Nanoprobes and method of testing electronic devices

Abstract

A nanoprobe, nanoprobe system, and methods of making measurements on devices using signals in the GHz range. The signals are made through a nanoprobe having an ultrasharp tip. Improved properties are delivered through enhanced, space-efficient shielding and system geometry. The probe tip may be angled and a trapezoidally-shaped circuit board containing electronic circuitry such as switches and amplifier can all be contained within a vacuum chamber in a multiple probe (typically 8 probe) system. The nanoprobe may be connected to the circuit board via an electrical snap connector.

Description

[0001] Nanoprobes and Method of Testing Electronic Devices

[0002] Related Applications

[0003] This application claims the priority benefit of United States Provisional Patent Application Ser. No. 63 / 713,024 filed 28 October 2024.

[0004] Introduction

[0005] Electronic circuits continue to get smaller and denser. Thus, there have been extensive efforts to develop nanoprobes for rapidly testing integrated circuits with high frequency signals. Numerous measurements can be made, often simultaneously, from closely spaced sites. There is a large patent literature describing nanoprobes; for example, US7659742, US8717053, US5512838, US2003173944, US2023168274, US2004164752, US2002229091, US2018335476, US2004211589, US2011140729, US2005052192, US2008149848, US2013119999, US2018246166, CN117949767, US2021270891, US2024255556, US6856129, US2022334144, US2003195713, US6573738, US2012306522, US6028423, JP2004279359, US2012306522, US2009167332, and US5274336.

[0006] Currently, nanoprobes (very sharp conductive wires) are used to test electrical devices with nanometer-scale features using direct current (DC) and alternating current (AC) up to about 300 megahertz (MHz) for low resistance devices using significant signal conditioning. Beyond that frequency, nanoprobes no longer function adequately because, among other reasons:

[0007] 1. They are unshielded, and the signal may be degraded by the escape of electrical signals from the core conductor or by the addition of signals to it, and

[0008] 2. They may act as an antenna and interfere with signal measurement on surrounding probes (“crosstalk effects”),

[0009] 3. They are prone to inherent system impedance, capacitance, and inductance which restrict and distort the signal.

[0010] As a result, failures that can only be detected at frequencies greater than 300 MHz go undetected. Since the clock speed of state-of-the-art chips is up to about 6.5 gigahertz GHz, many such undetectable soft failures are possible. As a result, there is a need for new and novel nanoprobes to test advanced electronic devices and integrated circuits using (AC) at ultra-high frequencies in the GHz range.

[0011] Summary of the Invention:

[0012] In one aspect, the invention provides a probe comprising: a conductive wire having a length of at least 0.5 cm (preferably at least 1 cm, or in the range of 1 to 7 cm or 1 to 4 cm) and an apex having a diameter of curvature of 50 nm or less; wherein the conductive wire comprises a straight section and an apex section and a bend having an angle of at least 10° disposed between the straight section and the apex section; a shielding disposed around the straight section; and a tapered shielding disposed around apex section wherein the tapered shielding is narrowest near the apex and the shielding ends at least 1 pm, or at least 10 pm, or at least 1 mm, or at least 2 mm prior to the apex, or in the range up to 5 mm or up to 3 mm.

[0013] In another aspect, the invention provides a nanoprobe, comprising: a conductive wire having a length of at least 1 cm (preferably at least 2 cm, or in the range of 1 to 10 cm or 1 to 5 cm) and an apex having a diameter of curvature of 50 nm or less; a shielding disposed around the conductive wire; a coaxial connector attached to an end of the conductive wire that is opposite the apex; a shielded circuit board electrically connected to the conductive wire through the coaxial connector; wherein the circuit board comprises a radio frequency amplifier where the distance to the apex is 30 mm or less, or 20 mm or less, or in the range of 10 mm to 30 mm.

[0014] In a further aspect, the invention provides a nanoprobe, comprising: a conductive wire having a length of at least 1 cm (preferably at least 2 cm, or in the range of 1 to 10 cm or 1 to 5 cm) and an apex having a diameter of curvature of 50 nm or less; a shielding disposed around the conductive wire; a shielded circuit board electrically connected to the conductive wire; wherein the circuit board comprises a radio frequency amplifier disposed between two MEMs switches.

[0015] In another aspect, the invention provides a nanoprobe, comprising: a conductive wire having a length of at least 1 cm (preferably at least 2 cm, or in the range of 1 to 10 cm or 1 to 5 cm) and an apex having a diameter of curvature of 50 nm or less; a shielding disposed around the conductive wire; a shielded circuit board electrically connected to the conductive wire; wherein the circuit board comprises a radio frequency amplifier. In still another aspect, the invention provides a nanoprobe, comprising: a conductive wire having a length of at least 1 cm (preferably at least 2 cm, or in the range of 1 to 10 cm or 1 to 5 cm) and an apex having a diameter of curvature of 50 nm or less; a shielding disposed around the conductive wire; a shielded circuit board electrically connected to the conductive wire; wherein the circuit board comprises a radio frequency amplifier and two switches; wherein the board has a trapezoidal shape with a first side perpendicular to the conductive wire and a second side perpendicular to the conductive wire; wherein the first side is closer to the apex than the second side; wherein the first side has a first length and the second side has a second length and wherein the second length is at least 10% (preferably at least 20% or at least 30% or at least 50%) larger than the first length; and a tapered shield disposed around the circuit board wherein the tapered shielding is narrowest near the apex.

[0016] The invention also includes an imaging system to guide the needle probe apex to the device under test. Preferably a scanning electron microscope, in which the probes and the device under test will be inside a vacuum. The invention also includes methods of testing devices by sending and / or receiving signals through any of the apparatus described here.

[0017] In a further aspect, the invention provides a method of measuring performance of an integrated circuit, comprising: passing a signal having a frequency of at least 1 GHz into the integrated circuit; and detecting the signal through the nanoprobe (or probe tip) of any of the above, or passing a signal having rise and fall times of less than 1 nanosecond (10‘9seconds) into the integrated circuit; and detecting the signal through the nanoprobe (or probe tip) of any of the above.

[0018] An apex having a diameter of curvature of 50 nm or less is a preferred feature of the invention; however, in any of the invention concepts, the apex can have a larger apex such as 500 nm or less, 300 nm or less, 100 nm or less, and / or down to 1 nm or 2 nm or 5 nm or 10 nm.

[0019] Any aspects of the invention can be further characterized by one or any combination of the following: the trapezoid preferably has a length of 1 to 10 cm, or 2 to 5 cm; the first length is preferably in the range of 1 to 8 cm; or 2 to 6 cm; the needle probe is removeable from the circuit board (for example via an electrical snap connection or the like), which allows the probe to be changed without discarding the electronics; where the bend angle is at least 20° or in the range of 20° to 50° or in the range of 20° to 40°; wherein the ength of the apex section is in the range of 1 to 5 mm or 2 to 4 mm; wherein the tapered shielding is a continuous taper or a stepped taper; wherein the tapered shielding varies in thickness from 2 mm to 1 pm or down to 10 nm; wherein the tapered shielding is comprised of a dielectric material inside of a tapered metallic shell; wherein the tapered shielding is comprised of a tapered dielectric that is coated with a metal layer; further comprising electronic circuitry capable of routing and amplifying an electrical signal that enters or exits through the needle apex; wherein the electronic circuitry comprises one or more switches located close to the probe apex that allow the nanoprobe to utilize: direct electrical current, alternating electrical current with a low impedance (50 Ohm or less) output, and alternating electrical current with a high impedance (1 Megaohm or greater) output; wherein the nanoprobe electrical circuitry has an amplifier which is used to convert a low current signal (100 or less, 50 or less, 20 or less (optionally in the range of 10 to 109or 10 to 106) femtoamps) to a robust output (1 or more, or 10 or more milliamps), which generates a robust signal from a delicate one; wherein the entire needle, except the sharp apex, and the conductive pathway through the probe device is shielded with electrical coax or shielding; wherein the cross section of the entire shielded needle has a diameter of 1.6 mm or less; wherein the nanoprobe assembly is built such that the nanoprobe tip apex of up to 8 probe assemblies is, or is adapted to be, brought into proximity with one another inside a circle whose radius is 500 nm or less; and / or further electronics to create and measure GHz frequency electrical signals.

[0020] Properties of the invention typically include the following characteristics:

[0021] 1. They deploy and measure high bandwidth signals, which differ from passive probes that are typically used only up to about 300 MHz. The nanoprobes can utilize one GHz and higher range frequencies (for example at least 1 or at least 2 or at least 3 or at least 4 or at least 5 GHz and optionally up to 20 or 30 or 40 or 50 or 60 or 100 GHz) that are crucial when working with high-speed digital signals or RF applications.

[0022] 2. They have amplification integrated into the probe system to improve signal strength and help measure faint signals. They require power inputs to run these electronics.

[0023] 3. They support differential measurements, which allows the measurement of voltage differences between two points without a direct connection to the ground.

[0024] 4. They have controllable input impedance across a wide frequency range and reduce loading effects that distort measurement signals. 5. They have low input capacitance, which minimizes the circuit’s impact on signal integrity, preferably 5 picofarads or less, or 2 picofarads or less, or 0.5 to 2 picofarads.

[0025] Glossary:

[0026] “Probe apex,” indicates the end of the point.

[0027] “Probe tip” indicates a region from the probe apex to a distance, such as 500 nm or another specified distance, away from the probe apex along the probe's longitudinal axis.

[0028] “Diameter of curvature” is typically determined by measuring the diameter of the largest circle that fits into the tip adjacent to the apex of a probe. The radius is half of the diameter. The tip dimensions are taken from an electron micrograph image of the probe tip. In cases where it is not clearly apparent, or where there is a reasonable dispute, the diameter of curvature is to be obtained by the method of Watanabe et al., U.S. Pat. No. 8,621,660, incorporated herein by reference.

[0029] Scanning probe and electron microscope (SPEM) probes are used in a device to interact with a surface. Examples include, but are not limited to, nanoprobers used in semiconductor circuit failure analysis, scanning probe microscopes such as scanning tunneling microscopes or atomic force microscopes, or any device wherein a probe tip interacts with a surface.

[0030] The phrase “tips that are substantially oxide free as characterized by having less than 5 nm of oxide as imaged by TEM” refers only to the section of the probe that is within 500 nm of the apex.

[0031] As is standard patent terminology, the term “comprising” means “including” and does not exclude additional components. Any of the inventive aspects described in conjunction with the term “comprising” also include narrower embodiments in which the term “comprising” is replaced by the narrower terms “consisting essentially of’ or “consisting of.” As used in this specification, the terms “includes” or “including” should not be read as limiting the invention but, rather, listing exemplary components.

[0032] Brief Description of the Figures:

[0033] Fig. 1 shows a comparison of frequency response (in Hz) of an unshielded probe and a shielded (coaxial) probe. Fig. 2 schematically illustrates a nanoprobe system. The switches are illustrated inside the vacuum chamber but some or all of the switches could be either inside or outside the vacuum chamber.

[0034] Fig. 3 schematically illustrates an active probe assembly including coaxial shielding around the nanoprobe wire and unshielded probe apex.

[0035] Fig. 4 shows features of the nanoprobe and electrical interface. The top of this figure shows a cross-sectional view of the electrical receptacle comprising a large through-hole receptacle to contact the probe shield and a small closed-pin receptacle to contact nanoprobe wire. The closed- pin receptacle is held in place by a formed or machined insulating material that also isolates the pin from the interface’s outer metallic shell. The bottom of this figure shows the nanoprobe with coaxial shield inserted into a coaxial electrical interface.

[0036] Fig. 5 shows a diagram of a multifunctional circuit board attached to a nanoprobe.

[0037] Fig. 6 is experimental data showing S12 transmission factors for two separate amplifiers as a function of frequency.

[0038] Fig. 7 is a photograph of three probes. The top and bottom probes are shielded.

[0039] Detailed Description of the Invention:

[0040] Transmission line factors

[0041] The first two problems identified above relate to the hardware used to transmit signals. With nonideal signal transmission, the signal -to-noise necessarily degrades. Additionally, non-ideal signal transmission can induce noise in the form of ringing or cross-talk. One solution to these problems is to use coaxial (coax) electrical lines, which means a concentric line with a center conductor, a width of insulator such as vacuum or non-conductive material, and an outer shell of conductor that is connected to an effective ground to act as a shield.

[0042] At GHz signal frequencies, the wavelength ( ) of the propagating AC wave is on the order of 1 cm to 15 cm, near to the length of an unshielded probe. To first order, the losses will be proportional to l / , where I is the length of exposed wire and X is the wavelength of the propagating electric field, with a rule of thumb being that deleterious effects start to appear at / >2i / 10. With A. being proportional to c' / f, where c' is the speed of light through the conductor (approximately 1.5xl08m / s) and f is the frequency of the signal being transmitted (for example 1x109 / s), this yields a of 15 cm for the values in this example. Because the wavelength of the radiation is near or less than the length of the probe, without shielding the electric field can start to escape from the conductor, reducing the transmission efficiency. Thus, the presence of a coax shield confines the electric wave and allows better transmission efficiency. To illustrate this effect, it can be shown that transmission efficiency for a coaxial probe is much greater than that for an unshielded probe, as seen in Fig. 1 .

[0043] Figure 1 shows that the unshielded 2 centimeter (cm) probe loses over half its energy at 1 GHz compared to the low-loss low frequency, in this case 9 kilohertz (kHz). At higher frequency up to 4 GHz, the losses of bare conductor increase to 90% while coax wires have losses <25%. One benefit of this reduction in losses is a greater signal to noise at higher frequency, resulting in new measurements becoming practical.

[0044] Another important factor to consider in propagating an AC wave down a coax line is impedance matching. Impedance is a measure of the ratio of voltage and current of a lossless infinite line for transmission of an AC current, akin to index of refraction for optics, as opposed to electrical resistance which represents a loss mechanism. While there are numerous ways to affect the impedance of a finite transmission line, one simple way is to create coax transmission line with consistent impedance. When transmission on a line encounters an abrupt change in the characteristic impedance along the line, for example where a coaxial section meets an unshielded section, a reflection along the transmission line may occur. These reflections may end up being large, approaching 100%. If there are multiple locations where a reflection may occur, ringing may appear (https: / / resources.altium.com / p / what-causes-gibbs-ringing-high-speed-channel- simulations). Besides reducing the overall power applied to a device under test (DUT), this makes understanding time dependent measurements very difficult; ringing is essentially a burst of noise that can contaminate signal for times much longer than the desired measurement.

[0045] Similar to how unshielded probes can emit electromagnetic radiation, unshielded probes can also absorb electromagnetic radiation with that absorption being proportional to the ratio / / I. What this means is that at GHz frequencies, probes near a probe that is emitting high frequency radiation will be able to absorb a portion of that high frequency radiation, resulting in possible signal artifacts on probes other than those where it is intended. Furthermore, when probes are placed within the evanescent field of an emitting probe (i.e., within ~ / 2) the electromagnetic coupling between probes can increase, necessitating a minimization of unshielded probe for both the probe with a high frequency signal and other nearby probes. The net impact of this is that cross-talk decreases with the increase in coax coverage of probes.

[0046] System factors

[0047] Practical nanoprober implementations will produce a characteristic maximum frequency due to system resistance and capacitance. A system with a current running through a resistor with a capacitor to ground will produce a low-pass filter which depends on the system resistance and capacitance as fc=(27tRC)’1where fcis the low pass filter cutoff frequency in Hertz, R is the resistance in Ohms, and C is the capacitance in Farads. Any measurement system (as shown for example in Fig. 2) will have wiring, usually coax or triaxial, to get from the probe apices and DUT to a measurement system such as an oscilloscope or vector network analyzer. The very nature of the coax cables includes an inherent capacitance across the insulator between the conductor and shield, typically on the order of 100 pF / m. With cables to detectors typically on the order of 1 meter, the total capacitance is typically 200 pF. The circuit between any high frequency signal source, across a DUT, and to a detector will also have an inherent resistance (not to be confused with impedance), most of which is usually due to the DUT. For a typical transistor, in its on (off) state it might add 1 kOhm (10 MOhm) to the system resistance. This means that in the on (off) state, a system measurement will have an fcof 5 MHz (50 Hz). Fortunately, many DUTs have lower resistances, and some of the effects of the cabling can be calibrated out of the signal. Still the very nature of the system has frequency limitations.

[0048] One way to bypass the problems inherent to DUT resistance and system capacitance is to insert a signal amplification system into measurement system close to the DUT. This way, cable capacitance depends on the capacitance of signal lines on the order of 20-30 mm instead of 1000- 2000 mm, decreasing the capacitance by a factor of 60-1000. Careful choice of the signal amplifier results in the rest of the system “seeing” a low resistance DUT, thus increasing the effective cutoff frequency to that defined by the DUT and short lead capacitance.

[0049] Implementation:

[0050] Nanoprobe System. Figure 2 schematically illustrates a nanoprobe system configuration (and corresponding method) of the invention described in this application. Its basic components comprise the following: 1 . A probe assembly that is contained inside the vacuum chamber of a scanning electron microscope (or Atomic Force Microscope), which preferably has a shielded probe whose tip apex has a diameter of curvature of 50 nm or less,

[0051] 2. A coax adapter that allows replaceable coax nanoprobes to interface with a nearby amplifier PC board,

[0052] 3. A switch, which may be inside or outside the vacuum chamber, that allows one or more nanoprobes to change between at least one of the three signals: direct current / altemating current, low impedance (50 Ohm), or high impedance (one megaohm), (the switch may be a MEMS switch such as that described below but could also be of any type),

[0053] 4. Electronics used to generate high bandwidth signals of at least one GHz that are electrically connected to the probe assembly, and

[0054] 5. Electronics, such as a high-speed oscilloscope, used for the detection and measurement of GHz frequency signals and are electrically connected to the probe assembly.

[0055] Nanoprobe Assembly. Figure 3 shows a shielded nanoprobe assembly 33, which comprises a tapered conductive and, preferably, shielded needle-like probe, wherein the shield 34 preferably spans essentially the entire length of the probe, exposing only the probe tip apex 32. The shielded nanoprobe contains a conductor 35 sharpened to a point 31 that preferably has a 50 nm or less diameter of curvature. The conductive wire 35 is surrounded by shielding that is coax in nature with an insulator 36 surrounding the conductor 35 inside the metallic shield 34, leaving a portion of the conductive wire at the distal end exposed to enable it to be plugged into a board interface (not shown in Fig. 3).

[0056] An electrical signal travels from the DUT through the apex and body of the conductor to a coax electrical interface (Fig. 4) which allows easy replacement of the coax probe. This electrical interface is attached to a multifunctional circuit board. Along the entire circuit path from near the nanoprobe apex through the electrical interface, the signal integrity is protected by the shielding. Typically, at least 90% or at least 95% of the length of the electrical pathway from the apex to an amplifier is shielded. The nanoprobe is removable from the multifunctional board and may be replaced when it becomes dull or otherwise no longer usable. Shown in the top of Fig. 4 as a hybrid cross-section, the interface comprises an open ended metallic receptacle 41 that is inserted into a metallic cylinder which may be stainless steel 42. This open ended metallic receptacle should have an internal interface that 1) is tight enough to make good mechanical and electrical contact with a coax probe shield, and 2) is loose enough to allow insertion and removal of the coax probe. The metallic receptacle 41 must also make good mechanical and electrical contact with the metallic cylinder 42. At the distal end of the interface, a smaller closed receptacle 44 with a metal extension 45 is housed in an insulated material 43 which is installed into the center of the metallic tube 42. Receptacle 44 must also have an internal interface that is 1) tight enough to make good mechanical and electrical contact with the coax probe conductor, and 2) loose enough to allow insertion and removal of the coax probe. The receptacle 44 should not make electrical contact with cylinder 42. The receptacle end 45 is then used for signal transmission.

[0057] The bottom of Fig. 4 shows a schematic of a coaxial probe installed in the electrical interface. In this simplified figure, the bent portion of probe is not shielded; however, in other implementations the shielding extends near the apex as shown in Fig. 3. The coaxial probe is inserted so that the shield 48 of the coax probe 49 makes mechanical and electrical contact with the open receptacle 41 while the distal end of the inner conductor 52 makes contact with the closed pin receptacle 44.

[0058] The length 49 of shielding between the front receptacle 41 and the bend 47 is preferably in the range of 1 to 25cm or 1 to 10 cm. The length 51 of shielding between the shield receptacle 41 and the conductor receptacle 44 is in the range of 0.1 to 10 mm, more preferably in the range of 0.1 to 2 mm. The coax shield 51 should not contact the closed pin receptacle 44 in order to avoid creating a short between the conductor and shield of the coax probe. The part of the conductor of the coax probe that extends out of the distal end of the probe 52 is inserted into an electrical receptacle with internal gripping flanges 44, socket, and electrical conduit 45. Once installed, the exposed wire 52 and the closed end receptacle 46 are shielded by the stainless steel housing 42.

[0059] Closed receptacle 44 must be well aligned with the center of open receptacle 41 in order to allow repeated and reliable insertion of the coax probe. Hence, the insulator 43 which holds closed receptacle 44 is formed or machined in such a way so that as the probe is being inserted, it will be aligned with the closed end receptacle, so the distance between the closed receptacle 44 and the open receptacle 41 should be as small as possible. This assembly is part of a moving nanoprobing system with motors providing very precise positioning in order to operate at advanced manufacturing nodes. As such, the distance between the closed receptacle 44 and the open receptacle 41 should be as great as possible to maximize mechanical rigidity of the nanoprobe. Since the design constraints show demand both minimal and maximal receptacle separation, a cylindrical geometry is chosen to reach an optimum of reliability and mechanical rigidity.

[0060] Figure 5 shows a probe attached to a circuit board 64 having a trapezoidal shape with the narrowest portion nearest the probe. In this configuration, a signal enters the board through the conductive metallic probe wire 61 and electrical interface 62 described above. The shielded probe assembly, including circuit board, is preferably inside a vacuum chamber. The trapezoidal shape allows the circuit boards for a multi-probe system to avoid the probe assemblies from spatially interfering with each other.

[0061] Once on the printed circuit board, the signal encounters a switch 63 that will be used to route the signal in different ways to enable several user selectable functions. The switch can be of any type that is compatible with high frequency signals, but a preferred option is a MEMS switch. One embodiment of the invention utilizes a switch with at least three outputs, which routes the signal as follows:

[0062] 1. Route 1 is a pass-through option in which the signal is routed to a coaxial cable leading out of the SEM chamber. This option will preserve nanoprobing functionality at DC and low-frequency electrical signals.

[0063] 2. Route 2 sends the signal to a high input impedance amplifier 65 on the printed circuit board (PCB). The low impedance output of this amplifier drives the coax to the external high frequency 50-ohm input impedance measurement equipment.

[0064] 3. Route 3 66 provides 50-ohm termination for high frequency signals sent in from the outside to drive devices on the chip.

[0065] These three modes of operation are user-selectable for each probe. Another alternative construction is a board with an amplifier and no switches; amplification local to the probe is an important feature.

[0066] Initial tests show that at high signal amplitudes, an amplifier can be inserted into the signal path to achieve effective amplification up to 500 MHz with 90% / 10% rise and fall times of less than 400 ps. See Fig. 6 for experimental data the frequency response of a 500 Ohm resistor, or device under test (DUT), with an amplifier in the measurement system. Forward transmission (i.e., with the amplifier on the output of the DUT) and reflection are shown. These signals were captured by a Keysight Vector Network Analyzer (VNA) with a frequency range of 9 kHz up to 20 GHz. High frequency coaxial cables with a length of 0.5 meters each were used to interface via SMA connectors to a surface mount 500 Ohm resistor. The output side of the board connected via a 6” SMA to UMCX high frequency coaxial cable to a custom high frequency amplifier board that is compatible with electrical interfaces described above. Output from the board connects to the VNA via a 0.5 meter length of high speed, SMA terminated coaxial cable. In this case, a high amplitude (+ / -1 V) input signal was provided, showing that this signal and a system in which it is installed will have a high fceven when driving a large signal with a high resistance “on” state. As a rule of thumb, the -3dB cutoff describes bandwidth. Without any data processing such as renormalization, this result shows a bandwidth of >250 MHz. Using a metric of 90% / 10% rise and fall time, this result corresponds to a bandwidth in excess of 500 MHz. This is in contrast to the ability of many DUTs which are unable drive the signal all of the way to the measurement system. Analogously, unamplified signals show much lower transmission across the frequency spectrum up to the bandwidth of the amplifier itself. Higher frequency amplification is expected simply by insertion of higher frequency amplifiers. The invention can be further characterized by having one or more characteristics of this data (or selected points within the data) or within ±30% or 20% or 10% of the results according to this measurement.

[0067] Shielding:

[0068] A preferred material for shielding dielectric is PTFE. Other known dielectric materials such as polyimide or parylene may also be used. Shielding can be assembled through insertion of the needle into an insulator such as a tube, or shielding can be deposited either through liquid or vapor mechanisms.

[0069] In Fig. 7, the top probe tip has a dielectric polymer inserted between a tungsten wire and stainless steel tube. The middle probe tip is not shielded, the wire and stainless steel tube are in electrical contact. The bottom probe tip shows a copper tube that shields the probe wire of the construction of the middle probe.

[0070] MEMS Switch:

[0071] One example of the MEMS switch for the subject invention is a Refurvo MM5130 rf MEMS switch. A signal entering the PCB board will first encounter a MEMS switch that will be used to route the signal in different ways to enable several user selectable functions. A Refurvo MM5130 rf MEMS switch is a good choice for this purpose: it can switch its input to any of four different outputs and it is rated for frequencies up to 26 GHz.

[0072] PCB Materials -

[0073] The material used to construct the PCB is a consideration. FR-4 is a favorite PCB material in many applications, but it is not acceptable as a PCB material for high-speed digital circuitry. Materials for high-speed PCB design include enhanced FR-4, polyamide, and PTFE. Rogers Corporation 3000 series and 4000 series materials are materials of choice, and a particular choice is Rogers 4350B, which has low dielectric constant (Dk) and low dissipation factor (Df) values. The Megatron 6 series of circuit board materials by Panasonic Corporation and high-speed digital and Rf / Microwave products of Isola Corporation are also materials of choice. Two preferred products from Isola are their MT40 and MT77 materials.

[0074] Probe Tips

[0075] The probe tips are described in US Patent No. 11,169,177, incorporated herein by reference as if reproduced in full below. The SPEM probe can be manufactured from a piece of wire (defined as a material having a length to diameter ratio of at least 5, preferably at least 10, more typically at least 100 or, in some embodiments, in the range of 10 to 1000). Wire pieces for the starting materials preferably have a diameter between 0.1 mm and 1 .00 mm and a length in the range of 0.5 to 3 cm, more preferably 1.5 to 2.5 cm and are etched or machined to a point. The probe materials may be any of the materials conventionally used for SPEM probes. Thus, in preferred embodiments, the probe comprises a material selected from the group consisting of beryllium copper (Be — Cu) alloy, platinum (Pt), iridium (Jr), platinum-iridium (Pt — Ir) alloy, tungsten (W), tungsten-rhenium (W — Re) alloy, palladium (Pd), palladium alloy, gold (Au), and commercial alloys (NewTek™, Paliney 7™ (Pd along with small percentages of Ag, Au, Pt, Cu, and Zn), Paliney H3C and Paliney C (Pd alloys with Pd, Ag, and Cu)), and cemented metal carbides, borides or nitrides, such as tungsten (W), titanium (Ti), niobium (Ni), or tantalum (Ta) carbide cemented with cobalt (Co), nickel (Ni), iron (Fe), chromium (Cr), molybdenum (Mo), platinum (Pt), iridium (Ir), rhodium (Rh), palladium (Pd), rhenium (Re), ruthenium (Ru), and osmium (Os), or mixtures thereof. A preferred list of probe body materials comprises tungsten, platinum iridium, and tungsten carbide cemented with cobalt, nickel, or mixtures of cobalt and nickel. These materials may be used by themselves or with a coating of one or more layers such as polytetrafluoroethylene (PTFE); magnetic coatings, such as iron, cobalt, chromium or platinum alloys; diamond; diamond-like-carbon (DLC), Ag; Au; C; boron nitride; silicon nitride; silicon dioxide; metal oxides, such as aluminum oxide; metal nitrides, such as titanium nitride or aluminum titanium nitride; metal carbides, such as tungsten carbide; metal borides such as hafnium diboride (HfB2) or titanium diboride; metal carbonitrides, such as titanium carbonitride; ceramics; or other hard coatings, such those containing chromium. Suitable methods for applying such coatings are known in the literature; for example, in Jensen et al., J. Am. Chem. Soc. 110, 1643-44 (1988); Jayaraman et al., J. Vac. Sci. Technol. 23, 1619 (2005); and Jayaraman et al., Surface & Coatings Technol. 200, 6629-6633 (2006). We have prepared SPEM probes from W and Pt — Ir having the advantageous properties of cone angle and diameter of curvature.

[0076] The wire pieces may be pre-sharpened by known methods. Preferably, this is done by electrochemical etching by a technique such as that described by Zhang et al., which is referenced above. Typically, a coating, if present, is applied after the electrochemical etch. The coating can be applied either before or after the ion milling process described here, and HfB2 coatings have been applied after the ion milling such that little or no additional sharpening is needed.

[0077] If the diameter of the cylindrical wire body is D, the profile of a bullet-shaped probe in the near apex region as defined above is described by two arcs of a circle of radius equal to a multiple of D, each arc being tangent to one of a pair of opposing parallel sides of the cylindrical wire body. The two arcs can be defined by a circle having a radius equal to between 1 and 20 times, preferably between 5 and 7 times the wire body diameter D. The two arcs meet at the apex of the probe. At this meeting point, the apex is defined by a diameter of curvature that in one embodiment is less than 10 nm. The two arcs may or may not be tangent at the point of intersection to the cylindrical portion of the wire. When the circles are tangent to the cylinder portion, this is a tangent shape. When the circles are not tangent to the cylinder portion, this is a secant shape.

Claims

What is claimed:

1. A probe comprising: a conductive wire having a length of at least 0.5 cm (preferably at least 1 cm, or in the range of 1 to 7 cm or 1 to 4 cm) and an apex having a diameter of curvature of 50 nm or less; wherein the conductive wire comprises a straight section and an apex section and a bend having an angle of at least 10° disposed between the straight section and the apex section; a shielding disposed around the straight section; and a tapered shielding disposed around apex section wherein the tapered shielding is narrowest near the apex and the shielding ends at least 1 pm, or at least 10 pm, or at least 1 mm, or at least 2 mm prior to the apex, or in the range up to 5 mm or up to 3 mm.

2. The probe of claim 1 wherein the bend has an angle in the range of 20° to 50°.

3. The probe of claim 1 wherein the apex section has a length in the range of 1 to 5 mm.

4. The probe of claim 1 wherein the tapered shielding has a continuous taper or a stepped taper.

5. The probe of claim 4 wherein the tapered shielding comprises varies in thickness between 2 mm to 1 pm.

6. The probe of claim 1 wherein the tapered shielding comprises a dielectric material inside of a tapered metallic shell.

7. The probe of claim 6 wherein the tapered shielding comprises a tapered dielectric that is coated with a metal layer.

8. A nanoprobe, comprising: a conductive wire having a length of at least 1 cm and an apex having a diameter of curvature of 50 nm or less; a shielding disposed around the conductive wire;a coaxial connector attached to an end of the conductive wire that is opposite the apex; a shielded circuit board electrically connected to the conductive wire through the coaxial connector; wherein the circuit board comprises a radio frequency amplifier where the distance to the apex is 30 mm or less.

9. A nanoprobe, comprising: a conductive wire having a length of at least 1 cm and an apex having a diameter of curvature of 50 nm or less; a shielding disposed around the conductive wire; a shielded circuit board electrically connected to the conductive wire; wherein the circuit board comprises a radio frequency amplifier disposed between two MEMs switches.

10. A nanoprobe, comprising: a conductive wire having a length of at least 1 cm and an apex having a diameter of curvature of 50 nm or less; a shielding disposed around the conductive wire; a shielded circuit board electrically connected to the conductive wire; wherein the circuit board comprises a radio frequency amplifier.

11. A nanoprobe, comprising: a conductive wire having a length of at least 1 cm and an apex having a diameter of curvature of 50 nm or less; a shielding disposed around the conductive wire; a shielded circuit board electrically connected to the conductive wire; wherein the circuit board comprises a radio frequency amplifier and two switches; wherein the board has a trapezoidal shape with a first side perpendicular to the conductive wire and a second side perpendicular to the conductive wire; wherein the first side is closer to the apex than the second side;wherein the first side has a first length and the second side has a second length and wherein the second length is at least 10% larger than the first length; and a tapered shield disposed around the circuit board wherein the tapered shielding is narrowest near the apex.

12. The nanoprobe of claim 11 wherein the tapered shield comprises a tapered dielectric that is coated with a metal layer.

13. The nanoprobe of claim 11 wherein the trapezoidal board has a length of 1 to 10 cm.

14. The nanoprobe of claim 11 wherein the first length is in the range of 1 to 8 cm.

15. The nanoprobe of claim 11 wherein the conductive wire is removeable from the circuit board which allows the probe to be changed without discarding the electronics.

16. An imaging system comprising the nanoprobe of any of the above claims comprising a scanning electron microscope in which the nanoprobe and a device under test are inside a vacuum chamber.

17. A method of measuring performance of an integrated circuit, comprising: passing a signal having a frequency of at least 1 GHz into an integrated circuit; and detecting the signal through the nanoprobe, or passing a signal having rise and fall times of less than 1 nanosecond (IO-9seconds) into the integrated circuit; and detecting the signal through the nanoprobe; wherein the nanoprobe comprises any of the nanoprobes described herein.

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