Pretreatment method for analyzing chloride ions on surface of silicon wafer by adopting liquid phase ion chromatograph
By combining liquid ion chromatography with ultrapure water pretreatment, the high cost and low efficiency of chloride ion detection on silicon wafer surfaces have been solved, achieving high-precision and low-cost chloride ion detection, which is suitable for the high cleanliness requirements of semiconductor manufacturing.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-15
- Publication Date
- 2026-04-07
AI Technical Summary
Existing technologies for detecting chloride ions on silicon wafer surfaces suffer from problems such as expensive equipment, high costs, the need for large amounts of ultrapure water, insufficient detection accuracy, and difficulty in achieving efficient chloride ion recovery and accurate detection.
A liquid ion chromatography (LICC) system combined with ultrapure water pretreatment was used. Chloride ions were dissolved by placing a polished disc in ultrapure water and then recovered with the aid of a nitrogen gun. A strict quality control system and repeated experiments were employed to ensure the accuracy and precision of the detection.
It achieves high-precision, low-cost detection of chloride ions on silicon wafer surfaces, meets the cleanliness standards for semiconductor manufacturing, and is suitable for quantitative analysis of extremely low concentrations of chloride ions, reducing detection costs and equipment requirements.
Smart Images
Figure CN121805489A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of semiconductor wafer processing technology, and specifically to a pretreatment method for analyzing chloride ions on the surface of silicon wafers using liquid phase ion chromatography. Background Technology
[0002] During the manufacturing of conductive silicon wafers or chip processing, chemical reagents such as SC2 are used to clean the silicon wafers with a mixture of HCl and H2O2, which may leave residual chloride ions. Cleanroom environments may also contain chloride ions, which, combined with ambient moisture, can adhere to the silicon wafer surface. Chloride ions on the silicon wafer surface have a significant impact on the gate oxide layer during chip processing, leading to premature oxide layer breakdown, threshold voltage drift, and increased leakage current. Furthermore, they can form contamination centers, inducing defects at high temperatures and affecting device performance. As device sizes continue to shrink, the detection of chloride ions on the silicon wafer surface is becoming increasingly important, and various analytical methods are being applied to chloride ion detection. In the semiconductor industry, UPW stands for ultrapure water.
[0003] Chloride ions on silicon wafer surfaces can be analyzed using the TREX method, which involves heating and chemical reactions to "drive out" chloride ions from the silicon wafer surface, then captures and measures them; this is one of the standard measurement methods, but the equipment and cost are expensive. Rapid, non-destructive surface screening and quantification can be performed using TOF-SIMS or TXRF, but the cost is quite high. Semi-quantitative detection can be performed using SEM-EDX; surface analysis can be done using ICP-MS, but it suffers from severe interference, requiring the use of collision reaction techniques to eliminate it; liquid ion chromatography can also be used for detection.
[0004] The first challenge in detecting chloride ions on silicon wafer surfaces using ion chromatography is collecting them. Methods such as rinsing the wafer surface with uplifted polyurethane (UPW) require specialized equipment, and manual rinsing necessitates large quantities of UPW, which can lead to excessive dilution and undetectable chloride ions when the chloride content is low. Alternatively, custom-made containers can be used to soak the silicon wafer surface with UPW, but this also presents the problem of requiring large quantities of UPW. Summary of the Invention
[0005] This invention addresses the shortcomings of existing technologies by providing a pretreatment method for analyzing chloride ions on silicon wafer surfaces using liquid chromatography-ion chromatography. This method offers advantages such as ease of operation, time and labor savings, and energy conservation and emission reduction. It enables chloride ion recovery using minimal amounts of ultrapure water and allows for more accurate chloride ion detection.
[0006] The above-mentioned technical problems of the present invention are mainly solved by the following technical solutions: A pretreatment method for analyzing chloride ions on the surface of silicon wafers using liquid ion chromatography includes the following steps: Step 1: Prepare the polishing plate and UPW; record the chloride ion analysis value of the freshly removed UPW using an ion chromatograph as a blank sample.
[0007] Step 2: Cover the surface of the polishing pad with UPW; in a fume hood, use a 100ml volumetric flask to weigh out 15-25ml of UPW and slowly pour it all into the center of the polishing pad. Be careful to do this slowly so that the UPW gradually covers the entire surface of the polishing pad without overflowing.
[0008] Step 3: Let the UPW stand to dissolve chloride ions on the surface of the polishing pad; let it stand for 5 to 10 minutes to allow the chloride ions to fully dissolve in the UPW.
[0009] Step 4: UPW recycling; Inside the fume hood, use a suction pen to pick up the back of the polishing pad and slowly pour the UPW back into a 100ml wide-mouth volumetric flask.
[0010] Step 5: Liquid Chromatography (LC) analysis; In a Class 100 cleanroom, analyze the chloride ions in UPW in a 100ml wide-mouth volumetric flask using an ion chromatograph and record the analytical values.
[0011] Step 6: Obtain chloride ion results on silicon wafer surface; repeat steps 1 to 5 twice, analyzing a total of 3 polished wafers and 3 blank samples.
[0012] As a preferred option, 10-20 ml of UPW is weighed in a 100 ml wide-mouth volumetric flask using an electronic balance; a polishing wafer is removed from the silicon wafer cassette using a vacuum pen in a fume hood and placed on the wafer support stage.
[0013] As a preferred method, in a Class 100 cleanroom, the chloride ions in UPW in a 100ml volumetric flask are analyzed using an ion chromatograph, and the analytical values are recorded as blank samples.
[0014] As a preferred method, due to the hydrophilicity of the polished wafer surface, the UPW film will cover the polished wafer surface and cannot be completely recycled. The water film on the polished wafer surface will have a relatively high chloride ion content because it is in direct contact with the silicon wafer surface. In the fume hood, a small flow of nitrogen is used to drive the water film into droplets, and then it is recycled into a 100ml wide-mouth volumetric flask.
[0015] As a preferred option, chloride ion detection requires a Class 100 or higher cleanroom environment equipped with chemical filters; the chlorine content in the cleanroom environment must be less than 10 ppt; the pretreatment process is completed in a fume hood, which requires a Class 10 cleanroom environment, and the chlorine content in the fume hood must also be less than 10 ppt.
[0016] The present invention can achieve the following effects: This invention provides a pretreatment method for analyzing chloride ions on the surface of silicon wafers using liquid ion chromatography. Compared with existing technologies, this method successfully transfers trace contaminants on the surface of silicon wafers to the liquid phase through ingenious pretreatment steps, achieving high-precision quantitative analysis. This method has high application value in the field of semiconductor material quality control.
[0017] High precision and high sensitivity: It combines precise sampling by weighing method, high-sensitivity detection by ion chromatography and nitrogen purging to improve recovery rate. The entire method chain is designed around the word "precision" and is suitable for detecting extremely low concentrations of chloride ion pollution.
[0018] A rigorous quality control system was implemented, including a blank sample control and requiring three replicate experiments. This design effectively eliminates interference from reagents, environment, and operational procedures, and statistical methods are used to assess the stability and reliability of the results.
[0019] Compliant with semiconductor industry standards: The method explicitly mentions key elements such as fume hoods, Class 100 cleanrooms, vacuum pens, and UPW (ultrapure water), fully complying with the stringent standards for cleanliness and contamination control in semiconductor manufacturing.
[0020] Highly operable and practical: The solution is described in great detail, with clear instructions on everything from water volume range and settling time to the specific operation of nitrogen purging, making it easy to standardize and repeat. Attached Figure Description
[0021] Figure 1 This is a process flow diagram of the present invention.
[0022] Figure 2 This is a table showing the results of ion chromatography analysis and TREX analysis verification of the pretreatment method of this invention. Detailed Implementation
[0023] The technical solution of the invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.
[0024] Example: Figure 1 As shown, a pretreatment method for analyzing chloride ions on the surface of a silicon wafer using liquid ion chromatography includes the following steps: Step 1: Preparation of polishing wafers and UPW; Weigh 10-20 ml of UPW into a 100 ml wide-mouth volumetric flask using an electronic balance; Remove one polishing wafer from the wafer cassette using a vacuum pen in a fume hood and place it on the wafer stage. In a Class 100 cleanroom, analyze the chloride ions in the 100 ml volumetric flask using an ion chromatograph and record the analytical value as a blank sample.
[0025] Chloride ion detection requires a Class 100 or higher cleanroom environment equipped with chemical filters; the chlorine content in the cleanroom environment must be below 10 ppt.
[0026] Step 2: Cover the surface of the polishing pad with UPW; in a fume hood, use a 100ml volumetric flask to weigh out 15-25ml of UPW and slowly pour it all into the center of the polishing pad. Be careful to do this slowly so that the UPW gradually covers the entire surface of the polishing pad without overflowing.
[0027] The pretreatment work is completed in a fume hood, which requires a Class 10 cleanroom environment and a chlorine content of less than 10 ppt.
[0028] Step 3: Let the UPW stand to dissolve chloride ions on the surface of the polishing pad; let it stand for 5 to 10 minutes to allow the chloride ions to fully dissolve in the UPW.
[0029] Step 4: UPW recycling; Inside the fume hood, use a suction pen to pick up the back of the polishing pad and slowly pour the UPW back into a 100ml wide-mouth volumetric flask.
[0030] Due to the hydrophilicity of the polished wafer surface, the UPW film will cover the polished wafer surface and cannot be completely recycled. The water film on the polished wafer surface will have a relatively high chloride ion content because it is in direct contact with the silicon wafer surface. In the fume hood, a small flow of nitrogen is used to drive the water film into droplets, and then it is recycled into a 100ml wide-mouth volumetric flask.
[0031] Step 5: Liquid Chromatography (LC) analysis; In a Class 100 cleanroom, analyze the chloride ions in UPW in a 100ml wide-mouth volumetric flask using an ion chromatograph and record the analytical values.
[0032] Step 6: Obtain chloride ion results on silicon wafer surface; repeat steps 1 to 5 twice, analyzing a total of 3 polished wafers and 3 blank samples.
[0033] like Figure 2 As shown, to verify whether the method of this invention can recover chloride ions from the silicon wafer surface, three 12-inch polished wafers were analyzed for chloride ions on the silicon wafer surface using the TREX method. The ion chromatography and TREX analysis results of the three polished wafers used in the pretreatment process are as follows: (1) The present invention collects chloride ions from the silicon wafer surface pretreatment and then analyzes the results by liquid ion chromatography. The results are not significantly different from those of TREX analysis and are at the same level.
[0034] (2) Compared with the TREX analysis method, the use of heating furnace + high temperature ventilation treatment + release gas collection + gas phase analysis greatly saves costs, is easy to operate, and is suitable for batch testing.
[0035] A pretreatment method is adopted in which a certain amount of UPW is added to the surface of the silicon wafer to fully dissolve chloride ions on the silicon wafer surface, and then the UPW is recovered with the assistance of a low-flow nitrogen gun. This method can recover chloride ions on the surface of the silicon wafer, making it possible to accurately measure chloride ions on the surface of the silicon wafer using ion chromatography.
[0036] In summary, this pretreatment method for analyzing chloride ions on silicon wafer surfaces using liquid ion chromatography (LICC) involves adding a certain amount of UPW (untreated polyvinyl chloride) to the silicon wafer surface and allowing it to stand to fully dissolve the chloride ions. The UPW is then recovered using a low-flow-rate nitrogen gun. This pretreatment method provides a standard approach for accurate LICC analysis of chloride ions on silicon wafer surfaces. It solves the problem of chloride ion recovery from large-area polished wafer surfaces, making accurate detection of chloride ions on silicon wafer surfaces by LICC a universal method.
[0037] 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 pretreatment method for analyzing chloride ions on the surface of silicon wafers using liquid ion chromatography, characterized in that... The following steps are included: Step 1: Prepare polishing discs and UPW; record the chloride ion analysis value of the freshly removed UPW using an ion chromatograph as a blank sample; Step 2: Cover the surface of the polishing pad with UPW; In the fume hood, use a 100ml volumetric flask to weigh 15-25ml of UPW again and slowly pour it all into the center of the polishing pad. Be careful to do this slowly so that the UPW can slowly cover the entire surface of the polishing pad without overflowing. Step 3: Let the UPW stand to dissolve chloride ions on the surface of the polishing pad; let it stand for 5 to 10 minutes to allow the chloride ions to fully dissolve in the UPW. Step 4: UPW recycling; Inside the fume hood, use a suction pen to pick up the back of the polishing pad and slowly pour the UPW back into a 100ml wide-mouth volumetric flask; Step 5: Liquid Chromatography (LC) analysis; In a Class 100 cleanroom, analyze the chloride ions in UPW in a 100ml wide-mouth volumetric flask using an ion chromatograph and record the analytical values; Step 6: Obtain chloride ion results on silicon wafer surface; repeat steps 1 to 5 twice, analyzing a total of 3 polished wafers and 3 blank samples.
2. The pretreatment method for analyzing chloride ions on the surface of silicon wafers using liquid ion chromatography according to claim 1, characterized in that: Weigh 10-20 ml of UPW into a 100 ml wide-mouth volumetric flask using an electronic balance; remove one polishing wafer from the wafer cassette using a vacuum pen in a fume hood and place it on the wafer support stage.
3. The pretreatment method for analyzing chloride ions on the surface of silicon wafers using liquid ion chromatography according to claim 2, characterized in that: In a Class 100 cleanroom, chloride ions in UPW were analyzed using an ion chromatograph, and the analytical values were recorded as blank samples.
4. The pretreatment method for analyzing chloride ions on the surface of silicon wafers using liquid ion chromatography according to claim 1, characterized in that: Due to the hydrophilicity of the polished wafer surface, the UPW film will cover the polished wafer surface and cannot be completely recycled. The water film on the polished wafer surface will have a relatively high chloride ion content because it is in direct contact with the silicon wafer surface. In the fume hood, a small flow of nitrogen is used to drive the water film into droplets, and then it is recycled into a 100ml wide-mouth volumetric flask.
5. The pretreatment method for analyzing chloride ions on the surface of silicon wafers using liquid ion chromatography according to claim 1, characterized in that: Chloride ion detection requires a Class 100 or higher cleanroom environment equipped with chemical filters; the chlorine content in the cleanroom environment must be below 10 ppt; pretreatment is performed in a fume hood, which must be a Class 10 cleanroom environment, with the chlorine content also below 10 ppt.