JPH0763667A - Method and device for measuring doped impurity - Google Patents

Abstract

PURPOSE:To detect the quantity of doped without interrupting an ion implantation process and diffusion process by irradiating the surface of a sample with probe light and modulation exciting light one over the other so as to detect the reflection spectrum of the surface of the sample synchronizing with the modulation. CONSTITUTION:An exciting light L from an exciting light source 1 is modulated by a chopper 2 and a sample 5 is irradiated with the modulation exciting light, then the same irradiation point is irradiated with a white light P from a white light source 3. The reflecting light H is detected spectroscopically by a spectroscope 6 and detector 7, and a photo-reflectance DELTAR synchronizing with the modulation is picked up, then, after it is standardized by the direct current element R of the reflecting light, the result is detected through scanning detection using the selected wavelength of the spectroscope 6 to obtain its photo-reflectance spectrum. Its wavelength lambdaG at the peak is equivalent to the band gap quantity of the sample 5 and the band gap quantity is shifted in proportion to the quantity of dopes impurities. Therefore, a metering line with their correlation is stored in a storage part 11 in advance and it is compared with the detected peak wavelength lambdaG in a calculation, so that the quantity of the doped impurities can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring an impurity doping amount in an ion implantation process and a diffusion process in semiconductor manufacturing.

[0002]

2. Description of the Related Art Conventionally, a four-probe method has been used to measure the amount of impurity doping in semiconductor manufacturing. The resistivity of the sample was detected by the 4-probe method, and the impurity doping amount was obtained from a calibration curve using known data showing the correlation between the resistivity and the impurity doping amount.

FIG. 7 shows a schematic configuration of the 4-probe method. In FIG. 7, 15 is a sample, 16, 17, 18, and 19 are probes,
20 is a voltmeter. The tip of tungsten or silicon carbide is used for the probe by a method such as electrolytic polishing.
What is thinned to about several μm is used.

Insufficient contact between the probe and the surface of the sample 15 causes an error. Therefore, the probe is pressed against the sample 15 using a spring or the like. When silicon is a sample, the mass is 10 when a 5 μm tip is used.
0 to 200 g is suitable. If the sample is a soft semiconductor such as gallium arsenide, it should be lighter than this to avoid damaging the surface.

When the sample surface is oxidized or dirty, the contact between the probe and the sample 15 is significantly deteriorated. Therefore, a high voltage pulse is applied between the probe and the sample 15 to melt them. Must be worn (or alloyed).

The probes 16, 17, 18, and 19 are arranged at equal intervals, and when the intervals are S, the resistivity ρ is ρ = 2π.
It is represented by S (V / I). I is the current flowing through the sample, and V is the measured voltage at that time. Usually, S is 1 mm, or 1.59 mm so that 2πS = 1.

This equation is satisfied only when the sample 15 is semi-infinitely wider than the probe spacing S. The distance L between the probe and the end of the sample 15 needs to be at least 10 S or more (L> 10 S). If L is larger than 2S, the error remains only a few percent, but if L> 10S is not satisfied, correction is necessary.

Further, the thickness of the sample 15 must be twice the thickness of S or more. When the sample 15 is thin, different corrections need to be applied depending on whether the bottom surface is in contact with a metal or an insulator.

In the measuring apparatus configured as described above, a constant current source having a large output impedance is used as a current source, and a current I is passed through the sample 15 using the probes 16 and 19. The current I is set so that a large current that heats the sample 15 does not flow.

On the other hand, a voltmeter having a large input impedance is used as the voltmeter 20, and the probes 17 and 18 are used to measure the voltage.

By this measurement, the voltage value V with respect to the current value I is read from the voltmeter 20 and is applied to the above equation to calculate the resistivity ρ.

The impurity doping amount was obtained from the known data showing the correlation between the resistivity ρ and the impurity doping amount thus obtained.

[0013]

The measurement using the 4-probe method is performed as described above. However, if the measurement conditions are not satisfied, it is necessary to add the above correction to the measurement result. Therefore, it is not always an efficient measurement method.

Further, since this is a contact measurement method in which a probe is brought into contact with the sample surface or fused (or alloyed), the sample is damaged and a measurement error occurs. Moreover, the sample used for the measurement is wasted. Further, in order to perform the measurement in the semiconductor manufacturing process, it was necessary to interrupt the ion implantation process and the diffusion process and take out the sample.

The present invention was devised to solve the above-mentioned problems, and it is easier than in the prior art without interrupting the ion implantation step and diffusion step in semiconductor manufacturing and without damaging the sample. It is an object of the present invention to provide a method and an apparatus capable of obtaining an impurity doping amount.

[0016]

The first invention of the present application is to irradiate a sample surface with probe light, and irradiate modulated excitation light to the irradiation position of the probe light to synchronize the sample surface with the modulation. It is characterized in that the reflection spectrum is detected from the reflected light from and the impurity doping amount is measured from the correlation between the band gap amount of the sample and the impurity doping amount obtained from this reflection spectrum.

A second invention of the present application is a probe light source for irradiating probe light, an excitation light source for irradiating a probe light irradiation position on a sample surface with modulated excitation light, and a reflected light of the probe light. Means for detecting a reflection spectrum in synchronism with the modulation, a data storage section for storing correlation data between the sample band gap amount and the impurity doping amount, and a sample band obtained from the detected reflection spectrum. It is characterized in that it comprises an arithmetic means for calculating the impurity doping amount by comparing the gap amount and the correlation data.

[0018]

[Function] The probe light is irradiated to the measurement point on the sample surface irradiated with the excitation light modulated by the chopper, and the reflected light is synchronized with the modulation from the reflected light signal spectrally detected by the spectroscope and the detector. After taking out the photoreflectance ΔR and normalizing the photoreflectance ΔR with the DC component R of the reflected light, the selected wavelength in the spectroscope is scanned and detected to obtain the photoreflectance spectrum.

Photoreflectance spectrum peak
The wavelength λ _G at the time of oscillation corresponds to the band gap amount of the sample. Here, when the doping amount of impurities (the number of atoms contained in 1 cubic cm) exceeds 10 ¹⁶ / cm ³ , the band gap amount shifts in proportion to the doping amount of impurities in the substance. There is a correlation.

Therefore, by estimating the band gap amount based on the photoreflectance spectrum and using the calibration curve using the correlation data between the band gap amount of the substance and the doping amount, the impurity doping The amount can be calculated.

[0021]

EXAMPLES Examples of the present invention will be described below.

FIG. 1 shows a schematic structure of an impurity doping amount measuring device of the present invention. In FIG. 1, 1 is an excitation light source, 2
Is a chopper, 3 is a white light source (probe light source), 4 is a beam
Splitter 5, 5 sample, 6 spectroscope, 7 detector, 8 smoothing circuit, 9 lock-in amplifier, 10 arithmetic control unit, 11 data storage unit, 12 display unit, 13, 1
Reference numeral 4 is a control circuit, L is excitation light, P is white light (probe light), H is reflected light, and F1, F2, and F3 are signals.

Next, the operation of the impurity doping amount measuring device of FIG. 1 will be described. Excitation light L emitted from the excitation light source 1
Is modulated by the chopper 2 controlled by the control circuit 13 and then irradiated on the sample 5. The periodic signal input to the chopper 2 is supplied from the control circuit 13 to the lock-in amplifier 9
Has also been entered.

On the other hand, the white light P emitted from the white light source 3 is reflected by the beam splitter 4 and is applied to the irradiation spot of the excitation light L on the sample 5.

The reflected light H from the sample 5 is transmitted through the beam splitter 4, and the light having the wavelength designated by the selection wavelength signal from the control circuit 14 is selected by the spectroscope 6 and then detected by the detector 7. The reflected light intensity for the wavelength as shown in 2 is detected, and the intensity signal F1 is input to the smoothing circuit 8 and the lock-in amplifier 9.

In FIG. 2, R is the reflected light signal when the excitation light is not irradiated, and ΔR is the difference between the reflected light signal when the excitation light is irradiated and R.

The smoothing circuit 8 outputs the DC component of the reflected light intensity signal F1, that is, the reflected light signal R when the excitation light is not irradiated, and inputs it to the arithmetic control unit 10. At this time, when the control circuit 14 scans the selected wavelength in the spectroscope 6, FIG.
A spectrum of R as shown in is obtained.

Although the DC component R of the reflected light actually contains the photoreflectance signal ΔR, ΔR is R
The error is negligible because it is extremely small compared to.

On the other hand, the lock-in amplifier 9 is also inputted with a periodic signal equal to the period of the modulation signal inputted from the control circuit 13 to the chopper 2, and a signal showing a periodic component equal to the modulation period of the chopper, that is, ΔR. F2 is input to the arithmetic and control unit 10.

At this time, when the control circuit 14 similarly scans the selected wavelength in the spectroscope 6, Δ as shown in FIG. 4 is obtained.
An R spectrum is obtained.

Therefore, when ΔR is standardized by R in the arithmetic control unit 10 while scanning the selected wavelength in the spectroscope 6 by the control circuit 14, a photoreflectance spectrum ΔR / R as shown in FIG. 5 is obtained. be able to.

In FIG. 5, the peak wavelength λ _G of the photoreflectance spectrum corresponds to the bandgap amount of the sample. Here, when the doping amount of impurities (the number of atoms contained in 1 cubic cm) exceeds 10 ¹⁶ / cm ³ , the band gap amount shifts in proportion to the impurity doping amount in the substance, Impurity doping as shown in FIG.
A correlation between the ping amount and the band gap amount can be obtained.

In the data storage unit 11, known data of the correlation between the impurity doping amount and the band gap amount in such a substance measured using a standard sample is stored as a calibration curve. .

Therefore, in the arithmetic and control unit 10, the wavelength λ _G at the peak of the photoreflectance spectrum is obtained.
Is detected and the obtained wavelength λ _G is compared with the calibration curve stored in the data storage unit 11, the impurity doping amount of the sample 5 is detected and displayed on the display unit 12.

In the above embodiment, the spectroscope 6 is arranged between the sample 5 and the detector 7 to disperse the reflected light H. However, the white light source 3 and the beam splitter 4 or the beam splitter 4 are separated. Even if it is arranged between the samples 5 to disperse the white light P,
Similarly, the impurity doping amount can be measured.

Also, without using the beam splitter 4,
The white light P is irradiated with the incident angle with respect to the surface of the sample 5 shifted from the vertical direction, and the spectroscope 6, at the position where the reflected light is detected,
Even if the detector 7 is arranged, the impurity doping amount can be measured.

Further, the data storage section 11 and the display section 12 of the above-mentioned embodiment are omitted, and the photoreflectance spectrum is simply obtained, and the measurer determines from the wavelength λ _G at the peak of the photoreflectance spectrum. May estimate the bandgap amount and detect the impurity doping amount of the sample 5 from a calibration curve using known data of the correlation between the impurity doping amount in the substance and the bandgap amount.

[0038]

Since the present invention is configured as described above, by incorporating this measuring device in the semiconductor manufacturing process, it is possible to perform the measurement without interrupting the ion implantation process and the diffusion process. Moreover, since it is possible to perform the measurement simply by irradiating with light, without damaging the sample,
The impurity doping amount can be calculated more easily than in the conventional case.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 2 is a diagram showing reflected light intensity.

FIG. 3 is a diagram showing a relationship between reflected light intensity and wavelength.

FIG. 4 is a diagram showing a relationship between photoreflectance and wavelength.

FIG. 5 is a diagram showing a photoreflectance spectrum.

FIG. 6 is a diagram showing a correlation between an impurity doping amount and a band gap amount.

FIG. 7 is a diagram showing a schematic configuration of a conventional 4-probe method.

Claims (2)

[Claims] 1. The sample surface is irradiated with probe light, and the irradiation position of this probe light is irradiated with modulated excitation light.
The feature is that the reflection spectrum is detected from the reflected light from the sample surface synchronized with the modulation, and the impurity doping amount is measured from the correlation between the sample band gap amount and the impurity doping amount obtained from this reflection spectrum. The method for measuring the amount of impurity doping. 2. A probe light source for irradiating probe light,
An excitation light source for irradiating the probe light irradiation position on the sample surface with the modulated excitation light, a means for detecting a reflection spectrum in synchronization with the modulation from the reflected light of the probe light, a band gap amount of the sample and impurity doping Calculation of the amount of impurity doping by comparing the above-mentioned correlation data with the band gap amount of the sample obtained from the above-mentioned detected reflection spectrum An impurity doping amount measuring device, comprising: