JPH02272743A - Life time measuring device of semiconductor - Google Patents

Abstract

PURPOSE:To increase conductance due to photo-excitation in positions near magnetic poles of a core and to increase output voltage, thereby improving measurement accuracy by directing a light beam to a semiconductor from the same side of the core which is wound with a coil. CONSTITUTION:A high frequency current is made to flow in a coil 19 of a U-shaped core 17. An alternating field occurred thereby is introduced from magnetic poles 18 to a semiconductor wafer 16 to generate eddy current. Meanwhile, light beams from LEDs 25, 26 are directed to the wafer 16 in the same direction as magnet lines of force through optical fiber cables 21, 22; then, excitation carriers develop and resistance reduces locally. Flux which enters the wafer 16 is maximum at an area near the magnetic poles 18. If light is directed in the same direction to the area, resistance change is developed in a position of a maximum electromotive force. Accordingly, an output voltage increases and is taken out by an electrode 29; then, life time of a carrier is measured. A life time measuring device of high measurement accuracy can be acquired in this way.

Description

[Detailed Description of the Invention] Field of Industrial Application] The present invention relates to a semiconductor lifetime measuring device, and in particular, it involves injecting light into a semiconductor to generate photoexcited carriers, and adjusting the magnetic flux introduced into the semiconductor in advance. occurs along with it. The present invention relates to a semiconductor lifetime measurement device that measures carrier lifetime from changes in voltage due to eddy current.

K Summary of the Invention: A gap is provided in a part of the magnetic path of a core made using a ferromagnetic material such as ferrite, and the current flowing through the coil wound around the core is induced and leaks through the magnetic poles of the core. A magnetic flux is guided into the semiconductor, and this magnetic flux generates an eddy current within the semiconductor.The voltage generated by this eddy current is extracted through an electrode provided on the surface of the semiconductor, and the light from the LED is passed through the semiconductor. In this device, the lifetime of a semiconductor is measured from the change in voltage by generating photo-excited carriers by injecting light into the semiconductor, and by winding the EO around the semiconductor with a coil. In addition, the light from a plurality of EDs that emit light of different wavelengths is made to enter the surface of the semiconductor between the magnetic poles of the core using optical fiber cables. This is what I did.

K. PRIOR ART A conventional semiconductor lifetime measuring device using eddy current has been constructed as shown in FIGS. 8 and 9. A coil 2 wound around a U-shaped core 1 is connected to a high frequency power supply circuit 3 with a 20 M
A high frequency current having a frequency of about 82 is caused to flow, thereby guiding the magnetic flux leaking from the gap in the core 1 into the semiconductor wafer 4, thereby causing an eddy current to flow within the semiconductor 4.

The voltage generated by the eddy current in the semiconductor 4 is detected through the electrode 5, and after this detection signal is amplified and detected by the amplification/detection circuit 6, changes in the voltage are observed using a waveform indicating device such as an oscilloscope 7. I try to do that.

An LED 8 is arranged on the opposite side of the semiconductor wafer 4 to be measured from the core 1 around which the coil 2 is wound, and the light from the LED 8 is made to enter the semiconductor 4 through a slit 9. I have to. Furthermore, the LED
8 is driven by an LED drive circuit 10. The light from the LED 8 generates carriers in the semiconductor 4 due to optical excitation, and the resistance locally decreases. This resistance change is extracted through the electrode 5 as a voltage change. The lifetime of the semiconductor is then measured from this change in voltage.

Problems to be Solved by the K Invention: According to such a conventional semiconductor lifetime measurement device, since the LED 8 is located on the opposite side of the semiconductor wafer 4 from the core 1 around which the coil 2 is wound, If the thickness of the semiconductor wafer 4 is thick, the increase in conductance due to optical excitation will occur in a region farther from the gap between the electrodes of the core 1, which will not only reduce the output voltage and lower the measurement accuracy, but also could become unmeasurable.

In addition, since such a device uses a single LED 8, only one type of wavelength of light can be incident, which makes it possible to change the lifetime of carriers generated near the surface and the lifetime of carriers generated inside. There was a problem in that it was difficult to separate the lifetime of the carrier A7.

The present invention was made in view of these problems, and it increases the output voltage by causing the increase in conductance due to optical excitation to occur in a portion of the core around which the coil is wound, which is close to the magnetic pole, thereby improving measurement accuracy. It is an object of the present invention to provide a semiconductor lifetime measuring device that can improve the lifetime of a semiconductor, or separately measure the lifetime of carriers generated near the surface and the lifetime of carriers generated inside. It is.

Means for Solving Problem K] The first invention is to pass a current through a coil, guide a magnetic flux into a semiconductor through the magnetic pole of a core around which the coil is wound, and cause a vortex in the semiconductor by the magnetic flux. In the device, the lifetime of the carriers is measured by generating a current and injecting light into the semiconductor to generate photo-excited carriers, and extracting the change in voltage generated in the semiconductor through an electrode. Light is made to enter the semiconductor from the same side of the semiconductor as the core around which the coil is wound.

Further, the second invention provides a method for passing current through the coil, guiding a magnetic flux into the semiconductor through the magnetic pole of the core around which the coil is wound, and causing an eddy current to flow in the semiconductor by the magnetic flux. In a device that measures the lifetime of carriers by injecting light into a semiconductor to generate photoexcited carriers and extracting the change in voltage generated in the semiconductor through an M pole, a plurality of types of carriers having different wavelengths are used. It is designed to allow light to enter.

"Effect χ Therefore, according to the first invention, light is incident on the semiconductor from the same side as the core, and this makes it possible to cause optical excitation near the magnetic pole of the core, making it possible to increase the output voltage. This makes it possible to improve measurement accuracy.

Furthermore, according to the second invention, it is possible to make multiple types of light with different wavelengths enter the semiconductor, thereby making it possible to measure the lifetime of carriers generated at a penetration depth corresponding to the wavelength. It becomes like this.

K Embodiment FIGS. 1 to 3 show a semiconductor lifetime measuring device according to an embodiment of the present invention, and this measuring device is adapted to measure a semiconductor 16 made of, for example, a silicon wafer. ing. A U-shaped core 17 is arranged on the wafer 16 which is the object to be measured. A pair of tips of the core 17 constitute magnetic poles 18, and the magnetic poles 18 are connected to the silicon wafer 1 through a small gap.
It is designed to face 6. Further, a coil 19 is wound around the U-shaped core 17, and this coil 19 is connected to a high frequency power circuit 20.

This measuring device also includes a pair of optical fiber cables 21.2.
2 are used, and their emission ends face the surface of the semiconductor wafer 16 and are located between a pair of magnetic poles 18. In addition, the input end of the optical fiber cable 21.22 is connected to the LED 25.2 via a condenser lens 23.24.
6 and facing each other. These E
D25.26 is the LED drive circuit 27.28 shown in Figure 2.
is connected to. Further, a pair of electrodes 29 are provided on the semiconductor wafer 16 , and these N poles 29 are connected to an amplification/detection circuit 30 . The detection circuit 30 is connected to an oscilloscope 31. Moreover, the oscilloscope 31 is connected to the LED drive circuits 27 and 28.

In the above configuration, for example, 20 MH2
Supplies high-frequency current at a frequency of This allows core 1
An alternating magnetic field is generated within 7, and this magnetic field creates a pair of f! 1 pole 1
It leaks between the electrodes 8 and is guided into the semiconductor wafer 16 (see FIG. 5). and semiconductor wafer 16
An eddy current flows inside the magnetic flux due to the magnetic flux. This eddy current generates a voltage within the semiconductor 16, and this voltage can be taken out by the pair of electrodes 8i29. The detected voltage is amplified and detected by an amplification/detection circuit 30, and changes in the voltage are observed by an oscilloscope 31.

Moreover, each of the LEDs 25 and 26 has a drive circuit of 27 and 28.
It is driven by and emits light. And these LED2
The light from 5.26 is focused by a condensing lens 23.24 and incident on the fiber optic cable 211.22.

The light passing through the optical fiber cables 21 and 22 is 1 each.
[The light enters the wafer 16 from the surface of the semiconductor wafer 16 during i18. Then, carriers are generated in the semiconductor due to optical excitation. This carrier locally reduces the resistance. Changes in resistance are therefore detected as changes in the voltage drawn through electrode 29.

FIG. 4 shows an equivalent circuit of this measuring device.

A change in magnetic flux due to one coil generates an electromotive force E that causes an eddy current to flow within the semiconductor 16. Go and GO represent the conductance of the irradiated portion of the semiconductor when not irradiated with light and the conductance increased when irradiated with light, respectively.

Re is the resistance of the semiconductor along the path through which the eddy current flows other than the portion hit by light. The eddy current flows through the magnetic pole 1 of the core 17.
Since the flow is concentrated in the narrow gap between 8 and 8, assuming that Re is smaller than the resistance 1/Go in this part, the voltage VO appearing at the detection electrode 29 is Vo=Re (Go+Gp)E..-( 1),
The output voltage is proportional to the increase in conductance. Therefore, the lifetime of the semiconductor can be measured from this output voltage.

Furthermore, the device according to this embodiment is characterized in that light is incident on the semiconductor wafer 16 from the same side as the core 17 around which the coil 19 is wound. An optical fiber cable 21 is installed in the gap between the pair of f11 poles 18 of the U-shaped core 17.
．． The light is made to enter the surface of the semiconductor wafer 16 at right angles through 22. Fiber optic cable 21.22
The diameters of each are small, less than 1111, so
It becomes possible to attach two or three or more as desired.

Since the direction of incidence of light is the same as the side on which the core 17 is provided, the following advantages arise.

As shown in FIG. 5, the lines of magnetic force entering the semiconductor wafer 16 from the magnetic pole 18 of the core 17 are strongest near the air gap.
The further away from this point, the weaker it becomes.

Therefore, the change in magnetic flux is large near the gap between the magnetic poles 18 of the core 17, and becomes smaller as the distance moves away. When light is incident directly under the gap, the light irradiation efficiency is highest because the resistance change due to photoexcitation occurs at the location where the electromotive force is greatest. Therefore, the output voltage increases and measurement accuracy improves. Furthermore, even if the semiconductor wafer 16 is thick, the inconvenience that measurement cannot be performed because the increase in conductance due to optical excitation occurs near the gap between the magnetic poles 18 can be solved.

Furthermore, in this device, two LEDs 25 and 26 are used to make light of different wavelengths incident on the semiconductor 16.
I am trying to irradiate it to In the case of silicon, as shown in FIG. 5, the thickness at which the light intensity becomes 1/2.7 is 0.2 μl when the wavelength is 400 ni. On the other hand, when the wavelength is 1000 nl11, it is 200 μm.
The depth is 1/2.7, and the difference in depth between the two is 1000
It's double. Therefore, carriers generated by the optical excitation method are concentrated on the surface when the wavelength of the incident light is 400 nm. On the other hand, in the case of light with a wavelength of 1000 na+, carriers spread to the back. The carrier lifetime consists of two components: one due to recombination on the surface of the semiconductor and the other due to recombination inside the semiconductor. Therefore, if you use light with a short wavelength, you will be able to measure the lifetime where surface recombination is dominant, whereas if you use light with a long wavelength, you will be able to measure the lifetime where internal recombination is dominant. It turns out.

As shown in equation (1), the voltage Vo appearing on the two detection electrodes is determined by the conductance GO when no light is incident on the semiconductor and the increase in conductance Gp when light is incident on the semiconductor.
is proportional to the sum of FIG. 7 shows only the change Gp in conductance when light is applied in an impulse manner, with the maximum value of the conductance width being normalized to 1. In the graph of this figure, the vertical axis is the logarithmic value of conductance, and the horizontal axis shows time. As shown in the figure, changes in conductance are not expressed by simple exponential decay.

Surface recombination is a phenomenon in which carriers excited by light that are within the range of the diffusion length diffuse to the surface, recombine at recombination centers on the surface of the semiconductor, and disappear. Carriers located deeper than the diffusion length recombine and disappear at recombination centers inside the semiconductor. Since there are usually far fewer recombination centers inside the semiconductor than at the surface, the change in conductance Gl) is: Gl) = AeXl) (-t/τ 1 )+
Bexp (-4/r2) ・ −・ ・
It is expressed as (2). The first term in the above equation is due to surface recombination, τ1 is its lifetime, and the second term is due to surface recombination.
The term is due to internal recombination, and τ2 is its lifetime. τ1 has a smaller value than τ2. A and B
is a constant that changes depending on the wavelength of incident light. When light reaches deep into the semiconductor, A/B is small, and when light reaches only shallowly, A/B becomes large. As shown in FIG. 6, A and 8 can be separated by performing measurements twice using light with a short wavelength of 400 nm or less and light with a long wavelength of 1100 Qn or more.

K Effects of the Invention The first invention is such that light is made to enter the semiconductor from the same side of the semiconductor as the core around which the coil is wound. Therefore, since the increase in conductance due to optical excitation occurs near the gap between the magnetic poles of the core, the output voltage increases and measurement accuracy improves.

In a second aspect of the invention, a plurality of types of light having mutually different wavelengths are made incident. Therefore, it becomes possible to separately measure the lifetime of carriers generated near the surface and the lifetime of carriers generated inside.

[Brief explanation of drawings]

FIG. 1 is a perspective view of the main parts of a semiconductor lifetime measuring device according to an embodiment of the present invention, FIG. 2 is a longitudinal cross-sectional view of the same, FIG. 3 is a plan view of the same, and FIG. Figure 5 is a cross-sectional view of the main part showing the behavior of magnetic lines of force within a semiconductor, Figure 6 is a graph showing the penetration depth according to wavelength, and Figure 7 is a circuit diagram of the circuit.
The figure is a graph showing changes in conductance, FIG. 8 is a longitudinal sectional view of a conventional measuring device, and FIG. 9 is a bottom view of the same. The names of the main parts in the drawings are as follows. 16... 17... 18... 19... 20... 21.22・ 25.26... ・Silicon wafer (semiconductor) ・U-shaped core, magnetic pole, coil, high frequency Power supply circuit, optical fiber cable, LED 29... Electrode 30... Amplification/detection circuit 31... Oscilloscope

Claims (1)

[Claims] 1. Passing current through the coil and guiding magnetic flux into the semiconductor through the magnetic pole of the core around which the coil is wound;
The magnetic flux generates an eddy current in the semiconductor, and light is incident into the semiconductor to generate photoexcited carriers, and the change in voltage generated in the semiconductor is extracted through electrodes, thereby reducing the lifetime of the carriers. 1. An apparatus for measuring lifetime of a semiconductor, characterized in that light is made to enter the semiconductor from the same side of the semiconductor as the core around which the coil is wound. 2. Passing current through the coil and guiding magnetic flux into the semiconductor through the magnetic pole of the core around which the coil is wound;
The magnetic flux generates an eddy current in the semiconductor, and light is incident on the semiconductor to generate photo-excited carriers, and the change in voltage generated in the semiconductor is taken out through electrodes, thereby changing the life of the carriers. What is claimed is: 1. A lifetime measuring device for a semiconductor, characterized in that the device is adapted to measure time, and is characterized in that a plurality of types of light having mutually different wavelengths are incident thereon.