JPS62257010A - Detection of height - Google Patents

Abstract

PURPOSE:To prevent the generation of a detection error caused by the interference of beams of light, by using low coherent light as irradiating light. CONSTITUTION:The surface of a specimen 11 is irradiated with the light from a light source 13 from an oblique direction. That is, the light from the light source 13 consisting of a white tungsten lamp passes through a filter 14 permitting the transmission of a long wavelength of 500nm or more and further passes through a slit 15 to be converged by a condenser 16 to irradiate the surface of the specimen 11. The reflected light 18 from the surface of the specimen 11 is converged by a lens 19 and passes through a slit 20 to be received by a light receiving element 21. The detection signal of the light receiving element 21 is supplied to a synchronous signal detection circuit 24 and the height position of the specimen 11 is detected on the basis of the detection output of said circuit 24. In this case, because light having a wide band width is used as the light irradiating the specimen 11 from an oblique direction, the interference of the reflected light from the surface of a Si-substrate and the reflected light from the surface of a resist can be prevented.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is directed to injecting light onto a sample to be measured from an oblique direction and determining the height of the sample surface from the amount of intensity distribution displacement of the reflected light. An optical height detection method is used to detect the position.

(Conventional technology In pattern transfer devices, defect detection devices, etc., it is necessary to accurately detect the height position of the sample in order to focus the lens on the surface of a semiconductor wafer, mask, etc.)
As shown in FIG. 3, this type of height detection method involves irradiating the surface of a sample 31 with light 32 from an oblique direction and detecting the height position based on the intensity distribution of reflected light 33 from the sample surface. is used. In this method, a slit image according to the intensity distribution 34 is projected onto the sample 31, and a slit image 35 is obtained using the obtained reflected light. This slit (gI3
5 is usually synchronously detected using a vibrating slit or the like to determine the vibration center, and the height position of the surface of the sample 31 is detected from the amount of displacement of this center point 36. Here, the center point 36 corresponds to the point where the left and right integral values of the intensity distribution 35 are equal, and highly accurate position detection is performed by detecting this center point.

However, this type of method has the following problems. That is, in the exposure process of semiconductor wafers, etc., a resist 42 is formed on the surface of the Si substrate 41 as shown in FIG.
Since a sample coated with is used, reflected light 43 is present not only from the surface of the resist 42 but also from the surface of the substrate 41.

Then, two slit image intensity distributions are formed. At this time, light interference occurs in the overlapping portion 44 of the two,
This results in an extremely unique waveform. Figure 5 shows an example based on theoretical calculations. When a resist 42 of 1.2 [μ77L] is coated on a 3i substrate 41, a reflected light intensity distribution P from the 3i substrate 41 and a reflected light intensity distribution Q from the resist 42 are obtained, and the two are synthesized. An abnormal peak S appears in the intensity distribution R due to interference.

It has been found that this abnormal peak causes an imbalance in the left and right integral values when synchronously detected, and as shown in FIG. 6, an abnormal error appears in the height measurement depending on the resist film thickness.

(Problems to be Solved by the Invention) In this way, in the conventional method, transparent tlgl is placed on the sample to be measured.
etc., an abnormal peak occurs in the detected light intensity distribution due to light interference, which causes problems such as height detection errors.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a height detection method that can prevent detection errors caused by light interference and improve detection accuracy. It is about providing.

[Configuration of the Invention (Means for Solving Problems) The gist of the present invention is to reduce the coherence of measurement light so as to reduce the interference effect of light.

A method for achieving low coherence is to reduce the spatial and temporal coherence of the light rays. To this end, it is conceivable to widen the wavelength range of the light beam, use it as a multi-wavelength light beam, or use so-called incoherent illumination as the illumination light of the measurement slit.

The present invention focuses on these points, and... ! ! ! The surface of the measurement sample is irradiated with light from an oblique direction, the reflected light from the sample surface due to this light irradiation is received, the center point of this reflected light intensity distribution is determined, and the height of the measurement sample is determined from the displacement m. This is a height detection method for detecting a position, in which low coherence light is used as the irradiation light.

(Function) With the above method, the interference of each reflected light from the substrate and the resist on the substrate is reduced, and the occurrence of abnormal peaks as shown in FIG. 5 is extremely small. Therefore, it is possible to prevent measurement errors caused by this abnormal peak.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 1 is a schematic configuration diagram showing a height detection device used in a method according to an embodiment of the present invention. In the figure, 11 is a sample to be measured, and this sample 11 is placed on a sample stage 12. The surface of the sample 11 is irradiated with light 17 from a light source 13 from an oblique direction.

That is, light from a light source 13 consisting of a white tungsten lamp or the like passes through a filter 14 that transmits long wavelengths of 500 nm or more, and then passes through a slit 15, and is focused by a focusing lens 16 and irradiated onto the surface of the sample 11. . Note that the filter 14 removes the wavelength component that sensitizes the resist applied to the surface of the sample 11, and is not necessarily necessary when the intensity of the irradiated light is sufficiently weak.

The reflected light 18 from the surface of the sample 111 is focused by a lens 19, passes through a slit 20, and is then received by a light receiving element 21. Here, the slit 20 is moved by an oscillator 23 that vibrates in response to an oscillation signal from an oscillator 22 in a direction perpendicular to the direction in which the light travels. The detection signal detected by the light receiving element 21 is supplied to a synchronous detection circuit 24. This synchronous detection circuit 24 detects the detection signal in synchronization with the oscillation cycle of the oscillator 22, and removes noise components from the detection signal. Based on the detection output of this synchronous detection circuit 24, the height position of the sample 11 is measured.

As the sample 11, a resist 42 coated on a Si substrate 41 as shown in FIG. 4 was used, and the height of the sample 11 was measured using the above-mentioned apparatus. As a result, the above-mentioned abnormal peak did not occur, and highly accurate measurements without abnormal measurement values could be performed. Furthermore, even when the thickness of the resist 42 was changed, no abnormal measurement values occurred.

Here, the occurrence of the abnormal peak is prevented because white light is used as the irradiation light and the band width of the irradiation light is widened to reduce the light interference effect. Furthermore, according to experiments conducted by the present inventors, the wavelength bandwidth of the irradiation light was increased by 3
It was confirmed that the occurrence of the above-mentioned abnormal peaks can be substantially suppressed by increasing the width to 0 [nm3 or more.

Thus, according to this *example method, since wide-band light (white light) is used as the light that irradiates the sample 11 from an oblique direction, interference of each reflected light from the 3i substrate surface and the resist surface is prevented. This makes it possible to prevent abnormal peaks from occurring in the reflected light intensity distribution.

Therefore, it is possible to prevent the occurrence of detection errors due to light interference, and it is possible to improve the accuracy in detecting the height of the sample surface. Further, there is an advantage that it can be easily realized simply by using a light source 13 with a wide band width.

Note that the present invention is not limited to the embodiments described above. For example, instead of using wide-bandwidth light as the irradiation light, it is possible to use polychromatic light having two or more wavelengths. Furthermore, instead of using a wide band width or multi-wavelength light as the irradiation light, as shown in Fig. 2, the parallelism of the slit illumination light is made poor and the angle θ at which the slit surface is viewed is made sufficiently large. Good too. Further, synchronous detection is not necessarily necessary, and any method that detects the integrated center point of the reflected light intensity distribution is sufficient. The present invention can be modified and implemented in various ways without departing from the spirit of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, by using low coherence light as the irradiation light, interference of reflected light from the sample surface can be reduced, and the measured sample Even if a transparent film such as a resist is applied to the surface, abnormal peaks can be prevented from occurring. Therefore, measurement errors caused by abnormal peaks can be prevented, and the height of the sample surface can be detected with high precision.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram showing a height detection device used in an embodiment method of the present invention, Fig. 2 is a schematic diagram for explaining a modified example, and Fig. 3 is a principle of oblique incidence type ^za detection. Figure 4 is a schematic diagram to explain the interference of light that causes measurement errors. Figure 5 is the intensity distribution of reflected light from the 3i substrate and resist, and the combined reflection of these. FIG. 6 is a characteristic diagram showing the light intensity distribution, and FIG. 6 is a characteristic diagram showing the change in the surface detection position with respect to the resist film thickness. 11...sample, 12...sample stage, 13...
Light source, 14... Filter, 15.20... Slit, 16° 19... Condensing lens, 17... Irradiation light,
18... Reflected light, 21... Light receiving element, 22... Oscillator, 23... Vibrator, 24... Synchronous detection circuit, 4
1...Si substrate, 42...resist. Applicant's agent, patent attorney Takehiko Suzue Figure 1 Figure 3

Claims (5)

[Claims] (1) Irradiate the surface of the sample to be measured with light from an oblique direction, receive the reflected light from the sample surface due to this light irradiation, find the center point of this reflected light intensity distribution, and calculate from the displacement of the center point. The height detection method for detecting the height position of the sample to be measured, characterized in that low coherence light is used as the irradiation light. (2) The wavelength bandwidth of the irradiation light is at least 30
The height detection method according to claim 1, wherein the height detection method is set to [nm] or more. (3) The height detection method according to claim 1, wherein polychromatic light having at least two wavelengths is used as the irradiation light. (4) The high light beam according to claim 1, characterized in that the irradiation light is light that has passed through a slit, and the slit illumination light has poor parallelism, and the angle at which the slit surface is viewed is sufficiently large. Detection method. (5) As a means for determining the center point of the intensity of the reflected light, the reflected light is vibrated and the received signal of the reflected light is periodically detected in synchronization with this vibration. Height detection method described.