Patent Application
20230136198
The present invention relates to a Wien filter and a multiple electron beam inspection apparatus.
As LSI circuits are increasing in density, the line width of circuits of semiconductor devices is becoming finer. To form a desired circuit pattern onto a semiconductor device, a method of reducing and transferring, by using a reduction-projection exposure apparatus, onto a wafer a highly precise original image pattern formed on a quartz is employed.
An improvement in yield is indispensable for the fabrication of LSI, which takes a massive fabrication cost. With miniaturization of the dimensions of the LSI pattern formed on a semiconductor wafer, the dimensions of pattern defects to be detected are also extremely small. Thus, high precision of a pattern inspection apparatus that inspects a hyperfine pattern transferred onto a semiconductor wafer for defects is needed.
As an inspection method for pattern defects, there is known a method of comparing a measurement image obtained by capturing a pattern formed on a substrate, such as a semiconductor wafer and a lithography mask, with design data or a measurement image obtained by capturing the same pattern on the substrate. Examples of the inspection method include “die-to-die inspection” that compares pieces of measurement image data obtained by capturing the same patterns at different locations on the same substrate and “die-to-database inspection” that generates design image data (reference image) based on pattern-designed design data and that compares the design image data with a measurement image that is measurement data obtained by capturing a pattern. When the compared images do not match, it is determined that there are pattern defects.
There has been developing an inspection apparatus that acquires a pattern image by scanning on a substrate to be inspected with electron beams and detecting secondary electrons emitted from the substrate with application of electron beams. Development of an apparatus using multiple beams as an inspection apparatus using electron beams has been proceeding.
When a substrate to be inspected is irradiated with multiple beams (multiple primary electron beams), a flux of secondary electrons (multiple secondary electron beams) including reflected electrons corresponding to respective ones of the multiple beams is emitted from the substrate to be inspected. The multiple beam inspection apparatus includes a Wien filter for separating multiple secondary electron beams from multiple primary electron beams.
In a plane orthogonal to a beam traveling direction (or path central axis), the Wien filter generates an electric field and a magnetic field in directions orthogonal to each other. The multiple primary electron beams that enter the Wien filter from above travel straight downward, because forces of the electric and magnetic fields acting on the multiple primary electron beams cancel each other out. On the other hand, the multiple secondary electron beams that enter the Wien filter from below are bent obliquely upward and separated from the multiple primary electron beams, because forces of the electric and magnetic fields act in the same direction on the multiple secondary electron beams.
In a conventional Wien filter, a plurality of electromagnetic poles are arranged at regular intervals on the same inner circumference of a cylindrical yoke, and the electromagnetic poles each have a coil wound thereon. A voltage applied to each electromagnetic pole and the amount of current passing through the coil are controlled, so that the electric and magnetic fields are superimposed.
The cylindrical yoke has a ground potential. Each electromagnetic pole is joined to the inner periphery of the cylindrical yoke, with an insulator therebetween. The insulator has a resistance (magnetic resistance) against a magnetic flux generated in the coil. To provide an efficient Wien filter that uses less coil current, the insulator is required to be reduced in thickness. With a thin insulator, however, there is an increased risk of discharge between the cylindrical yoke and the electromagnetic pole (high-voltage portion) to which a voltage is applied.
An object of the present invention is to provide a Wien filter that has a low risk of discharge and operates efficiently and stably, and to also provide a multiple electron beam inspection apparatus that includes the Wien filter.
According to one aspect of the present invention, a Wien filter includes a cylindrical yoke, a plurality of magnetic poles arranged at intervals along an inner periphery of the yoke, the magnetic poles each joined at one end thereof to the yoke, a coil wound on each of the plurality of magnetic poles, and an electrode disposed at the other end of each of the plurality of magnetic poles, with an insulator between the electrode and the magnetic pole.
According to one aspect of the present invention, a multiple electron beam inspection apparatus includes an optical system irradiating a substrate with multiple primary electron beams, a beam separator separating, from the multiple primary electron beams, multiple secondary electron beams emitted as a result of irradiating the substrate with the multiple primary electron beams, and a detector detecting the multiple secondary electron beams separated. The above Wien filter is used as the beam separator.
The present invention can reduce the risk of discharge in the Wien filter and allow the Wien filter to operate efficiently and stably.
Hereinafter, embodiments of the present invention will be described on the basis of the drawings.
Each magnetic pole 3 of the Wien filter 1 has a coil 4 wound thereon. The magnetic pole 3 extends in the radial direction of the yoke 2. The magnetic pole 3 is joined to the yoke 2 at one end thereof, and has an electrode 5 at the other end thereof (or at an end portion thereof adjacent to the yoke center), with an insulator 6 between the magnetic pole 3 and the electrode 5. A space in the yoke center surrounded by a plurality of electrodes 5 is a beam passage region.
Each coil 4 is connected to a current source (not shown) and configured to allow the amount of current to be independently controlled. Each electrode 5 is connected to a voltage source (not shown) outside the yoke and configured to allow a voltage applied thereto to be independently controlled. The yoke 2 has a ground potential.
The yoke 2 and the magnetic pole 3 may be made of a magnetic material, such as permalloy. The electrode 5 may be a conductive member, such as a copper plate. The insulator 6 may be made of, for example, a ceramic material.
As illustrated in
The first plate portion 31 has six surfaces: a first principal plate surface 31a, a second principal plate surface 31d opposite the first principal plate surface 31a, a proximal end 31b, a distal end 31e opposite the proximal end 31b, an upper surface 31c, and a lower surface 31f opposite the upper surface 31c. The first principal plate surface 31a and the second principal plate surface 31d are substantially parallel to the radial direction of the yoke 2.
The first plate portion 31 is joined at the proximal end 31b thereof to the inner periphery of the yoke 2. The distal end 31e of the first plate portion 31 is smaller than a first principal plate surface 32a of the second plate portion 32. The distal end 31e is joined to a center of the first principal plate surface 32a. The first plate portion 31 is joined to the second plate portion 32 in such a way as to be substantially perpendicular to the first principal plate surface 32a. The first plate portion 31 and the second plate portion 32 may be formed as an integral unit having the structure described above.
A second principal plate surface 32d opposite the first principal plate surface 32a of the second plate portion 32 is slightly curved toward the first principal plate surface 32a.
The coil 4 described above is wound around the first principal plate surface 31a, the upper surface 31c, the second principal plate surface 31d, and the lower surface 31f of the first plate portion 31. The electrode 5 is disposed on the second principal plate surface 32d of the second plate portion 32, with the insulator 6 therebetween.
An electric field is generated by controlling a voltage applied to each electrode 5. A magnetic field orthogonal to the electric field is generated by controlling current in each coil 4. For example, an electric field is generated by applying predetermined voltages (e.g., +5 kV for one electrode 5 and −5 kV for the other electrode) from the voltage source to the electrodes 5 at the 6 o'clock and 12 o'clock positions in
Referring to
In the present embodiment, on the other hand, a voltage for generating an electric field is applied to the electrode 5 separate from the magnetic pole 3 constituting a magnetic circuit. Since the insulator 6 interposed between the magnetic pole 3 and the electrode 5 has little impact on the magnetic resistance, it is possible to leave a sufficient insulation gap and reduce the risk of discharge. Also, since the yoke 2 and the magnetic pole 3 do not require an insulator therebetween, there is no need to increase coil current and the Wien filter can operate efficiently and stably.
As illustrated in
As illustrated in
As illustrated in
For example, by applying a voltage to the electrodes 5B (two separate electrodes) at the 12 o'clock position in
In the Wien filter that includes both the magnetic poles 3A and 3B, as illustrated in
The first plate portion 31 and the second plate portion 32 of any of the magnetic poles 3, 3A, and 3B may be formed as an integral unit or may be separate components coupled together. Also, the yoke 2 and any of the magnetic poles 3, 3A, and 3B may be formed as an integral unit or may be separate components coupled together.
In the embodiments described above, the electrode 5 is provided separately from the magnetic pole 3, and a voltage for generating an electric field is not applied to the magnetic pole 3. As illustrated in
With the configuration illustrated in
With the configuration Illustrated in
When the permanent magnet 7 is a permanent magnet member, such as a rubber magnet, that can be roughly regarded as an insulator, the high-voltage portion can be insulated from the ground portion and this can reduce the risk of discharge. Also, since the permanent magnet 7 provides a magnetomotive force for generating a magnetic field, it is possible to reduce magnetic-field control current flowing through the coil 4 and reduce the risk of heat generation.
Since the permanent magnet 7 allows a voltage drop and reduces the risk of discharge, the permanent magnet 7 and the yoke 2 may be provided with an insulator 8 therebetween, as illustrated in
Although the Wien filter includes eight magnetic poles 3 in the embodiments described above, the number of magnetic poles 3 is not limited, as long as orthogonal electric and magnetic fields can be generated. For example, the Wien filter may include four magnetic poles 3 as illustrated in
Next, a pattern inspection apparatus 100 including the Wien filter will be described with reference to
As illustrated in
A stage 105 movable in the horizontal direction, the rotational direction and the height direction is disposed in the inspection chamber 103. A substrate 101 (sample) to be inspected is placed on the stage 105. Examples of the substrate 101 include an exposure mask substrate and a semiconductor substrate, such as a silicon wafer. When the substrate 101 is a semiconductor substrate, a plurality of chip patterns (wafer dies) are formed on the semiconductor substrate. When the substrate 101 is an exposure mask substrate, a chip pattern is formed on the exposure mask substrate. The chip pattern is composed of a plurality of figure patterns. The chip pattern formed on the exposure mask substrate is exposed and transferred onto a semiconductor substrate multiple times, so that a plurality of chip patterns (wafer dies) are formed on the semiconductor substrate.
The substrate 101 is placed on the stage 105, with a pattern side thereof facing upward. The stage 105 has a mirror 216 disposed thereon. The mirror 216 reflects laser light for laser measurement emitted from a laser measurement system 111 disposed outside the inspection chamber 103.
The multi-detector 222 is connected to a detecting circuit 106 outside the electron beam column 102. The detecting circuit 106 is connected to a chip pattern memory 123.
In the control system circuit 160, a control computer 110 that controls the overall operation of the inspection apparatus 100 is connected through a bus 120 to a position circuit 107, a comparing circuit 108, a reference image generating circuit 112, a stage control circuit 114, a lens control circuit 124, a blanking control circuit 126, a deflection control circuit 128, a storage device 109 such as a magnetic disk device, a monitor 117, a memory 118, and a printer 119.
The deflection control circuit 128 is connected through a digital-to-analog converter (DAC) amplifier (not shown) to the main deflector 208, the sub-deflector 209, and the deflector 218.
The chip pattern memory 123 is connected to the comparing circuit 108.
The stage 105 is driven by a driving mechanism 142 under the control of the stage control circuit 114. The stage 105 is movable in the horizontal direction and the rotational direction. The stage 105 is also movable in the height direction.
The laser measurement system 111 measures the position of the stage 105 by receiving light reflected off the mirror 216 using the principle of laser interferometry. The position of the stage 105 measured by the laser measurement system 111 is sent to the position circuit 107.
The lens control circuit 124 controls the electromagnetic lens 202, the electromagnetic lens 205, the electromagnetic lens 206, the electromagnetic lens 207 (objective lens), the electrostatic lens 210, the electromagnetic lens 224, and the beam separator 214.
The electrostatic lens 210 is composed of, for example, three or more electrode substrates that are open in the center thereof. An electrode substrate in the middle of the electrostatic lens 210 is controlled by the lens control circuit 124 through a DAC amplifier (not shown), and upper and lower electrode substrates of the electrostatic lens 210 are supplied with a ground potential.
The collective blanking deflector 212 is composed of two or more electrodes, each of which is controlled by the blanking control circuit 126 through a DAC amplifier (not shown).
The sub-deflector 209 is composed of four or more electrodes, each of which is controlled by the deflection control circuit 128 through a DAC amplifier. The main deflector 208 is composed of four or more electrodes, each of which is controlled by the deflection control circuit 128 through a DAC amplifier. The deflector 218 is composed of four or more electrodes, each of which is controlled by the deflection control circuit 128 through a DAC amplifier.
A high-voltage power supply circuit (not shown) is connected to the electron gun 201. By applying an acceleration voltage from the high-voltage power supply circuit between a filament (cathode) and an extraction electrode (anode) (not shown) in the electron gun 201, applying a voltage to another extraction electrode (Wehnelt), and heating the cathode to a predetermined temperature, a group of electrons emitted from the cathode is accelerated and emitted as an electron beam 200.
An operation of the image acquiring mechanism 150 of the inspection apparatus 100 will now be described.
The electron beam 200 emitted from the electron gun 201 (emission source) is refracted by the electromagnetic lens 202 and illuminates the entire shaping aperture array substrate 203. The shaping aperture array substrate 203 has the plurality of apertures 203a as illustrated in
The multiple beams MB are refracted by the electromagnetic lens 205 and the electromagnetic lens 206 to repeatedly form an image and a crossover, and pass through the beam separator 214 disposed at a crossover of the multiple beams MB to reach the electromagnetic lens 207 (objective lens). The electromagnetic lens 207 focuses the multiple beams MB onto the substrate 101. The multiple beams MB brought into focus on the surface of the substrate 101 (sample) by the electromagnetic lens 207 are deflected together by the main deflector 208 and the sub-deflector 209 to the respective irradiation positions on the substrate 101.
When all the multiple beams MB are deflected together by the collective blanking deflector 212, the multiple beams MB are displaced from a center hole of the limiting aperture substrate 213 and blocked by the limiting aperture substrate 213. On the other hand, the multiple beams MB not deflected by the collective blanking deflector 212 pass through the center hole of the limiting aperture substrate 213, as illustrated in
When the substrate 101 is irradiated with the multiple beams MB at desired positions, a flux of secondary electrons (multiple secondary electron beams 300) including reflected electrons corresponding to respective ones of the multiple beams MB (multiple primary electron beams) is emitted from the substrate 101.
The multiple secondary electron beams 300 emitted from the substrate 101 pass through the electromagnetic lens 207 to reach the beam separator 214.
The Wien filter according to any of the embodiments described above is used as the beam separator 214. In a plane orthogonal to the direction in which a central beam of the multiple beams MB travels (i.e., in a plane orthogonal to the central axis of the path), the beam separator 214 generates an electric field and a magnetic field in directions orthogonal to each other. The electric field exerts force in the same direction regardless of the direction of travel of electrons. On the other hand, the magnetic field exerts force in accordance with the Fleming's left-hand rule. The direction of force acting on electrons can thus be changed by the direction of travel of the electrons.
The multiple beams MB that enter the beam separator 214 from above travel straight downward, because the forces exerted by the electric and magnetic fields and acting on the multiple beams MB cancel each other out. On the other hand, the multiple secondary electron beams 300 that enter the beam separator 214 from below are bent obliquely upward and separated from the multiple beams MB, because the forces exerted by the electric and magnetic fields act in the same direction on the multiple secondary electron beams 300.
The multiple secondary electron beams 300 bent obliquely upward and separated from the multiple beams MB are deflected by the deflector 218, refracted by the electromagnetic lens 224, and projected onto the multi-detector 222. Note that
The multi-detector 222 detects the multiple secondary electron beams 300 projected thereon. The multi-detector 222 includes, for example, a diode-type two-dimensional sensor (not shown). The secondary electrons of the multiple secondary electron beams 300 collide with the diode-type two-dimensional sensor at positions corresponding to respective beams of the multiple beams MB. This multiplies the electrons inside the sensor, and generates secondary electron image data for each pixel from an amplified signal.
Detection data of secondary electrons detected by the multi-detector 222 (i.e., measured image, secondary electron image, or image to be inspected) is output to the detecting circuit 106 in order of measurement. In the detecting circuit 106, analog detection data is converted to digital data by an analog-to-digital (A/D) converter (not shown) and stored in the chip pattern memory 123. The image acquiring mechanism 150 thus acquires a measured image of a pattern formed on the substrate 101.
The reference image generating circuit 112 generates a reference image for each mask die, on the basis of design data serving as a basis for forming a pattern on the substrate 101, or design pattern data defined by exposure image data of a pattern formed on the substrate 101. For example, design pattern data is read from the storage device 109 through the control computer 110, and each figure pattern defined by the read design pattern data is converted to binary or multilevel image data.
Figures defined by the design pattern data are composed of basic elements, such as a rectangle and a triangle. Figure data is stored, which defines the shape, size, position, and others of each pattern figure by using information, such as coordinates (x, y) of a reference position of the figure, lengths of sides of the figure, and a figure code serving as an identifier for identifying the figure type, such as rectangle or triangle.
When design pattern data used as figure data is received by the reference image generating circuit 112, the data is developed into data of each figure, and the figure code indicating the figure shape of the figure data and the figure dimensions are interpreted. Then, the figure data is developed into binary or multilevel image data of the design pattern as a pattern to be arranged within squares in units of grids of predetermined quantization dimensions, and output.
In other words, the design data is read, the occupancy of a figure in the design pattern is calculated for each of squares into which an inspection region is virtually divided in units of predetermined dimensions, and n-bit occupancy data is output. For example, it is preferable to set one square as one pixel. When one pixel is given a resolution of 1/28 (=1/256), small regions with a resolution of 1/256 are allocated to the region of a figure in the pixel to calculate the occupancy in the pixel. The calculated occupancy is output as 8-bit occupancy data to the reference image generating circuit 112. The square (inspection pixel) is simply sized to match the pixel of measured data.
The reference image generating circuit 112 then performs appropriate filter processing on design image data of the design pattern which is image data of the figure. Optical image data (measured image) is under the action of filtering performed thereon by the optical system or, in other words, in an analog state that continuously changes. Therefore, by also performing filter processing on image data of the design pattern which is design-side image data whose image intensity (gray value) is a digital value, it is possible to adjust the image data to the measured data. The generated image data of a reference image is output to the comparing circuit 108.
The comparing circuit 108 compares the measured image (image to be inspected) obtained by measuring the substrate 101 with the reference image corresponding thereto. Specifically, the image to be inspected and the reference image, which are positioned with respect to each other, are compared pixel-by-pixel. The comparing circuit 108 compares them pixel-by-pixel by using a predetermined determination threshold, in accordance with predetermined determination conditions, and determines whether there is a defect, such as a shape defect. For example, if a difference in pixel-by-pixel gray level is greater than a determination threshold Th, the comparing circuit 108 determines the pixel as a defect candidate, and outputs the result of the comparison. The result of the comparison may be stored in the storage device 109 or the memory 118, displayed on the monitor 117, or may be printed out from the printer 119.
Besides the die-to-database inspection described above, the die-to-die inspection may be performed. The die-to-die inspection compares data of measured images obtained by imaging the same patterns at different points on the same substrate 101. Accordingly, from the substrate 101 on which the same figure patterns (first and second figure patterns) are formed at different positions by the multiple beams MB (electron beams), the image acquiring mechanism 150 acquires measured images that are secondary electron images of one figure pattern (first figure pattern) and the other figure pattern (second figure pattern). In this case, the acquired measured image of the one figure pattern serves as a reference image, and the acquired measured image of the other figure pattern serves as an image to be inspected. The acquired images of the one figure pattern (first figure pattern) and the other figure pattern (second figure pattern) may be within the same chip pattern data, or may be separate in different pieces of chip pattern data. The inspection may be carried out in the same manner as the die-to-database inspection.
The Wien filter 1 according to any of the embodiments described above is used as the beam separator 214. This can reduce the risk of discharge in the image acquiring mechanism 150 and enables efficient and stable operation.
Although the present invention has been described in detail using specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the intent and scope of the present invention.
This application is based on Japanese Patent Application 2020-180675 filed on Oct. 28, 2020, which is incorporated by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-180675 | Oct 2020 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2021/023343 | Jun 2021 | US |
| Child | 18147263 | US |
