JPH09162251A - Method and apparatus for measuring interfacial state density - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize effective quality control and manufacture reliable products without defects by deriving the initial interfacial state density from the difference between the reciprocal of the initial lifetime of excessive carriers and the reciprocal of the saturation lifetime measured when it no longer decreases during the irradiation of a substrate with light. SOLUTION: A silicon substrate 1 is irradiated with a pulsed beam from a laser source 2 to produce electron-hole pairs as excessive carriers. Upon an interrupt of the pulsed beam, the attenuation of excessive carriers is measured by means of microwaves generated by a Gunn diode 3. The lifetime of excessive carriers is determined from the detected microwaves for each irradiation, and the initial interfacial state density is derived from the difference between the reciprocal of the saturation lifetime thus derived and the reciprocal of the initial lifetime. Since this measurement is independent from the processes of forming electrodes and ohmic contact on the reverse side, it is possible to reduce the costs of production systems and quality inspection and facilitate in-line measurements.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for measuring an interface state density of a silicon substrate and an apparatus for measuring an interface state density.

[0002]

2. Description of the Related Art An insulating film such as a silicon oxide film or a silicon nitride film formed on the surface of a silicon substrate, or a natural oxide film formed when the surface of a silicon substrate comes into contact with air or water, and an interface between silicon and The interface state exists. The interface state is an important property that influences the characteristics of silicon devices such as solar cells and dynamic RAMs.

Therefore, measurement of the interface state density is indispensable in the development of silicon devices, and several measurement methods have been proposed so far. That is, high frequency C
-V method, low frequency CV method, conductance method, Quasi-S
The tatic method, the charge-voltage method, the DLTS method, the charge pumping method, the thermally stimulated current method, the optical saturation method and the like.

In the high frequency CV method and the low frequency CV method, the capacitance is measured while sweeping the applied voltage, and the interface state density is obtained by using the charge / discharge frequency followability of carriers at the interface state. Is. The conductance method is a method of calculating the interface state density by measuring the conductance while sweeping the applied voltage, and the Quasi-Static method is an improvement of the low frequency CV method as a steady response method as a quasi steady response method. It is a thing. In the charge-voltage method, an interface state density is calculated by connecting a measurement sample in series with a known capacitance and measuring the amount of charge accumulated in the gate electrode. DLTS (De
The ep Level Transient Spectoroscopy) method and the thermally stimulated current method are methods for measuring the interface state density by making impedance changes caused by carrier capture / emission at the interface states correspond to changes in temperature. The charge pumping method is a method of measuring the substrate current when the source / drain current of the FET is recombined after being trapped at the interface state. This is a method of obtaining the interface state density from the bending characteristics.

[0005]

When manufacturing a VLSI, quality control of the manufacturing process is essential. Effective quality control of the manufacturing process makes it possible to prevent defects from occurring and improve product reliability. One of the important technologies in the quality control of the manufacturing process is a manufacturing process quality inspection technology.

The following method is one of the widely used means for quality inspection of manufacturing process. First, the manufacturing process to be inspected is determined. Next, in a manufacturing process to be inspected, a desired silicon substrate is subjected to desired treatment, and then the characteristics of the silicon substrate are measured. Then, the quality of the manufacturing process is evaluated from the measurement result. Excess carrier lifetime is a characteristic of the silicon substrate to be measured and evaluated in such a manufacturing process quality inspection. In particular, the measurement of excess carrier lifetime using the microwave photoconductivity decay method is widely used in VLSI manufacturing lines because of its simplicity.

On the other hand, the interface state density of the silicon substrate is a quantity closely related to the excess carrier lifetime, and is an important characteristic of the silicon substrate to be measured and evaluated along with the excess carrier lifetime. If two important quantities, the interface state density and the excess carrier lifetime, can be measured by one technique called the microwave photoconductivity decay method, the reliability and simplicity of the quality control of the manufacturing process can be improved.

As a means for measuring the interface state density of a silicon substrate using the microwave photoconductivity decay method, Japanese Patent Application No.
There is a specification of 7-114267. Here, a plurality of silicon substrates having different thicknesses are prepared, and the squared value of the reciprocal of each thickness and the reciprocal of the excess carrier lifetime measured by the microwave photoconductivity decay method for those silicon substrates are used. The proportionality constant is obtained and the correspondence with the interface state density actually measured on silicon substrates having different thicknesses is acquired. This interface state density was measured by forming C- after forming an electrode on a silicon substrate.
The V measurement method or the like is used. The correspondence obtained here is
It becomes the conversion basic data of the conventional method of measuring the interface state density of the silicon substrate by using the microwave photoconductivity decay method, and once the conversion basic data is acquired, it is not necessary to acquire it thereafter.

After obtaining the above-mentioned conversion basic data, a plurality of silicon substrates whose interface order density is to be measured are prepared. The multiple silicon substrates prepared at this time are
The samples should have the same interface state density and different thickness. The excess carrier lifetime of these silicon substrates is measured by the microwave photoconductive decay method.

FIG. 2 shows a state of measuring excess carrier lifetime of a silicon substrate by the microwave photoconductive attenuation method. The surface of the silicon substrate 1 is irradiated with pulsed light generated by the laser light source 2 to generate electron-hole pairs as excess carriers. The attenuation amount of excess carriers in the silicon substrate 1 immediately after the pulsed light is cut off is measured by the microwave generated by the Gunn diode 3. At this time, the microwave is transmitted through the waveguide C.
From 1 to the circulator 4, it passes through the waveguide C2, is absorbed and reflected by the silicon substrate 1, passes through the circulator 4 again, is guided to the waveguide C3, and reaches the detection diode 5. The detected attenuation signal of the excess carrier is input to the oscilloscope 7 through the conducting axis 6 and the lifetime is calculated from the measurement result.

After the measurement of the excess carrier lifetime, the proportional constant between the reciprocal value of the excess carrier lifetime measurement value and the square of the reciprocal number of the thickness of the silicon substrate is obtained. The interface state density can be obtained from this proportionality constant and the above-mentioned conversion basic data corresponding to each other.

In addition to using a plurality of silicon substrates having different thicknesses by the above method, means for using a single silicon substrate having a plurality of regions having different thicknesses formed on the surface of the substrate at a plurality of positions is also described above. It is described in Japanese Patent Application No. 7-114267. That is, the square value of the reciprocal of the thickness of each different thickness region in a single silicon substrate in which a plurality of regions of different thickness are formed on the surface of the substrate and the different thickness regions of the silicon substrate are respectively determined. The constant of proportionality with the reciprocal value of the excess carrier lifetime measured by the microwave photoconductivity decay method is obtained. Then, the correspondence relationship between the proportional constant and the interface state density actually measured in each of the regions having different thicknesses is acquired. This corresponds to the conversion basic data already described. Then, as a silicon substrate whose interface order density is to be measured, a single silicon substrate having a plurality of regions having different thicknesses formed in a plurality of locations on the substrate surface is prepared. The excess carrier lifetime of this silicon substrate is measured by the microwave photoconductive decay method. After measuring the excess carrier lifetime, the proportional constant between the reciprocal value of the excess carrier lifetime measurement value and the square value of the reciprocal number of the thickness of the silicon substrate is obtained. The interface state density can be obtained from this proportionality constant and the above-mentioned conversion basic data corresponding to each other.

In the above-mentioned prior application technique for measuring the interface state density of a silicon substrate using the microwave photoconductive attenuation method, a plurality of silicon substrates to be measured having different thicknesses are prepared, or Even with a single silicon substrate, it was necessary to prepare a special silicon substrate in which a plurality of regions having different thicknesses were formed on the substrate surface. That is, there is a problem in that a plurality of regions having different thicknesses are not formed on the surface of the substrate and it is not possible to measure with a single ordinary silicon substrate.

The problem to be solved by the present invention is to use a microwave photoconductive attenuation method by using only one ordinary silicon substrate in which a plurality of regions having different thicknesses are not formed on the surface of the substrate. Another object is to provide a method and a measuring apparatus for measuring the interface state density of a substrate.

[0015]

Means for Solving the Problems While irradiating a semiconductor substrate with light, an excess carrier lifetime is measured by a microwave photoconductive decay method. Then, the excess carrier lifetime decreases with time, and eventually becomes saturated. There is a proportional relationship between the value obtained by subtracting the reciprocal of the initial lifetime from the reciprocal of the excess carrier lifetime at the time of this saturation saturation and the initial interface state density. In the present invention, by obtaining this proportional relationship in advance, the value obtained by subtracting the reciprocal of the initial lifetime from the reciprocal of the excess carrier lifetime at the time of decreasing saturation is calculated using the microwave photoconductive decay method. By doing so, the interface state density is determined.

Alternatively, an apparatus in which the carrier lifetime measuring means, the data inputting means and the storing means are connected to the calculating means is prepared. In the storage means of this device, the correspondence relationship between the value obtained by subtracting the reciprocal of the initial lifetime from the reciprocal of the excess carrier lifetime at the time of the saturated saturation and the initial interface state density is held. Based on this correspondence, the calculation means calculates the interface state density from the measured carrier lifetime lifetime change of the semiconductor substrate and outputs it to the display means.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

(Example 1) First, a plurality of silicon substrates having the same thickness, which are continuously cut out from an arbitrary region of one silicon ingot, are prepared. Here, continuous cutting from an arbitrary region of one silicon ingot means that the bulk level density, the carrier concentration, and the carrier generation dopant of the silicon substrate are the same over a plurality of silicon substrates. The substrate may have any history as long as the bulk level density of the substrate, the carrier concentration, and the carrier generation dopant are the same for a plurality of substrates. In this embodiment, boron is added at 1 × 10 ¹⁵ atoms.
A silicon substrate containing / cm ³ was used. Further, the term "plurality of sheets" means that it is sufficient that the number of sheets is two or more.

Next, the same RCA cleaning and dilute hydrofluoric acid cleaning are performed on all four silicon substrates, and then a thermal oxide film of about 50 to 100 nm is formed on the substrate surface. At this time, the oxidation temperature and the oxidation method may be those well known in the art. In this example, dry oxidation was performed at 1000 ° C. for 1 hour.

Next, electrodes are formed on a part of the surfaces of all of these four silicon substrates. The electrode material and processing method may be those well known in the art. In this example, the phosphorus-doped polysilicon electrode was deposited and then microwave-etched to a desired shape. The location and size of the electrodes are
In the lifetime measurement by the microwave photoconductivity decay method which will be performed later, the size and location can be arbitrarily selected if a region larger than the waveguide cross section exists as a region without electrodes. In this embodiment, as shown in FIG. 3, a 5 mm square electrode 8 was formed in the right side region of the silicon substrate 1, and a region 9 without the electrode 8 was formed as shown by the broken line in the figure.

Next, hydrogen annealing is applied to all four silicon substrates. Then, the levels existing at the interface between silicon and the thermal oxide film are terminated by hydrogen, and a silicon substrate having a relatively low interface level density can be produced. When the low interface state density substrate is annealed in extremely low moisture nitrogen,
Hydrogen as a terminator is released to increase the interface state density.

Here, "in extremely low moisture nitrogen" has the following meaning. That is, when a small amount of water is present in the nitrogen annealing atmosphere, the water acts as a terminator for the interface level instead of the hydrogen released by the annealing,
This means that an increase in the interface state density is suppressed, or moisture oxidizes silicon, making it difficult to control the interface state, and thus a desired interface state density cannot be obtained. Therefore, in annealing for the purpose of increasing the interface state density, the amount of water in the atmosphere is set to several hundreds ppm or less. In this extremely low moisture nitrogen anneal, the interface state density can be controlled by controlling the moisture concentration in the atmosphere or the annealing temperature. The main annealing may be performed not only in nitrogen but also in a rare gas such as argon or xenon. In this example, four types of silicon substrates having different interface state densities were prepared by using the hydrogen annealing and the extremely low moisture nitrogen annealing described here.

Next, the electrodes 8 on the surface of these silicon substrates
Only the region corresponding to the back side of the device is brought into an ohmic state with respect to the terminal of the interface state density measuring device. In this embodiment, after removing the phosphorus-doped polysilicon film on the back surface, the area other than just the back surface of the surface of the silicon substrate on which the electrode 8 is formed is covered with a resist, the thermal oxide film is removed with dilute hydrofluoric acid, and the conductive paste is used. Was applied.

A needle is applied to the electrode 8 of the silicon substrate thus formed, and the interface state density is measured. As the measuring method at this time, any of the methods described in the section of the conventional art may be used, but in this embodiment, the high frequency CV method, which is easy to measure, was used. The interface state density measured here will be called the initial interface state density.

Next, the excess carrier lifetime of the region 9 without the electrode 8 is measured by the microwave photoconductive decay method. One of the features of the present invention is that in this excess carrier lifetime measurement, the silicon substrate is continuously irradiated with a certain amount of light to measure the change with time of the excess carrier lifetime.

FIG. 4 shows the measurement results. The horizontal axis represents the elapsed time when light irradiation is continued, and the vertical axis represents the excess carrier lifetime. The white circles, squares, triangles, and black circles in the figure are plots of changes in excess carrier lifetime over time for each initial interface state density measured by the high-frequency CV method. The initial interface state density of is as described in the figure. In the present embodiment, pulsed light emitted from the laser light source 2 shown in FIG. 2 was used as the fixed amount of light that is continuously emitted to the silicon substrate, but a commercially available fluorescent lamp, electric bulb, or the like may be used. You may use it for a light source.

It can be seen from FIG. 4 that the excess carrier lifetime of the silicon substrate decreases when the light irradiation is continued. This decrease in excess carrier lifetime is caused by the increase in interface state density due to light irradiation.

Next, the difference in reciprocal lifetime is defined. First, in this data, the data plotted at the elapsed time of 1 minute is called the initial lifetime. The difference between the reciprocal of the lifetime and the reciprocal of the lifetime at each time during the light irradiation elapsed time is subtracted from the reciprocal of the initial lifetime.

FIG. 5 shows the relationship between the elapsed time of light irradiation and the reciprocal difference of lifetime. As the light irradiation time elapses, the reciprocal difference of lifetime increases, and after a certain time or more,
It can be seen that the reciprocal difference in lifetime saturates to a different value for each initial interface state density. The difference in the reciprocal of the saturated lifetime is called the saturated reciprocal value.

The relationship between the saturation reciprocal value and the initial interface state density is shown in FIG. From this figure, it can be seen that the saturated reciprocal value and the initial interface state density have a linear relationship. If this linear relationship is used, the interface state density can be determined by measuring the saturation reciprocal value.

By the way, FIGS. 1 and 5 show data on samples having the same level density of the bulk of the silicon substrate.
We investigated that the same relationship holds for samples with different level densities of silicon substrate bulk. The level density of the bulk of the silicon substrate can be changed easily by changing the amount of dissolved oxygen in the substrate, doping with a metal element such as iron or copper, or a technique such as IG treatment or ion implantation. In this example, a low oxygen substrate and a silicon ion implantation process are used to change the level density of the bulk of the silicon substrate, and the hydrogen state annealing and the ultra-low moisture nitrogen annealing described above are used to obtain the same interface state density. Made of silicon substrate.

Using the silicon substrate thus manufactured, the silicon substrate is continuously irradiated with a certain amount of light as in the case where the silicon substrate bulk has the same level density.
The change in excess carrier lifetime with time was measured. FIG. 6 shows the result. In the figure, those with a high dose of silicon ion implantation have a high bulk level density, and those with a low dose of silicon ion implantation have a low bulk level density. All initial interface state densities are 5.4 ×
It is 10 ¹⁰ / cm ² .

FIG. 7 shows the relationship between the light irradiation elapsed time and the reciprocal lifetime difference calculated from the results shown in FIG. Here, the lifetime reciprocal difference is defined as the reciprocal of the initial lifetime subtracted from the reciprocal of the lifetime at each time during the light irradiation elapsed time, as described above. From FIG. 7, the relationship between the elapsed time of light irradiation and the reciprocal difference of lifetime is
It can be seen that it does not depend on the bulk level density, but only on the initial interface level density. Therefore, even when the bulk level densities are different, the relationship between the saturation reciprocal value and the initial interface state density agrees with that shown in FIG. 1, and the saturation reciprocal value and the initial interface state density have a linear relationship. You can see. If this linear relationship is used, the interface state density can be determined by measuring the saturation reciprocal value.

That is, once the data corresponding to FIG. 1 is acquired, the electrode formation and ohmic contact treatment on the back surface of the substrate are not necessary when the interface state density is measured thereafter. Further, it is not necessary to prepare a plurality of silicon substrates for measurement having different thicknesses, and even a single silicon substrate is prepared with a special silicon substrate having a plurality of regions having different thicknesses formed on the substrate surface. Therefore, it becomes possible to measure the interface state density of the silicon substrate in a non-contact manner by utilizing the microwave photoconductive attenuation method.

The method of using FIG. 1 will be described below.

When a quality inspection of a manufacturing apparatus or a manufacturing process is performed, a silicon substrate having the same thickness, the same carrier generation dopant and the same carrier concentration as those obtained in FIG. 1 is prepared. The prepared silicon substrate is inspected and processed in a desired manufacturing apparatus or manufacturing process. After the treatment, the excess carrier lifetime is measured by the microwave photoconductive decay method. Of course, at this time, the electrode forming process and the back surface ohmic contact process are unnecessary. Then, the same light source as that used to acquire FIG. 1 is used to measure the time-dependent decay of the excess carrier lifetime, and the above-mentioned saturation reciprocal value is calculated. The interface state density is obtained from the relationship between this saturation reciprocal value and FIG. The bulk level density of the silicon substrate used to obtain the interface state density here needs to be the same as the bulk level density of the silicon substrate used to derive the relationship in FIG. The absence is as shown in FIG. 7. Using the interface state density thus measured, the manufacturing apparatus and manufacturing process are quantitatively inspected and evaluated.

This method can be applied in the same manner even in manufacturing technology development support and product defect analysis. Similar to this method,
A silicon substrate having the same thickness, the same carrier generation dopant, and the same carrier concentration as when the relationship was obtained is prepared. A desired process is performed on the silicon substrate by a newly-developed silicon device manufacturing process or a newly-developed manufacturing apparatus. Alternatively, in the manufacturing line where the defect occurs, the silicon substrate is subjected to predetermined processing and processing under different conditions by a manufacturing apparatus or manufacturing process. After the treatment, the excess carrier lifetime is measured by the microwave photoconductive decay method. Then, the same light source as that used to acquire FIG. 1 is used to measure the time-dependent decay of the excess carrier lifetime, and the above-mentioned saturated reciprocal value is calculated. The interface state density is obtained from the relationship between this saturation reciprocal value and FIG. In this method, in-line measurement can be performed because the interface state density is obtained by non-contact measurement. As a result, high-precision technical development such as quick identification of defect occurrence devices in the production line and defect induction conditions, detailed defect analysis, fine adjustment of hardware and software aspects of the manufacturing device, and setting of optimum manufacturing conditions. I can help.

(Embodiment 2) FIG. 8 is a block diagram showing the structure of the present invention. The present invention has a display means 10 such as a CRT, a liquid crystal display, and a printer. Reference numeral 11A is a microwave photoconductive decay method excess carrier lifetime measuring means, and the one used in this embodiment has already been shown in FIG. 11B is CP
U execution control data input means, 11A, B
Each output is input to the CPU 14 as a calculation means via the interface I / F 13. This CPU14
The storage means 12 is connected to. And this CP
The interface state density of the measurement result is displayed on the display means 10 by the signal from U14.

The contents of the storage means 12 are obtained by tabulating the relationship shown in FIG. 1 and a work program, and are used as a guideline for executing the CPU 14. Here, what is made into a table means that if an arbitrary value of the reciprocal saturation value described in the first embodiment is given, the interface state density corresponding to it can be calculated.

By the way, if the carrier generation dopant species of the silicon substrate is different or the carrier concentration is changed, the relationship of FIG. 1 changes accordingly. Further, even if the excess carrier generation amount in the microwave photoconductive decay method excess carrier lifetime measurement changes, the relationship of FIG. 1 changes. Alternatively, the relationship in FIG. 1 changes even if the type of light source or the light irradiation amount for causing the excess carrier lifetime to decrease with time changes. In the present invention, the carrier generation dopant species of the silicon substrate to be measured, the carrier concentration, and a plurality of types of relationships corresponding to FIG. 1 according to the excess carrier generation amount and the light irradiation amount in the microwave photoconductive decay method excess carrier lifetime measurement, It is designed to be held in the storage means 5.

The operation of the constituent device of the present invention will be described with reference to the flowchart of FIG. Microwave photoconductivity decay method excess carrier lifetime measuring means 11A and data input means 11B are used to input measurement conditions (step S1). Here, the measurement condition input items from the microwave photoconductive decay method excess carrier lifetime measuring means 11A are a condition item that determines the excess carrier generation amount and a condition item that determines the change over time of the excess carrier lifetime. The applied voltage of the pulse laser for generation, the diameter of the pulse laser light, and the setting position of the pulse laser light source. In this embodiment, since the pulse carrier for generating excess carriers is also used as the light source for causing the change in the excess carrier lifetime to decrease with time, the input data may be the above items. However, if a light source other than the pulse carrier laser for generating excess carriers is used as the light source that causes the change in excess carrier lifetime over time, not only the condition items but also the light from the light source that causes decrease in excess carrier lifetime over time. It is necessary to input the irradiation amount and the wavelength of light. The measurement condition input items from the data input means 11B are the carrier generation dopant species of the silicon substrate, the carrier concentration, and the substrate thickness. Next, the tabled relationship corresponding to FIG. 1 under the same condition as the input measurement condition item is stored in the storage unit 12.
Whether or not it exists is checked by the condition determination in step S2. At this time, if the tabled relationship corresponding to FIG. 1 under the same condition as the input condition exists in the storage means 12, YES from step S2 in the flowchart of FIG.
Proceed to. Then, microwave photoconductive decay method excess carrier lifetime measurement and excess carrier lifetime decrease measurement with time are performed (step S3). This measured value is calculated through the interface I / F 13 as C which is a calculation means.
It is input to the PU 14, and there the interface state density is calculated from the tabulated relationship corresponding to FIG. 1 in the storage means 12 (step S4). The result is displayed on the display means 10 (step S5), and the measurement is completed.

In the condition determining step S2, if the tabled relation corresponding to FIG. 1 under the same condition as the input condition does not exist in the storage means 12, the process proceeds from step S2 to NO in the flowchart of FIG. In step S6, the storage unit 1 stores the relationship corresponding to FIG. 1 under the same conditions as the input conditions.
It is determined whether or not the data is input and stored in 2. The judgment data is the CPU execution control data input means 11B.
Then, enter YES or NO. If NO is input here, the measurement ends, and if YES is entered, the process proceeds to the step of inputting and storing the relationship corresponding to FIG. The case where YES is input will be described below.

A plurality of silicon substrates having the same carrier generation dopant species and the same carrier concentration as the silicon substrate to be measured are used as the silicon substrates having electrodes in a part as described in the first embodiment. prepare. Then, as also described in Example 1, the interface state density of the present substrate was measured in advance, and the microwave photoconductivity decay method excess carrier lifetime measurement and the excess carrier lifetime elapsed with respect to the region without electrodes were measured. Decrease change measurement is performed (step S7). The measured excess carrier lifetime and the applied voltage of the pulse laser for generating excess carrier, the diameter of the pulse laser light, the setting position of the pulse laser light source, and the excess carrier lifetime which are the measurement conditions of the excess carrier lifetime to be measured. The amount of light emitted from the light source and the wavelength of the light that cause a decrease with time are determined by the microwave photoconductive decay method excess carrier lifetime measuring means 11A through the interface I / F1.
3 is input to the CPU 14. The interface state density and the substrate thickness, and the carrier generation dopant species and the carrier concentration, which have been separately measured, are input from the data input unit 11B (step S8). From the input data, the relationship corresponding to FIG. 1 is obtained by the same procedure as the method described in the first embodiment, and the interface state density can be selected with respect to the slope of the linear relationship with the saturation reciprocal value. (Step S9). This table and the measurement conditions according to the table are stored in the storage means 12 (step S10).

Then, again, the condition determination is performed for the measurement condition input in step S1 (step S
2). It is checked in the condition determination in step S2 whether or not the tabled relationship corresponding to FIG. 1 under the same condition as the input measurement condition item exists in the storage unit 12. Step S
As long as there is no input error in 1 or step S8, the tabulated relationship corresponding to FIG. 1 under the same conditions as the input conditions should exist in the storage means 12, so the process proceeds from step S2 to YES. Then, the microwave photoconductivity decay method excess carrier lifetime measurement is performed (step S3). This measured value is the interface I / F13
It is input to the CPU 14 as a calculation means via the, and the interface state density is calculated from the tabled relation corresponding to FIG. 1 in the storage means 12 (step S4). The result is displayed on the display means 10 (step S5), and the measurement is completed.

When quality control of a manufacturing apparatus or a manufacturing process is performed using the apparatus of the present invention, if the contents of the measurement condition input items in step S1 are made constant, the condition determination in step 2 may be NO. Since it does not exist, the measurement can be performed without being aware of the relationship corresponding to FIG. Therefore, even a person who does not have the technical knowledge of reading a specific graph can easily measure the interface state density in a short time. Even if manufacturing technology development support or product failure analysis is performed, if the result of step 2 is NO in the condition determination, it is not necessary to be aware of the relationship corresponding to FIG. 1, and even a person who does not have the technical knowledge to read a specific graph. The interface state density can be easily measured in a short time. Also, in the condition judgment of step 2, N
Even if it becomes O, it is not necessary to pay attention to the details of the relationship corresponding to FIG. 1, and even a person who does not have the technical knowledge to create a specific graph can easily measure the interface state density in a short time.

[0045]

According to the present invention, it is possible to use a microwave photoconductive attenuation method without preparing a plurality of silicon substrates having different thicknesses or a silicon substrate having regions having different thicknesses formed on the substrate surface. It is possible to measure the interface state density, and it is possible to perform the measurement without the influence of the electrode forming process and the back surface ohmic treatment, and at the same time, the quality inspection cost of the manufacturing apparatus and the manufacturing process is reduced and the in-line measurement can be easily performed.

Also, the interface state density can be easily measured in a short time even by a person who does not have the technical knowledge of reading or creating a specific graph.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram of a saturation reciprocal value of excess carrier lifetime and initial interface state density when a silicon substrate is continuously irradiated with light.

FIG. 2 is a perspective view showing a state of measuring excess carrier lifetime by a microwave photoconductivity decay method.

FIG. 3 is a plan view showing electrodes on a silicon substrate used for description of the first embodiment.

FIG. 4 is a characteristic diagram showing a relationship between a light irradiation elapsed time and an excess carrier lifetime when a silicon substrate having different initial interface state densities is irradiated with light.

FIG. 5 is a characteristic diagram showing the relationship between the light irradiation elapsed time and the reciprocal of excess carrier lifetime when light is irradiated to silicon substrates having different initial interface state densities.

FIG. 6 is a characteristic diagram showing a relationship between light irradiation elapsed time and excess carrier lifetime when light is irradiated to silicon substrates having the same initial interface state density and different bulk state densities.

FIG. 7 is a characteristic diagram showing the relationship between the light irradiation elapsed time and the reciprocal of excess carrier lifetime when light is irradiated to silicon substrates having the same initial interface state density and different bulk state densities.

FIG. 8 is a block diagram showing an excess carrier lifetime measuring means in the measuring apparatus of the present invention used for the description of Example 2;

FIG. 9 is a flowchart of the measuring device of the present invention.

[Explanation of symbols]

1 ... Silicon substrate, 2 ... GaAs pulse laser, 3 ... Gunn diode, 4 ... Circulator, 5 ... Microwave detector, 6 ... Coaxial line, 7 ... Signal storage, 8 ... Electrode, 10 ... Display means, 11A ... Excess carrier Lifetime measuring means, 11B ... Control data input means, 12
... storage means, 13 ... interface, 14 ... calculation means CPU.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiko Sato 5-20-1 Kamimizuhoncho, Kodaira-shi, Tokyo Hiritsu Cho-LS Engineering Co., Ltd. (72) Inventor Takamitsu Nagara Kodaira, Tokyo Ichijomizu Honmachi 5-chome 20-20 Hitate Cho-LS Engineering Co., Ltd. (72) Inventor Jiro Yuue 1-280 Higashi-Kengikubo, Kokubunji-shi, Tokyo Inside Hitachi Central Research Laboratory (72) Inventor Satoshi Okura 1-280 Higashi Koigokubo, Kokubunji, Tokyo Inside Hitachi Central Research Laboratory, Hitachi, Ltd.

Claims (2)

[Claims] 1. A semiconductor substrate is continuously irradiated with light, and an excess carrier lifetime is measured by a microwave photoconductive decay method. When the excess carrier lifetime decreases and saturates with time, the excess carrier lifetime at the time of the decrease saturation is measured. A method for measuring an interface state density, which comprises obtaining an interface state density from a proportional constant of a value obtained by subtracting an inverse number of an initial lifetime from an inverse number and an initial interface state density. 2. A carrier lifetime measuring means, a data inputting means, and a storing means are connected to a calculating means, and in the storing means, from the reciprocal of the excess carrier lifetime at the time of decreasing saturation described in claim 1. The correspondence between the value obtained by subtracting the reciprocal of the initial lifetime and the initial interface state density is retained, and based on this correspondence, the calculation means calculates the interface state density from the change over time of the measured carrier lifetime, An interface state density measuring device for outputting to display means.