EU project provides better models for doping

Computer models created by a European project have been folded into the Sentaurus process simulator developed by Synopsys. The new models provide more accurate analysis of ion-implantation processes needed for integrated circuits.

The models created by the Atomics project team, funded under the European Union’s Sixth Framework programme, have been validated by STMicroelectronics. Modelling the fabrication processes for integrated circuits can slash production development time and costs by up to 40 per cent, the researchers claim.

Current research is preparing for the 32nm and 22nm nodes and even beyond. “At these nodes many new materials and processes are introduced and the devices become so small that we cannot be sure that the concepts developed for simulating the manufacture of larger devices can be transferred directly,” said Peter Pichler, a leading researcher in computer modelling of advanced manufacturing processes from the Fraunhofer Institute for Integrated Systems and Device Technology in Germany.

The Atomics team found new ways to model the activation or deactivation of dopants in silicon, generally introduced using ion implantation, which has the side effect of damaging the crystal lattice. Dopants are impurities added in small quantities to modify semiconductors’ electrical conductivity.

“As long as ion implantation remains the standard technique for doping, especially in this context, you will need very high doping concentrations, requiring very high dose ion implantations,” said Pichler. “However, ion implantation does a lot of damage to the crystal and a damaged crystal does not give you good performance in devices.”

Usually, annealing is used to repair implantation-induced crystal damage through the application of very high temperatures. The earliest annealing procedures were at temperatures of 900°C and above for hundreds of minutes. Miniaturisation required a reduction in the thermal budget.

Annealing in today’s production processes usually means a rapid increase to the peak temperature of around 1050°C followed by immediate cooling. New techniques such as flash annealing or non-melt laser annealing will reduce the annealing process from seconds to milliseconds. The work undertaken by Atomics has also helped to define the research route to computer modelling of processes such as flash annealing.

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