Obiettivo
The objective of this project was to develop an advanced physical analysis technique as a diagnostic and control tool for contamination detection and doping profile determination. The new technique is based on a fundamental improvement of the standard Secondary Ion Mass Spectroscopy (SIMS) technique through the use of resonant laser excitation of sputtered atoms into Rydberg states, followed by electric field ionisation. Hence the appellation LASIMS (Laser-Assisted SIMS).
The objective of this project was to develop an advanced physical analysis technique as a diagnostic and control tool for contamination detection and doping profile determination.
It was decided to use a modified commercial SMI-300 Cameca instrument, instead of constructing a totally new one, to experimentally verify the laser assisted secondary ion mass spectroscopy (LASIMS) concept. The original SMI-300 was fitted with a new spectrometer.
A new ultra high voltage (UHV) compatible chamber was constructed as well as a special interaction source and secondary ion optics.
A standard 4f-column was modified to a pulsed version which can be produce ion pulses of microsecond duration.
A specialised (and patented) raster system was designed and built which improves the speed during depth profiling by a factor of 100 and reduces the duty cycle problem due to the pulsed laser.
The prototype was evaluated in terms of sensitivity, detection limits and matrix effects for germanium.
The matrix effect was evaluated for germanium contained in silicon, silicon germanium (with varying germanium content) and germanium. The results achieved showed that the laser assisted secondary ion mass spectroscopy (SIMS) technique (LASIMS) has significant potential in improving the detection limits for those cases where mass interference limits the performance of standard SIMS. The elimination of matrix effects also makes the method particularly suitable for multilayer structure profiling. Due to the external ionisation, the technique can be combined with a liquid metal ion source for high spatial resolution without any loss in sensitivity.
Following the initial planning and feasibility study stages, the project entered an intensive construction phase, in 1988, carried out by IMEC and Cameca, with a consequent reduction in the involvement of Siemens and Philips.
Given the budget and time-scale of the project, it was decided to use a modified commercial SMI300 Cameca instrument, instead of constructing a totally new one, to experimentally verify the LASIMS concept.
The original SMI-300 was fitted with a new spectrometer resulting in a system very close to the latest Cameca3f configuration, which has the advantage of easy transferability of the LASIMS approach to already existing commercial systems.
A new UHV-compatible chamber was constructed as well as a special interaction source and secondary ion optics. The source is extremely versatile since is was shown to be capable of handling SIMS, RIS and LEFI ions with similar efficiency. This implies that one can select the method most appropriate for the analysis problem under investigation.
A standard 4f-column was modified to a pulsed version which can produce ion pulses of microsecond duration. The advantage of the present pulsing concept is that the beam is extinguished on its current position and does not move across the sample during the pulsing. At the same time, a specialised (and patented) raster system was designed and built which improves the speed during depth profiling by a factor 100 and reduces the duty-cycle problem due to the pulsed lasers.
The prototype was evaluated in terms of sensitivity, detection limits and matrix effects for Ge. It was shown that despite the compromises made in the source design (1 mm instead of 4 mm hole, due to time/budget constraints), a detection limit of 0.2 ppm for Ge in Si could be achieved. It was also shown that the LEFI technique leads to a reduction in background from SIMS ions by 7 orders of magnitude and for RIS and non-resonantly excited species by 3 orders of magnitude. The matrix effect was evaluated for Ge contained in Si, SiGe (with varying Ge content) and Ge. It was shown that the LEFI method was virtually matrix-independent, whereas the SIMS showed variations by as much as a factor of 20.
The results achieved showed that the laser-assisted SIMS technique (LASIMS) has significant potential in improving the detection limits for those cases where mass interference limits the performance of standard SIMS. The elimination of matrix effects also makes the method particularly suitable for multilayer structure profiling. Due to the external ionisation, the technique can be combined with a liquid metal ion source for high spatial resolution without any loss in sensitivity. The latter application wa s not part of the original project but is presently under implementation.
The SIMS builder, Cameca, is considering making a LASIMS option available for its future instrument series.
Campo scientifico (EuroSciVoc)
CORDIS classifica i progetti con EuroSciVoc, una tassonomia multilingue dei campi scientifici, attraverso un processo semi-automatico basato su tecniche NLP. Cfr.: Il Vocabolario Scientifico Europeo.
CORDIS classifica i progetti con EuroSciVoc, una tassonomia multilingue dei campi scientifici, attraverso un processo semi-automatico basato su tecniche NLP. Cfr.: Il Vocabolario Scientifico Europeo.
- scienze naturali scienze fisiche elettromagnetismo ed elettronica semiconduttività
- scienze naturali scienze fisiche ottica fisica dei laser laser a impulsi
- scienze naturali scienze chimiche chimica inorganica metalloidi
- scienze naturali scienze fisiche ottica spettroscopia
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Coordinatore
3030 HEVERLEE
Belgio
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