METHOD FOR MEASURING THE Fe CONCENTRATION IN A P-TYPE SILICON WAFER

Abstract

Method for measuring an iron concentration in a p-type silicon wafer (W) based on a measurement employing a surface photovoltage, hereinafter referred to as SPV, method, wherein the method for measuring comprises: Performing the measurement in a measurement mode in which the p-type silicon wafer (W) is irradiated with a plurality of lights having different wavelengths during the same time period, the measurement being performed under the following conditions: (i) the time between readouts is 35 ms or more and 120 ms or less, and a time constant is 20 ms or more, or the time between readouts is 10 ms or more and less than 35 ms and the time constant is 100 ms or more, and (ii) a number of readouts is 12 times or less, where the number of readouts means the number of SPV signals that are captured in an SPV measurement, The time constant represents the acquisition time during which each SPV signal is acquired, out of the number of SPV signals. The time between readouts means the time interval between times at which successive SPV signals are recorded.

Description

TECHNICAL AREA

[0001] This disclosure relates to a method for measuring the Fe concentration in a p-type silicon wafer using a surface photovoltage (SPV) method. STATE OF THE ART

[0002] Fe contamination of a p-type silicon wafer affects the characteristics of a device fabricated from the wafer. Therefore, simplified methods for evaluating the Fe concentration in p-type silicon wafers have been developed. One such method involves electrically measuring the diffusion length of minority carriers in a p-type silicon wafer using the SPV method and calculating the Fe concentration in the wafer from the measurement result.

[0003] In the SPV method, a p-type silicon wafer is irradiated with light of different wavelengths, and the surface photovoltage (SPV signal) of the wafer at that time is measured, thereby determining the diffusion length of minority carriers in the wafer. This procedure is also simply referred to below as "SPV measurement." The SPV method is an excellent technique that allows for shorter measurement times compared to other methods and enables non-contact and non-destructive measurements.

[0004] SPV measurement is known to have two measurement modes: Standard mode and Ultimate mode. The SPV method necessarily uses a variety of lights with different wavelengths to perform the measurement. Standard mode is a typical procedure for performing one SPV measurement using a specific wavelength, followed by sequential SPV measurements using wavelengths that are different from both the preceding wavelength and from each other. Ultimate mode is a specialized procedure for performing SPV measurements by irradiating a sample with a variety of lights with different wavelengths simultaneously within the same period.

[0005] JP 2004 - 503 100 A describes how, when a measurement is performed using Ultimate mode, the measurement can be completed in a shorter time compared to the standard mode. This can reduce measurement errors for the diffusion length of minority carriers due to environmental variations over time. Smaller measurement errors for the diffusion length of minority carriers mean that the detection limit for the Fe concentration can be lowered.

[0006] US 2010 / 0 085 073 A1 discloses a measurement of iron concentration using an SPV method.

[0007] JP 2007-53123A discloses a method for determining the stabilization of the surface of a p-type silicon wafer that has been treated with hydrofluoric acid. In this method, the diffusion length of minority charge carriers is measured using a single-phase vaporization (SPV) technique with at least two different time constants. The ratio of the diffusion lengths measured for these different time constants is then used to determine whether the surface has been stabilized. Furthermore, it is mentioned that the SPV technique can also be used to determine the iron concentration, with a time constant of 100 ms being disclosed.

[0008] US Patent 2006 / 066324A1 discloses a further method for measuring a metal concentration, in particular iron concentration, which measures a diffusion length of minority charge carriers. SUMMARY (Technical Problem Statement)

[0009] In recent years, the properties required of electronic components have increased significantly. This situation has created a greater need to lower the detection limit for iron concentration in p-type silicon wafers. On the other hand, the time required for SPV measurement impacts the production throughput of p-type silicon wafers, so this time must be as short as possible. The inventors recognized the new challenges of meeting these two requirements simultaneously and have conducted several studies.

[0010] In their studies, they considered the use of Ultimate mode based on the description in JP 2004-503 100 A. It is certain that the measurement time can be readily reduced when using Ultimate mode instead of Standard mode due to the difference in measurement approaches. According to the inventors' studies, although the measurement time was naturally reduced by switching from Standard to Ultimate mode, the detection limit for Fe concentration was not lowered, contrary to the description in JP 2004-503 100 A; in fact, the detection limit for Fe concentration was found to be higher.

[0011] In view of the problem mentioned above, it would be helpful to provide a method for measuring the Fe concentration in a p-type silicon wafer using the SPV method, which would lower the detection limit of a measurement for the Fe concentration and allow the measurement to be performed in a short time. (Solution to the problem)

[0012] As described in detail below, SPV measurement has various measurement parameters in addition to the measurement modes. With the aim of solving the problem mentioned above, the inventor investigated the influence of the parameter settings, which are configured on an SPV meter in addition to the measurement modes, on the detection limit for Fe concentration and the time required to measure the Fe concentration. It should be noted that JP 2004-503 100 A only describes how the error for the diffusion length of minority carriers is reduced when the measurement is performed using Ultimate mode, while JP 2004-503 100 A does not consider the optimization of the other setting parameters.

[0013] Given this situation, the inventors initially varied the measurement parameters in the standard mode recommended by the SPV device manufacturer, based on known values ​​also recommended by the manufacturer. They then discovered that one parameter, the number of readouts, described below, significantly affects the detection limit for the Fe concentration in standard mode. Specifically, increasing the number of readouts can lower the detection limit for the Fe concentration. However, a higher number of readouts also means a longer measurement time. Therefore, in standard mode, the detection limit for the Fe concentration can be lowered by adjusting any measurement parameters under conditions with a long measurement time, while shorter measurement time conditions increase the detection limit for the Fe concentration.Consequently, a shorter measurement time and a reduced detection limit for the Fe concentration were not achieved simultaneously in standard mode.

[0014] The inventors then varied the measurement parameters in Ultimate mode and discovered the following: Initially, even in Ultimate mode, there was a general tendency for the detection limit for Fe concentration to be lower under longer measurement time conditions, while the detection limit for Fe concentration was higher under shorter measurement time conditions. However, it was discovered that since Ultimate mode allows the measurement time to be easily reduced if the measurement parameters in Ultimate mode meet certain conditions, the detection limit for Fe concentration could be lowered in Standard mode if the measurement parameters were set to the aforementioned known values ​​(conditions recommended by the SPV device manufacturer), and the measurement time could be shortened.

[0015] Unlike in the standard mode, in the Ultimate mode it was found that the parameters "time between readouts" and "time constant," described below, have a significant influence on the detection limit for the Fe concentration. Based on these findings, the inventors discovered specific conditions under which both the detection limit for the Fe concentration and the time required for measurement can be reduced. This led to this disclosure.

[0016] The following will be provided: (1) a method for measuring an Fe concentration in a p-type silicon wafer, based on a measurement using an SPV method, the method comprising: Performing the measurement in a measurement mode in which irradiation with a multitude of lights having different wavelengths is performed during the same period under conditions in which (i) the Time Between Readings is 35 ms or more and 120 ms or less, and the Time Constant is 20 ms or more, or the Time Between Readings is 10 ms or more and less than 35 ms, and the Time Constant is 100 ms or more, and (ii) the Number of Readings is 12 times or less, where the Number of Readings means the number of SPV signals acquired in one SPV measurement. “Time constant” means the acquisition time during which each SPV signal is acquired, out of the number of SPV signals. “Time between readouts” means the time interval between times at which successive SPV signals of the number of SPV signals are recorded. (Beneficial effect)

[0017] According to the SPV method for measuring the Fe concentration in a p-type silicon wafer, the detection limit of a measurement for the Fe concentration can be reduced, and the measurement can be performed in a short time. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In the accompanying drawings: is Fig. 1 a schematic view illustrating the structure of an SPV measuring device that can be used for a method for measuring the Fe concentration in a p-type silicon wafer, according to an embodiment of this disclosure; and is Fig.2 a graph illustrating the relationship between the detection limit for Fe concentration and the process time. DETAILED DESCRIPTION

[0019] One embodiment of this disclosure relates to a method for measuring the Fe concentration in a p-type silicon wafer based on measuring the Fe concentration in a silicon wafer using an SPV method (SPV measurement).

[0020] First, the method for determining the Fe concentration at specific sections on the surface of the p-type silicon wafer is described. Fe present in the p-type silicon wafer in a normal state combines with a dopant (for example, boron) through electrostatic force to form Fe-B pairs. Conversely, when the wafer is irradiated with intense light, Fe dissociates from B. The minority carrier diffusion length, determined by SPV measurement, represents the distance over which the minority carriers generated by the light used for irradiation in the SPV measurement can travel. The minority carriers disappear, for example, by being trapped by a trap state formed by Fe within the wafer.Trap states formed by Fe in a p-type silicon wafer exhibit Fe-B (iron-boron pairs), which are normally present, and Fei (interstitial Fe), which is formed by light irradiation. The trap states formed by Fe in different forms have different minority carrier trapping capabilities. In particular, Fe can trap minority carriers more readily, and the diffusion length is shorter in the dissociated state than in the normal state. By using this difference, the Fe concentration in the wafer can be determined as follows.

[0021] First, the SPV measurement is performed under normal conditions, and the diffusion length L is determined. FeB The SPV measurement is then performed in a dissociated state, and the diffusion length L is determined. Fei The concentration of Fe [Fe] is determined by minority carriers. This concentration can be calculated using the following formula. [Fe]=C×(1 / LFei−1 / LFeB), where C is a constant.

[0022] Therefore, a map of the Fe concentration in the wafer can be obtained by performing SPV measurements in a normal state and in a dissociated state on a variety of sections of the wafer surface. The process for dissociating Fe-B pairs is carried out, for example, using a common method, but not limited to, irradiation with a flash lamp.

[0023] The structure of an SPV measuring device used for SPV measurement is described below. Fig. Figure 1 is a schematic view illustrating an example of the structure of an analog SPV measuring device 100. The SPV measuring device 100 has an optical module 10, a probe 18, a lock-in amplifier 20, and a stage 22. The optical module 10 has a light source 12, a chopper 14, and a filter turret 16.

[0024] The light source 12, for example, consists of white LEDs, and an optical path is designed such that light emitted from the light source is directed to the surface of a wafer W placed on the stage 22. The chopper 14 is a circular element with a multitude of openings arranged in a circular pattern. The rotation of the chopper allows the light emitted from the light source 12 to have a specific frequency. In other words, the surface of the wafer W is intermittently illuminated with the light. The frequency of the resulting light is called the "chopping frequency" (CF), which is one of the measurement parameters. The CF is typically set between 500 Hz and 3000 Hz.

[0025] The filter turret 16 has apertures 16A to 16D, which are fitted with filters that transmit only light of different wavelengths. This allows the surface of the wafer W to be irradiated with light of specific wavelengths.

[0026] This illustrates Fig. 1. Consider a case where the optical module 10 is an analog module; alternatively, it can be a digital module. In the case where the optical module 10 is a digital module, a plurality of individual color LEDs, each with a different emission wavelength, are modularized, and the surface of the wafer W can be illuminated with light of specific wavelengths and frequencies by blinking the LEDs.

[0027] The wavelengths of the irradiated light can be any different wavelengths between 780 nm and 1004 nm. However, if SPV measurements are performed using light with two wavelengths, a combination of 780 nm and 1004 nm can be given as an example of the wavelengths, and if the SPV measurements are performed using light with four wavelengths, a combination of 780 nm, 914 nm, 975 nm, and 1004 nm can be given as an example.

[0028] The intensity (amount) of the irradiated light is set as the injection level, which is one of the measurement parameters. The amount of light at level 2 is typically 2 × 10⁻⁶. 12 (Atoms / cm² 3 ), and that of level 3 is 3 × 10 12 (Atoms / cm² 3 ), and one of these two parameters is used.

[0029] Probe 18 has a capacitive sensor at its end that continuously measures the capacitance formed between the surface of wafer W and probe 18. Before the SPV measurement, the surface of wafer W undergoes RF treatment, resulting in a positive charge. When wafer W is irradiated with light from light source 12, minority carriers (electrons for a p-type wafer) are generated within the wafer and migrate to the positively charged surface. Upon reaching the surface, the electrons are annihilated by the positive charges on the surface, causing the electrical potential of the surface to decrease, resulting in reduced capacitance. This decrease in capacitance is detected as an SPV signal. If several electrons are trapped by Fe within the wafer, the surface potential is less likely to decrease.

[0030] The lock-in amplifier 20 amplifies and acquires an SPV signal corresponding to the capacitance measured by the probe 18. Therefore, an SPV signal can be obtained. Moving the stage 22 allows the SPV measurements to be performed on a variety of sections of the wafer W's surface.

[0031] The SPV device can be a well-known SPV device, such as a FAaST 330 manufactured by Semilab-SDi LLC, or an SPV Station 1020 manufactured by Strategie Diagnostics Inc.

[0032] The following describes a procedure for SPV measurement and how the diffusion length is determined. First, SPV measurement is performed using light with a first wavelength (for example, 780 nm) to obtain an SPV signal corresponding to the light. The "penetration length" as a function of the wavelength of the irradiated light is represented on the x-axis, and the "amount of light / SPV signal" is represented on the y-axis. The measurement results are plotted on the graph. Next, SPV measurement is performed using light with a second wavelength (for example, 1004 nm), which differs from the first wavelength, to obtain an SPV signal corresponding to the light. The measurement results are plotted on the graph in a similar manner. The x-intercept of the straight line connecting the two plots obtained in this way can be determined as the "diffusion length."It should be noted that when SPV measurements are performed using three or more wavelengths, the x-axis intercept is calculated by approximation, such as by the least squares method, since three or more representations are obtained.

[0033] The measurement modes here include two modes: Standard Mode and Ultimate Mode. In Standard Mode, an SPV measurement is performed using a specific wavelength, and subsequent SPV measurements are performed sequentially using wavelengths that differ from both the preceding wavelength and from each other, so that the representations are obtained sequentially. In Ultimate Mode, however, irradiation with a variety of lights with different wavelengths is performed simultaneously in a single SPV measurement, such that the representations are obtained from this one measurement. In this case, the chopping frequencies of the wavelengths are made different from each other, resulting in 20 SPV signals in the lock-in amplifier, each with a different frequency; SPV signals corresponding to the respective wavelengths can therefore be obtained separately.

[0034] Here, the measurement parameters on which one embodiment of this disclosure focuses are described. Number of Readings (hereinafter referred to as "NR") means the number of SPV signals acquired in an SPV measurement. Time Constant (hereinafter referred to as "TC") means the acquisition time during which each SPV signal is acquired. Time Between Readings (hereinafter referred to as "TB") means the time interval (waiting period) between the times at which the signals are acquired.

[0035] Specific parameter meanings are described with reference to known conditions, such as those recommended for the FAaST 330 (digital) manufactured by Semilab-SDi LLC (standard mode, CF: 1600 ± 100 Hz, light intensity: level 3, NR: 12 times, TC: 20 ms, and TB: 20 ​​ms). In this case, irradiation is performed with light of the first wavelength (e.g., 780 nm), which is configured to have a CF of 1600 ± 100 Hz for a predetermined time recommended by the manufacturer. SPV signals are then acquired for 20 ms, followed by a 20 ms waiting period. This procedure is repeated 12 times to obtain 12 SPV signals. The average of these 12 SPV signals is used as the single SPV signal corresponding to the light of the first wavelength.The system is then irradiated with light of the second wavelength (for example, 1004 nm), which is configured to have a frequency control (CF) of 1600 ± 100 Hz for a predetermined time mentioned above. SPV signals are then acquired for 20 ms, followed by a 20 ms waiting period. This procedure is repeated 12 times to obtain 12 SPV signals. The average of these 12 SPV signals is used as the single SPV signal corresponding to the light of the second wavelength.

[0036] Subsequently, in Ultimate mode, under the following conditions: CF: 1600 ± 100 Hz, Light Intensity: Level 3, NR: 12 times, TC: 20 ms, and TB: 20 ​​ms, a measurement is performed as follows. In this case, irradiation with light having the first wavelength (for example, 780 nm) is generated to have a frequency within the range of CF1: 1600 ± 100 Hz, and light having the second wavelength (for example, 1004 nm) is generated to have a frequency of CF2, which is 50 Hz higher than CF1, simultaneously for a predetermined time recommended by the manufacturer. SPV signals are then acquired for 20 ms, followed by a waiting period of 20 ms. This procedure is repeated 12 times to obtain 12 SPV signals.From each SPV signal, one can separately obtain a first SPV signal corresponding to the light with the first wavelength and a second SPV signal corresponding to the light with the second wavelength; the average of the first SPV signals and the average of the second SPV signals are therefore used as SPV signals corresponding to the lights with the respective wavelengths.

[0037] Here, as demonstrated in experimental example 1 described below, under the conditions recommended above in standard mode, the detection limit for the Fe concentration was 1.0 × 10 9 / cm 3 The time required for measurement on a wafer was 28 minutes. Changing NR, TC, and TB to arbitrary values ​​in standard mode did not result in a detection limit for the Fe concentration of less than 1.0 × 10⁻⁶. 9 / cm 3, and a time required for measurement on a wafer of less than 28 minutes.

[0038] Here, as demonstrated in experimental example 2, in Ultimate mode the measurement parameters, which met certain conditions described below, resulted in a detection limit for the Fe concentration of less than 1.0 × 10 9 / cm 3 , and in a time required for measurement on a wafer of less than 28 minutes. In one embodiment of this disclosure, it is therefore important to perform SPV measurement in Ultimate mode under the following conditions.

[0039] First, TB is set to 35 ms or more and 120 ms or less, and TC is set to 20 ms or more (first set of conditions), or alternatively, TB is set to 10 ms or more and less than 35 ms, and TC is set to 100 ms or more (second set of conditions). Under the conditions recommended above, the sum of TB and TC is 40 ms in standard mode, while in one embodiment of this disclosure, the sum of TB and TC is at least 55 ms. Therefore, if TB and / or TC are longer than in conventional techniques, the detection limit for the Fe concentration can be lowered. The inventors have concluded that such a result may be caused as follows. In the case of Ultimate mode, the total amount of light applied to the wafer at any given time is twice the amount in the case of standard mode, so that the wafer W heats up readily due to the light irradiation.

[0040] However, if the sum of TB and TC (i.e., the length of time during which light irradiation is not performed) is longer than with conventional techniques, a rise in wafer temperature, such as at the time of SPV signal readout, can be suppressed. This may lower the detection limit for the Fe concentration.

[0041] Referring to the first set of conditions, even if TB is 35 ms or more and 120 ms or less, the detection limit for the Fe concentration cannot be lowered if TC is less than 20 ms. Similarly, if TC is 20 ms or more and less than 100 ms, the detection limit for the Fe concentration cannot be lowered if TB is less than 35 ms. If TB exceeds 120 ms, this not only increases the time required for a measurement on a wafer but also promotes the recombination of Fe-B pairs, thus increasing the detection limit for the Fe concentration. The first set of conditions is therefore necessarily fulfilled.

[0042] Referring to the second set of conditions, if TB is 10 ms or more and less than 35 ms, the detection limit for the Fe concentration cannot be lowered if TC is less than 100 ms. Furthermore, even if TC is 100 ms or more, the detection limit for the Fe concentration cannot be lowered if TB is less than 10 ms. When the second set of conditions is applied, the upper limit of TC is preferably 1000 ms. If TB exceeds 1000 ms, this not only increases the time required for a measurement on a wafer but also promotes the recombination of Fe-B pairs, thus increasing the detection limit for the Fe concentration.

[0043] Secondly, NR is set to 12 times or less. If NR exceeds 12 times, it increases the time required for a measurement on a wafer. It should be noted that under the first and second sets of conditions above, sufficient detection sensitivity for the Fe concentration was achieved when NR was set to one. EXAMPLES (Experimental Example 1: Standard Mode)

[0044] The SPV measurement was performed using a FAaST 330, manufactured by Semilab-SDi LLC, as an SPV instrument in standard mode, with CF set to 1584 Hz, light intensity set to level 3, and NR, TC, and TB set to the values ​​presented in Table 1. The irradiation wavelengths were set to 780 nm and 1004 nm.

[0045] The detection limit for the Fe concentration was determined using the following technique. A boron-doped p-type silicon wafer, in which Fe-B pairs were dissociated, was prepared as a blank wafer based on the description in JP 2011-054784 A, and nine points on the surface of this wafer were subjected to RF treatment followed by SPV measurement. The minority carrier diffusion length obtained from the measurements was defined as the diffusion length L. FeB The minority carrier was treated in a normal state. The silicon wafer was then irradiated with light from a flash lamp 12 times at 5-second intervals, followed by a 5-minute waiting period. SPV measurements were then performed again at the nine points on the surface, and the diffusion length L was determined. FeiThe concentration of minority carriers in a dissociated state was determined. This measurement was repeated 10 times without interruption. Subsequently, 10 Fe concentrations [Fe] were determined from the 10 respective diffusion lengths L. FeB and L Fei The values ​​obtained for each point were calculated based on the formula mentioned above. Furthermore, the mean X and the standard deviation σ of [Fe], which has negative values, were calculated for each point. |X + 3σ| was calculated for each point, and the maximum value |X + 3σ| was determined as the "detection limit for Fe concentration," and the results are presented in Table 1. It should be noted that the "Detection Limit Rating" field in Table 1 is based on the following criteria: ++: 15% or more lower than in the conventional example +: less than 15% lower than in the conventional example -: less than 15% higher than in the conventional example --: 15% or more higher than in the conventional example

[0046] The process time was determined using the following technique. The diffusion lengths L FeB and L Fei Fe concentrations [Fe] were determined for 177 points on the surface of a boron-doped p-type silicon wafer using a technique similar to that described in the previous paragraph, and the Fe concentrations for these 177 points were calculated based on the formula mentioned above, resulting in an Fe concentration map. The time required from loading to unloading the wafer is defined as the "process time," and the results are presented in Table 1. It should be noted that the "process time rating" field in Table 1 is based on the following criteria. ++: 15% or more shorter than in the conventional example +: less than 15% shorter than in the conventional example -: less than 15% longer than in the conventional example --: 15% or more longer than in the conventional example Table 1 Nr. TC(ms) TB(ms) NR (Number of times) mode Processing time (min.) Process time assessment Fe concentration detection limit ( / cm³) 3 ) Recording limit assessment classification 1-1 20 20 12 standard 28 N / A 1,00E+09 N / A Traditional example 1-2 20 10 6 standard 25 + 1,40E+09 - Comparison example 1-3 10 50 12 standard 31 - 1,02E+09 - Comparison example 1-4 50 100 24 standard 58 - 4,14E+08 ++ Comparison example 1-5 10 10 24 standard 26 + 1,15E+09 - Comparison example 1-6 50 50 6 standard 32 - 7,59E+08 ++ Comparison example 1-7 50 10 24 standard 31 - 8,62E+08 + Comparison example 1-8 50 20 24 standard 34 - - 6,43E+08 ++ Comparison example 1-9 50 30 24 standard 37 - - 5,82E+08 ++ Comparison example 1-10 50 40 24 standard 41 - - 4,83E+08 ++ Comparison example 1-11 100 100 1 standard 36 - - 1,09E+09 - Comparison example

[0047] As shown in Table 1 and Fig. As stated in 2, under recommended conditions in standard mode (conventional example, No. 1-1) the detection limit for the Fe concentration was 1.0 × 10 9 / cm 3 The process time was 28 minutes. Furthermore, it was found that increasing NR lowered the detection limit for the Fe concentration. However, increasing NR would increase the process time. The relationship between the detection limit for the Fe concentration and the process time was derived from the measurement results in Table 1 and is shown in Fig.Given the above, a favorable detection limit for the Fe concentration and a favorable process time cannot be achieved simultaneously. Changing NR, TC, and TB to arbitrary values ​​did not result in an Fe concentration below 1.0 × 10⁻⁶ for the detection limit. 9 / cm 3 and in a process time of less than 28 minutes. Furthermore, even when TC and TB were increased, as in the comparison examples with numbers 1 to 11, the detection limit could not be reduced in this example. (Experimental Example 2: Ultimate Mode)

[0048] The SPV measurement was performed using a FAaST 330, manufactured by Semilab-SDi LLC, as a standard-mode SPV instrument. CF1 was set to 1584 Hz, CF2 to 1634 Hz, and the light intensity was set to level 3. NR, TC, and TB were set to the values ​​presented in Table 2. The irradiation wavelengths were set to 780 nm and 1004 nm. The Fe concentration detection limit and process time were determined using a similar technique to that used in Experimental Example 1, and the results are presented in Table 2. The evaluation results are also presented in Table 2, based on similar criteria. The relationship between the Fe concentration detection limit and the process time was derived from the measurement results in Table 2 and is also shown in [Table 2]. Fig. 2 given. Table 2 Nr. TC(ms) TB(ms) NR (Number of times) mode Processing time (min.) Process time assessment Fe concentration detection limit ( / cm³) 3 ) Recording limit assessment classification 1-1 20 20 12 standard 28 N / A 1,00E+09 N / A Traditional example 2-1 20 50 24 Ultimate 30 - 4,34E+08 ++ Comparison example 2-2 10 100 6 Ultimate 25 + 1,58E+09 - Comparison example 2-3 50 10 24 Ultimate 24 + 1,61E+09 - Comparison example 24 50 20 24 Ultimate 25 + 1,31E+09 - Comparison example 2-5 50 30 24 Ultimate 27 + 1,10E+09 - Comparison example 2-6 10 10 1 Ultimate 21 ++ 4,55E+09 - Comparison example 2-7 10 10 6 Ultimate 22 ++ 4,08E+09 - Comparison example 2-8 50 10 1 Ultimate 21 ++ 1,02E+09 - Comparison example 2-9 20 10 6 Ultimate 22 ++ 3,47E+09 - Comparison example 2-10 10 10 12 Ultimate 22 ++ 1,64E+09 - Comparison example 2-11 50 20 6 Ultimate 22 ++ 1,08E+09 - Comparison example 2-12 20 10 12 Ultimate 21 ++ 2,14E+09 - Comparison example 2-13 100 10 1 Ultimate 21 ++ 8,75E+08 + Example 2-14 50 10 12 Ultimate 22 ++ 1,30E+09 - Comparison example 2-15 100 10 12 Ultimate 22 ++ 9,69E+08 + Example 2-16 50 35 1 Ultimate 19 ++ 9,30E+08 + Example 2-17 20 20 1 Ultimate 21 ++ 1,49E+09 - Comparison example 2-18 50 40 1 Ultimate 22 ++ 7,00E+08 ++ Example 2-19 100 100 1 Ultimate 22 ++ 8,04E+08 ++ Example 2-20 50 35 6 Ultimate 23 ++ 6,31E+08 ++ Example 2-21 20 20 6 Ultimate 22 ++ 1,40E+09 - Comparison example 2-22 50 40 6 Ultimate 23 ++ 9,29E+08 + Example 2-23 100 100 6 Ultimate 25 + 3,32E+08 ++ Example 2-24 20 20 12 Ultimate 22 ++ 1,56E+09 - Comparison example 2-25 100 25 1 Ultimate 22 ++ 9,30E+08 + Example 2-26 50 25 1 Ultimate 21 ++ 1,58E+09 - Comparison example 2-27 50 25 6 Ultimate 22 ++ 1,43E+09 - Comparison example 2-28 20 25 1 Ultimate 22 ++ 1,11E+09 - Comparison example 2-29 20 25 6 Ultimate 22 ++ 1,06E+09 - Comparison example 2-30 50 30 1 Ultimate 22 ++ 1,93E+09 - Comparison example 2-31 50 30 6 Ultimate 23 ++ 1,42E+09 - Comparison example 2-32 20 30 1 Ultimate 21 ++ 1,46E+09 - Comparison example 2-34 50 35 12 Ultimate 24 + 8,18E+08 ++ Example 2-35 20 50 12 Ultimate 25 + 8,22E+08 ++ Example 2-36 50 120 1 Ultimate 22 ++ 7,75E+08 ++ Example 2-37 50 120 6 Ultimate 26 + 6,24E+08 ++ Example

[0049] As shown in Table 2 and Fig. As can be seen in Figure 2, if NR, TC, and TB in Ultimate mode were the same as in the conventional example No. 1-1 (comparative examples, Nos. 2 to 24), a shorter processing time was achieved, but the detection limit for the Fe concentration was higher. However, if TB was set to 35 ms or more and 120 ms or less, and TC was set to 20 ms or more (first set of conditions), or alternatively, if TB was set to 10 ms or more and less than 35 ms, and TC was set to 100 ms or more (second set of conditions), and NR was set to 12 times or less in Ultimate mode, an Fe concentration for the detection limit of less than 1.0 × 10⁻⁶ was achieved. 9 / cm 3 and a processing time of less than 28 minutes was achieved. COMMERCIAL APPLICABILITY

[0050] According to a method for measuring the Fe concentration in a p-type silicon wafer by the SPV method of this disclosure, the detection limit of a measurement for the Fe concentration can be reduced, and the measurement can be performed in a short time. REFERENCE MARK LIST 100 SPV measuring device 10 Optical Module 12 light sources 14 choppers 16 filter turrets 18 probe 20 Lock-In Amplifiers 22 Object table W silicon wafer

Claims

[1] Method for measuring an iron concentration in a p-type silicon wafer (W) based on a measurement using a surface photovoltage, hereinafter referred to as SPV, method, wherein the method for measuring comprises: Performing the measurement in a measurement mode in which the p-type silicon wafer (W) is irradiated with a plurality of lights having different wavelengths during the same time period, the measurement being performed under the following conditions: (i) the time between readouts is 35 ms or more and 120 ms or less, and a time constant is 20 ms or more, or the time between readouts is 10 ms or more and less than 35 ms and the time constant is 100 ms or more, and (ii) a number of readouts is 12 times or less, where the number of readouts means the number of SPV signals that are captured in an SPV measurement, The time constant represents the acquisition time during which each SPV signal is acquired, out of the number of SPV signals. The time between readouts means the time interval between times at which successive SPV signals are recorded.

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