JPH0236902B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting defects in insulating films that utilizes the dynamic scattering effect of nematic liquid crystals.

Film quality of insulating film, e.g. used in semiconductor industry
The quality of the SiO ₂ film has an extremely large effect on the manufacturing yield and reliability of semiconductor devices. If the insulating film is of poor quality and has pinhole defects or breakdown voltage defects, it is impossible to manufacture semiconductor devices with high production yield or high reliability. Therefore, a film-forming technology that can produce high-quality insulating films is required, but in order to improve film-forming technology, it is necessary to develop a film-forming technology that can accurately control the level of film-forming technology. Defect detection methods are needed.

One method for detecting defects in insulating films is to apply the dynamic scattering effect of nematic liquid crystals. In this method, a nematic liquid crystal film and a transparent conductive film are sequentially placed on an insulating film formed on a semiconductor substrate, and then a voltage is applied between the semiconductor substrate and the transparent conductive film. If there are pinhole defects or breakdown voltage defects in the insulating film, a dynamic scattering effect occurs in the nematic liquid crystal above these defects and scatters external light. This means that defects in the film can be detected.

This method of detecting defects in insulating films using nematic liquid crystals is a method that can detect defects with minute dimensions with high sensitivity.

However, this type of conventional defect detection method has the following drawbacks. In other words, when the insulating film whose defects are to be detected is not formed continuously on the same plane, for example, when a thick field oxide film and a thin gate oxide film are formed in a pattern, The disadvantage of this method is that external light is scattered by the step between the field oxide film and the gate oxide film, and it is difficult to distinguish between this scattered light and the scattered light due to the dynamic scattering effect from the gate oxide film used to detect defects. It was hot. This drawback is particularly noticeable when defects are automatically detected and counted by an image analysis device using a television camera tube, rather than by human vision. It is well known that the frequency of occurrence of defects in an insulating film differs depending on the configuration of the insulating film, for example, the coexistence of a field oxide film and a gate oxide film as described above. Therefore, defect detection is important in actual semiconductor devices when the insulating films whose defects are to be detected are not formed continuously on the same plane.

The present invention attempts to eliminate the conventional drawbacks by setting the focus of an optical microscope for observing dynamic scattering effects near the boundary between a nematic liquid crystal and a glass plate with a transparent conductive film.

Hereinafter, the present invention will be explained with reference to the drawings. In the explanation, we assume that the insulating film whose defects are to be detected is a gate oxide film with a small thickness.
A sample in which only this gate oxide film and a thick field oxide film are formed on a semiconductor substrate will be described as an example.

FIG. 1 is a sectional view for explaining a conventional method. In the figure, a gate oxide film 2 and a field oxide film 3 are formed on a semiconductor substrate 1. A step a appears at the boundary between the gate oxide film 2 and the field oxide film 3 due to the difference in film thickness, and a step b also appears on the surface of the semiconductor substrate due to the difference in the oxidation process and oxidation conditions of the two oxide films. A nematic liquid crystal film 4 and a glass plate 5 with a transparent conductive film are placed on the sample 100. The glass plate 5 with a transparent conductive film has a glass plate 7 surface coated with a transparent conductive film 6 such as a SnO ₂ film or an In ₂ O ₃ film. In this arrangement state, a DC voltage is applied between the semiconductor substrate 1 and the transparent conductive film 6 by the DC power supply 8. If there is a defect 9 such as a pinhole defect or a breakdown voltage defect in the gate oxide film 2 having a small film thickness, a dynamic scattering effect occurrence point 10 is located in the nematic liquid crystal film 4 on the defect 9.
occurs. Therefore, there is an external light area 11 on the sample 100 surface.
When observing with the optical microscope 12 while irradiating the defect, the defect scattered light 13, which is the scattered external light 11, is seen at the location 10 where the dynamic scattering effect occurs, and the defect 9 can be detected. However, within the field of view of the optical microscope 12, not only the defect scattered light 13 but also the steps a,
Step portion scattered light 14, which is the light scattered by b, also enters. Further, even if dust adheres to the gate oxide film 2 and the field oxide film 3, light scattered by the dust enters the field of view of the optical microscope 12. Scattered lights other than these defect portion scattered lights 13 interfere with accurate defect detection. Particularly, in an image analysis device in which a television image pickup tube is attached to the optical microscope 12, there is a risk of erroneous defect detection. The drawback of such a conventional method is that the focus c of the optical microscope 12 is placed on the surface of the gate oxide film 2 or the field oxide film 3, or on the step a,
This is caused by using a very common focusing method, which is set to .b.

FIG. 2 is a cross-sectional view for explaining the defect detection method according to the present invention. In the figure, the focal point c of the optical microscope 12 is set at the boundary between the nematic liquid crystal film 4 and the glass plate 5 with a transparent conductive film. Due to this focus setting, the step portion scattered light 1 enters the optical microscope 12.
As the amount of light 4 decreases, the image of the step portion scattered light 14 becomes blurred. However, the dynamic scattering effect occurs within the nematic liquid crystal film 4 up to the point where it contacts the glass plate 5 with a transparent conductive film, and the dynamic scattering effect reaches the area where it contacts the glass plate 5 with a transparent conductive film. The geometric range is the largest. Therefore, if the focal point c is set at the boundary between the nematic liquid crystal film 4 and the glass plate 5 with a transparent conductive film, the ratio of the amount of light entering the optical microscope 12 between the defect part scattered light 13 and the step part scattered light 14 increases, and the defect The image of the partial scattered light 13 is clearly contrasted with the dark and blurred image of the step scattered light 14, eliminating errors in defect detection and allowing accurate detection by the image analysis device.

Nematic liquid crystal film 4 and glass plate 5 with transparent conductive film
The focal point c is set at the boundary between the gate oxide film 2 and the field oxide film 3, or the step a,
After focusing on point c, the film thickness t of the nematic liquid crystal film 4 is determined using the vertical fine adjustment dial of the optical microscope 12.
It is only necessary to displace it toward the glass plate 5 with a transparent conductive film. In this state, the location 10 where the dynamic scattering effect occurs is detected, and if necessary, the focal point c is returned to its original state, so that the position of the defect 9 can be accurately determined.

Setting the focal point c at the boundary between the nematic liquid crystal film 4 and the transparent conductive film coated glass plate 5 is extremely easy using the optical microscope 12 having an automatic focusing mechanism.

As explained in detail above, the method of the present invention focuses the optical microscope on the surface or step of the insulating film, and then shifts it toward the glass plate with a transparent conductive film by the thickness of the nematic liquid crystal film. Since it is set near the boundary between the film and the glass plate with a transparent conductive film, it is possible to accurately detect defects in the insulating film even if the surface of the insulating film is not continuously flat but has uneven steps. Automatic defect detection using an image analysis device will become easier, and we can expect to improve insulating film deposition technology and, in turn, improve the manufacturing yield and reliability of semiconductor devices.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a conventional method, and FIG. 2 is a sectional view for explaining the method of the present invention. 1 is a semiconductor substrate, 2 is a gate oxide film, 3 is a field oxide film, 4 is a nematic liquid crystal, 5 is a glass plate with a transparent conductive film, 9 is a defect, 10 is a location where a dynamic scattering effect occurs, 11 is external light, 12 is an optical microscope, 1
3 is the defect part scattered light, 14 is the step part scattered light, 1
00 is the sample, a and b are the steps, and c is the focus. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In a method for detecting defects in an insulating film in which a step occurs due to a difference in film thickness by applying the dynamic scattering phenomenon of nematic liquid crystal, the focus of an optical microscope for observing the scattered light due to the dynamic scattering phenomenon is set to After aligning with the surface or step, the nematic liquid crystal film is displaced toward the glass plate with a transparent conductive film placed on the nematic liquid crystal film by the thickness of the nematic liquid crystal film placed on the insulating film. A method for detecting defects in an insulating film, the method comprising detecting defects in an insulating film, the method comprising detecting defects in an insulating film near a boundary between a liquid crystal film and the transparent conductive film-coated glass plate.