Research On Depth Control Technique Of Laser Annealing Process

The work focuses on the depth control technique of laser annealing process.With the continuous developing of integrated circuit manufacturing technology, laser annealing has been more and more widely used. There are different annealing depth requirements in the manufacture process of different device: during fabricating ultra shallow junctions or HBTs, annealing must not introduce large impurity redistribution, which results in strict control of the laser processing parameters; backside junction depth in some IGBTs may reach 2~3μm, which requires a deep annealing; in some FRDs where platinum is locally doped, the annealing need to be limited in a specific range. The common feature of these specific devices is the requirement of depth control in the laser annealing. Therefore our work focuses on how to control the annealing depth during process.Firstly, a532 nm laser annealing machine is developed and tested, based on which laser annealing experiments are carried out and some control strategies are obtained. The machine uses a 532 nm pulsed laser, with pulse width of 100 ns, repetition frequency of 1 k Hz. The laser power is user adjustable. SIMS and square resistance measurements are executed to evaluate the effect of annealing. In the experiments, laser energy, scanning speed and the overlap of laser spot are all the adjustable parameters to achieve better depth control.To explore the theoretical mechanism of laser annealing process, numerical calculations based on the thermal melt model are performed. The calculated data are then compared with those from the experiments. Using ANSYS thermal analysis, we calculate the temperature distribution of the wafer surface under given conditions, and get the impurity diffusion through solving the generalized Fick’ s equation. The thermal parameters of the material vary with temperature; this factor is included in our calculations. And phase transition is taken into consideration too.Devices such as FRD, IGBT and Si Ge HBT are experimentally studied; these devices have different depth requirements in the laser annealing.In the FRD experiment, a defect region are introduced through deep proton implantation, then the laser annealing is used for activating the shallower boron doping, while the defective area is retained to getter Pt atoms that are diffused later. Reverse recovery time is reduced by about 30% by using the local Pt doping method. In terms of IGBT, activation rate of the boron ions after laser annealing is significantly increased. The on-state Vce voltage drops down from 5~6 to 3.2 V. Epitaxial layer in the HBT device is irradiated by the laser. For junction depth less than 40 nm, the laser annealing energy should be confined in 6~7 m J.