The invention relates to methods and systems for preparing a sample for transmission electron microscopy.
Transmission electron microscopy (TEM) is a technique whereby a beam of electrons is transmitted through a thin sample, interacting with the specimen as it passes through. A high resolution image can be formed from the interaction of the electrons transmitted through the specimen. The thin sample can have a thickness of a few nano-meters.
The preparation of a TEM sample can start by receiving or manufacturing a sample that is connected to a sample holder element. The combination of the sample and the sample holder element, before being ion milled is referred to as an initial sample.
The sample holder element is much thicker than few microns and can be held by a manipulator. The sample holder element can be glued or otherwise connected to the sample. The edge area of the sample—or an area near the edge area of the sample can be thinned by a mechanical process and then be further thinned by an ion miller to provide a very thin area that can be transparent to electrons and can be used as a TEM sample.
The pre-thinned area 21(2) has a depth (height) 21(7) and a width 21(3). The pre-thinned area 21(2) includes an area of interest 21(4) that includes a target 21(5) that should be included in the TEM sample.
There is a growing need to provide methods and systems for generating thin samples for Transmission electron microscopy.
According to an embodiment of the invention a method for preparing a sample may be provided. The method may include:
The positioning of the mask and the initial sample in front of the ion miller may include rotating the mask and the initial sample by the manipulator.
The milling of the exposed portion of the edge area of the partially milled sample may include monitoring a thickness of the edge area of the milled sample, during the milling, by a transmissive detector of the imaging device.
The method may include changing a spatial relationship between the mask and the partially milled based on thickness feedback information obtained during the milling of the edge area of the partially milled sample. Thus—the mask can be moved to expose a previously masked region of the mask area in order to remove the previously masked region and thereby thin the edge area to a required thickness.
The method may include changing a spatial relationship between the mask and the partially milled based on thickness feedback information obtained after the milling of the partially milled sample. Thus—the mask can be moved to expose a previously masked region of the mask area in order to remove the previously masked region and thereby thin the edge area to a required thickness.
The imaging device optical axis may be normal to a milling tool optical axis. The manipulator may rotate the mask and the initial sample by ninety degrees so that they face the ion miller.
The method may include:
The edge area of the initial sample may have a thickness of at least one micros and wherein thickness of the edge area of the milled sample does not exceed 50 nanometers.
The milling may include milling the sample while rotating a milling beam about the optical axis of the ion miller.
The method may include removing, by ion milling, the exposed portion of the edge area of the partially milled sample.
The method may include stopping the milling of the edge area of the partially milled sample based on a thickness of the edge area of the partially milled sample.
The method may include monitoring the thickness of the edge area of the partially milled sample by a transmissive detector of the imaging device.
The method may include comparing a current outputted by a transmissive detector of the imaging device to a predefined relationship between current values and thickness values.
The method may include:
The obtaining of images can be executed by an imaging device that is an optical device, a scanning electron microscope or a combination of an optical device and a scanning electron microscope.
The method may include monitoring a progress of the milling of the initial sample by a backscattered electron detector; and monitoring a completion of a milling of the partially milled sample by a transmissive detector.
The method may include automatically stopping the milling of the partially milled sample when reaching a desired thickness of the edge area of the partially milled sample.
According to an embodiment of the invention a sample preparation system is provided and may include a manipulator, an imaging device; and an ion miller.
The imaging device may be an optical device, a scanning electron microscope or a combination thereof.
The system manipulator may be arranged to rotate the mask and the initial sample until the mask and the initial sample face the ion miller.
The imaging system may include a transmissive detector that may be arranged to provide detection signals indicative of a thickness of the exposed portion of the edge area of the partially milled sample, during a milling of the exposed portion of the edge area of the partially milled sample.
The manipulator may be arranged to change a spatial relationship between the mask and the partially milled based on thickness feedback information obtained during a milling of the edge area of the partially milled sample.
The system may include wherein the manipulator may be arranged to change a spatial relationship between the mask and the partially milled based on thickness feedback information obtained after a milling of the partially milled sample.
The imaging device optical axis may be normal to a milling tool optical axis; and wherein the manipulator may be arranged to rotate the mask and the initial sample until the mask and the initial sample face the ion miller.
The manipulator may be arranged to:
The edge area of the initial sample may have a thickness of at least one micros and wherein the system may be arranged to mill the edge area of the milled sample until a thickness of the edge area of the milled sample does not exceed 50 nanometers.
The ion miller may be arranged to mill while rotating a milling beam about the optical axis of the ion miller.
The ion miller may be arranged to remove the exposed portion of the edge area of the partially milled sample.
The system may include a controller that may be arranged to stop a milling of the edge area of the partially milled sample based on a thickness of the edge area of the partially milled sample.
The system may include a transmissive detector that may be arranged to assist in a monitoring of a thickness of the edge area of the partially milled sample. The transmissive detector assists in the monitoring by providing detection signals that are indicative of the thickness of the edge area of the sample. The detection signals represent known thicknesses and thus can be processed to detect the actual thickness of the edge area.
The system may include a controller that may be arranged to compare a current outputted by the transmissive detector of the imaging device to a predefined relationship between current values and thickness values.
The system may include a backscattered electron detector arranged to participate in a monitoring of a progress of a milling of the initial sample; and a transmissive detector that may be arranged to assist in a monitoring of a completion of a milling of the partially milled sample.
The system may include a controller that may be arranged to automatically stop a milling of the partially milled sample when reaching a desired thickness of the edge area of the partially milled sample.
The ion miller may be further arranged to mill the exposed portion of the edge area of the milled sample while the masked portion is being masked by the mask, to provide a further milled sample.
The manipulator may be further arranged to:
Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. In the drawings, like reference numbers are used to identify like or functionally similar elements. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale.
The foregoing and other objects, features, and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. In the drawings, similar reference characters denote similar elements throughout the different views.
Because the illustrated embodiments of the present invention may for the most part, be implemented using electronic components and circuits known to those skilled in the art, details will not be explained in any greater extent than that considered necessary for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention.
The term edge area may have its regular meaning. It may be interpreted as being an area that is proximate to an edge or may be delimited by an edge. An edge area of a sample can be proximate to the edge of the sample or delimited by the edge. It may include a target. The edge area of the sample can be thinned by ion milling to form a TEM sample. The thickness of the edge area, after milling can be below 51 nanometers. Its width and length can exceed one or more microns, but other dimensions can be provided. The edge area is illustrated as having a rectangular shape but this is not necessarily so and it can have other shapes.
According to an embodiment of the invention a method is provided. The method may include:
The system can view the sample continuously and in a real time mode during the entire milling process and may have a fully automatic control of the process accuracy, quality and termination.
Referring to
The system 10 may also include a vacuum system 90, a vacuum chamber 91, optical microscope 92, anti-vibration system 94, base 96, air-lock 1300 and a base plate 98. The ion beam unit 40 may include various components (some are illustrated in
The system 10 may generate or receive a mask 50. The mask can be manufactured by micro-cleaving to provide a highly accurate mask. If the system generates the mask 50 then it includes a micro-cleaving unit (not shown).
The manipulator 100 includes two separate subunits 110 and 120 both located on a main rotating stage 130.
The second subunit 120 may manipulate the sample and the mask and may have X, Y, Z and θ stages. In
The first subunit 110 may manipulate the sample—it may change the spatial relationship between the mask and the sample—for example by moving the mask in relation to any movement introduced by the second sub-unit 120. It is noted that each of the mask and sample can be moved by sub-units—each can move in relation to each other and not share stages such as rotating stage 130.
The first subunit 110 may have X, Y, Z and θ stages. In either one of
The second subunit 120 may manipulates the mask and may also manipulate technological accessories such as mask, calibrating plate, apertures, target for deposition etc.
The first subunit 110 may receive the sample or technological accessories from a sample holder (also referred to as shuttle 103). The shuttle 103 may be transferred until it is positioned on the sample angular stage 100(8).
The stages are connected between structural elements such as plates, beams, rails, guidelines and the like denoted 101(1)-101(5).
Referring to
The alignment process may include aligning the mask 50 and the initial sample 21 so that (a) they are parallel to each other (both can be horizontal) or be positioned on any other manner, and (b) the edge area of the mask 50 is positioned directly above an imaginary line that represents a desired milled edge of the initial sample 21 after being milled during a first milling sequence. This imaginary line can be located few nanometers from a center of the milled sample 21. Dashed line 55 illustrates that the mask 50 is horizontal at the end of the alignment process. The distance (D 23) between a trajectory of the edge 53 of the mask 50 on the edge 25 of the initial sample 21 and the center 22 of the initial sample 31 is few nano-meters. It is about a half of the final thickness of the milled sample.
The alignment process is aimed to guarantee that once the mask is placed between an ion miller and the initial sample 21, it (the mask) will prevent the ion miller from milling a pre-defined masked portion of the initial sample while allowing the ion miller to mill a pre-defined exposed portion of the initial sample.
Once the alignment process ends the mask 50 and the initial sample 21 are moved (for example—rotated). The rotation can be executed by the main rotating stage 130 and about an axis (for example—about the X axis), while maintaining the spatial relationship between the mask 50 and the initial sample 21 unchanged. The movement (rotation) can be stopped once the mask 50 and the initial sample 21 face the ion miller 40.
The ion miller 40 performs a first milling sequence that may include milling the exposed portion of the edge area of the initial sample 21 by a dual deflection while observing the milling by the scanning electron microscope (using detector 32 and/or detector 34). The milling may further thin the pre-thinned area of the initial sample 21 on one side to provide a milled side (denoted 24 in
After one side of the initial sample is milled (to provide partially milled sample 21′) the manipulator 100 changes the spatial relationship between the mask 50 and the partially milled sample 21′ in order to expose the other side of the edge area of the partially milled sample 21′ to the ion miller 40. This may include rotating the partially milled sample 21′ about its axis (112) by the sample rotational stage 100(8), and may also include changing the height of the mask 50.
According to an embodiment of the invention the change of spatial relationship is controlled during an alignment process during which the imaging system acquired images of the mask and the partially milled sample to guarantee that the desired alignment is obtained. The alignment may be preceded by moving (for example—rotating) that mask and the partially milled sample until they face the imaging system, performing the alignment and then moving (for example—rotating) the mask and the partially milled sample till they face the ion miller.
After the spatial relationship is changed, the ion miller 40 performs a second milling sequence that includes milling the other (now exposed) portion of the edge area of the partially milled sample 21′ while observing the milling by the scanning electron microscope and (optionally—when the partially milled sample starts to be partially transparent to electrons) by a TEM or STEM detector 33, until reaching a desired thickness. The milling process can be automatically stopped when the TEM detector 33 indicates that the thickness of the milled sample reached the desired thickness.
The system 10 can include a retractable BSE detector, a SE detector or a combination thereof. During initial ion milling at high sputtering rate, the viewing of the sample can be accomplished by the retractable BSE detector 32 that is illustrated in
To obtain high-resolution images at intermediate stages of ion milling when the sample is yet not transparent for incident primary electrons, a combination of SE detector 34 and BSE detector 32 can be used.
To obtain high-resolution images at final stages of ion milling when the sample becomes transparent for primary electrons a transmissive (TE) detection is used. A target identification for the sample alignment process can be carried out by operator by means of a combination of the three above-mentioned detectors; SE, BSE and TE.
The final thickness of the milled sample 21″ can be determined by measurement of output currents from a transmissive (TE) detector 33. Calibration curves of these output currents versus the sample thickness will be calculated for the predefined analytical conditions for different material constituents of the sample. An example of such a curve is illustrated in
The SE detector 34 can be an Everhart-Thornley type detector that includes a combination of a scintillator and a photo-multiplier. The SE detector 34 can be mounted on the sidewall of the system chamber. The SE detector 34 can operate in a current mode. During ion milling the SE detector 34 is protected by a protective shutter 35.
The BSE detector 32 can be a solid-state semiconductor detector, which can be located beneath the pole pieces of the objective lens 30 to allow its retracting in order to obtain high resolution observation mode when extremely short working distance is needed. The BSE detector 32 can operate in a current mode. The BSE 32 detector can be used during ion milling for observation of the sample surface.
The TE detector 33 may include three independent parts, which are electrically isolated one from another. A first part—referred to as a first bright field TE 33(1) detector may be a disk located on the microscope principal axis beneath the sample. It is dedicated to detection of transmitted electrons scattered at small angles. The second part is referred to as a second bright field TE detector 33(2) represents a ring coaxial with the first bright field TE detector. It is dedicated to detection of transmitted electrons scattered at small angles but bigger than for first bright field TE-detector. The third part—referred to as dark field TE detector 33(3) represents a ring coaxial with the second bright field TE detector. It is dedicated to detection of transmitted electrons scattered at relatively large angles. All three of these TE detector parts can be solid-state semiconductor detectors can have an atomic number resolution that equals to approximately 1 and can work in a current mode. During ion milling the TE detector 33 can be protected by a protective shutter Faraday cup located on its top on the microscope principal axis beneath the sample 21. It can be dedicated to measure electron probe current in order to provide subsequent calibration of the TE-detector for thickness measurement of a treated sample.
It is noted that the number of detectors, their location, the types of detectors and the number of parts of each detector (As well as their size and shape) can differ from the example illustrated above.
The manipulator 100 includes two separate subunits 110 and 120 both located on a main rotating stage 130. The rotating stage 130 is separated by and powered by engines 130(1)-130(4).
The second subunit 120 may manipulate the sample and the mask and may have X, Y, Z and θ stages. In
The first subunit 110 may manipulate the sample—it may change the spatial relationship between the mask and the sample—for example by moving the mask in relation to any movement introduced by the second sub-unit 120. It is noted that each of the mask and sample can be moved by sub-units—each can move in relation to each other and not share stages such as rotating stage 130.
The first subunit 110 may have X, Y, Z and θ stages. In either one of
The second subunit 120 may manipulates the mask and may also manipulate technological accessories such as mask, calibrating plate, apertures, target for deposition etc.
The first subunit 110 may receive the sample or technological accessories from a sample holder (also referred to as shuttle 103). The shuttle 103 may be transferred until it is positioned on the sample angular stage 100(8).
The stages are connected between structural elements such as plates, beams, rails, guidelines and the like denoted 101(1)-101(5).
Referring to
The ion miller 40 may include:
The ion beam source assembly 40(1) is fed by the non-ionized particle supply assembly 40(2) and the ion beam extractor assembly 40(3) outputs an ion beam that propagates along an optical axis 41 of the ion miller. The ion beam focusing assembly 40(4) focuses the ion beam and feeds the focused ion beam to ion beam first deflecting assembly 40(6) that rotates the ion beam and directs it along directions that are spaced apart from the optical axis of the ion miller to provide deflected and rotated ion beam 41(2). The ion beam second deflecting assembly 40(7) directs the rotating ion beam towards the optical axis, while maintaining the rotation of the ion beam 41(3). The rotation constantly changes milling angle and provide a smoother milled sample.
A non limiting example of an ion miller is provided in US patent application publication serial number 2008/0078750A1 titled “Directed Multi-Deflected Ion Beam Milling of a Work Piece and Determining and Controlling Extent Thereof”, which is incorporated herein by reference.
Referring to
The air lock 1300 function is to allow loading/unloading into the vacuum chamber (denoted 91 in
The air lock 1300 includes:
The air lock 1300 is proximate to an opening in the wall 91(1) of the vacuum chamber 91 such that when the shut-off valve 1350 is opened the feeding rod 1305 can enter the vacuum chamber 91 and especially the interior space 91(2) of the vacuum chamber 91. The Air lock 1300 and especially loading opening (space) are vacuumed before the feeding rod 1305 enters the vacuum chamber. When the shut-off valve 1350 is closed the air lock 1300 is sealed in a manner that prevents gases to enter the vacuum chamber 91.
The manipulator 100 can include the following stages and these stages can be characterized by the following parameters:
Main Rotating Stage 130:
Actuator type: Piezo motor
Actuation modes: stepping & scanning
Stroke: min 120 degrees
Maximal speed: 10 degrees/s
Maximal acceleration: 1000 degrees/ŝ2
Positioning accuracy with encoder closed loop: 150 m°
Resolution: 50 microns
First Sub-Unit 110:
Actuator type: Piezo motor
Actuation modes: stepping & scanning
Maximal speed: 5 mm/s
Maximal acceleration: 1000 mm/ŝ2
Positioning accuracy with encoder closed loop: 1000 nm
Actuator type: Piezo motor
Actuation modes: stepping & scanning
Maximal speed: 10 mm/s
Maximal acceleration: 1000 mm/ŝ2
Positioning accuracy with encoder closed loop: 1000 nm
Actuator type: Piezo motor
Actuation modes: stepping & scanning
Maximal speed: 5 mm/s
Maximal acceleration: 1000 mm/ŝ2
Positioning accuracy with encoder closed loop: 1000 nm
θ-Axis (May have No Thru-Hole in the Axis) 100(5)
Actuator type: Piezo motor
Actuation modes: stepping & scanning
Stroke: 360 degrees
Maximal speed: 45 degrees/s
Maximal acceleration: 1000 degrees/ŝ2
Positioning accuracy with encoder closed loop: 500 m°
Second Sub-Unit 120:
Actuator type: Piezo motor
Actuation modes: stepping & scanning
Maximal speed: 5 mm/s
Maximal acceleration: 1000 mm/ŝ2
Positioning accuracy with encoder closed loop: 1000 nm
Actuator type: Piezo motor
Actuation modes: stepping & scanning
Maximal speed: 10 mm/s
Maximal acceleration: 1000 mm/ŝ2
Positioning accuracy with encoder closed loop: 1000 nm
Actuator type: Piezo motor
Actuation modes: stepping & scanning
Maximal speed: 5 mm/s
Maximal acceleration: 1000 mm/ŝ2
Positioning accuracy with encoder closed loop: 1000 nm
Actuator type: Piezo motor
Actuation modes: stepping & scanning
Stroke: 360 degrees
Maximal speed: 45 degrees/s
Maximal acceleration: 1000 degrees/ŝ2
Positioning accuracy with encoder closed loop: 250 m°
Referring to
Method 1400 starts by stage 1410 of receiving or generating a mask. The mask can be generated by micro-cleaving to provide a highly accurate mask. An example for micro-cleaving is illustrated in U.S. Pat. No. 6,223,961 titled “Apparatus for cleaving crystals”, which is incorporated herein by reference.
Stage 1410 is followed by stage 1420 of receiving or generating an initial sample that has a thickness (near its edge) of few microns—as illustrated in
Stage 1420 is followed by stage 1430 of providing a mask and the initial sample to a manipulator.
Stage 1430 is followed by stage 1440 of aligning the mask and the initial sample (
Stage 1440 is followed by stage 1450 of moving (for example—rotating about an axis) the mask and the initial sample, by the manipulator, while maintaining the alignment so that the mask and initial sample face an ion miller.
Stage 1450 is followed by stage 1460 of performing a first milling sequence (
Stage 1460 is followed by stage 1470 of changing the spatial relationship between the mask and the partially milled sample (by the manipulator) in order to expose the other side of the edge area of the partially milled sample to the ion miller.
Stage 1470 may be followed by stage 1475 of aligning the mask and the partially milled sample by using the manipulator, and at least one out of the scanning electron microscope and the optical microscope. The mask is aligned to expose the other side of the partially milled sample to ion milling, and alignment may include moving the mask and/or the initial sample by the manipulator.
Stage 1475 is followed by stage 1480 of performing a second milling sequence (
Method 1400 starts by stage 1410 of receiving or generating a mask. The mask can be generated by micro-cleaving to provide a highly accurate mask. An example for micro-cleaving is illustrated in U.S. Pat. No. 6,223,961 titled “Apparatus for cleaving crystals”, which is incorporated herein by reference.
Stage 1410 is followed by stage 1420 of receiving or generating an initial sample that has a thickness (near its edge) of few microns—as illustrated in
Stage 1420 is followed by stage 1430 of providing a mask and the initial sample to a manipulator.
Stage 1430 is followed by stage 1440 of aligning the mask and the initial sample (
Stage 1440 is followed by stage 1450 of moving (for example—rotating about an axis) the mask and the initial sample, by the manipulator, while maintaining the alignment so that the mask and initial sample face an ion miller.
Stage 1450 is followed by stage 1460 of performing a first milling sequence (
Stage 1460 is followed by stage 1510 of moving (for example—rotating about an axis) the mask and the partially milled sample, by the manipulator, so that the mask and initial sample face the imaging device.
Stage 1510 is followed by stage 1520 of aligning the mask and the partially milled sample by using the manipulator, and at least one out of the scanning electron microscope and the optical microscope. The mask is aligned to expose the other side of the partially milled sample to ion milling, and the alignment may include moving the mask and/or the initial sample by the manipulator.
Stage 1520 is followed by stage 1480 of performing a second milling sequence (
It is noted that although
The outcome of each of the mentioned above methods may be a very thin area of interest that includes a target and is transparent to electrons so as to be a TEM or STEM sample.
The present invention can be practiced by employing conventional tools, methodology and components. Accordingly, the details of such tools, component and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, in order to provide a thorough understanding of the present invention. However, it should be recognized that the present invention might be practiced without resorting to the details specifically set forth.
Only exemplary embodiments of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.
This application claims priority from U.S. provisional patent Ser. No. 61/361,536, filing date Jul. 6, 2010, which is incorporated herein by reference.
Number | Date | Country | |
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61361536 | Jul 2010 | US |