Ion beam sample preparation apparatus and methods

Disclosed are embodiments of an ion beam sample preparation apparatus and methods for using the embodiments. The apparatus comprises a tilting ion beam irradiating means in a vacuum chamber that may direct ions toward a sample, a shield blocking a portion of the ions directed toward the sample, and a shield retention stage with shield retention means that replaceably and removably holds the shield in a position. The shield has datum features which abut complementary datum features on the shield retention stage when the shield is held in the shield retention stage. The shield has features which enable the durable adhering of the sample to the shield for processing the sample with the ion beam. The complementary datum features on both shield and shield retention stage enable accurate and repeatable positioning of the sample in the apparatus for sample processing and reprocessing. The tilting ion beam irradiating means may direct ions at the sample from more than one tilt angle. A rotating shield retention stage is also disclosed which works in concert with the tilting ion beam irradiating means to improve the flexibility and efficiency of the apparatus in preparing samples for microscopic observation.

Not Applicable.

DESCRIPTION OF ATTACHED APPENDIX

Not Applicable.

BACKGROUND

The present disclosure relates to the use of one or more ion beams to prepare materials for microscopic observation or spectroscopic analysis. Microscopic observational techniques include, but are not limited to, optical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), reflection electron microscopy (REM). Spectroscopic analysis techniques include, but are not limited to, x-ray micro-analysis, reflection electron energy-loss spectroscopy (REELS), electron back-scattered diffraction (EBSD), x-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). Materials to be viewed under any microscopic technique may require processing to produce a sample suitable for microscopic examination.

Ion beam milling of a material can produce samples that are well suited for microscopic examination. An ion beam irradiating device may generate, accelerate, and direct a beam of ions toward a sample. The impact of ions on the sample sputters material away from the area of ion impact. Furthermore, the sample surface may be polished by the ion beam to a substantially smooth condition further enhancing observational properties of the sample. Regions of interest in the sample may be exposed and polished by the use of ion beams thus making a suitable observational sample from the material under investigation.

Broad Ion Beam Slope-Cutting (BIBSC), also known as cross section cutting using broad ion beam sources or cross section polishing using broad ion beam sources, is a rapid method for removing sample material to expose a smooth and substantially artifact-free cross-sectional surface for ultimate analysis by various microscopies and spectroscopies. A notable advantage of the BIBSC technique is high rates of surface preparation that can exceed tens or hundreds or thousands of square microns per hour, often over sample milling times of tens or hundreds of minutes.

Important considerations to users of the BIBSC technique include: reducing or minimizing the effort and time that the user is occupied in processing the sample; reducing or minimizing the number of steps where delicate samples are directly handled and at risk for damage, such as during mounting to sample holders for processing or analysis; reducing or minimizing the time and effort the user is occupied transferring the sample into the ultimate analysis equipment (imaging or spectroscopy), and aligning the coordinates of the prepared sample region to the ultimate analysis equipment prior to analysis; ensuring high quality and high probability of success in processing and imaging the sample; reducing or minimizing the time that the BIBSC ion milling equipment and sample mounting equipment are occupied for each sample; and ensuring high-quality microscopy observation of the sample during sample mounting and ultimate analysis by reducing the working distance required between the sample and the objective or probe-forming lens used for observation.

A sample that has been prepared in the ion beam may be evaluated by various methods to determine if the region of interest has been adequately exposed and prepared for observation. It may happen that the region of interest in the sample has not been adequately exposed or prepared. Embodiments of the present disclosure address this common situation. Embodiments of the present disclosure teach methods and apparatus for repeatably positioning a sample within an ion beam sample preparation apparatus thereby facilitating accurate processing and reprocessing of a sample. Further embodiments of the present disclosure teach methods and apparatus for preparing the sample using a tilting ion beam, making use of controlled ion beam tilt angle to expose regions of interest in the sample. Further embodiments of the present disclosure teach methods and apparatus for rotating the sample during preparation using a tilting ion beam, thereby achieving a more consistent and more desirable surface for later observation.

In consideration of the foregoing points, it is clear that embodiments of the present disclosure confer numerous advantages and are therefore highly desirable.

SUMMARY

The present disclosure is directed to ion beam sample preparation apparatus and methods for using the disclosed apparatus to prepare samples for later observation. The apparatus has features to quickly and repeatably retain and release both unprepared samples and prepared samples thereby facilitating preparation of samples in the ion beam apparatus and also facilitating the observation of the prepared samples in an observation apparatus. Features of the disclosure enable accurate and repeatable positioning of the sample both within the ion beam sample preparation apparatus and also within observation apparatus later used for observing prepared samples. Tilting ion beam features of the present disclosure allow additional flexibility in exposing regions of interest in the sample. Tilting ion beam features allow the sample to be prepared by the ion beam using more than one tilt angle of the ion beam. A previously prepared sample may be replaced in the apparatus and then prepared using a different tilt angle of the ion beam thereby exposing and preparing a different region of the sample. Further features of the disclosure teach methods and apparatus for rotating the sample during preparation using a tilting ion beam thereby achieving a more consistent and more desirable surface for later observation.

An embodiment according to the present disclosure of an apparatus for ion beam sample preparation comprises: an ion beam sample preparation apparatus comprising: a tilting ion beam irradiating means disposed in a vacuum chamber and directing an ion beam toward a shield, characterized in that said tilting ion beam irradiating means projects an ion beam along a central ion beam axis, the direction of said central ion beam axis having a tilt angle with respect to said shield; a tilt drive operably coupled to said tilting ion beam irradiating means and configured to move the direction of said central ion beam axis between at least two different tilt angles; a shield retention stage disposed in the vacuum chamber; said shield retention stage comprising: a first datum feature; a second datum feature; a shield retention means having at least a shield releasing position and a shield retaining position; the shield having at least a rigid planar portion, removably and replaceably held in said shield retention stage, said shield further comprising: a proximal sample surface configured to durably adhere the sample to the shield; a first shielding surface disposed in the path of the ion beam and positioned to shield a portion of the ion beam directed at the sample when said shield is held in the shield retaining position of the shield retention means; a third datum feature formed integrally with said shield, wherein said shield retention means in said shield retaining position urges said third datum feature to abut said first datum feature; and, a fourth datum feature formed integrally with said shield, wherein said shield retention means in said shield retaining position urges said fourth datum feature to abut said second datum feature.

In a related embodiment of the ion beam sample preparation apparatus, the shield retention stage further comprises a fifth datum feature, and the shield further comprises a sixth datum feature formed integrally with the shield, wherein the shield retention means in said shield retaining position urges said sixth datum feature to abut said fifth datum feature.

In a related embodiment of the ion beam sample preparation apparatus, the first shielding surface meets said proximal sample surface at an angle of less than about 90 degrees and more than about 80 degrees.

In a related embodiment of the ion beam sample preparation apparatus, the first shielding surface meets said proximal sample surface at an angle of less than about 87 degrees and more than about 83 degrees.

In a related embodiment of the ion beam sample preparation apparatus, the first shielding surface is made of non-magnetic material having low sputtering-yield.

In a related embodiment of the ion beam sample preparation apparatus, at least a portion of the first shielding surface is made of tantalum or titanium.

In a related embodiment of the ion beam sample preparation apparatus, the third datum feature is a datum surface, and at least a portion of said datum surface is coextensive with at least a portion of said proximal sample surface.

In a related embodiment of the ion beam sample preparation, the proximal sample surface has at least one recessed portion configured for the flowing of adhesive between the shield and the sample.

In a related embodiment of the ion beam sample preparation apparatus, the shield further comprises a sample clamping means coupled to the shield and configured to hold the sample against said proximal sample surface.

In a related embodiment of the ion beam sample preparation apparatus, the shield further comprises: a second shielding surface having a portion disposed in the path of a portion of the ion beam; a shield edge formed where the first shielding surface meets the proximal sample surface; and a visible alignment mark on the second shielding surface, configured such that the location of said visible alignment mark is in a predetermined relationship to the region where the ion beam impinges on said shield edge when said shield is held in the shield retaining position of the shield retention means.

In a related embodiment of the ion beam sample preparation apparatus, the shield is made of a cladding material joined to a core material such that a portion of the cladding material forms at least a portion of the first shielding surface, and a portion of the core material forms the third and fourth datum features of the shield. In a related embodiment, the cladding material is a non-magnetic material having low sputtering-yield.

Another embodiment of the present disclosure is directed to an apparatus for ion beam sample preparation which comprises: a tilting ion beam irradiating means disposed in a vacuum chamber and directing an ion beam toward a shield, characterized in that said tilting ion beam irradiating means projects an ion beam along a central ion beam axis, the direction of said central ion beam axis having a tilt angle with respect to said shield; a tilt drive operably coupled to said tilting ion beam irradiating means and configured to move the direction of said central ion beam axis between at least two different tilt angles; a rotating shield retention stage disposed in the vacuum chamber; said shield retention stage comprising: a first datum feature; a second datum feature; a shield retention means having at least a shield releasing position and a shield retaining position; a rotation axis located substantially in the plane of the first datum feature; a rotation drive for rotating the shield retention stage around the rotation axis; the shield having at least a rigid planar portion, removably and replaceably held in said shield retention stage, said shield further comprising: a third datum feature formed integrally with the shield, wherein said shield retention means in said shield retaining position urges said third datum feature to abut said first datum feature; a fourth datum feature formed integrally with the shield, wherein said shield retention means in said shield retaining position urges said fourth datum feature to abut said second datum feature; a first shielding surface disposed in the path of the ion beam and positioned to shield a portion of the ion beam directed at the sample when said shield is held in the shield retaining position of the shield retention means; a proximal sample surface configured to durably adhere the sample to the shield; a shield edge formed where the first shielding surface meets the proximal sample surface, characterized in that said shield edge is held substantially perpendicular to said rotation axis when said shield is held in the shield retaining position of the shield retention means.

In a related embodiment of the ion beam sample preparation apparatus, the apparatus is further characterized in that the tilting ion beam irradiating means and tilt drive are adapted to provide at least two different tilt angles in which the central ion beam axis is substantially perpendicular to said shield edge.

In a related embodiment of the ion beam sample preparation apparatus, the apparatus is further characterized in that the tilting ion beam irradiating means and tilt drive are adapted to provide at least two different tilt angles in which the central ion beam axis substantially intersects said rotation axis.

LIST OF REFERENCE NUMBERS APPEARING IN THE FIGURES

DESCRIPTION

The Broad Ion Beam Slope-Cutting (BIBSC) sample preparation procedure can be described as a series of process steps, p1-p5:p1) Aligning the desired region of the sample to be processed to a usable portion of an ion shield;p2) Aligning the sample and shield in the BIBSC ion-milling system such that the desired region of the sample can be processed by the ion beam or beams;p3) Evacuating the ion-milling system to vacuum levels appropriate for ion beam milling;p4) Performing the ion-milling operation or operations, sometimes using a process monitoring step such as in situ light-microscopy imaging to verify sufficient cut depth and quality of the cross section;p5) Venting of the BIBSC ion-milling equipment and removal of the sample from the equipment.

The analysis of prepared BIBSC sample can be described as a series of process steps, p6-p9:p6) Introduction of the sample to the ultimate analysis microscope and initializing the microscope so that analysis can commence;p7) Finding the location of the prepared cross-sectional surface by adjusting any number of the microscope's translation stages, tilt stages, and rotation stages so that the desired area can be imaged;p8) Performing the desired microscopic or spectroscopic analyses;p9) Removing the sample from the microscope;p10) After analyzing the sample, a decision may be made to reprocess the sample to change the cut depth, position, or angle—traditionally requiring a repeat of p1-p9.

Embodiments of the present disclosure uniquely permit certain efficiencies and capabilities in the processing and subsequent observation and analysis of BIBSC produced samples. Beneficial features, functions, and aspects of the present disclosure include, but are not limited to:1. Datum features on the shield, shield retention device in the sample-to-shield mounting apparatus, shield retention device in the BIBSC ion-mill, shield retention device in the ultimate analysis equipment allow significant time efficiencies in processing steps p1, p2 and p7;2. The integral nature of the sample durably adhered to the shield, and to a lesser extent with the sample merely clamped to the shield, allows greater certainty in ensuring alignment of the shield to the sample remains consistent during p4 even over long time-scales and changes in temperature, whereas quality of the cross section cutting process is reduced if this precision alignment is not maintained;3. The integral nature of the sample durably adhered to the shield in processing step p1 eliminates the requirement for expensive and sizable fixturing apparatus to maintain their spatial relationship together throughout the milling operation, and enables multiple samples to be prepared in advance of milling without multiple fixturing apparatus;4. The integral nature of the sample durably adhered or clamped to the shield eliminates the requirement for dismounting the sample from the shield prior to observation in a microscope, even in cases where the smallest working distances between imaging objective and sample are employed. This permits reduction of both time and risk of damage to the sample during sample remounting in processing step p6;5. In the case where reprocessing the sample as in step p10 is performed, the integral nature of the sample durably adhered or clamped to the shield can eliminate the need for steps p1 and p2 entirely, which significantly reduces processing time and risk of damage to the sample during sample remounting; and,6. In the case where reprocessing the sample as in step p10 is performed, the integral nature of the sample durably adhered or clamped to the shield allows different cross-sectional planes to be cut very close to the originally cut cross-sectional plane by varying the angle of ion beam impinging on the sample and shield.

Turning now toFIG. 1, illustrated is a schematic cross sectional view of an embodiment of an ion beam sample preparation apparatus2according to the present disclosure. The embodiment ofFIG. 1is shown comprising: a vacuum chamber10in which a sample8is prepared; chamber cover18which seals vacuum chamber10from the outside atmosphere; vacuum pump means90and pumping manifold92, which together bring vacuum chamber10to vacuum levels appropriate for ion beam milling; tilting ion beam irradiating means36and tilt drive38, which creates and directs an ion beam having a central ion beam axis22toward sample8; a shield60, which shields at least a portion of sample8from at least a portion of the ion beam; a shield retention stage40, which holds and accurately positions shield60with respect to the direction and extent of the ion beam; a shield retention means42, which both retains shield60in shield retention stage40, and also urges shield60to remain in a position whereby the ion beam may prepare sample8.

With continuing reference toFIG. 1, the ion beam preferably comprises noble gas ions. Elements used for the ion beam may include but are not limited to: Argon, Xenon, and Krypton. The ion beam may also comprise a mixture of ions and neutrals. Shield retention stage40is disposed in vacuum chamber10in a predetermined position and orientation with respect to central ion beam axis22. Tilting ion beam irradiating means36and tilt drive38enable the ion beam to prepare the sample by directing central ion beam axis22toward sample8from more than one tilt angle with respect to shield60.FIG. 1shows tilting ion beam irradiating means36operating at a first tilt angle.

FIG. 2shows the same apparatus as inFIG. 1. However, the apparatus ofFIG. 2is shown after the tilt drive38has operated to move tilting ion beam irradiating means36to a different tilt angle than inFIG. 1. After the sample has been prepared by the ion beam in the vacuum chamber, chamber cover18may be opened; then the shield and sample may be removed for observation in a microscope.

The tilting ion beam irradiating means and drive shown in the embodiments ofFIG. 1andFIG. 2give the user additional flexibility in preparing a sample for later observation. In particular, a sample may be prepared at one tilt angle, observed in a microscope, prepared again at a different tilt angle, and observed again. The ability to direct central beam axis22along more than one tilt angle allows for considerable refinement in sample preparation in the region of interest. Other aspects of the embodiments shown inFIG. 1andFIG. 2may be better understood now with reference to the following descriptions and figures.

FIG. 3Ashows a perspective view of shield retention stage40on which sample8has been durably adhered to shield60prior to placing the shield and sample combination in a shield retaining position46in shield retention stage40. Shield60has a shielding surface61which is positioned in relation to sample8to shield at least a portion of said sample8from at least a portion of the ion beam. Also shown inFIG. 3Ais a section line indicating the section view shown inFIG. 3B.

FIG. 3Bshows a section view illustrating the position and function of the shield retention means which is part of shield retention stage40.FIG. 3Bshows an embodiment of the shield retention means comprising a shield retention means first member42aand a shield retention means second member42b. Shield retention means first member42aurges shield retention means second member42bagainst shield60. The action of shield retention means first member also urges shield60against shield retention stage40, and thereby maintains the position of shield60within shield retention stage40while the sample is prepared by ion beam. An embodiment of the shield retention means may comprise a spring for shield retention means first member42aand a solid member as shield retention means second member42bconfigured to slide within a cavity in shield retention stage40.

FIG. 4shows a view from the same sectional plane as inFIG. 3B. However, inFIG. 4the shield and sample have been removed to show a shield releasing position48of shield retention means. By means of the two positions provided by shield retention means, namely shield retaining position46, as shown inFIG. 3AandFIG. 3B, and shield releasing position48, as shown inFIG. 4, a shield may be removably and replaceably secured in shield retention stage40. A sample that has been durably adhered to shield60may be processed, removed, and then reprocessed by simply placing it in the shield retaining position and preparing the sample again in the ion beam.

FIG. 5Ashows a perspective view of shield retention stage40on which shield60is retained, wherein said shield has a shielding surface61.FIG. 5Aalso shows a sectional plane used forFIG. 5B.

FIG. 5Bshows a sectional perspective view illustrating physical features of both shield60and shield retention stage40that facilitate accurate and repeatable positioning of the shield with respect to the shield retention stage. The positioning of shield60assures that shielding surface61and shield edge63are accurately positioned and accurately oriented with respect to the shield retention stage, and are positioned with respect to central ion beam axis22to intercept at least a portion of the ion beam directed toward the sample.

FIG. 6shows a sectional perspective view as inFIG. 5B, in which preferred embodiments of both shield60and shield retention stage40have a plurality of datum features70a,70b,70c,70d,70e, and70f. In the exploded view shown inFIG. 6, shield60has been removed from shield retention stage40and the shield is turned to expose a proximal sample surface62, upon which a sample may be durably adhered prior to sample preparation by the ion beam. The plurality of datum features70a,70b,70c,70d,70e, and70fis provided on both shield60and shield retention stage40, and they enable accurate and repeatable positioning of the shield60with respect to the shield retention stage40. Datum features70b,70d, and70fon the shield are shaped and positioned such that when they are caused to abut complementary datum features70a,70c, and70eon the shield retention stage, the shield may be held in a predetermined position and a predetermined orientation with respect to the central ion beam axis22. Shield retention means42assures that datum features70b,70d, and70fof shield60abut the corresponding datum features70a,70c, and70eof the shield retention stage40when the shield is held in the shield retaining position. Shield edge63, also visible inFIG. 6, is also caused to be in a predetermined position and predetermined orientation when the shield is held in the shield retaining position.

Datum features are arranged in pairs such that a datum feature on the shield has a corresponding datum feature on the shield retention stage. InFIG. 6, one such pair of datum features is datum feature70aon the shield retention stage and datum feature70bon the shield. Another pair of datum features shown inFIG. 6is datum feature70con the shield retention stage and datum feature70don the shield. Another pair of datum features shown inFIG. 6is datum feature70eon the shield retention stage and datum feature70fon the shield. When the shield is in the shield retaining position, the shield retention means acts to urge the pairs of datum features to abut, thereby constraining the position of the shield with respect to the position of the shield retention stage. Datum features may be datum surfaces, as is shown in the preferred embodiment ofFIG. 6, or they may be datum edges or datum vertices, or combinations of datum surfaces, datum edges, and datum vertices.

Turning now to figuresFIG. 7A,FIG. 7B,FIG. 8A,FIG. 8B,FIG. 9, andFIG. 10, shown are various features and embodiments of shield60according to the present disclosure.

FIG. 7Ais a perspective view of a shield showing a first shielding surface61a, a second shielding surface61b, and shield edge63. Ions from the ion beam irradiating means that are blocked by the shield, and, in particular, the ions that are blocked by first shielding surface61a, are prevented from milling the sample. Ions not blocked by the shield may be used to prepare the sample for observation and analysis. When the ion beam is operating, ions may or may not impact second shielding surface61b. Whether ions do impact second shielding surface61bdepends on a number a factors including, but not limited to: the size of the ion beam; the angle at which the ion beam is directed; and, the position at which the ion beam is directed. It is a preferred embodiment of the shield that second shielding surface61bbe made of the same material as first shielding surface61a. In preferred embodiments, shield60is a generally planar rigid member, having one or more shielding surfaces that are smooth and may be polished, having a datum surface and at least an additional datum feature for facilitating accurate placement within the shield retention stage. Preferred materials for the shield are non-magnetic metals with low sputtering-yield including, but not limited to, tantalum or titanium. Lower cost embodiments of shield60may comprise core material66for the majority of the shield and cladding material67used for the shielding surfaces. Preferred core materials include, but are not limited to, copper. Preferred cladding materials include, but are not limited to, tantalum or titanium. FiguresFIG. 15AandFIG. 15Billustrate two different embodiments of a shield60, wherein each embodiment is shown comprising a combination of core material66and cladding material67.

FIG. 7Bshows the same shield as shown inFIG. 7A, but from a different angle thereby illustrating the position and nature of a plurality of datum features70dand70f.

FIG. 8Ashows the same shield as shown inFIG. 7AandFIG. 7B.FIG. 8Ashows a perspective view of shield60from the side of the shield closest to the sample during ion beam sample preparation. Proximal sample surface62may be used to adhere the sample material to be prepared in the apparatus. Datum surface72is a datum feature that is a surface. In a preferred embodiment, at least a portion of proximal sample surface62may be coextensive with at least a portion of datum surface72. Shield edge63is formed by the intersection of first shielding surface61aand proximal sample surface62. The angle between first shielding surface61aand proximal sample surface62has an impact on the quality of milling performed on the sample by the ion beam. A preferred embodiment is achieved when said first shielding surface61ameets said proximal sample surface62at an angle of less than about 90 degrees and more than about 80 degrees. An even more preferred embodiment is achieved when said first shielding surface61ameets said proximal sample surface62at an angle of less than about 87 degrees and more than about 83 degrees.

FIG. 8Bshows the same shield as shown inFIG. 8A, but from a different angle thereby illustrating the position and nature of a plurality of datum features70dand70f, and datum surface72, present on shield60.

FIG. 9shows a perspective view of shield60, having first shielding surface61a, second shielding surface61b, shield edge63, and additionally comprising a visible alignment mark65. When the shield is held in the shield retaining position, the visible alignment mark is positioned so that it indicates the approximate location where a portion of the ion beam will pass over shield edge63and impact the sample when the shield edge is substantially perpendicular to the central ion beam axis.

FIG. 10shows a perspective view of shield60from the side of the shield closest to the sample during ion beam sample preparation. Proximal sample surface62may be used to adhere the sample material to the shield prior to ion beam sample preparation in the apparatus. Recessed portion64provides a recessed portion of proximal sample surface62useful for flowing adhesive under the sample, thereby facilitating the durable adhering of sample to shield. Preferred materials used to adhere the sample to the shield include, but are not limited to: UV cured glue, light cured glue, superglue, silver paint, and wax.

Turning now toFIG. 11A, shown is a perspective view of shield60, shielding surface61, sample8durably adhered to the shield, and visible alignment mark65.FIG. 11Adepicts the sample prior to ion beam preparation.FIG. 11Bis a perspective view of the same objects depicted inFIG. 11A. However,FIG. 11Brepresents the sample after ion beam sample preparation. Shielding surface61intercepts a portion of the ion beam, which travels along central ion beam axis22. A portion of sample8is sputtered away by the ion beam during sample preparation, thereby exposing a portion of the sample lying in the plane defined by shield edge63and central ion beam axis22. A sample prepared in this way will be suitable for observation or analysis with a variety of microscopic or spectroscopic techniques, particularly those requiring a highly polished planar surface.

FIGS. 12A and 12Billustrate another embodiment of shield60, in which a sample clamping means68is formed integrally with the shield on the proximal sample surface62.FIG. 12Adepicts this shield prior to clamping a sample, whileFIG. 12Bdepicts this shield after sample8has been secured to the shield by means of sample clamping means68. In another embodiment, sample clamping means68may be formed separately, and then coupled to the shield prior to clamping the sample. Adhesive may be applied between the sample clamping means and the sample to further ensure the sample does not move with respect to the shield.

Use of the apparatus shown inFIG. 1may proceed with reference to the following steps: outside of the vacuum chamber, a sample may be durably adhered to a shield; with the chamber cover removed, the sample and shield combination may be set in the shield retaining position of the shield retention stage; the chamber cover may then be replaced; with the chamber cover in place on the vacuum chamber, the vacuum pump means may be operated to evacuate the vacuum chamber through the pumping manifold, thereby obtaining vacuum levels appropriate for ion beam milling; the ion beam irradiating means may then be operated to prepare the sample. When the sample is prepared to the extent desired by the user of the apparatus, the ion beam irradiating means may be turned off, the vacuum chamber may be returned to atmospheric conditions, the chamber cover may be removed, and the prepared sample may be removed from the apparatus along with the shield to which it was previously adhered. A microscope may be fitted with a shield retention stage so that the prepared sample and shield may be retained, and thereby the prepared region of the sample may be observed in the microscope. After observation the user may decide that additional sample preparation is needed. Since the sample is still durably adhered to the shield, it is a simple matter to return the sample and shield to the vacuum chamber for additional processing. The datum features on both the shield and the shield retention stage ensure that the shield may be retained in substantially the same position and orientation each time the sample is processed in the apparatus. A kit comprising a shield retention stage40with a plurality of datum features70a,70c, and70e, shield retention means42, and at least one shield60with a plurality of datum features70b,70d, and70fmay be supplied for fitting to a microscope. Such a kit facilitates the microscopic observation of samples prepared in the ion beam sample preparation apparatus2.

Turning now toFIG. 13AandFIG. 13B, shown are another embodiment of an ion beam sample preparation apparatus according to the present disclosure. The embodiment ofFIG. 13AandFIG. 13Bcomprises: a vacuum chamber10in which a sample8is prepared; chamber cover18which seals vacuum chamber10from the outside atmosphere; vacuum pump means90, and pumping manifold92which together bring vacuum chamber10to vacuum levels appropriate for ion beam milling; tilting ion beam irradiating means36and tilt drive38, which direct an ion beam having a central ion beam axis22toward sample8; a shield60, which shields at least a portion of sample8from at least a portion of the ion beam; a rotating shield retention stage50, which holds and accurately positions shield60with respect to the direction and extent of the ion beam; a shield retention means42, which both retains shield60in rotating shield retention stage50and also urges shield60to remain in a position whereby the ion beam may prepare sample8; a rotation drive52, which rotates the rotating shield retention stage50about rotation axis54; and vacuum seal56, which maintains the vacuum in vacuum chamber10, while allowing rotating shield retention stage50to move about rotation axis54. In preferred embodiment, rotation axis54lies substantially in the plane defined by the abutment of the proximal sample surface62with the sample8. Shield60of figuresFIG. 13AandFIG. 13Bhas the same features, functions, and aspects possessed by shield60shown in figuresFIG. 3A,FIG. 3B,FIG. 5A,FIG. 5B,FIG. 6,FIG. 7A,FIG. 7B,FIG. 8A, andFIG. 8B.

With continuing reference toFIG. 13AandFIG. 13B, the ion beam preferably comprises noble gas ions. Elements used for the ion beam may include but are not limited to: argon, xenon, and krypton. The ion beam may also comprise a mixture of ions and neutrals. Shield retention stage50is disposed in vacuum chamber10in a predetermined position and orientation with respect to central beam axis22. Rotating shield retention stage50may additionally comprise means for measuring the rotation angle of the stage. Rotation drive52may additionally comprise means to reach and maintain accurate angular position. Rotation drive52may additionally comprise means to reach and maintain accurate angular speed. Rotation drive52enables rotating shield retention stage50to rotate about rotation axis54. In a preferred embodiment, shield edge63is disposed substantially perpendicular to rotation axis54when shield60is held in the shield retaining position.

In the apparatus ofFIG. 13AandFIG. 13B, tilting ion beam irradiating means36and tilt drive38enable the ion beam to prepare the sample by directing central ion beam axis22toward sample8from more than one angle.FIG. 13Ashows tilting ion beam irradiating means36at a first angle, whileFIG. 13Bshows tilting ion beam irradiating means36at a second angle. In a preferred embodiment, tilting ion beam irradiating means36and tilt drive38are adapted to provide a variable degree of tilt angle while maintaining central ion beam axis22substantially perpendicular to shield edge63for at least a portion of tilt angle. In a preferred embodiment, tilting ion beam irradiating means36and tilt drive38are adapted to provide a variable degree of tilt angle while central ion beam axis22substantially intersects rotation axis54for at least a portion of tilt angle.

Features and aspects of rotating shield retention stage50may be better understood now with reference toFIG. 14AandFIG. 14Band the written description that follows.

FIG. 14Ashows a perspective schematic view of rotating shield retention stage50, on which sample8has been durably adhered to shield60prior to placing the shield and sample combination in a shield retaining position of rotating shield retention stage50. Shield60has a shielding surface61, which is positioned in relation to sample8to shield at least a portion of said sample8from at least a portion of the ion beam. Rotation drive52enables rotating shield retention stage50to rotate about rotation axis54. In a preferred embodiment, shield edge63is disposed to be substantially perpendicular to rotation axis54when shield60is held in the shield retaining position. Also shown inFIG. 14Ais a section line indicating the section view shown inFIG. 14B.

FIG. 14Bshows a section view illustrating the position and function of the shield retention means, which is part of rotating shield retention stage50. InFIG. 14Bshield retention means first member42aurges shield retention means second member42bagainst shield60. The action of shield retention means first member42aalso urges shield60against rotating shield retention stage50and thereby maintains the position of shield60within rotating shield retention stage50while the sample is prepared by the ion beam. An embodiment of the shield retention means may comprise a spring for shield retention means first member42aand a solid member as shield retention means second member42bconfigured to slide within a cavity in rotating shield retention stage50. The shield retention means also has a shield releasing position in which the shield and sample are not held in the rotating shield retention stage50. The shield releasing position may be identical to the shield releasing position48illustrated inFIG. 4. In a preferred embodiment, rotation axis54lies substantially in the plane defined by the abutment of the proximal sample surface62with the sample8.

The rotating shield retention stage50has the same plurality of datum features as shown on the non-rotating shield retention stage ofFIG. 6. In addition, the rotating shield retention stage50datum features allow the interchangeable use of shield60previously described. The datum features of the shield retention stage40and the rotating shield retention stage50are substantially identical in design, and thereby facilitate the easy interchange of shields between the stages. By means of the two positions provided by the shield retention means, namely shield retaining position46, as shown inFIG. 3B, and shield releasing position48, as shown inFIG. 4, a shield may be removably and replaceably secured in rotating shield retention stage50. A sample that has been durably adhered to shield60may be processed, removed, and then reprocessed by simply placing it in the shield retaining position and preparing the sample again in the ion beam. The datum features on both shield and shield retention stage assure that the shield may be positioned in a substantially identical position and orientation multiple times. In preferred embodiments that include rotating shield retention stage50, central ion beam axis22passes substantially through rotation axis54in the region above shield edge63. After the sample has been prepared by the ion beam in the vacuum chamber, chamber cover18may be removed, and then the shield and sample may be removed for observation in a microscope.

Use of the apparatus of figuresFIG. 13AandFIG. 13Bmay proceed according to all of the steps disclosed for the use of the apparatus ofFIG. 1andFIG. 2. However, the rotating shield retention stageFIG. 13AandFIG. 13Bgives the user additional capabilities. In particular, the use of the rotating shield retention stage during sample preparation may improve the evenness of the prepared region if that region of the sample has local variations in physical consistency that lead to different rates of preparation by the ion beam. Rotation during sample preparation may have a beneficial leveling effect on such a sample. In addition, the user may rotate the rotating shield retention stage about the rotation axis to a desired angle before sample preparation, during sample preparation, or after sample preparation. Also, the rotation drive and the tilt drive may operate in concert to accurately and repeatably control the ion beam tilt as a function of the rotation angle of the rotating shield retention stage. Thus, the user has increased flexibility in exposing and preparing a region of interest in the sample for later microscopic observation.

With continuing reference toFIG. 13AandFIG. 13B, the ion beam preferably comprises noble gas ions. Elements used for the ion beam may include but are not limited to: argon, xenon, and krypton. The ion beam may also comprise a mixture of ions and neutrals. Rotating shield retention stage50is disposed in vacuum chamber10in a predetermined position and orientation with respect to central ion beam axis22. Rotating shield retention stage50may additionally comprise means for measuring the rotation angle of the stage. Rotation drive52may additionally comprise means to reach and maintain accurate angular position. Rotation drive52may additionally comprise means to reach and maintain accurate angular speed. In addition, shield60ofFIG. 13AandFIG. 13Bhas the same features, functions, and aspects possessed by shield60shown in figuresFIG. 3A,FIG. 3B,FIG. 5A,FIG. 5B,FIG. 6,FIG. 7A,FIG. 7B,FIG. 8A,FIG. 8B,FIG. 14A, andFIG. 14B. In a preferred embodiment, as shown inFIG. 14AandFIG. 14B, rotation axis54lies substantially in the plane defined by the abutment of the proximal sample surface62with the sample8.

Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. For example, it may be desirable to combine features shown in various embodiments into a single embodiment. For example, materials or alloys that are both non-magnetic and have low sputtering-yield may be used with success for shielding surfaces and may be constructed and used entirely within the spirit and scope of the present disclosure. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.