Conan Weiland

Characterization of ALD copper thin films on palladium seed layers

A method for fabricating monolithic nanoscopic tunnel junctions (MNTJs) for tunneling spectroscopy measurements using atomic layer deposition (ALD) of Cu on Pd seed layers has recently been introduced [Gupta and Willis, Appl. Phys. Lett. 90, 253102 (2007)]. The ALD grown layers are characterized here using planar thin films as models for the nanoelectrode composition and structure. ALD Cu films grown on Pd seed layers using a varying number of deposition cycles were characterized using transmission electron microscopy, Auger electron spectroscopy (AES), and glancing incidence x-ray diffraction (GIXRD) to investigate the chemical composition and structure of the nanoelectrodes. Electron diffraction and GIXRD show that as Cu is deposited, the bulk composition progresses from being Pd rich to becoming predominately Cu. In contrast, AES data show that significant Pd consistently remains on the surface of the growing film. The divergence in surface and bulk behaviors is attributed to Pd surface segregation tha...

Hard x-ray photoelectron spectroscopy study of As and Ga out-diffusion in In0.53Ga0.47As/Al2O3 film systems

Hard x-ray photoelectron spectroscopy (HAXPES) was performed on In0.53Ga0.47As/Al2O3 gate stacks as deposited and annealed at 400 °C, 500 °C, and 700 °C to test for out-diffusion of substrate elements. Ga and As core-level intensities increase with increasing anneal temperature, while the In intensity decreases. HAXPES was performed at two different beam energies to vary the surface sensitivity; results demonstrate Ga and As out-diffuse into the Al2O3 film. Analysis suggests the presence of an interlayer containing Ga and As oxides, which thickens with increasing anneal temperature. Further diffusion, especially of Ga, into the Al2O3 film is also observed with increasing anneal temperature.

Reactivity and morphology of vapor-deposited Al/polymer interfaces for organic semiconductor devices

The chemistry and the morphology of metal-deposited organic semiconductor interfaces play a significant role in determining the performance and reliability of organic semiconductor devices. We investigated the aluminum metallization of poly(2-methoxy-5,2′-ethyl-hexyloxy-phenylene vinylene) (MEH-PPV), polystyrene, and ozone-treated polystyrene surfaces by chemical (x-ray and ultraviolet photoelectron spectroscopy) and microscopic [atomic force microscopy, scanning electron microscopy (SEM), focused ion beam (FIB)] analyses. Photoelectron spectroscopy showed the degree of chemical interaction between Al and each polymer; for MEH-PPV, the chemical interactions were mainly through the C–O present in the side chain of the polymer structure. The chemical interaction of aluminum with polystyrene was less significant, but it showed a dramatic increase after ozone treatment of the polystyrene surface (due to the formation of exposed oxygen sites). Results showed a strong relationship between the surface reactivity...

Effects of boron and phosphorus doping on the photoluminescence of self-assembled germanium quantum dots

The doping of Ge quantum dots grown on Si (100) was investigated using atomic force microscopy and photoluminescence spectroscopy. The dots produced photoluminescence in the energy range from 0.75 to 0.95 eV. Compared to the undoped dots, the boron and phosphorus doped dots demonstrated a shift in peak emission toward lower energy by 60–80 meV, which is attributed to the decrease in density of the smaller sized dots. Increased photoluminescence intensity with temperature indicated higher activation energy with doping, suggesting a higher probability of radiative transitions at elevated temperatures, potentially important for various applications.

Band alignment in Ge/GeOx/HfO2/TiO2 heterojunctions as measured by hard x-ray photoelectron spectroscopy

We investigate the interlayer (IL) thickness dependence of band offsets in a germanium based bilayer metal-oxide-semiconductor sandwich with an amorphous plasma enhanced atomic layer deposited (PE-ALD) HfO2 IL and PE-ALD grown TiO2 high k gate dielectric using hard x-ray photoelectron spectroscopy. The native Ge oxide shifts to higher oxidation state as the thickness of the IL layer was increased. The Hf 4f core line shows a broadening with increasing thickness, indicating the formation of Hf-Ge germanate. We observed a deviation from the bulk offset for films with ultra thin layers of HfO2.

Recent applications of hard x-ray photoelectron spectroscopy

Recent applications of hard x-ray photoelectron spectroscopy (HAXPES) demonstrate its many capabilities in addition to several of its limitations. Examples are given, including measurement of buried interfaces and materials under in situ or in operando conditions, as well as measurements under x-ray standing-wave and resonant excitation. Physical considerations that differentiate HAXPES from photoemission measurements utilizing soft x-ray and ultraviolet photon sources are also presented.

Atomic Layer Deposition of Rare-earth Oxide Thin Films for High-k Dielectric Applications

Many different organolanthanide molecules are being proposed as metal sources for depositing metal and metal oxide layers for semiconductors by atomic layer deposition (ALD). These precursors need particular physical and thermal properties to be used in the semiconductor manufacturing process. For example, the precursors need to have high volatility, reactivity, and thermal stability. Atomic layer deposition (ALD) is the preferred method for depositing metal oxide thin films where precise control of film composition and structure are highly desired. ALD deposition methods are very promising; however, new high-k metal oxide films will require new precursors to meet the very stringent requirements of the semiconductor process.

Note: Alignment/focus dependent core-line sensitivity for quantitative chemical analysis in hard x-ray photoelectron spectroscopy using a hemispherical electron analyzer.

X-ray photoelectron spectroscopy is an established technique for quantitative chemical analysis requiring accurate peak intensity analysis. We present evidence of focus∕alignment dependence of relative peak intensities for peaks over a broad kinetic energy range with a hemispherical electron analyzer operated in a position imaging mode. A decrease of over 50% in the Ag 2p₃/₂ to Ag 3d ratio is observed in a Ag specimen. No focus∕alignment dependence is observed when using an angular imaging mode, necessitating the use of angular mode for quantitative chemical analysis.

Spectroscopic analysis of Al and N diffusion in HfO2

X-ray photoelectron core level spectroscopy, secondary ion mass spectroscopy, spectroscopic ellipsometry, and extended x-ray absorption fine structure measurements have been employed to distinguish the effects of Al and N diffusion on the local bonding and microstructure of HfO2 and its interface with the Si substrate in (001)Si/SiOx/2 nm HfO2/1 nm AlOx film structures. The diffusion of Al from the thin AlOx cap layer deposited on both annealed and unannealed HfO2 has been observed following anneal in N2 and NH3 ambient. Both N2 and NH3 subsequent anneals were performed to decouple incorporated nitrogen from thermal reactions alone. Causal variations in the HfO2 microstructure combined with the dependence of Al and N diffusion on initial HfO2 conditions are presented with respect to anneal temperature and ambient.

Comparison of HfSiOx Thin Films Deposited by ALD with Moisture Using Different Silicon Sources

The scaling of semiconductor devices using various high-k materials have been investigated for replacing the gate dielectric and Hf-based materials are the preferred candidates. To improve integration of Hf into the gate dielectric, HfSiOx has been chosen for low power devices while HfZrOx are more common for highperformance. Currently, HfO2 can be easily deposited using various reducing agents such as ozone, oxygen or moisture by ALD. However, silicon deposition by ALD with moisture has been proven to be challenging. Nevertheless, the inevitable oxidation of the substrate during the ozone pulse in the standard ALD processes dramatically affects the electrical properties. The interfacial SiO2 growing during the first cycle needs to be avoided. There were many works attempting to suppress the oxidation on silicon substrates, one of the major step is to use moisture instead of ozone. Other sources such as NO and NO2 have also been tried but were not preferred so far. HfSiOx ALD deposition using SiCl4 is reported (1) but the reaction mechanism and absorption are complex and chlorine containing sources in presence of moisture can generate corrosive HCl. The Si incorporation is also temperature dependent and is thus difficult to control.