SWOP—Charge Carrier Depth Profiling of Boron Doped Single Crystalline Silicon

According to the subsequently continued shrinking of semiconductor device dimensions the fabrication of ultra shallow pn-junctions is the essential requirement for modern CMOS technology. Therefore the importance of measurement techniques for dopant depth profiles is rising and the demands in resolution and accuracy are increasing. The established methods like SIMS and spreading resistance profiling become less suitable for these applications because of their disadvantages at measurements near the silicon surface.
Stepwise Oxidation Profiling was applied to boron doped p+ layers as a new measurement technique for ultra shallow doped layers. Single crystalline n-type silicon (1…10 Ohmcm) with <100>- orientation was used as base material. One sample type was implanted with boron at an ion energy of 1 keV and an implantation fluence of 3x1014 cm^-2. After implantation the samples were annealed by rapid thermal annealing (RTA) at 1000 °C and 10 s annealing time. On the other sample type boron was deposited by e-beam evaporation. Following, a 400 keV Si pre-implant was done to avoid transient enhanced diffusion and then a flash lamp diffusion (FLD) was carried out with 600 °C preheating and a 1300 °C Xe flash of about 3 ms duration. The two sample types were fabricated as planar van der Pauw (VDP) test structures.
Compared to the Continuous Anodic Oxidation Technique (CAOT) developed by S. Prussin the measurement procedure of SWOP is similar and the dopant depth profiles are measured by altering between an electrical VDP measurement of the sheet resistance and the electrochemical growth of thin anodic SiO2 layers (in steps of 1 nm and below). The SWOP measurement can be done in one apparatus without removing the sample for anodic oxidation or electrical VDP measurement. The values of the active boron concentration are calculated using the hole mobility values based on the Thurber expression.