Patent Application
20060212977
This invention relates to electron beams, and more particularly to characterization of electron beams.
Electron beams (e-beams) are used in a variety of applications including certain computer memory devices, and e-beam lithography processing techniques. E-beam lithography is an etching process used in the production of some components of a semiconductor, superconductor, or other material. Using current techniques, a focused e-beam can have a diameter down to the order of nanometers or tens of nanometers. Such minutely focused e-beams are difficult to characterize and/or measure spatially or temporally.
In one aspect, e-beams are characterized or measured in e-beam based memory storage devices. Such e-beam characterizing or measuring devices may require an instrument to determine the location and spectral density of an e-beam. Increasing the precision with which the e-beam can be measured may improve the storage density of e-beam memory devices that can be incorporated into any given e-beam memory circuit. In another aspect, an improvement in the cross-sectional measurement and power can permit a more controlled application of e-beam to nano-scale workpieces such as semiconductor substrates. Accordingly, there is a need for improved techniques for characterizing an e-beam with the capability of being focused down to nanometer (or tens of nanometers) diameters.
The same numbers are used throughout the drawings to reference like features and components:
This disclosure provides a variety of embodiments of a nanowire electron-beam (e-beam) characterizing device 100. The e-beam characterizing device 100 performs a variety of metrology and calibration functions including measuring the dimensions of, and the intensity within, an e-beam. Certain embodiments of the nanowire e-beam characterizing device 100 are capable of characterizing, spatially or temporally, a focused electron beam whose diameter is on the order of nanometers or tens of nanometers. While this disclosure is directed to an “e-beam” characterizing device 100, ions (e.g., gas ions) could also be measured and characterized in a similar manner. As such, the term “e-beam” within this disclosure also applies to, and is intended to include, ion beams.
Certain embodiments of the nanowire e-beam characterizing device 100 can measure e-beam spot size and intensity. One embodiment of the nanowire e-beam characterizing device 100 as described in this disclosure is applicable to e-beam based storage devices that utilize an instrument that can measure in real time the X location or the X-Y location (depending on the embodiment) and/or stability of the centroid of the focused e-beam. The ability of the nanowire e-beam characterizing device 100 to measure the spatial profile (e.g., considering such factors as the e-beam location, the spot size stability, the centroid stability, and the current stability, etc.) can be utilized to enhance a memory scheme based on e-beam write, read, and erase processes. This is especially applicable with nano-scale devices since the present disclosure characterizes e-beams with nanowires.
The different embodiments of the nanowire e-beam characterizing device 100 include one or more nanowires 102 arranged in different configurations as described herein. In this disclosure, the term “nanowires” 102 is means to include nanowires, nanotubes, nanodots, and any other nanostructure having at least one dimension that is in the nano-scale (i.e., less than 100 nanometers). The configurations of the nanowires 102 in the nanowire e-beam characterizing device 100 include, but are not limited to, single nanowires 102, parallel (one dimensional) arrays of nanowires, rectangular arrays of nanowires, and arrays of nanodots as described in this disclosure.
Each one of the nanowires 102 that is included in the nanowire e-beam characterizing device 100 has a smaller width and/or pitch than the diameter of the focused electron beam. In one embodiment, a Faraday probe forms an active portion of the e-beam characterizing device. Faraday probes (not shown) are commercially available and include a current loop with a high permeability ferrite core in the center of the current loop. The Faraday probes provide an output indicative of the current produced by charged particles traversing, e.g., a chamber.
An electrically conductive nanowire, an array of individually addressable nanowires, or a crossed array of separated nanowires are used to measure electric current produced by the electron beam as the electron beam impinges on the nanowires. Each nanowire (whether in the single nanowire or the multiple nanowire array configuration) has a width that is a small fraction of the e-beam spot size which it is to characterize in order to effectively measure the e-beam impinging on the wire. This fraction of the e-beam spot size is a function of the level of accuracy for the measurements. The more accurate the measurement, the smaller the fraction should be. Conversely, the measuring device could actually be on the order of, or larger than the e-beam or the gas ion beam, in which case a deconvolution of the measured result would also be required.
One embodiment of the nanowire e-beam characterizing device 100 includes a single one of the nanowires 102. Other disclosed embodiments have a plurality of nanowires (arranged in arrays) and associated components.
The embodiment of nanowire e-beam characterizing device 100 shown in
The power source provides the voltage bias to collect the electrons. The electrometer 110 determines the electric current flowing through (or the electric voltage being applied across) the nanowire 102. The electric current flowing through the nanowire 102 is a function of the voltage that is applied across the nanowire 102 based on Ohm's Law. The current flowing through the nanowire 102 varies based on the number of electrons imparted from the e-beam to the nanowire.
An e-beam spot is illustrated as being scanned from left to right as shown in
The cross-sectional dimension of a nanowire is sufficiently small to function as a scanning slit. The current density profile, as the e-beam travels across the nanowire (or vice versa), can be mapped out as illustrated in
Single wire embodiments of nanowire e-beam characterizing devices 100 can effectively characterize the e-beam. Certain other embodiments of the nanowire e-beam characterizing device 100 that include, for example, arrays of nanowires can also be used. A variety of arrays of nanowires for the nanowire e-beam characterizing device 100 are therefore described in this disclosure that include, for example, parallel nanowires, crossed grids of nanowires, and arrays of nanodots.
One embodiment of the nanowire e-beam characterizing device 100 that includes two array sets 202, 204 of nanowires is illustrated in
For simplicity, the components 106, 108, and 110 shown in the embodiment of nanowire e-beam characterizing device 100 shown in
In one embodiment, the signal from each wire is monitored by an individual electrometer channel. In another embodiment, a plurality of the signals from each one of the multiple wires can be multiplexed using known electronic multiplexing systems that will not be further detailed herein. The combined data from each wire can be combined to produce a histogram of the current for each nanowire's X position. In this disclosure, the term “X” direction or position refers to the respective direction or position as taken along the horizontal axis as it appears on the paper. The term “Y” direction or position refers to the respective direction or position as taken along the vertical axis as it appears on the paper. As such, the terms “X” and “Y” are arbitrary when related to an actual product. In general, though, those embodiments having nanowires (and nanowire arrays) that are arranged only along a single axis are considered as extending along the Y axis and detect e-beam position and motion in the X direction.
Yet another embodiment of the nanowire e-beam characterizing device 100 is shown in
In the
Yet another embodiment of a nanowire e-beam characterizing device 100 includes a square grid array is illustrated in
In one embodiment of the nanowire e-beam characterizing device having the square grid 210, the individual nanowires from the array set 202 do not contact any of the individual nanowires from the array set 204. Instead, the crossing nanowires 102 are insulatively spaced apart from each other. The nanowires in one array set 204 of nanowires are separated a small distance from each wire of the array set 204 of the nanowires. This spacing of each nanowire in the array set 202 of nanowires from each nanowire in the array set 204 of nanowires can be maintained by, for example, a thin dielectric material or air space. This thin dielectric material can be fashioned as a sheet or strip that extends between the array set 202 and the array set 204. The crossing nanowires are thereby electrically isolated by an air space (not shown) in one embodiment that allows the electrons from the e-beam to physically contact both the horizontally extending nanowires in array 202, and the vertically extending nanowires in array 204.
Similarly, those embodiments of the nanowire e-beam characterizing device 100 that include nanodots 320 arranged in a square array as illustrated in
All of the embodiments of the nanowire e-beam characterizing devices 100 as described relative to
Certain disclosed embodiments of nanowire e-beam characterizing device 100 improve the time resolution of the measurement over so-called scanning knife-edge characterizing devices, one embodiment disclosed in U.S. Pat. No. 4,993,831 that issued on Feb. 19, 1991 to Vandenberg et al. (incorporated herein by reference). This improvement in certain embodiments of the present disclosure occurs by providing a plurality of nanowires, in an array, that can derive a precise one or two-dimensional image of an e-beam at any given time. In one embodiment, the disclosed embodiments of the nanowire e-beam characterizing device 100 have the ability to provide spatial stability information and current stability information simultaneously. Much of the improvement in the precision of the derived image and spatial stability in certain embodiments of the nanowire e-beam characterizing device 100 is due to the high spatial frequency of the nanowires and (nearly) simultaneous reading of the current values from the nanowires via an electrometer or other current measuring device. The spatial resolution of certain embodiments of the nanowire e-beam characterizing device 100 is a function of the width of the nanowires.
The substrate forms a platform on which the nanowire e-beam characterizing device 100 can be fabricated. In 704, a photosensitive layer is deposited on the substrate. The photosensitive layer is envisioned to be any layer, such as a polymer layer, that can be deposited the substrate which can be patterned. In 706, the photosensitive layer is patterned by applying a mold to the photosensitive layer. The remaining portions of the photosensitive layer following patterning are hardened. A variety of hardening techniques may be used depending on the type of imprint lithography used (such as thermal imprint lithography and step and flash imprint lithography). The patterning of the polymer layer is consistent with the configuration of the nanowire e-beam characterizing device 100.
Such materials as metals, semiconductors, and superconductors (of the desired conductivity) are deposited on both the imprinted portions and the non-imprinted portions of the photosensitive layer in 708. Those deposited active materials that are deposited in the imprinted portions of the photosensitive material to form an active layer. The height of the imprints of the photosensitive layer is thicker than the deposited active layer so that the deposited active layer is not continuous (the active layer within the imprinted portions of the active layer do not form a contiguous layer with the active layer above the non-imprinted portions of the active layer). The width of the active layer can be selected (down to the nanoscale) based on the dimensions of the imprinted portions of the active layer to provide the desired functionality.
In 710 as shown in
The active layer formed on the patterns formed in the photosensitive layer is then etched in 712. The etching can be performed for a duration sufficient to etch the active layer to a desired dimension. In certain embodiments, the active layer can be etched down to nanoscale dimensions. As such, this process allows patterning of the nanowire e-beam characterizing device 100 so certain portions of the active layer can be within the nanoscale within one or two perpendicular cross-sectional dimensions.
The controller or the computer 800 comprises a central processing unit (CPU) 852, a memory 858, support circuits 856 and input/output (I/O) circuits 854. The CPU 852 is a general purpose computer which when programmed by executing software contained in memory 858, becomes a specific purpose computer for controlling the hardware components of the processing portion 802. The memory 858 may comprise read only memory, random access memory, removable storage, a hard disk drive, or any form of digital memory device. The I/O circuits comprise well known displays for output of information and keyboards, mouse, track ball, or input of information. Such I/O circuits allow for programming of the controller or computer 800 to determine the processes performed by the process portion 802 (including the associated robot action included in the process portion). The support circuits 856 are well known in the art and include circuits such as cache, clocks, power supplies, and the like.
The memory 858 contains control software that, when executed by the CPU 852, enables the controller or the computer 800 that digitally controls the operation of the various components. In another embodiment, the computer or controller 800 can be analog. For instance, application specific integrated circuits are capable of controlling processes such as occur within the process portion 802.
Although the invention is described in language specific to structural features and methodological steps, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or steps described. Rather, the specific features and steps disclosed represents preferred forms of implementing the claimed invention.
