JP2012198239A - Inspection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce an inter-machine difference in inspection sensitivity among plural inspection devices (machines) by correcting a detection image signal from the inspection system.SOLUTION: In an inspection device processing a synthesized image to inspect a defect or a foreign material on the surface of an inspection object 001 by including: a light source for irradiating the inspection object 001 with a light flux; an optical system 100 for guiding reflected diffusion light reflected by the inspection object; a photoelectric image sensor 400 having plural photoelectric cells arrayed for converting the guided diffusion light into an electric detection signal; a detection signal transmission part composed of, for each of plural regions produced by dividing the photoelectric image sensor, a signal correction part, an A/D converter and an image generation part, all aforementioned three parts corresponding to each of the regions; an image synthesis part for generating an image produced by synthesizing partial images output from the detection signal transmission part, the detection signal transmission part has a detection signal correction function capable of correcting a detection signal from a photoelectric cell so as to be close to a reference target value of reference detection signal strength determined for each channel.

Description

  The present invention relates to an inspection apparatus and an inspection method for inspecting a defect image to be inspected in which an image formed on a wafer, a liquid crystal panel, a mask, or the like exists and an attached foreign matter.

  For example, in a semiconductor manufacturing process, a defect such as an insulation failure or a short circuit occurs due to a foreign substance existing on a semiconductor substrate or a pattern defect generated in the manufacturing process, thereby reducing the yield. Further, with the miniaturization of semiconductor elements, a smaller foreign matter or defect becomes fatal, so that a finer defect detection is required.

  For example, in a semiconductor production line, the defect and foreign matter are discovered early using a semiconductor inspection apparatus, the cause of the defect is identified, and feedback to the production process is performed to improve the yield.

  However, even the same type of inspection apparatus does not necessarily have the same inspection sensitivity, and even when the same inspection object is inspected, there may be a difference in the number of detected defects or defect types.

It is important to adjust the inspection sensitivity and maintain consistency in order to reduce the difference in inspection sensitivity (machine difference) between the airframes of such inspection devices (airframes). Due to characteristic variations, it is difficult to match the inspection sensitivities of the inspection apparatuses (machines). For this reason, there is a need for a correction method for reducing this.

  Conventionally, as described in Japanese Patent Application Laid-Open No. 2005-201782 (Patent Document 1), such a technique reduces noise caused by a detection system by combining a plurality of sensors and correcting a signal. Is disclosed.

  Further, in Japanese Patent Laid-Open No. 2003-346698 (Patent Document 2), a plurality of detectors are used in an electron beam apparatus, and gain and offset are individually corrected for each, thereby making the electron beam irradiation non-uniform. A method for correcting the effects of gender and time variations is disclosed.

  In Japanese Patent Laid-Open No. 2003-346698 (Patent Document 2), a two-dimensional sensor is divided into a plurality of regions, and the output signal is digitally corrected for each region, thereby correcting the nonuniformity of the signal intensity in the field of view. A method is disclosed.

  Japanese Laid-Open Patent Publication No. 4-362790 (Patent Document 3) discloses a method of correcting a light amount variation due to exposure time in a scan type sensor.

  Alternatively, as disclosed in Japanese Patent Application Laid-Open No. 2006-250739 (Patent Document 4), an example of performing illumination light correction by performing aberration correction by changing a reflecting surface shape in an illumination optical system is also disclosed.

Japanese Patent Application Laid-Open No. 2005-201782 JP 2003-346698 A JP-A-4-362790 JP 2006-250739 A

  However, in the prior art, although the inspection sensitivity or the image generation sensitivity can be adjusted by equalizing the individual detection signal level of each inspection apparatus (machine), the inspection sensitivity between the inspection apparatuses (machines) can be adjusted. No consideration has been given to maintaining consistency.

  Further, when a light source having a planar illumination distribution is used in the inspection visual field, the noise level is increased by forcibly increasing the detection signals of the inspection areas having different illumination intensities. Therefore, there is a problem that it cannot always be said that the inspection sensitivity is improved.

  An object of the present invention is to reduce an inspection device (machine) difference in an output signal from a photoelectric image sensor due to variations in optical characteristics of each inspection device (machine), and to maintain inspection sensitivity consistency and a method thereof. Is to provide.

  An object of the present invention is to correct a detection signal from a detection system, thereby performing a plurality of inspections due to variations in characteristics of components such as an illumination system having a light source, an optical system for guiding reflected scattered light, and a detection system having a photoelectric image sensor. The object is to reduce the difference in inspection sensitivity between devices (airframes).

  In the present invention, a light source for irradiating a light beam to an object to be inspected, an optical system that guides reflected / scattered light reflected from the object to be inspected, and a plurality of photoelectric cells that convert the reflected / scattered light thus guided into an electric detection signal are arranged. A photoelectric image sensor, and a plurality of regions obtained by dividing the photoelectric image sensor, a detection signal transmission unit having a channel constituted by a corresponding signal correction unit, an A / D converter, and an image generation unit, An image compositing unit that synthesizes partial images output by the detection signal transmission unit to create an image of the surface to be inspected, and inspects for defects or foreign matter on the surface to be inspected by processing the combined image In the inspection apparatus, the detection signal transmission unit is a detection signal corrector capable of correcting the detection signal from the photoelectric cell so as to approach the reference target value of the reference detection signal intensity determined for each channel. Characterized in that it has a.

  Further, the detection system of the photoelectric image sensor includes light receiving elements (photoelectric cells) arranged one-dimensionally or two-dimensionally, and each channel (detection signal transmission unit) that transmits a detection signal for each photoelectric cell.

  The detection signal transmission unit having the plurality of channels is configured to be able to correct the detection signal individually for each channel.

  In addition, the apparatus includes an external input means for sharing a correction target value (correction coefficient) serving as a correction target of the detection signal among a plurality of airframes.

  According to the present invention, the detection signal from each photoelectric cell can be corrected so as to be close to the reference target value of the reference detection signal intensity determined for each channel. The difference in inspection sensitivity can be reduced, and equivalent inspection sensitivity can be realized among a plurality of inspection apparatuses (machines). In addition, it is possible to easily correct a change in the detection signal due to a change with time of the light source or the element, thereby realizing a stable inspection.

FIG. 1 relates to an embodiment of the present invention and is a diagram showing a schematic configuration of an inspection apparatus. FIG. 2 is a plan view of the illumination optical system 100 according to the embodiment of the present invention. FIG. 3 relates to an embodiment of the present invention, and is a schematic diagram from the detection system 400 to the image processing system 500. FIG. 4 relates to an embodiment of the present invention, and is a flowchart of a correction coefficient calculation method. FIG. 5 relates to an embodiment of the present invention, and shows a target value management method.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  The outline | summary of the inspection apparatus which investigates the defect based on the Example of this invention is demonstrated along FIG.

  The inspection apparatus for examining defects includes a stage 300 for mounting an inspection target 001, a laser light source 101, a beam shaping unit 102, a plurality of irradiation units 120, 121, 122 branched by an optical path branching and switching optical system. The illumination optical system 100 is provided.

  The illumination optical system 100 irradiates the light beam of the light source (laser light source 101) onto the object to be inspected.

  The inspection apparatus for examining defects includes a condensing optical system 200 including an objective lens 201, a zoom lens group 202, and an imaging lens 203.

  By this condensing optical system 200, reflected / scattered light reflected from the object to be inspected is guided to a detection system described later.

  Further, the inspection apparatus for examining the defect has a light receiving element arranged one-dimensionally or two-dimensionally, has a light receiving surface 401 divided into a plurality of regions, and transmits a detection signal from the detection system for each region. And a channel group 501 for processing and an image processing system 500 for processing a detection signal from the detection system 400 and performing defect determination.

  The channel group 501 serves as a detection signal transmission unit, and has a correction function for correcting the intensity of the detection signal as described later.

  FIG. 2 is a plan view of the illumination optical system 100 for irradiating illumination light from three directions toward the inspection object.

  A laser beam emitted from the laser light source 101 is branched into two optical paths by a branching optical element 110 such as a half mirror, and one of them is reflected by mirrors 111 and 112 and is made incident downward to the beam shaping unit 102 by a mirror 113. Illumination light from 11 directions can be obtained, and the other proceeds to the branching optical element 114 such as a half mirror.

  One of the branched optical elements 114 is reflected by the mirror 115 and incident downward on the beam shaping unit 102 by the mirror 117, so that an illumination beam from 10 directions can be obtained, and the other is a mirror. Illumination light from 12 directions can be obtained by entering the beam shaping unit 102 downward at 116.

  By the way, when illuminating only from 11 directions, it can implement | achieve by switching from the branch optical element 110 to the mirror element 118. FIG.

  Further, in the case of illuminating only from the directions 10 and 12, it can be realized by exiting the branching optical element 110 from the optical path or switching to a normal optical element.

  Further, for example, in the illumination from 10 and 12 directions, for example, illumination from only 12 directions can be realized by switching from the branch optical element 114 to the mirror element 119.

  FIG. 3 is a schematic diagram showing the flow of detection signals from the detection system 400 to the processing system 500.

  The light receiving surface 401 is composed of light receiving elements arranged one-dimensionally or two-dimensionally, and is divided into regions 4011 to 4018.

  The intensity distribution 412 of the detection signal in each of the regions 4011 to 4018 on the light receiving surface 401 does not have the same shape in a plurality of apparatuses due to variations in components such as the illumination system 100 and the condensing optical system 200.

  By correcting the detection signal intensity 412 for each region by signal correction 5021 to 5028 individually provided for each channel, the corrected detection signal intensity distribution 512 can be obtained in an arbitrary shape. .

  Here, the correction units 5021 to 5028 are configured as simple proportional gains.

  The correction coefficient storage unit 505 stores different correction coefficients for each optical condition, and sets the correction coefficients in the correction units 5021 to 5028 according to the optical conditions. As a result, it is possible to perform correction in consideration of changes in optical characteristics when the illumination direction, magnification, and the like are changed.

  The corrected detection signals are digitized by A / D converters 5031 to 5038, imaged by image generation units 5061 to 5068, and the images are combined by an image synthesis unit 507 and transmitted to the image processing unit 504. .

  The image processing unit 504 performs a comparison process on the images arranged in the scan direction and inspects an image defect or attached dust to be inspected.

  The correction by the correction unit is determined by the correction coefficient shown in FIG. This correction coefficient will be further described.

  The detection signal of the photoelectric image sensor has an output intensity distribution 412 as shown in FIG. This output intensity distribution 412 is corrected to a corrected intensity distribution 512 (a quadratic distribution having a maximum at the center and a minimum at both ends in the arrangement direction of the eight photoelectric cells). The

  The target value storage unit 550 receives the reference target value of the reference detection signal intensity by the external input unit 530.

  The reference target value of the reference detection signal intensity corresponds to the array of eight photoelectric cells (channels CH1 to 8) and the optical conditions (A, B, C, D), and in column A, QA (1) to QA The reference target value of (8) is assigned. In the other conditions B to D, the reference target value is similarly assigned.

  The reference target value of the reference detection signal intensity has a quadratic distribution having a maximum at the center and a minimum at both ends in the arrangement direction of the eight photoelectric cells.

  The correction coefficient calculation unit 520 calculates a correction coefficient. The calculated correction coefficient is stored in the correction coefficient storage unit 505. The correction correction coefficient storage unit 505 corresponds to an array of eight photoelectric cells (channels CH1 to CH8) and optical conditions (A, B, C, and D), and CA (1) to CA (8) in the A column. Assigned. In other conditions B to D, correction coefficients are assigned in the same manner.

  FIG. 4 is a flowchart showing a correction method according to the embodiment of the present invention. It is a flowchart which shows the correction | amendment method for maintaining the consistency of the inspection sensitivity for every body of an inspection apparatus. The correction coefficient is determined according to the flow shown in FIG. 4 for each optical condition.

  First, a case where correction is performed for condition A will be described. In step S1 (test wafer inspection procedure 1), a reference inspection target (in this case, a test wafer) 001 is inspected, and the output intensity for each channel of the detected image signal is acquired.

  In this case, what is used is a bare wafer in which PSL (Poly Styrene Latex) standard particles are partially or entirely coated. Alternatively, it may be a wafer having a uniform reflectivity over the entire surface.

  At this time, scattered light from the test wafer 001 is received for each region, and the sum of the output for each pixel is set as the intensity of the detection signal in the region. Alternatively, the intensity of the detection signal may be the sum of the luminance within the search range of each area of the image acquired by inspection.

  The intensity of the detection signal thus obtained is PA1 [i] (i: sensor area number).

  At this time, the correction unit 502 does not correct the detection signal, and transmits the detection signal signal itself from the detection system 400 to the image processing unit 504.

  In step S1 (test wafer inspection procedure 1), the target detection signal intensity QA [i] corresponding to each set optical condition is acquired from the correction coefficient storage unit 505, and step S1 (test wafer inspection). The correction coefficient calculation unit 520 calculates a correction function such that the intensity PA1 [i] of the detection signal acquired in procedure 1) matches the target intensity QA [i] of the detection signal.

  Here, a simple proportionality is used as the correction function. That is, CA [i] = PA1 [i] / QA [i] with CA [i] as a coefficient. The calculated CA [i] is stored in the correction coefficient storage unit 505.

  In step S3 (test wafer inspection procedure 2), the correction coefficient CA [i] of the corresponding optical condition (here optical condition A) is called from the correction coefficient storage section 505 and set in the correction sections of the correction sections 5021 to 5028. To do.

  In this state, the test wafer 001 is inspected to acquire the intensity of the detection signal. The corrected intensity PA2 [i] of the detection signal is compared with the target value QA [i], and if the difference in the intensity of the detected image signal of each channel is within an allowable range, the correction ends.

  If there is a difference greater than the allowable value, the process proceeds to step S4 (optical system readjustment procedure), and optical system readjustment such as parameter review under the optical conditions is performed. Then, it returns to S1 again and follows a series of flows.

  In S2, T1 is a target match determination branch.

  FIG. 5 is a diagram illustrating some examples of correction target values when the inspection sensitivity of the inspection apparatus is corrected.

  The intensity QA [i] of the detection signal on the output side that is the target of the intensity of the detection signal of each channel may be an arbitrary function in consideration of the illumination intensity distribution by the illumination optical system or the detection optical system.

  For example, when a laser is used as the light source, the influence of the intensity distribution and the aberration of the lens of the illumination optical system is considered comprehensively, and a quadratic function QA [i] = a (ic) 2 + b () having a maximum value at the center. a, b, and c may be real numbers) or a normal distribution.

  Alternatively, a master is selected from a plurality, and (when correction is performed under the optical condition A), MA [i] of the detection signal on the actual output side becomes the target detection signal intensity B [i]. It is good. Alternatively, NA [i] obtained by approximating the output-side detection signal MA [i] with an arbitrary function may be used.

  FIG. 5 shows a means for sharing the target detection signal strength value QA [i] among a plurality of aircraft. For example, the target detection signal intensity QA [i] may be individually acquired by an external input unit 530 provided in each inspection apparatus 601 as shown in FIG.

  Alternatively, as shown in FIG. 5B, a plurality of inspection apparatuses are connected to the upper management apparatus 611, the target detection signal intensity B [i] is stored in the upper management apparatus 611, and the correction coefficient calculation is performed. Sometimes it may be transferred to a separate inspection device.

  Alternatively, the upper management apparatus 611 includes a correction coefficient calculation unit 530 and a correction target value storage unit 505. When calculating the correction coefficient, the detection signals PA1 [i] and PA2 [i] on the output side of the individual inspection apparatus 601 are used. , And the correction coefficient calculation may be performed inside the upper management apparatus 611, and the calculated correction coefficient may be transferred to the individual inspection apparatus 601 and stored in the correction coefficient storage unit 505.

  The upper management apparatus may be arranged in the same factory as shown in FIG. 1, or may be arranged at a remote place connected through a network such as the Internet. There may be a plurality of upper management devices or only one.

  The correction target value QA [i] may be just one type, or may be a uniform target value set in different production sites and unified within the same field or within a certain range.

  Alternatively, as shown in FIG. 5C, the correction target value QA [i] is the intensity of the detection signal when the master machine 621 is set from among a plurality of machine bodies and the inspection object serving as the reference is inspected. It is good.

  The master machine 621 may be connected through a network such as the Internet as shown in FIG.

  DESCRIPTION OF SYMBOLS 001 ... Inspection object, 100 ... Illumination optical system, 101 ... Laser light source, 102 ... Beam shaping unit, 120 to 122 ... Irradiation unit, 10 to 12 ... Irradiation direction, 110 ... Branching optical element, 111 to 113 ... Mirror, 114 ... Branch optical element, 115 to 119 ... mirror, 200 ... condensing optical system, 201 ... objective lens, 202 ... zoom lens group, 203 ... imaging lens, 300 ... stage, 400 ... detection system, 401 ... light receiving surface, 500 ... Image processing system, 501 ... channel group, 5011 to 5018 ... channel, 502 ... correction system, 5021 to 5028 ... correction unit, 5031 to 5038 ... A / D conversion unit, 504 ... image processing unit, 505 ... correction coefficient storage unit, 5061 to 5068: image generation unit, 512: intensity distribution of detection signal after correction, 520: correction coefficient calculation unit, 530: external input S1, test wafer inspection procedure 1, S2 ... correction coefficient calculation procedure, S3 ... test wafer inspection procedure 2, S4 ... optical system readjustment procedure, T1 ... target coincidence determination branch, 601 ... individual inspection device, 611 ... host Management device, 621... Master machine, 631... Network (Internet, etc.).

Claims (5)

A light source of luminous flux irradiated obliquely from a plurality of directions toward the object to be inspected;
An optical system for guiding reflected and scattered light reflected from the object to be inspected by irradiation of the light flux;
A photoelectric image sensor in which a plurality of photoelectric cells for converting the guided reflected scattered light into electrical detection signals are arranged;
A detection signal transmission unit having a channel composed of a signal correction unit, an A / D converter, and an image generation unit corresponding to each of a plurality of regions obtained by dividing the photoelectric image sensor,
An image compositing unit that synthesizes partial images output by the detection signal transmission unit to create an image of the surface to be inspected, and inspects for defects or foreign matter on the surface to be inspected by processing the combined image In the inspection device that performs
The detection signal transmission unit uses a correction coefficient set for each of the plurality of directions (illumination directions) to set a detection signal from the photoelectric cell to a reference target value of a reference detection signal intensity determined for each channel. An inspection apparatus having a detection signal correction function capable of correcting so as to approach each other. The inspection apparatus according to claim 1,
An inspection apparatus comprising external input means for obtaining a reference target value of the reference detection signal intensity from outside. The inspection apparatus according to claim 2,
The photoelectric image sensor is an inspection apparatus in which the photoelectric cells are arranged one-dimensionally or two-dimensionally on coordinates. The inspection apparatus according to claim 2,
A correction coefficient calculation unit for calculating a correction coefficient for correcting the intensity of a detection signal obtained from a reference inspection target inspection and the reference detection signal intensity to approach the reference target value;
A correction coefficient storage unit for storing the correction coefficient,
The inspection apparatus according to claim 1, wherein a correction coefficient of the correction coefficient storage unit is provided to the detection signal correction function. The inspection apparatus according to claim 4, wherein
The correction coefficient calculation unit calculates the correction coefficient for each channel,
An inspection apparatus, wherein a correction coefficient for each channel is stored in a correction coefficient storage unit.

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