Jessica Kachian

Sulfur versus Oxygen Reactivity of Organic Molecules at the Ge(100)-2×1 Surface

The adsorption behavior of sulfur- versus oxygen-containing organic molecules, including ethanol, ethanethiol, diethyl ether, and diethyl sulfide, at the Ge(100)-2 x 1 surface was investigated using a combination of multiple internal reflection infrared (MIR-IR) spectroscopy and density functional theory (DFT). The results show that ethanol and ethanethiol both adsorb via Ch-H dissociation at 310 K, where Ch (chalcogen) is either S or O. DFT calculations indicate that S-H dissociation is both kinetically and thermodynamically favored over O-H dissociation. IR spectra of diethyl ether and diethyl sulfide reveal that both molecules adsorb via dative bonding through the heteroatom for temperatures up to approximately 255 and 335 K, respectively, and reversibly desorb at higher temperatures. From these desorption temperatures, the S-Ge dative bond of a sulfide is calculated to be 5.9 kcal/mol stronger than the O-Ge dative bond of an ether, a trend consistent with results from DFT calculations. Moreover, for all of the molecules studied, SGe dative bonds are found to be stronger than O-Ge dative bonds, with the magnitude of the difference increasing with substitution of bulkier groups on the Ch atom of the adsorbate. Calculations on diethyl selenide show that the Se-Ge dative bond is slightly stronger than the S-Ge dative bond.

Nitride passivation of the interface between high-k dielectrics and SiGe

In-situ direct ammonia (NH3) plasma nitridation has been used to passivate the Al2O3/SiGe interfaces with Si nitride and oxynitride. X-ray photoelectron spectroscopy of the buried Al2O3/SiGe interface shows that NH3 plasma pre-treatment should be performed at high temperatures (300u2009°C) to fully prevent Ge nitride and oxynitride formation at the interface and Ge out-diffusion into the oxide. C-V and I-V spectroscopy results show a lower density of interface traps and smaller gate leakage for samples with plasma nitridation at 300u2009°C.

Passivation of InGaAs(001)-(2 × 4) by Self-Limiting Chemical Vapor Deposition of a Silicon Hydride Control Layer.

A saturated Si-Hx seed layer for gate oxide or contact conductor ALD has been deposited via two separate self-limiting and saturating CVD processes on InGaAs(001)-(2 × 4) at substrate temperatures of 250 and 350 °C. For the first self-limiting process, a single silicon precursor, Si3H8, was dosed at a substrate temperature of 250 °C, and XPS results show the deposited silicon hydride layer saturated at about 4 monolayers of silicon coverage with hydrogen termination. STS results show the surface Fermi level remains unpinned following the deposition of the saturated silicon hydride layer, indicating the InGaAs surface dangling bonds are electrically passivated by Si-Hx. For the second self-limiting process, Si2Cl6 was dosed at a substrate temperature of 350 °C, and XPS results show the deposited silicon chloride layer saturated at about 2.5 monolayers of silicon coverage with chlorine termination. Atomic hydrogen produced by a thermal gas cracker was subsequently dosed at 350 °C to remove the Si-Cl termination by replacing with Si-H termination as confirmed by XPS, and STS results confirm the saturated Si-Hx bilayer leaves the InGaAs(001)-(2 × 4) surface Fermi level unpinned. Density function theory modeling of silicon hydride surface passivation shows an Si-Hx monolayer can remove all the dangling bonds and leave a charge balanced surface on InGaAs.

Passivation of surface defects on InGaAs (001) and (110) surfaces in preparation for subsequent gate oxide ALD

In0.53Ga0.47As contains an intrinsically high electron mobility making it an attractive alternative semiconductor material for use in the channel region of MOSFET devices. The semiconductor/oxide interface can degrade device performance through interfacial roughness or formation of surface defects containing electronic trap states that act to pin the surface Fermi level. Tri-gate structured field effect transistors (finFETs) are currently being implemented into commercialized logic chips, making defect reduction and passivation of the semiconductor planar and sidewall crystallographic faces critical in order to create an ideal interface between the semiconductor and the gate oxide. For InGaAs(001) based finFETs to become potential for commercial implementation, in-situ III-V surface cleaning or defect passivation techniques must be compatible with both the InGaAs (001) and (110) surfaces. STM was employed to show air exposed InGaAs (001) and (110) samples can be restored to the cleanliness of MBE grown samples through atomic hydrogen dosing and thermal annealing. STM was also employed to characterize the in-situ self-limiting CVD of a silicon hydride control layer used to passivate the missing dimer defect unit cells of the arsenic rich InGaAs(001)-(2×4) surface. Surface defect densities are compared and quantified throughout several STM images following the surface cleaning and passivation techniques.

Formation of atomically ordered and chemically selective Si—O—Ti monolayer on Si0.5Ge0.5(110) for a MIS structure via H2O2(g) functionalization

Si0.5Ge0.5(110) surfaces were passivated and functionalized using atomic H, hydrogen peroxide (H2O2), and either tetrakis(dimethylamino)titanium (TDMAT) or titanium tetrachloride (TiCl4) and studied in situ with multiple spectroscopic techniques. To passivate the dangling bonds, atomic H and H2O2(g) were utilized and scanning tunneling spectroscopy (STS) demonstrated unpinning of the surface Fermi level. The H2O2(g) could also be used to functionalize the surface for metal atomic layer deposition. After subsequent TDMAT or TiCl4 dosing followed by a post-deposition annealing, scanning tunneling microscopy demonstrated that a thermally stable and well-ordered monolayer of TiOx was deposited on Si0.5Ge0.5(110), and X-ray photoelectron spectroscopy verified that the interfaces only contained Si-O-Ti bonds and a complete absence of GeOx. STS measurements confirmed a TiOx monolayer without mid-gap and conduction band edge states, which should be an ideal ultrathin insulating layer in a metal-insulator-semiconductor structure. Regardless of the Ti precursors, the final Ti density and electronic structure were identical since the Ti bonding is limited by the high coordination of Ti to O.

In0.53Ga0.47As(001)−(2x4) and Si0.5Ge0.5(110) surface passivation by self-limiting deposition of silicon containing control layers

Metal oxide semiconductor field effect transistors (MOSFETs) are diverging from the exclusive use of silicon and germanium to the employment of compound semiconductors such as SiGe and InGaAs to further increase transistor performance. A broader range of channel materials allowing better carrier confinement and higher mobility could be employed if a universal control monolayer (UCM) could be ALD or self-limiting CVD deposited on multiple materials and crystallographic faces. Silicon uniquely bonds strongly to all crystallographic faces of InGa1-xAs, InxGa1-xSb, InxGa1-xN, SiGe, and Ge enabling transfer of substrate dangling bonds to silicon, which may subsequently be passivated by atomic hydrogen. Subsequently, the surface may be functionalized with an oxidant such as HOOH(g) in order to create a UCM terminating Si-OH layer, or a nitriding agent such as N2H4(g) in order to create an Si-Nx diffusion barrier and surface protection layer. This study focuses on depositing saturated Si-Hx, and Si-OH seed layers via two separate self-limiting CVD processes on InGaAs(001)-(2x4), and depositing a Si-Nx seed layer on Si0.5Ge0.5(110) via an ALD process. XPS in combination with STS/STM were employed to characterize the electrical and surface properties of these silicon containing control layers on InGaAs(001)-(2x4) and Si0.5Ge0.5(110) surfaces. MOSCAP device fabrication was performed on n-type InGaAs(001) substrates with and without a Si-Hx passivation control layer deposited by self-limiting CVD in order to determine the effects on Cmax, frequency dispersion, and midgap trap states.

Cleaning and passivation of the four horseman of the silicon apocalypse

In-situ atomic imaging of cleaning and passivation of several systems has been studied. (1) For InGaAs (001), a low temperature in-situ cleaning process has been combined with low temperature HfO2 ALD to reduce the EOT below 0.4 nm. (2) For InGaAs (110), STM/STS studies have shown that both a metal precursor (TMA) and an oxidant (H2O) are required to remove trap states. (3) To assist in utilizing similar gate and contact processing on group IV and InGaAs surfaces, a silicon monolayer ALD process has been developed for InGaAs (001). (4) SiGe combines the most challenging components of cleaning Si and Ge; using a reaction with HOOH (g) and post deposition annealing, SiGe (001) becomes terminated with Si-OH which is nearly ideal for ALD nucleation.