Patent Description:
The present invention is directed to a microscope probe configured to analyze a sample.

In order to achieve low-powered high-performance electronics, the size of transistors forming the building block of very large scale integrated (VLSI) circuits are drastically decreasing. However, tool resolution and sensitivity continue to be major challenges in semiconductor device fault isolation and analysis. As transistors continue to scale down to <NUM> nodes and beyond, well-known optical microscopy techniques no longer work due to wavelength limitations. For instance, conventional failure analysis methods involve the use of Focused Ion Beam (FIB) deposited pads or Scanning Electron Microscope (SEM). However, minute charge currents from the FIB and SEM adversely affect measured results. The induced charge from the FIB and SEM can even break the ultra-thin transistor tunneling gate oxide layer. In addition to this, Passive Voltage Contrast (PVC) techniques lack the sensitivity to identify faulty vias and contacts.

Single-tip Scanning Probe Microscopy, such as Atomic Force Probing (AFP) and Atomic Force Microscopy (AFM), is a powerful tool for non-destructive determination of root causes of IC chip failure, including extension to the sub <NUM> node regimes. However, AFM effectiveness is severely limited by its single tip design. As a result, a range of fundamental phenomena that exist in thin film materials and devices are inaccessible. As just one example, the effects of dislocations and grain boundaries in thin films cannot be characterized, as the ability to perform trans-conductance (conduction between two tips) measurements at the nanoscale is a critical gap. Trans-conductance would enable a richer understanding of how electrons transport and interact with their surroundings by offering insight into the local density of states, tip-sample coupling, transport mechanisms, scattering phase shifts and inelastic free mean paths of electrons.

Multiple-tips SPMs have been proposed as a way of overcoming the inherent limitations of the single-tip SPM. <CIT> discloses a multi-tip nano-probe apparatus and a method for probing a sample while using the multi-tip nano-probe apparatus. <NPL> discloses silicon SPM multiprobes having lateral actuators. <CIT> discloses a nano-probe tip for advanced scanning probe microscopy comprising a layered probe material patterned by lithography and/or FIB techniques. <CIT> discloses a probe of a scanning atomic force microscope. However, there have been significant challenges to engineering a suitable multiple-tips SPM. Previous approaches to a multiple-tip SPM have relied on independent macroscopically-fabricated probes. These platforms are complex, difficult to actuate, and have limited scale-down. They are also prohibitively expensive to manufacture.

Accordingly, there is a continued need in the art for multiple-tips SPMs that are both cost-effective and easily manufactured and functionalized to the specific investigation for which they will be utilized. Also needed are efficient and cost-effective methods of manufacturing multiple integrated tip probes.

The present disclosure is directed to multiple integrated tip (MiT) probes for scanning probe microscopy. The MiT probe is a Nano-Electro-Mechanical System (NEMS) that integrates mechanical and electrical functionality in a monolithically-fabricated nano-structure which is tailored and functionalized to the specific investigation. The MiT scanning probe microscope provides two or more monolithically integrated cantilever tips that can be placed within nanometers of each other, with monolithically integrated transistors to amplify signals. As a result, the MiT SPM is able to perform atomic force microscopy without the need for laser tip alignment. Further, the MiT SPM is capable of nanoprobing surfaces where at least two of the integrated tips are in direct contact or in close proximity with the sample.

According to claim <NUM> the invention is about a microscope probe configured to analyze a sample. The microscope probe includes a movable probe tip comprising a terminal probe end, wherein the moveable probe tip comprises a metal layer affixed to a supporting layer, at least a portion of the metal layer at the terminal probe end extending past the supporting layer.

According to an embodiment, the microscope probe includes a first actuator configured to displace the movable probe tip along a first axis, and a detection component configured to detect motion of the movable probe tip in response to an applied signal.

According to an embodiment, the metal is platinum, gold, tungsten, or nickel.

According to an embodiment, the supporting layer is silicon, silicon dioxide, or silicon nitride.

According to an embodiment, the microscope probe includes a plurality of probe tips each comprising a terminal probe end, each of the plurality of probe tips further comprising a metal layer affixed to a supporting layer, at least a portion of the metal layer at the terminal probe ends extending past the supporting layer.

According to an embodiment, the probe further includes an insulated interdigitated structure positioned between each of the plurality of probe tips.

According to an aspect is a microscope probe configured to analyze a sample. The microscope probe includes: a plurality of probe tips and an insulated interdigitated structure positioned between each of the plurality of probe tips.

According to the invention, the probe includes a first actuator configured to displace at least one of the plurality of probe tips along a first axis; according to an embodiment the probe includes a detection component configured to detect motion of the at least one of the plurality of probe tips in response to an applied signal.

These and other aspects of the invention will be apparent from the embodiment(s) described hereinafter.

The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:.

The present disclosure includes various embodiments of a system and method for manufacturing multiple integrated tips (MiT) probes for use with a scanning probe microscope (SPM) system. The MiT-SPM enables nanoscale atomic imaging, electrical probing of trans-conductance, and parametric analysis of a transistor, among many other aspects.

Capacitive coupling and low signal-to-noise ratio leads to passive Nano-Electro-Mechanical-System (NEMS) devices generally having lower performance. <FIG> shows the small signal electrical equivalent circuit of a NEMS resonator structure. The resonator can be modeled as a typical Butterworth-Van Dyke equivalent circuit where Lx, Cx, and Rx represent the motional inductance, capacitance and resistance respectively. C<NUM> is the parasitic DC capacitance of the resonator and Cp represents the total parasitic capacitance introduced from the wirebonds, circuit board and packaging. If C<NUM> and Cp are large, they will generate large amounts of current that will obscure the motional current of the resonator. The current from the input (Vin) to the output of the NEMS resonator has three main paths: <MAT>.

The admittance of the NEMS resonator is given by the following equation: <MAT>.

From Equation <NUM>, if the feedback capacitor C<NUM> and parasitic capacitor Cp increases, their effective impedance decreases and would sink most of the input current thus masking the motional current Ix which is the parameter of interest. To minimize the effect of C<NUM> and Cp, either an on-board or off-board compensating capacitor can be added in parallel to cancel their effect. <FIG> illustrates the parallel connection of the compensation capacitor (Static) to the resonator. The compensation capacitor is fixed to the substrate so does not generate motional current. The current from the Static structure (Ico + Icp) is inverted into Icomp. Icomp is electrically combined with the current from the resonator If. ITotal is fed into an off board transimpedance amplifier. <MAT> <MAT>.

The compensation device is structurally identical to the resonator as shown in <FIG>. The comb-drives that form the static component <NUM> in <FIG> are fixed where as those that form the resonator component <NUM> are fully released from the substrate and capable of vibrating. Both AC and DC voltages are applied to electrode A2. The parasitic current (Ico + Icp) through the static component is inverted by on-board inverter into Icomp which is then combined with the resonator current If. The combined current is fed into a transimpedance amplifier. The probe tip device depicted in <FIG> has both a static component <NUM> and a resonating component <NUM>. The static structures are fixed on the substrate whereas the resonating structures are free to mechanically move and can be excited in a vibrational mode.

The probe tip can be used to image surfaces in both AFM and Scanning Tunneling Microscopy (STM) modes. In contact mode AFM, the tip is dragged across the surface of a sample. As the tip encounters different roughness of the surface, since the tip is supported by springs, it moves up and down. This up and down movement of the tip can be sensed by the differential capacitors B1 and B2. The device is biased as shown in <FIG>, where AC voltages are applied to B1 and B2 and DC voltage applied to the probe tip. STM images can also be acquired with the biased probe tip.

Vsense changes with the displacement of the probe tip and its value can be used to create a 3D topographical image of the surface. For small probe tip displacement the following equation is utilized: <MAT> where y is a small displacement caused by the probe tip in contact with a surface and y<NUM> is the default smallest gap between any of the fingers on B1 or B2 and a probe tip finger.

To ensure that there is good ohmics between the probe tip and the sample, the workfunction of the probe tip and sample should be closely matched. In most semiconductor technology nodes, tungsten plugs are used to connect a metal to the source, drain, and gate regions of the transistor. To probe these plugs, tungsten probe tips are usually used due to its hardness and high conductivity. But the tungsten probes are susceptible to oxidation which in effect render them insulating and non-ideal for electrical probing. Both chemical and mechanical techniques are used to remove the oxide on the probe tip.

Other structures with different workfunctions would require different conducting probe tip materials. Platinum and gold are metals of interest for nanoprobing due to their high conductivity and non-oxidation tendencies. Gold is pretty soft and might stick to surfaces. To this end, probe tip devices with different conducting materials or metals have been fabricated as shown in the SEM image in <FIG>. Table <NUM>, in accordance with an example not covered by the claims, provides a method for the nanofabrication of an all-metal integrated probe tip device. Referring to <FIG> is an image of the finalized probe device according to the method of Table <NUM>.

The stress gradient in the metal films might bend the probe tip either upwards or downward. To mitigate the effect of stress gradient, the metal can be mechanically attached to a supporting material.

According to an example not covered by the claims, <FIG>, for example, show a metal terminal probe end <NUM> of a probe tip which sits on, is supported by, or is affixed to, a silicon supporting layer <NUM>. The metal probe tip <NUM> extends past the silicon support layer <NUM> and during AFM/STM imaging and nanoprobing, only the metal probe tip <NUM> is in contact with the sample. The metal of choice is not limited to platinum, but gold and other conductive materials can also be utilized. Also, various materials such as silicon dioxide, silicon nitride can be used for the structural support layer. The platinum tip can be used for both AFM/STM imaging and nanoprobing. An example not covered by the claims of the nanofabrication method for the metal-overhang probe tip is outlined in Table <NUM>.

The support layer for the metal is not limited to silicon but other materials such as silicon dioxide, silicon nitride, and MoSi<NUM>, among others. Two or more individual probe tips can be synchronously and simultaneously used to perform AFM or STM imaging of a sample. Using the acquired image, individual tips can be navigated to specific points on the sample. For example, the plugs in an Integrated Circuit (IC) can be nanoprobed using the device, where all the four individual probe tips are scanned simultaneously to acquire STM or AFM image and subsequently navigated to specific plugs for nanoprobing. The 3D image can then be used as feedback for positioning each tip at a particular point on the sample.

According to an example not covered by the claims using the fabrication process outlined in Table <NUM> above, curved probe tips can be realized as shown in <FIG>. These tips could have integrated deflection electrodes that can actuate and sense the probe tip in resonance as well as integrated differential capacitive sensors for sensing the motion of the probe tip device. Two or more of these curved tips can be synchronized and used to perform Atomic Force Probing of a device.

According to an example not covered by the claims using the fabrication process outlined in Table <NUM>, pre-defined shaped single tips with extended metal overhangs can be realized. These probe tips can be used as fabricated, or soldered to metal shank, and inserted into manipulators. If the SOI device layer is thick, then the buried oxide layer can be fully etched away to release probe tips.

Freely released and suspended multiple integrated tips tend to pull-in to each other after the release process or during nanoprobing. To mitigate the pull-in effect, interdigitated structures can be monolithically inserted between the probes. Table <NUM> below illustrates the fabrication process for monolithically implementing the interdigitated structures, in accordance with an example not covered by the claims. Referring to <FIG> is an image of the finalized probe device according to the method of Table <NUM>. In <FIG>, for example, the probe includes a structure <NUM> with interdigitated structures <NUM> positioned between and on the outer side of the probe tips <NUM>.

The <NUM>-tip MiT probe can be considered as a Ground-Signal-Ground Signal (GSGS) probe device where two signals that are out-of- phase can be introduced on the Signal probes and shielded by the Ground probes. Bottom electrodes can also be placed below each probe tip for controlled downward deflection of each probe tip. The tips can be used for conventional <NUM>-point probing. Also, the <NUM> probes can be scanned across a sample surface and the current between any of the two tips can be used for imaging the surface.

Certain STM/AFM imaging and nanoprobing require that probe tips exhibit <NUM> Degrees of Freedom (DOF). <FIG> is the top view of a monolithically integrated tips device with <NUM> DOF. Applied voltages to electrode A2 move the middle probe tip in-plane whereas applied voltages to electrodes C1 or C2 laterally deflects the middle probe tip. Electrode E3 runs below the middle probe tip and applied voltages to E3 bends down the middle probe tip towards the substrate. The side probe tips also have electrodes E1 and E2 that bend down the tips when actuated. Table <NUM> illustrates the fabrication of MiT probe with <NUM> DOF where the bottom electrodes (E1, E2 and E3) are used to deflect the probe tips out of plane. Referring to <FIG> is an image of the finalized probe device according to the method of Table <NUM>.

The bottom electrodes are used to deflect the probes out-of-plane. The metal choice for the actuation electrodes (<NUM>st metal layer) and the probe tips (<NUM>nd metal layer) could be the same or different. The <NUM>-Tip MiT probe configuration allows these probes to be used as Ground-Signal-Ground (GSG) RF/microwave probes for testing microwave and RF circuits. The <NUM>-Tip MiT probe can also be used for AFP. Using the fabrication process outlined in Table <NUM> above, a <NUM>-point probe device can be realized. The middle probe tip is used for AFM/STM imaging then it is retracted and the remaining <NUM> probe tips are used for conventional <NUM>-point probe measurements.

According to an embodiment is the fabrication of monolithically integrated probe tips with bottom and side actuation electrodes, where the side tips are laterally deflected. The side probe tips can be independently controlled by applying voltages to electrodes E1 and E2 (bottom electrodes) and F1 and F2 (side electrodes) as shown in <FIG>. Illustrated in Table <NUM> below is the fabrication of an MiT probe with <NUM> DOF where the bottom electrodes (E1, E2 and E3) are used to deflect the probe tips out-of-plane. F1 and F2 are independently used to laterally deflect the side tips. Referring to <FIG> is an image of the finalized probe device according to the method of Table <NUM>.

In certain applications, the middle probe tip might be required to be deflected both down (towards the substrate) and up (away from the substrate). Table <NUM> illustrates the fabrication process steps in realizing such a device. The metal choice for the actuation electrodes (<NUM>st metal) and the probe tips (<NUM>nd metal) could be the same or different. Referring to <FIG> is an image of the finalized probe device according to the method of Table <NUM>, where the middle probe tip can deflect both up and down with respect to the substrate.

Several MiT probes can be monolithically vertically integrated to offer several probe tips that can be used to probe structures on a wafer. Table <NUM> illustrates the fabrication process for the vertically stacked MiT probes. The metal choice used in the MiT probe stack could be the same (<NUM>st metal is the same as <NUM>nd metal) or different (<NUM>st metal is different from <NUM>nd metal). The MiT probe stack is not limited to two layers but several layers can also be implemented using the outlined fabrication process flow. The stacked MiT probes can also be realized in standard CMOS processes where the different metal layers can be used as the probe tips. Referring to <FIG> is an image of the finalized probe device according to the method of Table <NUM>. The finalized probe comprises a first probe set <NUM> and a second probe set <NUM>, the first probe set being vertically stacked compared to the second probe set.

Each MiT probe that makeup the vertically stacked monolithically integrated probe tip devices that was illustrated in Table <NUM> above have the same number of probe tips. In certain applications, a modified probe tip configuration might be required. In such situations, the FIB can be used to remove unneeded probe tips, as shown in Table <NUM>. Removal of unneeded probe tips is not limited to the use of FIB but other means such as ion milling and reactive ion etching are possible. The metal choice used in the MiT probe stack could be the same (<NUM>st metal the same as <NUM>nd metal) or different (<NUM>st metal different from <NUM>nd metal). The MiT probe stack is not limited to two layers but several layers can also be implemented using the outlined fabrication process flow. Referring to <FIG> is an image of the finalized probe device according to the method of Table <NUM>.

SRAM, DRAM and flash memory are typically arrayed and the plug spacing for the source, drain and gate are fixed. These plugs could be relatively easily accessed with MiT probes that have predefined tip configurations that directly address these specific plug layouts. The MiT probes can be designed specifically for a particular technology node and semiconductor foundry. The metal choice used for the probe tips in the MiT probe could be the same (<NUM>st metal the same as <NUM>nd metal) or different (<NUM>st metal different from <NUM>nd metal), as shown in Table <NUM>. Referring to <FIG> is an image of the finalized probe device according to the method of Table <NUM>.

The out-of-plane MiT probe that was illustrated in Table <NUM> above had the middle probe tip fixed to the SiO<NUM> support layer. Table <NUM> below details out the fabrication of a fully suspended and movable out-of-plane middle probe tip device. Referring to <FIG> is an image of the finalized probe according to the method of Table <NUM>.

According to an example not covered by the claims, various combinations of the different probe configurations (single tip, <NUM>, <NUM> and/or <NUM>-Tip MiT probes) can be simultaneously used to scan and nanoprobe. According to one example, a <NUM>-Tip MiT probe could be utilized to access the source, drain, gate plugs of a transistor then bringing in an independent single tip device to probe the bulk (body) of the transistor.

Fabrication of monolithically integrated freely suspended out-of-plane probe tip device with bottom and side actuation electrodes.

Bottom electrodes are used to deflect the probe tips up or down with respect to the substrate. But in certain applications, the side probe tips might need to be laterally deflected. For instance, when the gate length of two transistors varies, the side tips must be laterally deflected in order to access the source and drain plugs. Table <NUM> below illustrates the fabrication process flow for making MiT probes with side actuation electrodes. Referring to <FIG> is an image of the finalized probe device according to the method of Table <NUM>.

According to an embodiment, the lateral actuation electrodes for the side probe tips can be implemented for all the above MiT probe designs.

The MiT probes can be used to implement various active and passive circuit components (transistor, resistor, diode and capacitor) on substrates. Since the MiT probe is capable of electrically mapping different regions of a substrate, at each spot, an active or passive component can be implemented on the substrate. Thus, these components are not lithographically fixed to the substrate but are mobile. For example, the <NUM>-Tips MiT probe can be used to implement a transistor on a substrate. The middle probe tip represents the gate and the side probe tips are the source and drain terminals as shown in <FIG>. The side tips are in soft contact with the substrate whereas the middle probe tip can either be in soft contact (the tip has a dielectric coating) or proximity (air gap serves as the gate dielectric). At any location on the substrate, a transistor can be formed. Thus, both the output and transfer curves of a transistor can be mapped at each point on the surface of a substrate. The substrate could be a 2D material such as graphene, molybdenum disulphide, silicon substrate, GaN wafer substrate, etc..

Referring to <FIG> is the design of the <NUM>-Tip MiT probe showing various actuation electrodes. <FIG> show the tip design of the <NUM>-Tip MiT probe and the gate capacitance between the middle probe tip and the substrate respectively. The middle tip is designed to be shorter than the side probe tips. The gate capacitance can be varied by applying DC voltages to electrode A2 which would retract or extend the middle probe tip. Thus, the effect of the gate capacitance on the transistor performance can be measured and investigated. <FIG> on the other hand shows a <NUM>-Tip MiT probe which has a few nanometers of either high or low-k dielectric that is deposited at the apex of the middle probe tip. The dielectric layer serves as the gate oxide and the middle probe tip is aligned with the side probe tips.

A variable resistor on the other hand can be implemented by changing the spacing between the middle probe tip and any of the side tips. Applied voltages to C1 or C2 would laterally deflect the middle probe tip. By varying the tip spacing and contacting the substrate, different substrate resistance values can be achieved as demonstrated in <FIG>.

Two or more active or passive circuit components that are implemented with two or more MiT probes can be cascaded to form various circuits such as common source amplifier, common gate amplifier, a source follower, etc. <FIG> shows the typical circuit configuration of a common source amplifier. This circuit could be implemented by at least a <NUM>-Tip MiT probe and either a <NUM>, <NUM>, or <NUM>-Tip MiT probe. As an example, two <NUM>-Tip MiT probes where one of the MiT probes would implement the transistor and the other would implement the resistor. Or a <NUM>-Tip MiT probe for the transistor and <NUM>-Tips or <NUM>-Tips MiT probe for the resistor.

While various embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims, embodiments may be practiced otherwise than as specifically described.

Claim 1:
A microscope probe configured to analyze a sample, the microscope probe comprising:
a moveable probe tip comprising a metal layer affixed to a top surface of a supporting layer, a portion of the metal layer forming a metal terminal probe end (<NUM>), the metal terminal probe end (<NUM>) extending past the supporting layer (<NUM>) in a plane parallel to the top surface of a fixed substrate;
wherein at least a portion of a bottom surface of the supporting layer (<NUM>) is attached to a spacer, the spacer fixedly secured to the top surface of a fixed substrate;
wherein at least a portion of the supporting layer (<NUM>) extends past the fixed substrate; and
wherein the microscope probe comprises first actuation electrodes (A2, C1, C2), which are configured to move the moveable probe tip in a plane parallel to the top surface of the fixed substrate when actuated, characterized in that the microscope probe comprises at least one second actuation electrode (E1, E2, E3), which is configured to move the moveable probe tip towards the fixed substrate in a plane perpendicular to the top surface of the fixed substrate when actuated, wherein the at least one second actuation electrode is a bottom electrode, wherein the bottom electrode runs below the moveable probe tip.