**5.1 Basic principles of TPD**

TPD, also called thermal desorption spectroscopy, is essentially a method of analyzing desorped gases from samples heated under vacuum conditions using quadruple mass spectroscopy (QMS). The sample is heated by infrared light at a linear rate and evolved gases are introduced into a quadruple mass spectroscope that indicates the intensity of the signal according to the mass (*m*) and electric charge (*z*). TPD is now widely used to investigate the surfaces of ceramics and also semiconductors. In typical TPD spectra, the vertical axis shows the variation of the ion intensity of QMS (in amperes) for a specific *m*/*z* and the horizontal axis is the desorption temperature (Figure 8) (Nishide et al., 2004).

Fig. 8. Typical TPD curves plotted as a function of temperature (Shimizu et al., 2007).

**5. Desorption of H2O from sol-gel-derived HfO2 and ZrO2 thin films on Si(001)** 

During the firing of hafnia gel films, H2O is not vaporized completely. Even after HfO2 films are crystallized on the Si(001) surface, Hf-OH bonds and/or H2O may be trapped between nanopores in HfO2 films. Thus, the thermal properties, especially the desorption of H2O from HfO2 films, must be clarified after firing hafnia gel films. The electrical properties of sol-gel-derived HfO2 films should also be characterized, in view of their possible application

Temperature-programmed desorption (TPD) is an excellent technique, not only for analyzing adsorbed gases on the surfaces of bulk sol-gel-derived HfO2 films, but also for

TPD, also called thermal desorption spectroscopy, is essentially a method of analyzing desorped gases from samples heated under vacuum conditions using quadruple mass spectroscopy (QMS). The sample is heated by infrared light at a linear rate and evolved gases are introduced into a quadruple mass spectroscope that indicates the intensity of the signal according to the mass (*m*) and electric charge (*z*). TPD is now widely used to investigate the surfaces of ceramics and also semiconductors. In typical TPD spectra, the vertical axis shows the variation of the ion intensity of QMS (in amperes) for a specific *m*/*z* and the horizontal axis is the desorption temperature (Figure 8) (Nishide et al., 2004).

Fig. 8. Typical TPD curves plotted as a function of temperature (Shimizu et al., 2007).

**wafers during firing** 

**5.1 Basic principles of TPD** 

as gate insulators in next-generation CMOS devices.

analyzing the species that evolve from the films.

TPD curves can be obtained for various *m*/*z*'s with increasing temperature, thereby enabling quantitative identification of species desorped from materials and films. Simultaneously, the desorped species can be physically and chemically analyzed. In addition, reaction rate analyses of desorped gases can be performed. Figure 8 shows examples of (a) a nonsymmetrical TPD curve indicated by the solid line (the first-order reaction) and (b) a symmetrical TPD curve indicated by the dashed line (the second-order reaction) as a function of temperature. The arrow on the nonsymmetrical TPD curve corresponds to the evolution of physisorbed and chemisorbed H2O, which is specified to be a liquid such as water and water molecules hydrogen-bonded to Si-OH bonds at nanopore sites in the films (Hirashita et al., 1993).

For chemical-vapor-deposited SiO2 films, three distinct H2O desorption states have been defined (Hirashita et al., 1993). They are physisorbed H2O evolved at temperatures between 100 and 200 °C and chemisorbed H2O evolved at temperatures between 150 and 300 °C in a TPD measurement. The higher desorption peak between 350 and 650 °C is ascribed to Si-OH bonds formed during film growth. Thus, TPD is a useful technique for evaluating surfaces and thin films of ceramics and semiconductors.
