JP2021128119A - Inspection device and inspection method - Google Patents

Abstract

To suppress decrease in accuracy of detecting defects.SOLUTION: An inspection device comprises: a stage 111; a light source 120; a first measurement unit 133 for measuring a first height position of a surface of a sample 2; a second measurement unit 140 for measuring a first stage position; a height control unit 181 for controlling the stage 111 to the second height position; and a controller 182 for transmitting a control signal of auto focus control of light with which a sample is irradiated and a focus offset value to the height control unit 181. The height control unit 181 executes auto focus control based on the data of the first height position measured by the first measurement unit 133 when a light irradiation position on the surface of the sample 2 exists within a first area, and changes the second height position on the basis of the focus offset value received from the controller 182 when the irradiation position exists in a second area.SELECTED DRAWING: Figure 2

Description

The present invention relates to an inspection device and an inspection method for inspecting a pattern formed on a sample.

With the increasing integration and capacity of large scale integration (LSI), the circuit dimensions required for semiconductor devices are steadily becoming smaller. In the manufacture of semiconductor devices, a pattern is exposed on a wafer in a reduced projection exposure apparatus (called a stepper or a scanner) using a mask on which a circuit pattern (hereinafter referred to as a pattern) is formed.

In the manufacture of LSI, one of the factors that reduce the yield is a defect (deformation) of a pattern formed on the mask.

For example, state-of-the-art devices require the formation of patterns with line widths of several nm. As the pattern becomes finer, the defects of the pattern in the mask also become finer. Therefore, mask inspection devices are required to improve the detection accuracy of defects in extremely small patterns.

In the mask inspection device, the mask is held and placed on a stage in the inspection device. Then, as the stage moves, the light emitted through the optical system scans on the mask. The light transmitted or reflected by the mask is imaged on the sensor through the lens. The defect inspection of the mask is performed, for example, by comparing the optical image captured by the sensor with the reference image generated from the mask design data (hereinafter referred to as design pattern data). Alternatively, since an optical image is acquired for each semiconductor element (die) formed on the wafer, the defect inspection of the mask can also be performed by comparing the optical images of each die. Therefore, the reference image includes not only the image generated from the design pattern data, but also the optical image acquired for a die.

The sample to be inspected by the inspection device is not limited to the mask. The sample may be a wafer, a substrate used for a liquid crystal display device, or the like.

In response to the miniaturization of the pattern formed on the mask, higher magnification and higher NA (Numerical Aperture) are being promoted in the optical system for capturing an optical image of the pattern. Therefore, the depth of focus, which is the allowable range of the distance between the optical system and the mask, becomes shallow. When the depth of focus becomes shallow, even a slight change in the distance between the optical system and the mask causes a shift in the focus of the light. As a result, the pattern image of the optical image is blurred, which hinders the acquisition of the optical image and the defect detection process. In order to suppress the focus shift, an inspection device provided with an autofocus mechanism that controls the autofocus of the light irradiating the mask is known.

As an autofocus mechanism, for example, Patent Document 1 discloses an autofocus mechanism that performs autofocus control at a preset position. Further, Patent Document 2 discloses an autofocus mechanism that turns off the autofocus control when the measurement position of the mask inspection deviates from a preset region. All of these patent documents specify a position or region where autofocus control is performed, and do not disclose a control mechanism or method corresponding to a step on the mask surface in a region where autofocus control is not performed.

JP-A-2009-168607 Japanese Unexamined Patent Publication No. 2012-78164

INDUSTRIAL APPLICABILITY The present invention provides a control mechanism and a method that enable focus to be followed at the edge of a step or a mesa portion even if there is a step or a mesa portion (protruding portion) on the pattern surface of the sample to be inspected. be. In the semiconductor manufacturing process, a halftone mask, which is one of the phase shift masks, is known as an example of a photomask that serves as a master for forming a fine pattern on a wafer. In the case of a halftone mask, for example, a pattern using a phase shift film having a certain degree of light transmittance and reversing the phase by 180 degrees is formed on a substrate using quartz glass, for example. Hereinafter, the region in which the pattern formed by the phase shift film is formed is referred to as a transmission region. Further, on the outer periphery of the transmission region where the pattern is not formed and does not contribute to the exposure, a light-shielding film using, for example, a chromium (Cr) film is provided on the substrate. Hereinafter, the region where the light-shielding film is formed will be referred to as a light-shielding region. In this case, the step (height) between the substrate and the light-shielding film on the mask surface is larger than the step between the substrate and the phase shift film.

When inspecting a defect of a halftone mask, the defect inspection area includes a transmission area and a part of a light-shielding area. The inspection device scans the light in the inspection area to acquire an optical image. The step between the substrate and the light-shielding film is larger than the step between the substrate and the phase shift film. Therefore, when scanning light, the autofocus control may not be able to follow the step between the substrate and the light-shielding film. For example, when light is scanned from a light-shielding region to a transmission region, the pattern image of the optical image may be blurred due to the influence that the autofocus control cannot follow. When the pattern image is blurred, there is a high possibility that pseudo defects will be detected or defects will not be detected due to the difference between the optical image and the reference image. Therefore, the defect detection accuracy may decrease.

The present invention has been made in view of these points. That is, an object of the present invention is to provide an inspection device and an inspection method capable of suppressing a decrease in defect detection accuracy for a sample having a step or a mesa portion to which it is difficult to follow the autofocus control.

According to the first aspect of the present invention, the inspection device is in a stage on which the sample is placed, a light source that emits light used for acquiring an optical image of the sample, and a first direction perpendicular to the surface of the stage. The first measuring unit that measures the first height position of the surface of the sample, the second direction that is parallel to the surface of the stage and intersects the first direction, and the first and second directions that are parallel to the surface and intersect the first direction. A second measuring unit that measures the stage position of the stage in the third direction intersecting with, a height control unit that controls the stage in the first direction to the second height position, and autofocus of the light irradiating the sample. A controller for transmitting a control signal for control and a focus offset value to a height control unit is provided. When the light irradiation position is within the first region on the surface of the sample, the height control unit executes autofocus control based on the data of the first height position measured by the first measurement unit, and the irradiation position is changed. If it is in a second area different from the first area, the second height position is changed based on the focus offset value received from the controller.

According to the first aspect of the present invention, the controller controls based on the stage position data measured by the second measuring unit, the position information regarding the first and second regions, and the surface height information of the sample. It is preferable to transmit the signal and the focus offset value to the height control unit.

According to the first aspect of the present invention, the position information further includes information about the step portion provided on the surface of the sample in the second region, and the controller has the irradiation position above the step portion in the second region. It is preferable to transmit the focus offset value to the height control unit when passing through.

According to the first aspect of the present invention, the position coordinates of the first region and the second region are coordinates based on the layout information of the pattern of the sample, and the controller controls the control signal when the irradiation position is within the first region. Is set to the first logic level, and when the irradiation position is within the second region, it is preferable that the control signal is set to the second logic level different from the first logic level.

According to the first aspect of the present invention, the focus offset value is preferably a value based on the height information of the surface of the sample.

According to the first aspect of the present invention, it is preferable to further include an actuator using a piezoelectric element that moves the stage in the first direction based on the control by the height control unit.

According to the second aspect of the present invention, the inspection method includes a step of placing the sample on the stage and a step of irradiating the sample with light to acquire an optical image. When the light irradiation position is within the first region, the steps of acquiring the optical image include the step of acquiring the data of the first height position of the surface of the sample in the first direction perpendicular to the surface of the stage and the acquisition. It includes a step of executing autofocus control of the light irradiating the sample based on the data of the first height position. When the irradiation position is within the second region, the step of acquiring the optical image is a step of changing the second height position of the stage in the first direction by using the focus offset value based on the height information of the surface of the sample. including.

According to the second aspect of the present invention, the step of changing the second height position is executed when the irradiation position passes over the step portion provided on the surface of the sample in the second region. Is preferable.

According to the sample inspection device and the sample inspection method of the present invention, it is possible to suppress a decrease in the detection accuracy of defects in a sample having a step that makes autofocus control difficult.

FIG. 1 is a diagram showing a configuration of an inspection device according to an embodiment. FIG. 2 is a diagram showing a configuration of an autofocus mechanism included in the inspection device according to the embodiment. FIG. 3 is a diagram showing a surface and a cross section of a mask to be inspected in the inspection apparatus according to the embodiment. FIG. 4 is a flowchart showing an inspection procedure in the inspection device according to the embodiment. FIG. 5 is an enlarged view of the region RA of FIG. 3 and a diagram showing the measurement result of the height position of the mask in the region RA. FIG. 6 is a diagram showing the height position of the stage when the autofocus control is always executed as a comparative example.

Hereinafter, embodiments will be described with reference to the drawings. The embodiments exemplify devices and methods for embodying the technical idea of the invention. The drawings are schematic or conceptual, and the dimensions and ratios of each drawing are not necessarily the same as the actual ones. The technical idea of the present invention is not specified by the shape, structure, arrangement, etc. of the components.

In the following, as a sample inspection device, a mask inspection device will be described as an example. In this embodiment, a sample to be inspected, that is, a case where a halftone mask is used as a mask will be described, but the present invention is not limited to the halftone mask.

Hereinafter, when the mask is not limited to the halftone mask, it is simply referred to as a mask.

1. 1. Overall configuration of the inspection device First, the overall configuration of the inspection device will be described with reference to FIG. FIG. 1 is a diagram showing an overall configuration of the inspection device 1.

As shown in FIG. 1, the inspection device 1 includes an optical image acquisition device 10 and a control device 20.

The optical image acquisition device 10 includes a first light source 120, a second light source 130, a stage 111, an XY drive unit 112, a Z drive unit 116, lenses 121, 123, and 124, mirrors 122, 131, and 132, and a photodiode. It includes an array 125, a sensor circuit 126, a height measuring system 133, a laser length measuring system 140, and an autoloader 150.

The first light source 120 irradiates the mask (sample) 2 with light for defect inspection of the mask 2. The light emitted from the first light source 120 passes through the lens 121, is turned by the mirror 122, and then is focused on the mask 2 by the lens 123. The light transmitted through the mask 2 is imaged on the photodiode array 125 by the lens 124 provided below the mask 2.

The second light source 130 irradiates the mask 2 with light for measuring the height of the mask 2. The light emitted from the second light source 130 is turned by the mirror 131 and radiated onto the mask 2. The light is then reflected on the mask 2 and then redirected by the mirror 132 to enter the height measurement system 133. The mirror 132 may be omitted. In this case, the light reflected on the mask 2 is directly incident on the height measurement system 133.

The stage 111 can move in the X direction parallel to the surface of the stage 111, the Y direction parallel to the surface of the stage 111 and intersecting the X direction, and the Z direction perpendicular to the surface of the stage 111. The mask 2 is placed on the stage 111.

The XY drive unit 112 has a drive mechanism for moving the stage 111 in the XY plane composed of the X direction and the Y direction. More specifically, the XY drive unit 112 includes an X-axis motor 113 that drives the stage 111 in the X direction and a Y-axis motor 114 that drives the stage 111 in the Y direction. For the X-axis motor 113 and the Y-axis motor 114, for example, a stepping motor can be used. The XY drive unit 112 may have, for example, a rotation axis motor that rotates the stage 111 around the rotation axis on the XY plane with the Z direction as the rotation axis.

The inspection area for inspecting the pattern defect of the mask 2 is virtually divided into a plurality of inspection areas along the Y direction, for example. Hereinafter, each of the divided inspection areas will be referred to as an “inspection frame”. The XY drive unit 112 controls the operation of the stage 111 so as to continuously scan the light for each divided inspection frame.

The Z drive unit 116 has a drive mechanism for moving the stage 111 in the Z direction. More specifically, the Z drive unit 116 includes a plurality of Z-axis actuators 117 that drive the stage 111 in the Z direction. As the Z-axis actuator 117, an actuator using a piezoelectric element such as a piezo element can be used.

The photodiode array 125 photoelectrically converts the light for defect inspection transmitted through the mask 2 to generate an electric signal. The photodiode array 125 transmits the generated electric signal to the sensor circuit 126. More specifically, the photodiode array 125 includes an image sensor (not shown). As the image sensor, for example, a line sensor in which CCD cameras as an image sensor are arranged in a row may be used. An example of a line sensor is a TDI (Time Delay Integration) sensor. For example, the pattern of the mask 2 is imaged by the TDI sensor while the stage 111 continuously moves in the X direction.

The sensor circuit 126 A / D (analog / digital) converts the electrical signal received from the photodiode array 125. The sensor circuit 126 transmits the converted digital signal, that is, optical image data, to the comparison circuit 173 of the control device 20. The optical image is an image of the mask 2 on which a figure based on the figure data included in the design pattern data is drawn. Further, the optical image is, for example, 8-bit unsigned data, and the brightness of each pixel obtained by dividing the inspection area on the XY plane is expressed by gradation.

Note that FIG. 1 shows an example having a configuration in which an image is acquired from the light transmitted through the mask 2, but the inspection device 1 is not limited to this. The inspection device 1 may have a configuration in which the light reflected by the mask 2 is guided to the photodiode array to acquire an image. Further, the inspection device 1 may have a configuration in which an image due to transmitted light from the mask 2 and an image due to reflected light from the mask 2 are simultaneously acquired.

The height measurement system 133 receives light for height measurement emitted from the second light source 130 and reflected on the surface of the mask 2. The height measuring system 133 is a measuring unit that measures the height position of the mask 2 (that is, the stage 111) in the Z direction based on the received light.

The laser length measuring system 140 is a measuring unit that measures the positions of the stage 111 in the X and Y directions (also referred to as “stage positions”). The laser length measuring system 140 transmits the measured data to the position circuit 174 of the control device 20.

A plurality of masks 2 are set in the autoloader 150. The autoloader 150 carries the mask 2 to be inspected into the stage 111. The autoloader 150 carries out the mask 2 for which the acquisition of the optical image has been completed from the stage 111, and carries in the next mask 2 to the stage 111.

The control device 20 includes a central processing unit (CPU) 160, a random access memory (RAM) 161, a read-only memory (ROM) 162, an external storage 163, a display device 164, an input device 165, and a communication device 166. Be prepared. These are connected to each other via a bus line.

The CPU 160 is a processor that controls the operation of each part of the inspection device 1, and is composed of one or a plurality of microprocessors. A part or all of the functions of the CPU 160 may be carried by other integrated circuits such as an application specific integrated circuit (ASIC), a field programmable array (FPGA), and a graphic processing unit (GPU).

The RAM 161 functions as, for example, the main storage device of the CPU 160. For example, the RAM 161 stores a program executed by the CPU 160, parameters and data necessary for executing the program, and the like.

The ROM 162 records, for example, a boot program, an operating system, a circuit inside the control device 20 for inspection, a program for controlling each part of the inspection device 1, and the like.

For the external storage 163, for example, various storage devices such as a magnetic disk storage device (HDD: Hard Disk Drive) and a solid state drive (SSD) are used. Various parameters and the like for the inspection process according to the present embodiment are recorded in the external storage 163. Further, the external storage 163 also records data acquired by the inspection device 1, data related to the inspection result processed by the control device 20, and the like.

Further, the external storage 163 of the present embodiment also stores position information and Z offset information about the inspection area of the mask 2. The position information includes an area in which the autofocus control is performed (hereinafter, referred to as "AF-ON area") and an area in which the autofocus control is not performed (hereinafter, referred to as "AF-OFF area") in the inspection area of the mask 2. ) And information indicating. The position coordinates of the AF-ON region and the AF-OFF region are based on the layout information of the pattern provided on the mask. Further, the position information includes information indicating a position (for example, a step portion on the surface of the mask 2 by the light-shielding film) in which the height position of the stage 111 needs to be adjusted (changed) in the AF-OFF region. .. The Z offset information is step (height) information on the surface of the mask 2. The Z offset information includes information for setting a focus offset value used for adjusting the height position of the stage 111 in the AF-OFF region. More specifically, for example, the Z offset information includes information about the film thickness of the light-shielding film (step between the substrate and the light-shielding film).

The position information and the Z offset information may be set by the user via the input device 165 or may be set by the CPU 160. For example, the CPU 160 may set the position information and the Z offset information based on the design pattern data, the mask information, the inspection conditions, and the like, and the height measurement result of the inspection area executed before acquiring the optical image. It may be set based on.

The display device 164 is a display device such as a CRT display, a liquid crystal display, or an organic EL display. The control device 20 may be provided with an audio output device such as a speaker.

The input device 165 is an input device such as a keyboard, a mouse, a touch panel, or a button switch.

The communication device 166 is a device for connecting to a network in order to send and receive data to and from an external device. Various communication standards can be used for communication. For example, the communication device 166 receives the design pattern data from the external device, and transmits the data acquired by the inspection device 1, the data related to the inspection result processed by the control device 20, and the like to the external device.

Further, the control device 20 includes an autoloader control circuit 167, a light source control circuit 168, an XY drive unit control circuit 169, a Z drive unit control circuit 170, a deployment circuit 171 and a reference circuit 172, a comparison circuit 173, and a position circuit 174. These may be configured by a program executed by an integrated circuit such as a CPU, ASIC, FPGA, or GPU, or may be configured by hardware or firmware included in those integrated circuits, and these integrated circuits may be configured. It may be composed of individual circuits controlled by. Hereinafter, a case where these are programs stored in the external storage 163 for performing the inspection process and executed by the CPU 160 will be described.

The autoloader control circuit 167 controls the operation of the autoloader 150 under the control of the CPU 160. The autoloader control circuit 167 operates the autoloader 150 to bring the mask 2 to be inspected into the stage 111. Further, the autoloader control circuit 167 operates the autoloader 150 to carry out the mask 2 from the stage 111.

The light source control circuit 168 controls the first light source 120 and the second light source 130 under the control of the CPU 160.

The XY drive unit control circuit 169 controls the XY drive unit 112 under the control of the CPU 160. More specifically, the XY drive unit control circuit 169 acquires the position measurement results of the stage 111 measured by the laser length measuring system 140 via the position circuit 174 in the X and Y directions, and based on the acquired results. The XY drive unit 112 is controlled.

The Z drive unit control circuit 170 controls the Z drive unit 116 under the control of the CPU 160. In the present embodiment, the Z drive unit control circuit 170 controls the Z drive unit 116 by dividing the inspection area of the mask 2 into an AF-ON area and an AF-OFF area. More specifically, in the AF-ON region, the Z drive unit control circuit 170 is the distance between the lens 123 and the pattern surface of the mask 2 based on the height data of the surface of the mask 2 received from the height measurement system 133. The height position of the stage 111 is controlled so that Further, in the AF-OFF region, the Z drive unit control circuit 170 changes the height position of the stage 111 according to the position coordinates of the stage 111 (mask 2).

The expansion circuit 171 generates binary or multi-valued image data (design pixel data) using, for example, the design pattern data held in the external storage 163. The generated image data is sent to the reference circuit 172.

The reference circuit 172 generates a reference image using the image data received from the expansion circuit 171. The reference circuit 172 transmits the generated reference image to the comparison circuit 173.

The comparison circuit 173 compares the optical image received from the sensor circuit 126 with the reference image generated by the reference circuit 172 using an appropriate algorithm. Then, when the error between the optical image and the reference image exceeds a preset value, the comparison circuit 173 determines that the coordinate positions of the corresponding masks 2 (stage positions in the X and Y directions) are defective. do. The coordinate position of the defect in the mask 2 and the optical image and the reference image on which the defect determination is based are stored in the external storage 163 as an inspection result, for example.

The position circuit 174 generates position data in the X and Y directions of the stage 111 based on the data received from the laser length measuring system 140.

2. Details of Height Measurement System and Z Drive Unit Control Circuit Next, details of the height measurement system 133 and Z drive unit control circuit 170 will be described with reference to FIG. FIG. 2 is an excerpt of the configuration of the autofocus mechanism, that is, the mechanism corresponding to the height position control of the stage 111 in the inspection device 1 shown in FIG.

As shown in FIG. 2, the autofocus mechanism includes a second light source 130, a stage 111, an XY drive unit 112, a Z drive unit 116, a lens 123, mirrors 131 and 132, a height measurement system 133, and a laser length measurement system. 140, an XY drive unit control circuit 169, a Z drive unit control circuit 170, and a position circuit 174 are included.

The height measurement system 133 includes a height position sensor 134 and a height measurement control unit 135.

The height position sensor 134 includes a light receiving element (not shown). As the light receiving element, for example, a position detection element (PSD: Position Sensitive Detector) is used. The PSD has a structure similar to that of a PIN-type photodiode, and measures the photocurrent at the incident position of light by the photovoltaic effect to realize the measurement of the position of the center of gravity of light.

The height measurement control unit 135 converts the signal output from the height position sensor 134 from the current value to the voltage value by the I / V conversion amplifier. After that, the height measurement control unit 135 amplifies the converted voltage value to an appropriate voltage level by the non-inverting amplification amplifier, and then converts it into digital data by the A / D conversion unit. Then, the height measurement control unit 135 creates the height data of the surface of the mask 2 according to the position of the light detected by the light receiving element.

The Z drive unit control circuit 170 includes a Z driver 180, a Z driver control unit 181 and a Z controller 182.

The Z driver 180 is a driver circuit that drives the Z-axis actuator 117 of the Z drive unit 116.

The Z driver control unit 181 is a height control unit of the stage 111 that controls the Z driver 180 based on the control of the Z controller 182. The Z driver control unit 181 switches the autofocus control on / off based on the AF control signal received from the Z controller 182. While executing the autofocus control, the Z driver control unit 181 matches the focal position of the light with the pattern surface of the mask 2 based on the height data of the surface of the mask 2 received from the height measurement system 133. The height position of the stage 111 is determined so as to control the Z driver 180. Further, while the autofocus control is not being executed, the Z driver control unit 181 controls the Z driver 180 so as to change the height position of the stage 111 based on the focus offset value received from the Z controller 182.

The Z controller 182 controls the Z driver control unit 181. More specifically, the Z controller 182 acquires the position data of the stage 111 (that is, the mask 2) in the X direction and the Y direction from the position circuit 174. Further, the Z controller 182 acquires the position information and the Z offset information about the mask 2 from the external storage 163, for example. The Z controller 182 transmits an AF control signal to the Z driver control unit 181 based on the position data, the position information, and the like. For example, when the Z controller 182 determines from the position data and the position information that the irradiation position of the light for defect inspection is in the AF-ON region, the Z controller 182 sends an AF control signal in order to turn on the autofocus control. The level is “High” (“H”). Alternatively, when the Z controller 182 determines from the position data and the position information that the irradiation position of the light for defect inspection is in the AF-OFF region, the Z controller 182 sends an AF control signal in order to turn off the autofocus control. Set to "Low" ("L") level.

The Z controller 182 sets the focus offset value according to the surface step (surface height information) of the mask 2 in the AF-OFF region based on the Z offset information. Then, when the Z controller 182 determines from the position data and the position information that the irradiation position of the light for defect inspection passes through, for example, the step portion between the substrate and the light-shielding film in the AF-OFF region, the Z controller 182 of the stage 111. The focus offset value is transmitted to the Z driver control unit 181 to change the height position.

3. 3. Mask inspection area Next, the inspection area of the mask 2 will be described with reference to FIG. FIG. 3 is a view showing the surface of the mask 2 and the cross section along the lines A1-A2.

As shown in FIG. 3, the substrate 200 of the mask 2 includes a transmission region and a light-shielding region.

The transmission region is a region in which a pattern formed by the phase shift film 202 is provided on the substrate 200. In the transmission region, light is transmitted through the substrate 200 and the phase shift film 202. In the reduced projection exposure apparatus, the pattern is exposed by the light transmitted through the transmission region.

The light-shielding region is a region in which the light-shielding film 201 is provided on the substrate 200. The light-shielding region is provided on the outer periphery of the transmission region and is a region that does not contribute to the exposure of the pattern in the reduced projection exposure apparatus. For example, the light-shielding region may be provided with an alignment pattern for adjusting the positions of the mask 2 in the X-direction and the Y-direction.

Assuming that the film thickness (height) of the light-shielding film 201 is Z1 and the film thickness of the phase shift film 202 is Z2, there is a relationship of Z1> Z2. The film thickness Z2 is within the depth of focus of the optical system, and when scanning the phase shift film 202, it is assumed that no focus error occurs due to the thickness of Z2.

The inspection area of the mask 2 includes a transmission area and a part of a light-shielding area. The inspection area of the mask 2 is virtually divided into a plurality of inspection frames having a scanning width W along the Y direction. In the example of FIG. 3, the inspection frames are divided into six inspection frames 211 to 216, but the number of inspection frames to be divided can be arbitrarily set. Then, the operation of the stage 111 is controlled by the XY drive unit 112 so that each of the divided inspection frames 211 to 216 is continuously scanned. More specifically, the inspection device 1 first scans the inspection frame 211 from the left side to the right side of the paper surface in the X direction to acquire an optical image. That is, the inspection device 1 moves the stage 111 in the X direction from the right side to the left side of the paper surface. At this time, the inspection device 1 continuously acquires optical images having a scanning width W in the sensor circuit 126. After acquiring the optical image in the inspection frame 211, the inspection device 1 continuously acquires the optical image while scanning the inspection frame 212 in the direction opposite to that in the case of the inspection frame 211. When acquiring the optical image in the inspection frame 213, the inspection device 1 scans the inspection frame 213 in the direction opposite to that in the case of the inspection frame 212. Similarly, for the other inspection frames 214, 215, and 216, optical images are acquired while alternately changing the scanning direction.

Alternatively, the inspection area of the present embodiment is divided into an AF-ON area and an AF-OFF area. In the example of FIG. 3, the boundary between the transmission region having a step of height Z1 and the light-shielding region, and the square frame-shaped region including the vicinity of the boundary are set as the AF-OFF region. Then, the inside and outside of the AF-OFF region in the inspection region, that is, the transmission region and the light-shielding region that do not include the AF-OFF region in the inspection region are set in the AF-ON region. The setting of the AF-OFF region is arbitrary. For example, at the boundary between the transmission region and the light-shielding region, the region including both sides in the Y direction along the scanning direction may be set as the AF-ON region. Further, the width in the vicinity of the boundary included in the AF-OFF region can be arbitrarily set. The AF-OFF area can be arbitrarily set according to the inspection area or inspection conditions (scanning speed, etc.).

4. Flow of inspection process Next, the flow of inspection process will be described with reference to FIG. FIG. 4 is a flowchart of the inspection process. In the following, an inspection method (Die to Database method) for comparing an optical image to be inspected with a reference image created based on drawing data (design pattern data) will be described.

As shown in FIG. 4, the inspection step includes an optical image acquisition step (step S1) for acquiring an optical image, a reference image acquisition step (step S2) for acquiring a reference image, and a comparison step between the optical image and the reference image. (Step S3) and the like.

4.1 Optical image acquisition process An example of the optical image acquisition process in step S1 will be described with reference to FIG. In the optical image acquisition step, the optical image acquisition device 10 acquires the optical image of the mask 2.

First, the CPU 160 starts acquiring an optical image (step S11). More specifically, the autoloader control circuit 167 carries in the mask 2 from the autoloader 150 and places it on the stage 111. Then, the XY drive unit control circuit 169 controls the XY drive unit 112 based on the position data acquired from the position circuit 174, and moves the stage 111 (mask 2) to the scanning start position. The light source control circuit 168 emits light from the first light source 120 and the second light source 130, respectively. When the XY drive unit control circuit 169 starts acquiring the optical image, the XY drive unit control circuit 169 moves the stage 111 according to the inspection frame. The optical image acquired in the sensor circuit 126 is transmitted to the comparison circuit 173. The Z controller 182 of the Z drive unit control circuit 170 first acquires position data, position information, and Z offset information.

When the Z controller 182 confirms that the scanning start position is in the AF-ON region, the Z controller 182 transmits an “H” level AF control signal to the Z driver control unit 181. Upon receiving the "H" level AF control signal, the Z driver control unit 181 turns on the autofocus control (step S12). More specifically, the Z driver control unit 181 makes the distance between the lens 123 and the surface of the mask 2 constant based on the height data of the surface of the mask 2 received from the height measurement system 133. The Z drive unit 116 is controlled via the Z driver 180 to adjust the height position of the stage 111.

In the AF-ON region, the height data of the surface of the mask 2 is used so that the distance between the lens 123 and the surface of the mask 2 becomes constant even if the height data of the surface of the mask 2 fluctuates due to the movement of the stage 111. Based on the feedback control, the height position of the stage 111 is adjusted.

When the stage 111 moves and the acquisition position of the optical image moves from the AF-ON region to the AF-OFF region (step S13_Yes), the Z controller 182 sets the AF control signal to the “OFF state” in order to turn off the autofocus control. Set to the L "level (step S14). Upon receiving the "L" level AF control signal, the Z driver control unit 181 turns off the autofocus control. When the Z driver control unit 181 receives the focus offset value from the Z controller 182, the Z driver control unit 181 changes the height position of the stage 111 (step S15).

For example, in the AF-OFF region, the Z controller 182 uses the position data acquired from the position circuit 174 and the position information acquired from the external storage 163 to determine that the acquisition position of the optical image is the boundary between the light-shielding region and the transmission region in the mask 2. That is, when it is determined that the step portion due to the light-shielding film 201 has been reached, the focus offset value for adjusting the height position of the stage 111 is transmitted to the Z driver control unit 181. More specifically, for example, the Z controller 182 sets a positive focus offset value so as to raise the height position of the stage 111 when the scanning direction is from the light-shielding region to the transmission region. Further, for example, the Z controller 182 sets a negative focus offset value so as to lower the height position of the stage 111 when the scanning direction is from the transmission region to the light-shielding region. Upon receiving the focus offset value, the Z driver control unit 181 controls the Z drive unit 116 so that the height position of the stage 111 becomes a set value obtained by adding the focus offset value. Therefore, in the AF-OFF region, the height position of the stage 111 is adjusted by open control based on the focus offset value.

When the stage 111 moves and the acquisition position of the optical image moves from the AF-OFF region to the AF-ON region (step S16_Yes), the Z controller 182 sets the AF control signal to the “ON state” in order to turn on the autofocus control. Set to H "level. Upon receiving the "H" level AF control signal, the Z driver control unit 181 turns on the autofocus control (step S17).

If the acquisition position of the optical image remains in the AF-OFF region even when the stage 111 moves (step S16_No), the process returns to step S15.

In a state where the acquisition position of the optical image is in the AF-ON region (step S13_Yes or step S17), the CPU 160 confirms whether the inspection region has been scanned (step S18).

If the scanning of the inspection area is not completed (step S18_No), the process returns to step S13, and the CPU 160 continues to acquire the optical image.

When the scanning of the inspection area is completed (step S18_Yes), the CPU 160 ends the optical image acquisition step (step S19). The acquired optical image is transmitted to the comparison circuit 173.

4.2 Reference image acquisition step Next, an example of the reference image acquisition step of FIG. 4 will be described. In the reference image acquisition process, a reference image based on the design pattern data is created.

First, the inspection device 1 acquires the design pattern data via the communication device 166 (step S21).

The acquired design pattern data is stored in, for example, the external storage 163 (step S22). The figures included in the design pattern are based on rectangles and triangles. The external storage 163 contains information such as coordinates at a reference position of a figure, side lengths, and a figure code that serves as an identifier for distinguishing a figure type such as a rectangle or a triangle, and the shape, size, and shape of each pattern figure. Graphic data that defines the position etc. is stored. Further, for example, a set of figures existing in a range of about several tens of μm is generally called a cluster or a cell, and data is layered using this. In the cluster or cell, the arrangement coordinates and the repetition description when various figures are arranged independently or repeatedly arranged at a certain interval are also defined. Cluster or cell data is further arranged for each inspection frame.

Next, the expansion circuit 171 reads out the design pattern data stored in the external storage 163. Then, the expansion circuit 171 converts (expands) the design pattern data into binary or multi-valued image data (design image data) (step S23). Then, this image data is sent to the reference circuit 172.

More specifically, when the design pattern data to be the graphic data is input to the expansion circuit 171, the expansion circuit 171 expands the design pattern data to the data for each graphic, and the graphic showing the graphic shape of the graphic data. Interpret codes, graphic dimensions, etc. Then, binary or multi-valued design image data is developed as a pattern arranged in a grid having a grid of predetermined quantization dimensions as a unit. The developed design image data calculates the occupancy rate of the figure in the design pattern for each area (square) corresponding to the sensor pixel. The figure occupancy rate in each pixel calculated in this way is the pixel value.

Next, the reference circuit 172 applies an appropriate filter process to the design image data, which is the image data of the graphic sent from the expansion circuit 171 (step S24).

More specifically, for example, the measurement data as an optical image obtained from the sensor circuit 126 is in a state in which the filter acts due to the resolution characteristics of the lens 124, the aperture effect of the photodiode array 125, or the like, in other words, continuously. It is in a changing analog state. Therefore, the reference circuit 172 filters the design image data whose image intensity (shade value) is a digital value, and creates a state in which it can be compared with the measurement data, that is, a reference image.

Then, the reference circuit 172 transmits the created reference image to the comparison circuit 173, and the reference image acquisition step ends (step S25).

4.3 Comparison step Next, an example of the comparison step in step S3 of FIG. 4 will be described. In step S3, the comparison circuit 173 compares the optical image sent from the sensor circuit 126 with the reference image sent from the reference circuit 172 using an appropriate comparison determination algorithm. Then, when the error exceeds a preset value, the comparison circuit 173 determines that the portion (coordinate position of the mask 2) is defective. For example, the coordinates of the defect, and the optical image and the reference image on which the defect determination is based may be displayed on the display device 164 after being stored in the external storage 163 as the inspection result, and may be displayed on the display device 164 via the communication device 166. It may be output to an external device (for example, a review device).

The defect determination can be performed by the following two types of methods. One is a method of determining a defect when a difference exceeding a preset threshold dimension is observed between the position of the contour line in the reference image and the position of the contour line in the optical image. The other one is a method of determining a defect when the ratio of the line width of the pattern in the reference image to the line width of the pattern in the optical image exceeds a preset threshold value. In this method, the ratio of the distance between the patterns in the reference image and the distance between the patterns in the optical image may be targeted.

5. Specific Examples of Auto Focus Control Next, specific examples of auto focus control will be described with reference to FIG. FIG. 5 is an enlarged view of the region RA of FIG. 3 and a view showing the height position of the stage 111. In the example of FIG. 5, the height position of the stage 111 when scanning the light for defect inspection from the transmission region to the light-shielding region is shown by a solid line. Further, the height position of the stage 111 when scanning the light for defect inspection from the light-shielding region to the transmission region is indicated by a broken line.

As shown in FIG. 5, first, a case of scanning from the transmission region toward the light-shielding region will be described. When the scan position (light irradiation position for defect inspection) is in the AF-ON region within the transmission region, the Z controller 182 sets the AF control signal to the “H” level. The Z driver control unit 181 executes autofocus control based on the “H” level AF control signal so that the distance between the lens 123 and the surface of the mask 2 becomes constant. More specifically, for example, the height position of the stage 111 when scanning the surface of the substrate 200 is T1, and the height position of the stage 111 when scanning the surface of the phase shift film 202 is T2. And. On the other hand, the Z driver control unit 181 sets the height position T2 of the stage when scanning the surface of the phase shift film 202 lower than the height position T1 when scanning the surface of the substrate 200, for example. When the thickness of the phase shift film 202 is Z2, T2 controls the Z drive unit 116 so that the value is substantially equal to that of T1-Z2. In the actual inspection, the area where the pattern is densely formed is scanned at high speed, and the Z position controlled by autofocus is between T1 and T2 due to the limitation of control responsiveness. ..

When the scan position moves from the AF-ON region in the transmission region to the AF-OFF region, the Z controller 182 sets the AF control signal to the “L” level. The Z driver control unit 181 turns off the autofocus control based on the "L" level AF control signal. The Z driver control unit 181 maintains the height position of the stage 111 during the period when the focus offset value is not received from the Z controller 182. For example, when the scanning position moves between the substrate 200 and the light-shielding film 201, the Z controller 182 sets a value (-Z1) based on the film thickness (Z1) of the light-shielding film 201 as a focus offset value. It is transmitted to the driver control unit 181. When the Z driver control unit 181 receives -Z1 as the focus offset value, -Z1 is added to the current height position T1 of the stage 111 to obtain T1-Z1. That is, the Z driver control unit 181 controls the Z drive unit 116 so that the height position of the stage 111 is lowered by Z1.

When the scan position moves from the AF-OFF region to the AF-ON region in the light-shielding region, the Z controller 182 sets the AF control signal to the “H” level. The Z driver control unit 181 executes autofocus control based on the "H" level AF control signal so that the distance between the lens 123 and the surface of the mask 2 (the surface of the light-shielding film 201) becomes constant. More specifically, for example, the height position of the stage 111 when scanning the surface of the light-shielding film 201 is T3. Then, the Z driver control unit 181 Z so that the height position T3 of the stage when scanning the surface of the light-shielding film 201 is lower than the height position T1 when scanning the surface of the substrate 200. Controls the drive unit 116. For example, when the film thickness of the light-shielding film 201 is Z1, T3 has a value substantially equal to that of T1-Z1.

Next, a case of scanning from the light-shielded area toward the transparent area will be described. First, when the scan position is in the AF-ON region within the light-shielding region, the Z controller 182 sets the AF control signal to the “H” level. The Z driver control unit 181 executes autofocus control based on the "H" level AF control signal.

When the scan position moves from the AF-ON region in the light-shielding region to the AF-OFF region, the Z controller 182 sets the AF control signal to the “L” level. The Z driver control unit 181 turns off the autofocus control based on the "L" level AF control signal. The Z driver control unit 181 maintains the height position of the stage 111 during the period when the focus offset value is not received from the Z controller 182. For example, when the scanning position moves between the substrate 200 and the light-shielding film 201, the Z controller 182 sets a value (+ Z1) based on the film thickness (Z1) of the light-shielding film 201 as the focus offset value of the Z driver. It is transmitted to the control unit 181. When the Z driver control unit 181 receives + Z1 as the focus offset value, + Z1 is added to the current height position T3 of the stage 111 to obtain T3 + Z1. That is, the Z driver control unit 181 controls the Z drive unit 116 so that the height position of the stage 111 is higher by Z1.

When the scan position moves from the AF-OFF region to the AF-ON region in the transmission region, the Z controller 182 sets the AF control signal to the “H” level. The Z driver control unit 181 executes autofocus control based on the "H" level AF control signal.

6. Effect of the present embodiment With the configuration of the present embodiment, an inspection device and an inspection method capable of suppressing a decrease in defect detection accuracy for a sample having a step that makes it difficult to follow the autofocus control are provided. can do. This effect will be described in detail.

For example, in a halftone mask, the film thickness of the light-shielding film 201 is thicker than the film thickness of the phase shift film 202. Therefore, when the light for defect inspection scans the surface of the halftone mask, the autofocus control may not be able to follow the stepped portion between the substrate 200 and the light-shielding film 201 having a relatively large stepped portion. An example of this is shown in FIG. FIG. 6 is a diagram showing an example of the height position of the stage 111 when the autofocus control is constantly executed in the region RA as a comparative example of FIG.

As shown in FIG. 6, the Z position of the autofocus is temporarily not determined at the stepped portion between the substrate 200 and the light-shielding film 201, and the autofocus control cannot follow due to the control delay of the autofocus mechanism. Therefore, for example, after passing through the stepped portion between the substrate 200 and the light-shielding film 201, an overshoot due to a control delay of the height position of the stage 111 causes an error in setting the height position. As a result, the height position of the stage 111 fluctuates regardless of the actual height position of the surface of the mask 2. Further, even when scanning is executed from the light-shielding region to the transmission region, the height position adjustment of the stage 111 corresponding to the phase shift film 202 is delayed due to the overshoot due to the control delay of the height position of the stage 111. The image of the optical image may be blurred. Therefore, the accuracy of defect inspection may deteriorate.

On the other hand, in the configuration according to the present embodiment, the autofocus control can be turned off in a region where it is difficult to follow the autofocus control. Further, in the region where the autofocus control is not executed, the height position of the stage 111 can be adjusted by the open control based on the focus offset value. As a result, it is possible to suppress a decrease in the detection accuracy of defects due to the focus shift of the optical image.

7. Deformation Examples, etc. The above-described embodiment has been described by exemplifying an inspection device for inspecting a mask (halftone mask) used as a sample in a photolithography method or the like. However, the scope of application of the technique according to this embodiment is not limited to this. For example, as a sample, a template used for nanoimprint lithography (NIL) may be used. As the sample, a wafer, a substrate used for a liquid crystal display device, or the like may be used. Further, the autofocus mechanism described in the above-described embodiment is not limited to the inspection device, and may be applied to other devices such as a charged particle beam drawing device used for manufacturing a mask.

The present invention is not limited to the above embodiment, and can be variously modified at the implementation stage without departing from the gist thereof. In addition, each embodiment may be carried out in combination as appropriate, in which case the combined effect can be obtained. Further, the above-described embodiment includes various inventions, and various inventions can be extracted by a combination selected from a plurality of disclosed constituent requirements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, if the problem can be solved and the effect is obtained, the configuration in which the constituent requirements are deleted can be extracted as an invention.

1 ... Inspection device, 2 ... Mask, 10 ... Optical image acquisition device, 20 ... Control device, 111 ... Stage, 112 ... XY drive unit, 113 ... X-axis motor, 114 ... Y-axis motor, 116 ... Z drive unit, 117 ... Z-axis actuator, 120 ... first light source, 121, 123, 124 ... lens, 122, 131, 132 ... mirror, 125 ... photodiode array, 126 ... sensor circuit, 130 ... second light source, 133 ... height Measurement system, 134 ... Height position sensor, 135 ... Height measurement control unit, 140 ... Laser length measurement system, 150 ... Autoloader, 160 ... CPU, 161 ... RAM, 162 ... ROM, 163 ... External storage, 164 ... Display device , 165 ... Input device, 166 ... Communication device, 167 ... Autoloader control circuit, 168 ... Light source control circuit, 169 ... XY drive unit control circuit, 170 ... Z drive unit control circuit, 171 ... Deployment circuit, 172 ... Reference circuit, 173. ... Comparison circuit, 174 ... Position circuit, 180 ... Z driver, 181 ... Z driver control unit, 182 ... Z controller, 200 ... Substrate, 201 ... Light-shielding film, 202 ... Phase shift film, 211-216 ... Inspection frame.

Claims (8)

The stage on which the sample is placed and
A light source that emits light used to acquire an optical image of the sample,
A first measuring unit that measures the first height position of the surface of the sample in the first direction perpendicular to the surface of the stage.
The stage position of the stage in a second direction parallel to the surface of the stage and intersecting the first direction and a third direction parallel to the surface and intersecting the first and second directions. The second measuring unit to measure and
A height control unit that controls the stage in the first direction to a second height position,
A controller for transmitting a control signal for autofocus control and a focus offset value of the light to irradiate the sample to the height control unit is provided.
When the light irradiation position is within the first region on the surface of the sample, the height control unit controls the autofocus based on the data of the first height position measured by the first measurement unit. When the irradiation position is in a second region different from the first region, the second height position is changed based on the focus offset value received from the controller.
Inspection equipment. The controller uses the control signal and the focus based on the stage position data measured by the second measurement unit, position information regarding the first and second regions, and surface height information of the sample. The offset value is transmitted to the height control unit.
The inspection device according to claim 1. The position information further includes information about a step portion provided on the surface of the sample in the second region.
The controller transmits the focus offset value to the height control unit when the irradiation position passes over the step portion in the second region.
The inspection device according to claim 2. The position coordinates of the first region and the second region are coordinates based on the layout information of the pattern of the sample, and the controller uses the control signal as the first logic when the irradiation position is within the first region. When the irradiation position is within the second region, the control signal is set to a second logic level different from the first logic level.
The inspection device according to any one of claims 1 to 3. The inspection device according to claim 1, wherein the focus offset value is a value based on the height information of the surface of the sample. An actuator using a piezoelectric element that moves the stage in the first direction based on control by the height control unit is further provided.
The inspection device according to any one of claims 1 to 5. The process of placing the sample on the stage and
The sample is provided with a step of irradiating the sample with light to acquire an optical image.
When the light irradiation position is within the first region of the sample, the step of acquiring the optical image is the data of the first height position of the surface of the sample in the first direction perpendicular to the surface of the stage. And a step of executing autofocus control of the light to irradiate the sample based on the acquired data of the first height position.
When the irradiation position is in a second region different from the first region of the sample, the step of acquiring the optical image is the first step using the focus offset value based on the height information of the surface of the sample. Including the step of changing the stage in the direction to the second height position.
Inspection method. The step of changing the second height position is executed when the irradiation position passes over a step portion provided on the surface of the sample in the second region.
The inspection method according to claim 7.

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