JP7026371B2 - Carbon concentration measuring method and carbon concentration measuring device - Google Patents

Description

The present invention relates to a carbon concentration measuring method and a carbon concentration measuring device for measuring a carbon concentration in a silicon crystal containing carbon.

Silicon crystals are a material widely used in semiconductor devices such as solar cells, LSIs, and power devices. Since it is known that a small amount of carbon impurities contained in this silicon crystal induces the formation of oxygen precipitation defects during the manufacture of a semiconductor device and causes deterioration of the performance of the semiconductor device, it is necessary to control the characteristics of the semiconductor device. In order to do so, it is indispensable to quantitatively measure the concentration of carbon contained in the silicon crystal.

As a method for measuring the carbon concentration in a silicon crystal, an electron beam is irradiated to the silicon crystal, carbon atoms contained in the semiconductor are displaced to interstitial positions, and an extremely low temperature (for example, 4.2 kelvin (K)) is used with a helium refrigerant. )), And a method of measuring the carbon concentration in a silicon crystal by a photoluminescence method (hereinafter referred to as “PL method”) is known (Non-Patent Document 1).

Further, Patent Document 1 discloses an example of a measuring device diagram for measuring a carbon concentration in a silicon crystal having the same configuration as that of Non-Patent Document 1.

In Non-Patent Document 1 and Patent Document 1, a particle beam is irradiated on a silicon crystal to displace carbon atoms at interstitial positions, and the carbon concentration in the silicon crystal is measured.

On the other hand, in Patent Document 2, a particle beam is irradiated on a silicon crystal to displace the silicon atom at an interstitial position, and the carbon concentration in the silicon crystal is measured.

Further, Patent Documents 3 and 4 disclose the room temperature PL method.

Patent No. 5615303 JP-A-2015-1111615 Japanese Unexamined Patent Publication No. 1-239863 Japanese Unexamined Patent Publication No. 2016-201461

Satoko Nakagawa, Kazuhiko Kashima, Michio Tajima, "Quantitative Analysis of Low-Concentration Carbon in Silicon Wafers by Luminescence Activation Using Electron Irradiation", The Forum on the Science and Technology of Silicon Materials 2010, Okayama Univ., Okayama City, Nov 14 to 17, 2010, p.326

However, in the means of Non-Patent Document 1 and Patent Document 1, since the measurement is performed at an extremely low temperature, the line width of the emission spectrum obtained by the PL method is narrow. A high-resolution spectroscope is required to measure this narrow line width spectrum. With a high resolution spectroscope, the dispersed light is widely dispersed. Since the size of the detector is finite, it is necessary to measure the light dispersed over a wide range in a plurality of times in order to measure the carbon concentration by the PL method. As a result of such restrictions on the device, there is a problem that the measurement time becomes long. For example, it takes at least 240 seconds to 360 seconds to measure the emission intensity in the wavelength range of 1653 nm to 1033 nm.

Further, in the means of Non-Patent Document 1 and Patent Document 1, since the measurement is performed at an extremely low temperature, a large amount of light emission derived from dopant impurities and multi-exciton-based light emission appear. The emission intensity of carbon-derived luminescence in a silicon crystal fluctuates due to the influence of luminescence derived from dopant impurities and multi-exciton-based luminescence. Therefore, the measurement accuracy of the carbon concentration measurement by the PL method at an extremely low temperature is low. Further, at an extremely low temperature, minute temperature fluctuations of the silicon crystal during measurement have a great influence on the measurement result, so that the measurement accuracy tends to decrease.

Patent Document 2 does not specifically disclose the cooling temperature of a silicon crystal after irradiating the silicon crystal with a particle beam.

Patent Document 3 discloses a method for evaluating a deep level in a crystal of a GaAs wafer, but does not disclose a method for measuring a carbon concentration in a silicon crystal.

Patent Document 4 discloses a method for evaluating an actual dose amount and a method for evaluating damage recovery using band-end emission having a wavelength of 1150 nm, but does not disclose a method for measuring a carbon concentration in a silicon crystal.

Further, in the PL method at an extremely low temperature, liquid helium used as a refrigerant is expensive. Furthermore, liquid helium always has a risk of exploding the container due to the vaporization pressure, and it takes time and effort to attach a safety valve having a large diameter to the container and to precool the container. It is also necessary to pay attention to the collection after use.

The present invention has been made in consideration of the above-mentioned problems, and it is possible to measure the carbon concentration in a silicon crystal containing carbon in a short time and with high accuracy by measuring a high temperature. It is an object of the present invention to provide a carbon concentration measuring method and a carbon concentration measuring device for measuring.

The carbon concentration measuring method of the present invention is a carbon concentration measuring method for measuring the carbon concentration in a silicon crystal containing carbon by a photoluminescence method, and (A) the carbon atom at the lattice position is displaced to the interstitial position. A step of cooling the resulting silicon crystal to a temperature range of 63K to 100K, (B) a step of exciting carriers to the silicon crystal after the step (A), and (C) a carrier in the step (B). A step of measuring the emission intensity of a plurality of wavelengths included in the emission spectrum of the excited silicon crystal, and (D) an emission intensity of a wavelength in a range including a specific wavelength selected from the plurality of wavelengths measured in the step (C). It is characterized by comprising a step of calculating the carbon concentration in the silicon crystal based on the integrated intensity of the emission peak obtained by integrating the above.

In the carbon concentration measuring method, the measurement of the emission intensity in the step (C) is characterized in that the emission intensity of the plurality of wavelengths is collectively measured.

The carbon concentration measuring method is characterized in that the plurality of wavelengths include one wavelength in the range of at least 1120 nm to 1140 nm, and further includes at least one of the plurality of wavelengths of 1278 nm or 1569 nm.

The carbon concentration measuring method is characterized in that, in step (D), the specific wavelengths are set to 1127 nm and 1278 nm, or 1127 nm and 1569 nm, and the carbon concentration in the silicon crystal is calculated.

The carbon concentration measuring method of the present invention is a carbon concentration measuring method for measuring a carbon concentration in a silicon crystal containing carbon, and is a silicon crystal in which the carbon atom at the (A) lattice position is displaced to an interstitial position. A step of exciting carriers in the atmosphere at room temperature, (B) a step of measuring the emission intensities of a plurality of wavelengths contained in the emission spectrum of the silicon crystal excited by the carrier in the step (A), and (C). The step (B) includes a step of calculating the carbon concentration in the silicon crystal based on the emission intensity of a specific wavelength selected from the plurality of wavelengths measured in the step (B) or the integrated intensity of the emission peak including the specific wavelength. In step (C), the specific wavelengths are 1140 nm and 1610 nm .

In the carbon concentration measuring method, the measurement of the emission intensity in the step (B) is characterized in that the emission intensity of the plurality of wavelengths is collectively measured.

The carbon concentration measuring device of the present invention is a carbon concentration measuring device that measures the carbon concentration in a silicon crystal containing carbon by a photoluminescence method, and is silicon in which the carbon atom at a child position is displaced to an interstitial position. A cooling unit that cools the crystal to a temperature range of 63K to 100K, an excitation unit that excites carriers in the silicon crystal, and a spectrum measurement that measures the emission intensity of a plurality of wavelengths contained in the emission spectrum of the excited silicon crystal. A concentration calculation unit that calculates the carbon concentration in the silicon crystal based on the integrated intensity of the emission peak obtained by integrating the emission intensity of a range including a specific wavelength selected from a plurality of wavelengths measured by the spectrum measurement unit and the unit. It is characterized by having and.

The carbon concentration measuring device of the present invention is a carbon concentration measuring device for measuring the carbon concentration in a silicon crystal containing carbon, and the carbon atom at the lattice position is displaced to the intergranular position on the silicon crystal at room temperature. From the excitation unit that excites carriers in the atmosphere, the spectrum measurement unit that measures the emission intensity of a plurality of wavelengths contained in the emission spectrum of the excited silicon crystal, and the plurality of wavelengths measured by the spectrum measurement unit. A concentration calculation unit for calculating the carbon concentration in the silicon crystal based on the emission intensity of the selected specific wavelength or the integrated intensity of the emission peak including the specific wavelength is provided, and the selected specific wavelengths are 1140 nm and 1610 nm. It is characterized by that.

In the carbon concentration measuring device, the spectrum measuring unit is characterized in that the emission intensity of a plurality of specific wavelengths is collectively measured.

According to the carbon concentration measuring method for measuring the carbon concentration in a silicon-containing silicon crystal of the present invention, the silicon crystal in which the carbon atom at the lattice position is displaced to the interstitial position is cooled to a temperature range of 63K to 100K. Steps, a step of exciting a carrier to the silicon crystal, a step of measuring the emission intensity of a plurality of wavelengths included in the emission spectrum of the silicon crystal excited with a carrier, and a specific wavelength selected from a plurality of measured wavelengths. By providing a step of calculating the carbon concentration in the silicon crystal based on the emission intensity of the above or the integrated intensity of the emission peak including the specific wavelength thereof, the measurement can be performed in a higher temperature region than before in a short time. It is possible to measure the carbon concentration in silicon crystals with high accuracy. In addition, the measurement sensitivity of the carbon concentration can be improved.

By having a step of collectively measuring the emission intensities of a plurality of wavelengths included in the emission spectrum, it is possible to measure the carbon concentration in the silicon crystal in a shorter time than in the prior art in which the batch measurement was not possible.

Further, in the carbon concentration measuring method for measuring the carbon concentration in a silicon-containing silicon crystal of the present invention, carriers are excited to the silicon crystal in which the carbon atom at the lattice position is displaced to the interstitial position in the air at room temperature. Steps to measure the emission intensity of a plurality of wavelengths contained in the emission spectrum of the silicon crystal excited by the carrier, emission intensity of a specific wavelength selected from the measured plurality of wavelengths, or emission peak including the specific wavelength. By providing a step of calculating the carbon concentration in the silicon crystal based on the integrated strength of the above, the carbon concentration in the silicon crystal can be measured in a short time and with high accuracy by measuring in a region higher than the conventional one. can do. In addition, the measurement sensitivity of the carbon concentration can be improved.

Further, according to the carbon concentration measuring device for measuring the carbon concentration in the carbon-containing silicon crystal of the present invention, the silicon crystal in which the carbon atom at the lattice position is displaced to the interstitial position is placed in a temperature range of 63K to 100K. A cooling unit that cools to the silicon crystal, an excitation unit that excites carriers in the silicon crystal, a spectrum measurement unit that measures the emission intensity of a plurality of wavelengths contained in the emission spectrum of the silicon crystal that excites the carrier, and the spectrum measurement unit. By providing a concentration calculation unit that calculates the carbon concentration in the silicon crystal based on the emission intensity of a specific wavelength selected from the plurality of wavelengths measured in 1 or the integrated intensity of the emission peak including the specific wavelength. By measuring in a higher temperature region, the carbon concentration in the silicon crystal can be measured in a short time and with high accuracy. In addition, the measurement sensitivity of the carbon concentration can be improved.

Further, according to the carbon concentration measuring device for measuring the carbon concentration in the carbon-containing silicon crystal of the present invention, the carbon atom at the lattice position is displaced to the interstitial position in the air at room temperature, and the carrier is transferred to the silicon crystal. A specific group selected from an excitation unit that excites a carrier, a spectrum measurement unit that measures the emission intensity of a plurality of wavelengths contained in the emission spectrum of the silicon crystal that excites a carrier, and a plurality of wavelengths measured by the spectrum measurement unit. By providing a concentration calculation unit that calculates the carbon concentration in the silicon crystal based on the emission intensity of the wavelength or the integrated intensity of the emission peak including the specific wavelength, the measurement can be performed in a higher temperature region than before for a short time. Moreover, the carbon concentration in the silicon crystal can be measured with high accuracy. In addition, the measurement sensitivity of the carbon concentration can be improved.

By having a spectrum measuring unit that collectively measures the emission intensity of a plurality of wavelengths, it is possible to measure the carbon concentration in the silicon crystal in a shorter time than in the conventional technique in which the batch measurement cannot be performed.

It is explanatory drawing of the carbon concentration measuring apparatus which concerns on 1st Embodiment of this invention. It is explanatory drawing of the calibration curve of C line which shows the correlation between the emission intensity ratio of C line measured at 77K, and the carbon concentration in a silicon crystal. It is explanatory drawing of the carbon concentration measuring method which concerns on 1st Embodiment of this invention. It is a figure which shows the example of the emission spectrum of the silicon crystal measured at 77K. It is a figure which shows the example of the emission spectrum of the silicon crystal measured at 4.2K. It is explanatory drawing of the carbon concentration measuring apparatus which concerns on 2nd Embodiment of this invention. It is explanatory drawing of the calibration curve of the 1610 nm emission band which shows the correlation between the emission intensity ratio of the 1610 nm emission band measured at room temperature, and the carbon concentration in a silicon crystal. It is explanatory drawing of the carbon concentration measuring method which concerns on 2nd Embodiment of this invention. It is a figure which shows the example of the emission spectrum of the silicon crystal measured at room temperature.

<Structure of carbon concentration measuring device according to the first embodiment>
Hereinafter, the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing a configuration of a carbon concentration measuring device 10 according to the first embodiment of the present invention.

The carbon concentration measuring device 10 includes a cooling unit 20, a laser light generating unit (exciting unit) 30, a spectrum measuring unit 40, and a concentration calculating unit 50.

The cooling unit 20 is a means for cooling the silicon crystal 22. The cooling unit 20 has a holder on which the silicon crystal 22 is placed. The cooling unit 20 is provided with a laser beam 32 irradiated from the laser light generating unit 30 and a window 24 through which the light emitted from the silicon crystal 22 can be transmitted.

The laser light generating unit 30 is a means for irradiating the laser beam 32 to excite carriers in the silicon crystal 22. The laser light generation unit 30 includes a laser oscillator and a light guide path.

The spectrum measuring unit 40 is a means for measuring the emission spectrum emitted from the excited silicon crystal 22. The spectrum measurement unit 40 efficiently condenses the light emitted from the silicon crystal 22 onto a spectroscope, a condensing optical device that disperses the focused light, and efficiently condenses light of a plurality of dispersed wavelengths. It is equipped with a condensing optical device that leads to a light detector and a light detector. Here, as the photodetector, for example, a multi-channel semiconductor diode array capable of simultaneously measuring the intensities of light having a plurality of wavelengths can be used. Examples of the multi-channel semiconductor diode array include an InGaAs diode array and a mercury cadmium tellurium diode array.

A laser light generation unit 30 and a spectrum measurement unit 40 are connected to the cooling unit 20.

The concentration calculation unit 50 is a means for calculating the carbon concentration in the silicon crystal 22 based on the emission intensity of the emission spectrum of the silicon crystal 22. It is equipped with a memory for storing the calibration curve, an input / output interface for measurement results and calculation results, and a CPU.

For the calibration curve, a plurality of types of silicon crystals 22 having a known carbon concentration are prepared, the emission spectrum of each silicon crystal 22 is measured, and the emission intensity ratio of two wavelengths used for calculating the carbon concentration and the emission intensity ratio in the silicon crystal. It expresses an approximate expression of the positive correlation with the carbon concentration. The approximate expression can be obtained, for example, by using the method of least squares. The two wavelengths used to calculate the carbon concentration are, for example, 1127 nm and 1278 nm. The emission in which a peak is seen around 1127 nm in the range of 1120 nm to 1140 nm is band-end emission of energy corresponding to the band gap of the silicon crystal. Emission with a peak at 1569 nm is commonly referred to as "C-line". C-rays are emitted from the energy level of the complex of carbon at the interstitial position and oxygen at the interstitial position of the silicon crystal. A calibration curve that expresses an approximate expression of a positive correlation between the emission intensity of C-line, the emission intensity ratio of band edge emission, and carbon concentration is called a "C-line calibration curve". Emissions with a peak at 1278 nm are commonly referred to as "G-rays". G-rays are luminescence derived from the energy level of the composite of carbon at the lattice position of the silicon crystal and carbon at the interstitial position. A calibration curve that expresses an approximate expression of a positive correlation between the emission intensity of G-rays, the emission intensity ratio of band-end emission, and the carbon concentration is called a "G-line calibration curve".

FIG. 2 is an explanatory diagram of a C-line calibration curve showing the correlation between the C-line emission intensity ratio measured at 77K and the carbon concentration in the silicon crystal. The vertical axis shows the logarithm of the emission intensity ratio of C line, and the horizontal axis shows the logarithm of the carbon concentration contained in the silicon crystal. The black circle plot is the measurement result. The straight line is a regression line that approximates the measurement result by the method of least squares. In this example, it is a straight line on the log-log graph, but it is not limited to this as long as it has a relationship of interpolating the measured value.

<Method for measuring carbon concentration according to the first embodiment>
Next, a method for measuring the carbon concentration in the silicon crystal will be described with reference to FIG. FIG. 3 is an explanatory diagram of the carbon concentration measuring method according to the first embodiment.

A silicon crystal 22 containing carbon and having the carbon atom at the lattice position displaced to the interstitial position is prepared in advance. For the displacement treatment, the publicly known technique (electron beam irradiation) disclosed in Non-Patent Document 1 and Patent Document 1 is generally used.

First, the silicon crystal 22 is placed on the holder inside the cooling unit 20 (step S1).

Next, the silicon crystal 22 is cooled (step S2). Specifically, a liquid nitrogen refrigerant introduced from the outside is circulated in the cavity inside the cooling unit 20, and the silicon crystal 22 is directly immersed in the refrigerant. When immersed directly in liquid nitrogen, in a thermal equilibrium state, the silicon crystal 22 is cooled to 77K, which is the same as the boiling point of liquid nitrogen.

Carriers are excited into the silicon crystal 22 (step S3). Specifically, the laser beam 32 having an energy larger than the bandgap energy of the silicon crystal 22 is irradiated to the silicon crystal 22 from the laser light generating unit 30 through the window 24 of the cooling unit 20. The laser light generating unit 30 is, for example, an all-solid-state laser using Nd: YVO ₄ as a laser oscillator, and the wavelength of the laser beam 32 is 532 nm.

The emission spectrum of the silicon crystal 22 is measured (step S4). Specifically, the spectrum measuring unit 40 arranged at a position facing the silicon crystal 22 is used to determine the emission intensity of a plurality of wavelengths included in the emission spectrum detected from the silicon crystal 22 through the window 24 of the cooling unit. Measure. The wavelength range to be measured includes band-end emission and further includes at least one of G and C rays.

FIG. 4 is a diagram showing an example of an emission spectrum of a silicon crystal measured at 77K. The vertical axis is the emission intensity measured in arbitrary units. The horizontal axis is the measured wavelength of emission. Band end emission 80, G line 70, and C line 60 are clearly observed.

The carbon concentration in the silicon crystal 22 is calculated based on the measured emission intensity of the specific wavelength (step S5). Specifically, the concentration calculation unit 50 reads out the calibration curve of C line stored in the memory in advance, and in the emission spectrum measured in step S4, the emission intensity of C line 60 is the emission intensity of the band end emission 80. By obtaining the divided value (hereinafter referred to as "C-line emission intensity ratio") and substituting the C-line emission intensity ratio into the formula (see FIG. 2) representing the C-line calibration curve, the silicon crystal 22 Calculate the carbon concentration.

The comparison with the conventional technique for measuring at an extremely low temperature will be described below.

FIG. 5 is a diagram showing an example of an emission spectrum of a silicon crystal measured at 4.2K. The vertical axis is the emission intensity measured in arbitrary units. For the sake of readability, the emission intensity at wavelengths of 1210 nm and above is described by being amplified eight times. The horizontal axis is the measured wavelength of emission.

In the emission spectrum measured at 4.2K, not only G-line 70 and C-line 60 but also emission of a plurality of wavelengths are measured. This includes light emission 92 and multi-exciton system light emission 90 derived from dopant impurities such as phosphorus. At extremely low temperatures, not only band-end emission 80 and carbon-derived emission (G-ray 70 and C-line 60), but also emission 92 and multi-exciton-based emission 90 derived from dopant impurities are generated, carbon in the silicon crystal. The emission intensity ratio of the emission light (G line 70 and C line 60) derived from the Therefore, the measurement accuracy is low.

On the other hand, in the emission spectrum measured at 77K in FIG. 4, only the G line 70, the C line 60, and the band end emission 80 are measured. At 77K, the excitons that are the origin of the light emission 92 derived from the dopant impurities are thermally dissociated from the impurities, so that there is no light emission 92 derived from the dopant impurities. Further, since the excitons are thermally dissociated, there is no multi-exciton system emission 90 generated by the aggregation of excitons. Therefore, the emission intensity ratio of carbon-derived emission (G-ray 70 and C-line 60) in the silicon crystal does not change due to the influence of the emission 92 derived from the dopant impurities and the multi-exciton emission 90. Therefore, the measurement accuracy is high.

From the above, the measurement accuracy in the first embodiment is higher than the measurement accuracy in the case of the conventional measurement at 4.2K.

The measurement at 4.2K requires a spectroscope with a narrow line width of the obtained emission spectrum and high resolution. With a high resolution spectroscope, the dispersed light is widely dispersed. Since the size of the detector is finite, it is not possible to measure a wide wavelength range with one measurement. Specifically, as a plurality of wavelengths required for measuring the carbon concentration in the silicon crystal, it is possible to collectively measure the emission spectrum in a range including at least band-end emission and further including at least one of G line or C line. Can not. Therefore, it is necessary to narrow the measurement range of one measurement and perform the measurement taking 80 seconds to 120 seconds in three times. Therefore, the measurement time takes at least 240 seconds to 360 seconds.

In the measurement at 77K, the line width of the obtained emission spectrum is wide, and the light dispersed by a low-dispersion spectroscope can be measured. Therefore, it is possible to measure a wide wavelength range with one measurement. Specifically, as a plurality of wavelengths required for measuring the carbon concentration in the silicon crystal, it is possible to collectively measure the emission spectrum in a range including at least band-end emission and further including at least one of G line or C line. can. As a result, the measurement time can be shortened. In the case of this embodiment, the measurement can be completed in 3 seconds.

From the above, the measurement time in the first embodiment can be shortened as compared with the measurement time in the case of the conventional measurement at 4.2K.

The minute temperature fluctuation ΔT of the silicon crystal during the measurement affects the measurement result. Specifically, ΔT / 4.2: ΔT / 77 is approximately 1: 0.05. This means that the magnitude of the effect of the same minute temperature fluctuation ΔT on the entire temperature is only about 5% of the measurement at 77K and the measurement at 4.2K.

From the above, the measurement accuracy in the first embodiment is higher than the measurement accuracy in the case of the conventional measurement at 4.2K.

The measurement at 77K is less susceptible to minute temperature fluctuations ΔT than the conventional measurement at 4.2K, the measurement time can be shortened, and the emission 92 and multi-exciton emission 90 derived from dopant impurities are silicon. It has the characteristic that it does not affect the light emission (G-ray 70 and C-ray 60) derived from carbon in the crystal.

In addition, since the measurement at 77K can be performed with a low-dispersion spectroscope, the focal length is shortened, and the light emission obtained by the PL method is shorter than that of the spectroscope used for the conventional 4.2K measurement. Of these, the amount of light that can be captured by the detector increases. In addition, the amount of light that can be detected per unit area of the detector increases. Due to these features on the device, the S / N ratio of the measurement result is improved.

From the above, the measurement sensitivity in the first embodiment is higher than the measurement sensitivity in the case of the conventional measurement at 4.2K.

The measurement at 4.2K uses liquid helium as the refrigerant, but helium is very expensive compared to liquid nitrogen because of its low abundance ratio in the elements on the earth. When cooling with liquid helium, it is necessary to attach a safety valve with a large diameter to the container in order to prevent the container from being destroyed by the sudden evaporation gas of liquid helium. In addition, it is necessary to precool the container with liquid nitrogen. It is also necessary to pay attention to the collection after use.

The measurement at 77K uses liquid nitrogen as the refrigerant, but since liquid nitrogen is made by cooling the air, it can be purchased at a relatively low cost. Liquid nitrogen does not require a large safety valve or precooling because the temperature difference from room temperature is not as large as that of liquid helium.

From the above, in the measurement in the first embodiment, the refrigerant is cheaper and easier to handle than in the case of the conventional 4.2K measurement.

Next, the second embodiment of the present invention will be described with reference to the drawings. FIG. 6 is an explanatory diagram showing the configuration of the carbon concentration measuring device 200 according to the second embodiment of the present invention.

The carbon concentration measuring device 200 according to the second embodiment of the present invention includes a mounting table 26, a laser light generating section (exciting section) 30, a spectrum measuring section 40, and a concentration calculating section 50. That is, with respect to the carbon concentration measuring device 10 according to the first embodiment, the carbon concentration measuring device 200 has a mounting table 26 instead of the cooling unit 20. The same components as those of the carbon concentration measuring device 10 shown in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

The mounting table 26 is a table on which the silicon crystal 22 is placed.

The two wavelengths used in the calculation of the carbon concentration in the concentration calculation unit 50 are, for example, 1140 nm and 1610 nm. The emission in which a peak is seen around 1140 nm in the range of 1130 nm to 1150 nm is band-end emission of energy corresponding to the band gap of the silicon crystal. Compared with the wavelength of the band edge emission in the first embodiment, the band edge emission in the second embodiment is on the long wavelength side in response to the decrease in the band gap as the temperature rises from liquid nitrogen to room temperature. It is out of alignment. Further, light emission in which a peak is observed around 1610 nm in the range of 1400 nm to 1700 nm, more preferably in the range of 1560 nm to 1660 nm is referred to as a “1610 nm emission band”. The 1610 nm emission band exhibits the same heat treatment behavior as the above-mentioned C line, and its intensity shows a positive correlation with the carbon concentration. Therefore, the emission is derived from the energy level of the carbon complex like the C line. It is estimated to be. A calibration curve expressing an approximate expression of a positive correlation between the emission intensity ratio of the 1610 nm emission band and the band end emission and the carbon concentration is called a "calibration curve of the 1610 nm emission band".

FIG. 7 is an explanatory diagram of a calibration curve of the 1610 nm emission band showing the correlation between the emission intensity ratio of the 1610 nm emission band measured at room temperature and the carbon concentration in the silicon crystal. The vertical axis shows the logarithm of the emission intensity ratio in the 1610 nm emission band, and the horizontal axis shows the logarithm of the carbon concentration contained in the silicon crystal. The black circle plot is the measurement result. The straight line is a regression line that approximates the measurement result by the method of least squares. In this example, it is a straight line on the log-log graph, but it is not limited to this as long as it has a relationship of interpolating the measured value.

<Method for measuring carbon concentration according to the second embodiment>
Next, a method for measuring the carbon concentration in the silicon crystal will be described with reference to FIG. FIG. 8 is an explanatory diagram of the carbon concentration measuring method according to the second embodiment of the present invention.

Similar to the first embodiment, a silicon crystal 22 containing carbon and having the carbon atom at the lattice position displaced to the interstitial position is prepared in advance.

Next, the silicon crystal 22 is placed on the mounting table 26 (step S11).

Carriers are excited into the silicon crystal 22 at room temperature (20 ° C to 30 ° C) in the atmosphere (step S12). The carrier excitation in step S12 is performed in the same manner as in step S3.

The emission spectrum of the silicon crystal 22 is measured (step S13). The measuring method in step S13 is the same as that in step S4, but the wavelength range to be measured is different from that in step S4. The wavelength range measured in step S13 includes at least one wavelength in the range of 1000 nm to 1200 nm including the band-end emission 110, and at least one wavelength in the range of 1400 nm to 1700 nm including the 1610 nm emission band 100. It is a range to include.

FIG. 9 is a diagram showing an example of an emission spectrum of a silicon crystal measured at room temperature. The vertical axis is the emission intensity measured in arbitrary units. The horizontal axis is the measured wavelength of emission. Band-end emission 110 and 1610 nm emission band 100 are clearly observed.

The carbon concentration in the silicon crystal 22 is calculated based on the measured emission intensity of the specific wavelength (step S14). Specifically, the concentration calculation unit 50 reads out the calibration curve of the 1610 nm emission band stored in the memory in advance, and of the emission spectrum measured in step S13, the emission intensity of the 1610 nm emission band 100 is the emission intensity of the band end emission 110. The value divided by the intensity (hereinafter referred to as "1610 nm emission band emission intensity ratio") is obtained, and the emission intensity ratio of the 1610 nm emission band 100 is substituted into the formula (see FIG. 7) representing the calibration curve of the 1610 nm emission band. , Calculate the carbon concentration in the silicon crystal 22.

In the emission spectrum measured at room temperature in FIG. 9, only the 1610 nm emission band 100 and the band end emission 110 are measured. At room temperature, as in 77K, the excitons that are the origin of the light emitting 92 derived from the dopant impurities are thermally dissociated from the impurities, so that there is no light emitting 92 derived from the dopant impurities. Further, since the excitons are thermally dissociated, there is no multi-exciton system emission 90 generated by the aggregation of excitons. Therefore, the emission intensity ratio of carbon-derived emission (1610 nm emission band 100) in the silicon crystal does not fluctuate due to the influence of the emission 92 derived from the dopant impurities and the multi-exciton emission 90. Therefore, the measurement accuracy is high.

Therefore, as described above, the measurement accuracy when measured at 4.2K is low, but the measurement accuracy in the second embodiment is higher than when measured at 4.2K.

Further, the measurement time in the second embodiment is about 60 seconds, which can be shorter than the measurement time in the case of the above-mentioned 4.2K measurement.

Further, the minute temperature fluctuation ΔT of the silicon crystal under measurement is ΔT / 4.2: ΔT / 300, which is about 1: 0.01, that is, only about 1%. Therefore, the measurement accuracy in the second embodiment is higher than the measurement accuracy in the case of the conventional measurement at 4.2K.

Further, the measurement in the second embodiment is less susceptible to the minute temperature fluctuation ΔT than the conventional measurement at 4.2K, the measurement time can be shortened, and the light emitting 92 and the multi-exciton derived from the dopant impurities are not affected. The system emission 90 is characterized in that it does not affect the emission (1610 nm emission band 100) derived from carbon in the silicon crystal.

Further, since the measurement in the second embodiment can be performed with a low-dispersion spectroscope, the focal length is shortened, and the light emission obtained by the PL method is higher than that of the spectroscope used for the conventional 4.2K measurement. Of these, the amount of light that can be captured by the detector increases. In addition, the amount of light that can be detected per unit area of the detector increases. Due to these features on the device, the S / N ratio of the measurement result is improved.

From the above, the measurement sensitivity in the second embodiment is higher than the measurement sensitivity in the case of the conventional measurement at 4.2K.

Further, the measurement in the second embodiment can be performed at room temperature in the atmosphere, and since it does not need to be cooled, a cooling unit is not required, and the device can be easily configured.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that various configurations can be taken without departing from the gist of the present invention.

The concentration calculation unit 50 of the above-described embodiment includes a memory, an input / output interface, and a CPU, but is limited to this if the carbon concentration in the silicon crystal can be calculated from the emission intensity measured by the spectrum measurement unit 40. It's not something. For example, the correspondence table between the emission intensity ratio of G-ray or C-line on the calibration line and the carbon concentration in the silicon crystal may be provided with a function of being displayed together with the emission intensity of G-ray or C-line measured in step S4. .. Further, the correspondence table between the emission intensity ratio of the 1610 nm emission band on the calibration line and the carbon concentration in the silicon crystal may be provided with a function of being displayed together with the emission intensity of the 1610 nm emission band measured in step S13.

The spectrum measuring unit 40 of the above-described embodiment includes a multi-channel detector that measures a plurality of wavelengths, but is not limited to this as long as it can measure a plurality of wavelengths. For example, a single channel detector that measures a plurality of wavelengths by rotating the diffraction grating of the spectroscope may be used.

The laser light generating unit 30 of the above-described embodiment excites carriers in the silicon crystal by generating laser light and irradiating the silicon crystal, but the present invention is limited to this as long as the carriers can be excited in the silicon crystal. It is not something that is done. For example, it may be an electron gun that can excite carriers in a silicon crystal by irradiating it with an electron beam.

In the above embodiment, the silicon crystal 22 is cooled to 77K, but it can be cooled with a refrigerant that is easier to handle than the conventional measurement at 4.2K, and the light emitting 92 and the multi-exciton-based light emitting 90 derived from the dopant impurities are produced. The temperature is not limited to 77K as long as it does not occur and the temperature is such that the emission spectra of a plurality of wavelengths necessary for measuring the carbon concentration in the silicon crystal can be measured.

For example, by using a cooling device using a closed circulation type helium compressor or by using a refrigerant obtained by further cooling liquid nitrogen by reducing the pressure, it is possible to cool down to 63 K, which is the melting point of nitrogen. Further, by providing a heater and a thermometer in the holder, temperature control in a temperature range of 77K or more becomes possible. The upper limit of the temperature at which the emission intensity of a specific wavelength is not buried in noise is about 100K. That is, in the range of 63K to 100K, the carbon concentration in the silicon crystal can be cooled by a closed circulation type helium compressor, liquid nitrogen, etc. It is possible to measure the emission spectra of a plurality of wavelengths required for the measurement of.

At 63K or less, the emission 92 and the multi-exciton emission 90 derived from the dopant impurities gradually increase, and the line width of the emission spectrum narrows. Even at 63 K or less, if the temperature is such that the emission 92 derived from the dopant impurities and the multi-exciton emission 90 are sufficiently small, the measurement accuracy of the emission spectra of a plurality of wavelengths required for measuring the carbon concentration in the silicon crystal is improved. Can be done. Further, even at 63 K or less, if the line width of the emission spectrum is wider than a certain level and the light dispersed by the low-dispersion spectroscope can be captured by the detector, the measurement can be performed collectively or in a short time. Further, among the light emitted by the PL method, the amount of light that can be taken into the detector increases, so that the measurement sensitivity can be increased. Further, even at 100 K or higher, by increasing the S / N ratio, if the emission intensity of a specific wavelength is not buried in noise, the emission spectra of a plurality of wavelengths necessary for measuring the carbon concentration in the silicon crystal are measured. can do.

In the above embodiment, a liquid or gas refrigerant such as liquid nitrogen introduced from the outside is circulated in the cavity inside the cooling unit 20 and directly immersed in the refrigerant to cool the silicon crystal 22. However, the silicon crystal 22 is cooled. If it can be cooled, it is not limited to this. For example, inside the vacuum chamber, the silicon crystal 22 may be cooled via a heat conductor made of a material having sufficiently high thermal conductivity, such as platinum or copper, in the holder portion on which the silicon crystal 22 is placed. In that case, for example, a cavity is provided in the heat conductor, a liquid or gas refrigerant such as liquid nitrogen introduced from the outside of the vacuum chamber is supplied to the cavity, and the silicon crystal 22 is cooled through the heat conductor. Alternatively, the heat conductor may be cooled by using a closed circulation type helium compressor, and the silicon crystal 22 may be cooled via the heat conductor.

In the above embodiment, the cooling unit 20 is provided with a window 24, but if the cooling unit 20 has a function of transmitting the light emitted from the laser beam 32 and the silicon crystal 22 emitted from the laser light generating unit 30, the window 24 is a laser beam. It may be provided separately for 32 and for light emission of the silicon crystal 22.

In the above embodiment, in steps S5 and S14, the carbon concentration is calculated based on the emission intensity of a specific wavelength, but the peak of the emission spectrum (here, the peak of the emission spectrum observed in a shape including a specific wavelength and having a chevron spread). , The spectrum of the mountain shape that spreads over a certain wavelength range is called "peak". The same applies hereinafter), and the value is the sum of the emission intensities of the wavelengths that spread over the mountain shape (hereinafter referred to as the integrated intensity of the emission peak). The carbon concentration may be calculated based on this. The range of wavelengths to be integrated is, for example, the range of half width, the range of wavelengths at which the emission intensity is higher than the noise level, or the peak obtained by fitting the peak shape with the Lorentz function, Gaussian function, or Maxwell-Boltzmann function. It is determined within the range of.

In the above embodiment, in step S5, the concentration calculation unit 50 reads out the C-line calibration curve stored in advance in the memory, and among the emission spectra measured in step S4, the C-line emission intensity ratio is C-line calibration. The carbon concentration in the silicon crystal 22 is calculated by substituting it into an equation representing a line, but the present invention is not limited to this as long as the carbon concentration in the silicon crystal 22 can be calculated. For example, the concentration calculation unit 50 reads out the calibration curve of the G line stored in the memory in advance, and divides the emission intensity of the G line 70 by the emission intensity of the band end emission 80 (hereinafter referred to as the G line emission intensity ratio). ), And the carbon concentration in the silicon crystal 22 may be calculated by substituting it into an equation representing the calibration curve of the G line. Further, it may be calculated by taking a large value, a small value, or an average value of the carbon concentration calculated by using the emission intensity ratio of C line and the emission intensity ratio of G line.

In the above embodiment, the calibration curve expresses an approximate expression of a positive correlation between the emission intensity ratio of a specific wavelength and the carbon concentration, but the emission from the silicon crystal 22 causes a difference in factors other than the carbon concentration. If it can be ignored or corrected and an approximate expression of the positive correlation with the carbon concentration can be expressed, the calibration curve is expressed as an approximate expression of the positive correlation between the emission intensity of a specific wavelength and the carbon concentration. It may be a thing. In this case, in step S5, the emission intensity of the specific wavelength (G line 70 or C line 60) is substituted into the equation representing the calibration curve. Further, in step S14, the emission intensity of a specific wavelength (1610 nm emission band 100) is substituted into the equation representing the calibration curve.

10, 200 ... Carbon concentration measuring device 20 ... Cooling unit 22 ... Silicon crystal 24 ... Window 26 ... Mounting table 30 ... Laser light generating unit 32 ... Laser beam 40 ... Spectrum measuring unit 50 ... Concentration calculation unit 60 ... C line 70 ... G line 80, 110 ... Band end emission 90 ... Multi-excitator-based emission 92 ... Emission 100 derived from dopant impurities ... 1610 nm emission band

Claims (9)

It is a carbon concentration measuring method that measures the carbon concentration in a silicon crystal containing carbon by the photoluminescence method .
(A) A step of cooling the silicon crystal in which the carbon atom at the lattice position is displaced to the interstitial position to a temperature range of 63K to 100K, and
(B) After the step (A), a step of exciting carriers to the silicon crystal and a step.
(C) A step of measuring the emission intensity of a plurality of wavelengths included in the emission spectrum of the silicon crystal whose carrier was excited in the step (B), and a step of measuring the emission intensity.
(D) A step of calculating the carbon concentration in the silicon crystal based on the integrated intensity of the emission peak obtained by integrating the emission intensity of the wavelength in the range including the specific wavelength selected from the plurality of wavelengths measured in the step (C). ,
A method for measuring a carbon concentration, which comprises. The carbon concentration measuring method according to claim 1, wherein in step (C), the emission intensity is measured collectively for the emission intensity of the plurality of wavelengths. The carbon concentration measuring method according to claim 1 or 2, wherein the plurality of wavelengths include one wavelength in the range of at least 1120 nm to 1140 nm, and further comprises at least one of the plurality of wavelengths of 1278 nm or 1569 nm. Carbon concentration measuring method. In the carbon concentration measuring method according to any one of claims 1 to 3,
A method for measuring a carbon concentration, which comprises calculating the carbon concentration in the silicon crystal by setting the specific wavelengths to 1127 nm and 1278 nm or 1127 nm and 1569 nm in the step (D). It is a carbon concentration measuring method for measuring the carbon concentration in a silicon crystal containing carbon.
(A) A step of exciting carriers in the air at room temperature to a silicon crystal in which the carbon atom at the lattice position is displaced to the interstitial position.
(B) A step of measuring the emission intensity of a plurality of wavelengths included in the emission spectrum of the silicon crystal whose carrier was excited in the step (A), and a step of measuring the emission intensity.
(C) A step of calculating the carbon concentration in the silicon crystal based on the emission intensity of a specific wavelength selected from the plurality of wavelengths measured in the step (B) or the integrated intensity of the emission peak including the specific wavelength.
Equipped with
The method for measuring a carbon concentration in the step (C), wherein the specific wavelengths are 1140 nm and 1610 nm . The carbon concentration measuring method according to claim 5, wherein in step (B), the emission intensity is measured collectively for the emission intensity of the plurality of wavelengths. It is a carbon concentration measuring device that measures the carbon concentration in a silicon crystal containing carbon by the photoluminescence method .
A cooling unit that cools a silicon crystal in which the carbon atom at the lattice position is displaced to the interstitial position in a temperature range of 63K to 100K, and a cooling unit.
The excited part that excites the carrier in the silicon crystal,
A spectrum measuring unit for measuring emission intensities of a plurality of wavelengths included in the emission spectrum of the excited silicon crystal, and a spectrum measuring unit.
A concentration calculation unit that calculates the carbon concentration in the silicon crystal based on the integrated intensity of the emission peak obtained by integrating the emission intensity of a wavelength in the range including a specific wavelength selected from a plurality of wavelengths measured by the spectrum measurement unit.
A carbon concentration measuring device characterized by being provided with. A carbon concentration measuring device that measures the carbon concentration in silicon crystals containing carbon.
An excited part that excites carriers in the atmosphere at room temperature on a silicon crystal in which the carbon atom at the lattice position is displaced to the interstitial position.
A spectrum measuring unit for measuring emission intensities of a plurality of wavelengths included in the emission spectrum of the excited silicon crystal, and a spectrum measuring unit.
A concentration calculation unit that calculates the carbon concentration in the silicon crystal based on the emission intensity of a specific wavelength selected from a plurality of wavelengths measured by the spectrum measurement unit or the integrated intensity of the emission peak including the specific wavelength.
Equipped with
A carbon concentration measuring device, characterized in that the selected specific wavelengths are 1140 nm and 1610 nm . In the carbon concentration measuring apparatus according to claim 7 or 8.
A carbon concentration measuring device, wherein the spectrum measuring unit collectively measures emission intensities of a plurality of specific wavelengths.

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