Analytical Methods MSE528 Chemical analysis Structural Analysis Physical 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 X. and the resolution (resolving power) is between 4 to 10 nm ( 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.backscatteredsecondaryproducing 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 26

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 27

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. 29

Gentle Beam 1KV X100,000 SEM Mode Resist Lines & Spaces Gentle Beam Mode 30

0.1kV in GB mode 50,000X200,000X Mesoporous Silica Ultra-High Resolution SEM JSM-7500F 31

STEM Data C Nano Tubes 32

EDS Spot Analysis in STEM Sample: Carbon nanotube with catalyst particles Mag: x 220,000 Acc. Voltage: 30kV Imaging mode: STEM EDS spot analysis clearly distinguishes between Fe-containing catalyst particles (Spot A) and carbon nanotube matrix (Spot B) 33

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 = keV) and magnesium (Mg K-alpha E = 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