Laser Ionization Mass Spectroscopy (LIMS)

Laser Ionization Mass Spectroscopy (LIMS) is a relatively new failure analysis technique used in the compositional analysis of a sample. 

LIMS operates by removing ions from the sample using a microfocused high-power density laser beam, and then analyzing the mass of these ions.  The removal of material for analysis is accomplished in one of two laser irradiation modes: 1)  by laser desorption (LD); and 2) by laser ionization (LI).

Once the ions are removed from the sample either by LD or LI, the ions are subjected to analysis using a mass spectrometer of time-of-flight design, wherein the mass values of the ions are quantified based on their transit time across a high vacuum region through which they are accelerated by an electric field of known value.

Laser ionization produces ions from the specimen during the vaporization of the material with the laser beam.  LI therefore operates under high irradiance levels of more than 10¹⁰ W/cm², and can sample well into the bulk of the specimen.  For instance, LI analysis can sample depths on the order of 1000 to 2000 angstroms per laser shot for GaP.

On the other hand, laser desorption can only produce ions from the specimen surface or from substances that are adsorbed on the specimen surface because it operates under relatively low irradiance levels of less than 10⁹ W/cm². LD sampling depths are on the order of 100 to 200 angstroms per laser shot.  

Typical applications of LIMS as a microanalytical tool include: 1) bulk microanalysis of conductor and insulator materials; 2) surface analysis of thin films, contamination, and adsorbed elements and molecules.

The main advantages offered by LIMS is its high elemental sensitivity, wide mass analysis range, and relatively small beam diameter (1 to 5 microns).  Because of these, LIMS can distinguish between the bulk material,  the materials that are just adsorbed on the surface of the specimen, and materials incorporated in a matrix.

See Also:  Failure Analysis;  All FA Techniques;  SIMS;  EDX/WDX Analysis;

Auger Analysis;  ESCA or XPS;  FTIR Spectroscopy;  Chromatography;

FA Lab Equipment;  Basic FA Flows;  Package Failures;  Die Failures