JP7018098B2 - Autofocus 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 for mass-produced devices. In order to realize a small feature size, an exposure technique capable of forming a smaller pattern is required.

Conventionally, a laser beam with a wavelength of 193 nm has been used for exposure, but since it has already greatly exceeded the limit of optical decomposition, exposure technology using EUV light with a wavelength of 13.5 nm has been energetically advanced in recent years. ing. This technology is said to have originated in Japan, but it 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 device is almost completed, the current EUV exposure device cannot obtain the light source power of 100 W to 200 W required for economical mass production, so it cannot be used for exposure of the 20 nm generation. It was skipped.

Instead, a so-called double or triple exposure technique, which can realize a smaller feature size by repeating the existing wavelength 193 nm exposure process a plurality of times, is used in an actual production site. In principle, it is possible to create any number of small patterns by repeating immersion lithography using a laser beam with a wavelength of 193 nm multiple times, but alignment accuracy on the order of nm, which is an order of magnitude higher than before, is required. It is known that the large roughness and the like resulting from the large molecular structure of the chemically amplified resist limit the repeated exposure process. Currently, double patterning, which repeats the exposure process twice, which is said to be the economical limit, is put into practical use. For memory devices with a relatively simple structure, it is used to realize lines and spaces of 20 nm to 16 nm. Has been done.

It is necessary to reduce the pattern of not only a memory device having a simple structure but also a CPU and a logic device in order to expand functions and reduce power consumption. Since the logic device uses a complicated pattern without repetition, 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 required result may not be obtained due to divergence of division calculation.

To avoid these complications, a technique called Complementary Lithography, which is mainly advocated 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 pattern of L & S such as a memory circuit. By doing this, the pattern of the complex logic device is limited to the L & S pattern that is most easily exposed and the process of cutting the line, so there is no need for complicated pattern division calculation, and the process is simple and computational. The upper part is said to go up to about 8 nm.

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

Electron microscopy technology is essential to determine if these masks are made to the correct dimensions, but autofocus technology is very important to obtain high-definition images. However, when the conventional autofocus is used, there is a problem that the autofocus fails depending on the mask. If the autofocus fails, not only the measurement cannot be performed, but also the erroneous measured value is provided to the process control, which causes the yield to decrease further and suffers a large loss, so the failure cannot be tolerated.

An optical height measuring method for non-contact measuring the sample height of an electron beam irradiation point has been developed for the purpose of assisting the autofocus of a conventional electron beam optical system. There is an objective lens at the tip of the electron beam column, and the tip of the pole piece is very close to the sample to be observed, so the distance is only a few millimeters. Conventionally, in order to measure the distance, an LED or a laser beam is incident at an angle, applied to an electron beam irradiation point, the position of the reflected light is detected by an optical sensor such as a CCD, and the height of the sample is measured. The method has been adopted.

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

Further, when the sample is tilted, it is indistinguishable from the change in the height of the sample, so that 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 and material of the sample surface.

On the other hand, since the optical path length of the LED, laser light source, or the optical system that composes them is as large as several tens of centimeters, the external environment is affected by deformation of the top plate due to changes in pressure, changes in the optical path length due to temperature expansion, and changes in the incident angle. Since it is easily caused by the change, there is also a problem that the measurement accuracy is lowered. Of course, it is possible to make corrections by measuring these changes in the external environment with a sensor or the like, but the system becomes more complicated, and there are 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 the usage time, which affects the measured value. There is also a problem that the measurement accuracy of only about 1 micron can be realized when these are integrated.

An object of the present invention is to accurately measure and set the height of a sample in an electron beam device (charged particle beam device), and to perform high-speed, precise and reliable autofocus.

Therefore, the present invention uses a charged particle beam in a charged particle beam device that narrows down a charged particle beam and scans it while irradiating the sample, and generates an image based on the signals emitted, reflected, and absorbed at that time. An objective lens and a scanning system that scans while irradiating the sample with a finely squeezed light are provided, and the outer surface of the objective lens or the hole provided in the objective lens that can be seen from the sample is irradiated with light rays toward the sample and the sample is used. A light guide that receives the reflected light rays, a sensor head that radiates the light rays to the light guide and receives the light rays emitted from the light guide, and a sensor head that radiates the light rays to the sensor head and emits the light rays from the sensor head. It is provided with a spectroscope that receives light rays and detects the irradiation position of the light rays on the sample based on the emitted light rays and the received light rays.

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

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

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

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

Also, based on the height of each sample measured by one or more light guides, or the height of the sample measured and stored in advance, the height of the location of the sample irradiated by the charged particle beam. Is provided with a height adjustment mechanism that adjusts to a constant value.

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 by the charged particle beam can be performed quickly and reliably. This is done to generate a focused image.

The present invention directly measures and sets the height of a sample near the electron beam irradiation point with one or more optical height sensors, and precision auto with an electron beam based on the measured or set height of the sample. Focusing makes it possible to set a stable ultra-high precision height exceeding 0.1 micron with an extremely simple configuration for the height of the sample, and at the same time, high speed and precision based on the measured or set height of the sample. Moreover, the autofocus of the electron beam can be reliably performed.

Further, when the sample is a semiconductor wafer, the light beam for measuring the height of the sample may change the conductivity in the irradiation region of the light beam and may affect the measured 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) in real time by the light beam, while the sample is irradiated by the electron beam to perform the measurement in parallel. Can be done.

The actual device will be described in detail below.

(1) By using the present invention, it is possible to realize a high-speed and accurate electron beam in-focus state without autofocus failure as compared with the case where only the conventional electron beam autofocus is used. Before performing electron beam autofocus, it is possible to create a state that is sufficiently close to the electron beam in-focus state, so the range in which electron beam autofocus searches for a focus value should be about one-tenth or less of the conventional range. It is possible, and autofocus can be performed at a higher 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) The optical height sensor is very compact unlike the conventional one, so it is easy to mount and maintain. Since the height is directly measured, the tilt correction of the sample 9, which was required 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) Since electromagnetic waves and heat are not generated when the sensor operates, the measurement can be made very stable.
Since the materials are crows and metal, vacuum contamination can be avoided. There are no moving parts and it has a long life.
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 a change in the external environment, the change can be measured in real time. , Electronic beam autofocus can be easily successful.

(6) Even if two optical height sensors cannot be measured in real time at the same time, it is possible to measure the height almost in real time by using the focus map created in advance. I can.

(7) Even for sample 9, which is difficult to autofocus with only an electron beam image, the height can be measured first with an optical height sensor and brought to a state close to the in-focus state, so very fine electrons can be obtained. You can swing the beam focus. This makes it easy to obtain an electron beam in-focus state in a three-dimensional object or a measurement target having a low edge contrast.

(8) When the Z stage 22 supported at 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, so that the electron beam irradiation can be made vertical. become. This makes it possible to acquire a more accurate electron beam image.

In the present invention, the height of the sample near the electron beam irradiation point is directly measured and set by one or a plurality of optical sensors, and the precision autofocus by the electron beam is performed based on the measured or set height of the sample. By doing so, it becomes possible to set a stable ultra-high precision height exceeding 0.1 micron with an extremely simple configuration for the height of the sample, and at the same time, it is fast, precise and reliable based on the measured or set height of the sample. The autofocus of the electron beam has been realized.

Further, when the sample is a semiconductor wafer, the light beam for measuring the height of the sample may change the conductivity in the irradiation region of the light beam and may affect the measured value by the electron beam. In the present invention, since the light beam does not directly irradiate the electron beam measurement point, it is possible to measure the height of the sample with the light beam in real time, while irradiating the sample 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, among the charged particle beams, a device using an electron beam, here, a scanning electron microscope will be described in detail in detail below with respect to an embodiment structure. It should be noted that a charged particle beam (ion or the like) other than the electron beam can also 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, the electron gun 1 is a known one that generates an electron beam, and generates an electron beam 2 accelerated to several hundred V to several tens of 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 deflection device 3 deflects the focused electron beam 2 in the X and Y directions (usually two-step deflection), and the electron beam 2 finely focused by the objective lens 5 is flat 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 / backscattered electrons 6 emitted from the sample (photomask) 9, and displays an image (secondary electron image, backscattered electron image, etc.) based on the detected signal. It is a known one.

The objective lens 5 is a known one in which an electron beam 2 is finely focused and irradiated onto a sample (photomask) 9.

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

The reflector 7 is a reflector which is one of the light guides 7, and reflects a light ray (laser ray) from the sensor head 8 and radiates (reflects) the sample (photomask) 9 toward the sample (photomask) 9. The light ray reflected by 9 is reflected in the direction of the sensor head 8. The light guide 7 includes an optical fiber and the like in addition to a reflector and a prism. The light beam output from the sensor head 8 is irradiated toward the sample 9, and the light ray reflected by the sample 9 is guided to the sensor head 8. Anything can be done. The size of the laser beam emitted from the laser head 8 is 0.1 to 1. It has a diameter of 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 one can be used.

The laser head 8 outputs the light rays from the spectroscope 11 to the light guide (reflector) 7 to irradiate the sample 9, and the light rays reflected by the sample 9 are taken in via the light guide (reflector) 7. Is sent to the spectroscope 11. The size of the laser beam emitted from the laser head 8 is 0.1 to 1. It has a diameter of about several mm, and in the experiment, a diameter of about 0.6 mm was used. The light rays emitted from the laser head 8 are reflected by the reflecting mirror 7 to irradiate the sample 9, and the light rays reflected by the sample 9 are reflected by the reflecting mirror 7 and the optical path length when incident on the laser head 8 changes. To prevent this, the part where the laser head 8 and the reflector 9 are attached (usually the objective lens 5 or its peripheral members) is not affected by the thermal change because it causes an error due to the expansion due to the thermal change, or the thermal expansion coefficient. It is necessary to devise so that the optical path length does not change, such as by using a material with a small thermal expansion coefficient or a material with the same thermal expansion coefficient.

The spectroscope 11 constitutes a spectroscopic interference type laser displacement measuring device integrally with the laser head 8 and the light guide (reflector) 7. Hereinafter, for convenience, the distance between the objective lens 5 and the surface of the sample (photomask) 9 is referred to as a height (sample height, Z). Of the spectroscope 11, the sensor head 8, and the light guide 7 that constitute the spectroscopic interference type laser displacement measuring device, the size of 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 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 is not normally present inside the sensor head 8, it is not a source of electrical 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 target (for example, sample 9) and the members in the vicinity thereof are not affected by the temperature. The sensor head 8 is covered with a non-magnetic 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 arranged inside the sample chamber and can withstand plasma cleaning and the like. Since the height measurement speed of the sample 9 is as high as 200 μs, the height measurement can be performed in almost real time.

Further, the measurement accuracy of the height sensor by the spectroscope 11, the sensor head 8 and the reflector (light guide) 7 has a measurement resolution of 1 nm, and the measurement reproducibility is also 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 does not necessarily have to be arranged symmetrically.

The focus control means 12 detects and generates secondary electrons and backscattered electrons when the electron beam 2 scans the sample 9 while irradiating the sample 9 based on the height data of the sample 9 from the spectroscope 11. Based on this, the current of the objective lens 5 is automatically controlled (to be exact, the current of a dynamic focus coil (not shown separately) 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 at which the value becomes the maximum value). At this time, since the height of the sample (photomask) 9 is precisely measured by the system using the spectroscope 11, the sensor head 8, and the reflector (light guide) 7, the height of the sample 9 is measured. The current of the objective lens 5 may be controlled so as to be focused, and the focus may be controlled slightly precisely around this, so that automatic focusing can be performed in a short time and reliably.

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 (transmits and receives a laser beam) the sensor head 8 and the spectroscope 11.

FIG. 2B shows a bottom view. Here, as shown in the figure, the height Ze of the sample at the center of the objective lens 5, the height Z1 of the sample of the reflector 7 that receives the light rays from the sensor head (Z1) 8 and reflects them on the sample 9. (Z2) The height Z2 of the sample of the reflector 7 that receives the light rays from 8 and reflects them on the sample 9. 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 the center (optical axis) of the objective lens 5 to the sensor. The distance between the positions of the reflector 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 the sample at the center of the objective lens 5 = Ze
-Sample height of the reflector 7 of the sensor head (Z1) = Z1
-Sample height of the reflector 7 of the sensor head (Z2) = Z2
Is 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 axisymmetrically with respect to the optical axis).

Next, the operation and features of the height measurement of the sample 9 by the spectroscope 11, the sensor head 8 and the light guide (reflector) 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. This laser beam is bent by a 90-degree reflector 7 in the traveling direction by 900 degrees, and irradiates the surface of the sample 9 substantially perpendicularly.

(2) The laser beam reflected on the surface of the sample 9 returns in 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 (wide wavelength band laser beam) to interfere with the laser beam reflected by the sample 9 to generate distance information (displacement data). Focus control is performed based on this.

(4) The method for measuring the height of the sample of the present invention is different from the conventional tilting height measuring method described above, and the incident angle is substantially perpendicular to the sample 9, so that the angle of incidence is substantially perpendicular to the tilt of the sample 9. Since the fluctuation (error) of the measured value is extremely small, it is not necessary to correct the inclination of the conventional sample 9, and it is easy to use. In addition, it is not easily affected by the pattern on the surface of the sample 9.

(5) Further, the laser beam guided from the sensor head 8 to the outside by an optical fiber is taken into the spectroscope 11 outside and converted into a distance (sample height). Although the spectroscope 11 generates heat, it does not usually 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 desired processing such as saving the correspondence with the measurement point coordinates (described later using a flowchart).

(6) The two sensor heads 8 and the reflector (light guide) 7 shown in FIGS. 1 and 2 measure the height of the electron beam 2 at a place different from the irradiation position on the sample 9, for example. When the two sensor heads 8 are arranged at the same distance from the center of the objective lens 5, the average value of the output values of both represents the height of the sample at the irradiation point on the sample 9 of the electron beam 2 (estimated). do). By performing such a calculation on a personal computer (see the 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 the height of the sample.

(7) Further, 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 mm, it is practically impossible to arrange the height sensor of the sample at that position, but the present invention. Then, the reflector (light guide) 7 can be arranged at a position away from the tip of the pole piece of the objective lens 5, and the light guide 7 can be arranged inside the objective lens 9 which will be described later by making a hole. A light guide (reflector, 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 and in real time.

3 and 4 show detailed structural views 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, and FIG. 4 shows an example of a detailed structure in which the light guide 7 is arranged in a hole provided inside the objective lens. This will be described in detail below.

FIG. 3 shows a detailed structural diagram (No. 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 drawing. In the illustrated structural example, the light beam (laser ray) emitted to the right from the sensor head (Z1) 8 is reflected downward by a 90-degree mirror (or prism) and irradiates the sample (photomask) 9 almost vertically. Then, the reflected light beam is incident on 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 reflector 7 and irradiates the sample 9 from the vertical direction, and the reflected light ray returns in the opposite direction and is incident on the spectroscope 11. In the spectroscope 11, the emitted laser beam (wide band) and the laser beam reflected by the sample 9 and returned are made to interfere with each other to generate displacement data of the height of the sample 9. This makes it possible to measure the height Z1 of the sample 9 at the position of the reflecting mirror 7 of the laser head (Z1) 8 in real time and with high accuracy. Similarly, for the sensor head (Z2) 8 on the right side, 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 drawing. In this case, the heights Z1 and Z2 of the sample at the position of the third reflecting mirror 7 irradiated with the photomask 9 from the vertical direction can be measured, and the optical axis of the objective lens 5 is aligned with the optical axis of FIG. 3 (a). The heights Z1 and Z2 of the sample at a position closer to each other can be measured.

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 photomask 9 from the vertical direction can be measured, and the optical axis of the objective lens 5 is aligned with (b) of FIG. The heights Z1 and Z2 of the sample at a position closer to the above can be measured.

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

Further, the reflecting mirror 7 is arranged symmetrically about the optical axis of the objective lens 5 so that the electron beam 2 does not cause direction dependence when scanning while irradiating the sample 9, or a dummy reflecting mirror 7. It is desirable to place.

FIG. 4 shows a detailed structural diagram (No. 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 a light ray transmitted through the hole in the center of the objective lens 5. In this case, the outer portion of the hole in the center of the objective lens 5 through which the electron beam 2 passes is used, and the light rays emitted from the sensor heads (Z1, Z2) 8 are substantially applied to the sample (photomask) 9. Since the light rays that are vertically irradiated and reflected are incident on the sensor heads (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 measured in real time and with high accuracy. Can be measured.

In FIG. 4 (e), the reflecting mirror 7 is placed inside a hole in the center of the objective lens 5 (if there is an existing hole, it is used, otherwise a small hole is made for light rays to pass through). An example of a structure in which a sample (photomask) 9 is irradiated with a light ray that has passed through a hole in the center of the objective lens 5 is shown. Similarly, in this case as well, the outer portion of the hole in the center of the objective lens 5 through which the electron beam 2 passes is used, and the light beam emitted from the sensor heads (Z1, Z2) 8 is used as the sample (photomask) 9. Since the light rays are irradiated almost vertically and the reflected light rays are incident on the sensor heads (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 set in real time and high. It can be measured accurately.

In FIG. 4 (f), 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 (if an existing hole is used, the existing hole is used, otherwise the optical fiber 15 is passed through). The optical fiber 15 is arranged in a small hole) and a hole 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 substantially perpendicular to the sample (photomask) 9. An example of the 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 beam emitted from the sensor heads (Z1, Z2) 8 is irradiated from the tip of the optical fiber 15 substantially perpendicular to the sample (photomask) 9. Since the reflected light rays are returned to the sensor heads (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 measured in real time. It can measure with high accuracy and eliminates the need for a reflector.

FIG. 5 shows a flow chart for creating a focus map of the present invention.

In FIG. 5, S1 moves the stage to the predetermined coordinates on the mask. As described on the right side, the stage is sequentially moved to the predetermined coordinates on the mask of 9 points or more symmetrically in the left-right and vertical directions, and S2 is repeated. For example, as shown in the photomask 9 of FIG. 6 to be described later, the photomasks 9 of FIGS. 1 to 4 are not shown at 9 points or more of (x0, y0), (x1.y0) ... (xn, yn). Move the stage to position it (position it while measuring it precisely with a laser interferometer (not shown)).

S2 measures and records the height with a height sensor. This is a height composed of the height sensors (spectrum 11, sensor head 8, and light guide 7) of FIGS. 1 to 4 in a state of being positioned at a predetermined position on the photo mask 9 using a stage in S1. The height of the sample at each position is measured by a sensor (hereinafter referred to as "height sensor"), and the height (Z) is recorded, for example, as shown in FIG. 7 described later, in correspondence with the coordinates (X, Y). Record.

S3 fits the parameters of the focus map approximation function. This is an approximate function (for example, Z ² = X ² + Y ² ) based on the data of the positions (x, y) of 9 points or more and the height Z of the sample at that time measured and recorded in S1 and S2. For example, as shown in FIG. 8 (a) described later, the parameters of the approximate curve of the focus map are fitted.

In S4, the focus map is completed.

Based on the above, the heights of the plurality of positions on the photomask 9 are measured by the height sensors of FIGS. 1 to 4 and the height Z of the sample is measured (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 of. After that, the height information of an arbitrary position on the photomask 9 is read out with reference to the focus map, and the automatic focus of the electron beam is performed at high speed and surely with the height of the read sample as the center. 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 measure the height of the sample 9 almost continuously regardless of the electron beam irradiation. Therefore, the height can be measured from the moment 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, it is located at almost the same height as long as the top plate does not move due to large atmospheric pressure fluctuations. On the other hand, the sample 9 to be measured is not always placed horizontally when it is placed in the sample holder, so that the sample 9 may be tilted. Further, the stage for moving the sample 9 has characteristics such as yawing, pitching, and rolling, and the height of the sample 9 may change slightly with the movement of the stage. That is, the change in the height of the sample 9 with respect to the change in the stage position is given by the synthesis of the above two values. Above all, the amount of change in the height of the sample due to the movement of the stage is an eigenvalue of the stage, and it is known that it is reproducible for repeated measurements, so that it can be described as an eigenfunction.

(2) Therefore, every time a new sample (photomask) 9 is placed in the sample holder, the amount of inclination of the sample is measured and synthesized with a known XY stage-specific function to obtain an arbitrary electron beam irradiation point. The height of the sample in 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 adjacent to the outer peripheral portion of the measurement target is measured by the optical height sensor as much as possible. When the measurement target is a photomask for semiconductors, it is extremely flat, so for example, about 9 points as shown in FIG. 6 are set as measurement points. The XY stage is moved to each position, and the height Z at that position is measured and recorded by the height sensor (S1 and S2 in FIG. 5). Repeat this several times to find the average value. Next, since the stage-specific function has symmetry with respect to the center of the stage, the offset component of the function is removed by using it. By doing so, it is possible to obtain a function representing the height change peculiar to the stage (S3, S4 in FIG. 5). With this function, a focus map for this measurement target can be obtained by installing a new measurement target in the holder and measuring the height at several points (FIGS. 5 to 9).

(4) Further, every time a new measurement target is installed in 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 to be measured can be obtained. Curve fitting is performed so that the above values can be expressed as a function of a plane so that the height with respect to arbitrary coordinates can be calculated, and an approximate curve is obtained. As the approximate curve, a function as simple as possible, such as a quadric 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 the focus map measurement point 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 has a length and width of 15 cm, and as shown in the figure, 3 × 3 measurement points (x0, y0), (x1, y0), (x2, yo) ... Provide as shown.

FIG. 7 shows an example of height measurement values of the present invention. Here, the height table corresponds to x and y on the photomask 9 of FIG. 6 and the height z (height measurement value) of the sample actually measured by the height sensor of FIGS. 1 to 4 at that time. An example of saving as shown in the figure 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 illustrated focus map example is measured based on the relationship of the height (z) actually measured at the position (x, y) on the photomask 9 measured in FIG. 7. An example is shown in which a focus map is obtained for an approximate curve through which a point (x, y, z) passes (here, the approximate curve Z ² = X ² + Y ² in (b) of FIG. 8).

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

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 points (Xn, Yn) on the XY stage (moves while making precise measurements with a laser interferometer).

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

In S13, YES in S12 indicates that the two height sensors (Z1 and Z2) are within the measurement region, so the average value of the two sensors is determined to be the height.

Since S14 is NO of S12 and it is found that the two height sensors (Z1 and Z2) are not within the measurement region, it is further determined whether the height of Z1 is OK. Since it was found that neither of the two height sensors (Z1 and Z2) was within the measurement area, it is further determined whether the height of Z1 is OK (within the measurement area). If 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 of the average value of (Z1 + Z (X + L, Y)) / 2 is calculated. On the other hand, in the case of NO in S14, the process proceeds to S16.

Since S16 was found to be NO in S14 and the height of Z1 was NG, it is further determined whether the height of Z2 is OK. Since it was found that the sensor of Z1 out of the two height sensors (Z1 and Z2) was not in the measurement area, it is further determined whether the height of Z2 is OK (in the measurement area). If YES, the height Z2 of the OK height sensor (Z2) and the height Z (XL, Y) of the position (XL, Y) of the NG height sensor (Z1) on the focus map. , Y) and the height of the average value (Z2 + Z (XL, Y)) / 2. On the other hand, in the case of NO in S16, since both height sensors of Z1 and Z2 were 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 is measured by the height sensors (Z1 and Z2) with the photomask 9 moved to the designated measurement point and positioned, and if both can detect it, the average value can be obtained with only one. When one is the height of the measured sample and the other is the average value of the height on the map, and when both cannot be measured, it is calculated as the height 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 flowchart 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. In this method, 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, a focus map of the sample (photomask) 9 is created, and the sample (photomask) 9 is prepared. The search lower limit (height of the smallest sample) of the photomask) 9 is obtained, and the electron beam focus value is set to the obtained search lower limit (value).

S22 scans the electron beam and acquires an image. This involves scanning the sample (photomask) 9 with an electron beam in a plane at the electron beam focus value set in S21, detecting the secondary electrons (or backscattered electrons, absorbed electrons) emitted at that time, and displaying an image. Generate.

S23 increases the electron beam focus value by a step width. This increases the electron beam focus value by a predetermined step width.

S24 scans the electron beam and acquires an image.

S25 determines whether it is 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.

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

As described above, the image of the sample (photomask) 9 is acquired while changing the electron beam focus value within 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 in-focus point thereof is obtained. By estimating the focus value and setting it to the estimated in-focus focus value, automatic focusing by the electron beam is performed only in the limited height range from the upper limit to the lower limit of the height of the sample (photomask) 9. , It is possible to automatically focus at high speed and surely.

The actual device will be described below.

Obtain the value measured by the optical height sensor corresponding to the coordinates to be measured (obtained in real time or from the focus map). Since this value is the value of the just focus obtained by the optical height sensor, there is no guarantee that it is the same as the just focus of the electron beam autofocus. Therefore, a range for swinging the focus (for example, plus or minus 0.5 micron) is set in order to obtain the electron beam autofocus, and the lower limit value minus 0.5 micron is added to the above optical just focus value to obtain the electron beam focus. The strength of is set (S21 in FIG. 10). In this state, the image information necessary for performing autofocus 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 described above to acquire image information (S24 in FIG. 10). This operation is repeated until the strength of the focus reaches the upper limit of the focus swing (S5 in FIG. 10). When all the information for obtaining the electron beam focus is collected, the focus state is calculated by using a focus algorithm such as the contrast method or the maximum edge tilt method (S26 in FIG. 10). From the above, the electron beam in-focus state can be obtained at high speed and accurately without failure.

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

In FIG. 11, the XY stage 21 precisely moves the photomask (sample) 9 in the X and Y directions, and is not shown while measuring 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 accurately moves the photomask (sample) 9 in the Z direction. Here, a predetermined voltage is applied to the piezo piezoelectric elements A, B, and C, and the element expands and contracts in the Z direction. It is a mechanism to move to. Here, the sample holder 23 is held by three piezoelectric piezoelectric elements, and a predetermined voltage is applied to each of the sample holders 23 so that the photomask (sample) 9 is horizontal and the distance (sample height) from the objective lens 5 is predetermined. The movement is controlled so that it 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 the signal from the laser interferometer.

The Z stage control means 32 controls the Z stage 22 (controls by applying predetermined voltages to the piezo piezoelectric elements A, B, and C, respectively), and controls the movement of the photomask (sample) 9 to the designated position (Z). It is something to do. Since Z movement (Z-axis drive) has vibration resistance, a piezo piezoelectric element capable of generating a large force is used. For example, a displacement of several centimeters in length, several centimeters in thickness, and a displacement of about several tens of microns can be obtained at 100 V. The sample holder 23 is supported at three points from the plane of the XY stage 21 which is the base. The three piezo piezoelectric elements A, B, and C are each equipped with a high-voltage amplifier and can be controlled independently. Therefore, using the data obtained when the focus map was created in advance, the tilt component of the photomask (sample) 9 is extracted, and the piezo piezoelectric element A, so that the displacement required to cancel the tilt is generated, 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, further control is performed so that the height of the photomask 9 becomes a desired height.

The sample height information processing means 33 controls an optical height sensor including a spectroscope 11, a sensor head 7, and a reflector (light guide) 7 to measure the height of the photo mask (sample) 9. be.

The auto focus control means 34 detects and generates a signal such as a secondary electron when the photomask (sample) 9 is scanned in a plane by the electron beam 2, and supplies the focus to the objective lens 5 from the lower limit of the search to the upper limit of the search. Based on the image associated with the current value, the current value of the objective lens at the time of focused focus (actually, the current value flowing through the dynamic coil provided separately from the objective lens 5) is estimated, and the estimated objective current value is estimated. It 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 of FIG. 11 in an integrated manner.

Under the above structure, a focus map of the photomask 9 is created as described with reference to FIGS. 5 to 9 described above with, for example, 9 points or more of the photomask (sample) 9, and the height of the photomask 9 is increased. By applying a predetermined voltage to each of the three piezo elements A, B, and C constituting the Z stage 22 so that is constant at any location, the height of the sample (photomask) 9 and the sample (photomask) are increased. ) It is possible to correct the inclination of 9 so that the height of the sample is always horizontal and constant. Then, after the height of the sample is constant and the sample is horizontally corrected by the Z stage 22, the automatic focus of the electron beam is performed between the lower limit of the search and the upper limit of the search, and the focused image can be obtained quickly and reliably. It will be possible.

FIG. 12 shows an autofocus flowchart (No. 2) of the present invention. This is the case where the electron beam is autofocused under the structure of FIG. 11 described above.

In FIG. 12, S31 moves the Z stage so that the height of the sample is constant. This applies a predetermined voltage to each of the three piezoelectric piezoelectric elements A, B, and C constituting the Z stage 22 of FIG. 11, corrects the height of the sample 9 and its inclination, and the height of the sample 8 is constant. And make the sample 8 horizontal.

S32 sets the electron beam focus value to the search lower limit of the specified value (search lower limit of the optical height measurement value). In this method, 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, a focus map of the sample (photomask) 9 is created, and the sample (photomask) 9 is prepared. The search lower limit (height of the smallest sample) of the photomask) 9 is obtained, and the electron beam focus value is set to the obtained search lower limit (value).

S33 scans the electron beam and acquires an image. This involves scanning the sample (photomask) 9 with an electron beam in a plane at the electron beam focus value set in S32, detecting the secondary electrons (or backscattered electrons, absorbed electrons) emitted at that time, and displaying an image. Generate.

S34 increases the electron beam focus value by a step width. This increases the electron beam focus value by a predetermined step width.

S35 scans the electron beam and acquires an image.

S36 determines whether it is the upper limit of the search range. If YES, the process proceeds to S37. If NO, repeat S34 and subsequent steps.

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

As described above, after the height of the sample is moved to be constant (height is constant and horizontal) by controlling the Z stage 22, the search lower limit to the search upper limit of the optical height measurement value of the present invention are reached. By acquiring an image of the sample (photomask) 9 while changing the electron beam focus value in a predetermined step width, estimating the focus focus value among them, and setting the estimated focus focus value to the sample 9. After moving the height constantly and horizontally on the Z stage, automatic focusing is performed at high speed and reliably 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. Is possible.

The procedure and features 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, the combination of detector signals that maximizes the image contrast is selected.

(3) By setting the signal so that it can be captured under the conditions of (2) and changing the voltage applied to the focus lens such as the objective lens 5 or the sample 9, the focus intensity can be changed in some ways such as underfocus, nearjust focus, and overfocus. The image signal is captured (S32 to S36 in FIG. 12).

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

(5) Using this function, an operation for finding the maximum / minimum or maximum / minimum is performed, and the focus intensity estimated to be able 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 an actual electron microscope to this focus intensity, an in-focus image can be obtained.

(7) Similarly, a function showing the relationship between the focus intensity and the maximum spatial frequency included in the image is obtained by acquiring a plurality of images obtained when the focus intensity is changed by using FFT (spatial frequency analysis) or the like. You can get it. By using this function to find the maximum and minimum and the maximum and minimum, the focus intensity including the highest spatial frequency may be set as the focal point. In addition to the above methods, all methods widely known in the world can be used as a method for finding the in-focus point, 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, electron beam focus can be obtained by changing the strength of the objective lens 5. However, unlike optical systems, in electronic optical systems, the image rotates when the focus is changed. When the image is rotated, image distortion occurs depending on the location, so it is necessary to make various corrections in order to perform dimensional measurement. In the present invention, the distance (the height of the sample) between the pole piece of the objective lens 5 and the surface of the sample 0 is measured in advance by an optical height sensor so that the distance is made parallel and the distance becomes constant. , The Z stage 22 is driven to change the height of the sample 9. After that, in order to correct a delicate focus error, electron beam focusing is performed. In this way, image rotation due to 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, in recent years, not only the distance measurement between two points but also the usage method of accurately reading the image itself and applying it to an optical simulation is increasing. 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 very small. The effect is particularly large when the FOV is large.

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

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

S42 measures the focus current of the objective lens. This measures (estimates) the focus current value of the objective lens at the time of focusing based on the image obtained by scanning the sample 9 in a plane with an electron beam with the sample 9 set to the reference height in S41. do.

S43 replaces the sample.

In S44, the sample is adjusted to the reference height in the Z stage. For the sample exchanged in S4, adjust it to the reference height (the height of the sample 9 is constant and horizontal) on the Z stage.

S45 checks the resolution with the line profile. This is because the line profile of the sample 9 is acquired by an 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 one). Check if it is sufficient for the purpose of use).

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

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

The S47 will use the information recorded in S46 (line profile resolution, Z stage information (sample height and horizontal information)) next time.

As described above, the sample 9 is set to the reference height by the Z stage 22 and the focus current of the objective lens is measured. After the sample 9 is replaced, the sample 9 is set to the reference height by the Z stage 22 and the line profile is obtained. Checks the resolution with, determines whether there is a charge, etc., and if it is found that there is a charge, etc., corrects only the charge, etc., so that high-speed and stable automatic focus can be achieved when the sample 9 is replaced. It will be possible to do.

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

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

In FIG. 14A, the detectors A, B, C, and D show an example of a detector arranged symmetrically with respect to the optical axis on the lower surface portion of the objective lens 5 in FIGS. 1 to 4 and 11. Now, let us show an electronic detector.

FIG. 14B shows an example in which the signals A, B, C, and D detected by the four detection devices A, B, C, and D of FIG. 14A are calculated to generate an emphasized signal.

Hereinafter, the features of the actual device will be described.

(1) When performing electron beam autofocus, there is a sample 9 having a very small contrast. For example, when a template for nanoimprint made of quartz, a thin film is placed on a photomask, or a resist covers the entire surface, a very small uneven shape made of the same material is surfaced. In the case of the sample contained in, it is impossible to autofocus using a normal SEM signal because even an image cannot be seen with a top-down image of a normal SEM.

(2) In such a case, if the signal obtained when the sample 9 is viewed from an angle is used, autofocus becomes easy. For that purpose, as shown in FIG. 14, for example, by arranging four electron detection devices A, B, C, and D, it becomes possible to detect signal electrons generated from the sample 9 depending on the angle. It is desirable that the placement position is axisymmetric when viewed from the primary electronic axis. For example, a difference image in the Y direction can be created by subtracting the C + D signal from the 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 when the sample 9 is viewed from an oblique direction can be obtained, so that 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 adopted, the contrast of the edge can be observed under the condition of the vicinity where the electron beam in-focus is obtained, but when the distance is further than that, the contrast of the edge is completely the same as that of the front image. The edges cannot be observed. In other words, it is not possible to find out the in-focus state by roughly shaking the focus intensity of the objective lens.

(4) By using the optical height sensor of the present invention, 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 autofocus can be achieved. The probability of success can be greatly improved.

FIG. 15 shows an example of arrangement 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 placement location, and the light beam emitted from the sensor head 8 is reflected by a light guide (reflection) (not shown). The height of the photomask 9 is optically measured by irradiating the photomask 9 vertically with a mirror (mirror, optical fiber, etc.) 7 and incident the reflected light rays on the sensor head 8 with a light guide (reflector, etc.) 7. can do. The sensor head 8 is connected to the spectroscope 11 of FIG. 1 described above by an optical fiber, and the sample 9 is caused by the interference between the laser beam (broadband) reflected inside the spectroscope 11 and the returned laser beam. It is possible to measure the height precisely.

With one sensor head 8 in the illustrated state, the entire photomask 9 can be measured on the XY stage with a stroke of 20 cm.

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

In FIG. 16, the region for estimating the mask height indicates a region where 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 area that can be measured by the two optical height sensors is the 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 Zc = (Z1A + Z2B) / (A + B) described on the right side.
-Zc: Sample height at the objective lens position (electron beam irradiation position) -A, B: Samples of light rays from the sensor head (Z1) and sensor head (Z2)
Distance from the electron beam irradiation center position on the sample 9 when irradiating with Z1A, Z1B: It can be obtained by the height of the sample 9 at the distances A and B.

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

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

It is 1 Example structural drawing (the 1) of this invention. It is 1 Example structural drawing (the 2) of this invention. It is a detailed structural drawing (the 1) of this invention. It is a detailed structural drawing (No. 2) of this invention. It is a focus map creation flowchart of this invention. This is an example of the focus map measurement point of the present invention. This is an example of the height measurement value of the present invention. It is an example of an approximate curved surface that passes through the measurement point of the present invention. It is a flow chart of height measurement of the sample of this invention. It is an autofocus flowchart (the 1) of this invention. It is a structural drawing of another Example of this invention. It is an autofocus flowchart (No. 2) of this invention. It is an autofocus flowchart (No. 3) of this invention. This is an example of image acquisition using the electron beam of the present invention. This is an example of arranging the sensor head of the present invention. It is explanatory drawing of the height estimation area of this invention.

1: Electron gun 2: Electron beam 3: Deflection device 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 scans while irradiating a sample with a finely focused charged particle beam and autofocuses the charged particle beam based on the signals emitted, reflected, and absorbed at that time.
An objective lens and a scanning system for scanning while irradiating the sample with a finely focused charged particle beam are provided, and an interference device and an optical fiber are connected to an outer surface portion of the objective lens or a hole portion provided in the objective lens. Fix the sensor head toward the sample and fix it.
The sensor head emits a light beam incident from the interfering device toward the sample, receives the reflected light beam, and emits the light beam to the interfering device.
The interfering device measures the distance between the sensor head and the sample in real time based on the emission and incidence of light rays, and the autofocus means uses the charged particle beam on the sample based on the measured distance. An autofocus device that autofocuses and focuses on the entire surface of a sample or a wider area than the area of the sample scanned by the charged particle beam . The autofocus device according to claim 1, wherein the interference device is a spectroscope using a plurality of wavelengths. The autofocus means uses a Z stage which is held by at least three piezoelectric elements and has a mechanism for correcting the height of the sample or the height and inclination of the sample, and charges the sample to which the charged particle beam focuses. The autofocus device according to any one of claims 1 to 2 , wherein the particle beam is moved in the axial direction to be focused and speeded up. While scanning while irradiating the sample with the charged particle beam and acquiring an image generated from the signals emitted, reflected, and absorbed at that time, the height of the sample is measured in real time by the one or more sensor heads. The autofocus device according to any one of claims 1 to 3, wherein the autofocus device is characterized in that.

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