JP2006337203A - Positioning method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve positioning precision by eliminating the restraint that the position of a mark for positioning is limited in the electric current path. <P>SOLUTION: A sample and a laser beam are relatively moved and the sample is scanned, and magnetism from the sample is detected by a SQUID magnetic detector to acquire an image made of a set of values, corresponding to the position of scanning according to the detection results. The positions of peaks or the positions of the center of gravity, within at least one area in the acquired image on the values of the image, is determined as a position mark in the sample. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sample positioning method and apparatus, and more particularly to a method and apparatus suitable for positioning a semiconductor integrated circuit (LSI) using a scanning laser SQUID microscope or the like.

  For example, Non-Patent Document 1 proposes a method for specifying an LSI position using a Pilot-OBIRCH (Optical Beam Induced Resistance Change) method. Non-Patent Document 1 describes that it has been clarified from experiments that 1σ at the observation position is about 65 nm under the condition of position resolution of 0.13 μm by Pilot light emission. In addition, the current that can be detected by Pilot-OBIRCH A method is disclosed in which a path image is used as a known contrast, a specific MOS transistor is repeatedly operated at high speed (a pattern is applied from a tester), and the transient current is observed as in the case of Pilot light emission.

  As shown in FIG. 4A, the IC chip is scanned with a laser beam and heated to detect a change in the current flowing through the external electrode, and a change in resistance corresponding to the irradiation position of the laser beam is imaged (FIG. 4). (See (B)). In this method, as shown in FIG. 4B, the portion where the image can be seen is limited to the current path connected to the external electrode in the IC chip.

Tatsuya Ishii, Hirotoshi Terada, "Pilot emission and Pilot-OBIRCH LSI pinpointing and its problems Pilot-Photon-Emission and Pilot-OBIRCH Techniques for LSI Fault Isolation," LSI Testing Symposium / 2003 Proceedings (H15.11.5 -7), pp. 225-229 Masashita Yamashita, Shindo Kawase, Tomoyuki Otani, Kiyoshi Futagawa, Masayoshi Touchi, “Non-contact evaluation of MOS transistors using laser terahertz emission microscope,” LSI Testing Symposium / 2004 Proceedings (H16.11.11-12), 347 -Page 351 Kiyoshi Futagawa, Shoji Inoue “Prototype / Evaluation of Scanning Laser SQUID Microscope and Application Proposal for Failure / Failure Analysis and Process Monitor-New Analytical Method for Complete Non-contact / Non-destructive” LSI Testing Symposium / 2000 Proceedings (H12. 11.9-10), pp. 203-208 Kiyoshi Futagawa, Tetsuya Sakai "Phase Imaging in Laser-SQUID Microscopy" LSI Testing Symposium / 2003 Proceedings (H15.11.5-7), 317-322

  As described above, in the case of the conventional technique shown in FIG. 4, there are many restrictions because it is necessary to apply a current or voltage to the IC chip from the outside.

  In addition, by applying an external current or voltage to the IC chip, only a portion where the current flows is set as an observation target. As a result, locations that can be selected as positioning marks in the IC chip are limited only to the current path. As described above, since the portion other than the current path cannot be used as a mark for positioning, its use is extremely limited.

  The method according to the present invention scans the sample by relatively moving the sample and the laser beam, detects magnetism or electromagnetic waves from the sample with a detector, corresponds to the scanning position and detects with the detector. A step of obtaining an image comprising an array of values according to the result, and an operation in the region relating to the value of the image as a mark of a position in the sample for at least one region of the obtained image And a step of obtaining

  The apparatus according to the present invention includes a means for scanning the sample by relatively moving the sample and laser light, a detector for detecting magnetism or electromagnetic waves from the sample, and corresponding to the scanning position and indicating a detection result. A means for acquiring a two-dimensional image composed of a collection of values corresponding to the position of the mark on the sample is obtained by calculating in the region regarding the value of the image for at least one region of the acquired image. Means. In the present invention, for example, a peak position or a gravity center position is obtained.

  In the present invention, the mark is used as a mark for narrowing down the sample.

  In the present invention, the detector includes a magnetic detector that detects a magnetic flux from the sample. Alternatively, the detector includes an electromagnetic wave detector that detects an electromagnetic wave emitted from the sample.

  According to the present invention, the position of the mark for positioning on the sample is not limited to the current path, and positioning can be performed with an accuracy of half or less of the half width.

  The above-described present invention will be described below with reference to the accompanying drawings in order to explain in more detail. A scanning laser SQUID (superconducting quantum interference device) microscope is a type of defect in which a current flows when a laser is irradiated to a defective portion or a related portion, and a magnetic field induced by the current is applied to a SQUID magnetometer. And an image is obtained by scanning the laser or the sample (see Non-Patent Document 3). In a scanning laser SQUID microscope, most defects or images associated therewith are isolated. For this reason, in the failure analysis, the positioning accuracy rather than the resolution is an index for determining the limit. That is, it is only necessary to know the position coordinates on the LSI chip.

  When the plane coordinates are (x, y), the (x, y) coordinates can be specified in an image of a scanning laser SQUID microscope or a laser terahertz emission microscope (LTEM). Note that Non-Patent Document 2 is referred to for non-contact evaluation of MOS transistors using a laser terahertz emission microscope (LTEM) (a device failure location narrowing technique that can be used under no-bias voltage conditions). The present invention acquires an image of a sample with a scanning laser SQUID microscope or a laser terahertz emission microscope (LTEM), and the value of the image in the region is used as a mark of the position in the sample for at least one region of the acquired images. Is calculated to obtain the peak position or the center of gravity position, thereby improving the positioning accuracy. Hereinafter, how to specify the position coordinates in one embodiment of the present invention will be described below.

  FIG. 1 is a diagram for explaining an embodiment of the present invention. FIG. 1A is a schematic diagram for explaining image acquisition by a scanning laser SQUID microscope. As shown in FIG. 1A, the LSI chip forming the sample and the laser beam are relatively moved to scan the LSI chip, and the magnetic flux from the LSI chip is detected by the SQUID magnetic sensor.

  As a result, for example, as shown in FIG. 1B, an image composed of a two-dimensional array of values corresponding to the scanning position and corresponding to the detection result (magnetic flux intensity) is acquired. FIG. 1B shows a part of an image of a well (256MDRAM) (image in an actual machine) by a scanning laser SQUID microscope. In the case of a scanning laser SQUID microscope, the observation time per pixel is as long as 100 μs or more, so the image has a spread of about μm due to the influence of the diffusion length of carriers generated by light irradiation. Nevertheless, as shown in FIG. 1B, there is a place having a line profile with a width of about 0.59 μm on the chip (sample).

  The profile (line profile) of FIG. 1C is a distribution of magnetic intensity along the line XX ′ of the cross section of the high brightness line that intersects the line XX ′ of the image of FIG. .

  FIG. 1D is a diagram illustrating a procedure for interpolating peak values from the image of FIG. As shown in FIG. 1D, for at least one region of the acquired images, a peak position in the region relating to the value of the image is obtained by interpolation as a position mark in the sample. As a result, positioning can be performed with an accuracy of half or less of the half-value width of 0.59 μm of the scanning laser SQUID microscope image.

  In the scanning laser SQUID microscope, a half-value width smaller than the diffraction limit obtained from the wavelength of light and the numerical aperture of the objective lens is obtained. The line limit of the optical system (= λ / (2NA); where λ is the wavelength and NA is the numerical aperture) is 0.7 μm (= 1065 nm / (2 * 0.76)), but half of the scanning laser SQUID microscope. The value width is 0.59 μm. In the present embodiment, by interpolating the peak, a value smaller than 0.59 μm can be obtained as the position accuracy. For example, peaks can be interpolated using extrapolation, interpolation, least squares, or other methods.

  Further, in the scanning laser SQUID microscope, by using a solid immersion lens, a half width of about 200 nm can be obtained, and the positioning accuracy can be set to 100 nm or less. A stage on which the LSI chip (sample) to be inspected is placed has a repeat positioning accuracy of 100 nm or less, and a mark location on the LSI chip to be inspected is specified with a positioning accuracy of 100 nm or less, for example. If it is possible, the specific accuracy of the specific position of the defect of the LSI chip can be reduced to 100 nm or less.

  In the present embodiment, the peak position is obtained by performing smoothing processing and obtaining two straight lines having different polarities in the image of FIG. 1D, and using the x coordinate of the intersection of the two straight lines as the peak position. A technique is used. Alternatively, an arbitrary method for obtaining the peak by interpolation is used.

  In this embodiment, instead of peak interpolation, in the region where the line profile is obtained (see FIG. 1B) or the like, the pixel value may be the density and the center (center of gravity) of the mass distribution may be obtained. This will be described below.

The image value (pixel value) at the lattice point (i, j) is defined as g (i, j). The centroids Gi and Gj of the region of l in the x direction and m in the y direction are as follows.

However,

  As a region of l in the x direction and m in the y direction, for example, a certain threshold is provided for a region where a sufficiently small point is originally blurred and spreads, and a region having luminance (gradation) equal to or higher than the threshold is selected. You may do it.

Further, in the present embodiment, when a sufficiently thin line is originally spread, a barycentric line may be obtained. The position G (i) of the center of gravity on the grid line i in the x direction is given below.

However, w (i) is

  Alternatively, a series of approximate lines of G (i) may be obtained by a least square method, spline approximation, or the like to obtain a centroid line.

Similarly, the position G (j) through which the center of gravity line passes in the grid line j in the y direction is given by

Where w (j) is

  In this embodiment, the peak value or barycentric position obtained as described above is used as a reference point for the coordinates of the LSI chip. Alternatively, several coordinate marks may be obtained to determine the coordinate system.

  According to the present embodiment, unlike the conventional method described with reference to FIG. 4, the position of the positioning mark is not limited to the current path, and contributes to improvement in the accuracy of failure analysis of the LSI chip.

  FIG. 2A is a diagram showing an embodiment of a device configuration for carrying out the present invention. FIG. 2B is a diagram for explaining an example of timing waveforms of the reference signal 1, the modulation signal 2, and the magnetic field signal 4 in FIG. Referring to FIG. 2A, this inspection apparatus generates modulated light that is intensity-modulated by a modulated signal 2 synchronized with a predetermined reference signal 1 and converges to generate a modulated beam 61. And an LSI chip forming the sample 70, mounted so that the modulated beam 61 is irradiated to a predetermined irradiation position of the sample, and generated when the sample 70 is irradiated with the modulated beam 61. A magnetic field detector 20 that detects a magnetic field (magnetic flux) induced by a current and outputs a magnetic field signal 4; a magnetic field intensity; and a phase difference 6 between the reference signal 1 and the magnetic field signal 4 (see FIG. 2B). A signal extraction unit 30 that extracts and outputs as the intensity signal 5 and the phase difference signal 7 respectively, controls the irradiation of the modulated beam 61 to the sample 70, and controls the positioning of the sample stage 71 according to the irradiation position information. A control unit 40 that inputs the signal 5 and the phase difference signal 7 and outputs the signal corresponding to the irradiation position information, and a display unit 50 that inputs at least one of the intensity signal 5 and the phase difference signal 7 and the irradiation position information and displays an image. It has.

  The modulated beam generator 10 includes a reference signal 1 and a pulse generator 11 that generates and outputs a modulated signal 2 (see FIG. 2B) synchronized with the reference signal 1, and a fiber laser with a modulation mechanism attached thereto. The laser light generator 12 that generates modulated light (laser light) intensity-modulated by the modulation signal 2 output from the pulse generator 11, the optical fiber 14 that guides the laser light, and the optical fiber 14 guides the laser light. An optical system unit 13 that converges the waved light to generate a modulated beam 61 is provided.

  The magnetic field detector 20 controls the SQUID magnetometer 21 and an electronic circuit (“SQUID electronic circuit”) that controls the SQUID magnetometer 21 to generate and output a magnetic field signal 4 from the output signal 3 (voltage output) of the SQUID magnetometer 21. 22). For example, the SQUID magnetometer 21 is a high-temperature superconducting SQUID magnetometer. The electronic circuit 22 can use a FLL (Flux-Locked Loop) circuit.

  Although not particularly limited, the signal extraction unit 30 includes, for example, a two-phase lock-in amplifier (not shown), receives the magnetic field signal 4 from the electronic circuit 22, receives the reference signal 1 from the pulse generator 11, The same frequency component as that of the reference signal 1 is extracted from the magnetic field signal 4, and the phase difference signal 7 corresponding to the intensity signal 5 and the phase difference 6 between the magnetic field signal 4 and the reference signal 1 (see FIG. 2B) is output.

  For example, the control unit 40 controls the position of the sample stage 71 (sample 70) by a stage scanning signal, controls the optical system unit 13 of the modulated beam generation unit 10 by a laser scanning signal, and scans the modulated beam 61 on the sample 70. Then, the sample 70 is irradiated.

  Further, the control unit 40 takes in the intensity signal 5 and the phase difference signal 7 from the signal extraction unit 30, and displays them as a scanning laser SQUID microscopic image in synchronization with the stage scanning, the laser light irradiation position, or the scanning of the SQUID magnetometer. Control for.

  The display unit 50 includes a PC (personal computer) 51 and a display 52, receives the image display signal 8 from the control unit 40, and the intensity image 81 of the magnetic field signal 4 corresponding to the magnetic field at the laser beam scanning position or the reference signal 1. A phase difference image 82 corresponding to the phase difference is output. In the description of FIG. 1, for simplicity of explanation, the magnetic field distribution image is shown as one kind, but preferably, an intensity image 81 and a phase difference image 82 are used.

  Although not particularly limited, since laser light having a wavelength of 1065 nm is used in the present embodiment, when the sample 70 is a Si wafer, the laser light is irradiated from the back surface thereof, transmitted through the Si substrate, and p near the surface of the Si wafer. The modulated beam can reach the -n junction. The back surface of the Si wafer is preferably mirror-polished. The modulated beam 61 irradiated from the back surface of the Si wafer can efficiently reach the pn junction. Note that the LSI chip forming the sample 70 is acquired with a magnetic field image in a non-bias voltage state.

  As the SQUID magnetometer 21, an HTS (High Temperature Superconductivity) SQUID magnetometer can be used to detect a minute magnetic field of 1 pT or less. A magnetic shield 65 is provided. The SQUID magnetometer detects a magnetic flux perpendicular to the normal sample 70.

  Since the noise is usually mixed in the magnetic field signal 4 output from the electronic circuit 22, only the same frequency component as the modulation frequency is extracted by the two-phase lock-in amplifier (signal extraction unit 30). The ratio has been improved. By using a two-phase lock-in amplifier as the signal extraction unit 30, not only the same frequency component as the reference signal 1 output from the pulse generator 11 can be extracted, but also the phase difference signal 7 from the reference signal 1 of the component. And the intensity signal 5 can be separated and output. A magnetic field distribution image is obtained by setting the size of the chip to 6 mm × 10 mm, for example, reducing the beam diameter of the modulation beam 61 to 10 μm, and scanning the sample stage 71 formed of a ceramic stage. The modulation frequency is, for example, 100 KHz. A chip intensity image 81 and a phase difference image 82 are obtained.

  The configuration shown in FIG. 2A has been described based on an example in which the intensity signal and the phase difference signal indicating the phase difference between the magnetic field signal and the reference signal are separately output from the magnetic field signal from the magnetic field detection unit. Of course, the present invention can also be applied to a configuration that outputs only an intensity signal.

  For the spatial resolution of the intensity image and the phase image (image of FIG. 1B) observed from the back surface of the 256MDRAM chip with the scanning laser SQUID microscope shown in FIG. 2, see, for example, the description of Non-Patent Document 4. Is done.

  Next, another embodiment of the present invention will be described. In the second embodiment of the present invention, an image of an LSI chip is obtained by a laser terahertz emission microscope (LTEM) instead of the scanning laser SQUID microscope used in the above embodiment. Also in the present embodiment, an electromagnetic field image is acquired and analyzed under a no-bias voltage condition as in the above-described embodiment. In FIG. 3, by scanning the semiconductor surface of the sample 101 with a femto laser, a temporally short electromagnetic wave pulse (terahertz (THz) electromagnetic wave) is emitted, and this THz electromagnetic wave is detected by the THz electromagnetic wave detector 102. Thus, it is possible to obtain information on the electric field distribution applied in the semiconductor. For non-bias voltage LTEM observation of the MOSFET, see Non-Patent Document 2 above. FIG. 3 shows LTEM images (images before actual disconnection and after disconnection, actual images) under no bias voltage. From the non-biased LTEM image thus obtained, the peak value or the center of gravity position is obtained in the same manner as described above for a predetermined line profile.

  In the case of a laser terahertz emission microscope, the laser beam cannot be narrowed down to a diffraction limit of 1 μm or less, but as long as an image narrowed down to about 2 μm is seen, the influence of the diffusion length (carrier diffusion) is not recognized. In the case of a laser terahertz emission microscope (LTEM), this is thought to be due to the time required for signal acquisition of one pixel being as short as ps order.

  For this reason, if a mark such as the line in FIG. 1B cannot be observed on the LSI chip being observed with the scanning laser SQUID microscope image, for example, the same procedure is performed on the LTEM image. Can be obtained.

  The LSI chip on which the position of the mark has been determined according to the above-described embodiment is aligned using the mark (for example, three marks) as a reference point (for example, alignment on the XY stage), and failure analysis is performed. As the failure analysis, for example, an OBIRCH method, an OBIC method, an LTEM, a laser SQUID microscope, or the like may be used. Alternatively, the coordinate coordinates of the LSI chip mark and the coordinate coordinates of the LSI layout pattern (for example, wiring pattern) are associated with each other, and the microscopic image and the layout pattern are associated with each other, or are displayed in an isometric manner. May be mapped. Currently, the accuracy of the layout pattern is higher than 100 nm, and can be associated with the position of the XY stage (as described above, 100 nm or less).

  For example, when the present invention is applied to failure analysis of an LSI chip under no bias, the position of the failure location can be specified with high accuracy, which contributes to improvement of accuracy of failure analysis.

  Although the present invention has been described with reference to the above embodiment, the present invention is not limited to the configuration of the above embodiment, and various modifications that can be made by those skilled in the art within the scope of the present invention. Of course, modifications are included.

It is a figure for demonstrating one Example of this invention. It is a figure which shows the apparatus structure of one Example of this invention. It is a figure explaining the structure of another Example of this invention. It is a figure explaining the conventional system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reference signal 2 Modulation signal 3 SQUID output signal 4 Magnetic field signal 5 Intensity signal 6 Phase difference 7 Phase difference signal 8 Image display signal 10 Modulated beam generation part 11 Pulse generator 12 Laser light generator 13 Optical system unit 14 Optical fiber 20 Magnetic field Detection unit 21 SQUID magnetometer 22 Electronic circuit (SQUID electronic circuit)
30 Signal Extractor 40 Control Unit 50 Display Unit 51 PC (Personal Computer)
52 Display 61 Modulated beam 63 Magnetic field (magnetic flux)
65 Magnetic shield 70 Sample 71 Sample stage 81 Intensity image 82 Phase contrast image 100 Inspection device (Non-destructive analysis device)
101 sample 102 THz electromagnetic wave detector

Claims (15)

The sample and the laser beam are moved relative to each other, the sample is scanned, and the magnetism or electromagnetic wave from the sample is detected by a detector. The value corresponding to the scanning position and the detection result of the detector Obtaining an image comprising an array;
Obtaining at least one region of the acquired image the position of the mark in the sample by calculation relating to the value of the image in the region;
A positioning method characterized by comprising:   The positioning method according to claim 1, wherein a position of a peak or a position of a center of gravity regarding the value of the image in the region is obtained as the position of the mark in the sample.   The positioning method according to claim 1, wherein the position of the mark in the sample is determined with higher accuracy than the half width of a microscope including the detector.   The positioning method according to claim 1, wherein the mark is used as a mark for failure analysis of the sample.   The positioning method according to claim 1, wherein the detector includes a magnetic detector that detects a magnetic flux from the sample.   The positioning method according to claim 1, wherein the detector includes an electromagnetic wave detector that detects an electromagnetic wave emitted from the sample.   5. The positioning method according to claim 4, wherein the sample is made of a semiconductor device, and the obtained position of the mark is associated with the layout data of the semiconductor device. Means for relatively moving the sample and the laser beam to scan the sample;
A detector for detecting magnetism or electromagnetic waves from the sample;
Means for acquiring an image corresponding to the scanning position and comprising an array of values corresponding to the detection result of the detector;
Means for determining the position of the mark in the sample by calculation related to the value of the image in the region for at least one region of the acquired images;
A positioning device characterized by comprising:   9. The position according to claim 8, wherein the means for obtaining the position of the mark in the sample obtains the position of the peak or the center of gravity regarding the value of the image in the region as the position of the mark in the sample. Ejecting device.   9. The positioning apparatus according to claim 8, wherein the position accuracy of the mark on the sample is higher than the half width of a microscope including the detector.   The positioning device according to claim 8, wherein the detector includes a magnetic detector that detects a magnetic flux from the sample.   The positioning device according to claim 8, wherein the detector includes an electromagnetic wave detector that detects an electromagnetic wave radiated from the sample. As the laser beam, a modulated beam that is intensity-modulated based on a modulated signal synchronized with a reference signal is generated, and a modulated beam that is converged on the sample is used.
Based on the magnetic field signal detected by the magnetic field detector and the reference signal, the magnetic field strength and the phase difference between the magnetic field signal and the reference signal are derived, and output as an intensity signal and a phase difference signal,
9. The positioning apparatus according to claim 8, wherein the intensity signal and / or the phase difference signal are displayed in correspondence with scanning position information.   12. The positioning apparatus according to claim 11, wherein the laser beam and the magnetic field detector constitute a scanning laser SQUID microscope.   The positioning apparatus according to claim 12, wherein the laser beam and the electromagnetic wave detector constitute a laser terahertz emission microscope.