Patent Publication Number: US-2021183608-A1

Title: Photon-induced ion source

Description:
FIELD OF THE INVENTION 
     The invention relates generally to ion sources, and specifically to photon-induced nano-aperture ion sources for use in charged particle systems. 
     BACKGROUND OF THE INVENTION 
     There are many types of ion sources available today, such as liquid metal ion sources, plasma-based ion sources, and sputter-based ion sources, to provide a few examples. While the liquid metal ion sources (usually in a Gallium flavor) may typically be used in many applications, there is a desire for ion sources that provide higher brightness and lower energy spread. Numerous attempts have been made at meeting these goals over the years, as indicated by the development of so many different types of ion sources, but there tend to be drawbacks and/or complicated engineering problems encountered. For example, plasma-based ion sources (either RF or ICP types) provide high brightness and high current, but typically require complicated power and thermal management design. 
     SUMMARY 
     Apparatuses and methods for an optical induced ion source are disclosed herein. An example apparatus at least includes an ionization volume arranged to receive a gas and first optical energy, the first optical energy to ionize the gas, and a channel formed between a first membrane and a second membrane, the first membrane having at least a transparent portion and the second membrane including an aperture, where the gas is provided to the ionization volume through the channel, the ionization volume formed inside the channel and adjacent to the aperture, and where the first optical energy ionizes the gas after passing through the at least transparent portion of the first membrane. 
     Another example includes a first membrane having a transparent portion, a second membrane having an aperture, a channel formed between the first and second membranes, a gas source coupled to provide gas to the channel, and first and second optical sources coupled to provide first and second optical energies, respectively, through the transparent portion to excite and ionize the gas to form ions, the ions emitted out of the aperture, where the first optical energy excites the gas to an intermediate energy state, and where the second optical energy ionizes the excited gas. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an example focused ion beam (FIB) system  100 A including a photon-induced NAIS in accordance with an embodiment of the present disclosure. 
         FIG. 1B  is an example dual-beam (DB) system  100 B including a photon-enabled NAIS in accordance with an embodiment of the present disclosure. 
         FIG. 1C  is an example triple-beam (TriBeam) system  100 C including a photon-induced NAIS in accordance with an embodiment of the present disclosure. 
         FIG. 2  is an example photon-enabled NAIS  204  in accordance with an embodiment of the present disclosure. 
         FIG. 3  is an illustration of an example photon-induced NAIS  304  in accordance with an embodiment of the present disclosure. 
         FIG. 4  is an example illustration of a NAIS  404  in accordance with an embodiment of the present disclosure. 
         FIG. 5  is an example illustration of NAIS  504  in accordance with an embodiment of the present disclosure. 
         FIG. 6  is an example illustration of a NAIS  604  in accordance with an embodiment of the present disclosure. 
         FIG. 7  is an illustration of NAIS  704  in accordance with an embodiment of the present disclosure. 
     
    
    
     Like reference numerals refer to corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention are described below in the context of a photon-induced nano-aperture ion source (NAIS). The photon-induced NAIS can be included in various charged particle systems that include an ion column, such as a focused ion column, and the photon-induced NAIS may provide a high brightness source, at least compared to a Gallium-based liquid metal ion source. However, it should be understood that the methods described herein are generally applicable to a wide range of different ion beam methods and apparatus, including both cone-beam and parallel beam systems, and are not limited to any particular apparatus type, beam type, object type, length scale, or scanning trajectory 
     As used in this application and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the term “coupled” does not exclude the presence of intermediate elements between the coupled items. 
     The systems, apparatus, and methods described herein should not be construed as limiting in any way. Instead, the present disclosure is directed toward all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The disclosed systems, methods, and apparatus are not limited to any specific aspect or feature or combinations thereof, nor do the disclosed systems, methods, and apparatus require that any one or more specific advantages be present or problems be solved. Any theories of operation are to facilitate explanation, but the disclosed systems, methods, and apparatus are not limited to such theories of operation. 
     Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed systems, methods, and apparatus can be used in conjunction with other systems, methods, and apparatus. Additionally, the description sometimes uses terms like “produce” and “provide” to describe the disclosed methods. These terms are high-level abstractions of the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art. 
     In some examples, values, procedures, or apparatuses are referred to as “lowest”, “best”, “minimum,” or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, or otherwise preferable to other selections. 
     Ion sources for focused ion beam (FIB) columns with higher brightness and lower energy spread than traditional Gallium (Ga) ion sources are very desirable. High brightness provides better performance in imaging, processing and material analysis, for example. While higher brightness is desirable, even a source having equal (or even a little less) brightness is also desirable, especially since the ion beam is not gallium, such as a noble gas. Prior attempts at a higher brightness source resulted in the development of a nano-aperture ion source (NAIS). The NAIS is composed of an electron beam system that provides an electron beam to ionize neutral gas in a reaction volume, a gas delivery system to deliver a gas to ionize, and (3) an aperture assembly. The aperture assembly includes two membranes that are separated by a 100-1000 nm gap. The aperture assembly confines the gas precursor in a small volume, e.g., the reaction volume, for ionization and ion extraction, which are then emitted to ion optics to form ion beam. The ion beam may then be used for imaging and/or processing, for example. 
     In addition to high brightness and low energy spread, a NAIS can also switch ion species during operation, which is very desirable in many applications. More importantly, a NAIS can be applied in some critical technology areas such as III-V semiconductors where Ga ion sources could be a source of device contamination. With all above advantages, NAIS may become very valuable and could have huge marketing opportunities. During implementation of a conventional NAIS system, some challenges were encountered. These challenges at least include the following: (1) the e-beam system needs to be electrically floated on the ion beam energy, which makes engineering difficult; (2) the gas delivery system should also be floated on the ion beam voltage to avoid potential arcing via high pressure gas inside the delivery line, which also makes engineering challenging; (3) the e-beam system requires a good vacuum to run and maintain, which becomes very hard when a high pressure gas is delivered to the nano-aperture device and leaks through the aperture into the space where the e-beam system resides (a sudden poor vacuum condition could kill the e-system); (4) a robust nano-aperture device is very difficult to fabricate; (5) gas ionization rate from an impacted electron beam is low and high electron beam current is required to produce sufficient ions, which is impractical in some high throughput applications; and (5) electron impact ionization results in a beam of ions having multiple charge states, for example 94% Ar+, 5% Ar++, and 1% Ar+++, and these components will unfortunately become separated in the beam line in the presence of even weak magnetic fields, leading to a multiplicity of ion beams at the sample. Considering the listed challenges, an improved NAIS is desirable. 
     One solution to reduce or eliminate one or more of the above-identified challenges is to use an optical source for ionizing the gas. To discuss a few of the challenges, replacing the e-beam system with the optical source alleviates the challenges with electrically floating the e-beam system on the ion producing system, the formation of multiple charge states, and reduces the vacuum constraints since the optical energy can be delivered through one or more transparent windows. The photon-induced NAIS system allows for the formation of desired ion species under better control and with improved/easier managed environmental, e.g., vacuum, conditions. 
     In general, the photon-induced NAIS will include two membranes separated by a gap with one membrane including at least one optically transparent window and the other membrane including an aperture. It will be appreciated by those skilled in the art that the term membrane is not limiting to thin flat electrodes, and that membrane can also include other electrode shapes, such as rings, discs, cones, plates, and combinations thereof. The at least one optically transparent window allows for introduction of one or two beams of optical energy for ionization of a gas, and the aperture is for emitting generated ions. The gap between the two membranes provides a channel for introduction of the gas to the reaction volume, which may also be referred to as the ionization volume or ionization region. The ionization volume may be adjacent to the aperture and comprise a volume of the channel between the aperture and other membrane where the ionization of the gas occurs. A potential difference established between the two membranes may induce the ions to drift toward the aperture for extraction into the ion beam column. Emitted ions may be attracted to ion optics, which form the ions into an ion beam for focusing and providing to a sample for imaging, milling, etching and/or deposition. The etching and deposition may be performed with a process gas present at the surface of the sample. 
     In some embodiments optical energy may be introduced into the ionization volume by more than one optical source. In such an embodiment, one optical source may provide optical energy at an intensity and energy to excite the gas to an intermediate state. This optical energy may be referred to as the excitation energy that is provided by an excitation source. A second optical source may provide optical energy at an intensity and energy to further excite the gas from the intermediate state to a desired ionization state. This optical energy may be referred to as the ionization energy that is provided by an ionization source. In some embodiments, both the excitation and the ionization sources are lasers. The lasers may be operated in either continuous wave (CW) or pulsed wave (PW) regimes. To note, by first exciting the gas with one source then ionizing the gas with another source, the number of charge states generated may be reduced to a single desired charge state in most, if not all, embodiments. It should be noted, however, that multiple optical sources are not necessary and the use of a single optical source to ionize the gas is within the scope of the present disclosure. 
     Some of the disclosed techniques use high power lasers to excite, ionize and produce ions from gas species in a small volume, followed by ion extraction to form an ion beam. The laser could operate in either CW mode or pulse mode, where lasers operated in pulse mode provide higher energy density that could ionize gas more efficiently. In general, a broad excitation laser beam illuminates gas inside the nano-aperture device and an ionization laser beam is focused into a small spot (e.g., 1 um in diameter) near the nano-aperture. Gas molecules inside a small volume near the aperture, which is determined by the focused laser beam and the gap between two membranes, are excited to excited states by the excitation laser and then ionized by the ionization laser. Ions produced in this small volume are extracted/transported out of the nano-aperture by a small potential between both plates and then form an ion beam via the downstream ion optics. With an optical window to block gas leakage, gas density inside the nano-aperture device should be higher than that in current electron-impacted NAIS assuming a similar geometry configuration. In addition, space above the aperture device should have better vacuum condition due to no gas leakage into it (the window prevents leakage). Considering gas ionization rate from laser is much higher than from electrons, thus higher ion current is expected in such photon-induced ion source. 
     Advantages of the disclosed techniques at least include: (1) the e-beam system is not a requirement, there would be no concerns about floating the e-beam system on ion beam energy; (2) the upper space (above the ion source) becomes available, multi-gas tanks can be installed inside and safely floated on the ion beam energy, laser components can also be installed in this space; (3) there is no critical vacuum constrain for the upper space; (4) gas ionization rate from high density photons (laser) is much higher than that from electrons leading to high ion beam current; and (5) ionization with laser beams may ensure that only singly ionized species are produced in and emitted from this source. 
     As will be discussed below, numerous examples of the photon-induced NAIS are possible, and all examples are within the scope of the present disclosure. For example, instead of a gas source providing a gas to the channel, a solid source may be housed within the photon-induced NAIS that provides a partial pressure of gas for exciting and ionizing. In such an embodiment, the solid source is disposed so that the optical energy can be delivered to the surface of the solid source or adjacent to where the gas may flow. Other examples include different arrangements for delivery of the optical energy and/or ionization region formation. 
       FIG. 1A  is an example focused ion beam (FIB) system  100 A including a photon-induced NAIS in accordance with an embodiment of the present disclosure. The FIB  100 A includes an ion column  102 A that delivers ions from an ion source  104 A to a sample  110 A. The ion column  102 A includes ion optics  106 A to form, shape, alter, manipulate the ion beam provided by ion source  104 A prior to the ion beam reaching the sample  110 A. The sample  110 A and at least a portion of the ion column  102 A are enclosed in a vacuum chamber  108 A that provides a low pressure environment for FIB milling and/or imaging. While not shown, one or more gasses may be delivered to the sample  110 A surface so that ion-induced deposition and/or etching may also be implemented. 
     The ion optics  106 A includes one or more lenses for manipulating the ion beam within the ion column  102 A. For example, ion optics  106 A may include a gun lens, an objective lens and other components, such as beam blankers, beam defining apertures, and scanning deflectors. The combination of these components allows the ion beam to be delivered at various energies and/or currents and moved across a surface of the sample  110 A so that specific areas of the sample  110 A may be imaged, milled, etched, and/or material deposition performed. 
     The ion source  104 A provides ions to the ion optics  106 A that have been ionized due to high intensity optical energy. The ions are generated, for example, by focusing high intensity optical energy onto a small volume of gas, e.g., an ionization volume, that is then ionized due to the optical energy. Once ionized, the ions emit out of a small aperture in a membrane of the ion source  104 A and are collected by the ion optics  106 A. In some embodiments, a potential difference between the membrane and a second membrane may promote the movement of the ions toward and out of the aperture. The second membrane is at least partially transparent for transmission of the optical energy. Additionally, the first and second membranes are arranged to form a channel for gas delivery. See at least  FIG. 2  for an example ion source in accordance with the disclosure. In some embodiments, the gas in the channel is illuminated with two different optical energies, a first optical energy to excite the gas to an intermediate state (e.g., from an excitation optical source) and a second optical energy to ionized the excited gas (e.g., from an ionization optical source). The first and second optical sources may be lasers, for example, of different intensities and/or wavelengths. 
       FIG. 1B  is an example dual-beam (DB) system  100 B including a photon-enabled NAIS in accordance with an embodiment of the present disclosure. The DB  100 B includes an ion column  102 B and an electron column  112 B, along with the other components discussed with respect to FIB  100 A, which, for sake of brevity, will not be discussed again. The electron column  112 B, or SEM column, is included to provide additional capabilities with imaging a sample  110 B. The ion column  102 B, like the ion column  102 A, incudes a photon-induced NAIS  102 B to generate and provide an ion beam. 
       FIG. 10  is an example triple-beam (TriBeam) system  100 C including a photon-induced NAIS in accordance with an embodiment of the present disclosure. The TriBeam  100 C is an extension of the DB  100 B in that it includes a laser “column”  114 C in addition to the FIB and electron columns  102 C and  112 C, respectively. The addition of the laser column  114 C allows for flexibility in sample processing, such as an increase in material removal rate with a laser provided by the laser column  114 C that can be augmented with more gentle processing by the FIB column  102 C. While the laser column  114 C is shown access a sample  110 C through the vacuum chamber  108 C, in other embodiments, the laser column  114 C may process a sample in a separate, but connected, chamber. 
     In general, each of the systems  100 A,  100 B and  100 C include a photon-induced NAIS to overcome or reduce the challenges discussed above so that a brighter ion source may be implemented to provide improved imaging and processing capabilities. 
       FIG. 2  is an example photon-enabled NAIS  204  in accordance with an embodiment of the present disclosure. The photon-enabled NAIS  204  (NAIS  204  for short) is one example of the ion sources  104 A- 104 C implemented in systems  100 A- 100 C. In general, the NAIS  204  provides a desired species of ions for an ion column implemented in any charged particle beam system, such as a FIB, a DB or a TriBeam system, and may be used to mill, etch, deposit material on and/or image samples. The NAIS  204  is a high brightness ion source that improves the various uses as discussed. 
     The NAIS  204  at least includes a first membrane  216 , a second membrane  218 , a gas source  226 , first and second optical energy sources  228 ,  230 , and a bias source  236 . These components may be arranged to form a restricted volume for ion generation, e.g., ionization volume  244 , using one or both of the optical energy sources  228 ,  230 . Some of the generated ions are emitted via an aperture  222 , e.g., an ion output aperture, formed in the second membrane  218  and are collected by ion optics  238 . The ion optics  238  are generally part of an ion column, not necessarily the NAIS  204 , but are included to complete the picture of providing an ion beam using ions generated by the NAIS  204 . 
     The first membrane  216  may have at least a portion that is transparent to optical wavelengths used to form the ions. For example, first membrane  216  includes transparent portion  220 , which may also be referred to herein as window  220 . While transparent portion  220  is shown to be located at a center location of first membrane  216  and to span a third of the shown length, such arrangement is only an example and other arrangements are contemplated. For example, the transparent portion  220  may be located at other locations of the first membrane  216 , or it may form the entirety of the first membrane  216 . The second membrane  218  includes the aperture  222  and is arranged to form the ionization volume  244  between the two membranes. The ionization volume  244  is where the optical energy is provided for generating the ions, and it may have a desired pressure of gas  224  to enable ionization. In general, the ionization volume  244  is defined by the gap between the two membranes  216 ,  218  and the exposure area of at least optical source  230 , which may be manipulated by one or more lenses. 
     The shape of the membranes  216  and  218 , from a plan view, may be formed to fit inside of an enclosure mounted to or incorporated into an ion column, such as ion columns  102 A- 1020 . Examples shapes include circular, rectangular, square, etc. In some embodiments, sidewalls may be disposed on the edges of the membranes  216  and  218  to form an enclosure for the channel  219  and the ionization volume  244 . In some embodiments, the membranes  216  and  218  may each have a thickness about 100-200 nm and the channel  219  between the two membranes may be up to a few millimeters. In some embodiments, the aperture  222  may have an diameter of around 50-200 nm. Of course, other dimensions are possible and contemplated and may only be limited by the ability to provide a gas at the ionization volume at a pressure that provides an efficient ionization cross-section. The membranes may be formed from silicon or silicon nitride using a MEMS process, for example, and the window  220  may be formed from silicon dioxide or quartz, to name a few examples. Additionally or alternatively, inside surfaces of membranes  216  and  218  may be reflective (not shown), at least to the wavelengths of optical sources  228  and  230 , so that incident radiation is reflected inside channel  219 . The reflectance may assist with illumination of the ionization volume  244 , and may reduce or prevent the optical energy from damaging the membranes. 
     A gas source  226  provides a desired gas to the volume  244 . The gas source  226  may be disposed outside of the NAIS  204  but be fluidly coupled to provide a desired gas  224  to the channel  219 . In some embodiments, the type or species of gas  224  may be switched to different types/species so that different ions are provided to ion optics  238 . Example gasses include argon, xenon, neon, krypton, for noble species micromachining applications; oxygen, nitrogen, or other reactive species for surface chemical functionalization applications; or the vapors of heated iodine, cesium, or other alkali metals for surface analysis by secondary ion mass spectrometry. 
     First and second optical energy source  228 ,  230  may be arranged to provide respective optical energies to the ionization volume  244  via the window  220  and adjacent to the aperture  222 . The optical energies may be provided via respective lenses  232 ,  234  selected to provide a desired optical beam spot size in the ionization volume  244 . For example, source  228  may be provided to a large area so that a large volume of gas is exposed to the excitation energy. On the other hand, the source  230  may be focused to a small area, e.g., 1 μm, so that the ionization efficiency is increased. Optical source  228  provides optical energy to excite the gas to an elevated energy state. The source  228 , which can be referred to as the excitation source, may energize the gas to enhance eventual ionization without promoting ionization. The gas  224  in the volume  244  may then be provided a second optical energy from optical source  230 , which provides energy to cause the excited gas to ionize. Optical source  230  may be referred to as the ionization optical source. Once ionized, a voltage difference between the first and second membranes  216 ,  218  may promote the ionized gas to drift toward the aperture  222  where they can be emitted to the ion optics  238  for formation of an ion beam, such as a focused ion beam. The voltage difference is provided by coupling a voltage source  236  between the first and second membranes, which may be a DC or an AC source. 
     In some embodiments, excitation and ionization sources  228  and  230  are lasers, such as solid state laser. Of course, other laser types are contemplated and available as well. For example, to ionize a Rubidium atom a photon of 4.2 eV energy is needed, corresponding to 296 nm wavelength, which is conventionally a difficult wavelength to generate. Instead of using this ultraviolet photon, a first excitation step can be made using a photon of 2.4 eV, corresponding to a 516 nm wavelength laser (provided by excitation source  228 ) to excite Rb to the 5p2P° level, followed by a second photon of 1.8 eV energy, corresponding to a 688 nm wavelength laser (provided by ionization source  230 ) to ionize the Rb atom. The same can be achieved using Cs atoms, instead of a direct ionization from the ground state (photons of 318 nm wavelength corresponding to 3.89 eV) a two-step process, exciting the atom using a 689 nm wavelength (1.8 eV) followed by a 592 nm wavelength photon (2 eV), is implemented. 
     In operation, a gas is provided to the channel  219  by the gas system  226 . The gas will flow into the ionization volume  244  and be irradiated by the first and second optical sources so that ions are formed. The ions, due to their charge, will be induced to move away from the first membrane  216  toward the second membrane  218  under the influence of the potential difference established by voltage source  236 . Some of the ions will eventually leave the volume through the aperture  222  to be formed into a focused ion beam by the ion optics  238 . In some embodiments, the gas pressure in the ionization volume  244  is around 1 atm. At this pressure and with the ionization source  230  providing 1 mJ pulses at a rate of 500 kHz (using a 532 nm wavelength laser), around 6 □A of ions may be provided by NAIS  204  assuming an ionization rate of 10% and ion extraction efficiency of 10%. With adding the excitation source  228  (532 nm wavelength laser or others operating in either CW or pulsed mode), comparable or more ion beam currents can be produced, while an ionization laser source of lower pulse energy and repetition rate can be used. In general, the excitation and ionization techniques disclosed herein may require either pulsed lasers to provide multi photon ionization or very short wavelengths for CW lasers. Multiple wavelengths to excite and ionize are possible but they likely need to be pulsed and coincident in time due to the short lived nature of the electronic states we are dealing with. 
       FIG. 3  is an illustration of an example photon-induced NAIS  304  in accordance with an embodiment of the present disclosure. The NAIS  304  has many, if not all, of the same components as NAIS  204 , but shows a number of different arrangements for the ionization optical source and how the ionization energy can be introduced to the ionization volume  344 . In general, the NAIS  304  can be implemented in any type of charged particle beam system, such as a FIB, DB or TriBeam, as shown in  FIGS. 1A-1C , respectively. The NAIS  304  is used to generate ions that are provided to a surface of a sample for imaging, milling, gas assisted etching and/or gas assisted deposition. 
     For sake of brevity, only the differences of NAIS  304  over NAIS  204  will be discussed in detail. Specifically, the ionization optical energy may be introduced to the ionization volume  344  by one of two different orientations over NAIS  204 . For example, the ionization optical energy may be provided through a second transparent window  346  if Option A is implemented. On the other hand, Option B may be implemented, which arranges the ionization optical energy to be provided to the ionization volume  344  via the channel  319  formed between the first and second membranes  316 ,  318 . In either embodiment, the inside surfaces of the first and second membranes may be reflective at least to the wavelengths of the introduced optical energies so to promote concentration of the optical energy in the ionization volume  344  instead of incurring losses through interaction with the surfaces of the membranes. 
       FIG. 4  is an example illustration of a NAIS  404  in accordance with an embodiment of the present disclosure. The NAIS  404  is yet another example NIAS source that can be implemented in systems  100 A through  100 C, for example. In general, the NAIS  404  includes a solid gas source disposed in a cell coupled to the ionization volume via a second aperture. This second aperture allows the gas and ions to be provided to the ion output aperture  422 . For brevity&#39;s sake, only the differences between NAIS  404  and NAIS  202  will be discussed in detail. 
     The NAIS  404  includes a solid gas precursor cell  450  coupled to the first membrane  416 . The solid gas precursor cell  450  houses a solid fuel source  542 , and is formed by a (optionally removeable) cover  454  (with heating function) and one or more transparent sides  456 . Due to vapor pressure of the solid fuel source, and the vacuum environment, vapor of the solid fuel source  452  is produced inside the cell  450 . The higher the vapor pressure of the solid fuel source, the more gas precursors are generated inside the cell  450 . To increase gas precursor density or pressure inside the cell  450 , laser ablation using the excitation source  428  or thermally heating using the cover  454  can be applied to the solid source precursor. Ions may be generated by providing excitation and ionization optical energies from optical sources  428  and  430 , respectively. Generated ions may then be induced to drift toward output aperture  422  through fuel cell aperture  458 . The potential difference inducing the drift of the ions may be established between the first and second membranes  416  and  418  as previously described. Ions that emit out of output aperture  422  may then be formed into a focused ion beam via ion optics  438 . To help confine the gas and ions within the channel between the membranes, structural barrier(s)  460  may be disposed between the two membranes adjacent to the apertures  458  and  422 . 
     The solid gas precursor cell  450  eliminates the need for coupling gas canisters via gas lines to a NAIS, which should simplify ion column design and tool placement. However, the use of a solid precursor  452  may limit the available ion species and additionally reduce or eliminate the ability to provide different ion species by a single ion column. Regardless, depending on the use of the NAIS  404 , the simplicity of the solid precursor based system may negate any other concerns. Example sold precursors include Cesium, lithium, rubidium, iodine and buckminsterfullerene. 
     It should be noted that in the NAIS  404 , the ionization volume  444  may be formed between the fuel source  452 , the aperture  458  and the exposure volume of the ionization source  430 . In some embodiment, the ionization volume  444  may extend into the volume between the membranes adjacent to the apertures  458 ,  422 . 
     While NAIS  404  includes two membranes  416 ,  418 , in other embodiments, only one membrane may be included, such as membrane  416 , for providing the output ions. In such an embodiment, a potential difference is formed between a side of the fuel container and the aperture for promoting movement of the ions toward the aperture. Additionally, in such an embodiment, the second aperture would also be the output aperture. 
       FIG. 5  is an example illustration of NAIS  504  in accordance with an embodiment of the present disclosure. The NAIS  504  is yet another example of a photon-induced NAIS that can be implemented in any of the systems  100 A through  100 C. In general, NAIS  504  generates ions using optical energy and provides the ions to ion optics for the formation of a focused ion beam for use in imaging, milling, ion induced etching and/or material deposition. In some aspects, the NAIS  504  may be easier to fabricate than NAISs  204 - 404 As due to having fewer components. As previous, only the differences between NAIS  504  and the previously discussed NAIS systems will be described in detail. 
     The NAIS  504  includes one membrane  518  with the aperture  522 . Instead of a first membrane that includes a transparent window, NAIS  504  includes a grid  562  for forming an ionization volume similar to that discussed with regards to NAISs  204 - 404 . A potential may be established between the grid  562  and the membrane  518  to promote drift of ions toward aperture  522 . In some embodiments, the gas  534  is provided in short duration, high pressure pulses to form an instance of high pressure gas in an ionization volume. To generate ions, the pressure of the gas in the ionization volume should be high enough to form an efficient ionization cross-section. 
       FIG. 6  is an example illustration of a NAIS  604  in accordance with an embodiment of the present disclosure. The NAIS  604  is yet another example of a photon-induced NAIS that can be implemented in any of the systems  100 A through  100 C. In general, NAIS  604  generates ions using optical energy and provides the ions to ion optics for the formation of a focused ion beam for use in imaging, milling, ion induced etching and/or material deposition. Additionally, NAIS  604  is a variation of NAIS  404  in that a solid source gas precursor is used to provide the gas supply. However, instead of disposing the solid source gas precursor in a separate cell attached to one of the membranes, the solid source gas precursor of NAIS  604  is disposed between the two membranes. 
     The NAIS  604  includes first and second membranes  616 ,  618 , with second membrane  618  having an aperture  622 . The NAIS  604  further includes a solid precursor source  652  disposed between the two membranes  616 ,  618 . As described above gas precursors  624  from the solid precursor source  652  can be produced adjacent to the aperture  622 , which is illuminated with ionization energy to form ions. The ionization energy may be provided through the channel  619  formed between the two membranes and may be incident on the gas  624  adjacent to the aperture  622 . A potential established between the first and second membranes will induce ions to drift toward the aperture  622  for emission to ion optics  638 . 
       FIG. 7  is an illustration of NAIS  704  in accordance with an embodiment of the present disclosure. NAIS  704  is another example of an ion source that may be implemented in system  100 A- 100 C, for example. In general, the NAIS  704  includes a laser that crosses with a delayed version of itself in an area adjacent to aperture  722  to generate ions. By crossing the laser with itself, the ionization energy can be confined to the ionization volume adjacent the aperture  722  while the optical energy is less everywhere else. By reducing the energy everywhere else, the potential for damage to the NAIS  704  outside of the ionization volume is reduced or eliminated. While other components of the NAIS  704  are not shown, such as a gas source, a voltage source for providing a potential difference across the membranes, etc., such components are included in the NAIS  704  as needed and are not shown for brevity&#39;s sake. 
     One embodiment of the NAIS  704  includes an ionization optical source  730 , first and second membranes  716  and  718 , and an optical delay  766 . The ionization source  730  provides optical energy to beam splitter  764 , which splits the beam into two branches  776  and  778 . Branch  778  is directed toward the membranes  716 ,  718  through lens  768 , and branch  776  is directed toward delay  766 . Delay  776  includes two mirrors  772  and  774  for routing the optical energy of branch  776  back toward the membranes  716 ,  718  via lens  770 . In some embodiments, branch  776  may approach the membranes  716 ,  718  in a direction orthogonal to branch  778 . Of course, other orientations between the two branches at the ionization volume are possible and contemplated herein. The two branches  776 ,  778  enter the channel, e.g., gap, between the two membranes and interact with each other in a volume adjacent the aperture  722 , e.g., the ionization volume. The interaction, based on the delay, should be additive so that an optical intensity obtained is strong enough to induce ionization of a gas present in the ionization volume. 
     While the NAIS  704  shows one arrangement for the optics and delay, there are many other arrangements capable of providing the same optical result at the ionization volume, which are contemplated herein. It should be understood that the arrangement of NAIS  704  is not limiting. 
     The embodiments discussed herein to illustrate the disclosed techniques should not be considered limiting and only provide examples of implementation. In general, the techniques disclosed herein are directed toward photon-induced ion beams formed from localized ionization regions provided with a desired ionizing gas. Those skilled in the art will understand the other myriad ways of how the disclosed techniques may be implemented, which are contemplated herein and are within the bounds of the disclosure.