JP2007049002A - Inspection device and foreign matter inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To readily and highly precisely detect a foreign matter, such as a growing foreign matter on a mask or a specific thin film, such as a phase shift film which is hardly detected by optical inspection and an edge edge-face reinforced secondary electron detection, by taking advantage of the characteristics of a mass reinforced type regarding an inspection device and a foreign-matter inspection method for generating a reflected electron image of the mask or the thin film by detecting/amplifying reflected reflection electron, by irradiating and scanning the mask or the thin film with electron beam. <P>SOLUTION: The device has a means for obtaining a maximum value and a minimum value, by obtaining a reflection electron image by irradiating and scanning a mask or a thin film with electron beam; and a means for detecting an image, having the strength of the obtained maximum value or higher (or at least the value obtained by adding a prescribed allowed value to the maximum value), or a minimum value or lower (or at least a value obtained by deducting a prescribed allowed value from the minimum value), regarding the reflection electronic image obtained from a region to be inspected on the mask or the thin film. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inspection apparatus and a foreign matter inspection method for irradiating and scanning an electron beam on a mask or a thin film, and detecting and amplifying reflected backscattered electrons to generate a reflected electron image of the mask or thin film. is there.

  Conventionally, a pattern inspection apparatus for a semiconductor LSI irradiates a mask to be inspected with light, displays images obtained by converting reflected light and transmitted light into electrical signals, respectively, and detects and inspects defects on these images. It was like that.

  Then, the stage is moved to the coordinate position of the detected defect, and the operator confirms the defect on the mask and decides a countermeasure. For example, the dust on the glass part of the mask is distinguished from the metal film (residue) on the glass part, and the former is judged to be able to be removed in the final cleaning process and left to the cleaning process. In the case of the latter residue, it is determined that the residue is removed by FIB (Focused Ion Beam) or laser.

  Recently, however, the determination of garbage has become simpler. There are many types of garbage. There are a variety of types, from those that can be easily peeled off by final cleaning to those that are firmly fixed to the mask substrate, such as metal thin films. There has been a problem that it has become impossible for an operator to judge them only from reflected light information and transmitted light information as in the past.

  For this reason, it is desired to detect and determine fine dust and foreign matter with high accuracy based on a high-resolution and characteristic signal obtained from an electron beam or the like for defects such as fine dust.

In particular, the detection of growth foreign substances on the phase shift film described in FIG. 6 is a problem.
FIG. 6 is an explanatory diagram of the prior art.

  FIG. 6A shows the state of the pattern on the mask (glass substrate) after cleaning before shipping the mask. (A-1) An example of a pattern on a mask is shown, and (a-2) shows a state in which (a-1) is enlarged and easily understood. As shown in (a-2), a state in which nuclei of small and thin growth foreign substances such as sulfides and ammonia salts of substances contained in the cleaning liquid are schematically shown.

  In FIG. 6B, the nuclei of the small and thin growth foreign matter in FIG. 6A cannot be detected by the above-described reflected light information and transmitted light information (for example, optical inspection at 440 nm) after cleaning before shipping the mask. Show the state.

  FIG. 6C shows a state where the pellicle is attached. In the state shown in the figure where the pellicle is attached, a pressure adjusting port is provided as shown in the figure to perform stepper exposure. During stepper exposure, UV light is irradiated, and gas, moisture, etc. contained in the surrounding atmosphere adhere to the nucleus of small and thin growth foreign substances on the glass substrate and grow as foreign substances, and become larger according to use.

  FIG. 6D shows an example of a foreign object failure. This is because the growing foreign matter grown by the stepper exposure of FIG. 6C starts with optical inspection (inspection using reflected light information and transmitted light information), and foreign matter (UV light or the like is present at the core of the growing foreign matter that originally existed). As a result, the surrounding gas grows and the nucleus becomes larger, and it can be detected as a growing foreign substance that has grown to the point of hindrance.

  As described above, especially for the mask formed with the phase shift film after cleaning before shipment, the core of these growing foreign matters cannot be found by conventional optical inspection (inspection by reflected light information and transmitted light information). There was a problem.

  In order to solve these problems, the present invention detects the maximum intensity and the minimum intensity of a reflected electron image generated by scanning an electron beam beam on a mask substrate or a specific thin film and detecting a reflected electron beam. Based on these, the backscattered electron image of the foreign material to be inspected such as the nucleus of the growing foreign material on the mask substrate or the specific thin film is acquired and detected, and the nucleus of the growing foreign material on the mask or the specific thin film is detected. The purpose of this method is to detect a foreign substance such as a simple and highly accurate utilizing the characteristics of the mass enhancement type.

  The present invention scans the electron beam beam on a mask substrate or a specific thin film, detects the reflected electron beam reflected, detects and stores the maximum intensity and the minimum intensity of the reflected electron image, and based on these, Phases that are difficult to detect by optical inspection and edge-enhanced secondary electron detection of patterns by acquiring and detecting reflected electron images of foreign objects to be inspected, such as nuclei of growing foreign substances on the substrate of the mask or on a specific thin film It becomes possible to detect foreign matter such as nuclei of growth foreign matter on a mask such as a shift film or a specific thin film simply and with high accuracy by utilizing the characteristics of mass enhancement.

  The present invention scans the electron beam beam on a mask substrate or a specific thin film, detects the reflected electron beam reflected, detects and stores the maximum intensity and the minimum intensity of the reflected electron image, and based on these, A mass-enhanced type that captures and detects reflected electron images of foreign objects to be inspected, such as nuclei of growing foreign substances on the mask substrate or specific thin film, and masses the foreign substances such as nuclei of growing foreign substances on the mask or specific thin film Using this characteristic, it was possible to detect easily and with high accuracy.

FIG. 1 shows a block diagram of an embodiment of the present invention.
In FIG. 1, a SEM 1 is a scanning electron microscope having a configuration as shown.

  The electron gun 2 generates an electron beam (for example, a tip of a tungsten wire is formed to have a sharp and predetermined surface, and a high voltage is applied to the anode 3 to extract the electron beam).

  The anode 3 applies a high voltage and accelerates electrons emitted from tungsten formed so that the tip of the cathode constituting the electron gun 2 is sharp and has a predetermined surface.

  The alignment coil 4 is for deflecting and aligning the electron beam emitted from the electron gun 2.

The condenser lens 5 focuses the electron beam emitted from the electron gun 2.
The deflection scanning coil 6 is for scanning an electron beam narrowly focused on a mask 11 as a sample by the objective lens 9 in the X direction and the Y direction.

  The backscattered electron detector 7 detects backscattered electrons reflected from the mask 11 when the mask 11 is scanned by irradiating the mask 11 with an electron beam. Based on the signal detected by the reflected electron detector 7, a reflected electron image is displayed on the display device 25.

  The secondary electron detector 8 collects, detects, and amplifies secondary electrons emitted from the mask 11 when the mask 11 is scanned with an electron beam. Based on the signal detected by the secondary electron detector 8, a secondary electron image is displayed on the display device 25.

The objective lens 9 narrows the electron beam on the mask 11.
The laser interferometer 10 is a known one that measures the position (positional coordinates) of the stage 12 with ultra-high accuracy by emitting a laser beam, reflecting it with a reflecting mirror attached to the stage 12 and capturing it.

The mask 11 is an example of a sample mounted (fixed) on the stage 12.
The stage 12 is mounted with a mask 11 and accurately moves to an arbitrary coordinate position, and is driven by a motor (or ultrasonic motor) 13.

  The motor 13 drives the stage 12 (X direction, Y direction), and is a servo motor or an ultrasonic motor.

  The PC 21 is a personal computer and performs various processes according to a program. Here, the inspection object extraction means 21, the reflected electron signal acquisition means 22, the foreign matter detection means 24, the display device 25, the input device 26, and the like are used. It is composed.

  The inspection object extraction means 22 extracts the inspection object on the mask 11 or a predetermined thin film formed on the mask 11. For example, a region having a predetermined size or less is extracted as an inspection target for a region where the mask 11 is exposed on the mask 11 having a predetermined region or less or a thin film region formed on the mask 11 (see FIG. 3).

  The reflected electron signal acquisition means 23 acquires a reflected electron signal of the mask 11 or a region formed on the mask 11 (see FIGS. 2 to 5).

  The foreign matter detection means 24 is an image having a predetermined size or more based on the reflected electron signal acquired from the mask 11 acquired by the reflected electron signal acquisition means 23 or an area formed on the mask 11 (area below the predetermined area). Are extracted and determined as a foreign object (see FIGS. 2 to 5).

The display device 25 displays a reflected electron image or the like.
The input device 26 inputs various instructions and data, and is a mouse or a keyboard.

  Next, the operation (reference value calculation) of the configuration of FIG. 1 will be described in detail according to the order of the flowchart of FIG.

FIG. 2 shows a flowchart for explaining the operation of the present invention (reference value calculation).
In FIG. 2, S1 moves the glass surface based on the reference point.

  S2 measures the maximum Rmax / minimum Rmin of the reflected electron intensity of the surface with the glass surface. These S1 and S2 move to the exposed surface (region) of the glass surface that is the substrate material of the mask, scan the surface while irradiating the surface with an electron beam, and detect and amplify the reflected signal reflected. The generated reflected electron signal (reflected electron image) is acquired, and the maximum value Rmax and the minimum value Rmin within a predetermined region of the glass surface are calculated as reference values (see FIG. 5A).

  As described above, the maximum value Rmax and the minimum value Rmin ((a) of FIG. 5) of the reflected electron image of the glass surface, which is the substrate material of the mask, are obtained, and the nuclei of the growth foreign matter formed on the glass surface of the mask are obtained. Preparation for detection (preparation of reference value) is completed.

  Next, the operation (foreign matter measurement) of the configuration of FIG. 1 will be described in detail according to the order of the flowchart of FIG.

FIG. 3 is a flowchart for explaining the operation of the present invention (foreign matter measurement).
In FIG. 3, S11 calculates the area | region below a predetermined glass area with reference to CAD. This refers to CAD data (design data), extracts a small area where the area where the glass is exposed is a predetermined value or less, and determines this as a foreign object detection area. The foreign matter is likely to be generated in an area where the glass surface is small to a certain extent, has a large effect when it occurs, and conversely, is hardly generated in an area where the glass surface is somewhat large, and has a small effect when it occurs.

  S12 measures the reflected electron intensity in the glass surface. This measures the backscattered electron intensity (backscattered electron image) in the small glass surface area below the predetermined area calculated in S11 and stores it in the memory.

  In step S13, a position that exceeds L0 in the pixel and becomes L0 or less is obtained. This is because, for example, as shown in FIG. 5B, the reflected electron image in the region of the glass surface stored in the memory in S12 is searched for each scanning line from left to right in the horizontal direction (X direction). , The value D that is equal to or greater than the maximum value Rmax (L0) calculated in S11 and then has a maximum length when the value is equal to or less than the maximum value Rmax (L0) is calculated. When the magnitude of the reflection signal of the foreign object is smaller than the minimum value Rmin of the reference value, a value D that maximizes the length when the value is less than the minimum value Rmin is calculated.

  In step S14, it is determined whether or not the threshold value is exceeded. This determines whether the value D calculated in S13 is equal to or greater than a threshold value. In the case of YES, it determines with the foreign material more than a threshold value having been detected, records, and progresses to S16. On the other hand, in the case of NO in S14, since it has been found that it is equal to or less than the threshold, the process proceeds to S16.

  In S16, it is determined whether or not the end. This determines whether or not the processing from S12 to S15 has been completed for all the regions extracted in S11. If YES, the process ends. In the case of NO, S12 and subsequent steps are repeated for all areas.

  Note that the recording may be performed in S15 when the foreign object is detected without determining whether the foreign object is equal to or greater than the predetermined threshold in S14, and the process may proceed to S16.

  As described above, a backscattered electron image is obtained for a region below a predetermined region on the glass surface of the mask substrate on the design data, and the image length D (or the reference value (minimum value Rmin) greater than or equal to the reference value (maximum value Rmax) is obtained. It is possible to automatically detect a foreign object (or a foreign object when the image length D can be detected) when the following image length D) is equal to or greater than a threshold value.

FIG. 4 is an explanatory diagram (signal strength) of the present invention. The horizontal axis represents the atomic number (mass), and the vertical axis represents the reflected electron signal corresponding to the atomic number of the substance at the irradiated position on the mask 11 when the electron beam is irradiated on the mask 11 (the dotted line is the secondary). The intensity of the electronic signal) is schematically represented. As the reflected electron signal increases in atomic number of the irradiated material, the reflectivity increases and the intensity of the reflected electron signal increases as shown by the solid curve in the figure, so that substances with different atomic numbers are detected as light and shade. It becomes possible. Here, due to the substances such as nitrogen and sulfur contained in the solvent used in the cleaning before shipping described above, growth foreign substances such as nitride and sulfide are small on the mask or a thin film formed on the mask. Thin nuclei are formed and grow during the stepper exposure shown in FIG. 6 as described above, resulting in failure. Therefore, a film is formed on the mask or the mask using the reflected electron image in advance before shipping the mask. It becomes possible to easily and accurately detect the nuclei of very small growth foreign substances formed on the thin film on the reflected electron image.

  On the other hand, in the case of a secondary electron signal indicated by a dotted line, when the atomic number is small, the intensity increases as the atomic number increases, but immediately becomes saturated. It becomes the same, and it is impossible to distinguish these substances having a large atomic number by the density of the secondary electron beam image.

FIG. 5 shows an explanatory diagram of the present invention.
(A) of FIG. 5 shows the calculation explanatory drawing of a reference value. This is a calculation explanatory view of the reference value calculated in S1 and S2 of FIG. 2 described above, and the solid line shown as the intensity of the reflected electron image from the left to the right in the predetermined area on the glass surface of the substrate of the mask. Is obtained. For this solid curve, a maximum value Rmax and a minimum value Rmin are obtained and determined as reference values.

  FIG. 5B shows an actual scanning example. It is assumed that the solid line curve shown in FIG. 5A is obtained as a reflected electron image for the glass surface region with reference to the reference values (maximum value Rmax, minimum value Rmin) for the glass surface. For the solid curve, the reference values (maximum value Rmax, minimum value Rmin) calculated in (a) of FIG. 5 are set as indicated by dotted lines, and here, the reference value is equal to or greater than the maximum value Rmax, The illustrated length (size) D that is equal to or less than the maximum value Rmax is repeated, and the maximum value of one closed image is calculated as D as illustrated. When the calculated size D is detected (or when D is larger than the threshold value), it is determined as the nucleus of the growing foreign matter, and the foreign matter that is not on the design data on the glass surface is an atom that is a characteristic of the reflected electron image. It can be detected as a difference in signal intensity due to a difference in number (mass). In FIG. 5B, foreign matter in the upper direction (mass is large) is detected, but conversely, foreign matter in the lower direction (mass is small) can be detected in the same manner.

  Here, the acquired foreign substance signal is equal to or greater than the maximum value Rmax. However, the foreign substance signal may be equal to or greater than a value obtained by adding a predetermined permissible value (optimal value is determined by experiment) to the maximum value Rmax, or the minimum value. A value equal to or less than a value obtained by subtracting a predetermined allowable value (an optimum value is obtained through an experiment) from Rmin may be used as a foreign object signal.

  In FIG. 5, foreign matter formed on the glass surface that is the substrate of the mask is detected. Similarly, foreign matter that is not on the design data may be detected on the thin film formed on the mask.

  The present invention makes use of mass-enhanced characteristics to remove foreign matters such as nuclei of growth foreign matters on a mask such as a phase shift film or a specific thin film, which are difficult to detect by secondary inspection of the edge-enhanced type of the optical inspection and pattern. The present invention relates to an inspection apparatus and a foreign matter inspection method that detect the object simply and with high accuracy.

1 is a configuration diagram of one embodiment of the present invention. It is an operation explanation flowchart (reference value calculation) of the present invention. It is an operation explanation flowchart (foreign matter measurement) of the present invention. It is explanatory drawing (signal strength) of this invention. It is explanatory drawing of this invention. It is explanatory drawing of a prior art.

Explanation of symbols

1: SEM (scanning electron microscope)
2: Electron gun 3: Anode 4: Alignment coil 5: Condenser lens 6: Deflection scanning coil 7: Reflected electron detector 8: Secondary electron detector 9: Objective lens 10: Laser interferometer 11: Mask 12: Stage 13: Motor 21: PC (PC)
22: Inspection object extraction means 23: Reflected electron signal acquisition means 24: Foreign object detection means 25: Display device 26: Input device

Claims (6)

In a device that irradiates and scans a mask or thin film with an electron beam, and detects and amplifies reflected backscattered electrons to generate a backscattered electron image of the mask or thin film.
Means for irradiating and scanning an electron beam on a mask or a thin film, acquiring a reflected electron image, and acquiring the maximum value and the minimum value;
For the backscattered electron image acquired from the inspection target area on the mask or thin film, the above acquired maximum value (or the maximum value plus a predetermined allowable value) or the minimum value (or the minimum value is subtracted from the predetermined allowable value) Means for detecting an image having an intensity less than or equal to the measured value).   2. The inspection apparatus according to claim 1, further comprising means for determining that the detected image is a foreign object when the detected image is larger than a threshold value.   The inspection apparatus according to claim 1, wherein the inspection target area is an area having a predetermined area or less of a mask or a thin film closed area.   4. The inspection apparatus according to claim 1, wherein the mask or thin film inspection target region or closed region is a closed region in which only the mask or thin film exists on the design data.   The inspection apparatus according to claim 1, wherein the thin film is a thin film formed on a mask. In a foreign matter inspection method in an apparatus that irradiates and scans a mask or thin film with an electron beam and detects and amplifies reflected backscattered electrons to generate a backscattered electron image of the mask or thin film.
Scanning a mask or thin film with an electron beam and scanning to obtain a reflected electron image and obtaining its maximum and minimum values; and
For the backscattered electron image acquired from the inspection target area on the mask or thin film, the above acquired maximum value (or the maximum value plus a predetermined allowable value) or the minimum value (or the minimum value is subtracted from the predetermined allowable value) A foreign substance inspection method including a step of detecting an image having an intensity less than or equal to a measured value.

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