JPS59148809A - Defect inspecting method of surface with lattice pattern - Google Patents

Abstract

PURPOSE:To perform easy, high-speed defect inspection by a simple device by irradiating a surface to be inspected which has a grating pattern with illumination luminous flux which is regarded substantially as parallel light in a direction which does not cross the grating pattern at right angles. CONSTITUTION:Light from an illumination light source is sent as substantially parallel luminous flux 21 and guided to the surface of a sample 16 through mirrors 19 and 20. The projection direction of the illumination flux luminous upon the sample 16 is set without crossing the grating pattern on the surface of the sample 16 at right angles, e.g. at 45 deg. to the grating for the orthogonal grating pattern of a mosaic type color filter. Thus, the simple device performs defect inspection easily at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention provides a lattice pattern that can inspect even defects of several microns or more on the surface of a color fumerta placed on a COD image sensor or cage, for example. The present invention relates to a surface defect inspection method having -1i.

Conventional configurations and their problems When electronic devices with fine structures such as ICs and LSis are used, defects such as scratches and foreign substances on the surface of the semiconductor materials that make up the device can impair device characteristics. Inspection is an essential part of the manufacturing process.

Although various inspection methods have been studied and implemented so far, the basic principle is common to all of them and is shown in Figure 1 of page 1. The surface 1a of the semiconductor material 1 etc. to be inspected is generally in a mirror state, and the illumination light 3 which forms an appropriate angle with the surface 1a and can be regarded as substantially parallel light is specularly reflected by the surface 111' and becomes reflected γC4.

When a foreign substance 2 is present on the surface 1a, the illumination light 3 is scattered and reflected by the foreign substance 2, and becomes scattered light 5. No. 1 in the darkroom, etc.
In the state shown in the figure, if you visually inspect the dish from directly above the surface 1a, you will see only the scattered light 5, and there will be a foreign object 6 in the darkness.
is recognized as a bright spot.

In addition to foreign matter, scratches are also observed in the same way, that is, by detecting light that is scattered and reflected at steps such as unevenness existing on the mirror-like surface 1a. In general, this type of inspection is performed directly with the naked eye, which is called full oblique light inspection or spot light inspection.The illumination system configured in this way with a microscope is called dark field illumination, and such a microscope is called dark field microscope.
Ru.

In ICs, LSis, etc., circuit patterns are formed on the surface of semiconductor materials by processes such as oxidation and etching, and there are fine irregularities. Therefore, when this is observed using a dark-field microscope, the illumination light is scattered and reflected by both the uneven step portion of the circuit pattern and the defect, making it extremely difficult to detect only the defect.

In recent years, television cameras that use solid-state image sensors such as COD image sensors are being put into practical use, but in order to make them all color, it is necessary to form a mosaic-like color filter on top of the image sensor. Ru. FIG. 2 is an example of such a color filter pattern.

Each color filter in a mosaic pattern corresponds to one pixel of the image sensor.The color filter is composed of a dyeing section 6 and a separator section 7, and the size of the dyeing section 6 is 20μ.
m x 25μm culm, and the width of the separate lake part 7 is 3am-
However, the separator portion 7 generally has a concave shape of 1aW1 or less, and when observed with a dark field microscope, the separator portion 7 appears shining. In the case of defect inspection on a surface with such a grid-like separator, the uniformity of L, grid-like patterns, etc. is conventionally used17, and the TV camera signal is processed by a computer to recognize only the defects'fc. In the past, defects were recognized by extracting signals from grid patterns using pattern matching methods.
All of these methods not only require large-scale equipment, but also take time to process the signals using a computer, which hinders high-speed inspection.

OBJECT OF THE INVENTION The present invention solves the above-mentioned conventional problems.
CC, D image sensors and COD image sensors are placed on the surface of the LSI line in a mosaic-like structure. It is an object of the present invention to provide a method for easily detecting all defects (to a degree larger than the size) of fine irregularities forming a pattern. A beam of illumination light that can be considered to be substantially parallel light is directed at a surface to be inspected that has a grid-like pattern from a direction perpendicular to the grid-like no-turn-n grating, forming an appropriate angle σ) with the surface to be inspected. flaws present on the surface to be inspected.

A defect inspection method in which light scattered by a defect such as a foreign object is received by a light detection means V provided in a direction perpendicular to the surface to be inspected, and the defect is recognized, and the illumination method:
The intensity of light scattered by the lattice) is made smaller than the intensity of the light scattered by the defect, and the defect is recognized. This makes it possible to perform the treatment easily, inexpensively, and at high speed.

DESCRIPTION OF THE EMBODIMENT FIGS. 3 and 4 are diagrams for explaining the principle of a method for inspecting defects on a surface having a lattice pattern according to an embodiment of the present invention. First, in FIG. 3 VC, when parallel light 8 is projected onto object 9 from an oblique direction, it is irradiated in the direction shown in the figure at peace part 9a, and the step 9bf scatters and reflects it. Observed from directly above object 9. In the case of No. L, the step 9b is clearly recognized by the scattered light, as in the case explained in FIG. 1.

Next, in FIG. 4, when the step 1ob of the object 10 is gentle, the reflected light from the flat portion 10a and the reflected light from the sloped portion of the step 10b are reflected in approximately the same direction, and as shown in FIG. Scattered light components like those in are minute. That is, object 10
Even when observed from above, it is extremely difficult to fully recognize the difference in level.

Therefore, as shown in FIG. 5, a color filter similar to that shown in FIG.
As shown in the figure, 11.11' from 8 directions, 12°12<1
Considering the case of projecting parallel light beams 3.13' and 14.14', the state of scattering and reflection due to the step of the separator section 7 is the same as that shown in Fig. 3 for illumination lights 11.11' and 12.12'. Yes, illumination light 13. '13' and 14.14'
The result will be similar to that shown in Figure 4. Although the state is not as shown in FIG. 4, the scattered light component in the direction perpendicular to the surface is sufficiently reduced. - On the other hand, since defects existing on the surface can be considered amorphous, the component of the scattered light in the direction perpendicular to the surface does not change rapidly depending on the direction in which the illumination light is projected.

That is, according to the illumination lights 13.13' and 14.14', the defect appears bright and shiny, and the separator portion 7 is almost invisible, so that the defect can be easily recognized.

However, very small defects, such as the separator part 70,
In the case of a defect that is smaller than the size of a step, the brightness of the illumination light source must be considerably increased in order to detect it, and in this case, the scattered light from the step of the separator section 7, especially at the corners, will be detected by the defect. The intensity of the scattered light is the same as that of
It becomes difficult to distinguish it from a defect. However, such minute defects (for example, size of 1 μm or less) can be ignored as color filter defects, and do not need to be detected by the present invention.

Next, the configuration of an embodiment of the present invention is shown in FIG. A sample 16 such as a color filter is placed on a sample stage 15 and fixed by means such as vacuum suction. Sample stand 15 is connected to the XY table and sample 16f! : Constructed so that it can be moved. An objective lens 17 of a microscope is positioned above the sample 16, and an observed image of the wipe 116 is captured by a television camera 18 and converted into an electrical signal.

The light from the illumination source is transmitted as a substantially parallel beam 21 and directed onto the surface of the sample 16 by mirrors 19 and 2o. The angle θ between the surface of the sample 16 and the illumination light may be selected as appropriate so as to produce the effect of dark-field illumination, but it is often restricted by the working distance of the objective lens 17.

As shown in FIG. 5, the direction in which the illumination light beam is projected onto the sample 16 is set in a direction that is not orthogonal to the grid pattern existing on the surface of the sample 16, and the orthogonal grid pattern like a mosaic color filter is formed. In this case, it is appropriate to project the illumination light from a direction forming an angle of 460 with the grating. General IC and LSi patterns are also a combination of almost orthogonal patterns, and inspection can be performed using a similar configuration.

FIG. 7 is a diagram illustrating the electrical signal output of the television camera 18. Taking the signal level V on the vertical axis, 23 and 26
is the scattered light due to the step part of the grid pattern, 24 and 2
7 is scattered light due to defects. Condition 22 in the case of 23.24 is a case where the intensity of the illumination light is low, and condition 26 in the case of 26.27 is a case where the intensity of the illumination light is high and the defect signal 27
has reached the camera saturation level Vs. Teru,
When the intensity of the bright light is further increased, the level of scattered light due to the stepped portions of the lattice-like pattern also reaches the saturation level Vs, and it becomes impossible to distinguish between lattices and defects.

In other words, the illumination light intensity is set so that the signal level based on the light scattered by the step part of the lattice pattern is larger than the size of the step □ It is smaller than the signal level of the light scattered by the defect, and the threshold level is set in the middle. VT is set, and only defects larger than the step portion of the grid pattern are detected and detected.

Effect of the invention As described above, the defect detection method of the present invention uses a grid.

Is the illumination light flux that can be considered as substantially parallel light to the surface to be inspected that has a shaped pattern? r, irradiate from a direction not perpendicular to the grid pattern at an appropriate angle with the surface to be inspected;
The light scattered by defects such as scratches and foreign objects existing on the surface to be inspected is received by a light detection means V installed in a direction perpendicular to the surface to be inspected, and the defects can be recognized using a simple device. It is possible to inspect defects easily and at high speed, and its industrial value is great.

[Brief explanation of drawings]

Fig. 1 is a principle diagram for explaining the principle of a conventional inspection method, Fig. 2 is a plan view showing an example of a surface to be inspected, and Fig. 3
5 to 5 are principle diagrams for explaining the principle of the method of inspecting defects on a surface having a lattice pattern according to the present invention, FIG. , solid mounting @ is a characteristic diagram for explanation. 16...Object to be inspected, 17...Objective lens, 1
8...TV camera, 1g, 20...
mirror. Name of agent: Patent attorney Toshio Nakao and one other person. Figure 1 Figure 2 Figure 3 Figure 6 /9 /'? Figure 7? ? ? 5

Claims (2)

[Claims] (1) An illumination beam that can be considered as substantially parallel light is applied to the surface to be inspected which has a lattice pattern formed by fine irregularities from a direction that is perpendicular to or not perpendicular to the lattice of the lattice pattern. Inspection surface and appropriate angle? flaws present on the inspected surface. A method for inspecting defects on a surface having a lattice pattern, characterized in that light scattered by a defect such as a foreign object is received by a light detection means provided in a direction perpendicular to the surface to be inspected, and the defect is recognized. (2) As a light detection means, the scattered light incident on the objective lens is received by a television camera or the like and converted into an electrical signal, and electricity is generated based on the light scattered on the fine uneven steps forming a grid pattern. Setting the illumination light intensity so that the signal level is smaller than the electrical signal level based on light scattered by a defect larger than the size of the step, and setting a threshold level between the two types of electrical signal levels. , the size of the defect b is larger than the step size of the unevenness forming the lattice pattern.