Radiant energy – Inspection of solids or liquids by charged particles – Methods
Reexamination Certificate
2003-05-01
2004-03-02
Berman, Jack (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Methods
C250S304000, C216S002000, C438S014000
Reexamination Certificate
active
06700121
ABSTRACT:
FIELD OF THE INVENTION
This disclosure concerns an invention relating generally to methods for obtaining and preparing specimens for microscopic analysis, and more specifically to methods of obtaining and preparing specimens for micron-scale and sub-micron-scale analysis, particularly specimens of multilayered materials, and materials upon which thin films have been deposited, implanted or otherwise incorporated (e.g., semiconductor wafers, photonic devices).
BACKGROUND OF THE INVENTION
In the manufacture of many modern devices containing microscopically thin layers of different materials, and/or zones of different materials segregated on a microscopic scale, it is important to be able to study the different layers and/or zones with analytical equipment after the deposition. As examples, it is often useful to be able to microscopically analyze the structures of semiconductor microelectronic devices; magnetic thin film memory storage devices (such as read/write hard disk heads and platters); thin film based optical devices; multilayered polymeric, organic and/or biochemical based thin film devices (as used in medicine); composites of inorganic materials, organic materials and/or biological materials (such as bioMEMs, biosensors, bioarray chips, and integrated labs on chips); and other devices wherein nanoscale structures are critical to device function. Common equipment used for such analysis (hereinafter referred to as “microanalysis”) includes electron microscopes (including TEMs, Transmission Electron Microscopes, and SEMs, Scanning Electron Microscopes); spectrometers (including Raman spectrometers and Auger spectrometers); photoelectron spectrometry (XPS); Secondary Ion Mass Spectrometry (SIMS); and more recently, the atom probe microscope, as described in U.S. Pat. Nos. 5,061,850 and 5,440,124. Of course, other microanalysis equipment is available, and new equipment having different principles of operation is expected to become available over time.
Generally, microanalysis of an entire device is not feasible owing to practical constraints, and thus specimens of portions of the device are studied. Ideally, the specimen of the device under study is formed from the actual material that is intended to perform a function in the device. Accordingly, destructive testing methods are known wherein study specimens are “biopsied” from the objects being studied, and are then subjected to microanalysis. As an example, Focused Ion Beam (FIB) milling processes are often used to excise study specimens from study objects. A good background discussion of FIB processes is set forth in U.S. Pat. No. 6,042,736 to Chung. U.S. Pat. No. 6,188,072 is then of interest for its discussion of a method (allegedly described by the FEI Company of Hillsboro, Oreg. USA) of cutting a study specimen from a study object by FIB milling, with the study specimen then being removed by a micromanipulator by use of electrostatic attraction. The study specimen is then subjected to TEM microanalysis. The remainder of the patent is directed to a micromanipulator suitable for performing this operation. U.S. Pat. No. 6,188,068 to Shaapur et al. appears to describe a similar method, and the Background section of U.S. Pat. No. 5,270,552 also appears to describe similar methods for preparing study specimens using FIB milling and mechanical cutting/polishing steps.
U.S. Pat. No. 6,194,720 to Li et al. describes a method wherein a study object is milled by FIB and other processes to produce a thin cross-sectional study specimen suitable for microanalysis by a TEM. One aspect of the method involves milling a pair of parallel trenches in the top surface of the study object to define a plate-like first study region therebetween (
FIGS. 2A-2C
of Li et al.), and then filling in the trenches with filler material (FIG.
2
D). Portions of the study object are then cut away along planes parallel to the first study region and intersecting the filled trenches (FIG.
3
B), or being spaced a short distance away from the filled trenches (FIG.
3
C). As a result, the study object is formed into a plate-like shape wherein the first study region defines an area of decreased thickness. The plate-like study object is then milled into a wedge-like form (
FIGS. 4A and 4B
) wherein the thinner side(s) of the study object define a second study region. The first and second study regions thereby define thin plate-like areas on the study object wherein the various deposited layers of the study object are displayed. A somewhat similar arrangement is described in U.S. Pat. No. 5,656,811, which is more directly devoted to methods of controlling the FIB milling process.
U.S. Pat. No. 5,270,552 describes a process wherein a study specimen is partially severed from a study object using FIB milling (with the study specimen remaining attached to the study object by a thin bridge of material), a probe is then connected to the partially-disconnected study specimen (as by “soldering” it thereon with FIB deposition), and then the study specimen is fully removed by cutting away the bridge with FIB milling so that the probe may carry the study specimen to a desired location for study. By using an electrically conductive probe, the voltage between the probe, study specimen, and bridge can provide a measure of whether the study specimen is intact. The probe may also serve as a support structure for further preparation of the study specimen, or for use during the study specimen's microanalysis. Use of the process to obtain multiple study specimens from points spaced about a semiconductor wafer is illustrated. The patent additionally discusses the use of the underlying process steps to separate elements from one chip, transport them to another chip by use of the probe, and then sever the probe and “solder” the elements to the second chip by use of FIB deposition.
Other patents note that study specimens can be formed from a study object by use of material removal processes other than FIB processes (and any accompanying polishing or other mechanical material removal processes). U.S. Pat. No. 6,140,652 to Shlepr et al. describes the formation of study specimens from a study object for TEM microanalysis using photolithography and chemical etching processes. Trenches are etched in the study object to form a circular plug-like study specimen, which then has its base cut free from the study object by further chemical etching techniques. The study specimen can then be microanalyzed using TEM techniques.
In many instances, destructive testing (as in the foregoing methods) is undesirable because it will effectively render the study object inoperable. Thus, in some cases “proxy” or “qualifier” study objects are used: objects which are not the true study objects of interest, but which are subjected to the same processes so that they (hopefully) serve as a reasonable representation of the product generated by these processes. As an example, in the field of semiconductors, many thin film deposition systems are designed to deposit layers over an area greater than the size of a typical semiconductor wafer. Qualifier wafers are often processed alongside actual wafers so that they receive the same deposited layers as the production wafer. The qualifier wafer is then destructively tested in place of the actual wafer. However, testing of a qualifier wafer assumes that the qualifier wafer receives the same treatment as the actual wafer within the deposition system, an assumption which is not always valid because the deposited coatings may vary in time or location within the deposition system.
One significant problem encountered with all known methods is the time and expense of subsequent testing. Often, individual study specimens, once obtained in accordance with the foregoing methods, must then be individually prepared for subsequent microanalysis. This can include steps such as polishing, mounting, application of protective or other layers, situating the study specimen in a vacuum environment, and so on. Because of the disadvantages of destructive test methods, and because of th
Goodman Steven L.
Kelly Thomas F.
Martens Richard L.
Berman Jack
DeWitt Ross & Stevens S.C.
Fieschko, Esq. Craig A.
Imago Scientific Instruments
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