DOPING CONCENTRATION MEASUREMENT TECHNIQUE IN TFSOI DEVICES
Original Publication Date: 1996-Nov-01
Included in the Prior Art Database: 2002-Apr-30
During development of thin film silicon-on- insulator (TFSOI) devices, there were die-by-die and wafer-by-wafer threshold voltage (Vt) variations: they may be due to a doping concentration issue and/or other process integration/material problems. To clar- ity the mechanism, the doping concentrations should first be known. However, SOI devices have unique characteristics of 1) buried oxide (BOX) layer (1 k-10 kA: thick oxide), thus floating devices, and 2) very thin Si thickness (5 1000 A), and thus nearly fully depleted. Because of these material restrictions, no bulk method is straightforwardly applicable to meas- ure doping concentrations (Na for NMOS and Nd for PMOS). In addition, SOI devices are either enhancement-mode (n+pn+ for NMOS and p+np+ for PMOS) or accumulation-mode (n+nn+ for NMOS and p+pp+ for PMOS), which requires a different kind ofmeasurement methodology.