JPS6253049B2 - - Google Patents

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, if the wafer surface deviates from the set height, the position and size of the exposed circuit may differ from the predetermined one. Especially 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 measuring 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 electron beam during measurement.
Therefore, the height measurement point must be located significantly away 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 difficult to traverse irregularities on the surface of the exposed material. If there is an interruption in the light, such as when the light is interrupted, subsequent measurements will be completely unreliable.

Recently, devices have been proposed that can solve these drawbacks. As shown in FIG. 1, this device projects light from a light source 1 obliquely onto the surface of a material to be exposed 2, irradiates this projected light onto a member 3 having an aperture, and directs the passed light through a lens. 4 to form an image near the surface of the material to be exposed, and a lens 5 is placed in the traveling direction of the light reflected from the material surface to form the image on the photoelectric detection surface of the image dissector tube 6. Instead, a signal corresponding to the position of the image is generated, and the height displacement is calculated from the signal.

In such an apparatus, if the material 2 changes by a height h from 2a to 2b as shown in FIG.
When the distance between the virtual images p' and p'' of the aperture image p is L, the magnification of the lens 5 is M, and the angle of incidence and reflection of light is θ, the amount of deviation △ of the aperture image on the detection surface is △ = M・It is given by Lcosθ=M・2hcosθ.Since the above M and θ are known,
If Δ is found, the height displacement h can be easily found.

This device is a non-contact, optical type and can measure the surface height at the point of irradiation of the electron beam without affecting the electron beam in any way, and does not use integration of interference pulses, so it is possible to measure the surface height at the point where the electron beam is irradiated. This has the effect that accurate height measurement is possible even when there is a problem.

However, the image dissector tube is composed of a photoelectric conversion surface, an aperture plate, a secondary electron multiplier, a collector electrode, an electrostatic lens, a deflection coil, a power source for each part, etc., so the structure is complex and large.
Another problem is that it is very expensive. especially,
The large size of the device makes it difficult to install it in a narrow exposure room, making it impossible to utilize the device, which has many advantages. Therefore, if a semiconductor array sensor is used in place of the image dissector tube, the above structural problem will be solved, but a new problem will arise. In other words, a semiconductor array sensor uses a semiconductor photodetector element with a thickness of 10 to 30μ.
They are arranged in large numbers at m pitch intervals, and the largest number currently commercially available is 2048. Now, if the pitch P of the array element is 25 μm, the length of the element is about 50 mm. In Fig. 1, the imaging lens 5
If the magnification M is 10 times and θ is small and cosθ is approximately 1, then from the above formula, the maximum height displacement h max
is approximately 2.5mm. In other words, the measurable height range is only about 2 mm to 3 mm. Also, to improve measurement accuracy, if M is multiplied by 100, the height range is 0.25.
It can only be 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 a plurality of bright and dark areas are arranged near the irradiation point. a light irradiation optical system that forms an image; an optical system that collects light reflected from the irradiation point to form the plurality of bright and dark images; and a number of semiconductor light detectors placed on the imaging plane of the bright and dark images. a semiconductor array sensor consisting of a semiconductor array sensor, and a circuit for determining the distance of bright and dark images on the semiconductor array sensor from a reference position, and the array length of the plurality of bright and dark images on the semiconductor array sensor is longer than the length of the sensor. much longer, and the interval between bright and dark images is such that at least one bright and dark image exists on the sensor;
Furthermore, 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.

An embodiment of the present invention will be described below 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. 10 is a deflector for deflecting the electron beam 8 and moving it on the exposed material 2 to draw a pattern;
A pattern signal is sent from a computer 12 via 1. Between the light source 1 and the lens 4 of the irradiation optical system, there is placed a slit plate 3' having a plurality of slits with minute intervals and array lengths as will be described later, and the light passing through the slit plate passes through the lens. 4, and after forming its bright and dark image at point p, it is projected onto material 2 at an angle θ. 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 in which a large number of semiconductor photodetecting elements are arranged. In other words, a virtual image p' of point p is projected onto the sensor. Incidentally, the image formation position of the slit plate 3' by the lens 4 is not limited to the front of the material irradiation point as shown in the figure, but is located in front of the material irradiation point or
It may be further back than that. The signal from the semiconductor array sensor 13 is amplified by the amplifier 14,
The signal is sent to the arithmetic circuit 15. In this arithmetic circuit, the distance from the reference position of the bright and dark image, which is the slit image, is determined and sent as a height signal to the display device 16 for display. Further, the signal is sent to the amplifier 11 of the deflector, the objective lens, the beam shift deflector, and the field rotation lens, etc., so that the drawing position of the drawing pattern and the exposure field are adjusted regardless of the height displacement of the exposed material. Control them so that the size, focusing, etc. are constant.

FIG. 4 is a diagram illustrating the operation of the present invention, and a
The figure shows the detection surface of the semiconductor array sensor 13, in which a large number of semiconductor photodetecting elements are arranged at regular intervals. Figure b shows the light intensity distribution of the slit image on the surface of the semiconductor array sensor 13.
C, D...N correspond to each slit image (light image). As can be seen from the figure, the array length of the slit images (length from A to N) is much longer (several to ten times) than the length of the detection surface of the array sensor 13. Also, the intervals between each of the optical images A, B, C...N are constant and are the same as the length of the detection surface, or
Or each is made smaller. In the figure, the length of the detection surface is 1/2, so two optical images are always projected onto the detection surface. Furthermore, each optical image A,
The widths of B, C...N are different from each other, so that it is possible to identify which optical image is projected onto the detection surface. 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 that it is possible to identify which light image is being projected. In the figure, optical images D and E are projected, and the distances d and e from the reference position (for example, the left end of the detection element) of the optical images are
is determined, and the height (relative height) is determined from these distance signals and sent as a control signal to the display device 16 and, for example, the amplifier 11 of the deflector 10.

When the height of the exposed material changes, the optical images D and E move to the right or left on the detection surface,
The distances d and e from the reference position change. Therefore, the display changes, and the control signal also changes. If the height displacement is extremely large, a light image different from the light images D and E, such as A and B, will be projected onto the detection surface of the semiconductor array sensor 13, and the height will change accordingly. value is displayed. Incidentally, only one of the distances d and e from the reference position may be used, but the measurement accuracy is improved by adding the two and calculating the average value. In this case, it is better to detect not only one edge but also both edges of each optical image, calculate the distance from the reference position, and average it.

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 of a limited length, and it can be used in a wide range of applications.

Note that the above is one embodiment of the present invention, and many modifications are possible in implementation. For example, although two slit images are shown in the figure to be projected onto the detection surface of the semiconductor array sensor, at least one slit image is sufficient. or,
In FIG. 4, the position of the element in a bright part, that is, the part irradiated with light, is detected, but it is also possible to detect the position of the element in a dark part, that is, a part not irradiated with light. Therefore, the slit plate 3'
Instead, a plurality of wires or strips may be arranged side by side. Furthermore, although FIG. 3 shows the 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]

Fig. 1 and Fig. 2 are diagrams for explaining conventional height measurement, Fig. 3 is a block diagram showing an embodiment of the present invention, and Fig. 4 is a diagram for explaining the operation of the present invention. . 1: Light source, 2: Material to be exposed, 3': Slit 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, 16:
Display device.

Claims (1)

[Claims] 1. 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. comprising: the array 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 one bright and dark image exists on the sensor; Furthermore, the apparatus for measuring the surface height of an object is characterized in that the widths of the bright and dark images are formed to have mutually different values.