Analysis of Desorbed Gases from Surface: Thermal Desorption Spectroscopy

Thermal desorption spectroscopy (TDS) has been commonly employed to evaluate the outgassing properties of both vacuum materials and thin films. Hydrogen, water, CO and CO2 —the most dominant gas species— can be easily detected and quantified by quadrupole mass spectrometry. This paper examines two calibration methods to convert ion current into outgassing rate: first, by using the standard leak of each gas and, second, by using an absolute pressure gauge. TDS is demonstrated for two different types of samples: stainless steel and amorphous Si (a-Si) film. In the case of stainless steel, samples blasted with glass beads were compared with chemically polished samples, and the TDS results' relationship to pumping down properties was investigated. The a-Si film examined was formed using a low temperature poly silicon process. Its hydrogen concentration as determined by TDS corresponded with that obtained by secondary ion mass spectrometry (SIMS). The outgassing temperature characteristics obtained for both the stainless steel and a-Si samples provided valuable information.