JPH01274040A - Material surface inspecting device - Google Patents

Abstract

PURPOSE:To achieve a higher measuring accuracy and a higher detection sensitivity about light absorption of the surface of a sample, by correcting dependence of a vertical deflection level of laser light on an inter-optical axis distance accompanying a change in refractive index using a measured value of a horizontal deflection level. CONSTITUTION:An excitation light 11 from a laser 1 for excitation is modulated in intensity with an excitation light modulator 2 and then, reflected with an excitation light scan mirror 3 to irradiate the surface of a sample 12 at a desired position on a sample base 5. A laser light 13 from a laser 4 for inspection is reflected with an optical path moving mirror 10 passes right on an irradiation point of the excitation light with an optical axis controlled so that it crosses the excitation light 11 and reflected again with the moving mirror 10 to be incident into a position detector 6. Then, a vertical deflection component and a horizontal deflection component of a cyclic deflection of the laser light are detected synchronously using a lock-in amplifier 7. Moreover, when measuring a light absorption level, the optical axis of the laser light 13 is adjusted so that a horizontal deflection component as obtained through the detector 6 and the amplifier 7 is down to zero to make the excitation light 11 cross the optical axis of the laser light 13 and then, a data processor is used to determine the light absorption from the vertical deflection component.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a material surface inspection device, and in particular, to quantitatively detect the distribution of slight changes in light absorption on the surface of a material in a non-contact and remote manner. This invention relates to a material surface inspection device suitable for.

[Conventional technology]

In the inspection of semiconductors, etc., it becomes necessary to detect the weak amount of light absorption on the surface. In particular, as semiconductors become more highly integrated, slight contamination and non-uniformity of the oxide film, which did not pose problems in the past, become causes of device failure. As a measurement method for this purpose, the usual laser light scattering method lacks sensitivity, so light is a highly sensitive detection method. ! Various heat wave measurement methods such as acoustic spectroscopy are being developed. However, microphone photoacoustic spectroscopy and piezoelectric element photoacoustic spectroscopy each require mounting a sample in a sample chamber and adhering a piezoelectric element to the sample, making inspection means for process control inappropriate. On the other hand, there are methods for detecting thermal deformation of the material surface due to excitation light irradiation as deflection of laser light (Japanese Patent Application Laid-Open No. 59-34138) and methods for detecting infrared rays from the point of excitation light irradiation (Japanese Patent Laid-Open No. 60-198).
No. 54224) is contactless and remote! However, there were problems in practical use, such as difficulty in adjusting the optical axis, and susceptibility to noise and relatively low sensitivity. In addition, a method of measuring the refractive index change of the atmosphere near the excitation light irradiation point (El Shearmot et al., Journal of Application
Hephisics, vol. 54, p581 (1983) (L
, C, Aamodt ct al, : Journa.
l of Applied Physics, VoQ,
54, 581 (lE'J 83)) have also been proposed, but the signal is also easily affected by optical axis adjustment.
In particular, there has been a problem in that the detection signal varies greatly depending on the distance between the optical axis of the laser beam used for detecting the change in refractive index and the optical axis of the excitation beam.

[Problem to be solved by the invention]

In conventional methods for detecting changes in refractive index, there is no means to maintain a constant distance between the laser beam optical axis and the excitation beam optical axis, so there is no possibility of changing the distance between the optical axes for each measurement or during measurement. The resulting measurement error could not be removed.

The main purpose of the present invention is to correct the dependence of the vertical deflection of the laser beam on the distance between the optical axes due to the change in the refractive index using the measured value of the Z deflection of water, thereby minimizing the weak light absorption. The object of the present invention is to provide a material surface inspection device capable of contact/remote measurement.

[Means to solve the problem]

The second purpose is to adjust the optical axis so that the horizontal deflection component becomes zero, taking advantage of the fact that the horizontal deflection component of the laser beam deflection becomes zero when the distance between the optical axes of the laser beam and the excitation light is zero. This is achieved by detecting the vertical deflection component in the state.

[Effect]

Periodic temperature changes (thermal waves) that occur when a sample is irradiated with intensity-modulated excitation light become smaller as they move away from the sample surface and from the excitation light optical axis, and are symmetrical with respect to the excitation light optical axis. Therefore, when the laser beam optical axis is parallel to the sample surface and perpendicular to the excitation light optical axis, the periodic deflection of the laser beam includes a vertical deflection component and a horizontal deflection component. Both the vertical and horizontal deflection components are proportional to the amount of light absorbed by the sample surface, but while the vertical deflection component's deflection intensity decreases symmetrically at the point where the optical axes of the laser beam and excitation light intersect, The horizontal deflection component reverses its deflection direction at the point where the laser beam optical axis and the excitation light optical axis intersect, and becomes zero when the optical axes intersect. Therefore, when the optical axis is adjusted so that the horizontal deflection component becomes zero, the measurement error due to the optical axis shift of the vertical deflection component is eliminated, its intensity is maximized, and statistical accuracy is also improved.

〔Example〕

An embodiment of the present invention will be explained with reference to FIG. In this embodiment, the excitation laser 1. Excitation light modulator 2. Excitation light scanning mirror 3.
Detection laser 4. Sample stage 51 position detector 6. lock-in amplifier 7, data processing device 8, controller 9, and
It is composed of a detection laser beam optical path moving mirror 10.

The excitation light 11 from the excitation laser 1 is intensity-modulated at a predetermined frequency by the excitation light modulator 2, and then reflected by the excitation light scanning mirror 3 to locate a desired position on the surface of the sample 12 on the sample stage S. irradiate. The irradiation position is adjusted by controlling the angle of the reflecting surface of the excitation light scanning mirror. The laser beam 13 from the detection laser 4 is reflected by the detection laser beam optical path moving mirror 1o, the optical axis is controlled so that the optical axis intersects with the excitation light, and the laser beam 13 passes directly above the excitation light irradiation point on the sample surface. , it is reflected again by the optical path movement fi 1.0 and enters the position detector 6. The vertical and horizontal deflection components of the periodic deflection of the laser beam are synchronously detected using a lock-in amplifier 7. The excitation light scanning mirror 3 and the optical path moving mirror 10 are controlled via a controller 9. The amount of light absorption is measured so that the optical axes of the excitation light 11 and the detection laser light 13 intersect.

The data processing device is used to start with the vertical deflection component when the optical axis is adjusted 8 so that the horizontal deflection component obtained through the position detector 6 and lock-in amplifier 7 becomes zero.

Optical axis adjustment is performed by moving the optical path moving mirror 10 in the horizontal direction, as shown in FIG. When the excitation light 11 is scanned over the surface of the sample 12 in the optical axis direction of the detection laser beam (in the left-right direction in FIG. 2), first move the optical path moving mirror 1o so that the horizontal deflection component becomes zero. Just let it happen. One step of scanning in the direction of the laser beam optical axis of the excitation light is completed, and in the direction perpendicular to this (
Even when the laser beam is scanned in the optical axis direction again after a step movement in the vertical direction (in FIG. 2), it is only necessary to adjust the optical axis at the first stage. The optical axis adjustment is performed by shifting the horizontal deflection component once from the zero point until it reverses, and then returning it.

Regarding the influence of the optical axis height of the detection laser beam 11, the optical axis height is determined from the phase of the vertical deflection component and corrected within the data processing device 8.

The amount of light absorbed by the sample surface can be determined by removing the influence of the distance between the optical axis of the detection laser beam and the optical axis of the excitation beam, as well as the height of the optical axis of the detection laser beam, using the above procedure. It is determined from the absolute value of the deflection component. A two-dimensional distribution of light absorption on the sample surface can be achieved by scanning the excitation light irradiation position.

Further, the optical absorption spectrum can be determined by changing the wavelength of the excitation light by using a dye laser as the excitation light source or by making another light emission source monochromatic.

According to this embodiment, by controlling the laser beam path shifting mirror a,
By intersecting the optical axes of the detection laser beam and the excitation light, it is possible to improve the measurement accuracy of the absolute value of the vertical polarization component, and to improve the detection sensitivity and accuracy of the amount of light absorption on the sample surface.

〔Effect of the invention〕

According to the present invention, it is possible to reduce measurement errors in the vertical polarization component of the laser beam due to variations in the distance between the optical axes of the laser beam and the excitation light, thereby improving the measurement accuracy and detection sensitivity of the amount of light absorption on the sample surface. be able to.

[Brief explanation of the drawing]

FIG. 1 is a side view of one embodiment of the present invention, and FIG. 2 is a plan view of FIG. 1. 1... Laser for excitation, 2... Excitation light modulator, 3...
・Excitation light scanning mirror.

Claims (1)

[Scope of Claims] 1. In a material surface inspection device that measures the amount of light absorption on a solid surface or the light absorption spectrum, the sample is irradiated with intensity-modulated excitation light, and the sample is heated as the sample periodically generates heat. The vertical deflection component and the horizontal deflection component of the optical path deflection of the laser beam caused by the periodic refractive index change of the atmosphere near the surface of the laser beam are measured alternately or simultaneously, and the light is A material surface inspection apparatus characterized in that the vertical deflection component is measured with the axis adjusted to detect the amount of light absorption on the sample surface.