Effect of Fluorine on the Dopant Diffusion of Through-Oxide Implanted Boron In Si - A Correlation with Microstructural D
- PDF / 2,695,198 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 44 Downloads / 188 Views
EFFECT OF FLUORINE ON THE DOPANT DIFFUSION OF THROUGH-OXIDE IMPLANTED BORON IN Si - A CORRELATION WITH MICROSTRUCTURAL DEFECTS J.G. HUANG, A. LAM, AND R.J. JACCODINE Sherman Fairchild Center for Solid University, PA 18015.
State
Studies,
Lehigh
ABSTRACT In case of boron through-oxide implant, it has been shown that the knocked-in oxygen atoms segregate at initially nucleated dislocation sites during the incubation and no significant junction movement is detected. The trapping of oxygen proceeds up to a certain time at which oxygen-precipitation occurs and this leads to an ejection of excess Si interstitials and further enhancing boron diffusion. However, with fluorine addition we believe that fluorine incorporation in Si0 2 and/or SiO2/Si interface not only releases the strain gradient but also suppresses the silicon interstitials ejection and by this means suppresses the oxidation-enhanced boron diffusion. Correlated results of TEM microdefect structures and spreading resistance profiles are used to further support our postulation.
INTRODUCTION Boron implant through a screen oxide into silicon provides a means of suppressing initial damage-enhanced diffusion during annealing. The recoil implanted oxygen atoms segregate at initially nucleated dislocations up to an incubation period. Beyond this incubation time oxygen precipitation starts, ejecting silicon interstitials and enhancing the diffusion of boron as that of directly implanted boron in silicon [1-3]. On the other hand, BF 2 implantation has been demonstrated very effective in forming narrow bases for high speed silicon bipolar devices [4) and also been applied on the P÷ polysilicon-gate MOSFET's as a diffusion source for gate dielectrics [5]. The common reason is based upon shallower junction formation, the advantages of fluorine in enhancing hot electron immunity and reducing interface trap density, and improvement of junction leakage. The introduction of fluorine into silicon has been shown to be effective in suppressing "incubated enhanced" boron diffusion [6]. Fluorine is effective in suppressing silicon interstitials only when it is incorporated in the SiO2 , and the silicon interstitials are a consequence of growth of oxide or precipitates. From our studies, fluorine enhances oxidation rate [7,8], reduces oxidation-induced stacking faults [9], retards oxidation-enhanced boron diffusion [10]. It is believed that the reaction of fluorine at Si0 2/Si interface results in increasing vacancy flux and depletion of silicon interstitials. Therefore, the interaction of boron-silicon interstitial is limited, which is responsible for the elimination of "incubated enhanced" diffusion. In this paper, we examined several possible approaches to introduce fluorine into silicon through a screen oxide. Correlated spreading resistance profiles and microstructure data suggest that a comparable dopant profile can be achieved by implanting boron through a fluorinated-oxide (F-ox). Furthermore, it is possible to totally eliminate the transient diffusion of boron by dua
Data Loading...
