analysis of semiconductor physics
...he source of the excess atoms is the supersaturated self-interstitials. 3. Oxygen plays several important roles in CZ grown silicon. It proves to be a very useful in gettering unwanted impurities from the active device regions. To prevent the precipitates from forming near the surface, a denuded zone is formed. Also, the presence of oxygen enhances the warpage resistance of silicon. 4. Intrinsic gettering is a process that uses gettering at oxygen precipitates or gettering by formation of impurity pairs. By doing this fast diffusing impurities are captured by sites that exist within the interior of the silicon wafer below the devices. Gettering at oxygen precipitates occurs when large amounts of oxygen form large clusters that can trap other ions. This only occurs if a three-step process is done. First a denuded zone is formed during a high temp step in a argon or nitrogen ambient. Second is a lower temperature step that creates the SiOx precipitates in a N2 ambient. Third, the wafers are heated to 900-1250 to allow the growth of dislocation loops. The formation of SiOx precipitates is a self-feeding process because stress from volume expansion causes Si self-interstitials which agglomerate to OISF’s, which nucleate to bulk SiOx which causes stress and so on. B: Oxide/Silicon Interface 1. Deal’s Triangle shows how temperature and annealing in inert gas affect fixed charge. The x-axis is annealing temperature, the y-axis is fixed charge and the hypotenuse is the affect of the oxidation temperature on fixed charge. Higher oxidation temperatures will produce lower fixed charge, and the vertical lines of the triangle represent the effect of cooling down from a higher temperature oxidation in inert gas. This helps in developing oxidation recipes with tight thermal budgets, because the triangle helps you determine what temperatures you can anneal at to achieve the desired fixed charge. 2. Fixed charge is a positive sheet charge near the Si/SiO2 interface. Once this region is established it is not affected by oxide thickness, doping type or concentration, and the polarity of the charge does not change with a change in applied voltage. So the charge is fixed. Interface traps are not “fixed” because the charge state of the trap depends on the bias condition, or Fermi level of the device. 3. With only one C-V curve it is difficult to determine the effects of fixed charge and interface traps due to their different e...