JP6751183B2 - Auto focus device - Google Patents

Description

The present invention relates to an autofocus device.

According to Moore's law, semiconductor devices are shrinking every year, and the minimum feature size of cutting-edge devices is about to be less than 20 nm even in mass production devices. To achieve a small feature size, an exposure technique capable of forming a smaller pattern is needed.

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, which is said to originate from Japan, has been researched and developed for practical use in ASML and the like for more than 10 years. Although the optical system of the main body of the exposure apparatus is almost completed, the current EUV exposure apparatus cannot obtain the light source power of 100 W to 200 W which is required for economical mass production. It was skipped.

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

In addition to the memory device having a simple structure, it is necessary to reduce the pattern of the CPU and the logic device in order to expand the function and reduce the power consumption. Since a logic device uses a complicated pattern that does not repeat, a considerably complicated pattern is required to make the logic device by double or triple exposure. A very complicated calculation is required to divide a pattern that can be originally realized by one exposure into a pattern on two photomasks so that it can be used by a plurality of exposures. Depending on the pattern, the necessary results may not be obtained due to the divergence of division calculation.

In order to avoid these complications, a lithographic facilitation technology called Complementary Lithography, which is mainly proposed by Intel, is about to be used. This exposure method is characterized by using a pattern in which a complicated logic circuit is reduced to a simple L&S pattern such as a memory circuit. By doing this, the complex logic device pattern is limited to only the L&S pattern that is the most easily exposed and the process of cutting the line, so there is no need for complicated pattern division calculation, the process is simple, It is said that the top reaches about 8 nm.

On the other hand, as described above, if the life of the 193 nm exposure technique is extended, the photomask used for it will increase by the number of exposures for each layer, requiring more mask inspections and precise dimension measurements than ever before. Become. For example, in double patterning, since two photomasks are used one after another, the absolute position accuracy and alignment accuracy of the line formed on the mask between the two masks are more important than ever. Optical correction for exposing finer patterns is also complicated and precise. A mask or the like using inverse lithography uses even higher diffraction heights, so the pattern size used for correction is even smaller.

Electron microscope technology is indispensable to check whether these masks are made in correct size, but autofocus technology is very important for acquiring high-definition images. However, when the conventional autofocus is used, there is a problem that the autofocus fails depending on the mask. If auto-focus fails, not only cannot the measurement be performed, but an incorrect measured value is provided to the process control, which causes an additional decrease in yield and suffers a large loss.

For the purpose of assisting the autofocus of the conventional electron beam optical system, an optical height measuring method for measuring the sample height at 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 there is a gap of only a few millimeters. Conventionally, in order to measure the distance, an LED or a laser beam is obliquely incident to hit the electron beam irradiation point, and the position of the reflected light is detected by an optical sensor such as a CCD to measure the height of the sample. The method has been adopted.

However, since the incident degree of the light beam and the height measurement resolution are in a proportional relationship, there is a problem that the height measurement resolution is hardly obtained when the incident angle is as small as 1 degree.

Further, if the sample is tilted, it is indistinguishable from the change in sample height, and there is a problem that a complicated correction for separating the height component and the sample tilt component is required. The measurement may become unstable depending on the pattern or material of the sample surface.

On the other hand, since the optical path length of the LED or laser light source or the optical system that constitutes them is as large as several tens of centimeters, deformation of the top plate due to atmospheric pressure changes, optical path length fluctuation due to temperature expansion, incident angle fluctuation, etc. There is also a problem that the measurement accuracy is lowered because it is easily caused by the change. 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 additional problems such as high cost and difficulty in maintenance.

Further, in the conventional system, since the system itself generates heat, there is a problem that the temperature of the peripheral portion of the device changes with use time, which affects the measured value. When these are combined, there is a problem that only a measurement accuracy of about 1 micron can be achieved at best.

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 high-speed, precise and reliable autofocus.

Therefore, the present invention is a charged particle beam apparatus that generates an image based on signals emitted, reflected, and absorbed at the time of scanning while irradiating a sample with a charged particle beam being narrowed down. An objective lens and a scanning system are provided to squeeze the sample down while irradiating the sample, and the light is directed toward the sample at the outer surface part of the objective lens or the hole part provided in the objective lens that is visible from the sample, A light guide that receives the reflected light, a sensor head that irradiates the light guide with the light and that receives the light emitted from the light guide, and a light that emits the light to the sensor head and is emitted from the sensor head. A spectroscope for receiving a light beam and 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.

Further, the light guide is equipped with a reflecting mirror, a prism, or an optical fiber in a portion visible from the sample so as to irradiate the sample with a light beam and receive the light beam reflected by the sample.

Further, when the light beam is applied to the sample, the light beam is applied almost vertically to the sample.

Also, a plurality of light guides are provided.

Further, the height of the sample at the electron beam irradiation position is determined 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 by one or a plurality of light guides, and the relationship between the location of the sample and the height is measured in advance.

In addition, the height of the location of the sample irradiated by the charged particle beam is 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 adjusting mechanism is provided for adjusting to a constant value.

Also, based on the height of the sample measured by one or a plurality of light guides or the height of the sample set to a constant value based on the measurement, autofocusing by the charged particle beam can be performed at high speed and reliably. It does so and produces an in-focus image.

According to the present invention, the height of a sample near an electron beam irradiation point is directly measured and set by one or a plurality of optical height sensors, and based on the measured or set height of the sample, a precision automatic measurement by an electron beam is performed. With focus, it becomes possible to set a stable ultra-high precision height of more than 0.1 micron with an extremely simple configuration for the height of the sample, and it is fast and precise based on the measured or set sample height. In addition, the electron beam can be surely autofocused.

Further, in the case where the sample height is a semiconductor wafer, the measurement beam of the height of the sample may change the conductivity in the irradiation region of the beam and may affect the measurement value by the electron beam. In the present invention, since the light beam does not directly irradiate the electron beam measurement point, the height of the sample is measured (estimated) with the light beam in real time, while the sample is irradiated with the electron beam to perform the measurement in parallel. You can

The actual device will be described in detail below.

(1) By using the present invention, as compared with the case where only the conventional electron beam autofocus is used, autofocus failure does not occur, and a high-speed and accurate electron beam focus state can be realized. Before performing electron beam autofocus, it is possible to create a state that is close enough to the electron beam in-focus state, so the range in which electron beam autofocus searches for the focus value can be reduced to about 1/10 or less of the conventional range. It is possible, and autofocus can be performed at 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) Unlike the conventional optical height sensor, it is very compact and easy to mount and maintain. Since the height is directly measured, the inclination correction of the sample 9 which is necessary in the conventional method is unnecessary. Since the measurement at the electron beam irradiation point is not required, it is not necessary to push the sensor into the narrow space between the tip of the pole piece of the objective lens 5 and the surface of the sample 9.

(4) Electromagnetic waves and heat are not generated during sensor operation, so measurement can be very stable.
Since the material is crow and metal, vacuum contamination can be avoided. Long life with no moving parts.
Since the distance between the sensor and the measurement point is short, the influence of disturbance is small.

(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 changes in the external environment, the change can be measured in real time. , Electron beam autofocus can be easily succeeded.

(6) Even if two optical height sensors cannot be measured in real time at the same time, the focus map created in advance can be used to perform height measurement similar to that in almost real time. I can.

(7) Even for the sample 9 that is difficult to autofocus with only the electron beam image, it is possible to measure the height with an optical height sensor first and bring it to a state close to the in-focus state. Beam focus can be changed. As a result, it becomes easy to obtain an electron beam focused state in a three-dimensional object or a measurement target with low edge contrast.

(8) When the Z stage 22 supporting three points is used, the inclination of the sample 9 can be set to 0 and the height of the sample 9 can be made constant, and the electron beam irradiation can be made vertical. become. This makes it possible to acquire a more accurate electron beam image.

According to the present invention, the height of a sample in the vicinity of an electron beam irradiation point is directly measured and set by one or a plurality of optical sensors, and precise autofocus by an electron beam is performed based on the measured or set height of the sample. With the extremely simple configuration of the sample height, it becomes possible to set a stable ultra-high precision height exceeding 0.1 micron, and at the same time, it is fast, precise and reliable based on the measured or set sample height. It is possible to automatically focus the electron beam.

Further, in the case where the sample height is a semiconductor wafer, the measurement beam of the height of the sample may change the conductivity in the irradiation region of the beam and may affect the measurement value by the electron beam. In the present invention, since the light beam does not directly irradiate the electron beam measurement point, the height of the sample is measured in real time by the light beam, while the sample is irradiated by the electron beam and the measurement is performed in parallel. ..

1 and 2 show a structural diagram of one embodiment of the present invention. An apparatus using an electron beam among charged particle beams, here, a scanning electron microscope will be described in detail below sequentially with reference to a first embodiment structure. It should be noted that charged particle beams (such as ions) other than electron beams can be configured in the same manner as described below according to each charged particle beam.

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

In FIG. 1A, an electron gun 1 is a known one that generates an electron beam, and generates an electron beam 2 accelerated to several hundreds V to several tens KV.

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 (normally two-stage deflection), and the electron beam 2 narrowed down by the objective lens 5 is flattened on a sample (photomask) 9. It is a known one for scanning (scanning in the X and Y directions).

The electron detector 4 detects secondary electrons/reflected electrons 6 and the like 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 known one.

The objective lens 5 is a known one that irradiates a sample (photomask) 9 with a finely focused electron beam 2.

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

The reflecting mirror 7 is a reflecting mirror that is one of the light guides 7, and reflects the light beam (laser beam) from the sensor head 8 and radiates (reflects) it toward the sample (photomask) 9, and the sample. The light beam reflected at 9 is reflected toward the sensor head 8. The light guide 7 includes an optical fiber in addition to the reflector and the prism. The light beam output from the sensor head 8 is directed toward the sample 9, and the light beam reflected by the sample 9 is guided to the sensor head 8. If it does, what kind of thing may be sufficient. The size of the laser beam emitted from the laser head 8 is 0.1 to 1. The diameter was about several mm, and in the experiment, a diameter of about 0.6 mm was used. Therefore, the reflecting mirror (light guide) 7 may have a reflecting portion of about 0.1 to 2 mm, and a very small reflecting mirror 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 captures the light reflected by the sample 9 via the light guide (reflecting mirror) 7. Is transmitted to the spectroscope 11. The size of the laser beam emitted from the laser head 8 is 0.1 to 1. The diameter was about several mm, and in the experiment, a diameter of about 0.6 mm was used. The light beam emitted from the laser head 8 is reflected by the reflecting mirror 7 to irradiate the sample 9, and 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. To avoid this, the portion where the laser head 8 and the reflecting mirror 9 are attached (usually the objective lens 5 or members around it) causes an error due to expansion due to thermal change, so is not affected by thermal change, or has a coefficient of thermal expansion. It is necessary to adopt a small material or a material having the same coefficient of thermal expansion so that the optical path length does not change.

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 device. Hereinafter, for convenience, the distance between the objective lens 5 and the surface of the sample (photomask) 9 is referred to as the height (height of the sample, Z). Of the spectroscope 11, the sensor head 8 and the light guide 7 which compose the spectral interference type laser displacement measuring device, the sensor head 8 is usually very small with a length of several centimeters and a width of several mm. An optical element is built in the inside of the sensor head 8, and an optical fiber for entering a laser beam from the outside (spectrometer 11) is attached to an 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 low as mW or less, it does not serve as a heat source, and the measurement target (for example, the sample 9) and members in the vicinity thereof are not affected by the temperature. The sensor head 8 is covered with a nonmagnetic metal housing. The lens for emitting the laser 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 height of the sample 9 can be measured at a maximum speed of 200 μs, the height can be measured almost in real time.

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

An image generated by the focus control means 12 by detecting secondary electrons and backscattered electrons when the electron beam 2 scans the surface of the sample 9 while scanning the surface based on the height data of the sample 9 from the spectroscope 11. Based on the above, the current of the objective lens 5 is automatically controlled (to be precise, the current of a dynamic focus coil (not shown) separately provided in the objective lens 5 is controlled) to perform focus control (for example, integration of a differential waveform of an image). The focus current is adjusted to the maximum focus current). 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 set to the measured height. It suffices to control the current of the objective lens 5 so as to focus, and slightly finely refocus control around this current, so that automatic focusing can be performed in a short time and reliably.

The image processing means 13 produces 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/receives a laser beam).

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

As mentioned above,
・Height of sample at center of objective lens 5 = Ze
・Height of the sample of the reflecting mirror 7 of the sensor head (Z1)=Z1
・Height of the sample of the reflecting mirror 7 of the sensor head (Z2)=Z2
Is defined as
・Height of sample at the center of objective lens Ze=(Z1+Z2)/2
Can be calculated (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 right beside the sample (photomask) 9. The direction of travel of this laser beam is bent by 90° by the 90-degree reflecting mirror 7, and the laser beam is irradiated almost perpendicularly to the surface of the sample 9.

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

(3) The spectroscope 11 causes the emitted laser beam (a laser beam in a wide wavelength band) and the laser beam reflected by the sample 9 to interfere with each other to generate distance information (displacement data). Focus control is performed based on this.

(4) Unlike the above-described conventional tilt-type height measuring method, the sample height measuring method of the present invention has an incident angle substantially perpendicular to the sample 9, so Since the fluctuation (error) of the measured value is extremely small, the inclination correction of the conventional sample 9 is not necessary, and the usage is easy. Further, the surface pattern of the sample 9 is not easily affected.

(5) Further, the laser beam guided from the sensor head 8 to the outside by an optical fiber is taken into the spectroscope 11 located outside and converted into a distance (height of the sample). The spectroscope 11 generates heat, but since it is not normally inside the vacuum sample chamber, it does not cause a measurement error. The data measured by the spectroscope 11 is guided to a personal computer by a communication means such as TCP/IP or USB, and is subjected to desired processing such as storing the correspondence with the measurement point coordinates (which will be 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 the electron beam 2 at a position different from the irradiation position on the sample 9. 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 the output values of the two sensor heads 8 represents the height of the irradiation point of the electron beam 2 on the sample 9 (estimation). To). By performing such a calculation with a personal computer (see a flow chart described later), the height of the sample at the irradiation point position of the electron beam 2 on the sample 9 can be obtained accurately and in real time without directly measuring it.

(7) Further, since the distance between the tip of the pole piece of the objective lens 5 and the sample 9 is usually as small as several mm, it is practically impossible to dispose the height sensor of the sample at that position. Then, a reflecting mirror (light guide) 7 can be arranged at a position away from the tip of the pole piece of the objective lens 5, or a light guide 7 can be arranged inside the objective lens 9 by making a hole in it, which will be described later. 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 any place, and the height of the sample can be measured with high accuracy and in real time.

3 and 4 show detailed structural diagrams of the present invention. 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. The details will be sequentially described below.

FIG. 3 is a detailed structural diagram (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 illustrated. In the illustrated structural example, a light beam (laser beam) emitted to the right from the sensor head (Z1) 8 is reflected downward by a 90-degree mirror (or prism) and is irradiated onto a sample (photomask) 9 almost vertically. Then, the reflected light beam enters the sensor head (Z1) 8 in the opposite direction. The sensor head (Z1) 8 is connected to the spectroscope 11 of 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 is applied to the sample 9 from the vertical direction, and the reflected light beam returns to the opposite direction and enters the spectroscope 11. The spectroscope 11 causes the emitted laser beam (broadband) and the laser beam reflected by the sample 9 and returned 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 as well, 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 the figure. In this case, the heights Z1 and Z2 of the sample at the position of the third reflecting mirror 7 where the photomask 9 is irradiated with light rays from the vertical direction can be measured, and the optical axis of the objective lens 5 can be measured by the optical axis of FIG. It is possible to measure the heights Z1 and Z2 of the sample at a position closer than that.

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

The reflecting mirror 7 is as small as about 1 to 2 mm, and the surface or the whole of the reflecting mirror 7 is made conductive so as to prevent electron charging.

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

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

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

FIG. 4E shows that the reflecting mirror 7 is disposed inside the hole (or a small hole that has been formed to allow the light beam to pass therethrough) in the center of the objective lens 5 if the existing hole is used. An example of a structure in which a sample (photomask) 9 is irradiated with a light beam that has passed through a hole in the center of the objective lens 5 is shown. Also in this case, similarly, the light beam emitted from the sensor head (Z1, Z2) 8 is used for the sample (photomask) 9 by using the portion outside the portion through which the electron beam 2 passes in the center hole of the objective lens 5. Since the light beam is emitted substantially vertically and the reflected light beam is incident on the sensor head (Z1, Z2) 8, the heights Z1 and Z2 of the sample near the position where the electron beam 2 irradiates the sample 9 can be easily increased in real time. Can measure with accuracy.

In FIG. 4(f), an optical fiber 15 is used instead of the reflecting mirror 7, and a hole at substantially the center in the vertical direction of the objective lens 5 is used (if there is an existing hole, it is used; otherwise, the optical fiber 15 is opened. The optical fiber 15 is arranged in a small hole), and in the hole portion in the center of the objective lens 5 through which the electron beam 2 does not pass, and the light beam emitted from the optical fiber 15 is made substantially perpendicular to the sample (photomask) 9. An example of the structure for irradiation is shown. In this case, the optical fiber 15 is passed through the hole of the objective lens 5, and the light beam emitted from the sensor head (Z1, Z2) 8 is radiated 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 and Z2 of the sample near the position where the electron beam 2 irradiates the sample 9 can be easily and in real time. The measurement can be performed with high accuracy and the reflector is not required.

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

In FIG. 5, S1 moves the stage to predetermined coordinates on the mask. As described on the right side, the stage is sequentially moved to the predetermined coordinates on the mask at 9 or more points symmetrically with respect to the left and right, and S2 is repeated. For example, as shown in a photomask 9 in FIG. 6 described later, the photomask 9 in FIGS. 1 to 4 is not shown in the figure, including nine points (x0, y0), (x1.y0)... (xn, yn). The stage is moved and positioned (the position is determined while performing precise measurement with a laser interferometer (not shown)).

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

In step 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 9 or more positions (x, y) measured and recorded in S1 and S2 and the height Z of the sample at that time. Parameter fitting, for example, parameter fitting of the approximate curve of the focus map as shown in FIG.

In S4, the focus map is completed.

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

The actual device 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 perform the height measurement of the sample 9 almost continuously irrespective of the electron beam irradiation. Therefore, the height measurement can be performed from the moment when the sample 9 to be measured is carried into the vacuum chamber. The focus map expresses 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 located at substantially the same height unless the top plate moves due to large atmospheric pressure fluctuations. On the other hand, the sample 9 to be measured is not always placed horizontally when installed in the sample holder, so the sample 9 may be inclined. In addition, 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 change in the stage position is given by the combination of the above two values. Above all, the amount of change in height of the sample due to the movement of the stage is an eigenvalue of the stage and is known to have reproducibility with respect to repeated measurement. Therefore, it can be described as a unique function.

(2) Therefore, each time a new sample (photomask) 9 is installed in the sample holder, the tilt amount of the sample is measured and combined with a known function specific to the XY stage to obtain an arbitrary electron beam irradiation point. The height of the sample at can be calculated.

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

The sample is placed in the sample holder, and the height distribution of the coordinates as close to the outer circumference of the measurement object as possible is measured by the optical height sensor. When the measurement target is a semiconductor photomask, it is extremely flat, and therefore, for example, about 9 points as shown in FIG. 6 are set as the measurement points. The XY stage is moved to each position, and the height Z measures the height Z at that position and records it (S1 and S2 in FIG. 5). Repeat this several times to obtain the average value. Next, since the function peculiar to the stage has symmetry with respect to the center of the stage, the offset component possessed by the function is removed by utilizing this. By doing so, it is possible to obtain a function representing the height change peculiar to the stage (S3 and S4 in FIG. 5). With this function, a focus map for the main measurement target can be obtained by setting a new measurement target on the holder and measuring heights at several places (FIGS. 5 to 9).

(4) Also, every time a new measurement target is installed 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 holder installation inclination of the measurement target can be obtained. In order to calculate the height for arbitrary coordinates, curve fitting is performed so that the above value can be expressed as a function of a plane, and an approximated curve is obtained. As the approximate curve, a simplest function 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 arbitrary coordinates can be obtained by calculation _.

FIG. 6 shows an example of focus map measurement points according to 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 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 height z (height measurement value) of the sample actually measured by the height sensor in FIGS. 1 to 4 at that time. In addition, an example of saving as shown is shown.

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

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

FIG. 9 shows a flowchart for measuring the height of the sample of the present invention. This shows a flow chart for measuring the height of the sample when actually measuring the height of the sample.

In FIG. 9, S11 moves the sample to the measurement coordinates (Xn, Yn). This moves the sample (photomask 9 in FIG. 1) to the designated measurement point (Xn, Yn) on the XY stage (moves while performing precise measurement with a laser interferometer).

In S12, it is determined whether the measurement point is within the area that can be measured by the two sensors. 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 area, this is YES in S12 and S13 is set. move on. In the case of NO, one of the two height sensors (Z1, Z2) or both of the two height sensors (Z1 and Z2) are determined not to be within the measurement region (outside the measurement region), and thus the determination in S12 is NO and the process proceeds to S14.

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

In S14, since the result of NO in S12 is that the two height sensors (Z1, Z2) are not within the measurement area, it is further determined whether the height of Z1 is OK. Since it is found that both of the two height sensors (Z1, Z2) are not within the measurement area, it is further determined whether the height of Z1 is OK (in the measurement area). 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 height (Z1+Z(X+L,Y))/2 of the average value of is calculated. On the other hand, if NO in S14, the process proceeds to S16.

In S16, since the result of NO in S14 is that the height of Z1 is NG, it is further determined whether or not the height of Z2 is OK. Since it has been found that the sensor of Z1 of the two height sensors (Z1, Z2) is not in the measurement area, it is further determined whether the height of Z2 is OK (in the measurement area). In the case of YES, the height Z2 of the OK height sensor (Z2) and the height Z (X-L) of the position (X-L, Y) of the NG height sensor (Z1) on the focus map. , Y) and the average height (Z2+Z(X-L,Y))/2 are calculated. On the other hand, in the case of NO in S16, since both height sensors Z1 and Z2 are found 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 sensor (Z1, Z2) measures the height while the photomask 9 is moved and positioned at the designated measurement point, and when both heights can be detected, only one average value is required. In this case, one is the height of the measured sample and the other is the average of the height on the map. If both cannot be measured, the height is calculated on the map. It is possible to measure the height of the upper position.

FIG. 10 shows an autofocus flowchart (No. 1) of the present invention. This shows a flow chart for performing electron beam autofocus at high speed without failure by 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 9 points, and a focus map of the sample (photomask) 9 is created. The search lower limit (height of the smallest sample) of the photomask 9 is calculated, and the electron beam focus value is set to the calculated search lower limit (value).

In S22, electron beam scanning and image acquisition are performed. This is because the sample (photomask) 9 is plane-scanned with the electron beam 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 displayed. To generate.

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

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

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

In step S26, the in-focus point focus value is estimated. This is to estimate the focus value at the in-focus point 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 S22 and S24. The method is a known contrast method (contrast maximum (focus value when an image is differentiated and the sum thereof is the maximum)), an edge inclination method (when an inclination of an edge portion of an image line profile is the maximum in an image). Known focus value), FFT method, or the like may be used.

As described above, the 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 focusing point thereof is obtained. By estimating the focus value and setting it to the estimated in-focus focus value, by performing automatic focusing by the electron beam only in a limited height range from the upper limit to the lower limit of the height of the sample (photomask) 9. It becomes possible to perform automatic focusing at high speed and reliably.

The actual device will be described below.

The value measured by the optical height sensor corresponding to the coordinate to be measured is obtained (real time or obtained from the focus map). Since this value is the just focus value obtained by the optical height sensor, it is not necessarily guaranteed to be the same as the just focus of the electron beam autofocus. Therefore, in order to obtain the electron beam autofocus, a range in which the focus is shaken (for example, plus or minus 0.5 micron) is set, and the lower limit value of minus 0.5 micron is added to the above optical just focus value. Is set (S21 in FIG. 10). In this state, the image information required for autofocusing is acquired by electron beam scanning (S22 in FIG. 10). Next, the electron beam focus value is increased by a predetermined value (S23 in FIG. 10). In this state, electron beam scanning is performed in the same manner as above to acquire image information (S24 in FIG. 10). This operation is repeated until the focus strength reaches the upper limit of focus swing (S5 in FIG. 10). When all the information for obtaining the electron beam in-focus point is collected, the in-focus point state is calculated by using the in-focus point algorithm such as the contrast method or the maximum edge inclination method (S26 in FIG. 10). As described above, the focused state of the electron beam can be accurately obtained at high speed without failure.

FIG. 11 shows a structural diagram of another embodiment of the present invention. In FIG. 11, the height value of the sample measured by the optical height sensor of the present invention is used so that the tip of the pole piece of the objective lens 5 and the surface of the sample (photomask) 9 are always constant. In addition, the Z stage 22 is controlled, and thereafter, two-step autofocus is performed by using electron beam autofocus. A Z stage 22 for realizing this is added to the structure of FIGS. 1 to 4. Others are the same, so description will be omitted.

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

The Z stage 22 precisely moves the photomask (sample) 9 in the Z direction, and here, a predetermined voltage is applied to the piezoelectric elements A, B, and C to expand and contract the elements, and thereby the Z direction. It is a mechanism to move to. Here, the sample holder 23 is held by three piezo piezoelectric elements, a predetermined voltage is applied to each of them, and the photomask (sample) 9 is horizontal and the distance between the photomask (sample) 9 and the objective lens 5 (the height of the sample) is predetermined. The movement is controlled so that the value becomes a value.

The sample holder 23 holds the 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 a predetermined voltage to each of the piezoelectric elements A, B, C) to control the movement of the photomask (sample) 9 to a designated position (Z). To do. Since the Z movement (Z axis drive) has vibration resistance, a piezo piezoelectric element that can generate a large force is used. For example, a length of several centimeters and a thickness of several centimeters, and a displacement of approximately several tens of microns can be obtained at 100V. The sample holder 23 is supported by three points from the plane of the XY stage 21, which is the base. 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 to cancel the tilt occurs. By properly 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 including 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 unit 34 supplies the focus to the objective lens 5 from the search lower limit to the search upper limit, which is generated by detecting signals such as secondary electrons when the photomask (sample) 9 is planarly scanned by the electron beam 2. The current value of the objective lens (actually, the current value flowing in the dynamic coil provided separately from the objective lens 5) at the time of focusing is estimated based on the image associated with the current value, 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 integrally controls the entire system of FIG.

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

FIG. 12 shows an autofocus flowchart (No. 2) of the present invention. This is a case where the electron beam is automatically focused under the structure shown in FIG.

In FIG. 12, in S31, the Z stage is moved so that the height of the sample becomes constant. This is because a predetermined voltage is applied to each of the three piezoelectric elements A, B, and C that form the Z stage 22 of FIG. 11, the height of the sample 9 and its inclination are corrected, 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 9 points, and a focus map of the sample (photomask) 9 is created. The search lower limit (height of the smallest sample) of the photomask 9 is calculated, and the electron beam focus value is set to the calculated search lower limit (value).

In S33, electron beam scanning and image acquisition are performed. This is because the sample (photomask) 9 is plane-scanned with the electron beam 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 displayed. To generate.

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

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

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

In S37, the in-focus focus value is estimated. This estimates the focus value at the in-focus point 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 well-known method such as a well-known contrast method, an edge inclination method, or an FFT method may be used.

As described above, after the height of the sample is moved so as to be constant (the 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. By acquiring an image of the sample (photomask) 9 while changing the electron beam focus value by a predetermined step width, estimating the in-focus point focus value of the images, and setting the estimated in-focus point focus value of the sample 9. High-speed and reliable automatic focusing is performed by performing automatic focusing with an electron beam in a limited height range from the upper limit to the lower limit of the height of the sample 9 after the height is constantly and horizontally moved by the Z stage. Is possible.

The procedure and characteristics of the actual device will be described below.

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

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

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

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

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

(6) A focused image can be obtained by setting the focus of the actual electron microscope to this focus strength.

(7) Similarly, a plurality of images obtained by changing the focus intensity using FFT (spatial frequency analysis) or the like are acquired, and a function indicating the relationship between the focus intensity and the highest spatial frequency included in the image is obtained. You can get it. The focus intensity including the highest spatial frequency may be used as the focal point by performing a calculation to find the maximum and minimum and the maximum and minimum using this function. As the method for finding the focal point, all the methods widely known in the art other than the above method can be used, and the scope of the present invention is not limited to the present 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, and therefore various corrections need to be performed in order to measure the dimensions. 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 the optical height sensor so that the distance is constant and the distance is constant. , Z stage 22 is driven to change the height of sample 9. After that, in order to correct a delicate focus error, electron beam focusing is performed. In this way, the image rotation due to the focus hardly occurs. Even if it occurs, it will be a very small value, so the measurement error caused by rotation correction can be reduced.

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

FIG. 13 shows an autofocus flowchart (No. 3) of the present invention.

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

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

In S43, the sample is replaced.

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

In S48, it is determined whether or not there is a charge. This is because it is determined whether the resolution checked by the line profile in the check in S45 is not sufficient and the resolution is lowered due to the influence of the charge of the sample 9 or the vicinity thereof. In the case of YES, in S49, only the charge amount is corrected (the current of the objective lens corresponding to the charge is corrected). On the other hand, if NO in S48, the process ends.

In step S46, the resolution information (including the height and horizontal information (Z stage information) of the sample) in the line profile checked in step S45 is stored.

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

As described above, after the sample 9 was exchanged after the sample 9 was set to the reference height by the Z stage 22 and the focus current of the objective lens was measured, the sample height was set to the reference height by the Z stage 22 and the line profile Check the resolution with, determine if there is a charge, etc., and if it is found that there is a charge, correct only that charge so that fast and stable automatic focusing can be performed when the sample 9 is replaced. It becomes possible to do.

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 the emphasized signal.

In (a) of FIG. 14, detectors A, B, C and D show examples of detectors arranged symmetrically with respect to the optical axis on the lower surface of the objective lens 5 in FIGS. 1 to 4 and 11. Then, an electron detector is shown.

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

The features of the actual device will be described below.

(1) When electron beam autofocusing is performed, there is a sample 9 having a very small contrast. For example, in the case of a nanoimprint template made of quartz, a thin film on the photomask, or a resist covering the entire surface, a very small uneven shape made of the same material is used as the surface. In the case of the sample in Table 1, even the image cannot be seen in the top-down image of the normal SEM, and therefore it is impossible to perform autofocus using the normal SEM signal.

(2) In such a case, if a signal obtained when the sample 9 is viewed obliquely is used, autofocusing becomes easy. For that purpose, by arranging four electron detectors A, B, C, and D as shown in FIG. 14, signal electrons depending on the angle generated from the sample 9 can be detected. It is desirable that the positions to be arranged are axisymmetric with respect to the primary electron axis. For example, a subtraction image in the Y direction can be created by subtracting the C+D signal from the A+B signal. Alternatively, the 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 when the sample 9 is viewed from the oblique direction can be obtained, so that an image with a clear pattern edge can be obtained as compared with a normal SEM image observed from the front.

(3) Even when the above-described contrast enhancement method is used, the edge contrast can be observed under the condition in the vicinity where the electron beam focusing point is obtained, but if the distance is further than that, just like the front image, No edges can be observed. In other words, it is not possible to find out the in-focus state by roughing the focus strength of the objective lens and examining it.

(4) If the optical height sensor of the present invention is used, the electron beam focus can be applied after the focus is brought close to 0.1 micron, so that the edge can be reliably captured and the auto focus can be performed. The probability of success can be greatly increased.

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 a sensor arrangable portion, and the light beam emitted from the sensor head 8 is guided by a light guide (reflector not shown). The height of the photomask 9 is optically measured by vertically irradiating the photomask 9 with a mirror, optical fiber, etc. 7 and making the reflected light beam enter the sensor head 8 with the light guide (reflector, etc.) 7. can do. An optical fiber is connected from the sensor head 8 to the spectroscope 11 of FIG. 1 described above, and the sample 9 is interfered with the laser beam (broadband) reflected by the spectroscope 11 and returned. It is possible to measure the height precisely.

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

FIG. 16 shows 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 where the height of the mask (sample) 9 can be estimated using the two sensor heads (Z1) 8 and the sensor heads (Z2) 8.

As the mask outer shape, an example of the outer shape of the sample (photomask) 9 is schematically shown.

The area that can be measured by the two optical height sensors is an area where 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 shown on the right side. Zc=(Z1A+Z2B)/(A+B)
-Zc: Height of sample at objective lens position (electron beam irradiation position)-A, B: Light beams from sensor head (Z1) and sensor head (Z2) are sample
Distance from the electron beam irradiation center position on the sample 9 when irradiating the object. Z1A, Z1B: The height of the sample 9 at the distances A and B can be obtained.

The principle of the height sensor used in the experiment of the present invention is described in, for example, the following URL of Keyence sensor, so please refer to it.

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

FIG. 1 is a structural diagram (1) of an embodiment of the present invention. FIG. 3 is a structural diagram (2) of the first embodiment of the present invention. It is a detailed structure figure (the 1) of the present invention. It is a detailed structure figure (the 2) of the present invention. It is a focus map creation flowchart of this invention. It is an example of a focus map measurement point of the present invention. It is an example of a height measurement value of the present invention. It is an example of the approximated 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 (1) of this invention. It is a structural diagram of another embodiment of the present invention. It is an autofocus flowchart (2) of this invention. It is an autofocus flowchart (3) of this invention. It is an example of image acquisition by the electron beam of the present invention. It is an example of arrangement of a 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: deflector 4: electron detector 5: objective lens 6: secondary electron/reflected electron 7: reflector, light guide, optical fiber 8: sensor head 9: photomask, sample 11 : Spectrometer 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 (4)

In an autofocus device that performs scanning while irradiating a sample with a charged particle beam narrowed down and irradiating the sample, and performing automatic focusing of the charged particle beam based on the emitted, reflected, and absorbed signals,
An objective lens and a scanning system for scanning while irradiating the sample with the charged particle beam narrowed down are provided. A light guide that irradiates and receives the light reflected by the sample,
A sensor head that irradiates the light guide with light rays and receives the light rays emitted from the light guide,
A spectroscope that emits light rays to the sensor head and receives the light rays emitted from the sensor head, and detects the irradiation position of the light rays on the sample based on the emitted light rays and the received light rays. ,
The light guide and the sensor head are integrally fixed to the objective lens, and the sensor head and the spectroscope are connected by an optical fiber, and the optical path length between the spectroscope and the light guide is always maintained. In a state in which the distance between the light guide and the position of the sample irradiated by the laser beam can be precisely measured while being held constant,
Furthermore, an autofocus means for autofocusing the charged particle beam on the sample is provided,
The autofocus means autofocuses the charged particle beam on the sample based on the position of the sample measured by the one or a plurality of light guides to focus the entire surface or a wide range of the sample. Auto focus device. The autofocus device according to claim 1, wherein the autofocus is speeded up by using a Z stage. While the sample is scanned while being irradiated with the charged particle beam and an image generated from signals emitted, reflected, and absorbed at that time is being acquired, the height of the sample is increased in real time by the one or more light guides. The autofocus device according to claim 1, wherein the autofocus device measures the height. 4. The Z stage is held by at least three or more piezoelectric elements, and has a mechanism for correcting the height of the sample or the inclination according to need. 4. Autofocus device.