JP2015087114A - Inspection equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide inspection equipment and an inspection method capable of accurately and quickly determining in a defect resulting from a foreign matter and a defect resulting from a shading film, while eliminating problems such as lowering of a yield or delay of a delivery date.SOLUTION: Inspection equipment 19 for detecting a defect of a photo mask includes: inspection means 1 based on an optical system using light to be always conducted; and inspection means 9 based on an optical system using an electron beam to be conducted when the inspection means 1 detects a defect. The inspection equipment 19 further includes: means for automatically switching the inspection means based on an optical system using light and the inspection means based on an optical system using an electron beam; and means for transmitting the coordinates of the defect detected by the inspection means based on an optical system using light to the inspection means based on an optical system using an electron beam.

Description

  The present invention relates to an inspection apparatus and an inspection method for detecting a defect on a photomask having a pattern formed by a light shielding film and determining the type of the detected defect.

  In a lithography process for manufacturing a semiconductor integrated circuit, an autofocus mechanism or the like is used to position an original image such as a circuit pattern on a wafer, and the same pattern is sequentially printed while being reduced and projected. At this time, if foreign matter or defects are present on the glass substrate of the photomask which is the pattern original, they may be transferred onto the wafer, causing a short circuit failure or the like of the circuit.

  In the photomask manufacturing process, after forming a pattern such as wiring by etching a light shielding film of a metal such as chromium (Cr) on the pattern formation surface of the glass substrate, the presence or absence of defects occurring on the pattern formation surface Is determined by the inspection device. In this inspection, pattern determination is performed by projecting laser light onto a photomask and detecting transmitted light and reflected light.

  When a defect is detected, removal of the defect is attempted by cleaning or correction. The correction method differs depending on the type of defect, and when a defect derived from a foreign substance is detected, the defect is removed by re-cleaning the mask or irradiating laser light. When a defect derived from the light shielding film is detected, the defect is removed by irradiation with FIB (Focused Ion Beam) or excavation using an AFM (Atomic Force Microscope) probe.

  However, in recent years, it is difficult to discriminate between a defect due to a foreign substance and a defect due to a light shielding film for reasons such as an allowable defect size miniaturization. In particular, when a defect is detected at the edge of the pattern, it cannot be determined whether the defect is a light shielding film or a foreign substance attached to the edge. Therefore, in most cases, as a next step when a defect is detected, a defect image is taken by a scanning electron microscope (SEM). However, since coordinate data indicating the position of a defect is required for SEM imaging, it is necessary to re-input coordinates at the time of defect imaging. Further, it is necessary to transport the mask from the inspection apparatus to the SEM.

JP 2003-185592 A JP 2008-166264 A

  The present invention has been made in view of the above-mentioned problems, and its problem is to accurately determine a defect derived from a foreign substance and a defect derived from a light-shielding film in a short time, thereby reducing yield and delaying delivery time. It is an object of the present invention to provide an inspection apparatus capable of solving such problems.

As means for solving the above-mentioned problems, the invention described in claim 1 is an inspection apparatus for detecting a defect of a photomask, which is always performed, and is based on an optical system using light and the inspection. An inspection unit based on an optical system using an electron beam, which is performed when a defect is detected by the unit, and an inspection unit based on an optical system using the light and an inspection unit based on an optical system using an electron beam. Means for automatically switching, and means for transmitting the coordinates of the defect detected by the inspection unit based on the optical system using the light to the inspection unit based on the optical system using the electron beam. It is an inspection device.

  The invention according to claim 2 is the inspection apparatus according to claim 1, wherein the light of the inspection means based on the optical system using the light is laser light.

  The invention according to claim 3 is characterized in that the inspection means based on the optical system using the electron beam is an inspection means based on an optical system for SEM imaging. Device.

  The invention according to claim 4 further comprises means for acquiring and storing an image of a defect detected by an inspection means based on the optical system using the electron beam. The inspection apparatus according to any one of the above.

  The invention according to claim 5 is the inspection apparatus according to claim 4, further comprising means for displaying defect information acquired by the inspection apparatus together with an image of the defect.

  According to the present invention, not only the presence / absence of a defect can be determined by a series of defect inspections, but also when a defect is detected, the type of defect can also be determined at the same time, and a correction method can be determined without separately performing SEM imaging of the defect. Can do.

It is a schematic diagram explaining an example of the structure of the inspection apparatus which concerns on this invention. It is a flowchart explaining an example of the defect inspection method at the time of using the inspection apparatus which concerns on this invention.

An embodiment according to the present invention will be described below with reference to FIGS.
FIG. 1 is a schematic view of an inspection apparatus according to claim 1 of the present invention. There are two apparatuses, an inspection means 1 based on an optical system using light such as laser light for defect inspection and an inspection means 9 based on an optical system using an electron beam such as SEM. Hereinafter, although the SEM will be described as an example of the inspection means 9 based on an optical system using an electron beam, the invention is not limited to this.

  An inspection means 1 based on an optical system using light includes a light source 2, a reflected light detector 6, a transmitted light detector 8, a light source 2, a photomask 18 to be inspected, and both detectors. It is a general one provided with a group of optical elements such as a reflected light condensing lens 5 and a transmitted light condensing lens 7 that form an optical path of reference light and an optical path of irradiation light. Laser light or the like is used for the light source 2. In addition, an acousto-optic beam scanner is also provided in the optical system, which makes it possible to deflect the light. The laser beam is finally focused on the photomask 18 to be inspected by the objective lens 4. The light reflected from the photomask 18 to be inspected is changed in direction by the beam splitter 3 and condensed on the reflected light detector 6 by the reflected light collecting lens 5 to form an image. On the other hand, the light transmitted through the photomask 18 to be inspected is condensed on the transmitted light detector 8 by the transmitted light condensing lens 7 to form an image. The presence or absence of a defect is determined by analyzing the detected image data. All these parts move during SEM photography and are stored so as not to interfere with photography.

The inspection means 9 based on an optical system using an electron beam has an electron source 10, a primary electron acceleration electrode 11, a condenser lens 12, a reflector 13, a scanning coil 14, an objective lens 15, and a secondary electron detector 16. It is general. During SEM imaging, a primary electron beam is generated from the electron source 10, accelerated by the primary electron acceleration electrode 11, converged by the condenser lens 12, passed through the central hole of the reflector 13, and deflected and scanned by the scanning coil 14. Thereafter, the light is focused on the photomask 18 to be inspected by the objective lens 15. The secondary electrons generated from the photomask 18 to be inspected collide with the reflector 13 and are detected by the secondary electron detector 16 and finally converted into an image. Since all parts at the time of defect inspection are stored, the principle of SEM imaging itself is not different from a general one.

  In addition, when the inspection apparatus shown in FIG. 1 confirms that there is a defect in the defect inspection by the inspection means 1 based on the optical system using light, the inspection means automatically inspects based on the optical system using the electron beam. At the same time as switching to the means 9, the inspection means 1 based on the optical system using light reads the coordinates of the detected defect, stores them, and sends them to the inspection means 9 based on the optical system using an electron beam. The inspection means 9 based on the optical system using the line can determine the photographing location. In order to make it possible to carry out the above, the inspection apparatus 19 of the present invention is inspected when the inspection means 1 based on the optical system using light inspects the photomask 18 to be inspected and detects a defect. Means is provided for transferring the target photomask 18 to the inspection means 9 based on an optical system using an electron beam and fixing it so that it can be inspected stably.

  In addition, after the SEM imaging by the inspection means 9 based on an optical system using an electron beam, defect information is automatically displayed on the display device of the inspection device 19, and at the same time, the captured SEM image is also displayed. The It is also possible to prevent such defect information and SEM images from being automatically displayed. Further, when the inspection means 9 based on an optical system using an electron beam is subjected to SEM imaging, the inspection device 19 of the present invention acquires and stores the image data, easily retrieves it as necessary, and displays it on the display device. Is possible. It is also possible to perform image processing of the image data and perform processing such as calculation processing for determining the type of defect and comparison calculation with reference data.

  FIG. 2 is a flowchart for explaining a defect inspection method when the inspection apparatus shown in FIG. 1 according to the present invention is used. First, the photomask 18 to be inspected is loaded into the inspection means 1 based on an optical system using light in step S101, inspection conditions are set in step S102, and inspection is started in step S103. When the inspection is completed, the presence or absence of a defect is confirmed in step S104. If there is no defect, the photomask 18 to be inspected is unloaded in step S109. If there is a defect, the inspection device 19 recognizes in step S105 and automatically switches from the inspection unit 1 based on the optical system using light to the inspection unit 9 based on the optical system using electron beam, and detected in step S106. In accordance with the defect coordinates, defect imaging is started. When the imaging of the defect is completed, each defect information is displayed on the display device of the inspection apparatus 19 of the present invention together with the captured SEM image in step S107. When the correction method for each defect is determined based on the information given in step S108, the inspection target photomask is unloaded in step S109. Thereafter, corrections can be made. As a method for determining the correction method, a person looks at the SEM image and determines from the characteristics whether the defect is derived from a foreign substance or a light shielding film. In addition, by storing and accumulating the characteristics of these images and the correct results of determination as digital data in a computer system in advance, it is possible to determine whether defects are derived from foreign matters or from light-shielding films from individually observed SEM images. It is also possible to automatically determine whether or not the

  By the inspection apparatus 19 of the present invention, the presence / absence of a defect and determination of a correction method can be achieved without separately performing defect imaging. The present invention is not limited to the above, and various modifications can be made within the scope of the invention described in the claims.

Example 1
A defect inspection by the inspection apparatus according to claim 3 of the present invention was performed on a photomask test product (photomask to be inspected). Specifically, first, a test product of a photomask composed of eight dies on which a pattern composed of lines and spaces having a line width of 1: 1 was drawn was produced.

  Next, the test product was loaded into the inspection apparatus, the inspection conditions for simultaneous transmission / reflection inspection between dies were set, and the inspection was performed. As a result of the inspection, a total of 11 actual defects were detected, so that the inspection means based on the optical system using light is automatically applied to the inspection means based on the optical system using an electron beam, specifically SEM (scanning electron microscope). The SEM imaging was executed at 11 defect detection locations.

  After completion of SEM imaging, an SEM image captured along with information on the detected 11 defects was displayed on the display device of the inspection apparatus of the present invention. The machine operator performed a classification of the 11 defects displayed. The SEM image is also displayed, so that one foreign substance on the light shielding film on the glass, three defects on the light shielding film, three foreign substances on the light shielding film, three pattern shape defects, It was confirmed that there was one large scum. The operator of the apparatus determined that the light shielding film on the glass had to be corrected by projecting a laser beam, and that the scratch was corrected by FIB, and unloaded the photomask to be inspected of the inspected test product.

  The apparatus operator does not need to operate the inspection apparatus until the defect information is displayed on the display apparatus after starting the inspection. That is, there is no need for separate SEM imaging, and there is no need for re-input of defect coordinates or transport of the photomask 18 to be inspected.

(Comparative Example 1)
For the same test product as in Example 1, defect inspection and SEM imaging were performed with separate apparatuses. Specifically, first, a test product was loaded into an inspection apparatus manufactured by KLA-Tencor Co., Ltd., and simultaneous transmission / reflection inspection between dies was performed under the same conditions as in Example 1. After the inspection was completed, information on 11 defects was displayed on the display device. The operator cannot correct a defect detected between lines, which is one of the defects, because the defect information alone cannot determine whether it is a light shielding film foreign object on glass or a protrusion defect on the light shielding film. The method was not decided. The operator of the apparatus unloaded the test product, printed out the defect information, and transported the test product to the SEM manufactured by Advantest.

  A test product was loaded into the SEM, and based on the printed defect information, defect coordinates were input and imaging conditions were set. SEM imaging was performed, and the SEM image after imaging was confirmed on the display device. As a result, 11 defects can be classified as in Example 1, and it was determined that correction by projection of laser light on the light-shielding film foreign material on the glass and that correction by FIB was necessary for scratches. The item was unloaded.

  Compared with Example 1, the operator of the apparatus needed to carry the test product and re-input the coordinates. Further, in the case of Example 1, it took about 3 minutes from the end of the inspection to the start of SEM imaging, but in Comparative Example 1, it took 10 minutes or more, leading to wasted time. From the above, Comparative Example 1 proved the effect of the present invention.

  INDUSTRIAL APPLICABILITY The present invention can be suitably used in a photomask manufacturing / management process for forming a semiconductor integrated circuit.

  DESCRIPTION OF SYMBOLS 1 ... Inspection means based on optical system using light, 2 ... Light source, 3 ... Beam splitter, 4 ... Objective lens, 5 ... Reflected light condensing lens, 6 ... Reflected light detector, 7 ... Transmitted light condensing lens, DESCRIPTION OF SYMBOLS 8 ... Transmitted light detector, 9 ... Inspection means based on optical system using electron beam, 10 ... Electron source, 11 ... Primary electron acceleration electrode, 12 ... Condenser lens, 13 ... Reflector, 14 ... Scanning coil, 15 ... Objective lens, 16 ... secondary electron detector, 17 ... stage, 18 ... photomask to be inspected, 19 ... inspection device

Claims (5)

  An inspection apparatus for detecting a defect in a photomask, which is always performed based on an inspection system based on an optical system using light, and an inspection based on an optical system using an electron beam performed when a defect is detected by the inspection means And means for automatically switching between the inspection means based on the optical system using the light and the inspection means based on the optical system using the electron beam, and the inspection means based on the optical system using the light detected. Means for transmitting the coordinates of the defect to an inspection means based on an optical system using the electron beam.   The inspection apparatus according to claim 1, wherein the light of the inspection unit based on the optical system using the light is a laser beam.   3. The inspection apparatus according to claim 1, wherein the inspection unit based on the optical system using the electron beam is an inspection unit based on an optical system for SEM imaging.   4. The inspection apparatus according to claim 1, further comprising means for acquiring and storing an image of a defect detected by an inspection means based on an optical system using the electron beam.   The inspection apparatus according to claim 4, further comprising means for displaying defect information acquired by the inspection apparatus together with an image of the defect.

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