Method for deep etching of GaN segmented pixel array of Micro-LED device with vertical structure

Abstract

The invention relates to the field of Micro-LEDs, in particular to a method for deep etching of a GaN segmented pixel array of a Micro-LED device with a vertical structure, which comprises the following steps: bonding a GaN epitaxial layer with an IC (integrated circuit) driving circuit wafer, grinding and polishing, then removing a silicon substrate by a wet method, etching the GaN epitaxial layer by a reactive ion etching technology, and finally etching the GaN epitaxial layer to form the GaN segmented pixel array of the Micro-LED device with the vertical structure. And preparing a passivation film on the surface of the GaN epitaxial layer by adopting a passivation technology, etching the GaN epitaxial layer covering the mask layer by adopting an inductively coupled plasma etching technology, and finally etching the bonding metal by adopting a plasma beam etching technology. According to the method, GaN deep etching is achieved while the high-quality mask silicon dioxide material is prepared, and meanwhile serious side wall damage to GaN can be avoided.

Description

Technical Field

[0001] The present invention relates to the field of Micro-LED, and in particular to a method for segmented deep etching of GaN pixel arrays of vertically structured Micro-LED devices. Background Art

[0002] Micro-LED devices are mainly made based on the third-generation semiconductor material GaN, which has excellent characteristics such as good luminous efficiency, high brightness, fast response time and high reliability. At present, the mainstream technology of Micro-LED device display technology is to reverse solder the IC drive circuit and GaN epitaxial wafer through reverse soldering technology. However, since the pixel size of Micro-LED devices is less than 7.5μm, the accuracy of the reverse soldering machine faces huge challenges. For Micro-LED devices with a pixel size of less than 7μm, vertically structured Micro-LED devices can be considered to meet production needs. The first technical barrier to be solved is GaN deep etching protection technology.

[0003] As one of the important process flows for preparing vertical structure Micro-LED displays, GaN deep etching protection technology has common problems such as difficulty in achieving deep etching, severe sidewall damage caused by etching, and slow etching rate of bonding metal. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the present invention provides a method for segmented deep etching of GaN pixel arrays in a vertically structured Micro-LED device.

[0005] The technical solution adopted by the present invention to solve the technical problem includes the following steps: Step 1), using a GaN epitaxial layer with a silicon substrate, bonding the GaN epitaxial layer to an IC drive circuit wafer; Step 2), removing the silicon substrate by first grinding and polishing and then removing by wet method; Step 3), etching the GaN epitaxial layer using reactive ion etching technology; Step 4), using a passivation technique to prepare a passivation film on the surface of the GaN epitaxial layer; Step 5), etching the GaN epitaxial layer covering the mask layer using an inductively coupled plasma etching technique; Step 6) Use plasma beam etching technology to etch the bonding metal.

[0006] In step 1), the size of the GaN epitaxial layer with the silicon substrate is 2 inches, the bonding pressure is 3000 kg-6000 kg, the temperature is 250°C-300°C, and the pressing time is 30 mins-50 mins. As another embodiment of the present invention, in step 1), the size of the GaN epitaxial layer with the silicon substrate is 4 inches, the wafer bonding pressure is 11000 kg-15000 kg, the temperature is 250°C-300°C, and the pressing time is 30 mins-50 mins.

[0007] In step 2), the ratio of the substrate removal solution is hydrofluoric acid: nitric acid: glacial acetic acid = 2:5:1.

[0008] Step 3) Inductively coupled plasma etching technology gas Cl 2 The flow rate is 50-100sccm, SiCl 4 The flow rate is 5-10sccm, the gas pressure is maintained at 0.5-1.0 Pa, and the RF etching power is 100-150 W.

[0009] In step 4), the passivation gas contains SiH with a purity exceeding 99.99%. 4 , O 2 ,Ar, among which SiH 4 The flow rate is 10-15sccm, O 2 The flow rate of is 5-10sccm, the flow rate of Ar is 120-150sccm, and the passivation film is made of silicon dioxide.

[0010] In step 5), the inductively coupled plasma etching technology gas contains O with a purity exceeding 99.99%. 2 and SF 6 , among which, SF 6 The flow rate is 20-60sccm, the flow rate of O2 is 5-15sccm, the gas pressure is maintained at 0.5-1.0 Pa, and the RF etching power is 220-300W.

[0011] Step 6) In the medium plasma beam etching technology, set the screen voltage to 600V, the acceleration voltage to 200V, the anode voltage to 50V, the cathode current to 20A, and the neutralization current to 8A, and wait until the ion beam current stabilizes at 100-300mA for etching.

[0012] The plasma etching technology used in step 3) and step 5) belongs to dry etching technology. The purpose of step 3) is the first stage of etching, and the purpose of step 5) is to avoid serious damage to the GaN side wall. The plasma beam etching technology is used in step 6) to achieve efficient etching of bonding metal. Through this method, while preparing high-quality mask silicon dioxide material to achieve deep etching of GaN, it can also protect GaN from causing serious side wall damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Schematic diagram of the structure of the ion etching GaN epitaxial process in preparing vertical structure Micro-LED devices.

[0014] Figure 2 Schematic diagram of the process structure for preparing high-quality mask material silicon dioxide for vertical structure Micro-LED devices.

[0015] Figure 3 Schematic diagram of the process structure of using inductively coupled plasma to etch silicon dioxide in the preparation of vertical structure Micro-LED devices.

[0016] Figure 4 Schematic diagram of the ion beam etching process in preparing vertical structure Micro-LED devices.

[0017] Figure 5 This is a diagram showing the effect of ion etching GaN epitaxy in a vertical structure Micro-LED device.

[0018] Figure 6 This is the effect of ion beam etching metal in a vertical structure Micro-LED device.

[0019] Figure 7 This is the SEM effect of segmented deep etching of a vertically structured Micro-LED device.

[0020] Figure 8 The IV curve of the vertically structured Micro-LED device illuminated by segmented deep etching. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Embodiment 1: In order to solve the problem of inductively coupled plasma etching (ICP) not being ideal for metal etching in the prior art of gallium nitride material dry etching, and the situation that ion beam etching (IBE) produces PN junction damage and leads to reduced device luminous efficiency, the present invention provides a segmented deep etching method, firstly, using reactive ion etching (RIE) to etch out pixels, then plasma enhanced chemical vapor deposition (PECVD) to plate a layer of high-quality mask silicon dioxide, then using inductively coupled plasma to etch silicon dioxide, and finally using ion beam etching (IBE) to etch bonding metal, which can etch different materials while ensuring the quality of deep etching. The specific scheme is as follows: Step 1. Use GaN on silicon epitaxial wafer to bond with IC circuit wafer.

[0023] Select wafers with small warpage, good surface condition, no black spots and no scratches.

[0024] Use acetone, alcohol, etc. to clean the wafer surface to reduce the impact of particles on bonding.

[0025] Bonding metal is prepared on the bonding wafer. The metal structure is Ti / Au with a thickness of 2000-10000A. The coating process ensures the quality of the film layer and improves the uniformity of the film thickness.

[0026] Use acetone, alcohol, etc. to clean the wafer surface again.

[0027] Align the edge of the bonded wafer and place it into the bonding fixture (using upper and lower spacers), and then place the fixture into the wafer bonding equipment.

[0028] In the vacuum state, the chamber temperature should be heated at a low rate to avoid film explosion caused by too fast a rate. After reaching the preset bonding temperature, the bonding pressure for 2-inch wafers is 3000 kg-6000 kg, the temperature is 250℃-300℃, and the bonding time is 30mins-50mins; the bonding pressure for 4-inch wafers is 11000 kg-15000 kg, the temperature is 250℃-300℃, and the bonding time is 30mins-50mins. After the bonding time is reached, the bonding is terminated after cooling at a low rate.

[0029] Step 2: After bonding, the silicon-based GaN epitaxy is removed by grinding and polishing and wet method.

[0030] A dual-axis grinding and polishing machine is used for thinning operations. The grinding liquid abrasive is boron carbide with a particle size of 15μm, the pressure is set to 1.2-1.5 kg, the grinding disc is an iron grinding disc, and the grinding and polishing speed is 30-60 rpm. After the silicon substrate epitaxial wafer is thinned to 600-700μm, the grinding and polishing is stopped, and the wafer is rinsed with deionized water.

[0031] The thinned wafer was placed in a corrosion solution of hydrofluoric acid: nitric acid: glacial acetic acid = 2:5:1, soaked for 20 minutes, the silicon substrate was removed, rinsed with deionized water for 10 minutes, and then dried with a spin dryer.

[0032] The gallium nitride sample with the substrate removed was subjected to spin coating of photoresist on the sample surface at a spin coating speed of 4000-5000 r / min and UV lithography to prepare a patterned mask with a table size of 8.6x8.6μm and a photoresist model of AZ6130.

[0033] Place the sample on a hot plate for hard film baking and remove it after heating for a period of time. The heating method is that the hot plate temperature is 80-90℃ and the heating time is 10-13 minutes.

[0034] The sample is placed in a plasma cleaning machine to clean and remove residual glue. The sample surface is subjected to a plasma cleaning process. The specific cleaning steps are to use a plasma cleaning machine with a power of 100-250 W, an oxygen flow rate of 150-250 cm, and a cleaning time of 60-80 s. In addition, an Ar flow rate of 150-250 sccm and a cleaning time of 50-70 s.

[0035] Step 3. Etch the GaN epitaxy using reactive ion etching (RIE).

[0036] The vacuum chamber in the reactive ion etching (RIE) etcher is evacuated to below 1Pa, the temperature is maintained at 10-25°C, SiCl4 and Cl2 process gases with a purity exceeding 99.99% are introduced, the flow rate of the process gas Cl2 is 50-100sccm, the flow rate of SiCl4 is 5-10sccm, and the gas pressure is maintained at 0.5-1.0 Pa. After stabilization for 20 seconds, 100-150 W of RF power is used for etching, and the etching rate is monitored by EDS to ensure that the etching angle is maintained at 80-90°.

[0037] Step 4. Prepare high quality mask material silicon dioxide passivation.

[0038] The vacuum chamber in the plasma enhanced chemical vapor deposition (PECVD) was evacuated to below 1 Pa, the temperature was maintained at 100-220°C, and process gas was introduced. The process gas contained SiH4, O2, and Ar with a purity exceeding 99.99%, wherein the flow rate of SiH4 was 10-15sccm, the flow rate of O2 was 5-10sccm, and the flow rate of Ar was 120-150sccm. The gas pressure was maintained at 0.5-1.0 Pa. After stabilization for 20 seconds, 280-310W of RF power was used for ignition.

[0039] After the silicon dioxide passivated sample, photoresist was spin-coated on the sample surface at a spin speed of 2000-3000 r / min and UV lithography was performed to prepare a patterned mask with a table size of 9.1x9.1 μm and a photoresist model of AZ6130.

[0040] Place the sample on a hot plate for hard film baking and remove it after heating for a period of time. The heating method is that the hot plate temperature is 80-90℃ and the heating time is 10-13 minutes.

[0041] The sample is placed in a plasma cleaning machine to clean and remove residual glue. The specific cleaning steps for the sample are to use a plasma cleaning machine: the power of the plasma cleaning machine is 200-300 W, the flow rate of oxygen is 150-250 cm, and the cleaning time is 80-100 s.

[0042] Step 5. Inductively coupled plasma (ICP) etching of the silicon dioxide mask layer protects the GaN epitaxy.

[0043] The vacuum chamber in the inductively coupled plasma (ICP) etcher is evacuated to below 1 Pa, the temperature is maintained at 10-25°C, and process gas is introduced. The process gas contains O2 and SF6 with a purity exceeding 99.99%, wherein the flow rate of SF6 is 20-60sccm, the flow rate of O2 is 5-15sccm, and the gas pressure is maintained at 0.5-1.0 Pa. After stabilization for 20 seconds, etching is performed using a RF power of 220-300W.

[0044] Silicon dioxide was etched using inductively coupled plasma (ICP) etching. The RF power of the upper electrode was 220-300 W, the RF power of the lower electrode was 120 W-160 W, the etching time was set to 12-15 minutes, the etching depth of gallium nitride was 1100-1200 nm, and the etching angle was 20°-80°.

[0045] Step 6. Ion beam etching (IBE) to etch the bonding metal The sample is posted and fixed on the stage, the chamber is evacuated to below 5x10-4 Pa, 10-15sccm of Ar gas is introduced, the chamber pressure is increased to 3.0-5.0x10-2 Pa, the etching angle is adjusted to 0°-10°, the etching rotation is 20-30rmp / min, the screen voltage is set to 600V, the acceleration voltage is 200V, the anode voltage is 50V, the cathode current is 20A, and the neutralization current is 8A. When the ion beam current stabilizes at 100-300 mA, open the baffle under this condition to etch the bonding metal (Ti, Au, Cu, Ni, Sn, etc.).

Claims

1. A method for segmented deep etching of GaN pixel arrays in a vertically structured Micro-LED device, characterized in that Implement it by following these steps: Step 1), using a GaN epitaxial layer with a silicon substrate, bonding the GaN epitaxial layer to an IC drive circuit wafer; Step 2), removing the silicon substrate by first grinding and polishing and then removing by wet method; Step 3), etching the GaN epitaxial layer using reactive ion etching technology; Step 4), using a passivation technique to prepare a passivation film on the surface of the GaN epitaxial layer; Step 5), etching the GaN epitaxial layer covering the mask layer using an inductively coupled plasma etching technique; Step 6) Use plasma beam etching technology to etch the bonding metal.

2. The method for segmented deep etching of GaN pixel array of vertical structure Micro-LED device according to claim 1, characterized in that In step 1), the size of the GaN epitaxial layer with the silicon substrate is 2 inches, the bonding pressure is 3000 kg-6000 kg, the temperature is 250°C-300°C, and the pressing time is 30 mins-50 mins.

3. The method for segmented deep etching of GaN pixel array of vertical structure Micro-LED device according to claim 1, characterized in that In step 1), the size of the GaN epitaxial layer with the silicon substrate is 4 inches, the wafer bonding pressure is 11000 kg-15000 kg, the temperature is 250°C-300°C, and the pressing time is 30 minutes-50 minutes.

4. The method for segmented deep etching of GaN pixel array of vertical structure Micro-LED device according to claim 1, characterized in that In step 2), the ratio of the substrate removal solution is hydrofluoric acid: nitric acid: glacial acetic acid = 2:5:

1.

5. The method for segmented deep etching of GaN pixel array of vertical structure Micro-LED device according to claim 1, characterized in that In step 3), the flow rate of Cl2 gas in the inductively coupled plasma etching technology is 50-100 sccm, the flow rate of SiCl4 is 5-10 sccm, the gas pressure is maintained at 0.5-1.0 Pa, and the RF etching power is 100-150 W.

6. The method for segmented deep etching of a GaN pixel array of a vertical structure Micro-LED device as claimed in claim 1, characterized in that In step 4), the passivation technical gas contains SiH4, O2, and Ar with a purity exceeding 99.99%, wherein the flow rate of SiH4 is 10-15sccm, the flow rate of O2 is 5-10sccm, and the flow rate of Ar is 120-150sccm, and the passivation film is made of silicon dioxide.

7. The method for segmented deep etching of GaN pixel array of vertical structure Micro-LED device according to claim 1, characterized in that In step 5), the inductively coupled plasma etching technology gas contains O2 and SF6 with a purity exceeding 99.99%, wherein the flow rate of SF6 is 20-60sccm, the flow rate of O2 is 5-15sccm, the gas pressure is maintained at 0.5-1.0 Pa, and the RF etching power is 220-300W.

8. The method for segmented deep etching of GaN pixel array of vertical structure Micro-LED device as claimed in claim 1, characterized in that Step 6) In the medium plasma beam etching technology, set the screen voltage to 600V, the acceleration voltage to 200V, the anode voltage to 50V, the cathode current to 20A, and the neutralization current to 8A, and wait until the ion beam current stabilizes at 100-300mA for etching.

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