

[0062] This embodiment uses chlorine-based gas, bromine-containing gas and boron-containing gas as etching gases. The chlorine-based gas can etch the hard mask and GaN at the same time, and the bromine-containing gas and the boron-containing gas play a role in correcting the morphology, thereby eliminating the micro-groove effect formed between the angle between the side wall of the etched groove and the bottom surface of the groove caused by the traditional dry etching method of high-angle GaN. The GaN etching morphology obtained by the method of this embodiment is as follows: Figure 4 As shown, it can be seen that the micro-groove effect is significantly improved.

[0063] At the same time, the etching method of this embodiment allows the hard mask to be opened wet / dry without a separate process. The patterned opening etching of the hard mask and the etching of the GaN epitaxial layer can be completed by etching in one step together with the GaN epitaxial layer. This effectively reduces the process flow while avoiding the problems of chamber state instability and particle contamination caused by mixing different gases due to the separate etching of the hard mask and the GaN epitaxial layer.

[0064] Example 2

[0065] The steps of the etching method of the GaN substrate in this embodiment are the same as those in Embodiment 1, see steps S1-S3 of Reference Document 1, except that: in step S3, the chlorine-based gas and the boron-containing gas used in the etching gas are selected differently, specifically:

[0066] Chlorine-based gases in etching gases include Cl 2 , BCl 3 At least one of, preferably including Cl 2 and BCl 3 Boron-containing gases include borane gases. 2 and BCl 3 When etching GaN, borane gases are used to enhance sidewall protection and repair the etching morphology.

[0067] The borane gas may include B 2 H 6 , B n H n+4 , B n H n+6 , B n H n+8 and B n H n+10 At least one of which B 4 H 10 It is gas, B 6 H 10 It is a liquid. When the number of boron atoms is larger, it becomes solid and cannot be used. Therefore, n≤6. The borane gas in this embodiment is preferably B 2 H 6 .

[0068] Borane can react with oxygen in silicon oxide etching to form boric acid or boron oxide oligomers, which adhere to the etched surface to protect the side walls, especially the bottom corners, from etching damage.

[0069] Reaction equation:

[0070] B 2 H 6 +O * →[BHO]n ↓, wherein the oxygen element mainly comes from the oxygen element generated during the etching process of the silicon oxide hard mask opening in step S3 and the oxygen element in the photoresist.

[0071] Boron oxide oligomer and boric acid oligomer structure:

[0072]

[0073] Borane gas can protect the sidewalls by forming boron oxide or boric acid oligomers adsorbed on the sidewalls, especially at the corners of the etched groove sidewalls and the groove bottom, effectively avoiding the occurrence of the groove effect.

[0074] Preferably, in this embodiment, the etching gas further comprises a nitrogen-containing gas, and the molar amounts of the boron element and the nitrogen element in the etching gas are equal. The nitrogen-containing gas comprises NH 3 、N 2 at least one of them.

[0075] Specifically, the B element has an empty orbital and lacks electrons, which is equivalent to p-type hole doping. After doping, the Fermi level of the GaN material will be reduced. On the contrary, the N element has a lone pair of electrons, which is equivalent to n-type electron doping. After doping, the Fermi level of the GaN material will be increased. When designing a device, its internal doping level and corresponding energy level have been determined. If unnecessary doping is introduced during the manufacturing process, it will affect the performance of the device. The prior art has not paid attention to BCl 3 The B doping problem introduced by GaN etching (relative to borane gases, BCl 3 The doping effect of B is limited, and doping occurs naturally during the etching process. The use of N-containing gas can neutralize the doping effect caused by B. Therefore, nitrogen-containing gas needs to be added to the etching gas to make the boron and nitrogen elements reach an equimolar amount, such as NH 3 、N 2 Etc., can effectively avoid changes in GaN doping characteristics.

[0076] In this embodiment, the bromine-containing gas in the etching gas may include HBr, H 2 +Br 2 , H 2 +BBr 3 , HBrO 3 , HBrO 4 At least one of the following. Preferably HBr.

[0077] Preferably, the present embodiment further includes fluorine-carbon gas, which can etch the silicon oxide in the first mask layer and increase the etching speed of the silicon oxide.

[0078] Fluorocarbon gases can include C 4 F 8 , C 2 F 6 , C 4 F 6 CF 4 , CHF 3 , CH 2 F 2 , CH 3 At least one of F. In this embodiment, CHF is preferred 3 .

[0079] The reaction equation of carbon fluorine gas and silicon oxide is:

[0080] Carbon-fluorine plasma formation:

[0081] C x F y →CF n ++CF 3 *+CF 2 *+CF*+F*+e-+photon

[0082] SiO 2 The etching mechanism is:

[0083] CF n *+SiO 2 →SiF 4 ↑+CO 2 ↑

[0084] The etching speed of silicon oxide can be increased by etching with fluorinated gases, forming an opening to expose the GaN epitaxial layer and completing the patterning of the hard mask. During the etching process, fluorinated gases can react chemically to generate polymers while etching. The generated polymers adhere to the bottom and sidewalls of the etched grooves, which have a certain protective effect on the corners of the pattern, significantly reducing the etching of the corners at the bottom of the groove by reactive ions, and further avoiding the generation of micro-grooves at this location.

[0085] Preferably, in this embodiment, the flow rate of borane gas is in the range of 5 to 20 sccm; the flow rate of fluorocarbon gas is in the range of 20 to 50 sccm; the flow rate of bromine-containing gas is in the range of 40 to 100 sccm; the flow rate of nitrogen-containing gas is in the range of 20 to 80 sccm; the flow rate of chlorine-based gas is in the range of 10 to 40 sccm. Preferably, the sum of the flow rates of borane gas, nitrogen-containing gas, fluorocarbon gas and bromine-containing gas is 60% to 80% of the total flow rate of etching gas.

[0086] Specifically, in actual use, the flow rates of various gases are controlled separately, and the total flow rate of borane gas (including nitrogen-containing gas to counteract it), carbon fluorine gas and bromine-containing gas / total etching gas flow rate is controlled to be 60% to 80%, which can effectively improve the smoothness of the side wall and avoid the formation of grooves at the corners of the side wall and bottom of the etched groove.

[0087] In a preferred implementation of this embodiment, the borane gas is selected as B 2 H 6 , fluorocarbon gas is CHF 3 , hydrobromic acid gas is HBr, nitrogen-containing gas is NH 3 , chlorine-based gas is Cl 2 and BCl 3 ; The typical process parameters of the corresponding dry etching process are as follows:

[0088] The process chamber pressure range is 2.5 to 5 mT;

[0089] The upper electrode RF power range is 400 to 1200W;

[0090] The lower electrode RF power range is 200-500W;

[0091] B 2 H 6 The gas flow rate range is 5 to 20 sccm;

[0092] CHF 3 The gas flow rate range is 20 to 50 sccm;

[0093] The HBr gas flow rate range is 40 to 100 sccm;

[0094] NH 3 The gas flow rate range is 20 to 80 sccm;

[0095] Cl 2 The gas flow rate range is 5 to 20 sccm;

[0096] BCl 3 The gas flow rate range is 5 to 20 sccm.

[0097] Based on the above process conditions, we can obtain Figure 6a-6c The etched morphology shown has smooth sidewalls and no micro-groove effect at the bottom corner.

[0098] The etching method of the GaN substrate provided in this embodiment can effectively prevent the micro-groove effect generated when dry etching GaN at a large angle, obtain smooth sidewall morphology and bottom morphology, and is of great significance to improving the electrical yield of Mini / Micro-LED chips. Moreover, for the method of using PR+hard mask to obtain a large etching angle, this solution can make the hard mask open wet / dry without a separate process, and only need to be etched in one step with GaN, and the etching step uses the same etching gas. Compared with the traditional process, it can effectively reduce the process and avoid the problem of chamber gas environment pollution caused by mixing different etching gases.

[0099] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for etching a GaN substrate, characterized in that: include: forming a first mask layer on the top surface of the GaN substrate, wherein the material of the first mask layer includes silicon oxide; forming a patterned photoresist layer on the surface of the first mask layer; An etching step, wherein the first mask layer and the GaN substrate are continuously etched by an etching gas to form a plurality of microstructures isolated from each other by etching grooves on the GaN substrate, wherein the microstructures have a set sidewall inclination angle; The etching gas includes a chlorine-based gas, a bromine-containing gas and a boron-containing gas, wherein the chlorine-based gas includes at least one of Cl2 and BCl3, and the boron-containing gas includes a borane-based gas; the bromine-containing gas is a gas containing hydrogen and bromine elements, and when the first mask layer is etched, the bromine-containing gas can form SiBr4 with the Si element, thereby having an etching effect, and can also absorb oxygen elements in the chamber and in the photoresist to form SiBr x O y The oligomer protects the sidewalls and forms volatile bromide of gallium during GaN etching, which has an etching effect and can also form Br x O y The borane gas can react with the oxygen element in the silicon oxide etching to form boric acid or boron oxide oligomers, which adhere to the etching surface to protect the side wall; The etching gas further comprises a nitrogen-containing gas, and the molar amounts of the boron element and the nitrogen element in the etching gas are equal.

2. The etching method according to claim 1, characterized in that: The etching gas also includes carbon-fluorine gas.

3. The etching method according to claim 1, characterized in that: The nitrogen-containing gas includes at least one of NH3 and N2.

4. The etching method according to claim 2, characterized in that: The borane gas flow rate range is 5-20 sccm; The flow rate of the carbon fluorine gas is in the range of 20 to 50 sccm; The bromine-containing gas flow rate ranges from 40 to 100 sccm; The nitrogen-containing gas flow rate range is 20-80 sccm; The chlorine-based gas flow rate ranges from 10 to 40 sccm.

5. The etching method according to claim 4, characterized in that: The sum of the flow rates of the borane gas, the nitrogen-containing gas, the carbon fluorine gas and the bromine-containing gas is 60% to 80% of the total flow rate of the etching gas.

6. The etching method according to claim 4, characterized in that: The borane gas is B2H6, the fluorocarbon gas is CHF3, the bromine-containing gas is HBr, the nitrogen-containing gas is NH3, and the chlorine-based gas is Cl2 and BCl3.

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