JPS61177723A - Exposure monitor - Google Patents

Abstract

PURPOSE:To make such a photometry that a proper exposure area on the transcription surface becomes widest with the difficulty of being affected by the positional variation of a light source, by providing a condenser lens, two-dimensional photo receptor array, and signal amplification system. CONSTITUTION:The title apparatus is composed of a condenser lens 5, two-dimensional photo receptor array 6, signal amplification system 7, signal processing system 8 etc., and the photo receiving surface of the array 6 and a mask surface 10 are arranged at a position conjugated optically. This configuration causes the light flux from a light source 1 to be amplitude-split into a transmitted light flux, i.e. pnotometry light flux and a reflected light flux, e.g. exposure light flux via half mirror 4, and the illuminance distribution on the mask surface 10 becomes similar to that on the photo receiving surface of said array 6. Therefore, detection of the illuminance distribution on the photo receiving surface of the array 6 informs about that on the mask surface 10. The signal amplification system 7 amplifier photo reception signals individually, and the signal processing system 8 chooses signals and averages the signals outputs.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an exposure apparatus, and particularly to an exposure monitoring apparatus used in an exposure apparatus for semiconductor manufacturing.

[Prior art] In exposure equipment for semiconductor manufacturing, an exposure monitoring device grasps illuminance information on the wafer surface and performs shutter control, thereby managing exposure time and keeping exposure energy constant to ensure reproducibility. It was a good exposure.

However, as semiconductor elements such as I'Cs and LSIs become more highly integrated and their patterns become finer, stricter exposure control in such exposure apparatuses has become necessary. Furthermore, in order to reduce the cost of semiconductor devices, it is necessary to maintain the island throughput (throughput). Therefore, the exposure monitoring device must also be able to perform accurate photometry without being affected by slight variations in the position of the light source, and ■measure light in a way that maximizes the appropriate exposure area on the wafer surface. It is necessary to satisfy two requirements.

Among these '11M's, an exposure monitoring device that satisfies the former is based on the combination of the light receiving surface of the exposure monitoring device and the transfer surface of the exposure device, as already proposed by the present applicant in Japanese Patent Application No. 59-34247. This can be achieved by optically conjugate arrangement.

However, a device that simultaneously satisfies the above two requirements has not yet been realized for the following reasons. This is because even devices of the same model have different illuminance distributions, and there is no known photometry method that is suitable for all illuminance distributions. This device difference in illuminance distribution is thought to be due to differences in the set positions of the light sources, slight eccentricity of the illumination optical system, and the like.

[Object of the Invention] An object of the present invention is to provide an exposure monitoring device that is not easily affected by positional fluctuations of a light source and can perform photometry that maximizes the appropriate exposure area on the transfer surface.

[Description of Examples] Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic layout diagram of a contact type or proximity type exposure apparatus to which an exposure monitoring apparatus according to an embodiment of the present invention is applied. In the figure, 1 is a light source such as a mercury lamp, 2 is an elliptical mirror, 3 is an optical integrator, 4 is a half mirror that partially transmits the light beam from the light source 2 and reflects the rest, and 15 is the light beam that has passed through the half mirror 4. 6 is a condenser lens that condenses light, and 6 is a light receiving surface having a plurality of light receiving elements (photoelectric conversion elements) 61.62. . . , a two-dimensional light-receiving element array configured by arranging 6 m of light-receiving elements 7, 61, 62 . . . , a signal amplification system that individually amplifies the electrical signals output from each of 6m+, and 8 is a light receiving element 61, 62, . ..., 6m
9 is a collimator lens for collimating the light beam reflected by the half mirror 4, 10 is a mask surface, that is, a transfer surface, and 11 is a wafer.

In FIG. 1, the exposure monitoring apparatus of the present invention is composed of a condenser lens 5, a two-dimensional light receiving element array 6, a signal amplification system 7, a signal processing system 8, etc.
The light receiving surface and the mask surface 10 are arranged at optically conjugate positions. Because of this arrangement, the luminous flux from the light source 1 is amplitude-divided into a transmitted luminous flux, that is, a photometric luminous flux, and a reflected luminous flux, that is, an exposure luminous flux via the half mirror 4, and the illuminance distribution on the mask surface 10 and the two-dimensional light receiving element array 6 The illuminance distribution on the light receiving surface has a similar shape. Therefore, by detecting the illuminance distribution on the light receiving surface of the two-dimensional light receiving element array 6, the illuminance distribution on the mask surface 10 can be known.

The signal amplification system 7 includes each element 61 of the two-dimensional light receiving element array 6.
．． 62. ..., the electrical signals (hereinafter referred to as light reception signals) output from 6 m corresponding to the illuminance distribution on the mask surface 10 are individually amplified, and the signal processing system 8 amplifies the plurality of electrical signals output from the signal amplification system 7. ``Selection of multiple signals'' and ``averaging of signal outputs'' are performed for the received light signals. For example, if all received light signals are taken in and averaged, average photometry will be obtained, and if only the received light signals from the light receiving elements corresponding to the center of the mask surface 10 are selected and taken in, center-weighted photometry will be obtained. In other words, the method for selecting the received light signals corresponds to various photometry methods.

Next, the relationship between the average photometry method, the center-weighted photometry method, and the appropriate exposure area will be explained.

Figures 2 to 5 show illuminance distribution curves 21 and 21' on the mask surface.
The respective photometry areas are indicated by arrows A when average photometry (Figs. 2 and 4) and center-weighted photometry (Figs. 2 and 4) are applied, respectively.

It is expressed by the intervals of A, B, and B, and the appropriate exposed area at that time is shown by the shaded area for comparison.

In these figures, the signal output obtained from the signal processing system 8 is defined as an average illuminance of 22.22', and a certain range above and below this is defined as the appropriate exposure range. 23.23' indicates the upper limit of permissible illuminance for proper exposure, and 24.24' indicates the lower limit of permissible illuminance. As can be seen from FIGS. 2 and 3, when the illuminance distribution curve is 21, the center-weighted photometry (FIG. 3) has a wider appropriate exposure area.

On the other hand, as shown in Figures 4 and 5, the illuminance distribution curve is
In a case like 1', average photometry (Fig. 4) provides a wider appropriate exposure area.

As can be seen from the above explanation, the average illuminance is 22°22'
In other words, how to choose the photometry method is important. Note that in the above description, for convenience of explanation, only average photometry and center-weighted photometry are used, but of course, if spot photometry or peripheral-weighted photometry more satisfies the above requirements, it may be used.

A method for determining the photometry method according to the situation of the transfer surface, that is, a method for selecting signals will be described below.

First, each light receiving element 61°62 of the two-dimensional light receiving element array 6
,..., To correct the sensitivity of 6m, the mask surface 10
The illuminance above and each light receiving element 61.62. ..., the ratio of the received light signal output of 61 is known in advance.

Next, the light receiving elements 61 constituting the two-dimensional light receiving element array 6
．． 62. ..., the number of 6m is m1, the signal output of each element is χk (k=1.2...2m), the number of signals used for averaging among these signals is n, and the average value z( n), the deviation yk from the average value, and the number N (n) of signals that result in proper exposure are calculated using the following formula.

yk=lχ to −z(n)l −・・−−−−<
2>N1n)=ΣH(a −yk)−=−・・・(3
)=/ However, )((a-yk) is 1 when O≦yh≦a,
When yk>a, it is O.

Here, 2a is the allowable illuminance range of appropriate exposure illuminance (i.e., the allowable illuminance limits 23 and 24 or 23' and 24 in Figs. 2 to 5).
′) is the signal output corresponding to the width.

As a result of the above calculation, the area for proper exposure is the number N (n)
Therefore, the optimal signal selection method for the above requirement is ``N (=1.2°..., m) for each combination of light receiving signals that can be selected for all n (=1.2°..., m).
This corresponds to calculating j) and finding a combination that maximizes N(n) among them.

However, the way to combine signals for one type of n is
mcn = ml/n! (m-n)! Since there are as many as n, it is extremely complicated to consider all n. On the other hand, there is not only one way to combine signals such that N(n> is the maximum).

Therefore, in order to perform efficient and accurate averaging processing, it is necessary to memorize several representative combinations of signals in advance, and compare them to find the received light signal that maximizes N(n). All you have to do is select a combination of

For example, in FIG. 6, a light-receiving element array 6 having 60 light-receiving elements is used.
This allows you to choose between two combinations. 3
Numerals 1 to 35 are light-receiving element groups composed of four adjacent light-receiving elements, and 36 is a light-receiving element group composed of all 60 light-receiving elements. Light receiving element groups 31 to 35
correspond to weighted photometry, and the light receiving element group 36 corresponds to average photometry.

In this case, the above equation (1) is expressed as χ+(4), . . . , Ts(4), respectively for the light receiving element groups 31 to 35.
For the light receiving element group 36, z(60) is obtained, and correspondingly, N+(4), . . . , N5(4) and N(60) of equation (3) are obtained. The most suitable one among the light receiving element groups 31 to 36 may be selected by comparing these sizes.

In the above description, as each light receiving element constituting the two-dimensional light receiving element array, a phototransistor, a photodiode, or the like which generates an electric signal corresponding to the illuminance of light is used. Moreover, an image pickup device such as a CCD or an image pickup tube can be used instead of this light receiving element array. In this case, for example, a gate circuit or the like may be used to extract only the portion of the output signal of the N image element at the timing corresponding to the desired light receiving area.

[Application Example of the Invention] In the above embodiment, the present invention was applied to a contact type or proximity type exposure apparatus. However, if a two-dimensional light receiving element is placed at a position optically conjugate with a wafer, The present invention can also be applied to a projection exposure apparatus using a projection method or a step-and-repeat method (stepper).

[Effects of the Invention] As explained above, according to the present invention, it is possible to select the optimal photometry method for each device, expand the appropriate exposure area on the wafer surface, and improve throughput. can.

[Brief explanation of the drawing]

FIG. 1 is a schematic layout diagram of an exposure device to which an exposure monitoring device according to an embodiment of the present invention is applied, and FIGS. 2 to 5 are mask surfaces for explaining the relationship between the photometry method and the appropriate exposure area, respectively. FIG. 6 is an explanatory diagram showing the relationship between the position and illuminance on the top, and FIG. 6 is a diagram showing the arrangement of light receiving elements on the light receiving surface to explain a specific method of combining signals. 1: light source, 4: half mirror, 5: condenser lens, 6: two-dimensional light receiving element array, 61, 62. ..., 6n: light receiving element, 8: signal processing section, 9: collimator lens, 10: mask surface, 11: wafer.

Claims (1)

[Claims] 1. An exposure monitoring device that monitors a light flux from a light source in order to control exposure energy on a transfer surface of an exposure device, comprising a condenser lens and a light flux that passes through the condenser lens. a two-dimensional light-receiving element disposed at a position optically conjugate with the transfer surface, and an output signal corresponding to the amount of light received in each region formed by dividing the light-receiving surface of the two-dimensional light-receiving element into a plurality of regions. storage means for storing a plurality of types of signal combinations to be averaged; means for selecting a desired one of the combinations; and a signal for calculating the illuminance of the transfer surface based on the output signal of the selected combination. An exposure monitoring device comprising: a processing system. 2. The exposure monitoring apparatus according to claim 1, wherein the two-dimensional light receiving element is a two-dimensional light receiving element array in which a plurality of photoelectric conversion elements are arranged corresponding to each of the areas. 3. The exposure monitoring apparatus according to claim 1, wherein the two-dimensional light receiving element is an image pickup device such as an image pickup tube or a CCD. 4. The exposure monitoring device according to claim 1, 2 or 3, wherein the condenser lens condenses one of the light fluxes obtained by amplitude-dividing the light flux from the light source using a half mirror.