CN117092146A - Probe structure, device and method for observing sample - Google Patents

Abstract

An apparatus for observing a sample using a charged particle beam includes an ion beam column configured to generate and direct an ion beam, an electron beam column configured to generate and direct an electron beam, a vacuum chamber for containing the sample, and a probe positioned in the vacuum chamber. The probe is configured to provide an electrical connection between the sample and a power source. Embodiments of the application also disclose a probe structure for a charged particle beam microscope and a method of observing defects in a sample.

Description

Probe structure, device and method for observing sample

Technical Field

Embodiments of the present application relate to probe structures, devices and methods for observing samples.

Background

Dual beam systems may include imaging capabilities using Focused Ion Beam (FIB) microscopy and Scanning Electron Microscopy (SEM), which are widely used for fault analysis of semiconductor devices and preparation of electron permeable samples for Transmission Electron Microscopy (TEM). FIB extraction procedure is a process consisting of several sequential steps, where the starting point is the delivery of a wafer, identifying the region of interest on the wafer, and operating the extraction probe in the FIB vacuum chamber to extract the sample from the wafer, and the end point is imaging the sample with SEM and/or TEM for further investigation. There is a need in the industry to automate the overall process, allowing for quick and safe handling of the removed samples without the need to vent the vacuum chamber through a airlock or remove probes and samples. Although in-situ extraction techniques are employed in the procedure, in which extraction probes (typically having tungsten pins as probe tips) are used to lift the sheet from the wafer and move the sheet to another sample holder for further analysis, the process of identifying the region of interest is typically performed ex-situ on the tester. One reason for this is that in order to identify a region of interest (e.g., a hot spot or circuit break on a wafer), it is often necessary to provide bias voltages and/or stimulus to one or more probe pads on the wafer, while existing extraction probes lack the ability to provide such electrical connections. Thus, while existing methods in FIB systems are generally adequate for their intended purpose, they are not entirely satisfactory in all respects. There is a need for a practical technique that allows the extraction probes to be provided in situ to the electrical connections of the wafer. Meeting this need would significantly improve wafer acceptance testing, process control monitoring, and/or failure analysis, as the entire process of FIB retrieval can be automated in the FIB vacuum chamber.

Disclosure of Invention

According to an aspect of an embodiment of the present application, there is provided an apparatus for observing a sample using a charged particle beam, comprising: an ion beam column configured to generate and direct an ion beam; an electron beam column configured to generate and guide an electron beam; a vacuum chamber for containing a sample; and a probe positioned in the vacuum chamber, wherein the probe is configured to provide an electrical connection between the sample and a power source.

According to another aspect of an embodiment of the present application, there is provided a probe structure for a charged particle beam microscope, comprising: a needle; a needle holder holding a needle, wherein the needle holder is electrically connected to the needle; a wire attached to the needle holder, wherein the wire provides an electrical connection between the needle holder and a power source; and an elongate shaft coupled to the needle holder, wherein the elongate shaft imparts motion control to the needle through the needle holder.

According to yet another aspect of an embodiment of the present application, there is provided a method of observing defects in a sample, comprising: loading a sample on a stage; detecting the sample with a probe; electrically connecting the probe to a ground line to discharge the sample; electrically connecting the probe to a voltage line to bias the sample; identifying a region having a defect; ion milling the sample to release a region from the sample; and extracting the region by the probe.

Drawings

The various aspects of the invention are best understood from the following detailed description when read in connection with the accompanying drawings. It should be emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale and are used for illustration purposes only. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

Fig. 1 illustrates a dual beam system according to some embodiments of the present disclosure.

Fig. 2 illustrates a top view of a semiconductor wafer having a test line structure, according to some embodiments of the present disclosure.

Fig. 3 illustrates a cross-sectional view of a test line structure with front side probe pads and back side probe pads, according to some embodiments of the present disclosure.

Fig. 4 illustrates a retrieval probe operable to provide electrical connection with a sample loaded in a dual beam system, according to some embodiments of the present disclosure.

Fig. 5 illustrates a TEM grid to which a sample is attached according to some embodiments of the present disclosure.

Fig. 6 illustrates a TEM sample extracted from a work piece according to some embodiments of the present disclosure.

Fig. 7 illustrates a TEM sample mounted on a TEM grid according to some embodiments of the present disclosure.

Fig. 8 illustrates a TEM sample and a tilted and rotated TEM grid using an ion beam to thin the TEM sample according to some embodiments of the present disclosure.

Fig. 9 illustrates a flowchart of a method of an ex situ extraction procedure utilizing the extraction probe shown in fig. 4, according to some embodiments of the present disclosure.

Detailed Description

The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific embodiments or examples of components and arrangements are described below to simplify the present disclosure. Of course, these are merely examples and are not intended to be limiting. For example, in the following description, forming a first component over or on a second component may include embodiments in which the first component and the second component are formed in direct contact, and may also include embodiments in which additional components may be formed between the first component and the second component, such that the first component and the second component may not be in direct contact. Furthermore, the present invention may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, for ease of description, spaced relationship terms such as "below …," "below …," "lower," "above …," "upper," and the like may be used herein to describe one element or component's relationship to another element or component as illustrated in the figures. In addition to the orientations shown in the drawings, the term spaced apart relationship is intended to include different orientations of the device in use or operation. The device may be otherwise positioned (rotated 90 degrees or at other orientations) and the spaced apart relationship descriptors used herein interpreted accordingly. Still further, in view of the specific techniques disclosed herein, when a number or a series of numbers is described using "about," "approximately," etc., the term includes numbers that are within some variation (e.g., +/-10% or other variation) of the number described, unless otherwise specified, according to the knowledge of one skilled in the art. For example, the term "about 5nm" may include a size range from 4.5nm to 5.5nm, 4.0nm to 5.0nm, and the like.

The present disclosure relates generally to preparation of samples for imaging in charged particle beam systems, and more particularly to methods and apparatus that allow extraction probes in dual beam systems to apply electrical connections (e.g., discharges, biases, and/or additive excitations) to a Device Under Test (DUT) (e.g., a semiconductor wafer) to assist in identifying regions of interest from which to extract lamellae for further analysis under a Transmission Electron Microscope (TEM) and/or a scanning transmission electron microscope.

Due to the technological requirements to build smaller and smaller structures in electronic, optical and micromechanical systems, defects on the order of nanometers or tens of nanometers may adversely affect the performance of the device. Such defects are routinely inspected using electron microscopy to determine and correct the cause of the defect. Defects may include contaminant particles embedded in the product during manufacturing or manufacturing defects, such as bridges that form a short circuit between two closely spaced conductors that are electrically separated from each other.

Charged particle beam microscopes, such as scanning ion microscopes and electron microscopes, provide higher resolution and greater depth of focus than optical microscopes, facilitating detection in the semiconductor industry. In a Scanning Electron Microscope (SEM), a primary electron beam is focused to a fine spot to scan a surface to be observed. The secondary electrons are emitted from the surface when they are impacted by the primary electron beam. The secondary electrons are detected and an image is formed, the brightness of each point on the image being determined by the number of secondary electrons detected when the beam strikes the corresponding point on the surface. A Scanning Ion Microscope (SIM) is similar to a scanning electron microscope, but uses an ion beam to scan a surface and eject secondary electrons.

In Transmission Electron Microscopy (TEM), a broadband electron beam impinges on a sample and electrons transmitted through the sample are focused to form an image of the sample. The sample must be thin enough to allow many of the electrons in the main beam to pass through the sample and exit from the opposite location. The thickness of the sample is typically less than 100nm.

In a Scanning Transmission Electron Microscope (STEM), a primary electron beam is focused to a fine spot and the fine spot is scanned over the sample surface. Electrons transmitted through the workpiece are collected by an electron detector at the distal end of the sample, and the intensity of each point on the image corresponds to the number of electrons collected when the main beam strikes the corresponding point on the surface.

Since the sample needs to be very Bao Cai to be able to be viewed with a transmission electron microscope (either TEM or STEM), sample preparation can be a delicate and time consuming task. The term "TEM" sample as used herein refers to a sample for TEM or STEM, and reference to preparing a sample for TEM is understood to also include preparing a sample for observation on STEM. One method of preparing a TEM sample is to cut the sample from a workpiece substrate using an ion beam. The withdrawal probe (or probes for simplicity) is attached to the sample either before or after the sample is completely released from the workpiece. For example, the extraction probe may be attached by static electricity, FIB deposition, or adhesive. The sample attached to the extraction probe is removed from the workpiece and is typically attached to the TEM grid using FIB deposition, static electricity or an adhesive.

Some dual beam systems include an ion beam that can be used to extract the sample and an electron beam that can be used for TEM observation. In some dual beam systems, the FIB column is oriented at an angle to the vertical, such as 52 degrees, and the electron beam column is oriented vertically. In other systems, the electron beam column is tilted, and the FIB column is vertically oriented or tilted as well. The stage on which the sample is mounted may be tilted, typically up to about 60 degrees in some systems.

Fig. 1 illustrates an example dual beam system 110 according to some embodiments of the disclosure. The dual beam system 110 includes a vertically mounted electron beam column and a Focused Ion Beam (FIB) column mounted at an angle (such as about 52 degrees) to vertical. Although examples of suitable hardware are provided below, the invention is not limited to implementation in any particular type of hardware.

The scanning electron microscope 141 and the power supply and control unit 145 are equipped with a dual beam system 110. By applying a voltage between the cathode 152 and the anode 154, the electron beam 143 is emitted from the cathode 152. The electron beam 143 is focused to a fine spot by a condenser lens 156 and an objective lens 158. The electron beam 143 is two-dimensionally scanned over the sample by the deflection yoke 160. The operation of the condenser lens 156, the objective lens 158 and the deflection coil 160 is controlled by the power and control unit 145.

The electron beam 143 may be focused onto a DUT 122, such as a semiconductor wafer, the DUT 122 being mounted on a movable stage 125 within the lower chamber 126. When an electron in the electron beam strikes DUT 122, a secondary electron is emitted. These secondary electrons are detected by the charged particle detector 140. STEM detector 162, located below TEM sample holder 124 and movable stage 125, may collect electrons transmitted through a sample mounted on TEM sample holder 124.

The dual beam system 110 further includes a FIB system 111, the FIB system 111 including an evacuated chamber having an ion column 112, an ion source 114 and a focusing column 116 positioned within the ion column 112, the focusing column 116 including an extractor electrode and an electrostatic optical system. In some embodiments, the axis of the focusing column 116 may be tilted about 52 degrees with respect to the axis of the electron column. The ion column 112 includes an ion source 114, an extraction electrode 115, a focusing element 117, a deflection plate 120, and a focused ion beam 118. The focused ion beam 118 passes from the ion source 114 through the focusing column 116 and between electrostatic deflection devices, schematically indicated at deflection plates 120, toward the DUT 122, the DUT 122 comprising, for example, semiconductor devices positioned on a movable stage 125 within a lower chamber 126.

The movable stage 125 may also support one or more TEM sample holders 124 so that samples can be extracted from the DUT 122 and moved to the TEM sample holders 124. The movable stage 125 can move in the horizontal plane (X-axis and Y-axis) and vertically (Z-axis). The movable stage 125 may also be tilted about sixty (60) degrees and rotated about the Z-axis. In some embodiments, a separate TEM sample stage (not shown) may be used. Such a TEM sample stage can also be moved in the X, Y and Z axes. The door 161 is opened for insertion of the DUT 122 onto the movable stage 125 and also for servicing the internal gas supply reservoir (if used). The doors are interlocked so that if the system is in a vacuum state, the doors cannot be opened.

An ion pump 168 is used for evacuating the ion column 112. The chamber 126 is evacuated with a turbo-molecular and mechanical pumping system 130 under the control of a vacuum controller 132. The vacuum system provides approximately 1 x 10 within the chamber 126 ^-7 Tong and 5X 10 ^-4 Vacuum between the trays. If an etch assist, etch delay gas, or deposition precursor gas is used, the chamber background pressure may rise, for example, to about 1 x 10 ^-5 And (5) a bracket.

The high voltage power supply provides a suitable acceleration voltage to the electrodes in the focusing column 116 for exciting and focusing the ion beam 118. When it hits the DUT 122, material is sputtered, i.e., physically ejected from the sample. Alternatively, the ion beam 118 may decompose the precursor gas to deposit the material.

A high voltage power supply 134 is connected to the ion source 114 and to appropriate electrodes in the focusing column 116 for forming and directing an ion beam 118 of about 1keV to 60keV to the DUT 122. A deflection controller and amplifier 136, operating in accordance with a prescribed pattern provided by a pattern generator 138, is coupled to the deflection plate 120, whereby the focused ion beam 118 can be manually or automatically controlled to trace a corresponding pattern on the upper surface of the DUT 122. In some systems, a deflector plate 120 is placed in front of the final lens. When a blanking controller (not shown) applies a blanking voltage to the blanking electrodes, beam blanking electrodes (not shown) within the focusing column 116 cause ion beam 118 to impinge on blanking apertures (not shown) instead of DUT 122.

The ion source 114 sometimes provides a focused ion beam 118 of gallium (Ga). The focused ion beam 118 can be focused into a beam less than one tenth of a micron wide at the DUT 122 for modifying the DUT 122 by ion milling, enhanced etching, material deposition, or for imaging the DUT 122.

Charged particle detector 140 for detecting secondary ion or electron emissions is connected to video circuit 142, video circuit 142 providing drive signals to video monitor 144 and receiving deflection signals from system controller 119. In various embodiments, the position of charged particle detector 140 within lower chamber 126 may vary. For example, the charged particle detector 140 may be coaxial with the ion beam 118 and include an aperture that allows the ion beam to pass through. In other embodiments, the secondary particles may be collected by a final lens and then offset from the axis used for collection.

The micromanipulator 147 can precisely move objects within the vacuum chamber. Micromanipulators 147 may sometimes be referred to as nanomanipulators. The terms "micromanipulator" and "nanomanipulator" are used interchangeably throughout this disclosure. Micromanipulator 147 may include a precision motor 148 positioned outside the vacuum chamber to provide X, Y, Z and θ control of a take-out probe 149 positioned within the vacuum chamber. The extraction probe 149 may be equipped with various end effectors for manipulating small objects. In the embodiments described herein, the end effector is a probe tip 150. In some embodiments, the probe tip 150 is in the form of a needle made of metal, such as tungsten of suitable hardness.

A gas delivery system 146 extends into the lower chamber 126 for introducing and directing gaseous vapors to the DUT 122. For example, iodine may be delivered to enhance etching, or a metal organic compound may be delivered to deposit the metal.

The system controller 119 controls the operation of the various portions of the dual beam system 110. Through the system controller 119, a user may scan the ion beam 118 or the electron beam 143 in a desired manner by commands entered into a conventional user interface (not shown). Alternatively, system controller 119 may control dual beam system 110 according to programmed instructions stored in memory 121. In some embodiments, the dual beam system 110 automatically identifies the region of interest in conjunction with image recognition software, and then the dual beam system 110 may manually or automatically extract the sample according to some embodiments of the present disclosure.

To identify a region of interest, such as a hot spot or circuit break point on a semiconductor wafer, it may be necessary to apply bias voltages and/or stimuli at one or more probe pads in the DUT 122. Reference is now made to fig. 2. FIG. 2 illustrates an example DUT 122 mounted on a movable stage 125, the DUT 122 including probe pads that are probed by a pick-off probe 149, in accordance with some embodiments of the disclosure.

DUT 122 may be a semiconductor wafer having a die region 210A and scribe line region 210B, a die 220 (including circuit region 222 and seal ring 224), and a test line structure (or test line) 230 (including probe pads 232). In some embodiments, each die 220 may include an integrated circuit, and the integrated circuit may be formed from a plurality of components connected in a desired connection relationship to construct a particular circuit. In some embodiments, each die 220 may be encapsulated, with the integrated circuits in the die 220 surrounded by a sealing ring 224. The die area 210A may refer to the area where the die 220 is located. The scribe line regions 210B may be distributed between the die regions 210A and may form a grid-like distribution in the semiconductor wafer. Test lines 230 may be disposed on layout areas within scribe area 210B and positioned between dies 220. Probe pads 232 are also disposed on scribe line region 210B.

In some embodiments, the test lines 230 may be formed on a semiconductor wafer by using processes and steps that form integrated circuits in the die 220. Thus, both the test line 230 and the die 220 include a plurality of components, such as transistors, and interconnect wiring, such as a redistribution layer, may be formed on the semiconductor wafer for connecting the components based on the desired design. After the transistors and the required wiring in die 220 are fabricated on the semiconductor wafer, a test such as a Wafer Acceptance Test (WAT) may be performed on test line 230 to determine the acceptance rate of the semiconductor wafer. In some embodiments, the WAT may be performed before die 220 is completed, such that the WAT may be an intermetallic WAT. In other words, after passing the intermetallic WAT, further fabrication processes may be performed on the semiconductor wafer. In some embodiments, WAT may be performed after forming the first level metal layer (M1) or the second level metal layer (M2) (a preceding layer of the metal layers in the interconnect structure). Conversely, if the intermetallic WAT does not pass, the semiconductor wafer may be considered a faulty wafer and no further fabrication process is performed thereon. Thus, the intermetallic WAT may facilitate inspection of faulty wafers at an intermediate stage of the manufacturing process. In wafer acceptance testing, test line 230 may be electrically connected to external circuitry via probe pads 232 to check the quality of the integrated circuit process. Probing is typically performed by a probe card on a tester that is external to dual beam system 110, rather than using pick-off probes 149 in situ. This is because the withdrawal probe is typically only a mechanical device and does not have the ability to provide an electrical connection. Furthermore, simply routing the extraction probe will not work because the extraction probe is typically formed of a stainless steel needle holder holding a tungsten needle, which constitutes a high resistance path unsuitable for the application of electricity. Rather, extraction probe 149 is specifically designed to accommodate the need for in-situ detection in a dual beam system, as will be discussed in further detail below.

Once the semiconductor wafers pass the test, subsequent processes for manufacturing the end product may be performed to form the desired end product. For example, die 220 may be packaged and singulated by dicing the semiconductor wafer along scribe areas 210B to obtain individual dies 220. Dicing the semiconductor wafer along scribe line region 210B, i.e., the singulation process, may also separate test lines 230 from die 220 such that singulated die 220 in the final product may not include test lines 230. Alternatively, depending on the scribe width and the scribe position during singulation, some or all of the test lines 230 may remain in the singulated die 220 and be packaged with the singulated die 220.

With the ever shrinking device feature sizes in integrated circuits, power rails in integrated circuits need to be further improved to provide the desired performance improvements and lower power consumption in order to meet the increasing demand for integrating more complex circuit functions on a single chip. In addition to the interconnect structures (which may also include power rails) on the front side (or front side) of the structure, the power rails (or power wiring) on the back side (or back side) of the structure, which contains transistors (e.g., fin field effect transistors (finfets) and/or full-gate-all-around (GAA) transistors), are also referred to as back side power rails. Implementation of backside power rails in IC fabrication increases the number of metal rails in the structure that can be used to directly power transistors. It also increases gate density compared to existing structures without backside power rails to achieve greater device integration. The back side power rail may be wider in size than the first level metal (M0) track on the front side of the structure, which advantageously reduces power rail resistance. The use of backside power rail technology also presents new challenges for dual beam system imaging. Referring now to fig. 3, fig. 3 illustrates a test line structure compatible with backside power rail technology.

FIG. 3 shows a cross-sectional view of an example test line in a portion of DUT 122 that includes two probe pads 232 associated with circuit assembly 234. The bottom surface of the test line 230 is fixed to the movable stage 125. This portion of the test line structure includes a substrate layer (or semiconductor substrate) 250, a front side insulating layer 252 formed on the substrate layer 250, a back side insulating layer 254 formed under the substrate layer 250, and a circuit assembly 234 formed in the front side insulating layer 252. The two probe pads 232 are electrically coupled to two terminals of the circuit assembly 234. Each probe pad 232 has an opposing backside probe pad 232'. Thus, the probe pads 232 are also referred to as front side probe pads. The structure extending from front side probe pad 232 to back side probe pad 232' and including the interconnect structure therebetween is referred to as probe pad structure 256. In the probe pad structure 256, the front side probe pad 232 is the uppermost metal sheet and the back side probe pad 232' is the lowermost metal sheet. The probe pad structure 256 is separated from adjacent probe pad structures 256. Each probe pad structure 256 includes a stacked via structure located below the front side probe pad 232. The stacked via structure includes a metal sheet (or referred to as a metal pad) on each metal layer that has the same shape as the probe pad 232 and is coupled to each other through one or more vias. In some embodiments, the metallic material of the front side probe pads 232 and the metal sheets in the underlying metal layer (M1, M2, … Mx-1) of the stacked via structure may be different. For example, the front side probe pad 232 may include AlCu or NiPdAu-Cu, and the metal sheet in the underlying metal layer may include tungsten (W), aluminum (Al), or copper (Cu).

In the illustrated embodiment, the resistance of a Via (denoted as Via 1) formed in the first level Via layer is measured by circuit assembly 234, which is used to make an electrical connection between metal layers M1 and M2. In order to perform resistance measurement of the Via Via1 with a desired test accuracy, a Via chain including a plurality of Via Via1 is first formed between M1 and M2. The resistance of the Via chain is measured and the resistance of the individual vias Via1 is estimated therefrom. The Via chain includes an M2 metal sheet extending from the M2 metal pad of the first probe pad structure 256, a Via1 connecting the M2 metal sheet to the M1 metal sheet, and another Via1 connecting the M1 metal sheet to another M2 metal sheet, and repeating this zigzag pattern. The zigzag pattern continues until the end M2 metal pieces of the via chain meet the M2 metal pads of the second probe pad structure 256.

Unlike some conventional probe pad structures formed only within front side insulating layer 252 (e.g., bottom-most metal sheet starting at M1), probe pad structure 256 is shown to include a front side portion formed in front side insulating layer 252, a back side portion formed in back side insulating layer 254, and a middle portion formed in substrate layer 250. The intermediate portion electrically connects the front side portion and the back side portion of the probe pad structure 256. The front portion of the probe pad structure 256 includes a square metal sheet over each metal layer (e.g., M1, M2, … Mx-1, mx) coupled to each other by one or more vias (e.g., via1, …, via x-1). The front side probe pad 232 is formed on the topmost metal layer Mx. The backside portion of the probe pad structure 256 includes a square metal sheet over each backside metal layer (e.g., BM1, BM 2) coupled to each other by one or more backside vias (e.g., BVia 1). The backside portion also includes backside probe pads 232' formed on a bottommost backside metal layer (e.g., BM2 in the illustrated embodiment). Accordingly, the probe pad structure 256 includes a front side probe pad 232 and a back side probe pad 232' electrically coupled to each other. In some embodiments, the metal material of the backside probe pad 232' and the metal sheets in the other backside metal layers (e.g., BM 1) may be different. For example, the backside probe pad 232' may include AlCu or NiPdAu-Cu, and the metal sheet in BM1 may include tungsten (W), aluminum (Al), or copper (Cu).

The number of metal layers in the front side portion of the probe pad structure 256 may be greater than the number of backside metal layers in the backside portion of the probe pad structure 256. In some alternative embodiments, the number of metal layers in the front side portion of the probe pad structure 256 may be equal to the number of backside metal layers in the backside portion of the probe pad structure 256. The front side portion is also referred to as a front side interconnect structure of probe pad structure 256; the backside portion is also referred to as a backside interconnect structure of probe pad structure 256.

The middle portion of probe pad structure 256 includes one or more doped epitaxial features 258, contact plugs formed on top of doped epitaxial features 258, contact vias (denoted as Via 0) connecting the contact plugs and M1, and backside contact vias (denoted as BVia 0) formed below doped epitaxial features 258 and connecting doped epitaxial features 258 with BM 1. Doped epitaxial feature 258 may be a source/drain feature of a transistor formed in a probe pad structure. Transistors formed in the probe pad structure are referred to as nonfunctional transistors because they do not provide circuit functions. By comparison, transistors formed as circuit elements in the circuit region of the die are referred to as functional transistors. As used herein, a source/drain feature may refer to the source or drain of a device. It may also refer to a region that provides a source and/or drain for multiple devices. The combination of contact Via Via0, contact plug, doped epitaxial feature 258, and backside contact Via BVia0 provides an electrical connection between the front side interconnect structure and the backside interconnect structure of probe pad structure 256.

To protect the backside power rails (including the backside probe pads), a passivation layer 257 is deposited on the bottom surface of the DUT 122. Passivation layer 257 may be formed of a dielectric material such as Undoped Silicate Glass (USG), silicon nitride, silicon oxide, silicon oxynitride, or a non-porous material. The passivation layer 257 electrically isolates the DUT 122 from the movable stage 125 underneath. The movable stage 125 is typically a conductor. For DUTs that do not employ backside power rail technology, the semiconductor substrate 250 is in direct contact with the movable stage 125. Accordingly, charges accumulated in the DUT 122 during the manufacturing process can be easily discharged to the movable stage 125 through the semiconductor substrate 250. However, by employing backside power rail technology, in the illustrated embodiment, the DUT 122 is isolated from the movable stage 125 by the passivation layer 257. The charge accumulated in DUT 122 during fabrication may not be discharged. The accumulated charge can interfere with the imaging process in a dual beam system, such as distorting the TEM image.

In this embodiment, dedicated extraction probes 149 are capable of providing electrical connections. In an example in-situ process, after DUT 122 is mounted on movable stage 125, probe tip 150 of take-out probe 149 is electrically connected to a ground line of a power supply. The power supply may be external to the dual beam system. By probing one of the front side probe pads 232, the charge accumulated in the DUT 122 can be discharged to ground through the extraction probe 149. After the accumulated charge is depleted, the probe tip 150 is switched to the voltage line of the power supply. By probing one of the front side probe pads 232, the probe tip 150 charges the circuit assembly 234. The charged portions of the circuit assembly 234 will be illuminated in images obtained by a focused ion beam microscope and/or a scanning electron microscope. If there is a circuit break point, such as a defective via 260 shown in fig. 3, then charge does not pass through the defective via 260. On the acquired image, the charged portions of the circuit elements 234 may appear as bright areas, while the uncharged portions of the circuit elements 234 may appear as dark areas. The contrast between the bright and dark areas indicates hot spots, identifying the area of interest. Alternatively, in addition to biasing probe pads 232, extraction probes 149 may be coupled to signal lines of a signal generator to feed stimulus to circuit assembly 234 and monitor responses from circuit assembly 234. The signal generator may be external to the dual beam system. The power source and the signal generator may be one device or two independent devices. In addition, two extraction probes may be applied simultaneously to two probe pads at both ends of the circuit assembly 234 to check whether the circuit assembly 234 is a through hole. Either way, after the region of interest is identified, the sheet containing at least circuit component 234 is ion milled. The extraction probe 149 then transports the slice to the TEM sample holder 124 for further investigation under TEM imaging. By employing specialized extraction probes 149, the entire process including releasing the DUT, biasing and/or exciting the probe pads, identifying the region of interest, ion milling the slice containing the region of interest, extracting the slice, and TEM imaging the slice can be performed in situ in the dual beam system without breaking the vacuum. The throughput of wafer testing can be greatly improved.

Fig. 4 illustrates an exemplary extraction probe (or probes) 149 according to some embodiments of the present disclosure. The extraction probe 149 includes a stem adapter 170, the stem adapter 170 being coupled to the precision motor 148 (fig. 1) and driven by the precision motor 148. In some embodiments, the precision motor 148 is positioned outside the vacuum chamber of the dual beam system 110 and the stem adapter 170 is positioned within the vacuum chamber. The precision motor 148 provides X, Y, Z and θ control of the stem adapter 170, which stem adapter 170 ultimately passes control to the probe tip 150.

The probe tip 150 takes the form of a needle. In some embodiments, the probe tip 150 may be made substantially of tungsten, considering the hardness of the probe tip to be able to manipulate the ion milled sample. In some embodiments, to reduce the resistance of the probe tip 150, an alloy of tungsten with a metal having a resistivity lower than tungsten, such as a copper tungsten (CuW) alloy, may be used. CuW is a mixture of copper and tungsten. Since copper and tungsten are not miscible, the material is composed of distinct particles of one metal dispersed in a matrix of another metal. Thus, the microstructure is more like a metal matrix composite than a true alloy. The probe tip 150 may be made of a copper-tungsten mixture by pressing tungsten particles into a desired shape, sintering the compacted portion, and then infiltrating with molten copper. The copper tungsten mixture combines the properties of both metals to form a material that is heat resistant, ablation resistant, highly thermally and electrically conductive, and easy to process. The copper-tungsten mixture may contain about 5% to about 50% by weight copper with the remainder being tungsten. Copper reduces the resistivity of the probe tip 150. The mixture with a smaller weight percentage of copper has a higher density, higher hardness and higher resistivity. In one example, the probe tip 150 is made of 10% copper by weight and 90% tungsten by weight. In some other embodiments, the probe tip 150 may be made of gold-plated tungsten in order to further reduce the resistance of the probe tip 150, particularly in order to achieve a lower resistance to the surface current flowing through the probe tip 150.

The stem adapter 170 is coupled to a probe shaft (or arm) 172. In some embodiments, the probe shaft 172 may be substantially made of stainless steel. Tapered retainers (or branches) 174 secure probe shaft 172 to stem adapter 170. The retainers 174 may be made of a dielectric material such as plastic. The end of the probe shaft 172 is embedded in a probe tip holder 176. The probe tip holder 176 has one end that grips the probe tip 150 and the other end that grips the probe shaft 172. The probe tip holder 176 is electrically conductive with the probe tip 150. To reduce the resistance of the probe tip holder 176, the probe tip holder 176 may be formed of an alloy of a metal having low resistivity, such as an alloy of copper gold (CuAu). The resistivity of the copper-gold alloy may be lower than 22nΩ m in some embodiments, depending on the weight percent of gold in the alloy. The probe tip holder 176 is electrically insulated from the probe shaft 172. Also shown in fig. 4 is a cross-sectional view along line A-A of the joint through the probe shaft 172 and the probe tip holder 176. In a cross-sectional view, the probe shaft 172 is rod-shaped with a hollow center, and the probe tip holder 176 is rod-shaped with a hollow center, with the probe shaft 172 and the insulator ring 175 being embedded in the center of the probe tip holder 176. The insulator ring 175 may be formed of a dielectric material such as plastic. An insulator ring 175 electrically isolates the probe tip holder 176 from the probe shaft 172.

The probe tip holder 176 provides at least one wire connection bond 178. In the illustrated embodiment, the probe tip holder 176 provides two wire connection bonds 178. Two wire connection bonds 178 may be positioned on opposite sides of the probe tip holder 176. The wire connection bond 178 secures the wires 180a and 180b in electrical connection with the outer surface of the probe tip holder 176. The wire collector 182 organizes the wire routing of the wires 180a and 180 b. A hub 182 is attached to the probe shaft 172. The wires 180a and 180b are further disposed inside the retainer 174 and are led out of the vacuum chamber. Alternatively, without the need for the wire collector 182, the wires 180a and 180b can be disposed internally through the hollow tube of the probe shaft 172 to be directed to the retainer 174 and ultimately out of the vacuum chamber.

Outside the vacuum chamber, wires 180a and 180b are connected to a switch control box 184. The switch control box 184 controls the connection between the wires 180a and 180b and the power source (or excitation source) 186. For example, the wire 180a may be used as a ground wire connected to the power supply 186, and the wire 180b may be used as a voltage line with a bias wire connected to the power supply 186. After the DUT is secured to the movable stage in the vacuum chamber, the probe tips 150 fall onto the probe pads of the DUT to release the accumulated charge. At the same time, switch control box 184 activates the connection between wire 180a and the ground of power supply 186 and leaves wire 180b electrically floating. The charge on the DUT discharges through a path that includes the probe tip 150, the probe tip holder 176, the wire 180a, and the ground line of the power supply 186. After discharging, the switch control box 184 activates the connection between the wire 180b and the voltage line of the power supply 186 and electrically floats the wire 180 a. A bias voltage is applied to the probe pads of the DUT through a path including voltage lines of power supply 186, wires 180b, probe tip holder 176, and probe tips 150. The magnitude of the bias voltage may be adjustable, for example, from about 0.1 volts to about 20 volts, by turning a knob on the power supply 186. In some applications, it is a signal stimulus provided to the DUT, and wire 180a may provide stimulus to the DUT, and wire 180b may obtain a response from the DUT. After identifying the region of interest, the switch control box 184 cuts off the electrical connection to the wires 180a and 180b, causing the probe tip 150 to float electrically, which allows the unbiased probe tip 150 to be used as a normal extraction probe tip for subsequent extraction operations in a dual beam system. Notably, providing an electrical connection to the DUT through the probe tip 150 is a different problem than applying an electrical charge to the probe to control the attractive force between the sample and the probe. The latter is a mechanical problem by enhancing the attractive force, which does not provide electrical functions (e.g., discharge, bias, and/or excitation) to the sample.

In addition to higher throughput testing efficiency, the complete in situ FIB extraction procedure provides other advantages. The probe tips 150 are typically smaller than other probe tips provided in the probe card of the ex-situ tester, which allows the probe pads of the test line structure to be smaller and saves more area for accommodating circuit area. In some embodiments, the probe pads for in situ probing may have dimensions of about 10 μm by 10 μm, which are typically smaller than the dimensions for ex situ probing. In addition, the probe tips 150 typically leave smaller probe marks than other probe tips provided in probe cards using ex-situ testers. In some embodiments, the probe tip 150 leaves probe labels generally less than about 5 μm by 5 μm.

Fig. 5 illustrates a TEM grid 300 according to some embodiments of the present disclosure. In the illustrated embodiment, the TEM grid 300 comprises a partial ring. In some applications, the sample 302 is attached to the fingers 304 of the TEM grid 300 by ion beam deposition or an adhesive. Sample 302 may be a sheet containing a region of interest, such as circuit assembly 234 having hot spot 260 as shown in fig. 3. The sample 302 extends from the finger 304 such that the electron beam will have a free path through the sample 302 to the detector below the sample. TEM samples can be broadly classified as either "plan view" samples or "cross-sectional view" samples, depending on the orientation of the sample on the workpiece. If the surface of the sample to be observed is parallel to the surface of the workpiece, the sample is referred to as a "plan view" sample. If the surface to be observed is perpendicular to the surface of the workpiece, the sample is referred to as a "cross-sectional view" sample. The TEM grid 300 can be mounted horizontally on a TEM sample holder 124 (FIG. 1) in a TEM, with the plane of the TEM grid perpendicular to the electron beam, and the sample is viewed.

Fig. 6 shows a perspective view of a TEM sample 302 partially extracted from DUT 122 using a FIB extraction process. The ion beam 118 cuts the grooves 306 and 308 on both sides of the sample to be extracted, leaving a sheet 310, the sheet 310 having a major surface 312 to be observed by the electron beam. The sample 302 is then released by tilting the DUT 122 relative to the ion beam and cutting around its sides and bottom. The take-out probe 149 is attached to the top of the sample 302 either before or after the sample 302 is released and the sample is transported to the TEM grid. Fig. 6 shows that the sample 302 is almost completely released, with one side still attached by the tab 318. Fig. 6 shows the ion beam 118 ready to sever the tab 318.

As shown in fig. 6, major surface 312 is vertically oriented. The transport of the sheet typically does not change its orientation, so that when the sample 302 is brought to the TEM sample holder 124, the major surfaces of the sheet remain vertically oriented. As shown in fig. 7, the plane of the TEM grid 300 may be oriented vertically such that the sample 302 may be attached to the fingers 304 of the TEM grid 300 with the major surface 312 extending parallel to the plane of the grid and the grid structure does not interfere with the transmission of electrons when the grid is mounted on a TEM sample holder. The ion beam may be used to attach the extracted sample to the TEM grid by ion beam deposition. After attachment, the ion beam may also be used to thin the surface of the sample 302. Fig. 7 shows a TEM grid 300 in a grid support 320 with a sample 302 attached to the TEM sample holder 124. The sample 302 is attached to the TEM grid 300 using the ion beam 118 and deposition precursor gas 330 from a nozzle 332. Fig. 8 shows TEM sample holder 124 rotated and tilted so that sample 302 is substantially perpendicular to ion beam 118 so that sample 302 can be thinned by ion beam 118.

Fig. 9 is a flowchart of a method 400 of utilizing an in-situ-complete FIB extraction procedure capable of providing extraction probes for electrical connection to a DUT, in accordance with various embodiments of the present disclosure. The present disclosure contemplates additional processing. Additional operations may be provided before, during, and after method 400, and some of the operations described may be moved, replaced, or eliminated for additional embodiments of method 400.

At operation 402, the method 400 loads a DUT, such as a semiconductor (e.g., silicon) wafer, into a vacuum chamber of a dual beam system. The DUT is fixed on a movable stage. The atmosphere is then evacuated from the vacuum chamber such that the DUT is under vacuum. At operation 404, the method 400 probes one or more probe pads of a DUT in situ in a vacuum chamber using one or more extraction probes. One or more of the probe pads may be part of a test line structure of the DUT. The probe pads may be about 10 μm by 10 μm in size. The probe label left by removal of the probe may be less than about 5 μm by 5 μm. At operation 406, the method 400 connects the probe tip of the extraction probe to a ground line through the switch control box, which allows charge accumulated in the DUT to discharge through the extraction probe. At operation 408, the method 400 connects the probe tip of the take-out probe to a voltage line through the switch control box, which allows circuit components in the DUT to be biased or charged to a reference voltage. In some embodiments, it is an stimulus that is sent through the probe tip into a circuit component in the DUT. At operation 410, the method 400 identifies a region of interest (e.g., a hot spot) on the DUT by imaging the DUT with a focused ion beam microscope and/or a scanning electron microscope under bias or stimulus. At operation 412, the method 400 performs ion milling of the slice containing the region of interest using the focused ion beam. During ion milling, the extraction probe is set to be electrically floating by a switch control box. At operation 414, the method 400 extracts the lamellae by withdrawing the probe and positioning the lamellae on the TEM grid. The lamellae may be further thinned by focusing the ion beam to make their thickness suitable for TEM imaging. At operation 416, the method 400 acquires a TEM image of the slice for further investigation.

The present disclosure provides a retrieval probe in a dual beam system. In addition to conventional extraction operations, the extraction probes can provide electrical connections (e.g., discharge, bias, and/or stimulus) with the DUT being probed. The extraction probe allows the entire FIB extraction procedure to be performed in-situ in a dual beam system without relying on an ex-situ tester to identify regions of interest of the DUT. Thus, the throughput of the wafer inspection process can be highly improved.

In one example aspect, the present disclosure relates to an apparatus for observing a sample using a charged particle beam. The device comprises: an ion beam column configured to generate and direct an ion beam; an electron beam column configured to generate and guide an electron beam; a vacuum chamber for containing a sample; and a probe positioned in the vacuum chamber. The probe is configured to provide an electrical connection between the sample and a power source. In some embodiments, the ion beam column is further configured to ion mill out the sheet from the sample, and the probe is further configured to remove the sheet from the sample. In some embodiments, the probe comprises: a probe tip; a probe tip holder, wherein the probe tip holder is electrically connected to the probe tip; and a probe shaft coupled to the probe tip holder. In some embodiments, the probe shaft is electrically insulated from the probe tip holder. In some embodiments, the probe shaft is electrically insulated from the probe tip holder by a dielectric ring stacked between the probe shaft and the probe tip holder. In some embodiments, the probe tip comprises tungsten and the probe tip holder is free of tungsten. In some embodiments, the probe tip holder comprises an alloy of copper and gold. In some embodiments, the probe shaft comprises stainless steel. In some embodiments, the probe further comprises: at least one wire attached to the probe tip holder, wherein the wire is electrically coupled to the power source. In some embodiments, the apparatus further comprises a motor configured to move and rotate the probe, wherein the motor is positioned outside the vacuum chamber.

In another example aspect, the present disclosure is directed to a probe structure for a charged particle beam microscope. The probe structure comprises: a needle; a needle holder holding a needle, wherein the needle holder is electrically connected to the needle; a wire attached to the needle holder, wherein the wire provides an electrical connection between the needle holder and a power source; and an elongate shaft coupled to the needle holder, wherein the elongate shaft imparts motion control to the needle through the needle holder. In some embodiments, the elongate shaft is electrically insulated from the needle holder. In some embodiments, the elongate shaft is partially embedded in the needle holder. In some embodiments, the needle and needle holder comprise different compositions of electrically conductive materials. In some embodiments, the wire is a first wire and the probe structure further comprises a second wire attached to the needle holder. In some embodiments, the probe structure further comprises a buncher configured to organize the first wire and the second wire, wherein the buncher is attached to the elongate shaft. In some embodiments, the needle is operable to extract a sheet from the sample for inspection under a charged particle beam microscope.

In another example aspect, the present disclosure is directed to a method of observing defects in a sample. The method comprises the following steps: loading a sample on a stage; detecting the sample with a probe; electrically connecting the probe to a ground line to discharge the sample; electrically connecting the probe to a voltage line to bias the sample; identifying a region having a defect; ion milling the sample to release the region from the sample; and extracting the region by the probe. In some embodiments, the sample includes an integrated circuit having a front side power rail and a back side power rail. In some embodiments, the probe comprises: a needle; a needle holder holding a needle; a first wire attached to the needle holder and providing an electrical coupling between the needle holder and a ground wire; and a second wire attached to the needle holder and providing an electrical coupling between the needle holder and the voltage line.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments described herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.

Claims (10)

1. An apparatus for observing a sample using a charged particle beam, comprising:

an ion beam column configured to generate and direct an ion beam;

an electron beam column configured to generate and guide an electron beam;

a vacuum chamber for containing a sample; and

a probe positioned in the vacuum chamber, wherein the probe is configured to provide an electrical connection between the sample and a power source.

2. The apparatus of claim 1, wherein the ion beam column is further configured to ion mill a sheet from the sample, and the probe is further configured to remove the sheet from the sample.

3. The apparatus of claim 1, wherein the probe comprises:

a probe tip;

a probe tip holder, wherein the probe tip holder is electrically connected with the probe tip; and

a probe shaft coupled to the probe tip holder.

4. The device of claim 3, wherein the probe shaft is electrically insulated from the probe tip holder.

5. The apparatus of claim 4, wherein the probe shaft is electrically insulated from the probe tip holder by a dielectric ring stacked between the probe shaft and the probe tip holder.

6. The apparatus of claim 3, wherein the probe tip comprises tungsten and the probe tip holder is free of tungsten.

7. The apparatus of claim 6, wherein the probe tip holder comprises an alloy of copper and gold.

8. The apparatus of claim 6, wherein the probe shaft comprises stainless steel.

9. A probe structure for a charged particle beam microscope, comprising:

a needle;

a needle holder holding the needle, wherein the needle holder is electrically connected to the needle;

a wire attached to the needle holder, wherein the wire provides an electrical connection between the needle holder and a power source; and

An elongate shaft is coupled to the needle holder, wherein the elongate shaft imparts motion control to the needle through the needle holder.

10. A method of observing defects in a sample, comprising:

loading a sample on a stage;

probing the sample with a probe;

electrically connecting the probe to a ground line to discharge the sample;

electrically connecting the probe to a voltage line to bias the sample;

identifying a region having the defect;

ion milling the sample to release the region from the sample; and

the region is removed by the probe.