A wet etching process for removing substrate after silicon wafer bonding
After bonding silicon wafers, wet etching is performed in alkaline solution, combined with polymer protection, the precise alignment and multiple grasping problems of pixel transfer and substrate removal in Micro-LED display technology are solved, achieving the goal of achieving Process simplification and cost reduction.
Patent Information
- Application Number
- CN202111522470.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-12-14
- Publication Date
- 2024-12-24
- Estimated Expiration
- 2041-12-14
AI Technical Summary
In Micro-LED display technology, there are problems of precise alignment and multiple grabbing during the transfer of huge pixels and substrate removal, resulting in complex and high cost.
A wet etching process of desubber after silicon wafer bonding is adopted. By selecting silicon wafers of different crystalline directions for high-temperature bonding, and heating etching is carried out in alkaline solution, and non-bonded use polymers to protect The junction surface realizes the removal of silicon substrate and the protection of the driving circuit.
The operation steps are simplified, process costs are reduced, short circuit problems caused by debris are avoided, etching speed and efficiency are improved, and precise alignment problems are solved during pixel transfer.
Smart Images
Figure CN114334640B_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of chemical etching, in particular to a wet etching process for removing a substrate after silicon wafer bonding. Background Art
[0002] With the continuous development of display technology, the size of LED is getting smaller and smaller until the micron level, and Micro-LED display has emerged accordingly, which has unique advantages compared to other displays. First, its micron-level pixel pitch allows each pixel to be controlled and driven individually, so the resolution, brightness, contrast and power consumption are no less than OLED.
[0003] Secondly, in terms of service life, since it is made of inorganic materials, its lifespan and stability are much stronger than the organic molecules of OLED screens, and the burn-in and aging phenomenon that is prone to occur on OLED screens is much less. In addition, Micro-LED has another very big advantage, which is its ultra-high resolution. This is also due to the use of micron-level pixel spacing. Because of its small size, the resolution is particularly high. However, due to the fineness of its size, there are also some difficulties in the process, among which mass transfer is very important and is also a bottleneck. Whether it is a TV or a mobile phone screen, the number of pixels is quite huge, and the size of the pixel is so small, and the display product has a low tolerance for pixel errors. No one wants to buy a display with "bright spots" or "dark spots", so it is very difficult to transfer these small pixels to a substrate with a good drive circuit and realize circuit connection. It is necessary to solve the problem of precise alignment and multiple captures during the transfer process. Summary of the invention
[0004] The present invention proposes a wet etching process for removing the substrate after silicon wafer bonding, which helps to solve the substrate removal part of the mass transfer problem in Micro-LED display technology, can simplify the operation steps and reduce process costs.
[0005] The present invention adopts the following technical solutions.
[0006] A wet etching process for removing substrate after silicon wafer bonding, comprising the following steps;
[0007] Step A, selecting a silicon wafer M with a crystal orientation of (111) and a silicon wafer N with a crystal orientation of (100), and cleaning the silicon wafers;
[0008] Step B, performing high-temperature bonding on the silicon wafer M and the silicon wafer N to form a combined silicon wafer;
[0009] Step C, sealing and protecting the non-bonding surface of the silicon wafer N of the combined silicon wafer with a high molecular polymer;
[0010] Step D, performing alkaline etching on one side of the silicon wafer M of the combined silicon wafer to roughen the surface;
[0011] Step E, placing the roughened silicon wafer into an alkaline solution, and heating and etching the wafer in an oil bath at a desired temperature;
[0012] Step F: ultrasonically clean the etched silicon wafer with deionized water, blow dry it with nitrogen, and dry it on a hot plate.
[0013] The heating etching in step E starts from one side of the silicon wafer M of the combined silicon wafer until the silicon wafer M is etched through.
[0014] The high molecular polymer is PDMS glue or PMMA glue; the alkaline solution is a KOH solution with a concentration of 30%; in step E, the required temperature of the oil bath thermostat is 100° C., and the temperature needs to be monitored in real time by a temperature measuring tool.
[0015] The silicon wafer M and the silicon wafer N are both gold-plated silicon wafers, both have a size of 20 mm×20 mm, and a thickness ranging from 20 μm to 2000 μm.
[0016] The cleaning of the silicon wafer in step A specifically comprises the following steps:
[0017] Step A1, placing the silicon wafer in a mixed solution of acetone, ethanol and deionized water and ultrasonically treating it at 30°C for 15-30 minutes, and then placing it in deionized water and ultrasonically treating it at 30°C for 5-10 minutes;
[0018] Step A2, drying the treated silicon wafer with nitrogen;
[0019] Step A3: drying the dried silicon wafer on a hot plate.
[0020] In step B, the bonding temperature is 200° C.-300° C. and the pressure is 0.5 MPa.
[0021] In step C, the high molecular polymer is scraped onto the surface and sidewalls of the silicon wafer to prevent the surface and sidewalls of the silicon wafer with a crystal orientation of (100) from being etched in step E. After scraping, vacuum is drawn to remove bubbles, and then high-temperature drying is performed.
[0022] The alkaline etching solution in step D is a mixed solution of NaOH, isopropanol and deionized water, which is etched in a constant temperature water bath at 80° C. for 30 minutes to form a large number of micro-pyramid structures on the surface of the silicon wafer with a crystal orientation of (111), thereby accelerating the etching speed of the silicon wafer with a crystal orientation of (111) in step E.
[0023] The etching time of the silicon wafer in step E is 25 hours.
[0024] The wet etching process is used in the substrate process of the Micro-LED preparation process. The substrate body of the LED component of the Micro-LED is a silicon wafer with a (111) crystal orientation, and the driving circuit body of the Micro-LED is a silicon wafer with a 100 crystal orientation. In the wet etching process, the (111) crystal orientation silicon wafer and the (100) crystal orientation silicon wafer are first bonded to form a combined silicon wafer, and then etching is started from the (111) crystal orientation silicon wafer side of the combined silicon wafer and the (111) crystal orientation silicon wafer is directly etched through to complete the substrate removal in the Micro-LED preparation process.
[0025] In the preparation process of Micro-LED devices, the present invention selects bonding first and then making devices, that is, bonding the LED and the driving circuit first and then removing the substrate, that is, removing the substrate after completing the mass transfer of Micro-LED, rather than removing the substrate first and then transferring. After the bonding is completed, etching is performed from one side and directly through to the other side, completing self-alignment, and solving the problem of precise alignment and multiple grabbing during the transfer process.
[0026] In order to solve the substrate removal problem in the mass transfer of Micro-LED display technology, the present invention provides a wet etching process for removing the substrate after bonding, bonds two silicon wafers with different crystal orientations, and peels off the silicon substrate while protecting the other side, which can simplify the operation steps and reduce the process cost.
[0027] The present invention can solve the problem of slow etching rate of (111) silicon by alkaline solution. Since alkaline solution etches silicon anisotropically, generally speaking, the etching rate of (100) silicon is much faster than that of (111) silicon. The present invention optimizes the process, protects (100) silicon with a high molecular polymer, and roughens the surface of (111) silicon to accelerate the etching rate, thereby achieving the technical effect of protecting (100) silicon from being etched while accelerating the etching rate of (111) silicon.
[0028] The advantages of the present invention are as follows: the bonding and substrate peeling process of Micro-LED is simulated by using silicon wafers with crystal orientations of (111) and (100), and the (111) silicon substrate is removed by chemical wet etching while PDMS glue is wrapped on the surface of the (100) silicon wafer to achieve a protective effect. This process simulates the actual chip substrate peeling process and uses alkaline etching. Compared with dry etching, it can avoid short circuit problems caused by debris, greatly reducing process costs and simplifying process difficulty.
[0029] The solution described in the present invention can be applied to Micro-LED chip processes and other processes that require bonding two silicon wafers with different crystal orientations, and has practical value. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:
[0031] Attached Figure 1 is a schematic diagram of the bonded composite silicon wafer of the present invention after the high molecular polymer is attached;
[0032] Attached Figure 2 This is a schematic diagram of micro-pyramids on the surface of a silicon wafer with a crystal orientation of (111) after roughening;
[0033] In the figure: 1-high molecular polymer; 2-silicon wafer with crystal orientation (100); 3-combined silicon wafer; 4-silicon wafer with crystal orientation (111). DETAILED DESCRIPTION
[0034] As shown in the figure, a wet etching process for removing the substrate after silicon wafer bonding includes the following steps:
[0035] Step A, selecting a silicon wafer M with a crystal orientation of (111) and a silicon wafer N with a crystal orientation of (100), and cleaning the silicon wafers;
[0036] Step B, performing high temperature bonding on the silicon wafer M and the silicon wafer N to form a combined silicon wafer 2;
[0037] Step C, sealing and protecting the non-bonding surface of the silicon wafer N of the combined silicon wafer with a high molecular polymer 1;
[0038] Step D, performing alkaline etching on one side of the silicon wafer M of the combined silicon wafer to roughen the surface;
[0039] Step E, placing the roughened silicon wafer into an alkaline solution, and heating and etching the wafer in an oil bath at a desired temperature;
[0040] Step F: ultrasonically clean the etched silicon wafer with deionized water, blow dry it with nitrogen, and dry it on a hot plate.
[0041] The heating etching in step E starts from one side of the silicon wafer M of the combined silicon wafer until the silicon wafer M is etched through.
[0042] The high molecular polymer is PDMS glue or PMMA glue; the alkaline solution is a KOH solution with a concentration of 30%; in step E, the required temperature of the oil bath thermostat is 100° C., and the temperature needs to be monitored in real time by a temperature measuring tool.
[0043] The silicon wafer M and the silicon wafer N are both gold-plated silicon wafers, both have a size of 20 mm×20 mm, and a thickness ranging from 20 μm to 2000 μm.
[0044] The cleaning of the silicon wafer in step A specifically comprises the following steps:
[0045] Step A1, placing the silicon wafer in a mixed solution of acetone, ethanol and deionized water and ultrasonically treating it at 30°C for 15-30 minutes, and then placing it in deionized water and ultrasonically treating it at 30°C for 5-10 minutes;
[0046] Step A2, drying the treated silicon wafer with nitrogen;
[0047] Step A3: drying the dried silicon wafer on a hot plate.
[0048] In step B, the bonding temperature is 200° C.-300° C. and the pressure is 0.5 MPa.
[0049] In step C, the high molecular polymer is scraped onto the surface and sidewalls of the silicon wafer to prevent the surface and sidewalls of the silicon wafer with a crystal orientation of (100) from being etched in step E. After scraping, vacuum is drawn to remove bubbles, and then high-temperature drying is performed.
[0050] The alkaline etching solution in step D is a mixed solution of NaOH, isopropanol and deionized water, which is etched in a constant temperature water bath at 80° C. for 30 minutes to form a large number of micro-pyramid structures on the surface of the silicon wafer with a crystal orientation of (111), thereby accelerating the etching speed of the silicon wafer with a crystal orientation of (111) in step E.
[0051] The etching time of the silicon wafer in step E is 25 hours.
[0052] The wet etching process is used in the substrate process of the Micro-LED preparation process. The substrate body of the LED component of the Micro-LED is a silicon wafer with a (111) crystal orientation, and the main body of the Micro-LED driving circuit is a silicon wafer with a 100 crystal orientation. In the wet etching process, the (111) crystal orientation silicon wafer 4 and the (100) crystal orientation silicon wafer 2 are first bonded to form a combined silicon wafer, and then etching is started from the (111) crystal orientation silicon wafer side of the combined silicon wafer and the (111) crystal orientation silicon wafer is directly etched through to complete the substrate removal in the Micro-LED preparation process.
[0053] Example:
[0054] This example specifically includes the following steps:
[0055] Step A, cleaning the silicon wafer, wherein the silicon wafer is single crystal silicon, the size is 20mm×20mm, the crystal orientation is (100) is P-type single crystal silicon, the thickness is 400μm±10μm, the resistivity is 1~10Ω / cm2, the crystal orientation is (111) is N-type single crystal silicon, the thickness is 540μm±10μm, and the resistivity is 0.003~0.0045Ω / cm2. Specifically comprising the following steps:
[0056] Step A1, placing the silicon wafer in a mixed solution of acetone, ethanol and deionized water and ultrasonically treating it at 30°C for 15 minutes, and then placing it in deionized water and ultrasonically treating it at 30°C for 5 minutes;
[0057] Step A2, drying the treated silicon wafer with nitrogen;
[0058] Step A3: drying the dried silicon wafer on a hot plate.
[0059] Step B: The silicon wafer 4 with a crystal orientation of (111) and the silicon wafer 2 with a crystal orientation of (100) are respectively coated with a metal layer 3 and then bonded at high temperature under non-vacuum conditions at a temperature of 300° C. and a pressure of 0.5 MPa.
[0060] Step C: Use PDMS glue to seal and protect the (100) silicon wafer. Apply the PDMS glue on the surface and sidewalls of the (100) silicon wafer. Figure 1 , the thickness reaches 1mm±0.5mm, and the bubbles are removed by vacuum to make the protective glue denser and without small holes. Then it is placed in an oven at 60℃ for 40 minutes for drying to form a protective film on the (100) surface and side walls to protect it from KOH etching.
[0061] Step D: Place the bonded and protected sample in a glass beaker containing a mixed solution of NaOH, isopropanol, and deionized water. The ratio of the mixed solution is NaOH: isopropanol: deionized water = 2.891g: 15ml: 50ml. Place the glass beaker in a constant temperature water bath at 80°C and etch for 30 minutes. During the etching process, cover the beaker with plastic wrap to prevent the isopropanol from volatilizing. This alkaline etching forms many tiny pyramid-shaped structures on the surface of the (111) silicon wafer, such as Figure 2 , which can achieve the purpose of coarsening (111) and thus shorten the time for etching (111) silicon.
[0062] Step E: Place the roughened sample into a polytetrafluoroethylene beaker containing a 30% KOH solution, and immerse the beaker in an oil bath to indirectly heat the KOH solution at 100°C. Constant temperature heating is 100°C, and the etching time is 25 hours. During the oil bath heating process, the temperature will vary between 100°C and 102°C. A thermometer should be inserted into the container to monitor the temperature in real time.
[0063] Step F: The etched silicon wafer was ultrasonically cleaned with deionized water for 3 minutes, then blown dry with nitrogen, and dried on a hot plate at 60° C. for 3 minutes.
[0064] The alkaline roughening solution of the present invention is prepared by mixing NaOH, isopropanol and deionized water. The method is used to roughen and etch the silicon wafer, and many tiny pyramid-shaped structures such as Figure 2, which can increase the roughness of the silicon wafer surface and thus shorten the etching time.
[0065] The PDMS glue used for protecting (100) silicon in the present invention is subjected to steps such as vacuuming and high-temperature drying after being scraped to improve the protection effect.
[0066] The present invention has the advantages of selective etching, simple etching process, low material cost, etc. The present invention can be used for etching of silicon wafers, and in the silicon substrate removal technology of Micro-LED, and can also be widely used in the fields of QLED display, etc.
[0067] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.
Claims
1. A wet etching process for removing the substrate after silicon wafer bonding, characterized in that: The steps include: Step A, selecting a silicon wafer M with a crystal orientation of (111) and a silicon wafer N with a crystal orientation of (100), and cleaning the silicon wafers; Step B, performing high-temperature bonding on the silicon wafer M and the silicon wafer N to form a combined silicon wafer; Step C, sealing and protecting the non-bonding surface of the silicon wafer N of the combined silicon wafer with a high molecular polymer; Step D, performing alkaline etching on one side of the silicon wafer M of the combined silicon wafer to roughen the surface; Step E, placing the roughened silicon wafer into an alkaline solution, and heating and etching the wafer in an oil bath at a desired temperature; Step F, ultrasonically cleaning the etched silicon wafer with deionized water, then drying it with nitrogen gas, and drying it on a hot plate; The wet etching process is used in the substrate process of the Micro-LED preparation process. The substrate body of the LED component of the Micro-LED is a silicon wafer with a (111) crystal orientation, and the driving circuit body of the Micro-LED is a silicon wafer with a (100) crystal orientation. In the wet etching process, the (111) crystal orientation silicon wafer and the (100) crystal orientation silicon wafer are first bonded to form a combined silicon wafer, and then etching is started from the (111) crystal orientation silicon wafer side of the combined silicon wafer and the (111) crystal orientation silicon wafer is directly etched through to complete the substrate removal in the Micro-LED preparation process.
2. The wet etching process for removing the substrate after silicon wafer bonding according to claim 1, characterized in that: The heating etching in step E starts from one side of the silicon wafer M of the combined silicon wafer until the silicon wafer M is etched through.
3. The wet etching process for removing the substrate after silicon wafer bonding according to claim 1, characterized in that: The high molecular polymer is PDMS glue or PMMA glue; the alkaline solution is a KOH solution with a concentration of 30%; in step E, the required temperature of the oil bath thermostat is 100° C., and the temperature needs to be monitored in real time by a temperature measuring tool.
4. The wet etching process for removing the substrate after silicon wafer bonding according to claim 3, characterized in that: The silicon wafer M and the silicon wafer N are both gold-plated silicon wafers, both have a size of 20 mm×20 mm, and a thickness ranging from 20 μm to 2000 μm.
5. The wet etching process for removing the substrate after silicon wafer bonding according to claim 1, characterized in that: The cleaning of the silicon wafer in step A specifically comprises the following steps: Step A1, placing the silicon wafer in a mixed solution of acetone, ethanol and deionized water and ultrasonically treating it at 30°C for 15-30 minutes, and then placing it in deionized water and ultrasonically treating it at 30°C for 5-10 minutes; Step A2, drying the treated silicon wafer with nitrogen; Step A3: drying the dried silicon wafer on a hot plate.
6. The wet etching process for removing the substrate after silicon wafer bonding according to claim 1, characterized in that: In step B, the bonding temperature is 200° C.-300° C. and the pressure is 0.5 MPa.
7. The wet etching process for removing the substrate after silicon wafer bonding according to claim 1, characterized in that: In step C, the high molecular polymer is scraped onto the surface and sidewalls of the silicon wafer to prevent the surface and sidewalls of the silicon wafer with a crystal orientation of (100) from being etched in step E. After scraping, vacuum is drawn to remove bubbles, and then high-temperature drying is performed.
8. The wet etching process for removing the substrate after silicon wafer bonding according to claim 1, characterized in that: The alkaline etching solution in step D is a mixed solution of NaOH, isopropanol and deionized water, which is etched in a constant temperature water bath at 80° C. for 30 minutes to form a large number of micro-pyramid structures on the surface of the silicon wafer with a crystal orientation of (111), thereby accelerating the etching speed of the silicon wafer with a crystal orientation of (111) in step E.
9. The wet etching process for removing substrate after silicon wafer bonding according to claim 1, characterized in that: The etching time of the silicon wafer in step E is 25 hours.