JPH0642163Y2 - Optical shape measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to an optical profile measuring apparatus, and improves the measurement accuracy of the optical profile measuring apparatus.

<Prior Art> FIG. 3 is a block diagram showing an example of a conventional optical shape measuring apparatus.

In FIG. 3, the light emitted from the laser diode 10 is collimated by the collimator lens 11 and reflected by the polarization beam splitter 12. The reflected light passes through the objective lens 14 and irradiates the DUT 15. Here, when the reflection surface of the DUT 15 is at the focal position of the objective lens 14, the reflected light becomes parallel light when passing through the objective lens 14, passes through the polarization beam splitter 12, and enters the critical angle prism 16. To be done. The critical angle prism 16 is adjusted to have a critical angle (θ) when parallel light is incident, and since all the parallel light is reflected and is incident on the two-division photodiode 18,
Since the A element and the B element of the two-divided photodiode 18 receive the same amount of light, the focus error signal after passing through the differential amplifier 20 becomes zero.

When the DUT 15 and the objective lens 14 are too close to each other, the light emitted from the objective lens 14 becomes divergent light, and the amount of light reflected at the point a of the critical angle prism 16 decreases, so that the two-division photodiode 18
The amount of light received by the A element is reduced, and the focus error signal becomes negative (-).

On the other hand, when the object to be measured 15 and the objective lens 14 are too far apart, the light incident on the critical angle prism 16 becomes convergent light, so the amount of light received by the B element of the two-divided photodiode 18 decreases and the focus error occurs. The signal is positive (+).

In these two cases, since the focus error signal has both polarities, it is sent to the control circuit (not shown) and the objective lens 14
Drive in the focus direction.

In such a configuration, there is an advantage that the focus error signal can be detected from the parallel light, and by repeating the reflection at the critical angle prism 16 several times, a high detection sensitivity can be obtained and the data around the measurement point can be captured. By
The shape of the object to be measured can be measured without contact.

<Problems to be Solved by the Invention> However, in the optical shape measuring apparatus shown in the above-mentioned prior art, the lateral resolution of the focus error signal is limited and determined by the light spot diameter. It was impossible to measure the groove 15a on the DUT 15 having a width narrower than the light spot diameter (1.6 μm in the figure) as shown in FIG. That is, when a light spot is applied to the groove 15a on the DUT 15, diffraction occurs at the edges and the center of both ends of the groove 15a. The light intensity pattern of the reflected light from is as shown in FIG. 4 (b), and since the minute deviation of the ± 1st order diffracted light cannot be read, there is a problem that the lateral resolution cannot be improved. there were.

The present invention has been made in view of the above problems of the prior art, and detects a slight displacement of ± first-order diffracted light on the array element in the light intensity pattern of the reflected light from the object to be measured,
By performing arithmetic processing, it is possible to measure a specific shape such as a groove width that is equal to or smaller than the spot diameter of light with a lateral resolution of 1 μm or less, and it is also possible to detect a tilt of the surface of an object to be measured, uneven reflectance, and the like. Therefore, by using these measurement data to correct the focus error signal obtained from the focus error detection optical system, it is possible to eliminate the influence of the tilt of the surface of the object to be measured or the unevenness of reflectance. Another object of the present invention is to provide an optical shape measuring device capable of further improving the lateral resolution.

<Means for Solving the Problems> A first configuration of the present invention for solving the above problems is to drive an objective lens in a focus direction to collect a light spot on an object to be measured and to reflect the reflected light. By measuring the light intensity pattern and performing arithmetic processing, in the optical shape measuring device configured to measure the shape of the DUT, for measuring the light intensity pattern of the reflected light from the DUT. An array element, an arithmetic processing section for adding the output signals of the array element, a focus error detection optical system for obtaining a focus error signal from the reflected light from the object to be measured, and a focus error detection optical system A second arithmetic processing unit for correcting the obtained focus error signal based on the arithmetic result from the arithmetic processing unit is provided.

In the second configuration, the optical shape measuring apparatus of the first configuration is provided with an image forming optical system for forming an enlarged image of a light spot on the object to be measured on the array element. It is characterized by that.

<Operation> According to the present invention, the array element can measure a specific shape such as a groove width with a lateral resolution of 1 μm or less by finely dividing the reflected light from the object to be measured,
Since it is possible to detect the inclination of the object surface and uneven reflectance,
By correcting the focus error signal using these signals, their influences can be eliminated and the measurement accuracy can be improved. In addition, by forming an enlarged image using the imaging optical system and measuring from the intensity pattern, the influence of aberration of the optical system can be reduced, the measurement accuracy is further improved, and the obtained image is Fourier transformed. Since it is not an image, data processing is simplified.

<Example> Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the optical shape measuring apparatus of the present invention. In FIG. 1, the same elements as those in FIG. 3 are designated by the same reference numerals, and duplicate description will be omitted.

In FIG. 1, 13 is a quarter-wave plate, 17 is a beam splitter that splits the reflected light from the DUT 15 into two, 19 is an array element that receives one of the beams split by the beam splitter 17, Reference numeral 21 is an arithmetic processing unit for adding the output signals of the array element 19, 22 is a focus error detection optical system for obtaining a focus error signal from the other light split by the beam splitter 17, and 23 is a focus error detection optical system 22. The second calculation processing unit corrects the focus error signal obtained from the calculation result from the calculation processing unit 21.

In such a configuration, the light emitted from the laser diode 10 is collimated by the collimator lens 11 and reflected by the polarization beam splitter 12. Reflected light is 1/4 wavelength plate 1
After passing through 3, the light is condensed by the objective lens 14 and irradiated onto the object to be measured 15. The irradiated light is reflected by the DUT 15, passes through the objective lens 14, the quarter-wave plate 13, and the polarization beam splitter 12, and is split into two by a beam splitter 17. One of the lights is incident on the array element 19 and is measured 15
It becomes a signal according to the light intensity pattern of the reflected light from
The pattern signal in the light spot such as the groove width, which is the measurement data, is sent to the arithmetic processing unit 21, and after the addition processing, the measurement data is sent to the arithmetic processing unit 23. The other light enters the focus error detection optical system 22, becomes a focus error signal, and is sent to the arithmetic processing unit 23. The arithmetic processing unit 23 corrects the measurement data from the arithmetic processing unit 21 and outputs it as a focus error signal.

In the above configuration, on the array element 19, FIG.
A minute displacement of the light intensity pattern due to the ± 1st-order diffracted light as shown in (1) is detected, and the signal is added by the arithmetic processing unit 21 to measure the groove width equal to or smaller than the light spot diameter. The lateral resolution is determined by the number of divisions of the array element. Further, by correcting the focus error signal using the measurement data of the arithmetic processing unit 21, it is possible to eliminate the influence of the inclination of the surface of the DUT 15, the unevenness of the reflectance, and the like, thereby further improving the lateral resolution. .

Further, by increasing the lateral resolution, not only the groove width but also the edge can be detected. Therefore, the calculation processing means is performed by correlating the stored bright and dark pattern of the edge with the measurement pattern. Alternatively, it is possible to measure the line or space of a pattern such as LSI.

FIG. 2 is a block diagram showing a second embodiment of the optical shape measuring apparatus of the present invention. The difference between FIG. 2 and FIG. 1 is that the object to be measured is branched by the beam splitter 17.
One of the reflected lights from 15 is made incident on the array element 19 through the imaging optical system 24. In FIG. 2, the same elements as those in FIG. Is omitted.

Here, in the apparatus of FIG. 1, it is possible to measure a groove width pattern or the like smaller than the light spot diameter, but the shape of the DUT 15 is measured by a light intensity pattern of parallel light. Therefore, it is easily affected by the aberration of the optical element in the optical path, which causes deterioration of measurement accuracy. Also, since the image obtained on the array element 19 is a Fourier transform image, the processing of the measurement data is complicated. It was

In consideration of this point, the second embodiment of the present invention provides a device under test 15
The reflected light is focused onto the array element 19 to form a magnified image of the light spot on the object to be measured 15, and the shape of the object to be measured 15 is determined by the light intensity pattern. Is being measured. Further, the focus error signal is corrected based on the measurement result. Therefore, the influence of the aberration of the optical element on the optical path can be reduced, so that the shape measurement can be performed with higher accuracy, and the obtained image is not the Fourier transform image, so that the measurement data processing can be simplified.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, the light intensity pattern of the reflected light from the object to be measured is slightly displaced by the ± first-order diffracted light on the array element. Is detected and arithmetic processing is performed. As a result, it is possible to measure a specific shape such as a groove width equal to or smaller than the spot diameter of light with a lateral resolution of 1 μm or less. Further, since it is possible to detect the inclination of the surface of the object to be measured, the unevenness of reflectance, and the like, by using the measurement data to correct the focus error signal obtained from the focus error detection optical system, the object to be measured can be Since it is possible to eliminate the effects of the surface inclination and unevenness of reflectance, and further improve the lateral resolution, it is possible to perform highly accurate shape measurement. Further, the shape of the DUT is not measured by measuring the light intensity pattern in the state of parallel light, but an imaging optical system is used to form a magnified image of the light spot on the DUT. By measuring from the intensity pattern, it is possible to reduce the influence of the aberration of the optical element on the optical path, which enables more accurate shape measurement, and the obtained image is not a Fourier transform image. It is possible to realize an optical shape measuring device having effects such as simplification of processing.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an optical shape measuring device of the present invention, FIG. 2 is a configuration diagram showing a second embodiment of the optical shape measuring device of the present invention, and FIG. FIG. 4 is a configuration diagram showing a conventional example, and FIG. 4 is a diagram showing a state of diffracted light by a groove and a diffracted light on a two-division photodiode. 10 ... Laser diode, 11 ... Collimator lens, 12
...... Polarizing beam splitter, 13 …… 1/4 wave plate, 14 ……
Objective lens, 15 ... DUT, 17 ... Beam splitter, 19 ... Array element, 21, 23 ... Arithmetic processing unit, 22 ...
Focus error detection optical system, 24 ... Imaging optical system.

Claims (2)

[Scope of utility model registration request] 1. A shape of the object to be measured by driving an objective lens in a focus direction, condensing a light spot on the object to be measured, measuring a light intensity pattern of the reflected light, and performing arithmetic processing. In the optical shape measuring device configured to measure, an array element for measuring the light intensity pattern of the reflected light from the object to be measured, an arithmetic processing unit that performs an addition process on the output signal of the array element, and A focus error detection optical system for obtaining a focus error signal from the reflected light from the object to be measured, and a second focus error signal obtained from the focus error detection optical system is corrected by the calculation result from the calculation processing section. An optical shape measuring device having a configuration including an arithmetic processing unit. 2. The optical shape measuring apparatus according to claim 1, wherein an image forming optical system for forming an enlarged image of a light spot on the object to be measured is formed on the array element. An optical shape measuring device characterized by.