The ever increasing interest in surface analysis techniques with excellent depth resolution, great detection sensitivity, and good throughput has been a driving force for development of dynamic secondary ion mass spectrometry using low energy primary beams. This work investigated sputtering erosion of Si and emission of secondary ions from Si bombarded by sub-keV O2+ beams at glancing incidence. It was demonstrated that surface roughening remained minimal for 250 and 500eV O2+ beams at an angle of incidence above 80° but developed rapidly at angles between 60° and 80°. The depth resolution for B and Ge appeared very different at the glancing incidence and changed dramatically in opposite ways as the angle of incidence decreased. The difference in the depth resolution was explained by the different diffusion/segregation behavior between B and Ge during O2+ bombardment. In general, the use of sub-keV O2+ beams at the glancing incidence (above 80°) favored a thinner altered layer, a short surface transient, a minimal apparent shift in depth profiles, a better depth resolution (not for B in Si), a good sputter rate, but a poor yield of the positive secondary ions. To address the issues with the low ion yield, we identified optimal cluster ions for common dopant such as boron and nitrogen. Good sensitivity was achieved for analyses of boron in Si by detecting BO2− as the characteristic secondary ion. A parallel study published elsewhere suggested SiN− as an ideal candidate for detection of nitrogen in ultrathin oxynitride [Z. X. Jiang et al., Surf. Interface Anal. (in press)]. For analyses of thin SiGe films in Si at glancing incidence, detection of Ge+ provided fairly good sensitivity. Applications of an O2+ beam at 250eV 83° for analyses of shallow boron implant demonstrated superior accuracy in the measured near-surface boron distribution. Also the characterization of thin SiGe films exhibited excellent depth resolving power for Ge in Si although the ion yield of Ge+ was low.

Good accuracy in depth profile analyses of nitrogen in ultrathin oxynitride films is desirable for process development and routine process monitoring. Low energy SIMS is one of the techniques that has found success in the accurate characterization of thin oxynitride films. This work investigated the artifacts in a typical depth profile analysis of nitrogen with the current SIMS technique and the ways to improve the accuracy by selecting optimal analytical conditions. It was demonstrated that surface roughness developed rapidly in a SiO 2 /Si stack when it was bombarded with an O 2 + beam at 250 eV and angle of incidence from 70 to 79° . The roughness caused distortion in the measured depth profiles of nitrogen and the major component elements. However, the above roughness and the distortion in the depth profiles can be eliminated by using a 250 eV O 2 + beam at an angle of incidence above 80° . Depth profile analyses with a 250 eV 83° O 2 + beam exhibited minimal surface roughening and insignificant variation in the secondary ion yield of SiN − from SiO 2 bulk to the SiO 2 /Si interface, facilitating an accurate analysis of nitrogen distribution in a SiO 2 /Si stack. In addition, depth profiles of the major component elements such as 18 O − and 28 Si − delivered clear information on the location of the SiO 2 /Si interface. Using the new approach, we compared nitrogen distribution in thin SiNO films with the decoupled‐plasma nitridation (DPN) at various powers. Copyright © 2008 John Wiley & Sons, Ltd.