JP2000171415A - Method and apparatus for measuring life time of semiconductor sample - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the subject method and apparatus for preventing the introduction of a new contaminant into a semiconductor sample and capable of rapidly and accurately measuring the life time of the interior of the semiconductor sample. SOLUTION: The correlation of a reduction ratio α of a measured life time due to surface re-bonding, which is obtained as the relation between an interior life time τm obtained by a photoconductive attenuation method in a state such that a surface re-bonding suppressing treatment such as oxide film treatment is preliminarily applied to a semiconductor sample and a life time measured value τ1 obtained in a treatment unapplied state, with an attenuation time τ2 of light with a specific wavelength obtained by a PL(photoluminescence) method is preliminarily calculated (S1). In an actual measurement, a life time τ1 due to the photoconductive attenuation method (S2-S5) and an attenuation time τ2 due to the PL method (S2→S6, S7) are measured in a state such that surface re-bonding suppressing treatment is not applied to the semiconductor sample and, on the basis of τ1, τ2 and the correlation, the life time of the interior of the semiconductor sample τm is calculated (S8).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for measuring the lifetime of a semiconductor sample for measuring the lifetime inside a semiconductor sample.

[0002]

2. Description of the Related Art A photoconductive decay method has been widely used as a method of measuring a lifetime until electrons and holes (hereinafter, referred to as carriers) injected into a semiconductor sample disappear. In this photoconductive decay method, a semiconductor sample is irradiated with microwaves, and at the same time, laser light is irradiated in a pulsed manner. If the photon energy of the irradiated laser beam is set to be larger than the band gap in the sample,
Carriers are generated in the sample. The generated carriers are recombined through the positions of energy levels at which defects and impurities in the semiconductor are formed in the band gap, and the number thereof gradually decreases. At this time, the intensity of the reflected or transmitted wave of the microwave changes with the amount of the carrier. Therefore, the intensity of the reflected or transmitted wave of the microwave is measured, and the time required for the intensity to reach a certain intensity from the maximum position is the time during which the carrier can exist in the semiconductor sample,
That is, it is obtained as a lifetime. The lifetime obtained by the photoconductive decay method can be generally expressed by the following equation.

(Equation 1) Here, τ ₁ is the lifetime determined by measurement, τ _m
Is the lifetime inside the semiconductor sample, and τ _s is the lifetime on the surface of the semiconductor sample.

In general, a semiconductor sample substrate has more defects on its surface than inside. Therefore, so-called surface recombination in which many carriers recombine on the surface in a short time becomes dominant. Therefore, the measured lifetime τ ₁ is different from the lifetime τ _m inside the semiconductor sample originally sought. Therefore, in order to determine the lifetime τ _m inside the semiconductor sample by the photoconductive decay method, it is necessary to suppress the surface recombination by some method. Therefore, as a method of suppressing the surface recombination,
For example, a method in which an oxide film is formed on the surface of a semiconductor sample and measurement is performed, and a method in which a semiconductor sample is immersed in a solution of iodine in an organic solution (chemical passivation method, hereinafter referred to as a CP method) are used. ing. Also,
Since the surface recombination cannot be completely suppressed in the above-described ordinary CP method, the semiconductor sample surface is irradiated with a bias light having a constant and predetermined light intensity different from the excitation light simultaneously with the excitation light. Japanese Patent Application Laid-Open No. 8-335 discloses a method capable of further suppressing surface recombination and measuring the lifetime inside a semiconductor sample with high accuracy without being affected by surface recombination.
No. 618 publication.

[0004]

However, when the above-described method of forming an oxide film on the surface or the process of suppressing surface recombination by the CP method are performed, a thermal oxidation process for forming an oxide film, In addition, since a pretreatment such as packing with an electrolytic solution and housing in an electrolytic solution is required, there is a problem that a large amount of time and labor is required for measurement. Also,
In the pretreatment as described above, new contamination may be introduced into the semiconductor sample. The present invention has been made in view of the above circumstances, and an object of the present invention is to quickly and accurately measure the lifetime of a semiconductor sample while preventing new contamination from being introduced into the semiconductor sample. It is an object of the present invention to provide a method and apparatus for measuring the lifetime of a semiconductor sample.

[0005]

As described above, the lifetime measurement using the photoconductive decay method without performing an oxide film treatment or the like can measure only the lifetime greatly affected by surface recombination. However, if the effect of surface recombination can be measured at the same time, it is possible to obtain the internal lifetime by obtaining the relationship between these two measured values and the internal lifetime in advance. is there. Here, as a method for obtaining information on surface recombination, for example, a photoluminescence method (hereinafter, referred to as PL) proposed in Japanese Patent Application Laid-Open No. 8-139146 has been proposed.
Is known). This is because the excitation light irradiates the surface of the semiconductor sample to generate carriers near the surface and the light (photoluminescence) generated when the carriers recombine has a wavelength at room temperature called band edge emission of about 1. Detects the intensity of 15 μm light (light of a specific wavelength)
The lifetime on the surface of the semiconductor sample is evaluated based on the decay time. Using this PL method,
As in the photoconductive decay method, the effect of surface recombination can be measured without subjecting the semiconductor sample to any special treatment. If the photoconductive decay method and the PL method are used, the relationship between the internal lifetime, the measurement lifetime by the photoconductive decay method, and the decay time by the PL method is determined in advance, so that the light Conduction decay method and PL
By performing measurement by the method and applying the measured value to the above relationship, the internal lifetime can be obtained without performing any special processing or the like on the semiconductor sample at the time of actual measurement.

Therefore, in order to achieve the above object, a method of the present invention is to irradiate a predetermined region of a semiconductor sample surface with a microwave and irradiate an excitation light, and to transmit a reflected wave or a reflected wave of the microwave by the semiconductor sample. A method of measuring a lifetime of the semiconductor sample based on a time change of the semiconductor sample by using a photoconductive decay method to measure a lifetime of the inside of the semiconductor sample. A first measuring step of measuring the lifetime by the photoconductive decay method without treatment, and irradiating a predetermined region of the semiconductor sample surface with excitation light, and specifying the light generated on the semiconductor sample surface by the excitation light. A second measurement step of extracting only light having a wavelength and detecting the decay time of the light; Reduction of measurement lifetime due to surface recombination obtained as a relationship between the lifetime measurement value obtained by the above-described photoconductive decay method in a state where the surface treatment has been performed and the lifetime measurement value obtained in the state without the above-mentioned treatment The correlation between the ratio and the decay time of light of a specific wavelength among the light generated on the surface of the semiconductor sample by irradiation with the excitation light, and the measured values obtained in the first and second measurement steps, respectively. An internal lifetime calculation step of calculating a lifetime inside the semiconductor sample based on the method. As the surface recombination suppression treatment, for example, an oxide film treatment on the surface of the semiconductor sample, a treatment for making the surface of the semiconductor sample passivated using a solution containing an electrolyte, or the like can be used. In addition, if the first and second measurement steps are performed in parallel using the same excitation light, there is no problem that the measurement time is increased by using the two measurement methods together.

In order to achieve the above object, an apparatus according to the present invention irradiates a predetermined area on a surface of a semiconductor sample with microwaves and irradiates excitation light, and transmits or reflects the microwaves through the semiconductor sample. In a semiconductor sample lifetime measuring apparatus for measuring the lifetime inside the semiconductor sample by using the photoconductive decay method for measuring the lifetime of the semiconductor sample based on the time change of the surface of the semiconductor sample, the surface of the semiconductor sample is re-equipped in advance. Of the measured lifetime by surface recombination obtained as a relationship between the lifetime measured value obtained by the photoconductive decay method and the lifetime measured value obtained without performing the above-described process in a state where the coupling suppression process is performed. The correlation between the decrease rate and the decay time of light of a specific wavelength among the light generated on the surface of the semiconductor sample by irradiation with the excitation light is stored. Storage means, first measurement means for measuring the lifetime by the photoconductive decay method without subjecting the semiconductor sample to surface recombination suppression treatment, and irradiating a predetermined region of the semiconductor sample surface with excitation light; A second measuring means for extracting only light of a specific wavelength from light generated on the surface of the semiconductor sample by the excitation light and detecting a decay time of the light; the correlation previously stored in the storage means; An internal lifetime calculator for calculating a lifetime inside the semiconductor sample based on the measured values obtained by the first and second measuring means, respectively. It is configured as a device.

[0008]

Embodiments and examples of the present invention will be described below with reference to the accompanying drawings to provide an understanding of the present invention. The following embodiments and examples are mere examples embodying the present invention, and do not limit the technical scope of the present invention. Here, FIG. 1 is a flowchart showing a processing procedure according to the lifetime measuring method according to the embodiment of the present invention, FIG. 2 is a detailed flowchart of the procedure of S1 in FIG. 1, and FIG. FIG. 4 is a schematic diagram showing a schematic configuration of a portion mainly related to the photoconductive decay method of the time measuring device Z, and FIG. 4 is a detailed view of a portion A in FIG. 3 and is a schematic diagram mainly showing a schematic configuration of a portion mainly related to the PL method. The semiconductor sample lifetime measuring apparatus Z according to the present embodiment is roughly composed of two parts. One is a configuration shown in FIG. 3, which is mainly for using the above-described conventional photoconductive attenuation method. The other is the configuration shown in FIG. 4, which is a detailed view of the part A in FIG.
This is a configuration mainly for using the PL method.

As shown in FIG. 3, a microwave transmission wave 22 oscillated from a microwave oscillator 1 passes through an attenuator 2 and a circulator 3 and is irradiated from an antenna 4 onto a semiconductor sample 20 mounted on a stage 21. Is done. A region on the semiconductor sample 20 to which the microwave 22 is irradiated is irradiated with pulsed laser light 23 (excitation light) oscillated from the pulsed short-wavelength laser light source 7 to inject carriers. The reflected wave 24 of the microwave 22 reflected by the semiconductor sample 20 passes through the antenna 4 and the circulator 3 and is detected by the microwave detector 5.
In this case the time variation of the reflection intensity of the detected microwave is calculated by the calculator 6, the lifetime tau ₁ is determined from the calculation result. The above configuration is the same as that of the conventional apparatus using the photoconductive decay method, and is an example of the first measuring means. Further, looking at the portion A in FIG. 3 in detail, as shown in FIG. 4, a lens 11, a cold filter 12, and a lens 13 are installed in the antenna 4. The fluorescent light 25 generated by the irradiation of the pulse laser light 23 oscillated from the short wavelength laser light source 7 is condensed by the lens 11,
The pulse laser light 23 (excitation light) is removed by the cold filter 12, and the light (here, infrared light) is
The light is guided to the spectroscope 14 via the light source 3, where only a specific wavelength is extracted and detected by the photodetector 15. At this time, the temporal change of the intensity of the light of the specific wavelength detected is calculated by the calculator 6, and the decay time τ ₂ is obtained. In order to efficiently obtain information on the surface of the semiconductor sample, the wavelength of the pulse laser beam 23 is set to a short wavelength of 800 nm or less, and the light receiving system is focused on the surface of the semiconductor sample as shown in FIG. desirable. The above configuration is based on the PL
This is the same as the device using the method, and is an example of the second measuring means. The measurement by the photoconductive decay method and the measurement by the PL method can be performed in parallel using the common pulse laser beam 23 (excitation light), so that the measurement process can be performed quickly. is there. The calculator 6 (storage means, and the internal one example of a lifetime calculating means), the according to the procedure described below, alpha obtained in advance _{(= τ 1 / τ m;} τ m
Using the correlation between τ ₂ and the internal lifetime of the semiconductor sample 20 and τ ₁ and τ ₂ determined above, the internal lifetime τ _m can be determined without performing an oxide film treatment or the like.

Hereinafter, a method for measuring the lifetime inside a semiconductor sample by the lifetime measuring apparatus Z will be described in detail with reference to the flowcharts shown in FIGS. First, prior to the actual measurement operation, a correlation between α (= τ ₁ / τ _m ) and τ ₂ is obtained (step S1). This step S1 will be described in more detail with reference to FIG. First, after applying the surface recombination suppression processing such as the semiconductor sample such as oxidation film process, for example using the apparatus shown in FIG. 3 for measuring the internal lifetime tau _m by photoconductive decay method (step S1
1). Subsequently, the life time τ ₁ is measured by a photoconductive decay method using, for example, the apparatus shown in FIG. 3 in a state where the surface recombination suppression processing such as the oxide film processing is not performed on the semiconductor sample (step S12). Further, the decay time τ ₂ of the light having the specific wavelength is measured by the PL method using, for example, the apparatus shown in FIG. 4 (step S13). Then, a correlation τ ₂ = F (α) (2) between α (= τ ₁ / τ _m ) and τ ₂ is determined using the respective values obtained above. Here, α indicates the decrease rate of the measured lifetime due to surface recombination, and τ ₂ is a value that captures information on surface recombination, so that there is naturally a correlation between the two. The obtained correlation (formula (2)) is stored in the arithmetic unit 6.

At the stage where the above correlation is obtained,
The actual lifetime measurement process to be described starts.
The processing of steps S2 to S5 described below (photoconductive
Measurement by the attenuation method) and the processing of steps S2 → S6, S7
(PL measurement) can be performed simultaneously and in parallel
You. First, a short wavelength laser light source 7 is applied to the semiconductor sample 20.
Then, pulse laser light 23 (excitation light) is irradiated (step
Step S2). Next, the measurement process using the photoconductive decay method was performed.
First, the microwave transmission wave 22 is transmitted from the microwave oscillator 1.
Is oscillated, passes through the attenuator 2 and the circulator 3, and
The semiconductor sample 20 is irradiated from the tener 4 (step S
3). Of the microwave 22 reflected by the semiconductor sample 20
The reflected wave 24 passes through the antenna 4 and the circulator 3,
Detected by the microwave detector 5 (step S
4). Then, in the arithmetic unit 6, the detected my
The time change of the reflection intensity of the black wave is measured and the measurement result
From lifetime τ₁Is obtained (step S5).
Also, regarding the measurement by the PL method, the above-described step S2
Generated from semiconductor sample by irradiation of excitation light
Is condensed by the lens 11 and is
Therefore, the pulse laser light 23 (excitation light) is removed, and the light
(Here, infrared light) passes through a lens 13 to a spectroscope 14.
Where only a specific wavelength is extracted and
15 (step S6). And the performance
In the calculator 6, the detected intensity of the light of the specific wavelength is detected.
The time change is measured and the decay time τ _TwoIs required
Step S7). In the computing unit 6, the phase stored in advance is stored.
The relationship (the above equation (2)) and the above steps S5 and S7
Τ obtained by₁, Τ_TwoSemiconductor sample based on
20 internal lifetime τ_mIs required (step S
8).

As described above, according to the lifetime measuring apparatus Z and the lifetime measuring method using the same according to the present embodiment, it is possible to perform a surface recombination suppressing process such as an oxide film process at the time of actual measurement. Since the internal lifetime can be measured simply by performing non-contact measurement by the ordinary photoconductive decay method and PL method, there is no danger of introducing new contamination into the semiconductor sample, and quick and accurate Measurement is possible. In addition, in the lifetime measuring apparatus Z, since the measurement by the photoconductive decay method and the measurement by the PL method are performed in parallel using the same excitation light, the measurement time is increased by using the two measurement methods together. The problem does not arise.

[0013]

In the above embodiment, the measurement of the internal lifetime τ _{m in} step S11 is performed by the photoconductive decay method in a state where the semiconductor sample is subjected to the oxide film treatment. Is also good. Further, any method other than the above may be used as long as the internal lifetime can be accurately obtained.

[0014]

As described above, the present invention irradiates a predetermined area on the surface of a semiconductor sample with a microwave and irradiates an excitation light, and the time change of a transmitted wave or a reflected wave of the microwave by the semiconductor sample. In the method for measuring the lifetime of the inside of the semiconductor sample using the photoconductive decay method for measuring the lifetime of the semiconductor sample based on the method, a surface recombination suppressing process is performed on the semiconductor sample. A first measuring step of measuring the lifetime by the photoconductive decay method in the absence of light, and irradiating a predetermined area of the semiconductor sample surface with excitation light, and generating light of a specific wavelength from light generated on the semiconductor sample surface by the excitation light. A second measurement step of extracting only the light and detecting the decay time of the light, and performing a surface recombination suppression treatment on the semiconductor sample previously determined. The reduction rate of the measured lifetime due to surface recombination obtained as the relationship between the lifetime measured value obtained by the photoconductive decay method in the above condition and the lifetime measured value obtained without the above treatment, and the excitation light Of the semiconductor sample based on the correlation with the decay time of light of a specific wavelength among the light generated on the surface of the semiconductor sample by the irradiation of the semiconductor sample, and the measured values obtained in the first and second measurement steps, respectively. Since the method is configured as a method for measuring the lifetime of a semiconductor sample, which comprises an internal lifetime calculation step for calculating the internal lifetime, there is no danger of introducing new contamination into the semiconductor sample. And quick and accurate measurements are possible. In addition, if the first and second measurement steps are performed in parallel using the same excitation light, there is no problem that the measurement time is increased by using the two measurement methods together.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a processing procedure according to a lifetime measuring method according to an embodiment of the present invention.

FIG. 2 is a detailed flowchart of a procedure of S1 in FIG. 1;

FIG. 3 is a schematic diagram showing a schematic configuration of a portion mainly related to a photoconductive decay method of a lifetime measuring apparatus Z according to an embodiment of the present invention.

FIG. 4 is a detailed view of a portion A in FIG. 3, which is a schematic diagram mainly showing a schematic configuration of a portion related to a PL method.

[Explanation of symbols]

6 arithmetic unit (an example of storage means and internal lifetime calculation means) 20 semiconductor sample 23 pulse laser light (an example of excitation light)

Continued on the front page F term (reference) 2G043 AA03 CA07 EA01 EA13 EA14 FA03 GA02 GB03 HA01 HA09 JA01 KA08 KA09 LA01 NA01 NA06 4M106 AA10 BA04 BA09 BA12 CB11 DH01 DH17 DH32 DH35 DH60 DJ20

Claims (8)

[Claims] 1. A semiconductor device, comprising: irradiating a predetermined region of a surface of a semiconductor sample with microwaves and irradiating excitation light; and setting a lifetime of the semiconductor sample based on a time change of a transmitted wave or a reflected wave of the microwave by the semiconductor sample. In the method for measuring the lifetime of the inside of the semiconductor sample using the photoconductive decay method for measuring, the life time of the semiconductor sample is measured by the photoconductive decay method without performing the surface recombination suppression treatment on the semiconductor sample. A first measuring step of measuring a time, irradiating a predetermined region of the semiconductor sample surface with excitation light, extracting only light of a specific wavelength from light generated on the semiconductor sample surface by the excitation light, and decay time of the light; A second measurement step of detecting the surface conductivity of the semiconductor sample, which is obtained in advance by the photoconductive decay method in a state where the surface recombination suppression processing is performed on the semiconductor sample. Of the measured lifetime reduction due to surface recombination obtained as a relationship between the measured lifetime measurement value and the lifetime measurement value obtained without performing the above treatment, and the rate of decrease in the measured lifetime caused by irradiation with excitation light. An internal lifetime for calculating a lifetime inside the semiconductor sample based on a correlation with a decay time of light of a specific wavelength of the light to be emitted and the measured values obtained in the first and second measurement steps, respectively. A method for measuring the lifetime of a semiconductor sample, comprising: a time calculating step. 2. The method for measuring the lifetime of a semiconductor sample according to claim 1, wherein the surface recombination suppression processing is an oxide film treatment on the surface of the semiconductor sample. 3. The method for measuring a lifetime of a semiconductor sample according to claim 1, wherein the surface recombination suppressing process is a process of putting the surface of the semiconductor sample into a passivation state using a solution containing an electrolyte. 4. The method for measuring the lifetime of a semiconductor sample according to claim 1, wherein the first and second measurement steps are performed in parallel using the same excitation light. 5. A method for irradiating a predetermined region of the surface of a semiconductor sample with microwaves and irradiating excitation light with the microwaves, and changing a lifetime of the semiconductor sample based on a time change of a transmitted wave or a reflected wave of the microwaves by the semiconductor sample. In the semiconductor sample lifetime measuring device for measuring the lifetime inside the semiconductor sample using the photoconductive decay method for measurement, the photoconductive decay method is performed in a state where the semiconductor sample is subjected to a surface recombination suppression treatment in advance. The reduction rate of the measured lifetime due to surface recombination obtained as the relationship between the measured lifetime obtained by the above and the measured lifetime obtained without performing the above treatment, and the surface of the semiconductor sample by irradiation with excitation light Storage means for storing a correlation with light decay time of light of a specific wavelength of light generated in the semiconductor device; First measuring means for measuring the lifetime by the photoconductive decay method in a state where no treatment is performed;
A second step of irradiating a predetermined area of the semiconductor sample surface with excitation light, extracting only light of a specific wavelength from light generated on the semiconductor sample surface by the excitation light, and detecting the decay time of the light;
And an internal life for calculating a lifetime inside the semiconductor sample based on the correlation previously stored in the storage and the measured values obtained by the first and second measurement, respectively. An apparatus for measuring the lifetime of a semiconductor sample, comprising: a time calculating means. 6. The apparatus for measuring a lifetime of a semiconductor sample according to claim 5, wherein the surface recombination suppression processing is an oxide film processing on the surface of the semiconductor sample. 7. The apparatus for measuring a lifetime of a semiconductor sample according to claim 5, wherein the surface recombination suppressing process is a process of putting the surface of the semiconductor sample into a passivation state using a solution containing an electrolyte. 8. The apparatus for measuring the lifetime of a semiconductor sample according to claim 5, wherein the first and second measurement steps are performed in parallel using the same excitation light.