SSL Seminar Series 2001 No. 14
Talks on Applications of SIMS Depth Profiling

Time: August 22, 2001, 5:00-6:00pm
Venue: Physics Resource Room, S13, 02-16

Speaker I: Yeo Kwee Liang (SSL, Physics Dept., NUS)
Title: SIMS Backside Depth Profiling of Ultra-Shallow Implants

Abstract
 In SIMS depth profiling, a more accurate junction depth can be acquired by sputtering from the backside of the wafer. Due to better depth resolution of the leading edge as compared to the trailing edge, a more accurate measurement of the concentration below the top concentration can be achieved by backside profiling. Furthermore by doing backside sputtering, the distortion of the dopant profiles caused by surface transient effect can be avoided. By using silicon-on- insulator (SOI) wafers, we have developed a backside depth profiling technique for studying ultra shallow implants. The abrupt interface between the SOI layer and the buried oxide (BOX) layer and the large selectivity of the chemical etching result in smooth after-etched surfaces, which facilitate high resolution SIMS profiling. The true dopant distribution of B 1keV implants was studied by performing front and backside depth profiling using SOI substrates. Low energy (1keV and below) O2+ primary ions were used at oblique incidence in a Cameca IMS-6f, with and without oxygen flooding and sample rotation. Capping was done on the front surface of the SOI samples with amorphous silicon. When compared to the conventional front profiling, the backside sputtering is able to distinguish the peak position from the interfacial native oxide enhancement. As compared to the one from the front, the backside sputtering gives a shallower dopant profile, which we believe better represents the dopant distribution. The effects of oxygen flooding and sample rotation on the depth resolution of backside profiling are also discussed. The effectiveness of backside SIMS profiling of the ultra shallow dopant implants using SOI substrates is evaluated.

Speaker II: Lau Gih Sheng (Materials Science Dept., NUS)
Title: SIMS Depth Profiling of Si / SiGe heterostructures

Abstract
In this seminar, our work on the applicability of SIMS technique for Ge segregation studies in Si / SiGe heterostructures is presented. In addition, we report about our most recent results on the formation of nanostructures in a Si / SiGe sample using low energy beam sputtering at oblique incidences with simultaneous rotation.