Germanium possesses higher electron and hole mobilities than silicon. There is a big leap, however, between these basic material parameters and implementation for high-performance microelectronics. Here we discuss some of the major issues for Ge metal oxide semiconductor field effect transistors ͑MOSFETs͒. Substrate options are overviewed. A dislocation reduction anneal Ͼ800°C decreases threading dislocation densities for Ge-on-Si wafers 10-fold to 10 7 cm −2 ; however, only a 2 times reduction in junction leakage is observed and no benefit is seen in on-state current. Ge wet etch rates are reported in a variety of acidic, basic, oxidizing, and organic solutions, and modifications of the RCA clean suitable for Ge are discussed. Thin, strained epi-Si is examined as a passivation of the Ge/gate dielectric interface, with an optimized thickness found at ϳ6 monolayers. Dopant species are overviewed. P and As halos are compared, with better short channel control observed for As. Area leakage currents are presented for pϩ/n diodes, with the n-doping level varied over the range relevant for pMOS. Germanide options are discussed, with NiGe showing the most promise. A defect mode for NiGe is reported, along with a fix involving two anneal steps. Finally, the benefit of an end-of-process H 2 anneal for device performance is shown.

The influence of the hydrophobicity of silica particles on the electrodeposition of Cu-SiO 2 composite coatings from acid copper sulfate solutions on rotating disk electrodes was studied. Spherical, nearly monodisperse hydrophilic and hydrophobic silica particles were used. The hydrophilic silica particles were prepared by the Stöber process. These particles were made hydrophobic by a treatment with oligodimethyl siloxane-␣,-diol. The effect of cetyl trimethyl ammonium hydrogen sulfate (CTAHS) and sodium 1-dodecane sulfonate on the codeposition behavior was investigated. Hydrophilic silica did not codeposit from surfactant-free nor from surfactant-containing acid copper sulfate solutions, but up to 4 wt % (Х 14 vol %) of hydrophobic silica codeposited from solutions containing 15 g/L of silica particles and 10 Ϫ4 M CTAHS. The codeposition rate of hydrophobic silica slowly decreased with time. The amount of codeposited particles was highest for a current density of 5 A/dm 2 and a rotation speed of 400 rpm.

The inverse relationship between film thickness and electrical resistivity of metallic films is usually studied by depositing a series of films with different thickness and measuring their sheet resistance with a four-point probe. However, the structure and uniformity of polycrystalline thin films typically depend on thickness, rendering it difficult to establish the dominant electron scattering mechanism. In order to circumvent the uniformity issue we now use beveled films to establish the thickness dependent resistivity of thin copper films. Here the resistivity of films down to a few nm’s can be studied without, e.g., a percolation effect. Additionally, the comparison of data obtained on samples where beveling took place either before or after anneal is used to study the impact of grain size on resistivity. It is shown that the normally observed strong increase in resistivity is dominated by grain boundary scattering. However, the influence of surface scattering can be clearly observed when thick films are thinned after a high temperature anneal in which case the grain size is considerably larger than the electron mean free path of copper at room temperature.

Germanium possesses higher bulk mobilities than silicon and was used for the first transistors. However, by the 1960s its use was largely supplanted with Si due largely to Si's high quality thermal oxide. Today, with the 45 nm technology node in production, high k dielectrics are beginning to replace SiO2 in the gate, and as such, one of the key reasons for using Si is no longer as relevant. This, combined with performance concerns for Si based devices for and beyond the 22 nm node has made Ge a worthy area for research for high performance devices. In this paper, we give an overview of some of the major issues for Ge MOSFETs, illustrating recent progress using data from IMEC. Key results include a factor of 10 reduction in threading dislocations for epi Ge on Si by the use of an ~850{degree sign}C anneal, the first successful use of As halo implants, progress on optimization of activation anneals, the use of a thin epitaxial Si passivation and its impact on threshold voltage, a 2-step anneal NiGe process flow to drastically reduce defects, and the importance of a hydrogen anneal following metallization.

Thin SiGe-on-insulator (SGOI) substrates with Ge content varying between 42 and 93% were produced by the Ge condensation technique and full structural characterization was carried out. In a second step, the electrical properties of these substrates were analyzed by the pseudo metal-oxide semiconductor field-effect transistor technique which allowed determination of the carrier low-field mobilities, as well as the density of fixed charges in the buried oxide (BOX) and the density of interface traps at the BOX-SiGe film interface. Optimization of intermediate anneals in argon during the condensation process made the production of high crystalline quality and high-mobility substrates possible (up to 400cm2normalV−1normals−1 for a 93% SGOI). Opposite trends were observed for holes and electrons: while the hole mobility increases with increasing Ge content, the electron mobility decreases. In addition, the density of interface traps and also the density of oxide charges were found to increase with increasing Ge content. Possible causes for this increase are discussed.