JP6548764B2 - Auto focus device - Google Patents

Description

  The present invention relates to an autofocus device.

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

  Conventionally, a laser beam with a wavelength of 193 nm has been used for exposure, but since it has already far exceeded the limit that can be resolved optically, in recent years exposure technology utilizing EUV light with a wavelength of 13.5 nm is vigorously promoted ing. This technology is a technology said to be from Japan, but has been researched and developed for practical use in ASML etc. from 10 years ago. Although the exposure system main body optical system is almost complete, the current EUV exposure system can not obtain the light source power of 100 W to 200 W required for economical mass production, so it can not be used for 20 nm generation exposure It was skipped.

  Instead, a so-called double or triple exposure technique is used in actual production sites, which can realize smaller feature sizes by repeating the existing 193 nm wavelength exposure process multiple times. In principle, it is possible to make a pattern as small as possible by repeating immersion lithography using a laser beam with a wavelength of 193 nm multiple times, but it is necessary to have an alignment accuracy on the order of nm higher than the conventional one. It is known that the large roughness etc. coming from the large molecular structure of the chemically amplified resist repeatedly becomes the limitation of the exposure process. At present, double patterning that repeats the exposure process twice, which is said to be an economic limit, is put to practical use, and a memory device with a relatively simple structure is used to achieve 20 nm to 16 nm lines and spaces. It is done.

  Not only simple memory devices but also CPUs and logic devices need to be reduced in size to expand their functions and reduce their power consumption. Since logic devices utilize complex patterns that do not repeat, considerable complexity of patterns is required to make logic devices with double or triple exposure. A very complicated calculation is required to divide a pattern that can be originally realized by one exposure into patterns on two photomasks so that it can be used by multiple exposures. Depending on the pattern, the required result may not be obtained due to divergence of division calculation.

  In order to avoid these complexities, lithography facilitation technology called "Complementary Lithography", mainly proposed by Intel, is being used. This exposure method is characterized by using a pattern obtained by reducing a complicated logic circuit into a simple L & S pattern such as a memory circuit. In this way, the complicated logic device pattern is limited to the process of cutting the L & S pattern and its lines that are most easily exposed, so there is no need for complicated pattern division calculation, and the process is simple. The top is said to go to about 8 nm.

  On the other hand, as described above, when the 193 nm exposure technology is extended, the photomasks used for it will increase by the number of exposures for each layer, and more mask inspection and precise dimension measurement will be required than ever before. Become. For example, in double patterning, since two photomasks are sequentially stacked and used, 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. A mask or the like using inverse lithography is used up to high-order diffraction height, so the pattern size used for correction is smaller.

  Although electron microscopy techniques are essential to determine whether these masks are made with the correct dimensions, autofocus techniques are 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 autofocus fails, not only can it not be measured, but erroneous measurements will be provided to the process control, which will cause extra yield loss, and it will not be tolerated because it will suffer large losses.

  In order to assist the autofocusing of the conventional electron beam optical system, an optical height measuring method has been developed which noncontactly measures the sample height of the electron beam irradiation point. There is an objective lens at the tip of the electron beam column, and the pole piece tip has a very close positional relationship with the sample to be observed, and therefore only a few millimeters are separated. In order to measure the distance, conventionally, an LED or a laser beam is obliquely incident on the electron beam irradiation point, the position of the reflected light is detected by a light sensor such as a CCD, and the height of the sample is measured. A scheme has been adopted.

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

  In addition, when the sample is inclined, it is indistinguishable from the change in sample height, so that there is a problem that complicated correction for separating the height component and the sample inclination component is required. The measurement may be unstable depending on the pattern and material of the sample surface.

  On the other hand, since the optical path length of the LED, the laser light source or the optical system constituting them has a large size of several tens of centimeters, the optical path length variation due to the deformation of the top plate due to the atmospheric pressure change There is also a problem that the measurement accuracy is reduced because the change is easily caused by the change. 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 causes problems such as high cost and maintenance difficulties.

  In addition, since the system itself generates heat in the conventional system, there is also a problem that the temperature of the peripheral portion of the apparatus changes with use time, which affects the measured value. There is also a problem that the measurement accuracy of only about 1 micron can be realized by combining these.

  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, in the charged particle beam apparatus according to the present invention, the charged particle beam is finely narrowed and scanned while irradiating the sample, and an image is generated based on the signal emitted, reflected, or absorbed at that time. An objective lens and a scanning system are provided which narrows and irradiates and scans the sample, and a light beam is directed to the sample and the sample is viewed on the outer surface of the objective lens or the hole provided in the objective lens as seen from the sample. A light guide for receiving a reflected light beam, a sensor head for emitting a light beam to the light guide and a light beam emitted from the light guide, a light beam emitted to the sensor head and emitted from the sensor head And a spectroscope for detecting the irradiation position of the light beam on the sample based on the received light beam and the received light beam.

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

  In addition, a light guide has a reflecting mirror, a prism, or an optical fiber attached to a portion seen from the sample to irradiate a light beam to the sample and to receive a light beam reflected by the sample.

  Also, irradiating the sample with a light beam causes the light beam to be irradiated substantially perpendicularly to the sample.

  In addition, a plurality of light guides are provided.

  In addition, 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.

  In addition, the height at a plurality of locations of the sample is measured by one or more light guides, and the relationship between the location of the sample and the height 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 The height adjustment mechanism is provided to adjust 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, autofocusing by the charged particle beam can be performed at high speed and reliably. It is done to generate an image that is in focus.

  According to the present invention, the height of the sample in the vicinity of the electron beam irradiation point is directly measured and set by one or a plurality of optical height sensors, and the precision auto by the electron beam is measured based on the measured or set sample height. While focusing, it is possible to set a stable ultra-high precision height setting of over 0.1 micron with a very simple configuration for the height of the sample, and high speed and precision based on the height of the measured or set sample. And, the electron beam can be reliably focused.

  Also, in the case where the sample is a semiconductor wafer, the light beam for measuring the height of the sample may change the conductivity in the irradiated area of the light beam and affect the measurement value by the electron beam in some cases. 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 measurement is performed in parallel by irradiating the sample with the electron beam Can.

  The actual device will be described in detail below.

  (1) By utilizing the present invention, it is possible to realize a high-speed and accurate electron beam focusing state without an autofocus failure as compared with the case where only the conventional electron beam autofocus is used. Before performing electron beam autofocusing, a state close to the electron beam in-focus state can be made sufficiently, so that the range in which the electron beam autofocusing searches for the focus value is about 1/10 or less of the conventional range. It is possible, and autofocus can be performed at high speed by that amount.

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

  (3) Since the optical height sensor is very compact unlike in the prior art, mounting and maintenance are easy. Since the height is directly measured, the inclination correction of the sample 9 which is required in the conventional method is unnecessary. There is no need to push the sensor into the narrow space of the pole piece tip of the objective lens 5 and the surface of the sample 9 because measurement at the electron beam irradiation point is not required.

(4) The measurement can be extremely stabilized because no electromagnetic wave or heat is generated at the time of sensor operation.
Because the materials are crows and metal, vacuum contamination can be avoided. No moving parts, long life.
Because 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 the external environment change, the change can be measured in real time Electron beam autofocus can be made more successful.

  (6) Even when two optical height sensors can not be measured at the same time in real time, height measurement similar to measuring in almost real time can be performed by utilizing the focus map created in advance It can.

  (7) Even for a sample 9 that is difficult to autofocus only with electron beam images, 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 You can shake the beam focus. As a result, it becomes easy to obtain an electron beam focused state in a three-dimensional object or a measurement target having a low edge contrast.

  (8) When the Z stage 22 with three points of support is used, the inclination of the sample 9 can be made zero 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 obtain a more accurate electron beam image.

  In the present invention, the height of the sample in the vicinity of the electron beam irradiation point is directly measured and set by one or a plurality of optical sensors, and precise autofocusing by the electron beam is performed based on the measured or set sample height. As a result, it becomes possible to set a stable ultra-high precision height setting exceeding 0.1 micron with a very simple configuration for the height of the sample, as well as high speed, precision and reliability based on the height of the measured or set sample. It was realized that the electron beam autofocus.

  Also, in the case where the sample is a semiconductor wafer, the light beam for measuring the height of the sample may change the conductivity in the irradiated area of the light beam and affect the measurement value by the electron beam in some cases. In the present invention, since the light beam does not directly irradiate the electron beam measurement point, while measuring the height of the sample in real time with the light beam, it is realized that the measurement is performed in parallel by irradiating the sample with the electron beam .

  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 sequentially described in detail as to the structure of one embodiment. In addition, charged particle beams (ions etc.) other than the electron beam can be configured in the same manner as described below in accordance with the respective charged particle beams.

  (A) of FIG. 1 shows a side view, and (b) of FIG. 2 shows a bottom view.

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

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

  The deflecting device 3 deflects the focused electron beam 2 in X and Y directions (usually two-step deflection), and flattens the electron beam 2 narrowed by the objective lens 5 on the sample (photomask) 9 It is known to scan (scan in X and Y directions).

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

  The objective lens 5 is a known lens that narrows the electron beam 2 finely and irradiates it onto a sample (photomask) 9.

  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. The reflecting mirror 7 reflects the light beam (laser beam) from the sensor head 8 and emits it (reflecting) toward the sample (photomask) 9, and the sample The light beam reflected by 9 is reflected in the direction of the sensor head 8. The light guide 7 may be, for example, an optical fiber other than a reflector or a prism, and 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 is, it may be anything. The size of the laser beam emitted from the laser head 8 is 0.1 to 1. The diameter was about several mm, and about 0.6 mm in diameter was used in the experiment. Therefore, the reflecting mirror (light guide) 7 may be any as long as it has a reflecting portion of about 0.1 to 2 mm, and a very small one can be used.

  The laser head 8 outputs the light beam from the spectroscope 11 to the light guide (reflecting mirror) 7 to illuminate the sample 9, and the light beam reflected by the sample 9 is taken in via the light guiding device (reflecting mirror) 7 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 about 0.6 mm in diameter was used in the experiment. The light beam emitted from the laser head 8 is reflected by the reflecting mirror 7 and illuminates the sample 9, and the light beam reflected by the sample 9 is reflected by the reflecting mirror 7 and changes the optical path length when it is incident on the laser head 8. The laser head 8 and the part to which the reflector 9 is attached (usually the objective lens 5 or members around it) generate errors due to expansion due to thermal change, so they are not affected by thermal change or have a thermal expansion coefficient It is necessary to devise that the optical path length does not change by adopting a small material or a material having the same thermal expansion coefficient.

  The spectroscope 11 is integrated with the laser head 8 and the light guide (reflecting mirror) 7 to constitute a spectral interference type laser displacement measuring device. Hereinafter, for convenience, the distance between the objective lens 5 and the surface of the sample (photomask) 9 is referred to as height (height of sample, Z). Among the spectroscope 11, sensor head 8 and light guide 7 constituting the spectral interference type laser displacement measuring apparatus, the size of the sensor head 8 is usually very small, such as several centimeters in length and several mm in width. An optical element is built in the inside of the sensor head 8, and an optical fiber for receiving a laser beam from the outside (spectrometer 11) is attached to an end of the sensor head 8. Since an electrical circuit is not usually present inside the sensor head 8, it does not become a source of electrical noise. Since the output of the laser beam used is also as small as mW or less, it does not serve as a heat source either, and the object to be measured (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 laser emission is made of glass, and in the case of the structure of FIG. 1, the lens is usually disposed inside the sample chamber and can withstand plasma cleaning and the like. Since the measurement speed of the height of the sample 9 is up to 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 reflecting mirror (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 arranged symmetrically here with respect to the center of the objective lens. It is not necessary to arrange symmetrically.

  An image is generated by detecting secondary electrons and reflected electrons when the electron beam 2 scans in a plane while irradiating the sample 9 based on the height data of the sample 9 from the spectrometer 11. Automatically controls the current of the objective lens 5 (precisely, controls the current of a dynamic focusing coil (not shown) separately provided on the objective lens 5) to perform focus control (eg, 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 accurately measured by the system of the spectroscope 11, the sensor head 8 and the reflecting mirror (light guide) 7, the height of the measured sample 9 is The current of the objective lens 5 may be controlled so as to focus, and the focus control may be slightly re-focused on the center of the current, and 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 the sensor head 8 and the spectroscope 11 (transmits and receives a laser beam).

  (B) of FIG. 2 shows a bottom view. Here, as illustrated, the height Ze of the sample at the center of the objective lens 5, the height Z1 of the sample of the reflecting mirror 7 that receives the light beam from the sensor head (Z1) 8 and reflects it to the sample 9 (Z2) The light beam from 8 is received, and the height Z2 of the sample of the reflecting mirror 7 reflected by the sample 9 is obtained. In addition, 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 at which a light beam is irradiated to the sample 9) is detected from the center (optical axis) of the objective lens 5 The distance of the position of the reflecting mirror 7 of the head (Z2) 8 (the position where the light beam is irradiated to the sample 9) is defined as Z1.

As above,
The height of the sample at the center of the objective lens 5 = Ze
· Height of sample of reflector 7 of sensor head (Z1) = Z1
· Height of sample of reflector 7 of sensor head (Z2) = Z2
If you define
・ 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 in axial symmetry with respect to the optical axis).

  Next, the operation and features of 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 just beside the sample (photomask) 9. The laser beam is bent by 900 degrees in the traveling direction by the 90-degree reflecting mirror 7 and is irradiated almost perpendicularly to the surface of the sample 9.

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

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

  (4) The method of measuring the height of the sample according to the present invention is different from the above-mentioned conventional method of measuring the height of inclination, and the incident angle is almost perpendicular to the sample 9. Since the variation (error) of the measured value is extremely small, there is no need for the inclination correction of the conventional sample 9 and it is easy to use. In addition, the pattern on the surface of the sample 9 is hardly affected.

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

  (6) The two sensor heads 8 shown in FIG. 1 and FIG. 2 and the reflector (light guide) 7 measure the height of a place different from the irradiation position of the electron beam 2 on the sample 9, but 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 the two represents the height of the sample at the irradiation point on the sample 9 of the electron beam 2 (estimate To do). By performing such calculation with 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 determined accurately and in real time without directly measuring it.

  (7) Also, since the distance between the pole piece tip of the objective lens 5 and the sample 9 is usually as narrow as several mm, it is virtually impossible to arrange the height sensor of the sample at that position, but the present invention In this case, the reflecting mirror (light guide) 7 can be disposed at a position away from the tip of the pole piece of the objective lens 5, or a hole can be formed in the objective lens 9 to 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 disposed at any place, and the height of the sample can be measured with high accuracy and in real time.

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

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

  FIG. 3A shows an example of the structure in which the reflector 7 is disposed on the side surface of the objective lens 5 as illustrated. In the illustrated structure example, a light beam (laser beam) emitted rightward from the sensor head (Z1) 8 is reflected downward by a mirror (or prism) at 90 degrees and irradiated almost perpendicularly to the sample (photomask) 9 The reflected light beam enters the sensor head (Z1) 8 in the reverse 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 illuminates the sample 9 from the vertical direction, and the reflected light beam returns in the reverse direction and enters the spectroscope 11. The spectroscope 11 causes the emitted laser beam (wide band) to interfere with the laser beam reflected back from the sample 9 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, also for the sensor head (Z2) 8 on the right side, it becomes possible to measure the height Z2 of the sample 9 at the position of the reflecting mirror 7 of the laser head (Z2) 8 in real time with high accuracy.

  FIG. 3B shows an example of the structure 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, it is possible to measure the heights Z1 and Z2 of the sample at the position of the third reflecting mirror 7 in which the light beam is irradiated from the vertical direction of the photomask 9 and the optical axis of the objective lens 5 is shown in FIG. It is possible to measure the heights Z1 and Z2 of the sample closer than the above.

  FIG. 3C shows a structural example in which the reflecting mirror 7 is disposed on the bottom surface of the objective lens 5 as illustrated. In this case, it is possible to measure the heights Z1 and Z2 of the sample at the position of the third reflecting mirror 7 in which the light beam is irradiated from the vertical direction of the photomask 9 and to the optical axis of the objective lens 5 as shown in 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 is made conductive so as to prevent the charge of electrons.

  Also, the reflecting mirrors 7 are disposed symmetrically about the optical axis of the objective lens 5 so that no directional dependence occurs when the electron beam 2 scans while irradiating the sample 9 or a dummy reflecting mirror 7 It is desirable to place

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

  FIG. 4D shows a structural example in which the reflecting mirror 7 is disposed on the objective lens 5 and a light beam transmitted through a hole at the center of the objective lens 5 is irradiated to the sample (photomask) 9. 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 substantially transmitted to the sample (photomask) 9. Since the light is irradiated vertically and the reflected light beam is incident on the sensor head (Z1, Z2) 8, the heights Z1, Z2 of the sample near the position where the electron beam 2 irradiates the sample 9 can be easily made real time and high precision Can be measured.

  In (e) of FIG. 4, the reflecting mirror 7 is placed inside the substantially central hole of the objective lens 5 (a small hole which is used to pass an existing hole if it is used, or a light beam is opened to pass it). The structural example which irradiates the sample (photo mask) 9 with the light ray which permeate | transmitted the hole of the center of the objective lens 5 is shown. Also 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 used as a sample (photomask) 9 Since the light beam is emitted almost perpendicularly and the reflected light beam is incident on the sensor head (Z1, Z2) 8, the heights Z1, Z2 of the sample near the position where the electron beam 2 irradiates the sample 9 can be easily made real time and high. It can measure to accuracy.

  In FIG. 4 (f), an optical fiber 15 is used instead of the reflecting mirror 7, and a substantially central hole in the vertical direction of the objective lens 5 (an existing hole is used and an optical fiber 15 is The optical fiber 15 is placed in the small hole and in the hole part where the electron beam 2 in the center of the objective lens 5 does not pass, and the light emitted from the optical fiber 15 is made approximately perpendicular to the sample (photomask) 9 The structural example to irradiate is shown. In this case, the optical fiber 15 is passed through the hole of the objective lens 5, and the light emitted from the sensor head (Z1, Z2) 8 is irradiated from the tip of the optical fiber 15 substantially perpendicularly to the sample (photomask) 9. Since the reflected light beam is returned to the sensor head (Z1, Z2) 8 through the optical fiber 15, the heights Z1, Z2 of the sample near the position where the electron beam 2 irradiates the sample 9 can be easily made in real time and While being able to measure with high precision, a reflecting mirror becomes unnecessary.

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

  In FIG. 5, S1 moves the stage to defined coordinates on the mask. In this case, the stage is sequentially moved to predetermined coordinates on nine or more masks on the left, right, upper and lower sides symmetrically as described on the right side, and S2 is repeated. For example, as shown in the photomask 9 of FIG. 6 described later, the photomask 9 of FIGS. 1 to 4 is not shown at nine or more points (x0, y0), (x1. Y0)... (Xn, yn) Move and position the stage of (position is precisely measured with a laser interferometer not shown).

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

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

  S4 completes the focus map.

  As described above, the heights of the plurality of positions on the photomask 9 are respectively measured by the height sensors of FIGS. 1 to 4 for the height Z of the sample (FIG. 6, FIG. 7). It is possible to perform fitting of the parameters of to create a focus map (FIG. 8). Thereafter, referring to the focus map, height information at an arbitrary position on the photomask 9 is read out, and the electron beam is automatically focused at high speed and reliably as 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 execute the height measurement of the sample 9 substantially continuously regardless of the electron beam irradiation. Therefore, height measurement can be performed from the moment the sample 9 to be measured is carried into the vacuum chamber. The focus map represents the distance from the tip of the objective lens pole piece to the measurement object (so-called height of the sample) as a function of the measurement object observation position (X, Y). Since the objective lens 9 is fixed to the top plate, it is positioned at substantially the same height unless the top plate moves largely due to pressure fluctuation. On the other hand, since the sample 9 to be measured is not necessarily placed horizontally when installed in the sample holder, the sample 9 may be inclined. 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 height of the sample 9 with respect to the change in stage position is given by the combination of the above two values. Above all, the height change amount of the sample accompanying the stage movement is an intrinsic value of the stage and is known to be reproducible for repeated measurement, so it is possible to describe it as an inherent function.

  (2) Therefore, every time a new sample (photomask) 9 is placed on the sample holder, the amount of tilt 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 determined by calculation.

  (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 circumference of the object to be measured is measured by an optical height sensor as much as possible. When the object to be measured is a semiconductor photomask, it is extremely flat, so, for example, about nine points as shown in FIG. 6 are taken as measurement points. The XY stage is moved to each position, and the height Z of the position is measured and recorded by the height sensor (S1, S2 in FIG. 5). Repeat this several times to find the average value. Next, since the stage-specific function is symmetrical about the center of the stage, it is used to remove the offset component of the function. By doing this, it is possible to obtain a function representing the stage-specific height change (S3, S4 in FIG. 5). With this function, a new measurement object can be placed in the holder and the heights of several points can be measured to obtain a focus map for this measurement object (FIGS. 5 to 9).

(4) Every time a new measurement target is placed on the sample holder, the height distribution of the sample with respect to the XY stage position can be acquired and used as an ad hoc focus map in the measurement. In this case, it is possible to obtain a focus map including the holder installation inclination to be measured. Curve fitting is performed so that the above value can be expressed as a function of a plane so that the height for any coordinate can be calculated, and an approximate curve is obtained. As the approximate curve, a function as simple as possible such as a quadratic plane function or a spline function as shown in FIG. 8 is used. By entering values into X and Y of this function, the height at any coordinate 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 is 15 cm wide and wide, and 3 × 3 measurement points (x0, y0), (x1, y0), (x2, yo). Set as shown.

  FIG. 7 illustrates an example height measurement of the present invention. Here, x, 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 FIG. 1 to FIG. 4 correspond to the height table Furthermore, an example stored as illustrated is shown.

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

In FIG. 8A, the example of the illustrated focus map is measured based on the relationship of the height (z) measured at the position (x, y) on the photomask 9 measured in FIG. point (x, y, z) is approximated curve passing through (in this case, the approximate curve ^{Z 2 =} X 2 + ^Y 2 in FIG. 8 (b)) shows an example of obtaining the focus map with.

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

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

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

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

  S14 is NO in S12, and it is found that the two height sensors (Z1, Z2) are not within the measurement area, so it is further determined whether the height of Z1 is OK. This proves that both of the two height sensors (Z1 and Z2) are not within the measurement area, and it is further determined whether the height of Z1 is OK (within 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, in the case of NO of S14, it progresses to S16.

  S16 is NO at S14, and the height NG of Z1 is found, so it is further determined whether the height Z2 is OK. Since it turns out that the sensor of Z1 of the two height sensors (Z1, Z2) is not within the measurement area, it is further determined whether the height of Z2 is OK (within the measurement area). If YES, the height Z2 of the OK height sensor (Z2) and the height Z (X-L, Y) of the position (X-L, Y) of the NG height sensor (Z1) on the focus map , Y) and calculate the height (Z2 + Z (X−L, Y)) / 2 of the average value. On the other hand, in the case of NO in S16, since both height sensors Z1 and Z2 are found to be NG, the height Z is calculated to be the same as the height Z of the map value (X, Y).

  By the above, with the photomask 9 moved and positioned at the designated measurement point, the height is measured by the height sensor (Z1, Z2), and when both can be detected, it is possible to use only one average value. When one is measured height of the sample and one that can not be measured, the average value with the height on the map, and when both can not be measured, it is calculated as the height on the map, and the photomask indicated in real time and with high accuracy It is possible to measure the height of the upper position.

  FIG. 10 shows an auto-focusing flowchart (part 1) of the present invention. This shows a flowchart for performing electron beam autofocusing at high speed without failure using values 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. This is because, as described in FIGS. 5 to 8 described above, the height of the sample (photomask) 9 is measured, for example, at least nine 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 obtained, and the electron beam focus value is set to the obtained search lower limit (value).

  S22 performs electron beam scanning and image acquisition. In this method, the electron beam is planarly scanned on the sample (photomask) 9 at the electron beam focus value set in S21, and the secondary electrons (or reflected electrons and absorbed electrons) emitted at that time are detected, and an image is displayed. 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 performs electron beam scanning and image acquisition.

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

  S26 estimates the in-focus point value. This is to estimate the focus value at the time of focusing for each image obtained when the electron beam focus value is changed with a predetermined step width from the search lower limit to the search upper limit obtained (generated) in S22 and S24. The method is a known contrast method (maximum contrast (focus value when the image is differentiated and the sum is the maximum image)), edge inclination method (image with the maximum inclination of the edge portion of the line profile of the image) A known focus value, an 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. By estimating the focus value and setting it to the estimated in-focus point, automatic focusing by the electron beam is performed 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 focus quickly and reliably.

  The actual device will be described below.

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

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

  In FIG. 11, the 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 with a laser interferometer (not shown), the XY stage 21 is not shown. It is driven by a servomotor.

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

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

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

  The Z stage control means 32 controls the Z stage 22 (by applying predetermined voltages to the piezoelectric elements A, B and C, respectively), and moves the photomask (sample) 9 to a designated position (Z) It is Since Z movement (Z axis drive) has vibration resistance, a piezoelectric element capable of generating a large force is used. For example, a length of several centimeters, a thickness of several centimeters, and a displacement of about several tens of microns can be obtained at 100V. The sample holder 23 is supported at three points from the plane of the base XY stage 21. The three piezoelectric elements A, B, and C have respective high voltage amplifiers and can be independently controlled. Therefore, using the data obtained when creating the focus map in advance, the tilt component of the photomask (sample) 9 is extracted, and the piezoelectric element A, so that the displacement necessary to cancel the tilt occurs. By appropriately applying voltages to B and C, respectively, 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 an optical height sensor comprising 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 autofocus control means 34 detects and generates signals such as secondary electrons when the photomask (sample) 9 is planarly scanned with the electron beam 2, and the focus supplied from the search lower limit to the search upper limit to the objective lens 5 Based on the image associated with the current value, the current value of the objective lens at the in-focus point (actually, the current value to be supplied to the dynamic coil provided separately from the objective lens 5) is estimated, and the estimated object current value 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 centrally controls the entire system of FIG.

  Under the above-described structure, the focus map of the photomask 9 is created as described in FIGS. 5 to 9 described above with, for example, nine or more points of the photomask (sample) 9, and the height of the photomask 9 The height of the sample (photo mask) 9 and the sample (photo mask) are applied by applying predetermined voltages to the three piezo elements A, B and C constituting the Z stage 22 so that It is possible to correct the inclination of 9) and to position the level of the sample constantly at a constant level. Then, after the height of the sample 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 an in-focus image can be acquired quickly and reliably. It becomes possible.

  FIG. 12 shows an autofocusing flowchart (part 2) of the present invention. This is the case in which 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 becomes constant. This applies a predetermined voltage to each of the three 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 becomes constant. And the sample 8 is horizontal.

  In step S32, the electron beam focus value is set to the search lower limit of the specified value (the search lower limit of the optical height measurement value). This is because, as described in FIGS. 5 to 8 described above, the height of the sample (photomask) 9 is measured, for example, at least nine 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 obtained, and the electron beam focus value is set to the obtained search lower limit (value).

  S33 performs electron beam scanning and image acquisition. This is performed by planarly scanning the electron beam on the sample (photomask) 9 at the electron beam focus value set in S32, detecting the secondary electrons (or reflected electrons, absorbed electrons) emitted at that time, and the 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 performs electron beam scanning and image acquisition.

  S36 determines whether the upper limit of the search range. In the case of YES, the process proceeds to S37. In the case of NO, the processes after S34 are repeated.

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

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

  The procedures and features of the actual device will be described below.

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

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

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

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

  (5) Using this function, an operation is performed to find the maximum minimum or maximum maximum and minimum, etc., and the focus intensity estimated to be able to realize the highest contrast state on the function is set as the in-focus point (S37 in FIG. 12).

  (6) An in-focus image can be obtained by setting the focus of the actual electron microscope to this focus intensity.

  (7) In addition, a plurality of images obtained when the focus intensity is changed similarly by using FFT (spatial frequency analysis) or the like is 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 set as the in-focus point by performing an operation of finding the maximum minimum and maximum maximum and minimum using this function. As a method for finding an in-focus point, all methods widely known in the world can be used besides the above methods, 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 the optical system, in the electron optical system, the image rotates when the focus is changed. When the image is rotated, image distortion occurs depending on the location, so that various corrections need to be made to perform dimension measurement. In the present invention, the distance (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 becomes constant after being parallel. , Z stage 22 is driven to change the height of the sample 9. After that, in order to correct a subtle focus error, it is a method of performing electron beam focusing. In this way, almost no image rotation due to focus occurs. Even if it happens, it will be a very small value, so the measurement error caused by the rotation correction can be reduced.

  (9) In particular, not only the distance measurement between two points, but in recent years, the method of reading the image itself accurately 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 large especially at large FOV.

  FIG. 13 shows an auto-focusing flowchart (part 3) of the present invention.

  In FIG. 13, S41 sets the sample to the reference height. The Z stage 22 sets the sample 9 to 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 is based on the image acquired by planarly scanning the sample 9 with the electron beam in a state where the sample 9 is set to the reference height in S41, and the focus current value of the objective lens at the time of focusing is measured (estimated) Do.

  S43 changes the sample.

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

  S45 checks the resolution in the line profile. This is performed by acquiring the line profile of the sample 9 by the electron beam and checking the resolution thereof (for example, the resolution of the line profile of the acquired image is current) while the new sample 9 is adjusted to the reference height in S44 in S44. Check if it is sufficient for the purpose of use).

  S48 determines whether there is a charge. This is because it is determined whether the resolution checked with the line profile in the check of S45 is not sufficient and the resolution is reduced due to the influence of the charge of the sample 9 or the like. In the case of YES, correction of only the charge (correction of the current of the objective lens corresponding to the charge) is performed in S49. On the other hand, in the case of NO of S48, it ends.

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

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

  As described above, in a state where the sample 9 is set to the reference height by the Z stage 22 and the focus current of the objective lens is measured, after replacing the sample 9, the sample 9 is set to the reference height by the Z stage 22 and a line profile The resolution is checked at step S5 to determine if there is a charge etc. If it is found that there is a charge etc., correction is made only for the charge so that fast and stable automatic focusing can be achieved when the sample 9 is replaced. It will be possible to do.

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

  (A) of FIG. 14 shows a top view, and (b) of FIG. 14 shows an example of an emphasizing signal.

  In (a) of FIG. 14, detection devices A, B, C, and D show an example of a detector disposed on the lower surface portion of the objective lens 5 in FIG. 1 to FIG. In the figure, an electronic detector is shown.

  FIG. 14 (b) shows an example in which signals A, B, C, D detected by the four detection devices A, B, C, D in FIG. 14 (a) are operated to generate an emphasis signal.

  The features of the actual device will be described below.

  (1) When electron beam autofocusing is performed, a sample 9 with very small contrast is present. For example, in the case of a template for nanoimprint made of quartz, a thin film on a photomask, or a case where a resist covers the entire surface, the surface of a very small uneven shape made of the same material In the case of the sample having the above, it is impossible to use the normal SEM signal for autofocusing because the top-down image of the normal SEM can not even see the image.

  (2) In such a case, using a signal obtained when the sample 9 is viewed obliquely makes autofocus easy. For this purpose, as shown in FIG. 14, for example, four electron detectors A, B, C and D can be arranged to detect signal electrons depending on the angle generated from the sample 9. It is desirable that the positions to be arranged be axially symmetrical with respect to the primary electronic axis. For example, by subtracting the C + D signal from the A + B signal, a Y-direction difference image can be created. Alternatively, the difference signal in the X direction can be produced 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 is obtained, so that an image can be obtained in which the pattern edge is clearer than a normal SEM image observed from the front.

  (3) Even when the contrast enhancement method as described above is taken, the contrast of the edge can be observed in the vicinity condition where the electron beam focusing point is obtained, but if it is further away, it will be totally the same as the front image. Edges can not be observed. In other words, it is not possible to find out the in-focus state if the focus intensity of the objective lens is shaken and examined roughly.

  (4) By using the optical height sensor according to the present invention, the electron beam focus can be applied after the lens is brought close to 0.1 micron of the in-focus point. The probability of success can be greatly improved.

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

  In FIG. 15, the sensor head 8 described above is disposed at any one position or a plurality of positions described as a sensor allocable location, and a light beam emitted from the sensor head 8 is not shown The height of the photomask 9 is optically measured by irradiating vertically to the photomask 9 with a mirror, an optical fiber, etc. 7 and entering the reflected light beam onto the sensor head 8 with a light guide (such as a reflecting mirror) 7. can do. The sensor head 8 is an optical fiber, which is connected to the spectroscope 11 of FIG. 1 described above, and the interference of the laser beam (wide band) with the laser beam reflected back inside the spectroscope 11 causes the sample 9 to It is possible to measure the height precisely.

  The entire photo mask 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 view of the height estimation area of the present invention.

  In FIG. 16, an 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 head (Z2) 8.

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

The area which can be measured by the two optical height sensors is an area in which the height of the irradiation position of the electron beam can be estimated (measured) by the two sensor heads (Z1) 8 and sensor heads (Z2) 8. The estimated (measured) value is described on the right Zc = (Z1A + Z2B) / (A + B)
Zc: height of the sample at the objective lens position (electron beam irradiation position) A, B: the light beam from the sensor head (Z1) and the sensor head (Z2)
Distance from the electron beam irradiation center position on the sample 9 when irradiating the light beam Z1A, Z1B: The height 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, for example, in the following URL of Keyence sensor, so please refer to it.

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

It is structural drawing (the 1) of one Example of this invention. It is structural drawing (the 2) of one Example of this invention. It is a detailed structural drawing (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 the present invention. It is an example of the focus map measurement point of this invention. It is an example of the height measurement value of the present invention. It is an example of the approximate curved surface which passes the measurement point of this invention. It is a height measurement flowchart of the sample of this invention. It is an auto-focusing flowchart (the 1) of the present invention. FIG. 6 is a structural diagram of another embodiment of the present invention. It is an auto-focusing flowchart (the 2) of the present invention. It is an auto-focus flowchart (the 3) of this invention. It is an example of image acquisition by the electron beam of this invention. It is an example of arrangement | positioning of the sensor head of this invention. It is explanatory drawing of the height estimation area | region 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 : Spectroscope 12: Focus control means 13: Image processing means 14, 15: Optical fiber 21: XY stage 22: Z stage 23: Sample holder 31: XY stage control means 32: Z stage control means 33: Sample height information processing means 34: Autofocus control means 35: Image processing means 36: Overall control means

Claims (5)

An auto-focusing apparatus for performing autofocusing of a charged particle beam based on emitted, reflected, and absorbed signals while scanning while irradiating the sample with the charged particle beam finely narrowed.
An objective lens and a scanning system are provided which narrows the charged particle beam and irradiates and scans the sample, and a light beam is provided to a portion of the outer surface of the objective lens or a portion of a hole provided in the objective lens which is visible from the sample. A light guide for irradiating the sample and receiving a light beam reflected by the sample;
A sensor head that emits light to the light guide and receives the light emitted from the light guide;
A spectroscope which emits a light beam to the sensor head and receives a light beam emitted from the sensor head, and detects an irradiation position of the light beam on the sample based on the emitted light beam and the received light beam;
A Z stage for correcting the tilt of the sample;
And autofocusing means for autofocusing the charged particle beam onto the sample,
Based on the height of the sample measured by the one or more light guides, the Z stage corrects the tilt of the sample, and then the autofocusing means applies the charged particle beam to the sample. An autofocusing apparatus characterized by autofocusing and focusing on the entire surface or a wide area of a sample.   Correcting the inclination of the sample, instead of correcting the inclination of the sample, correcting the height of the sample to a predetermined value, narrowing the focus and the autofocus range over the entire surface or wide area of the sample and speeding up The autofocus device according to claim 1, characterized in that:   3. The autofocus device according to claim 2, wherein the height of the sample is corrected to a predetermined value by setting the height of the sample set by the autofocus or the height of the sample designated in advance.   During scanning of the sample while irradiating the charged particle beam onto the sample, and while acquiring an image generated from the emitted, reflected, or absorbed signal at that time, the height of the sample is increased in real time by the one or more light guides. The autofocus device according to any one of claims 1 to 3, wherein the distance is measured. The Z stage is held by at least three or more piezoelectric elements, and has a mechanism for correcting the tilt of the sample, or correcting the tilt and height of the sample . The autofocus device described in.