We have investigated the effects of deliberate heavy metals contamination on dark current and image defects in CMOS Image Sensors (CIS). Analysis of dark current in these imager dice has revealed ...different behaviors among most important 3d metals present in the process line. We have implanted directly in 3 Mega array pixels the following metals: Cr, V, Cu, Ni, Fe, Ti, Mo, W, Al and Zn. Analyzing the dark current "spectrum" as obtained for fixed integration periods of time by means of standard image-testing equipment, these impurities can be identified and detected with a sensitivity of ∼ 109 traps/cm3 or higher.
In this work we report the results of a set of experiments carried out to assess the ability of recombination lifetime measurements for the detection of palladium contamination in silicon. Palladium ...is found to be a very effective recombination center, so recombination lifetime measurements are a very sensitive method to detect palladium in silicon. The surface segregation of palladium was monitored by the reduction of its recombination activity in the silicon volume. The palladium segregation at the wafer surface was checked by selective etching, and by Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray (EDX) analysis.After validating recombination lifetime measurements for palladium detection, we use these measurements to define suitable approaches to the prevention of palladium contamination of silicon devices. The efficiency of a diffusion barrier layer (silicon nitride) and of decontamination by wet cleaning are tested.
This paper collects the results of some experiments aimed at investigating the physical mechanisms of defect generation in devices. It is shown that suitable limits for the mechanical stress can be ...defined to prevent defect generation. In addition, a high temperature stress release annealing can be beneficial for stress reduction and defect prevention. The annealing of implanted layers may result in crystal defect formation even with no contribution from mechanical stress. In this case, the silicon surface plays a relevant role in reducing the point defect concentration and hence the nucleation of extended defects. In the annealing process of high energy implantations, the most damaged region is far from the wafer surface. Under these conditions, impurities in the silicon substrate play a relevant role in determining the resulting defect morphology. The presence of interstitial oxygen forces defects to grow along directions parallel to the silicon surface, thus preventing them to reach the device region.
In this paper, the paper addressed the problem of estimating the risk of crystal defect generation in a complex device process. The validity of numerical calculations of the mechanical stress ...developed in the device process flow is assessed by comparing these calculations to the results of the electrical tests of structures designed to monitor the formation of dislocations. The results show that, based upon numerical calculations, it is possible to define the mechanical stress criteria for preventing defect generation. By using this sort of criteria, potentially dangerous process variations can be easily identified. This method is quite general and can be applied to any device process flow
Contaminant reduction is a key issue for SOI substrate which cannot make use of back-side gettering. H 2 annealing has been proven to be effective in Si reconstruction, influencing diffusion by ...breaking strained Si bonds and generating cavities for contaminant gettering. These properties could help in reducing contaminants in BCD-SOI process. Unfortunately, H 2 annealing integration can be highly critical and the process optimization has to take into account 3-D morphology evolution and contaminant reduction efficiency. Aim of this work is to understand the physical mechanisms behind Si surface reconstruction and metallic contaminants reduction.
In this article the phenomenology related to the mechanisms of defect generation in Shallow Trench Isolation (STI) processes is discussed, and the role of the structure pattern is investigated. ...Defect formation is studied by plan and cross TEM analyses of wafers with different boron doses and after annealing at various temperatures. In addition, to obtain a wider statistics our analysis was extended by electrical measurements of defect-sensitive structures. It is shown that a modification of the STI flow suppresses the main mechanism of mechanical stress accumulation, hence stress-induced defects are eliminated. However, this approach is found to be critical from the point of view of the implantation damage recovery, specifically for what concerns the implantations carried out before the trench etch. This result can be explained by the role of the silicon surface in reducing the point defect excess generated in the implantation. As a consequence, in this example the presence of the STI structure is beneficial, in that it assists in annealing implantation-related defects. An attempt is also presented to model the evolution of implantation-induced defects by a Kinetic Monte Carlo code. The calculation results are promising, though the capabilities of the model are limited by the computation time.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this paper niobium is characterized as a silicon contaminant. It is shown that niobium is a relatively slow diffuser, with an intermediate diffusivity between very slow diffusers such as ...molybdenum and fast diffusers such as iron. Niobium is found to be very effective as a recombination center, and in addition prone to surface segregation. In addition, niobium shows optical activation, but no thermal activation. Three deep levels are revealed in niobium contaminated silicon, plus an additional level observed in high contamination dose samples only. One of these levels is located very close to midgap, and consistently niobium was also found very effective in degrading the generation lifetime.
Some examples of contamination by mass interference are studied in this work, specifically the molybdenum contamination in indium and boron implantations. This contamination is detected by Elymat and ...DLTS analyses, whereas it is missed by SPV, which is commonly used for routine line monitoring. Both Elymat and DLTS analyses consistently show molybdenum contamination clearly related to indium implantation conditions and to high dose boron implantations.
In this paper we show that nickel partially remains in the solid solution after Rapid Thermal Treatments (RTPs), so it can be detected by recombination lifetime techniques such as SPV and Elymat ...(based on photocurrent measurements). A quantification of nickel contamination based on lifetime measurements is provided. However, partial nickel segregation at wafer surface is observed even in RTPs by surface recombination velocity measurements. As a consequence, the near-surface region is depleted by nickel and a specific thermal treatment with very fast quenching is required to detect nickel in the volume by DLTS. Finally, the results about the electrical activity of nickel in carrier recombination and generation are compared to TOF-SIMS analyses at the oxide-silicon interface and to TEM analyses of nickel precipitates at wafer surface.
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