I. Mica

Crystal defects and junction properties in the evolution of device fabrication technology

In this paper, the correlation between dislocation density and transistor leakage current is demonstrated. The stress evolution and the generation of defects are studied as a function of the process step, and experimental evidence is given of the role of structure geometry in determining the stress level and hence defect formation. Finally, the role of high-dose implantations and the related silicon amorphization and recrystallization is investigated.

Oxide Thinning in Shallow Trench Isolation

Aim of this work is to study the thinning of thick HV gate oxides in flash and embedded flash processes due to the shallow trench isolation (STI) induced stress on oxide growth

The Role of High Temperature Treatments in Stress Release and Defect Reduction

In this work we discuss an original analysis about a method to reduce the dislocation density in the devices that use the Shallow Trench Isolation (STI). It is well known that a high mechanical stress in silicon combined with an amorphizing implantation damage can generate many dislocations. So we propose to release the mechanical stress in silicon before implanting. A high temperature treatment indeed can trigger the viscous behaviour of the filling oxide inducing the relaxation of the stress field in silicon. For the first time a systematic study of the effect of different furnace and RTP annealings in the stress relaxation was done by Raman measurements. Different temperatures (from 3000C to 11000C) and different durations (from few seconds to one hour) were explored and the experimental results were compared with the numerical simulation with a good agreement. Finally we study the effect of the most promising annealings selected by Raman in a complete process flow.

H 2 annealing for metallic contaminant reduction in BCD-SOI process: Benefits and drawbacks

Contaminant reduction is a key issue for SOI substrate which cannot make use of back-side gettering. H2 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, H2 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.

Detection and Prevention of Palladium Contamination in Silicon Devices

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.

The Role of the Interstitial Oxygen in the Recovery and Evolution of the Boron Implantation Damage

The recovery of the boron implantation damage can be very difficult. Depending on the energy and the dose many dislocations are generated at the projected range of the boron implantation. The morphology of these dislocations depends on the silicon substrate. In this work we demonstrate that the interstitial oxygen concentration ([Oi]) is related with the dislocation dimension, density end morphology. Particularly long dislocation dipoles were generated by the boron implantation in substrate with interstitial oxygen, and their density is connected with the [Oi] concentration.

Mechanical Stress and Defect Formation in Device-Processing: Validity of the Numerical Models for Mechanical Stress Calculation

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