Mousumi Bhat

Multiple-pulse laser annealing of preamorphized silicon for ultrashallow boron junction formation

Advantages of multiple-pulse laser annealing with a moderate energy fluence over a single-pulse annealing with a high energy fluence are demonstrated on the formation of shallow p+/n junction. When the silicon surface is preamorphized, the multiple-pulse laser annealing with a fluence adjusted to a value which can melt the amorphous layer but not crystal silicon shows that the successive pulses do not increase junction depth further but decrease sheet resistance significantly. Under this condition, the junction depth is still controlled by the depth of the preamorphized layer. However, when the laser fluence is high enough to melt the crystal silicon, the successive pulses result in the deepening of junction depth. This is attributed to the increase of surface roughness by the successive pulses, thereby increasing the total absorbed energy.

Boron Profile Narrowing in Laser-Processed Silicon after Rapid Thermal Anneal

The narrowing or broadening of the boron profile during annealing of laser-processed samples is observed to occur depending on which of two competing mechanisms, uphill diffusion of boron due to a highly defective single-crystal layer near the surface or transient-enhanced diffusion due to end-of-range defects, dominates during the post-laser processing anneal. The results show that uphill diffusion of boron is found to dominate during annealing of a single-pulse laser-processed sample because the defects near the surface cannot be efficiently removed with a single laser pulse adjusted to a value that can melt the amorphous silicon but not the underlying crystalline substrate. Junctions thus become shallower with the post-laser processing anneal. However, with successive laser pulses, the dopants are observed to move deeper into the silicon with subsequent rapid thermal annealing cycles. This could be due to the reduced contribution of uphill boron diffusion when the defects near the surface decrease with successive pulses. The end-of-range defects, which cannot be sufficiently annealed because the melt depth is not beyond the amorphous layer, thus play the key role in broadening the boron concentration profile for multiple-pulse laser-annealed silicon.

Multiple-pulse laser annealing of boron-implanted preamorphized silicon and the process optimization

Advantages of multiple-pulse Laser Thermal Annealing (LTA) with a moderate energy fluence on preamorphized silicon are described. Re-distribution of laser annealed boron junction during subsequent RTA is also studied. A method to optimize the multiple-pulse LTA condition is proposed. It is also demonstrated that Hall analysis can be used as a quick evaluation tool of the integrity of the junctions.

Dependence of Texture in Al Bondpads on Ta/TaN Bilayer Barrier and its Correlation to Optical Reflectivity in 0.13μm IC Technology

In this paper, the dependence of crystallographic orientation in Aluminum thin films grown on different barrier-metal substrate schemes (Ta or Ta/TaN) will be presented. The orientation of Al grains will be shown to have a bearing on the material characteristics, which are important in IC fabrication from the perspective of both the device functionality and reliability. X-ray powder diffraction studies indicate that the films deposited on a single Ta layer are randomly oriented. On the other hand, a Ta/TaN bilayer substrate scheme results in preferred orientation along Al(111). A correlation will be established between the grain orientation and optical reflectivity properties of Al films. Moreover, the optical appearance of bondpads and their bondability are also influenced by the orientation of Al grains.