Diffusion and activation of ultrashallow B implants in silicon on insulator: End-of-range defect dissolution and the buried Si∕SiO2 interface

Abstract

The fabrication of preamorphized p-type ultrashallow junctions in silicon-on-insulator ͑SOI͒ has been investigated. Electrical and structural measurements after annealing show that boron deactivation and transient enhanced diffusion are reduced in SOI compared to bulk wafers. The reduction is strongest when the end-of-range defects of the preamorphizing implant are located deep within the silicon overlayer of the SOI silicon substrate. Results reveal a very substantial increase in the dissolution rate of the end-of-range defect band. A key player in this effect is the buried Si/ SiO 2 interface, which acts as an efficient sink for interstitials competing with the silicon surface. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2240257͔ Formation of highly activated, ultrashallow, and abrupt profiles is a key requirement for the next generation of complementary metal oxide semiconductor ͑CMOS͒ devices, particularly for source-drain extensions.1 For p-type ͑boron͒ dopant implants, a promising method of increasing junction abruptness is to use Ge preamorphizing implants ͑PAI͒ prior to ultralow energy B implantation. Advantages of this method are a reduction in B channeling and an increase in B electrical activation due to the solid-phase-epitaxial ͑SPE͒ regrowth process. 2 SPE regrowth of the amorphized silicon does not remove interstitial defects located at depths greater than the initial amorphous/crystalline ͑a / c͒ interface. Excess interstitial atoms in this region agglomerate into "end-of-range" ͑EOR͒ defects situated just below the former a / c interface. During higher temperature annealing these defects undergo a series of transitions from self-interstitial clusters to ͕113͖ defects to dislocation loops depending on the initial PAI and subsequent conditions.3 These defects dissolve during annealing and the silicon self-interstitials so released migrate to nearby sinks such as the silicon surface.3 Transient enhanced diffusion and B electrical deactivation result from the interstitials that diffuse towards the silicon surface during annealing. 3,4 In the absence of sinks within the silicon, all of the released interstitials diffuse towards the surface. Thus they either end up reacting with B atoms in the implant or migrating unscathed through the B-doped layer to the silicon surface-the former being the more probable event in the case of highdose B implants.One possible method to reduce the number of interstitials that migrate to the B implanted region is to provide an efficient alternative sink for the interstitials. In this letter we investigate whether the buried oxide interface of the silicon top layer in silicon on insulator ͑SOI͒ may function in this way. This question is of considerable importance as SOI emerges as a candidate technology for future CMOS applications. 5Experiments were performed on n-type ͗100͘ Czochralski silicon wafers with a resistivity of ϳ10-25 ⍀ cm and on SOI wafers with a 145-nm-thick buried oxide and a 55-nm-thick p-type Si overlayer. Silicon and Soitec© SOI wafers were i...

Boron pile-up phenomena during ultra shallow junction formation

“…6 as a function of the annealing temperature. For temperatures higher than 850°C a shallower Xj in SOI material with respect to bulk Si is obtained in agreement with previous observations [19]. This effect was attributed to the interstitial recombination on the buried oxide layer [20,19].…”

Uphill diffusion of ultralow-energy boron implants in preamorphized silicon and silicon-on-insulator

“…For temperatures higher than 900°C a shallower X j in SOI material with respect to bulk Si is obtained, in agreement with previous observations. 26 This effect was attributed to the interstitial recombination on the buried oxide layer. 25,26 In order to point out the role of surface trapping on junction depth, a simulation performed without taking into account this effect ͑dashed line͒ is also reported in Fig.…”

“…23 The advantages of the use of SOI with respect to bulk samples regarding electrical activation and TED reduction have been explored in recent papers. [24][25][26] The purpose of this work is to investigate the uphill diffusion in ultrashallow p + / n junctions obtained by low-energy boron ͑B͒ implantation in both bulk Si and SOI material. In particular, the dependence of this phenomenon on the implanted dose, depth of the amorphous layer, and annealing conditions has been analyzed with the support of a simulation program which takes into account dopant trapping at the surface and allows a satisfactory prediction of the dopant redistribution upon annealing.…”

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

“…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.…”