Thermal desorption of Ge native oxides and the loss of Ge from the surface

The annealing behavior of Ge native oxides has been studied with x-ray photoemission spectroscopy (XPS). The native oxides were primarily GeO₂ with small amounts of GeO_x (x<2). Annealing was performed using a rapid thermal processor (RTP) with a N₂ purge at atmospheric pressure. Ion-implanted Ge substrates were used to investigate the loss of Ge from the surface due to thermal desorption of Ge oxides. It was found that thermal desorption of volatile Ge oxides and oxidization of Ge take place successively, which results in the loss of Ge from the surface.     

Encapsulation of ion-implanted GaAs using native oxides

It was found that oxidation at 500 to 600°C produced uniform layers, which, when used as protective coatings for ion-implanted GaAs, gave rise to donor activity, but with poor reproducibility. The addition of a thin layer of evaporated aluminium to the oxide layer gave donor activities very similar to results obtained with other coating materials and with good reproducibility.     

Crystallisation phenomena of native anodic oxides for GaAs devices

Results are presented which show the crystallisation processes and changes in the composition of native anodic oxides produced by annealing in a nitrogen atmosphere.     

Characteristics of InAIAs/InP and InAIP/GaAs native oxides

Characteristics of InAlAs/InP and InAlP/GaAs wet oxidation layers were measured for the first time. These oxidation layers can be a current blocking or an optical confining layer in laser diodes. These layers were well made at 500–575 °C. The oxidation rates at 525 °C are approximately 340 nm/h and 120 nm/h for InAlAs and InAlP oxides, respectively. The refractive index are 1.82–1.90 for InAlAs oxide and 1.565–1.595 for InAlP oxide between 0.6 μm and 1.65 μm wavelength. The characteristics are not much varied with processing temperatures except the oxidation rate. And a 200 nm thick InAlAs oxidation layer has a current–voltage characteristic that currents rapidly flow at about 10 V, which is much lower than that of SiO₂.     

Hydrogen desorption from the surface under the conditions of epitaxial growth of silicon layers from monosilane in vacuum

For the first time, the desorption coefficient of hydrogen and activation energy of desorption are directly determined during the growth of an Si epitaxial layer from silane in vacuum using experimental data on the degree of surface coverage of an Si wafer with hydrogen. The results obtained are compared with earlier results obtained under low-temperature conditions, for example, by thermodesorption spectrometry. The found values are used to calculate the crystallization coefficient and its dependence on the growth temperature and decomposition rate for monosilane at the growth surface.     

The influence of vapor phase cleaning on the composition and the surface roughness of rapid thermal oxides and nitrided oxides

In this paper, the influence of various pre-oxidation cleanings on the Si/SiO₂ interface and the oxide surface roughness is investigated. Different types of Vapor Phase Cleanings (VPC) are performed in an integrated STEAG AST cluster module and are compared to a standard wet cleaning process. The VPC uses Anhydrous Hydrogen Fluoride (AHF) and additional ozone cleaning. Directly after the cleaning, oxidation in pure oxygen (O₂) is carried out in an integrated STEAG AST Rapid Thermal Processing (RTP) cluster module. Nitrided oxides are formed by annealing in pure nitric oxide (NO) gas directly after the oxidation. The nitrogen incorporation and distribution in the oxide is investigated using secondary ion mass spectroscopy (SIMS). The nitrogen concentration at the Si/SiO₂ interface depends on the time and/or temperature of the NO annealing. For a 900°C annealing, the nitrogen incorporation varies from 0.5 at.% for a 5 s anneal to 2.5 at.% for a 60 s anneal. The nitrogen concentration of the oxides can be correlated with the different types of precleaning sequences which seems to be an effect of the different fluorine contents obtained after various cleaning procedures. The surface roughness of oxide layers formed after different pre-cleaning sequences is analyzed by Atomic Force Microscopy (AFM). A decrease in surface roughness is measured for oxidation performed at higher temperature. and for rapid thermal oxides produced after a cleaning procedure using AHF and ozone.     

Ge-related impurities in high-k oxides: Carrier traps and interaction with native defects

Volatilization of a Ge substrate may generate a large number of impurities inside the gate dielectric of a Ge-based device. Here we use density-functional theory calculations to probe the stability of Ge atoms and GeO molecules inside Al₂O₃ and Y₂O₃ high-k oxides. We identify the most stable impurity configurations and we show that both types of extrinsic species generate levels inside the energy band gap of the host systems. We also find that Ge and GeO impurities get trapped at O vacancies and replace the vacancy-related carrier traps with different types of levels in the gap. The results identify atomic-scale mechanisms that underlie gate leakage and charge trapping in Ge-based electronic systems.     

Chemical contamination of thin oxides and native silicon for use in modern device processing

The characterization of native oxide residuals and contaminants during the clean-up of silicon substrates prior to oxide growth is crucial for the development of accurate growth algorithms. Studies of contaminant concentrations based on Auger analysis are reported, showing carbon to be the critical contaminant. A critical etching time is established, for which carbon content and residual native oxide thickness are minimal. Variations in refractive index with etching period and native oxide thickness are also reported, showing an increase in refractive index with increase in native oxide thickness. These results should prove useful in improving the accuracy of ellipsometric techniques, and will aid in growth algorithm development.     

Effect of nanoimprinted surface relief on Si and Ge nucleation and ordering

Surface relief formed by nanoimprinting and etching into a thermally grown SiO₂ layer on Si was used to position the initial nuclei formed by chemically vapor deposited Si and Ge. By controlling the deposition conditions, the surface diffusion length was adjusted to be comparable to or larger than the spacing between features, thus favoring nucleation adjacent to steps, rather than random nucleation. Random nucleation was further suppressed by a two-stage deposition process. Ge nucleation on oxide by chemical vapor deposition was enhanced by coating the oxide surface with an organic self-assembled monolayer (SAM) and by the nanoimprinted surface relief. The nanoimprinted surface relief also provides long-range order in the SAM.     

Effects of residual surface nitrogen on the dielectric breakdowncharacteristics of regrown oxides

Effects of residual surface nitrogen, remaining on the Si surface after stripping off tunneling oxynitrides (N₂O-grown or NH ₃-nitrided oxides), on the quality of the regrown gate oxides are studied. Residual surface nitrogen is observed to reduce the breakdown field and degrade the time-dependent dielectric breakdown (TDDB) characteristics of the subsequently grown gate oxides. Results show that oxide regrowth in N₂O, rather than O₂, can significantly suppress these undesirable effects     

Ge/Si(001)多层纳米岛材料的快速热退火特性

通过X射线双晶衍射、光致发光谱等手段,系统研究了Ge/Si(001)多层纳米岛材料的快速热退火特性.研究表明:退火过程中纳米岛区的Ge/Si原子互扩散作用比浸润层区强烈;并且随着退火时间增加,这种互扩散作用加大,晶体质量下降,影响材料性能.而在800℃退火12s,材料保持了较小的Ge/Si原子互扩散水平和较高的晶体质量,并且经硼离子注入后的样品在这一条件退火后,超过50%的杂质原子可被激活.     

Ge/Si(001)多层纳米岛材料的快速热退火特性

通过X射线双晶衍射、光致发光谱等手段,系统研究了Ge/Si(001)多层纳米岛材料的快速热退火特性.研究表明:退火过程中纳米岛区的Ge/Si原子互扩散作用比浸润层区强烈;并且随着退火时间增加,这种互扩散作用加大,晶体质量下降,影响材料性能.而在800℃退火12s,材料保持了较小的Ge/Si原子互扩散水平和较高的晶体质量,并且经硼离子注入后的样品在这一条件退火后,超过50%的杂质原子可被激活.     

Ge/Si(001)多层纳米岛材料的快速热退火特性

通过X射线双晶衍射、光致发光谱等手段，系统研究了Ge/Si(001)多层纳米岛材料的快速热退火特性. 研究表明：退火过程中纳米岛区的Ge/Si原子互扩散作用比浸润层区强烈；并且随着退火时间增加，这种互扩散作用加大，晶体质量下降，影响材料性能. 而在800℃退火12s，材料保持了较小的Ge/Si原子互扩散水平和较高的晶体质量，并且经硼离子注入后的样品在这一条件退火后，超过50%的杂质原子可被激活.     

Thermal oxidation of indium phosphide in the presence of lead, zirconium, and titanium oxides

A nonlinear effect of activation of InP thermal oxidation by lead, titanium, and zirconium oxides introduced during the process was discovered. The source of the activating admixtures was their solid solution. Under such conditions, mass transfer of metal cations towards the outer interface of the solid-phase source becomes the reaction-rate-limiting process. Oxide formation in an InP film is the governing process     

Thermal evaporation of Ge on Si for near infrared detectors: Material and device characterization

Using a low-temperature process, we thermally evaporated Ge thin films on Si substrates and investigated both structural and electrical properties of samples grown at various temperatures. The characterization included X-ray diffraction, atomic force microscopy and Hall measurements and aimed at determining a suitable temperature range in terms of crystal quality and transport properties. Finally, we employed Ge films on Si to fabricate near infrared photodiodes and test them in terms of dark current and responsivity.     

Thermal Stability of Poly-Si Phototransistors Incorporating Ge Quantum Dots for Near-Ultraviolet Light Detection and Amplification

We investigated temperature-dependent ( 300 K– 120 K ) subthreshold characteristics and transient photoresponses of poly-Si phototransistors (PTs) incorporating germanium (Ge) quantum dots (QDs) in the gate oxide for near-ultraviolet light detection and amplification. Incorporating Ge QDs into the poly-Si PT structure improves the device thermal stability in the subthreshold characteristics and transient photoresponse, due to better light absorption efficiency and photovoltaic effect suppression.      

Characterization of surface states in HCl-grown oxides using MOS transient currents

A fast transient current (TC) technique has been developed for the characterization of majority carrier charge emission from surface states using MOS capacitors excited by a voltage step-function. This technique, with appropriate choice of initial and final biasing conditions, allows a rapid determination of the density of surface states (N_ss) and their capture cross section values (σ_n) in preselected regions of band gap using suitable temperature ambients. A low temperature (113°K) was used for regions close to the bottom of conduction band and room temperature and moderately low temperatures were used for the mid-gap region. Results of transient current measurements were compared with those obtained from thermally stimulated current and low frequency C-V measurements. The MOS devices were fabricated using [100] oriented n-type (6–8 Ω-cm) silicon on n⁺ substrates with HCl added to the oxidizing ambient. The detectability limit of the TC technique has been found to be approximately 1 × 10¹⁰ cm^?2 eV^?1 for the device area used.     

基区不同Ge组分分布的多指SiGe HBT热学特性

基于半导体器件仿真工具SILVACO TCAD,研究了三种常见的基区Ge组分分布(矩形、梯形和三角形)对多指功率SiGe异质结双极型晶体管(HBT)的热学特性的影响。结果表明,基区Ge组分为梯形分布和三角形分布的多指SiGe HBT的增益随温度变化比较平缓,各发射极指的峰值温度明显小于矩形分布的各指峰值温度,器件纵向和表面温度分布也更加均匀,因此,与矩形分布相比,梯形分布和三角形分布的多指SiGe HBT在热学特性上有了很大的改善,电学特性也相对热稳定。在这三种结构中,梯形分布可以更好地兼顾增益特性和热学特性。     

Electroluminescence from the Ge quantum dot MOS tunneling diodes

A Ge quantum dot (QD) light-emitting diode (LED) is demonstrated using a MOS tunneling structure for the first time. The oxide film was grown by liquid phase deposition at 50/spl deg/C to reduce the thermal budget. The infrared emission of /spl sim/1.5 /spl mu/m was observed from Ge QD MOS LEDs, similar to the p-type-intrinsic-n-type structure reported previously. At the negative gate bias, the electrons in the Al gate electrode tunnel to the Ge QD through the ultrathin oxide and recombine radiatively with holes to emit the /spl sim/1.5/spl mu/m infrared. The electrons also recombine with holes in the Si cap, and the band edge emission from Si is also observed.     

Laser-induced desorption of atomic and molecular fragments from a tin dioxide surface modified by a thin organic covering of copper phthalocyanine

The systematic features of laser-induced desorption from an SnO₂ surface exposed to 10-ns pulsed neodymium laser radiation are studied at the photon energy 2.34 eV, in the range of pulse energy densities 1 to 50 mJ/cm². As the threshold pulse energy 28 mJ/cm² is achieved, molecular oxygen O₂ is detected in the desorption mass spectra from the SnO₂ surface; as the threshold pulse energy 42 mJ/cm² is reached, tin Sn, and SnO and (SnO)₂ particle desorption is observed. The laser desorption mass spectra from the SnO₂ surface coated with an organic copper phthalocyanine (CuPc) film 50 nm thick are measured. It is shown that laser irradiation causes the fragmentation of CuPc molecules and the desorption of molecular fragments in the laser pulse energy density range 6 to 10 mJ/cm². Along with the desorption of molecular fragments, a weak desorption signal of the substrate components O₂, Sn, SnO, and (SnO)₂ is observed in the same energy range. Desorption energy thresholds of substrate atomic components from the organic film surface are approximately five times lower than thresholds of their desorption from the atomically clean SnO₂ surface, which indicates the diffusion of atomic components of the SnO₂ substrate to the bulk of the deposited organic film.