Patent Application
20240290571
Embodiments described herein relate to a charged particle optics for a charged particle beam apparatus, for example in an electron microscope, particularly in a scanning electron microscope (SEM). Embodiments further relate to a method for scanning a charged particle beam over a sample in a charged particle beam device. Specifically, embodiments relate to a charged particle optics for a charged particle beam apparatus, a charged particle beam apparatus and method of imaging a sample in a charged particle beam device.
Modern semiconductor technology has created a high demand for structuring and probing specimens in the nanometer or even in the sub-nanometer scale. Micrometer and nanometer-scale process control, inspection or structuring, is often done with charged particle beams, e.g. electron beams, which are generated, shaped, deflected and focused in charged particle beam apparatuses, such as electron microscopes or electron beam pattern generators. For inspection purposes, charged particle beams offer a superior spatial resolution compared to, e.g., photon beams.
Apparatuses using charged particle beams, such as scanning electron microscopes (SEM), have many functions in a plurality of industrial fields, including, but not limited to, inspection of electronic circuits, exposure systems for lithography, detecting systems, defect inspection tools, and testing systems for integrated circuits. In such particle beam systems, fine beam probes with a high current density can be used. For instance, in the case of an SEM, the primary electron beam generates signal particles like secondary electrons (SE) and/or backscattered electrons (BSE) that can be used to image and/or inspect a sample.
Reliably inspecting and/or imaging samples with a charged particle beam apparatus at a good resolution is, however, challenging. Further, particularly in the semiconductor industry, throughput, for example, for image generation is beneficially high. Further, low energy particle beams are beneficial for in-line inspection and/or imaging. The throughput influencing factors like the size of the field of view (FOV), particularly the FOV size being limited relative to the size of the wafer, and the collection efficiency of signal particles, and factors like the resolution and the beam energy on a specimen, for example, a wafer, can contradict each other for the beneficial design of an electro-optical component.
In light of the above, providing an improved charged particle optics for a charged particle beam apparatus, an improved charged particle beam apparatus, and an improved method of scanning a charged particle beam over a sample are beneficial.
In light of the above, a charged particle optics for a charged particle beam apparatus, a charged particle beam apparatus, and a method of focusing the charged particle beam are provided according to the independent claims.
According to an embodiment, a charged particle optics for a charged particle beam apparatus having a charged particle beam and a beam propagation direction of the charged particle beam apparatus is provided. The charged particle optics includes a focusing lens. The focusing lens includes a first electrode with a first aperture; a second electrode with a second aperture, the second electrode being mechanically movable at least in a first direction perpendicular to the beam propagation direction; and an actuator coupled to the second electrode to move the second electrode in at least the first direction for displacement of the second aperture with respect to the first aperture. The charged particle optics further includes a deflection system positioned upstream of the second electrode to deflect the charged particle beam, based on the displacement, to guide the charged particle beam through the second aperture.
According to an embodiment, a charged particle beam apparatus is provided. The charged particle beam apparatus includes an emitter configured a emit a charged particle beam; a scan deflector to scan the charged particle beam within a field of view; and a charged particle optics according to any of the embodiments described herein, wherein the charged particle optics is configured to focus the charged particle beam and to deflect the charged particle beam within a field of movement.
According to an embodiments, a method for imaging a sample in a charged particle beam device having a charged particle optics with at least a first electrode with a first aperture and a second electrode with a second aperture is provided. The method includes (a) moving the second electrode with the second aperture at least in a first direction perpendicular to a beam propagation direction for displacement of the second aperture with respect to the first aperture; (b) guiding a charged particle beam through the first aperture of a first electrode; (c) deflecting the charged particle beam based on the displacement of the second aperture with respect to the first aperture; (d) guiding the charged particle beam through the second aperture onto the sample; (e) focusing the charged particle beam with a focusing lens including the first electrode and the second electrode; and (f) scanning the charged particle beam over the sample.
Further advantages, features, aspects and details that can be combined with embodiments described herein are evident from the dependent claims, the description and the drawings.
So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to one or more embodiments and are described in the following.
Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in the figures. Within the following description of the drawings, same reference numbers refer to same components. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation and is not meant as a limitation. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the description includes such modifications and variations.
According to an embodiment, a charged particle optics for a charged particle beam apparatus having a charged particle beam and a beam propagation direction of the charged particle beam apparatus is described. The charged particle optics includes a focusing lens having a first electrode with a first aperture; a second electrode with a second aperture, the second electrode being mechanically movable at least in a first direction perpendicular to the beam propagation direction; and an actuator coupled to the second electrode to move the second electrode in at least the first direction for displacement of the second aperture with respect to the first aperture. The charged particle optics further includes a deflection system positioned upstream of the second electrode to deflect the charged particle beam, based on the displacement, to guide the charged particle beam through the second aperture.
The second electrode can be very light, which results in the second electrode being easier to move than the substrate. Particularly, the second electrode can be moved faster than the substrate. By moving the second electrode to a new position where an image can be acquired the overhead time between images is reduced as compared to moving the sample, e.g. the substrate. Moving the charged particle beam correlated with moving the second electrode can increase the throughput of apparatuses using charged particle beams, such as scanning electron microscopes (SEM).
The charged particle beam can be deflected by the deflection system, based on the displacement of the second electrode, to guide the charged particle beam through the second aperture. Throughout this disclosure, based on the displacement of the second electrode, it is understood, unless otherwise indicated, that the charged particle beam is deflected in a way that the deflection of the charged particle beam results in a displacement of the charged particle beam, measured in the plane of the second electrode, equal to the displacement of the second electrode. The second electrode being mechanically movable at least in a first direction perpendicular to the beam propagation direction results in an increased main field of view as compared to a lens without a movable electrode. The main field of view is a combination of a field of movement of the second electrode and a field of view of a scanning system, i.e. a sub-field of view corresponding to scanning of the scanning deflector. Advantageously, the deflection system can deflect the charged particle beam based on the displacement, to guide the charged particle beam through the center of the second aperture. The first aperture and the second aperture can be at the position of the charged particle beam, even for a larger off-axis position as compared to a FOV without movement of the second electrode. By moving the second electrode to view the desired location on the wafer, e.g. the specified surface region, off-axis aberrations can be reduced. In some embodiments, which can be combined with other embodiments described herein, the displacement can be at least in the range of tens of microns, for example 20 μm or more. The displacement may be up to several millimeters, e.g. up to 10 mm. The displacement can be in the first direction and a second direction respectfully. Particularly, the second direction can be perpendicular to the beam propagation direction. The first direction and the second direction can form a plane, with the beam propagation direction being perpendicular to the plane.
Throughout this disclosure, the beam propagation direction 12 is understood, unless otherwise indicated, as the direction in which the charged particle beam travels from the charged particle source towards the charged particle optics. The charged particle beam can be deflected in the charged particle optics by the deflection system. After deflection of the charged particle beam by a deflection system, the charged particle beam can travel along a further direction. The direction of the charged particle beam after deflection by the deflection system is understood to be a deflected beam propagation direction. The beam propagation direction can be, for example, along the z-axis of the charged particle beam apparatus, as shown in
The charged particle beam apparatus 100 further includes a sample stage 108. The sample 10 can be placed on the sample stage 108. The charged particle beam apparatus 100 further includes a charged particle optics 200 for moving the charged particle beam over a sample and for focusing the charged particle beam according to embodiments described herein. The charged particle optics 200 includes a focusing lens and an actuator as described e.g. with respect to
An image generation unit (not shown) may be provided. The image generation unit can be configured to generate one or more images of the sample 10. The image generation unit can generate the one or more images based on the signal received from the charged particle detector 118.
The sample stage 108 may be a movable stage. In particular, the sample stage 108 may be movable in the Z-direction, i.e., in the direction of the optical axis A, such that the distance between the focusing lens and the sample stage 108 can be varied (see arrow 112 in
The beam-optical components of the charged particle beam apparatus 100 can be placed in a vacuum chamber 101 that can be evacuated. A vacuum can be beneficial for propagation of the charged particle beam 11, for example, along the optical axis A from the charged particle source 105 toward the sample stage 108. The charged particle beam may hit the sample 10 under a sub-atmospheric pressure, e.g. a pressure below 10−3 mbar or a pressure below 10−5 mbar.
For example, the charged particle beam apparatus 100 may be an electron microscope, particularly a scanning electron microscope. A condenser lens system 106 may be arranged downstream of the charged particle source 105. The condenser lens system 106 can collimate the charged particle beam 11 propagating toward the charged particle optics 200.
One or more surface regions of the sample 10 can be inspected and/or imaged with the charged particle beam apparatus 100. The term “sample” as used herein may relate to a substrate, for example, with one or more layers or features formed thereon, a semiconductor wafer, a glass substrate, a flexible substrate, such as a web substrate, or another sample that is to be inspected. The sample can be inspected for one or more of (1) imaging a surface of the sample, (2) measuring dimensions of one or more features of the sample, e.g. in a lateral direction, i.e. in the X-Y-plane, (3) conducting critical dimension measurements and/or metrology, (4) detecting defects, and/or (5) investigating the quality of the sample.
For inspecting the sample 10 with the charged particle beam 11, the charged particle beam 11 can be focused on a sample surface with the focusing lens. Focusing of the focusing lens can be improved by correcting spherical aberration. Secondary electrons and/or backscattered electrons (referred to as “signal electrons”) are emitted from the sample when the charged particle beam 11 impinges on the sample surface. The signal electrons provide information about spatial characteristics and dimensions of features of the sample. The signal electrons can be detected with the charged particle detector 118.
The scan deflector 107 can scan the charged particle beam 11 over the sample. The signal electrons can be detected as a function of time and, thus, the generation position of the signal electrons can be determined. The sample surface or a portion thereof can be imaged, e.g., with the image generation unit that may be configured to provide an image of the sample 10 based on the received signal electrons.
A scan deflector 107 may be provided for scanning the charged particle beam 11 over a surface of the sample 10 along a predetermined scanning pattern, for example, in the X-direction and/or in the Y-direction. The scan deflector 107 can scan the charged particle beam 11 over the sample. The scanning range of the scan deflector 107 can be limited in the X-direction and/or in the Y-direction, for example, by the tilt angle or the first aperture and/or the second aperture. The scan deflector 107 has a field of view (FOV) corresponding to the scanning range. The FOV is an area or a projected area on the sample surface, which can be scanned by the scan deflector. Particularly, the FOV is a projected area on the sample surface, which defines an area that can be scanned by the scan deflector for a set position of the second electrode and a set position of the sample.
The charged particle optics 200 can deflect or move the charged particle beam, for example, in the X-direction and/or the Y-direction. The deflection by the charged particle optics 200 can superposition the deflection by the scan deflector 107, such that the position of the FOV on the surface of the sample 10 can be changed. The deflection range of the charged particle optics 200 can be provided in the X-direction and/or the Y-direction, for example, by the deflection system and/or the displacement of the second electrode. The charged particle optics 200 has a field of movement (FOM) corresponding to the range of movement of the second electrode and/or the deflection range of the deflection system of the charged particle optics. The charged particle optics 200 can deflect the charged particle beam to a position within the FOM. Particularly, the charged particle optics 200 can deflect the FOV to a position within the FOM. Superposition of the FOV of the scan deflector 107 and the FOM of the charged particle optics 200 results in a main FOV of the charged particle beam apparatus. The FOV of the scan deflector can provide a sub-field of view within the main field of view. The main FOV is larger than the sub-field of view of the scan deflector.
The main FOV provides for faster imaging of a specified surface region to be imaged. Multiple surface regions (FOVs), which can be independent from each other, can be scanned for a set sample position, i.e. without moving the sample. Throughout this disclosure, unless otherwise indicated, two surface regions are independent from each other if the two surface regions have no overlap and/or the two surface regions cannot be scanned in a single FOV. For example, to image a specified surface region, the sample stage 108 can be moved to place the specified surface region within the main field of view of the charged particle optics 200. The charged particle optics 200 can move the FOV of the scanning deflector 107, such that a surface region to be scanned is located in the FOV. The FOM can be adjusted faster and more precisely than the sample stage 108, which allows for faster adjustment. After scanning the surface region, the charged particle optics 200 can move and/or deflect the FOV to a further surface region within the main field of view, such that the FOV at the further surface region is independent from the surface region, e.g. has no overlap with the FOV at the previous surface region.
The first electrode and the second electrode can be configured such that a voltage can be applied to the first electrode and the second electrode. In some embodiments, which can be combined with other embodiments described herein, the charged particle optics can include a voltage supply assembly connected to the first electrode and the second electrode and configured to provide a voltage difference between the first electrode and the second electrode. For example, the voltage supply assembly can include a voltage supply connected to the first electrode and the second electrode. For example, the voltage supply assembly may include a first voltage supply connected to the first electrode and ground and a second voltage supply connected to the second electrode and ground, wherein the second voltage of the second voltage being independent from the first voltage. The first voltage supply and the second voltage supply can be configured to provide the first voltage to the first electrode and the second voltage to the second electrode to decelerate charged particles of the charged particle beam by the second electrode. particularly to provide a first voltage to the first electrode which is higher than a second voltage supplied to the second electrode for charged particles with negative charge, and to provide a first voltage to the first electrode which is lower than a second voltage supplied to the second electrode for charged particles with positive charge.
The focusing lens 210, particularly the electrostatic lens of the focusing lens 210, comprises a first electrode 220 with a first aperture 225 and a second electrode 230 with a second aperture 235. The charged particle beam 11 can be guided through the first aperture 225 and through the second aperture. In some embodiments, which can be combined with other embodiments described herein, the first aperture and the second aperture are spaced apart at least 1 mm, and particularly up to 20 mm along the beam propagation direction.
The second electrode is mechanically movable at least in a first direction perpendicular to the beam propagation direction. An actuator 250 is coupled to the second electrode to move the second electrode in at least the first direction. The first direction is perpendicular to the beam propagation direction. The first direction can be, for example, along the x-direction shown in
According to some embodiments of the present disclosure, the actuator 250 can move the second electrode from a first position within the FOM to a second position within the FOM. Particularly, the second electrode can be moved after an image or sub-image of a FOV at the first position has been generated. After each generation of an image or sub-image of a FOV, the FOV can be moved to a new position within the FOM. As described above, by moving the second electrode to a new position where an image can be acquired the overhead time between images is reduced as compared to moving the sample. Accordingly, the actuator 250 and/or the second electrode can be configured to be moved within 1 second or less, particularly within 100 milliseconds or less, or even within 20 millisecond or less.
The charged particle optics includes a deflection system 240. The deflection system 240 is upstream of the second electrode 230. According to some embodiments of the present disclosure, the deflection system can in include one or more deflectors, particularly one or more deflectors for each of the x-direction and the y-direction. For example, a first deflector of the deflection system can be an alignment deflector to align the charged particle beam to the second electrode, i.e. to deflect the charged particle beam to the aperture of the second electrode, e.g. after movement of the second electrode. According to further implementations, the deflection system may include (for each direction) an alignment deflector and an inverse alignment deflector. As exemplarily shown in
The deflection system 240 or at least one deflector of the deflection system can be placed upstream of the first electrode. According to some embodiments, a magnetic deflector may also be placed between the first electrode and the second electrode. In some embodiments, which can be combined in other embodiments described herein, the deflection system includes a magnetic deflector. In alternative embodiments, the deflection system includes an electrostatic deflector, particularly an electrostatic deflector placed upstream of the first electrode. The deflection system 240 can deflect the charged particle beam by an angle α, such that the charged particle beam propagates along a deflected beam propagation direction 212 having an angle α to the beam propagation direction 12.
The deflected charged particle beam impacts the sample at a tilt angle measured to the surface normal. The tilt angle can be the angle α. By adjusting the position of the FOV of the scan deflector 107 within the FOM of the charged particle optics 200, the tilt angle α can be adjusted. According to some embodiments, which can be combined with other embodiments described herein, tilt angles of up to αmax 30°. For example, as exemplarily shown for a beam path depicted in
The charged particle optics can include the deflection system having an alignment deflector and an inverse alignment deflector, as shown by the dotted line in
In some embodiments, which can be combined with other embodiments described herein, the charged particle optics can include the deflection system having an inverse alignment deflector, configured to deflect the charged particle beam inverse to the deflection of the charged particle beam by the alignment deflector of the deflection system, resulting in a parallel displacement of the charged particle beam. Particularly, the second deflection can be based on the first deflection to create a z-displacement, resulting in parallel displacement of the charged particle beam. According to some embodiments, which can be combined with other embodiments described herein, the deflection system can include an alignment deflector and an inverse alignment deflector, wherein the alignment deflector and the inverse alignment deflector impose deflection angles in opposite directions.
As shown in
According to an embodiment, a method 300 for imaging a sample in a charged particle beam device is described. The method includes the following operations: (a) moving the second electrode with the second aperture at least in a first direction perpendicular to a beam propagation direction for displacement of the second aperture with respect to the first aperture; (b) guiding the charged particle beam through a first aperture of a first electrode; (c) deflecting the charged particle beam based on the displacement of the second aperture with respect to the first aperture; (d) guiding the charged particle beam through the second aperture onto the sample; (e) focusing the charged particle beam with a focusing lens including the first electrode and the second electrode; and (f) scanning the charged particle beam over the sample.
According to some embodiments, which can be combined with other embodiments described herein, the charged particle beam can be guided through the first aperture off-axis with respect to a first axis of the first aperture and can be guided through the second aperture on-axis with respect to a second axis of the second aperture. For example, the charged particle beam can be guided through the first aperture off-axis and can be guided through the second aperture to be parallel to the beam propagation direction before entering the charged particle optics. The deflection system may deflect the charged particle beam by inversing the deflection of the charged particle beam to provide a parallel displacement of the charged particle beam.
According to some embodiments, which can be combined with other embodiments described herein, as exemplarily shown by the beam path in
Embodiments of the present disclosure allow to generate images at various FOVs without movement of the sample. Accordingly, the operations (a) moving the second electrode, (b) guiding the charged particle beam through a first aperture, (c) deflecting the charged particle beam, (d) guiding the charged particle beam through the second aperture, (e) focusing the charged particle beam, and (f) scanning the charged particle beam over the sample can be repeated one or more times. Particularly, between repeating the operations, the second electrode can be moved from a first position within a field of movement to a second position with the field of movement. Alternatively, the second electrode may be continuously moved and the beam is guided through the second aperture by continuously deflecting the charged particle beam in a manner corresponding to the continuous movement of the second electrode. For example, moving the second aperture can be a continuous movement and deflecting the charged particle beam can be a corresponding continuous deflection.
In some embodiments, which can be combined with other embodiments described herein, the focusing the charged particle beam can further include providing a voltage difference between the first electrode and a second voltage to the second electrode, particularly for decelerating the charged particle beam.
In some embodiments, which can be combined with other embodiments described herein, the method 300 further includes deflecting the charged particle beam inversing the deflection of the charged particle beam, to provide a parallel displacement of the charged particle beam. The charged particle beam is deflected by the inverse alignment deflector by an angle α′=−α, such that the charged particle beam propagates along the beam propagation direction. The charged particle beam has a parallel displacement with respect to the optical axis.
According to some embodiments, which can be combined with other embodiments described herein, the deflection of the charged particle beam through the first aperture and/or the second aperture can be adapted to optimize the spot size on the sample, and/or provide minimum chromatic aberrations and/or coma. In light of the stronger focusing field of the second electrode, particularly the deflection through the second aperture can be optimized as described above.
In some embodiments, which can be combined with other embodiments described herein, the method 300 further includes focusing the charged particle beam with a magnetic lens. The magnetic lens can focus the charged particle beam on the surface of the sample to reduce a spot size of the charged particle beam.
In light of the above, a plurality of embodiments are provided in the present disclosure, some of which are as follows:
Embodiment 1. A charged particle optics for a charged particle beam apparatus having a charged particle beam and a beam propagation direction of the charged particle beam apparatus, the charged particle optics comprising: a focusing lens, comprising: a first electrode with a first aperture; a second electrode with a second aperture, the second electrode being mechanically movable at least in a first direction perpendicular to the beam propagation direction; and an actuator coupled to the second electrode to move the second electrode in at least the first direction for displacement of the second aperture with respect to the first aperture; the charged particle optics further comprising: deflection system positioned upstream of the second electrode to deflect the charged particle beam, based on the displacement, to guide the charged particle beam through the second aperture.
Embodiment 2. The charged particle optics of embodiment 1, wherein the displacement can be at least 20 μm mm in the first direction and a second direction respectfully.
Embodiment 3. The charged particle optics of any one of embodiments 1 to 2, further comprising: a voltage supply assembly connected to the first electrode and the second electrode and configured to provide a voltage difference between the first electrode and the second electrode.
Embodiment 4. The charged particle optics of embodiment 3, wherein the voltage supply assembly comprises a first voltage supply and a second voltage supply, which are configured to provide a first voltage relative to ground to the first electrode and a second voltage relative to ground to the second electrode to decelerate charged particles of the charged particle beam by the second electrode.
Embodiment 5. The charged particle optics of any one of embodiments 1 to 4, wherein the first aperture and the second aperture are spaced apart at least 1 mm along the beam propagation direction.
Embodiment 6. The charged particle optics according to any one of embodiments 1 to 5, wherein the deflection system comprises an electrostatic deflector placed upstream of the second electrode.
Embodiment 7. The charged particle optics according to any one of embodiments 1 to 6, wherein the deflection system comprises a magnetic deflector placed upstream of the second electrode.
Embodiment 8. The charged particle optics according to any one of embodiments 1 to 7, wherein the focusing lens comprising a magnetic lens for focusing the charged particle beam, particularly wherein the magnetic lens is placed upstream from the second aperture.
Embodiment 9. The charged particle optics according to any one of embodiments 1 to 8, wherein the deflection system comprises: an alignment deflector; and an inverse alignment deflector, wherein the alignment deflector and the inverse alignment deflector imposing deflection angles in opposite directions.
Embodiment 10. A charged particle beam apparatus, comprising: an emitter configured a emit a charged particle beam; a scan deflector to scan the charged particle beam within a field of view; and a charged particle optics according to any of embodiments 1 to 9, wherein the charged particle optics is configured to focus the charged particle beam and to deflect the charged particle beam within a field of movement.
Embodiment 11. A method for imaging a sample in a charged particle beam device having a charged particle optics with at least a first electrode with a first aperture and a second electrode with a second aperture, the method comprising: (a) moving the second electrode with the second aperture at least in a first direction perpendicular to a beam propagation direction for displacement of the second aperture with respect to the first aperture; (b) guiding a charged particle beam through the first aperture of a first electrode; (c) deflecting the charged particle beam based on the displacement of the second aperture with respect to the first aperture; (d) guiding the charged particle beam through the second aperture onto the sample; (e) focusing the charged particle beam with a focusing lens including the first electrode and the second electrode; and (f) scanning the charged particle beam over the sample.
Embodiment 12. The method of embodiment 11, wherein the charged particle beam is guided through the first aperture off-axis with respect to a first axis of the first aperture and is guided through the second aperture on-axis with respect to a second axis of the second aperture.
Embodiment 13. The method of any of embodiments 11 to 12, wherein the charged particle beam is guided through the first aperture off-axis with respect to the first axis of the first aperture and is guided through the second aperture to be parallel to the beam propagation direction before entering the charged particle optics.
Embodiment 14. The method of any one of embodiments 11 to 13, further comprising: deflecting the charged particle beam by inversing the deflection of the charged particle beam to provide a parallel displacement of the charged particle beam.
Embodiment 15. The method of embodiment 11, wherein the charged particle beam is guided through the first aperture on-axis with respect to a first axis of the first aperture and is guided through the second aperture on-axis with respect to a second axis of the second aperture.
Embodiment 16. The method of any of embodiments 11 to 15, further comprising: decelerating the charged particle beam by the second electrode.
Embodiment 17. The method of any one of embodiments 11 to 16, further comprising: additionally focusing the charged particle beam with a magnetic lens.
Embodiment 18. The method of any of embodiments 11 to 17, further comprising: repeating operations (a) to (f), wherein the second electrode is during operation (a) moved from a first position within a field of movement to a second position with the field of movement.
Embodiment 19. The method of any of embodiments 11 to 17, wherein moving the second aperture is a continuous movement and deflecting the charged particle beam is a corresponding continuous deflection.
While the foregoing is directed to embodiments, other and further embodiments may be devised without departing from the basic scope, and the scope thereof is determined by the claims that follow.
