JP2007042513A - Inspection device and adjustment method of irradiation beam size of inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection device in which, when a testpiece is irradiated with an electron beam and scanned and a reflecting electron which increases corresponding with a mass is detected and amplified to form a reflecting electron image, conditions before a change of magnification and after a change of magnification of irradiating and scanning a testpiece by an electron beam is set at almost the same and a reflecting electron image having an adequate shade can be formed even if a magnification is changed, and provide an adjustment method of an irradiating beam size of the inspection device. <P>SOLUTION: An inspection device in which a testpiece is irradiated with an electron beam and scanned and a reflecting electron which increases corresponding to a mass will be detected and amplified to form a reflecting electron image is provided with an adjustment means to adjust a spot size of the electron beam so that a condition before a change of magnification can remain almost same with the condition after a change of magnification is instructed, and a means to irradiate and scan a testpiece corresponding to a magnification instructed and changed by the electron beam after adjustment. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inspection apparatus that scans a sample by irradiating a sample with an electron beam, and detects and amplifies reflected electrons corresponding to the mass to generate a reflected electron beam image, and an irradiation beam size adjustment method for the inspection apparatus. Is.

  Conventionally, a large mask (for example, 8 inch size) or the like is mounted on an SEM (scanning electron microscope) stage to measure and inspect patterns such as LSI masks in the semiconductor field, and the mask is applied with a finely focused electron beam. The secondary electrons emitted by scanning the entire surface are collected, detected and amplified to display a secondary electron image, and a pattern is measured and inspected on the secondary electron image.

  At this time, when the magnification is too small or too large, the scanning range is changed by irradiating the mask with the electron beam, and as a result, the size of the secondary electron image is varied.

  As described above, when changing the magnification, for example, the electron beam beam is irradiated to the mask at a high magnification and scanned, the focus is adjusted so that the secondary electron image becomes clear, and then the magnification is changed to a low magnification. For this reason, scanning is performed with the same electron beam spot size that is finely focused at low magnification, and a gap that is not irradiated with the electron beam is created between the scanning lines, at high magnification and at low magnification. However, there is a problem that a secondary electron image scanned under the same conditions cannot be obtained.

  In particular, in the case of a backscattered electron image generated by detecting and amplifying backscattered electrons whose signal amount increases corresponding to the mass on the sample when irradiating and scanning the sample with an electron beam, the Although it is required that the same conditions are satisfied when the magnification is changed from a magnification to a low magnification (for example, there is no gap that is not scanned with an electron beam between the scanning lines when the magnification is low or the same). There is also a problem that the above-described conventional method cannot satisfy this.

  In order to solve these problems, the present invention irradiates and scans a sample with an electron beam, and generates a reflected electron beam image generated by detecting and amplifying reflected electrons that increase in accordance with mass. An object of the present invention is to generate a reflected electron beam image having an appropriate gradation even if the magnification is varied by making the scanning condition by irradiating the sample with an electron beam beam substantially the same before and after the magnification change.

  The present invention irradiates a sample with an electron beam when scanning the sample by irradiating the sample with an electron beam and generating a reflected electron beam image generated by detecting and amplifying reflected electrons that increase in response to mass. By making the scanning conditions substantially the same before the magnification change and after the magnification change, it is possible to generate a reflected electron beam image having an appropriate shading even if the magnification is varied.

  The present invention irradiates a sample with an electron beam when scanning the sample by irradiating the sample with an electron beam and generating a reflected electron beam image generated by detecting and amplifying reflected electrons that increase in response to mass. Thus, the scanning conditions are made substantially the same before and after the magnification change, and a reflected electron beam image having an appropriate gray level can be generated even if the magnification is changed.

FIG. 1 shows a block diagram of an embodiment of the present invention.
In FIG. 1A, a SEM 1 is a scanning electron microscope having the configuration shown in the figure.

  The electron gun 2 generates an electron beam (for example, a tip of a tungsten wire is formed to have a sharp and predetermined surface, and a high voltage is applied to the anode 3 to extract the electron beam).

  The anode 3 applies a high voltage and accelerates electrons emitted from tungsten formed so that the tip of the cathode constituting the electron gun 2 is sharp and has a predetermined surface.

  The alignment coil 4 is for deflecting and aligning the electron beam emitted from the electron gun 2.

The condenser lens 5 focuses the electron beam emitted from the electron gun 2.
The deflection scanning coil 6 is for scanning an electron beam narrowly focused on a mask 11 as a sample by the objective lens 9 in the X direction and the Y direction.

  The backscattered electron detector 7 detects backscattered electrons reflected from the mask 11 when the mask 11 is scanned by irradiating the mask 11 with an electron beam. Based on the signal detected by the reflected electron detector 7, a reflected electron image is displayed on the display device 25. The backscattered electron detector 8 is usually a disk-shaped hole in which an electron beam passes, and the entire circumference is, for example, a fan shape that is divided into four parts. A reflected electron image having a dependent gray level is displayed, and the unevenness of the shape is highlighted by the difference between the two left and right signals.

  The secondary electron detector 8 collects, detects, and amplifies secondary electrons emitted from the mask 11 when the mask 11 is scanned with an electron beam. Based on the signal detected by the secondary electron detector 8, a secondary electron image is displayed on the display device 25.

The objective lens 9 narrows the electron beam on the mask 10.
The laser interferometer 10 is a known one that measures the position (positional coordinates) of the stage 12 with ultra-high accuracy by emitting a laser beam, reflecting it with a reflecting mirror attached to the stage 12 and capturing it.

The mask 11 is an example of a sample mounted (fixed) on the stage 12.
The stage 12 is mounted with a mask 11 and accurately moves to an arbitrary coordinate position, and is driven by a motor (or ultrasonic motor) 13.

  The motor 13 drives the stage 12 (X direction, Y direction), and is a servo motor or an ultrasonic motor.

  The PC 21 is a personal computer and performs various processes according to a program. Here, the PC 21 includes a condition storage means 22, an adjustment means 23, a scanning means 24, a display device 25, an input device 26, and the like. is there.

  The condition storage means 22 irradiates and scans the mask 11 with the electron beam, detects the reflected electrons reflected from the mask 11 by the reflected electron detector 7, and displays the reflected electron image on the display device 25. The conditions for irradiating the mask 11 with the electron beam (for example, the spot size of the electron beam, the current density of the electron beam (current value per unit area of the spot), the acceleration voltage, etc.) are stored.

  When the magnification of the reflected electron image of the mask 11 displayed on the display device 25 is changed, the adjusting means 23 adjusts to substantially the same conditions according to the changed magnification (for example, the beam spots of the electron beam are almost the same). Further, the current density of the electron beam is adjusted so as to be substantially the same) (to be described later with reference to FIGS. 2 to 5).

  When the magnification is changed, the scanning unit 24 adjusts the electron beam under the conditions after the adjustment by the adjusting unit 23 (conditions after adjusting the beam spot size of the electron beam, the current density of the electron beam, etc.). The beam is irradiated and scanned (described later with reference to FIGS. 2 to 5).

The display device 25 displays an image such as a reflected electron image.
The input device 26 is a mouse, a keyboard, or the like for inputting various instructions.

Next, the operation of the configuration of FIG. 1 will be described in detail according to the order of the flowchart of FIG.
FIG. 2 shows a flowchart for explaining the operation of the present invention.

  In FIG. 2, S1 displays a reflected electron image with a high magnification and a just focus. This is because an automatic focus program that moves on the operator or the PC 21 adjusts the current value of the objective lens 9 in FIG. 1, the electron beam beam irradiates and scans the mask 11, and the reflected backscattered electron detector 7 detects the reflected backscattered electrons. The reflected electron image that has been detected and amplified by and enlarged and displayed on the display device 25 is adjusted so as to be the sharpest (just focus). Then, the spot size and current density of the electron beam at the time of this just focus are stored (here, as shown, spot size S0 = 2 nm, current density I0 = 2A is stored). As the spot size S0, for example, the size diameter S0 = 2 nm at the time of just focus measured in advance for SEM1 is stored and read out, or used, or a very sharp edge portion formed on the mask 11 is scanned. It is obtained as the inclined width of the edge portion in the obtained image (the spot size S0 = 2 nm is automatically measured as the distance where the amplitude is between 10% and 90%). The current density of the electron beam is calculated as I0 = 2A here from the current of the electron beam beam that is currently flowing and the spot size.

  S2 displays a low magnification, reflected electron image with just focus. This is performed under the same conditions as when scanning by irradiating the mask 11 with the electron beam in S1, and only the magnification is low (the area where the electron beam is scanned with the mask 11 is large (scanning through the deflection scanning coil 6). The low-magnification backscattered electron image instructed by increasing the current)) is displayed on the display device 25.

  In S3, defocusing is performed so as not to cause missing teeth corresponding to the low magnification. This is because the reflected electron beam image in which only the magnification is changed to the low magnification in S2 is scanned with the spot of the electron beam radiated as shown in FIG. 3), as shown in FIG. 3C, defocusing (adjusting the current of the objective lens 9 or passing a current through a focus coil not shown in the figure) is performed so as not to cause tooth loss even when the spot size of the electron beam is low. The electron beam spot is defocused (focused at a position out of focus)). As a result, the spot size of the electron beam to irradiate the mask 11 is increased and the current density is substantially the same. The bias voltage of the gun 2 is adjusted (or the current of the condenser lens 5 is adjusted).

  In S4, an image is acquired. This is because the reflected electron beam image is displayed on the display device 25 in a state where the tooth missing state is eliminated by defocusing in S3, and a reflected electron beam image for length measurement and inspection is acquired and stored outside the figure. Store in the device.

  In step S5, the reference (CAD) image is compared with the acquired image. This compares the image of the CAD data of the reference LSI with the acquired reflected electron beam image by irradiating the mask 11 with the electron beam after eliminating the tooth-missing state acquired in S4, and scanning. For example, the widths of patterns to be inspected are compared).

  S6 evaluates. The result of the comparison in S5 is evaluated. If it is within the predetermined allowable range, it is determined as a non-defective product in S7, and if it is outside the predetermined allowable range, it is determined as a defective product in S8, and the process ends.

  In the case of the comparison, CAD data of the fixed pattern is obtained by obtaining a reflected electron beam image of a fixed pattern serving as a reference on the mask 11 and changing the threshold value when the acquired reflected electron beam image is binarized. Compared with the upper image (image of setting data), the binarized threshold value when matching is stored, and the reflected electron beam image obtained by binarizing the reflected electron beam image acquired with the threshold value in subsequent comparisons (After binarization with a threshold value) is compared with the pattern image on the CAD data, and it is determined as a non-defective product when it is within the allowable range and as a defective product when outside the allowable range.

  As described above, a reflected electron beam image is displayed with high magnification and just focus, and the spot size S0 and current density I0 of the electron beam at that time are stored. At this time, the electron beam is defocused and adjusted to an appropriate spot size so that tooth loss does not occur, and the current of the electron beam is adjusted so that the current density becomes substantially the same value. As a result, the same scanning conditions can be used for the high magnification before the magnification change and the low magnification after the magnification change (when the electron beam is applied to the mask 11 for scanning, the scanning of the beam spot is not lost). The current density at which the electron beam spot irradiates the mask 11 can be made substantially the same), and for the reflected electron beam image obtained by irradiating the mask 11 with the reflected electron beam and scanning, the reflected electron is the mass of the mask 11. Taking full advantage of the characteristic that the reflectivity increases as the (average atomic number) increases, and the conditions are the same before and after the magnification change, the density of the reflected electron beam image is almost the same, and evaluation and inspection ( Good products and defective products) can be performed with good accuracy. This will be described in detail below.

FIG. 3 is an explanatory diagram of the present invention.
FIG. 3A shows the spot size of the electron beam of the high-magnification reflected electron beam image. Here, as an example, a case where a rectangular range of 0.8 μm × 1.0 μm is scanned with an electron beam beam spot size of 0.1 μmφ is schematically shown. Since the horizontal is 0.8 μm, scanning is performed by sequentially shifting the spots of eight electron beam beams in the horizontal direction. Since the vertical length is 1.0 μm, scanning is performed by repeating sequential scanning of the spot of the electron beam 10 times in the horizontal direction. Now, the pattern on the mask 11 having a size of 200 nm × 800 nm is scanned with a total of 16 beam spots as shown in the figure, and a reflected electron beam image corresponding thereto can be displayed.

  FIG. 3B schematically shows an example of low magnification (before adjustment). This schematically shows a state in which only the magnification is changed to the low magnification after the adjustment in the high magnification state of FIG. At the low magnification shown in the figure, the beam spot of the electron beam remains at a high magnification, so that tooth loss occurs, and there are five electron beam beams at the upper left in the rectangular portion (rectangular portion of 200 nm × 800 nm). However, there is a disadvantage that the density is greatly reduced from 16 in FIG. 3 (a) to 5 and the density of the rectangular portion is greatly darkened. FIG. 3C of the present invention solves this.

  FIG. 3C schematically shows an example of low magnification (after adjustment). This is a solution to the state in which the tooth is missing in FIG. 3B, and the overall spot size of the electron beam is large (in the drawing, 0.2 μmφ) and the current density is substantially the same (current 4 and the current density is substantially the same), and the amount of the electron beam scanned by irradiating the rectangular portion (200 nm × 800 nm) is the rectangular shape in FIG. The rectangular portion can be displayed with substantially the same density even if the magnification is lowered on the reflected electron beam image.

  As described above, when the magnification is changed, the beam spot to be scanned by irradiating the mask 11 with the electron beam after the magnification change is made large (or small so as not to overlap) and the current is changed. By increasing (or decreasing) the current so that the densities are substantially the same, the density of the rectangular portion shown in the figure is reflected on the reflected electron beam image after the magnification change, and the pattern image on the CAD data and the magnification It is possible to easily compare with the reflected electron beam image when changing, and to inspect non-defective products and defective products with good accuracy and ease.

  In the above description, a case is described in which scanning is performed in dot units digitally in the scanning line direction and points on the mask 11 are sequentially irradiated with a predetermined spot of the electron beam. However, in the case of analog scanning in the scanning line direction, digital scanning is performed. As in the case of scanning in dot units, scanning is performed at a predetermined analog scanning speed at a predetermined spot of the electron beam.

  In addition, the case where the magnification is changed from the high magnification to the low magnification is described in FIGS. 3C and 3C. However, the case where the magnification is changed from the low magnification in FIG. 3C to the high magnification in FIG. 3B. In other words, the spot size of the electron beam is reduced so as not to overlap, and the current is adjusted to be small so that the current density is substantially the same.

FIG. 4 shows the relationship between the spot size of the present invention and the objective lens current.
FIG. 4A shows an example of a relationship curve between the spot size and the objective lens current. The horizontal axis represents the current of the objective lens, and the vertical axis represents the beam spot size of the electron beam on the mask 11. When the current of the objective lens is adjusted from the smaller one to the just focus and further larger, as shown in the figure, the spot size (spot size of the electron beam on the mask 11) is the smallest spot from the large size to the just focus. It becomes a size and changes to a larger spot size again. Measure the relationship between the objective lens current shown in the figure and the spot size accurately, and then use the just focus as the starting point to find the amount of current change required when adjusting to the required spot size based on the curve shown in the figure. Just flow into it. Although the horizontal axis is the objective lens 9, the objective lens 9 is provided with another independent shift coil coaxially with an air core, and a current change amount necessary for changing the magnification is passed through the shift coil so that hysteresis or the like can be obtained. It becomes possible to reduce the influence of.

  FIG. 4B shows an example in the case of high magnification. At high magnification, when the just focus is set, the spot size of the electron beam is normally in a state where there is no missing teeth as shown in the figure.

FIG. 5 is an explanatory view of the reflected electron beam image of the present invention.
FIG. 5A shows the intensity of the reflected electron signal. The horizontal axis represents the atomic number (mass), and the vertical axis represents the reflected electron signal corresponding to the atomic number of the substance at the irradiated position on the mask 11 when the electron beam is irradiated on the mask 11 (the dotted line is the secondary). The intensity of the electronic signal) is schematically represented. As the reflected electron signal increases in atomic number of the irradiated material, the reflectivity increases and the intensity of the reflected electron signal increases as shown by the solid curve in the figure, so that substances with different atomic numbers are detected as light and shade. It becomes possible. In particular, by appropriately setting a threshold value when binarizing the acquired backscattered electron image as described above, it becomes possible to distinguish a substance having a large atomic number on the image. At this time, when the magnification is changed, a binary image obtained by generating a reflected electron image before the magnification change and a reflected electron image after the magnification change with substantially the same density in the present invention and binarizing with an appropriate threshold value. And the image on the design data (CAD data) can be compared, and it can be automatically determined as a non-defective product when it is within the allowable range and as a defective product when outside the allowable range.

  On the other hand, in the case of a secondary electron signal indicated by a dotted line, when the atomic number is small, the intensity increases as the atomic number increases, but it is saturated immediately. It becomes the same, and it is impossible to distinguish these substances having a large atomic number by the density of the secondary electron beam image.

  FIG. 5B illustrates a comparison between a reflected electron beam image and a CAD (design data) image.

  FIG. 5B-1 shows an example of a reflected electron beam image, and FIG. 5B-2 shows an example of a CAD data image. As described above, the reflected electron beam image is acquired under substantially the same conditions (conditions where the beam spot size of the electron beam beam and the current density of the beam spot are substantially the same) even when the magnification is changed, and the density is substantially as shown on the left side. Are displayed in the same manner, the reflected electron image on the left side and the CAD data image shown on the right side can be easily matched, and it is possible to evaluate (determine) a non-defective product and a defective product easily and accurately.

  At this time, as described above, a comparison is made between a plurality of binary images obtained by binarizing the backscattered electron image acquired for the fixed pattern on the mask 11 with various threshold values and a binary image on the CAD data of the fixed pattern. Then, a matching threshold value is calculated, and an image obtained by binarizing the backscattered electron beam image acquired from the mask 11 with the calculated threshold value (a binarized image of the backscattered electron image of (b-1) in FIG. 5). ) And the corresponding binarized image on the CAD data, and when it is within the allowable range, it is determined to be a non-defective product and when it is out of the allowable range, the reflected electron image is used for high accuracy. It is possible to determine whether the pattern is non-defective.

  The present invention irradiates a sample with an electron beam when scanning the sample by irradiating the sample with an electron beam and generating a reflected electron beam image generated by detecting and amplifying reflected electrons that increase in response to mass. Thus, the present invention relates to an inspection apparatus for generating a reflected electron beam image having an appropriate gray level even when the magnification is changed, and a method for adjusting the irradiation beam size of the inspection apparatus. .

1 is a configuration diagram of one embodiment of the present invention. It is an operation | movement explanatory flowchart of this invention. It is explanatory drawing of this invention. FIG. 4 is a relationship diagram between a spot size and an objective lens current according to the present invention. It is explanatory drawing of the reflected electron beam image of this invention.

Explanation of symbols

1: SEM (scanning electron microscope)
2: Electron gun 3: Anode 4: Alignment coil 5: Condenser lens 6: Deflection scanning coil 7: Reflected electron detector 8: Secondary electron detector 9: Objective lens 10: Laser interferometer 11: Mask 12: Stage 13: Motor 21: PC (PC)
22: Condition storage means 23: Adjustment means 24: Scanning means 25: Display device 26: Input device

Claims (7)

In an inspection device that irradiates and scans a sample with an electron beam, and detects and amplifies the number of reflected electrons corresponding to the mass to generate a reflected electron beam image.
Means for adjusting the spot size of the electron beam so that the conditions before the change are substantially the same when the magnification is instructed to change when the magnification is instructed;
An inspection apparatus comprising: means for irradiating and scanning the sample in accordance with the magnification instructed to change with the adjusted electron beam.   The inspection apparatus according to claim 1, wherein the current density of the electron beam is adjusted at the time of adjusting the spot size of the electron beam.   Assuming that the spot size of the electron beam is adjusted so that the conditions are substantially the same, the number of spots of one scanning line (or the scanning time of one scanning line) and the number of scanning lines of one image are before and after the magnification change. Are the same, and the number of spots of one scanning line (or the scanning time of one scanning line) substantially satisfies the one scanning line (or scans one scanning line almost uniformly), so that no gap is formed, or 1 3. The inspection apparatus according to claim 1, wherein the spot size is such that the one image is substantially filled with the number of scanning lines of the image and no gap is formed.   The electron beam density is adjusted so that the conditions are substantially the same, and the current per unit area of the electron beam beam spot is made substantially the same before and after the magnification change. The inspection apparatus according to any one of claims 1 to 3. A binary image obtained by changing a threshold value for binarizing the reflected electron beam image acquired for a predetermined pattern on the mask is compared with a binary image of the pattern on the design data of the predetermined pattern on the mask. Means for calculating a matching threshold;
The inspection apparatus according to claim 1, further comprising: a unit that generates a binarized image obtained by binarizing the acquired reflected electron beam image with the calculated threshold value.   The binary image obtained by binarizing the acquired reflected electron beam image with the calculated threshold value is compared with the binary image of the pattern on the design data. 6. The inspection apparatus according to claim 5, further comprising means for sometimes determining that the product is defective. In the irradiation beam size adjustment method of the inspection apparatus that irradiates and scans the sample with an electron beam and detects and amplifies the reflected electrons that increase in response to the mass to generate a reflected electron beam image
When a magnification change instruction is given, the electron beam spot size and, if necessary, the electron beam beam current density are adjusted so that the conditions before the change are almost the same when the magnification is specified. And steps to
An irradiation beam size adjustment method for an inspection apparatus, the method comprising: irradiating and scanning the sample in accordance with the magnification instructed to change with the adjusted electron beam beam.

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