TCAD Application Advanced Examples (2D) 

Simulation of Scanning Laser Annealing in Sentaurus Process 

Figure 1
Temperature solutions in the wafer at: (a) t=0 ms; (b) t=0.4 ms; (c) t=0.8 ms; and (d) t=1.2 ms.

The laser beam is 60 um wide and scans from left edge towards right at a speed of 15 cm/s.

Figure 2
Temperature profile inside the device region. A fast up and down rate leads to much reduced thermal cycle for dopant diffusion.

Overview
Shallow junctions with low sheet resistance are required for future generation short channel devices. This dual requirement on junctions imposes great difficulties for the conventional rapid thermal annealing technology, for which the thermal ramp down rate is limited by the cooling speed of the entire wafer. This sets a lower limit on the thermal cycle, which will become insufficient to produce quality junctions for future devices. The anticipation of such difficulties has prompted development of new technologies which include laser and flash annealing. A common feature of these two new technologies is that they can ramp up and down temperature at a very fast pace, therefore allowing a much shortened thermal cycle which typically only lasts a few milliseconds. This short heating cycle combined with the very high peak temperature that can be reached in a laser/flash setup has proven to be efficient in producing ideal junctions of box shape and high dopant activation.

The introduction of these new technologies in process flow presents additional challenges for process simulation. For laser and flash annealing, the main challenge for simulation is the thermal temperature used for mechanics and diffusion simulation, which is typically known in a rapid thermal annealing simulation but unknown in a laser/flash annealing simulation. To meet this challenge, new models have been added in Sentaurus Process to solve the heat balance equations built on user-defined laser/flash light conditions and the thermal properties of the device components. The solution of the equations leads to time-dependent temperature distribution inside the wafer (see Figure 1). This temperature solution is then applied to the mechanics and diffusion simulations as the temperature ramps defined in the regular rapid thermal annealing simulations.

This month's featured application example demonstrates the capabilities of laser/flash annealing simulation in Sentaurus Process with focus on scanning laser simulation. The specific setup used for scanning laser simulation as well as the general characteristics of the results are discussed. In general, the heat simulation and the regular mechanics and dopant simulations are coupled together in a laser annealing simulation in Sentaurus Process. This example also discusses the possibility of separating the heat simulation from the mechanics and diffusion simulations to improve the overall simulation time while maintaining a high level of accuracy.

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