JP2016011896A - Height measuring device in charged particle beam device, and autofocus device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a height measuring device and an autofocus device for precisely measuring and setting and for fast, precisely and surely auto-focusing a height of a specimen in a charged particle beam device.SOLUTION: An objective lens 5 and a scanning system are provided for scanning a specimen 9 while narrowing down a charged particle beam 2 and irradiating the specimen 9 with the charged particle beam 2. In a portion of an outer surface of the objective lens 5 or in a portion of a hole provided in the objective lens 5 visible from the specimen 9, a light guide 7 is provided for irradiating the specimen 9 with a light beam and receiving a light beam reflected on the specimen 9, a sensor head 8 is provided for irradiating the light guide 7 with a light beam and receiving a light beam emitted from the light guide 7, and a spectrometer 11 is provided for radiating a light beam to the sensor head 8, receiving a light beam emitted from the sensor head 8 and detecting a position on the specimen irradiated with the light beam on the basis of the emitted light beam and the received light beam.

Description

  The present invention relates to an autofocus apparatus and an autofocus method in a charged particle beam apparatus.

  Semiconductor devices are shrinking every year according to Moore's Law, and the latest feature devices are trying to cut the minimum feature size to 20 nm even in mass production devices. In order to realize a small feature size, an exposure technique capable of forming a smaller pattern is required.

  Conventionally, a laser beam having a wavelength of 193 nm has been used for exposure, but since the limit that can be optically resolved has already been greatly exceeded, in recent years, an exposure technique using EUV light having a wavelength of 13.5 nm has been vigorously advanced. ing. This technology is said to have originated in Japan, but has been researched and developed for practical use by ASML for more than 10 years. Although the optical system of the exposure apparatus main body is almost completed, the current EUV exposure apparatus cannot obtain the light source power of 100W to 200W required for economical mass production. Skipped.

  Instead, a so-called double or triple exposure technique that can realize a smaller feature size by repeatedly performing an existing wavelength 193 nm exposure process a plurality of times is used in actual production sites. In principle, it is possible to make any number of small patterns by repeating immersion lithography using a laser beam with a wavelength of 193 nm, but it is necessary to have alignment accuracy on the order of nm, which is one digit higher than before. It is known that large roughness and the like resulting from the large molecular structure of the chemically amplified resist limit the repeated exposure process. At present, double patterning that repeats the exposure process, which is said to be the economic limit, is used for practical purposes. For relatively simple memory devices, it is used to realize lines and spaces from 20 nm to 16 nm. Has been.

  In addition to memory devices with a simple structure, CPUs and logic devices need to be reduced in pattern for function enhancement and power consumption reduction. Since a logic device uses a complicated pattern without repetition, a considerably complicated pattern is required to make a logic device by double or triple exposure. In order to divide a pattern that can be originally realized by one exposure into patterns on two photomasks for use in a plurality of exposures, a very complicated calculation is required. Depending on the pattern, the division calculation may diverge and the required result may not be obtained.

  In order to avoid these complexities, a technology for facilitating lithography called “complementary lithography” mainly proposed by Intel is about to be used. This exposure method is characterized by using a pattern obtained by reducing a complicated logic circuit to a simple L & S pattern such as a memory circuit. In this way, complex logic device patterns are limited to the most easily exposed L & S pattern and the process of cutting the line, so there is no need for complicated pattern division calculations, and the process is simple and easy to calculate. The top is supposed to go up to about 8 nm.

  On the other hand, as described above, when the 193 nm exposure technology is extended, the photomask used for it will increase by the number of exposures for each layer, so that more mask inspections and precise dimensional measurements are required than before. Become. For example, in double patterning, since two photomasks are used one after another, the absolute position accuracy and alignment accuracy of lines formed on the mask between the two masks are more important than ever. Optical correction for exposing a finer pattern becomes complicated and precise. Since masks using inverse lithography are used up to higher diffraction heights, the pattern size used for correction is even smaller.

  An electron microscope technique is indispensable for checking whether or not these masks have the correct dimensions, but an autofocus technique is very important for obtaining a high-definition image. However, when the conventional autofocus is used, there is a problem that the autofocus fails depending on the mask. If autofocus fails, not only will the measurement be impossible, but an erroneous measurement value will be provided to the process control, causing a further drop in yield and incurring a large loss, so failure is not allowed.

  For the purpose of assisting the autofocus of the conventional electron beam optical system, an optical height measurement method for measuring the sample height of the electron beam irradiation point in a non-contact manner has been developed. There is an objective lens at the tip of the electron beam column, and the tip of the pole piece has a very close positional relationship with the sample to be observed, so that only a few millimeters are spaced apart. Conventionally, in order to measure the distance, an LED or laser beam is incident obliquely, hits an electron beam irradiation point, the position of the reflected light is detected by a photosensor such as a CCD, and the height of the sample is measured. A scheme has been adopted.

  However, since the incident degree of the light beam and the height measurement resolution are proportional to each other, there is a problem that the height measurement resolution is hardly obtained when the incident angle is reduced to 1 degree.

  In addition, if the sample is tilted, it cannot be distinguished from the change in the sample height, so that there is a problem that complicated correction for separating the height component and the sample tilt component is required. Depending on the pattern and material of the sample surface, measurement may become unstable.

  On the other hand, the optical path length of LEDs, laser light sources, or the optical systems that make them is as large as several tens of centimeters. Therefore, deformation of the top plate due to changes in atmospheric pressure, fluctuations in optical path length due to temperature expansion, incident angle fluctuations, etc. Since it is easily caused by a change, there is a problem that the measurement accuracy is lowered. Of course, it is possible to perform correction by measuring these changes in the external environment with a sensor or the like, but there is a problem that the system becomes more complicated and causes problems such as high cost and difficulty in maintenance.

  In addition, since the system itself generates heat in the conventional system, there is a problem in that the temperature around the apparatus changes with the usage time and affects the measured value. When these are combined, there is also a problem that only a measurement accuracy of about 1 micron can be realized.

  An object of the present invention is to accurately measure and set the height of a sample in an electron beam apparatus (charged particle beam apparatus), and to perform autofocus at high speed, precision, and reliability.

  Therefore, the present invention is a charged particle beam apparatus that scans a charged particle beam while squeezing a charged particle beam while irradiating the sample, and generates an image based on the emitted, reflected, and absorbed signals at that time. An objective lens and a scanning system that scan while irradiating the sample with a narrow aperture are provided, and the sample is irradiated with light toward the outer surface of the objective lens or the hole provided in the objective lens, which is visible from the sample. A light guide that receives the reflected light, a sensor head that emits light to the light guide and receives light emitted from the light guide, and radiates light to the sensor head and is emitted from the sensor head. And a spectroscope for detecting the irradiation position of the light beam on the sample based on the emitted light beam and the received light beam.

  At this time, the light guide and the sensor head are integrated.

  In addition, the light guide is provided with a reflecting mirror, a prism, or an optical fiber in a portion that can be seen from the sample, so that the sample is irradiated with the light beam and the light beam reflected by the sample is received.

  In addition, the sample is irradiated with a light beam so that the sample is irradiated almost perpendicularly.

  A plurality of light guides are provided.

  Further, the height of the sample at the electron beam irradiation position is obtained based on the height of each sample of the plurality of light guides.

  Further, the height of the sample at a plurality of locations is measured with one or a plurality of light guides, and the relationship between the location of the sample and the height is measured in advance.

  The height of each sample irradiated by the charged particle beam based on the height of each sample measured by one or a plurality of light guides or the height of the sample measured and stored in advance. A height adjustment mechanism for adjusting the value to a constant value is provided.

  In addition, based on the height of the sample measured by one or more light guides or the height of the sample set to a constant value based on the measurement, autofocus with a charged particle beam can be performed quickly and reliably. To generate a focused image.

  In the present invention, the height of the sample in the vicinity of the electron beam irradiation point is set by directly measuring with one or a plurality of optical height sensors. Focusing is possible, and the height of the sample can be set to a stable ultra-high accuracy exceeding 0.1 microns with a very simple configuration, and at the same time, high-speed and precise based on the measured or set sample height. In addition, the electron beam can be automatically focused.

  In addition, when the sample is a semiconductor wafer, the measurement light of the sample height may change the conductivity in the irradiation region of the light beam and affect the measurement value by the electron beam. In the present invention, since the electron beam measurement point is not directly irradiated with the light beam, the height of the sample is measured (estimated) in real time with the light beam, while the sample is irradiated with the electron beam and the measurement is performed in parallel. Can do.

  The actual apparatus will be described in detail below.

  (1) By using the present invention, compared with the case where only conventional electron beam autofocus is used, there is no failure of autofocus, and a high-speed and accurate electron beam focusing state can be realized. Before the electron beam autofocus is performed, a state close enough to the electron beam in-focus state can be created. Therefore, the range in which the electron beam autofocus searches for the focus value can be reduced to about one-tenth or less of the conventional range. It is possible and autofocus can be performed at that high speed.

  (2) When the Z stage 22 is used, since the height is always constant, there is no image rotation, and highly accurate measurement can be realized.

  (3) Since the optical height sensor is very compact unlike the conventional one, it is easy to mount and maintain. Since the height is measured directly, the tilt correction of the sample 9 that was necessary in the conventional method is unnecessary. Since measurement at the electron beam irradiation point is not required, it is not necessary to push the sensor into a narrow space between the tip of the pole piece of the objective lens 5 and the surface of the sample 9.

(4) Since the sensor does not generate electromagnetic waves or heat, the measurement can be very stabilized.
Since the material is crow and metal, vacuum contamination can be avoided. Long life with no moving parts.
The effect of disturbance is small because the distance between the sensor and the measurement point is short.

  (5) Since the distance between the pole piece of the objective lens 5 and the surface of the sample 9 can be measured in real time, even if the height of the sample 9 changes due to a change in the external environment, the change can be measured in real time. , Electron beam autofocus can be easily succeeded.

  (6) Even when the two optical height sensors cannot be measured simultaneously in real time, by using a focus map created in advance, it is possible to perform height measurement similar to that measured in real time. I can do it.

  (7) Even with a specimen 9 that is difficult to autofocus only with an electron beam image, the height can be measured first with an optical height sensor and brought close to the in-focus state. You can shake the beam focus. Thereby, it becomes easy to obtain a focused state of the electron beam in a measurement object having a low three-dimensional object or edge contrast.

  (8) When the Z stage 22 supported by three points is used, the inclination of the sample 9 can be made zero and the height of the sample 9 can be made constant, so that the electron beam irradiation can be made vertical. become. Thereby, a more accurate electron beam image can be acquired.

  In the present invention, the height of the sample in the vicinity of the electron beam irradiation point is set by directly measuring with one or a plurality of optical sensors, and precision auto-focusing by the electron beam is performed based on the measured or set height of the sample. It is possible to set the height of the sample to a stable ultra-high accuracy exceeding 0.1 microns with a very simple configuration, and at the same time, it is fast, accurate and reliable based on the measured or set sample height. The autofocus of the electron beam was realized.

  In addition, when the sample is a semiconductor wafer, the measurement light of the sample height may change the conductivity in the irradiation region of the light beam and affect the measurement value by the electron beam. In the present invention, since the light beam is not directly irradiated to the electron beam measurement point, the sample height is measured in real time with the light beam, while the sample is irradiated with the electron beam to perform the measurement in parallel. .

  1 and 2 show a structural diagram of one embodiment of the present invention. Hereinafter, an apparatus using an electron beam among charged particle beams, here, a scanning electron microscope, one embodiment structure will be described in detail below. Note that charged particle beams (eg, ions) other than electron beams can be configured in the same manner as described below in accordance with the respective charged particle beams.

  FIG. 1A shows a side view, and FIG. 2B shows a bottom view.

  In FIG. 1A, an electron gun 1 is a known electron beam generating device that generates an electron beam 2 accelerated to several hundred volts to several tens of kilovolts.

  The electron beam 2 is an electron beam generated and emitted by the electron gun 1. The electron beam 2 is focused by a focusing lens (not shown).

  The deflecting device 3 deflects the focused electron beam 2 in the X and Y directions (usually two-stage deflection), and the electron beam 2 narrowed by the objective lens 5 is flattened on the sample (photomask) 9. It is a known one that scans (scans in the X and Y directions).

  The electron detector 4 detects secondary electrons / reflected electrons 6 emitted from the sample (photomask) 9 and displays an image (secondary electron image, reflected electron image, etc.) based on the detected signal. It is a publicly known thing.

  The objective lens 5 is a known lens that irradiates the sample (photomask) 9 with the electron beam 2 narrowed down.

  The secondary electrons / reflected electrons 6 are secondary electrons and reflected electrons emitted when the electron beam 2 is scanned on the sample (photomask) 9 in a plane.

  The reflecting mirror 7 is a reflecting mirror that is one of the light guides 7, which reflects the light beam (laser beam) from the sensor head 8 to emit (reflect) toward the sample (photomask) 9, and the sample The light beam reflected at 9 is reflected in the direction of the sensor head 8. As the light guide 7, there is an optical fiber or the like in addition to the reflector and the prism. The light beam output from the sensor head 8 is irradiated toward the sample 9, and the light beam reflected by the sample 9 is guided to the sensor head 8. Anything can be used. The size of the laser beam emitted from the laser head 8 is 0.1 to 1. A diameter of about several mm was used, and a diameter of about 0.6 mm was used in the experiment. For this reason, the reflecting mirror (light guide) 7 only needs to have a reflecting portion of about 0.1 to 2 mm, and a very small one can be used.

  The laser head 8 outputs the light beam from the spectroscope 11 to the light guide (reflecting mirror) 7 to irradiate the sample 9, and takes in the light beam reflected by the sample 9 via the light guide (reflecting mirror) 7. Is sent to the spectroscope 11. The size of the laser beam emitted from the laser head 8 is 0.1 to 1. A diameter of about several mm was used, and a diameter of about 0.6 mm was used in the experiment. The light beam emitted from the laser head 8 is reflected by the reflecting mirror 7 and irradiates the sample 9. The light beam reflected by the sample 9 is reflected by the reflecting mirror 7 and changes in the optical path length when entering the laser head 8. In order to prevent this, the portion to which the laser head 8 and the reflecting mirror 9 are attached (usually the objective lens 5 or its peripheral members) generates an error due to expansion due to thermal change, and thus is not affected by thermal change or has a thermal expansion coefficient. It is necessary to devise so as not to change the optical path length by adopting a small material or a material having the same thermal expansion coefficient.

  The spectroscope 11 is integrated with the laser head 8 and the light guide (reflecting mirror) 7 to constitute a spectral interference type laser displacement measuring apparatus. Hereinafter, for the sake of convenience, the distance between the objective lens 5 and the surface of the sample (photomask) 9 is referred to as height (the height of the sample, Z). Of the spectroscope 11, the sensor head 8 and the light guide 7 constituting the spectral interference type laser displacement measuring device, the size of the sensor head 8 is usually a very small size of several centimeters in length and several mm in width. An optical element is built in the sensor head 8, and an optical fiber for inserting a laser beam from the outside (spectrometer 11) is attached to the end of the sensor head 8. Since the electric circuit does not normally exist inside the sensor head 8, it does not become a source of electric noise. Since the output of the laser beam used is as small as mW or less, it does not serve as a heat source, and the measurement object (for example, the sample 9) and its nearby members are not affected by the temperature. The sensor head 8 is covered with a nonmagnetic metal housing. The lens for laser emission is made of glass, and in the case of the structure shown in FIG. 1, it is usually placed inside the sample chamber and can withstand plasma cleaning. Since the measurement speed of the height of the sample 9 is 200 μs at the maximum, the height measurement can be executed almost in real time.

  Further, the measurement accuracy of the height sensor by the spectroscope 11, the sensor head 8, and the reflecting mirror (light guide) 7 has a measurement resolution of 1 nm, and a measurement reproducibility of 10 nm is obtained. In this embodiment, two height sensors are used. The two height sensors are here arranged symmetrically with respect to the objective lens center. It is not always necessary to arrange them symmetrically.

  The focus control means 12 detects, based on the height data of the sample 9 from the spectroscope 11, an image generated by detecting secondary electrons and reflected electrons when the electron beam 2 scans the surface while irradiating the sample 9. Based on the above, the current of the objective lens 5 is automatically controlled (more precisely, the current of a dynamic focus coil (not shown) provided separately on the objective lens 5) is controlled to control the focus (for example, integration of the differential waveform of the image) Focus control is performed on the focus current having the maximum value. At this time, since the height of the sample (photomask) 9 is precisely measured by the system including the spectroscope 11, the sensor head 8, and the reflecting mirror (light guide) 7, the height of the measured sample 9 is measured. It is only necessary to control the current of the objective lens 5 so as to focus, and to perform focus control slightly more precisely around this, so that automatic focusing can be performed reliably in a short time.

  The image processing means 13 generates an image (secondary electron image, reflected electron image, etc.) based on the signal detected by the electron detector 4.

  The optical fiber 14 is an optical fiber that connects the sensor head 8 and the spectroscope 11 (transmits and receives laser beams).

  FIG. 2B shows a bottom view. Here, as shown in the drawing, the height Ze of the sample at the center of the objective lens 5, the height Z 1 of the sample of the reflecting mirror 7 that receives the light beam from the sensor head (Z 1) 8 and reflects it to the sample 9, and the sensor head. (Z2) The light beam from 8 is received, and the height of the sample of the reflecting mirror 7 that reflects to the sample 9 is set to Z2. Further, the distance from the center (optical axis) of the objective lens 5 to the position of the reflecting mirror 7 of the sensor head (Z1) 8 (the position where the light beam is applied to the sample 9) is measured from Z1, the center (optical axis) of the objective lens 5. The distance of the position of the reflecting mirror 7 of the head (Z2) 8 (the position where the sample 9 is irradiated with the light beam) is defined as Z1.

As above
The height of the sample at the center of the objective lens 5 = Ze
The height of the sample of the reflecting mirror 7 of the sensor head (Z1) = Z1
The height of the sample of the reflecting mirror 7 of the sensor head (Z2) = Z2.
Defined as
The height of the sample at the center of the objective lens Ze = (Z1 + Z2) / 2
(When the sensor heads (Z1) and (Z2) are arranged symmetrically with respect to the optical axis).

  Next, the operation and characteristics of the height measurement of the sample 9 by the spectroscope 11, the sensor head 8, and the light guide (reflecting mirror) 7 according to the present invention will be described.

  (1) The laser beam emitted from the sensor head 8 is emitted directly to the sample (photomask) 9. The traveling direction of the laser beam is bent by 90 ° by the 90 ° reflecting mirror 7, and the surface of the sample 9 is irradiated almost perpendicularly.

  (2) The laser beam reflected by the surface of the sample 9 returns again through the same path, passes through the sensor head 8, and reaches the spectroscope 11 by an optical fiber.

  (3) The spectroscope 11 causes the emitted laser beam (wide wavelength band laser beam) to interfere with the laser beam reflected by the sample 9 to generate distance information (displacement data). Based on this, focus control is performed.

  (4) Unlike the conventional tilt-type height measurement method described above, the method for measuring the height of the sample of the present invention is substantially perpendicular to the sample 9. Since the fluctuation (error) of the measured value is extremely small, the tilt correction of the conventional sample 9 is not necessary, and the usage is easy. In addition, the surface pattern of the sample 9 is hardly affected.

  (5) Further, the laser beam guided from the sensor head 8 to the outside by an optical fiber is taken into the spectrometer 11 outside and converted into a distance (the height of the sample). Although the spectroscope 11 generates heat, it usually does not cause a measurement error because it is not inside the vacuum sample chamber. The data measured by the spectroscope 11 is guided to a personal computer by a communication means such as TCP / IP or USB, and performs a desired process such as storing a correspondence relationship with measurement point coordinates (described later using a flowchart).

  (6) The two sensor heads 8 and the reflecting mirror (light guide) 7 shown in FIGS. 1 and 2 measure the height of a place different from the irradiation position of the electron beam 2 on the sample 9, for example, When the two sensor heads 8 are arranged at the same distance with respect to the center of the objective lens 5, the average value of both output values represents the height of the sample at the irradiation point on the sample 9 of the electron beam 2 (estimation). To do). By performing such calculation with a personal computer (refer to a flowchart described later), the height of the sample at the irradiation point position on the sample 9 of the electron beam 2 can be obtained accurately and in real time without directly measuring.

  (7) Since the distance between the tip of the pole piece of the objective lens 5 and the sample 9 is usually as narrow as several millimeters, it is practically impossible to place a sample height sensor at that position. Then, a reflecting mirror (light guide) 7 can be disposed at a position away from the tip of the pole piece of the objective lens 5, and further, a light guide 7 can be disposed inside the objective lens 9 to be described later by making a hole, A light guide (reflecting mirror, prism, optical fiber, etc.) 7 having a size of about 0.1 to 2 mm can be easily arranged at an arbitrary place, and the height of the sample can be measured with high accuracy in real time.

  3 and 4 show detailed structural views of the present invention. FIG. 3 shows a detailed structure example in which the light guide 7 is arranged outside the objective lens 5, and FIG. 4 shows a detailed structure example in which the light guide 7 is arranged in a hole provided inside the objective lens. Details will be sequentially described below.

  FIG. 3 is a detailed structural diagram (part 1) of the present invention. FIG. 3 shows an example of a detailed structure in which the light guide 7 is arranged outside the objective lens 5.

  FIG. 3A shows a structural example in which the reflector 7 is arranged on the side surface of the objective lens 5 as shown in the figure. In the illustrated structural example, a light beam (laser beam) emitted from the sensor head (Z1) 8 in the right direction is reflected downward by a 90-degree mirror (or prism), and irradiates the sample (photomask) 9 almost perpendicularly. The reflected light beam enters the sensor head (Z1) 8 in the reverse direction. The sensor head (Z1) 8 is connected to the spectrometer 11 shown in FIG. 1 by an optical fiber. The light beam emitted from the spectroscope 11 passes through the sensor head (Z1) 8 and the reflecting mirror 7 and irradiates the sample 9 from the vertical direction, and the reflected light beam returns to the reverse direction and enters the spectroscope 11. In the spectroscope 11, the emitted laser beam (broadband) and the laser beam reflected and returned from the sample 9 are caused to interfere with each other to generate displacement data of the height of the sample 9. As a result, the height Z1 of the sample 9 at the position of the reflecting mirror 7 of the laser head (Z1) 8 can be measured in real time and with high accuracy. Similarly, for the right sensor head (Z2) 8, the height Z2 of the sample 9 at the position of the reflecting mirror 7 of the laser head (Z2) 8 can be measured in real time and with high accuracy.

  FIG. 3B shows a structural example in which three reflecting mirrors 7 are arranged on the side surface of the objective lens 5 as shown. In this case, the heights Z1 and Z2 of the sample at the position of the third reflecting mirror 7 irradiated with light from the vertical direction on the photomask 9 can be measured, and the optical axis of the objective lens 5 is shown in FIG. It is possible to measure the heights Z1 and Z2 of the sample at a closer position.

  FIG. 3C shows a structural example in which the reflecting mirror 7 is arranged on the bottom surface of the objective lens 5 as shown in the drawing. In this case, the heights Z1 and Z2 of the sample at the position of the third reflecting mirror 7 irradiated with the light from the vertical direction on the photomask 9 can be measured, and the optical axis of the objective lens 5 is shown in FIG. It is possible to measure the heights Z1 and Z2 of the sample at a position closer to that.

  The reflecting mirror 7 is as small as about 1 to 2 mm, and the surface or the entire surface is made conductive so as to prevent charge of electrons.

  Further, the reflecting mirror 7 is arranged symmetrically with respect to the optical axis of the objective lens 5, and is arranged so that direction dependency does not occur when the electron beam 2 is scanned while irradiating the sample 9 or a dummy reflecting mirror 7. It is desirable to arrange.

  FIG. 4 is a detailed structural diagram (part 2) of the present invention.

  FIG. 4D shows a structural example in which the reflecting mirror 7 is disposed on the objective lens 5 and the sample (photomask) 9 is irradiated with the light beam that has passed through the central hole of the objective lens 5. In this case, the light beam emitted from the sensor head (Z1, Z2) 8 is substantially applied to the sample (photomask) 9 by using a portion outside the portion of the central hole of the objective lens 5 through which the electron beam 2 passes. Irradiated vertically and reflected light is incident on the sensor head (Z1, Z2) 8, so that the sample heights Z1, Z2 near the position where the electron beam 2 irradiates the sample 9 can be easily measured in real time and with high accuracy. Can be measured.

  FIG. 4 (e) shows that the reflecting mirror 7 is disposed inside a substantially central hole of the objective lens 5 (the existing hole is used if it is not used, otherwise it is a small hole opened for the passage of light rays). An example of a structure in which a sample (photomask) 9 is irradiated with a light beam transmitted through a central hole of the objective lens 5 is shown. Similarly, in this case, the light beam emitted from the sensor head (Z1, Z2) 8 is applied to the sample (photomask) 9 by using a portion outside the portion of the center hole of the objective lens 5 through which the electron beam 2 passes. Irradiation is performed almost vertically and the reflected light beam is incident on the sensor head (Z1, Z2) 8. Therefore, the heights Z1, Z2 of the sample near the position where the electron beam 2 irradiates the sample 9 can be easily increased in real time. It can be measured accurately.

  In FIG. 4F, an optical fiber 15 is used instead of the reflecting mirror 7, and a hole in the center of the objective lens 5 in the vertical direction is used (if there is an existing hole, it is used; otherwise, the optical fiber 15 is opened. A small hole), and the optical fiber 15 is arranged in a hole portion through which the electron beam 2 at the center of the objective lens 5 does not pass, and the light beam emitted from the optical fiber 15 is substantially perpendicular to the sample (photomask) 9. An example of a structure to be irradiated is shown. In this case, the optical fiber 15 is passed through the hole of the objective lens 5, and the light emitted from the sensor head (Z1, Z2) 8 is irradiated from the tip of the optical fiber 15 almost perpendicularly to the sample (photomask) 9, Since the reflected light beam is returned to the sensor head (Z1, Z2) 8 via the optical fiber 15, the heights Z1, Z2 of the sample in the vicinity of the position where the electron beam 2 irradiates the sample 9 can be easily and in real time. Measurement can be performed with high accuracy and a reflecting mirror is not required.

  FIG. 5 shows a focus map creation flowchart of the present invention.

  In FIG. 5, S1 moves the stage to a predetermined coordinate on the mask. As described on the right side, the stage is sequentially moved to predetermined coordinates on nine or more masks symmetrically in the horizontal and vertical directions, and S2 is repeated. For example, as shown in a photomask 9 of FIG. 6 to be described later, the photomask 9 of FIGS. 1 to 4 is not illustrated at 9 points or more of (x0, y0), (x1.y0)... (Xn, yn). The stage is moved and positioned (the position is determined while accurately measuring with a laser interferometer not shown).

  In S2, the height is measured and recorded by the height sensor. This is the height sensor (spectrometer 11, sensor head 8, and light guide 7) shown in FIGS. 1 to 4 in a state where the stage is positioned at a predetermined position on the photomask 9 in S1. The height of the sample at each position is measured with a sensor (hereinafter referred to as a “height sensor”) and recorded, for example, as shown in FIG. 7 described later, the height (Z) is associated with coordinates (X, Y). Record.

In S3, the parameters of the focus map approximation function are fitted. This is an approximate function (for example, Z ² = X ² + Y ² ) based on the data of nine or more positions (x, y) measured and recorded in S1 and S2 and the height Z of the sample at that time. For example, as shown in FIG. 8A, which will be described later, the parameters of the approximate curve of the focus map are fitted.

  In S4, the focus map is completed.

  As described above, the heights of a plurality of positions on the photomask 9 are actually measured with the height sensors of FIGS. 1 to 4 (FIGS. 6 and 7), and the focus map approximation curve is based on these. It is possible to create a focus map (FIG. 8) by fitting the parameters. Thereafter, referring to the focus map, the height information at an arbitrary position on the photomask 9 is read out, and the electron beam is focused automatically at a high speed as will be described later with the read sample height as the center. Is possible.

  The actual apparatus will be described in detail below.

  (1) As described with reference to FIG. 5, the apparatus (optical height sensor) of the present invention can optically measure the height of the sample 9 almost continuously regardless of electron beam irradiation. Therefore, height measurement can be executed from the moment when the sample 9 to be measured is carried into the vacuum chamber. The focus map represents the distance from the tip of the objective lens pole piece to the measurement target (so-called sample height) as a function of the measurement target observation position (X, Y). Since the objective lens 9 is fixed to the top plate, the objective lens 9 is positioned at substantially the same height unless the top plate moves due to a large fluctuation in atmospheric pressure. On the other hand, since the sample 9 to be measured is not necessarily placed horizontally when placed on the sample holder, the sample 9 may be inclined. Further, the stage for moving the sample 9 has characteristics such as yawing, pitching, and rolling, and the height of the sample 9 may slightly change as the stage moves. That is, the change in the height of the sample 9 with respect to the stage position change is given by the combination of the above two values. In particular, the amount of change in the height of the sample that accompanies the stage movement is an eigenvalue of the stage and is known to be reproducible for repeated measurements, and can be described as an intrinsic function.

  (2) Therefore, every time a new sample (photomask) 9 is placed on the sample holder, the tilt amount of the sample is measured and synthesized with a function specific to a known XY stage, so that an arbitrary electron beam irradiation point can be obtained. The height of the sample at can be obtained by calculation.

  (3) For example, the eigenfunction of the stage is calculated as follows.

  The sample is placed on the sample holder, and the height distribution of the coordinates adjacent to the outer periphery of the measurement target is measured with an optical height sensor as much as possible. When the object to be measured is a semiconductor photomask, it is extremely flat. For example, about nine points as shown in FIG. The XY stage is moved to each position, and the height Z of the position is measured by a height sensor and recorded (S1, S2 in FIG. 5). Repeat this several times to find the average value. Next, since the stage-specific function is symmetric with respect to the center of the stage, the offset component of the function is removed using the function. By doing so, it is possible to obtain a function representing the stage-specific height change (S3 and S4 in FIG. 5). With this function, a new measurement object is placed on the holder and several heights are measured to obtain a focus map for this measurement object (FIGS. 5 to 9).

(4) Also, every time a new measurement object is placed on the sample holder, the height distribution of the sample with respect to the XY stage position can be acquired and used as an ad hoc focus map in the measurement. In this case, a focus map including the inclination of the holder to be measured can be obtained. Curve fitting is performed so that the above value can be expressed as a function of a plane so that the height for an arbitrary coordinate can be calculated, and an approximate curve is obtained. As an approximate curve, a function as simple as possible such as a quadratic plane function or a spline function as shown in FIG. 8 is used. By entering values in X and Y of this function, the height at an arbitrary coordinate can be obtained by calculation _.

  FIG. 6 shows an example of focus map measurement points of the present invention. This is an example in which nine or more measurement points are provided on the photomask 9. In this example, the photomask 9 is 15 cm in length and width, and as shown in the figure, 3 × 3 measurement points (x0, y0), (x1, y0), (x2, yo),... Provided as shown.

  FIG. 7 shows an example of the height measurement value of the present invention. Here, the height table corresponds to x and y on the photomask 9 in FIG. 6 and the sample height z (height measurement value) actually measured by the height sensor in FIGS. 1 to 4 at that time. An example stored as shown is shown.

  FIG. 8 shows an example of an approximate curve passing through the measurement point of the present invention. FIG. 8A shows an example of a focus map, and FIG. 8B shows an example of an approximate curve.

In FIG. 8A, the example of the focus map shown in FIG. 8 is measured based on the relationship of the height (z) measured at the position (x, y) on the photomask 9 measured in FIG. An example is shown in which a focus map is obtained for an approximate curve (here, approximate curve Z ² = X ² + Y ² in FIG. 8B) through which a point (x, y, z) passes.

  FIG. 9 shows a height measurement flowchart of the sample of the present invention. This shows a sample height measurement flowchart when the sample height is actually measured.

  In FIG. 9, in S11, the sample is moved to the measurement coordinates (Xn, Yn). This moves the sample (photomask 9 in FIG. 1) to the instructed measurement point (Xn, Yn) on the XY stage (moves while precisely measuring with a laser interferometer).

  In step S12, it is determined whether the measurement point is in an area that can be measured by the two sensors. This is because when the two height sensors (Z1, Z2) shown in FIG. 1 are used and both of these two height sensors (Z1, Z2) are within the measurement region, S12 is YES, and S13 move on. In the case of NO, since one or two of the two height sensors (Z1, Z2) are found not to be within the measurement region (outside the measurement region), the result of S12 is NO, and the process proceeds to S14.

  S13 is YES in S12, and since the two height sensors (Z1, Z2) are found to be within the measurement region, the average value of the two sensors is determined as the height.

  S14 is NO in S12, and since it has been found that the two height sensors (Z1, Z2) are not within the measurement region, it is further determined whether the height of Z1 is OK. Since it has been found that both of the two height sensors (Z1, Z2) are not within the measurement region, it is further determined whether the height of Z1 is OK (within the measurement region). In the case of YES, the height Z1 of the OK height sensor (Z1) and the height Z (X + L, Y) of the position (X + L, Y) of the NG height sensor (Z2) on the focus map The average height (Z1 + Z (X + L, Y)) / 2 is calculated. On the other hand, if NO in S14, the process proceeds to S16.

  S16 is NO in S14, and it is determined that the height of Z1 is NG. Therefore, it is further determined whether the height of Z2 is OK. Since it has been determined that the sensor of Z1 is not within the measurement region among the two height sensors (Z1, Z2), it is further determined whether the height of Z2 is OK (within the measurement region). In the case of YES, the height Z2 of the OK height sensor (Z2) and the height Z (XL) of the position (XL, Y) of the NG height sensor (Z1) on the focus map. , Y), the average height (Z2 + Z (XL, Y)) / 2 is calculated. On the other hand, in the case of NO in S16, since both the height sensors Z1 and Z2 are determined to be NG, it is calculated to be the same as the height Z of the map value (X, Y).

  As described above, the height is measured with the height sensors (Z1, Z2) while the photomask 9 is moved and positioned at the designated measurement point, and if both can be detected, only one average value can be obtained. One is the height of the measured sample, and the one that cannot be measured is the average value of the height on the map. If both cannot be measured, the photomask is indicated in real time and with high accuracy by calculating the height on the map. It becomes possible to measure the height of the upper position.

  FIG. 10 shows an autofocus flowchart (part 1) of the present invention. This shows a flow chart for performing electron beam autofocus at high speed without failure using the value measured by the optical height sensor of the present invention.

  In FIG. 10, S21 sets the electron beam focus value to the search lower limit of the optical height measurement value. As described above with reference to FIGS. 5 to 8, the height of the sample (photomask) 9 is measured, for example, at least nine points to create a focus map of the sample (photomask) 9, and the sample (photomask) The search lower limit (the smallest sample height) of the photomask 9 is obtained, and the electron beam focus value is set to the obtained search lower limit (value).

  In step S22, electron beam scanning and image acquisition are performed. This is because the electron beam is scanned on the sample (photomask) 9 at the electron beam focus value set in S21, secondary electrons (or reflected electrons, absorbed electrons) emitted at that time are detected, and an image is obtained. Generate.

  In step S23, the electron beam focus value is increased by a step width. This increases the electron beam focus value by a predetermined step width.

  In step S24, electron beam scanning and image acquisition are performed.

  S25 determines whether the upper limit of the search range. If YES, the process proceeds to S26. In the case of NO, S23 and subsequent steps are repeated.

  In S26, an in-focus focus value is estimated. This estimates the focus value at the in-focus position for each image acquired when the electron beam focus value is changed with a predetermined step width from the search lower limit to the search upper limit acquired (generated) in S22 and S24. The method is a known contrast method (maximum contrast (focus value when the image is differentiated and the sum is the maximum)), edge tilt method (when the image has the maximum tilt of the edge of the line profile of the image) In other words, a known value such as an FFT method may be used.

  As described above, an image of the sample (photomask) 9 is acquired while changing the electron beam focus value with a predetermined step width from the search lower limit to the search upper limit of the optical height measurement value of the present invention, and the focal point thereof is obtained. By estimating the focus value and setting it to the estimated focus value, the automatic focusing by the electron beam is executed only in the limited height range from the upper limit to the lower limit of the height of the sample (photomask) 9 High-speed and reliable automatic focusing becomes possible.

  The actual apparatus will be described below.

  The value measured by the optical height sensor corresponding to the coordinates to be measured is obtained (obtained from the real time or focus map). Since this value is the just focus value obtained by the optical height sensor, there is no guarantee that it is necessarily the same as the just focus of the electron beam autofocus. Therefore, in order to obtain electron beam autofocus, a focus range (for example, plus or minus 0.5 microns) is set, and the lower limit value of minus 0.5 microns is added to the above-mentioned optical just focus value. Is set (S21 in FIG. 10). In this state, image information necessary for performing autofocus is acquired by electron beam scanning (S22 in FIG. 10). Next, the value of the electron beam focus is increased by a predetermined value (S23 in FIG. 10). In this state, electron beam scanning is performed in the same manner as described above to acquire image information (S24 in FIG. 10). This operation is repeated until the focus intensity reaches the upper limit of the focus swing (S5 in FIG. 10). When all the information for obtaining the electron beam in-focus is gathered, the in-focus state is obtained by calculation using an in-focus algorithm such as the contrast method or the maximum edge tilt method (S26 in FIG. 10). As described above, the focused state of the electron beam can be obtained quickly and accurately without failure.

  FIG. 11 shows a structural diagram of another embodiment of the present invention. This FIG. 11 uses the sample height value measured by the optical height sensor of the present invention so that the tip of the pole piece of the objective lens 5 and the height of the surface of the sample (photomask) 9 are always constant. The second embodiment is characterized in that the Z stage 22 is controlled, and thereafter, two-stage autofocus is performed using electron beam autofocus. A Z stage 22 for realizing this is added to the structure shown in FIGS. Since others are the same, description is abbreviate | omitted.

  In FIG. 11, an XY stage 21 precisely moves a photomask (sample) 9 in the X and Y directions, and measures the coordinates in the X and Y directions with a laser interferometer (not shown). It is driven by a servo motor.

  The Z stage 22 moves the photomask (sample) 9 accurately in the Z direction. Here, a predetermined voltage is applied to the piezoelectric elements A, B, and C, and the elements are expanded and contracted to expand in the Z direction. It is a mechanism to move to. Here, the sample holder 23 is held by three piezoelectric elements, a predetermined voltage is applied to each of them, and the distance (the height of the sample) between the photomask (sample) 9 and the objective lens 5 is predetermined. The movement is controlled so as to be a value.

  The sample holder 23 holds a photomask (sample) 9.

  The XY stage control means 31 controls the XY stage 21 and controls the movement of the photomask (sample) 9 to a designated position (X, Y) based on a signal from the laser interferometer.

  The Z stage control means 32 controls the Z stage 22 (controls by applying predetermined voltages to the piezoelectric elements A, B, and C, respectively), and controls the movement of the photomask (sample) 9 to the designated position (Z). To do. Since the Z movement (Z-axis drive) has vibration resistance, a piezoelectric element that can generate a large force is used. For example, a displacement of several centimeters in thickness and several centimeters in thickness is obtained at 100 V, and approximately several tens of microns can be obtained. The sample holder 23 is supported from the plane of the XY stage 21 serving as a base with three-point support. Each of the three piezoelectric elements A, B, and C has a high-voltage amplifier, and can be controlled independently. Therefore, by using the data obtained when the focus map is created in advance, the tilt component of the photomask (sample) 9 is extracted and the piezo piezoelectric element A, so that the displacement necessary for canceling the tilt occurs. By appropriately applying voltages to B and C, the surface Z of the photomask 9 can be made perpendicular to the electron beam irradiation axis. In this state, control is further performed so that the height of the photomask 9 becomes a desired height.

  The sample height information processing means 33 controls the optical height sensor composed of the spectroscope 11, the sensor head 7, and the reflecting mirror (light guide) 7, and measures the height of the photomask (sample) 9. is there.

  The auto-focus control means 34 detects the focus signal supplied to the objective lens 5 from the search lower limit to the search upper limit, which is generated by detecting a signal such as secondary electrons when the photomask (sample) 9 is planarly scanned with the electron beam 2. Based on the image associated with the current value, the current value of the objective lens at the time of focusing is estimated (actually, the current value passed through a dynamic coil provided separately from the objective lens 5), and the estimated objective current value Is set to

  The image processing means 35 generates an image (secondary electron image, reflected electron image, etc.) based on the signal detected by the electron detector 4.

  The overall control means 36 controls the entire system shown in FIG.

  Based on the above structure, a focus map of the photomask 9 is created as described with reference to FIGS. By applying predetermined voltages to the three piezo elements A, B, and C constituting the Z stage 22 so as to be constant at any location, the height of the sample (photomask) 9 and the sample (photomask) ) The inclination of 9 can be corrected so that the height of the sample can be always kept horizontal and constant. Then, after the sample height is fixed and the sample is corrected horizontally by the Z stage 22, the electron beam is automatically focused between the search lower limit and the search upper limit, and a focused image can be acquired quickly and reliably. It becomes possible.

  FIG. 12 shows an autofocus flowchart (part 2) of the present invention. This is a case where the electron beam autofocus is performed under the structure of FIG. 11 described above.

  In FIG. 12, in S31, the Z stage is moved so that the height of the sample is constant. This is because a predetermined voltage is applied to each of the three piezoelectric elements A, B, and C constituting the Z stage 22 of FIG. 11 to correct the height of the sample 9 and its inclination, and the height of the sample 8 is constant. And the sample 8 should be horizontal.

  In S32, the electron beam focus value is set to the search lower limit of the specified value (search lower limit of the optical height measurement value). As described above with reference to FIGS. 5 to 8, the height of the sample (photomask) 9 is measured, for example, at least nine points to create a focus map of the sample (photomask) 9, and the sample (photomask) The search lower limit (the smallest sample height) of the photomask 9 is obtained, and the electron beam focus value is set to the obtained search lower limit (value).

  In step S33, electron beam scanning and image acquisition are performed. This is because the electron beam is scanned on the sample (photomask) 9 at the electron beam focus value set in S32, secondary electrons (or reflected electrons, absorbed electrons) emitted at that time are detected, and an image is obtained. Generate.

  In step S34, the electron beam focus value is increased by a step width. This increases the electron beam focus value by a predetermined step width.

  In S35, electron beam scanning and image acquisition are performed.

  S36 determines whether the upper limit of the search range. If YES, the process proceeds to S37. In the case of NO, S34 and subsequent steps are repeated.

  In S37, an in-focus focus value is estimated. This estimates the focus value at the in-focus position for each image acquired when the electron beam focus value is changed by a predetermined step width from the search lower limit to the search upper limit acquired (generated) in S33 and S35. As the method, a known method such as a known contrast method, an edge tilt method, or an FFT method may be used.

  As described above, after the sample height is moved so as to be constant (height is constant and horizontal) by controlling the Z stage 22, from the search lower limit to the search upper limit of the optical height measurement value of the present invention. The image of the sample (photomask) 9 is acquired while changing the electron beam focus value with a predetermined step width, and the in-focus focus value is estimated and set to the estimated in-focus focus value. After moving on the Z stage at a constant and horizontal height, autofocusing with a limited height range from the upper limit to the lower limit of the height of the sample 9 is performed automatically and reliably by high speed. Is possible.

  The procedure and features in the actual apparatus will be described below.

  (1) First, the height of the sample 9 is moved uniformly and horizontally on the Z stage 22 (S31 in FIG. 12).

  (2) Next, the combination of detector signals that maximizes the image contrast is selected.

  (3) Set so that the signal can be captured under the conditions of (2), and change the focus intensity such as the objective lens 5 or the voltage applied to the sample 9 to change the focus intensity, such as under focus, near focus, over focus, etc. The captured image signal is captured (S32 to S36 in FIG. 12).

  (4) The contrast of these images is evaluated with respect to the focus intensity, and a function indicating the relationship between the focus intensity and the contrast value is obtained.

  (5) Using this function, an operation for finding the maximum minimum or maximum / minimum is performed, and the focus intensity estimated to realize the state with the highest contrast in the function is set as the focal point (S37 in FIG. 12).

  (6) By setting the focus of the actual electron microscope to this focus intensity, a focused image can be obtained.

  (7) Similarly, a function indicating the relationship between the focus intensity and the highest spatial frequency included in the image is obtained by acquiring a plurality of images obtained by changing the focus intensity using FFT (spatial frequency analysis) or the like. Can be obtained. The focus intensity including the highest spatial frequency may be set as the focal point by calculating the maximum minimum and maximum / minimum using this function. In addition to the above method, any method widely known in the world can be used as the method for finding the focal point, and the scope of the present invention is not limited to this embodiment.

  (8) When the distance between the tip of the objective lens pole piece and the surface of the sample 9 is different, the electron beam focus can be obtained by changing the strength of the objective lens 5. However, unlike the optical system, in the electron optical system, the image rotates when the focus is changed. When the image rotates, image distortion occurs depending on the location. Therefore, various corrections need to be made in order to perform dimension measurement. In the present invention, the distance between the pole piece of the objective lens 5 and the surface of the sample 0 (the height of the sample) is measured in advance by an optical height sensor, and the distance is made constant after being parallelized. Then, the Z stage 22 is driven to change the height of the sample 9. Thereafter, in order to correct a fine focus error, electron beam focusing is performed. In this way, image rotation due to focus hardly occurs. Even if it occurs, it becomes a very small value, so that the measurement error caused by the rotation correction can be reduced.

  (9) In particular, recently, not only the distance measurement between two points, but also an increasing number of usages that accurately read the image itself and apply it to an optical simulation. In these cases, if the image is rotated or distorted, it causes a simulation error. In the structure of FIG. 11 of the present invention, these error factors can be made extremely small. The effect is particularly great when the FOV is large.

  FIG. 13 shows an autofocus flowchart (part 3) of the present invention.

  In FIG. 13, S41 sets a sample to the reference height. This is set by the Z stage 22 so that the sample 9 is set to a predetermined reference height (the height of the sample 9 is constant and the sample 9 is horizontal).

  In step S42, the focus current of the objective lens is measured. This is to measure (estimate) the focus current value of the objective lens at the time of focusing based on an image obtained by scanning the sample 9 with an electron beam in a plane with the sample 9 set to a reference height in S41. To do.

  In S43, the sample is exchanged.

  In S44, the sample is adjusted to the reference height on the Z stage. The sample after the replacement in S4 is adjusted to the reference height (the height of the sample 9 is constant and horizontal) on the Z stage.

  In S45, the resolution is checked with the line profile. In S44, the new sample 9 is adjusted to the reference height in S44, and the line profile of the sample 9 is acquired by the electron beam and its resolution is checked (for example, the resolution of the line profile of the acquired image is the current resolution). Check if it is sufficient for the intended use).

  In S48, it is determined whether there is a charge. This is to determine whether the resolution checked by the line profile in the check of S45 is insufficient and the resolution is lowered due to the influence of the sample 9 or the nearby charge. In the case of YES, only the charge is corrected in S49 (the current of the objective lens corresponding to the charge is corrected). On the other hand, if NO in S48, the process ends.

  S46 stores resolution information (including sample height and horizontal information (Z stage information)) in the line profile checked in S45.

  In S47, the information (line profile resolution, Z stage information (sample height and horizontal information)) recorded in S46 is used next time.

  As described above, in a state where the sample 9 is set to the reference height by the Z stage 22 and the focus current of the objective lens is measured, the sample 9 is replaced and then the sample 9 is set to the reference height by the Z stage 22 and the line profile is set. The resolution is checked to determine if there is a charge, etc., and if it is found that there is a charge, etc., by correcting only the charge, fast and stable automatic focus is achieved when the sample 9 is replaced. Can be done.

  FIG. 14 shows an example of image acquisition by the electron beam of the present invention.

  14A shows a top view, and FIG. 14B shows an example of an emphasis signal.

  In FIG. 14A, detection devices A, B, C, and D are examples of detectors arranged symmetrically on the lower surface of the objective lens 5 in FIGS. Then, an electron detector is shown.

  FIG. 14B shows an example in which signals A, B, C, and D detected by the four detection devices A, B, C, and D shown in FIG.

  Hereinafter, characteristics of the actual apparatus will be described.

  (1) When performing electron beam autofocus, there is a sample 9 having a very small contrast. For example, a nanoimprint template made of quartz, a thin film on a photomask, or a resist that covers the entire surface. In the case of the sample in FIG. 1, since even an image cannot be seen in a normal SEM top-down image, it is impossible to perform autofocus using a normal SEM signal.

  (2) In such a case, auto-focusing is facilitated by using a signal obtained when the sample 9 is viewed obliquely. For this purpose, as shown in FIG. 14, for example, four electron detectors A, B, C, and D are arranged so that signal electrons depending on the angle generated from the sample 9 can be detected. It is desirable that the arrangement position is axisymmetric as viewed from the primary electron axis. For example, a difference image in the Y direction can be created by subtracting a C + D signal from an A + B signal. Alternatively, a difference signal in the X direction can be created by subtracting the B + D signal from the A + C signal. When the detected signal electrons are processed as described above, the same effect as that obtained when the sample 9 is viewed from an oblique direction can be obtained. Therefore, an image having a clearer pattern edge than a normal SEM image observed from the front can be obtained.

  (3) Even when the contrast enhancement method as described above is employed, the edge contrast can be observed in the vicinity of the electron beam in-focus, but if it is further away, it is completely the same as the front image. The edge cannot be observed. That is, it is rough and it is impossible to find out the in-focus state by examining the focus intensity of the objective lens.

  (4) If the optical height sensor of the present invention is used, the electron beam focus can be applied after reaching the focal point near 0.1 micron, so that the edge can be reliably captured and the auto focus is The probability of success can be greatly improved.

  FIG. 15 shows an arrangement example of the sensor head of the present invention.

  In FIG. 15, the sensor head 8 described above is arranged at any one position or a plurality of positions described as sensor placement positions, and the light emitted from the sensor head 8 is guided to a light guide (reflective) (not shown). The height of the photomask 9 is optically measured by irradiating the photomask 9 vertically with a mirror (optical fiber, etc.) 7 and making the reflected light beam enter the sensor head 8 with a light guide (reflector mirror, etc.) 7. can do. The sensor head 8 is connected to the spectroscope 11 shown in FIG. 1 by an optical fiber, and the sample 9 is interfered with the laser beam (broadband) reflected by the spectroscope 11 and the laser beam returned. It becomes possible to accurately measure the height.

  The entire photomask 9 can be measured with an XY stage having a stroke of 20 cm with one sensor head 8 in the state shown in the figure.

  FIG. 16 is an explanatory diagram of the height estimation region of the present invention.

  In FIG. 16, the area for estimating the mask height indicates an area in which the height of the mask (sample) 9 can be estimated using the two sensor heads (Z1) 8 and the sensor head (Z2) 8.

  The mask outer shape schematically shows an example of the outer shape of the sample (photomask) 9.

The region that can be measured by the two optical height sensors is a region in which the height of the irradiation position of the electron beam can be estimated (measured) by the two sensor heads (Z1) 8 and the sensor head (Z2) 8. The estimated (measured) value is indicated on the right side as follows: Zc = (Z1A + Z2B) / (A + B)
Zc: Height of the sample at the objective lens position (electron beam irradiation position) A, B: Sample the light beam from the sensor head (Z1) and sensor head (Z2)
Distance from the electron beam irradiation center position on the sample 9 when irradiating the sample 9 Z1A, Z1B: It can be obtained from the height of the sample 9 at the distances A and B.

  For the principle of the height sensor used in the experiment of the present invention, refer to the following URL of the Keyence sensor.

  http://www.keyence.co.jp/henni/laser_henni/si/

FIG. 1 is a structural diagram (part 1) of an embodiment of the present invention. It is 1st Embodiment structural drawing (the 2) of this invention. FIG. 3 is a detailed structural diagram (part 1) of the present invention. It is a detailed structure figure (the 2) of this invention. It is a focus map creation flowchart of the present invention. It is an example of the focus map measurement point of this invention. It is an example of the height measurement value of this invention. It is an example of an approximate curved surface which passes the measurement point of this invention. It is a height measurement flowchart of the sample of this invention. It is an autofocus flowchart (the 1) of the present invention. It is another Example structure figure of this invention. It is an autofocus flowchart (the 2) of the present invention. It is an autofocus flowchart (the 3) of this invention. It is an example of the image acquisition by the electron beam of this invention. It is an example of arrangement of the sensor head of the present invention. It is explanatory drawing of the height estimation area | region of this invention.

1: electron gun 2: electron beam 3: deflecting device 4: electron detector 5: objective lens 6: secondary electron / reflected electron 7: reflecting mirror, light guide, optical fiber 8: sensor head 9: photomask, sample 11 : Spectroscope 12: Focus control means 13: Image processing means 14, 15: Optical fiber 21: XY stage 22: Z stage 23: Sample holder 31: XY stage control means 32: Z stage control means 33: Sample height information processing means 34: Autofocus control means 35: Image processing means 36: Overall control means

Claims (9)

In a charged particle beam apparatus that scans a charged particle beam while squeezing a charged particle beam and generating an image based on the signal emitted, reflected, and absorbed at that time,
An objective lens and a scanning system for scanning while squeezing the charged particle beam finely and irradiating the sample are provided. A light guide that irradiates the sample and receives the light beam reflected by the sample; and
A sensor head for irradiating the light guide with light and receiving the light emitted from the light guide;
A spectroscope that emits light to the sensor head and receives light emitted from the sensor head, and detects an irradiation position of the light on the sample based on the emitted light and the received light. Height measuring device in charged particle beam equipment.   The height measuring device in the charged particle beam device according to claim 1, wherein the light guide and the sensor head are integrated.   2. The light guide device according to claim 1, wherein a reflection mirror, a prism, or an optical fiber is attached to a portion that is visible from the sample, and the sample is irradiated with the light beam and the light beam reflected by the sample is received. 3. A height measuring device in the charged particle beam device according to 2.   4. The height measuring device in the charged particle beam apparatus according to claim 1, wherein the light beam is irradiated on the sample substantially perpendicularly to the sample.   The height measuring device in the charged particle beam device according to any one of claims 1 to 4, wherein a plurality of the light guides are provided.   6. The height measuring device in a charged particle beam apparatus according to claim 5, wherein the height of the sample at the electron beam irradiation position is obtained based on the height of each sample of the plurality of light guides.   7. The height of the sample at a plurality of locations is measured with the one or a plurality of light guides, respectively, and the relationship between the location of the sample and the height is measured in advance. A height measuring device in the charged particle beam device according to claim 1.   The location of the sample irradiated by the charged particle beam based on the height of each sample measured by the one or more light guides or the height of the sample measured and stored in advance in claim 7 8. A height measuring device in a charged particle beam apparatus according to claim 1, further comprising a height adjusting mechanism for adjusting the height of the charged particle beam to a constant value.   Based on the height of the sample measured by the one or more light guides, or the height of the sample set to a constant value based on the measurement, autofocus with a charged particle beam is performed at high speed and reliably. 9. The autofocus device in the charged particle beam device according to claim 1, wherein the focused image is generated by generating a focused image.