A cleaning method for inhibiting water streak defects after epitaxy of a germanium wafer

Abstract

The present application relates to the technical field of semiconductor material preparation, and particularly relates to a cleaning method for inhibiting water streak defects of a germanium wafer after epitaxy, which comprises the following steps: wafer placement, alcohol rinsing, deionized water rinsing, alkaline solution rinsing and wafer drying. The form and thickness of the liquid film attached to the wafer surface are effectively controlled by synergistically controlling the spindle speed, the chemical liquid, the deionized water flow, the air supply and exhaust wind speed, and particularly setting the interval time between the last water valve closing and the start of the spin-drying program, so that the liquid film can be more uniformly and quickly separated from the surface during spin-drying, and water streaks caused by local liquid film residues or uneven drying can be avoided. The method is directly integrated into the existing automatic cleaning equipment, without the need to change the hardware structure, and only by optimizing the process parameters, the surface quality of the germanium wafer before epitaxy can be significantly improved, and the method has good industrial application value.

Description

Technical Field

[0001] This invention relates to the field of semiconductor material preparation technology, and in particular to a cleaning method for suppressing watermark defects after epitaxy of germanium wafers. Background Technology

[0002] In existing germanium wafer cleaning processes, after cleaning, etching, and rinsing, the wafers must be manually transferred to a spin dryer. This process involves a time interval of at least 3-5 seconds, and the liquid film on the wafer surface is easily lost due to wafer tilting during the transfer, resulting in uneven liquid film thickness when the wafer arrives at the spin dryer. Ultimately, before the final drying stage, residual watermarks or chemical solutions on the wafer surface are not effectively and uniformly removed, leading to surface defects such as uneven watermarks in subsequent epitaxial processes. Once watermark defects appear on the germanium wafer surface, the entire wafer must be scrapped, with no usable area, severely impacting product quality, increasing substrate processing and epitaxial growth costs, and reducing substrate availability. This invention aims to solve this problem. Summary of the Invention

[0003] This invention provides a cleaning method for suppressing watermark defects after germanium wafer epitaxy. It aims to address the problem that if residual watermarks or chemical solutions on the surface of germanium wafers are not effectively and uniformly removed before the final drying stage after cleaning and rinsing, surface defects such as watermarks can easily occur in subsequent epitaxial processes, affecting product quality. The core of this invention lies in optimizing the spindle speed, chemical flow rate, and air supply and exhaust velocity of the automatic cleaning machine, as well as optimizing the process parameters and control logic during the critical transition stage from the end of final rinsing to the start of spin-drying. Through coordinated control, the wafer surface is etched uniformly, and the morphology and thickness of the attached liquid film are effectively controlled, allowing for more uniform and rapid removal from the surface during spin-drying. This avoids defects such as watermarks formed after epitaxy due to localized liquid film residue or uneven drying. This method can be directly integrated into existing automatic cleaning equipment without changing the hardware structure. It significantly improves the surface quality of germanium wafers before epitaxy and avoids surface defects after epitaxy simply by optimizing process parameters, demonstrating significant industrial application value.

[0004] Specifically, the present invention provides the following technical solutions:

[0005] A cleaning method for suppressing watermark defects after epitaxy of germanium wafers, the method employing a single-wafer cleaning machine, the cleaning machine comprising a multi-channel spray pipe, a cleaning tank, an FFU (Fan Filter Unit) air supply unit, and an exhaust duct, wherein a rotating stage is installed in the cleaning tank, the germanium wafer is placed in the center of the stage, and the multi-channel spray pipe is positioned above the wafer, the method comprising the following steps:

[0006] S1, wafer placement, operated by a robotic arm;

[0007] S2, alcohol rinse to remove organic matter from the surface;

[0008] S3, rinse with deionized water to remove alcohol residue from the surface;

[0009] S4, alkaline solution rinse, uniformly etch the wafer surface, and remove the oxide layer;

[0010] S5, deionized water rinsing to remove alkaline solution residue: During deionized water rinsing, the rotational spindle speed of the stage is 800-900 r / min, the deionized water flow rate is 400-500 ml / min, and the deionized water rinsing time is 100-120 s.

[0011] S6, Wafer Drying: Start the spin-drying program immediately 3 seconds before the deionized water valve closes. Set the stage spindle acceleration to 400 rpm / s, with a final rotation speed of 3500-4000 r / min. Control the drying time to 100-120 seconds. Starting the spin-drying program immediately 3 seconds before the deionized water valve closes in step S6 is crucial because the spindle acceleration at 400 rpm / s takes 6-8 seconds to reach the target rotation speed. Starting the spin-drying program 3 seconds in advance ensures that the liquid on the wafer surface is evenly ejected by the centrifugal force of the high-speed rotation. This prevents uneven detachment of the liquid film on the wafer surface during the transition between rinsing and spin-drying steps, which could lead to uneven watermarks on the wafer surface and ultimately watermark defects after epitaxy.

[0012] Furthermore, in step S1, the robot arm operates at a speed of 100-120 mm / s when placing the wafer, and the negative pressure of the fingers during wafer suction is 30-50 kPa, ensuring that the wafer is placed in the center of the stage.

[0013] Furthermore, during the alcohol rinsing step S2, the rotational speed of the stage spindle is maintained at 400-500 r / min, the flow rate is controlled at 400-500 ml / min, and the rinsing time is controlled at 60-80 s. This ensures that the wafer surface can be uniformly rinsed to remove organic matter. The alcohol purity level is UP grade, with water content ≤0.1%, total metal impurities ≤1 ppb (of which key elements such as sodium, potassium, and iron must be ≤0.1 ppb), and particulate matter (≥0.5 μm) ≤25 particles / mL.

[0014] Furthermore, during the deionized water rinsing step S3, the spindle speed is 800-900 r / min, the deionized water flow rate is 400-600 ml / min, and the rinsing time is controlled at 80-100 s. The deionized water pipe is located directly above the center of the wafer and moves back and forth, with a movement distance of approximately 20-30 mm. The temperature of the deionized water is within the range of 14±2℃, and the water resistance is <18.5 MΩ.

[0015] Furthermore, in step S4, during alkaline solution rinsing, the spindle speed of the rotating stage is 400-500 r / min, the flow rate of the alkaline solution is 400-500 ml / min, and the rinsing time is 100-120 s. The spindle speed in step S4 is lower than in step S3 to ensure a more thorough and uniform reaction between the solution and the wafer surface, effectively reducing surface roughness. The alkaline solution flow rate is 400-500 ml / min, and the rinsing time is 100-120 s. The alkaline solution channel is positioned directly above the center of the wafer and moves back and forth approximately 20-30 mm to ensure more uniform and reliable etching of the wafer surface. The alkaline solution contains NH3·H2O, H2O2, and deionized water.

[0016] Furthermore, all steps are performed in a Class 10 cleanroom environment, with a temperature requirement of 14±2℃, an ambient temperature of 21℃~25℃, and a relative humidity of 20%~65%. During spin-drying, the air supply velocity of the cleaning machine is 0.5-0.6m / s, and the exhaust velocity is 1-1.2m / s. The air supply and exhaust of the chamber need to maintain a certain balance to meet the requirements of a Class 10 cleanroom environment, removing particulate matter, moisture, and volatile chemicals from the environment, while ensuring that it does not interfere with the wafer surface.

[0017] The technical effects achieved by this invention are as follows:

[0018] This invention relates to a cleaning method for suppressing watermark defects after epitaxy of germanium wafers. This method effectively improves the surface quality of germanium wafers, reduces surface roughness, and avoids post-epitaxy watermark defects. It also offers advantages such as simplicity, speed, stability, and increased yield. This invention not only prevents the generation of post-epitaxy watermark defects but also reduces the proportion of other defects, such as white spots and bright spots. Ultimately, it aims to reduce substrate processing and epitaxial growth costs and improve the utilization rate of germanium wafers. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the implementation of the present invention;

[0020] Figure 2 This is a simplified schematic diagram of a single-crystal cleaning machine, where: 1. Multi-channel spray pipe; 2. Cleaning tank; 3. Rotating stage; 4. FFU (Fan Filter Unit) air supply unit; 5. Exhaust duct.

[0021] Figure 3 This is a schematic diagram showing the surface roughness of the germanium wafer after cleaning by the method of the present invention and the comparative method;

[0022] Figure 4This is a schematic diagram of the microstructure of the epitaxial layer surface of the wafer after cleaning by the method of the present invention and the comparative method. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0024] Example 1

[0025] See process Figure 1 , Prepare germanium polished substrate: Use a finely polished 4-inch wafer with a crystal plane of (100) to

[111] 9°±0.2°, a thickness of 145±15μm, a total thickness variation (TTV) <7μm, a total flatness (TIR) ​​<7μm, a bending degree (BOW) <7μm, a warp degree (Warp) <10μm, and no obvious mechanical damage on the surface.

[0026] Cleaning was performed using a single-crystal cleaning machine (product model: Zhongke Micro ZQX6-150-3Y1DZ). Figure 2 The cleaning machine includes a multi-channel spray pipe 1, a cleaning tank 2, an FFU air supply unit 4, and an exhaust pipe 5. A rotating stage 3 is installed inside the cleaning tank. A robotic arm (product model: ZKM RD-Z270-RL200-T360) removes the wafer from the cassette at a speed of 120mm / s and places it in the center of the rotating stage. The robotic arm then disconnects the negative pressure and retracts, and the wafer falls onto the stage. The negative pressure of the robotic fingers during wafer suction is 30Kpa.

[0027] After the wafer is placed in the center of the rotating stage, the multi-channel spray pipe 1 is placed above the wafer. The main shaft of the rotating stage 3 begins to accelerate, eventually reaching a speed of 500 r / min. At the same time, the alcohol tube moves forward to the center of the wafer to begin supplying the alcohol, and then moves back and forth with a movement of 20 mm. During this process, the flow rate is controlled at 400 ml / min, and the alcohol rinsing time is controlled at 60 s to ensure that the alcohol can evenly rinse and remove organic matter from the wafer surface.

[0028] After the alcohol rinsing is completed, the deionized water needs to be connected immediately without any gaps. The spindle speed is accelerated to 800 r / min, which increases the centrifugal force and shear force. At this time, the deionized water can better remove the residues from the previous process on the wafer surface. The deionized water flow rate is 400 ml / min, and the deionized water rinsing time is controlled at 80 seconds. The deionized water pipe is directly above the center of the wafer and moves back and forth, with a moving distance of about 20 mm.

[0029] After rinsing with deionized water, the spindle speed is reduced to 500 r / min during alkaline solution rinsing. This allows the solution to react more fully and evenly with the wafer surface, effectively reducing the surface roughness of the wafer. The flow rate of the alkaline solution is 400 ml / min, and the rinsing time is 100 s. The alkaline solution channel is located directly above the center of the wafer and moves back and forth, with a moving distance of approximately 20 mm, ensuring more uniform and reliable corrosion of the wafer surface.

[0030] After the alkaline solution corrosion, the spindle speed is accelerated to 900 r / min and the deionized water flow rate is 500 ml / min. The deionized water rinsing time is 100 s to fully remove the residual solution from the wafer surface.

[0031] The spin-drying program starts immediately after the deionized water valve closes for 3 seconds. Within 6 seconds, the spindle speed reaches 4000 r / min, initiating the drying process, which lasts for 100 seconds. This ensures that the liquid on the wafer surface is evenly ejected by the centrifugal force of the high-speed rotation, preventing uneven detachment of the liquid film on the wafer surface due to wind action during the rinsing and spin-drying steps. This avoids uneven watermarks on the wafer surface, which could ultimately lead to watermark defects after epitaxy.

[0032] After spin-drying, the robotic arm retrieves the wafer back to its corresponding holder and places it under a strong light to carefully observe its surface for defects such as chemical residue, stains, and scratches. If none are found, a particle size analyzer is used to scan the surface for particle count, and an AFM (Anti-Fluorescence Membrane) device is used to test the surface roughness. This method cleans wafers with fewer than 50 particles larger than 0.3 μm, and also significantly reduces particles smaller than 0.3 μm, achieving a surface roughness of approximately 0.1 nm.

[0033] All the above steps are carried out in a Class 10 clean environment. The water used is deionized water, the temperature is required to be 14±2℃, the ambient temperature is 21℃~25℃, the relative humidity is 20%~65%, the air supply speed is 0.5m / s during spin drying, and the exhaust speed is 1m / s.

[0034] Comparative Example 1

[0035] The wafer is placed in a wafer holder and first manually transferred to an alcohol solution for 60 seconds. Then, it is transferred to a spray system for 80 seconds of rinsing. Next, it is immersed in an alkaline solution for 100 seconds of etching, rinsed for 100 seconds, and finally transferred to a spin dryer for drying. After the wafer is dried, it is inspected under a strong light. If there are no problems, the surface grain size and roughness are then tested.

[0036] All of the above operations involve manually transferring the wafer from one stage to another. During this transfer, the wafer is exposed to air for more than 1 second, and especially before the final drying, it is exposed to air for more than 3 seconds, resulting in uneven drying of the liquid film on its surface. This Example 2 is a traditional cleaning method.

[0037] Comparing Example 1 and Comparative Example 1 above, as shown in Table 1 below, the number of particles on the surface of the germanium wafer after cleaning by the technology of the present invention is significantly better than that of Comparative Example 1, as follows: Figure 3 The surface roughness shown is also significantly better than that of Comparative Example 1. (See below) Figure 4 The substrate epitaxial layer after cleaning with the technique of the present invention and the epitaxial layer on the substrate surface of comparative example 1 were tested by scanning electron microscopy. It was found that the microstructure of the substrate surface after epitaxy was significantly better after cleaning with the technique of the present invention, while water ripple defects appeared on the surface of the epitaxial layer of comparative example 1.

[0038] Table 1. Surface particle size of germanium wafers cleaned using the method of the present invention and comparative methods.

[0039]

[0040] Example 2

[0041] This cleaning method is not only applicable to solving the water ripple problem of 4-inch germanium wafers, but also applicable to 6-inch wafers. A finely polished 6-inch wafer with a crystal orientation of (100) to

[111] 9°±0.2°, a thickness of 225±15μm, a total thickness variation (TTV) of <10μm, a total flatness (TIR) ​​of <10μm, a bending degree (BOW) of <10μm, a warp of <10μm, and no obvious mechanical damage on the surface.

[0042] The robotic arm removes the wafer from the cassette at a speed of 100 mm / s and places it in the center of the rotating stage. The arm then retracts after the negative pressure is disengaged, and the wafer falls onto the stage. The negative pressure of the fingers during wafer suction is 50 kPa.

[0043] After the wafer is placed in the center of the stage, the spindle begins to accelerate and rotates to a final speed of 400 r / min. At the same time, the alcohol tube moves forward to the center of the wafer to begin supplying the alcohol, and then moves back and forth with a movement of 30 mm. During this process, the flow rate is controlled at 500 ml / min, and the alcohol rinsing time is controlled at 80 s to ensure uniform rinsing of the wafer surface and removal of organic matter.

[0044] After the alcohol rinsing is completed, the deionized water needs to be connected immediately without any gaps. The spindle speed is accelerated to 800 r / min, which increases the centrifugal force and shear force. At this time, the deionized water can better remove the residues from the previous process on the wafer surface. The deionized water flow rate is 500 ml / min, and the deionized water rinsing time is controlled at 100 s. The deionized water pipe is directly above the center of the wafer and moves back and forth, with a moving distance of about 30 mm.

[0045] After rinsing with deionized water, the spindle speed is reduced to 400 r / min during alkaline solution rinsing. This allows for a more thorough and uniform reaction between the solution and the wafer surface, effectively reducing wafer surface roughness. The alkaline solution flow rate is 500 ml / min, and the rinsing time is 120 s. The alkaline solution channel is positioned directly above the center of the wafer and moves back and forth over a distance of approximately 30 mm to ensure more uniform and reliable corrosion of the wafer surface.

[0046] After the alkaline solution corrosion, the spindle speed is accelerated to 800 r / min and the deionized water flow rate is 600 ml / min. The deionized water rinsing time is 120 s to fully remove the residual solution from the wafer surface.

[0047] The spin-drying program starts immediately after the deionized water valve closes for 3 seconds. Within 6 seconds, the spindle speed reaches 3500 r / min, initiating the drying process, which lasts for 120 seconds. This ensures that the liquid on the wafer surface is evenly ejected by the centrifugal force of the high-speed rotation, preventing uneven detachment of the liquid film on the wafer surface due to wind action during the rinsing and spin-drying steps. This avoids uneven watermarks on the wafer surface, which could ultimately lead to watermark defects after epitaxy.

[0048] After the spin-drying is completed, the robotic arm retrieves the wafer back to the corresponding cartridge and places the wafer under a strong light to carefully observe its surface for defects such as drug marks, chemicals, scratches, etc. If no defects are found, a particle size detection device is used to scan the number of particles on the surface and an AFM device is used to test the surface roughness.

[0049] All the above steps are carried out in a Class 10 clean environment. The water used is deionized water, the temperature is required to be 14±2℃, the ambient temperature is 21℃~25℃, the relative humidity is 20%~65%, the air supply speed of the spin dryer is 0.6m / s, and the exhaust speed is 1.2m / s.

[0050] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A cleaning method for suppressing watermark defects after epitaxy of germanium wafers, the method employing a single-wafer cleaning machine, the cleaning machine comprising a multi-channel spray pipe, a cleaning tank, an FFU (Fan Filter Unit) air supply unit, and an exhaust pipe, wherein a rotating stage is provided in the cleaning tank, the germanium wafer is placed in the center of the stage, and the multi-channel spray pipe is positioned above the wafer, characterized in that... Includes the following steps: S1, wafer placement, operated by a robotic arm; S2, alcohol rinse to remove organic matter from the surface; S3, rinse with deionized water to remove alcohol residue from the surface; S4, alkaline solution rinse, uniformly etch the wafer surface, and remove the oxide layer; S5, deionized water rinsing to remove alkaline solution residue: During deionized water rinsing, the rotational spindle speed of the stage is 800-900 r / min, the deionized water flow rate is 400-500 ml / min, and the deionized water rinsing time is 100-120 s. S6, wafer drying: The spin-drying program is started immediately 3 seconds after the deionized water valve is closed. The stage spindle acceleration is set to 400 rpm / s, the final rotation speed is 3500-4000 r / min, and the drying time is controlled at 100-120 seconds.

2. The cleaning method according to claim 1, characterized in that, In step S1, when placing the wafer, the robot arm operates at a speed of 100-120 mm / s, and the negative pressure of the fingers during wafer suction is 30-50 kPa, ensuring that the wafer is placed in the center of the stage.

3. The cleaning method according to claim 1, characterized in that, During the alcohol rinsing step S2, the rotational speed of the stage spindle is 400-500 r / min, the flow rate is controlled at 400-500 ml / min, and the alcohol rinsing time is controlled at 60-80 s.

4. The cleaning method according to claim 1, characterized in that, During the deionized water rinsing in step S3, the spindle speed is 800-900 r / min, the deionized water flow rate is 400-600 ml / min, and the rinsing time is controlled at 80-100 s. The deionized water spray pipe is directly above the center of the wafer and moves back and forth, with a moving distance of about 20-30 mm.

5. The cleaning method according to claim 1, characterized in that, In step S4, during the alkaline solution rinsing, the rotational speed of the stage spindle is 400-500 r / min, the flow rate of the alkaline solution is 400-500 ml / min, and the rinsing time of the alkaline solution is 100-120 s.

6. The cleaning method according to any one of claims 1-5, characterized in that, All steps are carried out in a Class 10 clean environment with a temperature requirement of 14±2℃, an ambient temperature of 21℃~25℃, a relative humidity of 20%~65%, and an air supply velocity of 0.5-0.6m / s and an exhaust velocity of 1-1.2m / s during spin drying.

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