JPS6021017A - Optical system of scanning photon microscope - Google Patents

Abstract

PURPOSE:To prevent resolution at the peripheral part of a picture from reduction by increasing the thickness of a transparent electrode arranged on a sample inside the surface intersecting with the optical axis of a lens system opposed to the transparent electrode at right angles in accordance with a distance from the optical axis to correct the aberration of curve on the image surface of the lens system. CONSTITUTION:The glass plate 3 provided with the transparent electrode 4 arranged on the sample 5 supported by a supporting board 6 is curved at its lens 2 side. The shape of the curved surface of the glass plate 3 is set up so that the aberration of curve on the image surface which is formed by a lens 2 can be corrected. A bright point in a point A on the optical axis of a light source 1 is formed at its image on a point A' on the surface of the sample 5 and a bright point in a point B separated from the optical axis is also formed at its image in a point B' on the surface of the sample 5, so that the resolution at the peripheral part of the picture is prevented from reduction.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a device for measuring the distribution of electrical characteristics of a semiconductor by scanning a light spot and detecting a photovoltage generated thereby, and Related to optical systems that improve

[Background of the Invention] FIG. 1 shows an example of the optical system of a conventional scanning photon 3#rj microscope. In FIG. 1, light emitted from a bright spot of a light source 1, which emits light based on the basic principle of scanning bright spots, such as a cathode ray tube, is focused by a lens 2, and a transparent material coated on, for example, a glass plate 3 and its lower surface is used. Through the conductive film 4, the semiconductor sea urchin
- Image is formed on the surface of the sample 50. As a result, semiconductor ueno・
A photovoltage is induced in the sample 5, but if the light emission from the MA of the light source 1 is made into intermittent light, an alternating current photovoltage will be induced in the sample 5. A photovoltage is extracted by capacitive coupling, and the distribution of the photovoltage is displayed as a grayscale image by an image display device synchronized with the bright spot scanning of the light source 1.

However, in the example shown in Figure 1, if the arrangement of the optical system is adjusted so that the bright spot A on the optical axis of lens 2 is best imaged at point A' on the sample surface, the bright spot A on the optical axis of lens 2 is For example, a bright spot t at point B is imaged at point B' due to the field curvature aberration of the lens 2, and does not form a point on the surface of the sample 5. In general, if the light emitting surface of the light source 1 is a flat surface, the image of each point on the light emitting surface will be formed along a curved surface as shown by the broken line in Figure 1, and as a result, the resolution of the scanning photon microscope will increase. The problem is that although the image is good in the vicinity of the light beam 111 (near the point N'), it is poor in the peripheral region, resulting in only a so-called blurred image being obtained.

[Purpose of the invention]

An object of the present invention is to provide an optical system for a scanning photon microscope that prevents deterioration of the M image at the periphery of the image due to field curvature aberration in the conventional optical system for a scanning photon microscope.

[Summary of the invention]

In general, in a lens formation system 1, if a transparent medium plate of Jll + refractive index n1 thickness d is inserted into the optical path on the image plane side,
Due to the effect of refraction, the effective optical path length is ΔZ =
= d...Mountain...(1) Shortened by ΔZ shown by 1. In other words, the imaging point moves in a direction farther away from the lens by ΔZ compared to the case where no transparent material is inserted. Therefore, the 11th PI
In this step, the thickness of the glass plate 3 is changed depending on the part,
It is possible to correct the curved image plane shown by the broken line in FIG. 1 so that it coincides with the surface of the sample 5. As shown in FIG. 1, this correction [l increases as the distance from the optical axis 7 increases, and accordingly, the thickness of the glass plate 3 may also increase as the distance from the optical axis 7 increases.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In this embodiment, the lens-side surface of the parallel flat glass plate 3 forming the transparent electrode in the optical system of the conventional scanning photon microscope shown in FIG. 1 is curved. That is, the thickness of the glass plate 3 is varied depending on the location so that all the bright spots at each point of the light source 1 are imaged on the surface of the sample 5 in FIG. The shape of the curved surface of the glass plate 3 is determined based on the amount of field curvature aberration caused by the lens 2 by a method such as ray tracing. Still, the amount of field curvature aberration of lens 2 can be determined by ray tracing of lens 2 or by experimental methods.

According to this embodiment, a bright spot located at a point A on the optical axis of the light source 1 is imaged at a point A' on the sample surface, and at the same time a bright spot located at a point away from the optical axis of the light source 1, for example, a point B. Since the bright spot is also imaged at point B' on the sample surface, there is an effect of correcting field curvature aberration.

〔Effect of the invention〕

As explained below, according to the present invention, in a scanning photon microscope, it is possible to correct the field curvature aberration of the lens system, thereby preventing the reduction in resolution at the periphery of the image in the conventional method. A sharp image can be obtained over the entire screen, and as a result, the entire large semiconductor wafer can be observed in detail.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an optical system of a conventional scanning photon microscope, and FIG. 2 is a block diagram of an optical system according to an embodiment of the present invention. 1...Light source, 2...Lens, 3...Glass plate, 4
・・・Conductivity Calendar 1 Figure 2

Claims (1)

[Claims] 1. A light source that emits light by scanning a bright spot, a lens system that images the bright spot on the sample surface, and a lens system that focuses the bright spot on the sample surface to extract the photovoltage generated within the sample by irradiating the bright spot. The thickness of the transparent electrode is increased in accordance with the distance from the optical axis in a plane directly parallel to the optical axis of the lens system. An optical system for a scanning photon microscope, characterized in that it corrects field curvature aberration of the lens system.