JPS5999215A - Measuring device of surface height of body - Google Patents

Abstract

PURPOSE:To expand the measurement range of the surface height of a body by irradiating the surface of the body with light at a specific angle and forming a light and dark image, and converging its reflected light for image formation on a semiconductor array and finding the distance from the reference position of the light and dark image. CONSTITUTION:The light emitted from a light source 1 is made incident to the surface of a material 2 to be exposed through a slit plate 3' and a lens 4 at the specific angle to form the light and dark image. Its reflected light is expanded by an image forming lens 5 to form an image on the semiconductor array sensor 13. Its output is sent to an arithmetic circuit 15 through an amplifier 14 to find the surface height of the material on the basis of the distance from the reference position of the light and dark image, and the height is displayed on a display device 16 and also sent as a control signal to an amplifier and the deflector 11 of an electron gun 8. The image forming light of slanting incidence is used, so the measurement range of the surface height is expanded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus capable of extremely accurately detecting the height of an object, such as the height of a mask blank or wafer surface in a charged particle beam exposure apparatus.

For example, when drawing a fine circuit pattern on a semiconductor wafer etc. using an electron beam exposure device, the wafer surface may deviate from the set height or the position or size of the exposed circuit may differ from the predetermined one. In particular, when multiple exposure is performed on a semiconductor wafer, the drawing accuracy is significantly reduced. Therefore, accurately measuring the height of the exposed material is extremely important for highly accurate drawing.

In conventional height measurement devices, an electrode is placed opposite the surface of the material to be exposed, and the capacitance of a capacitor formed between this surface and the electrode changes as the surface moves up and down. There are two types of laser beams in use: one that irradiates the surface of a material to be exposed with laser light and uses interference fringes between the reflected light on the surface and the irradiated light.

However, in the former case, an electrostatic field is generated, which adversely affects the measured special electron beam. Therefore, the height measurement point must be located at a point that stands out from the most important electron beam irradiation point, and high measurement accuracy cannot be expected. In addition, since the latter is an optical measurement, it is possible to match the electron beam irradiation point and the measurement point, but since it uses the integration of the number of interference pulses, it is possible to traverse the unevenness of the exposed surface. If there is an interruption in the light, subsequent measurements will be completely unreliable.

Recently, devices have been proposed that solve these drawbacks. As shown in FIG. 1, this device projects light from a light source 1 obliquely onto the surface of an exposed object 2, and irradiates this projected light onto a member 3 on the right side of an aperture, so that the light that passes through it is is imaged near the surface of the material to be exposed by the lens 4, and the lens 5 is directed in the traveling direction of the light reflected by the material surface.
is placed so that the image is formed on the photoelectric detection surface 1 of the image dissector tube 6, a signal corresponding to the position of the image is generated, and the height displacement is calculated from the signal. This is what I did.

In such a device, the monthly charge 2 is 2 as shown in FIG.
When the height changes from a by 211 times h, the distance between ramp' and p'' of the aperture image ρ is set to 1-, and the lens 50
When the magnification is M and the angle of light deviation is θ, the deviation of the aperture image on the detection surface Φ△ is △-M・1-cosθ-M・
It is given by 2hcosθ. Since M and θ are known, if Δ is found, the height displacement can be easily found.

This device is a non-contact, optical type that can measure the surface height of the electron beam at the irradiation point without affecting the electron beam in any way, and since it does not use the integration of interference pulses, it can measure unevenness, etc. This has the effect that accurate height measurement is possible even if there is a light interruption part.

However, the image dissector tube is composed of a photoelectric conversion surface, an aperture plate, a secondary electron multiplier tube, a collector electrode, an electrostatic lens, a deflection coil, a power source for each part, etc., so the structure is complicated and large. Another problem is that it is very expensive. In particular, the large size of the apparatus makes it difficult to install it in a narrow exposure room, making it impossible to utilize the apparatus, which has many advantages. Now, if a semiconductor array sensor is used in place of the image dissector tube, the orientation problem can be solved, but a new problem arises. That is, the semiconductor array sensor is a 1ζ type in which a large number of semiconductor photodetecting elements are arranged at a pitch interval of 10 to 3Qp%, but the largest number of arrays currently available on the market is 2oz+8 drops.

Now, if the pitch P of the array elements is 251111, the length of the elements is about 50 mm. In Fig. 1, the magnification M of the imaging lens 5 is 10 times, θ is small, and COS θ is assumed to be approximately 1. From the above formula, the maximum height displacement tiihma
x is approximately 2.5 mm. In other words, the measurable height range is only about 2 mm to 3 mm.

Furthermore, if M is increased by 100 times to improve measurement accuracy, the height range becomes only 0.25 mm.

The purpose of the present invention is to expand the measurement range using a semiconductor array sensor, and its configuration is such that light is irradiated onto the surface of an object at a constant angle θ, and the irradiation point is a light irradiation optical system that forms a plurality of bright and dark images in the vicinity; and a light irradiation optical system that focuses light reflected from the irradiation point to form the plurality of bright and dark images.
a semiconductor array sensor consisting of a large number of semiconductor photodetecting elements placed on the imaging plane of the bright and dark images, and a circuit for determining the distance from the reference position of the bright and dark images placed on the semiconductor array sensor. The arrangement length of the plurality of bright and dark images on the semiconductor array sensor is much longer than the length of the sensor, and the interval between the bright and dark images is so large that at least - bright and dark images are present on the sensor. In short, the present invention is characterized by an apparatus for measuring the surface height of an object, in which the widths of the bright and dark images are formed to have mutually different values.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 3, numeral 7 indicates an electron gun, and an electron beam 8 emitted from the electron gun is focused by an electron lens system 9 and projected onto the material 2 to be exposed. A deflector 10 is used to deflect the electron beam 8 and move it on the exposed material Y312 to draw a pattern.A pattern signal is sent from the computer 12 via the amplifier 11. Between the light source 1 and the lens 4 of the irradiation optical system, there is a slit plate 3' having a plurality of slits with minute intervals and array lengths as will be described later. The image is formed at 4,
After forming its bright and dark image at point p, /υ, it is projected onto the moonlight 2 at an angle O. The light reflected by the material 2 is imaged by an imaging lens 5, and is magnified and imaged onto a semiconductor array sensor 13'2, which has a large number of semiconductor photodetecting elements arranged. In other words, a virtual image 1)' of point p is projected onto the sensor. still,
The position where the lenses 1 to 3' are imaged by the lens 4 is not limited to the front of the shrine illumination point as shown in the figure, but may be at or behind the illumination point. The signal from the semiconductor array sensor 13 is amplified by the amplifier 14 and sent to the performance circuit 15. In this arithmetic circuit, the distance -1 from the reference position of the bright and dark image, which is the slit image, is calculated, and it is sent to the display device 16 as the height (i) and displayed.
The signal is sent to the amplifier 11 of the deflector, the objective lens, the deflector for beam shift 1~, and further to the field rotation lens, etc., so that the drawing position of the drawing pattern and the exposure field can be adjusted regardless of the height displacement of the exposed target. They are pricked so that the serrations, focusing, etc. are constant.

FIG. 4 is a diagram explaining the present invention in detail, and FIG. 4(a) shows the detection surface of the semiconductor array sensor 13, in which a large number of semiconductor photodetecting elements are arranged at regular intervals. Further, the figure (b) shows the light intensity distribution of the slit images on the surface of the semiconductor array sensor 'v13, where A, B, C, D...N correspond to each slit image (light image). As can be seen from the figure, the array length of the slit 1 to the image (length from Δ to N) is much longer than the length of the detection surface of the array sensor 13 (several times to N).
Furthermore, the intervals between the optical images Δ, B, C, . . . , N are constant, and are equal to or smaller than the length of the detection surface. In the figure, 1/2 of the length of the detection surface
Therefore, two optical images are always projected onto the detection surface. Furthermore, the widths of each of the optical images Δ, B, C, . In other words, by making the widths of each light image different, the number of elements that produce outputs in the photodetecting element differs, so it is impossible to identify which light image is being projected.

In the figure, optical images D and E are projected, and the 2Ht of the optical images is
The distances IWld and e from the base Q position (for example, the left end of the detection element) are determined, and these distances (relative height from the signal) are determined and sent to the display device 16 and, for example, the amplifier 11 of the deflector 10. Sent as a control signal.

When the height of the monthly exposure rate changes, the light image and E
moves to the right or left on the detection surface, and the distances (j and e) from the base level stomach change.Therefore, the display also changes, and the control signal also changes.The height displacement is significantly large. In this case, a light image different from the light image E, such as A or B, is projected onto the detection surface of the semiconductor array sensor 13, and a corresponding height value is displayed. Note that either one of the distances 1flld and e from the reference position may be used, but if the two are added and the average value is determined, the measurement accuracy will be improved.In this case, each optical image It is even better if not only one edge but both edges are detected, and the distance from the reference position is calculated and averaged.

With the configuration described in detail above, it becomes possible to measure heights in a range comparable to several times the length using a semiconductor array sensor with a limited size, and it can be widely used.

It should be noted that the above is one embodiment of the present invention, and many modifications are possible in implementation. For example, although the figure shows two slit images projected onto the detection surface of a semiconductor array sensor,
It is good to have at least one. Also, in Fig. 4, the position of the element in the bright part, that is, the part irradiated with light, was detected, but conversely, the position of the element in the part 1, that is, the part not hit by light, was detected. Also good. Therefore, the slit plate 3
′ may be replaced by a plurality of wires or strips arranged side by side.

Furthermore, although FIG. 100 shows a case where the present invention is applied to an electron beam exposure apparatus, there is no particular restriction on the applicable apparatus.

[Brief explanation of the drawing]

1 and 2 are diagrams for explaining conventional height measurement, FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG.
The figure is a diagram for explaining the present invention in detail. 1: light source, 2: monthly exposure rate, 3' Nislit plate, 4.
5: Optical lens, 7: Electron gun, 8: Electron beam, 9: Electron lens system, 10: Deflector, 11: Amplifier, 12: Computer, 13: Semiconductor array sensor, 14: Amplifier, 15
: Arithmetic circuit, 162 display device. Patent Applicant JEOL Ltd. Representative Ito - Husband Nippon Telegraph and Telephone Public Corporation Representative Hisashi Shindo

Claims (1)

[Claims] A light irradiation optical system that irradiates the surface of an object with light at a constant angle θ and forms a plurality of bright and dark images near the irradiation point, and a light irradiation optical system that collects light reflected from the irradiation point to form the plurality of bright and dark images. An optical system for forming an image, a semiconductor array sensor consisting of a large number of semiconductor photodetecting elements placed on an imaging plane of the bright and dark images, and a circuit for determining the distance of the bright and dark images from a reference position on the semiconductor array sensor. The arrangement length of the plurality of bright and dark images on the semiconductor array sensor is much longer than the length of the sensor, and the interval between the bright and dark images is such that at least - bright and dark images are present on the sensor. , and further characterized in that the widths of the bright and dark images are formed to have mutually different values.