JPS58193426A - Light detector - Google Patents

Abstract

PURPOSE:To obtain the accurate output proportional to the amount of received light when the light is received by a plurality of light guides, by expanding the light received by the light guides to the entire surface of a photoelectric plane of a photoelectric multiplier tube and inputting the light in the tube. CONSTITUTION:The light reflected by a sample is received by a plurality of light guides 4-7, and transmitted to a photoelectric multiplier tube 8. For this purpose, a holder 11 supports the light guides 4-7 so that the end surfaces of the light guides 4-7 are located at the points separated from the central part of the photoelectric plane of the photoelectric multiplier tube 8 by an equal distance R. The distance R is determined in such a way that the light emitted from the light guides 4-7 is expanded to the approximately entire surface of the photoelectric plane of the photoelectric multiplier tube 8.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a photodetector using a light guide and a photomultiplier tube (hereinafter abbreviated as PMT).

One of the non-contact, non-destructive measurements is to irradiate the source beam onto the object.
There is a device that detects reflected light, scattered light, rotating street light, etc., and calculates the characteristics tl-of the object.

These devices are widely used for inspecting minute patterns formed on semiconductor wafers.

When performing the needle side using such a device, a light kite and a PMT are used as photodetectors that receive all reflected light and scattered light.
I can think of a combination of and.

That is, the light is received in one direction of the light guide, and the next light is transmitted to the photocathode of the PMT by the light guide.
Detects light as an electrical signal. Since this light receiving method allows the end face of the light guide to be made small, it is possible to receive only the light traveling in the direction of the light with high selectivity.

In order to create a photodetector that effectively utilizes this feature, one end of several light kites is redirected to just in front of one P M 'I' photocathode, and the other light receiving end is oscillated at a certain multiplier. A photodetector arranged so as to receive light at a certain angle can be considered. By using several sets of these sophisticated photodetectors at the same time, it becomes possible to carefully measure the characteristics of the engineered pi test.

According to this unconventional photodetector, even if the light is received by a light guide connected to one PMT, the receiving beam is the same and the output of the PMT must be the same. n must not be.

However, experiments have revealed that even if the above-mentioned photodetector receives N-light beams, the output of the PMT varies greatly depending on the receiving light guide. In this way, even if the same light '1k is received, the magnitude of the output signal varies greatly from the detector 4e! This is a major drawback that reduces R properties.

Therefore, this cause tl--the result is PM'l
The problem lies in the non-uniformity of the sensitivity distribution of the original 11LI11] (see References 1 and 2).

Therefore, the object of the invention is that if a photodetector in which several light guides are connected to one PMT receives light of a constant violet at 7'C, the same PMT will be detected no matter which light guide receives the light. The output is in the form of a photodetector that provides an additional photodetector.

In order to achieve the above objectives, in the present invention, in order to eliminate the shadow w of the PMT light turtle photoelectric sensing east distribution, when the source of light received by the valley-going point is made to be incident on the MT light turtle photoelectric sensor, PMTyt,
The configuration was such that the light was incident on the entire surface of allLI.

In this way, the optical sound light '#LIl! is made incident on the PMT! When n is widened to the entire surface of 0, there is no shadow change in the sensitivity distribution of the photocathode, and
With the same photoelectric system, the same PMT output number can be obtained no matter which light guide the light enters from.

The present invention will be explained below with reference to Examples.

FIG. 1 shows the basic structure of a photodetector according to the present invention. In Figure 1, in V), 1 is the irradiation light, 2 is the irradiation light t
- Lens for condensing light, 3 is the sample to be inspected, 4
~7 is a light kite and the reflected light and scattered light from sample 3 gt
Receives light and transmits the light to PMT8. 9 is P M'I
' 8 is the power supply, 10 is the output terminal of PMT 8.

In this detector, irradiation light 1 is focused onto a sample 3 using a lens 2. The light guides 4 to 7 receive reflected light, diffracted light, scattered light, etc. from the sample 3, and the received light tPMT
Tell 8. 7'c receiving light from light kites 4-7
PMT8 converts to IIL accent with the incident i-mode photoelectric conversion direction,
Output end 10) as an electrical signal.

Output to.

FIG. 2 shows the combined structure of the light guides 4 to 7 and the PMT 8, which are the characteristic parts of this embodiment.

In the figure, 4 to 7 are light guides, 11 is a holder for light kites 4 to 7, and the end faces of light guides 4 to 7 are
M 'l'' 80 is designed to be held equidistantly from the center of the photocathode. 12 is a holder for PMT8. Holders 11 and 12 are designed to prevent light from entering the PMT8 from parts other than light guides 4 to 7. It is designed to prevent it from entering.

Here, the aperture of the light guides 4 to 7 is i [kNA, and light is emitted from the light kites 4 to 7; the wide angle at b is 20
Then, θ appears in the following equations by NA.

θ=sin-' (NA) In this way, the light emitted from the light guides 4 to 7 has 20 wide angles, so the end faces of the light kites 4 to 7 are violet)' M 'l' 8 light 11i1. +1111 Eri's fist is released, Light Kite 4-7 is the light, PM'I
You can make a fist that widens the area of light that enters the '8 photoelectric ■. now,
Distance 1 between light kites 4 to 7 and the middle large part of the photocathode of PMT8
111: The light incident on the PMT 8 from the light guides 4 to 7 spreads over almost the entire length of the photocathode of the PMT 8 so as to satisfy the LTT physician's formula.

However, D is the diameter of the photocathode of PMT8.

In other words, if the distance 111R is set to satisfy the above formula, the incident light will spread over the entire length of the photocathode of PMT8, so if the amount of incident light is constant, it will not matter which light guide it enters from. The constant output of PMT8 is the main point.

In addition, although the number of light kites is t4 in the description of the non-embodiments, the present invention is not limited to this number of 1 to 4 light kites.

FIG. 3 shows a light guide and P according to a second embodiment of the present invention.
This shows the attached part of iiB with MT. In FIG. 3, numerals 14 to 17 are prisms attached near the end faces of the valleys 2 and 4 to 7. The basic configuration of the non-embodiment is the same as that of the first embodiment.

The connecting portion between the light guides 4 to 7 and P M 'I' 8 is arranged such that the end faces of the valley light guides 4 to 7 are parallel to the photocathode of the PMT 8.
The distance between the MT8 and the photocathode is the same as in the first embodiment. 14 to 17 prisms are arranged on the end face of each light guide 4 to 7, and the light from each light guide 4 to 7 is transmitted to the prism 1.
4 to 17, and spreads out to the entire photoelectric path of PMT8.

Therefore, the influence of non-uniformity in sensitivity of the photocathode of the PMT 8 is eliminated, and no matter which light guide the light enters the PMT 8 from, the amount of light is the same and an electrical output having the same value n can be obtained.

FIG. 4 shows the structure of a connecting portion of a third embodiment of the present invention. In the four circles, 18 is the light guide 4
Holter 119 of 7 to 7 is a ground glass plate. In this embodiment, the optical sound ground glass plate 19 from each light guide 4 to 7 is
The light is applied to and diffused so that the light is incident on the entire surface of the photocathode of P1'vt T8. In this case, the distance II between the light guides 4 to 7 and the photocathode of PM 'l' 8
II can make a fist of any value.

As explained above, in the photodetector according to the present invention, PM
By connecting the light guide and the PMT without being affected by the sensitivity distribution of the photocathode of the T, it is now possible to obtain an electrical signal output from the PMT that is proportional to the light received by the valley light guide.

References 1) E, A, Ballik rArea and
'VvavelengLh8enst t ivi
ty of a Photomultipl
1erJ Appl.

opt, 10 No.3)'689~691 (19
71) 2) G-8, Birth and
D, P, Dewitt rFurtherCo
mmment on the Real 5ens+L
ivity ofEna on Photomul
tiplierJ Appl, opt, Luri No3
P687-689 (1971)

[Brief explanation of drawings]

Figure 1 is a basic configuration diagram of the present invention - Figure 2 is a configuration diagram of a light kite and PMT coupling part according to the first embodiment of the present invention, and Figure 3 is a diagram of the light guide and PMT according to the second embodiment. of the joining part with! FIG. i and FIG. 4 are configuration diagrams of a connecting portion between a light guide and a PMT according to a third embodiment. 1... Irradiation light, 2... Lens, 3... Sample, 4~
7... Light guide, 8... PMT, 9... Power supply, 10... Output end, 11.12.13.18... Holder, 14-171 1st Figure 2nd

Claims (1)

[Claims] 1. In a detector that receives light at one end face of a plurality of light guides and directs the light emitted from the other end face into a single photomultiplier tube to detect the light as an electrical signal, from each of the above light guides. A photodetector characterized by being configured so that the emitted light is spread over the entire surface of the photocathode of the photomultiplier tube.