Exploring Materials Engineering

Materials Characterization: Page I

Page II: Scanning Probe Microscopy
Page III: Non-Destructive Testing

Materials Characterization represents many different disciplines depending upon the background of the user. These concepts range from that of the scientist, who thinks of it in atomic terms, to that of the process engineer, who thinks of it in terms of properties, procedures, and quality assurance, to that of the mechanical engineer, who thinks of it in terms of stress distributions and heat transfer. The definition selected for the ASM-International Materials Characterization Handbook is as follows: "Characterization describes those features of composition and structure (including defects) of a material that are significant for a particular preparation, study of properties, or use, and suffice for reproduction of the material." This definition limits the characterization methods included in the Handbook [and this web page] to those that provide information about composition, structure, and defects and excludes those methods that yield information primarily related to materials properties, such as thermal, electrical, and mechanical properties.

Taken from Metals Handbook Ninth Edition, Volume 10: Materials Characterization, ASM Handbook Committee, ASM-International, Metals Park, Ohio.

An important component of the materials engineering methodology involves knowledge of the structure of materials. Typical structure is necessarily viewed through a microscope.... an optical microscope, the electron microscope (imaging of electrons passed through a thin specimen in the transmission electron microscope TEM; or imaging by collecting electrons emitted from the surface of the material of interest in the scanning electron microscope SEM). Here are some structure related Internet images:

Here is a typical optical microscope. The principles are the same for the operation of a SEM or TEM; except the light source for an electron microscope is an electron gun, and the lenses are electromagnetic (they are not made from optical-grade glass). Electron microscopes require a vacuum column because electrons readily interact with air molecules and would become rapidly adsorbed. The reference source URL for the optical microscope image was the Lucent Technologies Microscapes site, which is no longer available. Do visit the Bell Labs web pages to see related images.

On the upper right we see a photomicrograph of pyramid-shaped etch pits on the surface of a silicon wafer. What is the reason for formation of an 'etch-pit?' Well, there are defects in crystalline materials called dislocations. Where dislocations intersect a surface, a feature called an etch-pit can form. The pit will form if atomic impurities in the crystal are segregated to the dislocation (by thermal treatment) and if the specimen is subsequently etched (ie, the surface chemically attacked with an appropriate chemical etchant). The reference source URL is the Bell Labs web pages.

This is a scanning electron micrograph (left) of a dendrite. When solid metal grows from the liquid state, a tree-like feature grows which is called a dendrite. The dendrite is, essentially, a single crystal feature. The growth of dendrites occurs when liquid metals solidify, and the phenomenon is analogous to the process of formation of ice crystals from supersaturated water vapor, for example. For a most interesting look at the dendrite growth process, visit this Cal Tech web site.

Here is a scanning electron micrograph of a device region (right) on an integrated circuit. The white features are metallization lines. Here, we are looking normal to the surface of the silicon wafer and see the top-level of connective lines. In the next image, we will see a cross-section through metallization lines. The reference source URL is Philips Research, part of Philips Electronics.

Next, let us consider a cross-section through an integrated circuit (IC). View the series of images below.

First, to get a good idea as to the various layers that make-up a modern IC, go to the following LINK where a schematic of a typical cross-section of a complementary metal oxide semiconductor (CMOS) device is presented (origin is Texas Instruments). For cross-sectional views and an operational description of different IC devices, visit these Wikipedia web pages.

The SEM image below, left, is an actual cross-section of a modern IC device showing the various metallization lines (yellow) embedded in passivation material (silicon nitride, for example). Being able to deposit a number of planar layers has made possible the scaling-down of the size of device regions and made possible more punch per chip! The reference source URL is IBM Corporation.

On the right is an SEM section through 4 MB DRAM (Dynamic Random Access Memory) cells. The section was made by a new instrument called the Focused Ion Beam Microscope. It is capable of performing corrective micro-surgery on IC chips. The reference source for this cross-section was FIB International of Santa Clara, CA; but this company (and its web pages) no longer exist. Visit the following web pages at IMEC, Belgium to learn more about focused ion-beam technique for IC analysis. IMEC is a world-leading independent research center in nanoelectronics and nanotechnology.

To see impressive detail within the FIB section, click here.

If you have further interest into the structure and operation of IC devices, I encourage you to download the following .pdf file.

This is a polycrystalline array of grains in an aluminum metallization line on an integrated circuit. It is a color photomicrograph. Each colored grain is a single crystal of aluminum, oriented differently with respect to its neighbors. The reference source URL is the Bell Labs web page.

Photomicroscopy is an important tool in the characterization of engineering materials. A good overview of 'Metallography', the photomicroscopy of metals and alloys is provided at the following Wikipedia web site. Another look-see at micrographs is provided at the this mircolab gallery: lots of photomicrographs.

The scanning electron micrograph (left) shows a typical TiC coating of 150 micrometers on Poco AXF-5Q graphite. These TiC coatings feature both an equiaxed structure adjacent to the coating-substrate interface, and columnar grains away from the interface. Additionally, these coatings adhere well to their graphite substrates even after fracture. Thicknesses for these coatings can be controlled from a few micrometers to 250 micrometers. The reference source URL is Lanxide Coated Products

If you wish to know more about materials characterization, I invite you to turn to PAGE II. PAGE II will introduce you to other examples of materials characterization, including scanning probe microscopy, which offers the possibility to view, and manipulate, individual atoms and molecules on surfaces. Then, there is PAGE III. Page III will introduce you to Non-Destructive Testing, useful methods to find and characterize internal flaws within a material, for example. Make sure to visit these two additional pages.

The materials engineer is often involved in a function called failure analysis. Materials characterization is an important component of any failure analysis. For further information about this most interesting aspect of materials engineering, please visit the Failure Analysis web pages at this site.

Continue Tour of Commercial Material's Links to ...

Metals and Alloys
Concept of Structure
Failure Analysis

Return to the Chemical and Materials Engineering Department Home Page at San Jose State University.

Please send any comments to Patrick P. Pizzo, Professor of Materials Engineering

Created by Dr. Pizzo on August 1, 1997.

Last Revision, December 31, 2014