Patent Application
20090114620
Embodiments of the present invention relate to treatments for atom probe electrodes, including treatments for atom probe electrodes used in atom probe devices (e.g., atom probe microscopes).
An atom probe (e.g., atom probe microscope) is a device which allows specimens 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 is intermittently applied to the specimen. With each pulse, one or more atom(s) on the specimen surface is ionized. The ionized atom(s) separate or “evaporate” from the surface, pass though an aperture in the electrode, and impact the surface of the detector. The identity of an ionized atom can be determined by measuring its time of flight between the surface of the specimen and the detector, which varies based on the mass/charge ratio of the ionized atom. The location of the ionized atom on the surface of the specimen can be determined by measuring the location of the atom's impact on the detector. Accordingly, as the specimen is evaporated, a three-dimensional map of the specimen's constituents can be constructed.
A problem with current atom probes is that irregularities associated with the electrodes can distort the electrical fields created by the electrical charges that are applied during analysis of a specimen. This distortion can interfere with the operation of the atom probe. For example, field distortion can cause electrode field emission where the electric field causes the electrode to emit one or more electrons and/or ions. These emissions can cause reduced data quality because the emissions can show up as “noise” on the detector. Additionally, these emissions can damage the electrode and/or damage the specimen by removing material from the electrode, removing material from the specimen, and/or transferring material between the electrode and the specimen. Damage to the electrode and/or the specimen can further reduce data quality and/or prevent operation of the atom probe.
The present invention relates to treatments for atom probe electrodes, including treatments for atom probe electrodes used in atom probe devices (e.g., atom probe microscopes). For example, certain embodiments are directed toward treating atom probe electrodes to reduce a potential of the atom probe electrode creating a non-uniformity in an electric field when the atom probe electrode is used in an atom probe device during specimen analysis. Other embodiments are directed at processes of treating an atom probe electrode to reduce a potential of the atom probe electrode creating a field emission or a thermionic emission when the atom probe electrode is used in an atom probe device during specimen analysis. Some of the treatments can include processes that make a surface of the atom probe electrode smoother and/or increase a consistency or uniformity of material on the surface of the atom probe electrode. For example, in certain embodiments the treating processes can include depositing material on a surface of the atom probe electrode, removing material from the surface, heating the surface, cooling the surface, impacting the surface with ionized gas atoms, and/or applying laser energy to the surface.
In the following description, numerous specific details are provided in order to give a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well known structures, materials, or operations are not shown or described in order to avoid obscuring aspects of the invention.
References throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrase “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
Accordingly, various embodiments of the invention are described below. First the structure and operation of atom probe devices are discussed. Then, various treatment processes in accordance with embodiments of the invention are described.
In the illustrated embodiment, each chamber 101 is operatively coupled to a fluid control system 105 (e.g., a vacuum pump and/or an ion pump) that is capable of lowering the pressure in the chambers 101 individually. Additionally, the atom probe device 100 can include sealable passageways 104 that allow items to be placed in, removed from, and/or transferred between the chambers 110. In the illustrated embodiment, a first passageway 104a is positioned between the interior of the load lock chamber 101a and the exterior of the atom probe device 100, a second passageway 104b is positioned between the interior of the load lock chamber 101a and the interior of the buffer chamber 101b, and a third passageway 104c is positioned between the interior of the buffer chamber 101b and the interior of the analysis chamber 101c. In certain embodiments, a transfer device (e.g., a mechanical arm) can be positioned to move items between the chambers 104 and/or place or remove items on/in the atom probe assembly 110.
In
The fluid control system 105 can then lower the pressure in the buffer chamber 101b (e.g., reduce the pressure to 10−8-10−9 torr). The pressure in the analysis chamber 101c can be set at approximately the same or a lower pressure than the buffer chamber 101b. The third passageway 104c can be opened, the specimen 130 can be transferred to the analysis chamber 101c, and the third passageway 104c can be sealed.
The fluid control system 105 can then reduce the pressure in the analysis chamber 101c (e.g., the pressure can be lowered to 10−10-10−11 torr) prior to analysis of the specimen 130. In the illustrated embodiment, a getter 192 is positioned in the analysis chamber 101c to aid in lowering the pressure. In other embodiments, a getter 192 can be used in other chambers 101 or not used in the atom probe device. In still other embodiments, multiple items can be loaded or positioned in the chambers 101 of the atom probe device 100 using a similar method. For example, multiple specimens 130 can be positioned in the buffer chamber 101b and rotated through the analysis chamber 101c for analysis and/or multiple electrodes can be stored in the buffer chamber 101b and used to replace damaged electrodes in the analysis chamber 101c as required.
During analysis of the specimen 130, a positive electrical charge (e.g., a baseline voltage) can be applied to the specimen. The detector can be negatively charged and the electrode can be either grounded or negatively charged. A positive electrical pulse (above the baseline voltage) can be intermittently applied to the specimen 130 or a negative electrical pulse can be applied to the electrode 120. The electric field(s) created by the electrical charges can provide energy to ionize one or more atom(s) on the surface of the specimen 130. These ionized atom(s) can separate or “evaporate” from the surface, pass though an aperture in the electrode 120, and impact the surface of the detector 114. As the specimen 130 is evaporated, a three-dimensional map of the specimen's constituents can be constructed.
In certain embodiments, laser energy from the emitting device 150 can be used to thermally pulse a portion of the specimen 130 to assist with the evaporation process (e.g., the removal of ionized atoms). Additionally, in certain embodiments a temperature control device 116 can be used to cool the specimen 130 to reduce thermal motion and thermionic emission from the specimen. Thermionic emission includes the flow of one or more electrons from a metal or metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface. Thermionic emission from portions of the specimen 130 (or specimens in a multiple array) can reduce the accuracy of the analysis process.
In other embodiments, the atom probe device 100 can have more, fewer, and/or other arrangements of components. For example, in certain embodiments the atom probe device 100 can include more or fewer chambers, or no chambers. In other embodiments, the atom probe device can include multiple atom probe electrodes 120 and/or electrode(s) 120 having different configurations (e.g., planar electrode(s)). In still other embodiments, the atom probe device 100 includes more or fewer emitting devices 150, more or fewer temperature control systems 116, and more or fewer electrical sources 112.
During the analysis process, non-uniformities (e.g., distortions) in the electric field(s) can interfere with the operation of the atom probe. For example, distorted electrical field(s) can interfere with the orderly evaporation of the specimen 130 and/or cause electrode or specimen field emission, both of which can reduce data quality, damage the electrode 120, and/or damage the specimen 130. One cause of non-uniformities in the electric field(s) can be irregularities associated with the electrode 120.
In
In the illustrated embodiment, the first surface 323a includes a first irregularity 324a where the material is inconsistent with that of the surrounding area. This inconsistency in material can create portions on the first surface 323a that have differing work functions (e.g., where work function is the minimum amount of energy required to remove an electron from a material). Accordingly, this inconsistency in material can cause non-uniformities (e.g., asymmetries and/or areas of concentration) in the electric field(s) F proximate to the electrode and/or the specimen 330. In
As discussed above and illustrated in
In certain embodiments, process portions discussed above can be accomplished on newly manufactured atom probe electrodes (e.g., used to treat newly formed probes and/or prepare the probes for use). In other embodiments, process portions discussed above can be used to refurbish or repair old and/or damaged electrodes. In various embodiments, process portions discussed above can be accomplished in a lab or in a controlled environment where various environmental characteristics (e.g., temperature, pressure, and the composition of the surrounding fluid) can be selected and/or controlled. Accordingly, certain process portions can be accomplished under selected environmental conditions (e.g., in a high or low pressure environment). In certain embodiments, process portions discussed above can also be accomplished in the atom probe device, with the electrode installed in or removed from the atom probe assembly. When process portions are accomplished in the atom probe device, in certain embodiments they can be accomplished in a low pressure environment (e.g., less than atmospheric pressure) and in other embodiments they can be accomplished at atmospheric pressure or above.
In the illustrated embodiment, an atom probe electrode 720, having a surface and an aperture, is positioned in the container 790 and coupled to an electrical source 712 and a thermal control device 716. In
As discussed above, in certain embodiments material can be removed from a surface 723 of the electrode 720 to reduce the potential of the electrode 720 creating non-uniformity in an electric field and/or field emission when the electrode 720 is used in an atom probe device during specimen analysis. For example, a chemical polishing process can be used where the electrode 720 is immersed in one or more chemical baths that attack contaminants on the surface 723 of the electrode 720 and/or the bulk material of the electrode 720, smoothing the surface 723 (e.g., removing contaminants and/or protrusions). For example, the fluid 755 in the container 790 can include an acid (e.g., a solution of 30% hydrofluoric acid in nitric acid) and the electrode 720 can be comprised of silicon, nickel, stainless steel, and/or other suitable material(s). The fluid 755 will then attack the bulk material of the electrode 720. In other embodiments, the fluid 755 can include an acid such as hydrofluoric acid and the electrode 720 can be comprised of silicon, nickel, stainless steel, and/or other suitable material(s). The fluid 755 will then attack oxides on the electrode 720.
In other embodiments, removing material from a surface 723 can include an electro-polishing process. For example, the electrode 720 can be immersed in one or more chemical baths. The electrical source 712 coupled to the electrode 720 can apply an electrical current (e.g., an AC or positive DC current) to the electrode 720. The interaction of the electric field created by the voltage and the chemical bath can cause protrusions to be removed from the surface 723. In one embodiment, the fluid 755 can include a 20%-70% orthophosphoric acid in water and the electrode 720 can be comprised of copper. When 1-20 volts are applied to the electrode 720, the surface 723 can be electro-polished or smoothed. In other embodiments, the electro-polishing process can include grounding the electrode 720 and applying an electrical current to the fluid 755 (e.g., an AC or negative DC current).
In still other embodiments, a vapor or plasma etching process can be used to remove material form the surface 723 of the electrode 720. For example, a chemical vapor or plasma-assisted etching process can be used to remove material from the surface 723 with or without an electrical current or radio-frequency (RF) bias applied to the electrode 720 and/or the fluid 755. In one embodiment, the fluid 755 can include a fluorocarbon (e.g., a sulfur hexafluoride (SF6) vapor), the container 790 can be maintained at a pressure of 0.6-2 mbar, and the resulting reaction can etch away protrusions on electrodes 720 having selected compositions (e.g., electrodes 720 comprised of silicon, nickel, stainless steel, and/or other suitable material(s)). In still other embodiments, the fluid 755 can include a plasma generated by exposing a gas (e.g., oxygen, carbon tetrafluoride, or argon) to an electrical current or RF energy (e.g., via the emitting device 750). The plasma can be used to clean contaminants from the electrode 720 and/or etch protrusions from the electrode 720. Although in the illustrated embodiment, the vapor and plasma etching processes are shown being accomplished in the container 790, many of the vapor or plasma etching processes are also particularly well suited to be accomplished in the atom probe device (e.g., in the load lock or buffer chamber).
In still other embodiments an ion beam milling process can be used to remove material from the surface 723 of the electrode 720. For example, in one embodiment a focused ion beam can be emitted by the emitting device 750 and used to remove small protrusions from the surface 723. Although in the illustrated embodiment, the ion beam milling process is shown being accomplished in the container 790, this process is also particularly well suited to be accomplished in the atom probe device (e.g., in the load lock or buffer chamber). When this process is accomplished in the atom probe device, the fluid control system 105, shown in
As discussed above, in certain other embodiments material can be deposited on the surface 723 of the electrode 720 to reduce the potential of the electrode 720 creating non-uniformity in an electric field and/or field emission when the electrode 720 is used in an atom probe device during specimen analysis. For example, a thick film deposition process (e.g., electroplating) can be used to deposit material on the surface 723. In certain embodiments, the electrode 720 can be immersed in one or more chemical baths and the electrical source 712 coupled to the electrode 720 can apply a voltage (e.g., a negative AC or DC voltage) to the electrode 720 causing material to be added proximate to and/or over the protrusions on the surface 723, thereby smoothing the surface 723. For example, in one embodiment the fluid 755 can include a solution of 20%-70% sulphuric acid and copper sulphate in water, and 1-20 volts (e.g., negative DC) can be applied to the electrode 720 causing the copper to be deposited on the electrode 720. In other embodiments, a material having a high work function can be deposited on the surface 723 (e.g., platinum can be electroplated to the surface 723). By depositing a material with a high work function, the effective work function of the electrode 720 can be increased. As the effective work function of the electrode is increased, the likelihood of field emission can be reduced.
In other embodiments, a thin film coating process (e.g., a process depositing material at an atomic level) can be used to deposit material onto the surface 723, thereby making the surface 723 smoother. For example, a thin film coating process can include vapor or plasma deposition, chemical vapor deposition, physical vapor deposition, electron beam deposition, and/or molecular beam epitaxy. Additionally, a thin film coating process can be used to deposit a material having a high work function (e.g., tungsten or platinum) onto the surface 723, thereby increasing the effective work function of the electrode 720 and potentially reducing the likelihood of field emission. For example, in one embodiment a self-limiting formation of a thin layer of tungsten on the surface 723 can result when the electrode 720 is comprised of silicon and the fluid 755 is comprised of tungsten hexafluoride (WF6) maintained in the container 790 at a low pressure.
In still other embodiments, an ion beam assisted deposition process can be used to deposit material onto the surface 723. For example, the fluid 755 can include a vapor comprising platinum or tungsten and the emitting device 750 can be configured to emit an ion beam causing the deposition of platinum or tungsten on the surface 723. Although in the illustrated embodiment, the ion beam assisted deposition process is shown being accomplished in the container 790, this process is also particularly well suited to be accomplished in the atom probe device (e.g., in the load lock or buffer chamber). When this process is accomplished in the atom probe device, the fluid control system 105, shown in
In certain embodiments, at least a portion of the atom probe electrode 720 can be made more robust or stronger (e.g., mechanically or physically stronger) by depositing material on a surface 723 of the atom probe electrode 720. For example, material can be deposited on a surface 723 of the electrode 720 proximate to the aperture of the electrode 720. The added material can strengthen at least the portion of the electrode 720 proximate to the surface 723 (e.g., because of the amount of added material or because of the properties of the added material). This added material can make the electrode more resistant to damage from piece(s) of a specimen that impact the electrode 720 when a specimen fractures during specimen analysis. Additionally, the coating can make the electrode more durable and damage resistant in general (e.g., during transport, storage, and loading into an atom probe device). In one embodiment, a silicon nitride and/or a silicon carbide coating can be deposited (e.g., using a chemical vapor deposition process) on a surface 723 of the electrode 720. The coating can strengthen the portion of the electrode 720 proximate to the surface 723 and/or reduce the potential of the electrode 720 creating non-uniformity in an electric field and/or field emission when the electrode 720 is used in an atom probe device during specimen analysis.
As discussed above, in yet other embodiments the surface 723 of the electrode 720 can be heated and/or cooled to reduce the potential of the electrode 720 creating non-uniformity in an electric field and/or field emission when the electrode 720 is used in an atom probe device during specimen analysis. For example, in certain embodiments the electrode 720 can be annealed to smooth the surface 723 (e.g., by rapidly heating and slowly cooling the surface 723). In one embodiment, the temperature control device 716 can be used to heat the surface 723 above approximately two-thirds of the melting point of a material of the surface 723 (e.g., approximately 500° C. for aluminum) to make the surface 723 smoother. In other embodiments, other temperature control devices 716 can be used, including a radiant heat source. Although in the illustrated embodiment, the annealing process is shown being accomplished in the container 790, this process is also particularly well suited to be accomplished in the atom probe device (e.g., in the load lock or buffer chamber).
In other embodiments a cooling process can be used to reduce the temperature of the electrode 120 (shown in
Referring back to
Referring again to
As discussed above, aspects of various embodiments described above can be combined. For example, in certain embodiments one or more materials can be deposited on the electrode 720 to facilitate cleaning the electrode 720 after the electrode 720 has been contaminated (e.g., after the electrode has been stored, transported, and/or used to analyze one or more specimen(s)). In certain embodiments, silicon nitride (including all of its stoiciometric combinations), silicon dioxide, molybdenum, and/or platinum can be deposited on the surface 723 of the electrode 720 (e.g., to form a coating or film). After the electrode 720 has collected contaminants, material (e.g., the contaminants) can be removed or cleaned from the electrode 720 using a cleaning process (e.g., a refurbishing process, an acid bath, and/or plasma-etching process). In certain embodiments, the cleaning process “attacks” selected materials, but does not attack or is slow to attack the deposited material. In further embodiments, after removing at least some of the contaminants, additional material can be deposited on the electrode 720 (e.g., the electrode 720 can be re-coated) to facilitate the removal of contaminants in the future and/or to cover contaminants that remain after the cleaning process. In certain embodiments, the original deposited material (e.g., original coating) can be completely removed before new material is deposited on the surface 723. In other embodiments, only a portion of the original deposited material is removed before new material is deposited or none of the originally deposited material is removed.
In still other embodiments, one or more material(s) can be deposited on the surface 723 of the electrode 720 to act as a sacrificial layer during the cleaning process (e.g., a refurbishing process). During the cleaning process, the deposited material comprising the sacrificial layer can be partially or completely removed (e.g., stripped), thereby removing contaminants that have accumulated on portions of the sacrificial layer. For example, in certain embodiments an etching process that selectively removes the deposited material from the material used to fabricate the electrode can be utilized to remove at least a portion of the deposited material, along with contaminants that have accumulated on the deposited material. New material can then be deposited onto the surface 723 of the electrode 720 to act as a new sacrificial layer to facilitate future contaminant removal. For example, in one embodiment an electrode 720 can be comprised of nickel, and silicon dioxide can be deposited on the surface 723 of the electrode 720. After the electrode 720 has collected contaminants, a buffered hydrogen fluoride can be used to strip the silicon dioxide coating from the electrode 720 without removing a significant amount of nickel, thereby removing at least a portion of the contaminants that have collected on the silicon dioxide coating. Another sacrificial layer can then be deposited on the surface 723 of the electrode 720 to facilitate contaminant removal in the future.
A feature of some of the embodiments discussed above is that an atom probe electrode can be treated to reduce a potential of the atom probe electrode creating non-uniformity in an electric field when the atom probe electrode is used in an atom probe device during specimen analysis. By reducing non-uniformities in the electric field, the atom probe device can operate more efficiently, more accurately, and/or with lower field emission. Additionally, the electrode can be treated specifically to reduce a potential of the atom probe electrode creating field emission and/or thermionic emission when the atom probe electrode is used in an atom probe device during specimen analysis. By reducing emissions, the electrode and specimen can be less likely to sustain damage from emitted particles and the atom probe device can operate more efficiently and/or more accurately. Certain processes for reducing non-uniformities and/or reducing the potential for emissions can include making the surface of the electrode smoother and/or increasing a consistency or uniformity of material on the surface of the electrode. Making a surface smoother and/or increasing the consistency or uniformity of material on the surface of the electrode can also increase the consistency or the uniformity of work function over the surface of the electrode. Advantages of these features include better specimen analysis and less atom probe device downtime caused by damaged electrodes and specimens.
Another feature of some of the embodiments discussed above is that electrodes can be refurbished and/or repaired. Because electrodes are difficult and costly to manufacture, an advantage of this feature is that operating costs can be reduced by repairing/refurbishing electrodes versus replacing electrodes. Additionally, many of the treatment processes discussed above can be used to correct production defects in newly manufactured electrodes. An advantage of this feature is that manufacturing costs can be reduced by repairing electrodes with production defects instead of discarding defective electrodes. Additionally, smaller apertures can be formed in the electrodes during the manufacturing process because various treatment processes can be used to correct aperture defects that occur during the production of electrodes with smaller apertures. Smaller apertures can enable the analysis of smaller (e.g., shorter) micro-tip specimens, which are easier to manufacture and can be more densely packed over a given area enabling more regions of interest to be analyzed. Another feature of some of the embodiments discussed above is that electrodes can be repaired/refurbished without removing them from the atom probe device. An advantage of this feature is that atom probe device downtime can be reduced.
Yet another feature of some of the embodiments discussed above is that treatment processes that reduce electric field non-uniformities and emissions can allow electrodes to be positioned closer to specimens during data acquisition. Because the electrode and specimen can be closer to one another, a lower voltage can produce the electric field used to evaporate the specimen. Accordingly, smaller voltage pulses can be used during the evaporation process. Smaller pulse voltages can be generated with faster rise times, and the pulses can be applied more rapidly resulting in improved resolution.
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.
This application claims the benefit of U.S. Provisional Patent Application No. 60/690,997 filed on Jun. 16, 2005, Entitled ATOM PROBE ELECTRODE TREATMENTS.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2005/025740 | 7/21/2005 | WO | 00 | 7/21/2008 |
| Number | Date | Country | |
|---|---|---|---|
| 60690997 | Jun 2005 | US |
