JP2016110865A - Scanning electron microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning electron microscope that is configured in a small size by omitting a condenser lens constituting a convergent lens and shortening the dimension in the axial line direction of an electron optics system.SOLUTION: An electron gun for generating an electron beam is provided with a gun lens 46 for varying the current density, the peripheral portion of an electron beam is removed, and an aperture 58 for restricting the size of the electron beam flux is disposed at the emission side of the gun lens 46. And the electron beam passing through the aperture 58 is passed through an objective lens and applied to a sample on a stage.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a scanning electron microscope, and in particular, irradiates an electron beam while scanning it relative to a sample, detects secondary electrons from the sample by a detector, and outputs secondary electrons detected at the scanning position. The present invention relates to a scanning electron microscope that forms an image from the above.

  In the case of manufacturing a semiconductor, a chemical process is performed on a silicon wafer to form a wiring pattern, and each element formed on the silicon wafer is connected via the wiring pattern. Therefore, if the wiring pattern is not correctly formed and properly connected, a state in which the semiconductor does not operate correctly occurs, leading to the generation of defective products. Therefore, in order to check whether or not the drawing pattern formed on the semiconductor wafer is correctly formed in the semiconductor manufacturing process, a scanning electron microscope is used as disclosed in, for example, Japanese Patent Application Laid-Open No. 2006-138864. It is used for inspection or evaluation.

  A scanning electron microscope used for such an application focuses an electron beam from an electron beam source by a converging lens or a condenser lens, deflects it in a predetermined direction by a deflection coil, and then places it on a stage by an objective lens. Irradiation is performed on a predetermined position of the semiconductor wafer made of the arranged sample. In such a configuration, it is necessary to provide a condenser lens constituting a converging lens on the emission side of the electron gun. Since the condenser lens is an electromagnetic coil and has a large dimension in the axial direction, the dimension in the height direction of the electron optical system becomes very large, which increases the size of the scanning electron microscope, especially in the height direction. There was a drawback of becoming longer.

JP 2006-138864 A

  The subject of this invention is providing the scanning electron microscope which shortened the dimension of the height direction and enabled size reduction by this.

  Another object of the present invention is to provide a scanning electron microscope that eliminates a converging lens made up of a condenser lens, thereby reducing the size of the electron optical system.

  Still another object of the present invention is to provide a compact scanning electron microscope having a resolution equal to or higher than that of an electron microscope using a condenser lens without using a converging lens made of a condenser lens.

  Still another object of the present invention is to provide a compact scanning electron microscope in which the function of a condenser lens is achieved by a gun lens composed of an electrostatic lens provided in an electron gun.

  Still another object of the present invention is to provide a scanning electron microscope in which a blanking function is achieved by a gun lens composed of an electrostatic lens provided in an electron gun.

  The above-described problems and other problems of the present invention will be made clear by the technical idea of the present invention described below and the embodiments thereof.

In the main invention of the present application, an electron beam is irradiated while being scanned relative to a sample, secondary electrons from the sample are detected by a detector, and an image is obtained from the detection output of the secondary electrons with respect to a scanning position. In a scanning electron microscope designed to form,
The electron gun that emits the electron beam is provided with a gun lens that includes an electrostatic lens and changes the current density of the electron beam, and the electron beam bundle is removed by removing the peripheral portion of the electron beam from the output side of the gun lens. The present invention relates to a scanning electron microscope in which an aperture for regulating the thickness is arranged and an electron beam that has passed through the aperture is irradiated onto the sample through an objective lens.

  Here, two pairs of the gun lens and the aperture are provided, the pair of gun lenses on the front stage side is provided on the electron beam source side with respect to the anode, and the aperture corresponding to the gun lens on the front stage side is provided on the anode side. May be formed. The electron gun may be directly attached to the objective lens. A deflecting device may be attached to the incident side of the objective lens, and the electron gun including the gun lens may be directly connected to the incident side of the deflecting device. The electron beam source of the electron gun may be a W / ZrO thermal field emission type electron beam source.

  The gun lens comprises an insulating cylinder, and is formed by forming electrodes divided into four or more poles in the circumferential direction on the inner peripheral surface of the center hole, and a control voltage is applied to each electrode. The electron beam may be converged by applying. In addition, blanking may be performed by applying an asymmetric voltage to the multi-polarized electrode of the gun lens to move the electron beam laterally with respect to the aperture. The aperture may be a circular hole having a diameter in the range of 0.3 to 1.2 mm. The scanning may be performed by placing the sample on a stage and moving the sample in a predetermined direction by the stage.

  The invention according to each claim of the present application was created in a strategic basic technology advancement support project that was made under the leadership of the National Institute of Advanced Industrial Science and Technology.

In the main invention of the present application, an electron beam is irradiated while being scanned relative to a sample, secondary electrons from the sample are detected by a detector, and an image is obtained from the detection output of the secondary electrons with respect to a scanning position. In a scanning electron microscope designed to form,
The electron gun that emits the electron beam is provided with a gun lens that includes an electrostatic lens and changes the current density of the electron beam, and the electron beam bundle is removed by removing the peripheral portion of the electron beam from the output side of the gun lens. An aperture for regulating the thickness is arranged, and the sample is irradiated with an electron beam that has passed through the aperture through an objective lens.

  Therefore, according to such a scanning electron microscope, it is possible to achieve the function of a converging lens composed of a conventional condenser lens by a gun lens provided in an electron gun, and the condenser lens constituting the converging lens can be omitted. It becomes possible. Accordingly, the size of the electron optical system, particularly the height direction can be significantly shortened, and a compact and compact scanning electron microscope can be provided. Further, the current density of the electron beam can be changed by the gun lens, and the blanking function can also be achieved by the gun lens.

1 is a block diagram of a scanning electron microscope according to an embodiment of the present invention. It is the external appearance perspective view of the electron microscope (A), and the longitudinal cross-sectional view (B) which shows arrangement | positioning in the housing | casing of each unit. It is the longitudinal cross-sectional view (A) of an electron optical system, and the longitudinal cross-sectional view (B) of an electron gun. It is a block diagram which shows the state of radiation | emission of an electron beam. FIG. 2 is a plan view (A) showing a multipolar structure of a gun lens, and a plan view (B) of an aperture arranged on the exit side of the gun lens. It is the perspective view (A) and longitudinal cross-sectional view (B) of the gun lens which consists of an electrostatic lens. It is an expansion cross-sectional view of the gun lens which consists of an electrostatic lens.

  The present invention will be described below with reference to embodiments shown in the drawings. FIG. 1 shows a system configuration of a scanning electron microscope according to the present embodiment, and this scanning electron microscope includes an electron optical system 10. The electron optical system 10 includes an electron beam source that generates electrons, and includes a high vacuum pump 11. The inside of the electron optical system 10 is maintained in a vacuum state by the high vacuum pump 11. A vacuum chamber 14 is disposed below the electron optical system 10, and a stage 15 is disposed on the bottom side inside the vacuum chamber 14.

  A transport system 17 is provided on the side of the vacuum chamber 14, and the sample 16 is supplied from the transport system 17 without breaking the vacuum of the vacuum chamber 14 and is placed on the stage 15. The vacuum chamber 14 is vacuum-sucked by a diaphragm pump 18 and a turbo molecular pump 19 disposed at the lower part thereof, and is maintained at a predetermined degree of vacuum. The vacuum chamber 14 is mounted on the mounting table 20 and is supported via a vibration isolation system 21 so as not to be affected by vibrations caused by the diaphragm pump 18 and the turbo molecular pump 19 in particular.

  A secondary electron detector 23 is attached to the side of the vacuum chamber 14. The secondary electron detector 23 is for detecting the intensity of secondary electrons generated when the sample 16 is irradiated with an electron beam by the electron optical system 10, and the detection output is a signal in the control system. The signal supplied to the processing system 24 and then processed by the signal processing system 24 is transferred to the image processing system 25. The image processing system 25 forms an image from the intensity of secondary electrons taken out via the signal processing system 24, and the intensity of secondary electrons on the surface of the sample 16 at each scanning position. Output to.

  The control system further includes a high voltage power supply 29, a lens control system 30, a stage control system 31, and a vacuum control system 32. The high voltage power source 29 is for applying a high voltage power source to the electron optical system 10. The lens control system 30 controls each lens in the electron optical system 10. The stage control system 31 controls the stage 15 in the vacuum chamber 14 to scan the sample 16 in a predetermined direction with respect to the electron beam of the electron optical system 10.

  Each unit of the scanning electron microscope having such a configuration is housed in an outer casing 35 shown in FIG. 2A. The outer casing 35 includes four support legs 36 at a lower portion thereof, and a recess 37 is formed on the front side of the outer casing 35. An operation element 38 is provided in the recess 37. The display device 26 is attached to the upper portion of the recess 37.

  The arrangement of each block in the outer casing 35 is as shown in FIG. 2B. The high voltage power supply 29 is accommodated at the top, and the lens control system 30 and the signal processing system 24 are accommodated below the high voltage power supply 29. . An intermediate transport system 17 is disposed below the electron transport system 10, and an electron optical system 10 is mounted below the intermediate transport system 17. A high vacuum pump 11 is connected to the side of the electron optical system 10. A vacuum chamber 14 is provided below the electron optical system 10. The vacuum chamber 14 is mounted on the mounting table 20, and has a structure in which a vibration isolation system 21, a turbo molecular pump 19, and a diaphragm pump 18 are housed on the lower side of the mounting table 20.

  Next, the internal structure of the electron optical system 10 will be described. The electron optical system 10 is configured as shown in FIG. 3A, and includes an electron beam source 42, and an extraction electrode 43 is disposed below the electron beam source 42. A suppress electrode 44 is attached below the extraction electrode 43. The lower end side of the suppress electrode 44 is an anode 45. An alignment / condenser combined gun lens 46 is provided immediately below the electron gun having such a structure. That is, it has a characteristic configuration in which the gun lens 46 is provided in the lower part of the electron gun. Such an electron gun is arranged on the incident side on the deflection unit 47 side. The deflection unit 47 is attached to a portion immediately above the objective lens 48. An OL alignment 49 and an astigmatism correction 50 are attached to the center of the deflection unit 47. In the center hole portion of the objective lens 48, the shift coil 51 is disposed on the upper side and the deflection coil 52 is disposed on the inner side, the shift coil 53 is disposed on the inner side, and the deflection coil 54 is disposed on the outer side. Has been.

  FIG. 3B is an enlarged view of an electron gun portion in which the gun lens 46 in the electron optical system 10 is directly attached to the lower end.

  Next, a schematic operation of the scanning electron microscope according to the above configuration will be described with reference to FIGS. The electron beam emitted from the electron beam source 42 of the electron optical system 10 passes through each unit of the electron optical system 10, is focused by the objective lens 48, and is irradiated onto the sample 16 placed on the stage 15. The Here, since the stage 15 moves the sample 16 in a predetermined direction by the stage control system 31, the electron beam irradiated through the objective lens 48 scans in a predetermined direction relative to the sample 16 on the stage 15. Will be. The secondary electrons emitted from the sample 16 at each scanning position at this time are detected by the secondary electron detector 23, and the detection output is processed by the signal processing system 24. The processed signal is supplied to the image processing system 25, and the image processing system 25 forms an image from the intensity of secondary electrons corresponding to each scanning position. An image formed by the image processing system 25 is displayed on the display device 26.

  In such a scanning electron microscope, as shown in FIGS. 3A and 3B in particular, a gun lens 46 is directly attached to a lower portion of an electron gun comprising an electron beam source 42 and a condenser constituting a converging lens. The lens is omitted. As shown in FIGS. 6 and 7, the gun lens 46 is an electrostatic lens and is a ceramic cylinder. And the flange 61 is provided in the outer peripheral side of the cylinder. On the inner peripheral surface of the center hole of the cylindrical body, a conductive metal electrode 63 is formed by being divided into eight in the circumferential direction. When a voltage is applied to each electrode 63, a substantially circular electrostatic field is formed, resulting in an electrostatic lens with a maximum of about 1,000 times. Since the electrostatic lens can adjust the skirt-like spread of the electron beam according to the electric field strength, it is possible to adjust the current density of the electron beam. Accordingly, in such a configuration, since there is no condenser lens having a long dimension in the axial direction, the dimension of the electron optical system 10 in the height direction becomes very short, and the electron optical system 10 can be assembled compactly. . For this reason, the height dimension of the entire scanning electron microscope can be significantly shortened.

  As the electron beam source 42, an electron beam source of a W / ZrO thermal field emission type and comprising a field effect type emitter is used. This electron beam source has a sharp spindle-shaped tip that emits electrons, and the tip itself constitutes a virtual light source. The electron beam has a resolution of about 10 nm and is a minute light source. This makes it possible to omit the condenser lens.

  Further, as shown in FIG. 4 in particular, the scanning electron microscope of the present embodiment has a skirt formed by an upper gun lens 46 after the electron beam from the electron beam source 42 has passed through the extraction electrode 43 and the saplus electrode 44. The spread of the shape is adjusted according to the electric field strength, whereby the current density is changed, and the outer electron beam bundle is removed by the aperture of the anode 45. The combination of the gun lens 46 and the aperture may be a pair, but two pairs may be provided in two upper and lower stages. FIG. 4 shows a configuration in which two pairs are provided in two upper and lower stages. In this case, distribution control is performed by the electric field of the lower gun lens 46 when passing through the lower gun lens 46, and as a result, the power density changes. Also here, the electrons on the outer peripheral side are removed by the aperture 58 in the lower stage.

  The electron beam whose current density has been changed by the lens action (voltage change) by the gun lens 46 then passes through the center of the deflection unit 47, is focused by the objective lens 48, and is irradiated onto the sample 16 on the stage 15. In particular, the adjustment of the current density by the gun lens 46 shown in FIG. 4 omits the use of a converging lens composed of a condenser lens constituted by an electromagnetic coil, and the function of the condenser lens is provided by a compound gun lens 46 provided in the electron gun. Can be achieved. Accordingly, it is possible to ensure a resolution equal to or higher than that when a condenser lens is used without using a condenser lens.

  Further, as shown in FIG. 5A, the scanning electron microscope according to the present embodiment enables a blanking function by generating a deflection electric field by applying an asymmetric voltage to four opposing poles among eight magnetic poles. To do. As shown in FIG. 5A, when an asymmetric voltage is applied to the opposite four poles, the center of the beam shifts to the side as shown in FIG. 5B, and the center of the electron beam moves to the side with respect to the aperture 58. Will do. Therefore, the electron beam can be blocked by the plate-like body having the aperture 58, and the blanking function is added as a basic function.

  Although the present invention has been described above with reference to the illustrated embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the technical idea of the present invention. For example, although the above embodiment is used as a length measuring microscope for measuring the width of a pattern formed on a semiconductor wafer, the scanning electron microscope according to the present invention is used for various other purposes. It can be used for a scanning electron microscope that can be widely used. In the configuration shown in FIG. 4, the pair of the gun lens and the aperture is arranged in two upper and lower stages in the axial direction of the electron beam, but the pair of the gun lens and the aperture is not necessarily arranged in two upper and lower stages. It may be a step.

  The present invention can be widely used as a measuring microscope and a scanning electron microscope for obtaining enlarged images of various samples.

DESCRIPTION OF SYMBOLS 10 Electro-optic system 11 High vacuum pump 14 Vacuum chamber 15 Stage 16 Sample 17 Conveyance system 18 Diaphragm pump 19 Turbo molecular pump 20 Mounting stand 21 Vibration isolation system 23 Secondary electron detector 24 Signal processing system 25 Image processing system 26 Display apparatus 29 High-voltage power supply 30 Lens control system 31 Stage control system 32 Vacuum control system 35 Outer casing 36 Support leg 37 Recess 38 Operation element 42 Electron beam source 43 Extraction electrode 44 Suppress electrode 45 Anode 46 Alignment / condenser compound gun lens 47 Deflection unit 48 Objective lens 49 OL alignment 50 Astigmatism correction 51 Shift coil 52 Deflection coil 53 Shift coil 54 Deflection coil 57 Pole 61 Flange 62 Center hole 63 Electrode

Claims (9)

A scanning type in which an electron beam is irradiated while scanning relative to a sample, secondary electrons from the sample are detected by a detector, and an image is formed from the detection output of the secondary electrons at a scanning position. In electron microscope,
The electron gun that emits the electron beam is provided with a gun lens that includes an electrostatic lens and changes the current density of the electron beam, and the electron beam bundle is removed by removing the peripheral portion of the electron beam from the output side of the gun lens. The scanning electron microscope which arranged the aperture which controls thickness and irradiated the electron beam which passed the said aperture through the objective lens to the sample.   Two pairs of the gun lens and the aperture are provided, the pair of gun lenses on the front stage side is provided on the electron beam source side from the anode, and the aperture corresponding to the gun lens on the front stage side is formed on the anode. The scanning electron microscope according to claim 1.   The scanning electron microscope according to claim 1, wherein the electron gun is directly attached to the objective lens.   The scanning electron microscope according to claim 3, wherein a deflecting device is attached to the incident side of the objective lens, and the electron gun including the gun lens is directly connected to the incident side of the deflecting device.   The scanning electron microscope according to claim 1, wherein the electron beam source of the electron gun is a W / ZrO thermal field emission electron beam source.   The gun lens comprises an insulating cylinder, and is formed by forming electrodes divided into four or more poles in the circumferential direction on the inner peripheral surface of the central hole, and applying a control voltage to each electrode. The scanning electron microscope of Claim 1 which converges an electron beam by this.   The scanning type according to claim 6, wherein blanking is performed by applying an asymmetric voltage to the multi-polarized electrode of the gun lens to move the electron beam laterally with respect to the aperture. electronic microscope.   The scanning electron microscope according to claim 1, wherein the aperture is a circular hole having a diameter in a range of 0.3 to 1.2 mm.   The scanning electron microscope according to claim 1, wherein the scanning is performed by placing the sample on a stage and moving the sample in a predetermined direction by the stage.

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