Boron deactivation in preamorphized silicon on insulator: Efficiency of the buried oxide as an interstitial sink

Abstract

Preamorphization of ultrashallow implanted boron in silicon on insulator is optimized to produce an abrupt boxlike doping profile with negligible electrical deactivation and significantly reduced transient enhanced diffusion. The effect is achieved by positioning the as-implanted amorphous/ crystalline interface close to the buried oxide interface to minimize interstitials while leaving a single-crystal seed to support solid-phase epitaxy. Results support the idea that the interface between the Si overlayer and the buried oxide is an efficient interstitial sink. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2778749͔Highly activated ultrashallow boxlike doping profiles are an important requirement for advanced planar complementary metal oxide semiconductor ͑MOS͒ applications. 1 A promising fabrication approach for p-channel MOS transistors is the use of Ge preamorphizing implants ͑PAIs͒ prior to ultralow energy B implantation. This reduces channeling and increases electrical activation due to solid-phase epitaxial regrowth ͑SPER͒. 2 For future technology nodes, bulk Si wafers may be replaced by silicon on insulator ͑SOI͒. 3 Unfortunately, in both bulk Si and SOI, the PAI implantation step causes an interstitial-rich "end-of-range" ͑EOR͒ defect band to form on further annealing. As this EOR band evolves, it releases self-interstitials, causing transient enhanced diffusion ͑TED͒ and boron-interstitial cluster ͑BIC͒ formation which manifests itself as electrical deactivation. 4 In SOI, a proportion of the emitted self-interstitials may migrate to nearby sinks such as the silicon/buried oxide ͑BOX͒ interface, thus reducing the amount of B deactivation that occurs. 5 This letter quantifies the role of the BOX and shows the dramatic advantages-in terms of reduced diffusion and deactivation-that can be achieved by exploiting the positioning of the EOR defect band within the silicon top layer in SOI. We will show that two distinct physical processes are involved: the removal of interstitials at the BOX interface following diffusion within the Si overlayer and the cutting off of the "as-implanted" excess interstitial profile within the BOX.Experiments were performed on n-type ͗100͘ Czochralski Si wafers with a resistivity of ϳ10-25 ⍀ cm, and on SOITEC© SOI wafers with a nominal 145 nm BOX and a 55 nm p-type Si overlayer. The wafers were implanted with Ge + at 8, 20, 24, 28, 32, or 36 keV to a dose of 1 ϫ 10 15 cm −2 , amorphizing to depths of ϳ20, 40, 45, 50, 55, and 60 nm, respectively, as determined by Rutherford backscattering spectrometry ͑RBS͒ and cross-sectional transmission electron microscopy ͑XTEM͒. Boron was subsequently implanted at 500 eV to a dose of 2 ϫ 10 15 cm −2 at 0°tilt and 0°twist. RBS used a 1.5 MeV He beam at 45°to the sample. 6 After implantation, samples received isochronal rapid thermal annealings in N 2 ambient, using a Process Products Corporation 18-lamp system ͑with lamps above and below the sample͒ operating with a set time of 60 s at temperatures in the range of 700-1000°C, considere...

Evolution of end-of-range defects in silicon-on-insulator substrates

“…The possible effect of the Si top layer/BOX interface acting as a sink, for example, has been confirmed by some already published experimental analysis [2,5], and ruled out by others [3,7].…”

“…Moreover, no direct quantitative data concerning the surface influence on extended defect evolution have been reported yet, since interstitial recombination at Si/BOX and the implanted profile cut-off effects are mixed up in some of the reported data [2], and in other published articles [5] measured defects size and densities are too small to obtain quantitative data.…”

“…It is commonly accepted [2,3,[5][6][7] that the density and size of EOR defects decreases when passing from Bulk Silicon to SOI but different arguments are used in the literature to explain this reduction. The possible effect of the Si top layer/BOX interface acting as a sink, for example, has been confirmed by some already published experimental analysis [2,5], and ruled out by others [3,7].…”

“…The presence of the BOX can alter the interstitial concentration in the Si top layer in two ways: by reducing the initial concentration of interstitial created by the implant [2,3] or acting as a sink for interstitial recombination [4,5].…”

Interaction of interstitials with buried amorphous layer in silicon

“…We are therefore able to create a well-defined two regions system with a region rich in vacancies and a region rich in interstitial spatially well separated. As recently shown, the use of silicon on insulator (SOI) wafer and therefore a silicon/buried oxide interface could be a solution to avoid the EOR defects after recrystallization [22], thus combining it with the buried amorphous layer could be a way to get rid of most interstitial defects. This is important for the development of defect engineering in silicon and other materials.…”