JPS61218902A - Position measuring method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a position measurement method for optically measuring the position of an object to be measured, and particularly to a position measurement method for optically measuring the position of an object to be measured, and particularly to a position measurement method for optically measuring the position of an object to be measured. Regarding measurement methods.

[Technical background of the invention and its problems]

In L8I manufacturing equipment, for example, electron beam exposure equipment,
When drawing and forming a pattern on a sample such as a semiconductor wafer or a mask substrate, if the angle of the sample (i.e., the height of the sample surface and the distance to the optical system) changes due to other factors, errors will occur in the drawn pattern. Conventionally, therefore, a method has been adopted in which the amount of variation in the height direction of the sample is measured and the variation is corrected according to the variation in the height of the sample. There is a method using an optical method as shown in (Japanese Unexamined Patent Publication No. 56-2632). In this device, the light emitted from the laser light source is focused into a spot by the lens L1 and irradiated onto the sample surface, and the reflected light is directed by the lens L onto the semiconductor device detector using the lateral light effect. form an image. The height position of the sample surface is measured by processing the detection output of this detector.

However, this type of measuring device has the following problems. In other words, within the light beam irradiated onto the sample surface,
As shown in FIG. 7, a portion 7 with high reflectance on the surface of the sample 700
1 and a portion 72 with low reflectance, the difference in reflectance causes an imbalance in the light amount distribution within the luminous flux, resulting in a measurement error. For example, P8D (semiconductor device detection element 4) t, which measures the center of gravity of light quantity, is used in many places these days.
- When used as a detector, the difference in light intensity distribution as shown in FIG. 8(a) causes the center of gravity to vary as shown in FIG. 8(b), resulting in measurement errors. -! The same thing can be said for position detection means using the vibrating slit method, which is well known in the Koryu microscope, for example, and measurement errors occur due to changes in the light intensity distribution within the light beam.Therefore, there is a method to reduce such errors. As one of the methods, the slit-shaped incident light is formed into a pattern (often orthogonal) K on the surface to be measured.
There is a method described in Japanese Unexamined Patent Application Publication No. 56-42205, in which the irradiation is performed while being tilted. According to this method, the maximum effect can be obtained by tilting the pattern by 45'' with respect to the orthogonal pattern.

However, in semiconductor IC patterns, in addition to orthogonal patterns, patterns with arbitrary inclinations are often created, and the above method has not been able to sufficiently reduce pressure measurement errors.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and its purpose is to reduce measurement errors caused by differences in reflectance of the surface to be measured, and to improve measurement accuracy. The objective is to provide a measurement method.

[Summary of the invention]

The key point of the present invention is to vibrate the incident light to average out the errors in order to reduce measurement errors caused by changes in the distribution of the amount of reflected light within the light beam.

That is, the present invention irradiates the surface of the object to be measured with focused light in a pattern from an oblique direction, detects the reflected light from the surface of the object with a photodetector, and detects two positions on the surface of the object. In the position measuring method, the incident light incident on the surface of the object to be measured is vibrated, and a detection signal of the photodetector that varies due to the imaging or a pattern on the surface of the object to be measured or a difference in reflectance is detected. This is an averaging process.

Further, in addition to the above configuration, the present invention vibrates the reflected light from the surface of the object to be measured to eliminate positional fluctuations of the reflected light on the detector due to vibration of the incident light.

〔Effect of the invention〕

According to the present invention, the incident light incident on the surface of the object to be measured is oscillated and is irradiated at an angle of 100 degrees, and a large number of measurement points on the surface of the object to be measured are averaged. As a result, measurement errors caused by differences in reflectance on the surface of the object to be measured can be significantly reduced. Furthermore, compared to conventional methods, this method has the advantage that it can be easily realized by simply adding a configuration that vibrates the incident light, for example, by adding a vibrating mirror. Furthermore, by also vibrating the reflected light from the surface of the object to be measured, reduction in the dynamic range due to vibration of the incident light can be prevented.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing a sample surface height measuring device used in an embodiment of the present invention. In this example, it is arranged in a sample chamber of an electron beam exposure apparatus, and the height of the sample surface inside the sample chamber is measured. In the figure, 10 is a vacuum container forming a sample chamber of an electron beam exposure apparatus, and an electron beam optical column (hereinafter abbreviated as BO8) 20 is attached to the earthen wall of this container 10. BO820 consists of an electron gun, various lenses, various deflection systems, etc.
The electron beam from O320 is irradiated onto a sample 30 as an object to be measured placed inside the container 10.

On the left and right sides of the GOS 20, an irradiation system 40 and a light receiving system 50, which constitute the sample surface height measuring device according to this embodiment, are provided, respectively. The irradiation system 40 includes a laser light source 41, a slit 429 and a reflecting mirror 43, 44. Focusing lens 45, reflecting mirror (vibrating mirror) 46. It is composed of a vibrator 47, a drive circuit 48, and the like. The light emitted from the laser light source 41 passes through the slit 42 and is reflected by the reflecting mirrors 43 and 44.
The light is reflected by the focusing lens 45 and is focused onto the vibrating mirror 46 . The surface of the sample 30 is irradiated with focused light 49 reflected by the vibrating mirror 46. Here, the focused light 49 becomes incident light on the sample 30.

As shown in FIG. 9, the incident slit image 9 on the sample surface is irradiated with an inclination of, for example, 45'' with respect to the orthogonal pattern 100 on the sample surface (i.e., the pattern that causes a change in reflectance). An angle other than 456 may be used.

The vibrating mirror 46 is attached to a vibrator 47 made of a piezoelectric element, and the vibrator 47 is vibrated by a drive circuit 48. Here, the frequency of the vibrating mirror 46 is sufficiently higher than the sample surface height fluctuation measurement frequency. Further, the vibration amplitude may be determined depending on the length of the light-receiving surface of a photodetector such as PSO, which will be described later, or the rate at which the error is reduced.

On the other hand, the light receiving system 50 includes a reflecting mirror 51 . Focusing lens 52
, semiconductor device detector (P8D) using lateral light effect, known as a photodetector 53. Adder 54. Subtractor 55.
Divider 56. Averaging processing circuit 57 and position measurement circuit 58
It is composed of etc. The reflected light 59 resulting from the irradiation of the incident light 49 onto the surface of the sample 30 is reflected by the reflecting mirror 51 and is imaged on the light receiving surface of the P 8 D 53 via the focusing lens 52. P8D53 is a product in which a resistive thin film is formed on a semiconductor substrate, output terminals are provided at both ends of the thin film, and the semiconductor substrate is grounded.Unbalance is generated from a pair of output terminals due to displacement of the resistive thin film irradiation position of the light spot. A signal is output.

The detection signal of P8D 53 is sent to adder 54. The signal is processed by a signal processing circuit including a subtracter 55, a divider 56, etc., and is input to an averaging processing circuit 57. The averaging processing circuit 57 averages the input signal through, for example, a low-pass filter, and this averaged signal (position signal) is supplied to the position measuring circuit 58. The position measurement circuit 58 moves the sample 30 according to the input position signal.
The 0 surface height position is calculated.

With such a configuration, the effect of irradiating the slit-shaped incident light at an angle with respect to the pattern and the effect of vibrating the incident light are combined, and a position detection device with very few errors can be provided. That is, as shown in FIG. 10, the effect of irradiating the slit-shaped incident light 101 at an angle with respect to the pattern 102 is, for example, when the slit width in the irradiated light is W and the slit length is l/W = 10. When calculating the measurement error for the case, it is found that θ=00 in Fig.
Figure f) a=45''.Furthermore, 1cP8D53 and signal processing circuit 9.

The detection output obtained at 56 becomes a sine wave corresponding to the frequency and amplitude of the vibrating mirror 46, as shown by curve 1 in FIG. At this time, if the light beam passes through a place where there is a difference in reflectance along the way, an error signal as shown by the broken line in the figure is generated. However, by averaging the signal, for example through a filter in the simplest way, the error signal will be averaged over the entire oscillation amplitude, as shown by line 2, and the incoming light will be oscillated. The error will be significantly reduced compared to when it is not used. That is, by vibrating the incident angle of the incident light 49 and averaging a large number of measurement points on the sample surface, the measurement error is significantly reduced compared to the conventional method.

As described above, according to this embodiment, by vibrating the incident light 49 tilted with respect to the pattern, it is possible to significantly reduce measurement errors caused by differences in reflectance of the sample surface. Therefore, the height of the sample surface can be measured with high precision. Furthermore, compared to conventional devices, there is an advantage that it can be realized with a simple structure that only requires a mechanism for vibrating the mirror 46.

FIG. 3 is a schematic configuration diagram of an apparatus used in another embodiment of the present invention. Note that the same parts as in FIG. 1 are given the same reference numerals, and detailed explanation thereof will be omitted. This embodiment differs from the previously described embodiments in that not only the mirror catch on the irradiation system side but also the mirror 51 on the light receiving system side vibrates. That is, the mirror 51 is attached to a vibrator 61, and this vibrator 61 is driven by the drive circuit 48. Here, the vibration of the mirror 51 is exactly in opposite phase to the vibration of the mirror 46. In addition, the vibration amplitude of K so as to cancel the optical magnification is
The adjustment is made so that the vibration of the light beam on the P8D 53 does not occur due to the vibration of the P8D 53. In other words, even if the incident light 49 vibrates, the position on the reflected light 590P8D 53 on the light receiving side does not change.

With such a configuration, the vibration of the incident light 49 is canceled by the correction of the reflected light 59, and since the movement of the light flux in the height direction of the actual sample surface is different from the vibration component of the incident light 49, This appears as a movement of the luminous flux. That is, when the reflected light 59 is not vibrated, the incident light 49 is input to the detection output as shown in FIG.
However, when the reflected light 59 is vibrated, the vibration component of the incident light 49 does not appear, as shown in FIG. 4(b). Therefore, the movement of the light beam on the P8D 53 is only due to the actual height variation of the sample surface, and the measurement dynamic range of the detector is expanded.

Furthermore, it becomes possible to use a smaller detector, and the resolution of the detector increases accordingly.

Here, in the apparatus shown in FIG. 1, the light flux on the detector (P8D) side fluctuates as shown in FIG. 5 due to the vibration of the incident light 49. In FIG. 5, 53a indicates the light receiving surface of the P8D 53, and 59a indicates the imaging light beam of the reflected light 59. These are averaged through a filter etc. by the signal processing circuit after the detector and calculated as accurate position coordinates, but the light flux on the detector side is need to be expanded by In this case, even if the incident light 49 is slightly vibrated, the light beam will vibrate within the measurement range of the detector. This point can be covered by using a large detector, but in this case, there is a risk that the measurement resolution will decrease, so an unnecessarily large detector cannot be used. For these reasons, it becomes difficult to increase the dynamic range of measurements.

On the other hand, in this embodiment, the reflected light 59 is converted into the incident light 49.
Because it vibrates in an opposite phase in synchronization with the vibration of K, even if the incident light 49 is vibrated, the light flux will not move within the measurement range of the detector. Therefore, according to this embodiment, not only the same effect as the previous embodiment can be obtained, but also the dynamic range of measurement can be expanded, and the effect is enormous.

Note that the present invention is not limited to the embodiments described above. For example, the incident light incident on the sample surface is not limited to a slit-shaped focused beam, but may be a circular spot-shaped beam. In addition to mechanically vibrating the angle of incidence, as a means of vibrating the incident light incident on the sample surface, for example, acoustic means may be used, and the transmittance of the light deflection surface may be increased by applying a voltage. A material having a different refractive index may also be used. As a mechanical driving method, a piezoelectric element or an electromagnetic method may be used.

Moreover, instead of vibrating the incident angle, it is also possible to vibrate by parallelizing the position of the incident light. Further, the averaging processing circuit may be installed before the divider or before and after the adder/subtractor.

Furthermore, although the embodiment describes the measurement of the height of the sample surface, the present invention can be widely used for position measurement.

Further, regarding signal processing, although the method of averaging through a low-pass filter has been described as the simplest method, it goes without saying that other methods may be used. Furthermore, the larger the vibration amplitude, the greater the averaging effect and the ability to reduce errors, but it may be determined as appropriate depending on the specifications of the device. Further, the vibration waveform is not limited to a sine wave, but can be appropriately changed to a triangular wave, a sawtooth wave, or the like. Furthermore, the light source may be continuously lit or modulated. Furthermore, the position measuring circuit is not necessarily required; for example, the output of the averaging circuit can be sent directly to the height control mechanism. In addition, various modifications can be made without departing from the gist of the present invention.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing a sample surface height measuring device used in an embodiment of the present invention, Fig. 2 is a signal waveform diagram for explaining the operation of the above embodiment, and Fig. 3 is a diagram showing a sample surface height measuring device used in an embodiment of the present invention. Fig. 4 is a signal waveform diagram for explaining the operation of the above-mentioned embodiment, and Fig. 5 is a diagram for explaining the problem when the incident light is vibrated. The schematic diagrams, FIGS. 6 to 8 are diagrams for explaining the problems of the conventional method, respectively. FIG. 12 is a characteristic diagram showing the effects of the present invention. 10... Vacuum container, 20... Electron optical lens barrel, 30...
Sample, season...Irradiation system, 41...Laser light source, 45,
52...Focusing lens, 46.51...Reflecting mirror (
Vibration mirror), 47.61... Vibrator, 48. Drive circuit, 53.. Detector (P13D), 54.55.56.
...Signal processing circuit, 57...Averaging processing circuit, 58
Position measurement circuit, 100, 102... Sample surface pattern, 99.101... Incident slit image on the sample surface. (7317) Agent: Patent Attorney Noriyuki Chika (
Figure 1 Figure 2 Figure 4 Figure 53a Figure 6 Figure w-4 Figure 8 Figure 9 Figure 10 Pattern edge amount -%/w Figure 11 Figure 12

Claims (11)

[Claims] (1) The surface of the object to be measured is irradiated with slit-shaped focused light obliquely to the pattern on the surface to be measured, and the incident light incident on the surface of the object to be measured is vibrated; It is characterized by detecting the reflected light reflected on the surface of the object to be measured by the irradiation to obtain a signal corresponding to the position of the object to be measured that changes due to the vibration, and averaging the detected signal. position measurement method. (2) The position measuring method according to claim 1, wherein a semiconductor device detection element using a lateral light effect is used for the light detection. (3) In order to vibrate the incident light, a piezoelectric element is used as a driving source, and the piezoelectric element vibrates a mirror that reflects the focused light and irradiates it onto the surface of the object to be measured. The position measuring method according to scope 1. (4) Claim 1, characterized in that a low-pass filter is used to average the detection signal.
Position measurement method described in section. (5) The surface of the object to be measured is irradiated with slit-shaped focused light obliquely to the pattern on the surface to be measured, and the incident light incident on the surface of the object to be measured is vibrated; Vibrating the reflected light reflected on the surface of the object to be measured by the light irradiation, detecting the vibrated reflected light to obtain a signal corresponding to the position of the object to be measured, and averaging the detected signal. A position measurement method characterized by: (6) The position measuring method according to claim 5, wherein a semiconductor device detection element using a lateral light effect is used for the light detection. (7) In order to vibrate the incident light, a piezoelectric element is used as a driving source, and the piezoelectric element vibrates a mirror that reflects the focused light and irradiates it onto the surface of the object to be measured. The position measuring method according to scope 5. (8) In order to vibrate the reflected light, a piezoelectric element is used as a driving source, and the piezoelectric element vibrates a mirror that reflects the reflected light from the surface of the object to be measured and irradiates it onto the photodetecting section. A position measuring method according to claim 5. (9) The position measuring method according to claim 5, characterized in that a low-pass filter is used for the averaging process. (10) The position measuring method according to claim 5, wherein the vibrations of the incident light and the reflected light are in opposite phases to each other. (11) The vibration amplitude of the reflected light is adjusted so that the position of the reflected light does not change on the photodetector due to the vibration of the incident light. Measuring method.