JP5744248B2 - Sample observation method - Google Patents

Description

  The present invention relates to a sample observation method and apparatus, and a sample inspection method and apparatus using them, and more specifically, a sample obtained by irradiating a sample surface on which an insulating region and a conductive region are formed with a low-energy imaging electron beam. The present invention relates to a technique for acquiring a surface image.

  Conventionally, a sample surface such as a semiconductor wafer is irradiated with an electron beam, and electrons emitted from the sample surface are detected to obtain an image of the wafer surface. Based on this, an open defect or missing defect of the semiconductor wafer is obtained. A sample surface observation method for detecting defects such as (short defects) is known (see, for example, JP-A-2005-235777 (Patent Document 1)).

  In such a conventional sample surface observation method, light and shade (gradation difference) in an image generated in a portion where an open defect or a missing defect exists is used. In a portion where there is a defect such as an open defect or a missing defect, shading (gradation difference) that does not occur in the normal portion appears in the image. In the conventional sample surface observation method, the wafer surface image obtained from the surface of the semiconductor wafer is compared with the original (defect-free sample) surface image, and when the shade that should not appear originally is recognized, the relevant part is opened. A method of determining as a defect or a missing defect is adopted.

  However, the observation method disclosed in Patent Document 1 has a problem that the gray level difference of the observation site is originally small depending on the structure or material of the observation target, and it may be difficult to detect missing defects or open defects. It was.

  In addition, particularly with respect to the open defect, the image of the part where the open defect exists may be darker (blacker) or lighter (whiter) than the image of the normal part. For this reason, there is a problem that it is extremely difficult to detect defects and classify types of defects.

  The present inventors have obtained a sample surface observation method in which a defect surface and a normal region have a large gradation difference, a sample surface image having a clear difference in shades of black and white is obtained in defect detection of a wiring structure, and defect detection is easy As a result of repeated examinations for the purpose of providing the above, the problem that the above-described conventional specimen surface observation method has is that it is in the point of simultaneously detecting missing defects and open defects under the same conditions, A new sample surface observation method was proposed (Japanese Patent Laid-Open No. 2009-87893: Patent Document 2).

  In Patent Document 2, a sample surface image is obtained by irradiating an electron beam onto a sample surface on which a wiring including an insulating material and a conductive material is formed, and detecting electrons obtained from the structure information of the sample surface. A sample surface observation method for observing the sample surface, wherein the insulating material and the conductive material are irradiated by irradiating the sample surface with an electron beam in a state where the brightness of the insulating material and the conductive material in the sample surface image is equal. In addition, it is possible to easily and reliably detect a portion other than the above, and further, by detecting a point of luminance different from the luminance of the insulating material and the conductive material in the sample surface image as an open defect on the sample surface, the open defect can be easily and A sample surface observation method that enables reliable detection is disclosed.

  In Patent Document 2, it is easy to discriminate from the periphery of a missing defect by irradiating the sample surface with an electron beam in a state where the luminance difference between the insulating material and the conductive material in the sample surface image is maximized. The sample surface image is acquired and the defect defect is easily and reliably detected. Further, the state in which the luminance difference is maximized is determined in the mirror electron region where the electrons obtained from the structure information of the sample surface become mirror electrons. As a definition, a sample surface observation method that enables effective detection of missing defects is also disclosed.

JP 2005-235777 A JP 2009-87893 A

  When the insulating surface and the conductive region are formed on the sample surface, the inventors perform high-contrast observation of the sample surface and not only detect missing defects and open defects but also easily classify defect types. As a result of further studies on the technique and apparatus to be achieved, it was concluded that the invention disclosed in Patent Document 2 has room for further improvement.

  That is, the object of the present invention is to perform observation of the sample surface on which the insulating region and the conductive region are formed with high contrast, and to easily detect missing defects and open defects and classify defect types. It is an object to provide a sample observation method and apparatus, and a sample inspection method and apparatus using them.

  In order to achieve the above-described object, a sample observation method according to the present invention is a method of observing a sample surface having an insulating region and a conductive region by electron beam irradiation, wherein the sample surface is irradiated with an imaging electron beam. And a second step of obtaining an image of the sample surface by detecting electrons obtained from the structure information of the sample surface, and the irradiation energy (LE) of the imaging electron beam in the first step In the second step, the electrons obtained from the structural information of the sample surface are adjusted to a transition region including both mirror electrons and secondary electrons, and the second step is such that the luminance of the conductive region is higher than the luminance of the insulating region. Sub-step A in which image acquisition is performed under conditions, and Sub-step B in which image acquisition is performed under conditions in which the luminance of the insulating region is higher than the luminance of the conductive region, To do.

  With this configuration, an image is acquired under conditions where the luminance of the conductive region is higher than that of the insulating region, and an image is acquired under conditions where the luminance of the insulating region is higher than the luminance of the conductive region. Therefore, it is possible to detect both missing defects and open defects on the sample surface with high accuracy based on these images.

  The sample observation method according to the present invention may include a step of charging the insulating region by irradiating the surface of the sample with a charged electron beam before irradiation with the imaging electron beam.

With such a configuration, separation of the electron e _i obtained structural information conductive region and electrons e _c to obtain structural information of the insulating region becomes more pronounced, it is easy to obtain a high contrast.

  The sample observation method according to the present invention may be configured such that the condition selection of the sub-step A and the sub-step B is performed by adjusting a position of a movable NA aperture that is provided in the optical system and determines a numerical aperture (NA). Good.

With such a structure, directing the electron e _c to obtain structural information conductive regions on the detector, on the contrary, as easily can lead to electronic e _i obtained structural information of the insulating region to the detector Become.

In addition, the sample observation method according to the present invention provides imaging electrons that maximize the contrast generated by the difference between the luminance of the conductive region and the luminance of the insulating region before the first step and after irradiation with the charged electron beam. It is good also as a structure which comprises the step which determines the irradiation energy (LE) of a beam, and performs the irradiation of the imaging electron beam in the said 1st step with the irradiation energy (LE) which becomes the said contrast maximum.

With such a configuration, acquisition of the high contrast of an image in a state in which the separation is made of the electron e _c to obtain structural information conductive region and electrons e _i obtained structural information of the insulating region is facilitated.

  Further, the sample observation method according to the present invention includes a step of determining a dose amount at which charging of the insulating region by electron beam irradiation is saturated prior to irradiation of the charged electron beam, and charging in the step of charging the insulating region. It is good also as a structure which performs irradiation of an electron beam with the said dose amount.

With such a configuration, it is possible to separate the electron e _c to obtain structural information conductive region and electrons e _i obtained structural information of the insulating region effectively.

  In addition, the sample observation method according to the present invention includes a step of obtaining in advance an orbit shift amount of electrons obtained from the structure information of the insulating region before and after irradiation of the charged electron beam, and based on the orbit shift amount. The NA aperture may be adjusted in position.

With such a structure, directing the electron e _c to obtain structural information conductive regions on the detector, on the contrary, to lead the electrons e _i obtained structural information of the insulating region to the detector, performed quickly can do.

  In the sample observation method according to the present invention, when the minimum irradiation energy of the transition region is LEA and the maximum irradiation energy is LEB, the irradiation energy (LE) of the imaging electron beam is set to LEA ≦ LE ≦ LEB + 5 eV. It is preferred that

  By setting the irradiation energy, an image with a high material contrast can be acquired.

  The sample observation method according to the invention is executed using, for example, a mapping projection type low acceleration electron beam apparatus.

  By using the projection type low acceleration electron beam apparatus, the sample observation method of the present invention can be executed without any special apparatus improvement.

  The sample inspection method according to the present invention is a sample inspection method for determining the presence / absence of a defect on the sample surface using an image of the sample surface obtained by the sample observation method described above, and obtained by the sub-step A. The presence or absence of a missing defect (short defect) is determined from the image A, and the presence or absence of an open defect (open defect) is determined from the image B obtained in the sub-step B.

  With this configuration, an image acquired under conditions where the luminance of the conductive region is higher than that of the insulating region and an image acquired under conditions where the luminance of the insulating region is higher than the luminance of the conductive region It is possible to detect both missing defects (short defects) and open defects (open defects) with high sensitivity and high accuracy.

The sample observation apparatus according to the invention includes an electron beam source that irradiates an imaging electron beam to a sample surface having an insulating region and a conductive region, and electrons that obtain structural information of the sample surface by irradiation of the imaging electron beam. The electromagnetic field generating means (E × B) directs the electrons by an electric field and a magnetic field according to the speed of traveling in the direction opposite to the incident direction of the electron beam, and the electromagnetic field generating means (E × B) A detector that detects the electrons and acquires an image of the sample surface from the detected electrons, and sets the irradiation energy of the imaging electron beam in a transition region in which the electrons include both mirror electrons and secondary electrons. Irradiation energy setting means, an NA aperture moving mechanism that enables adjustment of the position of the NA aperture that determines the numerical aperture (NA) within the plane, and the sample surface is irradiated with an electron beam to form the insulating region. A charging electron beam irradiating means for charging, and the NA aperture moving mechanism is configured such that the NA aperture obtains structural information of the conductive region whose orientation is different by the action of E × B and the insulating region. The electrons that have obtained the structure information are selectively guided to the detector.

  With this configuration, an image is acquired under conditions where the luminance of the conductive region is higher than that of the insulating region, and an image is acquired under conditions where the luminance of the insulating region is higher than the luminance of the conductive region. Therefore, it is possible to detect both missing defects and open defects on the sample surface with high accuracy based on these images.

  In the sample observation apparatus according to the invention, the electron beam source may also serve as the charged electron beam irradiation unit.

In this case, it is assumed that the separation of the electron e _c obtained from the structural information of the conductive region and the electron e _i obtained from the structural information of the insulating region is significant without providing a separate charged electron beam irradiation means. Can be obtained.

  Further, in the sample observation apparatus according to the present invention, a plurality of types of the NA apertures are provided, and the plurality of NA apertures are NA adjustment apertures having different diameters, and the conductive aperture region is formed by the NA aperture moving mechanism. It is also possible to adopt an aspect in which an NA aperture that optimizes the contrast of the image can be selected by passing at least one of electrons that have obtained structural information or electrons that have obtained structural information of the insulating region.

With such a structure, directing the electron e _c to obtain structural information conductive regions on the detector, on the contrary, as easily can lead to electronic e _i obtained structural information of the insulating region to the detector Become.

  The detector of the sample observation apparatus according to the invention is, for example, an EB-CCD or an EB-TDI that directly detects the electrons.

  By adopting such a configuration, it is possible to directly detect electrons and output an electrical signal as it is without undergoing photo-electron conversion, so that a fluorescent screen or MCP is not required, and there is no signal loss on the way. Therefore, high-resolution image acquisition is possible.

  The sample observation apparatus according to the invention is, for example, a mapping projection type low acceleration electron beam apparatus.

  By using the projection type low acceleration electron beam apparatus, the sample observation method of the present invention can be executed without any special apparatus improvement.

  The sample inspection apparatus according to the invention determines the presence or absence of a missing defect (short defect) based on the above-described sample observation apparatus and an image obtained by electrons obtained from the structure information of the conductive region, and obtains the structure information of the insulating region. And an arithmetic unit that determines the presence or absence of an open defect (open defect) from an image obtained by the obtained electrons.

With this configuration, an image acquired under conditions where the luminance of the conductive region is higher than that of the insulating region and an image acquired under conditions where the luminance of the insulating region is higher than the luminance of the conductive region It is possible to detect both missing defects (short defects) and open defects (open defects) with high sensitivity and high accuracy.

  As described above, according to the sample observation method and the sample observation apparatus according to the present invention, an image is acquired under the condition that the luminance of the conductive region is higher than the luminance of the insulating region, and the luminance of the insulating region is higher than the luminance of the conductive region. Images are acquired under high conditions, and it is possible to detect both missing defects and open defects on the sample surface with high accuracy based on these images.

Further, according to the sample observation method and sample observation apparatus according to the present invention, the separation of electrons e _i obtained structural information conductive region and electrons e _c to obtain structural information of the insulating region becomes more pronounced, high It becomes easy to obtain contrast.

  Furthermore, according to the sample inspection method and the sample inspection apparatus according to the present invention, the image acquired under the condition that the luminance of the conductive region is higher than the luminance of the insulating region and the luminance of the insulating region is higher than the luminance of the conductive region. By determining whether or not there is a defect based on the image acquired below, it is possible to detect both a missing defect (short defect) and an open defect (open defect) with high sensitivity and high accuracy.

  The present invention can be applied to, for example, observation and inspection of the surface of a semiconductor wafer after it is processed in a semiconductor manufacturing process. By using a sample observation apparatus and a sample observation method according to the present invention, a semiconductor wafer having an insulating region and a conductive region on the sample surface is observed, and a high contrast image is acquired to check the quality of the semiconductor wafer. It becomes an effective means for the production of a semiconductor wafer free from defects.

  As described above, according to the present invention, the sample surface on which the insulating region and the conductive region are formed is observed with high contrast, and the detection of the missing defect and the open defect and the classification of the defect type are facilitated. Provided are a sample observation method and apparatus, and a sample inspection method and apparatus using them. The present invention can be used for, for example, a sample observation apparatus that observes the surface of a substrate such as a semiconductor wafer or a reticle, or a sample defect detection apparatus that detects defects.

FIG. 1 is a diagram showing an overall configuration example of a sample observation apparatus according to the present invention. FIG. 2 is a diagram showing an example of the relationship between the irradiation energy of the imaging electron beam and the material contrast in the acquired image. FIG. 2A is a diagram showing an example of an image obtained by the irradiation energy band, and FIG. 2B is a diagram showing a correlation between the irradiation energy of the imaging electron beam and the detector current. FIG. 3 is a diagram schematically showing the difference in angle between the mirror electrons and the secondary electrons obtained from the structure information of the sample surface, and the horizontal axis is the effective landing energy (LE). FIG. 4 is a diagram showing a change in gradation of the sample surface with respect to landing energy (LE). FIG. 5 is a schematic diagram showing an example of an electron trajectory obtained from the structure information of the sample surface. 5A is a side view of the electron trajectory, and FIG. 5B is a partially enlarged view of the electron trajectory as viewed from the lower side of the movable NA aperture. FIG. 6 is a diagram for explaining the optimum position of the NA aperture for obtaining a high material contrast in each of mirror electrons and secondary electrons. FIG. 6A is a diagram showing the optimum NA aperture position of the NA adjustment aperture in the case of mirror electrons, and FIG. 6B is a diagram showing the optimum NA aperture position in the case of secondary electrons. is there. FIG. 7 is a diagram showing an example of the structure of the sample already described in relation to FIG. 2 and an image acquired by observing the sample. FIG. 7A is a diagram illustrating a cross-sectional structure of a contact plug that is a sample, and FIG. 7B is a diagram illustrating an example of an acquired image of a sample surface having a contact plug structure. FIG. 8 is a diagram for explaining by way of example the results of studying the landing energy (LE) condition for acquiring a high-contrast image. FIG. 8A is a table summarizing the results of measuring the contrast when observing the contact plug having the cross-sectional structure shown in FIG. 7A by changing the landing energy (LE) of the electron beam. FIG. 8B is a graph of the measurement result of FIG. FIG. 9 is a diagram for explaining the correlation between the dose amount of the charged electron beam and the contrast. 9A is a table of measurement results showing the correlation between the dose amount of the charged electron beam and the contrast, and FIG. 9B is a graph of the measurement results of FIG. 9A. is there. FIG. 10 is a diagram for supplementarily explaining that a high contrast can be obtained by separating the electron e _c obtained from the structural information of the conductive region and the electron e _i obtained from the structural information of the insulating region. . FIG. 10A shows each of the conductive region (Cu) and the insulating region (SiO ₂ ) when the electron e _c obtained from the structural information of the conductive region and the electron e _i obtained from the structural information of the insulating region are not separated. 6 is a table summarizing the landing energy (LE) dependence of the secondary electron emission efficiency and contrast of the material. FIG. 10B is a graph showing this table. FIG. 11 is a diagram showing a result of comparing the contrast when the area ratio (pattern width) between the conductive region and the insulating region on the sample surface is changed between the LEEM method using the low acceleration electron beam apparatus and the SEM method. It is. FIG. 11A is a table of measurement results showing the correlation between the sample surface and contrast, and FIG. 11B is a graph of the measurement results of FIG. 11A. FIG. 12 is a diagram showing a second overall configuration example of the sample observation apparatus according to the present invention. FIG. 13 is a diagram illustrating a configuration example of a movable NA adjustment aperture. FIG. 13A is a top view illustrating an example of a slide movement type NA adjustment aperture, and FIG. 13B illustrates an example of a rotation movement type NA adjustment aperture. FIG. FIG. 14 is a diagram showing an example of a preferred detector configuration for high-resolution observation. FIG. 15 is a diagram showing a third overall configuration example of the sample observation apparatus according to the present invention. FIG. 16 illustrates an image acquired under a condition (A condition) where the luminance of the conductive area is higher than that of the insulating area and an image acquired under a condition (B condition) where the luminance of the insulating area is higher than the luminance of the conductive area. It is a figure for showing notionally how a missing defect (short defect) and an open defect (open defect) appear in each. FIG. 17 shows an image acquired under a condition (A condition) where the luminance of the conductive area is higher than that of the insulating area and an image acquired under a condition (B condition) where the luminance of the insulating area is higher than the luminance of the conductive area. It is a figure for showing notionally how a missing defect (short defect) and an open defect (open defect) appear in each. FIG. 18 shows the result of an experiment conducted to determine the optimum value of the irradiation energy (LE) of the imaging electron beam irradiated on the sample surface. FIG. 18A summarizes the irradiation energy (LE), the luminance [DN] of each of the conductive material and the insulating material, and the contrast as a table. FIG. 18B is a diagram showing this table as a graph. FIG. 19 shows the result of an experiment conducted to determine the optimum value of the dose amount of the charged electron beam irradiated on the sample surface. FIG. 19A summarizes the beam dose [mC / cm ² ], the luminance [DN] of each of the conductive material and the insulating material, and the contrast as a table. FIG. 19B is a diagram showing this table as a graph. FIG. 20 is a diagram for explaining the result of confirming the position of the electron distribution in the NA imaging mode. FIG. 20 (A) beam dose amount [mC / cm ^2] and when irradiated with charged electron beam of the dose, the deviation of the distribution state of the electronic e _i to obtain a surface structure information of an insulating material, i.e., conductive it is a table that summarizes how much shifted from the distribution state of the electronic e _c to obtain a surface structure information of the material. FIG. 20B is a diagram showing this table as a graph. FIG. 21 shows the result of an experiment conducted to determine the optimum value of the irradiation energy (LE) of the imaging electron beam irradiated on the surface of the charged sample. FIG. 21A summarizes the irradiation energy (LE), the luminance [DN] of each of the conductive material and the insulating material, and the contrast as a table. FIG. 21B is a graph showing this table. FIG. 22 is a diagram for explaining the reversal of contrast by adjusting the position of the NA aperture. FIG. 22 (A) moves the center position of the NA aperture substantially matched positions in the center of the orbit of the electron e _c emitted from the conductive area from the (normalized position = 0) in the Y direction (normalized position = 1 The brightness [DN] and contrast of each of the conductive material and the insulating material are summarized as a table. FIG. 22B is a diagram showing this table as a graph. FIG. 23 is a diagram for conceptually explaining the state of contrast inversion accompanying the adjustment of the position of the NA aperture. FIG. 24 is a flowchart for exemplifying the procedure for determining the dose dependency of the electron orbit shift amount and the procedure for confirming the reversal of the material contrast in the sample observation method of the present invention. FIG. 25 is a flowchart for illustrating the procedure of the sample observation method of the present invention by way of example. FIG. 26 is a flowchart for explaining another example of the procedure of the sample observation method of the present invention. FIG. 27 is a diagram for explaining the result of performing the defect inspection by the method of the present invention. FIG. 27A is a table summarizing whether or not defects can be detected by an image acquired under the condition that the luminance of the conductive region is higher than the luminance of the insulating region. FIG. 27B is a table showing the luminance of the insulating region. FIG. 27C is a table summarizing the possibility of defect detection by combining the two defect detection results, and a table summarizing the possibility of defect detection using images acquired under conditions higher than the luminance.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

[Example of overall configuration of sample observation device]
FIG. 1 is a diagram showing an overall configuration example of a sample observation apparatus according to the present invention. This sample observation device is a mapping projection type low acceleration electron beam device, and includes an electron beam source 10, a primary lens 20, a condenser lens 30, an electromagnetic field generating means (E × B) 40, and a transfer lens 50. And an NA adjustment aperture 60 for adjusting a numerical aperture (NA), a projection lens 70, a detector 80, an image processing device 90, and a stage 100 for placing a sample 200 to be observed. And an irradiation energy setting means 110 and a power source 115.

  The NA adjustment aperture 60 is provided with at least one NA aperture 61, and the numerical aperture (NA) is determined by the NA aperture 61. The position of the NA aperture 61 can be adjusted in a plane, and the electrons obtained from the structure information of the conductive region and the electrons obtained from the structure information of the insulating region are selectively selected by the action of E × B40 described later. To the detector 80. Note that this sample observation apparatus may include a charged beam irradiation unit 120 for irradiating the surface of the sample 200 with an electron beam to charge the sample surface 201 as necessary.

  The sample surface 201 has an insulating region and a conductive region, and the sample surface 201 is observed by irradiation with an imaging electron beam from the electron beam source 10. The electron beam source 10 includes, for example, an electron source 11, a Wehnelt electrode 12, and an anode 13. The electron source 11 generates electrons, the electrons are extracted by the Wehnelt electrode 12, and the electrons are accelerated by the anode 13. The sample surface 201 is irradiated.

  The electron beam source 10 may generate a planar electron beam having a predetermined area that can include a plurality of pixels so that a plurality of pixels can be imaged simultaneously. Thereby, a plurality of pixels can be imaged simultaneously by one-time irradiation of the sample surface 201 with an electron beam, and a two-dimensional image having a large area can be acquired at high speed.

  The irradiation energy setting means 110 is a means for setting the irradiation energy of the electron beam emitted from the electron beam source 10. The power source 115 of the irradiation energy setting unit 110 supplies power to the electron beam source 10 and generates electrons from the electron source 11. Since the power source 115 generates electrons from the electron source 11, the negative electrode is connected to the electron source 11. The irradiation energy of the electron beam is determined by the potential difference between the potential of the sample 200 and the cathode of the electron source 11 of the electron beam source 10. Therefore, the irradiation energy setting means 110 can adjust and set the irradiation energy by adjusting the voltage of the power source 115 (hereinafter referred to as “acceleration voltage”).

  In the sample observation apparatus according to the present invention, the irradiation energy setting means 110 sets the irradiation energy of the electron beam to an appropriate value, and increases the contrast of the acquired image. In the present invention, the irradiation energy of the electron beam is set in a transition region in which electrons obtained from the structural information of the sample surface 201 by irradiation of the imaging electron beam include both mirror electrons and secondary electrons. A specific method for setting the irradiation energy will be described later.

  The primary lens 20 is a means for deflecting the electron beam emitted from the electron beam source 10 by the action of an electromagnetic field and guiding it to a desired irradiation region on the sample surface 201. A plurality of primary lenses 20 may be provided. As such a primary lens 20, for example, a quadrupole lens is used.

  The E × B 40 is a means for applying an electric field and a magnetic field to the electron beam or the electron, directing the electron beam or the electron by Lorentz force, and directing the electron beam or the electron in a predetermined direction. In the E × B 40, an electric field and a magnetic field are set so as to generate a Lorentz force that directs the electron beam emitted from the electron beam source 10 in the direction of the sample surface 201.

  In the E × B 40, the electrons obtained from the structure information of the sample surface 201 by irradiating the sample surface 201 with the electron beam are directly moved upward and the electric field and the magnetic field are directed toward the detector 80. Is set. As will be described later, the electrons that have obtained the structural information of the sample surface 201 by the irradiation of the imaging electron beam are subjected to the electric field according to the speed of traveling in the direction opposite to the incident direction of the imaging electron beam by the action of E × B40. And the direction is made by the magnetic field.

  By such an action of E × B40, the electron beam incident on the sample surface 201 and the electron generated from the sample surface 201 side traveling in the opposite direction to the incident electron beam can be separated. Note that E × B may be referred to as a Wien filter.

  The condenser lens 30 is a lens for focusing an electron obtained from the structural information of the sample surface 201 while forming an image of the electron beam on the sample surface 201. Therefore, the condenser lens 30 is disposed closest to the sample 200.

  The transfer lens 50 is an optical means for guiding the electrons that have passed through the E × B 40 in the direction of the detector 80 and for forming a crossover near the NA aperture 61 of the NA adjustment aperture 60.

  The NA adjusting aperture 60 is a means for adjusting the number of passing electrons. The NA adjusting aperture 60 has an NA aperture 61 which is a hole for determining a numerical aperture (NA) at the center thereof. The NA aperture 61 allows electrons from the sample surface 201 side guided by the transfer lens 50 to pass therethrough and becomes a path to the detector 80, and blocks electrons that become imaging noise from moving toward the detector 80. Adjust the number of passing electrons. Further, as described above, the position of the NA aperture 61 can be adjusted in the plane, and the structure information of the conductive region and the insulating region obtained by the action of E × B40 has been obtained. Electrons can be selectively directed to the detector 80. Details thereof will be described later. Note that a plurality of types of NA apertures having different hole diameters may be provided. In this case, a desired NA aperture is selected by the NA aperture moving mechanism.

  The projection lens 70 is final focus adjustment means for forming an image on the detection surface 81 of the detector 80 with respect to electrons that have passed through the NA adjustment aperture 60.

The detector 80 is a means for acquiring an image of the sample surface 201 by detecting the electrons obtained by irradiating the sample surface 201 with the electron beam and obtaining the structural information of the sample surface 201. Although various detectors 80 can be applied to the detector 80, for example, a CCD (Charge Coupled Device) detector that enables parallel image acquisition or a TDI (Time Delay Integration) -CCD detector can be applied. Good. By using a two-dimensional image pickup type detector 80 such as a CCD or a TDI-CCD and using a surface beam that can irradiate a predetermined area including a plurality of pixels to the electron beam source 10, parallel imaging is performed with one beam irradiation. A wide area image can be acquired, and the specimen surface 201 can be observed at high speed. The CCD or TDI-CCD is a detection element that detects light and outputs an electrical signal. Therefore, when the CCD or TDI-CCD is applied to the detector 80, a fluorescent plate that converts electrons into light, Since an MCP (microchannel plate) for multiplying electrons is required, the detector 80 includes them.

  The detector 80 may use EB-CCD or EB-TDI. An EB-CCD 81 is used for the detector 80 of the sample observation apparatus illustrated in FIG. EB-CCD and EB-TDI are the same as CCD and TDI-CCD in that they are two-dimensional image pickup type detectors, but directly detect electrons and do not undergo photo-electron conversion. The electrical signal is output as it is. Therefore, the above-described fluorescent plate and MCP are not required, and signal loss along the way is reduced, so that high-resolution image acquisition is possible.

  The image processing device 90 is a device that generates an image of the sample surface 201 based on the electrical signal output from the detector 80. Specifically, a two-dimensional image is generated based on the coordinate information and luminance information output from the detector 80. In the sample observation apparatus according to the present embodiment, since the sample 200 including the insulating material and the conductive material is observed on the sample surface 201, a luminance difference is generated between the insulating region and the conductive region, and an image with high contrast is acquired. The image processing apparatus 90 performs necessary image processing and image generation so that a good image can be acquired.

The stage 100 is means for supporting the sample 200 by placing the sample 200 on the upper surface. The stage 100 can be moved in the X and Y directions in the horizontal plane (in the XY plane) or can be rotated in the horizontal plane so that the entire observation area of the sample surface 201 can be irradiated with the electron beam. May be. In addition, the height of the sample surface 201 may be adjusted so that it can be moved in the vertical direction (Z direction) as necessary. When the stage 100 is configured to be movable, for example, a moving means such as a motor or air may be provided.

  The charged electron beam irradiation means 120 is provided to charge the sample surface 201 before irradiating the imaging electron beam for imaging from the electron beam source 10. The charged electron beam irradiation means 120 may be provided as necessary.

  If the sample surface 201 is irradiated with an electron beam in advance before imaging the sample surface 201, the conductive region is not charged and the potential remains at the ground potential, whereas the insulating region is negatively charged. Therefore, a potential difference corresponding to the material can be formed between the conductive region and the insulating region. The potential difference can increase the contrast between the conductive region and the insulating region. Therefore, when it is desired to irradiate the sample surface 201 with the charged electron beam before the imaging electron beam, the charged electron beam irradiation means 120 may be provided.

  In addition, it is good also as a sample observation apparatus of the structure where the electron beam source 10 serves as the said charged electron beam irradiation means, without providing the charged electron beam irradiation means 120 separately.

  That is, the above-described charged electron beam may be irradiated from the electron beam source 10 without using the charged electron beam irradiation means 120. Then, following the irradiation of the charged electron beam, the sample electron beam 201 may be irradiated with the imaging electron beam.

  Therefore, the charged electron beam irradiation means 120 is provided, for example, when it is desired to irradiate the sample surface 201 with the charged electron beam and when it is desired to irradiate the imaging electron beam immediately after the irradiation with the charged electron beam. It may be. Generally, since the imaging electron beam and the charged electron beam have different irradiation energies, the adjustment of the irradiation energy between the charged electron beam irradiation and the imaging electron beam irradiation is not required by providing the charged electron beam irradiation means 120. And rapid imaging can be performed. Therefore, when the request for shortening the observation time is high, the charged electron beam irradiation means 120 can be provided to meet the request for shortening the observation time.

  The sample 200 includes an insulating region made of an insulating material and a conductive region made of a conductive material on the sample surface 201 of the surface. Although the sample 200 can be applied in various shapes, for example, a substrate-like sample 200 such as a semiconductor wafer or a reticle may be applied. The sample observation apparatus according to the present invention may be configured so that the sample surface 201 can be preferably observed even when the insulating region of the sample surface 201 has a larger area ratio than the conductive region. With such a configuration, for example, an image of the sample surface 201 can be satisfactorily acquired and observed also for a contact plug of a semiconductor wafer and a contact structure of a reticle.

Various materials can be applied to the conductive material and the insulating material. For example, the conductive material is a plug material such as W (tungsten), and the insulating material is SiO ₂ (silicon used as an insulating layer of a semiconductor wafer). An oxide film) or the like may be applied.

[Specific contents of sample observation]
Next, the contents of sample observation using the sample observation apparatus having the configuration illustrated in FIG. 1 will be specifically described.

  FIG. 2 is a diagram showing an example of the relationship between the irradiation energy of the imaging electron beam and the material contrast in the acquired image. Here, the material contrast means a contrast formed due to a difference between electrons generated from the conductive material and electrons generated from the insulating material. FIG. 2A is a diagram showing an example of an image obtained by the irradiation energy band, and FIG. 2B is a diagram showing a correlation between the irradiation energy of the imaging electron beam and the detector current.

  In FIG. 2B, the horizontal axis indicates the irradiation energy (also referred to as landing energy (LE)) of the imaging electron beam, and the vertical axis indicates the magnitude of the detector current in the detector 80. In FIG. 2 (B), the solid line is a characteristic curve when the NA adjusting aperture 60 having an aperture diameter of 10 to 300 [μm] is used, and the alternate long and short dash line is 1000 to 3000 [μm] BR> Characteristic curve when NA adjustment aperture 60 having A is used. In the example shown in this figure, landing energy (LE) 2 to 10 [eV] is “secondary electron region”, −2 to 2 [eV] is “transition region”, and −2 [eV] and below are “mirror electrons”. "Region".

  Here, “secondary electrons” refer to electrons emitted from the sample 200 when the electron beam collides with the sample surface 201. As long as the secondary electrons are electrons emitted from the sample 200 when the electron beam collides with the sample surface 201, in addition to so-called secondary electrons, reflected electrons having substantially the same incident energy and reflected energy, and backward scattered back. Although it may contain scattered electrons and the like, it is secondary electrons that are mainly detected in the “secondary electron region” according to the cosine law in the manner of emission from the sample 200.

  The “mirror electron” means an electron that is reflected by the electron beam irradiated toward the sample surface 201 with the traveling direction being reversed in the vicinity of the sample surface 201 without colliding with the sample surface 201. For example, when the potential of the sample surface 201 is a negative potential and the landing energy of the electron beam is small, the electron beam does not collide with the sample surface 201 due to the electric field near the sample surface 201 and changes the traveling direction in the opposite direction. A phenomenon is observed. In the sample observation apparatus and the sample observation method according to the present invention, such electrons that are reflected with the traveling direction in the reverse direction without colliding with the sample surface 201 are referred to as mirror electrons.

  In FIG. 2B, in the secondary electron region of landing energy (LE) 2 to 10 [eV], the detected current is greatly different due to the difference in the aperture diameter of the NA adjusting aperture 60. This is because the electron emission at the position of the NA adjustment aperture 60 is large because the sample surface emission angle of secondary electrons is expressed by the cosine law.

  Next, as the landing energy (LE) is decreased to 2 [eV] or less, the mirror electrons increase little by little and become a “transition region” in which mirror electrons and secondary electrons are mixed. The difference in detector current due to the difference in aperture diameter is small.

  Next, when the landing energy (LE) becomes −2 [eV] or less, the emission of secondary electrons is not recognized by entering the mirror electron region, and the amount of emission of mirror electrons becomes constant. In this region, the detector current does not depend on the aperture diameter of the NA adjustment aperture 60. From this, it is considered that the mirror electrons are focused around φ300 [μm] or more and φ10 [μm] or more at the position of the NA adjusting aperture 60. This is because the mirror electrons are reflected without colliding with the substrate surface, so that directivity is good and straightness is high.

  In the example shown in FIG. 2 (B), the characteristic curve when the aperture diameter is less than 10 [μm] is the same as that shown by the solid line, and when the aperture diameter is larger than 3000 [μm]. The characteristic curve is considered to be the same as that shown by the broken line. However, here, it is set to 10 [μm] or more and 3000 [μm] or less because of a measurement limit due to noise increase.

FIG. 3 is a diagram schematically showing the difference in angle between the mirror electrons and the secondary electrons obtained from the structural information of the sample surface 201, and the horizontal axis is the effective landing energy (LE). FIG. 3 shows the relationship between effective landing energy and electron behavior for each of the mirror electron region and the transition region.

  FIG. 3 shows an example in which a region having an effective landing energy (LE) of 0 [eV] or less becomes a mirror electron region. As shown in this figure, the mirror electrons are reflected in front of the sample surface 201 without the irradiation electron beam colliding with the sample surface 201. In this case, when the irradiation beam is incident on the sample surface 201 perpendicularly, the mirror electrons are reflected perpendicularly on the sample surface 201. As a result, the traveling direction of the mirror electrons is constant.

  On the other hand, in the transition region, a certain part of the irradiation electron beam becomes a mirror electron reflected in front of the sample surface 201 without colliding with the sample surface 201, but a part of the irradiation electron beam is reflected on the sample surface. It collides with 201 and enters a state in which secondary electrons are emitted from the inside of the sample 200 to the outside. Here, similarly to the mirror electron region, when the irradiation beam is incident perpendicular to the sample surface 201, the mirror electrons are reflected perpendicular to the sample surface 201, and the traveling direction of the mirror electrons is constant. . On the other hand, secondary electrons are emitted in various directions according to the so-called “cosine law” so that the emission amount is proportional to the cosine of the angle formed by the normal line of the sample surface 201 and the emission direction (observation direction). Has been. As the landing energy increases (as shown on the right side in FIG. 3), the ratio of secondary electrons to mirror electrons increases.

  That is, as shown in FIG. 3, it can be seen that the mirror electrons have a constant direction of travel and good directivity, but the secondary electrons travel in various directions according to the cosine law and the directivity is not high.

  In the example described above, the landing energy range of −2 [eV] to 2 [eV] is a transition region, that is, a region where mirror electrons and secondary electrons are mixed. However, such a landing energy range can vary depending on the sample to be observed. From the experience of various experiments, the inventors have made use of the irradiation electron beam having the landing energy in the transition region, and the high contrast observation of the pattern on the sample surface, in particular, the sample in which the insulating region and the conductive region are formed. It was found to be very effective for observing the surface with high contrast.

  According to the study by the present inventors, when the minimum irradiation energy of the transition region is LEA and the maximum irradiation energy is LEB, the irradiation energy (LE) of the primary imaging electron beam is LEA ≦ LE ≦ LEB, Alternatively, LEA ≦ LE ≦ LEB + 5 eV is preferably set.

  Hereinafter, this content will be described in detail.

  FIG. 4 is a diagram showing a change in gradation of the sample surface 201 with respect to landing energy (LE). Here, the gradation is proportional to the number of electrons acquired by the detector 80.

  As shown in FIG. 4, the region where the landing energy (LE) is LEA or less is the mirror electron region, the region where the landing energy (LE) is LEB or more is the secondary electron region, and the region where the landing energy (LE) is LEA or more and LEB or less. Is a transition region.

  According to the experience that the present inventors have made various experiments, it has been confirmed that LEA to LEB are preferably in the range of −5 [eV] to +5 [eV].

A gradation difference is generated due to a difference in the formation state of mirror electrons between the insulating region and the conductive region, and a higher contrast is formed as the gradation difference is larger. That is, a difference in the formation state of mirror electrons occurs due to a difference in material and structure, and a gradation difference is formed. How to set the above-mentioned landing energy (LE) is extremely important in order to generate a high contrast between the insulating region and the conductive region in the acquired image. Specifically, the region of LEA ≦ LE ≦ LEB (for example, −5 [eV] to +5 [eV]), or LEA
Using the landing energy (LE) in the region of ≦ LE ≦ LEB + 5 [eV] (for example, −5 [eV] to +10 (5 + 5) [eV]) is very effective for obtaining high contrast.

Returning to FIG. 2 again, the contrast between the insulating material and the conductive material in each generated electron region will be described. Note that various materials may be used as the conductive material and the insulating material as long as they are formed of a conductor or an insulator. For example, the conductive material is W (tungsten), and the insulating material is SiO ₂ (silicon oxide). Film) or the like may be applied.

  FIG. 2A shows an example of material contrast in an image acquired by an irradiation electron beam having landing energy (LE) in each generated electron region. FIG. 2A shows an example of material contrast in the secondary electron region, transition region, and mirror electron region. First, focusing on the material contrast in the mirror electron region, there is no difference in luminance between the conductive material and the insulating material, and the material contrast cannot be obtained. This is because, in the mirror electron region, all irradiated electrons are reflected before the sample surface 201, so that a difference in luminance, that is, a difference in the number of electrons does not occur between the conductive material and the insulating material.

  In addition, in both the transition region and the secondary electron region, there is a luminance difference between the conductive material and the insulating material. However, the transition region has a larger luminance difference between the conductive material and the insulating material. The contrast is high. This is probably because not only secondary electrons but also highly directional mirror electrons are detected in the transition region, so that the amount of signal increases and the luminance increases accordingly.

  Thus, if an image of the sample surface 201 is acquired in the transition region where secondary electrons and mirror electrons are mixed, the material contrast between the conductive material and the insulating material can be increased.

  In the transition region, if the sample surface 201 is irradiated with an electron beam in advance before imaging, the potential of the conductive material remains at the ground potential, while the insulating material is charged and has a potential of about a few [eV]. Change. As a result, the energy (velocity) differs between the electron that has obtained the structural information of the conductive material and the electron that has obtained the structural information of the insulating material.

  When electrons having different velocities pass through the E × B 40, orbital shift (orbit shift) occurs according to the respective velocities for the following reasons.

E × B40 is a means for generating an electric field E and a magnetic field B, and electrons passing through the E × B40 are generated by the force of F _E = e · E due to the electric field and F _B = e · (v × B) due to the magnetic field. Receive the power of Here, e is an electric charge of 1.602 × 10 ⁻¹⁹ [C], and E and B are an electric field [V / m] and a magnetic field [Wb / m ² ], respectively.

Among these forces, the force of F _E = e · E due to the electric field does not depend on the velocity of the electrons v [m / s], whereas the force of F _B = e · (v × B) due to the magnetic field is It depends on the speed v [m / s].

  Normally, the condition (Vienna condition) in which electrons emitted from the conductive substrate travel straight through E × B40 is set. However, if the electron velocity v [m / s] changes due to the above-described reason, the magnetic field Since the force received by this action changes, the trajectory of the electrons that have passed through E × B40 shifts.

That is, as described above, the E × B 40 directs the electron trajectory obtained from the structure information of the sample surface 201 by irradiation of the imaging electron beam according to the speed of traveling in the direction opposite to the incident direction of the imaging electron beam. Means. Then, using the above-described shift of the electron orbit, either the electron that has obtained the structural information of the conductive region or the electron that has obtained the structural information of the insulating region passes through the NA aperture 61 and is selectively detected. 80 is possible.

  Since the transition region is an energy region in which secondary electrons and mirror electrons are mixed, in this energy region, the electron trajectories of the secondary electrons and mirror electrons from the insulating region both shift.

  FIG. 5 is a schematic diagram showing an example of an electron trajectory obtained from the structural information of the sample surface 201, FIG. 5 (A) is a side view of the electron trajectory, and FIG. 5 (B) is under the movable NA aperture. It is the elements on larger scale of the electron orbit seen from the side.

  In FIG. 5A, a negative potential is applied to the sample 200 by the sample power source 101. In the sample 200, the insulating material 203 covers the conductive material 202, and the conductive material 202 is exposed from a hole 204 that is a break in the insulating material 203 to form the sample surface 201. For example, the contact structure of the reticle often has a shape in which the bottom surface of the hole 204 is formed of the conductive material 202 as in the sample 200 shown in FIG. For simplification, only the E × B 40, the NA adjustment aperture 60, and the detector 80 are shown as components of the sample observation apparatus.

In FIG. 5A, an electron beam EB is emitted from the upper right, and the electron beam is deflected by E × B 40 and vertically incident on the sample surface 201. Then, among the electrons to obtain structural information of a sample surface 201, electrons e _c to obtain structural information conductive region 202 passes through the NA aperture 61 of the NA adjusting aperture 60 and straight. On the other hand, the electron e _{i that} has obtained the structure information of the insulating region 201 shifts its trajectory by the action of E × B 40, collides with a member of the NA adjustment aperture 60 around the NA aperture 61, and does not pass through the NA aperture 61. . As a result, while the electron e _c to obtain structural information conductive region 202 reaching the detector 80, an electronic e _i obtained structural information of the insulating region 201 does not reach the detector 80.

In the contact structure of the reticle, in many cases, the insulating material 201 occupies most of the sample surface 201 and the conductive material 202 is included in a part (the bottom surface of the hole 204). In this structure, only the electrons e _c to obtain a surface structure information of the conductive material 202 introduced into a detector 80, by not reach the electron e _i to obtain a surface structure information of an insulating material 201 to the detector 80, An image with a specifically high contrast can be acquired.

On the contrary, also by not reach only electrons e _i to obtain a surface structure information of the insulating material 201 introduced into a detector 80, an electronic e _c to obtain a surface structure information of the conductive material 202 to the detector 80 It is possible to acquire an image with a specifically high contrast.

  Such a contrast inversion method is particularly effective in detecting missing defects (short defects) and open defects (open defects) present in a pattern having the same area of conductive material and insulating material on the sample surface. is there. In a pattern in which the area of one of the conductive material and the insulating material is significantly narrower than the area of the other material, a material area having a remarkably narrow area is scattered in a material area having a large area. . Because electrons from a large area of material diffuse slightly in the optical path to the detector, this diffusion action results in an image obtained from electrons from a small area of material that is smaller than the original image. This makes it difficult to detect defects. For example, in a structure in which contact plug-shaped conductive regions with a remarkably small area are interspersed in a wide insulating region provided on a silicon substrate (contact plug structure), it is formed by electrons from the conductive region. The image to be obtained is obtained as an image narrower than the original area due to diffusion (wraparound) of electrons from the insulating region.

Here, it is assumed that the electrons e _c and e _i include both mirror electrons and secondary electrons. Further, the separation and detection of the generated electrons according to the kind of material can be similarly applied not only to the reticle but also to a line / space pattern such as a semiconductor wafer.

FIG. 5B shows the NA aperture 61 and the electrons e _c obtained from the surface structure information of the conductive material 202 and the electrons e obtained from the surface structure information of the insulating material 201 as viewed from below the NA adjustment aperture 60. It is an enlarged view for _{demonstrating} the relationship of _i .

In the example shown in this FIG., NA aperture 61 is a hole portion formed on a part of the rectangular NA adjusting aperture 60, the electron e _c to obtain structural information conductive region 202 is passed through the NA aperture 61 while for, it is adjusted to a position which can not pass through the NA aperture 61 most of the electrons e _i obtained structural information of the insulating region 203 intercepts the NA adjusting aperture 60.

As for the mirror electrons, the electron trajectories of the conductive material 202 and the insulating material 203 are the minimum spot of 100 [μm] at the position of the NA adjusting aperture 60 as a crossover point. Therefore, utilizing track shift by E × B40, the NA adjusting aperture 60, it is easy to selectively separate electronic e _c to obtain structural information of the conductive material 202 without loss of optical resolution .

The greater the potential difference between the conductive material and the insulating material due to the above-described charging, the greater the positional movement at the position of the NA adjustment aperture 60. Accordingly, the if the charging potential greatly, larger even by using a NA aperture 61 having a pore size, can be separated electrons e _i obtained structural information of the electronic e _c and the insulating region 203 to obtain structural information conductive region 202 It becomes. By using the NA aperture 61 having a large hole diameter, it is possible to increase the number of detected electrons and form an image.

  When the charged electron beam is irradiated onto the insulating region 203 of the sample surface 201 before the imaging electron beam is irradiated, the electron beam source 10 or the charged electron beam irradiation means 120 is installed when it is installed. It is only necessary to irradiate the sample surface 201 of the sample 200 with the charged electron beam in a state where imaging by the detector 80 is not performed. In this case, the charged electron beam may be irradiated only to the insulating region 203. However, the surface potential of the conductive region 202 is zero even when the charged electron beam is irradiated. It is also possible to irradiate the imaging region of the sample surface 201 with a charged electron beam having an irradiation energy of 1.

FIG. 6 is a diagram for explaining the optimum position of the NA aperture 61 for obtaining a high material contrast in each of the case of mirror electrons and the case of secondary electrons. FIG. 6A is a diagram showing the optimal NA aperture 61 position of the NA adjustment aperture 60 in the case of mirror electrons, and FIG. 6B shows the optimal NA aperture position in the case of secondary electrons. FIG. Further, in FIG. 6, a circle indicated by black, shows an electronic e _c to obtain structural information conductive region 202, a circle indicated by gray, the electrons e _i obtained structural information of the insulating region 203 Show. As shown in this figure, the optimum position of the NA aperture 61 at the position of the NA adjustment aperture 60 differs depending on the difference in the spread of the trajectories of the mirror electrons and the secondary electrons.

In FIG. 6 (B), the in the position of the NA adjusting aperture 60, the electron orbit shift amount of the secondary electrons e _i obtained structural information was obtained structural information conductive regions 202 secondary electrons e _c and the insulating region 203 Is approximately 100 μm, but most of these electron distributions overlap. This is because, as described above, the secondary electrons travel in various directions according to the cosine law, and thus the directivity is not high. Therefore, in order to increase the material contrast due to secondary electrons, N
The center of the NA aperture 61 of the A-adjusting aperture 60, the center of the orbit of emitted electrons e _c from the conductive region 202 that match the substantially matched positions, considered optimal. Together the center of the NA aperture 61 in such a position, it is possible to detect the electron e _c around the most electron density high portion of the electron e _c emitted from the conductive region 202 of the sample surface 201.

However, as shown in FIG. 6 (B), the electron orbit of the electron e _i emitted from the insulating region 203 also, because of overlap with the trajectory of the electron e _c emitted from the substantially conductive region 202, separate the two Cannot be detected. Therefore, in the secondary electron regions, the material contrast, based on the difference of the secondary electrons e _i itself signals emitted as emitted secondary electrons e _c from the insulating region 203 from conductive region 202, distinguished from each other Will do.

In contrast, in FIG. 6 (A), the mirror electrons e _i to obtain structural information mirror electrons e _c and the insulating region 203 to obtain structural information conductive regions 202, remarkable difference in electron orbit shift amount Appear in In the example shown in FIG. 6 (A), in the position of the NA adjusting aperture 60, an electron orbit of mirror electrons e _i obtained structural information mirror electrons e _c and the insulating region 203 to obtain structural information conductive region 202 The difference in shift amount is approximately 100 μm, but most of these electron distributions do not overlap and are substantially separated. This is because, as described above, mirror electrons have a constant traveling direction and good directivity.

In such a case, for example, while the electron e _c to obtain structural information conductive region 202 passes all the NA aperture 61, electrons e _i obtained structural information of the insulating region 203 can not pass through the NA aperture 61 so Such an arrangement is easily possible. Then, when the position of the NA aperture 61 is adjusted, the electron e _c obtained from the structure information of the conductive region is separated from the electron e _i obtained from the structure information of the insulating region, thereby obtaining the structure information of the conductive region. only it can be guided more to the detector 80 electrons e _c. As a result, the material contrast between the conductive region 202 and the insulating region 203 can be increased. That is, by utilizing the mirror electrons generated in the transition region, it is possible to separate the electron e _i obtained structural information of the electronic e _c and the insulating region 203 to obtain structural information conductive region, Acquisition of an image with high material contrast is facilitated.

  Usually, in order to perform such separation, a chromatic aberration corrector (monochromator) composed of a plurality of magnetic fields and electric fields is required. However, according to the sample observation apparatus and the sample observation method according to the present invention, chromatic aberration is obtained. Even without installing a corrector, an image with a high material contrast can be obtained only by adjusting the position of the NA aperture 61 that is a hole in the NA adjustment aperture 60.

In FIGS. 5 and 6 guides the electrons e _c to obtain structural information conductive region 202 to selectively detector 80, guide to the detector 80 electrons e _i obtained structural information of the insulating region 203 Explains an example. However, the electron e _i obtained from the structural information of the insulating region 203 is selectively guided to the detector 80 by setting the E × B 40, the arrangement of the NA adjusting aperture 60 and the adjustment of the aperture diameter, and the structural information of the conductive region 202 is obtained. it is also possible to embodiments does not lead to the detector 80 electrons e _c got.

Depending on the application, which electron is selectively introduced to the detector 80 and detected from the electron e _c obtained from the structural information of the conductive region 202 and the electron e _i obtained from the structural information on the insulating region 203 depends on the application. Can be set freely.

As described above, the sample observation apparatus according to the present invention includes an electron beam source that irradiates an imaging electron beam onto a sample surface having an insulating region and a conductive region, and an electron that obtains structural information on the sample surface by irradiation of the imaging electron beam. , An electromagnetic field generating means (E × B) for directing the electrons by an electric field and a magnetic field in accordance with a speed traveling in a direction opposite to the incident direction of the imaging electron beam, and the electromagnetic field generating means (E
XB) detects the electron directed by the detector, acquires an image of the sample surface from the detected electron, and the irradiation energy of the imaging electron beam. The electron is both a mirror electron and a secondary electron. Irradiation energy setting means for setting the transition region including the NA aperture moving mechanism for adjusting the position of the NA aperture for determining the numerical aperture (NA) within the surface, and charging the insulating region by irradiating the sample surface with an electron beam Charging electron beam irradiating means. Then, by adjusting the position of the NA aperture by the NA aperture moving mechanism, the electrons that have obtained the structure information of the conductive region and the electrons that have obtained the structure information of the insulating region are selectively detected by the action of E × B. It is configured to be guided to a vessel.

  Further, the image processing device 90 determines whether or not there is a missing defect (short defect) based on the image obtained from the electrons obtained from the structure information of the conductive region, and uses the image obtained from the electrons obtained from the structure information of the insulating region. The sample observation apparatus can be used as a sample inspection apparatus provided that a calculation function (calculation unit) for determining the presence or absence of an open defect (open defect) is provided.

  Furthermore, the sample observation method of the present invention can be executed using the sample observation apparatus having the above-described configuration, and the image acquisition under the condition that the luminance of the conductive region is higher than the luminance of the insulating region and the luminance of the insulating region is the conductive region. By acquiring images under conditions higher than the brightness of the sample, the sample surface on which the insulating and conductive regions are formed can be observed with high contrast, and the detection of missing defects and open defects and classification of defect types It should be easy.

  The sample observation method of the present invention will be described below.

  In the sample observation method of the present invention, the imaging electron beam is adjusted so that electrons obtained from the structure information of the sample surface are adjusted to a transition region including both mirror electrons and secondary electrons on the sample surface having the insulating region and the conductive region. The irradiation energy (LE) is adjusted, and image acquisition under the condition that the luminance of the conductive region is higher than the luminance of the insulating region and image acquisition under the condition where the luminance of the insulating region is higher than the luminance of the conductive region are performed. That is, in the sample observation method of the present invention, image acquisition is performed under conditions where the contrast is inverted between the conductive region and the insulating region.

[Contrast formation between conductive and insulating regions]
As described above, by using a mirror electrons generated in the transition region, it is possible to separate the electron e _i obtained structural information of the electronic e _c and the insulating region 203 to obtain structural information conductive region, As a result, it is easy to obtain a high-contrast image. Since the present invention uses this principle, in order to facilitate understanding of the characteristics of the sample observation method of the present invention, the basic examination results regarding the formation of the contrast between the conductive region and the insulating region will be described in advance. Keep it.

  FIG. 7 is a diagram showing an example of the structure of the sample 200 already described with reference to FIG. 2 and an image acquired by observing the sample 200. FIG. 7A is a diagram illustrating a cross-sectional structure of a contact plug that is the sample 200, and FIG. 7B is a diagram illustrating an example of an acquired image of the sample surface 201 having the contact plug structure.

In FIG. 7A, an insulating region 203 and a conductive region 202 are formed over a silicon substrate 205 which is a semiconductor substrate. Insulating region 203 is formed of SiO _2. The conductive region 202 is made of tungsten (W) and has a contact plug shape. The sample surface 201 has a planar structure in which the conductive region 202 is formed as a dot or a circle while the insulating region 203 is used as a base.

FIG. 7B is a diagram illustrating an example of an image of the sample surface 201 acquired by sample observation. In this image, the position of the NA aperture 61 of the NA adjustment aperture 60 is adjusted so that electrons generated from the conductive region 202 are selectively detected, and the luminance of the conductive region is higher than the luminance of the insulating region. It has been acquired. As a result, the insulating region 203 is black and occupies the base of the image, and a high-contrast image is formed such that the white circular conductive region 202 emerges from the black region.

In this way, the contrast can be increased by separating the electron e _c obtained from the structural information of the conductive region and the electron e _i obtained from the structural information of the insulating region 203. As a result, an image in which the insulating region 203 can be easily distinguished from the conductive region 202 can be acquired, and observation and inspection of defects and the like can be easily performed.

  On the contrary, if the position of the NA aperture 61 of the NA adjustment aperture 60 is adjusted so as to selectively detect electrons generated from the insulating region 203, the luminance of the insulating region is higher than the luminance of the conductive region. Since an image is acquired under the conditions, an image in which the insulating region 203 becomes white with high luminance and the conductive region 202 becomes white with low luminance is acquired, contrary to FIG. 7B.

  Next, an example of setting conditions for acquiring a high-contrast image will be described.

FIG. 8 is a diagram for explaining by way of example the results of studying the landing energy (LE) condition for acquiring a high-contrast image. In this example, the voltage of the cathode of the electron source 11 of the electron beam source 10 is set to −3995 to −4005 [eV], and the voltage of the sample surface 201 is set to −4000 [eV]. The transition region was optimized with landing energy (LE) set to -1 [eV]. The irradiation current density of the electron beam was 0.1 [mA / cm ² ], and the pixel size of the detector 80 was 50 [nm / pix]. The aperture diameter of the NA aperture 61 of the NA adjusting aperture 60 was φ150 [μm], and the pre-dose amount by the charged electron beam was 1 [mC / cm ² ].

  FIG. 8A shows the result of measuring the contrast when the contact plug having the cross-sectional structure shown in FIG. 7A is observed by changing the landing energy (LE) of the electron beam under the above-described conditions. FIG. 8B is a table in which the measurement results of FIG. 8A are graphed.

  In FIG. 8B, the horizontal axis represents the landing energy (LE), and the vertical axis represents the average gradation of the acquired image. The characteristic curve of the insulating region is shown as a curve connecting substantially square points, and the characteristic curve of the conductive region is shown as a curve connecting diamond points. The result of calculating the contrast from the average gradation of the insulating region and the conductive region is shown as a curve connecting triangular points. The contrast is calculated using the following formula (1).

  8A and 8B, when the landing energy (LE) = − 1 [eV], the contrast is the highest at 0.8. As already described with reference to FIG. 2, the landing energy (LE) = − 1 [eV] is in the transition region where mirror electrons and secondary electrons are mixed in the sample 200. Further, as shown in FIG. 2, −5 [eV] is the landing energy (LE) of the mirror electron region, and 5 [eV] is the landing energy (LE) of the secondary electron region. The contrast is low.

  That is, it can be seen that the highest contrast is obtained when the landing energy (LE) is in the transition region.

  FIG. 9 is a diagram for explaining the correlation between the dose amount of the charged electron beam and the contrast. 9A is a table of measurement results showing the correlation between the dose amount of the charged electron beam and the contrast, and FIG. 9B is a graph of the measurement results of FIG. 9A. is there. Note that various setting conditions of the sample observation apparatus and the sample 200 to be measured are as described above, and thus the description thereof is omitted.

The contrast was measured by the above equation (1) from the average gradation of the insulating region and the conductive region in the image obtained by imaging the sample surface 201 after irradiating the sample surface 201 with the charged electron beam. As shown in FIGS. 9A and 9B, the contrast increases as the dose of the charged electron beam increases, but the contrast is saturated at a certain dose. In the example shown in FIG. 9, the contrast remains 0.8 even when the sample surface 201 before imaging is irradiated with a charged electron beam of 1 [mC / cm ² ] or more in advance. That is, the contrast is saturated when the dose amount of the charged electron beam is 1 [mC / cm ² ] or more. This means that when the dose amount of the charged electron beam is 1 [mC / cm ² ] or more, the charging of the insulating region 203 on the sample surface 201 is saturated and becomes a negative potential, and a stable contrast can be obtained. Yes.

FIG. 10 is a diagram for supplementarily explaining that a high contrast can be obtained by separating the electron e _c obtained from the structural information of the conductive region and the electron e _i obtained from the structural information of the insulating region 203. is there. FIG. 10A shows each of the conductive region (Cu) and the insulating region (SiO ₂ ) when the electron e _c obtained from the structural information of the conductive region and the electron e _i obtained from the structural information of the insulating region are not separated. 6 is a table summarizing the landing energy (LE) dependence of the secondary electron emission efficiency and contrast of the material. FIG. 10B is a graph showing this table.

In the case where the electron e _c obtained from the structural information of the conductive region and the electron e _i obtained from the structural information of the insulating region 203 are not separated, the contrast obtained is the brightness corresponding to the emission efficiency of the secondary electrons of each material. It depends only on the difference. That is, the contrast obtained by acquiring an image in which only the electrons that have obtained the structural information from any region are acquired by adjusting the position of the NA aperture 61 cannot occur.

FIG. 10 (A), the according to the results shown in (B), in the case where no separate electronic e _i obtained structural information of the electronic e _c and the insulating region 203 to obtain structural information conductive regions, resulting contrast The contrast (for example, 0.8 described above) obtained by separating the electron e _c obtained from the structural information of the conductive region and the electron e _i obtained from the structural information of the insulating region 203 is about 0.4 at most. In comparison, it is only significantly lower.

In other words, as in the present invention, by separating the electronic e _i that utilizes mirror electrons generated, to obtain to obtain structural information conductive regions electrons e _c and structural information of the insulating region 203 in the transition region, the conductive If the image is acquired under the condition that the luminance of the region is higher than the luminance of the insulating region, or conversely, if the image is acquired under the condition that the luminance of the insulating region is higher than the luminance of the conductive region, compared to the image obtained by sample observation without separation of electrons e _i obtained structural information of the electronic e _c and the insulating region 203 to obtain structural information of the conductive region, it is possible to obtain a remarkably high contrast It becomes possible.

FIG. 11 shows the contrast when the area ratio (pattern width) between the conductive region 202 and the insulating region 203 on the sample surface 201 is changed. The contrast is shown by LEEM (Low-energy) using a low acceleration electron beam apparatus.
It is the figure which showed the result compared with the Electron Microscopy (low energy electron microscope) system and the SEM system. FIG. 11A is a table of measurement results showing the correlation between the sample surface 201 and contrast, and FIG. 11B is a graph graphed with the measurement results of FIG. Note that the measurement results shown here are based on images obtained under conditions where the luminance of the conductive region is higher than that of the insulating region, and are obtained under the various setting conditions described above. The description is omitted.

  As shown in FIG. 6B, the LEEM-type sample observation apparatus and sample observation method mainly cause the conductive region 202 to be bright and bright, so that if the area ratio of the conductive region 202 is reduced, interference from the surroundings is prevented. Contrast is high because it is hard to receive. In the SEM method (for example, landing energy of about 1000 eV), the insulating material 203 is brighter in terms of the secondary electron emission coefficient of the material, and when the ratio increases, the signal of the conductive region 202 expands the trajectory of the secondary electrons. The contrast is extremely low.

  As shown in FIGS. 11A and 11B, when the area ratio of the conductive region 202 to the insulating region 203 is small, the difference in contrast is still relatively small, and when the conductive region 202: insulating region 203 = 1: 2. The difference in contrast is suppressed to about 0.3. However, as the area of the insulating region 203 on the sample surface 201 increases, the contrast of the LEEM method increases, but the contrast of the conventional SEM method decreases. In the case of conductive region 202: insulating region 203 = 1: 10, the contrast difference reaches 0.75.

  As described above, the LEEM-type sample observation is particularly effective for observation of the sample surface 201 of the sample 200 in which the proportion of the conductive material 202 is low, and observation in the case where the sample surface 201 has a contact structure in which the proportion of the insulating material 203 is large. Can obtain a high-contrast image and has a great advantage. On the other hand, if the image is acquired under the condition that the luminance of the insulating region is higher than the luminance of the conductive region, the sample surface 201 has a low ratio of the insulating material 203 and a high ratio of the conductive material 202. It is possible to effectively observe the sample 200 having the above.

[Configuration example of aperture for NA adjustment with selectable numerical aperture (NA)]
FIG. 12 is a diagram showing a second overall configuration example of the sample observation apparatus according to the present invention, and the basic configuration is the same as that shown in FIG. That is, the configuration shown in FIG. 12 includes an electron beam source 10, a primary lens 20, a condenser lens 30, an E × B 40, a transfer lens 50, an NA adjustment aperture 60a, a projection lens 70, 1 is common to the configuration shown in FIG. 1 in that the detector 80, the image processing device 90, the stage 100, the energy setting means 110, and the power source 115 are provided.

  FIG. 1 also shows that the charged electron beam irradiation means 120 may be provided if necessary, and that the sample 200 is placed on the stage 100 with the sample surface 201 as the upper surface as a related component. The configuration is the same as that shown.

  On the other hand, the configuration shown in FIG. 12 is different from the configuration shown in FIG. 1 in that the NA adjustment aperture 60a includes a movable and multiple-selection NA adjustment aperture moving mechanism. In other words, the NA adjusting aperture 60a is provided with a plurality of types of NA apertures 61 and 62 having different aperture diameters, and these NA apertures 61 and 62 that determine the numerical aperture (NA) are used as an NA aperture moving mechanism (not shown). ), The position can be adjusted (switchable) in the plane.

  In the sample observation apparatus shown in FIG. 12, the same components as those in the sample observation apparatus shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

In the sample observation apparatus shown in FIG. 12, the NA adjustment aperture 60a includes a plurality of NA apertures 61 and 62 having different sizes, and the NA adjustment aperture 60a is movable in the horizontal direction (in-plane). Therefore, a desired numerical aperture (NA) can be obtained by switching between the NA aperture 61 and the NA aperture 62. Accordingly, an NA aperture having an optimum numerical aperture (NA) is selected according to various conditions such as the type of the sample 200 and the structure of the sample surface 201, and an image of the sample surface 201 having a high material contrast is acquired. Is possible.

  FIG. 13 is a diagram illustrating a configuration example of the movable NA adjustment aperture 60a described above. FIG. 13A is a top view showing an example of a case where the slide moving NA adjustment aperture 60b is configured, and FIG. 13B is a case where the rotary movement NA adjustment aperture 60c is configured. It is the top view which showed an example.

  In FIG. 13A, the NA adjustment aperture 60b includes a plurality of NA apertures 61, 62, and 63, and the aperture diameters of these NA apertures are different from each other. Further, the NA adjustment aperture 60b includes a sliding NA adjustment aperture moving mechanism 65 on both sides in the longitudinal direction. In this way, a plurality of NA apertures 61, 62, 63 are formed in the rectangular plate-shaped NA adjustment aperture 60b, and the slide-type NA adjustment aperture moving mechanism 65 can be moved in the horizontal direction. The aperture diameter and NA aperture position of the NA adjustment aperture 60b can be adjusted according to the application, and an optimal image of the sample surface 201 can be acquired corresponding to various samples 200 and applications.

  The sliding NA adjustment aperture moving mechanism 65 may have a moving mechanism such as a linear motor by sandwiching the NA adjustment aperture 60b from above and below with a rail-like member, or a rotary rail member. Then, the NA adjusting aperture 60b may be sandwiched, and the rotary rail member may be rotated and moved by a rotary motor. The sliding NA adjustment aperture moving mechanism 65 can take various forms depending on the application.

  In FIG. 13B, the NA adjustment aperture 60c has a plurality of NA apertures 61 to 64 on a disk-like plate, and includes a rotary NA adjustment aperture moving mechanism 66 at the center. The aperture diameters of the NA apertures 61 to 64 are different from each other, the NA aperture 61 is the largest, the NA aperture 62 has a smaller aperture diameter than the NA aperture 61, and the NA aperture 63 has a smaller aperture diameter than the NA aperture 62. The aperture diameter is small, and the NA aperture 64 is the smallest.

  The rotary NA adjustment aperture moving mechanism 66 may be a rotary motor or the like. Thus, for example, a configuration may be adopted in which the aperture diameter of the NA adjustment aperture 60c is switched by rotational movement.

  According to the sample observation apparatus having the configuration illustrated in FIGS. 12 and 13, the NA adjustment apertures 60 a to 60 c can be selected from a plurality of NA apertures 61 to 64 and the position can be adjusted. In addition, it is possible to flexibly cope with the use and the type of the sample 200, and an optimal contrast image can be acquired even under various conditions.

[Example of detector configuration for high-resolution observation]
FIG. 14 is a diagram showing an example of a configuration of a detector 80a preferable for high-resolution observation. When an electron direct-incidence type EB-CCD or EB-TDI is used for the detector 80a, compared to the conventional configurations of MCP, FOP (Fiber Optical Plate), fluorescent plate, and TDI, it is based on MCP and FOP transmission. Since there is no deterioration, it is possible to obtain a contrast image about three times that of the prior art. In particular, when detecting light from the hole bottom 202 of the contact structure, the conventional detector is effective because the spots (dots) become gentle. Further, since there is no gain deterioration due to the use of MCP, there is no luminance unevenness on the effective screen and the replacement cycle is long. Therefore, the maintenance cost and time of the detector 80 can be reduced.

  Thus, EB-CCD and EB-TDI are preferable in terms of obtaining a high-contrast image and durability. Below, an example of the usage aspect of EB-CCD and EB-TDI is demonstrated.

  The detector 80a illustrated in FIG. 14 is configured so that the EB-TDI 82 and the EB-CCD 81 can be switched and can be used interchangeably depending on the application. In FIG. 14, the detector 80 a includes an EB-CCD 81 and an EB-TDI 82. The EB-CCD 81 and the EB-TDI 82 are electronic sensors that receive an electron beam, and cause electrons to directly enter the detection surface. In this configuration, the EB-CCD 81 is used for adjusting the optical axis of an electron beam and adjusting and optimizing image capturing conditions. On the other hand, when the EB-TDI 82 is used, the EB-CCD 81 is moved to a position away from the optical axis by the moving mechanism M, and then the condition obtained when the EB-CCD 81 is used is used. Imaging with the EB-TDI 82 is performed with reference, and the sample surface 201 is observed.

  The detector 80a having such a configuration can perform image acquisition of the semiconductor wafer by the EB-TDI 82 using or referring to the electro-optical condition obtained when the EB-CCD 81 is used. After the inspection of the sample surface 201 by the EB-TDI 82, it is also possible to perform a review imaging using the EB-CCD 81 and perform a pattern defect evaluation. At this time, the EB-CCD 81 can accumulate images, thereby reducing noise, and review imaging of a defect detection site can be performed with high S / N. At this time, it is effective to use a pixel whose EB-CCD 81 is smaller than the pixel of the EB-TDI 82. In other words, it is possible to image with a large number of pixels for the signal size expanded by the mapping projection optical system, and it is possible to perform imaging for classification and determination of inspection, defect type, etc. with higher resolution. Become.

  The EB-TDI 82 has, for example, a rectangular shape in which pixels are two-dimensionally arranged so that it can be used to directly receive electrons and form an electronic image. The pixel size is, for example, 12 to 16 [ μm]. On the other hand, the pixel size of the EB-CCD 81 is, for example, 6 to 8 [μm].

  The EB-TDI 82 is formed in the shape of a package 85. The package 85 itself serves as a feedthrough, and the pins 83 of the package are connected to the camera 84 on the atmosphere side.

  When the configuration shown in FIG. 14 is adopted, optical conversion loss due to FOP, hermetic optical glass, optical lens, etc., aberration and distortion at the time of light transmission, resulting in image resolution degradation, detection failure, high cost, large size, etc. Can be eliminated.

[Configuration example as a composite sample observation device]
FIG. 15 is a diagram showing a third overall configuration example of the sample observation apparatus according to the present invention. This sample observation apparatus is a composite sample observation apparatus capable of sample observation with an optical microscope and sample observation with an SEM. It is configured.

The composite sample observation apparatus shown in FIG. 15 includes a sample carrier 190, a mini-environment 180, a load lock 162, a transfer chamber 161, a main chamber 160, an electronic column 130, an image processing apparatus system 90, and the like. It has. The mini-environment 180 is provided with an atmospheric transfer robot, a sample alignment device, a clean air supply mechanism, and the like (not shown). Further, the transfer chamber 161 always in a vacuum state is provided with a vacuum transfer robot (not shown), whereby generation of particles and the like due to pressure fluctuations can be minimized.

The main chamber 160 is provided with a stage 100 that can move in the x direction, the y direction, and the θ (rotation) direction in the horizontal plane (in the xy plane), and an electrostatic chuck is installed on the stage 100. ing. The sample 200 itself or the sample 200 placed on a pallet or jig is placed on the stage 100 by this electrostatic chuck.

  The inside of the main chamber 160 is pressure controlled by the vacuum control system 150 so that a vacuum state is maintained. Further, the main chamber 160, the transfer chamber 161, and the load lock 162 are placed on the vibration isolation table 170 so that vibration from the floor is not transmitted.

  An electronic column 130 is installed in the main chamber 160. The electron column 130 includes a primary optical system including the electron beam source 10 and the primary lens 20, a condenser lens 30, an E × B 40, a transfer lens 50, NA adjustment apertures 60, 60 a to 60 c, and a projection lens 70. And a detector 80 for detecting secondary electrons and mirror electrons from the sample 200 are installed. Further, as related components of the electronic column 130, an optical microscope 140 used for alignment of the sample 200 and an SEM 145 used for review observation are provided.

  The signal from the detector 80 is sent to the image processing apparatus system 90 for signal processing. Signal processing can be performed both during on-time processing during observation and offline processing in which only images are acquired and processed later. Data processed by the image processing apparatus 90 is stored in a recording medium such as a hard disk or memory. Further, it can be displayed on the console monitor as necessary. For example, an observation area, a defect map, a defect classification, a patch image, and the like. In order to perform such signal processing, system software 95 is provided. An electron optical system control power supply 118 is provided to supply power to the electron column system 130. The electron optical system control power supply 118 includes a power supply 115 that supplies power to the electron source 11 of the electron beam source 10 and an irradiation energy control means 110 that controls the power supply 115.

  Next, a transport mechanism for the sample 200 will be described.

  A sample 200 such as a wafer or mask is transferred from the load port 190 into the mini-environment 180, and alignment work is performed therein. Further, the sample 200 is transferred to the load lock 162 by the atmospheric transfer robot. In the load lock 162, the vacuum pump (not shown) exhausts the air from the atmospheric state to the vacuum state. When the pressure in the load lock 162 is reduced to a predetermined pressure (for example, about 1 [Pa]) or less by this exhaust, the sample 200 is transferred from the load lock 162 to the main chamber 160 by the vacuum transfer robot provided in the transfer chamber 161, and the stage It is installed on the electrostatic chuck mechanism 100 has.

[Basic Principle of the Present Invention]
As described above, by separating the electronic e _i that utilizes mirror electrons generated to obtain structural information of the electronic e _c and an insulating region to obtain structural information conductive regions in the transition region, the luminance of the conductive regions insulated If the image is acquired under conditions higher than the brightness of the region, or conversely, if the image is acquired under conditions where the brightness of the insulating region is higher than the luminance of the conductive region, the structure information of the conductive region is obtained. compared to the image obtained by sample observation without separation of electrons e _i obtained structural information of the electronic e _c and the insulating region 203 was obtained, it is possible to obtain a significantly higher contrast.

  However, according to the study by the present inventors, an insulating region and a conductive region are formed on the surface of the sample to be observed, and it is necessary to detect both missing defects and open defects on the sample surface with high accuracy. If there is, the image is acquired under the condition that the luminance of the conductive area is higher than the luminance of the insulating area, or conversely, the image is acquired under the condition that the luminance of the insulating area is higher than the luminance of the conductive area. It has been found that it is easy to detect any one type of defect by acquiring only the error, but it may be difficult to detect the other type of defect.

  Specifically, when an image is acquired under the condition that the luminance of the conductive region is higher than the luminance of the insulating region, it is easy to detect a missing defect, but it is difficult to detect an open defect (open defect). There is a case. On the other hand, when an image is acquired under the condition that the brightness of the insulating region is higher than that of the conductive region, open defects (open defects) can be easily detected, but missing defects (short defects) can be detected. It may be difficult to detect.

  Based on such knowledge, the sample observation method according to the present invention acquires images under conditions where the luminance of the conductive region is higher than the luminance of the insulating region, and the condition where the luminance of the insulating region is higher than the luminance of the conductive region. In this case, images are acquired, and based on these images, both missing defects and open defects on the sample surface are detected with high accuracy.

  In other words, in the sample observation method according to the present invention, irradiation is performed in which the electrons obtained from the structure information of the sample surface are adjusted to a transition region including both mirror electrons and secondary electrons on the sample surface having the insulating region and the conductive region. An imaging electron beam of energy (LE) is irradiated, and an image of the sample surface that has been irradiated with the imaging electron beam has a condition (A condition) where the luminance of the conductive region is higher than the luminance of the insulating region and the luminance of the insulating region. It is acquired under a condition (B condition) higher than the luminance of the conductive region. These images may be acquired under the B condition following the A condition, or may be acquired under the A condition following the B condition.

  FIG. 16 illustrates an image acquired under a condition (A condition) where the luminance of the conductive area is higher than that of the insulating area and an image acquired under a condition (B condition) where the luminance of the insulating area is higher than the luminance of the conductive area. It is a figure for showing notionally how a missing defect (short defect) and an open defect (open defect) appear in each. Here, the missing defect (short defect) is a state in which a short circuit (short) exists in a part of a region (conductive region) formed in a line shape with a conductive material such as W or Cu, and an open defect (open defect). Is a state where a part of a region (conductive region) formed in a line shape with a conductive material is disconnected (open).

Specifically, as already described in FIG. 6 (A), the each of these A conditions and B conditions, the position adjustment of the NA aperture 61, the electron e _c only many detectors to obtain structural information conductive region it leads to 80 and only electrons e _i obtained structural information of the insulating region is achieved by directing a number detector 80.

FIG. 16A schematically shows a part 300 on the sample surface having a region (conductive region) 310 of a conductive material such as W or Cu and a region (insulating region) 320 of an insulating material such as SiO ₂ . 16 (A) and 16 (a) show a state in which there is a missing defect (short defect) 330 in a partial region of the conductive material formed in a line shape, and FIGS. 16 (A) and 16 (b) show the line. A state in which there is an open defect (open defect) 340 in a partial region of the conductive material formed in the shape is shown.

FIG. 16B shows an imaging electron beam of irradiation energy (LE) in which the electrons obtained from the sample surface structure information are adjusted to a transition region including both mirror electrons and secondary electrons on the sample surface. The image of the sample surface irradiated with the imaging electron beam is schematically represented by an image obtained under the condition (A condition) where the luminance of the conductive region is higher than the luminance of the insulating region. 16 (B) (a) corresponds to FIGS. 16 (A) and 16 (a), and FIGS. 16 (B) and 16 (b) correspond to FIGS. 16 (A) and 16 (b).

  Further, FIG. 16C schematically shows an image obtained by inverting the contrast under the imaging condition opposite to the above and under the condition (B condition) where the luminance of the insulating region is higher than the luminance of the conductive region. 16C and 16A correspond to FIGS. 16A and 16A, and FIGS. 16C and 16B correspond to FIGS. 16A and 16B.

  Referring to FIG. 16B, in an image acquired under a condition (A condition) in which the luminance of the conductive region is higher than the luminance of the insulating region, the defect defect ( (Short defects) are emphasized and appear larger than the actual defect size (FIGS. 16B and 16A). On the contrary, due to the relatively low brightness of the insulating region, open defects (open defects) appear smaller than the actual defect size (FIGS. 16B and 16B).

  On the other hand, referring to FIG. 16C, an image acquired under a condition (B condition) in which the luminance of the insulating region is higher than the luminance of the conductive region is lost due to the relatively high luminance of the insulating region. Defects (short defects) appear smaller than the actual defect size (FIGS. 16C and 16A). On the contrary, due to the relatively low luminance of the conductive region, open defects (open defects) appear larger than the actual defect size (FIGS. 16B and 16B).

  A similar phenomenon occurs even when the defect is incomplete.

  FIGS. 17A and 17A show a state in which an incomplete missing defect (short defect) 335 is present in a partial region of the insulating material formed in a line, and FIGS. 17A and 17B show a line. A state in which an incomplete open defect (open defect) 345 is present in a partial region of the insulating material formed in the shape is shown.

  FIG. 17B is a diagram schematically showing an image acquired under the condition (A condition) where the luminance of the conductive region is higher than the luminance of the insulating region under the above-described irradiation condition of the imaging electron beam. FIGS. 17B and 17A correspond to FIGS. 17A and 17A, and FIGS. 17B and 17B correspond to FIGS. 17A and 17B.

  Further, FIG. 17C schematically shows an image obtained by inverting the contrast under the imaging condition opposite to the above and under the condition (B condition) where the luminance of the insulating region is higher than the luminance of the conductive region. 17C and 17A correspond to FIGS. 17A and 17A, and FIGS. 17C and 17B correspond to FIGS. 17A and 17B.

  Referring to FIG. 17B, in an image acquired under the condition where the luminance of the conductive region is higher than the luminance of the insulating region (A condition), incomplete omission is caused by the relatively high luminance of the conductive region. Defects (incomplete short defects) are emphasized and appear larger than the actual defect size (FIGS. 17B and 17A). On the other hand, due to the relatively low brightness of the insulating region, the incomplete open defect (incomplete open defect) appears smaller than the actual defect size (FIG. 17B, (b) )).

  On the other hand, referring to FIG. 17C, an image acquired under a condition (B condition) where the luminance of the insulating region is higher than the luminance of the conductive region is not good due to the relatively high luminance of the insulating region. Completely missing defects (incomplete short defects) appear smaller than the actual defect size (FIGS. 17C and 17A). On the contrary, due to the relatively low luminance of the conductive region, the incomplete open defect (incomplete open defect) appears larger than the actual defect size (FIG. 17B, (b) )).

  The reason why such a phenomenon occurs is considered to be as follows. That is, when an image is acquired under the condition where the luminance of the conductive region is higher than the luminance of the insulating region (A condition), it is emitted from the conductive material in the vicinity of the missing defect (short defect) or the open defect (open defect). Electrons are diffused, and due to the action, a missing defect (short defect) portion is wider and an open defect (open defect) portion is narrower, and an image is taken. On the contrary, when an image is acquired under a condition (B condition) where the luminance of the insulating region is higher than the luminance of the conductive region, electrons emitted from missing defects (short defects) or open defects (open defects). As a result, the missing defect (short defect) portion is narrowed and the open defect (open defect) portion is imaged wider.

  As described above, if the image acquisition is performed under the condition that the luminance of the conductive region is higher than the luminance of the insulating region, and the image is acquired under the condition that the luminance of the insulating region is higher than the luminance of the conductive region, Based on these contrast-inverted images, it is possible to detect both missing defects and open defects on the sample surface with high accuracy.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Optimization of material contrast]
The sample used in this example has a pattern in which a line and space (L & S) similar to that shown in FIGS. 16 and 17 is formed, and Cu is a conductive material on the surface thereof. Region (conductive region) 310 and a region (insulating region) 320 of SiO ₂ that is an insulating material are formed, and the line width and space width are both 43 nm.

FIG. 18 shows the results of an experiment conducted to determine the optimum value of the irradiation energy (LE) of the imaging electron beam irradiated on the surface of the sample. FIG. 18A summarizes the irradiation energy (LE), the luminance [DN] of each of the conductive material and the insulating material, and the contrast as a table. FIG. 18B is a graph showing this table. The horizontal axis represents the irradiation energy (LE), the left vertical axis represents the luminance [DN] of the conductive material and the insulating material, and the right vertical The axis shows contrast. The imaging of this time, the center of the NA aperture 61 of the NA adjusting aperture 60, have gone to suit almost matched positions in the center of the orbit of emitted electrons e _c from the conductive area 202. [DN] indicating gradation is a meaning of “Digital Number”, and black and white gradations are represented by 8 bits. DN = 0 indicates black, DN = 255 indicates pixel information. is there.

  In this example, the highest contrast (0.41) is obtained when the irradiation energy (LE) is 3.2 [eV].

[Optimization of charged electron beam dose]
FIG. 19 shows the result of an experiment conducted to determine the optimum value of the dose amount of the charged electron beam irradiated on the surface of the sample. FIG. 19A summarizes the beam dose [mC / cm ² ], the luminance [DN] of each of the conductive material and the insulating material, and the contrast as a table. FIG. 19B is a graph showing this table. The horizontal axis represents the beam dose [mC / cm ² ], and the left vertical axis represents the luminance [DN] of each of the conductive material and the insulating material. The right vertical axis indicates contrast. The imaging of this time also, the center of the NA aperture 61 of the NA adjusting aperture 60, have gone to suit almost matched positions in the center of the orbit of emitted electrons e _c from the conductive area 202. Here, the beam dose is defined by the product of the beam current density and the irradiation time.

In this example, the contrast increases with the dose, but the contrast is saturated at a dose of approximately 2 [mC / cm ² ]. That is, it can be seen that the dose amount of the charged electron beam to be irradiated for imaging with high contrast is about 2 [mC / cm ² ].

[Position confirmation of electron distribution by NA imaging mode]
In the present invention, to obtain a high contrast by separation of electrons e _i obtained structural information conductive region and electrons e _c to obtain structural information of the insulating region, missing defect (short defect) and an open defect ( Both open defects) are detected with high sensitivity and high accuracy. The separation of the electron e _c obtained from the structure information of the conductive region and the electron e _i obtained the structure information from the insulating region can be performed by adjusting the position of the NA aperture. By directly observing the distribution of electrons from the conductive region and insulating region on the sample surface in the imaging mode, the position adjustment of the NA aperture can be performed with high accuracy. Below, the example of a specific procedure is demonstrated.

The projection lens 70 provided between the NA adjustment aperture 60 and the detector 80 is set to a predetermined voltage of 5500 V, and the surface structure information of the conductive material 202 at the position of the NA adjustment aperture 60 is determined by the NA imaging mode. The positional relationship between the distribution of the electron e _c obtained and the electron e _i obtained the surface structure information of the insulating material 201 was confirmed. Specifically, charging electron beam by changing the dose amount of, with a change of the dose distribution state of the electronic e _i to obtain a surface structure information of the insulating material 201 (the center of the track) is, the conductive material 202 confirming how much to shift the distribution of electrons e _c to obtain a surface structure information (the center of the track).

FIG. 20 is a diagram for explaining the result of confirming the position of the electron distribution in the NA imaging mode. FIG. 20 (A) beam dose amount [mC / cm ^2] and when irradiated with charged electron beam of the dose, the deviation of the distribution state of the electronic e _i to obtain a surface structure information of an insulating material 201, i.e., to obtain surface structure information of the conductive material 202 from the distribution of the electron e _c is a table summarizing how much shifted. FIG. 20B is a graph showing the table. The horizontal axis represents the beam dose [mC / cm ² ], and the left vertical axis represents the surface structure information of the insulating material 201. The shift amount of the distribution state of _i is shown. Here, the shift direction was taken as the Y direction.

Note that the shift amount of the distribution of electrons e _i shown in the left vertical axis represents a value normalized. The shift amount was normalized by setting the position of the NA aperture through which electrons from the conductive material pass to 0 and setting the position of the NA aperture to 1 under the condition that the contrast is inverted. Further, based on the result of the optimization experiment of the dose amount of the charged electron beam described above, the upper limit value of the dose of charged electron beam was set to 2 [mC / cm ² ]. Further, for the sake of reference, the same experiment was performed on a sample having an L & S width of 35 nm and a sample having an L & S width of 65 nm.

According to the results shown in FIG. 20, the deviation amount of the distribution of electrons e _i to obtain a surface structure information of the dose and the insulating material 201 charged electron beam is approximately proportional. Therefore, considering the result of the optimization experiment of the dose amount of the charged electron beam, the electron e _c obtained from the structural information of the conductive region and the electron e _i obtained from the structural information of the insulating region are separated to obtain a high contrast. In this case, the irradiation amount of the charged electron beam is set to about 2 [mC / cm ² ], and the NA aperture 61, which is the hole of the NA adjustment aperture 60, is shifted in the Y direction by a predetermined amount. the electronic e _c to obtain structural information selectively can be be performed imaging under conditions leading to electron e _i obtained structural information conditions as the insulating region 203 leading to the detector 80 to selectively detector 80 I understand.

Further, according to the result shown in FIG. 20, in the sample having a wide wiring width (L & S width), the change in substrate potential (ΔV) increases as the volume of the insulating material increases, so that the surface structure of the insulating material 201 is increased. The shift amount of the distribution of the electron e _{i from} which information is obtained is also large. On the contrary, since the volume of the insulating material becomes smaller as the wiring width (L & S width) becomes smaller, the change (ΔV) in the substrate potential becomes smaller, and it becomes difficult to obtain high contrast.

[Optimum irradiation energy (LE) during substrate charging]
As described above, facilitates the separation of the electrons e _i obtained structural information with the electronic e _c to obtain structural information conductive region by the irradiation of the charged electron beam insulating region, easily obtain a high contrast. This substrate potential by the irradiation of the charged electron beam is changed ([Delta] V), thereby by shifting the distribution of the electron e _i to obtain a surface structure information of an insulating material. This is the amount of change in the substrate potential from ([Delta] V), the distribution of electrons e _i to obtain a surface structure information of an insulating material which means that it is possible to estimate the shift amount.

FIG. 21 shows the result of an experiment conducted to determine the optimum value of the irradiation energy (LE) of the imaging electron beam irradiated on the surface of the charged sample. FIG. 21A summarizes the irradiation energy (LE), the luminance [DN] of each of the conductive material and the insulating material, and the contrast as a table. FIG. 21B is a graph showing this table. The horizontal axis represents irradiation energy (LE), the left vertical axis represents the luminance [DN] of the conductive material and the insulating material, and the right vertical The axis shows contrast. Also imaging of this time, the center of the NA aperture 61 of the NA adjusting aperture 60, have gone to suit almost matched positions in the center of the orbit of emitted electrons e _c from the conductive area 202.

When FIG. 21B is compared with FIG. 18B, when the surface of the charged sample is irradiated with the imaging electron beam (FIG. 21B), the surface of the uncharged sample is irradiated. A high contrast (7.8) is obtained as compared with the case where the imaging electron beam is irradiated (FIG. 18B), and the irradiation energy (LE) corresponding thereto is shifted to the low energy side. This is because, as already explained, changes in the substrate potential to the insulating region of the sample surface is charged state (approximately 1V), as a result, the center of the orbit of the electron e _i emitted from the insulating region 203 is charged to significantly shift the center of the orbit of emitted electrons e _c from the area 202, the degree of separation of electrons e _i obtained structural information conductive region and electrons e _c to obtain structural information of the insulating region is increased This is because.

Therefore, in advance, by to know what the optimal irradiation energy (LE) how changes by the charging state of the sample surface (the substrate potential), the deviation of the center of the orbit of emitted electrons e _i from the insulating region 203 It is possible to estimate the quantity. That is, the shift amount of the center position of the trajectory of the electrons e _i from the substrate potential can be estimated. Specifically, the shift amount of the substrate potential is read from the shift amount of the irradiation energy (LE) before and after charging. As described above, when the charged state changes, the energy (velocity) of electrons changes accordingly, and the force of F = e · (v × B) received when passing through the electromagnetic field generating means (E × B) is also obtained. Since it changes, it is possible to calculate the trajectory shift amount when passing E × B. Then, because it calculates the shift amount in the position of the NA aperture from the track shift amount of the E × B during the passage, it is possible to verify the actual shift amount of the center position of the orbit of the electron e _i.

[Contrast inversion by adjusting the position of the NA aperture]
FIG. 22 is a diagram for explaining the reversal of contrast by adjusting the position of the NA aperture. FIG. 22 (A) moves the center position of the NA aperture substantially matched positions in the center of the orbit of the electron e _c emitted from the conductive area from the (normalized position = 0) in the Y direction (normalized position = 1 The brightness [DN] and contrast of each of the conductive material and the insulating material are summarized as a table. FIG. 22B is a graph showing this table. The horizontal axis indicates the center position [normalized position] of the NA aperture, and the left vertical axis indicates the luminance [DN] of the conductive material and the insulating material. ] And the right vertical axis indicates contrast. The imaging at this time was performed by irradiating the sample surface with 2 [mC / cm ² ] of the charged electron beam and setting the center position of the NA aperture at which the luminance of the conductive material is maximized as the normalized position = 0. Here, as described above, the “normalized position” indicates relative coordinates when the position of the NA aperture through which electrons of the conductive material pass is 0 and the position of the NA aperture where the contrast is inverted is 1.

  As shown in this figure, when the position of the NA aperture is shifted from the normalized position = 0 in the Y direction, the luminance of the conductive material decreases while the luminance of the insulating material increases, and as a result, the contrast gradually increases. Lower. When the center position of the NA aperture is the normalized position = 0.6, the luminance of the conductive material is equal to the luminance of the insulating material, and contrast cannot be obtained. Further, when the position of the NA aperture is shifted in the Y direction, the luminance of the conductive material is further reduced while the luminance of the insulating material is further increased. As a result, the contrast is reversed and gradually increased. In this way, the contrast can be reversed by adjusting the position of the NA aperture.

Figure 23 is a diagram for conceptually explaining how contrast reversal caused by positional adjustment of the NA aperture and substantially coincides with the center of the orbit of emitted electrons e _c center position of the NA aperture a conductive region located when in the (normalized position NP = 0) is mainly electrons e _c is guided to the detector. When the center position of the NA aperture Yuku shifted in the Y direction, the amount of electrons e _i the amount of electrons e _c that can pass through the NA aperture can pass through the NA aperture while decreases increase, normalized position NP = 0. In No. 6, the amount of electrons of the two coincides and no difference in brightness occurs, so that contrast cannot be obtained. Further Yuku shifting the center position of the NA aperture in the Y direction, the amount of electrons e _i amounts that can pass through the NA aperture while reducing further the electronic e _c that can pass through the NA aperture further increases, normalized position NP At 1.0, the amount of electrons of both is reversed and the contrast is reversed.

[Procedure for Sample Observation Method of the Present Invention]
FIG. 24 is a flowchart for exemplifying the procedure for determining the dose dependency of the electron orbit shift amount and the procedure for confirming the reversal of the material contrast in the sample observation method of the present invention. The details of the parts already described for each step are omitted.

  First, the irradiation energy (LE) of the imaging electron beam is adjusted to the transition region described above (S102), and the imaging electron beam is irradiated onto the surface of the observation target sample having the insulating region and the conductive region (S103).

By adjusting the position of the NA aperture in the plane by NA aperture movement mechanism, aligning the center position of the NA aperture in the center of the orbit of the electron e _c to obtain structural information conductive region (S104). In this state, the irradiation energy (LE) of the imaging electron beam is adjusted so that the difference in luminance between the insulating region and the conductive region, that is, the material contrast is maximized (S105).

Next, the sample surface is irradiated with the charged electron beam of a predetermined dose amount is charged an insulating region (S106), how much the center position of the NA aperture of the trajectory of the electrons e _i from the insulating area in the charged state It is confirmed whether the shift has been performed (S107). Thereafter, repeat Step S106 and Step S107, obtains the track shift amount of the dose dependence of the electron _{e i} from the insulating area in the charged state (S108).

When the track shift of the dose dependence of the electron e _i from the insulating area in the charged state is determined (S108: Yes), it determines the appropriate dose on the basis of the data (S109).

After determining the appropriate dose amount, the irradiation energy (LE) of the imaging electron beam is adjusted again. Specifically, the charged electron beam having the appropriate dose determined in the above procedure is irradiated onto the sample surface, and the irradiation energy (LE) that maximizes the material contrast in this state is determined (S110).
Then, an image of the sample surface irradiated with the imaging electron beam having the irradiation energy (LE) is acquired, and the material contrast is measured (S111). As described in relation to step S107, since the center position of the NA aperture in this case lies in the center of the orbit of the electron e _c to obtain structural information conductive region, the brightness in the captured image, the conductive region is relatively The insulation area is relatively low.

Subsequently, only the track shift amount of the electron e _i when performing a charging electron beam irradiation of the proper dose by moving the center position of the NA aperture to match the center position of the NA aperture track center of the electron e _i. In this state, the material contrast is measured again (S112).

  As described above, if the center position of such an NA aperture is adjusted, the material contrast should be reversed, and an image with relatively high brightness in the insulating area and relatively low brightness in the conductive area should have been acquired. It is. Therefore, if the reversal of the material contrast is confirmed (S113: Yes), the process is finished (S114). If inversion of the material contrast is not confirmed (S113: No), there should be some problem in the procedure so far, so the process returns to step S102 and starts again.

  According to the above procedure, the dose dependence of the electron orbit shift amount and the reversal confirmation of the material contrast are confirmed, and the condition setting necessary for the sample observation of the present invention is completed.

  FIG. 25 is a flowchart for illustrating the procedure of the sample observation method of the present invention by way of example. The details of the parts already described for each step are omitted.

  In a sample observation method according to a preferred aspect of the present invention, a sample surface having an insulating region and a conductive region is irradiated with an imaging electron beam having an irradiation energy (LE) that maximizes material contrast (S203), and the imaging electron beam The step (S205, S207) which acquires the sample surface image by detecting the electron which acquired the structure information from the sample surface which received irradiation of is provided. As described above, the irradiation energy (LE) of the imaging electron beam is adjusted to the transition region in which the electrons obtained from the structure information of the sample surface include both the mirror electrons and the secondary electrons. In this step, an image is acquired under the condition that the luminance of the conductive region is higher than the luminance of the insulating region (S205), and the image is acquired under a condition where the luminance of the insulating region is higher than the luminance of the conductive region. Step (S207).

As described above, if the insulating region is charged by irradiating the sample surface with a charged electron beam of an appropriate dose before the imaging electron beam irradiation step (S203) (S202), the substrate potential changes. result, the deviation of the center of the orbit of emitted electrons e _c from the center and the charged area of the trajectory of the electrons e _i emitted from the insulating region is increased, the electron e _c and an insulating region to obtain structural information conductive region also increases the degree of separation of electrons e _i obtained structural information. The appropriate dose amount described above is determined in advance in step S109 as described above, and is preferably set to a dose amount at which charging of the insulating region by electron beam irradiation is saturated.

The imaging electron beam while irradiating the sample surface with a step 203, to maximize the material contrast centered position of the NA aperture in the center of the orbit of the electron e _c to obtain structural information conductive region (S204). An image obtained under this condition is an image in which the luminance of the conductive region is relatively high and the luminance of the insulating region is relatively low (S205).

Then, to maximize the material contrast centered position of the NA aperture in the center of the orbit of the electron e _i obtained structural information of the insulating region (S206). An image obtained under this condition is an image in which the luminance of the insulating region is relatively high and the luminance of the conductive region is relatively low (S207). That is, the image obtained in step S205 is an image with the contrast reversed.

The position adjustment of the NA aperture in step S206, based on the track shift amount of the electron e _i that is determined in advance at step S107, may be to adjust the position of the NA aperture only the track shift amount.

  FIG. 26 is a flowchart for explaining another example of the procedure of the sample observation method of the present invention. In the procedure shown in FIG. 25, following the step (S305) in which an image is acquired under the condition that the luminance of the insulating region is higher than the luminance of the conductive region, the luminance of the conductive region is higher than the luminance of the insulating region. The difference is that the step (S307) in which an image is acquired under the conditions is executed.

  That is, in the sample observation method of this aspect, the step (S303) of irradiating the sample surface having the insulating region and the conductive region with the imaging electron beam having the irradiation energy (LE) that maximizes the material contrast, and the irradiation of the imaging electron beam. The method includes the steps (S305 and S307) of acquiring a sample surface image by detecting electrons obtained structural information from the received sample surface. The sample surface image acquisition step includes a step (S305) in which an image is acquired under the condition that the luminance of the insulating region is higher than the luminance of the conductive region, and the luminance of the conductive region is higher than the luminance of the conductive insulating region. A step (S307) of acquiring an image under high conditions.

As in the procedure of FIG. 25, prior to the imaging electron beam irradiation step (S303), if the insulating region is charged by irradiating the sample surface with a charged electron beam of an appropriate dose (S302), the substrate potential is set. As a result, the shift between the center of the orbit of the electron e _i emitted from the insulating region and the center of the orbit of the electron e _c emitted from the charged region becomes large, and the electron e _c obtained from the structural information of the conductive region. and also it increases the degree of separation of electrons e _i obtained structural information of the insulating region.

The imaging electron beam while irradiating the sample surface with a step 303, to maximize the material contrast centered position of the NA aperture in the center of the orbit of the electron e _i obtained structural information of the insulating region (S304). An image obtained under this condition is an image in which the luminance of the insulating region is relatively high and the luminance of the conductive region is relatively low (S305).

Then, to maximize the material contrast centered position of the NA aperture in the center of the orbit of the electron e _c to obtain structural information conductive region (S306). An image obtained under this condition is an image in which the luminance of the conductive region is relatively high and the luminance of the insulating region is relatively low (S307). That is, the image obtained in step S305 is an image with contrast reversed.

The position adjustment of the NA aperture at step S306, on the basis of the track shift amount of the electron e _i that is determined in advance at step S107, only the track shift amount, in a direction opposite to the shift direction, the position of the NA aperture You may make it adjust.

  As described above, when an image is acquired under the condition that the luminance of the conductive region is higher than that of the insulating region, it is easy to detect a missing defect (short defect), but an open defect (open defect) is detected. May be difficult to remove. On the other hand, when an image is acquired under the condition that the luminance of the insulating region is higher than that of the conductive region, it is easy to detect open defects (open defects), but missing defects (short defects). ) May be difficult to detect. Therefore, in order to detect both missing defects and open defects on the sample surface on which the insulating region and the conductive region are formed with high accuracy, an image is obtained under the condition that the luminance of the conductive region is higher than the luminance of the insulating region. It is not sufficient to acquire the image or, conversely, to acquire the image only under the condition that the luminance of the insulating region is higher than the luminance of the conductive region.

  According to the sample observation method according to the present invention, an image is acquired under a condition where the luminance of the conductive region is higher than that of the insulating region, and an image is acquired under a condition where the luminance of the insulating region is higher than the luminance of the conductive region. Therefore, based on these images, it is possible to detect both missing defects and open defects on the sample surface with high accuracy.

  That is, if an image of the sample surface obtained by the sample observation method according to the present invention described above is used, missing defects (short defects) are caused by an image obtained under the condition that the luminance of the conductive region is higher than the luminance of the insulating region. Presence / absence can be detected with high sensitivity and high accuracy, and the presence / absence of open defects (open defects) can be detected with high sensitivity and high accuracy from images acquired under conditions where the luminance of the insulating region is higher than that of the conductive region. Therefore, it can be used as a highly sensitive and highly accurate sample inspection method.

[Sample inspection according to the present invention]
Below, the example which implemented the defect inspection of the sample surface by the above-mentioned method is demonstrated.

As the object to be observed, the line and space (L & S) of the Cu region (conductive region) as the conductive material and the SiO ₂ region (insulating region) as the insulating material are the same as those shown in FIGS. A sample having a pattern was prepared. The line width and space width were both 43 nm. Various sizes of missing defects (short defects) and open defects (open defects) were formed in a part of the conductive region of the L & S pattern, and these defects were detected.

In observing the sample, the acceleration voltage of the electron source beam was set to −4005V, and the potential of the sample surface 201 was set to −4002.6V. Therefore, the irradiation energy (LE) of the imaging electron beam is 2.4 eV in which the electrons obtained from the structural information of the sample surface are in a transition region including both mirror electrons and secondary electrons. The aperture of the NA aperture 61 is 100 to 300 μm, the insulating region is charged by irradiation with a charged electron beam prior to imaging (charge amount ² mC / cm ² ), and the current density of the imaging electron beam is 1 mA / cm ² for imaging. went. The inspection pixel size at the time of defect inspection was set to 29 nm square depending on the magnification setting of the electron optical system lens. The inspection speed was 50 MPPS (Mega Pixels Per Second).

  FIG. 27 is a diagram for explaining the result of the defect inspection performed under the above conditions. FIG. 27A is a table summarizing whether or not defects can be detected by an image acquired under the condition that the luminance of the conductive region is higher than the luminance of the insulating region. FIG. 27B is a table showing the luminance of the insulating region. FIG. 27C is a table summarizing the possibility of defect detection by combining the two defect detection results, and a table summarizing the possibility of defect detection using images acquired under conditions higher than the luminance. In these tables, “◯” indicates that the defect was detected, “X” indicates that the defect was not detected, and “「 ”indicates that the defect was detected in both inspections.

  As can be seen from these results, according to the image acquired under the condition that the luminance of the conductive region is higher than the luminance of the insulating region, the missing defect (short defect) can be detected with high accuracy, while the luminance of the insulating region is high. According to an image acquired under a condition higher than the luminance of the conductive region, open defects (open defects) can be detected with high accuracy. This is because, according to an image acquired under the condition that the luminance of the conductive region is higher than that of the insulating region, an open defect may be overlooked, and the luminance of the insulating region is higher than the luminance of the conductive region. This means that missing images (short defects) may be overlooked according to images acquired under conditions.

In contrast, as in the present invention, an image acquired under conditions where the luminance of the conductive region is higher than the luminance of the insulating region, and an image acquired under conditions where the luminance of the insulating region is higher than the luminance of the conductive region. Thus, if it is determined whether or not a defect exists, it is possible to detect both a missing defect (short defect) and an open defect (open defect) having a size larger than at least 25 nm with high sensitivity and high accuracy.

  The sample observation apparatus and sample observation method of the present invention described so far can be used for, for example, observation and inspection of the surface of a semiconductor wafer after processing the semiconductor wafer in a semiconductor manufacturing process. By using a sample observation apparatus and a sample observation method according to the present invention, a semiconductor wafer having an insulating region and a conductive region on the sample surface is observed, and a high contrast image is acquired to check the quality of the semiconductor wafer. It becomes an effective means for the production of a semiconductor wafer free from defects. Thus, the sample observation apparatus and sample observation method according to the present invention can be suitably applied to a semiconductor manufacturing method.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be added to these embodiments.

  The present invention provides a sample observation method and apparatus for performing high-contrast observation of a sample surface on which an insulating region and a conductive region are formed, and facilitating detection of missing defects and open defects and classification of defect types, A sample inspection method and apparatus using the same are also provided. The present invention can be used for, for example, a sample observation apparatus that observes the surface of a substrate such as a semiconductor wafer or a reticle, or a sample defect detection apparatus that detects defects.

10 Electron Beam Source 11 Electron Source 12 Wehnelt Electrode 13 Anode 20 Primary System Lens 30 Condenser Lens 40 E × B
50 Transfer lens 60, 60a, 60b, 60c NA adjustment aperture 61, 62, 63, 64 NA aperture 65, 66 NA adjustment aperture moving mechanism 70 Projection lens 80, 80a Detector 81 EB-CCD
82 EB-TDI
83 pin 84 camera 85 package 90 image processing apparatus 95 system software 100 stage 110 irradiation energy setting means 115 power supply 118 electron optical system control power supply 120 charged electron beam irradiation means 130 electron column 140 optical microscope 145 SEM
150 Vacuum Control System 160 Main Chamber 161 Transfer Chamber 162 Load Lock Chamber 170 Vibration Isolation Stand 180 Mini Environment 190 Sample Carrier 200 Sample 201 Sample Surface 202 Conductive Region (Conductive Material)
203 Insulation region (insulating material)
204 hole 205 silicon substrate 300 part of sample surface 310 region of conductive material (conductive region)
320 Insulating material region (insulating region)
330 Missing defect (short defect)
335 Incomplete missing defect (short defect)
340 Open defect (open defect)
345 Incomplete open defect (open defect)

Claims (8)

A method for observing a sample surface having an insulating region and a conductive region by electron beam irradiation, comprising the following steps.
Step A: Acquiring the first image in a state where the center position of the NA aperture is aligned with the center of the orbit of the electron (e _c ) from which the structure information of the conductive region is obtained.
The insulating surface is charged by irradiating the sample surface with a charged electron beam having a predetermined dose, and the center position of the NA aperture is set to the center of the trajectory of electrons (e _i ) from the insulating region in the charged state. Step B for obtaining the second image in the combined state:
Step C for confirming reversal of material contrast between the first image and the second image:
Step D in which the predetermined dose is changed and the steps A to C are repeated when the reversal of the material contrast is not confirmed. 2. The sample observation according to claim 1, wherein the change of the predetermined dose in the step D is made based on the dose dependency of the orbit shift amount of electrons (e _i ) from the insulating region in the charged state. Method.   3. The sample observation according to claim 1, wherein the electron beam has irradiation energy (LE) adjusted in a transition region in which electrons obtained from the sample surface structure information include both mirror electrons and secondary electrons. Method. The sample observation method according to claim 3 , wherein in the step A, the first image is acquired by adjusting the irradiation energy (LE) so that the material contrast is maximized. The sample observation method according to any one of claims 1 to 4,
The predetermined dose amount at which the reversal of the material contrast is confirmed by the steps A to D is determined as an appropriate dose amount,
Irradiating the sample surface with a charged electron beam of the appropriate dose to charge the insulating region,
The sample surface having the insulating region and the conductive region is irradiated with an imaging electron beam having an irradiation energy (LE) that maximizes the material contrast,
The NA aperture center position electrons e _c raceway center to suit brightness of the conductive region under the conditions of the maximum the material contrast is relatively high in the insulating region of obtaining the structure information of the conductive regions of the Acquire an image with relatively low brightness,
The brightness of the insulating region is relatively high in the conductive region under conditions the central position of the NA aperture to maximize the center the material contrast to match the trajectory of an electron e _i obtained structural information of said insulating region A sample observation method for acquiring an image with relatively low luminance. The sample observation method according to any one of claims 1 to 4,
The predetermined dose amount at which the reversal of the material contrast is confirmed by the steps A to D is determined as an appropriate dose amount,
Irradiating the sample surface with a charged electron beam of the appropriate dose to charge the insulating region,
The sample surface having the insulating region and the conductive region is irradiated with an imaging electron beam having an irradiation energy (LE) that maximizes the material contrast,
The brightness of the insulating region is relatively high in the conductive region under conditions the central position of the NA aperture to maximize the center the material contrast to match the trajectory of an electron e _i obtained structural information of said insulating region Acquire an image with relatively low brightness,
The NA aperture center position electrons e _c raceway center to suit brightness of the conductive region under the conditions of the maximum the material contrast is relatively high in the insulating region of obtaining the structure information of the conductive regions of the A sample observation method for acquiring an image with relatively low luminance. Irradiation energy (LE) of the imaging electron beam when the electron having obtained the structural information of the sample surface has the minimum irradiation energy LEA and the maximum irradiation energy LEB in the transition region including both mirror electrons and secondary electrons. Is the sample observation method according to claim 5, wherein LEA ≦ LE ≦ LEB + 5 eV is set.   The sample observation method according to claim 5, wherein the observation of the sample surface is executed using a mapping projection type low acceleration electron beam apparatus.