Thermal interface process considerations

By employing a laser for the photoionization (not to be confused with laser desorption/ ionization, where a laser is irradiating a surface, see Section 2.1.21) both sensitivity and selectivity are considerably enhanced. In 1970 the first mass spectrometric analysis of laser photoionized molecular species, namely H2, was performed [54]. Two years later selective two-step photoionization was used to ionize mbidium [55]. Multiphoton ionization mass spectrometry (MPI-MS) was demonstrated in the late 1970s [56—58]. The combination of tunable lasers and MS into a multidimensional analysis tool proved to be a very useful way to investigate excitation and dissociation processes, as well as to obtain mass spectrometric data [59-62]. Because of the pulsed nature of most MPI sources TOF analyzers are preferred, but in combination with continuous wave lasers quadrupole analyzers have been utilized [63]. MPI is performed on species already in the gas phase. The analyte delivery system depends on the application and can be, for example, a GC interface, thermal evaporation from a surface, secondary neutrals from a particle impact event (see Section 2.1.18), or molecular beams that are introduced through a spray interface. There is a multitude of different source geometries. 

Using GIR to investigate the thickness of the ultrathin oxide layer in Al-SiO c-Si devices, the number of Al—O bonds (band of 849 cm" ) was found to increase with thermal annealing [13] (Fig. 6.3). The decrease in the SiO thickness is a temperatnre-activated process with an activation energy of 0.98 eV and can be well described within the fi amework of an Al-A10y-SiO t Si model. In addition, contamination by aluminum can considerably influence the characteristics of the SiOj -Si interface, causing an increase in the density of electronic states, the effect being more pronounced for thinner silicon oxide layers [22, 23]. 

---