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WO2020079770A1 - Dispositif d'alignement, dispositif d'inspection et procédé d'alignement - Google Patents

Dispositif d'alignement, dispositif d'inspection et procédé d'alignement Download PDF

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Publication number
WO2020079770A1
WO2020079770A1 PCT/JP2018/038634 JP2018038634W WO2020079770A1 WO 2020079770 A1 WO2020079770 A1 WO 2020079770A1 JP 2018038634 W JP2018038634 W JP 2018038634W WO 2020079770 A1 WO2020079770 A1 WO 2020079770A1
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WIPO (PCT)
Prior art keywords
alignment
reflected light
filter
image
light
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Ceased
Application number
PCT/JP2018/038634
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English (en)
Japanese (ja)
Inventor
幸一 名古屋
波多野　央
展明 広瀬
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Hitachi High Tech Corp
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Hitachi High Tech Corp
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Priority to PCT/JP2018/038634 priority Critical patent/WO2020079770A1/fr
Publication of WO2020079770A1 publication Critical patent/WO2020079770A1/fr
Anticipated expiration legal-status Critical
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/95—Investigating the presence of flaws or contamination characterised by the material or shape of the object to be examined
    • G01N21/956—Inspecting patterns on the surface of objects
    • H10P72/50—

Definitions

  • the present invention relates to an alignment apparatus that measures and adjusts the positional relationship of a sample (for example, a patterned wafer with a film) with respect to a stage, an inspection apparatus including the alignment apparatus, and an alignment method.
  • the pattern formed on the wafer (sample) and the defects (scratches, foreign substances, etc.) on the surface of the wafer greatly affect the yield.
  • the defect inspection is performed by the inspection apparatus, the positional relationship between the stage and the wafer loaded on the stage varies from a microscopic point of view. If the positional relationship between the stage and the wafer is not specified in advance, it is high. Cannot perform accurate defect inspection. Therefore, in some cases, the inspection apparatus is equipped with an alignment device that measures the positional relationship between the stage and the wafer loaded on the stage prior to the defect inspection, and aligns them with high accuracy (see Patent Document 1, etc.).
  • the demand for stacked-layer semiconductor devices such as 3D-NAND has increased, and the number of deposition processes (film formation processes) for forming a thin film on the surface of a sample has also increased in the semiconductor manufacturing process.
  • the stage of the inspection device and the wafer to be inspected are aligned with each other, and then the inspection for defects and the like is performed.
  • alignment is performed based on the images of the reference patterns of the plurality of chips covered with the thin film.
  • An object of the present invention is to obtain a precise alignment image of a pattern and perform accurate alignment even on a wafer that could not be aligned by an alignment device for in-line inspection due to the material or thickness of a thin film formed on the surface.
  • An object of the present invention is to provide an alignment apparatus capable of performing the inspection, an inspection apparatus equipped with the alignment apparatus, and an alignment method.
  • the present invention provides an illumination optical system that illuminates a sample held on a stage with illumination light, an imaging unit that receives and images reflected light from the sample due to the illumination light, and An illumination optical system and a processing unit that controls the image capturing unit are provided.
  • the illumination optical system is capable of switching the wavelength of the illumination light, and the image capturing unit selects color reflection light according to the wavelength.
  • At least one of the element or the filter device and a plurality of sensors of which at least one is selected corresponding to the wavelength of the selected reflected light are provided, and the processing unit is based on the image captured by the selected sensor.
  • An alignment circuit for adjusting the positions of the sample and the stage is provided.
  • the present invention it is possible to obtain an alignment image with a clear pattern and perform accurate alignment even when it is covered with a thin film having a material or a thickness that is difficult to transmit light with illumination light having a uniform wavelength.
  • an alignment process is performed to align the coordinates (position) of the stage of the inspection device and the wafer. For example, a sample on a stage (described later) of the inspection device is irradiated with illumination light, and the reflected light is imaged by a sensor to acquire an alignment image. Based on the acquired alignment image, the coordinates of the wafer and the stage and their positional relationship are calculated in advance.
  • a broadband light source with a wide wavelength band is used as the light source of the alignment illumination optical system.
  • the wavelength of light emitted from this light source is selected according to the step of inspecting.
  • a filter device is used to select the wavelength.
  • a filter device is installed in the emission light path of the illumination light from the light source (optical axis of the light source), and by switching the filter, only the illumination light in the desired wavelength band is transmitted.
  • switching the wavelength band of the illumination light it is also possible to switch the wavelength band of the illumination light by configuring the illumination light source with a plurality of light sources having different wavelength bands of the illumination light instead of the broadband light source and changing the light source to be used. .
  • a color separation optical element for splitting the reflected light into a plurality according to the wavelength band is installed together with the sensor in the image pickup unit that receives and captures the reflected light from the sample due to the illumination light.
  • the effective reflected light used for alignment is selectively picked up by a sensor.
  • a filter device similar to that used for the illumination optical system in the image pickup section can be used. Effective reflected light is selectively imaged using at least one sensor having a different sensitivity depending on the wavelength band (sensitivity is adjusted so as to be suitably exposed in the wavelength band to be detected).
  • the optimal wavelength is selected in the illumination optical system according to the material and film thickness of the thin film, and the effective reflected light of the reflected light from the wafer is selectively picked up by the image pickup unit, which enables clear alignment. It is possible to obtain an image for use.
  • a pattern or the like which is not reflected in an image because it is difficult for the illumination light having a uniform wavelength (light whose wavelength band is not selected) to pass through normally has a specific wavelength which is easily transmitted through the thin film.
  • the selective use of the illumination light in the band may allow clear recognition on the image.
  • an image obtained from only the effective reflected light is used as an alignment image, and the positional relationship between the sample and the stage is calculated based on this alignment image, whereby the alignment that could not be performed inline can be performed. Therefore, it contributes to the improvement of the inspection efficiency of the defect inspection and the improvement of the yield of the semiconductor manufacturing process.
  • a configuration example of an apparatus for performing such an alignment method will be described below.
  • FIG. 1 is a schematic diagram of an inspection apparatus according to an embodiment of the present invention.
  • the inspection apparatus 100 shown in the figure includes a stage 101, a wafer transfer apparatus 102, a defect inspection unit 200, an overall control apparatus 300, an input apparatus 401, an output apparatus 402, and an alignment apparatus 1.
  • the stage 101 is for holding a wafer W (for example, a patterned wafer with a film) to be a sample, and includes a chuck 101a, a Y stage 101y, an X stage 101x, a Z stage 101z, and a ⁇ stage 101t. There is.
  • the chuck 101a attracts and holds the wafer W.
  • the wafer W is placed (loaded) on the chuck 101 a of the stage 101 by the robot arm of the wafer transfer device 102.
  • the wafer transfer device 102 includes a robot arm, a wafer pod, a pre-aligner, and the like.
  • the Y stage 101y is a drive unit for moving the chuck 101a in the Y axis direction.
  • the X stage 101x is a drive unit that moves the chuck 101a in the X axis direction and the Z stage 101z is a Z axis direction.
  • the ⁇ stage 101t is a drive unit that rotates the chuck 101a around the Z axis. Thereby, the wafer W mounted on the chuck 101a can be translated in the XYZ directions and rotated in the XY plane.
  • the X axis and the Y axis are, for example, coordinate axes orthogonal to each other in a horizontal plane, and the Z axis is an axis orthogonal to the XY plane.
  • the defect inspection unit 200 is a unit for inspecting a defect of the wafer W held on the stage 101, and includes an inspection light source 201, an objective lens 202, a spatial filter 203, an imaging lens 204, and a sensor 205.
  • the defect inspection unit 200 is arranged side by side with the alignment apparatus 1 in the X-axis direction, and by moving the chuck 101a of the stage 101 in the X-axis direction, the defect inspection unit 200 and the alignment apparatus 1 can be illuminated with each other.
  • the wafer W can be moved between them.
  • the inspection light source 201 is a device for emitting inspection light to the wafer W held on the stage 101 to form an illumination area on the wafer W, and is configured to include, for example, a mirror and a lens.
  • the shape of the illumination area can be changed by driving a mirror or a lens, and can be, for example, dot-shaped or linear.
  • the scattered light from the illumination area is condensed by the objective lens 202. Unwanted light of the scattered light collected by the objective lens 202 is blocked by the spatial filter 203, and the light passing through the spatial filter 203 is imaged on the light receiving surface of the sensor 205 by the imaging lens 204. In this way, the sensor 205 receives scattered light from the wafer W due to the inspection light.
  • the signal output from the sensor 205 upon reception of light is transmitted to the overall control device 300, and the signal from the sensor 205 is compared with a threshold value (set value) to perform inspection (defect detection).
  • the inspection result (presence / absence of a defect) is synchronized with the movement signal of the stage 101 in the overall control device 300, is associated with the coordinates on the wafer W, and is output from the output device 402 in response to an operation from the input device 401.
  • the overall control device 300 is, for example, a computer, and the input device 401 is a keyboard, a mouse or other operation device.
  • the output device 402 is, for example, a monitor, and a printer or a recording device for a recording medium can also be used. When a touch panel is used as the output device 402, it can also serve as the input device 401.
  • the alignment apparatus 1 is a unit for measuring (aligning) the positional relationship of the wafer W with respect to the stage 101 (chuck 101a), and is, for example, a so-called bright field type that detects specularly reflected light.
  • the alignment device 1 includes an illumination optical system 1A, an image pickup section 1B, and a processing device 10.
  • the illumination optical system 1A includes an illumination light source 2, an aperture stop 8, a filter device 9, a half mirror 3 and an objective lens 4.
  • the image pickup unit 1B includes an imaging lens 5, a color separation optical element 6, and a plurality of sensors 7, 7C, 7I.
  • the processing device 10 is illustrated separately from the overall control device 300 in FIG. 1, the processing device 10 is, for example, a computer, and the overall control device 300 may also serve as the processing device 10.
  • the illumination optical system 1A of the alignment apparatus 1 is a device for emitting the illumination light from the illumination light source 2 to the wafer W held on the stage 101 to form an illumination area on the wafer W, and can switch the wavelength band of the illumination light. .
  • the illumination optical system 1A includes a mirror and a lens, for example, to form a Keilor illumination.
  • the illumination light source 2 is preferably a broadband light source, but may include a plurality of light sources having different wavelength bands of illumination light as shown in FIGS. 2B and 2C. Further, the illumination light source 2 may have a light amount adjustable or a fixed light amount.
  • a filter device 9 provided in the illumination optical system 1A is a device that selectively transmits illumination light having a different wavelength band for each switching position, and an emission light path of the illumination light from the illumination light source 2 (optical axis of the illumination light source 2). ) Has been installed.
  • the filter device 9 can be exemplified by a roulette device having at least one color filter, and the wavelength band of the illumination light with which the wafer W is irradiated is switched by switching the switching position.
  • the filter device 9 of this embodiment is provided with, for example, five switching positions. Filters for selectively passing mainly blue light rays, blue-green light rays, green light rays, red light rays, and near infrared rays are installed at the five positions, respectively.
  • To selectively pass light means to shield light other than the target wavelength band.
  • a switching position that does not limit the wavelength band may be added.
  • the illumination light source 2 is composed of a plurality of light sources having different wavelength bands of illumination light
  • the illumination light source 2 is composed of a plurality of light sources emitting blue light rays, blue to green light rays, green light rays, red light rays, and near infrared rays.
  • the filter device 9 is omitted, and the light source that emits the illumination light is selected by the control circuit 13 of the processing device 10 described later according to the selection sensor, and the illumination light is emitted from only one light source of the plurality of light sources. It may be configured to irradiate.
  • the filter device 9 can also be used when the illumination light source 2 is composed of a plurality of light sources.
  • the illumination optical system 1A is configured so that not only the wavelength band but also the amount of illumination light can be adjusted using the aperture stop 8.
  • the aperture stop 8 is a variable stop that adjusts the amount of illumination light, and is installed in the emission light path of the illumination light (optical axis of the illumination light source 2).
  • the reference opening of the aperture stop 8 is set to an intermediate opening between the maximum opening and the minimum opening.
  • the aperture stop 8 and the filter device 9 are arranged along the optical axis of the illumination light source 2 between the illumination light source 2 and the half mirror 3, and in the present embodiment, the aperture stop 8 and the illumination device 2 are arranged in the illumination light source 2 rather than the filter device 9. Although they are placed near each other, this context can be reversed.
  • the illumination light emitted from the illumination light source 2 passes through the aperture stop 8 and the filter device 9, is reflected by the half mirror 3, and is applied to the wafer W.
  • the image pickup unit 1B collects the reflected light from the illumination area of the wafer W by the objective lens 4 and receives the light on any one of the light receiving surfaces of the plurality of sensors 7, 7C, 7I via the half mirror 3 and the imaging lens 5. Take an image.
  • the sensor 7 is, for example, an RGB 3CCD camera (FIG. 2A), the sensor 7C is a sensor highly sensitive to blue to green light rays, and the sensor 7I is a sensor highly sensitive to near infrared rays.
  • the optical path to the sensors 7, 7C, 7I is switched by a movable mirror.
  • the sensors 7, 7C, 7I transmit signals generated by photoelectrically converting the reflected light to the processing device 10.
  • an image of the wafer W is generated based on the signals of the sensors 7, 7C and 7I.
  • the image generated by the processing device 10 and the measurement result can be output to the output device 402 by an operation from the input device 401.
  • FIG. 2A is a diagram in which the color separation optical element 6, the sensor 7, and the processing device 10 of the alignment device are extracted and shown.
  • the color separation optical element 6 splits the reflected light from the wafer W due to the illumination light into a plurality of rays according to the wavelength band.
  • the color separation optical element 6 is configured by combining a plurality of (three in this embodiment) prisms 6R, 6G, 6B, and makes incident light RGB (red, green, blue) having different wavelength bands. Disassemble into each color. Light in the red wavelength band is emitted from the prism 6R, light in the green wavelength band is emitted from the prism 6G, and light in the blue wavelength band is emitted from the prism 6B.
  • the sensor 7 includes a plurality of sensors (imaging elements) 7R, 7G, 7B.
  • the sensors 7R, 7G, and 7B are provided in the light emitting portions of the prisms 6R, 6G, and 6B, respectively, and receive the corresponding reflected light among the plurality of reflected lights separated by the color separation optical element 6. That is, for example, the sensor 7R is configured to receive only the red light emitted from the prism 6R, and is adjusted so that the sensitivity and the dynamic range for the wavelength band of the red light are good.
  • the sensors 7G and 7B are configured to receive only the green light and the blue light emitted from the prisms 6G and 6B, respectively, so that the sensitivity and the dynamic range for the wavelength bands of the green light and the blue light respectively become good. It has been adjusted to.
  • at least one of the sensors 7R, 7G, 7B, 7C, 7I is selected as a selection sensor according to the characteristics of the observation target of the alignment apparatus 1 and is used to capture an alignment image of the wafer W (described later). ).
  • a filter device 9 similar to that provided in the illumination optical system 1A may be installed in place of the color separation optical element 6 on the reflection optical path before entering the sensor 7. Yes ( Figure 2C).
  • the color separation optical element 6 does not separate the other wavelength bands to extract the effective reflected light, but the filter device cuts the other wavelength bands to extract the effective reflected light.
  • the movable mirror can guide the reflected light to the corresponding sensor as shown in FIG. 2C. Even with such a configuration, a clear alignment image can be obtained by selecting at least one of the sensors 7R, 7G, 7B, 7C, and 7I as a selection sensor and using it for capturing the alignment image of the wafer W.
  • the color separation optical element 6 and the filter device 9 may be used in combination in the image pickup section 1B (FIG. 2B).
  • the filter device 9 can be omitted as shown in FIGS. 2B and 2C, but the illumination optical system 1A has a filter device in FIGS. 2B and 2C. It is also possible to use 9.
  • the illumination light source 2 including a plurality of light sources as shown in FIGS. 2B and 2C can also be used.
  • the illumination light source 2 including the broadband light source as shown in FIG. 2A can also be used.
  • the processing device 10 is a computer that controls the illumination optical system 1A and the imaging unit 1B, and includes an alignment circuit 11, a memory 12, and a control circuit 13.
  • the alignment circuit 11 is a circuit that adjusts the positions of the wafer W and the stage 101 (chuck 101a) based on the alignment image captured by the selection sensor, and is, for example, a CPU.
  • the selected sensor is at least one sensor selected from the sensors 7R, 7G, 7B, 7C, and 7I as a sensor that outputs a signal that is a basis of the alignment image.
  • the memory 12 is a storage device for storing programs and constants necessary for alignment operation, numerical values in the process of calculation, etc. In particular, in the present embodiment, a lookup table (FIG.
  • a storage device provided in a computer such as a RAM (random access memory), a ROM (read-on memory), and an HDD (hard disk drive) can be used.
  • various recording media that can be connected to a computer, such as a CD, a DVD, a disc such as a Blu-ray disc, and a USB memory, can be used as the memory 12.
  • the control circuit 13 is a circuit that drives the filter device 9 according to the selected sensor and limits the wavelength band of the illumination light with which the wafer W is irradiated, and is, for example, a CPU.
  • the control circuit 13 controls the illumination light source 2 instead of the filter device 9 (for example, a light source to be used from a plurality of light sources is selected according to a sensor). Select and illuminate with illumination light).
  • the filter device 9 will be read as the illumination light source 2 and replaced.
  • the control circuit 13 performs the operation of selecting the wavelength band of the illumination light in the illumination optical system 1A and the operation of selecting the sensor according to the wavelength band in the imaging unit 1B in an interlocking manner.
  • the control circuit 13 also has a function of driving the aperture stop 8 according to the switching position of the filter device 9 to control the amount of illumination light with which the wafer W is irradiated.
  • the control circuit 13 further includes an automatic image pickup circuit 14 and a simulation circuit 15, in addition to a circuit that controls a basic function of driving the filter device 9 based on a look-up table according to input information from an operator.
  • the automatic image pickup circuit 14 is a circuit for automatically acquiring a good alignment image from the viewpoint of executing alignment. As will be specifically described later, the automatic image pickup circuit 14 sequentially changes the combination of the selection sensor and the switching position of the filter device 9 until the alignment image having the contrast equal to or higher than the set value is obtained, and repeatedly acquires the image. It has functions.
  • the automatic image pickup circuit 14 in the present embodiment also has a function of driving the stage 101 to change the focus position when the contrast of the image is less than the set value.
  • the automatic image pickup circuit 14 further has a function of correcting the gain of the signal of the selection sensor when the contrast of the image is less than the set value.
  • the focus position changing function and the gain correcting function may be executed in place of the switching position of the filter device 9, or may be executed together with the switching position of the filter device 9. Both functions of changing the focus position and correcting the gain can be executed at the same time.
  • the execution procedure of the automatic image pickup of the alignment image by the automatic image pickup circuit 14 will be described later.
  • the simulation circuit 15 is a circuit for identifying a good alignment condition based on known information that can be known at present. Specifically, the simulation circuit 15 executes a simulation based on the input information (refractive index, film thickness, etc.) regarding the thin film formed on the surface of the wafer W, and determines the wavelength band in which the alignment image is optimized. It has a function to specify. As an example of a configuration for executing this function, in the present embodiment, the simulation circuit 15 is configured to include a reflected light amount calculation circuit 16, a filtered reflected light amount calculation circuit 17, and a filter selection circuit 18. The simulation function of the simulation circuit 15 will be described later.
  • the reflected light amount calculation circuit 16 calculates the reflected light amount based on the thickness (known) and the refractive index (known) of the thin film formed on the surface of the wafer W.
  • the reflected light amount calculated here is the reflected light amount in the pattern covered with the thin film (first reflected light amount) and the reflected light amount in the wafer substrate outside the pattern (second reflected light amount). The amount of reflected light and its calculation principle will be described later.
  • the post-filter reflected light amount calculation circuit 17 determines the first filter for each switching position based on the first reflected light amount and the second reflected light amount calculated by the reflected light amount calculation circuit 16 and the filter characteristic of each switching position of the filter device 9. The back-reflected light amount and the second-filter back-reflected light amount are calculated.
  • the post-filter reflection light amount is the reflection light amount of the wafer W with respect to the illumination light that has passed through the filter.
  • the post-filter reflected light amount calculation circuit 17 calculates the first post-filter reflected light amount and the second post-filter reflected light amount on the assumption that the switching position of the filter device 9 is switched.
  • the filter selection circuit 18 specifies the position where the alignment image is optimized based on the calculation result of the filtered reflected light amount calculation circuit 17.
  • a switching position is extracted in which either the amount of reflected light after the first filter or the amount of reflected light after the second filter is equal to or greater than the set amount of light. Then, of the extracted switching positions, the one that maximizes the ratio of the amount of reflected light after the first filter and the amount of reflected light after the second filter is specified as the position where the alignment image is optimized.
  • FIG. 3 is a schematic diagram of a look-up table stored in the memory 12.
  • the switching position (“filter No.”) and the sensor (“Camera No.”) of the filter device 9 are set for each wavelength band (“selected wavelength”) of the illumination light with which the wafer W is irradiated through the selected filter. )) Combinations are specified.
  • the switching position of the filter device 9 in which the No. 1 filter (center wavelength L12) is installed and the No. 1-B camera (for example, the sensor 7B) are selected.
  • the amount of illumination light that passes through the filter device 9 used differs depending on the switching position. Therefore, the opening degree (not shown) of the aperture diaphragm 8 is also defined in the look-up table, and the aperture is changed according to the switching position. The opening of the diaphragm 8 is selected.
  • FIG. 4 is a diagram showing an example of an operation screen of the alignment apparatus according to the present embodiment.
  • the operation screen 40 is displayed on the output device 402 as a monitor according to the operation of the input device 401, for example.
  • the alignment apparatus according to the present embodiment has three modes including a manual mode, a simulation mode, and an automatic mode, and check boxes 41-43 for selecting each mode are displayed on the operation screen.
  • the manual mode is a mode in which the operator arbitrarily sets the switching position of the filter device 9 based on his own judgment.
  • the control circuit 13 by inputting and designating the wavelength of the illumination light in the wavelength input field 44, the control circuit 13 causes the switching position of the filter device 9 and the opening of the aperture stop 8 according to the lookup table shown in FIG. , The corresponding sensor is set. Then, by operating the execute button 45, the illumination light source 2, the filter device 9, and the aperture stop 8 are driven by the control circuit 13, and the alignment process is executed based on the signal of the selected sensor.
  • the simulation mode is a mode in which a condition (here, the wavelength of illumination light) suitable for alignment is specified by a simulation based on known information about the thin film.
  • a condition here, the wavelength of illumination light
  • the refractive index n1 of the thin film, the extinction coefficient k1, the thickness t1, the refractive index n2 of the pattern, and the extinction coefficient are displayed in the condition input field 47 (details are shown in FIG. 5). Input k2 and thickness t2.
  • the simulation circuit 15 specifies the conditions suitable for the alignment according to the program stored in the memory 12. The principle of this simulation will be described later.
  • the model of the amount of reflected light after the first filter and the amount of reflected light after the second filter are displayed in the window 49, and the specified wavelength is displayed in the window 50.
  • a bar 51 is displayed in the window 49 together with a model of the amount of reflected light after filtering, and the wavelength displayed in the window 50 is linked to the wavelength indicated by the bar 51.
  • the wavelength specified by the simulation circuit 15 is displayed, but by looking at the model in the window 49 and moving the bar 51 left and right, the wavelength value displayed in the window 50 is displayed. Can be adjusted.
  • the wavelength displayed in the window 50 becomes the designated wavelength.
  • the execute button 52 When the execute button 52 is operated while the wavelength is displayed in the window 50, the illumination light source 2, the filter device 9, and the aperture stop 8 are driven by the control circuit 13 as in the case of the manual mode, and the signal of the selected sensor is displayed. Alignment processing is executed based on this.
  • the difference between the manual mode and the simulation mode in that the selection of the wavelength is based on the operator's input or the simulation is performed, but the subsequent alignment process itself is the same in both modes.
  • the automatic mode is a mode in which a good alignment image can be obtained only by operating the execute button 53 in a state where the wafer W is set in the alignment apparatus without any data input work.
  • the conditions most suitable for alignment are specified by the automatic imaging circuit 14 according to the program stored in the memory 12, and the alignment image is acquired under the conditions.
  • the alignment processing can be automatically executed by the alignment image acquired in the automatic mode.
  • the alignment process itself is similar to other modes. The processing of the automatic image pickup circuit 14 in the automatic mode will be described later.
  • a setting registration field 54 is also prepared on the operation screen, and a combination of the switching position of the filter device 9 and the sensor to be added to the lookup table can be arbitrarily registered.
  • the end button 55 is operated, the operation screen of FIG. 4 is closed.
  • FIG. 6 is a sectional view of a model of the wafer W.
  • the first reflected light amount refers to the intensity of the first reflected light shown in the figure
  • the second reflected light amount refers to the intensity of the second reflected light.
  • the first reflected light is the reflected light of the illumination light applied to the portion of the wafer W on which the pattern is formed
  • the second reflected light is the reflected light of the illumination light applied to the portion of the wafer W on which the pattern is not formed. Light.
  • the first reflected light in the model shown in the figure is strictly the interference light of each reflected light from the substrate surface of the wafer W and the pattern surface and the thin film. It becomes interference light with the reflected light from the surface. Therefore, the first reflected light amount changes depending on the material of the thin film and the thickness t1, the material of the pattern and the thickness t2, and the wavelength of the illumination light. Since the second reflected light is an interference light between the reflected light from the substrate surface of the wafer W and the reflected light from the thin film surface, the amount of light changes depending on the material of the thin film (the same), the thickness t1, and the wavelength of the illumination light. To do.
  • n1, n2, k1, and k2 are values that depend on the material, they may be input by selecting the material.
  • the relationship between the amount of reflected light and the wavelength of the illumination light applied to the thin film portion is as shown in Fig. 7. That is, the number of peaks and troughs of the reflected light amount in the same wavelength band generally increases as the thin film becomes thicker and decreases as it becomes thinner. Since the extinction coefficient of the material of the pattern is usually larger than that of the material of the thin film, the amount of light transmitted through the pattern is small, and when the illumination light of the same wavelength is used, the difference between the first reflected light amount and the second reflected light amount. Occurs mainly depending on the thickness of the thin film. Therefore, in the model of FIG. 6, the number of peaks and troughs of the reflected light amount in the same wavelength band is smaller in the first reflected light of the thin film portion than in the second reflected light of the thick film portion.
  • the post-filter reflected light amount calculation circuit 17 determines, based on the characteristics of the first reflected light amount and the second reflected light amount and the filter characteristics of each switching position of the filter device 9, the first post-filtered reflected light amount and the second post-filtered light amount for each switching position. The amount of reflected light is obtained.
  • the filter selection circuit 18 When forming an alignment image from the amount of reflected light after the first filter and the amount of reflected light after the second filter, it is desirable that at least one of the amounts of light has a certain value or more. Even if the amount of light is sufficient, if the difference between the amount of reflected light after the first filter and the amount of reflected light after the second filter is small, the contrast of the image becomes low, and the pattern under the thin film is not clear on the image. From this point of view, it is possible to improve the filter selection circuit 18 by specifying the switching position with the maximum ratio of the two light amounts from the switching positions in which at least one of the first filter reflected light amount and the second filter reflected light amount is equal to or greater than the set light amount. Conditions for obtaining a proper alignment image can be obtained. For example, in FIG. 10, when the set light amount is S, the switching position of the filter No. 1-G can be selected. When the filter No. is determined, the sensor used and the aperture opening are also determined according to the look-up table (FIG. 3
  • FIG. 11 is a flowchart showing the procedure of defect inspection including the procedure of automatically capturing the alignment image by the automatic image capturing circuit.
  • steps S12 to S18 are procedures relating to automatic image capturing for alignment
  • steps S21 to S23 are procedures relating to alignment
  • step S31 is procedures relating to defect inspection.
  • the overall control device 300 first drives the wafer transfer device 102 to load the wafer W at a predetermined position on the chuck 101a of the stage 101 (step S11). The overall control device 300 then drives the stage 101 to move the wafer W into the field of view of the alignment device 1, and instructs the processing device 10 of the alignment device 1 to perform alignment processing (steps S12-S18, S21-S23). Run.
  • the processing apparatus 10 drives the automatic image pickup circuit 14, picks up an image of the entire wafer W by using the illumination light source 2, the sensor 7, and the like to acquire an image, and recognizes the wafer matrix formed on the wafer W (step S12).
  • the image is acquired by scanning the wafer W concentrically or spirally in the R ⁇ coordinate system of the stage 101 (by driving the ⁇ stage 101t and the X stage 101x). It is also possible to obtain an image by scanning the wafer W with the XY coordinate system (driving the X stage 101x and the Y stage 101y). For example, the pattern repeating distance (pitch) in the Xw-axis direction and the Yw-axis direction is calculated from the acquired image by image processing.
  • a wafer matrix is a matrix in which a large number of chips of the same type (semiconductor devices also called dies) are arranged in a plurality of rows in two directions (Xw axis direction and Yw axis direction) of the orthogonal coordinate system on the wafer as shown in FIG. It is in the form of a shape.
  • the automatic imaging circuit 14 determines the first chip T1 and the second chip T2 in the wafer matrix as shown in FIG. 12 (step S13). After determining the chips T1 and T2, the automatic imaging circuit 14 registers the coordinates of the chip origin O of the chip T1 (for example, the starting point for repeating the above pattern) in the memory 12 (step S14).
  • the reference pattern P (FIG. 12) is a pattern located at a fixed distance of the X coordinate ⁇ X1 and the Y coordinate ⁇ Y2 from the chip origin O, and ⁇ X1 and ⁇ Y2 are stored in advance in the memory 12 as information at the time of alignment.
  • the chips T1 and T2 are reference chips for measuring the rotation deviation of the wafer W, and have the same Yw coordinate on the wafer matrix (they are arranged on the same axis parallel to the Xw axis on the wafer W). Exist).
  • the chips T1 and T2 are preferably separated from each other in terms of correction accuracy of the rotation deviation of the wafer W.
  • the chip T2 is out of the field of view when the observation position moves from the chip T1 to the chip T2, and an operation of searching for an alignment pattern image is required, which is necessary for image recognition. There are cases where it takes time.
  • FIG. 12 shows an example in which four chips (first to fourth chips T1 to T4) having the same Yw coordinate are selected.
  • it is possible to extend the inter-chip distance by, for example, first performing the alignment with the chips T3 and T4 having a short inter-chip distance, and then performing the alignment with the chips T3 and T2, and then the chips T2 and T1. .
  • the automatic image pickup circuit 14 searches for the reference pattern P in each selected chip (step S15), and determines whether each reference pattern P is recognizable (contrast is a set value or more) (step S16). If there is a reference pattern P that cannot be recognized due to the low contrast of the image, the automatic image pickup circuit 14 changes the switching position of the filter device 9 and the selection sensor according to the setting order, and then acquires a new image of the wafer W (step S17). . At this time, the stage 101 is driven to move the focus position of the illumination light to the inside of the thin film, or the gain of the sensor signal used to generate the image is corrected to adjust the brightness and contrast of the image. Good.
  • a combination of the focus position and the gain is prepared in advance, and the combination of the switch position of the lookup table, the sensor, and the aperture opening of the lookup table of FIG. 3 is sequentially changed for each combination of the focus position and the gain.
  • an image can be taken by sequentially changing the imaging conditions such as the wavelength of the illumination light and the focus position each time the procedure moves to step S17.
  • the automatic imaging circuit 14 uses the image as an alignment image (effective image), for example. It is registered in the memory 12 (step S18).
  • the automatic image pickup circuit 14 drives the stage 101 to move the wafer W, and thus picks up a clear alignment image of the reference pattern P on the chips T1 to T4 (at least the chips T1 and T2) by the image pickup unit 1B. Then, it is registered in the memory 12.
  • the processing device 10 causes the alignment circuit 11 to execute the alignment process (step S21).
  • the alignment processing the positional deviation of the center of the wafer W from the rotational center of the stage 101 and the rotational deviation of the wafer W are first calculated in the coordinate system of the stage 101. Details of this alignment processing are described in JP-A-2005-40698, and similar processing can be adopted in this embodiment. However, in the present embodiment, since the plurality of reference patterns P can be satisfactorily recognized through the procedure of step S16, the rotation of the wafer W using the reference pattern P instead of the method disclosed in the same document. The deviation (deviation in the ⁇ direction) can be calculated. The method will be described.
  • the reference patterns P of the chips T1 to T4 are lined up along the Xw axis, and the Yw coordinates are the same for both. Therefore, the straight line passing through the four reference patterns P is parallel to the Xw axis of the wafer coordinate system. Therefore, the rotation deviation (tilt) of the wafer W can be calculated by calculating the tilt of the straight line passing through the four reference patterns P in the stage coordinate system (R ⁇ coordinate system or XY coordinate system). In order to obtain a straight line parallel to the Xw axis, it is sufficient to select two reference patterns P along the Xw axis, but four are selected in this embodiment.
  • FIG. 12 illustrates the case where four reference patterns P are selected in consideration of both the accuracy and the calculation load.
  • FIG. 12 illustrates an example of selecting the reference pattern P for obtaining a straight line parallel to the Xw axis
  • a plurality of reference patterns P may be selected along the Yw axis.
  • the rotation deviation of the wafer W can also be calculated by the inclination of the Yw axis in the stage coordinate system (R ⁇ coordinate system or XY coordinate system).
  • the alignment circuit 11 determines whether the deviations are within a preset allowable value (step S22). If both the rotational deviation and the center position deviation exceed the allowable value, it is judged as exceeding the allowable range, or if either one of them exceeds the allowable value, it is judged as exceeding the allowable range. Can be changed, but the latter is adopted here. If either the rotational deviation or the central positional deviation exceeds the allowable value, the alignment circuit 11 corrects at least one of the position and the angle of the alignment image and executes image processing to bring the wafer coordinate system closer to the stage coordinate system (step S23), and returns the procedure to step S21.
  • the alignment circuit 11 outputs a signal to that effect, and It is transmitted from the device 10 to the overall control device 300.
  • the overall control apparatus 300 drives the stage 101 and executes the defect inspection of the wafer W using the inspection light source 201 and the sensor 205 (step S31).
  • FIG. 11 has been described as the procedure of the automatic mode, but the only difference is that the imaging conditions are arbitrarily input or set with reference to the simulation result.
  • the procedure from step S18 is the same in the simulation mode and the manual mode. is there.
  • the reflected light from the wafer W due to the illumination light is split by the color separation optical element 6, and each split reflected light is received by the corresponding sensor. Then, at least one (for example, a long-wavelength red ray) is selected from the plurality of dispersed reflected lights, and an alignment image is generated based on only the selected reflected lights. For example, in a wafer on which a thin film of a specific material that reflects most of the blue light on the surface is formed, if the reflected light of the blue light is reflected in the image generation signal when the wavelength band is not limited, the thin film of the alignment image The lower structure becomes invisible.
  • the reflected light that has passed through the thin film and reflected by the structure under the thin film is extracted and used as the basis of the alignment image, so it is difficult to see normally.
  • An alignment image is obtained in which the structure under the thin film is clearly shown.
  • the wavelength band of the reflected light to be the basis of the alignment image is selected, the light in the wavelength band outside the selected wavelength band is cut from the illumination light by the filter device 9 in advance, so that the alignment image is obtained.
  • the filter the wavelength band can be more accurately limited than the color separation optical element 6, and the wavelength distribution of the reflected light incident on the selected sensor can be controlled with higher precision according to the sensor sensitivity.
  • the same effect can be obtained when the image pickup unit 1B is configured to extract the reflected light in the specific wavelength band by the filter device and receive the reflected light by the corresponding sensor. be able to. Similar effects can be obtained when the illumination optical system 1A uses the illumination light source 2 configured by a plurality of light sources having different wavelength bands instead of the broadband light source. When the illumination light source 2 is composed of a plurality of light sources, the filter device 9 can be omitted. Further, in these cases, the following effects (2) to (7) can be similarly obtained.
  • the aperture of the aperture diaphragm 8 is changed according to the switching position of the filter device 9. As a result, it is possible to suppress variation in the brightness of the alignment image due to the filter used.
  • the interlocking function of the filter device 9 and the aperture stop 8 is not always necessary. Further, in changing the amount of illumination light, it may be possible to adjust the amount of light emitted from the illumination light source 2 instead of adjusting the opening of the aperture stop 8.
  • a lookup table (FIG. 3) in which a combination of a sensor and a filter is associated with a selected wavelength is stored in the memory 12 in advance, so that the wavelength used for creating the alignment image is designated, and thus the sensor and the filter can be selected.
  • the combination can be determined automatically. Therefore, when the spectral data or the like of the thin film is obtained in advance, the imaging condition can be set only by designating the wavelength without manually selecting the sensor and the filter.
  • the sensor selection and the filter selection may be performed only by manual operation, and in this case, the lookup table is not always necessary.
  • the simulation circuit 15 By implementing the simulation circuit 15, it is possible to specify appropriate imaging conditions for the alignment image by inputting known information (refractive index, film thickness, etc.) about the thin film. Even if the information of the thin film is known, it is useful when it is not possible to determine what imaging condition should be set based on the information. However, the simulation function is not always necessary to obtain the effect (1). Further, the case where the simulation circuit 15 is configured to include the reflected light amount calculation circuit 16, the filtered reflected light amount calculation circuit 17, and the filter selection circuit 18 is illustrated. However, it is needless to say that when the simulation is executed by a different method, the function of the simulation circuit 15 can be changed accordingly.
  • the alignment apparatus 1 By mounting the automatic image pickup circuit 14, even if the information about the thin film is ambiguous, the alignment apparatus 1 sequentially changes the conditions and repeatedly picks up the image of the wafer W, and automatically obtains a good alignment image. You can get it. In the case of such an auto sequence, it is possible to save the operator the trouble of changing the imaging conditions and manually operating one by one. It is efficient because the operator can perform other tasks while executing the process of automatic imaging. However, the automatic image capturing function is not always necessary to obtain the effect (1).
  • the automatic image pickup circuit 14 drives the stage 101 in the Z direction in place of the switching position of the filter device 9 or together with the switching position of the filter device 9 to change the focus position. I implemented the function to do. By moving the focus position inside the thin film, the appearance of the wafer W in the image may be changed, and the structure of the lower portion of the thin film may become clear.
  • the automatic image pickup circuit 14 it is not always necessary for the automatic image pickup circuit 14 to have the function of adjusting the focus position. It should be noted that changing the focus position instead of the switching position of the filter device 9 means changing the focus position without changing the filter when a good alignment image cannot be obtained by repeatedly picking up the image by changing the filter. Refers to trying to improve image quality.
  • the automatic image pickup circuit 14 has a function of correcting the gain of the signal of the selection sensor instead of the switching position of the filter device 9 or together with the switching position of the filter device 9. .
  • the structure of the lower part of the thin film may become clear by correcting the gain of the image signal and adjusting the appearance of the image afterwards.
  • correcting the gain of the signal instead of the switching position of the filter device 9 means correcting the gain without changing the filter when a good alignment image cannot be obtained even if the image is repeatedly captured by changing the filter. Refers to trying to adjust the image.
  • the patterned wafer with a film is described as an example of the positioning target of the alignment apparatus 1.
  • the alignment is performed with a bare wafer, a patterned wafer without a film, and other samples. be able to.
  • the inspection apparatus 100 equipped with the optical defect inspection unit 200 has been described as an example, the alignment apparatus 1 is also applicable to an inspection apparatus equipped with the SEM, TEM, STEM or the like as the defect inspection unit 200. .
  • the switching positions of the filter device 9 need only be plural, and need not be five.
  • the number of switching positions of the filter device 9 can be changed as needed.
  • the number of switching positions of the filter device 9 does not necessarily correspond to the number of sensors. For example, even when a plurality of filters are associated with a single sensor and the same sensor is used, it is conceivable to change the imaging condition by changing the filter. In this case, the number of switching positions of the filter device 9 tends to increase with respect to the number of sensors. The same applies to the number of light sources when the illumination light source 2 is composed of a plurality of light sources having different wavelength bands.
  • any one of the sensors 7R, 7G, 7B, 7C, and 7I is selectively used has been described, but a plurality of selection sensors may be used to create one alignment image.
  • a sample for which it is not necessary to limit the wavelength by adding a switching position that does not limit the wavelength to the filter device 9 and obtains an alignment image by using the signals of all the sensors 7R, 7G, 7B of all the RGB of the sensor 7 as usual.
  • SYMBOLS 1 Alignment device, 1A ... Illumination optical system, 1B ... Imaging part, 2 ... Illumination light source, 6 ... Color separation optical element, 7, 7B, 7C, 7G, 7I, 7R ... Sensor, 8 ... Aperture stop, 9 ... Filter Device, 10 ... Processing device (processing unit), 11 ... Alignment circuit, 12 ... Memory, 13 ... Control circuit, 14 ... Automatic imaging circuit, 15 ... Simulation circuit, 16 ... Reflected light amount calculation circuit, 17 ... Filtered reflected light amount calculation Circuit, 18 ... Filter selection circuit, 100 ... Inspection device, 101 ... Stage, 200 ... Defect inspection unit, n1, n2 ... Refractive index of thin film, O ... Chip origin, P ... Reference pattern, t1, t2 ... Thin film thickness , W ... Wafer (sample)

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Abstract

Lors du réglage des positions d'une platine et d'un échantillon sur la platine sur la base d'une image pour l'alignement acquise par l'émission d'une lumière d'éclairage sur l'échantillon, la présente invention : disperse une lumière d'éclairage qui a été réfléchie par l'échantillon en une pluralité de bandes de longueur d'onde; sélectionne, parmi la lumière réfléchie dispersée, la lumière réfléchie efficace à utiliser pour l'alignement; limite la bande de longueur d'onde de la lumière d'éclairage irradiée sur l'échantillon en fonction de la lumière réfléchie efficace sélectionnée; et ajuste les positions de l'échantillon et de la platine sur la base d'une image pour l'alignement obtenue à partir de la lumière réfléchie efficace.
PCT/JP2018/038634 2018-10-17 2018-10-17 Dispositif d'alignement, dispositif d'inspection et procédé d'alignement Ceased WO2020079770A1 (fr)

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Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4669884A (en) * 1985-10-30 1987-06-02 Harris Corporation Variable wavelength optical alignment system
JPH05226220A (ja) * 1992-02-10 1993-09-03 Toshiba Corp アライメント測定装置
JP2007147475A (ja) * 2005-11-29 2007-06-14 Hitachi High-Technologies Corp 光学式検査装置及びその方法
JP2009085826A (ja) * 2007-10-01 2009-04-23 Nikon Corp 観察装置及び観察方法
JP2010171448A (ja) * 2005-08-16 2010-08-05 Asml Netherlands Bv 位置合わせ測定機構及び位置合わせ測定方法
JP2011075280A (ja) * 2009-09-29 2011-04-14 Hitachi High-Technologies Corp 検査装置及び検査方法

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4669884A (en) * 1985-10-30 1987-06-02 Harris Corporation Variable wavelength optical alignment system
JPH05226220A (ja) * 1992-02-10 1993-09-03 Toshiba Corp アライメント測定装置
JP2010171448A (ja) * 2005-08-16 2010-08-05 Asml Netherlands Bv 位置合わせ測定機構及び位置合わせ測定方法
JP2007147475A (ja) * 2005-11-29 2007-06-14 Hitachi High-Technologies Corp 光学式検査装置及びその方法
JP2009085826A (ja) * 2007-10-01 2009-04-23 Nikon Corp 観察装置及び観察方法
JP2011075280A (ja) * 2009-09-29 2011-04-14 Hitachi High-Technologies Corp 検査装置及び検査方法

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