Solid State Phenomena Vols. 108-109

Abstract: The electrical activity of stacking faults (SFs) in multicrystalline sheet silicon has been examined by correlating EBIC(electron beam induced current), preferential defect etching, and microwave photo-conductance decay (PCD) lifetime measurements. Following a three hour 1060 0C annealing the interstitial oxygen concentration decreased from 14 to 4.5 x 1017 cm-3, during which time a high density of SFs were generated in the center of individual large grains. Subsequent EBIC contrast variation within individual large grains was correlated with the local SF density revealed by preferential etching. In addition, a more quantitative intra-grain lifetime was obtained from high spatial resolution PCD measurements. It was found that an SF density of 1 to 2 x 106 cm-2 produces a lifetime limitation in sheet silicon which corresponds to a recombination lifetime of ~2 µs.

Abstract: The build-up of strain fields caused by the precipitation of oxygen in Czochralski-silicon during annealing up to 1200°C and for process times up to 70 hours has been observed in real time by high energy x-ray diffraction. Five different processes are distinguished in the temperature evolution of the intensity and of the rocking width of the silicon 220-reflection. These features are attributed to different precipitation mechanisms. A fit to part of the data with a diffusion limited precipitation model leads to an activation energy for oxygen diffusion in silicon of 2.2 eV in the temperature range from 700°C to 950°C.

Abstract: Contamination controls are very important issues in microelectronics. Any wrong substance introduction in process chambers can cause damages to the production line. Therefore, an extensive control is important because every operation in the process flow (also the most insignificant) can become fatal for the correct functioning of a microelectronic device. The aim of this work is to evaluate the impact of small metallic contamination in the range of 1011÷1012 at/cm2 on silicon substrates implanted with different ion species (As, B and P). An important example of failure related to metallic contamination in a wet bench is reported in this work. The problem appears in a particular class of flash memory devices processing. The electrical parametric test shows a wrong gate oxide thickness and Qbd values out of range, confirmed by early breakdown events and anomalous C-V characteristics. The cause of the failure is morphologically identified off-line by using TEM: the cross section shows a wrong gate oxide thickness and an anomalous interface between gate oxide and silicon substrate. It appears clear that the root failure cause is related to the ion implantation (As in this case) and to the cleaning before gate oxide growth. A short process flow was performed and analyzed step by step in order to identify the failure cause. Many different analytical techniques have been used for each step and all of these provide consistent results. In particular TXRF analysis on wafers processed immediately after cleaning do not show any contamination while Cu and Fe contaminants are observed after sample oxidation and As implant. Metallic contaminants are captured by the substrate after it is implanted with As, and the following RCA cleaning is not able to remove them. In addition, the presence of these metallic contaminants induces roughness of the Si surface and the growth of gate oxide is not controlled (faster oxidation). If different substrates are used, e.g. silicon implanted with B or un-implanted, this contamination level is not detected and does not lead to oxide reliability problems. Once the mechanism of metal contaminant interaction with dopant is identified the introduction of an in-line monitoring is possible, thus allowing to prevent the device failure. The short process loop can be considered as a good method to prepare the substrate before TXRF analysis. After this study the monitor has been integrated in the production line controls

Abstract: We compare SPV technique with µ−PCD for the determination of recombination activity of copper precipitates in p-Si. The copper precipitates were formed in bulk silicon through illumination at room temperature. We observed that the recombination activities of copper precipitates measured with SPV are higher than the ones measured with µ−PCD technique. However, it seems that the copper detection sensitivity is about the same with SPV and µ−PCD techniques.

Abstract: In this work we studied the cathodoluminescence (CL) of thin silicon oxide and natural silicon oxide grown on different types of silicon substrates (p-silicon and n-silicon with different content of boron and phosphor). At the same time we studied the distribution of intrinsic defects on depth for thermal silicon oxide films with depth resolution 10-20 nm. The method of local cathodoluminescence was used for definition the structure defects in SiO2 think layer and control of the quality of SiO2-Si interface.

Abstract: The content of interstitially solved oxygen (Oi) in heavily boron doped silicon (9- 29 m
cm) were measured by low temperature Fourier transform infrared (FTIR) spectroscopy. Therefor an alternative thinning technique for silicon is used: by alkaline potassium hydroxide etching (KOH) prepolished silicon specimens are thinned down to 8 - 60 microns. The optimal end thickness depends on the boron concentration which specifies the free carrier concentration. Specimens with three different boron concentrations (9/19/29 m
cm) were examined. The results are compared with gas fusion analysis (GFA) measurements. Furthermore the precipitated oxygen Oi was measured for a RTA process (20s@1250°C) with subsequent growth steps (4h@780°C + 16h@1000°C).

Abstract: In this paper, some basic aspects related to defects and SiC devices performances are discussed. Our recent work is reviewed and inserted in the international research scenario. In particular, some issues relative to rectifying metal/SiC contacts will be treated in more detail. In fact, establishing a correlation between material defects, processing induced defects and irradiation induced defects with the electrical behaviour of Schottky contacts is extremely important for the future optimization of almost all electronic devices, sensors and particle detectors.

Abstract: Using first principles molecular dynamics simulations, we have recently determined the threshold displacement energies and the associated created defects in cubic silicon carbide. Contrary to previous studies using classical molecular dynamics, we found values close to the experimental consensus, and also created defects in good agreement with recent works on interstitials stability in silicon carbide. We have also investigated the stability of several Frenkel pairs, using transition state theory and constrained path calculations.

Abstract: 4H-SiC epitaxial layers were hydrogenated by means of plasma treatment and annealing, aiming at passivating the surface by forming bonds with Si atoms. Ni/SiC Schottky contacts were processed, and investigated by electrical methods (I-V-T, C-V-T, EBIC, DLTS). The annealings were performed at two different temperatures (300°C and 400°C) in H2 ambient. The Inductively Coupled Plasma (ICP) treatment was effected before and after the Schottky contact metallization, and two integrated hydrogen doses were imposed for the same low energy (500 eV/atom). Two deep levels were detected in the gap of the sample hydrogenated at the highest dose before contact deposition, similar to the double defect RD1/2 associated to the vacancy pair VSi-VC. No deep level was found on other plasma-hydrogenated samples, which electrical characteristics are the same than for virgin SiC. A slight improvement of electrical parameters (lowering of ideality factor, increasing of minority carrier diffusion length, better switching behaviour) was only measured on the sample annealed at 400°C.

Abstract: Recent progress is presented in the understanding of grown-in defects in Czochralskigrown germanium crystals with special emphasis on intrinsic point defects, on vacancy clustering and on interstitial oxygen. Whenever useful the results are compared with those obtained for silicon.