Heavily doped n-type regions are one of the basic components of semiconductor device technology. Because of its high solubility and low diffusivity, arsenic is the most commonly used dopant for the formation of $n^+$ regions in silicon. Crystal defects are generated because of implant damage, solid solubility, and two-dimensional solid phase epitaxial regrowth of amorphous layers. Understanding the details of the generation, evolution, and dissolution of the crystal defects is important for an evaluation of the effect of the crystal defects on the electrical properties of devices.
We first investigate the generation, evolution, and dissolution of the crystal defects in high-dose $As^+$-implanted silicon during thermal annealing. $As^+$ implantation at an energy of 80 keV with a dose of $3×10^15/㎠$ completely amorphized a 100-nm-thick silicon surface. After annealing at 500 ℃ for 4 h, no crystal defects were generated near the implant projected range, but {311} defects having a size of 2~5 nm were generated at the end-of-range region. Lattice contraction induced by the substitutional As in the regrown layer and lattice expansion due to the end-of-range defects were observed. After annealing at temperature range 650~950 ℃, the projected range defects and the end-of-range defects were generated near the maximum As concentration region and the original amorphous/crystalline interface, respectively. The crystal defects evolved in the sequence {311} defects → {100} defects →faulted Frank loop → perfect prismatic loop with the increase of the annealing temperature. Lattice contraction was reduced with the increase of the annealing temperature and completely disappeared after annealing at 950 ℃ for 10 min. With the increase of the annealing temperature, lattice expansion was also reduced. After annealing at 1000 ℃ for 1 h, the crystal defects were mostly annealed out and lattice strain completely disappeared. Meanwhile, during annealing the stress in chemical vapor deposited $SiO_2$ films increased with temperatures and a maximum stress of $1.0×10^10dyne/㎠$ was developed at 650 ℃. However, the stress induced by the films had little influence on amorphous layer the regrowth, crystal defect generation, and As diffusion.
In Si ultralarge-scale integration fabrication, high-dose As implantation is usually performed through fine mask patterns. As a result, two-dimensional amorphous layers are formed under mask-opening regions. Two-dimensional solid phase epitaxial regrowth and crystal defect generation under the mask edges have been studied in $As^+$-implanted Si. Chemical vapor deposited $SiO_2$ films are often deposited on $As^+$-implanted amorphous layers to isolate these layers from various interconnections. The effect of stress induced by the chemical vapor deposited $SiO_2$ films on the solid phase epitaxial regrowth and crystal defect generation under the mask edges has been also studied. Trench structures were used to form the two-dimensional amorphous layer and to induce the stress in the Si substrate. $As^+$ implantation at an energy of 80 keV with a dose of $3×10^15/㎠$ completely amorphized a 100-nm-thick silicon surface under the trench bottom and produced a sharply curved amorphous/crystalline interface under the bottom corner of the trenches. In the case of the absence of the stress vacancy-type dislocation half loops were generated on {111} planes at the corner of the regrowth regions after annealing. The trenches filled with a high-tensile stressed chemical vapor deposited $SiO_2$ film induced a high stress field in the Si substrate. The solid-phase epitaxial regrowth and the corner defect microstructure were strongly influenced by the stress induced by the trenches. In the case of the presence of the stress induced by the trenches, the regrowth of the amorphous layers was retarded and a notch remained for a long time in the amorphous/crystalline interface just under the bottom corner of the trenches during the regrowth process. The regrowth retardation and the remaining notch were explained by the effect of the stress induced by the trenches filled with the chemical vapor deposited $SiO_2$ film on the activation barrier of the regrowth. Microtwins were formed on the {111} planes at the corner of the regrowth regions in the case of the presence of trench-induced stress. It was also found that the microstructure of the corner defects was determined by the regrowth behavior at intermediate stages of the regrowth process.
Continued shrinkage of Si device dimensions and increasing complexity of device processing have led to increase in stress levels in the Si substrate. The stress can alter the evolution kinetics of the crystal defects created by ion implantation. The effect of stress on the nucleation of the crystal defects in $As^+$-implanted, amorphized Si has been studied by transmission electron microscopy. Trench structures filled with a high-tensile stressed chemical vapor deposited $SiO_2$ film were used to induce the stress in the Si substrate. In the case of the presence of the stress induced by the trenches, the crystal defects were less dense under the bottom corner of the trenches. The decrease in the defect density was explained by the effect of the resolved normal stress on the nucleation of the crystal defects on their habit planes.
