Here you will find descriptions of some of the specific techniques and instrumentation used by CE&A which are representative of the state-of-the-art in materials characterization. They are listed under their generic headings.
Jump to a table of capabilities summarizing surface
analytical techniques.
Jump to a chart of detection limit vs. lateral resolution
(58K) for the techniques.
Jump to a tutorial on theory and instrumentation
used in SIMS, AES, and RBS.
In this mass spectrometry technique, a very small aliquot of sample (about 1 pmole) is greatly diluted in a supporting matrix, dried and inserted into the vacuum chamber of the instrument. A pulse of UV laser light (337 nm) a few nanoseconds in duration illuminates the sample and is absorbed by the matrix. This rapid pulse of energy causes the matrix to eject charged molecular ions into the vapor phase. They are then accelerated into the mass spectrometer and analyzed by mass-to-charge ratio, similar to the way analysis is performed using TOF SIMS.
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An energetic primary ion beam sputters a sample surface. Secondary ions
formed in this sputtering process are extracted frm the sample and analyzed
in a double-focusing mass spectrometer system. The lateral distribution
of the ions is maintained through the spectrometer so that the mass resolved
image of the secondary ions can be projected onto several types of image
detectors. Alternatively, microfocusing the primary ion beam permits analysis
in ion microprobe mode.
A more detailed tutorial on SIMS is also available.
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A large area or microfocused pulsed primary ion beam sputters the top surface layer of the sample. The secondary ions produced in this sputtering process are extracted from the sample surface and injected into a specially designed time-of-flight mass spectrometer. The ions are dispersed in time according to their velocity (which is proportional to their mass-to-charge ratio m/z) and the discrete packets of different massed ions are detected on either a microchannel plate (MCP) or resistive anode encoder (RAE) detector. The TOF SIMS technique is capable of detecting secondary ions produced over a large mass range (typically 0 to around 5000 atomic mass units) and performs this mass analysis at relatively high mass resolutions (>6000). The technique also is capable of generating an image of the lateral distributions of these secondary ions at spatial resolutions of better than 1 micron.
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A focused beam of electrons is rastered across a sample surface, the raster scan being synchronous with that of a cathode ray tube (CRT). The brightness of the CRT is modulated by the detected secondary electron current from the sample, such that the viewing CRT displays an image of the variation of secondary electron intensity with position on the sample. This variation is largely dependent on the angle of incidence of the focused beam onto the sample, thus yielding a topographical image. Different detectors can be used to provide alternative information, e.g., a backscattered electron detector will provide average atomic number information. An auxiliary energy dispersive X-ray (EDS) detector provides elemental identification analyses from boron to uranium. Some high performance instruments have enhanced abilities due to use of a special field-emission electron source (FE-SEM).
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The Field Emission Scanning Electron Microscope (FE-SEM) is similarly configured to a conventional SEM, except that a cold field emission electron source is used, which permits higher image resolution to be attained, increased signal to noise ratio, and increased depth of field.
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An EDS attachment to an SEM permits the detection and identification of the x-rays produced by the impact of the electron beam on the sample thereby allowing qualitative and quantitative analysis. The electron beam of an SEM is used to excite the atoms in the surface of a solid. These excited atoms produce characteristic X-rays which are readily detected. By utilizing the scanning feature of the SEM, a spatial distribution of elements can be obtained. For flat, polished homogeneous samples, quantitative analysis can provide relative accuracy of 1-3% when appropriate standards are available.
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A focused electron beam irradiates a sample surface producing Auger electrons,
the energies of which are characteristic of the element from which they
are generated. Compositional depth profiling is accomplished by using an
independent ion beam to sputter the sample surface while using AES/SAM to
analyze each successive depth.
A more detailed tutorial on AES is also available.
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Samples are irradiated with Mg or Al X-rays which cause the ejection of photoelectrons from the surface. The electron binding energies, as measured by a high resolution electron spectrometer, are used to identify the elements present and, in many cases, provide information about the valence state(s) or chemical bonding environment(s) of the elements thus detected. The depth of the analysis, typically the outer 3 nm of the sample, is determined by the escape depth of the photoelectrons and the angle of the sample plane relative to the spectrometer.
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A beam of He ions (with an energy of about 2.3 MeV) impinges on the target.
The He ions backscatter from the near surface region of the sample and are
collected by a solid state detector. The energy of the backscattered ions
provides information on both the composition and depth distribution of elements
in the target. Alignment of the ion beam with sample crystallographic axes
permits crystal damage to be measured quantitatively.
A more detailed tutorial on RBS is also available.
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This is a variation on RBS for measuring hydrogen in materials. An energetic beam of helium ions impinges on the target at a glancing angle (15 degrees). Hydrogen atoms are scattered forward out of the sample by the He atoms, which also scatter forward, after collisions with lighter atoms. The forward scattered H atoms are collected by a solid state detector, while the He atoms are stopped by a foil placed between the sample and the detector. The number of forward scattered H atoms provides information on the concentration of H in the sample, while the energy of the H provides depth information.
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These are variations on a method of imaging surfaces with atomic or near-atomic resolution, collectively called scanning probe microscopy (SPM). A small tip is scanned across the surface of a sample in order to construct a 3-D image of the surface. Fine control of the scan is accomplished using piezoelectrically-induced motions. If the tip and the surface are both conducting, the structure of the surface can be detected by tunneling of electrons from the tip to the surface (STM). Any type of surface can be probed by the molecular forces exerted by the surface against the tip (AFM). The tip can be constantly in contact with the surface, it can gently tap the surface while oscillating at high frequency, or it can be scanned just minutely above the surface. By coating the tip with a magnetic material, the magnetic fields immediately above a surface can be imaged (MFM). Image processing software allows easy extraction of useful surface parameters.
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X-rays from a tungsten anode or molybdenum tube impinge the sample surface at a glancing angle, within the critical angle for total external reflectance, and excite the electrons on atoms in the top few monolayers of the sample, causing them to emit photons (fluoresce). The X-ray photons emitted by the surface atoms have energies that are characteristic of the particular element. They are detected by an Si(Li) energy dispersive spectrometer. Quantification is achieved using a sample with a known areal density of impurity atoms (e.g. Ni) on the surface, and corrections with relative sensitivity factors are used for the other elements.
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The sample to be studied is placed on the stage of a microscope that is specially designed to transmit light at far-infrared wavelengths. Light generated by a broad-spectrum infrared source passes through a Fourier-transform spectrometer, is focused through (or reflected from)the sample, and travels on to a sensitive infrared detector. A computer performs a Fourier transform to convert the time-modulated intensity changes at the detector into an absorption spectrum vs. wavelength for the sample. Analysis of the spectral absorption bands allows identification of the composition of the sample.
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A non-destructive technique known as the Electrolytic Metal Tracer (ELYMAT) measures and maps minority carrier lifetime and diffusion length and provides contamination maps in semiconductor wafers. The measurements can be made in BPC or FPC mode. In the backsurface photo current (BPC) mode, the technique is sensitive to metals, such as Fe, Ni, Cr, and Cu, which form single atom recombination centers in the wafer bulk. The frontsurface photo current (FPC) mode is used to detect defects in the sub-surface layer, to measure highly contaminated wafers or where diffusion length is much smaller than the wafer thickness. The technique may also be used in injection level spectroscopic (ILS) mode for the elemental identification of a defect or recombination center, or in differential photo current (DPC) mode to determine the conditions of surface recombination.
The Model 670 features a thermal field emitter allowing the instrument
to routinely achieve a spatial resolution of 15 nm for elemental analysis
of particles and very small features found on semiconductors, metals, electronic
devices, and other materials. An in-vacuo cold fracture stage allows interfaces
to be studied without atmospheric contamination. It features spatial resolution
of better than 100 nm, a fracture stage, and Zalar Rotation for high resolution
depth profiling.
The Model 4300 has Zalar Rotation and is configured for high resolution
(1 nm) depth profiling.
Data output of these instruments is designed for use with PHI MATLAB Target
Factor Analysis (TFA) for post processing, which gives excellent quantitation
of TiN, WSi(x), Si and Cu in Al, etc.
An assortment of measuring heads is available to perform AFM/SPM (ambient), electrochemical, magnetic, and tapping mode SPM analyses. This AFM can accept full 200 mm (8 inch) wafers. The primary purpose of these instruments is to quantitatively measure surface roughness with a nominal 5 nm lateral and 0.01nm vertical resolution on all types of samples. Typical applications include measuring the surface roughness of semiconductor wafers, optical components, and hard disk drives.
This instrument currently has a spot size of 75 microns and will soon be upgraded with a new monochromator and lens to achieve a 25 micron analytical area. This instrument provides depth profiling of insulating materials and performs thickness measurements on organic films such as lubricants on magnetic media. XPS is a versatile tool capable of analyzing both inorganic and organic contamination on dielectric materials, stainless steel, semiconductor materials, circuit boards, magnetic media, polymers, and ceramics.
This FTIR has micro spot capability with the Spectra Tech infrared microscope
which can analyze areas as small as 5 microns. The FTIR is capable of analyzing
samples in transmission, reflectance, and total internal reflectance modes.
This instrument is used for bulk and surface identification of organic materials,
including thin films, fibers, solids, and liquids. It is especially useful
in the identification of polymers.
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Rutherford backscattering spectrometry uses a 1 MV NEC Pelletron tandem accelerator with a Charles Evans & Associates RBS-400 analytical end station. This instrument is configured with two surface barrier detectors for backscattering spectrometry in the normal and grazing exit detection modes and a 4-axis goniometer for ion beam channeling studies. A third detector provides quantitative hydrogen analysis by hydrogen forward scattering (HFS). The resulting energy spectrum of the scattered ions provides elemental identification and quantitative characterization of the near surface regions of the material, including the thickness of thin films.
This instrument has less critical vacuum requirements than the field emission electron microscopes, and supplies a high electron beam current for good X-ray production. Elements can be identified, and quantified with an accuracy of around 15% using appropriate standards.
The single crystal <310> tungsten cold cathode of these electron microscopes creates a tiny, bright source of electrons to allow 1.5 nm resolution at 30 kV, and enhanced surface contrast at lower voltages. They have the ability to image both secondary and backscattered electrons. The 6300F and 6400F are used mainly for imaging precision polished cross sections of semiconductor devices with very high spatial resolution. The 6400F additionally has a digital image system used for CD metrology, a 6-inch wafer capability and a symmetric channel plate electron detector. The 890 has a TEM-like column design that holds the sample within the objective lens, providing a unique contrast mechanism for dramatically enhanced image contrast and resolution down to 0.7 nm. The 890 additionally has a transmitted electron detector for high-resolution STEM imaging.
This is the largest concentration of CAMECA SIMS instruments in any laboratory in the world. The variety of instruments permits dedication of an instrument to a specialized analysis. They are used for trace elemental analysis of materials with ppb detection limits. Typical applications include depth profiling and microanalysis of high purity semiconductor materials, verification of controlled O content of Si substrate materials, and B contamination in N+ Si substrates. The use of the resistive anode encoder (RAE) ion imaging detector allows us to make direct ion maps of any element on the surface and changes in their lateral distribution as a function of depth
This is a relatively new technique for biochemicals. Applications include rapid and accurate mass determination of carbohydrates, proteins, and peptides, and molecular weight determination of oligomers and polymers. This instrument offers an extended mass range to 500,000 Da and superior mass resolution, which aids in unambiguous identification of compounds and chemically or proteolytically generated fragments, even in mixtures.
The TOF SIMS instruments offer extremely high mass resolution and exceptional mass accuracy for unambiguous identification of organic compounds and inorganic elemental contamination on surfaces. They are extremely surface-sensitive. TOF SIMS analyzes over a mass range of one to >10,000 amu and performs microanalysis with submicron resolution. Typical applications include surface haze composition, inorganic and organic particle analysis, and surface chemistry of inorganic, polymeric, and surface treated materials.
This instrument features both Mo and W anodes to cover a wide element
range, and is equipped with a 9 kW rotating anode X-ray source, a 2 kW Mo
x-ray tube and two monochromators. It will automatically load and analyze
a cassette of 4-, 5-, 6-, or 8-inch wafers or other smaller pieces of optically
flat materials. The X-ray beam strikes the sample surface at a glancing
angle and is totally reflected. The instrument uses a Si(Li) detector for
energy dispersive X-ray spectrometry. A typical application is for quantitative
measurement of surface impurities on semiconductor wafers or similar optically
flat samples. Detection limits are 1e10 atoms/cm2 to 1e12 atoms/cm2
and the elemental range is from S to U.