JP4627731B2 - Height detection apparatus and height detection method used for charged particle beam apparatus - Google Patents

Description

  The present invention relates to an apparatus and method for detecting the height of a sample in a charged particle beam apparatus.

  The charged particle beam apparatus is used to inspect a fine circuit pattern formed on a semiconductor wafer or the like, or to measure a line width of the pattern. Inspection of a fine circuit pattern formed on a semiconductor wafer or the like is performed by comparing electron microscope images of a pattern to be inspected and a good product pattern of the same type. Further, the line width and hole diameter of the fine circuit pattern are measured by measuring with a scanning electron microscope. In these inspections and measurements, the quality of the obtained image greatly affects the reliability of the inspection results. The image quality deteriorates due to image distortion caused by deflection or aberration of the electron optical system, or a reduction in resolution due to defocusing. Due to such deterioration of the image quality, the performance of comparative inspection and length measurement deteriorates.

  Another factor of the performance deterioration in the charged particle beam apparatus is that an appropriate inspection image cannot be obtained because the height of the sample surface cannot be accurately detected. If the entire surface of the sample is inspected under the same conditions even though the sample surface is not constant in height due to warpage or deflection, the electron beam image changes depending on the inspection location. As a result, an appropriate inspection image cannot be obtained. For example, as shown in FIG. 4, when there are regions A, B, and C having different heights on the sample wafer, if the entire sample wafer is inspected according to the height of the region A, the regions B and C are A defocused electron beam image is acquired. With such an inappropriate electron beam image, the line width of the pattern and the edge of the image cannot be accurately detected. Conventionally, focusing in an electron microscope or the like has been performed by the operator adjusting the control current of the objective lens while viewing the electron beam image. Since the sample surface is scanned many times, there is also a problem that damage to the sample increases.

JP 63-254649 A Japanese Patent Laid-Open No. 11-149895 Japanese Patent Laid-Open No. 11-183154

  In order to solve such a problem, a method of performing focusing using a scanning electron microscope or the like using an optical height detection means has been proposed (see Patent Document 1). However, in this method, since the optical system for height detection is arranged in the vacuum apparatus, it is difficult to adjust the optical axis and the amount of light emitted from the light source is limited by a slit or the like. There was a problem that the detection performance deteriorated. As another technique for measuring the height of a sample with an optical method, for example, it is known that the latter stage of the light source is slit or multi-slit (see Patent Documents 2 and 3). In this case as well, there is a problem in that the amount of light emitted from the light source is limited by slits or the like and cannot be detected.

  There are other problems as follows. In a charged particle beam apparatus typified by a scanning electron microscope, first, the height of a sample surface is measured by each function, and a finely focused charged particle beam is scanned over the sample to obtain desired information (for example, a sample). Image). In such charged particle beam equipment, as the resolution increases year by year, the material, film type, and film thickness of the sample observation film are diversified, and the light source, polarization, and multiple reflections for measuring the height of the sample In some cases, the height cannot be measured sufficiently accurately due to error factors such as diffraction. In particular, if the sample stage on which the sample is placed is moving, more accurate measurement becomes difficult. Also in a processing apparatus using a converged charged particle beam, focusing of the charged particle beam will affect the processing accuracy, so that it becomes a very important issue as in the case of an observation apparatus. Yes. Here, the processing apparatus using the converged charged particle beam is, for example, an electron beam type semiconductor pattern exposure apparatus or a FIB circuit correction apparatus.

  In addition, there are the following problems. When measuring the sample height of the charged particle beam apparatus using an optical height detection means, it is necessary to ensure a certain working distance between the objective lens and the sample surface. However, when this working distance is increased, the amount of movement of the sample surface in the height direction is increased, and there is a problem in that it may be outside the detection range in the height direction. When the optical system of the height detection means is incorporated in the charged particle beam device, the objective lens and other parts projecting to the sample surface side, so the working distance from the sample surface cannot be sufficiently widened, and the light source is incident. The dynamic range is secured by taking a large corner. For this reason, the detection system has become large and it has been difficult to secure an optical path. Furthermore, in recent years, since the sample has become larger, it is difficult to ensure a sufficient height detection range for a sample having a large amount of warping or bending.

  The present invention has been made in view of such circumstances, and in a charged particle beam apparatus, a sufficient amount of sample height detection light can be projected between the objective lens and the sample surface. It is an object of the present invention to provide a height detection device and a height detection method using an optical system that does not require a large working distance.

  As a result of diligent research in view of the above-described problem, the present inventors adjusted the light beam emitted from one light source into parallel light with a collimator lens in the sample height detection optical system of the charged particle beam device, This parallel light is distributed to a plurality of light beams by a plurality of cylindrical lenses that collect light in the same direction, and each distributed light beam passes through each opening of a slit having a plurality of openings and is projected onto the sample surface. With this configuration, it is possible to project a sufficient amount of sample height detection light, and there is no need to secure a large working distance between the objective lens and the sample surface, so that a stable sample height can be obtained. I came up with the idea of being able to make measurements.

  That is, the present invention is a sample height detection apparatus used in a charged particle beam apparatus, comprising: a light source; a collimator lens that adjusts the light beam projected from the light source to parallel light; and the parallel light into a plurality of light beams. A plurality of cylindrical lenses for condensing, a slit having a plurality of openings for forming each of the plurality of condensed light beams, and a first image for imaging each light beam formed by the slits on the sample surface An imaging lens, a second imaging lens that forms an image of a reflected light beam reflected from the sample surface, and a detector that acquires an image of the reflected light and detects the height of the sample surface The height detection apparatus provided is provided.

  In the height detection apparatus of the present invention, it is preferable that the collimating lens is configured so that the height detection ranges of the plurality of light beams are different. Further, it is preferable to further include means for selectively making one of a plurality of reflected light beams reflected from the sample surface incident on the second imaging lens.

  Further, the present invention is a method for detecting the height of a sample in a charged particle beam apparatus, wherein a light beam projected from a light source is arranged into parallel light by a collimator lens, and a plurality of the parallel lights are formed by a plurality of stages of cylindrical lenses. Each of the plurality of condensed light beams is formed by a slit having a plurality of openings, and each light beam formed by the slit is imaged on the sample surface by a first imaging lens. Providing a height detection method in which a reflected light beam reflected from the sample surface is imaged by a second imaging lens, and an image of the reflected light is acquired to detect the height of the sample surface. is there.

  In the height detection method of the present invention, it is preferable that the collimating lens is configured so that height detection ranges of the plurality of light beams are different. Further, it is preferable that one of a plurality of reflected light beams reflected from the sample surface is selectively incident on the second imaging lens.

  As described above, according to the present invention, the charged particle beam apparatus can project a sufficient amount of sample height detection light, and a large working distance can be provided between the objective lens and the sample surface. A height detection apparatus and a height detection method using an optical system that is not required are provided. The height information data obtained by the height detection device and the height detection method is often used for adjustment and adjustment such as focusing on the beam information of the charged particle device by applying feedback to the information. Necessary height information can be obtained in the height information acquisition range of the sample. In addition, a large working distance for the height detection optical system is not required, and the beam conditions can be suitably adjusted.

  Hereinafter, the best mode for carrying out a height detection apparatus and a height detection method used in the charged particle beam apparatus of the present invention will be described in detail with reference to the accompanying drawings. 1 to 3 are diagrams illustrating embodiments of the present invention. In these drawings, the same reference numerals denote the same components, and the basic configuration and operation are the same. To do.

  FIG. 1 is a diagram schematically showing an overall configuration of a scanning electron microscope according to an embodiment of the present invention. In FIG. 1, a scanning electron microscope includes a cathode 1, a first anode 2, a second anode 3, a focusing lens 5, an objective lens 7, an aperture plate 8, a sample 9, a secondary electron 10, a deflector 11, and a secondary electron detection. 12, secondary electron detector output signal amplifier 13, control arithmetic device 20, high voltage control power supply 21, convergent lens control power supply 22, objective lens control power supply 23, deflection coil control power supply 24, stage control 25, sample image display device 26, an input device 27, a drawing image device 28, a height detection light projecting portion 29, a height detection detection portion 30, a height detector signal amplifier Z 31, and a sample stage 41.

  In this scanning electron microscope, a voltage is applied between the cathode 1 and the first anode 2 by a high voltage control power source 21 controlled by a control arithmetic unit 20 (control processor), and a predetermined emission current is drawn from the cathode 1. It is. In addition, since an acceleration voltage is applied between the cathode 1 and the second anode 3 by a high voltage control power source 21 controlled by the control arithmetic unit 20, the electron beam 4 emitted from the cathode 1 is accelerated to a subsequent stage. Proceed to the lens system. The electron beam 4 is converged by the focusing lens 5 controlled by the focusing lens control power source 22, and an unnecessary area of the electron beam 4 is removed by the diaphragm plate 8. Thereafter, the electron beam 4 is focused as a fine spot on the sample 9 by the objective lens 7 controlled by the objective lens control power source 23 and controlled to scan the sample two-dimensionally by the deflection coil 11. In the vicinity of the deflector 11, an image shift deflector (not shown) for deflecting the electron beam 4 from the optical axis of the electron beam 4 (orbit of the electron beam 4 not subjected to deflection) is provided. And Using this image shift deflector, the scanning position of the electron beam 4 with respect to the sample 9 can be changed. Further, by deflecting the electron beam from the optical axis of the objective lens 7, the irradiation angle of the electron beam 4 on the sample 9 can be changed. The scanning signal of the deflector 11 is controlled by the deflector control power source 24 in accordance with the observation magnification. The sample 9 is fixed on a sample stage 41 that can move two-dimensionally. The movement of the sample stage 41 is controlled by the stage control unit 25.

  The secondary electrons 10 generated from the sample 9 by the irradiation of the electron beam 4 are detected by the secondary electron detector 12, and the drawing device 28 converts the detected secondary signals into visible signals and arranges them appropriately on another plane. By performing the control as described above, an image corresponding to the surface shape of the sample is displayed on the sample image display device 26 as a sample image. The signal detected by the secondary electron detector 12 is amplified by the signal amplifier 13 and then stored in the image memory in the drawing device 28. In measuring the dimensions of the pattern, the sample image display device 26 displays two vertical or horizontal cursor lines together with the sample image, and the two cursors are placed on the two edges of the pattern via the input device 27. Based on the information of the image magnification of the image and the distance between the two cursors, the control arithmetic unit 20 calculates the measurement value as the dimension value of the pattern.

  The input device 27 serves as an interface between the operator and the control arithmetic unit 20, and the operator controls the above-described units via the input device 27, and also designates measurement points and commands for dimension measurement. The control arithmetic unit 20 is provided with a storage device (not shown) so that the obtained length measurement value, control conditions for each unit, and the like can be stored.

  Further, the scanning electron microscope includes a height detection unit including a height detection light projecting side portion 29, a height detection detection side portion 30, and a signal amplifier Z31, and a height obtained from the height detection portion. The information can be fed back to the objective lens 7 via the control arithmetic unit 20, and the control power source 23 of the objective lens 7 can be changed and adjusted according to the height of the sample 9 to perform focusing. ing. The function and operation of this height detector will be described later.

  Next, a method for automatically inspecting and measuring a fine circuit pattern formed on an object to be inspected in the scanning electron microscope of this embodiment will be described. Inspecting a fine circuit pattern formed on a semiconductor wafer or the like is often performed by comparing a pattern to be inspected with a pattern similar to the pattern to be inspected or by comparing with a non-defective pattern. Even in the appearance inspection of an image (SEM image) using a charged particle beam apparatus, the inspection is performed by comparing the pattern images. In addition, in the determination of manufacturing process conditions in semiconductor manufacturing equipment, and in the measurement (SEM measurement) of scanning charged particle beam equipment that measures the pattern line width and hole diameter used for monitoring The length measurement is automated by processing. When measuring line widths and hole diameters by using comparison inspections that consist of comparing images with similar patterns or using charged particle beam images, the quality of the obtained image affects the reliability of the inspection results. It will be. The image quality deteriorates due to image distortion caused by deflection or aberration of the electron optical system or a decrease in resolution due to defocusing.

  It is known that such image quality deterioration deteriorates comparative inspection and length measurement performance. When the height of the sample to be inspected is not constant, when the inspection and measurement are performed under the same conditions for all ranges, the image quality changes depending on the inspection location as shown in FIG. As a result, when FIG. 4B is used as a focused image, FIG. 4B is compared with defocused images such as FIG. 4C and FIG. Even if the inspection is performed, a sufficient inspection result cannot be obtained. In these images, the width of the pattern changes, and the inspection result of the edge detection of the image cannot be obtained stably, so that the pattern having a stable line width and hole diameter cannot be obtained.

  The optical system of the height detection light projecting side portion 29 in the scanning electron microscope of this embodiment will be described with reference to FIG. As shown in FIG. 2A, in the height detection light projecting side portion 29, the light beam projected from one light source 51 is adjusted to parallel light by the collimator lens 52, and then in the same direction in two steps. The parallel light is divided into two light beams by a cylindrical lens 53 having a condensing characteristic, and each of the divided light beams is irradiated to each of the two-stage slits 54, and the light beams are adjusted and connected by the first imaging lens 55. The sample is illuminated. FIG. 2B shows a configuration example of the cylindrical lens 53 having the light condensing property in the same direction. In this example, the cylindrical lenses having the same direction of light condensing property are stacked in two stages. However, the cylindrical lens 53 may be configured by stacking three or more stages of the cylindrical lenses having light condensing characteristics in the same direction. FIG. 2C shows a configuration example of the two-stage slit 54 described above. In the actual example, it is configured as a two-stage slit having two openings according to the condensing position of the cylindrical lens shown in FIG. 2B. However, any number of stages may be selected according to the number of condensing numbers and positions of the cylindrical lens. Can be used.

  Next, in the scanning electron microscope of the present embodiment, a method for detecting the height of the sample by the height detection unit will be described with reference to FIG. As shown in each figure of FIG. 3, in the height detection unit, the light beam projected from the light source 51 is adjusted to parallel light by the collimator lens 52, and then a cylindrical lens having two stages of light condensing properties. 53 divides the parallel light into two light beams, irradiates each of the divided light beams to each of the two-stage slits 54, arranges the light beams, forms an image with the first imaging lens 55, and irradiates the sample surface 56. ing. The reflected light from the sample surface 56 is imaged on the detection sensor 59 by the second imaging lens 58 via the aperture 57. In the present embodiment, by utilizing the fact that two light beams are irradiated on the sample surface, as shown in FIGS. 3A and 3B, at two sample height positions with different sample heights Z. The sample height can be detected. As a result, the required working distance is reduced as compared with a height detection device in a conventional charged particle beam device.

  In the scanning electron microscope of the present embodiment, the configuration of the height detection unit is not limited to the above-described form. For example, it is possible to change the cylindrical lens to three or four stages. Further, a configuration may be adopted in which parts such as the aperture 57 are installed in the height detection light projecting side portion 29 to actively limit the light flux. Although not shown, when using two light beams, it is desirable to adjust so that when the light beam exceeds the measurement range of one light beam, the other light beam falls within the measurement range.

  The height detection apparatus and the height detection method used in the charged particle beam apparatus of the present invention have been described above with specific embodiments, but the present invention is not limited to these. A person skilled in the art can make various changes and improvements to the configurations and functions of the invention according to the above-described embodiments or other embodiments without departing from the gist of the present invention.

1 is a diagram schematically showing an overall configuration of a scanning electron microscope according to an embodiment of the present invention. The optical system of the height detection light projecting side portion in the scanning electron microscope shown in FIG. 1 will be described. In the scanning electron microscope shown in FIG. 1, it is a figure explaining the method of performing the height detection of a sample by a height detection part. It is a figure which illustrates the sample wafer and electron beam image obtained from it with a non-constant height. It is a figure which shows the example of the height detection apparatus and height detection method which are used for the conventional charged particle beam apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cathode 2 1st anode 3 Second anode 4 Electron beam 5 Focusing lens 7 Objective lens 8 Diaphragm plate 9 Sample 10 Secondary electron 11 Deflector 12 Secondary electron detector 13 Secondary electron detector output signal amplifier 20 Control arithmetic unit 21 High Voltage Control Power Supply 22 Convergent Lens Control Power Supply 23 Objective Lens Control Power Supply 24 Deflection Coil Control Power Supply 25 Stage Control 26 Sample Image Display Device 27 Input Device 28 Drawing Image Placement 29 Height Detection Projection Side 30 Height Detection Detection Side part 31 Height detector signal amplifier Z
41 Sample stage 51 Light source 52 Collimator lens 53 Cylindrical lens 54 Two-stage slit (two-open slit)
55 First imaging lens 56 Sample surface 57 Aperture 58 Second imaging lens 59 Detection sensor

Claims (6)

A device for detecting the height of a sample used in a charged particle beam device,
A light source;
A collimating lens that adjusts the light beam projected from the light source into parallel light;
A plurality of cylindrical lenses for condensing the parallel light into a plurality of light fluxes;
A slit having a plurality of openings for shaping each of the condensed light fluxes;
A first imaging lens for imaging each light beam formed by the slit on the sample surface;
A second imaging lens that forms an image of a reflected light beam reflected from the sample surface;
And a detector for detecting the height of the sample surface by acquiring an image of the reflected light. The height detection apparatus according to claim 1, wherein the collimating lens is configured so that height detection ranges of the plurality of light beams are different from each other. Height of claim 1 or 2, characterized in that it further comprises a means for entering the selectively the second imaging lens one of the plurality of beams of light reflected from the sample surface Detection device. A method for detecting the height of a sample in a charged particle beam device,
The collimating lens adjusts the light beam projected from the light source into parallel light,
The parallel light is condensed into a plurality of light beams by a plurality of cylindrical lenses,
Each of the condensed light fluxes is shaped by a slit having a plurality of openings,
Each light beam formed by the slit is imaged on the sample surface by the first imaging lens,
The reflected light beam reflected from the sample surface is imaged by the second imaging lens,
A height detection method for detecting the height of the sample surface by obtaining an image of the reflected light. The height detection method according to claim 4, wherein the collimating lens is configured so that height detection ranges of the plurality of light beams are different from each other. 6. The height detection method according to claim 4, wherein one of a plurality of reflected light beams reflected from the sample surface is selectively incident on the second imaging lens.

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