JPH09126892A - Ellipsometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an ellipsometer to accurately measure an object to be measured while securing the laser light output required for measurement by providing a light detecting mechanism and a means which judges the intensity deterioration of laser light. SOLUTION: The ellipsometer is provided with a cap 1 which covers the light projecting end section of a lens barrel 7 for projecting laser light so that no light can leak out and carrying a photodetector 2 which measures the intensity of the laser light on its bottom and a microcomputer 4 which is a deterioration mode judging means for judging the intensity deterioration of the laser light. It is also possible to use a slide on which the photodetector 2 inserted into the lens barrel 7 in the preceding stage of a deflector 6 inserted of the cap 1 which is a switching mechanism. When the photodetector 2 and deterioration mode judging means are provided in the optical path of the laser light, the laser light output of a laser oscillator can be maintained at a required level and objects to be measured can always be measured accurately, because the detecting frequency of the service life of a laser oscillator and the measuring frequency of the laser light output of the oscillator can be decided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ellipsometer for projecting a laser beam onto an object to be measured and for analyzing the substance intervening on the surface of the object to be measured by the reflected light or measuring the film thickness.

[0002]

2. Description of the Related Art Conventionally, an ellipsometer irradiates a surface of an object to be evaluated with a laser beam, and the polarization state of the reflected laser beam is intervened on the surface as compared with the polarization state of the radiated laser beam. An ellipsometer for analyzing substances.

FIG. 2 is a diagram showing an outline of an example of a conventional ellipsometer. As shown in FIG. 2, this ellipsometer is mounted on a sample stage 11 and a lens barrel 7 for laser light projection, which has a light source 8 for generating laser light and a polarizer 6 for linearly polarizing the generated laser light. The light receiving unit includes an analyzer 9 for receiving reflected light of a laser beam projected on a wafer 12, which is an object to be measured, and a detecting unit 10.

To analyze the impurities present in the thin film on the surface of the wafer 12 with this ellipsometer, first, the polarizer 6 is used.
The surface of the wafer 12 is irradiated with the laser light linearly polarized by the rotation of the laser light, and the laser light reflected from the wafer 12 passes through the analyzer 9 and enters the detection unit 8. At this time, the wafer 10
Therefore, the laser light becomes elliptically polarized light. The state of this polarization is measured by the detector 10 for each angle of rotation of the analyzer 9, and the phase difference Δ and the amplitude reflectance ratio are calculated from the light intensity and the rotation angle of the analyzer 9. The optical constant of the film of the wafer 12 was obtained by calculating Ψ and fitting the Δ and the Ψ value of the wafer 12 on which the thin film was formed with a model.

[0005]

In the above-described conventional ellipsometer, the laser oscillator used for the light source has a long life and cannot be used for many years. Even in this life, the output does not suddenly disappear and the output gradually deteriorates like a bathtub curve. Normally, the output measurement of the laser light is carried out in a regular inspection about once a year to determine whether or not it can be used.

However, until the life is judged by the measurement in the periodic inspection, the measurement is carried out even if the output value is close to the limit value. When the laser output enters the descending region, there is a problem that the output becomes unstable and the reliability of measurement accuracy is significantly reduced.

Although it is sufficient to measure the laser output in advance in order to always measure accurately, the work of measuring the output by attaching the laser beam detector to the optical axis so that light does not leak from the outside is great. This is not necessarily a good method because it consumes man-hours and lowers the operation rate of the device.

Therefore, an object of the present invention is to provide an ellipsometer which can secure the output of laser light necessary for measurement and can accurately measure an object to be measured.

[0009]

The features of the present invention are a lens barrel for laser light projection for irradiating an object to be measured with laser light, and a rotary analyzer for receiving the laser light reflected from the object to be measured. And a light receiving section for measuring the light intensity due to rotation of the lens barrel, the photodetection mechanism for measuring the light intensity of the laser light of the lens barrel, the switch having a photodetector in the optical axis of the lens barrel. And a deterioration mode determination means for determining deterioration of the light intensity of the laser light.

Further, it is desirable to determine the frequency of the light intensity measurement of the laser light by the deterioration mode determination means. Further, it is preferable that the switching mechanism includes a lid-like member that is fitted around the light emitting end of the lens barrel to dispose the photodetector on the bottom and that can be inserted into and removed from the lens barrel.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIGS. 1 (a) and 1 (b) are a diagram and a flow chart showing the configuration and the vicinity of a lens barrel portion for explaining an ellipsometer according to an embodiment of the present invention. As shown in FIG. 1 (a), this ellipsometer covers a light emitting end 7a of a lens barrel 7 for laser light projection so that light does not leak and a photodetector 2 for measuring the light intensity of laser light at the bottom. That is, the cap 1 to be mounted on and the microcomputer 4 which is the deterioration mode determination means for determining the deterioration of the light intensity of the laser light are provided. Otherwise, it is the same as the conventional example.

The cap 1 which is a switching mechanism for inserting the photodetector 2 into the lens barrel 7 has an inner diameter finished so as to be slidably engaged with the outer diameter of the light emitting end portion 7a. It is fixed so that it does not come off. As the photodetector 2, for example, a solar cell which is an inexpensive photodiode is used. It should be noted that instead of the cap 1 which is a switching mechanism, a slide plate on which a photodetector to be inserted into the barrel of the deflector 6 is mounted may be used. In this case, there is a risk of light leakage from the outside, so it is advisable to cover the whole with a bandpass filter that transmits only the laser light, if necessary.

Next, the operation of whether or not the measurement is possible in this ellipsometer will be described. First, in step A, a cap is attached to the light emitting end 7a of the lens barrel 7. Next, the laser oscillator is operated to generate laser light. This allows
The photodetector 2 promotes the laser light and converts it into an electric current. The converted current is converted by the digital conversion unit 3. Next, in step B, the current value digitized by the microcomputer 4 is counted and compared with the count value P0 of the reference power. If the count value rises, the process proceeds to step C and the measurement is started.

If the result is NG in step B, the process proceeds to step D to measure the laser power (output). Then, similarly to the above, in step E, the count value is compared with the reference count value P1 smaller than the reference count value P0. If the measured count value is larger, the process proceeds to step C and the measurement is started. If it is lower than P1 and NG, the process proceeds to step F and is compared with the limit count value P2.
If the measured count value is lower than P2, the process proceeds to step G, where a signal is sent from the microcomputer 3 to the control unit 5 to turn on the red lamp and at the same time generate an alarm. In this case, the device is stopped and the laser oscillator is replaced.

If the measured count value exceeds P2 in step F, the flow advances to step H to compare the reference count value P3 exceeding P2 with the measured count value. At this time, if the measured count value exceeds P3, a signal is sent from the microcomputer 4 to the control unit 5, and the yellow lamp is turned on in step I. If the measured count value is lower than P3, a signal is sent from the computer 4 to the control unit 5, and the orange lamp is turned on in step K.

The lighting of the yellow lamp and the lighting of the orange lamp indicate the degree of the deterioration mode of the laser beam.
If the yellow lamp is on, for example, the power of the laser beam is measured once a week to perform the actual measurement. If the orange lamp is on, the laser light output measurement is performed once a day.

Further, in addition to the microcomputer 4 for judging the deterioration mode of the laser beam, it is possible to see the trend of the laser power measurement value on the CRT, and according to the trend, the judgment is artificially made instead of turning on the lamp. You can also In setting the measurement frequency, it is desirable to judge by the deterioration speed of the output, and the judgment standard should be judged by the trend.

[0019]

As described above, according to the present invention, the photodetector for measuring the light intensity of the laser light in the middle of the laser light path and the deterioration mode for judging the transition of the deterioration state from the output measurement value obtained by the photodetector are used. By providing the determining means, the life of the laser oscillator can be detected and the frequency of measuring the laser light output can be determined, so that the output of the laser light required for the measurement can be maintained and an accurate measurement can always be performed.

[Brief description of the drawings]

FIG. 1 is a diagram and a flowchart showing a configuration around a lens barrel and a configuration for explaining an ellipsometer according to an embodiment of the present invention.

FIG. 2 is a diagram showing an outline of an example of a conventional ellipsometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cap 2 Photodetector 3 Digital conversion unit 4 Microcomputer 5 Control unit 6 Polarizer 7 Lens barrel 7a Light emitting end 8 Light source 9 Analyzer 10 Detector 11 Sample stage 12 Wafer

Claims (3)

[Claims] 1. A lens barrel for projecting a laser beam onto the object to be measured, and a light receiving section for receiving the laser beam reflected from the object to be measured and measuring the light intensity due to the rotation of a rotary analyzer. And an optical detection mechanism for measuring the light intensity of the laser light of the lens barrel, which includes a switching mechanism for inserting a photodetector in the optical axis of the lens barrel, and deterioration of the light intensity of the laser light. An ellipsometer, comprising: a deterioration mode determining means for determining. 2. The ellipsometer according to claim 1, wherein the deterioration mode determination means determines the frequency of measuring the light intensity of the laser light. 3. The switching mechanism includes a lid-like member which is fitted to the outer periphery of a light emitting end of the lens barrel, has the photodetector arranged at the bottom, and is insertable into and removable from the lens barrel. The ellipsometer according to claim 1 or 2, which is characterized in that