KEYWORDS: Particles, Photodiodes, Back end of line, Surface roughness, Optical spheres, Diodes, Dielectrics, Monte Carlo methods, Semiconducting wafers, Scanning electron microscopy
In this work the influence of nanoscale particles caused by processing excursions during back end of line (BEOL) processing on top of the photodiode active region was examined. To investigate the influence of the particles on the photodiode performance, wafer level optical responsivity measurements were done. In addition to the measurements the effect of the particles was simulated with a simplified model based on a modified transfer matrix method (MTMM)1 . The simulation and measurements are in very good agreement with each other and lead to the conclusion that even though some decrease of sensitivity was observed, the overall system variability was reduced by the presence of particles. Furthermore, the influence of the dielectric stack layer thickness variability on the photon flux density is reduced.
In this work the characterization of CMOS diodes with Electron Beam Induced Current (EBIC) measurements in a
Scanning Electron Microscope (SEM) are presented. Three-dimensional Technology Computer Aided Design (TCAD)
simulations of the EBIC measurement were performed for the first time to help interpret the experimental results. The
TCAD simulations provide direct access to the spatial distribution of physical quantities (like mobility, lifetime etc.)
which are very difficult to obtain experimentally. For the calibration of the simulation to the experiments, special designs
of vertical p-n diodes were fabricated. These structures were investigated with respect to doping concentration, beam
energy, and biasing. A strong influence of the surface preparation on the measurements and the extracted diffusion
lengths are shown.
The 0.35μm HV-CMOS process technology utilizes several junctions with different doping levels and depths. This process supports complete modular 3V and 5V standard CMOS functionality and offers a wide set of HV transistor types capable for operating voltages from 20V to 120V made available with only 2 more mask adders [1]. Compared to other reported integration of photo detection functionalities in normal CMOS processes [2] or special modified process technologies [3] a much wider variety of junction combinations is already intrinsically available in the investigated technology. Such junctions include beside the standard n+ and p+ source/drain dopings also several combinations of shallow and deep tubs for both p-wells and n-wells. The availability of junction from submicron to 7μm depths enables the selection of appropriate spectral sensitivity ranging from ultraviolet to infrared wavelengths. On the other side by appropriate layouts the contributions of photocurrents of shallower or deeper photo carrier generation can be kept to a minimum. We also show that by analytically modelling the space charge regions of the selected junctions the drift and diffusion carrier contributions can be calculated with a very good match indicating also the suppression of diffusion current contribution. We present examples of spectral responsivity of junction combinations optimized for peak sensitivity in the ranges of 380-450nm, 450-600nm or 700-900nm. By appropriate junction choice the ratios of the generated photo currents in their respective peak zones can exhibit more than a factor of 10 compared to the other photo diode combinations. This enables already without further filter implementation a very good spectral resolution for colour sensing applications. Finally the possible junction combinations are also assessed by the achievable dark current for optimized signal to noise characteristic.
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