TW416116B - Process for mapping metal contaminant concentration on a silicon wafer surface - Google Patents

Abstract

A process is provided for preparing a reference wafer having a surface which is substantially uniformly contaminated with one or more metals of interest and which is suitable for use in the calibration of a total reflection fluorescent X-ray apparatus. The process comprises immersing a virgin wafer in a treatment solution obtained by mixing an aqueous stock solution containing a water-soluble salt of a metallic contaminant of interest with an organic solvent, and then drying thus immersed wafer.

Description

416116 V. Description of the invention (π Background of the invention The method of the present invention is generally related to the detection of metal contamination on the surface of a semiconductor substrate. More specifically, this method involves mapping the surface of a single-crystal silicon wafer to determine its surface. Method for the distribution of metal contamination. This method is further related to the preparation of reference or calibration wafers for the mapping method. Semiconductor wafers suitable for integrated circuit manufacturing are manufactured by cutting thin wafers from monocrystalline silicon ingots After slicing, the wafer is polished to have a substantially uniform thickness. The wafer is then etched to remove damage and produce a smooth surface. At a uniform thickness, the wafer is then etched to remove damage and produce a smooth surface. The next step in the conventional wafer forming process is a polishing step to produce a highly reflective and undamaged surface on at least one side of the wafer. Electronic_device manufacturing occurs on this polished surface. Known contaminants are on the semiconductor wafer table The presence of ®, especially metal contaminants, can greatly reduce the quality and performance of integrated circuits manufactured by it. Therefore, the manufacturers of integrated circuits are The surface concentration of impurities is set to a strict limit, and wafers exceeding this concentration are rejected. As a result, Shi Xi wafers are generally cleaned after some or all of the preparation steps to help reduce the amount of surface contamination present in the final wafer product. Many methods exist to analyze the surface of a wafer to determine the concentration of metal impurities thereon. These methods can generally be divided into two groups based on whether they provide partial or full concentration data of surface contaminants. For example, provide all or a total of surface contaminants. The method of concentration data generally involves dissolving the oxide layer present on the wafer surface by hydrofluoric acid vapor or solution, and then analyzing the condensed vapor or solution to determine the concentration of metal contaminants therein. This method is advantageous,

Page 5 416116 V. Description of the invention (2) Because it generally causes detection of very low levels of metal contaminants; that is, this method is advantageous because it generally has a relatively low method for determining the local concentration of metal contaminants Detection limit. In addition, this method effectively provides data on the contamination concentration of the entire wafer surface. Methods for providing local concentration data of metal contaminants generally involve analyzing the wafer surface by using a secondary ion mass spectrometer, Auger spectrum analysis, neutron activation analysis, or total X-ray reflection fluorescence spectrum (TXRF) analysis. This method is advantageous because it is essentially non-destructive to the surface of the wafer, which means that multiple analyses can be performed on the same wafer. For example, after any step in a wafer manufacturing method, the wafer can be analyzed before proceeding to the next step. This method therefore provides a method for monitoring manufacturing methods and evidence of possible sources of metal contamination. In addition, because these methods provide local results on the wafer surface, the surface can be effectively " enantiomer " that is, these methods can be used to determine where metal contamination is on the surface. This data is beneficial because specific pollution patterns can suggest the source of the pollutant. E.g. For wafers with circular patterns in the center of the wafer, it is recommended that the wafer be processed. The chuck is the source of contamination | and for the approximately uniform distribution of contaminants, it is recommended that the etching solution or polishing slurry be the source of contamination. Therefore, these partial methods of surface analysis provide very useful information not only on wafers, but also on wafer manufacturing methods. However, in order for these methods to provide reliable and reproducible results, the methods and instruments used must be properly calibrated. In general, the instrument used for this method must be calibrated because of any factors that can affect the measurement, such as changes in the background noise of the instrument, changes in the detector and collection efficiency, and changes in the response from the detected impurities. Accurate calibration generally requires the preparation of standard products, or in this case crystals.

V. Description of the invention (3) For circles, the concentration of metal pollutants on the surface must meet very strict specifications. In this way, the actual reflection of the known impurity concentration correction device of the reference wafer can be compared. One of the important conditions set for these wafers is that they are uniformly contaminated on all surfaces, and that a correct and reliable calibration is determined regardless of the position used on the reference wafer surface. For specific wafer manufacturing equipment, it is also desirable that the surface be uniformly contaminated with all the various metal contaminants of interest. As a result, although the reference wafer is commercially available, it cannot necessarily exhibit the characteristics required for the specific manufacturing location where the test occurs. In addition, it cannot necessarily perform the correction with high accuracy. In addition, gettering is often a desirable silicon wafer feature, which is characteristic of various performance test investigations. However, it is not easy to obtain a reference wafer for this test. Therefore, the results of this test need to be checked using i I CP-MS or flameless atomic absorption spectroscopy to improve the accuracy of this test. Therefore, there continues to be a need for reference or calibration wafers, which are easy to prepare to have uniformly contaminated surfaces, and which can serve as a comparative comparison of the manufacturing conditions and getter characteristics of the wafers that appropriately meet the final evaluation. SUMMARY OF THE INVENTION Therefore, it should be noted that the object of the present invention is to provide a method for preparing a reference wafer, which is suitable for non-destructive surface analysis of silicon wafers to determine the concentration and distribution of metal contaminants thereon; Implementation and time-saving method; providing a reference wafer with a uniformly contaminated surface; providing a reference wafer particularly suitable for surface analysis of a silicon wafer by total reflection X-ray fluorescence; and providing a reflection Surface of silicon wafer surface

416116 V. Description of the invention (4) Method for the concentration of pollutants, in which this reference wafer is used. Therefore, in short, the present invention relates to a method for preparing a reference crystal suitable for the correction of a total reflection X-ray fluorescence spectrometer. This method includes preparing an aqueous salt solution comprising water and a water-soluble metal salt, and then mixing a portion of the aqueous salt solution with an organic solvent to form a treatment solution. Substantially metal-free silicon wafers are immersed in a processing solution and removed. The processed wafer is then dried. The invention further relates to a method for measuring the concentration of metal contaminants on the surface of Shi Xi wafer by a total reflection X-ray fluorescence spectrometer. This method is characterized in that the reference wafer for calibrating the spectrometer is prepared by immersing the original wafer in the mixture for a predetermined time. Then, the wafer thus prepared is dried before use. Other objects and features of the present invention are obvious and partly indicated below. Brief Description of the Drawings Figure 1 is a bar-shaped chart describing the results of investigating the deposition distribution on the surface of a reference wafer prepared according to the method of the present invention, as measured by a full X-ray reflection fluorescence spectrometer. Fig. 2 is a bar-shaped graph describing the results of investigating the distribution of nickel deposition on the surface of a reference wafer prepared by spin coating performed by a method commonly used in this technique, as measured by a full X-ray reflection fluorescence spectrometer. Detailed description of a preferred embodiment The method of the present invention results in the preparation of a reference or calibration wafer for the purpose of measuring the concentration of metal contaminants on the surface of a silicon wafer prepared by conventional manufacturing methods

Page 8 416116 V. Description of the invention (5) For the purpose of instrument calibration for distribution, its surface is substantially uniformly contaminated with one or more metal impurities of interest. More specifically, this method results in the preparation of a reference wafer for calibration of a full X-ray reflection fluorescent instrument with a substantially uniformly polluted surface. In order to determine the concentration and distribution of metal contaminants thereon, the TXRF instrument is thus made. Applicable to the surface of anti-Shi Xi wafer. According to the method of the present invention, a common metal water-soluble salt (commonly used to prepare the purity for the purpose of calibration standards of this type of instrument) is used to prepare an aqueous solution to analyze a sample wafer. Conventional silicon wafer manufacturing conditions or the environment generally produce crystals. Surfaces are contaminated by metals such as zinc, nickel, copper, iron, calcium, and chromium. Therefore, this aqueous solution can be prepared by adding one or more salts to a certain amount of pure water. However, in general, the raw material or standard solution for preparing each metal salt is to have a concentration of about 10 ppm (parts per million). Once prepared, all raw material solutions are mixed in quantities of commercially available volatile organic solvents (purity suitable for the purpose of preparing calibration standards for this type of instrument), which are miscible with water, for example, generally low molecular weight Alcohol or Brew 1, making it easy to evaporate at room temperature. Preferably, these low molecular weight alcohols have three carbons or less and include methanol, ethanol, propanol, isopropanol, and propanol is the preferred ketone. In a particularly preferred embodiment, isopropanol is used. In general, the raw material solution and the solvent can be mixed in any proportion sufficient to cause the salt to remain in the solution and at an appropriate metal contaminant concentration sufficient to cause substantially uniform deposition on the reference wafer surface to prepare a processing solution. However, in general, in terms of volume ratio, the ratio of the raw material solution to the solvent in the processing solution ranges from about 1: 1 to about 1: 1. Once the raw material solution and the solvent have been completely mixed,

Page 9 416116 V. Description of the invention (6) The liquid is substantially uniformly contaminated to prepare a wafer contact processing solution for a reference wafer. Generally speaking, by using full or partial wafer rotation to immerse the wafer to determine the complete treatment of the entire surface, it is sufficient to determine the complete surface treatment and also the time to substantially uniformly impart an appropriate degree of contamination to the entire wafer surface. Processing, therefore, it generally means that the wafer surface is in contact with the processing solution for about 1 minute to about 10 minutes. -In general, the wafer in contact with the processing solution can be any wafer suitable for the preparation of this type of calibration standard, which has been prepared under strict manufacturing conditions. In other words, essentially any silicon wafer can be processed on the condition that it first accepts this technology's clean processing standard, which is effective enough to reduce the concentration of metal impurities of interest to a sufficiently low level so that these impurities do not interfere with the calibration method. Therefore, a "primary crystal circle" or a wafer having a substantially metal-free surface is used. Once the processing time is exceeded, the wafer sores are removed (ie, excess processing solution is removed from the wafer surface) and the wafer is at room temperature (ie, at a temperature generally in the range of about 20 to about 25 ° C) Dry in a conventional clean room setting (ie, a room that is essentially free of metal contaminants that interfere with the calibration method). Because of the volatility that the organic solvent imparts to the processing solution, wafers that are crystal-processed dry quickly without the need for an accelerated drying process. The dried wafer can now be used as a reference wafer for the purpose of calibrating a specific instrument in accordance with a common calibration method for a specific instrument, which is used to analyze the surface of a sample wafer obtained from a manufacturing method. In a preferred embodiment, the reference wafer of the present invention can be used to calibrate a full X-ray reflection fluorescence meter (such as the > MTREX61 0T model), which is commonly obtained by this technology from the Technos Corporation ).

Page 10 416116 V. Description of the invention (7) Regarding the above, it can be seen that according to the method of the present invention, a reference wafer having a concentration of one or more metal contaminants of interest is prepared, and this concentration is distributed substantially uniformly throughout On the wafer surface. The method thus provides a more efficient and cost-effective method for preparing such wafers, as it can be performed in situ where wafer fabrication occurs. In addition, for the purpose of preparing a reference wafer, by implementing the method in a wafer manufacturing facility and using a wafer obtained from a production line, more accurate and reliable data can be collected. As described in the following example, a reference wafer suitable for calibration of a full X-ray reflection fluorescence can be easily and efficiently prepared to have a substantially uniform contaminant concentration on the entire wafer surface. It should be noted, however, that the method conditions provided herein and above may be other than those described without departing from the scope of the invention. _ EXAMPLE '' An aqueous raw material solution of iron, copper, zinc, chromium 1 and sodium was prepared so that the concentration of each metal in the solution was about 10 PPII. Take out equal parts from each raw material solution in the range of about 1 to about 200 cc each, and add isopropanol to make the total volume of each solution about 100 c c. Each of the treatment solutions thus prepared was shaken to ensure complete mixing, and then placed in an immersion tank. The cleaned six-inch silicon wafer (cleaned by standard techniques) is then immersed in a bath containing a nickel-containing treatment solution for about 3 to about 4 minutes. The wafer is then removed from the tank * so that excess solution will drip from it, and the wafer is dried in a clean room at room temperature. After drying, the reference wafers were then analyzed by X-ray reflection fluorescence (TREX610YT, available from Technos) at nine different locations on the wafer surface. Referring now to FIG. 1, a bar chart is shown, the description of which is integrated 11111 __ ill; 1 1 _ II 1 416116 V. Description of the invention (8) Nickel deposition from all 9 locations. In addition, referring now to FIG. 2, staggered deposits are also determined by repeating the steps shown on a commercially available reference wafer prepared by spin coating. Metals were deposited on reference samples prepared by the methods described above and commercially available reference samples prepared by spin coating using a total reflection fluorescent X-ray apparatus manufactured by Technos. The test results are shown in Table 1 below. Table 1 Analysis No. Commercially available samples of the method of the invention 1 13.0441 77. 4742 2 8.0963 89. 8240 3 11.5328 81.2665 4 11.8583 85. 5087 5 11.2154 118.6100 6 10. 5565 75. 6795 7 7.4390 71.8325 8 9. 6834 99.7520 9 8.6127 83.1578 Mean 10.2265 87.0118 Standard deviation 1.8983 14.4421

Page 12 416116 V. Description of the invention (9) As proved by these test results, it can be observed that the nickel deposition of the reference wafer prepared by the present invention is substantially uniform, and the uniformity of nickel contamination is relatively relative to commercially available reference wafers. Greatly improved. Therefore, it has been found that the reference wafer of the present invention is acceptable for industrial use, and the present invention is therefore suitable for preparing a calibration wafer for quantitative analysis. It should be noted that the metal deposition was actually measured using the reference sample of the present invention, and the measurement results obtained were found to be highly reproducible. As described above, for example, zinc, nickel, copper, iron, calcium, and chromium can be deposited on the surface of the original wafer by a predetermined amount by preparing an aqueous salt solution and mixing it with a specific organic solvent to prepare a reference sample. The reference sample thus prepared therefore uses a total reflection fluorescent X-ray device for the measurement of metal deposition on the surface of the sample wafer. In this way, the present invention can exhibit the effect of more accurately measuring the metal deposition on the surface of the crystallite. It is easy to carry out wafer inspection at the manufacturing location. 1Quality control temple.

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Claims (1)

416116 VI. Application for Patent Scope 1, A method for preparing a reference wafer suitable for total reflection X-ray fluorescence spectrometer calibration. One surface of the reference wafer has a substantially uniform distribution of metal contaminants deposited thereon, This method includes: preparing an aqueous salt solution of an aqueous salt containing metal contaminants; mixing a portion of the aqueous salt solution with an organic solvent to form a processing solution; immersing a substantially metal-free silicon wafer in the processing solution; self-processing The solution removes the processed wafer; and dries the processed wafer. 2. —A method of reflecting the metal deposition distribution on the sample wafer by a full X-ray reflection fluorescence meter. This method is characterized by immersing the original wafer in the water-solubility of the required metal contaminants. A reference wafer prepared with a mixture of a salt and an organic solvent selected from the group consisting of a lower alcohol and a ketone is used for calibration of the instrument. _ — 3. The method according to item 2 of the scope of patent application, wherein isopropyl alcohol is used as the organic solvent. 苐 Page 14