Patent Application
20160299103
1. Field
Various embodiments of the present invention generally relate to the non-mechanical contact probing of electronic devices and surface modification of devices and tissue. In particular, the various embodiments relate to application of electron-beam induced plasma probes for metrology and surface modification.
2. Related Arts
The ability to measure and apply voltages and currents on patterned structures without having to establish mechanical contact is of importance to the functional (electrical) testing of semiconductor devices and flat panel displays, e.g., liquid crystal and organic light emitting diode (OLED) displays, backplanes, and printed circuit boards, since non-mechanical contact probing minimizes the likelihood of damage to the device/panel under test and is also conducive to improved testing throughput.
Photon Dynamics', an Orbotech company, Voltage Imaging® optical system (VIOS) employs electro-optical transducers to translate the electrical fields on the devices under test into optical information captured by an optical sensor. Other techniques provide an indirect measurement of the voltage on the devices under test by means of secondary electrons and require the devices to be placed in vacuum. These approaches are mostly geared towards voltage measurements and still require mechanical contacts to pads on the periphery of the devices in order to drive the signals used for inspection.
The need for a non-mechanical probe emerged as a new class of current-driven devices such as OLEDs was developed. As opposed to voltage-driven devices such as conventional LCDs, the preferred way of testing OLED-based flat panel displays after array fabrication is by allowing a current to indestructively pass through the unsealed pixel electrode, especially in those OLED architectures in which the cell holding capacitance is small. A separate class of inspection methods based on conductive plasmas has recently emerged. The main concept behind these methods is that a directional plasma, which contains mobile secondary electrons besides stationary ions, may act as a non-mechanical contact probe. Several such “plasma probing” approaches have been proposed in the past. They may roughly be divided into two categories, one category being based on high intensity laser-induced ionization, which presents possible risks of laser-induced damage to the device under tests given the high ionization thresholds, and another category being based on high voltage corona discharges, in which ionized species have a wide range of scattering angles (little directional control) and also presents damage risks, especially related to arcing.
Electron beam imaging systems using membranes and differentially pumped apertures have been used to propagate e-beams into a gas ambient for electron beam characterization of live/wet specimens in scanning electron microscopes (SEM) or X-ray diffraction on live samples.
State-of-the-art electron-beam based inspection and registration systems used in semiconductor manufacturing mostly rely on secondary electron (SE) and/or backscattered electron (BSE) imaging in vacuum. This technology involves large vacuum enclosures and complex electron optics, leading to high system costs, large factory foot prints and potentially impacting throughput. Examples of electron beam applications used in semiconductor manufacturing include Voltage Contrast measurements using SE for via short inspection (at some process steps in the IC fabrication process), high aspect ratio feature (e.g. deep trenches and through-silicon vias (TSV)) imaging and sample registration with backscattered electrons.
In the previously filed PCT application number PCT/US2012/046100, an atmospheric plasma prober, for testing of flat panel displays is described. Further work led to the development of additional applications, detailed herein, that may use the same or a similar plasma prober.
The following summary is included in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below.
Various disclosed embodiments utilize electron-beam induced plasmas (eBIP) to establish a non-mechanical, electrical contact to a device of interest. This plasma source may be referred to as atmospheric plasma source and may be configured to provide a plasma column of very fine diameter and controllable characteristics. The plasma column traverses the atmospheric space between the plasma source into the atmosphere (through membrane or pinhole) and the device of interest and acts as an electrical path to the device of interest in such a way that a characteristic electrical signal can be collected from the device. Additionally, by controlling the gases flowing into the plasma column the probe may be used for surface modification, etching and deposition.
In various disclosed embodiments the electron beam and the generated plasma are used for multiple functions simultaneously or serially. For example, the electron beam is used both to generate and sustain the plasma and also to stimulate a sample of interest, e.g., to generate electron-hole pairs inside the sample. Then, the conductive plasma sustained by the driving electron beam is used to pass an electrical signal to an external measurement apparatus, thus providing a sensor for the amount of current generated by the stimulus of the electron beam. Using this method, stimulus and sensing is done in situ, i.e., the current is collected at the exact point where it is generated, forming a closed-loop operation.
According to disclosed aspects an atmospheric plasma apparatus is provided, comprising: a vacuum enclosure having an orifice at a first side thereof; an electron source positioned inside the vacuum enclosure and having an electron extraction opening; an extractor positioned at the vicinity of the extraction opening and configured to extract electrons from the electron source so as to form an electron beam and direct the electron beam through the orifice, wherein the electron bean is configured to have a diameter smaller than diameter of the orifice; an aperture plate positioned so as to cover the orifice, the aperture plate being electrically conductive and having a conductive line attached thereto, and wherein the aperture plate has an aperture of diameter smaller than the diameter of the electron beam such that the aperture plate reduces the diameter of the electron beam as it passes through the aperture; and, wherein the electron beam is configured to ionize the atmosphere as it exits the aperture so as to sustain a column of plasma.
According to further aspects, a method for performing voltage contrast imaging of a sample is provided, comprising: extracting an electron beam from an electron source in a vacuum enclosure; transmitting the electron beam from the vacuum enclosure into an adjacent ambient gas to thereby ionize gas molecules around the electron beam to generate a column of ionized species; scanning the electron beam over a selected area of a sample located opposite the entry point of the electron beam into the gas ambient; applying a voltage potential across the plasma so as to drive an electron current from the sample to a pick-up electrode; measuring the amount of electron current flowing between the pick-up electrode and the sample; and generating an image using the amount of electron current measured at each location on the selected area and displaying the image on a monitor. The method may further include a step of using the image or the measured current to detect defects in the sample.
According to other disclosed aspects a method is provided for performing dimensional registration using an electron-beam induced plasma probe, comprising: extracting an electron beam from an electron source in a vacuum enclosure; transmitting the electron beam from the vacuum enclosure in to an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species, thereby defining a plasma probe; scanning the plasma probe over a selected area of a sample located opposite the entry point of the electron beam into the gas ambient; applying a voltage potential across the plasma so as to drive an electron current from the sample to a pick-up electrode; measuring the amount of electron current flowing between the pick-up electrode and the sample; and using the measurement of the electron current to determine the vertical registration of the plasma prober. The method may further include measuring back scattered electrons scattered from the sample and using the measurement of back scattered electrons to determine lateral registration of the plasma probe, thereby providing three-dimensional registration. In some aspects the registration is used for performing LED, OLED or LCD Array testing.
According to yet further aspects, a method is provided for inspecting material composition profile of a sample using electron beam induced plasma probes, comprising: extracting an electron beam from an electron source in a vacuum enclosure; transmitting the electron beam from the vacuum enclosure in to an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species defining a plasma probe; scanning the plasma probe over a selected area of a sample located opposite the entry point of the electron beam into the gas ambient; applying a voltage potential across the plasma so as to drive an electron current from the sample to a pick-up electrode; measuring amount of electron current flowing from the pick-up electrode into the sample or vice-versa; de-convolving changes in the measurement of the electron current caused by topographical features of the sample; using the de-convolved changes in the measured electron current to determine changes in material composition of the sample.
In other aspects, a method is provided for measuring topography of a sample using electron-beam plasma prober, comprising: extracting an electron beam from an electron source in a vacuum enclosure; transmitting the electron beam from the vacuum enclosure in to an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species defining a plasma probe; scanning the plasma probe over a selected area of a sample located opposite the entry point of the electron beam into the gas ambient; applying a voltage potential across the plasma so as to drive an electron current from the sample to a pick-up electrode; measuring the amount of electron current flowing from the pick-up electrode into the sample or vice-versa; de-convolving changes in the measurement of the electron current caused by material composition of the sample; using the de-convolved changes in the measured electron current to determine changes in topography of the sample.
According to further aspects, a method for inspecting high aspect ratio structures, both vias (i.e., holes) and pillars, in a sample is provided. The vias maybe open unfilled holes or filled with other material. This method comprises: extracting an electron beam from an electron source in a vacuum enclosure; transmitting the electron beam from the vacuum enclosure in to an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species defining plasma probe; scanning the plasma probe over a selected area of a sample located opposite the entry point of the electron beam into the gas ambient; scanning the plasma probe over a selected area of the sample over the high aspect ratio structure; applying a voltage potential across the plasma so as to drive an electron current from the sample to a pick-up electrode; measuring amount of electron current flowing from the pick-up electrode into the sample or vice-versa; generating an image using the amount of electron current measured at each pixel over the selected area and displaying the image on a monitor. The measurement of the high aspect ratio feature may be performed by calibrating the produced signal with height or depth of the high aspect ratio feature to generate a measurement of the depth or height of the feature. The method may further include a step of detecting defects or process deviations in the inspected high aspect ratio structures based on the measured currents.
Other aspects provide a method for performing atmospheric electron beam induced current measurement of embedded defects in a sample, comprising: extracting an electron beam from an electron source; transmitting the electron beam from the vacuum enclosure in to an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species defining; scanning the electron beam over a selected area of the sample located opposite the entry point of the electron beam into the gas ambient so as to generate electron-hole pairs in the sample; using the column of plasma probe to collect current from the sample; and, measuring the amount of current flowing from the sample. The method may further include controllably injecting gas into the plasma.
According to further aspects, a method for neuron excitation is provided, comprising: extracting an electron beam having a defined diameter from an electron source; transmitting the electron beam from the vacuum enclosure in to an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species; directing the ionized species onto selected neurons.
A further aspect provides a method for 3D printing of metals, comprising: extracting an electron beam up to 10's of keV of energy having a defined diameter from an electron source; transmitting the electron beam from the vacuum enclosure into an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species defining a plasma probe; using the plasma to prepare a surface for applications; melting sputtered metal particles, fine metal powder or thin metal wire using the primary electron beam to deposit a layer based on a pre-designed pattern; repeating the process above to perform printing action over an extended area and multiple vertical layers. The electron beam may be scanned using electromagnetic lens or a moving stage. The 3D printing apparatus may be connected to and controlled by CAD capable computer. The method may include directing the ionized species over selected area of a printed sample to thereby adhere the additive elements to the printed sample.
According to yet further aspects, methods for treatment of live tissue are provided, comprising: extracting an electron beam having a defined diameter from an electron source; transmitting the electron beam from the vacuum enclosure into an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species; manipulating the lateral dimension of the electrons beam as it exist into the gas ambient; directing the plasma ionized species over selected area of the live tissue. The treatment may comprise one of therapeutic application, sterilization, decontamination, wound healing, blood coagulation, cancer cell treatment.
Other aspects include methods for modifying surface characteristics of a sample, comprising: extracting an electron beam having a defined diameter from an electron source; transmitting the electron beam from the vacuum enclosure in to an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species forming a plasma probe; manipulating lateral dimension of the electrons beam as it exist into the gas ambient; scanning the plasma probe over selected area of the sample so as to modify the surface characteristics of the sample. The surface modification may comprise one of ashing, etching, surface activation, passivation, wetting, and functionalization.
In any of the disclosed embodiments, the ambient gas may comprise air or a mix of one or more inert gasses. Also, transmitting the electron beam from the vacuum enclosure may comprise passing the electron beam via pinhole provided in an aperture plate separating the vacuum environment from the ambient gas. Transmitting the electron beam from the vacuum enclosure may further comprise passing the electron beam through a membrane prior to passing the electron beam through the pinhole. A voltage potential may be applied to at least one of the sample, the aperture plate or the membrane. The aperture plate or the membrane may comprise a pick-up electrode. The methods may further comprise the use of electron beam and/or plasma for sensing before interaction with or modifying the sample; then processing, interacting or modifying the sample, then sensing again after the processing, interaction or modifying the sample. As such, the methods establish closed-loop processing (sense-process-sense).
The accompanying drawings, which are incorporated in and constitute a part of this specification, exemplify the embodiments of the present invention and, together with the description, serve to explain and illustrate principles of the invention. The drawings are intended to illustrate major features of the exemplary embodiments in a diagrammatic manner. The drawings are not intended to depict every feature of actual embodiments nor relative dimensions of the depicted elements, and are not drawn to scale.
Various embodiments described below provide solutions based on a high resolution, high sensitivity, and compact atmospheric electron beam induced plasma probe technology. This technology essentially relies on the fact that the cold plasma (a few eV) generated by collisional ionization events driven by the electron beam in air acts as a non-mechanical conductive contact, allowing voltages on the devices under test (DUT) to be measured via the resulting secondary plasma electron current. As implied by the name, this technology does not require the DUT to be held in vacuum. Rather, only the electron emitter (cathode) and electron optics need to be kept in a vacuum enclosure. Furthermore, the implementation of this technology only requires simple electron optics configurations, e.g., an extraction grid and an electrostatic lens, keeping the gun cost low and its size, and hence the size of the enclosure, compact. The electron beam exits the vacuum enclosure containing the electron gun into the surrounding atmospheric environment either by means of a thin, electron transparent-membrane (made of, e.g., SiN, SiC, Be, etc.) and/or a microscopic pinhole subjected to differential pumping. The signal carried by the mobile secondary electrons in the plasma probe can be picked up by a conductive thin film (Ti, Cr, etc. of thickness less than 20 nm) applied to the side of the membrane facing the DUT or, in case a pinhole is used, the pinhole itself (assuming it is made of conductive material and isolated from the rest of the electron gun enclosure). From there, the signal is fed to the appropriate acquisition device, e.g. a high precision, high speed electrometer for further signal processing.
Without any loss of novelty or practicality of this invention, the spatial resolution required for the various applications listed below can be also achieved by using a small diameter e-beam emitter and highly focusing e-beam column. While this approach may add to the system cost, it still offers differential advantage over systems requiring vacuum and load-lock sample enclosures. The physics associated with the plasma probe to implement the applications described herein is independent of the method by which the final e-beam spot is generated.
However, the simplest approach to generate a high-resolution final e-beam spot is to aperture the output e-beam using a pinhole. This approach decouples the electron beam diameter from the beam energy, thereby reducing the need for high-end electron optics to achieve small and stable focal spots and offering more potential for system compactness. Moreover, the pinhole can serve as a biasing and signal collection electrode and it can allow the use of higher incident electron beam currents than a stand-alone membrane. Furthermore, an adequately thick pinhole can be sectioned into 4 isolated quadrants to allow for beam deflection control. This aperture can be implemented in such a way that it may be attached to the membrane, or on a secondary chamber.
The edges of the pinhole should be thick enough to stop the incident primary e-beam so that a top-hat beam profile is formed. This in turn produces a plasma probe with well-defined edges minimizing skin-depth and cross-talk from arrayed targets. Furthermore, the pinhole should be adequately smaller than the incident e-beam, as well have a conductive surface, in order to that it contacts the plasma “wire” produced on the air side of cathode chamber. It should also be substantially thick: (typically thicker than 50 micron) to allow for an enameled wire to be attached to its edge and to prevent charge accumulation. Finally, it should be electrically insulated from chamber body; i.e., it should not short to ground.
In order to better understand the various embodiments described below, a brief description of the atmospheric electron-beam induced plasma source will first be provided. Electron beams can provide efficient ionization of air or other gasses, and generate highly directional plasma columns with little risk of damage to the device under test (hereinafter alternatively referred to as structure under test). Electron beams also may provide control of the lateral size of the plasma probe, which is an important advantage for the measurement of electrical signals on small, high-density conductors on the device.
Upon entering the ambient gas, the electrons in the portion of the electron beam directed into the gas collide with the gas atoms and are deflected or lose energy through ionization. Thus, the portion of the electron beam that is directed into the gas induces a plasma 160 (hereinafter alternatively referred to as plasma probe) in the gas where the electron beam passes through it. Aside from slow gas ions, these electron-gas collisions create low-energy secondary electrons that are free to conduct. Therefore, voltages and currents may be measured or applied through the plasma. The plasma may then act as a non-mechanical contact electrical or plasma probe. Backscattered electrons are not used to carry the voltage or current signals in the plasma probe, but can be collected using an appropriate detector for added benefit of the invention.
Second conductor 180 may be coupled to an electrical measurement device 185 or a signal source 190. A data storage and system control block 198 controls testing routines and stores measured data and is coupled to inspection head 195, electrical measurement device 185, and signal source 190. The data storage unit within data storage and system control block 198 may be coupled to the measurement device and adapted to store a plurality of data values from measurement device 185. A control unit within data storage and system control block 198 may be coupled to the data storage unit, measurement device 185, and signal source 190. The data storage unit, measurement device 185, and signal source 190 may be responsive to the control unit.
As illustrated in
Voltage contrast is a failure isolation technique that is useful in isolating yield problems to a particular circuit or circuit block in IC fabrication. In the prior art voltage contrast measurements are performed by placing the sample in a vacuum chamber and charging the sample using an electron beam, following which the sample is imaged using secondary electrons. This is generally a two-step process and requires a high vacuum chamber and an elaborate electron beam source. Open vias, i.e., metal contacts that have no connection to ground, will retain the charge and appear differently on the secondary electron image than those that are connected to ground. In other words, open vias locally trap charge and change the surface voltage of the sample. This can be used, for example, to examine which contacts in an integrated circuit are closed and which are open.
According to one embodiment, a pinhole of several 10's of nanometer diameter is made using, e.g., lithographic technology. Using relatively short working distances between the pinhole and the DUT (10-50 microns), plasma beam diameters of 50 nm and less should be achievable, while retaining sufficient e-beam current to generate plasma signals of more than 10 pA. This combination of resolution and signal levels allows detecting defects in critical IC structures such as open gate contacts for example. Unlike conventional Voltage Contrast Imaging techniques, the e-beam induced plasma probe approach does not require a two-step measurement (pre-charging and probing) of the inspected via in order to determine whether it is open by modifying the secondary electron emission cross-section. The plasma probe can perform an open/short measurement in a single step by measuring the plasma current and comparing it to a golden reference, simplifying tool recipe and enabling throughput advantage (see
The testing can be performed by scanning the electron beam, and as a consequence the plasma column, over the sample. A bias potential is applied, such that electrons from the plasma are driven into the sample. The current flow from the sample is measured through a detector connected to the metallic aperture where the primary e-beam exits the apparatus. If the feature that is being scanned is electrically connected to the common ground, current will flow and the current reading will register at the detector. Conversely, if the feature being scanned is isolated, i.e., there is an open circuit, current will not flow and the current reading would register a different value at the detector. As the resistance of the open, or partially open circuit changes, different current would flow, such that a different current reading would be obtained. These current readings can be mapped to provide a voltage contrast image of the scanned area.
One example for such an arrangement is illustrated in
Additionally, in
Note that under the appropriate sample bias, the plasma current can be up to two orders of magnitude larger than the incident e-beam current. This is due to the fact that a single electron in the primary e-beam current, which typically has an energy in the 5-50 keV range, undergoes a cascade of multiple random inelastic collisions, producing many secondary electrons that are sufficiently mobile to carry the plasma signal along the entire length of the probe (typically less than a few 100 microns). The plasma current can be further boosted by using a local noble gas environment (Ar, Ne, . . . ), which leads to higher ionization rates. On the other hand, with He, for example, smaller plasma diameters, i.e., higher resolutions down to several nanometers should be achievable. The trade-off between probe resolution and conductivity can be pre-engineered in a stable manner by flooding the working space between the entry point of the electron e-beam and sample with a suitable gas mixture for a given application.
As can be appreciated, since the plasma prober can be used to perform voltage contrast inspection in an atmospheric environment, without requirement for the inspected substrate to be in vacuum, the tool according to this embodiment may be integrated into a processing tool, rather than being a stand-alone tool. For example, the plasma prober may be integrated onto an etcher or CMP tool to perform inspection immediately after processing of the wafer is completed. Additionally, the plasma prober may be installed in the front end, also called mini-environment, of a cluster tool used to process integrated circuits, e.g. for pre-mapping or alignment purposes.
Moreover, the achievable resolution of the plasma probe can be much higher than that of a conventional voltage contrast measurement system. This is because, at least in part, the lateral size of the plasma probe relative to that of the structure under test needs to be small enough to detect the differential signal between the structure and the surrounding background. Since the Signal-to-Noise-Ratio (SNR) of the plasma current is very high, the plasma probe can be quite large, i.e., having a large diameter or footprint, compared to the structure under test. Thus, the effective resolution can be reduced down to about 5 nanometers while using a plasma probe of much larger lateral size. On the other hand, secondary electron imaging as used in conventional voltage contrast measurement systems requires the incident electron beam to be smaller than the size of the structures being probed.
Furthermore, since the plasma probe does not require separate platform and vacuum, its throughput can be much higher than a standard stand-alone tool. Also, it requires a single-step illumination and imaging, while standard tools require a two-step pre-dosing and imaging process.
E-beam induced plasma probes currents are very sensitive to the separation between the pick-up electrode and the device under test. Preliminary laboratory tests demonstrated sub-micron sensitivity, but much better sensitivity can be achieved with better current detectors. The dependence of the probe column resistivity on the separation is a combination of the plasma sheath effect and the sheer Ohmic resistance due to the finite mean-free-path of the secondary electron carriers in the probe. Therefore, electron beam-induced plasma probes can be used to image and inspect high aspect ratio semiconductor features such as deep trenches and Through-Substrate (or silicon) Vias (TSV); see
The HAR structure may be inspected using a set-up similar to that illustrated in
Electron beam induced plasma probes offer the unique capability of 3-D registration (see
Since backscattered electrons (BSE) have enough energy (keV range) to propagate in atmosphere over the working distance, full 3-D registration can also be facilitated by complementing the plasma current measurements with BSE data from BSE detector 181, illustrated in
The 3-D registration capability is important for any application in which it is critical to maintain a precise gap to the sample, e.g., semiconductor wafer, and helps eliminate dependence on knowledge of wafer or glass placement on the chuck. Additionally, plasma probes should provide better Z-sensitivity than the optical sensors that are typically used in high-end sample stages. Therefore, not only do inspection and imaging applications based on e-beam induced plasma probes do not require a separate registration capability; e-beam induced plasma probes may also be used as stand-alone registration capability for other applications, especially when Z-registration is important, as in flat panel inspection, profilometry, and as pre-aligner in e-beam load lock systems. This 3-D registration system can be integrated into a feedback loop to provide real-time gap control.
It should be emphasized here that unlike electron beam imaging, where the electron beam diameter must be much smaller than the feature size in order to properly register the feature, using the embodiment disclosed herein the probe diameter, i.e., the diameter of the plasma column, need not be smaller than the feature size. This is because the image is not formed using secondary or back scattered electron from the sample, but rather using current attenuation. Thus, even if the plasma column is larger than the feature size, a change in plasma current measurement indicating the edge of a feature, can still be detected when traversing said feature with the plasma probe by virtue of the high SNR of the plasma current. Thus, features much smaller than the diameter of the plasma column can be imaged.
As noted above, measuring the current flowing from the plasma into the sample can provide image of the sample. Changes in the image, i.e., in the measured current, are caused by convolution of topography changes and material changes (e.g., different materials having different compositions, thereby different impedances). On the one extreme, if the sample is of pure and uniform material composition, the resulting image would reflect changes in topography only. Conversely, if the sample is perfectly flat, but has areas of non-uniform material composition, the image would reflect changes in material composition only (e.g., changes in grains or doping). Note that the image is not resolution dependent, but rather sensitivity dependent, i.e., so long as the probe can detect changes in the current, the prober can generate a high resolution image even with a relatively low resolution (e.g., large footprint). This utility of the plasma probe resistance mapping lends itself to applications in metal lines metrology, doping metrology and protrusion defects, to name a few. A combination of compositional and topographical changes may also be discerned if the collected signal can be de-convolved with the aid of a model for the samples under test using certain algorithms.
For example, one may calibrate the prober using a sample of known uniform material composition and known topography. Then the prober can be used to inspect other samples and compare to the “golden sample” to determine the material composition uniformity of the scanned sample. Conversely, the variation in topography can be mapped by similarly de-convolving the signal generated from the topography and the material impedance. Other calibrations and algorithms can be used to de-convolve a signal generated from a mixed material/topography change. For example, if the spatial scale of the signal change or the level change of the signal is outside a certain expected range, the change of the signal can be interpreted as one over the other.
EBIC is another isolation technique which can provide more precise failure location information, typically down to 500 angstrom resolution. It is particularly powerful when performed using a probe station in an SEM. In addition to providing fine fault location resolution, EBIC has the benefit of being non-destructive with respect to the electrical and physical characteristics of the fault region.
EBIC is a technique used for buried defect inspection in semiconductor devices. The electron beam is used to stimulate the sample and generate electron-hole pairs in p-n or Schottky junctions present in the device under test, resulting in a current. In conventional EBIC, the incident electrons are generated in vacuum by means of a Scanning Electron Microscope (SEM) and the current generated in semiconductor junction is collected via physical probes at the periphery of the device. See, e.g., H. J. Leamy, “Charge Collection scanning electron microscopy,” Journal of Applied Physics, V53(6), 1982, P. R51. On the other hand, with e-beam induced plasma probe technology, the primary electrons in the probe can be used to excite the electron-hole pairs and the plasma can be used as a conductor to collect and sense this current. Thus, the probe is utilized both as stimulus and sensor.
The plasma probe presented in this invention provides better implementation of the traditional EBIC techniques. First, EBIC with electron-beam induced plasma probes can be performed in air or a controlled gas mixture in the working distance, providing advantages in system configuration, cost and throughput over SEM-based EBIC. Second, the plasma probe is more sensitive to the EBIC signal fluctuation since the current from the sample is sensed directly in-situ by the plasma probe and does not have to travel through the entire sample to probe contacts (as is the case with the conventional implementation of EBIPP, especially in large samples such as Si wafers). As such the plasma probe sensitivity to buried defects will be larger than in SEM-EBIC, especially for weak semiconductors or even for some insulators.
The example illustrated in
Some applications require selective surface modifications. For example, in some application selective ashing or etching is needed. Other applications entail surface activation, passivation, wetting, functionalization or any other form of plasma-assisted surface interaction including but not limited to chemical and physical interaction. Conventionally this is achieved by means of a mask (including lithographically defined masks) covering the areas that are not to be modified, while exposing the areas to be modified, e.g., ashed, etched or modified in any of the ways aforementioned. Plasma is then provided over the entire wafer, such that the mask provides selective contact of the plasma with selective areas of the wafer.
Electron beam-induced plasma probes offer the capability of performing this spatially selective processing without masks (see
According to one embodiment, the plasma column is used for edge shunt, detection, isolation and removal in solar cells. Specifically, the primary electron beam and the plasma it induces is scanned around the edge of the solar cell so as to remove the conductive layer and thereby isolate the potential shunt. The e-beam driven plasma probe can perform a closed-loop operation to treat solar cell shunts. The e-beam induced plasma probe can be used to map the impedance response after flashing a solar sample to identify shunt areas and to detect shunts based on the measured impedance. Shunt sensing can also be performed by e-beam excitation of the solar sample and measuring the electrical or optical response of the sample, otherwise known in the prior art as Electro-luminescence or Photo-luminescence, respectively. After shunt sensing, the e-beam driven plasma probe can isolate the shunt, ablate the shunt with e-beam or etch it with the generated plasma. Sensing of the resulting treatment can then be performed and the shunt treatment process can be repeated as necessary. The advantage of the e-beam driven plasma probe over existing art (e.g., laser treatment) is the closed-loop and all-in-one operation along with the spatial selectivity of the plasma probe.
Embodiments described herein utilize plasma creation by e-Beams with energies in the keV range. Gas mixtures can be introduced in the space between source and sample and ionized by the e-beam, providing a wider range of reactive chemistry.
Electron beam-induced plasma probe technology has a number of advantages over other technologies used for plasma-assisted surface modification. For instance, with electron beam-induced plasmas, there is no risk of contamination, as opposed to what may occur with DC discharge plasma-based systems, in which the electrode can evaporate. In general, electron-beam induced plasmas involve much lower temperatures than DC discharge plasmas since the energy of the plasma electrons at the target is on the order of a few eV. Moreover, no air flow is required to convey electron-beam-induced plasmas to the target (since the plasma follows the direction of the primary beam), as opposed to RF discharge-induced plasmas or plasma jets.
The lateral dimension of the e-beam incident in the ionizing medium, and hence that of the resulting plasma, can be scaled down to one micron or lower by means of hard apertures or by focusing the beam using the appropriate electron optics elements. This implies that electron beam-induced plasmas enable spatially selective surface modifications with submicron resolution. Such resolutions are not possible with the other plasma-assisted surface modification methods since aperturing (masking) beyond a certain limit will lead to catastrophic turbulent flow and would significantly limit the efficiency of the plasma or destroy the substrate under treatment. To our knowledge, the existing resolution of the concurrent gas-backed atmospheric plasma technology is not better than 1 mm. The high resolution capability of electron beam-induced plasma probes make them a good candidate for (subtractive) maskless patterning applications as used, e.g., in MEMS, in-situ patterning on polymer surfaces and 3D printing.
Electron beam-induced plasmas can be tuned over a wide range of parameters (beam current, spot size, energy, ambient gas, working distance, etc. . . . ). As a consequence, electron beam-induced plasma probes can be used in a number of different ways. For instance, by setting the parameters of the electron beam-induced plasma appropriately, the plasma probe can be configured to either sense or perform a process. This could allow the probe to be used for surface composition sensing, followed by surface modification and subsequently for post-process sensing to assess the impact of the modification. This in-situ sensing capability in turn should allow closed loop processing—substrates do not need to be taken out of the processing tool for metrology, reducing contamination, improving yield and allowing for the development of more efficient process recipes. Furthermore, different gas ambients can be used to allow different surface reaction chemistries. Moreover, both the plasma and the primary beam can be operative to modify the surfaces, giving access to processing powers ranging from a few to hundreds of Watts.
Owing to the micron-level resolution, the plasma probe can be used for metal deposition in high-resolution 3-D printing applications, as illustrated in
The plasma probe can be also used as an in-situ sensor for post printing verification. This provides a closed-loop printing function. The e-beam operating parameter space for melting and sensing are different, as one might expect. For example, the beam current used for printing should be adjusted to provide for uniform thermal dose deposition on metal to insure uniform melting and adhesion rate, while the sensing action is done at smaller current enough to merely drive a conducing non-mechanical contact (plasma) probe to the surface. This action can be repeated point-by-point or line-by-line either by scanning the e-beam or by a moving stage where the printed sample is placed. An extended layer can then be formed and layers can be stacked vertically to complete the 3D printing function.
The most likely embodiment of a 3D printing device based on this invention is one in which the e-beam printing head is controlled by a computer that can load Computer Aided Drawing (CAD) designs with standard format and implement them. The e-beam printing head can be used as a stand-alone or complimentary head to another 3D printing head that uses conventional, state-of-the-art 3D printing techniques; e.g. plastic fused deposition or laser melting. A further advantage of the atmospheric e-beam system is that it can perform additive printing per the above description as well as subtractive printing, since the e-beam can be used to perform high-resolution ablation over small areas, especially with non-metallic materials.
The properties of electron beam induced plasma probe, specifically their low temperature, high resolution and tunability (to sensing or processing conditions), make them uniquely suited for therapeutic applications such as sterilization and decontamination (e.g. in oxygen atmosphere), blood coagulation and wound cauterization (healing), as well as cancer cell treatment. Other applications include dendrite and neuron probing, for which spatial selectivity is an important property.
For example, in one application a wound is treated by injecting oxygen around the wound and scanning the wound with the electron beam. The generated oxygen-gas plasma helps in sterilization and decontamination of the wound.
In the foregoing specification, specific exemplary embodiments of the invention have been described. It will, however, be evident that various modifications and changes may be made thereto. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. Various features and advantages disclosed in the specification may be described as follows.
In general, an atmospheric plasma apparatus is disclosed, comprising: a vacuum enclosure having an orifice at a first side thereof; an electron source positioned inside the vacuum enclosure and having an electron extraction opening; an extractor positioned at the vicinity of the extraction opening and configured to extract electrons from the electron source so as to form an electron beam and direct the electron beam through the orifice, wherein the electron beam is configured to have a diameter smaller than diameter of the orifice; a membrane or aperture plate positioned so as to cover the orifice, the surface of membrane or aperture plate being electrically conductive and having a conductive line attached thereto, and wherein the aperture plate has an aperture of diameter smaller than the diameter of the electron beam such that the aperture plate reduces the diameter of the electron beam as it passes through the aperture; and, wherein the electron beam is configured to ionize the atmosphere as it exits the aperture so as to sustain a column of plasma. The apparatus may further comprise one or more of the following: an electrical insulation member configured to electrically isolate the aperture plate from the vacuum enclosure, a membrane positioned between the aperture plate and the first side of the vacuum enclosure, a differential pumping chamber attached to the first side of the vacuum enclosure and wherein the aperture plate is attached to a lower portion of the differential pumping chamber, an electrostatic lens situated inside the vacuum enclosure. The aperture plate may comprise a plurality of electrically isolated sectors, each coupled to a respective conductive line.
Also, a method for performing voltage contrast imaging of a sample is disclosed, comprising: extracting an electron beam from an electron source in a vacuum enclosure; transmitting the electron beam from the vacuum enclosure into an adjacent ambient gas to thereby ionize gas molecules around the electron beam to generate a column of ionized species; scanning the electron beam over a selected area of a sample located opposite the entry point of the electron beam into the gas ambient; applying a voltage potential across the plasma so as to drive an electron current from the sample to a pick-up electrode; measuring the amount of electron current flowing between the pick-up electrode and the sample; and generating an image using the amount of electron current measured at each location on the selected area and displaying the image on a monitor.
Another method disclosed is for performing three dimensional registration using an electron-beam induced plasma probe, and comprising: extracting an electron beam from an electron source in a vacuum enclosure; transmitting the electron beam from the vacuum enclosure in to an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species defining a plasma probe; scanning the plasma probe over a selected area of a sample located opposite the entry point of the electron beam into the gas ambient applying a voltage potential across the plasma so as to drive an electron current from the sample to a pick-up electrode; measuring the amount of electron current flowing between the pick-up electrode and the sample; measuring back scattered electrons scattered from the sample; using the measurement of back scattered electrons to determine lateral registration of the plasma probe; and using the measurement of the electron current to determine the vertical registration of the plasma prober. The method may further comprise using prior knowledge of at least one of material composition and topography of the sample for more accurate registration. Three dimensional registration using electron beam induced plasma probes may be used as registration capability in conjunction with electron beam induced plasma probe based processing or measurement applications or as registration capability in conjunction with LCD Array testing using a voltage imaging optical system. The lateral dimension of the electron beam induced plasma may be larger than that of the registration features.
A further method disclosed is for inspecting a sample using electron beam induced plasma probes, comprising: extracting an electron beam from an electron source in a vacuum enclosure; transmitting the electron beam from the vacuum enclosure in to an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species defining a plasma probe; scanning the plasma probe over a selected area of a sample located opposite the entry point of the electron beam into the gas ambient; applying a voltage potential across the plasma so as to drive an electron current from the sample to a pick-up electrode; measuring amount of electron current flowing between the pick-up electrode and the sample; de-convolving changes in the measurement of the electron current caused by the sample; using the de-convolved changes in the measured electron current to determine at least one of: changes material composition and changes in topography of the sample. The method may further comprise using prior knowledge of material composition of the sample to determine topography. The method may further comprise: measuring the amount of electron current flowing from the plasma into the sample or vice-versa; de-convolving changes in the measurement of the electron current caused by topography of the sample; and using the de-convolved changes in the measured electron current to determine changes in material composition of the sample.
The above methods may further comprise passing the electron beam through a diameter limiting aperture prior to scanning the electron beam. Also, the methods may further comprise applying bias to the sample and the diameter limiting aperture.
Another disclosed method is for edge shunt detection, isolation and repair in a solar cell, comprising: extracting an electron beam from an electrons source; and exciting the solar sample with the e-beam and measure the sample optical and electrical response. The method may comprise maintaining plasma using the e-beam to generate a plasma probe and measuring impedance of the solar cell locally using the e-beam plasma probe, and detecting shunts based on the measured impedance. The method may further comprise scanning the electron beam over peripheral area of the solar cell so as to ablate or remove material at the peripheral edge of the solar cell at the location of the detected shunt.
Also, a method for modifying surface characteristics of a sample is disclosed, comprising: extracting an electron beam having a defined diameter from an electron source; transmitting the electron beam from the vacuum enclosure in to an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species forming a plasma probe; manipulating lateral dimension of the electrons beam as it exist into the gas ambient; and scanning the plasma probe over selected area of the sample so as to modify the surface characteristics of the sample. The surface modification may comprise one of ashing, etching, surface activation, passivation, wetting, and functionalization. The method may further comprise using precursor gasses to modify surface chemistry of the sample.
Another method disclosed is for treatment of live tissue, comprising: extracting an electron beam having a defined diameter from an electron source; transmitting the electron beam from the vacuum enclosure into an adjacent gas ambient to thereby ionize gas molecules around the electron beam to generate a column of ionized species; manipulating the lateral dimension of the electrons beam as it exist into the gas ambient; and directing the plasma ionized species over selected area of the live tissue. The treatment may comprise one of therapeutic application, sterilization, decontamination, wound healing, blood coagulation, cancer cell treatment.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US14/58899 | 10/2/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61886625 | Oct 2013 | US |
