JP7215886B2 - inspection equipment - Google Patents

Description

The present invention relates to an inspection device. For example, the present invention relates to an apparatus for inspecting pattern defects of an exposure mask substrate used in semiconductor manufacturing.

2. Description of the Related Art In recent years, as large-scale integrated circuits (LSIs) have become highly integrated and have large capacities, the circuit line width required for semiconductor elements has become increasingly narrow. These semiconductor elements are manufactured by exposing and transferring the pattern onto a wafer using a reduction projection exposure apparatus called a stepper using an original image pattern (also called a mask or reticle, hereinafter collectively referred to as a mask) on which a circuit pattern is formed. Manufactured by circuit forming. Therefore, a pattern drawing apparatus using an electron beam capable of drawing a fine circuit pattern is used to manufacture a mask for transferring such a fine circuit pattern to a wafer. A pattern circuit may be drawn directly on a wafer using such a pattern drawing apparatus. Alternatively, attempts have been made to develop a laser beam drawing apparatus that uses a laser beam for drawing in addition to the electron beam.

In addition, the improvement of yield is essential for the manufacture of LSIs, which requires a great manufacturing cost. However, as typified by 1 gigabit class DRAMs (random access memories), patterns constituting LSIs are on the order of nanometers. One of the major causes of yield reduction is the pattern defect of the mask used when exposing and transferring an ultra-fine pattern onto a semiconductor wafer by photolithography. In recent years, as the dimensions of LSI patterns formed on semiconductor wafers have become finer, the dimensions that must be detected as pattern defects have become extremely small. Therefore, it is necessary to improve the precision of pattern inspection apparatuses for inspecting defects in transfer masks used in LSI manufacturing.

As an inspection method, an optical image of a pattern formed on a sample, such as a lithography mask, captured at a predetermined magnification using a magnifying optical system is compared with an optical image of the design data or the same pattern on the sample. It is known to perform the inspection by For example, as a pattern inspection method, there is a "die to die inspection" that compares optical image data obtained by imaging the same pattern at different locations on the same mask, and a pattern is inspected using pattern-designed CAD data as a mask. The drawing data (design pattern data) converted into the device input format for input by the drawing device at the time of drawing is input to the inspection device, and based on this, the design image (reference image) is generated, and the pattern is imaged. There is a "die to database inspection" that compares the measured data to the optical image. In the inspection method for such an inspection apparatus, an inspection object is placed on a table, and the table is moved to scan a light beam over the sample for inspection. An object to be inspected is irradiated with a light beam by a light source and an illumination optical system. The light transmitted or reflected by the object to be inspected is imaged on the sensor via the optical system. The image captured by the sensor is sent to the comparison section as measurement data. After aligning the images, the comparison unit compares the measurement data and the reference data according to an appropriate algorithm, and determines that there is a pattern defect if they do not match.

As described above, pattern inspection methods include transmission inspection for inspecting a transmitted image transmitted through an object to be inspected and reflection inspection for inspecting a reflected image reflected from the object to be inspected. In some cases, transmission/reflection inspection is performed to inspect both of these simultaneously. When conducting a transmission/reflection inspection, the light from the light source is split into two, one for the transmission inspection and the other for the reflection inspection, which are simultaneously irradiated to different positions on the object to be inspected via different illumination optical systems. .

By the way, if the amount of light is changed due to the light source or the optical system, the gradation value of the optical image data is changed, and the accuracy of the pattern inspection may be lowered. A portion of the inspection light is used as correction light to detect the variation in the amount of light, thereby improving the inspection accuracy. If the amount of light required for defect inspection changes, the amount of correction light also changes, making it impossible to appropriately correct the variation in the amount of light.

JP 2014-222175 A

Accordingly, one aspect of the present invention provides an inspection apparatus capable of adjusting the amount of correction light.

An inspection apparatus according to one aspect of the present invention can change the amount of the correction light by dividing the light from the light source into the light that illuminates the object to be inspected and the correction light that does not pass through the surface of the object to be inspected. An optical element, a sensor for receiving the correction light, a displacement rate calculator for calculating the displacement rate of the light amount of the correction light received by the sensor, and an inspection target based on the light amount of the light reflected by illuminating the inspection object. It includes an optical image creating unit that creates optical image data, and a light amount correcting unit that corrects the optical image data based on the displacement rate.

In the inspection apparatus described above, the optical element includes a first light branching element, a half-wave plate, a first quarter-wave plate, a second quarter-wave plate, and a mirror. The light passes through the half-wave plate, and the light passing through the half-wave plate is split by the first light splitting element into light for illuminating the object to be inspected and correction light. The correction light branched by the light branching element passes through the first quarter-wave plate and is reflected by the mirror , and the correction light reflected by the mirror passes through the first quarter-wave plate. The corrected light that passes through and is reflected by the first light branching element is received by the sensor, and the light that is branched by the first light branching element and illuminates the inspection object is , the light passing through the second quarter-wave plate and illuminating the object to be inspected after passing through the second quarter-wave plate preferably illuminates the surface of the object to be inspected.

In the inspection apparatus described above, the first optical branching element is a polarizing beam splitter, and by adjusting the optical axis direction of the half-wave plate, the first optical branching element illuminates the object to be inspected. and correction light are preferably adjusted.

In the inspection apparatus described above, the optical element has a second light branching element, a light control filter, and a mirror, and the light from the light source is converted into light correction light that illuminates the object to be inspected by the second light branching element. The correction light branched and branched by the second light branching element passes through the light control filter and is reflected by the mirror, and the correction light reflected by the mirror passes through the light control filter and enters the second light branch. The corrected light reflected by the element and reflected by the second light splitting element is received by the sensor, and the light split by the second light splitting element to illuminate the object to be inspected irradiates the surface of the object to be inspected. preferably.

In the inspection apparatus described above, it is preferable that the second light branching element is a reflection-transmission member, and adjusts the light amount of the correction light by adjusting the light transmittance of the light control filter.

In the inspection apparatus described above, the difference between the amount of light received by the sensor receiving the light and the amount of light reflected by the object to be inspected is within ±0.5% with respect to the amount of light received by the sensor. It is preferable to adjust the optical element so that

The inspection apparatus described above includes a transmission illumination optical system for illuminating an object to be inspected with light from the light source, and a third light splitting element for splitting the light from the light source into the transmission illumination optical system side and the optical element side. The difference between the amount of light received by the sensor that receives the light and the amount of light reflected by the object to be inspected is within ±0.5% of the amount of light received by the sensor, and the correction light is received by the sensor. The difference in the amount of light received by the sensor that receives the light transmitted through the transmitted illumination optical system and the object to be inspected is within ±0.5% of the amount of light received, and the object to be inspected is illuminated and reflected. The difference between the amount of light received by the sensor that receives the light and the amount of light that has passed through the inspection object through the transmission illumination optical system with respect to the amount of light received by the sensor that receives the light is within 0.5%. It is preferable to adjust the optical element and the third optical branching element so that

According to one aspect of the present invention, it is possible to suitably correct the influence of light intensity variation due to a light source or optical factors.

1 is a configuration diagram showing the configuration of a pattern inspection apparatus according to Embodiment 1; FIG. 4 is a flow chart diagram showing main steps of a pattern inspection method according to the first embodiment; FIG. FIG. 10 is a configuration diagram showing the configuration of a pattern inspection apparatus according to Embodiment 2; FIG. 10 is a flow chart showing main steps of a pattern inspection method according to a second embodiment;

Embodiment 1
FIG. 1 is a configuration diagram showing the configuration of the pattern inspection apparatus according to the first embodiment. In FIG. 1, an inspection apparatus 100 for inspecting defects in a pattern formed on an object to be inspected Ma includes a control unit 110 for controlling the inspection apparatus 100 and an optical image acquisition mechanism 150 for imaging the object to be inspected Ma. The object to be inspected Ma is, for example, a mask.

The control unit 110 includes, for example, a control computer 121, a bus 122, a table control unit 131, a position calculation unit 132, a reference image creation unit 133, a comparison unit 134, a light amount correction unit 135, a displacement rate calculation unit 136, and an optical image creation unit 137. , a storage device 141 , a pattern monitor 142 , a monitor 143 and a printer 144 . The optical image forming section 137 has a reflection signal processing section 137a and a transmission signal processing section 137b.

The optical image acquisition mechanism 150, for example, the light source 161, the magnifying optical system 162, the third light branching element 163, the mirror 164, the XYθ table 165, the laser length measurement system 166, the mirror 167, the light from the light source 161 to the inspection object. An optical element (hereinafter referred to as a light branching and adjusting element) 180 that can split the light illuminating Ma and the correction light that does not pass through the surface of the object to be inspected Ma and change the light amount of the correction light, an objective lens 168, and a mirror 169. , a mirror 170 , a lens 171 , a transmission TDI (Time Delay Integration) sensor 172 , a mirror 173 , a lens 174 and a reflection TDI sensor 175 .

A control computer 121 that controls the entire inspection apparatus 100 provides a table control unit 131 , a position calculation unit 132 , a reference image creation unit 133 , a comparison unit 134 , a light intensity correction unit 135 , a displacement rate calculation unit 136 , an optical It is connected to the image forming section 137 , storage device 141 , pattern monitor 142 , monitor 143 and printer 144 .

The table control unit 131 is connected to and controlled by the XYθ table 165 . The XYθ table 165 is driven by, for example, an X-axis motor, a Y-axis motor, and a θ-axis motor. The comparison section 134 is connected to the position calculation section 132 , the reference image creation section 133 and the light amount correction section 135 . The position calculator 132 is connected to the laser length measurement system 166 . The light amount correction section 135 is connected to the displacement rate calculation section 136 and the optical image generation section 137 . The reflection signal processor 137 a of the optical image generator 137 is connected to the reflection TDI sensor 175 , and the transmission signal processor 137 b is connected to the transmission TDI sensor 172 .

The branching light control element 180 of Embodiment 1 includes a half wavelength plate 181, a first optical branching element 182, a first quarter wavelength plate 183, a mirror 184 and a second quarter wavelength It has a plate 185 . A polarizing beam splitter is preferable as the first optical branching element 182 . A half-wave plate 181 and a polarizing beam splitter 182 are combined to split the light from the light source 161 into light for illuminating the object to be inspected Ma and correction light not passing through the surface of the object to be inspected Ma at an arbitrary ratio. can be done.

The light (solid line) emitted from the light source 161 is adjusted to an arbitrary imaging magnification by the magnifying optical system 162, and is split by the third light splitting element 163 into the transmitted illumination optical system side (broken line) and the optical path light splitting/adjusting element 180. side (chain line). The third optical branching element 163 includes, for example, a transmissive reflector or a half-wave plate and a polarizing beam splitter. When the object to be inspected Ma is not inspected by the light passing through the object to be inspected Ma, the third light branching element 163 can be replaced with a mirror. The amount of light transmitted through the object to be inspected Ma received by the sensor that receives the light, the amount of light reflected by the object to be inspected Ma received by the sensor that receives the light, and the correction light received by the sensor The branching ratio of the third light branching element 163 is adjusted so that the amount of light received by the sensors is approximately the same.

Transillumination optics includes mirror 164 . The light that has passed through the transmission illumination optical system illuminates the object to be inspected Ma placed on the XYθ table 165 . The light that has passed through the object to be inspected Ma passes through the objective lens 168 , the second quarter-wave plate 185 of the light branching and adjusting device 180 , and the first light branching device 182 . The light that has passed through the object to be inspected Ma and passed through the first optical branching element 182 is reflected by the mirror 169 and further reflected by the mirror 170 . The light transmitted through the object to be inspected Ma and reflected by the mirror 170 passes through the lens 171 and is received by the transmission TDI sensor 172 . The light received by the transmission TDI sensor 172 is photoelectrically converted, the signal is processed by the transmission signal processing unit 137b of the optical image generation unit 173, and optical image data is generated based on the light transmitted through the object to be inspected Ma. be. Although the TDI sensor is mentioned as the sensor, it is not limited to the TDI sensor.

The light branched to the light branching and adjusting device 180 side is reflected by the mirror 167 . The light reflected by the mirror 167 passes through the half-wave plate 181 and is reflected by the first optical branching element 182 to illuminate the object to be inspected Ma (long dashed line) and the first optical branching element 182 is branched into the correction light (short dashed line) that has passed through the . The ratio of splitting into the light for illuminating the object to be inspected Ma and the correction light is selected in consideration of the reflectance of the object to be inspected Ma and loss due to other optical elements. The ratio of splitting into the light reflected by illuminating the inspection object Ma and the correction light is the amount of light reflected by the inspection object Ma received by the sensor that receives the light and the correction light receiving the light. It is preferable that the ratio of the amount of light received by each sensor is adjusted to be approximately the same.

The light (correction light) that has passed through the first optical branching element 182 passes through the first quarter-wave plate 183 and is reflected by the mirror 184 . The light reflected by the mirror 184 passes through the first quarter-wave plate 183 again, is reflected by the first optical branching element 182, and is guided to the mirror 169 side. The correction light guided to the mirror 169 side is reflected by the mirror 169 . The correction light reflected by the mirror 169 is reflected by the mirror 173 , passes through the lens 174 , and is received by the correction light area of the reflection TDI sensor 175 . The light received by the reflection TDI sensor 175 is photoelectrically converted, the signal is processed by the displacement rate calculator 136, and the displacement rate of the light amount of the correction light (time light amount change rate) is obtained. In FIG. 1, the inspection apparatus 100 is configured such that the correction light is received by the reflection TDI sensor 175, but the inspection apparatus 100 is configured so that the correction light is received by the transmission TDI sensor 172. may have been

The temporal change in the amount of correction light is due to optical factors such as changes in the amount of light emitted from the light source 161 and fluctuations. The change in the amount of correction light over time occurs in both the light that illuminates and passes through the object to be inspected Ma and the light that illuminates and reflects from the object to be inspected Ma. The light transmitted through the object to be inspected Ma and the light reflected by the object to be inspected Ma are the inspection light. In addition, the amount of light received varies depending on the inspection itself of the object to be inspected Ma. Therefore, it is not possible to distinguish whether the change in the amount of received light is due to the change in the amount of light emitted from the light source 161, optical factors, or the like, or due to the inspection of the object to be inspected Ma. The change in the amount of correction light is not affected by the inspection of the object to be inspected Ma, and is not reflected by the object to be inspected Ma. It is possible to accurately measure the change in the amount of light emitted, the temporal change in the amount of light caused by fluctuations, and the like. Even if the amount of light emitted from the light source 161 is measured, the change in amount of light due to optical factors cannot be measured. The correction light is light that illuminates and passes through the object to be inspected Ma, light that illuminates and reflects from the object to be inspected Ma, or light that illuminates and passes through the object to be inspected Ma, and illuminates the object to be inspected Ma. Since the light is received by the sensor at the same time as the reflected light, the light intensity variation rate at the inspection position of the object to be inspected Ma can be easily obtained.

The light illuminating the inspection target Ma reflected by the first optical branching element 182 passes through the second quarter-wave plate 185 . The light that illuminates the object to be inspected Ma that has passed through the second quarter-wave plate 185 illuminates the object to be inspected Ma. The light reflected by illuminating the object to be inspected Ma passes through the second quarter-wave plate 185 again. The light reflected by the object to be inspected Ma and passed through the second quarter-wave plate 185 passes through the first optical branching element 182 and is reflected by the mirror 169 . The light reflected by the object to be inspected Ma, passed through the second quarter-wave plate 185 and reflected by the mirror 169 is reflected by the mirror 173 . The light reflected by the mirror 173 passes through the lens 174 and is received by the reflection TDI sensor 175 . The area of the reflective TDI sensor 175 that receives the light reflected by the object to be inspected Ma is different from the area of the reflective TDI sensor 175 that receives the correction light. The light received by the reflective TDI sensor 175 is photoelectrically converted, the signal is processed by the reflective signal processing unit 137a of the optical image creating unit 173, and optical image data is created based on the light reflected by the object to be inspected Ma. be done.

The gradation value of the optical image data is corrected by the light amount correction unit 135 in consideration of the light amount change rate of the correction light. Optical image data may also be subjected to other image processing.

The movement position of the XYθ table 165 from the laser length measurement system 166 is sent to the position information section 132 . Then, the position information of the object to be inspected Ma is calculated by the position information unit 132 . The corrected optical image data is sent to the comparing section 134 together with the reference optical image data created by the reference image creating section 133 and the position information. The comparison unit 134 compares the optical image data and the reference optical image data to detect defects in the inspection object Ma. The detected defects are stored in the storage device 141 together with the position information.

In the embodiment, the correction light can be branched and dimmed by a relatively simple optical element and guided to the sensor. Further, the correction light is received by a sensor that illuminates the object to be inspected Ma and receives the light transmitted therethrough or by a sensor that receives light that is reflected by illuminating the object to be inspected Ma and is photoelectrically converted. The correction light can be measured with the same configuration (method) as that for inspecting the object Ma for the light amount variation rate caused by factors other than the inspection, which occurs in the light for inspecting the object Ma to be inspected. Therefore, it is possible to accurately measure the change in the amount of light due to optical factors that occur in the optical path through which the light inspecting the object to be inspected Ma passes. If the correction light passes through a completely different optical path from the light for inspecting the object to be inspected Ma, it is impossible to accurately measure the change in the amount of light due to optical factors.

Here, in FIG. 1, constituent parts necessary for explaining the first embodiment are described. It goes without saying that other configurations normally required for the inspection apparatus 100 may be included. Also, although FIG. 1 includes an optical element, a sensor, and a signal processing system for performing pattern inspection from light transmitted through the object to be inspected Ma, these can be omitted.

FIG. 2 is a flow chart showing main steps of the pattern inspection method according to the first embodiment. 2, the pattern inspection method according to the first embodiment includes a first inspection light measurement step (S101), a second inspection light measurement step (S102), a first branch ratio adjustment step (S103), a second Branch ratio adjustment step (S104), total light amount adjustment step (S105), scanning step (S106), optical image creation step (S107), light amount displacement rate calculation step (S108), optical image correction step (S109), reference image creation Each step of the step (S110) and the comparison step (S111) is performed. Before performing the above steps, it is preferable to perform calibration by adjusting the characteristics of the TDI sensor to reduce (or eliminate) variations in the sensor characteristics. Each step will be described below.

<First Inspection Light Measurement Step (S101)>
The first inspection light measurement step (S101) is a step of illuminating the inspection object Ma and measuring the amount of light transmitted therethrough. Preferably, after performing calibration, the first inspection light measurement step is performed. Specifically, the light emitted from the light source 161, passes through the magnifying optical system 162, is branched by the third light branching element 163, and is reflected by the mirror 164 to illuminate the inspection object Ma. The object to be inspected Ma is illuminated, the amount of transmitted light is received by the transmission TDI sensor 172, the object to be inspected Ma is illuminated, and the amount of transmitted light is measured. The analog signal photoelectrically converted by the transmission TDI sensor 172 is processed including digital conversion by the transmission signal processing unit 137b. Then, optical image data is created from the light transmitted by illuminating the object to be inspected Ma by the transmission signal processing unit 137b.

By measuring the amount of light transmitted through the object to be inspected Ma in advance, it is possible to reduce the difference between the amount of light transmitted through the object to be inspected Ma and the amount of light received by the correction light. can do it This process may be carried out when inspecting the object to be inspected Ma for defects using light that illuminates the object to be inspected and passes through the object to be inspected.

This step is omitted when there is no transmission illumination optical system or when the object to be inspected Ma is not inspected by light that illuminates and passes through the object to be inspected Ma.

<Second Inspection Light Measurement Step (S102)>
The second inspection light measurement step (S102) is a step of illuminating the inspection target Ma and measuring the amount of reflected light. Specifically, the light is emitted from the light source 161 , passes through the magnifying optical system 162 , is branched to the light branching and adjusting device 180 side by the third light branching device 163 , is reflected by the mirror 167 , and is reflected by the half-wave plate 181 . , is branched (reflected) by the first optical branching element 182, passes through the second quarter-wave plate 185, passes through the objective lens 168, and illuminates the object to be inspected Ma. At this time, the optical axis direction of the half-wave plate 181 is adjusted so that no light passes through the polarization beam splitter 182 (reflection:transmission=1:0). The TDI sensor 175 for reflection receives the amount of light reflected by illuminating the object to be inspected Ma to measure the amount of light. The analog signal photoelectrically converted by the reflection TDI sensor 175 is processed including digital conversion by the reflection signal processing unit 137a. The amount of light received by the reflection TDI sensor 175 changes depending on the reflectance of the object to be inspected Ma.

By illuminating the object to be inspected Ma in advance and measuring the amount of reflected light, the difference between the amount of light reflected and received by the object to be inspected Ma and the amount of light received by the correction light can be reduced. can be adjusted.

<First branch ratio adjustment step (S103)>
The first branch ratio adjustment step (S103) is a step of changing the ratio between the light reflected by illuminating the inspection object Ma and the correction light. The optical axis direction of the half-wave plate 181 of the light branching/adjusting element 180 is adjusted in order to change the ratio of the light that illuminates the inspection target Ma and the correction light. In Embodiment 1, the light from the light source 161 is split into the light that illuminates the object to be inspected Ma and the correction light that does not pass through the surface of the object to be inspected Ma. A plate 181 and a polarizing beam splitter 182 are combined. Therefore, by adjusting the optical axis direction of the half-wave plate 181, the ratio of the light reflected by the polarization beam splitter 182 and the light transmitted through the polarization beam splitter 182 can be adjusted. The correction light passes through polarizing beam splitter 182 , through first quarter-wave plate 183 , is reflected off mirror 184 , and passes through first quarter-wave plate 183 again. The light that has passed through the first quarter-wave plate 183 again is reflected by the polarization beam splitter 182 and received by the reflection TDI sensor 175 .

When calibration is performed, the sensitivity of the TDI sensor is adjusted in advance, so the splitting ratio of the polarizing beam splitter 182, that is, 1/2, is calculated from parameters including the measured reflectance of the object to be inspected Ma. The optical axis direction of the wave plate 181 can be determined. Also, while adjusting the optical axis direction of the half-wave plate 181, the amount of light received by the reflecting TDI sensor 175 is measured to illuminate the object to be inspected Ma, and the reflected light receives the light. The ratio of the amount of light received by the sensor and the amount of correction light received by the sensor that receives the light can be adjusted.

The difference Δ1 (=([illuminating the inspection object Ma Amount of light received by the sensor that receives the light reflected by the light] - [Amount of light that the correction light received by the sensor that receives the light]) / [Correction light received by the sensor that receives the light] The amount of light applied]) is preferably ±0.5% or less. When the light quantity difference Δ1 is small, the S/N ratio of the correction light and the S/N ratio of the light reflected and received by illuminating the inspection object Ma are approximately the same, and the accuracy of correction using the correction light is improved. From the same point of view, the difference Δ1 in the amount of light is more preferably ±0.25% or less.

<Second branch ratio adjustment step (S104)>
As the second branching ratio adjustment step (S104), the branching ratio of the third optical branching element 163 is adjusted. By adjusting the branching ratio of the third light branching element 163, the ratio of the light branched to the transmitted illumination optical system side and the light branching and adjusting element 180 side is adjusted. More specifically, the amount of light transmitted by illuminating the object to be inspected Ma received by a sensor that receives the light and the amount of light that is reflected by illuminating the object to be inspected Ma by the sensor that receives the light and the ratio of the amount of light received by the sensor that receives the light transmitted by illuminating the object to be inspected Ma and the amount of correction light received by the sensor that receives the light. It is preferred that the ratios are comparable. The difference Δ2 between the amount of light received by the sensor that receives the correction light and the amount of light that is received after illuminating the object to be inspected Ma (=([light that is transmitted by illuminating the object to be inspected Ma is the amount of light received by the sensor that receives the light] - [the amount of light received by the sensor that receives the correction light]) / [the amount of light received by the sensor that receives the correction light]) is , ±0.5% or less. From the same point of view, the difference Δ2 in the amount of light is more preferably ±0.25% or less.

Comparing the optical image data created based on the light transmitted by illuminating the object to be inspected Ma and the optical image data created based on the light reflected by illuminating the object to be inspected Ma In view of the fact that the amount of light is changed, it is preferable that the amount of correction associated with the change in the amount of light be the same or approximately the same. If the amount of correction is greatly different between the optical image data based on reflection and the optical image data based on transmission, it is not preferable that the accuracy of correction of both image data will be greatly different. Therefore, the difference Δ3 (=([ Amount of light received by a sensor that illuminates and passes through the inspection target Ma]−[Amount of light that is reflected by illuminating the inspection target Ma and received by a sensor that receives the light ])/[amount of light received by the sensor that receives the light reflected by illuminating the inspection target Ma]) is preferably ±0.5% or less. From the same point of view, the difference Δ3 in the amount of light is more preferably ±0.25% or less.

<Overall Light Amount Adjustment Step (S105)>
In the overall light intensity adjustment step (S105), the light intensity emitted from the light source 161 is adjusted. Since the light amount of each branched light is reduced by performing the above steps, the output of the light source 161 is adjusted so as to obtain an appropriate light amount. It is preferable that the differences .DELTA.1 to .DELTA.3 between the amounts of light are suitable values even after the adjustment of the total amount of light. The amount of correction light received by the sensor that receives the light after the overall light amount adjustment step (S105) is defined as a reference light amount (reference light amount of correction light). The reference light quantity is used as a reference value for light quantity fluctuations during scanning.

<Scanning step (S106)>
The scanning step (S106) is a step of scanning the inspection target area of the inspection target Ma. In the scanning process, the object to be inspected Ma is scanned, and the signal received by the transmission TDI sensor 172 is sent to the transmission signal processing unit 137b, and the signal received by the reflection TDI sensor 175 is used as a reflection image. It is sent to the processing unit 137a. In the scanning process, a signal of the inspection light received by the reflection TDI sensor 175 is sent to the displacement rate calculator 136 so that the change in the amount of light during inspection can be reflected in the optical image data. During the scanning step (S106), the laser length measurement system 166 measures the position of the XYθ table 165. FIG. The acquired position information is output to the position calculator 132 . The position calculation unit 132 calculates the position of the object to be inspected Ma using the measured position information. The calculated position of the object to be inspected Ma is used for specifying a defect position, creating optical image data, comparing and correcting the data.

<Optical Image Creation Step (S107)>
The optical image creation step (S107) is a step of processing the signals obtained in the scanning step to create optical image data. A signal received by the transmission TDI sensor 172 is sent to the transmission signal processing section 137b and converted from an analog signal to a digital signal. The converted digital signal is optionally subjected to amplification processing and the like, and is stored in the storage device 141 as optical image data. A signal received by the reflection TDI sensor 175 is sent to the reflection signal processing section 137a and converted from an analog signal to a digital signal. The converted digital signal is optionally subjected to amplification processing and the like, and is stored in the storage device 141 as optical image data.

<Light amount variation rate calculation step (S108)>
The light quantity change rate calculation step (S108) is a step of calculating the light quantity change rate during scanning. A signal obtained by receiving the correction light by the reflection TDI sensor 175 is sent to the displacement rate calculation unit 136 and converted into a digital signal in the same manner as the signal obtained by scanning the object to be inspected Ma. The signal is processed in the same manner as the signal obtained by scanning the object to be inspected Ma, and is stored in the storage device as image data or data including position information and gradation value information. The light amount displacement rate is obtained from the reference light amount of the correction light and the measured light amount of the correction light (more specifically, the reference gradation value, which is the gradation value of the reference light amount of the correction light, is obtained, and the reference gradation value and the measured The light amount displacement rate is obtained from the gradation value of the corrected light that has been corrected). Specifically, the light amount displacement rate is obtained by [measured light amount of correction light]/[reference light amount of correction light] (more specifically, [measured gradation value of correction light]/[correction light gradation value of the reference light amount of light]). The light amount variation rate is stored in the storage device as correction data for optical image data including image data or position information and the light amount variation rate.

<Optical Image Correction Step (S109)>
The optical image correction step (S109) is a step of correcting the optical image data using the obtained light amount displacement rate (correction data). Specifically, the gradation value of the optical image data is corrected. The corrected optical image data is stored in storage device 141 . The correction of the light amount change rate is a process of dividing the light amount (gradation value) of the inspection target area of the inspection target Ma in the optical image data by the light amount change rate when the inspection target area is inspected.

When correcting the optical image data created from the light reflected by illuminating the object to be inspected Ma, the amount of light received by the sensor that receives the light reflected by the object to be inspected (more specifically Specifically, the gradation value of the amount of light received by the sensor that receives the light reflected by illuminating the object to be inspected is divided by the light intensity displacement rate ([illuminating the object to be inspected and reflected Quantity of light received by the sensor that receives the light]÷[Light quantity change rate] The gradation value of the amount of light applied]÷[the rate of change in the amount of light]) to correct the optical image data. Similarly, when correcting the optical image data created from the light that illuminates and passes through the object to be inspected Ma, the amount of light ( More specifically, the gradation value of the amount of light received by the sensor that receives the light transmitted by illuminating the object to be inspected Ma is divided by the light intensity displacement rate ([illuminating the object to be inspected Quantity of light received by the sensor that receives the light] ÷ [Light quantity change rate] The gradation value of the amount of light applied]÷[the rate of change in the amount of light]) to correct the optical image data. According to this method, the effects of changes in the amount of light during inspection can be accurately and easily corrected without being affected by the level of the gradation value or whether the light is reflected or transmitted by the object to be inspected Ma. can do By comparing optical image data that is not affected by changes in the amount of light (processed to reduce the influence) by the method shown in the steps below, the accuracy of defect detection is improved.

<Reference Image Creation Step (S110)>
The reference image creation step (S110) is a step of creating image data to be compared with the measured and corrected optical image data. In the case of die to database inspection, optical image data for reference is created based on pattern data defined in design data (drawing data) that is the basis for forming the object to be inspected Ma. In the case of die to die inspection, optical image data inspected in the past is prepared as image data for reference.

<Comparison step (S111)>
Comparison step (S111) This is a step of comparing the measured and corrected optical image data with the reference optical image data to detect defects. The positions of the measured and corrected optical image data and the reference optical image data are aligned, and, for example, if the difference in gradation value for each pixel is larger than the determination threshold Th, the defect is determined. The detected defect information is stored in the storage device 141 together with the position information.

Even if the light amount displacement amount is corrected, the light amount of the correction light and the light amount of the inspection light (the amount of light reflected by illuminating the object to be inspected Ma and the amount of light received by the sensor that receives the light and the amount of light to be inspected Ma If there is a large difference in the amount of light received by the sensor that receives the light, the accuracy of correction of the optical image data is lowered, and defect determination may not be performed accurately. In the embodiment, since the amounts of received light of the inspection light and the correction light are matched, the optical image data can be corrected in the same or the same degree as the light amount displacement amount of the correction light, so that highly accurate correction is possible. . Since the inspection apparatus according to the embodiment is configured to be able to adjust the light amount of the correction light according to the reflectance of the object to be inspected Ma, the light amount displacement amount is can be corrected with high accuracy. For example, if the difference in the amount of received light between the correction light and the inspection light is large, for example, several times, the error in the correction by the correction light may affect the defect determination. By suppressing the received light amount to the above difference, the correction error can be extremely reduced, and the accuracy of the defect inspection is improved. Therefore, the light amount differences Δ1, Δ2 and Δ3 are preferably values within the above range.

Embodiment 2
FIG. 3 is a configuration diagram showing the configuration of the pattern inspection apparatus according to the second embodiment. In FIG. 2, an inspection apparatus 200 for inspecting defects in patterns formed on an object to be inspected Ma includes a control unit 110 for controlling the inspection apparatus 200 and an optical image acquisition mechanism 150 for imaging the object to be inspected Ma. The object to be inspected Ma is, for example, a mask. The second embodiment is a modification of the first embodiment. Configurations of the second embodiment that are different from those of the first embodiment will be described below.

The light branching and adjusting element 190, which is an optical element capable of branching the light from the light source into the light for illuminating the object to be inspected and the correction light that does not pass through the surface of the object to be inspected Ma, and changing the light amount of the correction light, It includes a second light branching element 191 , a light control filter 192 and a mirror 193 . The second light branching element 191 is preferably a transmissive reflector. Dimming filter 192 uses one or more filters that reduce the amount of light transmitted. As the light control filter 192, a filter whose light control amount is fixed or a filter whose light control amount is variable can be used.

In Embodiment 1, the correction light is received by the TDI sensor 175 for reflection, but in Embodiment 2, the correction light is received by the TDI sensor 172 for transmission. . In the second embodiment, inspection apparatus 200 may be configured such that correction light is received by reflection TDI sensor 175 .

The light (solid line) emitted from the light source 161 is adjusted to an arbitrary imaging magnification by the magnifying optical system 162, and is split by the third light splitting element 163 into the transmission illumination optical system side (dashed line) and the light splitting/adjusting element 190 side. (chain line). The third optical branching element 163 includes, for example, a polarizing beam splitter or a transmissive reflector. When the object to be inspected Ma is not inspected by the light passing through the object to be inspected Ma, the third light branching element 163 can be replaced with a mirror. , the amount of received light transmitted through the object to be inspected Ma, the amount of received light reflected by the object to be inspected Ma, and the amount of received correction light are approximately the same. 163 branch ratios are adjusted.

The transmission illumination optical system includes a mirror 164 and illuminates an object to be inspected Ma placed on an XYθ table 165 . The light transmitted through the object to be inspected Ma passes through the objective lens 168 and the second light branching element 191 of the light branching light control element 190 . The light that has passed through the second optical branching element 191 and passed through the object to be inspected Ma is reflected by the mirror 169 and further reflected by the mirror 170 . The light transmitted through the object to be inspected Ma reflected by the mirror 170 passes through the lens 171 and is received by the transmission TDI sensor 172 . The light received by the transmission TDI sensor 172 is photoelectrically converted, the signal is processed by the transmission signal processing unit 137b of the optical image generation unit 173, and optical image data is generated based on the light transmitted through the object to be inspected Ma. be. Although the TDI sensor is mentioned as the sensor, it is not limited to the TDI sensor.

The light branched to the light branching and adjusting device 190 side is reflected by the mirror 167 . The light reflected by the mirror 167 passes through the second light branching element 191 and the light (long dashed line) that illuminates the object to be inspected Ma and is reflected by the second light branching element 191 of the light branching/adjusting element 190. It is branched into correction light (short dashed line). The ratio of splitting into the light for illuminating the object to be inspected Ma and the correction light is selected in consideration of the reflectance of the object to be inspected Ma and losses due to other optical elements. The ratio of splitting into the light for illuminating the object to be inspected Ma and the correction light is adjusted so that the ratio of the light quantity of the received light reflected by the object to be inspected Ma and the light quantity of the received correction light is approximately the same. preferably.

The correction light that has passed through the second light branching element 191 passes through the light control filter 192 and is reflected by the mirror 193 . The light reflected by the mirror 193 passes through the dimmer filter 192 again, is reflected by the first light branching element 182, and is guided to the mirror 169 side. The correction light guided to the mirror 169 side is reflected by the mirror 169 . The correction light reflected by the mirror 169 is reflected by the mirror 170 , passes through the lens 171 , and is received by the correction light area of the transmission TDI sensor 172 . The light received by the transmission TDI sensor 172 is photoelectrically converted, the signal is processed by the displacement calculation unit 136, and the light amount change rate of the correction light (time light amount change rate) is obtained.

FIG. 4 is a flow chart showing main steps of the pattern inspection method according to the second embodiment. 4, the pattern inspection method according to the second embodiment includes a first inspection light measurement step (S101), a second inspection light measurement step (S202), a third branch ratio adjustment step (S203), a second Branch ratio adjustment step (S104), total light amount adjustment step (S105), scanning step (S106), optical image creation step (S107), light amount displacement rate calculation step (S108), optical image correction step (S109), reference image creation Each step of the step (S110) and the comparison step (S111) is performed. Other than the difference in the optical path described above, the second inspection light measurement step (S202), the third branch ratio adjustment step (S203), and the correction light are received by the transmission TDI sensor 172 and photoelectrically converted. are common to the inspection method of the first embodiment. Before performing the above steps, it is preferable to perform calibration by adjusting the characteristics of the TDI sensor to reduce (or eliminate) variations in the sensor characteristics. Each step will be described below.

<Second Inspection Light Measurement Step (S202)>
The second inspection light measurement step (S202) is a step of illuminating the object to be inspected Ma and measuring the amount of reflected light. Specifically, the light is emitted from the light source 161 , passes through the magnifying optical system 162 , is branched by the third light branching element 163 to the light branching/adjusting element 190 side, is reflected by the mirror 167 , and passes through the second light branching element 191 . , passes through the objective lens 168 and illuminates the object to be inspected Ma. At this time, since a transmissive reflector is used for the second light branching element 191, the branching ratio of the light for illuminating the inspection object Ma and the correction light is fixed. The TDI sensor 175 for reflection receives the amount of light reflected by illuminating the object to be inspected Ma to measure the amount of light. The analog signal photoelectrically converted by the reflection TDI sensor 175 is processed including digital conversion by the reflection signal processing unit 137a. The amount of light received by the reflection TDI sensor 175 changes depending on the reflectance of the object to be inspected Ma.

<Third branch ratio adjustment step (S203)>
The third branch ratio adjustment step (S203) is a step of changing the ratio of the light illuminating the inspection object Ma and the correction light. The light transmittance of the light control filter 192 of the optical splitter light control element 190 is adjusted in order to change the ratio of the light that illuminates the object to be inspected Ma and the correction light. Since the correction light passes through the light control filter 192 twice, the light transmittance of the light control filter is adjusted so that half of the target light reduction amount is corrected. The adjustment of the light transmittance includes replacing the light control filter 192 with one having a different light transmittance, using a plurality of light control filters 192, and adjusting the light transmittance of the variable light control filter 192. or one or a combination. By the operation including this step, it is possible to adjust the light amount of the correction light so as to be appropriate regardless of the reflectance of the object to be inspected Ma. In the second embodiment, since the transmissive reflector 191 with a fixed transmittance (reflectance) is used, the amount of light that illuminates the inspection object Ma is not adjusted. The corrected light passes through the transmissive reflector 191, passes through the light control filter 192, is reflected by the mirror 193, and passes through the light control filter 192 again. The light passing through the dimmer filter 192 again is reflected by the transmissive reflector 191 and received by the transmissive TDI sensor 172 . A signal of the correction light received by the transmission TDI sensor 172 is subjected to signal processing in the light amount variation rate calculation step (S108).

Also in the second embodiment, it is possible to adjust the light amount of the correction light so as to be appropriate according to the reflectance of the object to be inspected Ma. Therefore, it is possible to correct the optical image data with high accuracy based on the change in the amount of light from the light source 161 due to the change in the amount of light.

In the above description, each "-part" includes hardware, software, and a combination of hardware and software.

The embodiments have been described above with reference to specific examples. However, the invention is not limited to these specific examples.

In addition, descriptions of parts that are not directly necessary for the explanation of the present invention, such as the device configuration and control method, are omitted, but the required device configuration and control method can be appropriately selected and used.

In addition, all pattern inspection apparatuses and pattern inspection methods that have the elements of the present invention and whose designs can be modified as appropriate by those skilled in the art are included in the scope of the present invention.

100 inspection apparatus 110 control system 121 control computer 122 bus 131 table control unit 132 position calculation unit 133 reference image creation unit 134 comparison unit 135 light amount correction unit 136 displacement rate calculation unit 137 optical image creation unit 137a reflection signal processing unit 137b for transmission Signal processing unit 141 Storage device 142 Pattern monitor 143 Monitor 144 Printer 150 Optical image acquisition mechanism 161 Light source 162 Enlargement optical system 163 Third light branching element 164 Mirror 165 Table Ma Object to be inspected 166 Laser length measurement system 167 Mirror 168 Objective lens 169 Mirror 170 Mirror 171 Lens 172 Transmissive TDI sensor 173 Mirror 174 Lens 175 Reflective TDI sensor 180 Light from the light source is split into light for illuminating the object to be inspected and correction light not passing through the surface of the object to be inspected. Optical element that can change the amount of light (optical branch light control element)
181 half-wave plate 182 first optical branching element (polarization beam splitter)
183 First quarter-wave plate 184 Mirror 185 Second quarter-wave plate 190 Light from the light source is split into light for illuminating the object to be inspected and correction light not passing through the surface of the object to be inspected. , an optical element that can change the amount of correction light (optical splitter light control element)
191 transmissive reflector 192 light control filter 193 mirror

Claims (6)

a light source;
an optical element capable of branching the light from the light source into light for illuminating the object to be inspected and correction light not passing through the surface of the object to be inspected, and changing the amount of the correction light;
a sensor that receives the correction light;
a displacement rate calculator that calculates a displacement rate of the amount of the correction light received by the sensor;
an optical image creating unit that creates optical image data of the object to be inspected based on the amount of light reflected by illuminating the object to be inspected;
a light amount correction unit that corrects the optical image data from the displacement rate;
with
The optical element includes a first optical branching element, a half-wave plate, a first quarter-wave plate, a second quarter-wave plate and a mirror;
light from the light source passes through the half-wave plate,
The light passing through the half-wave plate is split by the first light splitting element into light for illuminating the object to be inspected and the correction light,
the correction light split by the first light splitting element passes through the first quarter-wave plate and is reflected by the mirror;
the correction light reflected by the mirror passes through the first quarter-wave plate and is reflected by the first optical branching element;
the correction light reflected by the first light branching element is received by the sensor;
The light split by the first light splitting element and illuminating the object to be inspected passes through the second quarter-wave plate,
An inspection apparatus in which the light passing through the second quarter-wave plate and illuminating the object to be inspected irradiates the surface of the object to be inspected . a light source;
an optical element capable of branching the light from the light source into light for illuminating the object to be inspected and correction light not passing through the surface of the object to be inspected, and changing the amount of the correction light;
a sensor that receives the correction light;
a displacement rate calculator that calculates a displacement rate of the amount of the correction light received by the sensor;
an optical image creating unit that creates optical image data of the object to be inspected based on the amount of light reflected by illuminating the object to be inspected;
a light amount correction unit that corrects the optical image data from the displacement rate;
with
The optical element has a second light branching element, a light control filter and a mirror,
Light from the light source is split by the second light splitting element into light for illuminating the inspection object and the correction light,
the correction light split by the second light splitting element passes through the light control filter and is reflected by the mirror;
the correction light reflected by the mirror passes through the light control filter and is reflected by the second light branching element;
the correction light reflected by the second light branching element is received by the sensor;
The inspection apparatus according to claim 1, wherein the light split by the second optical branching element and illuminating the object to be inspected irradiates the surface of the object to be inspected . The first optical branching element is a polarizing beam splitter,
2. The method according to claim 1 , wherein by adjusting the optical axis direction of said half-wave plate, said first optical branching element adjusts a ratio of branching into light for illuminating said object to be inspected and said correction light. inspection equipment. The second optical branching element is a reflective and transmissive member,
3. The inspection apparatus according to claim 2 , wherein the light amount of the correction light is adjusted by adjusting the light transmittance of the light control filter. The correction light is arranged so that the difference between the amount of light received by the sensor and the amount of light received by the sensor that receives the light is within ±0.5%. 5. Inspection apparatus according to any one of claims 1 to 4 , wherein an optical element is adjusted. a transmission illumination optical system that illuminates the inspection object with light from the light source;
a third light splitting element that splits the light from the light source into the transmission illumination optical system side and the optical element side;
A difference in the amount of light received by the sensor that receives the light and the amount of light reflected by the object to be inspected is within ±0.5% with respect to the amount of light received by the sensor with the correction light, and The difference between the amount of light received by the sensor and the amount of light transmitted through the transmission illumination optical system and received by the sensor is within ±0.5%, and and the amount of light transmitted through the object to be inspected through the transmission illumination optical system is received by the sensor for receiving the light with respect to the amount of light reflected by illuminating the object to be inspected and received by the sensor for receiving the light. 5. The inspection apparatus according to any one of claims 1 to 4 , wherein the optical element and the third light branching element are adjusted so that the difference in the amount of light obtained is within 0.5%.

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