JPH10270514A - Method and apparatus for evaluating semiconductor wafer - Google Patents

Abstract

(57) [Problem] To provide a semiconductor wafer evaluation method capable of improving measurement accuracy by a photoluminescence method and an apparatus used for carrying out the method. In An optical path of the argon laser oscillator 1 laser light emitted from the light deflector 2 comprising a filter 22a and TeO ₂ are arranged. The luminescence light emitted from the wafer 15 by the irradiation of the laser light passes through the condenser lens 25a, the filter 22b, and the spectroscope 27, and is detected by the photodetector 26, which is a photomultiplier tube. The signal thus obtained is supplied to the boxcar integrator 4. The irradiation time control signal output from the signal generator 5 is supplied to an RF oscillator 7 for controlling the light deflection time of the optical deflector 2, and the irradiation intensity control signal output from the computer 45 is an RF oscillator for driving the RF oscillator 7 Power is supplied to the power supply 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a semiconductor wafer such as a silicon wafer used for an integrated circuit, and an apparatus used for carrying out the method.

[0002]

2. Description of the Related Art In a process of manufacturing a silicon wafer used for an integrated circuit from a silicon single crystal ingot pulled by a single crystal pulling method such as a CZ method (Czochralski method), the surface of the wafer is contaminated by heavy metal or heat treatment. Crystal defects occur in the vicinity. Also in the subsequent integrated circuit manufacturing process, crystal defects are similarly generated near the surface of the wafer, and the manufacturing yield of devices is reduced. Since it is difficult to identify the cause of the crystal defect, the occurrence of the crystal defect is accurately detected, and the wafer determined to be defective is removed from the process. In addition, it is necessary to clarify a factor that caused a defective product, for example, a failure of a manufacturing apparatus and not to generate a new defective product, in order to keep manufacturing costs low.

One of the methods for evaluating the crystal quality near the wafer surface is a photoluminescence method. FIG. 8 is a block diagram showing a configuration of a silicon wafer evaluation apparatus used for a conventional photoluminescence method. Unnecessary light such as infrared light contained in the laser light emitted from the laser oscillator 21 is removed by a filter 22a, and the laser light is passed through an optical chopper 23 for intermittently irradiating the laser light.

FIG. 9 shows the structure of the optical chopper 23. As shown in FIG. FIG.
9A is a plan view of a rotating plate of the optical chopper 23, and FIG.
(b) is a side view of the optical chopper 23. Disk-shaped rotating plate
The center of 23a is supported by the rotating shaft of motor 23b,
The transmission window 23 is provided at two locations in the peripheral portion that are opposed to each other in one diameter direction.
c is provided. Optical chopper 23 is a laser oscillator
The optical axis of the laser light emitted from 21 is arranged to pass through one transmission window 23c. At this time, the other transmission window
A light emitting diode 23d is provided to allow light to pass through 23c, and a photo sensor 23e is arranged with the rotating plate 23a interposed therebetween. The signal output from the photosensor 23e is provided to the lock-in amplifier 28 as a synchronization pulse signal.

[0005] The light from the laser oscillator 21 that has passed through the optical chopper 23 is reflected by a plane mirror 24 for changing the optical path and guided to a silicon wafer 15 as a sample. Light (luminescence light) having a wavelength of 1.14 μm emitted from the silicon wafer 15 by the irradiation of the laser light is condensed by the condensing lens 25a, and only the necessary wavelength region is converted to the long-pass filter 22a.
Transmit b. The light transmitted through the long-pass filter 22b is made incident on the spectroscope 27 to be separated into a light and a condensing lens.
The light passes through 25b and is detected by the photodetector 26. The detected signal is supplied to the lock-in amplifier 28, where the signal is amplified in synchronization with the synchronization pulse signal from the optical chopper 23. The computer 45 performs a predetermined operation on the amplified signal to determine the intensity of the photoluminescence light. It is known that the presence of crystal defects lowers the photoluminescence intensity at a wavelength of 1.14 μm, and the quality determines the quality of the crystal. Then, the data is printed and displayed by the plotter 46 in a predetermined data format. The photoluminescence method allows non-destructive, non-contact evaluation,
Can be incorporated into manufacturing processes.

[0006]

However, the luminescence light intensity measured by such an apparatus may change every second, and the instability of the measured value is a problem. Further, in a silicon wafer whose impurity concentration changes in the depth direction, for example, an epitaxial wafer, there is a problem that the luminescence light intensity changes depending on the thickness of the epitaxial layer.

Therefore, electron-hole pairs are generated near the surface of the semiconductor thin layer using excitation light having energy greater than the band gap of the semiconductor, and the intensity of a specific wavelength emitted by the recombination is detected. A method for evaluating the lifetime of a layer is disclosed in JP-A-8-139146. According to this method, the region where excited carriers are generated can be made shallower by shortening the wavelength of the excitation light.

However, the diffusion length of minority carriers is as large as several hundred μm, and carriers generated on the surface are diffused inside. As a result, the number of carriers in the deep part of the wafer increases, and the luminescence light therefrom becomes dominant, and LS
It is difficult to independently and accurately measure the lifetime near the surface that affects the device characteristics of I.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is intended to improve the accuracy of measurement by a photoluminescence method by controlling the irradiation time or the irradiation time and the irradiation intensity. It is an object of the present invention to provide an evaluation method and an apparatus used for implementing the method.

[0010]

As a result of investigating a change in the measured value of the luminescence light intensity, the surface temperature of the semiconductor wafer increases as the intensity of the laser light applied to the semiconductor wafer increases, and the luminescence light intensity decreases. It turned out to change. Silicon wafers having different impurity concentrations in the depth direction, for example, 1 × 10 ¹⁵ / cm from the surface to 10 μm.
³ and 1 × 10 ¹⁸ / cm ³ in the region deeper than 10 μm, the carrier excited by the laser beam diffuses to the high concentration region when the irradiation time of the laser beam becomes longer, and as a result, It became clear that the luminescence light in the high concentration region became dominant.

From the above experimental results, it has been found that the measurement accuracy can be improved by controlling the irradiation time or the irradiation time and the irradiation intensity of the laser light to be applied to the semiconductor wafer in accordance with the variation amount of the luminescence light intensity. I got

Accordingly, the present invention provides a method for evaluating luminescence light emitted from a semiconductor wafer by irradiating the semiconductor wafer with light, and evaluating the semiconductor wafer based on its spectrum. The semiconductor wafer is irradiated with light while controlling the irradiation intensity.

[0013] By controlling the irradiation time or the irradiation time and irradiation intensity of the laser light irradiating the semiconductor wafer in response to the detection signal of the luminescence light detected in time series, the wafer surface temperature rise and excitation Measurement errors due to diffusion of carriers into the wafer can be reduced.

According to a second aspect of the present invention, there is provided an apparatus for receiving luminescence light emitted by irradiating a semiconductor wafer with light and evaluating the semiconductor wafer based on the spectrum thereof, wherein the luminescence is detected in time series. Irradiation time control means for controlling the irradiation time of light irradiating the semiconductor wafer in response to a light detection signal, or irradiation intensity control means for controlling the irradiation intensity of the light in addition to the irradiation time control means It is characterized by.

By controlling the irradiation time, or the irradiation time and the irradiation intensity of the laser light for irradiating the semiconductor wafer,
It is possible to reduce a measurement error due to an increase in the wafer surface temperature and diffusion of the excited carriers into the inside of the wafer.

According to a third aspect of the present invention, in the second aspect, the light generation source is a continuous wave laser, and the irradiation time control means for controlling the irradiation time of the laser light from the continuous wave laser, or the irradiation time The time control means and the irradiation intensity control means for controlling the irradiation intensity of the laser light from the continuous wave laser include an optical deflector.

The irradiation time control means controls the diffraction time of the optical deflector and the diffracted light reaches the semiconductor wafer, whereby the irradiation time of the laser beam can be controlled by the diffraction time. The irradiation intensity control means controls the voltage applied to the optical deflector, whereby the intensity of light passing through the optical deflector is controlled.

According to a fourth aspect of the present invention, in the second aspect, the light source is a continuous wave laser, and the irradiation time control means for controlling the irradiation time of the laser light from the continuous wave laser, or the irradiation time The time control means and the irradiation intensity control means for controlling the irradiation intensity of the laser light from the continuous wave laser include an optical modulator.

The irradiation time control means controls the modulation time of the optical modulator and the modulated light reaches the semiconductor wafer, so that the irradiation time of the laser light can be controlled by the modulation time. The irradiation intensity control means controls the voltage applied to the optical modulator, whereby the intensity of light passing through the optical modulator is controlled.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. Embodiment 1 FIG. 1 is a block diagram showing a configuration of a semiconductor wafer evaluation apparatus according to the present invention. In FIG. 1, reference numeral 1 denotes a continuously oscillating argon laser oscillator, and an optical deflector _{2 including} a filter 22a and TeO 2 is arranged on an optical path of laser light emitted from the argon laser oscillator. A slit 3 is provided at a position where predetermined light deflected by the optical deflector 2 is transmitted, and a mirror 24 for irradiating the wafer 15 with light transmitted through the slit 3 is provided at an appropriate position.

The luminescence light emitted from the wafer 15 by the irradiation of the laser beam passes through a condenser lens 25a, a long-pass filter 22b, and a spectroscope 27, and is detected by a photodetector 26 comprising a photomultiplier tube. The detected signal is supplied to the boxcar integrator 4. The boxcar integrator 4 generates a control signal to the signal generator 5 for generating an irradiation time control signal, a detection control signal to the boxcar integrator 4, and an irradiation intensity control signal, and performs a predetermined operation. The computer 45 and the recorder 6 are connected. The irradiation time control signal is transmitted from the optical deflector 2
The irradiation intensity control signal is supplied to an RF oscillator 7 for controlling the polarization time of the
To be given to

The operation of the evaluation device configured as described above will be described. The laser light having a wavelength of 514.5 nm and a diameter of 0.5 mm emitted from the argon laser oscillator 1 is filtered.
Unnecessary components such as infrared rays are cut at 22 a and deflected by the optical deflector 2. The light that has been deflected and transmitted through the slit 3 has its optical path changed by the mirror 24 and is irradiated onto the wafer 15.

The luminescence light emitted from the wafer 15 by the irradiation of the laser light is condensed by the condenser lens 25a, and only the necessary wavelength region passes through the long-pass filter 22b. The light that has passed through the long-pass filter 22b is made incident on the spectroscope 27 to be separated, and light of 1.14 μm is detected by the photodetector. Since the detected signal is very weak, the boxcar integrator 4 uses the computer
On the basis of the detection control signal as shown in FIG. That is, the output of the photodetector 26, which is a photomultiplier tube, has a pulse-like waveform, and integrates a pulse-like voltage generated for a certain period of time and outputs the value as a voltage. The integration timing and period are controlled from the outside (computer 45) by the detection control signal. The obtained detection signal is supplied to the computer 45 and subjected to data processing to determine the quality of the crystal.

The irradiation time data determined by the computer 45 based on the detection signal output from the boxcar integrator 4 is also supplied as a control signal to the signal generator 5, where the irradiation time as shown in FIG. A time control signal is generated in synchronization with the detection control signal. The RF oscillator 7 supplies an RF voltage of 0.5 V (frequency of 80 V) according to the pulse width of the irradiation time control signal.
MHz) is applied to the optical deflector 2. The optical deflector 2 is provided with an electrode for generating an ultrasonic wave perpendicular to the incident direction of the laser light, and diffracts 5% of the incident laser light intensity when receiving an RF voltage of 0.5V. As a result, the irradiation time of the laser light applied to the wafer 15 is synchronized with the irradiation time, as shown in FIG.
It changes as shown in FIG. Accordingly, the output of the recorder 6 (for example, an oscilloscope) based on the luminescence light emitted by the wafer 15 becomes as shown in FIG. That is, after the luminescence light is integrated and detected, the detected signal output is sequentially output to the computer 45.

The detection is performed in a time-series manner. As shown in FIG. 2B, the pulse width of the irradiation time control signal is sequentially reduced every 250 detections, whereby the irradiation time (FIG. 2E) ) Is shortened. When the irradiation time is shortened, the intensity of the luminescence light that is integrated and amplified by the boxcar integrator 4 that performs integration in a predetermined time decreases. Therefore, to compensate for this, it is necessary to increase the irradiation intensity. Therefore, if the irradiation intensity control signal is increased as shown in FIG.
The voltage applied by the RF oscillator power supply 8 to the RF oscillator 7 increases, and the RF oscillator 7 outputs R to the optical deflector 2.
The F voltage increases (for example, from 0.5 V to 0.8 V). Then, the intensity of the diffracted light in the optical deflector 2 increases (for example, from 5% to 8%), so that an irradiation intensity that increases in a sequential manner as shown in FIG.

FIG. 3 shows the number of detections and the output of a detection signal when the pulse width, ie, the irradiation time is 0.5, 1.5 msec, for a wafer on which crystal defects are intentionally formed by polishing. 6 is a graph showing a relationship with the graph. Pulse width is 0.
In the case of 5 msec, a substantially constant signal value can be obtained regardless of the number of detections even if the number of detections exceeds 200. However, it can be seen that the larger the pulse width, the larger the detection signal increases as the number of detections increases.

Here, it is possible to determine that a wafer whose output of the detection signal greatly changes depending on the irradiation time may have crystal defects on its surface.

Next, a case where an epitaxial wafer having an epitaxial layer having a thickness of 10 μm is evaluated will be described. When the irradiation time is long (for example, 5 msec), FIG.
As shown in the figure, the carriers generated near the surface of the wafer by the laser light diffuse from the surface where the impurity concentration is low to the region where the impurity concentration is high, so that the luminescence light from the region other than the epitaxial layer which is not to be evaluated is This makes it impossible to accurately measure the luminescence light from the epitaxial layer on the surface, which is the object of the evaluation. Therefore, when the irradiation time is reduced to about 5 μsec, the ratio between the luminescence light intensity and the laser light irradiation intensity becomes almost constant,
As shown in FIG. 4B, the luminescence light from the epitaxial layer can be detected before the excited carriers diffuse to the high concentration region. At this time, even if the irradiation time is shortened, by controlling to increase the irradiation intensity as described above, a luminescence light intensity sufficient for detection can be obtained.

Next, a method for evaluating a semiconductor wafer according to the present invention will be described. FIG. 5 is a flowchart for evaluating a normal silicon wafer having no epitaxial structure. First, an initial value and a variation width of the irradiation time and an irradiation intensity are set (step S1). That is, the initial pulse width of the irradiation time control signal and the pulse width that are sequentially changed so that the diffraction time of the optical deflector 2 becomes these values are set, and the voltage of the irradiation intensity control signal is set. The luminescence light intensity is measured 250 times with the selectively set irradiation time and irradiation intensity (step S2). Then, a change rate of the measured luminescence light intensity is calculated (step S3), and it is determined whether or not this is within an allowable range (step S4).

If it is not within the allowable range, the irradiation time is shortened based on the set change width (step S5), that is, the pulse width of the irradiation time control signal is reduced, and the process returns to step S2. Then, the luminescence light intensity is measured 250 times with the changed (shortened) irradiation time, and if the measured value falls within the allowable range in step S4, it is set as the optimum irradiation time for the wafer (step S6). ), The wafer is evaluated in the manufacturing process (step S7).

FIG. 6 is a flowchart for evaluating a silicon wafer having an epitaxial structure. First, an initial value and a variation width of the irradiation time and the irradiation intensity are set (step S11). That is, the initial pulse width of the irradiation time control signal and the pulse width to be sequentially changed so that the diffraction time of the optical deflector 2 becomes these values are set, and the initial voltage and the initial voltage of the irradiation intensity control signal are sequentially changed. Set the voltage. The luminescence light intensity is measured 250 times with the selectively set irradiation time and irradiation intensity (step S
2). Then, it is determined whether or not the measured luminescence light intensity is equal to or more than a predetermined value (step S12).

If not, the irradiation intensity is increased based on the set change width (step S13), that is, the voltage of the irradiation intensity control signal is increased, and step S2 is performed.
Return to If it is not less than the predetermined value in step S12, the ratio between the luminescence light intensity and the irradiation intensity is calculated (step S14), and it is determined whether or not this is not less than the predetermined value (step S15). The irradiation intensity is obtained by the following equation. Irradiation intensity = constant x diffraction time x diffraction intensity

If not, the irradiation time is shortened based on the set change width (step S5), that is, the pulse width of the irradiation time control signal is reduced, and the process returns to step S2. Then, the luminescence light intensity is measured 250 times with the changed (shortened) irradiation time, and when the luminescence light intensity exceeds a predetermined value in step S15, the optimum irradiation time and irradiation intensity of the wafer are set. (Step S16) The wafer is evaluated in the manufacturing process (Step S7).

In this way, by detecting the luminescence light in a time-series manner and changing the irradiation time on the wafer, or the time and the intensity, the conditions which are not affected by the factors causing the measurement error are clarified. The luminescence light intensity is measured at the optimum irradiation time and irradiation intensity. By setting the irradiation time and the irradiation intensity for each type of wafer in this manner, the influence of a rise in the wafer surface temperature, the diffusion of excited carriers to other than near the surface, and the like is reduced, and the measurement of the luminescence light intensity is improved. Can be implemented with precision. As a result, the accuracy of the quality evaluation of the semiconductor wafer by the photoluminescence method is improved, and the effect of reducing the wafer evaluation cost is obtained.

Embodiment 2 In the first embodiment, an optical deflector is used as means for controlling the light irradiation time or the light irradiation intensity. In the second embodiment, as shown in FIG. 7, an optical modulator 11 is used instead of the light deflector 2. . The optical modulator 11 includes an ADP crystal 12
And a polarizer 13 provided on the filter 22a side, and an analyzer 14 provided in place of the slit 3. Further, a voltage generator is used instead of the RF oscillator 7 and the RF oscillator power supply 8.
17, voltage generator power supply 18 is installed. Voltage generator 17
Applies a voltage of about 100 V to the optical modulator 11 according to the pulse width, that is, the irradiation time, based on the irradiation time control signal.

When a voltage is applied to the crystal 12, the plane of polarization of the incident light rotates, so that the transmittance of the analyzer 14 changes. As a result, an irradiation intensity as shown in FIG. 2E synchronized with the detection control signal is obtained. The other configuration is the same as that of the first embodiment, and the description is omitted.

In this apparatus, when an ordinary wafer is evaluated, the initial value and the change width of the irradiation time in step S1 in FIG. 5 are set by the light modulation time of the light modulator 11 (the time for transmitting light, ie, the time for transmitting light. This is performed by setting the initial value of the pulse width of the irradiation time control signal and the pulse width to be sequentially changed so that the voltage application time) becomes these values.

In this apparatus, when evaluating a wafer having an epitaxial structure, step S in FIG.
The setting of the initial value and the change width of the irradiation time and the irradiation intensity of 11 are such that the light modulation time of the light modulator 11 becomes these values, and the initial pulse width of the irradiation time control signal and the pulse width to be sequentially changed. And an initial voltage of the irradiation intensity control signal and a voltage that is sequentially changed so that the light transmittance of the light modulator 11 (the light transmittance adjusted by the applied voltage) becomes these values. It is done by doing. The irradiation intensity when the ratio between the luminescence light intensity and the irradiation intensity is obtained in step S13 is obtained by the following equation. Irradiation intensity = constant x light modulation time x light transmittance

In this embodiment, as described above,
The luminescence light intensity can be measured with high accuracy.

[0040]

As described above, the method and the apparatus for evaluating a semiconductor wafer according to the present invention control the irradiation time or the irradiation time and the irradiation intensity of the light applied to the semiconductor wafer, and optimize the type of the wafer. By detecting the luminescence light using the irradiation time and the irradiation intensity, the present invention has an excellent effect such that the measurement accuracy by the photoluminescence method can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a semiconductor wafer evaluation apparatus according to a first embodiment.

FIG. 2 is a waveform diagram of each control signal and each output in the device shown in FIG.

FIG. 3 is a graph showing the relationship between the number of detections and the output of a detection signal.

FIG. 4 is an explanatory view showing diffusion of carriers in an epitaxial wafer.

FIG. 5 is a flowchart showing a processing procedure for evaluating a normal wafer.

FIG. 6 is a flowchart illustrating a processing procedure for evaluating an epitaxial wafer.

FIG. 7 is a block diagram illustrating a configuration of a semiconductor wafer evaluation device according to a second embodiment.

FIG. 8 is a block diagram showing a configuration of a semiconductor wafer evaluation apparatus used for a conventional photoluminescence method.

9 is a diagram showing a configuration of an optical chopper in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Argon laser oscillator 2 Optical deflector 3 Slit 4 Boxcar integrator 5 Signal generator 7 RF oscillator 8 RF oscillator power supply 11 Optical modulator 12 Crystal 13 Polarizer 14 Analyzer 15 Wafer 17 Voltage generator 18 Voltage generator power supply 26 Photodetector 27 Spectrometer 45 Computer

Claims (4)

[Claims] 1. A method of receiving luminescence light emitted by irradiating a semiconductor wafer with light and evaluating the semiconductor wafer based on the spectrum thereof, comprising:
Alternatively, the method for evaluating a semiconductor wafer includes a step of irradiating the semiconductor wafer with light while controlling an irradiation time and an irradiation intensity. 2. An apparatus for receiving luminescence light emitted by irradiating a semiconductor wafer with light and evaluating the semiconductor wafer based on the spectrum thereof, wherein the irradiation time controlling the irradiation time of the light applied to the semiconductor wafer is controlled. An apparatus for evaluating a semiconductor wafer, comprising: time control means; or irradiation intensity control means for controlling the irradiation intensity of the light in addition to the irradiation time control means. 3. The light source is a continuous wave laser, irradiation time control means for controlling the irradiation time of the laser light from the continuous wave laser, or the irradiation time control means and the laser from the continuous wave laser. 3. The apparatus for evaluating a semiconductor wafer according to claim 2, wherein the irradiation intensity control means for controlling the irradiation intensity of light includes an optical deflector. 4. The light source is a continuous wave laser, irradiation time control means for controlling the irradiation time of the laser light from the continuous wave laser, or the irradiation time control means and the laser from the continuous wave laser. 3. The apparatus for evaluating a semiconductor wafer according to claim 2, wherein the irradiation intensity control means for controlling the irradiation intensity of light includes a light modulator.