Energy Dependence of Transient Enhanced Diffusion and {311} Defect Kinetics
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Energy Dependence of Transient Enhanced Diffusion and {311} Defect Kinetics Hugo Saleha, Mark E. Lawa, Sushil Bharatana, Kevin S. Jonesa, Wish Krishnamoorthya, and Temel Buyuklimanlib a. SWAMP Center, University of Florida, Gainesville, FL 32611 b. Evans East, East Windsor, NJ 08520 ABSTRACT Boron, a P-type dopant, experiences Transient Enhanced Diffusion (TED) via interstitials. The Boron TED and {311} dissolution rates are explored as a function of implant energy dependence. Silicon implants of 1014/cm2 at 20, 40, 80, and 160 keV were used to damage the surface of a wafer with an epitaxially grown boron marker layer. Samples were annealed at 750°C for 15 to 135 minutes and 800˚C for 10 to 30 minutes to observe the diffusion exhibited by the marker layer and to correlate this with the dissolution of {311} type defects. The diffusion enhancement depends strongly on implant energy but the {311} dissolution rate is weakly dependent. INTRODUCTION Transient Enhanced Diffusion (TED) of boron is caused by the release of interstitials from implantation damage. TED is well known to exhibit an energy dependence; as the implant energy is increased so does the enhanced diffusion1,2. Lim and Rafferty showed that TED depends on the distance to the surface by using surface polishing with a fixed implant dose and energy3. These effects are thought to be correlated, since an increase in implant energy moves the damage farther from the surface. The surface is thought to control TED. Below the implant amorphization threshold dose, most of the damage recombines quickly. An excess of interstitials remains from the implanted ions, and these condense into {311} defects. This is known as the “plus one” dose of interstitials4. The {311} defects dissolve and release interstitials. Eaglesham, et al., first proposed that these {311} defects are the source of interstitials for TED 5. Since TED depends on the distance to the surface, it has been assumed that the dissolution of {311} defects should be dependent on the distance to the surface. However, there have been some experiments that have suggested that this may not be true. Agarwal, et al., showed that some {311} defects could be very long lived just 40Å from the surface6. Moller, et al., showed that the width of the {311} layer is almost constant during dissolution, and that the {311} defects do not dissolve faster closer to the surface7. This study investigates simultaneously the energy dependence of TED and {311} dissolution. EXPERIMENT Si+ was implanted at 20, 40, 80, and 160 keV to a dose of 1x1014/cm2 into a Czochralski wafer to introduce damage above a CVD (Chemical Vapor Deposition) grown buried Boron marker layer about 5600Å deep. These implants were then annealed at 750°C for a range of times from 15 to 135 minutes and 800˚C for 10 to
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30 minutes in an N2 ambient. Plan-view TEM (Transmission Electron Microscopy) samples were prepared and the pictures were then used to measure the average length of {311}s, atomic concentration of trapped interstitials, and areal density o
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