JPH06138058A - Instrument for measuring energy level of semiconductor wafer - Google Patents

Abstract

PURPOSE:To measure the energy level of a semiconductor wafer in a non- contacting and nondestructive state at an ordinary temperature by measuring the lifetime variation of the minority carrier of the semiconductor wafer by forcibly changing the lifetime by changing the wavelength of bias light. CONSTITUTION:A wavelength setter 10 changes the wavelength of bias light from a bias light generator 9 so as to obtain the thermal equilibrium state corresponding to the wavelength. In addition, when an exciting light generator 4 starts/stops the emission of exciting light for irradiating a semiconductor wafer 2, the carrier concentration in the wafer 2 changes due to the generation/ reduction of excessive carriers and level variation occurs in the reflected wave of microwaves radiated 5 upon the wafer 2. The level variation is detected 7. The setter 10 forcibly changes the lifetime of the minority carrier of the wafer 2 by changing the wavelength of the bias light and a measurement circuit 11 measures the lifetime variation of the minority carrier in a thermal equilibrium state. The energy level of the wafer 2 is measured 11 basing on the wavelength of the bias light at the point at which the lifetime changes stepwise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor wafer energy level measuring apparatus used for evaluating a semiconductor wafer.

[0002]

2. Description of the Related Art With the recent trend toward ultra-precision semiconductor devices represented by VLSI, stricter quality control of semiconductor materials has been required. Conventionally, as a method for detecting a minute amount of metal contamination on a semiconductor material, D
A contact breakdown inspection method called an LTS (Deep Level Transient Spectroscopy) method for measuring impurities of a semiconductor wafer to identify impurities due to contamination is generally used. However, for the management as described above, it is desirable to use an inspection method that does not cause contamination or damage to the semiconductor wafer. Therefore, a technique has been developed for measuring the energy level of a semiconductor wafer by using a non-contact and non-destructive inspection method called a microwave photoconductive attenuation method (Japanese Patent Application No. 61-101045).
Japanese Patent Application No. 2-248062). FIG. 4 is a block diagram showing a measurement principle in an example of a conventional microwave energy level measuring apparatus, FIG. 5 is a graph showing a level change of reflected microwaves by the conventional measuring apparatus, and FIG. It is a graph which shows the relationship of the constant (tau) and temperature. As shown in FIG. 4, the conventional measuring apparatus A includes a sample holder 1,
A semiconductor wafer 2 that is a sample to be measured held on a sample holder 1, an excitation light generator 4 that irradiates the semiconductor wafer 2 with excitation light, and a microwave generator 5 that generates a microwave radiated to the semiconductor wafer 2. A waveguide 3 for radiating the microwave radiated by the microwave generator 5 to the semiconductor wafer 2, and a detector 6 for detecting the microwave reflected by the surface of the semiconductor 2 through the waveguide 3. , A synchroscope 7 for displaying the level change of the microwave detected by the detector 6, and a semiconductor wafer 2 incorporated in the sample holder 1.
A heater 11 for heating from below, a temperature controller 12 for adjusting the heating temperature by the heater 11, a temperature controller 12,
It is composed of an excitation light generator 4, a microwave generator 5, a detector 6 and a control circuit 8 for controlling the synchroscope 7. The measurement principle will be described below. Carriers, which are free electron-hole pairs, are excited in the semiconductor wafer 2 by the excitation light emitted from the excitation light generator 4. This carrier is in excess of the carrier concentration of the semiconductor wafer 2 in the thermal equilibrium state, and increases the carrier concentration. And
If the irradiation of excitation light is interrupted, excess carriers recombine and gradually disappear, decreasing the carrier concentration. Since such a change in carrier concentration changes the electric conductivity of the semiconductor wafer 2, the microwave incident on the wafer 2 changes in level. The microwave after the level change becomes a reflected wave, passes through the waveguide 3 again, and is transmitted to the detector 6. The attenuation of the microwave (reflected wave) detected by the synchroscope 7 is displayed as an attenuation curve as shown in FIG. 5, for example. In the figure, t ₀ is the time when the excitation light is irradiated, and τ is the time constant at a predetermined attenuation point. Next, FIG. 6 is a graph in which the temperature of the semiconductor wafer 2 heated by the heater 11 is changed using the temperature controller 12 and the change of the time constant τ at this time is plotted. It can be seen from FIG. 6 that the time constant τ has temperature dependence. The peaks in the figure correspond to deep impurity levels EL6 and EL9, respectively.
Therefore, a slight amount of metal contamination of the semiconductor wafer 2 could be estimated from this peak.

[0003]

In the conventional measuring method, the energy level of the semiconductor wafer 2 is calculated from the waveform analysis of the attenuation curve. However, the decay curve is a linearity (probe function) when the carrier concentration is determined by the injection state of carriers by excitation light or microwaves as a probe.
Therefore, it is difficult to directly obtain the energy level of the semiconductor wafer 2 from the waveform of the attenuation curve, which includes many errors caused by the above. For this reason, there are cases where the theoretical level and the energy level measured by another measurement method (for example, the capacitance DLTS measurement method) do not match. Further, in the conventional measuring method, since the heating temperature of the semiconductor wafer 2 is changed, for example, the semiconductor wafer 2, which is the sample to be measured, is put in the vacuum container together with the heater 11 so as not to be affected by the ambient temperature, and the measurement is performed. It was Therefore, it is difficult to measure a large amount of semiconductor wafers 2 quickly. On the other hand, although it is a contact / destructive inspection method, excess carriers are generated by irradiating a semiconductor wafer with monochromatic light while changing the wavelength, and the energy level of the semiconductor wafer 2 is detected at the wavelength of the monochromatic light at that time. The technique to do so has been known (Japanese Patent Laid-Open No. 53-50983). In order to solve the problems in the conventional art, the present invention provides
It is an object of the present invention to improve a semiconductor wafer energy level measuring device and provide a semiconductor wafer energy level measuring device capable of non-contact / non-destructive measurement of energy levels at room temperature.

[0004]

In order to achieve the above object, the present invention provides an irradiation means for irradiating a semiconductor wafer with excitation light, a radiation means for radiating a microwave to the semiconductor wafer, and radiation by the radiation means. Detecting means for detecting a transmitted wave or a reflected wave of the generated microwave, and lifetime forcing for forcibly changing the lifetime of the minority carrier of the semiconductor wafer corresponding to the level change of the microwave detected by the detecting means. An energy level measuring device for a semiconductor wafer comprising: a changing means; and an energy level measuring means for measuring an energy level of the semiconductor wafer based on a change in the lifetime forced by the lifetime forced changing means. Bias light for irradiating the semiconductor wafer with the wavelength changing the wavelength by the forced lifetime changing means. It is morphism means configured as an energy level measuring apparatus for a semiconductor wafer characterized by.

[0005]

According to the present invention, the semiconductor wafer is irradiated with the excitation light and the bias light is irradiated with the wavelength changed, and the life of minority carriers is changed from the level change of the reflected wave of the microwave radiated to the semiconductor wafer. Measure the change in time. At this time, the energy level of the semiconductor wafer can be measured based on the wavelength of the bias light at the point where the minority carrier lifetime changes stepwise.
That is, the energy level of the semiconductor wafer can be measured at non-contact, non-destructive and at room temperature. As a result, a very small amount of metal contamination of the semiconductor wafer can be detected with high accuracy and speed based on this energy level.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings for the understanding of the present invention. still,
The following examples are examples of embodying the present invention, and do not limit the technical scope of the present invention. FIG. 1 is a block diagram showing the measurement principle of a microwave energy level measuring apparatus for a semiconductor wafer according to an embodiment of the present invention, and FIG. 2 is an explanatory view of the energy level of a semiconductor wafer.
Shows a graph showing the relationship between the change in wavelength of bias light and the change in lifetime of minority carriers. In addition, in FIG.
The same symbols are used for the elements common to the block diagram showing the measurement principle in the example of the conventional microwave energy level measuring apparatus shown in FIG. As shown in FIG. 1, the measuring apparatus A'according to this embodiment has a sample holder 1 similar to that of the conventional example.
A semiconductor wafer 2 as a sample to be measured, an excitation light generator 4 as an example of irradiation means, a microwave generator 5 as an example of radiation means, a waveguide 3, and an example of detection means. In addition to the detector 6, the synchroscope 7 and the control circuit 8, a bias light generator 9 for generating bias light,
The wavelength setting device 10 forcibly changes the lifetime of a small number of carriers by changing the wavelength of the bias light generated by the bias light generator 9 (the bias light generator 9 and the wavelength setting device 10 are bias light irradiation means). (It is an example of (lifetime forced change means)) and the wavelength setting device 1
The measuring circuit 11 is an example of energy level measuring means for measuring the energy level of the semiconductor wafer 2 based on the change of the minority carrier lifetime forced by 0.

Next, the measurement principle of this embodiment will be described with reference to FIG. For example, when an electron exists at the energy level Et of the semiconductor wafer 2, the energy ΔE required to raise this electron to a conductor having the energy level Ec.
Is hC / (Ec-E when converted to the wavelength of bias light
t). When holes are present, the energy Δ required to lower the holes to the valence band of the energy level Ev.
E ′ is hC / (Ev− when converted to the wavelength of bias light.
Et). Where h is Planck's constant and C is the speed of light. Therefore, when the wavelength of the bias light is changed by the wavelength setting device 10, the carrier of the energy level corresponding to the wavelength is excited, and the wavelength of each bias light is changed as in the case of changing the heating temperature in the conventional example. A thermal equilibrium state corresponding to is obtained. Then, a change in carrier concentration due to generation / disappearance of excess carriers due to irradiation / interruption of the excitation light from the excitation light generator 4 on the semiconductor wafer 2 is generated by the microwave generator 5 to generate a waveguide. Three
Is detected by the wave detector 6 and the synchroscope 7 as a level change of the reflected wave of the microwave radiated via. The lifetime of a small number of carriers in the thermal equilibrium state is measured from this level change. At this time, the energy levels Ec and Ev are values unique to the semiconductor wafer 2,
Further, since the energy level Et is a value inherent to impurities due to contamination, the change in the minority carrier lifetime when the wavelength of the bypass light is changed is a wavelength corresponding to the above energy ΔE or ΔE ′. Occurs only at times. That is, the lifetime of a small number of carriers changes in steps as shown in FIG. Based on this step change, the energy level of impurities due to contamination is measured. The measurement circuit 11 measures the minority carrier lifetime and energy level. As described above, according to the energy level measuring apparatus A'of the semiconductor wafer according to the present embodiment, the energy level can be measured at non-contact, non-destructive, and room temperature. Furthermore, since the energy level is measured based on the step change in the lifetime of a few carriers,
The detection accuracy is higher than that of the conventional method of directly reading from the waveform of the attenuation curve. As a result, a minute amount of metal contamination of the semiconductor wafer 2 can be detected with high accuracy and speed. Incidentally, the control circuit 8 and the measuring circuit 11 in the above embodiment
It is also possible to combine and in one computer. Further, in the present embodiment, the method of measuring the change in the number of minority carriers using the reflected microwave as a probe is applied, but in the actual use, the method of detecting the increase or decrease of all the minority carriers such as infrared laser and transmitted microwave is applied. However, there is no problem.

[0008]

Since the semiconductor wafer energy level measuring apparatus according to the present invention is configured as described above, it is possible to measure the energy level non-contact and non-destructive at room temperature. As a result, a minute amount of metal contamination of the semiconductor wafer can be detected with high accuracy and speed.

[Brief description of drawings]

FIG. 1 is a block diagram showing the measurement principle of a microwave energy level measuring apparatus for semiconductor wafers according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of energy levels of a semiconductor wafer.

FIG. 3 is a graph showing a relationship between a change in wavelength of bias light and a change in lifetime of minority carriers.

FIG. 4 is a block diagram showing the measurement principle in an example of a conventional microwave energy level measuring apparatus.

FIG. 5 is a graph showing a level change of reflected microwaves by a conventional measuring device.

FIG. 6 is a graph showing the relationship between time constant τ and temperature by a conventional measuring device.

[Explanation of symbols]

A '... Microwave energy level measuring device for semiconductor wafer 2 ... Semiconductor wafer 4 ... Excitation light generator 5 ... Microwave generator 6 ... Detector 7 ... Synchroscope 9 ... Bias light generator 10 ... Wavelength setting device 11 … Measuring circuit

Claims (1)

[Claims] 1. A radiating means for irradiating a semiconductor wafer with excitation light, a radiating means for radiating a microwave to the semiconductor wafer, and a detecting means for detecting a transmitted wave or a reflected wave of the microwave radiated by the radiating means. And a lifetime forced change means for forcibly changing the lifetime of minority carriers of the semiconductor wafer corresponding to the microwave level change detected by the detection means, and a life forced by the lifetime forced change means. An energy level measuring device for a semiconductor wafer, comprising: an energy level measuring means for measuring the energy level of the semiconductor wafer based on a change in time; Of a semiconductor wafer, which is a bias light irradiating means for changing and irradiating Gi level measuring device.