Patent Application
20120117696
The present invention relates generally to specimen analysis in semiconductor device manufacturing and, more particularly, to an integrated metallic microtip coupon structure for atom probe tomographic (APT) analysis.
An atom probe (also referred to as an atom probe microscope) is a device that allows specimens appropriately sized or taken from larger samples, such as semiconductor wafers or large parts thereof, to be analyzed on an atomic level. For example, a typical atom probe includes a specimen mount, an electrode, and a detector. During analysis, a specimen is carried by the specimen mount and a positive electrical charge (e.g., a baseline voltage) is applied to the specimen. The detector is spaced apart from the specimen and is negatively charged. The electrode is located between the specimen and the detector, and is either grounded or negatively charged. A positive electrical pulse (above the baseline voltage) and/or a laser pulse (e.g., photonic energy) is intermittently applied to the specimen. Alternately, a negative pulse can be applied to the electrode.
With each pulse, one or more atoms on the specimen surface are ionized. As shown in
Specimens are often formed by removing a section or wedge from the sample that represents the structure of the sample throughout at least a portion of its depth. Such a specimen is typically attached to a pre-made post and then sharpened by ion milling. The specimen-post combination is then aligned in a specimen holder with its axis extending toward the detector, so that the collected atoms demonstrate the depthwise structure of the sampled object. The rod-like structure of the prepared specimen also beneficially concentrates the electric field of the charged specimen about its apex (its area closest to the detector), thereby enhancing evaporation from the apex.
In order to increase the throughput of APT analysis, the posts to which specimens are mounted have been manufactured as prefabricated arrays of posts. For example, a 6×6 microtip array may be formed into a small coupon of about 3 millimeters (mm)×7 mm in area. The coupon is then attached to a metal carrier that is then loaded into the atom probe. Thus, such coupons having an array of individual microtips reduces sample transfer overhead with respect to single post structures.
However, these coupons are typically made out of silicon (Si), and doped with antimony (Sb) or arsenic (As) to improve conductivity of the posts. Unfortunately, even with the doping, silicon or other semiconductor materials do not provide the optimal electrical and thermal conduction characteristics desirable for preventing sample fracturing and data quality degradation.
In one aspect, an integrated coupon structure for atom probe tomography (APT) analysis includes a base portion; an array of microtip posts protruding from the base portion, with both the base portion and the microtip posts formed from a same metal material; and the microtip posts being shaped at an apex thereof so as to be adapted to receive a sample attached thereto.
In another aspect, a method of forming an integrated coupon structure for atom probe tomography (APT) analysis includes thinning a metal material base portion having an original thickness so as to define an array of microtip posts protruding from the base portion; and shaping the microtip posts so as to be adapted to receive a sample attached at an apex of the posts.
In another aspect, a method of performing for atom probe tomography (APT) analysis includes attaching one or more samples to an integrated coupon structure, the coupon structure comprising a base portion, an array of microtip posts protruding from the base portion, with both the base portion and the microtip posts formed from a same metal material, and the microtip posts being shaped at an apex thereof so as to be adapted to receive a sample attached thereto; mounting the integrated coupon structure to a sample holder housed within a chamber of an atom probe; and operating the atom probe so as to cause evaporation of individual atoms at a tip of the sample.
Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:
a) is an image of a conventional silicon microtip array coupon having individual posts to which APT samples are mounted;
b) is a more detailed image of one of the posts of the coupon of
c) is a more detailed image of the topmost portion of the post of
d) is an image illustrating an intermediate stage of sharpening of the post tip and sample of
e) illustrates the test-ready sharpened post tip and sample of
f) is an even further detailed image of the sharpened sample of
Disclosed herein is an integrated metallic microtip coupon structure for APT analysis. As indicated above, APT requires the placement of the sample to be analyzed on a conductive post. Conventional silicon or doped silicon posts provide limited electrical and thermal conductivity. Therefore, by integrating a coupon into a metal holder to create a single, electrically and thermally conductive solid structure for insertion into an atom probe, a more effective sample preparation path is achieved. This in turn enhances sample preparation and the operation of imaging and analytical techniques such as, for example, APT, transmission electron microscopy (TEM), scanning electron microscopy (SEM), focused ion beam (FIB), and scanning probe microscopy (SPM).
Referring now to
a) is an image of a conventional silicon microtip array coupon 300 having a plurality of individual posts 302 defined thereon, such as by etching into a silicon substrate. As shown more particularly in
c) is a more detailed image of the top portion 308 of the post 302 of
In
As further indicated above, a conventional silicon microtip array coupon, such as the coupon 300 in
Accordingly,
The metallic microtip coupon structure 500 of the present embodiment may be formed by micromachining a starting metal block having an initial thickness, selectively removing areas not corresponding to the post regions until a desired shape, height and number of posts 502 are obtained. As is the case with a silicon coupon, the integrated metallic microtip coupon structure 500 may include one or more marker posts 504 that are formed at a greater height than the microtip posts. Thus, when the coupon structure 500 is mounted the APT, the posts may be counted, starting from the marker post(s) 504 until the specific post 502 carrying the specimen to be analyzed is found.
While the invention has been described with reference to a preferred embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
