Method for evaluating semiconductor sample, device for evaluating semiconductor sample, and method for manufacturing semiconductor wafer

Abstract

Provided is a method for evaluating a semiconductor sample, the method including: acquiring an attenuation curve by performing a plurality of times of measurement by a photoconductivity attenuation method on a semiconductor sample to be evaluated by changing a surface charge density; performing signal data processing on at least one attenuation curve among the attenuation curves obtained by the plurality of measurements using a model formula including an exponential attenuation term and a constant term; calculating the composite lifetime [tau] eff of the semiconductor sample according to an exponential decay formula obtained by processing the signal data; obtaining a quadratic function using a surface charge density-related value as a variable x and a value related to the constant term as a variable y on the basis of measurement results obtained by the plurality of measurements; and obtaining the surface composite lifetime [tau] s of the semiconductor sample according to the quadratic function.

Description

Technical Field

[0001] The present invention relates to a method for evaluating a semiconductor sample, an apparatus for evaluating a semiconductor sample, and a method for manufacturing a semiconductor wafer. Background Art

[0002] The photoconductivity decay method, generally referred to as the PCD method, is widely used in the evaluation of semiconductor samples.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-012740

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 58-181549

[0007] Non-patent literature

[0008] Non-patent document 1: Usami Akira, Sone Fukuyasu, Murai Koji, and Sano Kenji, Laser Research, Vol. 12, No. 10, 1984, pp. 585-594

[0009] Non-patent document 2: Usami Akira, Shinichi Kamitsu, and Hiroshi Kudo, Applied Physics, Vol. 49, No. 12, 1980, pp. 1192-1197 Summary of the Invention

[0010] Technical problem to be solved by the invention

[0011] For example, for silicon wafers as an example of semiconductor samples, a method for measuring recombination lifetime based on the PCD method is standardized (SEMI MF1535. Test Methods for Carrier Recombination Lifetime in Silicon Wafers by Noncontact Measurement of Photoconductivity Decay by Microwave Reflectance. 2007; hereinafter referred to as “SEMI standard”).

[0012] The SEMI standard describes the first-order mode method and the 1 / e life method as methods for determining the recombination lifetime using the PCD method. In the first-order mode method, the time constant within the range that can be regarded as exponential decay in the decay curve obtained by measurement using the PCD method is defined as the first-order mode lifetime τ1. The first-order mode lifetime τ1 is calculated based on the SRH (Shockley-Read-Hall) recombination lifetime (i.e., bulk lifetime) τ band surface recombination lifetime τ s , by the formula: 1 / τ1=1 / τ b +1 / τ s On the other hand, in the 1 / e lifetime method, when the time for the light pulse to excite excess carriers in the semiconductor sample is t0, the time until the signal intensity becomes 1 / e times the peak value V0 of the signal intensity V (V1 = V0 / e) is t1, and the 1 / e lifetime τ e By the formula: τ e =t1-t0.

[0013] In the above method, the recombination lifetime is calculated under the assumption that the decay of excess carrier concentration is exponentially due only to the contribution of SRH recombination (i.e., bulk recombination). However, as described in Patent Document 2, for example, the recombination lifetime (described as "effective lifetime τ eff ”), in addition to the SRH recombination lifetime (bulk lifetime) τ determined by the purity of the semiconductor crystal of the semiconductor sample to be evaluated, crystal defects, etc. b In addition, it also involves the surface recombination life τ s For example, in highly clean silicon wafers, the contribution of SRH recombination is relatively weak, so the contribution of surface recombination and other factors cannot be ignored. Therefore, when PCD measurements are performed on highly clean silicon wafers, for example, the decay curve is distorted by the influence of surface recombination at the end of the decay, resulting in a non-exponential decay. In this case, for example, the above-mentioned method, which assumes that the decay of excess carrier concentration is exponential due solely to the contribution of SRH recombination, makes it difficult to accurately measure the recombination lifetime.

[0014] Regarding surface recombination, evaluation methods that take surface recombination into account are proposed in Patent Document 1, Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2. However, the method proposed in Patent Document 1 requires two measurements for each sample, making the recombination lifetime unsuitable for samples with a time dependency from surface treatment, and requiring the creation of a database for analysis, which lacks versatility. Furthermore, the methods proposed in Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2 all eliminate deviations from exponential decay in the early stages of decay due to the influence of higher-order modes than the first-order mode as the influence of surface recombination. Therefore, these methods cannot reduce or eliminate the influence of deviations from exponential decay in the late stages of decay.

[0015] In view of the above circumstances, an object of one embodiment of the present invention is to provide a new evaluation method for evaluating the recombination lifetime of a semiconductor sample with high accuracy.

[0016] Means for solving technical problems

[0017] The present inventors have conducted intensive research and have found that the recombination lifetime τ can be obtained with high accuracy by performing signal data processing on the decay curve as follows: eff Furthermore, the present inventors have newly discovered that by using the model formula in the following manner, in addition to the recombination life τ eff In addition, the surface recombination lifetime τ can also be calculated s .

[0018] One embodiment of the present invention is as follows.

[0019] [1] A method for evaluating a semiconductor sample, comprising:

[0020] The surface charge density is varied and the photoconductivity decay method is repeatedly performed on the semiconductor sample to be evaluated to obtain a decay curve.

[0021] performing signal data processing using a model formula on at least one of the decay curves obtained through the multiple measurements, the model formula including an exponential decay term and a constant term;

[0022] According to the exponential decay formula obtained by the above signal data processing, the recombination lifetime τ of the above semiconductor sample is calculated eff ;

[0023] Based on the measurement results obtained by the above multiple measurements, a quadratic function is obtained, wherein the value related to the surface charge density is a variable x and the value related to the above constant term is a variable y; and

[0024] According to the above quadratic function, the surface recombination lifetime τ of the above semiconductor sample is calculated. s .

[0025] [2] The method for evaluating a semiconductor sample according to [1], wherein:

[0026] In the following formula (11)':

[0027] C min =τ eff / τ s ×n0…(11)'

[0028] (In formula (11), n0: equilibrium carrier concentration)

[0029] In the min The surface recombination lifetime τ is calculated as the minimum value of y in the quadratic function. s .

[0030] [3] The method for evaluating a semiconductor sample according to [1] or [2], wherein:

[0031] The evaluation method of the semiconductor sample further includes: according to the above-mentioned recombination lifetime τ eff And the above surface recombination lifetime τ s , calculate the SRH recombination lifetime τ of the above semiconductor sample b .

[0032] [4] The method for evaluating a semiconductor sample according to [3], wherein:

[0033] According to the following formula (1):

[0034] 1 / τ eff =1 / τ b +1 / τ s …(1)'

[0035] Calculate the above SRH composite life τ b .

[0036] [5] The method for evaluating a semiconductor sample according to any one of [1] to [4], wherein:

[0037] The evaluation method of the semiconductor sample further includes: determining the thickness d of the semiconductor sample and the surface recombination lifetime τ S , through the following formula (12):

[0038] S r =d / (2τ S )…(12)

[0039] Calculate the surface recombination velocity S of the above semiconductor sample r .

[0040] [6] The method for evaluating a semiconductor sample according to any one of [1] to [5], wherein:

[0041] The evaluation method of the semiconductor sample further includes:

[0042] By performing the above-mentioned signal data processing, the constant term in the above-mentioned model formula is offset to obtain the above-mentioned exponential decay formula; and

[0043] According to the above exponential decay formula, the time constant τ is obtained b -1 +τ S -1 ,

[0044] τ b is the SRH recombination lifetime, τ S is the surface recombination life.

[0045] [7] The semiconductor sample evaluation method according to [6], wherein:

[0046] The signal data processing includes repeatedly sampling the time series signal modeled by the model formula and obtaining a difference.

[0047] [8] The method for evaluating a semiconductor sample according to [7], wherein:

[0048] The semiconductor sample evaluation method further includes performing automatic scaling for determining a sampling region for performing the sampling.

[0049] [9] The semiconductor sample evaluation method according to [8], wherein:

[0050] By the automatic scaling described above, a region with little influence of Auger recombination and little influence of noise is determined as a sampling region.

[0051]

[10] The method for evaluating a semiconductor sample according to any one of [1] to [9], wherein:

[0052] The above model formula is the following formula (10)':

[0053] xi(ti)=A×exp[-(τ b -1 +τ S -1 )ti]-C…(10)'

[0054] (In formula (10), ti: the time after the excitation light irradiation, xi(ti): the signal intensity at the time ti, τ b : SRH recombination lifetime, τ S : surface recombination lifetime, A, C: constants).

[0055]

[11] The method for evaluating a semiconductor sample according to any one of [1] to

[10] , wherein:

[0056] In the following formula (11)':

[0057] C min =τ eff / τ s ×n0…(11)'

[0058] (In formula (11), n0: equilibrium carrier concentration)

[0059] In the min The surface recombination lifetime τ is calculated as the minimum value of y in the quadratic function. s ,

[0060] The evaluation method of the semiconductor sample further includes: according to the above-mentioned recombination lifetime τ effAnd the above surface recombination lifetime τ s , calculate the SRH recombination lifetime τ of the above semiconductor sample b ,

[0061] According to the following formula (1):

[0062] 1 / τ eff =1 / τ b +1 / τ s …(1)'

[0063] Calculate the above SRH composite life τ b ,

[0064] The evaluation method of the semiconductor sample further includes:

[0065] By performing the above-mentioned signal data processing, the constant term in the above-mentioned model formula is offset to obtain the above-mentioned exponential decay formula; and

[0066] According to the above exponential decay formula, the time constant τ is obtained b -1 +τ S -1 ,

[0067] τ b is the SRH recombination lifetime, τ S is the surface recombination life,

[0068] The signal data processing includes repeatedly performing the following operations: sampling the time series signal modeled by the above model formula to obtain a difference,

[0069] The semiconductor sample evaluation method further includes: performing automatic scaling for determining a sampling area for performing the sampling;

[0070] By the above automatic scaling, the region with little influence of Auger recombination and little influence of noise is determined as the sampling region.

[0071] The above model formula is the following formula (10)':

[0072] xi(ti)=A×exp[-(τ b -1 +τ S -1 )ti]-C…(10)'

[0073] (In formula (10), ti: the time after the excitation light irradiation, xi(ti): the signal intensity at the time ti, τ b : SRH recombination lifetime, τ S : surface recombination lifetime, A, C: constants).

[0074]

[12] The method for evaluating a semiconductor sample according to any one of [1] to

[11] , wherein:

[0075] In the following formula (11)':

[0076] C min =τ eff / τ s ×n0…(11)'

[0077] (In formula (11), n0: equilibrium carrier concentration)

[0078] In the min The surface recombination lifetime τ is calculated as the minimum value of y in the quadratic function. s ,

[0079] The evaluation method of the semiconductor sample further includes: determining the thickness d of the semiconductor sample and the surface recombination lifetime τ S , through the following formula (12):

[0080] S r =d / (2τ S )…(12)

[0081] Calculate the surface recombination velocity S of the above semiconductor sample r ,

[0082] The evaluation method of the semiconductor sample further includes:

[0083] By performing the above-mentioned signal data processing, the constant term in the above-mentioned model formula is offset to obtain the above-mentioned exponential decay formula; and

[0084] According to the above exponential decay formula, the time constant τ is obtained b -1 +τ S -1 ,

[0085] τ b is the SRH recombination lifetime, τ S is the surface recombination life,

[0086] The signal data processing includes repeatedly performing the following operations: sampling the time series signal modeled by the above model formula to obtain a difference,

[0087] The semiconductor sample evaluation method further includes: performing automatic scaling for determining a sampling area for performing the sampling;

[0088] By the above automatic scaling, the region with little influence of Auger recombination and little influence of noise is determined as the sampling region.

[0089] The above model formula is the following formula (10)':

[0090] xi(ti)=A×exp[-(τ b -1 +τ S -1 )ti]-C…(10)'

[0091] (In formula (10), ti: the time after the excitation light irradiation, xi(ti): the signal intensity at the time ti, τ b : SRH recombination lifetime, τ S : surface recombination lifetime, A, C: constants).

[0092]

[13] A semiconductor sample evaluation device for implementing the semiconductor sample evaluation method described in any one of [1] to

[12] , the evaluation device comprising:

[0093] a measuring unit that performs measurement on a semiconductor sample to be evaluated using a photoconductivity decay method; and

[0094] The processing unit performs signal data processing on the decay curve using a model equation including an exponential decay term and a constant term, and obtains the quadratic function.

[0095]

[14] The evaluation device according to

[13] , wherein

[0096] In the above-mentioned measuring unit, the intensity of the light pulse is variable.

[0097]

[15] The evaluation device according to

[13] or

[14] , wherein:

[0098] The measuring unit further includes a corona charging treatment unit.

[0099]

[16] The evaluation device according to any one of

[13] to

[15] , wherein

[0100] The measurement unit further includes a surface charge density-related value measurement unit for measuring a surface charge density-related value of the semiconductor sample subjected to the measurement.

[0101]

[17] The evaluation device according to any one of

[13] to

[16] , wherein

[0102] In the above-mentioned measuring unit, the intensity of the light pulse is variable.

[0103] The measurement unit further includes a corona charging treatment unit and a surface charge density-related value measurement unit for measuring a surface charge density-related value of the semiconductor sample being measured.

[0104]

[18] A method for manufacturing a semiconductor wafer, comprising:

[0105] manufacturing a semiconductor wafer batch comprising a plurality of semiconductor wafers;

[0106] extracting at least one semiconductor wafer from the batch of semiconductor wafers;

[0107] evaluating the extracted semiconductor wafer by the evaluation method described in any one of [1] to

[12] ; and

[0108] Semiconductor wafers from the same semiconductor wafer lot as the semiconductor wafers determined as non-defective products as a result of the above evaluation are prepared for shipment as product semiconductor wafers.

[0109]

[19] A method for manufacturing a semiconductor wafer, comprising:

[0110] manufacturing a semiconductor wafer for evaluation under test manufacturing conditions;

[0111] Evaluating the manufactured semiconductor wafer for evaluation using the semiconductor sample evaluation method described in any one of [1] to

[12] ;

[0112] Based on the evaluation result, determining the manufacturing conditions obtained by modifying the test manufacturing conditions as the actual manufacturing conditions, or determining the test manufacturing conditions as the actual manufacturing conditions; and

[0113] Semiconductor wafers are manufactured under the actual manufacturing conditions determined above.

[0114] Effects of the Invention

[0115] According to one embodiment of the present invention, the recombination lifetime τ can be obtained with high accuracy. eff , and then we can also calculate the surface recombination lifetime τ s . BRIEF DESCRIPTION OF THE DRAWINGS

[0116] Figure 1 This is an explanatory diagram of a specific example of signal data processing.

[0117] Figure 2 This is an explanatory diagram of a specific example of signal data processing.

[0118] Figure 3 This is an explanatory diagram of a specific example of signal data processing.

[0119] Figure 4 It is an explanatory diagram of an example of a method for evaluating a semiconductor sample according to one embodiment of the present invention.

[0120] Figure 5Results of comparison between an example (new method) of a semiconductor sample evaluation method according to one embodiment of the present invention and a conventional method are shown.

[0121] Figure 6 Results of comparison between an example (new method) of a semiconductor sample evaluation method according to one embodiment of the present invention and a conventional method are shown.

[0122] Figure 7 Results of comparison between an example (new method) of a semiconductor sample evaluation method according to one embodiment of the present invention and a conventional method are shown.

[0123] Figure 8 is used to derive the surface recombination lifetime τ S Schematic diagram of the drawing.

[0124] Figure 9 The quadratic curve obtained in Example 1 is shown.

[0125] Figure 10 It shows the quadratic curve obtained in Example 2.

[0126] Figure 11 The figure shows a decay curve obtained by performing a chemical passivation treatment on an n-type silicon wafer (single crystal silicon wafer) as a surface treatment and then measuring the surface using the μ-PCD method.

[0127] Figure 12 Express Figure 11 The decay curve shown is a fitting curve obtained by fitting the first-order mode lifetime and a fitting curve obtained by fitting the 1 / e lifetime. DETAILED DESCRIPTION

[0128] [Evaluation Method for Semiconductor Samples]

[0129] A method for evaluating a semiconductor sample according to one embodiment of the present invention comprises: performing a plurality of photoconductivity decay measurements on the semiconductor sample to be evaluated, while varying the surface charge density, to obtain decay curves; performing signal data processing using a model formula comprising an exponential decay term and a constant term on at least one of the decay curves obtained by the plurality of measurements; and determining a recombination lifetime τ of the semiconductor sample based on the exponential decay formula obtained by the signal data processing. eff ; Based on the measurement results obtained by the above multiple measurements, a quadratic function is obtained with the value associated with the surface charge density as the variable x and the value associated with the above constant term as the variable y; and the surface recombination lifetime τ of the above semiconductor sample is obtained based on the above quadratic function s .

[0130] Hereinafter, the above-mentioned evaluation method will be described in more detail.

[0131] <Evaluation target semiconductor samples>

[0132] The evaluation object of the above-mentioned evaluation method can be any semiconductor sample. Examples of semiconductor samples include single crystal silicon, polycrystalline silicon, SiC, and other semiconductor samples. The shape and size of the semiconductor sample to be evaluated are not particularly limited. As an example, the semiconductor sample to be evaluated can be a wafer-shaped semiconductor sample, i.e., a semiconductor wafer, such as a single crystal silicon wafer. However, the semiconductor sample to be evaluated can also be in a shape other than a wafer. In addition, the conductivity type of the semiconductor sample to be evaluated is not particularly limited and can be either n-type or p-type.

[0133] <Measurement by the photoconductivity decay method>

[0134] For the measurement using the photoconductivity attenuation method in the above-mentioned evaluation method, known techniques can be applied. As a specific example of the photoconductivity attenuation method, the microwave photoconductivity attenuation (μ-PCD) method can be cited. However, the measurement using the photoconductivity attenuation method in the above-mentioned evaluation method is not limited to the measurement using the μ-PCD method. For example, if the maximum carrier injection amount of a general μ-PCD device is considered, when the semiconductor sample to be evaluated is p-type silicon, its resistivity is preferably about 1 to 100 Ωcm, and when it is n-type silicon, the resistivity is preferably about 0.5 to 100 Ωcm.

[0135] During measurement, excess carriers are first excited in the semiconductor sample being evaluated using a light pulse. Therefore, a PCD device with a measurement unit capable of setting the light pulse intensity to a desired value (i.e., variable) is used, and measurement is performed with the light pulse intensity set to an appropriate value.

[0136] In addition, as described later, in order to change the surface charge density and perform multiple measurements, a PCD device having a corona charging treatment unit in the measurement unit is used, and the surface charge density can be changed and multiple measurements can be performed, for example, by changing the number of corona charging times. For example, a PCD device having a corona charging treatment unit can be used, and the corona charging treatment unit can apply positive charge, negative charge, or positive and negative charges to the surface of a semiconductor sample by a corona charging method, or apply positive charge or negative charge to the surfaces of multiple semiconductor samples by a corona charging method. Alternatively, in order to change the surface charge density and perform multiple measurements, the surface charge density of the semiconductor sample of the measurement object can also be changed by changing the concentration of the reagent (such as iodine, hydroquinone, etc.) used in the chemical passivation treatment and / or changing the treatment time. In this case, it is preferred to use a PCD device having a device structure corresponding to chemical passivation. Examples of such PCD devices include a device having a mechanism for applying a chemical solution (such as an iodine-ethanol solution) on the front and back surfaces of a semiconductor sample and performing measurements while the sample is placed in a transparent bag such as polyethylene; a device having a mechanism for applying a chemical solution (such as an iodine-ethanol solution) on the front and back surfaces of a semiconductor sample outside the device and directly performing measurements on the substance placed in a transparent bag such as polyethylene; and the like.

[0137] Furthermore, a PCD device equipped with a device for measuring surface charge density-related values, such as surface charge amount and surface potential, can be used. For example, by measuring the surface charge amount and surface potential using a surface charge density-related value measuring device such as a Kelvin probe or a non-contact CV measurement device, the surface charge density in each measurement can be determined. An example of a surface charge density-related value measuring device is a non-contact CV measurement device that measures surface charge density-related values ​​by applying a voltage across a gap provided between the surface of a semiconductor sample and an electrode facing the surface.

[0138] The above-mentioned measurement using the photoconductivity decay method produces a decay curve. Specifically, a decay curve represents the temporal variation of signal intensity relative to the time elapsed after excitation light irradiation. Specifically, "time elapsed after excitation light irradiation" refers to the time elapsed from the end of excitation light irradiation. Furthermore, in the μ-PCD method, for example, signal intensity refers to the intensity of the reflected microwaves. Figure 11 The figure shows a decay curve obtained by performing a chemical passivation treatment on an n-type silicon wafer (single crystal silicon wafer) as a surface treatment and then measuring the surface using the μ-PCD method. Figure 11 The decay curve shown is deformed from the mid- to the end-stage region due to the effects of surface recombination. Figure 12 Express Figure 11 The decay curves shown are fitted curves obtained by fitting the first-order mode lifetime described in the SEMI standard and the 1 / e lifetime described in the SEMI standard. Figure 12 Both fitting curves shown do not fit the decay curve from the mid- to late-stage regions. This is because the first-order mode method and the 1 / e lifetime method are fitted under the assumption that the decay of excess carrier concentration is exponential due solely to the contribution of SRH recombination.

[0139] In contrast, in the above evaluation method, by performing signal data processing on the decay curve as described in detail below, the recombination lifetime τ can be obtained with high accuracy. eff .

[0140] <Recombination life τ eff Export >

[0141] (Signal data processing of attenuation curve)

[0142] In the above evaluation method, a model formula including an exponential decay term and a constant term is used to perform signal data processing on at least one decay curve obtained by measuring the semiconductor sample to be evaluated using the photoconductivity decay method. The decay curves for which signal data processing is performed may be only one or two or more. In the case of two or more decay curves, for example, the average value of the recombination lifetimes obtained by signal data processing of the decay curves may be used as the recombination lifetime τ of the semiconductor sample to be evaluated. eff As the attenuation curve for signal data processing, it is preferred to use the attenuation curve obtained by measuring under the measurement condition with a small surface charge density among the multiple attenuation curves obtained by the above-mentioned multiple measurements, and it is more preferred to use the attenuation curve obtained by measuring under the measurement condition with the smallest surface charge density among the multiple measurements. For example, in the case of changing the surface charge density by changing the number of corona charging times, it is preferred to use the attenuation curve obtained by measuring with a corona charging number of zero. It is most preferred to use the attenuation curve obtained by measuring under the measurement condition with a surface charge density of zero, but in practice, the surface charge density can generally be measured at a value exceeding 0.

[0143] In the above model equation, the constant term is included in addition to the exponential decay term. The inventors believe that it is appropriate to express the decay curve when surface recombination occurs using an equation containing an exponential decay term and a constant term, preferably an equation in which the constant term is subtracted from the exponential decay term. By subjecting such an equation to signal data processing that cancels out the constant term, only the exponential decay term remains. In other words, an exponential decay equation is obtained. By using this exponential decay equation, the recombination lifetime can be calculated as a value that includes the effects of SRH recombination and surface recombination. This allows the recombination lifetime of the semiconductor sample being evaluated to be determined with high accuracy. The above signal data processing is described in more detail below.

[0144] If the excess carrier concentration is set to x[1 / cm 3 ], let the function of time be x(t), then the function x(t) can be approximately expressed by the following formula (1).

[0145] x(t)=A×exp[-(τ b -1 +τ S -1 )t]-C…(1)

[0146] In formula (1), τ b Indicates the SRH recombination lifetime, in units such as μsec, τ S represents the surface recombination lifetime, and its unit is, for example, μsec. A and C each independently represent a constant [1 / cm 3 ], preferably represents a positive constant. A and C are based on τ b -1 +τ S -1 The above formula (1) is a function that expresses the excess carrier concentration as a function of time x(t) when both SRH recombination and surface recombination based on surface energy levels contribute to the recombination lifetime, and is preferably used when the excess carrier concentration is greater than the carrier concentration in the equilibrium state.

[0147] As a model equation for performing signal data processing based on equation (1), the following equation (10)' can be cited.

[0148] xi(ti)=A×exp[-(τ b -1 +τ S -1 )ti]-C…(10)'

[0149] In formula (10), ti is the time after the excitation light is irradiated, xi(ti) is the signal intensity at the time ti, and the unit is, for example, mV. b is the SRH recombination lifetime, τ S is the surface recombination lifetime, A and C are independent constants, and the unit is, for example, mV. The above model equation (10)' contains an exponential decay term and a constant term. Specifically, it is derived from the exponential decay term "A×exp[-(τ b -1 +τ S -1 )ti]" minus the constant term "C". Equation (10)' is an example of the above-mentioned model equation. For example, if a model equation containing a constant term such as Equation (10)' is subjected to signal data processing to cancel the constant term, only the exponential decay term remains. Therefore, the time constant τ can be obtained by the exponential decay approximation method.b -1 +τ S -1 (The sum of the inverse of the surface recombination life and the inverse of the SRH recombination life). b -1 +τ S -1 The reciprocal of the recombination lifetime τ of the semiconductor sample to be evaluated eff As the exponential decay approximation method, a general exponential decay approximation method such as the first-order lifetime method and the 1 / e lifetime method can be used.

[0150] Hereinafter, a specific example of signal data processing will be described using the case where the model equation is equation (10)'. However, the signal data processing described below is an example, and the present invention is not limited to the above example.

[0151] Signal data processing involves determining a sampling region within the attenuation curve obtained by measurement using the photoconductivity attenuation method. Within this sampling region, the time series signal modeled using the above-described model formula (specifically, measurement points on the attenuation curve) is repeatedly sampled and differentiated. The sampling region can be determined, for example, through automatic scaling. A specific example is the following method. For example, the following method can be used to determine a region with minimal influence from Auger recombination and minimal influence from noise as the sampling region. Specifically, by excluding regions of high signal intensity where Auger recombination is strongly influenced and regions of low signal intensity where noise is strongly influenced, the sampling region can be selected as the sampling region.

[0152] First, set an arbitrary signal strength (e.g., 60% of the peak value) as the starting point of the sampling area and perform signal data processing. 2 The value, residual sum of squares, etc. can be used as an index of the degree of suitability for exponential decay. The degree of suitability for exponential decay is evaluated based on whether the calculated value of the above index meets a preset threshold.

[0153] When the above calculated value meets the preset threshold (for example, R 2 ≥0.99), the starting point of the sampling region set as described above can be determined as the starting point of the sampling region when the signal data processing is executed.

[0154] When the above calculated value does not meet the preset threshold (for example, R 2≥0.99), the starting point of the sampling area is moved toward the side with lower signal strength and recalculation is performed. Recalculation can be performed once or twice or more. If the evaluation result of the recalculation meets a predetermined threshold, the starting point of the recalculation can be determined as the starting point of the sampling area.

[0155] The end point of the sampling area can be set to the position where the signal-to-noise ratio (SN) falls below a preset threshold. The SN ratio can be calculated, for example, using the following formula. The SN ratio threshold can be, for example, 5 dB or less. The end point is preferably determined as the position where the SN ratio of the signal reaches 0 dB, i.e., where the noise and signal are at the same level.

[0156] SN ratio [dB] = 20log 10 [(Dispersion of the signal at any time) / (Dispersion of the noise at equilibrium)]

[0157] Figures 1 to 3 This diagram illustrates a specific example of signal data processing. For example, signal data processing can be performed as follows, assuming the number of sampling points is 3N. Here, N is an arbitrary integer, for example, 2 or greater. Furthermore, for example, if the total number of signal data points is 1000, N can be 333 or less. That is, for example, if the total number of signal data points is T, N can be an integer less than "T × 1 / 3."

[0158] First, taking the starting point (point 1) as the reference, calculate the average A1 of points 1 to N and the average B1 of points N+1 to 2N (refer to Figure 1 ).

[0159] A1={x(t1)+x(t2)+…+x(t N )} / N

[0160] B1={x(t N+1 )+x(t N+2 )+…+x(t 2N )} / N

[0161] The value obtained by subtracting B1 from A1 is set to Y(t1).

[0162] Y(t1)=A1-B1

[0163] Next, taking the second point as the reference, calculate the average A2 of the second point to the N+1 point and the average B2 of the N+2 point to the 2N+1 point (refer to Figure 2 ).

[0164] A2={x(t2)+x(t3)+…+x(t N+1 )} / N

[0165] B2={x(t N+2 )+x(t N+3 )+…+x(t 2N+1 )} / N

[0166] The value obtained by subtracting B2 from A2 is set to Y(t2).

[0167] Y(t2)=A2-B2

[0168] Continue the same calculation and finally calculate the average A from point N+1 to point 2N N+1 and the average B from point 2N+1 to point 3N N+1 (Refer to Figure 3 ).

[0169] A N+1 ={x(t N+1 )+x(t N+2 )+…+x(t 2N )} / N

[0170] B N+1 ={x(t 2N+1 )+x(t 2N+2 )+…+x(t 3N )} / N

[0171] Will start from A N+1 Subtract B N+1 The value after is set to Y(t N+1 ).

[0172] Y(t N+1 )=A N+1 -B N+1

[0173] The time series signal data obtained by continuing the above calculation cancels out the constant term in equation (10)', resulting in the following exponential decay equation (2). By applying the general exponential decay approximation method to equation (2), the time constant τ can be obtained. b -1 +τ S -1 . The “τ” obtained in this way can be used b -1 +τ S -1 "The recombination lifetime τ of the semiconductor sample to be evaluated eff As the exponential decay approximation method, for example, the first-order mode method and the 1 / e lifetime method can be cited.

[0174] Y(t)=A'×exp[-(τ b -1 +τS -1 )t]…(2)

[0175] (A': arbitrary constant)

[0176] (compound life τ eff Specific calculation method)

[0177] Figure 4 It is an explanatory diagram of an example of a method for evaluating a semiconductor sample according to one embodiment of the present invention.

[0178] Figure 4 The decay curve shown on the left is Figure 11 The same decay curve is shown, obtained by measuring an n-type silicon wafer (single crystal silicon wafer, resistivity: 10Ωcm) using the μ-PCD method after chemical passivation as a surface treatment. The maximum carrier injection rate of the μ-PCD here is approximately 1E17 / cm 3 In addition, "E17" means "×10 17 ”.

[0179] for Figure 4 The attenuation curve shown in the left figure uses formula (10)' as the model formula, referring to Figures 1 to 3 As explained above, the number of sampling points is set to 3N points and the signal data processing is performed. The starting point of the sampling area is set by setting the threshold value to "R 2 ≥0.99” is determined as described above. The end point of the sampling area is the position where the SN ratio is 0 dB as described above.

[0180] By performing the above signal data processing, the constant term of equation (10)' is canceled, and a straight line ( Figure 4 The solid line in the right figure). For this linear equation, the time constant τ is obtained by applying the first-order model method. b -1 +τ S -1 , as the time constant τ b -1 +τ S -1 The composite life obtained by the reciprocal of (in Table 1, Example A) is the value shown in Table 1.

[0181] for Figure 4 Table 1 also shows the decay curve shown in the left figure, and the composite lifetimes obtained by applying the first-order mode method and the 1 / e method described in the SEMI standard.

[0182] [Table 1]

[0183] First-order model method 3453.1μsec 1 / e lifespan method 3510.5μsec Example A 6323.3μsec

[0184] From the results shown in Table 1, it can be confirmed that the value of the composite lifetime is underestimated by about 60% compared with Example A in the conventional first-order model method and the 1 / e lifetime method.

[0185] Next, it was confirmed by the following method that the function of equation (1) is a function close to the actually measured decay time.

[0186] First, in order to determine the remaining undetermined parameter constants A and C in equation (1), fitting is performed as follows.

[0187] If we use the time constant τ obtained in the above example b -1 +τ S -1 , then formula (1) is relative to exp[-(τ b -1 +τ S -1 )t] becomes a straight line. That is, in the sampling area determined by automatic scaling, the attenuation curve is as follows Figure 5 As shown in the left figure, it can be compared with exp[-(τ b -1 +τ S -1 )t] is approximated by a straight line, and constants A and C can be obtained as its slope and intercept.

[0188] If we use the time constant τ obtained in this way b -1 +τ S -1 and constants A and C and apply formula (1), then Figure 5 As shown in the figure on the right, the case of fitting by the first-order model method or the 1 / e lifetime method ( Figure 5 In the right figure, the first-order mode lifetime fitting and 1 / e lifetime fitting are compared to obtain a fitting curve that is suitable for a wide range of the decay curve ( Figure 5 (right figure, new method fitting).

[0189] From the above results, it can be confirmed that the function of formula (1) is a function close to the actually measured decay time.

[0190] Figure 6 as well as Figure 7 Results of comparison between an example (new method) of a semiconductor sample evaluation method according to one embodiment of the present invention and a conventional method are shown.

[0191] Figure 6The left figure shows the composite lifetime values ​​( Figure 6 The new method) and the composite life value obtained by the first-order model method as a conventional method ( Figure 6 in the “Previous Methods” section). Figure 6 The right picture shows Figure 6 The left graph shows the CV values ​​of the measurement results (standard deviation / arithmetic mean × 100, unit: %). Figure 6 The results shown confirm that the new method suppresses variations in composite life values ​​compared to the conventional method.

[0192] Figure 7 Indicates Figure 6 In the conventional method, for sample mark 1 with the largest difference in the positive direction and sample mark 2 with the largest difference in the negative direction, the attenuation curve obtained by the measurement based on the μ-PCD method is fitted by equation (1) as described above, and the fitting curve is obtained by fitting by the first-order mode method as the conventional method. Figure 7 In the figure, the composite life values ​​of each sample obtained by the new method and the conventional method are also shown. Figure 7 The results shown also confirm that the function of equation (1) is close to the actually measured decay time function.

[0193] <Surface recombination life τ s 、SRH composite life τ b , surface recombination velocity S r Export >

[0194] On the surface recombination lifetime τ s The inventors' in-depth research has led to a new understanding that, using Poisson's equation, the constant term C in equation (10)' can be expressed as equation (11) regarding the charge distribution near the surface of a semiconductor sample (the relationship between carrier concentration and surface charge density). Equation (11) shows that the constant term is a quadratic function of the surface charge density Qs, allowing analysis to be performed as a quadratic function.

[0195] C=(τ eff / τ s ) / (2kTε s ε0)×Q s 2 +τ eff / τ s ×n0…(11)

[0196] In formula (11), k is the Boltzmann constant [eV / K], T is the absolute temperature [K], ε sis the dielectric constant of the semiconductor sample [F / m], ε0 is the dielectric constant of vacuum [F / m], Q s is the surface charge density [F / m 2 ], n0 is the equilibrium carrier concentration [cm -3 ].

[0197] τ in formula (11) eff As described above, it can be derived by performing fitting calculation based on the formula (10)' on the attenuation curve obtained by measuring the semiconductor sample to be evaluated using the photoconductivity attenuation method.

[0198] then, Figure 8 is used to derive the surface recombination lifetime τ s Schematic diagram of the plot. In order to derive τ s , changing the surface charge density, repeatedly performing the measurement of the semiconductor sample to be evaluated by the photoconductivity attenuation method to obtain the attenuation curve. For the attenuation signal obtained at each different surface charge density, if the constant term C calculated using formula (10) is plotted against the surface charge density Qs, it becomes a quadratic function as shown in formula (11) (refer to Figure 8 ). Figure 8 The minimum value C of the quadratic function shown min The second term "τ eff / τ s ×n0" is represented by the following formula (11)'.

[0199] C min =τ eff / τ s ×n0…(11)'

[0200] Therefore, by setting the minimum value C of the quadratic function min , equilibrium carrier concentration n0 and τ eff Substituting into formula (11)', the surface recombination lifetime τ can be calculated S However, in the μ-PCD method, the microwave reflectivity signal intensity is measured using voltage, and the unit of C is voltage. Therefore, the relationship between the reflectivity signal intensity and the carrier concentration is converted using the amount of carriers injected by the light pulse and the initial reflectivity signal intensity of the microwave. The equilibrium carrier concentration n0 is the equilibrium carrier concentration of the semiconductor sample being measured.

[0201] The second term “τ eff / τ s ×n0” minimum value C min For example, Figure 8As shown, the measurement points can be plotted on a graph with C on the vertical axis (y-axis) and the surface charge density on the horizontal axis (x-axis), and the minimum value of the vertical axis y in the quadratic function (quadratic curve) obtained by fitting these plots using a well-known method such as the least squares method can be obtained.

[0202] exist Figure 8 In the example shown, the vertical axis (y-axis) is taken as the absolute value of the constant term C, and the horizontal axis (x-axis) is taken as the surface charge density. However, the variable x of the horizontal axis is not limited to the value of the surface charge density itself. For example, the surface charge density can be changed according to the number of corona charging treatments (i.e., the number of corona charging times). In the case where the surface charge density is changed according to the number of corona charging times, the number of corona charging times can also be used as the variable x of the horizontal axis. As an example, as the variable x of the horizontal axis, the number of corona charging times for applying positive charges can be set to a positive value (for example, if it is one time, x=1), and the number of corona charging times for applying negative charges can be set to a negative value (for example, if it is one time, x=-1). In addition, the variable y of the horizontal axis is not limited to the absolute value of the constant term C. For example, the value of the constant term C itself can be used as the variable y of the vertical axis.

[0203] That is, a quadratic function is obtained by fitting a plot using the value associated with the surface charge density as the variable x and the value associated with the constant term as the variable y using a known method: y = ax 2 +bx+c. a is a positive constant, b and c are positive or negative constants or zero. The minimum value of y in this quadratic function is taken as C in formula (11). min , the surface recombination lifetime τ can be calculated according to formula (11) s .

[0204] Then, by setting τ eff and τ S Substitute into formula (1)':

[0205] 1 / τ eff =1 / τ b +1 / τ s …(1)'

[0206] The SRH composite life (body life) τ can be calculated b .

[0207] In addition, the surface recombination velocity S r It can be calculated based on the thickness d of the semiconductor sample and the surface recombination lifetime τ S , is calculated using the following formula (12).

[0208] S r =d / (2τ S )…(12)

[0209] [Evaluation equipment for semiconductor samples]

[0210] One embodiment of the present invention relates to an evaluation device for a semiconductor sample that implements the aforementioned evaluation method. The evaluation device includes: a measurement unit that measures the semiconductor sample to be evaluated using the photoconductivity decay method; a processing unit that performs signal processing on the decay curve using a model equation containing an exponential decay term and a constant term; and a processing unit that calculates the aforementioned quadratic function.

[0211] The measurement unit performs measurement on the semiconductor sample being measured using the photoconductivity decay method. The measurement unit can vary the intensity of the light pulse. This is as previously described. Furthermore, in one embodiment, the measurement unit may include a corona charging treatment unit to change the surface charge density. Details of the measurement unit are as previously described. Furthermore, as previously described for the PCD device, the measurement unit may also include a surface charge density correlation value measurement device.

[0212] To implement the semiconductor sample evaluation method according to one embodiment of the present invention, the processing unit of the evaluation device performs signal data processing on a decay curve using a model equation including an exponential decay term and a constant term, and calculates the quadratic function. The processing unit can be configured using a known analysis program.

[0213] In addition, the processing unit can process the signal data using a model formula including an exponential decay term and a constant term on the decay curve, cancel the constant term in the model formula, obtain the exponential decay formula, and calculate the time constant τ based on the exponential decay formula. b -1 +τ S -1 .

[0214] The signal data processing may include repeatedly sampling the time series signal modeled by the model formula and obtaining a difference.

[0215] Furthermore, the processing unit may perform automatic scaling to determine a sampling area for the sampling. The processing unit may use the automatic scaling to determine an area with less influence from composites and noise as the sampling area. The automatic scaling is as described above.

[0216] In the above-mentioned evaluation device, the measuring unit or the calculating unit provided separately from the measuring unit can derive the recombination lifetime τ of the above-mentioned semiconductor sample based on the exponential decay formula obtained by the above-mentioned signal data processing. eff . Calculate the surface recombination life τ after the quadratic function S 、SRH composite life τ band the surface recombination velocity S r The derivation of the values ​​may be performed by the measuring unit or the calculation unit provided separately from the measuring unit. These derivations may also be performed using a known analysis program provided in the measuring unit or the calculation unit.

[0217] In one embodiment, in the evaluation device described above, a PCD measuring device having a measuring unit that performs measurements using the PCD method may further include the processing unit and / or the computing unit. Furthermore, in another embodiment, one or more computers separate from the PCD measuring device having a measuring unit that performs measurements using the PCD method may include the processing unit and / or the computing unit. Various information, such as measurement results, processing results, and computing results, may be transmitted and received between the computers and the PCD measuring device, or between multiple computers, via wired or wireless communication. A single computer may include both the processing unit and the computing unit, or different computers may each include both the processing unit and the computing unit.

[0218] [Method for manufacturing semiconductor wafer]

[0219] One embodiment of the present invention relates to a method for manufacturing a semiconductor wafer (hereinafter also referred to as “manufacturing method 1”), comprising:

[0220] manufacturing a semiconductor wafer batch comprising a plurality of semiconductor wafers;

[0221] extracting at least one semiconductor wafer from the batch of semiconductor wafers;

[0222] evaluating the extracted semiconductor wafer by the above-mentioned evaluation method; and

[0223] Semiconductor wafers from the same semiconductor wafer lot as the semiconductor wafers determined as non-defective products as a result of the above evaluation are prepared for shipment as product semiconductor wafers.

[0224] Furthermore, one embodiment of the present invention relates to a method for manufacturing a semiconductor wafer (hereinafter also referred to as “manufacturing method 2”), comprising:

[0225] manufacturing a semiconductor wafer for evaluation under test manufacturing conditions;

[0226] evaluating the manufactured semiconductor wafer for evaluation using the semiconductor sample evaluation method;

[0227] Based on the evaluation result, determining the manufacturing conditions obtained by modifying the test manufacturing conditions as the actual manufacturing conditions, or determining the test manufacturing conditions as the actual manufacturing conditions; and

[0228] Semiconductor wafers are manufactured under the actual manufacturing conditions determined above.

[0229] In manufacturing method 1, semiconductor wafers from the same batch as those determined to be acceptable after so-called spot checks are prepared for shipment as product semiconductor wafers. On the other hand, in manufacturing method 2, semiconductor wafers manufactured under test manufacturing conditions are evaluated, and actual manufacturing conditions are determined based on the evaluation results. In both manufacturing methods 1 and 2, semiconductor wafer evaluation is performed using the evaluation method according to one embodiment of the present invention described above.

[0230] In manufacturing method 1, the manufacture of semiconductor wafer batches can be carried out in the same manner as the manufacturing method of general semiconductor wafers. For example, as an example of a silicon wafer as a mode of semiconductor wafer, a polished wafer can be cited. The polished wafer can be manufactured by the following manufacturing process, which includes cutting (slicing) of a silicon wafer from a silicon single crystal ingot grown by the Czochralski method (CZ method) or the like, chamfering, rough grinding (e.g., grinding), etching, mirror grinding (fine grinding), and cleaning performed between or after the above-mentioned processing steps. In addition, an annealed wafer can be manufactured by subjecting the polished wafer manufactured in the above manner to a heat treatment, in particular, an annealing treatment. An epitaxial wafer can be manufactured by vapor-growing (epitaxially growing) an epitaxial layer on the surface of the polished wafer manufactured in the above manner.

[0231] The total number of semiconductor wafers included in a semiconductor wafer batch is not particularly limited. The number of semiconductor wafers sampled from a manufactured semiconductor wafer batch and subjected to so-called spot inspection may be at least one or two or more, and the number is not particularly limited.

[0232] Semiconductor wafers extracted from a semiconductor wafer batch are evaluated using the evaluation method according to one embodiment of the present invention. For example, the composite lifetime value obtained by the above evaluation can be used as an indicator to determine whether the evaluated semiconductor wafer is qualified. For example, the greater the amount of metal contamination, the longer the composite lifetime τ measured by the PCD method. eff Therefore, the value of the recombination lifetime measured by the PCD method can be used to evaluate the presence or absence of metal contamination of the semiconductor wafer and / or the degree of metal contamination. Therefore, for example, the recombination lifetime τ eff The criterion for determining a pass product is that the value of is greater than or exceeds a predetermined threshold. The threshold can be set based on the quality required of the product wafers. Semiconductor wafers from the same semiconductor wafer batch as the semiconductor wafers determined to be pass products can be prepared (e.g., packaged) for shipment as product semiconductor wafers.

[0233] Regarding Manufacturing Method 2, test manufacturing conditions and actual manufacturing conditions include various conditions in various steps used to manufacture semiconductor wafers. The various steps used to manufacture semiconductor wafers are the same as those described above for Manufacturing Method 1. Furthermore, "actual manufacturing conditions" refer to the manufacturing conditions for the finished semiconductor wafer.

[0234] In manufacturing method 2, as a pre-stage for determining actual manufacturing conditions, test manufacturing conditions are set, and semiconductor wafers for evaluation are manufactured under these test manufacturing conditions. The manufactured semiconductor wafers are evaluated using the evaluation method according to one embodiment of the present invention. The composite lifetime τ obtained by the above evaluation is eff The value of can be used as an indicator to determine whether the test manufacturing conditions are suitable for use as actual manufacturing conditions, or whether the manufacturing conditions modified from the test manufacturing conditions should be used as actual manufacturing conditions. For example, from the same point of view as that described above for manufacturing method 1, the obtained composite life τ can be eff The determination of whether the manufacturing conditions are suitable for actual manufacturing is based on the fact that the value of is above or exceeds a predetermined threshold. As a result of this determination, manufacturing conditions that may be modified include, for example, those that may cause metal contamination. For example, modifications to the heat treatment furnace used (e.g., replacement of components, cleaning of components, cleaning of the furnace interior, etc.) may be cited.

[0235] Known techniques related to semiconductor wafer manufacturing methods can be applied to other details of the manufacturing methods 1 and 2. The manufacturing methods 1 and 2 enable, for example, stable supply of semiconductor wafers with low metal contamination to the market.

[0236] Example

[0237] Hereinafter, the present invention will be further described based on examples. However, the present invention is not limited to the embodiments shown in the examples.

[0238] [Example 1]

[0239] μPCD measurements were performed on n-type silicon wafers (single crystal silicon wafers) using varying corona charging cycles. Positive corona charging was performed once, three, or five times, while negative corona charging was performed once, three, or five times, with the charge amount (absolute value) being the same for each cycle. The number of corona charging cycles was used as the surface charge density-related value, defined as the variable x. Positive values ​​correspond to positive corona charging cycles, while negative values ​​correspond to negative corona charging cycles. The absolute value of the constant term C, calculated by fitting the decay curves obtained from each measurement, was used as the variable y.

[0240] The decay curve obtained by measuring corona charging 0 times was selected from the decay curves obtained by multiple measurements, and the fitting calculation was performed using formula (10)' in the same manner as described in Example A. τ eff Calculated to be 5300 μs.

[0241] For each of a plurality of decay curves obtained through a plurality of measurements, a constant term C is calculated based on the fitting calculation results.

[0242] The above values ​​are used as the values ​​of the horizontal axis (x-axis) and the vertical axis (y-axis). Based on the minimum value of the vertical axis (the minimum value calculated by fitting a quadratic function to the average value of the values ​​measured at 50 points in each plane) and formula (11)' (the second term "τ eff / τ s ×n0”), surface recombination lifetime τ S Calculated to be 115000 μs (in this embodiment, n0 is 5 mV).

[0243] Furthermore, according to formula (1)', the SRH composite life (body life) τ b Calculated to be 5560μs.

[0244] Table 2 shows the above calculation results. Figure 9 The quadratic curve obtained in Example 1 is shown.

[0245] [Table 2]

[0246] <![CDATA[τ eff (μs)]]> <![CDATA[τ s (μs)]]> <![CDATA[τ b (μs)]]> 5300 115000 5560

[0247] Furthermore, according to the thickness d of the silicon wafer and the surface recombination life τ S , calculate the surface recombination velocity S of the silicon wafer by formula (12) r , the result is 0.34cm / s.

[0248] [Example 2]

[0249] An embodiment using a μPCD device equipped with a corona charging treatment unit and a non-contact CV device is shown.

[0250] First, an n-type silicon wafer (single crystal silicon wafer) is subjected to a corona charging treatment.

[0251] Next, the surface charge amount of the wafer surface was measured using a non-contact CV device, and μPCD measurement was performed after calculating the surface charge density.

[0252] These series of treatments, measurements, and calculations are performed by changing the number of corona charging times and the positive and negative charges.

[0253] The decay curve obtained by measuring corona charging 0 times was selected from the decay curves obtained by multiple measurements, and the fitting calculation was performed using formula (10)' in the same manner as described in Example A. τ eff Calculated to be 5300 μs.

[0254] The surface charge density is plotted on the horizontal axis and the absolute value of the constant term is plotted on the vertical axis for the measurement results obtained by multiple measurements. The minimum value of the vertical axis (the minimum value calculated by fitting a quadratic function to the average value of the values ​​measured at 50 points in each plane) and the second term "τ" of the formula (11) are used to calculate the surface charge density. eff / τ s ×n0”), surface recombination lifetime τ S The calculation is 121000 μs (n0 in this embodiment is 5 mV).

[0255] Furthermore, according to formula (1)', the SRH composite life (body life) τ b Calculated to be 5540μs.

[0256] Table 3 shows the above calculation results. Figure 10 It shows the quadratic curve obtained in Example 2.

[0257] [Table 3]

[0258] <![CDATA[τ eff (μs)]]> <![CDATA[τ s (μs)]]> <![CDATA[τ b (μs)]]> 5300 121000 5540

[0259] Furthermore, according to the thickness d of the silicon wafer and the surface recombination life τ S , calculate the surface recombination velocity S of the silicon wafer by formula (12) r , the result is 0.32cm / s.

[0260] Industrial Applicability

[0261] One embodiment of the present invention is useful in various technical fields of semiconductor wafers.

Claims

1. A method for evaluating a semiconductor sample, characterized in that: include: The surface charge density is varied and the photoconductivity decay method is repeatedly performed on the semiconductor sample to be evaluated to obtain a decay curve. performing signal data processing using a model formula on at least one of the decay curves obtained through the multiple measurements, the model formula including an exponential decay term and a constant term; The recombination lifetime τ of the semiconductor sample is calculated based on the exponential decay formula obtained by processing the signal data. eff ; Based on the measurement results obtained by the multiple measurements, a quadratic function is obtained, wherein the value associated with the surface charge density is a variable x and the value associated with the constant term is a variable y; and The surface recombination lifetime τ of the semiconductor sample is calculated according to the quadratic function s .

2. The semiconductor sample evaluation method according to claim 1, wherein: In the following formula (11)': C min =t eff / t s ×n0…(11)' (In formula (11), n0: equilibrium carrier concentration) In the min The surface recombination lifetime τ is calculated as the minimum value of y in the quadratic function s .

3. The semiconductor sample evaluation method according to claim 1, wherein: The semiconductor sample evaluation method further includes: according to the recombination lifetime τ eff and the surface recombination lifetime τ s , calculate the SRH recombination lifetime τ of the semiconductor sample b .

4. The semiconductor sample evaluation method according to claim 3, wherein: According to the following formula (1): 1 / t eff =1 / t b +1 / t s …(1)' Calculate the SRH composite lifetime τ b .

5. The semiconductor sample evaluation method according to claim 1, wherein: The semiconductor sample evaluation method further includes: according to the thickness d of the semiconductor sample and the surface recombination lifetime τ S , through the following formula (12): S r =d / (2τ S )…(12) Calculate the surface recombination velocity S of the semiconductor sample r .

6. The semiconductor sample evaluation method according to claim 1, wherein: The semiconductor sample evaluation method further includes: Pass By performing the signal data processing, the constant term in the model formula is offset to obtain the exponential decay formula; and According to the exponential decay formula, the time constant τ is obtained b -1 +τ S -1 , τ b is the SRH recombination lifetime, τ S is the surface recombination life.

7. The semiconductor sample evaluation method according to claim 6, wherein: The signal data processing includes repeatedly sampling the time series signal modeled by the model formula and obtaining a difference.

8. The semiconductor sample evaluation method according to claim 7, wherein: The semiconductor sample evaluation method further includes performing automatic scaling for determining a sampling region where the sampling is performed.

9. The semiconductor sample evaluation method according to claim 8, wherein: By the automatic scaling, a region with little influence of Auger recombination and little influence of noise is determined as a sampling region.

10. The semiconductor sample evaluation method according to claim 1, wherein: The model formula is the following formula (10)': xi(ti)=A×exp[-(τ b -1 +τ S -1 )ti]-C…(10)' (In formula (10), ti: the time after the excitation light irradiation, xi(ti): the signal intensity at the time ti, τ b : SRH recombination lifetime, τ S : surface recombination lifetime, A, C: constants).

11. The semiconductor sample evaluation method according to claim 1, wherein: In the following formula (11)': C min =T eff / t s ×n0…(11)' (In formula (11), n0: equilibrium carrier concentration) In the min The surface recombination lifetime τ is calculated as the minimum value of y in the quadratic function s , The semiconductor sample evaluation method further includes: according to the recombination lifetime τ eff and the surface recombination lifetime τ s , calculate the SRH recombination lifetime τ of the semiconductor sample b , According to the following formula (1): 1 / t eff =1 / t b +1 / t s …(1)' Calculate the SRH composite lifetime τ b , The semiconductor sample evaluation method further includes: By performing the signal data processing, the constant term in the model formula is offset to obtain the exponential decay formula; and The time constant τ is obtained according to the exponential decay formula b -1 +τ S -1 , τ b is the SRH recombination lifetime, τ S is the surface recombination life, The signal data processing includes repeatedly performing the following operations: sampling the time series signal modeled by the model formula to obtain a difference, The semiconductor sample evaluation method further includes: performing automatic scaling for determining a sampling area for performing the sampling, By the automatic scaling, a region with little influence of Auger recombination and little influence of noise is determined as a sampling region. The model formula is the following formula (10)': xi(ti)=A×exp[-(τ b -1 +τ S -1 )ti]-C…(10)' (In formula (10), ti: the time after the excitation light irradiation, xi(ti): the signal intensity at the time ti, τ b : SRH recombination lifetime, τ S : surface recombination lifetime, A, C: constants).

12. The semiconductor sample evaluation method according to claim 1, wherein: In the following formula (11)': C min =t eff / t s ×n0…(11)' (In formula (11), nn0: equilibrium carrier concentration) In the min The surface recombination lifetime τ is calculated as the minimum value of y in the quadratic function s , The semiconductor sample evaluation method further includes determining the thickness d of the semiconductor sample and the surface recombination lifetime τ S , through the following formula (12): S r =d / (2τ S )…(12) Calculate the surface recombination velocity S of the semiconductor sample r , The semiconductor sample evaluation method further includes: By performing the signal data processing, the constant term in the model formula is offset to obtain the exponential decay formula; and The time constant τ is obtained according to the exponential decay formula b -1 +τ S -1 , τ b is the SRH recombination lifetime, τ S is the surface recombination life, The signal data processing includes repeatedly performing the following operations: sampling the time series signal modeled by the model formula to obtain a difference, The semiconductor sample evaluation method further includes performing automatic scaling for determining a sampling area for performing the sampling, By the automatic scaling, a region with little influence of Auger recombination and little influence of noise is determined as a sampling region. The model formula is the following formula (10)': xi(ti)=A×exp[-(τ b -1 +τ S -1 )ti]-C…(10)' (In formula (10), ti: the time after the excitation light irradiation, xi(ti): the signal intensity at the time ti, τ b : SRH recombination lifetime, τ S : surface recombination lifetime, A, C: constants).

13. A semiconductor sample evaluation device for implementing the semiconductor sample evaluation method according to any one of claims 1 to 12, the evaluation device comprising: a measuring unit for measuring the semiconductor sample to be evaluated using a photoconductivity decay method; as well as The processing unit performs signal data processing on the attenuation curve using a model equation, the model equation including an exponential attenuation term and a constant term, and obtains the quadratic function.

14. The evaluation device according to claim 13, wherein: In the measuring unit, the intensity of the light pulse is variable.

15. The evaluation device according to claim 13, wherein The measuring unit further includes a corona charging treatment unit.

16. The evaluation device according to claim 13, wherein: The measurement unit further includes a surface charge density-related value measurement unit that measures a surface charge density-related value of the semiconductor sample being measured.

17. The evaluation device according to claim 13, wherein: In the measuring unit, the light pulse intensity is variable. The measurement unit further includes a corona charging treatment unit and a surface charge density-related value measurement unit that measures a surface charge density-related value of the semiconductor sample being measured.

18. A method for manufacturing a semiconductor wafer, characterized in that: include: manufacturing a semiconductor wafer batch comprising a plurality of semiconductor wafers; extracting at least one semiconductor wafer from the batch of semiconductor wafers; evaluating the extracted semiconductor wafer by the evaluation method according to any one of claims 1 to 12; as well as, Semiconductor wafers from the same semiconductor wafer lot as the semiconductor wafers determined as non-defective products as a result of the evaluation are prepared for shipment as product semiconductor wafers.

19. A method for manufacturing a semiconductor wafer, characterized in that: include: manufacturing a semiconductor wafer for evaluation under test manufacturing conditions; evaluating the manufactured semiconductor wafer for evaluation by the semiconductor sample evaluation method according to any one of claims 1 to '12; determining, based on a result of the evaluation, a manufacturing condition obtained by modifying the test manufacturing condition as an actual manufacturing condition, or determining the test manufacturing condition as an actual manufacturing condition; as well as A semiconductor wafer is manufactured under the determined actual manufacturing conditions.

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