SSL Seminar Series 2001 No. 15
Combined talks (two speakers) on Time-of-Flight Mass Spectrometry, some results obtained at IMRE

Time: September 19, 2001, 5:00-6:00pm
Venue: Physics Resource Room, S13, 02-16
Speakers: Dr Nikolai Yakovlev (IMRE, NUS) and Ms Lena Lui (Physics Dept, NUS)
Title: Time-of-Flight Mass Spectrometry, some results obtained at IMRE

Abstract
 Secondary ion mass spectrometry with time-of-flight detection of ions (ToF SIMS) is a technique applied for surface studies due to its high sensitivity and high mass resolution. In the presentation, we shall describe the principles of ToF SIMS, modes of its operation and results of two studies: laser ablation of polyimides and electroplated Cu films.

Organic polymers form a class of organic molecules of considerable technological importance in the field of materials processing, hence their interactions with laser radiation have generated interest from various fields. When laser ablation of polyimide occurs, the absorbed energy exceeds the energy that is needed to break the bonds of the material or the melted polyimide is superheated, the fragments are ejected from the surface to form a plume, which is deposited on a silicon substrate. This silicon substrate is subsequently analysed using the imaging mode of ToF-SIMS. It has been found that the size and the chemical composition of the plume depend on the repetition rate of the laser pulses.

Copper is a candidate to replace aluminium as interconnect material in integrated circuits. Preferred method of depositing Cu films is electroplating. At room temperature, the sheet resistance of these films decreases by 20% during about 16 hours. This process is known as self annealing and is attributed to increase in grain size. We used focused ion beam induced electron emission and monitored the grain growth. The observed contrast in secondary electron images, as well as secondary ion images is due to different crystallographic orientation of the grains. We found that at channelling condition, 25 kV Ga ions penetrate 20 nm deeper than at random orientation.

About the speakers
Ms Lena Lui, Honours year student, Department of Physics, National University of Singapore.

Dr Nikolai Yakovlev - Research Associate, Institute of Materials Research and Engineering. He obtained his MSc degree at Leningad Polytechnic Institute and PhD degree at Ioffe Physico-Technical Institute, Russia. He worked in the fields of molecular beam epitaxy, optcal spectroscopy, X-ray and electron diffraction, AFM and STM. At present, he works on SIMS.