JP2012032179A - Defect inspection method and apparatus - Google Patents

Abstract

Provided is a technique capable of accurately detecting the distance and contact between a probe tip and a sample by a simple method.
A defect inspection apparatus comprising: an electron optical system that irradiates a sample with an electron beam; at least one probe that causes the sample to touch the probe; and a plurality of detectors that detect secondary electrons or reflected electrons from the sample. Is used to measure the electrical characteristics of the inspection object formed on the sample. First, the probe is brought close to the inspection object on the sample. Next, signals from a plurality of detectors are input to generate an image to be inspected so as to include an image of the tip of the probe. An image to be inspected is generated based on a signal from a detector selected by the user among the plurality of detectors.
[Selection] Figure 2

Description

  The present invention relates to a probe type defect inspection method and apparatus for measuring electrical characteristics of a sample by bringing a probe into contact with the sample.

  Patent Document 1 describes a technique for measuring electrical characteristics by bringing a plurality of probes into contact with a wiring formed on a semiconductor chip in order to detect a defect in a fine wiring formed on the semiconductor chip. ing. When the probe is brought into contact with the sample, if the distance between the probe and the sample is not accurately detected, the probe tip collides with the sample and breaks. Therefore, when the probe is brought into contact with the sample, the relative position between the probe and the sample is confirmed using an optical camera image or SEM image. For example, an optical camera is used until the distance between the probe and the sample is about several hundred μm, and then an SEM image is used. While observing the SEM image, the probe is moved until the distance between the probe and the sample becomes about 50 to 100 μm using the focus value of the electron optical system between the probe tip and the sample surface. Thereafter, the probe is repeatedly moved in smaller units (several micrometers to several nanometers). When the probe tip comes into contact with the sample, movement of the probe position occurs. By observing this with an SEM image, the contact between the probe and the sample can be confirmed.

JP 2002-343843 A

  In recent years, circuit patterns formed on semiconductor elements such as LSIs have become complicated and miniaturized, and probe tips have also been miniaturized. Accordingly, it is essential to increase the magnification of the observation image. When the radius of curvature of the probe tip is about several tens of nanometers, the allowable pressure that can maintain the shape of the probe tip becomes small. For this reason, the probe tip tends to be damaged frequently in the final step of contacting the probe.

  An object of the present invention is to provide a technique capable of accurately detecting the distance and contact between a probe tip and a sample by a simple technique.

  In the present invention, a defect inspection apparatus having an electron optical system that irradiates a sample with an electron beam, at least one probe that causes the sample to touch, and a plurality of detectors that detect secondary electrons or reflected electrons from the sample. Is used to measure the electrical characteristics of the inspection object formed on the sample.

  First, the probe is brought close to the inspection object on the sample. Next, signals from a plurality of detectors are input to generate an image to be inspected so as to include an image of the tip of the probe. Here, an image to be inspected is generated based on a signal from a detector selected by the user among the plurality of detectors.

  According to the present invention, the distance and contact between the probe tip and the sample can be accurately detected by a simple method.

It is a figure explaining the example of the defect inspection apparatus by this invention. It is a figure explaining the example of the SEM image of a probe and a sample by the defect inspection apparatus by this invention. It is a figure explaining the example of arrangement | positioning of the probe and detector in the defect inspection apparatus by this invention. It is a figure explaining the example of the method of measuring the distance between a probe and a sample with the defect inspection apparatus by this invention.

  An example of a defect inspection apparatus according to the present invention will be described with reference to FIG. In a defect inspection apparatus, a probe is brought into direct contact with a circuit pattern formed on a semiconductor element as a sample, and the logical operation and electrical characteristics of the circuit are measured. In order to confirm the contact state and the contact position between the sample and the probe, a scanning microscope (SEM) or a focus ion beam (FIB) apparatus is provided. Here, an example of an SEM type defect inspection apparatus provided with a scanning microscope will be described, but the defect inspection apparatus of the present invention may be a defect inspection apparatus using another charged particle beam apparatus.

  The SEM type defect inspection apparatus of this example includes an SEM type electron optical system 100 and a sample chamber 108. The electron optical system 100 is provided in the housing of the sample chamber 108. In the sample chamber 108, a sample holder 102 for placing the sample 101, a sample stage 103 for supporting the sample holder 102, probe holders 106A and 106B for supporting probes 107A and 107B, and probe holders 106A and 106B are supported. Probe stages 105A and 105B, and a sample stage 103 and a base stage 104 that supports the probe stages 105A and 105B are provided. The housing of the sample chamber 108 is supported by a gantry 117 having a vibration isolation function indicated by a one-dot chain line. Detectors 109A and 109B are further provided in the housing of the sample chamber 108.

  The probes 107A and 107B, the probe holders 106A and 106B, and the probe stages 105A and 105B are referred to as probe units. In FIG. 1, a pair of probe units is shown, but in the SEM type defect inspection apparatus of this example, three or more probe units can be provided. In FIG. 1, a pair of detectors 109 </ b> A and 109 </ b> B is illustrated, but in the SEM type defect inspection apparatus of this example, three or more detectors 109 can be provided.

  By moving the probe stages 105A and 105B, the probes 107A and 107B supported by the probe holders 106A and 106B can be moved in a three-dimensional direction. By moving the sample stage 103, the sample 101 mounted on the sample holder 102 can be moved in a three-dimensional direction. Furthermore, by moving the base stage 104, the probe stages 105A and 105B and the sample stage 103 can be moved simultaneously. That is, the probes 107A and 107B and the sample 101 can be simultaneously moved in the three-dimensional direction without changing the relative position between the probes 107A and 107B and the sample 101.

  The SEM type defect inspection apparatus of this example further includes a control unit 112 having a signal processing system 113 and a power supply unit 114, an image display unit 115, and an electrical characteristic evaluation unit 116.

  A turbo molecular pump (TMP) 110 and a dry pump (DRP) 111 connected thereto are connected to the sample chamber 108. These pumps 110 and 111 are driven by a signal from the control unit 112, and the inside of the sample chamber 108 is evacuated.

  The operation of the SEM type defect inspection apparatus of this example will be described. First, operation information is supplied to the control unit 112. The control unit 112 converts the operation information into a control signal and transmits it to the probe stages 105A and 105B, the sample stage 103, and the base stage 104. Thereby, the relative positions between the probes 107A and 107B and the sample 101 change, and the probes 107A and 107B come into contact with the sample 101. Electrical signals from the probes 107A and 107B are sent to the electrical characteristic evaluation unit 116. The electrical property evaluation unit 116 analyzes the signal from the probe, evaluates the electrical property, and transmits the evaluation result to the control unit 112. The graph or table indicating the evaluation result is displayed by the image display unit 115 or the electrical characteristic evaluation unit 116.

  On the other hand, the electron optical system 100 irradiates the sample 101 with a charged particle beam. Secondary electron signals or reflected electron signals generated from the sample 101 are detected by the detectors 109A and 109B and sent to the signal processing system 113 of the control unit 112. The image signal generated by the signal processing system 113 is sent to the image display unit 115, and an SEM image is displayed.

  In the SEM type defect inspection apparatus of this example, the signal processing system 113 generates a single SEM image by selecting a desired signal from signals from a plurality of detectors, and further generates a desired SEM image from the signals from the plurality of detectors. These signals are selected and combined (integrated) to generate one SEM image. By generating a desired SEM image in this manner, the contact between the sample and the probe can be confirmed accurately and accurately, which will be described in detail below.

  With reference to FIG. 2, in the SEM type defect inspection apparatus according to the present invention, the relationship between the position and direction of the detector and the SEM image will be described. FIG. 2 shows a state in which the sample 101 is viewed from above. A probe 107 and detectors 109A, 109B, and 109C are arranged above the sample 101. Secondary electron signals or reflected electron signals generated from the sample 101 are detected by the detectors 109A, 109B, and 109C, and an SEM image is generated. A first SEM image 201 is generated by the first detector 109A on the left side, a second SEM image 202 is generated by the second detector 109B on the right side, and a third SEM image 202 is generated by the upper third detector 109C. It is assumed that the SEM image 203 has been generated.

  In this example, the interval between the probe 107 and the sample 101 is about 10 μm. In this case, secondary electron signals or reflected electron signals generated from the sample 101 are shielded by the probe 107 before reaching the detector. Therefore, detectors are arranged on both sides of the probe 107. The first and second detectors 109A and 109B are arranged on the lateral side of the probe 107. In the first and second SEM images 201 and 202, probe images 2011 and 2021 and their shadows 2012 and 2022 appear. Shadows 2012 and 2022 indicate that the signal from the detector is decreasing. The shape and size of the shadows 2012 and 2022 vary depending on the height of the probe 107, that is, the distance between the probe 107 and the sample 101. The shadows 2012 and 2022 are darker as the distance between the probe 107 and the sample 101 is smaller, and the shadows 2012 and 2022 are lighter as the distance between the probe 107 and the sample 101 is larger. When the distance between the probe 107 and the sample 101 is about several tens of micrometers, there is no signal difference due to the direction of the detector.

  The third detector 109C is disposed on the tip side of the probe 107. In this case, secondary electron signals or reflected electron signals generated from the sample 101 are not shielded by the probe 107. Accordingly, in the third SEM image 203, only the probe image 2031 appears, and the shadow thereof does not appear.

  Thus, when the distance between the probe 107 and the sample 101 is about 10 μm, the SEM image varies depending on the position and direction of the detector. That is, different SEM images are obtained by using a plurality of detectors arranged at different positions and directions. From these SEM images, a desired SEM image can be selected according to the observation purpose and the observation object. That is, the user can select and use a desired detector among a plurality of detectors.

  (1) When the probe and the sample are close to each other, the signal detected by the detector changes. In the example of FIG. 2, in the first and second SEM images 201, 202 obtained by the signals from the first and second detectors 109A, 109B, shadows 2012, adjacent to the probe images 2011, 2021, 2022 appears. Thus, when the shadows 2012 and 2022 appear, it can be determined that the probe is close to the sample.

  (2) When shadows 2012 and 2022 appear in the SEM images 201 and 202, the sample image becomes unclear. Therefore, in order to generate an SEM image in which no shadow is generated, the third SEM image 203 obtained by the signal from the third detector 109C may be used. However, when the third detector 109C is not provided, a combined signal is generated by adding the signals from the first and second detectors 109A and 109B, and an SEM image is generated using the combined signal. do it. As a result, the shadow is erased and an image without a shadow is obtained.

  With reference to FIG. 3, the example of arrangement | positioning of a probe and a detector is demonstrated. In the defect inspection apparatus of the present invention, a plurality of probes 107A, 107B, 107C, and 107D and a plurality of detectors 109A, 109B, and 109C arranged at different positions and directions are mounted. The directions of the center axis of the probe and the center axis of the detector shown in the figure are examples, and in fact, the directions of the center axis of the probe and the center axis of the detector are in arbitrary directions. The number of probes used for the evaluation of electrical characteristics varies depending on the inspection object. For example, when a semiconductor element transistor is to be inspected, four probes are used. When a wiring pattern of a semiconductor element such as an LSI is to be inspected, one or two probes are used. The number of probes used and the number of detectors are not necessarily the same.

  The user can generate a desired SEM image by selectively using signals from a desired detector among signals from a plurality of detectors for each probe. For example, when detecting contact of the first probe 107A, a signal from a desired detector is selected from the signals from the three detectors 109A, 109B, and 109C, and an SEM image is generated. When the first probe 107A approaches the sample, a shadow appears adjacent to the probe image in any one of the SEM images obtained from the signals from the three detectors 109A, 109B, and 109C. Thereby, the contact of the probe 107A can be confirmed. Similarly, in order to confirm the contact of the second probe 107B, a signal from a desired detector is selected from the signals from the three detectors 109A, 109B, and 109C, and an SEM image is generated.

  Next, when detecting the contact of the first probe 107A, an SEM image in which no shadow is generated may be required. In this case, an SEM image may be generated by selecting a signal from a desired detector from among the signals from the three detectors 109A, 109B, and 109C. In these SEM images, when there is an SEM image in which no shadow is generated, it is used. When there is no SEM image in which no shadow occurs, the shadow disappears and there is no shadow by adding signals from a plurality of desired detectors among the signals from the three detectors 109A, 109B, and 109C. SEM images can be generated.

  With reference to FIGS. 4A, 4B, and 4C, a method of measuring the distance between the probe and the sample in the SEM type defect inspection apparatus according to the present invention will be described. First, the relative positions of the probe 107 and the detector 109A will be described with reference to FIG. 4A. The detector 109A is disposed on the lateral side of the probe 107. That is, the detector 109A is arranged so that its central axis is orthogonal to the axis of the probe 107. The inventors of the present application observed the shadow appearing in the SEM image by changing the angle of the detector with respect to the sample. The angle formed by the central axis of the detector 109A with respect to the upper surface of the sample 101 is θ, and the angle formed by the central axis of the probe 107 with respect to the upper surface of the sample 101 is α. In general, 0 ° <θ <α. It is assumed that the probe attachment angle α is predetermined. For example, α = 30-60 °. Here, it is assumed that α = 45 °.

  The inventor of the present application has found that the mounting angle θ of the detector 109A should be as small as possible. That is, it was found that the shadow appearing in the SEM image is clarified when the mounting angle θ of the detector 109A is reduced. It has been found that the mounting angle θ of the detector 109A is preferably θ = 0 to 45 °, and more preferably θ = 0 to 10 °. Next, the SEM image was observed while bringing the probe close to the surface of the sample.

  FIG. 4B shows an example of the SEM image 301 when the probe is not in contact with the sample, and FIG. 4C shows an example of the SEM image 302 when the probe is in contact with the sample. As shown in FIG. 4B, when the probe is not in contact with the sample, the shadow image 3012 is separated from the probe image 3011. As shown in FIG. 4C, the shadow image 3022 is adjacent to the probe image 3021 when the probe is in contact with the sample. Therefore, by measuring the distance x between the shadow image 3012 and the probe image 3011, it can be determined whether or not the probe is in contact with the sample.

  For example, first, the actual distance y between the probe and the sample is accurately measured by an appropriate method. At the same time, the distance x between the shadow image and the probe image is measured. Thus, the relationship between the distance x between the shadow image and the probe image and the distance y between the probe and the sample is obtained in advance and stored in the signal processing system 113. Therefore, when the distance x between the shadow image and the probe image is measured, the distance y between the probe and the sample can be accurately obtained from the relationship between the two distances x · y stored in the signal processing system 113.

  According to the present invention, a secondary electron signal or a reflected electron signal from a sample is detected by a detector in a defect inspection apparatus that measures electrical characteristics with high sensitivity by directly contacting an LSI or the like using an SEM image. This signal amount changes immediately before the probe contacts the sample. By detecting this change in the signal amount, it is possible to reduce the repetitive work of the final process of bringing the probe into contact with the sample. In addition, according to the present invention, since the probe contact process is facilitated, it is possible to provide a failure analysis apparatus with high reliability and good operability.

  Further, according to the present invention, in the SEM type probing apparatus that measures the electrical characteristics by directly contacting a plurality of mechanical probes, when the probe is brought into contact with the sample, in the SEM image, the image of the probe and the shadow of the probe are displayed. By measuring the distance between the images, the distance between the probe and the sample can be measured. That is, according to the present invention, the relative position immediately before the contact between the probe and the sample can be quantified regardless of the arrangement of the probe. Therefore, it is possible to avoid the probe tip from colliding with the sample to be deformed, and a stable failure analysis can be performed. Furthermore, since the relative position between the probe and the sample can be known without bringing the probe into contact with the sample, the probe can be automatically moved without damaging the probe tip.

  Although the examples of the present invention have been described above, the present invention is not limited to the above-described examples, and it is easy for those skilled in the art to make various modifications within the scope of the invention described in the claims. Will be understood.

DESCRIPTION OF SYMBOLS 100 ... Electro-optic system, 101 ... Sample, 102 ... Sample holder, 103 ... Sample stage, 104 ... Base stage, 105 ... Probe stage, 106 ... Probe holder, 107 ... Probe, 108 ... Sample chamber, 109 ... Detector, 110 ... Turbo molecular pump (TMP), 111 ... Dry pump (DRP), 112 ... Control unit, 113 ...・ Signal processing system, 114 ... Power supply unit, 115 ... Image display unit, 116 ... Electrical characteristic evaluation unit, 117 ... Stand

Claims (12)

Using a defect inspection apparatus having an electron optical system that irradiates a sample with an electron beam, at least one probe that causes the sample to touch, and a plurality of detectors that detect secondary electrons or reflected electrons from the sample, In a defect inspection method for measuring electrical characteristics of an inspection object formed on a sample,
A probe moving step for bringing the probe closer to the inspection object on the sample;
An image generation step of inputting signals from the plurality of detectors and generating an image of the inspection target so as to include an image of the tip of the probe, respectively.
An image display step for displaying the image to be inspected on an image display unit;
Generating an image of the inspection object based on a signal from a detector selected by a user among the plurality of detectors;
A defect inspection method. The defect inspection method according to claim 1,
Combining image signals from a plurality of detectors selected by a user to generate one combined image signal;
Generating an image to be inspected based on the composite image signal;
A defect inspection method characterized by comprising: The defect inspection method according to claim 1,
A defect inspection method, wherein an angle formed by a central axis of the detector with respect to the sample is θ, and the angle θ is 10 ° or less. The defect inspection method according to claim 1,
A defect inspection method, wherein 0 ° <θ <α, where θ is an angle formed by the central axis of the detector with respect to the sample and α is an angle formed by the central axis of the probe with respect to the sample. The defect inspection method according to claim 1,
The defect inspection apparatus is used to measure the distance between the probe image and a shadow generated adjacent to the probe image, and the distance between the probe image and the shadow between the actual probe and the sample. Determining a relationship between the distances and storing the relationship between the two distances;
Obtaining a distance between an image of the probe and a shadow generated adjacent to the image of the probe in the image to be inspected;
Obtaining the distance between the probe and the sample using the relationship between the two stored distances from the distance between the image and the shadow of the probe obtained in the image to be inspected;
A defect inspection method characterized by comprising: A sample stage on which the sample is placed, an electron optical system that irradiates the sample with an electron beam, a probe unit that causes the sample to touch at least one probe, and a plurality of detections that detect secondary electrons or reflected electrons from the sample An electrical signal from the probe, and a signal processing system for generating an image of the sample by inputting signals from the plurality of detectors for each probe and an image display unit for displaying the image In the defect inspection apparatus that measures the electrical characteristics of the wiring pattern formed on the sample by
The signal processing system includes an image of a tip of the probe based on a signal from a detector selected by a user among the plurality of detectors when the probe is brought close to an inspection target on a sample. A defect inspection apparatus that generates an image to be inspected and displays the image on the image display unit. The defect inspection apparatus according to claim 6,
The signal processing system generates an image to be inspected using a composite signal obtained by adding signals from a plurality of predetermined detectors selected by a user, and displays the image on the image display unit. A feature defect inspection device. The defect inspection apparatus according to claim 6,
A defect inspection apparatus, wherein an angle formed by a central axis of the detector with respect to the sample is θ, the angle θ is 10 ° or less. The defect inspection apparatus according to claim 6,
A defect inspection apparatus, wherein 0 ° <θ <α, where θ is an angle formed by the central axis of the detector with respect to the sample and α is an angle formed by the central axis of the probe with respect to the sample. The defect inspection apparatus according to claim 6,
The signal processing system stores a relationship between a distance between the probe image and a shadow generated adjacent to the probe image, and an actual distance between the probe and the sample;
When the distance between the image of the probe and the shadow generated adjacent to the probe image is determined in the image to be inspected, the two stored images are calculated from the distance between the image of the probe and the shadow. A defect inspection apparatus characterized in that a distance between the probe and the sample is obtained using a distance relationship. Using a defect inspection apparatus having an electron optical system that irradiates a sample with an electron beam, at least one probe that causes the sample to touch, and a plurality of detectors that detect secondary electrons or reflected electrons from the sample, In a defect inspection method for measuring electrical characteristics of an inspection object formed on a sample,
The defect inspection apparatus is used to measure the distance x between the probe image and the shadow generated adjacent to the probe image, and the distance between the probe image and the shadow and the actual probe and sample. Determining the relationship between the distances y and storing the relationship between the two distances x · y;
A probe moving step for bringing the probe closer to the inspection object on the sample;
An image generation step of inputting signals from the plurality of detectors and generating an image of the inspection object so as to include an image of the tip of the probe;
Obtaining a distance between an image of the probe and a shadow generated adjacent to the image of the probe in the image to be inspected;
Obtaining the distance between the probe and the sample using the relationship between the two stored distances from the distance between the image and the shadow of the probe obtained in the image to be inspected;
A defect inspection method characterized by comprising: The defect inspection method according to claim 11,
The defect inspection method, wherein the image to be inspected is generated based on a signal from a detector selected by a user among the plurality of detectors.

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