In this study 300keV and 1MeV Si vacancy engineering implants have been used to optimise the activation of a 2keV 1×1015cm-2 B implant into SOI. Although the two implants generate a similar areal density of excess vacancies in the SOI top layer, Hall Effect measurements show that low temperature activation is possible to a greater level with the 300keV Si co-implant than with the 1MeV implant. Hall and SIMS data are consistent with a high level of activation of the B at 700°C, with no significant diffusion at the metallurgical junction depth.

In recent years, experimental studies [1-3] have suggested that Si interstitials may play a role in facilitating As transient enhanced diffusion during pn junction formation in silicon. These studies contradict conventional models that assume vacancy-mediated As diffusion. Using density functional theory calculations within the generalized gradient approximation, we have examined the structure, stability, and diffusion of the neutral As-Sii pair. We find the lowest energy structure is comprised of an As and Sii atom pair that is aligned in the [110] direction while sharing a lattice site. We have calculated the binding energy as well as diffusion pathways and barriers for the neutral As-Sii pair. Our results suggest that the neutral As-Sii pair has a binding energy relative to neutral Sii and neutral As of 0.63 eV. We also find an overall diffusion activation energy of 3.3 eV, which is similar to experimental observations for As diffusion and preVious calculations for As-vacancy complex diffusion. These results clearly support that interstitials can contribute significantly to As transient enhanced diffusion, especially in regions where interstitials exist in excess. In addition, interstitial-mediated arsenic diffusion suggests that interstitials may also play a role in arsenic agglomeration.

Ab initio electronics structure calculations have been carried out in a series of RPb2n-1Te2n, n=16, compounds to understand the nature of “defect” states introduced by R where R = vacancy, monovalent Na, K, Rb, Cs, Ag atoms and divalent Cd atoms. We find that the density of states (DOS) near the top of the valence band and the bottom of the conduction band get significantly modified. The Na atom seems to perturb this region least (ideal acceptor in PbTe) and the other monovalent atoms enhance the DOS near the top of the valence band. Cd is an interesting case, since it introduces a strong resonance state near the bottom of the conduction band.

Hydrogen implanted, boron doped (100) Czochralski silicon wafers, which were annealed after implantation up to 600 °C, are investigated by μ-Raman spectroscopy (μRS). We have studied the thermal evolution of hydrogen related defects, including vacancy-hydrogen (VnHm) complexes, H-saturated dangling bonds and trapped H2 molecules. Applying temperatures above ∼ 400 °C, the hydrogen related defects and the formation of voids/platelets are distinctly modified. The measured intensity of the local vibration mode (LVM) of H2 molecules trapped in multi-vacancy complexes at a frequency of ∼ 3820 cm-1 decreases while the LVM of H2 in platelets or larger voids (∼ 4150 cm-1) is increasing. This indicates that multi-vacancy complexes coalesce and form larger voids/platelets. Most of the VnHm complexes (∼ 2000 – 2200 cm-1) are dissolved during annealing at 600 °C, where a thin silicon layer exfoliates due to the ion-cut mechanism. However, the Raman modes of the characteristic V2H6 complex, of Si-Hx bonds stemming from H-terminated surfaces and of H2 located in voids/platelets still can be observed after a short time annealing (≤2 min) at 600 °C.

A theoretical modeling of the oxygen diffusivity in silicon and germanium crystals both at normal and high hydrostatic pressure has been carried out using molecular mechanics, semiempirical and ab-initio methods. It was established that the diffusion process of an interstitial oxygen atom (Oi) is controlled by the optimum configuration of three silicon (germanium) atoms nearest to Oi. The calculated values of the activation energy δEa (Si) = 2.59 eV, δEa (Ge) = 2.05 eV and pre-exponential factor D0 (Si) = 0.28 cm2 s-1, D0 (Ge) = 0.39 cm2 s-1 are in a good agreement with experimental ones and for the first time describe perfectly an experimental temperature dependence of the Oi diffusion constant in Si crystals (T=350 - 1200°C). Hydrostatic pressure (P≤80kabar) results in a linear decrease of the diffusion barrier (∂PδEa(P)= -4.38 10-3 eV kbar-1 for Si crystals). The calculated pressure dependence of Oi diffusivity in silicon crystals agrees well with the pressure-enhanced initial growth of oxygenrelated thermal donors.

SiGe/SOI films have been investigated by transmission electron microscopy (TEM), atomic force microscopy (AFM) and Raman spectroscopy. For low Ge composition (∼ 20%), strain relaxation in the SiGe layer is minimal (<0.25%). For higher Ge content (32%), the tensile strain in a Si capping layer grown on top of SiGe/SOI is 0.46% (a stress of 0.81 GPa). TEM has revealed that most of the resulting defects at the SiGe/SOI interface and move downward. The misfit dislocation (MD) linear density is 17/μm, being consistent with the strain relaxation of the SiGe layer as determined by Raman spectroscopy. Upon thermal annealing, residual strain in the SiGe films has been further relaxed via two major routes (a) introduction of more MDs, and (b) development of surface undulation. High strain relaxation has been achieved in a SiGe layer grown on a higher-Ge content buffer layer.

Hydrogenated amorphous silicon carbide (a-SiC:H) films have been deposited using magnetron sputtering technique. Investigation of the effect of the vacuum annealing temperature on photoluminescence properties and paramagnetic defects, and its correlation with structural transformation of a-SiC:H have been performed. Significantly enhanced light emission efficiency after low-temperature vacuum treatment (450 °C) is found due to enhanced passivation of paramagnetic defects associated with carbon-rich chemically disordered structure. Subsequent high-temperature vacuum annealing results in a decrease of luminescent intensity that is associated with increase of carbon related paramagnetic defect states, shown to be the primary nonradiative recombination centres. For the first time silicon-related dangling bonds in a-SiC:H have been detected reliably by electron paramagnetic resonance measurements in annealed samples.

We investigated the process of Pb center generation during silicon oxidation following oxygen termination on a clean Si surface, based on which we discuss the microscopic origin of Pb centers. We constructed a UHV-ESR system which enabled measurements to be carried out at a low temperature of around 100 – 120 K, and used the system to study the Si(111)-7×7 surface after slight exposure to O2. Based on the observed ESR spectra, we discuss the electronic structure of the Si(111)-7×7 surface.

Auger Electron Spectroscopy (AES) is one of the few techniques that has surface sensitivity and small analysis volume to make it the ideal analytical technique for the compositional characterization of submicron defects. However, the integration of defect inspections at only a few processing steps during device fabrication results in the detection of many buried defects. In order to identify these defects, it is necessary to determine their composition. Combined with Focused Ion Beam (FIB) technique to expose the cross section of the buried defect, Auger analysis provides accurate identification of buried defects that are critical for quickly ramping to higher yields and recovering from yield excursions. This paper reports two examples of the use of AES combined with FIB to diagnose processing problems.

The methods of microwave-detected photo-induced current transient spectroscopy (MD-PICTS) and microwave-detected photoconductivity (MDP), which proved themselves as very successful for defect investigations in GaAs wafers, were applied to Fe-doped SI-InP samples. It was possible to observe characteristic defect levels. One important defect center showed a similar behavior as the well known EL2 defect in GaAs. This defect exhibits positive and negative PICTS signals depending on the Fe concentration. The associated activation energies show that these signals can be interpreted as an interaction of the Fe2+/3+ level in InP with both, the valence and the conduction band.

Beside this major defect we discovered a wide range of shallow defects which may be important for material properties.

This result and successful microwave detected photoconductivity mappings of InP wafers show that the new non-destructive investigation methods provide valuable information on defect distribution and characteristics.

We studied the electroluminescence (EL) of boron-implanted p-n junction Si LEDs in correlation with the implant-induced extended defects of different types. By varying the post implant annealing conditions to tune the extended defects and by using plan-view transmission electron microscopy to identify them, we found that {113} defects along Si<110> are the ones that result in strong silicon light emission of the p-n junction Si LEDs other than {111} perfect prismatic and {111} faulted Frank dislocation loops. The EL peak intensity at about 1.1 eV of {113} defect-engineered Si LEDs is about twenty-five times higher than that of dislocation defect-engineered Si LEDs. The EL measured at temperatures from room temperature to 4 K indicated that the emissions related to the extended defects are from silicon band edge radiative recombination.

We have studied the influence of a deuterium diffusion on the electrical characteristics of the 2D gas present in AlGaN/GaN heterostructures. The deuterium diffusion is performed by exposing the structures to a rf remote deuterium plasma. We find that both the sheet carrier concentration and the electron mobility decrease and that these effects are partly reversible under thermal annealing. These results suggest that deuterium behave as acceptors in the 2D gas region. The negatively charged deuterium act as additional scattering centers for electrons.

Infrared absorption (IR) and electron paramagnetic resonance (EPR) spectroscopies are used to study the V3+ impurity and the vanadium acceptor level in 6H semi-insulating SiC. IR and EPR data obtained from samples cut from the same wafer support the assignment of the 0.60 and 0.62 eV IR absorption lines to substitutional V3+. Photo-induced EPR measurements reveal identical photo-thresholds for V3+ and V4+ ions. A peak at 0.8 eV, where the intensity of the three plus charge state decreases and the four plus charge state increases by an equal amount, is thought to represent excitation of an electron from V3+ to the conduction band edge. The 0.8 eV peak is therefore attributed to the V3+/4+ level. The difference between the optically measured value reported here and that measured previously using temperature dependent techniques is attributed thermal relaxation.

We fabricated narrow fins structures and non-planar MOSFETs like FinFETs and triple-gate MOSFETs using plasma doping with substrate heating under 350··, and measured their I-V characteristics. Fins and MOSFETs using low-temperature doping process show good current drivability and low subthreshold slope. However, without post high-temperature thermal annealing, this process could not avoid generating defects and traps as well as mobile protons on the gate and gate oxide interface and junctions, and therefore degraded device reliability. The results of ultra-small MOSFET research show possibility of new memory devices with these traps and ions in devices.

The precipitation of interstitial oxygen (Oi) in heavily arsenic doped Czochralski (CZ) silicon wafers (As-wafer) has been studied for both polysilicon and damaged back surfaces. After annealed at 1200°C for 45 minutes and 950°C for 15hrs sequentially, the As-wafers with polysilicon show no Oi precipitation in the bulk while polyhedral Oi precipitates are observed at the interface between polysilicon and the silicon substrate. They exhibit a habit plane of {100}. The lack of the Oi precipitation in the bulk may reduce the total gettering efficiency of the polysilicon layer on the As-wafer. The same annealing led to rod-like SiOx precipitates in the wafers with damaged back surface. These precipitates extended about 1um into the bulk and had a habit plane of {111}. This morphology has high interfacial energy and is only possible when strain relief is dominant. The Oi outdiffusion has been observed to be same for both backside surface conditions and is only determined by annealing process.

Previously, defect D (VO+) was barely detected in ultra-thin (physical thickness < 10 nm) Ta2O5 capacitors for DRAM applications using zero-bias thermally stimulated current (ZBTSC) spectroscopy and correlated with leakage current. Our explanation is that defect D (VO+) behaves like an electron trap with an electron-repulsive energy barrier and thus small electron capture cross section at low temperature such that it is difficult for defect D to capture electrons during ultraviolet illumination at low temperature. We modified our experimental technique to a twoscan ZBTSC technique and managed to detect oxygen vacancies much more efficiently in ultrathin Ta2O5 films for the first time. Two-scan ZBTSC can also be applied to other high-K dielectric materials for process diagnosis.

Tantalum oxide has demonstrated promise as a high-K dielectric for charge storage in Gb dynamic random access memories (DRAMs) [1]-[2]. For DRAM applications, the two most important requirements are high capacitance, limiting film thickness to < 10 nm, and low leakage current, which may be related to defect states in Ta2O5. Ta is not volatile while O is volatile; therefore the presence of O vacancies (VO) in Ta2O5 is expected. O vacancies are double donors [3], which will make Ta2O5 a very weakly n-type large bandgap semiconductor, resulting in leakage current. Thus it is important to develop a technique to detect O vacancies in capacitor structures with an ultra-thin Ta2O5 insulating film. In 1995, we explained the principle of zerobias thermally stimulated current (ZBTSC) spectroscopy and demonstrated the detection of defect states in capacitors with relatively thick Ta2O5 [4]. Subsequently, we demonstrated the application of ZBTSC to capacitors with ultra-thin Ta2O5 [5]-[6]. However, the signal from defect D (the first ionization state of the O vacancy double donor) was weak such that the detection of defect D was marginal [6]. In this paper, we tried to give a theoretical explanation why the detection of defect D is quite frequently inefficient and how the problem can be handled.

Ta2O5 was deposited onto (100) p+-Si or n+-Si wafers by low-pressure metal-organic chemical vapor deposition (LP-MOCVD). The physical thickness of the film was about 8 nm. Post-deposition anneal of Ta2O5/p+-Si or Ta2O5/n+-Si samples was done by RTP (rapid thermal processing) in O2 or N2O at 700-800°C for 30 s. ZBTSC measurements were performed at a ramp rate of 0.5 K/s as before [4]-[6]. Our old method to fill the defect states was UV illumination at about 90 K. With the UV source off, the current is then recorded as a function of temperature when the temperature is ramped from 90 K to 400 K. The energy level of the defect was estimated using ET = 23kTm, where Tm is the peak temperature and k the Boltzmann constant [7]. Table I shows 3 main kinds of electron traps detected by ZBTSC: (A) the ionized Si/O vacancy complex shallow single donor (Si- -VO++), (B) the ionized C/O vacancy complex shallow single donor (C- -VO++) and (C) the first ionization state of the oxygen vacancy deep double donor (VO+) which is also known as defect D [6]. Smaller leakage current can be easily correlated with lower ZBTSC signal from D (0.8 eV) [6]. We observed that C/O vacancy complex can be more easily removed by an oxidizing anneal when the Ta2O5 film is very thin [6]. The physics why Si/O vacancy complex and C/O vacancy complex are shallower donors compared with the first ionization energy level of the O vacancy double donor has been explained by us in another paper [8]. The traps previously reported by Seve and Lassabetere [9] in 1974 based on their conventional thermally stimulated current (TSC) study are probably the Si/O vacancy complex and the C/O vacancy complex; they did not report about defect D. The trap previously reported by Oehrlein and Reisman [10] in 1983 based on conventional TSC is probably the C/O vacancy complex; they also did not report about defect D. Nishioka [11] pointed out that it was difficult to correlate leakage current in Ta2O5 with defect states detected by conventional TSC. We suspected that the difficulty mentioned by Nishioka [11] is related to the difficulty in the detection of defect D, as discussed in the following paragraph. For example, the leakage decreases with O2 annealing temperature while the Si/O vacancy complex TSC peak increases with O2 annealing temperature because of Si diffusion from the Si substrate into the Ta2O5 film, resulting in a wrong impression that the leakage current does not decrease with the decrease in defect states detected by TSC.

After we realized that defect D (0.8 eV) is probably the first ionization energy level of the oxygen vacancy double donor, our results and the results of other scientists become more consistent with each other. For example, Sawada and Kawakami [12] estimated that the first ionization energy of the oxygen vacancy double donor in Ta2O5 film is 0.8 eV below the conduction band by their theoretical calculations; their results appear to be consistent with our findings.

Float Zone (FZ) silicon samples have been cascade-implanted with helium ions at energies decreasing from 1.9 MeV to 0.8 MeV in steps of 0.1 MeV, with flux maintained between 5 × 1012 and 1 × 1013 He cm-2-1s. The dose was 5×1016 He cm-2 for all the energies except 0.8 MeV where a lower dose of 3×1016 He cm-2 was used. After thermal annealing, the sample was studied by cross section transmission electron microscopy (XTEM) using a Field Emission Gun Microscope (Jeol 2010F). Our results clearly demonstrate that these cavities mainly grow by the Ostwald ripening mechanism. This means a growth by exchange of He and vacancies from smaller to bigger cavities. Further this study provides essential data for resolving the controversy on the growth mechanism governing He-cavities.

We have studied the evolution of the structure of boron-doped hydrogenated amorphous silicon films exposed to a hydrogen plasma. From the early stages of exposure, hydrogen diffuses and forms a thick H-rich subsurface. At longer times, hydrogen plasma leads to the formation of a microcrystalline layer via chemical transport without crystallization of the initial layer. We observe that the hydrogen content increases in the films during a plasma exposure and once the microcrystalline layer is formed hydrogen diffuses out of the sample accompanied with a decrease in the boron content. This effect can be attributed to the electric field developed within the heterojunction a-Si:H/μc-Si:H that drives the positively charged hydrogen atoms in the boron-doped layer towards the μc-Si:H layer.

A rather large amount of shallow donors is created in p-type Czochralski silicon (Cz Si) wafers after a hydrogen plasma exposure at ∼270 °C (substrate temperature) and a subsequent annealing in the temperature range of 350-450 °C. This two-step process has been used for the fabrication p-n junction diodes at low temperatures. Current-voltage characteristics show that the breakdown voltages of these diodes are higher than 100 V. The diode leakage is found to be improved after slow ramp annealing at temperatures up to 250 °C. Deep level transient spectroscopy measurements reveal that the oxygen related thermal donor is not the dominant doping species as expected before.

A comprehensive experimental and theoretical investigation was performed for the system of As-Sb nanoclusters and nanoscale dislocation loops in GaAs:Sb films grown by molecular beam epitaxy at low temperature and subsequently annealed. A model was developed for the elastic stress relaxation, self-energies and interactions in such cluster-loop nanosystems. The model was based on the experimental investigation of the microstructure of the As-Sb nanoclusters by transmission electron microscopy. The atomic structures of the As-Sb nanoclusters and dislocation loops, as well as their orientation relationships were determined. A strong anisotropic mismatch between the As-Sb nanoclusters and GaAs matrix has been revealed. This mismatch was proven to be a reason for the formation of the prismatic nanoscale dislocation loops nearby the nanoclusters. Our theoretical model explores the elastic properties of an inclusion with uniaxial dilatation. For such inclusions, the elastic stresses and stored energy are determined in a closed analytical form. The theoretical analysis predicts a specific non-linear dependence of the dislocation loop diameter on the cluster diameter, which fits well the experimentally observed one. It is demonstrated that both the change in the inclusion self energy due to diminishing dilatation and the interaction between the dislocation loop and inclusion are important in the relaxation phenomena at stressed nanoscale inclusions in semiconductors.