Preparation and characterization of ultrathin crystalline silicon membranes

The electrochemical etch-stop behaviour of ion-implanted n-type layers has been investigated as a function of the ion-implantation and post-annealing conditions. A three-electrode potentiostatic configuration and a KOH/H2O etch solution were used for these studies. Energy-loss spectrometry of alpha particles was applied to measure the absolute membrane thickness with an accuracy of +/-3.5%. The smallest membrane thickness has been measured as 1.15-1.45 fm. The thickness investigation shows that the etch-stop takes place 1.0-1.2 fm before the implanted metallurgical p-n junction is reached, which is less than the value found by other authors. Finally, the experimental results of anisotropically and selectively etched membrane thicknesses have been compared with calculated dopant profiles, depletion layers and electrical-field distributions in the region of the p-n junction during the electrochemical etch-stop process.