Boron Activation During Solid Phase Epitaxial Regrowth
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Boron Activation During Solid Phase Epitaxial Regrowth C. D. Lindfors , K. S. Jonesa, M. E. Lawa, D. F. Downeyb, and R. W. Murtoc a Swamp Center, University of Florida, Gainesville, FL b Varian Semiconductor Equipment Associates, Gloucester, MA c International SEMATECH, Austin, TX a
Abstract To continue scaling dimensions of transistors, higher dopant concentration levels are needed for ultra-shallow contacts. Therefore studies of dopant activation have been performed in preamorphized silicon wafers with various boron implant conditions to determine the maximum achievable dopant concentrations after Solid Phase Epitaxial Regrowth (SPER) alone. In the first experiment a silicon piece was preamorphized with a 30 keV, 1x1015 cm-2 and 90 keV, 1x1015 cm-2 Si+ implant followed by a 30 keV, 1x1015 cm-2 B+ implant. Solid phase epitaxial regrowth at 500 °C indicates that boron can be activated at low temperatures. Ultra Low Energy (ULE) implants were studied in the second experiment. Silicon wafers were implanted with 2.5 keV, 1x1015 cm-2 Si+ to amorphize and then B+ was implanted at 0.5 keV in the dose range of 1x1015 to 9x1015 cm-2. Samples were annealed in the temperature range of 500 to 650 °C. High concentrations of boron make it difficult to fully regrow amorphous layers and thus yield marginal electrical properties. Much of the boron remains inactive, particularly at the higher dose implants. In both experiments Variable Angle Spectroscopic Ellipsometry (VASE) is used to measure amorphous layer thickness and Hall effect measures active boron dose. For the first experiment, Secondary Ion Mass Spectrometry (SIMS) data compares chemical dose to active dose during the regrowth process. Sheet resistance data is obtained from a four point probe for the ULE implant experiment. Introduction Alternate processing and annealing techniques are being examined as a means to produce smaller dimensions needed for scale-down. One technique for exploring formation of ultra shallow junctions is amorphizing the substrate prior to boron doping and then taking advantage of Solid Phase Epitaxial Regrowth (SPER) at low temperatures (500 – 650 °C) to activate the boron. The advantage to this technique is boron can be incorporated while the regrowth process is occurring and at the same time low temperatures allow very little diffusion of dopant atoms. Indeed work has been done showing SPER is successful for incorporating high concentrations of boron into silicon1,2. However, as the need arises for shallower junction materials there are several tradeoffs to producing the optimum junction depth and sheet resistance3. The work below describes two experiments to examine boron activation during and after SPER. The first experiment was set up to determine if moderate boron concentrations could be incorporated during SPER. This was accomplished by using a medium energy, high dose implant and choosing an anneal temperature that easily controls the regrowth of the amorphous layer. The second experiment involves Ultra Low Energy (ULE), high dose implan
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