JP2015064279A - Inspection device and method for generating image data for inspection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspection device capable of suppressing occurrence of luminance unevenness in image data associated with fluctuation of emission current.SOLUTION: An inspection device comprises: a first primary optical system including an electron source which radiates a charged particle as a beam; a current detection unit which detects an emission current value of the beam radiated from the electron source; an imaging unit including an imaging element which detects an amount of primary charged particles obtained by irradiating an inspection object with a beam; an image data generation unit which generates image data on the basis of the imaging results of the imaging unit; and a correction unit which corrects the imaging results or the image data on the basis of the detected emission current value.

Description

  The present invention relates to a technique for generating inspection image data in order to inspect defects and the like of a pattern formed on a surface of an inspection object by irradiating the inspection object with charged particles.

  An inspection target such as a semiconductor wafer is irradiated with charged particles from an electron source, and secondary charged particles obtained according to the properties of the surface of the inspection target are detected by an imaging device, and generated based on the detection result. An inspection apparatus for inspecting a pattern or the like formed on the surface of an inspection object using image data is widely known (for example, Patent Document 1 below). In such an inspection apparatus, when the emission current from the electron source fluctuates, the luminance of the electronic image changes. As a result, luminance unevenness occurs in the output image, and the inspection accuracy decreases. For this reason, a technique is known in which the emission current is monitored and the emission current is controlled to a set value by feedback control (for example, Patent Document 2 below).

International Publication No. 2002/001596 JP 2006-324124 A

  However, in the feedback control, since the control for reducing the fluctuation is performed after detecting the fluctuation of the emission current, the influence on the image data due to the fluctuation of the emission current cannot be completely eliminated. Therefore, there is a need for another technique that can suppress the occurrence of luminance unevenness in image data due to fluctuations in emission current.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as, for example, the following forms.

  A first aspect of the present invention is provided as an inspection apparatus. This inspection apparatus is obtained by a primary optical system having an electron source that irradiates charged particles as a beam, a current detection unit that detects an emission current value of a beam irradiated from the electron source, and irradiation of the inspection target of the beam. An imaging unit having an imaging device for detecting the amount of secondary charged particles, an image data generation unit for generating image data based on an imaging result of the imaging unit, and an emission current detected from the imaging result or the image data And a correction unit that performs correction based on the value.

  According to such an inspection apparatus, even if the emission current value fluctuates, the imaging result or the image data can be corrected so as to reduce the influence on the image data due to the fluctuation. Accordingly, it is possible to suppress the occurrence of luminance unevenness in the image data due to the fluctuation of the emission current.

  As a second aspect of the present invention, in the first aspect, the correction unit may perform correction based on a target value predetermined for the emission current value and the detected emission current value. According to this aspect, the image data can be corrected so as to approach the image data obtained when the emission current value is as the target value. Therefore, the occurrence of uneven brightness can be suppressed while adjusting the brightness value of the image data to a desired level.

  As a third aspect of the present invention, in the second aspect, the correction unit performs correction to increase the luminance value represented by the imaging result or the image data when the detected emission current value is smaller than the target value. Also good. According to this aspect, when the emission current value fluctuates to a side smaller than a desired level, it is possible to suppress the occurrence of luminance unevenness in the image data due to the fluctuation.

  As a fourth aspect of the present invention, in the second or third aspect, the correction unit corrects the luminance value represented by the imaging result or the image data when the detected emission current value is larger than the target value. May be performed. According to this aspect, when the emission current value fluctuates to a larger side than a desired level, it is possible to suppress the occurrence of uneven brightness in the image data due to the fluctuation.

  As a fifth aspect of the present invention, the inspection apparatus according to any one of the first to fourth aspects further performs feedback control based on the detected emission current value so that fluctuations in the emission current value are suppressed. You may provide the feedback control part to perform. According to this aspect, since the fluctuation of the emission current value itself is suppressed, the occurrence of uneven brightness can be further suppressed.

  As a sixth aspect of the present invention, the inspection apparatus according to any one of the first to fifth aspects is a moving unit capable of holding the inspection object, and the inspection object is irradiated with a beam by the primary optical system. You may provide the moving part which moves to a predetermined direction on a position. The imaging unit is a TDI sensor in which an imaging device is arranged in a predetermined direction by a predetermined number of stages, and secondary charged particles obtained by irradiating the inspection target with a beam while moving the moving unit in the predetermined direction There may be provided a TDI sensor that integrates the amount of the signal along a predetermined direction by a time delay integration method. According to such a form, even when high-sensitivity imaging is performed using a TDI sensor, occurrence of luminance unevenness can be suppressed.

  As a seventh aspect of the present invention, in the sixth aspect, the correction unit includes an emission current detected by the current detection unit during an integration period in which the TDI sensor integrates the amount of secondary charged particles by a predetermined number of stages. Based on the average value, the imaging result or image data corresponding to the amount of secondary charged particles accumulated during the accumulation period may be corrected. According to such a form, the period during which the image of the predetermined area to be inspected is projected on the TDI sensor and the period for detecting the emission current value used for correction for the predetermined area match. Good correction accuracy can be obtained, and as a result, the occurrence of uneven brightness can be satisfactorily suppressed.

  The eighth aspect of the present invention is provided as a method for generating inspection image data. This method includes a step of irradiating an inspection target from an electron source with charged particles as a beam, a step of detecting an emission current value of the beam irradiated from the electron source, and a secondary charge obtained by irradiation of the beam onto the inspection target. The step of detecting the amount of particles, the step of generating image data based on the detection result of the amount of secondary charged particles, the detection result of the amount of secondary charged particles, or the image data, the detected emission current And a step of correcting based on the value. According to this method, the same effect as that of the first embodiment is obtained. It is also possible to add any of the second to seventh forms to the eighth form.

  In addition to the above-described embodiments, the present invention can be realized in various forms such as an inspection image data generation device, an inspection image data correction device, and a program for generating inspection image data.

1 is a schematic elevation view of an inspection apparatus as an embodiment of the present invention. It is a schematic plan view of the inspection apparatus shown in FIG. It is explanatory drawing which shows schematic structure of an electron optical apparatus. It is explanatory drawing which shows typically a mode that the quantity of the secondary charged particle in a TDI sensor is integrated | accumulated. It is explanatory drawing which shows schematic structure of an electron source. It is explanatory drawing which shows the specific example of the correction process with respect to the imaging result in a TDI sensor. It is a block diagram which shows an example of the structure for performing a correction process.

A. Example:
1 and 2 show a schematic configuration of a semiconductor inspection apparatus (hereinafter also simply referred to as an inspection apparatus) 5 as an embodiment of the inspection apparatus of the present invention. FIG. 1 is a schematic elevation view (indicated by arrows AA in FIG. 2) of the inspection apparatus 5, and FIG. 2 is a schematic plan view of the inspection apparatus 5 (indicated by arrows BB in FIG. 1). The inspection apparatus 5 is an apparatus that inspects a defect of a pattern formed on the surface of the inspection target, the presence of foreign matter on the surface of the inspection target, and the like. Examples of inspection targets include semiconductor wafers, exposure masks, EUV masks, nanoimprint masks (and templates), optical element substrates, optical circuit substrates, and the like. Examples of foreign substances include particles, cleaning residues (organic substances), reaction products on the surface, and the like. Such foreign matter is made of, for example, an insulator, a conductive material, a semiconductor material, or a composite thereof. In the following description, it is assumed that a semiconductor wafer (hereinafter also simply referred to as wafer W) is inspected by the inspection apparatus 5. The inspection of the wafer is performed after the wafer processing process is performed in the semiconductor manufacturing process or during the processing process. For example, the inspection is performed on a film forming process, a wafer that has undergone CMP or ion implantation, a wafer having a wiring pattern formed on the surface, a wafer on which a wiring pattern has not yet been formed, and the like.

  As shown in FIG. 1, the inspection device 5 includes a cassette holder 10, a mini-environment device 20, a main housing 30, a loader housing 40, a stage device 50, an electro-optical device 70, and an image processing device 80. And a control device 89. As shown in FIGS. 1 and 2, the cassette holder 10 is configured to hold a plurality of cassettes C (two in FIG. 2). In the cassette C, a plurality of wafers W to be inspected are stored in a state of being arranged in parallel in the vertical direction. In the present embodiment, the cassette holder 10 is configured so that the cassette C can be automatically set at a position indicated by a chain line in FIG. The cassette C set in the cassette holder 10 has a position indicated by a solid line in FIG. 2, that is, a rotation axis OO (see FIG. 1) of the first transport unit 61 in the mini-environment device 20 described later. It is automatically rotated to the facing position.

  As shown in FIGS. 1 and 2, the mini-environment device 20 includes a housing 22, a gas circulation device 23, a discharge device 24, and a pre-aligner 25. A mini-environment space 21 whose atmosphere is controlled is formed inside the housing 22. A first transport unit 61 is installed in the mini-environment space 21. The gas circulation device 23 performs atmosphere control by circulating a clean gas (here, air) in the mini-environment space 21. The discharge device 24 collects a part of the air supplied into the mini-environment space 21 and discharges it to the outside. The pre-aligner 25 roughly positions the wafer.

The first transport unit 61 is installed in the mini-environment space 21. The first transport unit 61 has a multi-node arm that can rotate around an axis OO. This arm is configured to be extendable and contractable in the radial direction. A gripping device that grips the wafer W, for example, a mechanical chuck, a vacuum chuck, or an electrostatic chuck is provided at the tip of the arm. Such an arm is movable in the vertical direction. The first transfer unit 61 holds a required wafer W among a plurality of wafers held in the cassette holder 10 and transfers it to a wafer rack 41 in a loader housing 40 described later.

Inside the loader housing 40, as shown in FIGS. 1 and 2, a wafer rack 41 and a second transfer unit 62 are installed. The housing 22 and the loader housing 40 of the mini-environment device 20 are separated by a shutter device 27, and the shutter device 27 is opened only when the wafer W is delivered. The wafer rack 41 supports a plurality (two in FIG. 1) of wafers W in a horizontal state with a vertical separation. The second transport unit 62 has basically the same configuration as the first transport unit described above. The second transfer unit 62 transfers the wafer W between the wafer rack 41 and a holder 55 of the stage apparatus 50 described later. The inside of the loader housing 40 is controlled in an atmosphere to a high vacuum state (the vacuum degree is 10 ⁻⁵ to 10 ⁻⁶ Pa), and an inert gas (for example, dry pure nitrogen) is injected.

  As shown in FIGS. 1 and 2, a stage device 50 as an example of a moving unit that moves the wafer W is provided in the main housing 30. The stage device 50 rotates on the fixed table 51 arranged on the bottom wall, the Y table 52 that moves in the Y direction on the fixed table, the X table 53 that moves in the X direction on the Y table, and the X table. A possible rotary table 54 and a holder 55 arranged on the rotary table 54 are provided. The Y table 52 is moved in the Y direction by a servo motor 56 that is an actuator provided outside the main housing 30. The X table 53 is moved in the X direction by a servo motor 57 that is an actuator provided outside the main housing 30. The holder 55 holds the wafer W on the mounting surface so as to be releasable by a mechanical chuck or an electrostatic chuck. The position in the Y direction of the wafer W held by the holder 55 is detected by a position detection unit (position sensor) 58. The position detector 58 is a laser interference distance measuring device that uses the principle of an interferometer, and detects the reference position of the mounting surface of the holder 55 with a fine-diameter laser. 1 and 2, the position of the position detector 58 is schematically shown. For example, the position detection unit 58 irradiates a laser beam onto a mirror plate fixed to the Y table 52 (or the holder 55), and a laser interferometer detects the incident wave of the laser and the reflected wave from the mirror plate. Based on the phase difference, the coordinates of the wafer W, strictly speaking, the Y table 52 (or holder 55) are detected. The laser interferometer may be provided inside the main housing 30 or outside. The laser interferometer may be connected to an optical pickup provided in the optical path of the laser via an optical cable and provided at a position away from the main housing 30.

  The electron optical device 70 irradiates the wafer W moving in the Y direction (see FIG. 2) with charged particles as a beam, and detects the amount of secondary charged particles obtained thereby. The movement of the wafer W is performed by the stage device 50. Details of the electro-optical device 70 will be described later.

  The image processing device 80 shown in FIG. 1 generates image data based on the amount of secondary charged particles obtained by the electron optical device 70. The generated image data has a luminance value as a gradation value. In this embodiment, the image processing apparatus 80 includes a memory and a CPU, and functions as a correction unit 81 and an image data generation unit 82 by executing a program stored in advance. These functions will be described later. Note that at least a part of each functional unit of the image processing apparatus 80 may be configured by a dedicated hardware circuit.

The image data generated by the image processing apparatus 80 is used for inspecting the presence or absence of a defect of a pattern formed on the surface of the wafer W or the presence of foreign matter by an arbitrary method. This inspection may be automatically performed using an information processing apparatus or the like. For example, the information processing apparatus may detect an area having a luminance value higher than a threshold value, or may perform pattern matching between generated image data and reference image data prepared in advance. Alternatively, the inspection may be performed by an inspector based on the image represented by the image data or the gradation value of each pixel constituting the image data.

  A control device 89 shown in FIG. 1 controls the overall operation of the inspection device 5. For example, the control device 89 sends a movement command to the stage device 50 and moves the holder 55 holding the wafer W in the Y direction at a predetermined movement speed. The control device 89 may include a memory and a CPU, and may implement a required function by executing a program stored in advance. Alternatively, the control device 89 may implement at least a part of required functions with a dedicated hardware circuit in addition to or instead of realizing the functions with software.

  FIG. 3 shows a schematic configuration of the electron optical device 70. In this embodiment, the electron optical device 70 is a mapping projection type electron microscope that collectively irradiates an electron beam onto a wide surface to be inspected and collectively detects the amount of secondary charged particles obtained thereby. However, the electron optical device 70 is another type of electron microscope, for example, a finely focused electron beam is scanned on the surface of the inspection object, and the amount of secondary charged particles obtained thereby corresponds to the diameter of the electron beam. It may be a scanning electron microscope that acquires and detects pixel by pixel. As illustrated, the electron optical device 70 includes a primary optical system 72, a secondary optical system 73, and a TDI sensor 75. The primary optical system 72 generates charged particles as a beam and irradiates the wafer W held by the holder 55 with the beam. The primary optical system 72 includes an electron source 90, lenses 72a and 72d, apertures 72b and 72c, an E × B filter 72e, lenses 72f, 72h, and 72i, and an aperture 72g. The electron source 90 is an electron gun that generates an electron beam, and details thereof will be described later.

  By irradiating the wafer W with charged particles, secondary charged particles corresponding to the state of the wafer W (pattern formation state, foreign matter adhesion state, etc.) are obtained. In the present specification, the secondary charged particles are any of secondary emission electrons, mirror electrons, and photoelectrons, or a mixture of these. The secondary emission electrons are any of secondary electrons, reflected electrons, and backscattered electrons, or a mixture of at least two of these. Secondary emission electrons are generated by collision of charged particles with the surface of the wafer W when the surface of the wafer W is irradiated with charged particles such as an electron beam. When the surface of the wafer W is irradiated with charged particles such as an electron beam, the mirror electrons are generated when the irradiated charged particles are reflected near the surface of the wafer W without colliding with the surface of the wafer W.

  The lenses 72a and 72d and the apertures 72b and 72c shape the electron beam generated by the electron source 90, control the direction of the electron beam, and guide the electron beam to the E × B filter 72e so as to enter from an oblique direction. . The electron beam incident on the E × B filter 72e is deflected vertically downward under the influence of the Lorentz force due to the magnetic field and electric field, and is directed toward the wafer W through the lenses 72f, 72h, 72i and the aperture 72g. It is burned. The lenses 72f, 72h, 72i adjust the landing energy by controlling the direction of the electron beam and appropriately decelerating.

  By irradiating the wafer W with the electron beam, the foreign matter on the wafer W is charged up, so that a part of the incident electrons are rebounded without contacting the wafer W. As a result, the mirror electrons are guided to the TDI sensor 75 via the secondary optical system 73. Further, when some of the incident electrons come into contact with the wafer W, secondary emission electrons are emitted.

Secondary charged particles (here, mirror electrons and secondary emission electrons) obtained by irradiation with the electron beam pass through the objective lens 72i, the lens 72h, the aperture 72g, the lens 72f, and the E × B filter 72e again, Guided to the secondary optical system 73. The secondary optical system 73 guides secondary charged particles obtained by electron beam irradiation to the TDI sensor 75. The secondary optical system 73 includes lenses 73a and 73c, an NA aperture 73b, and an aligner 73d. In the secondary optical system 73, secondary charged particles are collected by passing through the lens 73 a, the NA aperture 73 b, and the lens 73 c, and are adjusted by the aligner 64. The NA aperture 73b has a role of defining the transmittance and aberration of the secondary system.

  The TDI sensor 75 has an image sensor arranged in a predetermined number (plural) of stages in the Y direction, and detects the amount of secondary charged particles guided by the secondary optical system 73. In the present embodiment, the image pickup elements of the TDI sensor 75 are also arranged in the X direction. In the detection by the TDI sensor 75, the stage W 50 moves the wafer W along the Y direction while irradiating the wafer W with an electron beam, and the amount (charge) of secondary charged particles obtained thereby is integrated with time delay. This is performed by integrating the number of steps in the Y direction along the Y direction according to the method. The moving direction of the wafer W and the direction of integration by the TDI sensor 75 are the same direction. The amount of secondary charged particles is integrated by one stage each time a transfer clock is input to the TDI sensor 75. In other words, the electric charge accumulated in one pixel of the TDI sensor 75 is transferred to an adjacent pixel in the Y direction every time a transfer clock is input. Then, the detection amount integrated by the number of stages in the Y direction, that is, the detection amount integrated up to the final stage (also referred to as an integrated detection amount) is transferred to the image processing device 80 every time a transfer clock is input. . The integration direction of the TDI sensor 75 is not limited to the Y direction, and may be the X direction. In this case, the wafer W is moved in the X direction.

  FIG. 4 schematically shows how the TDI sensor 75 integrates the amount of secondary charged particles. Since the configuration of the TDI sensor is known, only the manner in which the amount of secondary charged particles is integrated will be described here. Here, for convenience of explanation, the TDI sensor 75 has five pixels arranged in the first direction D1 (the above-mentioned X direction) and is not arranged in the second direction D2 (the above-mentioned Y direction). Will be described. In FIG. 4, P1 to P5 indicate the respective image sensors (pixels) arranged in the first direction D1. In the illustrated example, the wafer W moves in the direction from the pixels P1 to P5 when detected by the TDI sensor 75. In FIG. 4, T11 to T15 indicate times (periods) actually required for the wafer W to move by one pixel. For example, the time T11 is a time required for moving the distance corresponding to the pixel P1, and the time T12 is a time required for moving the distance corresponding to the pixel P2.

  As shown in FIG. 4, in the detection by the TDI sensor 75, first, the charge Q1 corresponding to the amount of the sensed secondary charged particles is accumulated in the pixel P1 during the time T11. This charge Q1 is transferred to the pixel P2 adjacent to the pixel P1 according to the transfer clock input to the TDI sensor 75 at the timing immediately after the elapse of time T11. During time T12 following time T11, the charge P2 is accumulated in the pixel P2 in addition to the charge Q1 transferred from the pixel P1. As a result, when the time T12 has elapsed, the charge Q1 + Q2 is accumulated in the pixel P2. This charge Q1 + Q2 is transferred to the pixel P3 at a timing immediately after the elapse of time T12. During time T13 following time T12, the charge P3 is accumulated in the pixel P3 in addition to the charge Q1 + Q2 transferred from the pixel P2. As a result, when the time T13 has elapsed, charges Q1 + Q2 + Q3 are accumulated in the pixel P3. In this way, the charges are sequentially accumulated, so that the charges Q1 + Q2 + Q3 + Q4 + Q5 are accumulated in the pixel P5 and transferred to the image processing device 80 after the time T11 to T15 has elapsed. In this way, the amount of secondary charged particles obtained from the same position on the wafer W is integrated, so that even when the wafer W is moved at high speed along the first direction D1, it is sufficient as a whole. Exposure time is ensured, and highly sensitive imaging data is obtained. In this embodiment, the transfer clock is input to the TDI sensor 75 every time the holder 55 (wafer W) moves by a distance corresponding to one pixel of the TDI sensor 75. However, the input timing of the transfer clock is not particularly limited, and may be input at regular intervals, for example.

The luminance data obtained in this manner suitably reflects, for example, the presence or absence of foreign matter on the wafer W. This is because the above-described mirror electrons do not scatter, whereas secondary emission electrons scatter. Therefore, the amount of secondary charged particles obtained from the region where the foreign matter exists on the wafer W is in other regions. This is because it is much larger than the amount of secondary charged particles obtained from the above. That is, an area where a foreign object exists is imaged as an area having a higher luminance than an area where no foreign object exists. However, when the emission current of the electron beam emitted from the electron source 90 varies, the amount of secondary charged particles also varies. Therefore, the luminance data obtained by the TDI sensor 75 includes luminance unevenness that does not depend on the presence or absence of foreign matter. Will occur.

  The inspection apparatus 5 of the present embodiment has two configurations that can suppress the occurrence of such luminance unevenness. One is a configuration for performing feedback control of the emission current value, and the other is a configuration for performing correction processing. In the present embodiment, the correction process is a process of correcting the luminance value for the imaging result of the TDI sensor 75 based on the emission current value detected by the emission ammeter 96. This correction process is performed by the correction unit 81 of the image processing apparatus 80. The integrated detection amount whose luminance has been corrected by the correction unit 81 is output to the image data generation unit 82. The image data generation unit 82 combines the integrated detection values received from the correction unit 81 and generates image data composed of pixel values (luminance values) arranged in the X direction and the Y direction. Note that the order of the correction process and the image data generation process may be reversed. That is, the image data generation unit 82 may combine the data transferred from the TDI sensor 75 to generate image data, and then the correction unit 81 may perform correction processing on the generated image data. It is also possible to omit the feedback control and perform only the correction process. Hereinafter, feedback control and correction processing will be described.

  FIG. 5 shows a schematic configuration of an electron source 90 for performing feedback control. The electron source 90 includes a Wehnelt 91, a filament 92, and a power supply device 93. The power supply device 93 includes an acceleration power supply 94, a Wehnelt power supply 95, a heat current source 97, a filament ammeter 98, an emission ammeter 96, and a feedback control unit 99. The filament 92 is heated by applying a current from the heat current source 97, and as a result, thermoelectrons are easily emitted from the filament 92. The filament ammeter 98 measures the amount of current actually flowing through the filament 92. The thermoelectrons are emitted as an electron beam by being accelerated by the voltage of the acceleration power supply 94, and the amount of emitted electrons is controlled by the voltage applied to the Wehnelt 91.

  The amount of electrons emitted from the filament 92 (emission current value) is detected by an emission ammeter 96. The current value detected by the emission ammeter 96 is input to the feedback control unit 99. The feedback control unit 99 operates the Wehnelt power supply 95 based on the input emission current value, and controls the voltage value applied to the Wehnelt 91 so that the emission current value is maintained at the target value. I do.

In this embodiment, the correction process is performed by the following equation (1). IV0 is an integrated detection amount before the correction process, and IV1 is an integrated detection amount after the correction process. K is a correction coefficient, and is calculated by the following equation (2). A0 is a target value for the emission current value. An (n is an integer of 1 or more) is an emission current value detected by the emission ammeter 96 (hereinafter also referred to as an actual emission current value).
IV1 = K × IV0 (1)
K = A0 / An (2)

  The target value A0 is set by the user so that the inspection image has a desired luminance, and may be stored in advance in the image processing apparatus 80, or may be set by the user adjusting the luminance at the time of inspection. May be. In the present embodiment, the actual emission current value An is the characteristic amount of the emission current value detected by the emission ammeter 96 during the period Tn in which the TDI sensor 75 accumulates the amount of secondary charged particles by the number of stages in the Y direction ( Here, it is a simple average value).

  As is clear from the above equations (1) and (2), in the correction process, when the actual emission current value An is smaller than the target value A0, the imaging result of the TDI sensor 75 is the luminance value of the imaging result. Is corrected so as to increase. On the other hand, when the actual emission current value An is larger than the target value A0, the imaging result of the TDI sensor 75 is corrected so that the luminance value of the imaging result becomes small. In this embodiment, assuming that the emission current and the amount of secondary charged particles are in a directly proportional relationship, the correction coefficient K is set as shown in the above equation (2). With such a configuration, on the premise of the direct proportional relationship, the influence of the fluctuation of the emission current value on the imaging result can be completely eliminated as the average value in the period Tn.

  FIG. 6 shows a specific example of the correction process for the imaging result of the TDI sensor 75. In this example, image data is first generated and then correction processing is performed. FIG. 6A shows a pixel arrangement of image data before correction processing. The pixel group with Y = 1 is a pixel group that is first transferred to the image processing apparatus 80 by the TDI sensor 75. The Y = 2 pixel group is a pixel group transferred next to the Y = 1 pixel group. That is, the arrangement of numbers in the Y direction represents the order of transfer from the TDI sensor 75. FIG. 6B shows the actual emission current value An for each period Tn (in this example, n = 1 to 8) along the X direction. For example, the actual emission current value A1 is an average value of the emission current in the period T1 (for example, corresponding to the times T11 to T15 shown in FIG. 4). FIG. 6C shows the pixel value of each pixel of the image data generated by combining the integrated detection values. That is, FIG. 6C shows the integrated detection amount IV0 before the correction process. Here, the integrated detection amount IV0 (pixel value) before correction processing is a luminance value of 256 gradations. FIG. 6D shows a correction coefficient K applied to each Y = n pixel group. FIG. 6E shows the post-correction processing calculated by the equation (2) based on the pre-correction integrated detection amount IV0 shown in FIG. 6C and the correction coefficient K shown in FIG. 6D. This is the integrated detection amount IV1.

  An example of a configuration for realizing such correction processing is shown in FIG. The example shown in the figure is a configuration when image data is generated after correction processing. As illustrated, the correction unit 81 includes an average calculation unit 83, a division unit 84, and a multiplication unit 85. When a movement command is given from the control device 89 to the stage device 50 (servo motor 56), the Y table 52 is moved in the Y direction. The amount of movement of the Y table 52 is detected by the position sensor 58. Then, the position information detected by the position sensor 58 is input to the TDI clock generator 74. The TDI clock generator 74 inputs a TDI clock (transfer clock) to the TDI sensor 75 every time the Y table 52 moves one pixel in the Y direction based on the received position information. The TDI sensor 75 accumulates charges according to the TDI clock, and transfers the accumulated charges up to the final stage to a built-in A / D converter (not shown). The pre-correction integration detection amount IV0 converted into a digital value by the A / D conversion unit is input to the multiplication unit 85. Further, every time the amount (charge) of the secondary charged particles is transferred, the TDI sensor 75 inputs a transfer signal indicating that the transfer has been performed to the average calculation unit 83.

  On the other hand, in the correction unit 81, the average calculation unit 83 calculates the actual emission current value An using the emission current value output from the emission ammeter 96 via a sampling circuit (not shown). Specifically, the average calculation unit 83 calculates the average value of the emission current values input during the time required to receive the transfer signal for the most recent predetermined number of times (in the example of FIG. 4, 5 times). To do. The calculated average value, that is, the actual emission current value An is input to the division unit 84. The division unit 84 calculates the correction coefficient K using the above equation (2) based on the target value A0 input from the control device 89 and the actual emission current value An input from the average calculation unit 83. To do. The calculated correction coefficient K is input to the multiplication unit 85, and the correction process in the multiplication unit 85, that is, the calculation according to the above equation (1) is performed. The calculation result of the multiplication unit 85, that is, the post-correction integrated detection amount IV1 is input to the image data generation unit 82.

  Although illustration is omitted, the image data generation unit 82 combines the data transferred from the TDI sensor 75 to generate image data, and then the correction unit 81 performs a correction process on the generated image data. In this case, the correction unit 81 can perform correction processing as follows, for example. First, as in FIG. 7, the correction unit 81 sequentially calculates the actual emission current value An, or sequentially calculates the correction coefficient K, and stores each actual emission current value An or the correction coefficient K in the buffer. deep. Next, the correction unit 81 sequentially extracts data groups received in one transfer from the TDI sensor 75 from the image data generated by the image data generation unit 82 in the order received. Then, correction processing is performed on the extracted data group.

  According to the inspection apparatus 5 described above, since the correction processing for correcting the imaging result of the TDI sensor 75 or the image data is performed based on the actual emission current value An, the emission current value of the electron source 90 varies. Even so, it is possible to suppress the occurrence of luminance unevenness in the image data due to fluctuations in the emission current. In addition, since the correction process is performed based on the target value A0, the luminance value of the generated image data can be brought close to a desired level. More specifically, according to the inspection apparatus 5, the correction unit 81 performs correction to increase the luminance value represented by the imaging result or the image data when the actual emission current value An is smaller than the target value A0. Therefore, when the emission current value fluctuates to a side smaller than the target value A0, it is possible to suppress the occurrence of luminance unevenness in the image data due to the fluctuation. Further, according to the inspection apparatus 5, the correction unit 81 performs correction to reduce the luminance value represented by the imaging result or the image data when the actual emission current value An is larger than the target value A0. Therefore, when the emission current value fluctuates to the side larger than the target value A0, it is possible to suppress the occurrence of luminance unevenness in the image data due to the fluctuation. It is desirable that both the control in the case of An> A0 and the control in the case of An <A0 are performed, but only one of them may be performed. For example, when the characteristics of the electro-optical device 70 are biased toward any one of An> A0 and An <A0, only one control may be performed.

  Furthermore, according to the inspection apparatus 5, feedback control is performed based on the detected emission current value so that fluctuations in the emission current value are suppressed, and correction processing is performed based on the emission current value subjected to feedback control. . Therefore, combined with the feedback control and the correction process, it is possible to further suppress the occurrence of luminance unevenness that cannot be completely eliminated by the feedback control.

B. Variation:
B-1. Modification 1:
The actual emission current value An is a feature amount (for example, an average value) of the emission current value detected by the emission ammeter 96 in a period shorter than the period Tn in which the TDI sensor 75 accumulates the amount of secondary charged particles by the number of stages in the Y direction. Value). For example, when the number of stages in the Y direction of the TDI sensor 75 is 2048, the actual emission current value An may be an average value of emission current values during a period in which the amount of secondary charged particles is accumulated by 2000 stages. According to such a configuration, it is possible to increase the generation speed of the image data without greatly affecting the accuracy of the correction process.

B-2. Modification 2:
The imaging means for detecting the amount of secondary charged particles is not limited to the TDI sensor 75, but may be any imaging means such as EB (Electron Bombardment) -CCD, I (Intensified) -CCD, or the like.

B-3. Modification 3:
The correction formula used for the correction process is not limited to the above example. For example, the correction coefficient K may be an arbitrary function having the actual emission current value An and the target value A0 as variables. In this case, the function may be set by experimentally grasping the correlation between the emission current value and the amount of secondary charged particles. Of course, the correction process is not necessarily performed using the target value A0, and the actual emission current value is reduced so that the influence on the image data due to the fluctuation of the emission current value, that is, the fluctuation of the luminance value is alleviated. It may be performed based only on An. For example, the average value Aav of the current value is calculated from each emission current value detected in the process of detecting secondary charged particles for each pixel of the image data (or for each pixel data in the imaging result). The correction coefficient K may be calculated by the following equation (3). Even in such a configuration, fluctuations in the emission current value are equalized, so that occurrence of luminance unevenness in the image data can be suppressed.
K = Aav / An (3)

  The embodiments of the present invention have been described above based on some examples. However, the above-described embodiments of the present invention are for facilitating the understanding of the present invention and limit the present invention. It is not a thing. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes the equivalents thereof. In addition, any combination or omission of each constituent element described in the claims and the specification is possible within a range where at least a part of the above-described problems can be solved or a range where at least a part of the effect is achieved. It is.

DESCRIPTION OF SYMBOLS 5 ... Inspection apparatus 10 ... Cassette holder 20 ... Mini-environment device 21 ... Mini-environment space 22 ... Housing 23 ... Gas circulation device 24 ... Discharge device 25 ... Pre-aligner 27 ... Shutter device 30 ... Main housing 40 ... Loader housing 41 ... Wafer Rack 50 ... Stage device 51 ... Fixed table 52 ... Y table 53 ... X table 54 ... Rotary table 55 ... Holder 56, 57 ... Servo motor 58 ... Position sensor 61,62 ... Transport unit 64 ... Aligner 70 ... Electro-optical device 72 ... Primary optical system 72a, 72d, 72f, 72h, 72i ... Lens 72b, 72c, 72g ... Aperture 72e ... ExB filter 73 ... Secondary optical system 73a, 73c ... Lens 73b ... NA aperture 73d ... Aligner 75 ... TDI sensor 80 ... Image processing device 81 ... correction unit 82 ... image data generation unit 83 ... average calculation unit 84 ... division unit 85 ... multiplication unit 89 ... control unit 90 ... electron source 91 ... Wenert 92 ... filament 93 ... power supply device 94 ... acceleration power supply 95 ... Wehnelt power supply 96 ... Emission ammeter 97 ... Heat current source 98 ... Filament ammeter 99 ... Feedback control unit W ... Wafer C ... Cassette

Claims (8)

An inspection device,
A primary optical system having an electron source for irradiating charged particles as a beam;
A current detector for detecting an emission current value of the beam irradiated from the electron source;
An imaging unit having an imaging element for detecting the amount of secondary charged particles obtained by irradiating the inspection target of the beam;
An image data generation unit that generates image data based on an imaging result of the imaging unit;
An inspection apparatus comprising: a correction unit that corrects the imaging result or the image data based on the detected emission current value. The inspection apparatus according to claim 1,
The said correction | amendment part is an inspection apparatus which performs the said correction | amendment based on the target value predetermined about the said emission current value, and the said detected emission current value. The inspection apparatus according to claim 2,
The said correction | amendment part correct | amends which enlarges the luminance value which the said imaging result or the said image data represents, when the detected emission electric current value is smaller than the said target value. The inspection apparatus according to claim 2 or 3, wherein
The said correction | amendment part performs the correction | amendment which makes small the luminance value which the said imaging result or the said image data represents, when the detected emission electric current value is larger than the said target value. The inspection apparatus according to any one of claims 1 to 4, wherein
Furthermore, an inspection apparatus comprising a feedback control unit that performs feedback control based on the detected emission current value so that fluctuations in the emission current value are suppressed. An inspection apparatus according to any one of claims 1 to 5,
And a moving unit capable of holding the inspection object, the moving unit moving the inspection object in a predetermined direction on the irradiation position of the beam by the primary optical system,
The imaging unit is a TDI sensor in which the imaging element is arranged in a predetermined number of stages in the predetermined direction, and the irradiation of the beam to the inspection object performed while moving the moving unit in the predetermined direction An inspection apparatus comprising: a TDI sensor that integrates the amount of the secondary charged particles obtained by the step along the predetermined direction by a time delay integration method. The inspection apparatus according to claim 6,
The correction unit is based on an average value of the emission current value detected by the current detection unit during an integration period in which the TDI sensor integrates the amount of the secondary charged particles by the predetermined number of stages. An inspection apparatus that corrects the imaging result or the image data corresponding to the amount of the secondary charged particles accumulated during the accumulation period. A method for generating image data for inspection,
Irradiating a charged particle as a beam from an electron source to an inspection object;
Detecting an emission current value of the beam emitted from the electron source;
Detecting the amount of secondary charged particles obtained by irradiating the inspection target of the beam;
Generating image data based on the detection result of the amount of the secondary charged particles;
A method of generating inspection image data, comprising: correcting the amount of secondary charged particles or correcting the image data based on the detected emission current value.

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