Sample preparation method for annealed wafer spread resistance detection

Abstract

The application relates to a sample preparation method for annealing wafer extension resistance detection, belonging to the technical field of silicon crystal detection, and comprising the following operation steps: first step: breaking a silicon wafer into two pieces; second step: repeating the first step to break the silicon wafer into a square; third step: after heating a goniometer, taking down the goniometer with a pincer and placing the goniometer on a sample preparation table; fourth step: taking a paraffin stick and uniformly coating the goniometer surface, dissolving the goniometer in hot state, and attaching a silicon wafer sample to the center of the goniometer; fifth step: starting the machine, and adjusting the position of a grinding liquid by using a cotton swab rod; sixth step: setting the grinding rotating speed and grinding time; seventh step: after grinding is completed, cleaning and wiping the silicon wafer sample; eighth step: after heating the cleaned silicon wafer sample, taking down the silicon wafer sample and placing the silicon wafer sample for cooling; ninth step: checking the state of a grinding surface.

Description

Technical Field

[0001] This invention relates to the field of silicon crystal testing technology, specifically to a sample preparation method for testing the extended resistance of annealed wafers. Background Technology

[0002] Secondary processing, such as annealing, on polished wafers yields silicon wafers with special properties. These high-performance wafers meet the needs of various applications and are an indispensable part of the semiconductor industry. Annealing is a common process in integrated circuit manufacturing, especially for modern CMOS chips, which, after ion implantation, undergo rapid high-temperature annealing (RTP) to repair defects and achieve a regular lattice arrangement. The annealing process involves heating and cooling the polished wafer in hydrogen or argon gas before annealing. Compared to polished wafers, annealed wafers have a higher gettering capacity and significantly reduced oxygen content, resulting in better crystal integrity.

[0003] Annealing typically uses a diffusion furnace as the heat treatment method. Dopant contaminants present on the wafer surface do not change the resistivity before heat treatment, but after high-temperature heat treatment, diffusion affects the resistivity at a depth of 0 to 5 μm from the device design surface, causing resistivity changes. Furthermore, severe contamination can lead to PN junction and type inversion. Achieving uniform resistivity in the near-surface region of the silicon wafer is crucial for high-frequency applications; detecting the resistivity uniformity of the annealed wafer from the surface to the depth of the substrate layer effectively monitors contamination by unwanted dopants during the manufacturing process.

[0004] The SCP method can rapidly measure the resistivity values ​​at various points on a wafer without damaging it, and the uniformity of resistivity values ​​at each point can be used to evaluate the quality of the annealed wafer. However, it cannot obtain the resistivity variation along the longitudinal direction from the surface to the substrate layer. The preparation of SRP samples, especially the grinding and surface condition of the bevels, has a significant impact on the accuracy of extended resistivity (SRP) testing. SRP sample preparation is a meticulous process that requires mastering the correct methods and paying attention to operational details; otherwise, accurate data may not be obtained. SRP testing of annealed samples particularly focuses on the resistivity at a depth of 1–2 μm on the surface. Poor sample surface preparation may reduce accuracy and repeatability, and increase noise in the data. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a sample preparation method for extended resistance testing of annealed wafers. By performing a rapid thermal annealing process on the polished annealed wafer sample, impurities are volatilized and removed from its surface, the exposed Si-SiO2 interface dangling bonds and surface damage layer after sample preparation and polishing are repaired, recombination centers are reduced, electroactivity is improved, resistivity is reduced, and the phenomenon of unstable resistivity within 1-2 μm depth of the polished surface is improved.

[0006] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions:

[0007] A sample preparation method for extended resistance testing of annealed wafers includes the following steps:

[0008] Step 1: Place the silicon wafer on a clean cloth. Using the notch as a reference, use a diamond pen to draw a short line on the edge of the silicon wafer. Using a pin as a reference, gently press down from below the silicon wafer to break it into two pieces.

[0009] Step 2: Repeat step 1 to split the silicon wafer into squares about 2-5mm wide. Three sides must be smooth cut surfaces after separation, and the other side can be an uneven cut surface drawn with a diamond pen.

[0010] Step 3: Place the angle gauge on the heating table and heat it at 200℃ for about 3 to 5 minutes. Then, use pliers to remove the angle gauge and place it on the sample preparation table.

[0011] Step 4: Take the paraffin stick from the clean box and spread it evenly on the surface of the angle gauge to melt it while it is hot. Place the silicon wafer sample face up on the center of the angle gauge. Under the LED desktop magnifying glass, align the end of the dissociated surface that needs to be ground with the center line of the angle gauge.

[0012] For confirming the position of the silicon wafer sample during placement and initially inspecting the polished surface, conventional methods relying on visual observation are not only prone to errors but also time-consuming. After placement, an LED desktop magnifying glass is used to observe whether the end of the release surface to be polished is aligned with the center line of the angle gauge, check the condition of the polished surface, and observe whether the polished surface is skewed. The LED light is bright, the visibility is good, the desktop magnifying glass is easy to observe, and the higher the magnification, the clearer the view and the smaller the error.

[0013] Step 5: Pour 5-10 ml of 0.1μm diamond polishing slurry into the center of the frosted glass surface of the polishing equipment, turn on the machine, and use the handle of a cotton swab to adjust the position of the polishing slurry so that it is fully and evenly coated on the frosted glass surface; align the center line of the angle gauge with the line at the bottom of the fixture, fix it on the fixture, and then place it on the frosted glass plate at a suitable angle so that the cleavage surface of the silicon wafer sample to be polished is perpendicular to the polishing direction.

[0014] Step 6: Turn on the machine, set the grinding speed and grinding time. During the grinding process, use the cotton swab handle to adjust the position of the grinding fluid to ensure that the silicon wafer sample is fully ground.

[0015] Step 7: After grinding, remove the angle gauge with the silicon wafer sample attached from the fixture, place it in a beaker containing isopropanol, clean it with an ultrasonic cleaner for 8-10 minutes, and then wipe the sample surface with a lint-free cloth.

[0016] Conventional sample preparation methods, such as directly wiping the polished surface with a cotton swab dipped in solvent, have limited cleaning effect and can easily contaminate the inside of the machine. To address this, the polished silicon wafer samples are cleaned using an ultrasonic cleaner. Analytical grade isopropanol is used as the cleaning solvent, and appropriate power, temperature, and cleaning time are set to effectively remove residual polishing fluid, organic contaminants, and polishing debris from the silicon wafer sample surface, significantly improving the surface cleanliness of the silicon wafer samples.

[0017] Step 8: Place the cleaned silicon wafer sample on the heating stage and heat it at 200°C for about 5 minutes. Then, remove it with pliers and place it on the cooling stage to cool for 10 minutes.

[0018] Step 9: Under an LED desktop magnifying glass, check the condition of the polished surface. If the polished surface is obviously skewed, the sample needs to be prepared again. If there are foreign objects on the surface, use an ultrasonic cleaner to clean it until the surface is completely clean.

[0019] As a preferred method, when placing the silicon wafer sample on the angle gauge, fold the lint-free cloth several times and press the sample several times with your thumb on the lint-free cloth to make the sample firmly stick to the angle gauge and ensure that the sample is flat and that no end is raised.

[0020] As a preferred method, avoid moving the sample during the pressing process to prevent it from changing its position; if the sample moves slightly, tweezers can be used to reset it.

[0021] Ideally, if the polishing slurry is insufficient, it needs to be replenished in time; otherwise, not only will the polished surface be in poor condition, but the wear of the frosted glass will also be accelerated.

[0022] As a preferred option, if the square shape of the silicon wafer does not meet the requirements, it needs to be re-cracked. During the cracking process, care must be taken to keep the front side of the silicon wafer facing up, and it must be clearly marked to avoid confusion.

[0023] The present invention can achieve the following effects:

[0024] This invention provides a sample preparation method for extended resistance testing of annealed wafers. Compared with the prior art, by performing a rapid thermal annealing process on the polished annealed wafer sample, impurities are volatilized and removed from its surface, the exposed Si-SiO2 interface dangling bonds and surface damage layer after sample preparation and polishing are repaired, recombination centers are reduced, electroactivity is improved, resistivity is reduced, and the phenomenon of unstable resistivity within 1-2 μm depth of the polished surface is improved. Detailed Implementation

[0025] The technical solution of the invention will be further described in detail below through examples.

[0026] Example: A sample preparation method for extended resistance testing of annealed wafers, comprising the following steps:

[0027] Step 1: Place the silicon wafer on a clean cloth. Using the notch as a reference, use a diamond pen to draw a short line on the edge of the silicon wafer. Using a pin as a reference, gently press down from below the silicon wafer to break it into two pieces.

[0028] Step 2: Repeat step 1 to split the silicon wafer into squares about 3.5mm wide. Three sides of the squares must be smooth cut surfaces from the separation process, while the other side can be a rough cut surface marked with a diamond pen.

[0029] If the square shape formed by the silicon wafer is not satisfactory, it needs to be re-cracked. During the cracking process, it is important to always keep the front side of the silicon wafer facing up and to clearly mark it to avoid confusion.

[0030] Step 3: Place the angle gauge on the heating table and heat it at 200℃ for about 4 minutes. Then, use pliers to remove the angle gauge and place it on the sample preparation table.

[0031] Step 4: Take the paraffin stick from the clean box and spread it evenly on the surface of the angle gauge to melt it while it is hot. Place the silicon wafer sample face up on the center of the angle gauge. Under the LED desktop magnifying glass, align the end of the dissociated surface that needs to be ground with the center line of the angle gauge.

[0032] When placing the silicon wafer sample onto the angle gauge, fold the lint-free cloth several times and press the sample down several times with your thumb on the cloth to ensure it adheres firmly to the gauge and is flat with no one end sticking up. Do not move the sample during the pressing process to avoid changing its position; if the sample moves slightly, use tweezers to reposition it.

[0033] Step 5: Pour 7ml of 0.1μm diamond polishing slurry into the center of the frosted glass surface of the polishing equipment, turn on the machine, and use the handle of a cotton swab to adjust the position of the polishing slurry so that it is fully and evenly coated on the frosted glass surface; align the center line of the angle gauge with the line at the bottom of the fixture, fix it on the fixture, and then place it on the frosted glass plate at a suitable angle so that the cleavage surface of the silicon wafer sample to be polished is perpendicular to the polishing direction.

[0034] Step 6: Turn on the machine, set the grinding speed and grinding time. During the grinding process, use the handle of a cotton swab to adjust the position of the grinding fluid to ensure the silicon wafer sample is thoroughly ground. If the grinding fluid is insufficient, it needs to be replenished in time; otherwise, not only will the ground surface be in poor condition, but the wear of the frosted glass will also be accelerated.

[0035] Step 7: After grinding, remove the angle gauge with the silicon wafer sample attached from the fixture, place it in a beaker containing isopropanol, clean it with an ultrasonic cleaner for 9 minutes, and then wipe the sample surface with a lint-free cloth.

[0036] Step 8: Place the cleaned silicon wafer sample on the heating stage and heat it at 200°C for about 5 minutes. Then, remove it with pliers and place it on the cooling stage to cool for 10 minutes.

[0037] Step 9: Inspect the condition of the polished surface under an LED desktop magnifying glass. If the polished surface is significantly skewed, the sample needs to be prepared again. If there are foreign objects on the surface, clean it with an ultrasonic cleaner until the surface is completely clean. In summary, this sample preparation method for annealed wafer extended resistance testing promotes the volatilization and removal of impurities from the surface of the polished annealed wafer sample through a rapid thermal annealing process. It repairs the exposed Si-SiO2 interface dangling bonds and surface damage layer after sample preparation and polishing, reduces recombination centers, improves electroactivity, reduces resistivity, and improves the phenomenon of unstable resistivity within a depth of 1-2 μm of the polished surface.

[0038] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A sample preparation method for annealed wafer extended resistance testing, characterized in that... The following steps are included: Step 1: Place the silicon wafer on a clean cloth. Using the notch as a reference, use a diamond pen to draw a short line on the edge of the silicon wafer. Using a pin as a reference, gently press down from below the silicon wafer to break it into two pieces. Step 2: Repeat step 1 to split the silicon wafer into squares about 2-5mm wide. Three sides must be smooth cut surfaces after separation, and the other side can be an uneven cut surface drawn with a diamond pen. Step 3: Place the angle gauge on the heating table and heat it at 200℃ for about 3 to 5 minutes. Then, use pliers to remove the angle gauge and place it on the sample preparation table. Step 4: Take the paraffin stick from the clean box and spread it evenly on the surface of the angle gauge to melt it while it is hot. Place the silicon wafer sample face up on the center of the angle gauge. Under the LED desktop magnifying glass, align the end of the dissociated surface that needs to be ground with the center line of the angle gauge. When placing the silicon wafer sample on the angle gauge, fold the cleanroom cloth several times and press the sample several times with your thumb on the cleanroom cloth to make the sample firmly stick to the angle gauge and ensure that the sample is flat and that no end is raised; be careful not to move it during the pressing process to avoid changing the position of the sample. If the sample has moved slightly, use tweezers to reset it; Step 5: Pour 5-10 ml of 0.1μm diamond polishing slurry into the center of the frosted glass surface of the polishing equipment, turn on the machine, and use the handle of a cotton swab to adjust the position of the polishing slurry so that it is fully and evenly coated on the frosted glass surface; align the center line of the angle gauge with the line at the bottom of the fixture, fix it on the fixture, and then place it on the frosted glass plate at a suitable angle so that the cleavage surface of the silicon wafer sample to be polished is perpendicular to the polishing direction; Step 6: Turn on the machine, set the grinding speed and grinding time. During the grinding process, use the cotton swab handle to adjust the position of the grinding fluid to ensure that the silicon wafer sample is fully ground. Step 7: After grinding, remove the angle gauge with the silicon wafer sample attached from the fixture, place it in a beaker containing isopropanol, clean it with an ultrasonic cleaner for 8-10 minutes, and then wipe the sample surface with a lint-free cloth. Step 8: Place the cleaned silicon wafer sample on the heating stage and heat it at 200°C for about 5 minutes. Then, remove it with pliers and place it on the cooling stage to cool for 10 minutes. Step 9: Under an LED desktop magnifying glass, check the condition of the polished surface. If the polished surface is obviously skewed, the sample needs to be prepared again. If there are foreign objects on the surface, use an ultrasonic cleaner to clean it until the surface is completely clean.

2. The sample preparation method for annealed wafer extended resistance detection according to claim 1, characterized in that: If the polishing slurry is insufficient, it needs to be replenished in time; otherwise, not only will the polished surface be in poor condition, but the wear and tear of the frosted glass will also be accelerated.

3. The sample preparation method for annealed wafer extended resistance detection according to claim 1, characterized in that: If the square shape formed by the silicon wafer is not satisfactory, it needs to be re-cracked. During the cracking process, it is important to always keep the front side of the silicon wafer facing up and to clearly mark it to avoid confusion.