Controlling the diffusion of implanted boron in Si and silicide by multiple implants

To form an ultra-shallow p(+)-n junction by direct low energy BF2+ implantation is difficult. The channeling of the baron during implant and the transient enhanced diffusion of boron during annealing prohibit the tight control of the boron profile. Using the germanium preamorphization implant, the channeling probability of the boron is suppressed. However, the thickness of the pre-amorphized layer is crucial in alleviating the transient enhanced diffusion of boron. The excess point defects below the original amorphous/crystalline interface play a key role in enhancing the diffusion of boron. Introducing the carbon into the BF2+ implanted Si, the diffusion of the boron is retarded, Combining with the germanium pre-amorphization implant, low energy BF2+ implant and carbon implant, an ultra-shallow p(+)-n junction with a junction depth of about 70 nm is realized after rapid thermal annealing at 1050 degrees C, 10 s, Using the baron implanted TiSi2 as diffusion source to form an ultra-shallow p(+)-n junction is prohibited by the trapping of boron inside the TiSi2. The fabrication of high quality p(+)-n junction using this technique is difficult to achieve. Incorporation of germanium into the baron containing TiSi2, the diffusion of boron inside the TiSi2 is enhanced. Boron easily out-diffuses from the TiSi2 layer into the Si substrate and forms a high quality p+-n shallow junction. Manipulating the diffusion behavior of implanted boron in the Si and TiSi2 could be achieved by the multiple implants of germanium and carbon. The chemical interaction of co-implanted ions with the boron is the key to control the baron profile inside the silicon. (C) 1998 Elsevier Science S.A. All rights reserved.