Wet Chemical Cleaning of Germanium Surfaces for Growth of High-k Dielectrics
- PDF / 316,507 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 111 Downloads / 165 Views
0917-E01-05
Wet Chemical Cleaning of Germanium Surfaces for Growth of High-k Dielectrics Sandrine Rivillon Amy1, Yves J Chabal1, Fabrice Amy2, Antoine Kahn2, Cristiano Krugg3, and Paul Kirsch3 1 Department of Chemistry and Chemical Biology, Rutgers University, 136 Frelinghuysen Rd, Piscataway, NJ, 08854 2 Electrical Engineering Department, Princeton University, Princeton, NJ, 08544 3 AGS dielectrics, Sematech, Austin, Tx, 78741 ABSTRACT One of the major difficulties preventing the wide use of germanium (epi or bulk) as a gate material is the poor stability of its oxide, leading to reproducibility and reliability issues. In contrast to silicon, the nature and thickness of Ge “native” oxides are history dependent, and most phases of germanium oxide are water-soluble. As a result, the procedures for passivating Ge surfaces with hydrogen (HF last) are more complex and less forgiving. We have used infrared absorption spectroscopy and x-ray photoelectron spectroscopy to investigate the nature of oxidized and H-terminated Ge surfaces. The GeO2, GeO and GeC phases have been identified and quantified as a function of processing conditions. The stability of the H-terminated surfaces has been examined in air and in controlled environments. The Hpassivated Ge surfaces are found to be much less stable in air than H-terminated Si surfaces. INTRODUCTION Passivation of germanium (Ge) surfaces is challenging because most of the commonly accepted passivation layers (oxide, H, etc..) are much less stable than on silicon (Si). For instance, germanium oxide exhibits various chemical forms. Specifically, studies on germanium dioxide powder reveals a polymorphism at room temperature with three possible structures: the tetragonal phase (insoluble in water), and the hexagonal and amorphous phases (both soluble in water). The respective water solubility is 4.5 g/l for the hexagonal and 5.2 g/l for the amorphous phases.[1] Early reports on surface germanium oxides and Ge cleaning have been difficult to integrate into a clear picture beause the reported results depend on the specific chemical treatment used. For instance, X-rays photoemission spectroscopy of the Ge3d core level have shown varying intensities of the peak corresponding to GeO2 (+3.2 eV), suggesting that the initial thickness of the “native” oxide is different for different groups.[2-6] If the thickness (and possibly composition) of the starting “native” oxides can vary, we can expect that the cleaning procedures may also vary depending on the starting conditions. Furthermore, most work described in the literature has focused on the germanium dioxide and less on possible germanium suboxides[2-4,6] that may be also formed on the surface. Finally, very few papers mention hydrocarbon contamination,[5] which we will show plays a key role for the germanium. Similarly, passivation of Ge surfaces with hydrogen or halides (and their respective stability) is also less well understood than for Si surfaces. Hydrogen passivation has been previously achieved using electrochemistry[7] althoug
Data Loading...
