CA2543396A1 - Method for manipulating microscopic particles and analyzing the composition thereof - Google Patents
Method for manipulating microscopic particles and analyzing the composition thereof Download PDFInfo
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- CA2543396A1 CA2543396A1 CA002543396A CA2543396A CA2543396A1 CA 2543396 A1 CA2543396 A1 CA 2543396A1 CA 002543396 A CA002543396 A CA 002543396A CA 2543396 A CA2543396 A CA 2543396A CA 2543396 A1 CA2543396 A1 CA 2543396A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
- G01N23/22—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by measuring secondary emission from the material
- G01N23/2204—Specimen supports therefor; Sample conveying means therefore
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B21/00—Microscopes
- G02B21/32—Micromanipulators structurally combined with microscopes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/30—Electron or ion beam tubes for processing objects
- H01J2237/317—Processing objects on a microscale
- H01J2237/3174—Etching microareas
- H01J2237/31745—Etching microareas for preparing specimen to be viewed in microscopes or analyzed in microanalysers
Abstract
We disclose a method for analyzing the composition of a microscopic particle (100) resting on a first sample surface (110). The method comprises positioning a micro-manipulator probe (120) near the particle (100); attaching the particle (100) to the probe (120); moving the probe (120) and the attached particle (100) away from the first sample surface (110); positioning the particle (100) on a second sample surface (150); and, analyzing the composition of the particle (100) on the second sample surface (150) by energy-dispersive X-ray analysis or detection of Auger electrons. The second surface (150) has a reduced or non-interfering background signal during analysis relative to the background signal of the first surface (110). We also disclose methods for adjusting the electrostatic forces and DC potentials between the probe (120), the particle (100), and the sample surfaces (110, 150) to effect removal of the particle (100), and its transfer and relocation to the second sample surface (150).
Description
to METHOD FOR MANIPULATING MICROSCOPIC PARTICLES AND
14 Fatent Application of Thomas M. Moore and John M. Anthony 1 ~ TECHNICAL FIELD
18 The invention relates to techniques for removing and analyzing microscopic 19 particles from a sample surface, particularly from semiconductor samples.
2o BACKGROUND
21 In the semiconductor industry, unexpected particles due to contamination will 22 cause yield loss during the manufacturing process. Since a major focus of this industry is 23 aggressive reduction in feature size for pattern line widths, the minimum size of particles 24 that can cause performance loss also decreases rapidly. A reasonable estimate for a "killer defect" size is that greater than one-third the size of the smallest feature on the 26 semiconductor wafer.
27 Although semiconductor manufacturing is performed in clean rooms with 28 stringent particle standards, unexpected contamination will occur due to sources such as 29 moving parts, human presence, gas condensation, and chamber wear. Control and removal of these particles is a continuous process. In many cases, removal of the source 31 of particles requires an understanding of their origin. Many of these particles or defects 32 are too small for detection in a general purpose optical inspection microscope, so higher 33 resolution methods are required, using charged-particle microscopes, such as scanning 1 electron microscopes (SEM), transmission electron microscopes (TEM), scanning Auger 2 microprobes (SAM), or focused ion beam (FIB) instruments, are required.
3 Even an image of the particle is usually insufficient to trace the origin of the 4 particle, and more information is required. Elemental composition is valuable in identifying the defect. This can be done in various ways using the charged-particle 6 systems mentioned above. Unfortunately, most of the analytical methods are limited by 7 background signals from the environment of the particle.
8 Throughput is also a critical parameter in semiconductor manufacturing.
9 Existing strategies for compositional analysis of particles on a semiconductor wafer, for l0 example, usually require removal of the wafer from the fabrication area for off line i i analysis using methods such as those described below. Removal from the line severely 12 reduces the throughput of the manufacturing process.
13 Particle identification on sample surfaces using electron-beam based identification 14 is complicated by the size of the particle relative to the electron penetration depth, and by the nature of surrounding materials in the sample. As an electron beam interacts with 16 bulls solid materials, it expands to fill a teardrop-shaped volume as it loses energy. As 17 the primary beam interacts with atoms in this volume, it generates low energy Auger i8 electrons and X~rays that are characteristic of the elements involved.
19 The particular X-ray line generated will depend on the atomic number of the 2o element, the energy of the electron during the interaction; and other factors. When 21 trying to identify an unknown particle using conventional Energy-dispersive X-ray 22 Spectrophotometry (EDS), the energy of the electron beam must be large enough to 23 generate inner-shell X-rays from all possible relevant elements, which, for semiconductor 24 applications, may include elements of high atomic number such as tungsten.
Unfortunately, this energy results in a penetration depth that may be much larger than the 26 particle of interest, resulting in X-ray generation from the sample surface. These X-rays 27 interfere with any signal from the particle, making unique identification of the particle 28 material difficult. Conventional strategies for solving this problem involve either 29 resolving the X-ray lines of different elements, or reducing the energy of the exciting 3o electron beam.
31 For example, it is possible to detect and analyze electron-beam generated X-rays 32 from a particle by measuring the intensity and diffraction angle of the X-rays diffracted 33 by a reference crystal, or Wavelength Dispersive X-ray Spectrometry (WDS).
One 1 chooses the crystal atomic spacing to deflect (with very high resolution) X-rays of a 2 given energy, thus allowing separation between X-ray lines of different elements. This 3 method has higher energy resolution than EDS but much slower throughput. In addition, 4 if the particle could be, as it often is, of the same composition as the sample surface, this method will not uniquely determine the particle composition.
6 Other solutions involve reducing the energy of the primary electron beam to 7 guarantee the activated volume is less than the volume of the particle of interest. This 8 reduction in primary electron-beam energy results in characteristic X-rays of much lower 9 energy (M or L shell X-rays, rather than K shell). Conventional cooled semiconductor-based detectors use the generation and collection of electron-hole pairs as a measure of 11 the energy of the ionizing radiation (a few eV for each electron-hole pair, depending on 12 the detecting material). A reduction in the X-ray energy therefore leads to a reduced 13 number of electron-hole pairs and reduced sensitivity to the particle material. In addition 14 the resolution of these detectors is governed by the statistics of the electron-hole generation process, and reducing the energy of the detected X-ray often leads to 16 ambiguous identification of the element of interest. X-ray micro-calorimeter methods 17 have been used to detect these weak X-ray signals, using heat transferred to the detector 18 rather than the generation of electron-hole pairs. This process does allow measurement 19 of small X-ray energies, but micro-calorimeter instruments are expensive, have 2o complicated cooling requirements, and are slow compared to other methods.
Also, the 21 electron beam must be kept smaller than the smallest dimension of the particle of interest, 22 rendering the method impractical for small, unsymmetrical particles.
23 Scanning Auger microprobe analysis also uses an electron beam to irradiate a 24 particle of interest, but rather than detecting any X-rays generated it focuses on the detection of Auger electrons ejected from the atoms of the material. These Auger 26 electrons come from outer shells and have relatively low energies. The Auger electron 27 energies from a material produce a pattern that is characteristic of each element in the 28 material, and the shape and exact energy of the Auger transitions provide information on 29 the chemical bonding of the elements in the material (such as, phase or compound information). The escape depth of these electrons is quite small (a few nm), so Auger 31 analysis focuses mainly on the surface of a sample. This is an advantage for the analysis 32 of small diameter particles (<10 nm). For the analysis of larger particles, one can 33 generate depth profiles by using an ion beam to sputter through the particle and take 1 periodic measurements, but this is inherently destructive of the surrounding sample due 2 to ion milling in the SAM, and requires background analyses on the sample near the 3 location of the particle. Auger analysis is typically more sensitive to light elements than 4 standard EDS analysis, making it more suitable to identify organic materials. However, to improve counting statistics, high electron beam currents are typically employed. This 6 exaggerates the issues of thermo-mechanical drift and drift due to electrical charging of 7 the sample. This means that operating the SAM in the "spot mode," with the electron 8 beam positioned on the particle, involves a risk that over time the electron beam spot will 9 drift onto the sample that surrounds the particle. And the use of a raster pattern for the io electron beam will be more tolerant of drift for keeping the beam on the particle, but will i i involve significant contamination of the results with signal from the surrounding material.
12 In either case, background contamination of the Auger results is a serious issue, and 13 Auger analyses of the surrounding material are required to uniquely identify the signal 14 from the particle. The acquisition of background analyses reduces throughput and inherently damages the sample.
16 TEM can often be used for analysis of particles in or on surfaces. There are a 17 variety of methods for isolating the particle for analysis, including replication, lift-out or is cross sectioning the area of interest. These methods all destroy the sample surface and 19 must be done off line, thereby increasing cost and cycle time.
2o Moving the particle from the first sample surface to a more controlled 21 environment for testing can dramatically improve the chance of success and throughput 22 for elemental identification with either EDS or Auger analysis. A critical part of this 23 process is the strategy for moving the particle. This disclosure describes a novel method 24 for removing a particle of interest from a sample surface, transporting that particle to a second sample surface with a controlled X-ray or Auger background, and performing 26 electron beam-induced X-ray analysis or Auger electron analysis there, using any of the 27 methods discussed above. This eliminates the requirement that the analyzing technique 28 have high spatial resolution, although a technique with high spatial resolution, such as 29 EDS analysis in the SEM and SAM analysis, is generally preferred. For example, 3o techniques without high spatial resolution that could be successfully applied to the 31 situation of a particle on a reduced or non-interfering background include X-ray 32 Photoelectron Spectroscopy (XPS) and X-ray Fluorescence analysis (XRF), which may 33 offer an advantage in unique and specific situations.
-S-1 The proposed method for particle manipulation and EDS X-ray analysis can be 2 done in-line on existing wafer-manufacturing tools. An in-line procedure using existing 3 manufacturing and inspection tools represents a significant reduction in cycle time for 4 contamination removal. SEM is a routine method for wafer inspection, and analytical methods using the electron beam in an SEM system provide a substantial throughput 6 advantage over the off line strategies.
7 Although this disclosure primarily illustrates the use of the novel technique to 8 manipulate and examine particles that are contaminants in the context of semiconductor 9 manufacturing, the reader should note that the term "particle" may be taken to include objects that may not be contaminants in other environments, such as chemical deposits, 0 11 biological material, or micro-mechanical machines. In the latter cases, the novel methods 12 of manipulation described in this application may be applied to manipulate these objects 13 generally, for purposes other than electron-beam X-ray analysis or Auger electron 14 analysis.
DRAWINGS
16 Figure 1 shows the steps of attaching a particle to a micro-manipulator probe and 17 removing the particle to a second surface for analysis.
18 Figure 2 shows three other methods of attaching a particle to a micro-19 manipulator probe.
2o Figure 3 shows the process of modifying electrostatic forces by bombardment 21 with polarizable molecules.
22 Figure 4 shows the method of simultaneously viewing a particle and modifying 23 the charge state of the particle.
24 Figure 5~ shows several methods for fixing a particle to a second surface for analysis.
26 Figure 6 shows the analysis of a particle while the particle is fixed to the tip of a 27 micro-manipulator probe.
28 Figure 7 shows the process of analyzing the composition of a particle removed to 29 a second surface for analysis.
SITMMARY
31 We disclose a method for analyzing the composition of a microscopic particle 32 resting on a first sample surface. Usually, the particle will be a contaminant in a 33 semiconductor processing system, although the method is not limited to those 1 circumstances. The method comprises positioning a micro-manipulator probe near the 2 particle; attaching the particle to the probe; moving the probe and the attached particle 3 away from the first sample surface; positioning the particle on a second sample surface;
4 and, analyzing the composition of the particle on the second sample surface by energy-dispersive X-ray analysis, Auger microprobe analysis or any other suitable analytical 6 technique. The second surface has a reduced or non-interfering background signal 7 during analysis, relative to the background signal of the first surface. (We call such a 8 reduced or non-interfering background signal a "controlled" background signal in the 9 claims.) We also disclose methods for adjusting the electrostatic forces and DC
l0 potentials between the probe, the particle, and the sample surfaces to effect removal of 11 the particle, and its transfer and relocation to the second sample surface.
These include 12 adjusting electrostatic forces to create an attractive force between the probe and particle.
13 Adjustment of the electrostatic forces may include locally adjusting the energy or 14 intensity (intensity means beam current for electron and ion beams) of an electron beam, ion beam or photon beam incident on the individual components of the sample system, 16 which includes the probe tip, particle and first sample surface, to create an electrostatic 17 attraction between the particle and probe tip, or an electrostatic repulsion between the 18 particle and the first sample surface. This procedure is reversed to transfer the particle 19 from the probe tip to the second sample surface.
The second sample surface may be the probe tip itself. In this case the probe tip 21 is composed of a controlled background material. Due to the possibility of transmission 22 of the energetic beam through a tiny particle, or scattering of the energetic beam onto the 23 underlying surface, it may be necessary to translate the probe tip with the particle 24 attached over a surface composed of a controlled background material, or alternatively translate such a controlled background surface beneath the probe tip with the particle 26 attached. In this description, "under" and "beneath" refer to the side of the particle 27 opposite the side on which the energetic beam is incident (i.e.: the transmitted side).
29 The analysis of microscopic particles, particularly in semiconductor manufacturing, is typically done inside a Scanning Electron Microscope (SEM), Focused 31 Ion Beam (FIB) instrument, or Scanning Auger Microprobe (SAM). The FIB
instrument 32 may be either a single-beam model, or a dual-beam (both SEM and ion beam) model.
33 Typical FIB instruments are those manufactured by FEI Company of Hillsboro, Oregon, _7-1 as models 200, 235, 820, 830, or 835. The probe (120) referred to below is a 2 component of a micro-manipulator tool attached to the FIB instrument with vacuum 3 feed-through. A typical such micro-manipulator tool is the Model 100 manufactured by 4 Omniprobe, Inc. of Dallas, Texas. Typical SAM instruments include the JAMP-and JAMP-7830F manufactured by JEOL USA, Inc. of Peabody, Massachusetts.
6 Figure 1 depicts the general setup for particle manipulation and analysis.
Fig. lA
7 shows a particle (100) of interest resting on a first sample surface (110).
A micro-8 manipulator probe (120) is positioned near the particle (1d0). The probe tip can be 9 electrostatically charged relative to the particle and the first sample surface.
Alternatively, a voltage source (130) may be connected between the probe (120) and the 11 first sample surface (110). The local electrostatic charge on the particle can be modified 12 by the irradiation of the particle by a charged particle beam. Figs. 1 B
through 1 D show, 13 respectively, the irradiation of the particle (100) and first sample surface (110) by 14 photons or a charged-particle beam (140) to cause attachment of the particle (100) to the probe (120), the removal of the probe (120) and attached particle (100) from the first 16 sample surface (110), and the deposition of the particle (100) on a second sample surface 17 (150) for analysis. The drawings are not to scale.
18 Attaching the particle to the probe 19 Strong electrostatic forces exist on particles in a vacuum. The presence of static charges on the particle (100) and the probe (120) leads to the creation of image charges 21 on the opposite surfaces. These image charges create forces that are proportional to the 22 area exposed and inversely proportional to the distance between the objects. Reducing 23 or increasing the exposed area will therefore either reduce or increase the force acting on 24 the particle (100), and the resultant adhesion between probe (120) and particle (100).
This can be used as a straightforward method to remove particles of interest from the 26 sample, using either a conducting or insulating probe (120). Conducting probes allow 27 more versatility through the introduction of static or time varying voltages or 28 electrostatic charges to the probe (120) from a voltage or electrostatic charge source 29 (130), as shown generally in Fig. lA.
The shape of the tip of the probe (120) will also influence the electric fields at the 31 tip. Static electric charges on a blunt tip will exext stronger influence on a particle in line 32 with the tip than a sharply pointed tip. In contrast, in the case of a DC
potential on a 33 conductive tip, a sharp tip will produce the strongest field concentration at the tip. The _g_ 1 probe ( 120) can be moved into proximity to the particle ( 100) while imaging with, for 2 example, the electron beam (140) available in the FIB instrument, as shown in Fig. 1B.
3 The electron beam will also affect the charge distribution in the surface-particle-probe 4 system, and thus can assist attraction of the particle (100) to the probe (120). An application of this effect is discussed below. The electron beam (140) depicted in Fig.
6 1B and other drawings should be understood to also be a charged-particle beam or 7 photon beam generally, and may, for example, consist of an ion beam. These, and beams 8 of photons, such as from a laser, are referred to collectively in the claims as "energetic"
9 beams.
l0 In general, the adjustment of electrostatic forces on the system may comprise 11 adjusting the energy of an electron beam (140) incident on the particle (100), probe 12 (120), and first sample surface (110) to create a relative electrostatic attraction between 13 the particle (100) and the probe (120), and a relative electrostatic repulsion between the 14 particle (100) and the first sample surface (110). The process may be assisted by a voltage source (130) connected between the first sample surface (110) and the probe 16 ( 120). Clearly, the impinging beam ( 140) could also be a beam of photons, having 17 sufficient energy to release photoelectrons, which thus change the charge distribution in 18 the system, and the electrostatic forces involved.
19 The preferred embodiment may also be carried out using an adhesive (160) on the probe (120), as shown in Fig. 2A. An acceptable adhesive (160) could be any having a 21 low vapor pressure, such as vacuum grease, low melting point waxes, or other low vapor 22 pressure glues. In this case, the forces of adhesion simply capture the particle (100), 23 notwithstanding existing electrostatic forces.
t 24 In another embodiment, shown in Fig. 2B, tweezers (170) connected to the probe (120) grasp the particle (100) and remove it from the first sample surface (110). Suitable 26 device having tweezers (170) or similar grippers are those manufactured by MEMS
27 Precision Instruments in Berkeley, CA.
28 The probe (120) can touch the particle (100), but this is not necessary in many 29 cases, as the particle (100) will jump to the probe (120) due to the electrostatic attraction. The electrostatic field is controlled by surface area and therefore enhanced 31 with a blunt tip on the probe (120), or the blunt side of a particle (100) or the probe 32 (120), whereas DC potentials are enhanced by a pointed tip that concentrates the field 33 lines. Figs. 2C and 2D show examples of strategies for particle (100) attachment and 1 transfer by controlling the surface area of the particle (100) exposed to the manipulator, 2 by applying the tip (125) of the probe (120) and the side (135) of the probe (120) to the 3 particle to achieve the desired movement of the particle (100).
4 An additional method of adjusting the electrostatic fields in the particle-probe-surface system, for both attaching and removing the particle (100) comprises depositing 6 a conductive material on the first sample surface (110) or second sample surface (150), 7 as the case may be, to distribute and modify the electrostatic charge on the surface at the 8 location of the particle to create either an attractive or a repulsive force on the particle, 9 as desired. Figure 3A depicts the deposit of polarizable molecules (250), such as water, l0 on the sample surface (110). Figure 3B depicts the deposit of a conductive film (255) by 1 i evaporation of a source. Figure 3C depicts a directed jet (240) of gas (245) applied to a 12 surface (110) having a particle (100) resting upon the surface (110). The gas (245) is 13 decomposed by an energetic beam (140), which may be an electron beam, an ion beam, 14 or photons, such as from a laser.
A method of simultaneously viewing a particle (100) in a vacuum system and 16 adjusting the charge state of the paxticle is shown in Figure 4. The SEM
beam and the 17 ion beam in typical FIB instruments are scanned over the object of interest in a raster 18 pattern (260). This scanning, synchronized with emitted secondary electrons, generates 19 the electrical signal that is displayed as an image to the operator of the instrument. Since 2o the scanning beam necessarily comprises charged particles, and causes charged particles, 21 such as secondary electrons, to be emitted from the sample, it may itself be used to 22 change the charge state of the particle (100). FIB instruments typically use digital scan 23 generators that digitally increment the position of the beam spot through a raster pattern, 24 one line at a time, often reversing direction between lines to eliminate the flyback after each line that characterizes traditional analog scanners. So the operator, or the computer 26 program controlling the scan, can determine the dwell time on a per-pixel basis. For 27 example, a box covering the particle (or the exact outline shape of the particle) can be 28 programmed with zero dwell time, and therefore blanked during the scan. Any dwell 29 time can be set up to the maximum time allowed by the line rate to avoid image distortion in a single scan. It is also possible to alternately scan around the box, and then 31 scan in the box with different parameters, and do this so quickly that the human eye 32 would not see an interruption.
1 Fig. 4 shows the steps of rastering a primary electron beam (270) over a field of 2 view that includes the particle (100); generating and detecting secondary electrons (2~0) 3 that are synchronized with the primary beam (270); and modifying the raster scan pattern 4 (260) to specify dwell time and location for specific pixels in the field of the raster (260) associated with the particle (100) to be incorporated and added to the standard raster 6 pattern. The particle (100) then experiences an excess or a reduction of negative charge 7 relative to the sample surface (150) under the rest of the raster (260).
Thus the 8 electrostatic field .between the particle (100) and the probe (120) and sample surface 9 (150) can be adjusted to achieve attraction or repulsion, as desired. The raster may be l0 generated by ion beams as well, and in the same fashion, by a scanning laser.
11 Transferring the particle 12 ~nce the particle ( 100) is attached to the probe ( 120) by any of the means just 13 described, the probe (120) can be moved within the vacuum environment either manually 14 or via automated probe (120) hardware. An alternative method would be to raise or retract the probe (120) slightly and move the sample stage to bring a controlled 16 background material under the probe (120).
17 The particle (100) can also be transferred by the probe (120) to the second 18 sample surface (150) consisting substantially of a controlled background material having 19 a low background' or non-interfering background signal. For analysis by EDS, low 2o atomic-number materials such as carbon or beryllium produce low-energy X-rays that 21 will not interfere with most non-organic particle-analysis processes. An atomic number 22 less than or equal to 12 is preferred. ~rganic particles will obviously require a non-23 organic background material. Examples of the low-background materials for the second 24 sample surface (150) include photoresist, carbon planchette, beryllium foil, conductive carbon-based paste (colloidal graphite suspensions), polymer membranes, or carbon 26 nanotube needles. Any material whose X-ray background does not interfere with the 27 typical materials in the fabrication process may be acceptable for the second sample 28 surface (150). In some cases, the second sample surface (150) may be a different part of 29 the first sample surface (110). In other cases, where the composition of the particle (100) is partly known or suspected, the material of the second sample surface (150) 31 should have a background signal different that the signals expected from the particle 32 (100). Care must be taken that the choice of the second sample surface (150) does not 33 obscure possible signals from contaminants from outside the fabrication facility, such as 1 impurities in incoming gases or chemicals. For Auger analysis of the particle on the 2 second surface, the second surface should consist of low Auger electron background or 3 non-interfering Auger electron background. The composition of the second surface 4 should be consistent to a depth greater than that of any depth profiling that will be performed on the particle. It will be helpful, but not necessary for the second surface 6 material to be electrically and thermally conductive to minnvze any charging or thermo-7 mechanical drift problems associated with high incident electron beam currents. A pre-8 sputtering of the second surface, before transfer of the particle will.
remove any native 9 surface coating (mostly carbon and oxygen) and simplify the analysis. This pre-sputtering can be performed, for example, with the depth profiling ion source in the 11 Auger, or the ion beam in the FIB. That the composition of the second surface is well 12 known eliminates the need to acquire background analyses which improves throughput.
13 Figure 5 shows several methods for transferring the attached particle (100) from 14 the probe (120) to the second sample surface (150) for the analysis. Fig.
5A shows the particle suspended on an underlying framework (190), thin relative to the penetration 16 depth of the analysis beam (140). The framework (190) would typically be a TEM grid, 17 possibly having a polymer membrane (195) such as FC)RMVAR across the grid 18 openings.
19 Fig. 5B shows the particle attached to the second sample surface (150) by an adhesive (200) on the second sample surface (150). Fig. 5C shows a second sample 21 surface (150) comprising a background material (210) having a low modulus of 22 elasticity, such as vacuum grease, low-melting point wax, or low-modulus polymer. In 23 this case the particle (100) can be pushed into the low-modulus material (210) and stuck 24 there.
Fig. 5D shows a wrinkled surface (220) on an insulating second sample surface 26 (150). The wrinkled surface (220) allows an increased area of contact between the 27 particle (100) and the second sample surface (1~0), thus changing the electrostatic forces 28 between them.
29 Fig. 5E shows an electrified pattern (230) written on the ~ second sample surface (150) by the charged-particle beam (140). The electrostatic field of such a pattern can 31 assist in the transfer of the particle from the probe (120) to the second sample surface 32 (150).
1 Figure SF shows a porous second sample surface (150) having holes or pores 2 (290). Such surfaces may be micro-pore filters, such as the MICROPORE series of 3 filters manufactured by 3M Corporation of St. Paul, Minnesota, glass fiber filters such as 4 the FILTRETE or EMPORE series of filters manufactured by 3M Corporation of St.
Paul, Minnesota, or "holey carbon" films, such as the QUANTIFOIL series manufactured 6 by Structure Probe, Inc. of West Chester, PA. These surfaces have the advantage that 7 particles (100) will rest or be electrostatically captured in the holes or pores and be held 8 there for analysis.
9 In some cases it may be necessary to search for areas of high local static fields l0 sufficient to remove the particle (100) from the probe (120) without contact (if that is 11 desired).
12 Of course, the methods described in the previous section for adjusting the 13 electrostatic forces in the particle-probe-sample surface system for attaching the particle 14 (100) to the probe (120) can also be used to remove the particle (100) from the probe (120) and attach it to the second sample surface (150). In particular, the voltage or 16 charge source (130) may generate a rapid transient or resonant phenomenon, for 17 example, by rapidly switching stored negative charge from a capacitor through the probe is (120), or by a time-varying voltage, such as a square wave or pulse, applied to the probe 19 (120) from the source (130).
Analog the particle 21 X-ray analysis or Auger analysis can be performed with the particle (100) directly 22 on the probe tip (125), as shown in Fig. 6. This will of course result in X-ray or Auger 23 electron generation from the probe tip (120) itself. Other interfering signals can be 24 reduced by either using a low-background or non-interfering background material for the probe tip material, as discussed above, placing a low background or non-interfering 26 background material under the probe (120) during this analysis, or by dropping the stage 27 and all other hardware from near the probe (120). Removal of the particle (100) a$er 28 this step can be performed destructively since the particle ( 100) analysis has already been 29 done. Example destructive methods might include inserting the probe (120) in a plasma cleaner of some kind, rubbing the particle (100) off on a mechanical transfer structure 31 such as a V-groove, irradiating the probe optically either in vacuum or a$er exposure to 32 the atmosphere, or ablating the particle (100).
1 Usually, however, the particle ( 100) will be analyzed on a second sample surface 2 (150), as depicted generally in Fig. 7, where the particle (100) is irradiated with a 3 charged-particle analysis beam (140), causing it to emit characteristic Auger electrons or 4 X-rays (180) for compositional analysis, by any of the methods described in the Background section of this application. In the claims, the term "emissions"
denotes 6 either Auger electrons or X-rays.
7 Analog the particle on the probe tip s The second sample (150) surface may be the probe tip (135) itself. In this case 9 the probe tip (135) is composed of a controlled background material. In the case of a to analysis instrument such as SAM or FIB in which ion beam milling of the surface is 11 possible, the surface of the probe tip (135) can be ion milled prior to attachment of the 12 particle (100) to the tip (135) to reduce signals from the native surface coating and 13 debris on the probe tip (135) surface. Due to the possibility of transmission of the 14 energetic beam ( 140) through a tiny particle, or scattering of the energetic beam ( 140) onto the underlying surface, it may be necessary to translate the probe tip (135) with the 16 particle (100) attached over a surface composed of a controlled background material, or 17 alternatively translate such a controlled background surface beneath the probe tip (135) 18 with the particle ( 100) attached. In this description, "under" and "beneath" refer to the 19 side of the particle (100) opposite the side on which the energetic beam (140) is incident (i.e.: the transmitted side).
21 Since those skilled in the art can modify the specific embodiments described 22 above, we intend that the claims be interpreted to cover such modifications and 23 equivalents.
24 We claim:
14 Fatent Application of Thomas M. Moore and John M. Anthony 1 ~ TECHNICAL FIELD
18 The invention relates to techniques for removing and analyzing microscopic 19 particles from a sample surface, particularly from semiconductor samples.
2o BACKGROUND
21 In the semiconductor industry, unexpected particles due to contamination will 22 cause yield loss during the manufacturing process. Since a major focus of this industry is 23 aggressive reduction in feature size for pattern line widths, the minimum size of particles 24 that can cause performance loss also decreases rapidly. A reasonable estimate for a "killer defect" size is that greater than one-third the size of the smallest feature on the 26 semiconductor wafer.
27 Although semiconductor manufacturing is performed in clean rooms with 28 stringent particle standards, unexpected contamination will occur due to sources such as 29 moving parts, human presence, gas condensation, and chamber wear. Control and removal of these particles is a continuous process. In many cases, removal of the source 31 of particles requires an understanding of their origin. Many of these particles or defects 32 are too small for detection in a general purpose optical inspection microscope, so higher 33 resolution methods are required, using charged-particle microscopes, such as scanning 1 electron microscopes (SEM), transmission electron microscopes (TEM), scanning Auger 2 microprobes (SAM), or focused ion beam (FIB) instruments, are required.
3 Even an image of the particle is usually insufficient to trace the origin of the 4 particle, and more information is required. Elemental composition is valuable in identifying the defect. This can be done in various ways using the charged-particle 6 systems mentioned above. Unfortunately, most of the analytical methods are limited by 7 background signals from the environment of the particle.
8 Throughput is also a critical parameter in semiconductor manufacturing.
9 Existing strategies for compositional analysis of particles on a semiconductor wafer, for l0 example, usually require removal of the wafer from the fabrication area for off line i i analysis using methods such as those described below. Removal from the line severely 12 reduces the throughput of the manufacturing process.
13 Particle identification on sample surfaces using electron-beam based identification 14 is complicated by the size of the particle relative to the electron penetration depth, and by the nature of surrounding materials in the sample. As an electron beam interacts with 16 bulls solid materials, it expands to fill a teardrop-shaped volume as it loses energy. As 17 the primary beam interacts with atoms in this volume, it generates low energy Auger i8 electrons and X~rays that are characteristic of the elements involved.
19 The particular X-ray line generated will depend on the atomic number of the 2o element, the energy of the electron during the interaction; and other factors. When 21 trying to identify an unknown particle using conventional Energy-dispersive X-ray 22 Spectrophotometry (EDS), the energy of the electron beam must be large enough to 23 generate inner-shell X-rays from all possible relevant elements, which, for semiconductor 24 applications, may include elements of high atomic number such as tungsten.
Unfortunately, this energy results in a penetration depth that may be much larger than the 26 particle of interest, resulting in X-ray generation from the sample surface. These X-rays 27 interfere with any signal from the particle, making unique identification of the particle 28 material difficult. Conventional strategies for solving this problem involve either 29 resolving the X-ray lines of different elements, or reducing the energy of the exciting 3o electron beam.
31 For example, it is possible to detect and analyze electron-beam generated X-rays 32 from a particle by measuring the intensity and diffraction angle of the X-rays diffracted 33 by a reference crystal, or Wavelength Dispersive X-ray Spectrometry (WDS).
One 1 chooses the crystal atomic spacing to deflect (with very high resolution) X-rays of a 2 given energy, thus allowing separation between X-ray lines of different elements. This 3 method has higher energy resolution than EDS but much slower throughput. In addition, 4 if the particle could be, as it often is, of the same composition as the sample surface, this method will not uniquely determine the particle composition.
6 Other solutions involve reducing the energy of the primary electron beam to 7 guarantee the activated volume is less than the volume of the particle of interest. This 8 reduction in primary electron-beam energy results in characteristic X-rays of much lower 9 energy (M or L shell X-rays, rather than K shell). Conventional cooled semiconductor-based detectors use the generation and collection of electron-hole pairs as a measure of 11 the energy of the ionizing radiation (a few eV for each electron-hole pair, depending on 12 the detecting material). A reduction in the X-ray energy therefore leads to a reduced 13 number of electron-hole pairs and reduced sensitivity to the particle material. In addition 14 the resolution of these detectors is governed by the statistics of the electron-hole generation process, and reducing the energy of the detected X-ray often leads to 16 ambiguous identification of the element of interest. X-ray micro-calorimeter methods 17 have been used to detect these weak X-ray signals, using heat transferred to the detector 18 rather than the generation of electron-hole pairs. This process does allow measurement 19 of small X-ray energies, but micro-calorimeter instruments are expensive, have 2o complicated cooling requirements, and are slow compared to other methods.
Also, the 21 electron beam must be kept smaller than the smallest dimension of the particle of interest, 22 rendering the method impractical for small, unsymmetrical particles.
23 Scanning Auger microprobe analysis also uses an electron beam to irradiate a 24 particle of interest, but rather than detecting any X-rays generated it focuses on the detection of Auger electrons ejected from the atoms of the material. These Auger 26 electrons come from outer shells and have relatively low energies. The Auger electron 27 energies from a material produce a pattern that is characteristic of each element in the 28 material, and the shape and exact energy of the Auger transitions provide information on 29 the chemical bonding of the elements in the material (such as, phase or compound information). The escape depth of these electrons is quite small (a few nm), so Auger 31 analysis focuses mainly on the surface of a sample. This is an advantage for the analysis 32 of small diameter particles (<10 nm). For the analysis of larger particles, one can 33 generate depth profiles by using an ion beam to sputter through the particle and take 1 periodic measurements, but this is inherently destructive of the surrounding sample due 2 to ion milling in the SAM, and requires background analyses on the sample near the 3 location of the particle. Auger analysis is typically more sensitive to light elements than 4 standard EDS analysis, making it more suitable to identify organic materials. However, to improve counting statistics, high electron beam currents are typically employed. This 6 exaggerates the issues of thermo-mechanical drift and drift due to electrical charging of 7 the sample. This means that operating the SAM in the "spot mode," with the electron 8 beam positioned on the particle, involves a risk that over time the electron beam spot will 9 drift onto the sample that surrounds the particle. And the use of a raster pattern for the io electron beam will be more tolerant of drift for keeping the beam on the particle, but will i i involve significant contamination of the results with signal from the surrounding material.
12 In either case, background contamination of the Auger results is a serious issue, and 13 Auger analyses of the surrounding material are required to uniquely identify the signal 14 from the particle. The acquisition of background analyses reduces throughput and inherently damages the sample.
16 TEM can often be used for analysis of particles in or on surfaces. There are a 17 variety of methods for isolating the particle for analysis, including replication, lift-out or is cross sectioning the area of interest. These methods all destroy the sample surface and 19 must be done off line, thereby increasing cost and cycle time.
2o Moving the particle from the first sample surface to a more controlled 21 environment for testing can dramatically improve the chance of success and throughput 22 for elemental identification with either EDS or Auger analysis. A critical part of this 23 process is the strategy for moving the particle. This disclosure describes a novel method 24 for removing a particle of interest from a sample surface, transporting that particle to a second sample surface with a controlled X-ray or Auger background, and performing 26 electron beam-induced X-ray analysis or Auger electron analysis there, using any of the 27 methods discussed above. This eliminates the requirement that the analyzing technique 28 have high spatial resolution, although a technique with high spatial resolution, such as 29 EDS analysis in the SEM and SAM analysis, is generally preferred. For example, 3o techniques without high spatial resolution that could be successfully applied to the 31 situation of a particle on a reduced or non-interfering background include X-ray 32 Photoelectron Spectroscopy (XPS) and X-ray Fluorescence analysis (XRF), which may 33 offer an advantage in unique and specific situations.
-S-1 The proposed method for particle manipulation and EDS X-ray analysis can be 2 done in-line on existing wafer-manufacturing tools. An in-line procedure using existing 3 manufacturing and inspection tools represents a significant reduction in cycle time for 4 contamination removal. SEM is a routine method for wafer inspection, and analytical methods using the electron beam in an SEM system provide a substantial throughput 6 advantage over the off line strategies.
7 Although this disclosure primarily illustrates the use of the novel technique to 8 manipulate and examine particles that are contaminants in the context of semiconductor 9 manufacturing, the reader should note that the term "particle" may be taken to include objects that may not be contaminants in other environments, such as chemical deposits, 0 11 biological material, or micro-mechanical machines. In the latter cases, the novel methods 12 of manipulation described in this application may be applied to manipulate these objects 13 generally, for purposes other than electron-beam X-ray analysis or Auger electron 14 analysis.
DRAWINGS
16 Figure 1 shows the steps of attaching a particle to a micro-manipulator probe and 17 removing the particle to a second surface for analysis.
18 Figure 2 shows three other methods of attaching a particle to a micro-19 manipulator probe.
2o Figure 3 shows the process of modifying electrostatic forces by bombardment 21 with polarizable molecules.
22 Figure 4 shows the method of simultaneously viewing a particle and modifying 23 the charge state of the particle.
24 Figure 5~ shows several methods for fixing a particle to a second surface for analysis.
26 Figure 6 shows the analysis of a particle while the particle is fixed to the tip of a 27 micro-manipulator probe.
28 Figure 7 shows the process of analyzing the composition of a particle removed to 29 a second surface for analysis.
SITMMARY
31 We disclose a method for analyzing the composition of a microscopic particle 32 resting on a first sample surface. Usually, the particle will be a contaminant in a 33 semiconductor processing system, although the method is not limited to those 1 circumstances. The method comprises positioning a micro-manipulator probe near the 2 particle; attaching the particle to the probe; moving the probe and the attached particle 3 away from the first sample surface; positioning the particle on a second sample surface;
4 and, analyzing the composition of the particle on the second sample surface by energy-dispersive X-ray analysis, Auger microprobe analysis or any other suitable analytical 6 technique. The second surface has a reduced or non-interfering background signal 7 during analysis, relative to the background signal of the first surface. (We call such a 8 reduced or non-interfering background signal a "controlled" background signal in the 9 claims.) We also disclose methods for adjusting the electrostatic forces and DC
l0 potentials between the probe, the particle, and the sample surfaces to effect removal of 11 the particle, and its transfer and relocation to the second sample surface.
These include 12 adjusting electrostatic forces to create an attractive force between the probe and particle.
13 Adjustment of the electrostatic forces may include locally adjusting the energy or 14 intensity (intensity means beam current for electron and ion beams) of an electron beam, ion beam or photon beam incident on the individual components of the sample system, 16 which includes the probe tip, particle and first sample surface, to create an electrostatic 17 attraction between the particle and probe tip, or an electrostatic repulsion between the 18 particle and the first sample surface. This procedure is reversed to transfer the particle 19 from the probe tip to the second sample surface.
The second sample surface may be the probe tip itself. In this case the probe tip 21 is composed of a controlled background material. Due to the possibility of transmission 22 of the energetic beam through a tiny particle, or scattering of the energetic beam onto the 23 underlying surface, it may be necessary to translate the probe tip with the particle 24 attached over a surface composed of a controlled background material, or alternatively translate such a controlled background surface beneath the probe tip with the particle 26 attached. In this description, "under" and "beneath" refer to the side of the particle 27 opposite the side on which the energetic beam is incident (i.e.: the transmitted side).
29 The analysis of microscopic particles, particularly in semiconductor manufacturing, is typically done inside a Scanning Electron Microscope (SEM), Focused 31 Ion Beam (FIB) instrument, or Scanning Auger Microprobe (SAM). The FIB
instrument 32 may be either a single-beam model, or a dual-beam (both SEM and ion beam) model.
33 Typical FIB instruments are those manufactured by FEI Company of Hillsboro, Oregon, _7-1 as models 200, 235, 820, 830, or 835. The probe (120) referred to below is a 2 component of a micro-manipulator tool attached to the FIB instrument with vacuum 3 feed-through. A typical such micro-manipulator tool is the Model 100 manufactured by 4 Omniprobe, Inc. of Dallas, Texas. Typical SAM instruments include the JAMP-and JAMP-7830F manufactured by JEOL USA, Inc. of Peabody, Massachusetts.
6 Figure 1 depicts the general setup for particle manipulation and analysis.
Fig. lA
7 shows a particle (100) of interest resting on a first sample surface (110).
A micro-8 manipulator probe (120) is positioned near the particle (1d0). The probe tip can be 9 electrostatically charged relative to the particle and the first sample surface.
Alternatively, a voltage source (130) may be connected between the probe (120) and the 11 first sample surface (110). The local electrostatic charge on the particle can be modified 12 by the irradiation of the particle by a charged particle beam. Figs. 1 B
through 1 D show, 13 respectively, the irradiation of the particle (100) and first sample surface (110) by 14 photons or a charged-particle beam (140) to cause attachment of the particle (100) to the probe (120), the removal of the probe (120) and attached particle (100) from the first 16 sample surface (110), and the deposition of the particle (100) on a second sample surface 17 (150) for analysis. The drawings are not to scale.
18 Attaching the particle to the probe 19 Strong electrostatic forces exist on particles in a vacuum. The presence of static charges on the particle (100) and the probe (120) leads to the creation of image charges 21 on the opposite surfaces. These image charges create forces that are proportional to the 22 area exposed and inversely proportional to the distance between the objects. Reducing 23 or increasing the exposed area will therefore either reduce or increase the force acting on 24 the particle (100), and the resultant adhesion between probe (120) and particle (100).
This can be used as a straightforward method to remove particles of interest from the 26 sample, using either a conducting or insulating probe (120). Conducting probes allow 27 more versatility through the introduction of static or time varying voltages or 28 electrostatic charges to the probe (120) from a voltage or electrostatic charge source 29 (130), as shown generally in Fig. lA.
The shape of the tip of the probe (120) will also influence the electric fields at the 31 tip. Static electric charges on a blunt tip will exext stronger influence on a particle in line 32 with the tip than a sharply pointed tip. In contrast, in the case of a DC
potential on a 33 conductive tip, a sharp tip will produce the strongest field concentration at the tip. The _g_ 1 probe ( 120) can be moved into proximity to the particle ( 100) while imaging with, for 2 example, the electron beam (140) available in the FIB instrument, as shown in Fig. 1B.
3 The electron beam will also affect the charge distribution in the surface-particle-probe 4 system, and thus can assist attraction of the particle (100) to the probe (120). An application of this effect is discussed below. The electron beam (140) depicted in Fig.
6 1B and other drawings should be understood to also be a charged-particle beam or 7 photon beam generally, and may, for example, consist of an ion beam. These, and beams 8 of photons, such as from a laser, are referred to collectively in the claims as "energetic"
9 beams.
l0 In general, the adjustment of electrostatic forces on the system may comprise 11 adjusting the energy of an electron beam (140) incident on the particle (100), probe 12 (120), and first sample surface (110) to create a relative electrostatic attraction between 13 the particle (100) and the probe (120), and a relative electrostatic repulsion between the 14 particle (100) and the first sample surface (110). The process may be assisted by a voltage source (130) connected between the first sample surface (110) and the probe 16 ( 120). Clearly, the impinging beam ( 140) could also be a beam of photons, having 17 sufficient energy to release photoelectrons, which thus change the charge distribution in 18 the system, and the electrostatic forces involved.
19 The preferred embodiment may also be carried out using an adhesive (160) on the probe (120), as shown in Fig. 2A. An acceptable adhesive (160) could be any having a 21 low vapor pressure, such as vacuum grease, low melting point waxes, or other low vapor 22 pressure glues. In this case, the forces of adhesion simply capture the particle (100), 23 notwithstanding existing electrostatic forces.
t 24 In another embodiment, shown in Fig. 2B, tweezers (170) connected to the probe (120) grasp the particle (100) and remove it from the first sample surface (110). Suitable 26 device having tweezers (170) or similar grippers are those manufactured by MEMS
27 Precision Instruments in Berkeley, CA.
28 The probe (120) can touch the particle (100), but this is not necessary in many 29 cases, as the particle (100) will jump to the probe (120) due to the electrostatic attraction. The electrostatic field is controlled by surface area and therefore enhanced 31 with a blunt tip on the probe (120), or the blunt side of a particle (100) or the probe 32 (120), whereas DC potentials are enhanced by a pointed tip that concentrates the field 33 lines. Figs. 2C and 2D show examples of strategies for particle (100) attachment and 1 transfer by controlling the surface area of the particle (100) exposed to the manipulator, 2 by applying the tip (125) of the probe (120) and the side (135) of the probe (120) to the 3 particle to achieve the desired movement of the particle (100).
4 An additional method of adjusting the electrostatic fields in the particle-probe-surface system, for both attaching and removing the particle (100) comprises depositing 6 a conductive material on the first sample surface (110) or second sample surface (150), 7 as the case may be, to distribute and modify the electrostatic charge on the surface at the 8 location of the particle to create either an attractive or a repulsive force on the particle, 9 as desired. Figure 3A depicts the deposit of polarizable molecules (250), such as water, l0 on the sample surface (110). Figure 3B depicts the deposit of a conductive film (255) by 1 i evaporation of a source. Figure 3C depicts a directed jet (240) of gas (245) applied to a 12 surface (110) having a particle (100) resting upon the surface (110). The gas (245) is 13 decomposed by an energetic beam (140), which may be an electron beam, an ion beam, 14 or photons, such as from a laser.
A method of simultaneously viewing a particle (100) in a vacuum system and 16 adjusting the charge state of the paxticle is shown in Figure 4. The SEM
beam and the 17 ion beam in typical FIB instruments are scanned over the object of interest in a raster 18 pattern (260). This scanning, synchronized with emitted secondary electrons, generates 19 the electrical signal that is displayed as an image to the operator of the instrument. Since 2o the scanning beam necessarily comprises charged particles, and causes charged particles, 21 such as secondary electrons, to be emitted from the sample, it may itself be used to 22 change the charge state of the particle (100). FIB instruments typically use digital scan 23 generators that digitally increment the position of the beam spot through a raster pattern, 24 one line at a time, often reversing direction between lines to eliminate the flyback after each line that characterizes traditional analog scanners. So the operator, or the computer 26 program controlling the scan, can determine the dwell time on a per-pixel basis. For 27 example, a box covering the particle (or the exact outline shape of the particle) can be 28 programmed with zero dwell time, and therefore blanked during the scan. Any dwell 29 time can be set up to the maximum time allowed by the line rate to avoid image distortion in a single scan. It is also possible to alternately scan around the box, and then 31 scan in the box with different parameters, and do this so quickly that the human eye 32 would not see an interruption.
1 Fig. 4 shows the steps of rastering a primary electron beam (270) over a field of 2 view that includes the particle (100); generating and detecting secondary electrons (2~0) 3 that are synchronized with the primary beam (270); and modifying the raster scan pattern 4 (260) to specify dwell time and location for specific pixels in the field of the raster (260) associated with the particle (100) to be incorporated and added to the standard raster 6 pattern. The particle (100) then experiences an excess or a reduction of negative charge 7 relative to the sample surface (150) under the rest of the raster (260).
Thus the 8 electrostatic field .between the particle (100) and the probe (120) and sample surface 9 (150) can be adjusted to achieve attraction or repulsion, as desired. The raster may be l0 generated by ion beams as well, and in the same fashion, by a scanning laser.
11 Transferring the particle 12 ~nce the particle ( 100) is attached to the probe ( 120) by any of the means just 13 described, the probe (120) can be moved within the vacuum environment either manually 14 or via automated probe (120) hardware. An alternative method would be to raise or retract the probe (120) slightly and move the sample stage to bring a controlled 16 background material under the probe (120).
17 The particle (100) can also be transferred by the probe (120) to the second 18 sample surface (150) consisting substantially of a controlled background material having 19 a low background' or non-interfering background signal. For analysis by EDS, low 2o atomic-number materials such as carbon or beryllium produce low-energy X-rays that 21 will not interfere with most non-organic particle-analysis processes. An atomic number 22 less than or equal to 12 is preferred. ~rganic particles will obviously require a non-23 organic background material. Examples of the low-background materials for the second 24 sample surface (150) include photoresist, carbon planchette, beryllium foil, conductive carbon-based paste (colloidal graphite suspensions), polymer membranes, or carbon 26 nanotube needles. Any material whose X-ray background does not interfere with the 27 typical materials in the fabrication process may be acceptable for the second sample 28 surface (150). In some cases, the second sample surface (150) may be a different part of 29 the first sample surface (110). In other cases, where the composition of the particle (100) is partly known or suspected, the material of the second sample surface (150) 31 should have a background signal different that the signals expected from the particle 32 (100). Care must be taken that the choice of the second sample surface (150) does not 33 obscure possible signals from contaminants from outside the fabrication facility, such as 1 impurities in incoming gases or chemicals. For Auger analysis of the particle on the 2 second surface, the second surface should consist of low Auger electron background or 3 non-interfering Auger electron background. The composition of the second surface 4 should be consistent to a depth greater than that of any depth profiling that will be performed on the particle. It will be helpful, but not necessary for the second surface 6 material to be electrically and thermally conductive to minnvze any charging or thermo-7 mechanical drift problems associated with high incident electron beam currents. A pre-8 sputtering of the second surface, before transfer of the particle will.
remove any native 9 surface coating (mostly carbon and oxygen) and simplify the analysis. This pre-sputtering can be performed, for example, with the depth profiling ion source in the 11 Auger, or the ion beam in the FIB. That the composition of the second surface is well 12 known eliminates the need to acquire background analyses which improves throughput.
13 Figure 5 shows several methods for transferring the attached particle (100) from 14 the probe (120) to the second sample surface (150) for the analysis. Fig.
5A shows the particle suspended on an underlying framework (190), thin relative to the penetration 16 depth of the analysis beam (140). The framework (190) would typically be a TEM grid, 17 possibly having a polymer membrane (195) such as FC)RMVAR across the grid 18 openings.
19 Fig. 5B shows the particle attached to the second sample surface (150) by an adhesive (200) on the second sample surface (150). Fig. 5C shows a second sample 21 surface (150) comprising a background material (210) having a low modulus of 22 elasticity, such as vacuum grease, low-melting point wax, or low-modulus polymer. In 23 this case the particle (100) can be pushed into the low-modulus material (210) and stuck 24 there.
Fig. 5D shows a wrinkled surface (220) on an insulating second sample surface 26 (150). The wrinkled surface (220) allows an increased area of contact between the 27 particle (100) and the second sample surface (1~0), thus changing the electrostatic forces 28 between them.
29 Fig. 5E shows an electrified pattern (230) written on the ~ second sample surface (150) by the charged-particle beam (140). The electrostatic field of such a pattern can 31 assist in the transfer of the particle from the probe (120) to the second sample surface 32 (150).
1 Figure SF shows a porous second sample surface (150) having holes or pores 2 (290). Such surfaces may be micro-pore filters, such as the MICROPORE series of 3 filters manufactured by 3M Corporation of St. Paul, Minnesota, glass fiber filters such as 4 the FILTRETE or EMPORE series of filters manufactured by 3M Corporation of St.
Paul, Minnesota, or "holey carbon" films, such as the QUANTIFOIL series manufactured 6 by Structure Probe, Inc. of West Chester, PA. These surfaces have the advantage that 7 particles (100) will rest or be electrostatically captured in the holes or pores and be held 8 there for analysis.
9 In some cases it may be necessary to search for areas of high local static fields l0 sufficient to remove the particle (100) from the probe (120) without contact (if that is 11 desired).
12 Of course, the methods described in the previous section for adjusting the 13 electrostatic forces in the particle-probe-sample surface system for attaching the particle 14 (100) to the probe (120) can also be used to remove the particle (100) from the probe (120) and attach it to the second sample surface (150). In particular, the voltage or 16 charge source (130) may generate a rapid transient or resonant phenomenon, for 17 example, by rapidly switching stored negative charge from a capacitor through the probe is (120), or by a time-varying voltage, such as a square wave or pulse, applied to the probe 19 (120) from the source (130).
Analog the particle 21 X-ray analysis or Auger analysis can be performed with the particle (100) directly 22 on the probe tip (125), as shown in Fig. 6. This will of course result in X-ray or Auger 23 electron generation from the probe tip (120) itself. Other interfering signals can be 24 reduced by either using a low-background or non-interfering background material for the probe tip material, as discussed above, placing a low background or non-interfering 26 background material under the probe (120) during this analysis, or by dropping the stage 27 and all other hardware from near the probe (120). Removal of the particle (100) a$er 28 this step can be performed destructively since the particle ( 100) analysis has already been 29 done. Example destructive methods might include inserting the probe (120) in a plasma cleaner of some kind, rubbing the particle (100) off on a mechanical transfer structure 31 such as a V-groove, irradiating the probe optically either in vacuum or a$er exposure to 32 the atmosphere, or ablating the particle (100).
1 Usually, however, the particle ( 100) will be analyzed on a second sample surface 2 (150), as depicted generally in Fig. 7, where the particle (100) is irradiated with a 3 charged-particle analysis beam (140), causing it to emit characteristic Auger electrons or 4 X-rays (180) for compositional analysis, by any of the methods described in the Background section of this application. In the claims, the term "emissions"
denotes 6 either Auger electrons or X-rays.
7 Analog the particle on the probe tip s The second sample (150) surface may be the probe tip (135) itself. In this case 9 the probe tip (135) is composed of a controlled background material. In the case of a to analysis instrument such as SAM or FIB in which ion beam milling of the surface is 11 possible, the surface of the probe tip (135) can be ion milled prior to attachment of the 12 particle (100) to the tip (135) to reduce signals from the native surface coating and 13 debris on the probe tip (135) surface. Due to the possibility of transmission of the 14 energetic beam ( 140) through a tiny particle, or scattering of the energetic beam ( 140) onto the underlying surface, it may be necessary to translate the probe tip (135) with the 16 particle (100) attached over a surface composed of a controlled background material, or 17 alternatively translate such a controlled background surface beneath the probe tip (135) 18 with the particle ( 100) attached. In this description, "under" and "beneath" refer to the 19 side of the particle (100) opposite the side on which the energetic beam (140) is incident (i.e.: the transmitted side).
21 Since those skilled in the art can modify the specific embodiments described 22 above, we intend that the claims be interpreted to cover such modifications and 23 equivalents.
24 We claim:
Claims (65)
1. A method for analyzing the composition of a particle; the particle resting on a first sample surface; the method comprising the steps of:
positioning a micro-manipulator probe near the particle, the probe having a tip;
attaching the particle to the probe tip;
moving the probe and the attached particle away from the first sample surface;
removing the particle from the probe tip to a second sample surface; and, analyzing the composition of the particle on the second sample surface;
where the second sample surface has a controlled background signal during analysis relative to the background signal of the first surface.
positioning a micro-manipulator probe near the particle, the probe having a tip;
attaching the particle to the probe tip;
moving the probe and the attached particle away from the first sample surface;
removing the particle from the probe tip to a second sample surface; and, analyzing the composition of the particle on the second sample surface;
where the second sample surface has a controlled background signal during analysis relative to the background signal of the first surface.
2. The method of claim 1 carried out in an atmosphere.
3. The method of claim 1 carried out in a vacuum.
4. The method of claim 1 where the particle is attached, moved, and removed while being irradiated by an electron beam.
5. The method of claim 1 where the particle is attached, moved, and removed while being irradiated by an ion beam.
6. The method of claim 1 where the particle is attached, moved, and removed while being irradiated by a photon beam.
7. The method of claim 1 where the second sample surface is a portion of the first sample surface.
8. The method of claim 1 where the step of moving the probe and the attached particle away from the first sample surface comprises:
fixing the location of the probe;
moving the first sample surface relative to the fixed probe, so as to separate the first sample surface from the probe and the attached particle.
fixing the location of the probe;
moving the first sample surface relative to the fixed probe, so as to separate the first sample surface from the probe and the attached particle.
9. The method of claim 1 where the second sample surface comprises material having an atomic number less than or equal to 12.
10. The method of claim 1 where the second sample surface comprises material having a background signal different than that of the signals expected to be generated by analysis of the particle.
11. The method of claim 1 where the step of attaching the particle to the probe tip comprises adjusting electrostatic forces to create an attractive force between the probe and particle.
12. The method of claim 11 where the adjustment of electrostatic forces further comprises:
adjusting the energy of an energetic beam incident on the particle to electrostatically charge the particle, the first sample surface, and the probe tip so as to create an electrostatic attraction between the particle and the probe tip and to create an electrostatic repulsion between the first sample surface and the particle.
adjusting the energy of an energetic beam incident on the particle to electrostatically charge the particle, the first sample surface, and the probe tip so as to create an electrostatic attraction between the particle and the probe tip and to create an electrostatic repulsion between the first sample surface and the particle.
13. The method of claim 11 where energetic beam is an electron beam.
14. The method of claim 11 where energetic beam is an ion beam.
15. The method of claim 11 where the energetic beam comprises photons.
16. The method of claim 11 where the adjustment of electrostatic forces further comprises:
the particle having an electrostatic charge; end, depositing a conductive material on the first sample surface to distribute and modify the electrostatic charge of the first sample surface at the location of the particle.
the particle having an electrostatic charge; end, depositing a conductive material on the first sample surface to distribute and modify the electrostatic charge of the first sample surface at the location of the particle.
17. The method of claim 16 where the conductive material deposited on the first sample surface comprises polarizable molecules.
18. The method of claim 16 where the conductive material deposited on the first sample surface is an evaporated conductive film.
19. The method of claim 16 where the step of depositing a conductive material on the first sample surface comprises bombarding the first sample surface with a directed jet of a gas, and decomposing the gas with an energetic beam.
20. The method of claim 19 where the energetic beam is an electron beam.
21. The method of claim 19 where the energetic beam is an ion beam.
22. The method of claim 19 where the energetic beam comprises photons.
23. The method of claim 11 where the adjustment of electrostatic forces further comprises:
rastering a energetic beam over a field of view that includes the particle;
programming the raster scan to have a pre-determined dwell time and location, where the location includes the location of the particle, so as to impart an electrostatic charge to the particle.
rastering a energetic beam over a field of view that includes the particle;
programming the raster scan to have a pre-determined dwell time and location, where the location includes the location of the particle, so as to impart an electrostatic charge to the particle.
24. The method of claim 23 where the energetic beam is an electron beam.
25. The method of claim 23 where the energetic beam is an ion beam.
26. The method of claim 23 where the energetic beam comprises photons.
27. The method of claim 11 where the adjustment of electrostatic forces comprises controlling the surface area of the particle exposed to the probe by applying the tip of the probe or the side of the probe to the particle to achieve attachment of the particle to the probe.
28. The method of claim 1 where the step of attaching the particle to the probe tip comprises adjusting a DC bias voltage between the probe and the first sample surface.
29. The method of claim 1 where the step of attaching the particle to the probe tip comprises grasping the particle with tweezers.
30. The method of claim 1 where the step of attaching the particle to the probe tip comprises the probe tip having an adhesive.
31. The method of claim 1 where the step of removing the particle from the probe to the second sample surface comprises adjusting a DC bias voltage between the probe and the second sample surface.
32. The method of claim 1 where the step of removing the particle from the probe to the second sample surface comprises applying a time-varying potential to the probe.
33. The method of claim 32 where the time-varying potential is a pulse.
34. The method of claim 32 where the time-varying potential is generated by rapidly switching stored negative charge from a capacitor through the probe.
35. The method of claim 32 where the time-varying potential is a sinusoidal voltage.
36. The method of claim 1 where the step of removing the particle from the probe to the second sample surface comprises adjusting electrostatic forces to create a repulsive force between the probe and the particle.
37. The method of claim 36 where the adjustment of electrostatic forces further comprises:
adjusting the energy of an energetic beam incident on the particle to electrostatically charge the particle, the second sample surface, and the probe tip, so as to create an electrostatic repulsion between the particle and the probe tip and to create an electrostatic attraction between the second sample surface and the particle.
adjusting the energy of an energetic beam incident on the particle to electrostatically charge the particle, the second sample surface, and the probe tip, so as to create an electrostatic repulsion between the particle and the probe tip and to create an electrostatic attraction between the second sample surface and the particle.
38. The method of claim 37 where energetic beam is an electron beam.
39. The method of claim 37 where energetic beam is an ion beam.
40. The method of claim 37 where the energetic beam comprises photons.
41. The method of claim 36 where the adjustment of electrostatic forces further comprises the particle having an electrostatic charge; and, depositing a conductive material on the second sample surface to distribute and modify the charge on the second sample surface at the location of the particle.
42. The method of claim 41 where the conductive material deposited on the second sample surface comprises polarizable molecules.
43. The method of claim 41 where the conductive material deposited on the second sample surface is an evaporated conductive film.
44. The method of claim 41 where the step of depositing a conductive material on the first sample surface comprises bombarding the second sample surface with a directed jet of a gas, and decomposing the gas with an energetic beam.
45. The method of claim 44 where the energetic beam is an electron beam.
46. The method of claim 44 where the energetic beam is an ion beam.
47. The method of claim 44 where the energetic beam comprises photons.
48. The method of claim 36 where the adjustment of electrostatic forces further comprises:
rastering a energetic beam over a field of view that includes the particle;
programming the raster scan to exhibit a pre-determined dwell time and location, where the location includes the location of the particle, so as to impart an electrostatic charge to the particle.
rastering a energetic beam over a field of view that includes the particle;
programming the raster scan to exhibit a pre-determined dwell time and location, where the location includes the location of the particle, so as to impart an electrostatic charge to the particle.
49. The method of claim 48 where the energetic beam is an electron beam.
50. The method of claim 48 where the energetic beam is an ion beam.
51. The method of claim 48 where the energetic beam comprises photons.
52. The method of claim 1 where the second sample surface comprises an adhesive, for engaging the particle.
53. The method of claim 1 where the second sample surface has an elastic modulus low compared to the compliance of the probe and the elastic modulus of the particle.
54. The method of claim 1 where the second sample surface is insulating; the second sample surface having electrified patterns written into it; the charge of the electrified patterns being opposite to that of the particle.
55. The method of claim 1 where the second sample surface is wrinkled.
56. The method of claim 1 where the step of analyzing the composition of the particle further comprises:
irradiating the particle with an analysis beam; and, detecting emissions from the particle.
irradiating the particle with an analysis beam; and, detecting emissions from the particle.
57. The method of claim 56 where the analysis beam is an electron beam.
58. The method of claim 56 where the analysis beam is an ion beam.
59. The method of claim 56 where the analysis beam comprises photons.
60. The method of claim 1 where the second sample surface is self-supporting, but is thin relative to the penetration depth of the analysis beam.
61. The method of claim 1 where the second sample surface is a porous surface.
62. The method of claim 1 where the second sample surface is thin relative to the penetration depth of the analysis beam, and the second sample surface is supported by an underlying framework.
63. The method of claim 62 where the underlying framework is a grid.
64. The method of claim 1 where the second sample surface is the probe tip;
and, where the step of analyzing the composition of the particle comprises analyzing the composition of the particle on the probe tip.
and, where the step of analyzing the composition of the particle comprises analyzing the composition of the particle on the probe tip.
65. The method of claim 64 where the probe and the attached particle are moved away from the first sample surface by holding the position of the probe fixed and moving the first sample surface away from the probe and the attached particle.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/US2004/018206 WO2005123227A2 (en) | 2004-06-08 | 2004-06-08 | Method for manipulating microscopic particles and analyzing the composition thereof |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2543396A1 true CA2543396A1 (en) | 2005-12-29 |
Family
ID=35510284
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002543396A Abandoned CA2543396A1 (en) | 2004-06-08 | 2004-06-08 | Method for manipulating microscopic particles and analyzing the composition thereof |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP1754049A2 (en) |
| CN (1) | CN1977159A (en) |
| CA (1) | CA2543396A1 (en) |
| WO (1) | WO2005123227A2 (en) |
Families Citing this family (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE102006045620B4 (en) | 2006-09-25 | 2009-10-29 | Roland Dr. Kilper | Device and method for receiving, transporting and storing microscopic samples |
| EP1953789A1 (en) * | 2007-02-05 | 2008-08-06 | FEI Company | Method for thinning a sample and sample carrier for performing said method |
| US8283631B2 (en) * | 2008-05-08 | 2012-10-09 | Kla-Tencor Corporation | In-situ differential spectroscopy |
| JP5849331B2 (en) * | 2011-08-31 | 2016-01-27 | 国立大学法人静岡大学 | Micro-adhesion peeling system and micro-adhesion peeling method |
| CN104236978B (en) * | 2014-09-30 | 2017-03-22 | 中国原子能科学研究院 | Method for measuring isotope ratio of uranium in single particle |
| CN105797867B (en) * | 2016-05-09 | 2018-05-04 | 长安大学 | A kind of electrostatic mineral microparticle Chooser |
| CN110595848B (en) * | 2018-06-12 | 2022-04-01 | 中国科学院苏州纳米技术与纳米仿生研究所 | Preparation method of micron-sized particle transmission electron microscope sample |
| CN111521623B (en) * | 2020-04-28 | 2023-04-07 | 广西大学 | Method for improving sample preparation success rate of powder sample transmission electron microscope in-situ heating chip |
| CN113804607A (en) * | 2020-06-17 | 2021-12-17 | 阅美测量系统（上海）有限公司 | Method for fixing particles in detection of scanning electron microscope and energy spectrometer (SEM-EDX) |
| CN111693555B (en) * | 2020-06-18 | 2021-08-10 | 中国科学院地球化学研究所 | Method for in-situ preparation of TEM (transmission electron microscope) sample of nano-scale particles in complex-structure sample |
| CN112180124A (en) * | 2020-08-31 | 2021-01-05 | 上海交通大学 | Preparation method of submicron probe for atomic force microscope |
| WO2022178903A1 (en) * | 2021-02-28 | 2022-09-01 | 浙江大学 | Method and device for manufacturing microdevice |
| CN116477566B (en) * | 2023-03-23 | 2024-04-09 | 清华大学 | Single-particle microelectrode preparation method based on microcapillary injection |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4590792A (en) * | 1984-11-05 | 1986-05-27 | Chiang William W | Microanalysis particle sampler |
| US6188068B1 (en) * | 1997-06-16 | 2001-02-13 | Frederick F. Shaapur | Methods of examining a specimen and of preparing a specimen for transmission microscopic examination |
| US6777674B2 (en) * | 2002-09-23 | 2004-08-17 | Omniprobe, Inc. | Method for manipulating microscopic particles and analyzing |
-
2004
- 2004-06-08 EP EP04754729A patent/EP1754049A2/en not_active Withdrawn
- 2004-06-08 WO PCT/US2004/018206 patent/WO2005123227A2/en not_active Application Discontinuation
- 2004-06-08 CN CNA2004800379489A patent/CN1977159A/en active Pending
- 2004-06-08 CA CA002543396A patent/CA2543396A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| WO2005123227A2 (en) | 2005-12-29 |
| CN1977159A (en) | 2007-06-06 |
| EP1754049A2 (en) | 2007-02-21 |
| WO2005123227A3 (en) | 2006-12-14 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |