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Crystalline Silicon Properties and Uses Part 5

Tham khảo tài liệu 'crystalline silicon properties and uses part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | High Mass Molecular Ion Implantation 89 where N is the number of interstitials trapped in the defects approximately equal to the implanted dose and Rp is the projected ion range where the excess interstitials are initially located . The linear dependence on Rp has been demonstrated experimentally as shown in fig. 6. The activation energy of Axj2 is negative because the interstitial supersaturation due to the presence of the extended defects is larger at lower temperatures. This implies that the final junction will be deeper if the defects are annealed out at a lower temperature than at a higher temperature. This is a key reason why junction anneals are done in a rapid thermal annealing RTA rather than in a conventional furnace with a ramp-up rate of a few degrees per minute. An RTA spends significantly less time during the temperature ramp-up at lower temperatures where the diffusivity enhancement is larger. Since the increase in junction depth due to TED depends on the implant dose Eq. 1 it is possible that for a high dose implant some damage will remain after a fast ramp-up allowing TED to continue during the ramp down Agarwal 1999 . As the ramp-up rate is increased the temperature at which TED runs out is pushed up until the TED is pushed over to the ramp-down side of the anneal Agarwal 2000 . This is illustrated in fig. 8. Fig. 8. Schematic illustration of TED continuing during ramp down of a spike anneal that is sufficiently fast Agarwal 2000 . In the sub-keV regime there is more than one way to arrive at the same junction properties. It is very important to minimize the dose first before reducing the energy further. The dependence of the sheet resistance and junction depth data on the different implant and annealing parameters is summarized in fig. 9. Increasing the ramp-up rate leads to a more shallow junction with higher resistivity. The same is also true when a smaller dose or energy is used. Modifying the implant parameters first helps avoid the risk of .