Effects of lattice damage on impurity depth profiles in $BF_2^+$ ion implanted silicon have been investigated. $BF_2^+$ ions were implanted on n-type (100) silicon wafers and were annealed in rapid thermal annealing furnace as well as in conventional diffusion furnace. The morphologies of the lattice damage caused by ion implantation and the crystal defects originated from the lattice damage during subsequent annealing process have been characterized by cross-section transmission electron microscopy and Rutherford backscattering ion beam channeling technique. The effects of these crystal defects on the redistribution of the implanted impurities, boron and fluorine, were analyzed by depth profiling technique of secondary ion mass spectrometry.
In as-implanted states, it have been found that considerable amounts of lattice damage was formed in silicon substrate and the surface region of the silicon was amorphized by higher doses of implanted ions than critical value, which have been measured to be $8.0\times10^{14}/㎠$. The amorphized layer have clear boundary to the crystalline silicon which include much damages as shown to be micro-amorphous clusters originated from point defect clusters. RBS channeling reveals that the integrated damage in implanted layers increase linearly with increasing ion dose until critical value, and above this value the increasing rate decrease, which have been analyzed with modeling of damage formation. Since there's no increase of lattice damage in an amorphous layer, the integrated damages show reduced increasing rate, which only due to the increase of the thickness of amorphous layer. The calculated values of this integrated damage by computer program agree well with the measured value.
After annealing in diffusion furnace at 950℃ for 40min, the depth profiles for boron and fluorine show double peaks at the same depth from silicon surface. Micrographs of transmission electron microscopy revealed only one type of defects, dislocation loop, at depth of secondary peak, whereas RBS data indicated the possible presence of another type of defects in the depth of primary peak, which clearly show the gettering effect of crystal defects to impurities. in the SIMS profiles of the specimens rapid thermally annealed at various temperatures without capping oxide, evidence of out-diffusion was shown, and the double peaks in fluorine depth profiles were observed in all annealing temperatures, while those for boron were observed only in the temperatures above 1100℃, which indicate that the $BF_2^+$ion implantation produce two types of defects where the boron and fluorine can be gettered and that the boron is gettered at higher temperature due to a lower value of diffusion coefficient.
Thermal behavior of crystal defects at various ion doses and various annealing temperatures have been investigated. It was found that the implant dose strongly influence to the formation and distribution of residual crystal defects and redistribtuion of implanted impurities. At the dose of $1\times10^{15}/㎠$, the thickness of amorphous layer is relatively thin and the amounts of lattice damage at the crystalline region just below the a/c interface is much higher in as-implanted state. After annealing, the damaged crystalline layer changed to dislocation loops of stable structure, remaining defect-free at surface region, which had been amorphous before annealing process. These dislocation loop-like defects show weak gettering effects to the impurities, showing secondary peaks of boron at the temperatures below 1000℃ and that of fluorine, disappear at the temperature over 1100℃. On the other hands, at the dose of $5\times10^{15}/㎠$, the behavior of residual defects show different features. The RBS analysis results revealed that the residual damage at the depth of the secondary peak have highest value at RTA temperature of 1000℃, but the total amounts of damage increase with RTA temperature. By transmission electron micrographs, the dislocation network was observed at this depth, which also show strong gettering effects of impurities, and the stacking fault was observed at the silicon surface. At the dose of $1\times10^{16}/㎠$, the thickness of amorphous layer is thick and the damage in crystalline region is relatively low. Though the amount of residual damages after RTA showed the highest value in this dose, the gettering effects was not the highest and the morphology of the residual defects was the dislocations of irregular shapes distributed at wide range of depth from silicon surface.
