BACKSIDE SAMPLE PREPARATION ON BULK SUBSTRATE FOR SECONDARY ION MASS SPECTROSCOPY (SIMS) ANALYSIS

Abstract

Secondary ion mass spectrometry (SIMS) is an effective and powerful analytical technique that is widely used in semiconductor industry. With the continuing shrinking of the devices, quantification of dopant concentration profile, especially at the interface become increasing important in controlling the device performance. There is an urgent need for accurate dopant profile determination as well as high depth resolution of SIMS depth profiling. There are various artifacts associated with conventional trailing SIMS technique, including ion beam induced roughness, mixing and knock-on effects, etc. These artifacts play a negative role on achieving high depth resolution. Theoretically, these artifacts can be relieved by backside SIMS depth profiling as for improved depth resolution. In the light of improved SIMS quality, a backside sample preparation technique should be developed to leave the substrate thin, flat and smooth for SIMS analysis. However, current studies mainly focus on the backside SIMS sample preparation on Silicon on Insulator (SOI) substrate by chemical etching, as SOI substrate has a etch stopper underlying. It lacks of the study on the backside sample preparation method for bulk substrate that is widely used in microelectronics industry. Therefore this thesis aims to develop a novel backside sample preparation method for bulk substrate for high resolution backside SIMS depth profiling. The method and a standard procedure for backside sample preparation have been developed. The method can prepare backside SIMS sample with a surface roughness less than 1 nm, with a good control on remaining sample thickness on the scale of ~500 nm and with a good sample flatness, which are desired for high depth resolution depth profiling. A site-specific sample preparation method for SIMS backside analysis has also been developed. A case study on the comparison between the front side and backside SIMS analysis for the phosphorus depth profiling on a poly-Si/SiO2/Si-substrate test structure has also been studied, the result showed that the backside SIMS analysis could achieve better depth resolution at the interface and provide more accurate information about the dopant distribution.