JPS5823584B2 - buttaibutsukankansokuhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for observing or inspecting defects on the surface and inside of a transparent object, in particular macroscopic defects such as waviness on the surface of a transparent object and internal refractive index distribution, as well as minute irregularities and foreign objects. This invention relates to a method that allows simultaneous observation of microscopic defects such as

Traditionally, direct visual observation and observation using a microscope have been used to observe defects such as irregularities, waviness, refractive index distribution, foreign matter, and bubbles on the surface or inside of transparent objects. A method has been proposed in which the average value of the amount of defects in the observed object is measured by projecting coherent fi plane wave light onto the object and observing the Fourier transform pattern obtained by converging the reflected light or transmitted light with a convex lens, etc. ing.

However, with this method, defects such as surface irregularities are averaged out within the region of the object, so defects such as large undulations occurring on the object surface, large refractive index distribution inside a transparent object, and fine It is difficult to individually observe defects such as unevenness or bubbles.

In view of the above points, the present inventors proposed a method for two-dimensionally simultaneously observing minute surface conditions such as unevenness and macroscopic surface conditions such as waviness of an object to be observed, in Japanese Patent Application No. 48-36372.
We proposed a method for observing the surface state of objects, which is shown in the issue.

This method projects coherent toner spherical wave light onto an observed object and observes the reflected light two-dimensionally.

According to this method, the diffraction pattern of the undulations and irregularities on the surface of the object to be observed is observed, so the smaller the undulations, the larger the magnification. Since it can be observed as a circular pattern, it is possible to simultaneously observe the microscopic surface state and the macroscopic surface state.

An object of the present invention is to provide a novel object defect observation method that can further expand the scope of application of the above-mentioned object surface state observation method.

A specific object of the present invention is to provide a method for observing or inspecting defects such as unevenness and waviness on the surface of a transparent object, and defects such as refractive index distribution and foreign matter inside the transparent object.

The object defect observation method of the present invention is characterized in that coherent spherical wave light is irradiated onto an observed object, and defects in the observed object are two-dimensionally observed using the transmitted light.

The present invention will be explained in detail below.

FIGS. 1a and 1b are diagrams illustrating the object defect observation method according to the present invention.

Figure 1a shows that when the observed surface 3 is placed between the convergence point 1 of coherent spherical wave light and the observation surface 2, the observed surface 3 is placed in front of the convergence point 1 of coherent spherical wave light. was placed.

Indicate the case.

In Fig. 1, 4 indicates each defect to be observed, and curve 5
, 6 show the light intensity distribution of the defect projection pattern on the observation plane.

Here, the defect 4 is considered to be a light-transmitting obstacle with a finite width d.

Consider a system in which a plane 3 including this defect 4 is irradiated with coherent spherical wave light that diverges or converges, and the transmitted diffracted light is projected onto an observation surface 2 placed a finite distance Z apart.

The diffraction observed here can be considered to be Fresnel diffraction because the distances from the plane 3 including the defect 4 to the point 1 of divergence (or convergence) of the spherical wave light and the observation surface 2 are both finite.

As a result, if we do not consider the diffraction phenomenon, only a geometrical optical shadow will appear on the observation surface, as indicated by the broken line T in Figure 1.
Actually, due to diffraction, an intensity distribution of the diffracted light appears as shown by curve 5, which includes the first maximum value.

This creates the effect of magnifying the defect.

That is, when actually observing, for example, the first maximum value portion of the light intensity distribution is observed as a defective projection pattern.

The defect projection dimension Y is the defect dimension d, the distance between the divergence (or convergence) point 1 of the spherical wave light and the observed surface 3° (hereinafter referred to as illumination distance) X, and the distance between the observed surface 3 and the observed surface 2 ( (hereinafter referred to as observation distance) 2 and the wavelength λ of the light used.

Regarding the illumination distance X, the case where the observed surface 3 is irradiated with a diverging spherical wave is shown in FIG. 1a.

In the case of a configuration where
That is, in the case of the configuration shown in FIG. 1, it is defined as Xku0.

The relationship between these parameters will be quantitatively explained below.

If we consider a semi-infinite plane in which the observed plane 3 and the observed plane 2 are placed on the ξ axis and the η axis, respectively, and an obstacle is placed in the area of ξ × d/2 on the observed plane ξ, the intensity distribution of the Fresnel diffraction pattern is The relationship between ξ and η at the first maximum value (u=1.217) can be expressed by diffraction theory.

Details of the diffraction theory are explained, for example, on page 237 of the book "Wave Optics" by Hiroshi Kubota published by Iwanami Shoten.

Here, an obstacle of width d considered as defect 4 is defined as -d/2 x ξ d/2 on the observed surface 3, and when considering its Fresnel diffraction pattern, ξ - d/2 and ξ d/2
It can be considered that the respective Fresnel diffraction patterns of the two semi-infinite planes are synthesized on the observation surface 2.

From equation (1), the defect projection size Y is given by the following equation, also taking into account the sign of the illumination distance X.

However, X+Z>O.

In equation (2), the first term on the right side represents a diffraction component, and the second term represents a geometrical optical projection component. As is clear from this equation, the diffraction component does not depend on the defect size d.

This diffraction component has a positive value and has the effect of making the defect projected dimension Y larger than the geometric projected dimension.

Therefore, according to the object defect observation method described above, as the defect size d increases, the defect projected size Y increases, while the defect magnification rate Y/d increases as the defect size d decreases. Simultaneous observation of visual defects and macroscopic defects becomes possible.

As an example, the wavelength λ-6,328X10-' (i→He
A case will be described in which a -Ne laser is used as a coherent light source.

By substituting this value of λ into equation (2), the relationship between the defect size d, the defect projected size Y, and the defect expansion rate M=Y/d is shown in Figure 2a for the cases of X>O and X<O, respectively. and b.

That is, FIG. 2 a and b correspond to FIG. 1 a and b, respectively.
Defect size d, defect projection size Y, and defect expansion rate M=Y/d
Indicates the relationship between

In Figures 2 a and b, curve group B shows the defect projected size Y, curve group A shows the defect expansion rate M, and the numbers in the curves are the illumination distance X (unit: mrrt).
shows.

Note that the observation distance Z here was 500 (mi).

As is clear from FIG. 2, according to the object defect observation method of the present invention, it is possible to simultaneously observe microscopic defects at different magnifications, and by adjusting the illumination distance Defects can be observed at a magnification of .

The relationship between the defect size and the defect projected size in the experiment conducted by the present inventors matched the theoretical value shown in FIG.

As is clear from the above description, according to the present invention, it is possible to simultaneously observe microscopic defects and macroscopic defects on the surface and inside of a transparent object. The law is very strong.

It can be said that it is useful.

When it is desired to observe or inspect only defects inside an object using the method of the present invention, the object surface state observation method previously proposed by the present inventor can also be used.

That is, defects on the surface and inside of a transparent object are observed according to the present invention, only defects on the surface are observed using the method shown in Japanese Patent Application No. 48-36372, and defects inside the object to be observed are determined by comparing the respective observation results. can only be observed or inspected.

In the present invention, the reason for using coherent light, especially laser light, is that it has good monochromaticity and convergence, so that
This is because the maximum value in the light intensity distribution of the diffraction pattern can be clearly observed.

According to experiments conducted by the present inventor, when an incoherent white light source is used, a projection pattern that is simply geometrical optics is produced.

Only 10% of the time was observed.

Therefore, when carrying out the present invention, it is particularly preferable to use a laser as a light source in terms of monochromaticity and convergence.

Defects that can be observed by the method of the present invention include unevenness, wrinkles, undulations, dirt, and objects on the surface of objects.

Obstacles with different amplitude transmittances of light such as air bubbles inside the body, refractive index analysis, foreign objects, etc., and gaps that give a phase difference to transmitted light are included.

Furthermore, in the above explanation, the object to which the object defect observation method of the present invention is applied is described as a transparent object, but the term transparent object herein includes all objects that allow transmission of the spherical wave light irradiated according to the present invention. is clear.

An additional effect of the present invention is that defects in an observed object can be objectively evaluated.

In other words, when inspecting object defects by direct visual inspection or microscopic inspection as in the past, it is important to avoid the subjectivity of the observer when evaluating the shape, size, etc. of minute irregularities on the surface of the object. Although unavoidable, according to the present invention:
The size, light intensity, etc. of the maximum light intensity distribution portion of the defect projection pattern are measured at a desired magnification, and based on the results, the size, shape, etc. of the defect in the observed object can be objectively evaluated.

[Brief explanation of drawings]

Figures 1 a and b are diagrams showing the principle of the object defect observation method of the present invention, and Figures 2 a and b are diagrams showing the relationship between defect size, defect projection size, and defect enlargement rate in the object defect observation method of the present invention. FIG. In the drawing, 1 is a divergence or convergence point of coherent spherical wave light, 2 is an observation surface, 3 is a surface to be observed, 4 is a defect, 5,
6 is the light intensity distribution of the defect projection pattern, 7 is a line indicating the geometrical optical shadow of the defect, X is the illumination distance, Y is the defect projection dimension,
Z is the observation distance, A is a group of curves showing the defect projected size, and B is a group of curves showing the defect expansion rate.

Claims (1)

[Claims] 1. In an object defect observation method in which the object to be inspected is inspected for defects by irradiating the object with coherent toner spherical wave light, the relative distance between the divergence point or the convergence point and the object to be inspected can be changed. Irradiating the object to be inspected with coherent spherical wave light and projecting the transmitted light onto an observation surface,
The transmitted light distribution of the projected image corresponding to defects existing on the surface and inside of the object to be inspected on the observation surface is calculated by 2 in the Fresnel region.
A method for observing defects in an object, characterized in that the presence or absence and size of defects in the object to be inspected are observed by dimensional scaling.