analytical methods mse528

Analytical MethodsMSE528

Chemical analysisStructural AnalysisPhysical Properties

• X-Ray method– Laue Techniques: rotating Xtal– Debye-Scherrer: Powder Method– Diffraction

• Electron Microscope– Transmission Electron Microscope (TEM)– Scanning Electron Microscope (SEM)– SPM & AFM

• Microanalysis: EDAX, AES and XPS

• X-Ray method– Laue Techniques: rotating Xtal– Debye-Scherrer: Powder Method– Diffraction

• X-ray powder diffraction (XRD) is one of the most powerful technique for qualitative and quantitative analysis of crystalline compounds. The technique provides information that cannot be obtained any other way. The information obtained includes types and nature of crystalline phases present, structural make-up of phases, degree of crystallinity, amount of amorphous content, microstrain & size and orientation of crystallites.

• X-ray diffraction has application in most fields dealing with solid materials. XRD identifies crystalline compounds as opposed to X-ray Fluorescence (XRF) or other spectro-chemical methods that identifies just the elements. Areas of application are quite wide and include metals, organic and inorganic compounds.

Some of the relevant areas are listed and discussed below: • Airborne dusts and particulate • Hazardous Inorganic chemicals • Asbestos • Metals • Biomaterials • Pharmaceuticals • Catalysts • Polymers • Ceramics and Composites • Rocks and minerals • Clays & Soils • Semiconductors • Corrosion Products

A schematic of typical optics is shown below.

Typically for a fine filament tube the filament length Lx is 12-16mm and its width Wx is 0.04mm.

nl = 2d sin

• In the scanning electron microscope (SEM) a very fine 'probe' of electrons with energies up to 40 keV is focused at the surface of the specimen in the microscope and scanned across it in a 'raster' or pattern of parallel lines. A number of phenomena occur at the surface under electron impact: most important for scanning microscopy are the emission of secondary electrons with energies of a few tens eV and re-emission or reflection of the high-energy backscattered electrons from the primary beam. The intensity of emission of both secondary and backscattered electrons is very sensitive to the angle at which the electron beam strikes the surface, i.e. to topographical features on the specimen. The emitted electron current is collected and amplified; variations in the resulting signal strength as electron probe is scanned across the specimen are used to vary the brightness of the trace of a cathode ray tube being scanned in synchronism with the probe. There is thus a direct positional correspondence between the electron beam scanning across the specimen and the fluorescent image on the cathode ray tube.

The magnification produced by scanning microscope is the ratio between the dimensions of the final image display and the field scanned on the specimen. Usually magnification range of SEM is between 10 to 200 000 X. and the resolution (resolving power) is between 4 to 10 nm (40 - 100 Angstroms) .

• How the SEM Works • • The SEM uses electrons instead of

light to form an image. A beam of electrons is produced at the top of the microscope by heating of a metallic filament. The electron beam follows a vertical path through the column of the microscope. It makes its way through electromagnetic lenses which focus and direct the beam down towards the sample. Once it hits the sample, other electrons ( backscattered or secondary ) are ejected from the sample. Detectors collect the secondary or backscattered electrons, and convert them to a signal that is sent to a viewing screen similiar to the one in an ordinary television, producing an image.

JEOL JSM-7500

• Mag: 25 to 1,000kX• kV: 0.1 to 30kV• SEI: 1.0nm (15kV)• SEI: 1.5nm (1kV)• SEI: 4.0nm (0.1kV)• BEI*: 1.5nm (5kV)• BEI*: 1.7nm (3kV)• GB mode / r-filter / in-

lens BSE Detector

Highlights of the 7500F

• 5 axis tilt eucentric stage with automation standard on all axes including compeucentric rotation.

• Smooth mechanical stage movement at high mags via TEM trackball & touch pad

• Great low kV SE, low kV BSE and STEM Imaging• Enhanced environmental resistance• GB Mode and in column SE energy filter• In lens BSE Detector for ultra high res. BSE imaging• LABE detector• r-Filter

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Live Image Comparison

The main image window can also be a live split or live quad display of different detector signals with independent control of each signal

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Specimen stub Specimen

Electron probe

Electron

Electron probe

－

＋

Gentle Beam

Reduces the effect of charging 　 28

Gentle Beam

• Increases resolution by maintaining higher kV in the gun & column. (Reduces Aberrations)

• Accelerates secondary electrons off the sample, especially at very low accelerating voltages.

• Reduces charging.

• Reduces contamination.

• Lowers the kV to the sample increasing pure surface topographic detail due to reduced beam penetration.

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Gentle Beam

1KV X100,000 1KV X100,000

SEM Mode Resist Lines & Spaces Gentle Beam Mode

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0.1kV in GB mode

50,000X 200,000XMesoporous Silica

Ultra-High Resolution SEM JSM-7500F

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STEM Data

C Nano Tubes

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EDS Spot Analysis in STEMSample: Carbon nanotube with catalyst particlesMag: x 220,000Acc. Voltage: 30kVImaging mode: STEM

EDS spot analysis clearly distinguishes between Fe-containing catalyst particles (Spot A) and carbon nanotube matrix (Spot B)

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Electron Spectroscopy for Chemical Analysis (ESCA) or X-ray Photoelectron Spectroscopy (XPS)

In a failure analysis technique primarily used in the identification of compounds on the surface of a sample.  It utilizes X-Rays with low energy (typically 1-2 keV) to knock off photoelectrons from atoms of the sample through the photoelectric effect.  The energy content of these ejected electrons are then analyzed by a spectrometer to identify the elements where they came from.         The incident X-Rays used in knocking off the electrons must possess energy that is both monochromatic and of accurately known magnitude.  The X-ray source material must also be a light element since X-ray line widths, which must be as narrow as possible in ESCA, are proportional to the atomic number of the source material. It is for these reasons that commercial XPS systems typically use the K-alpha X-rays of aluminum (Al K-alpha E = 1.487 keV) and magnesium (Mg K-alpha E = 1.254 keV).          

Schematic representation of the energies produced from electron beam interaction with solid matter.

Luminescence is the emission of light from a solid which is 'excited' by some form of energy. The term broadly includes the commonly-used categories of fluorescence and phosphorescence.

• Field Emission Scanning Electron Microscopy (FESEM) is a high-resolution imaging technique providing topographical and structural information in plan view or in cross-section. Often used in conjunction with SEM, Energy Dispersive X-Ray Spectroscopy (EDX) is used to qualitatively and quantitatively analyze the elements present in a selected area of the SEM image. Together FE-SEM and EDX capabilities allow the irradiation by a focused electron beam, imaging secondary or backscattered electrons and energy analysis of x-rays.Typical SEM applications include plan view and cross-sectional imaging for process development and failure analysis. EDX applications include specific defect analysis or compositional analysis (for boron and heavier elements).

2.1nm resolution at 1kV 1.5nm resolution at 15kV Cold finger and specimen exchange chamber as standard Optional integrated EDX system with 30 degree take-off angle Fully digital imaging, image processing and archiving system Dual SE detectors for versatile imaging New ExB energy filter

Compositional analysis Elemental Chemical

Electron diffraction/crystalographic identification

Phase identification

Silicon devices Precise Location

Compound semiconductors Magnetic disks Film Thickness Gate Ox thickness

III - IV Superlattice Step coverage

Gate Ox thickness Gate to Silicon Interface

Interfacial oxide

• Chemical analysis (microanalysis) in the scanning electron microscope (SEM) is performed by measuring the energy or wavelength and intensity distribution of X-ray signal generated by a focused electron beam on the specimen. With the attachment of the energy dispersive spectrometer (EDS) or wavelength dispersive spectrometers (WDS), the precise elemental composition of materials can be obtained with high spatial resolution. When we work with bulk specimens in the SEM very precise accurate chemical analyses (relative error 1-2%) can be obtained from larger areas of the solid (0.5-3 micrometer diameter) using a n EDS or WDS. Bellow is a example of EDS spectrum collected in the SEM with EDS. The spectrum shows presence of Al, Si, Ca, Mn and Fe in the steel slag phase.

• Scanning Acoustic Microscopy (SAM) is an excellent technique for studying buried solid interfaces of dissimilar materials. SAM is an internal imaging analysis technique produced via ultrasonic waves reflecting or transmitting at sample interfaces. The images are constructed by detecting reflection (echo) or transmission of ultrasound from a solid state device shortly after pulse-excitation by a focusing transducer. Features such as bonded interfaces, density gradients or defects (delaminated interfaces, voids and cracks) can be imaged non-destructively.

FTIR application

• What is FTIR?• Applications of FTIR (general)• Applications of FTIR for semiconductor

industry• Remarks

FTIR

• Fourier Transform Infrared Spectroscopy• Used for identifying or characterizing

organic (and some inorganic) compounds (solid, powders, residues, solvents, liquids, gas)

• IR radiation is absorbed/transmitted; resulting spectrum characteristic of molecular structure

FTIR• “Fingerprint” type method (no 2 are same)• Detection of individual chemical compounds

or characteristic absorptions of chemical functional groups (organic and some inorganic)

• Detection limit: picogram range (monomolecular layers detectable on metal surfaces)

• Qualitative, quantitative• Reference libraries, spectral interpretation• Sampling techniques: transmission,

external reflection, internal reflection (ATR), diffuse reflection, emission, and photoacoustic spectroscopy

• Detectors: triglycine sulfate (TGS), mercury-cadmium-telluride (MCT)

FTIR with microscope

General Applications• Identify unknown compounds -e.g. plastics, drugs (i.e. cocaine), contamination (i.e. flux residues, silicone, esters, grease, etc.)• Obtain structural information (organic functional groups) -e.g. alkanes, alkenes, alkynes, aromatics, alcohols, ethers, amines, aldehydes and ketones, carboxylic acids, amides, etc.

Common uses in semiconductor industry

• Determination of interstitial oxygen and substitutional carbon in processing wafers

• Epitaxial film thickness measurements• Monitoring phosphorus in phosphosilicate thin films and both

phosphorus and boron in borophosphosilicate thin films• Measurement of the hydrogen content in oxide and nitride thin

films• Identification of particles and residues (most common)• Incoming materials characterization• Trace gas analysis• Carrier concentration measurements• Characterization of Si surfaces after cleaning operations

Measurement of Interstitial Oxygen and Substitutional Carbon in Si

Wafers• Si-C, Si-O-Si

Advantages of FTIR for measurement of Cs and Oi

• Non-destructive• Cheaper• Faster• Reproducible• Sensitive (to dopants)• Excellent spatial resolution (5-10 um)• Specific to the Oi and Cs in Si

Epitaxial Film Thickness Applications

• To determine epitaxial (Epi) layer film thickness (the most commonly used high-resistivity Epi layers are transparent to IR radiation)

• 3 methods (constant-angle observations making use of either direct or modified measurement of interference phenomena):

1) Interferogram Subtraction 2) Constant Angle Reflection Interference Spectroscopy 3) Cepstrum

Interferogram Subtraction

Constant Angle Reflectance Interference

Advantages of FTIR for Epi thickness measurements

• speed of measurement• Non-destructive• Reproducible• Lends itself to automation• Operator independent

Particle/residue identification in Failure Analysis

Remarks

• Many applications• May use other instruments/tools/techniques to

obtain additional information or confirmation• Relatively cheap, quick, accurate, internally

calibrated (self-calibrated)• Even with software and automation, still

recommend a chemist familiar with spectral interpretation