JP2019114662A - MEASURING METHOD OF Fe CONCENTRATION IN P-TYPE SILICON WAFER AND SPV MEASURING APPARATUS - Google Patents

Abstract

To provide a measuring method of Fe concentration in a p-type silicon wafer by an SPV method capable of improving measurement accuracy of Fe concentration of 1×10/cmor less.SOLUTION: A measuring method of an Fe concentration in a p-type silicon wafer is performed under an atmosphere in which the total concentration of Na, NH, and Kis 1.750 μg/mor less, and the total concentration of F, Cl, NO, PO, Br, NO, and SOis 0.552 μg/mor less to determine the Fe concentration in the p-type silicon wafer on the basis of the measurement by an SPV method performed on the p-type silicon wafer.SELECTED DRAWING: None

Description

  The present invention relates to a method of measuring Fe concentration in a p-type silicon wafer by SPV method (Surface Photo-Voltage), and an SPV measuring device.

  Contamination of p-type silicon wafers with Fe adversely affects the characteristics of devices made from the wafers. Therefore, methods have been developed to simply evaluate the Fe concentration in p-type silicon wafers. As one of the methods, there is known a method of electrically measuring the diffusion length of minority carriers by the SPV method and determining the Fe concentration in a p-type silicon wafer from the measurement result.

  In the SPV method, light of a specific wavelength is irradiated to a p-type silicon wafer, surface electromotive force (SPV signal) of the wafer at that time is measured, and the diffusion length of minority carriers in the wafer is determined. This is hereinafter also referred to simply as "SPV measurement". The SPV method is an excellent method that can measure non-contact and nondestructively in addition to having a short measurement time as compared with other methods.

  In SPV measurement, it is known that there are two measurement modes, Standard Mode and Ultimate Mode. In the SPV method, it is necessary to perform the above-described SPV measurement using light of a plurality of different wavelengths. Standard mode is a general method of performing SPV measurement using one wavelength and then performing SPV measurement using another wavelength sequentially. Ultimate mode is a special method that simultaneously emits light of different wavelengths and performs SPV measurement at one time.

  In Patent Document 1, the SPV measurement is performed in the Ultimate mode, and the detection limit of Fe concentration is lowered by setting three measurement parameters of Time Between Readings, Time Constant and Number of Readings in a predetermined numerical range, And the technique which makes it possible to measure in a short time is described.

International Publication No. 2017/061072

  The installation environment of the SPV measuring device when performing such SPV measurement is conventionally recommended to be temperature: 24 ± 2 ° C., relative humidity: 30 to 50%, and cleanliness: class 7 (JIS standard) This is described in the manufacturer's specification of a general SPV measuring device. Conventionally, SPV measurement has generally been performed under this recommended environment. Here, the present inventors came to recognize that there are the following problems.

That is, as long as the SPV measurement is performed under the above-mentioned recommended environment, sufficient measurement accuracy is obtained in the determination of the Fe concentration of 1 × 10 ⁹ / cm ³ order or 1 × 10 ¹⁰ / cm ³ order. However, in the determination of Fe concentration of 1 × 10 ⁹ / cm ³ or less, even if SPV measurement is performed under the above-mentioned recommended environment, measurement values when SPV measurement of the same wafer is performed multiple times vary, that is, sufficient It turned out that a good measurement accuracy could not be obtained. The conventional recommended environment considers only temperature, humidity, and air particles (cleanness), and does not define any other conditions. Further, also in Patent Document 1, the installation environment of the SPV measurement device is not considered at all.

Therefore, in view of the above problems, the present invention provides a method of measuring Fe concentration in a p-type silicon wafer by SPV method and an SPV measuring device capable of improving the measurement accuracy of Fe concentration of 1 × 10 ⁹ / cm ³ or less. The purpose is to

In order to solve the above-mentioned subject, the present inventor optimizes the installation environment of the SPV measuring device at the time of performing SPV measurement from viewpoints other than temperature, humidity, and air particles (cleanliness), and 1x10 ⁹ It was earnestly examined whether it was possible to improve the measurement accuracy of Fe concentration in a low concentration region such as not more than ³ cm ³ . As a result, the ion concentration of the installation environment of the SPV measuring device influences the measurement accuracy of the Fe concentration, and by setting the ion concentration to a predetermined value or less, the measurement accuracy of the Fe concentration of 1 × 10 ⁹ / cm ³ or less Found that it can improve.

The essential features of the present invention completed based on the above findings are as follows.
(1) In order to determine the Fe concentration in the p-type silicon wafer based on the measurement by the SPV method performed on the p-type silicon wafer,
The measurement indicates that the total concentration of Na ⁺ , NH ₄ ⁺ and K ⁺ is 1.750 μg / m ³ or less, and F ⁻ , Cl ⁻ , NO ₂ ⁻ , PO ₄ ³⁻ , Br ⁻ , NO ₃ ⁻ and SO _{3 4. A} method of measuring Fe concentration in a p-type silicon wafer, characterized in that the method is performed under an atmosphere in which the total concentration of ^2- is not more than 0.552 μg / m ³ .

(2) An SPV measuring device for determining the Fe concentration in a p-type silicon wafer based on measurement by the SPV method,
A measurement stage for placing a p-type silicon wafer during SPV measurement;
An optical module for irradiating the p-type silicon wafer with light;
A probe for measuring a capacitance generated between a capacitance sensor provided at a tip and the surface of the p-type silicon wafer;
A lock-in amplifier for amplifying and detecting an SPV signal corresponding to the capacitance measured by the probe;
Calibration chip for calibration to reduce measurement error;
A separation stage on which the p-type silicon wafer is placed when the Fe-B pair in the p-type silicon wafer is separated;
A flash lamp for separating Fe-B pairs in the p-type silicon wafer;
A robot arm that transports and unloads the p-type silicon wafer with respect to the measurement stage and the separation stage;
A robot controller that controls the robot arm;
Have
A first housing that accommodates the measurement stage, the probe, and the calibration tip for calibration;
A second housing accommodating the light module and the lock-in amplifier;
A third housing accommodating the deviation stage and the flash lamp;
A fourth housing housing the robot arm and the robot controller;
And have
A first chemical filter and a second chemical filter are respectively installed on the windward side of the air flow with respect to the first housing and the third housing, and the inside of the first housing and the third housing is , The total concentration of Na ⁺ , NH ₄ ⁺ and K ⁺ is 1.750 μg / m ³ or less, F ⁻ , Cl ⁻ , NO ₂ ⁻ , PO ₄ ³⁻ , Br ⁻ , NO ₃ ⁻ and SO ₄ ²⁻ An SPV measurement device characterized in that the atmosphere has a total concentration of 0.552 μg / m ³ or less.

(3) A third chemical filter is installed on the windward side of the air flow with respect to the fourth case, and the total concentration of Na ⁺ , NH ₄ ⁺ and K ⁺ is 1. The atmosphere was 750 μg / m ³ or less, and the total concentration of F ⁻ , Cl ⁻ , NO ₂ ⁻ , PO ₄ ^3- , Br ⁻ , NO ₃ ⁻ and SO ₄ ^2- was 0.552 μg / m ³ or less. And the SPV measuring device as described in said (2).

  (4) The SPV measurement device according to (2), wherein the first chemical filter and the second chemical filter are disposed above the first housing and the third housing, respectively.

  (5) The SPV measurement device according to (3), wherein the third chemical filter is disposed above the fourth housing.

According to the method of measuring the Fe concentration in a p-type silicon wafer and the SPV measuring device according to the SPV method of the present invention, the measurement accuracy of the Fe concentration of 1 × 10 ⁹ / cm ³ or less can be improved.

It is a schematic diagram which shows the structure of the SPV measuring apparatus 100 by one Embodiment of this invention. It is the schematic diagram which extracted and showed only the structure relevant to the SPV measurement which measures Fe concentration in a p-type silicon wafer about the SPV measuring apparatus 100. FIG. It is a graph which shows the change rate of the Signal value acquired using the calibration chip for calibration.

  One embodiment of the present invention relates to a method of determining the Fe concentration in a silicon wafer based on measurement (SPV measurement) performed on a p-type silicon wafer by SPV method.

  First, how to determine the Fe concentration at a specific place in the plane of a p-type silicon wafer will be described. Under normal conditions, Fe present in a p-type silicon wafer is electrostatically coupled to a dopant (for example, boron) to form an Fe-B pair. On the other hand, when the wafer is irradiated with strong light, Fe is separated from B. The diffusion length of the minority carriers obtained as a result of the SPV measurement means the distance that the minority carriers generated by the light irradiated in the SPV measurement can move before disappearing. The minority carriers are trapped and annihilated, for example, by trap levels formed by Fe in the wafer. The level which Fe forms in a p-type silicon wafer includes Fe-B (iron boron pair) which usually exists, and Fei (interstitial iron) formed by light irradiation. The trap levels created by each differ in the ease of capturing minority carriers. Therefore, Fe tends to trap minority carriers more easily in the above separated state than in the above normal state, and the diffusion length becomes smaller. Using this difference, the Fe concentration in the wafer can be determined as follows.

First, SPV measurement is performed in a normal state to determine the diffusion length L _FeB of minority carriers. Next, SPV measurement is performed in the separated state to determine the diffusion length L _Fei of the minority carrier. The Fe concentration [Fe] can be calculated by the following equation (1).
[Fe] = C × (1 / L _Fei ² − 1 / L _FeB ² ) (1)
However, C is a constant.

  Therefore, a map of the Fe concentration in the wafer can be obtained by performing the SPV measurement in a normal state and in a separated state at a plurality of locations in the wafer surface. The treatment for separating the Fe-B pair is a standard method and is not particularly limited. For example, irradiation with a flash lamp can be mentioned.

  Next, with reference to FIG. 2, a configuration related to SPV measurement will be described for the SPV measurement device 100 according to an embodiment of the present invention. The SPV measurement apparatus 100 includes an optical module 10, a probe 18, a lock-in amplifier 20, and a measurement stage 22. The light module 10 has a light source 12, a chopper 14 and a filter wheel 16.

  The light source 12 is, for example, a white LED, and the light path is set so that the light emitted therefrom is irradiated onto the surface of the p-type silicon wafer W mounted on the measurement stage 22. The chopper 14 is a disk member having a plurality of holes in a circumferential shape, and when it rotates, gives a frequency to the light emitted from the light source 12. That is, light is intermittently applied to the surface of the p-type silicon wafer W. The frequency of light given here is defined as "Chopping Frequency (CF)" and is one of measurement parameters. CF is usually set to about 500 to 3000 Hz.

  In the filter wheel 16, filters that allow only light of different wavelengths to pass through are installed in the holes 16 </ b> A to 16 </ b> D, so that light of specific wavelengths can be irradiated to the surface of the p-type silicon wafer W.

  Here, FIG. 2 shows the case where the optical module 10 is an analog type, but may be a digital type. In the case of the digital type, it is possible to irradiate light of a specific wavelength onto the surface of the p-type silicon wafer W at a specific frequency by modularizing a plurality of single color LEDs having different emission wavelengths and blinking each LED.

  The wavelength of the irradiation light is not particularly limited as long as it is a plurality of wavelengths between 780 and 100 nm, but when SPV measurement is performed with light of two types of wavelengths, a combination of 780 nm and 1004 nm can be exemplified. In the case of performing SPV measurement with light of four types of wavelengths, a combination of 780 nm, 914 nm, 975 nm, and 1004 nm can be exemplified.

The intensity (light amount) of the irradiation light is set as the injection level and is one of the measurement parameters. Generally, the light quantity of Level 2 is 2 × 10 ¹² (atoms / cc), and the light quantity of Level 3 is 3 × 10 ¹² (atoms / cc), and either of these is used.

  The probe 18 has a capacitance sensor at its tip and constantly measures the capacitance generated between the surface of the p-type silicon wafer W and the probe 18. Prior to the SPV measurement, the surface of the p-type silicon wafer W is subjected to HF treatment to positively charge the surface. When the light from the light source 12 is irradiated to the wafer W, minority carriers (electrons because of p-type) are generated in the wafer and move toward the positively charged surface. When the electrons reach the surface, they cancel the positive charge on the surface, so the potential on the surface decreases, and as a result, the capacitance also decreases. The difference in capacitance at this time is detected as an SPV signal. The more electrons that are trapped in Fe in the p-type silicon wafer, the lower the surface potential.

  The lock-in amplifier 20 amplifies and detects the SPV signal corresponding to the capacitance measured by the probe 18. Thus, the SPV signal can be obtained. By moving the measurement stage 22, it is possible to perform SPV measurement at a plurality of locations in the p-type silicon wafer W plane.

  Examples of SPV devices include known SPV devices, for example, FAaST 330 manufactured by Semilab-SDi LLC, and SPV-Station-1020 manufactured by Strategic Diagnostics.

  Next, the method of SPV measurement and how to obtain the diffusion length will be described. First, SPV measurement is performed using light of a first wavelength (for example, 780 nm) to obtain an SPV signal corresponding to the light. Here, the “penetration length” depending on the wavelength of the irradiation light is taken on the X axis, the “light quantity / SPV signal” is taken on the Y axis, and the measurement results are plotted. Subsequently, SPV measurement is performed using light of a second wavelength (for example, 1004 nm) different from the first wavelength to obtain an SPV signal corresponding to the light. Then, the measurement results are plotted in the same manner. The X-intercept when two plots obtained in this way are connected by a straight line can be taken as the "diffusion length". When SPV measurement is performed at three or more types of wavelengths, three or more plots are obtained, so the X-intercept is determined by an approximation process such as the least squares method.

  Here, there are two types of measurement modes, Standard Mode and Ultimate Mode. In the Standard mode, the above plots are sequentially obtained because SPV measurement using a certain wavelength is performed and then SPV measurement using another wavelength is sequentially performed. On the other hand, in the Ultimate mode, light of a plurality of different wavelengths is emitted during the same period, and the SPV measurement is performed at one time, so the above plot can be obtained by one measurement. In this case, by making the chopping frequency of light different for each wavelength, SPV signals having different frequencies can be obtained in the lock-in amplifier 20, so SPV signals corresponding to the respective wavelengths can be separated and obtained. The measurement mode is not particularly limited in the present embodiment.

Here, in the present embodiment, SPV measurement is carried out as follows ^: the total concentration of Na ⁺ , NH ₄ ⁺ and K ⁺ is not more than 1.750 μg / m ³ , F ⁻ , Cl ⁻ , NO ₂ ⁻ , PO ₄ ^3- , Br ^-, NO ₃ ^- and SO ₄ total concentration of ² it is imperative that conducted in an atmosphere at 0.552μg / m ³ or less. That is, in the present embodiment, by reducing the ion concentration in the SPV measurement atmosphere, it is possible to improve the measurement accuracy of the Fe concentration of 1 × 10 ⁹ / cm ³ or less.

The following can be considered as a mechanism by which such an effect is obtained. First, with regard to anions, as described above, in SPV measurement of p-type silicon wafers, it is necessary to positively passivate the surface by pretreatment such as HF cleaning. Here, when the acid-based gas (anion) adheres to the surface passivation (weak charge), the measurement value of the diffusion length varies. And, in the case of measurement of Fe concentration of 1 × 10 ⁹ / cm ³ or less, the difference in diffusion length before and after divergence becomes smaller (L _FeB LL _Fei ), and therefore the influence of measurement variation of diffusion length becomes large. Therefore, it is considered that the removal of the anion stabilizes the measurement of the diffusion length and can improve the quantification of the Fe-B level density.

  Next, with regard to the cation, the SPV measurement device incorporates a built-in calibration chip for calibrating the device, and this chip is an n-type silicon wafer. In n-type silicon wafers, the surface is negatively passivated in reverse to p-type. If an alkaline gas (cation) is present in the measurement atmosphere, the measurement accuracy of the calibration chip is degraded, which affects the calibration of the diffusion length measurement. Therefore, by removing the cation, it is considered that the absolute value of the diffusion length can be ensured and the quantitativity of the Fe-B level density can be improved.

In the silicon wafer manufacturing process, sodium hydroxide or potassium hydroxide is mainly used as an alkaline etching solution, and hydrofluoric-nitric acid is mainly used as an acid etching solution. Bromate may be added to the alkaline etching solution, and phosphoric acid or sulfuric acid may be added to the acid etching solution. In addition, ammonia water, hydrochloric acid and hydrogen peroxide are mainly used as cleaning solutions for wafers. Considering the gas generated when using these chemicals, three of Na ⁺ , NH ₄ ⁺ and K ⁺ as cations, F ⁻ , Cl ⁻ , NO ₂ ⁻ , PO ₄ ³⁻ , Br ⁻ , NO ₃ as anions ^- and it is sufficient to consider SO ₄ seven ^2. Furthermore, Na ⁺ and Cl sea breeze due to the outside air ^- but contains ions such as, there is no problem if monitoring the previously mentioned ions.

  As one mode which makes the ion concentration of SPV measurement atmosphere as mentioned above, setting the ion concentration of the installation environment of a SPV measuring device as mentioned above is mentioned. Specifically, a chemical filter such as a cation filter for removing cations or an anion filter for removing anions is installed in a clean room where the SPV measurement device is installed, and the ion concentration of the atmosphere in the clean room is made as described above. As a cation filter, "Purelight" PF590F4H by Nippon Puretex Co., Ltd., PL-C-25-4 GI by Dan-Takuma, etc. can be illustrated. As an anion filter, "Purelight" P592E5H manufactured by Japan Puretex Co., Ltd., PL-A-30-4 GO manufactured by Dan Takuma Co., Ltd., and the like can be exemplified. The installation position of the chemical filter with respect to the clean room may be appropriately determined from the viewpoint of suitably reducing the ion concentration of the atmosphere in the clean room. Generally, the air in the clean room is composed of circulating air and outside air intake air for compensating for pressure loss. The circulating air is cleaned by passing through a HEPA filter installed in the middle of the air flow formed by the circulating fan (preferably the ceiling of the clean room) and introduced into the clean room. The air introduced from the outside air intake port is also designed to be led to the circulating fan. Therefore, it is preferable that the chemical filter be installed in the outside air intake and further be installed between the circulating fan and the HEPA filter.

  As another aspect which makes the ion concentration of SPV measurement atmosphere as above, setting the atmosphere of the specific space of SPV measuring device 100 used for measurement to the above-mentioned ion concentration is mentioned. Hereinafter, the aspect will be described with reference to FIG.

  The SPV measurement apparatus 100 is divided into a plurality of spaces by a plurality of housings. The first housing 38 accommodates the measurement stage 22 and the probe 18 already described with reference to FIG. 2 and the calibration chip 24 for calibration to reduce measurement errors. The second housing 40 houses the optical module 10 and the lock-in amplifier 20 already described with reference to FIG. The third casing 42 has a separation stage 26 on which the p-type silicon wafer is placed when the Fe-B pair in the p-type silicon wafer is separated, and the Fe-B pair in the p-type silicon wafer A flash lamp 28 for separating is accommodated. The fourth case 44 includes a robot arm 30 for transporting and unloading a p-type silicon wafer to and from the measurement stage 22 and the separation stage 26, a robot controller 32 for controlling the robot arm 30, and a notch of the p-type silicon wafer And an aligner 34 for aligning the positions of The fifth housing 46 houses a control computer 36 for controlling the entire apparatus.

  The p-type silicon wafer W is transported as follows and subjected to SPV measurement. First, a plurality of p-type silicon wafers W accommodated in a load port (not shown) are mounted one by one on the robot arm 30 installed in the fourth housing 44, and the positions of the notches can be aligned by the aligner 34. . Next, the robot arm 30 transports it into the first housing 38 and places it on the measurement stage 22. Next, SPV measurement is performed on the measurement stage 22 in a normal state. Next, it is carried out of the first housing 38 by the robot arm 30, transported into the third housing 42, and placed on the separation stage 26. Next, the light is irradiated with the flash lamp 28 on the separation stage 26, and the separation process is performed to be in the separated state. Next, the robot is taken out of the third housing 42 by the robot arm 30, conveyed again into the first housing 38, and placed on the measurement stage 22. Next, SPV measurement is performed on the measurement stage 22 in a separated state. Finally, the robot arm 30 carries it out of the first housing 38, unloads it from the SPV measuring device 100, and returns to the load port.

Here, the first chemical filter 48 and the second chemical filter 50 are installed on the windward side of the air flow with respect to the first housing 38 and the third housing 42, respectively. The total concentration of Na ⁺ , NH ₄ ⁺ and K ⁺ is less than 1.750 μg / m ^{3 in the} interior of the rod 42, and F ⁻ , Cl ⁻ , NO ₂ ⁻ , PO ₄ ³⁻ , Br ⁻ , NO ₃ ⁻ and SO ₄ total concentration of ² it is imperative that an atmosphere is 0.552μg / m ³ or less. In the SPV measurement, it is necessary to control at least the atmosphere in the first housing 38 for actually performing the measurement and the atmosphere in the third housing 42 for performing the separation process. In this manner, by controlling the atmosphere in the first and third housings, ions are not deposited on the measurement stage 22 or the dissociation stage 26 and are not attached to the back surface of the wafer, so that the measurement value is measured. Not adversely affect As the first chemical filter 48 and the second chemical filter 50, the above-described cation filter or anion filter can be suitably used.

  Further, from the viewpoint of further improving the measurement accuracy, it is preferable that the third chemical filter 52 be installed on the windward side of the air flow with respect to the fourth housing 44 and the inside of the fourth housing 44 be also the above atmosphere. . As a result, ions do not deposit on the robot arm 30 in the fourth housing 44 and adhere to the back surface of the wafer, thereby further improving the measurement accuracy.

  The first housing 38, the third housing 42 and the fourth housing 44 may be integrated so as to define one measurement space (measurement area, separation processing area, and transfer area).

  Further, since the turbulent flow is unlikely to occur in the air flow, the first, second and third chemical filters 48, 50 and 52 are located above the first, third and fourth casings 38, 42 and 44, respectively. It is preferable to install.

(Invention example)
An SPV measuring device (FAaST 330 (digital type) manufactured by Semilab-SDi LLC) was installed in a clean room. In the clean room, an anion filter (manufactured by Nippon Puretech Co., Ltd .: Purelight P592E5H) and a cation filter (manufactured by Japan Puretech Co., Ltd .: Purelight PF590F4H) were newly installed to reduce the ion concentration. Table 1 shows the ion concentration measured by the following method. No. 1 to 6 are measured on different days. In addition, as environmental conditions other than ion concentration, the temperature recommended by the manufacturer: 24 ± 2 ° C., relative humidity: 30 to 50%, and cleanliness: class 7 (JIS standard).

<Method for measuring ion concentration>
The measurement of the ion concentration was performed by a pure water impinger bubbling method.
Pure water: 100 mL
-Aspiration speed: 1 L / min-Aspiration time: 360 minutes-Analyzer: Ion chromatography For conversion to the ion concentration in the atmosphere in 1 m ³ , the following conversion equation was used.
Analysis value [ppb] × amount of recovered pure water [mL] ÷ amount of suction [m ³ ] = ion concentration [μg / m ³ ]

^Three p-type silicon wafers with an Fe concentration of 10 ⁸ / cm ^{3, three} p-type silicon wafers with an Fe concentration of 10 ⁹ / cm ^{3 in the} first half, and an Fe concentration of 10 ⁹ / cm ^{3 in the} second half to 10 ¹⁰ / It was prepared a total of nine three p-type silicon wafer cm ³ order. Table 1 No. Under the atmosphere of 1 to 6, Fe concentration at 177 points in the plane of each wafer was measured three times using the above-mentioned SPV measuring device. The measurement conditions were set as manufacturer recommended conditions, and the irradiation wavelengths were set to 780 nm and 1004 nm.

<Evaluation of measurement accuracy>
For each wafer, three variations of the average Fe concentration of in-plane 177 points (dispersion value of three average Fe concentrations / 3 average value of average Fe concentrations x 100 times) are shown in Table 2 as CV values. . The CV value is preferably 10% or less.
In addition, the number of missing points (Undefine points) where L _Fei > L _FeB among the measured values of 177 points of each wafer was counted, and the average of the three times was shown in Table 3 as an average UD value.
In Tables 2 and 3, wafers with an Fe concentration of 10 ⁸ / cm ³ order are “WF 1 to ³ ”, those with an Fe concentration of 10 ⁹ / cm ³ half order are “WF 4 to 6”, and Fe concentration is 10 Wafers in the second half of ⁹ / cm ³ to 10 ¹⁰ / cm ³ were displayed as “WF 7 to 9”. The average value of the average Fe concentration of three times of each wafer measured according to the invention example is shown in Table 4.
Further, separately from the above-mentioned SPV measurement, the measurement of the Signal value using the calibration chip for calibration was performed daily for one month, and the change rate was determined with the Signal value on the first day as 1. The results are shown in FIG.

(Comparative example 1)
The measurement accuracy was evaluated in the same manner as in the invention example except that the chemical filter was not installed in the clean room and the ion concentration was not reduced. The results are shown in Table 1.

(Comparative example 2)
The measurement accuracy was evaluated by the same method as in the invention example and the SPV measurement apparatus of the same type as the invention example installed in a clean room where the chemical filter in a factory different from the comparative example 1 was not installed. The results are shown in Table 1.

<Evaluation result>
As shown in Tables 2 and 3, in the invention example, the CV value is suppressed to 10% or less and the average UD value is suppressed to almost zero even at an Fe concentration of 1 × 10 ⁹ / cm ³ or less. . On the other hand, in Comparative Examples 1 and 2, the CV value exceeds 10% at an Fe concentration of 1 × 10 ⁹ / cm ³ or less, and the average UD value is also large. Further, as shown in FIG. 3, in the invention example, the change of the Signal value is small. On the other hand, in Comparative Examples 1 and 2, the change in Signal value is large, and in Comparative Example 2 in which the number of cations is large, the amount of decrease in Signal value is particularly large.

According to the method of measuring the Fe concentration in a p-type silicon wafer and the SPV measuring device according to the SPV method of the present invention, the measurement accuracy of the Fe concentration of 1 × 10 ⁹ / cm ³ or less can be improved.

100 SPV measuring apparatus 10 light module 12 light source 14 chopper 16 filter wheel 18 probe 20 lock-in amplifier 22 measurement stage 24 calibration tip for calibration 26 separation stage 28 flash lamp 30 robot arm 32 robot controller 34 aligner 36 control computer 38 1st Housing 40 Second housing 42 Third housing 44 Fourth housing 46 Fifth housing 48 First chemical filter 50 Second chemical filter 52 Third chemical filter W p-type silicon wafer

Claims (5)

In order to determine the Fe concentration in the p-type silicon wafer based on the measurement by the SPV method performed on the p-type silicon wafer,
The measurement indicates that the total concentration of Na ⁺ , NH ₄ ⁺ and K ⁺ is 1.750 μg / m ³ or less, and F ⁻ , Cl ⁻ , NO ₂ ⁻ , PO ₄ ³⁻ , Br ⁻ , NO ₃ ⁻ and SO _{3 4. A} method of measuring Fe concentration in a p-type silicon wafer, characterized in that the method is performed under an atmosphere in which the total concentration of ^2- is not more than 0.552 μg / m ³ . An SPV measuring device for determining Fe concentration in a p-type silicon wafer based on measurement by SPV method,
A measurement stage for placing a p-type silicon wafer during SPV measurement;
An optical module for irradiating the p-type silicon wafer with light;
A probe for measuring a capacitance generated between a capacitance sensor provided at a tip and the surface of the p-type silicon wafer;
A lock-in amplifier for amplifying and detecting an SPV signal corresponding to the capacitance measured by the probe;
Calibration chip for calibration to reduce measurement error;
A separation stage on which the p-type silicon wafer is placed when the Fe-B pair in the p-type silicon wafer is separated;
A flash lamp for separating Fe-B pairs in the p-type silicon wafer;
A robot arm that transports and unloads the p-type silicon wafer with respect to the measurement stage and the separation stage;
A robot controller that controls the robot arm;
Have
A first housing that accommodates the measurement stage, the probe, and the calibration tip for calibration;
A second housing accommodating the light module and the lock-in amplifier;
A third housing accommodating the deviation stage and the flash lamp;
A fourth housing housing the robot arm and the robot controller;
And have
A first chemical filter and a second chemical filter are respectively installed on the windward side of the air flow with respect to the first housing and the third housing, and the inside of the first housing and the third housing is , The total concentration of Na ⁺ , NH ₄ ⁺ and K ⁺ is 1.750 μg / m ³ or less, F ⁻ , Cl ⁻ , NO ₂ ⁻ , PO ₄ ³⁻ , Br ⁻ , NO ₃ ⁻ and SO ₄ ²⁻ An SPV measurement device characterized in that the atmosphere has a total concentration of 0.552 μg / m ³ or less. A third chemical filter is installed on the windward side of the air flow with respect to the fourth housing, and the total concentration of Na ⁺ , NH ₄ ⁺ and K ⁺ is 1.750 μg / m for the inside of the fourth housing. ³ or ^{less, F -, Cl -, NO} 2 -, PO 4 3-, Br -, NO 3 - and SO ₄ total concentration of ² has an atmosphere at 0.552μg / m ³ or less, claims The SPV measuring device as described in 2.   The SPV measurement device according to claim 2, wherein the first chemical filter and the second chemical filter are disposed above the first housing and the third housing, respectively.   The SPV measurement device according to claim 3, wherein the third chemical filter is disposed above the fourth housing.

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