Method for accurately detecting heavy metal content in silicon wafer body

Abstract

The invention relates to a method for accurately detecting the content of heavy metals in a silicon wafer body, which belongs to the technical field of silicon wafer detection and comprises the following operation steps of: 1, cleaning the surface of the silicon wafer by adopting a VPD machine, and simultaneously finishing a metal impurity scanning and collecting process; and 2, measuring the metal impurities collected by the VPD by using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) to confirm the metal content condition. And 3, the silicon wafer which is confirmed to be clean enough is placed in a VPD machine table in sequence and is weighed in the machine table, VPD corrosion is carried out, and then drying and weighing are carried out again. And 4, carrying out bulk metal collection on the silicon wafer. And 5, testing the collected sample solution by using ICP-MS (Inductively Coupled Plasma Mass Spectrometry) And 6, calculating the thickness of the corroded surface of the silicon wafer according to the mass difference before and after corrosion, calculating the corrosion volume, and obtaining the specific metal content according to the test value of the sample solution. The method has the advantages of convenient operation, time and labor saving, high accuracy and good effect. The precision and accuracy of test data are ensured, and result difference caused by test is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of silicon wafer detection, and in particular to a method for accurately detecting the content of heavy metals in a silicon wafer. Background Art

[0002] At present, the device size of integrated circuits is shrinking, and the degree of integration is becoming higher and higher. Any tiny process defect will cause the integrated circuit to fail. Therefore, the requirements for the development and management of production and processing technology and various process parameters of raw materials are also becoming higher and higher.

[0003] Silicon wafers are one of the important raw materials in the integrated circuit manufacturing process. Metal impurities in silicon wafers will affect the performance and reliability of the device, and have a significant impact on the component yield and integrated circuit performance. Therefore, the control of various metal impurities in silicon wafers is extremely strict, and various institutions have always attached great importance to the detection of metal elements in the production and processing of silicon wafers.

[0004] Metal elements are commonly found in the silicon wafer processing process. The study of the chemical behavior of various metal elements in silicon wafers has always been a key topic of concern for relevant scholars and experts. According to the diffusion coefficient of metal elements in silicon, they can be roughly divided into three categories: high, medium and low. Fe, Ni, Cu, and Ru have extremely fast diffusion rates and are elements that need to be paid special attention to; the diffusion rates of Pt, W, Zr, Cr, are slightly lower; the diffusion rates of Pb, Sr and other elements are even lower, and it is generally believed that almost no diffusion occurs in the silicon wafer body. Due to the high diffusion coefficients of elements such as Cu and Ni, the heat treatment temperature during processing and the cooling rate during cooling will affect the diffusion degree of metal in silicon. In addition, the contamination of heavy metal elements such as Fe, Mn, and Zn can shorten the life of components or increase the current during operation, leading to device failure.

[0005] It is extremely important to detect the heavy metal content in silicon wafers, which is one of the necessary items for metal quality control during the production and processing of silicon wafers. The traditional testing method mainly uses a mixed acid solution to dissolve the silicon wafer and detects it with ICP-MS. The traditional testing method has the following disadvantages: the pre-treatment time of the dissolution method is long and the test efficiency is extremely low; a variety of mixed acids are required in the dissolution process, which is easy to cause harm to the operator, and has high requirements for personnel operation and high requirements for the quality of the liquid medicine, otherwise it will affect the test accuracy. The mixed acid solution is corrosive to laboratory equipment and will affect the clean room environment. Therefore, the cost of the dissolution method to test the metal is high; the silicon wafer involves heating operation during the dissolution process, which is easy to cause burns to personnel. External impurities are easily introduced during the test and pre-treatment process, which interferes with the test results and affects the judgment of the corresponding conclusions. Another mainstream detection method is the silicon wafer baking method to test copper and nickel, but the operation process involves heating operation, which has high requirements for personnel operation, and it is easy to introduce external pollution during the heating process, which affects the accuracy of the test results. Summary of the invention

[0006] The present invention mainly solves the deficiencies in the prior art and provides a method for accurately detecting the heavy metal content in silicon wafers, which has the advantages of convenient operation, time-saving and labor-saving, high accuracy and good effect. The precision and accuracy of the test data are guaranteed, the metal content in the silicon wafer sample is truly and accurately reflected, and unnecessary pollution is avoided during the detection process. Large-scale standardized operations are achieved, and the differences in results caused by the test are avoided.

[0007] The above technical problems of the present invention are mainly solved by the following technical solutions: A method for accurately detecting the heavy metal content in a silicon wafer comprises the following steps: Step 1: Use the VPD machine to clean the surface of the silicon wafer, remove the natural oxide film and other metal impurities on the surface of the silicon wafer, and complete the metal impurity scanning and collection process.

[0008] Step 2: Use ICP-MS to measure the metal impurities collected by VPD to confirm the metal content and confirm that the surface is dry. Only when the metal content is low enough will the next step be performed.

[0009] Step 3: Place the silicon wafer that has been confirmed to be sufficiently clean in the VPD machine again and weigh it in the machine, perform VPD etching, then dry it and weigh it again.

[0010] Step 4: Collect the bulk metal from the silicon wafer. Use 2ml of a 2% HF + 2% H2O2 mixed solution to extract the metal from the dried silicon wafer. During the extraction process, ensure that the metal on the entire surface is extracted.

[0011] Step 5: Use ICP-MS to test the collected sample solution.

[0012] Step 6: Calculate the thickness of the silicon wafer surface corroded and the volume of the corrosion based on the mass difference before and after corrosion, and obtain the specific metal content based on the test value of the sample solution.

[0013] The ICP-MS test uses an element detection machine. The ICP-MS machine model is ICP-MS-8900. Its detection accuracy must be at the ppt level. Before using the machine, it is necessary to confirm that the instrument is in normal condition and the calibration curve linearity must be above 0.995. A blank sample should be tested in advance to confirm that the machine is not contaminated.

[0014] The VPD in the VPD machine stands for Vapor Phase Decomposition. The PD machine uses IASExpert. The etching liquid is mainly made of high-purity HF and H2O2 in a certain ratio. Its configuration is automatically completed by the VPD machine, which can reduce unnecessary pollution caused by corresponding human factors. The HF used requires metal elements ≤ 10ppt, the H2O2 used requires metal element impurities ≤ 10ppt, and the H2O2 used to prepare the corrosion solution is 35% concentration hydrogen peroxide from Duomo Chemical. In order to reduce the impact of external metal impurities on the detection precision and accuracy, the water used in the detection process is ultrapure water with a resistivity of ≥ 18MΩ.cm.

[0015] Preferably, HF vapor is generated by VPD to perform meteorological corrosion on the surface of the silicon wafer, and the surface of the silicon wafer is changed from hydrophilic to hydrophobic. Then, the VPD scanning head scans and collects metal contamination on the surface of the silicon wafer. The scanning head needs to scan and collect metal impurities on the entire surface of the silicon wafer. After the metal impurities are collected, the corrosive liquid is properly scrapped, and finally the silicon wafer is dried by VPD.

[0016] The silicon wafer that has been surface cleaned is placed on a ceramic heating plate for heating. The transfer process is operated with a vacuum pen. Be careful not to let foreign objects touch the cleaned surface of the silicon wafer during the transfer process. The temperature of the heating plate is set to 420 degrees Celsius, and the heating time is 2 hours. The temperature of the heating plate should be uniform to avoid excessive local temperature differences on the silicon wafer. After stopping the heating, wait for the surface temperature of the silicon wafer to cool to room temperature, and then use a vacuum pen to transfer the silicon wafer to the wafer box. VPD takes the silicon wafer out of the wafer box to collect the metal on the surface.

[0017] Since the operation involves heating, you need to wear relevant protective equipment during the heating process of the ceramic heating plate to avoid burns.

[0018] Preferably, when the metal impurity content on the surface of the silicon wafer tested by ICP-MS is not low enough, it needs to enter the VPD machine for re-cleaning and drying, and at the same time scan and collect the metal impurities on the entire surface of the silicon wafer.

[0019] Preferably, O3 is introduced into the etching chamber of the VPD machine to oxidize the surface Si into SiO2, and then HF vapor is introduced to perform meteorological etching on the surface of the silicon wafer, and SiF4 is discharged along with the HF vapor. The above process is repeated continuously, and after a period of time, the silicon wafer is dried and weighed again, and the weights of the two times are recorded.

[0020] Preferably, a nitrogen gun is used to purge the silicon wafer during bulk metal collection.

[0021] The present invention can achieve the following effects: The present invention provides a method for accurately detecting the heavy metal content in silicon wafers. Compared with the prior art, the method has the advantages of convenient operation, time-saving and labor-saving, high accuracy and good effect. The precision and accuracy of the test data are guaranteed, the metal content in the silicon wafer sample is truly and accurately reflected, and unnecessary pollution is avoided during the detection process. Large-scale standardized operations are achieved, and the differences in test results are avoided.

[0022] The purpose of this technical solution is to provide relevant testing units and departments with an analytical method to accurately determine the heavy metal content in silicon wafers, thereby improving the quality of silicon wafers, helping relevant technical personnel to improve the process and promote the improvement of process yield. The scope of application is for various types of doped large-size silicon wafers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0024] The technical solution of the invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0025] Example: Figure 1 As shown, a method for accurately detecting the heavy metal content in a silicon wafer includes the following steps: Step 1: Use the VPD machine to clean the surface of the silicon wafer, remove the natural oxide film and other metal impurities on the surface of the silicon wafer, and complete the metal impurity scanning and collection process.

[0026] The HF vapor generated by VPD is used to perform meteorological corrosion on the surface of the silicon wafer, and the surface of the silicon wafer changes from hydrophilic to hydrophobic. Then the VPD scanning head scans and collects the metal contamination on the surface of the silicon wafer. The scanning head needs to scan and collect the metal impurities on the entire surface of the silicon wafer. After the metal impurities are collected, the corrosive liquid is properly scrapped, and finally the silicon wafer is dried by the VPD.

[0027] The silicon wafer that has been surface cleaned is placed on a ceramic heating plate for heating. The transfer process is operated with a vacuum pen. Be careful not to let foreign objects touch the cleaned surface of the silicon wafer during the transfer process. The temperature of the heating plate is set to 420 degrees Celsius, and the heating time is 2 hours. The temperature of the heating plate should be uniform to avoid excessive local temperature differences on the silicon wafer. After stopping the heating, wait for the surface temperature of the silicon wafer to cool to room temperature, and then use a vacuum pen to transfer the silicon wafer to the wafer box. VPD takes the silicon wafer out of the wafer box to collect the metal on the surface.

[0028] Step 2: Use ICP-MS to measure the metal impurities collected by VPD to confirm the metal content and confirm that the surface is dry. Only when the metal content is low enough will the next step be performed.

[0029] When the metal impurity content on the surface of the silicon wafer tested by ICP-MS is not low enough, it needs to enter the VPD machine for re-cleaning and drying, and at the same time scan and collect the metal impurities on the entire surface of the silicon wafer.

[0030] Step 3: Place the silicon wafer that has been confirmed to be sufficiently clean in the VPD machine again and weigh it in the machine, perform VPD etching, then dry it and weigh it again.

[0031] O3 is introduced into the etching chamber of the VPD machine to oxidize the surface Si into SiO2, and then HF vapor is introduced to perform meteorological etching on the surface of the silicon wafer. SiF4 is discharged along with the HF vapor, and the above process is repeated continuously. After a period of time, the silicon wafer is dried and weighed again, and the weights of the two times are recorded.

[0032] Step 4: Collect the bulk metal from the silicon wafer. Use 2ml of a 2% HF + 2% H2O2 mixed solution to extract the metal from the dried silicon wafer. During the extraction process, ensure that the metal on the entire surface is extracted.

[0033] A nitrogen gun is used to purge the silicon wafer during bulk metal collection.

[0034] Step 5: Use ICP-MS to test the collected sample solution.

[0035] Step 6: Calculate the thickness of the silicon wafer surface corroded and the volume of the corrosion based on the mass difference before and after corrosion, and obtain the specific metal content based on the test value of the sample solution.

[0036] In summary, the method for accurately detecting the heavy metal content in silicon wafers has the advantages of convenient operation, time-saving and labor-saving, high accuracy and good effect. It ensures the precision and accuracy of the test data, truly and accurately reflects the metal content in the silicon wafer sample, and avoids unnecessary pollution during the detection process. It realizes large-scale standardized operations and avoids the differences in test results.

[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 any technician in the field of the present invention are included in the patent scope of the present invention.

Claims

1. A method for accurately detecting the heavy metal content in a silicon wafer, characterized in that The steps are as follows: Step 1: Use the VPD machine to clean the surface of the silicon wafer, remove the natural oxide film and other metal impurities on the surface of the silicon wafer, and complete the metal impurity scanning and collection process; Step 2: Use ICP-MS to measure the metal impurities collected by VPD to confirm the metal content and confirm that the surface is dry. Only when the metal content is low enough can the next step be performed; Step 3: Place the silicon wafer that has been confirmed to be sufficiently clean in the VPD machine again and weigh it in the machine, perform VPD etching, then dry it and weigh it again; Step 4: Collect the bulk metal from the silicon wafer. Use 2ml of 2% HF + 2% H2O2 mixed solution to extract the metal from the dried silicon wafer. During the extraction process, ensure that the metal on the entire surface is extracted. Step 5: Use ICP-MS to test the collected sample solution; Step 6: Calculate the thickness of the silicon wafer surface corroded and the volume of the corrosion based on the mass difference before and after corrosion, and obtain the specific metal content based on the test value of the sample solution.

2. The method for accurately detecting the heavy metal content in a silicon wafer according to claim 1, characterized in that: The HF vapor generated by VPD is used to perform meteorological corrosion on the surface of the silicon wafer, and the surface of the silicon wafer changes from hydrophilic to hydrophobic. Then the VPD scanning head scans and collects the metal contamination on the surface of the silicon wafer. The scanning head needs to scan and collect the metal impurities on the entire surface of the silicon wafer. After the metal impurities are collected, the corrosive liquid is properly scrapped, and finally the silicon wafer is dried by the VPD.

3. The method for accurately detecting the heavy metal content in a silicon wafer according to claim 2, characterized in that: When the metal impurity content on the surface of the silicon wafer tested by ICP-MS is not low enough, it needs to enter the VPD machine for re-cleaning and drying, and at the same time scan and collect the metal impurities on the entire surface of the silicon wafer.

4. The method for accurately detecting the heavy metal content in a silicon wafer according to claim 1, characterized in that: O3 is introduced into the etching chamber of the VPD machine to oxidize the surface Si into SiO2, and then HF vapor is introduced to perform meteorological etching on the surface of the silicon wafer. SiF4 is discharged along with the HF vapor, and the above process is repeated continuously. After a period of time, the silicon wafer is dried and weighed again, and the weights of the two times are recorded.

5. The method for accurately detecting the heavy metal content in a silicon wafer according to claim 1, characterized in that: A nitrogen gun is used to purge the silicon wafer during bulk metal collection.

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