SCANNING ELECTRON MICROSCOPE

SCANNING ELECTRON MICROSCOPY (SEM) &

FIELD EMISSION SCANNING ELECTRON MICROSCOPY (FE-SEM)

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).

SEM provides topographical and elemental information at magnifications of 10x to 100,000x with virtually unlimited depth of field.

SEM Applications Include:

Materials evaluation: Grain size, Surface roughness, PorosityParticle, size distributions, Material homogeneity, Intermetallic distribution and diffusion
Failure analysis: Contamination location, Mechanical damage assessment, Electrostatic discharge effects, Micro-crack location
Quality Control screening: "Good" to "bad" sample comparison, Film and coating thickness determination, Dimension verification, Gate width measurement, Mil Std. screening

SEM Principle of Operation

A finely focused electron beam scanned across the surface of the sample generates secondary electrons, backscattered electrons, and characteristic X-rays. These signals are collected by detectors to form images of the sample displayed on a cathode ray tube screen. Features seen in the SEM image may then be immediately analyzed for elemental composition using EDS or WDS.

Secondary Electron Imaging shows the topography of surface features a few nm across. Films and stains as thin as 20 nm produce adequate-contrast images. Materials are viewed at useful magnifications up to 100,000x without the need for extensive sample preparation and without damaging the sample.

Backscattered Electron Imaging shows the spatial distribution of elements or compounds within the top micron of the sample. Features as small as 10 nm are resolved and composition variations of as little as as 0.2% determined.

Data Output is generated in real time on the CRT monitor. Hard copies are photographed from this high resolution (2000 line pairs) display onto Polaroid film, with negatives available for later production of multiple copies.

FE-SEM Principle of Operation

A field-emission cathode in the electron gun of a scanning electron microscope provides narrower probing beams at low as well as high electron energy, resulting in both improved spatial resolution and minimized sample charging and damage.

FE-SEM Applications Include:

Semiconductor device cross section analyses for gate widths, gate oxides, film thicknesses, and construction details
Advanced coating thickness and structure uniformity determination
Small contamination feature geometry and elemental composition measurement

Why Field Emission SEM?

FESEM produces clearer, less electrostatically distorted images with spatial resolution down to 1 1/2 nm. That's 3 to 6 times better than conventional SEM.
Smaller-area contamination spots can be examined at electron accelerating voltages compatible with Energy Dispersive X-ray Spectroscopy.
Reduced penetration of low kinetic energy electrons probes closer to the immediate material surface.
High quality, low voltage images are obtained with negligible electrical charging of samples. (Accelerating voltages range from 0.5 to 30 kV.)
Need for placing conducting coatings on insulating materials is virtually eliminated.