Tem Observation of the Damages in Heavily Ion-Implanted Fine Si Columns
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ABSTRACT Si nanometer structures are promising for exhibiting the quantum size effect at temperatures even as high as a room temperature. The present work investigates by TEM the damages induced by a heavy ion-implantation to the fine Si columns, aim of fabrication of 1-D tunneling PN diode in Si columns are fabricated by electron beam lithography and reactive ion etching, future. followed by thinning by thermal oxidation of Si. Ultra fine Si column with a diameter of 8 nm are successfully formed. TEM lattice image observations for fine Si columns, which are subject to ion-implantation and subsequent annealing, are carried out. In the case of heavy doping of As, as well as BF2, as-doped structure is amorphous, and recrystallization is observed after annealing Typical damages such as dislocations which are parallel to the {1111} at 1000 *(C for 30 min. planes and Si micro-crystals which are differently oriented from the Si single crystal substrate are However, it should be noted that observed for Si columns with diameters larger than 40nm. no damage is observed for fine Si columns with diameters less than 20nm. It is suggested that defects are diffused out to the surface or the Si/SiO2 interface for ultra fine Si columns during annealing.
INTRODUCTION Si nanometer structures are promising for exhibiting the quantum size effect at It is of great interest to fabricate one temperatures even as high as a room temperature. dimensional PN junction which is embedded in a fine Si quantum wire, since there is a possibility of the direct electron tunneling between one dimensional (l-D) sub bands across P and N regions. Though there have been numerous works of low dimensional electron gases which are obtained in an inversion layer or a heterostructure interface [1,2], it should be noted that the 1-D PN junction can be obtained only by thinning of a semiconductor into a nano meter wire. Further, in order to realize a tunneling effect across a depletion layer in 1-D PN diode, a depletion layer width must be less than 10nm, and heavy doping of impurities are necessary. Fine Si columns with a few nanometer diameter have been successfully fabricated recently by the combination of the anisotropic dry etching and the subsequent isotropical thinning by oxidation or chemical etching [3,4]. The interesting point is that these fine column are easy to be observed by TEM (transmission electron microscopy) observations. Since heavy doping of impurities is a crucial point in fabricating 1-D tunneling PN diode, which is the same situation as the shallow junction formation in Si sub-micron meter devices [5], evaluation of the implanted damages is essential. The aim of the present work is to evaluate damages which are introduced by heavy ion implantation in fine Si columns, by TEM, and to obtain optimal conditions for the maximum doping with the least damage. 641 Mat. Res. Soc. Symp. Proc. Vol. 3540©1995 Materials Research Society
FABRICATION
OF FINE SI COLUMNS
At first, silicon dioxide (SiO2) with 200 nm thickness is deposited by APCVD (atm
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