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Maskless implants of 20 keV Ga+ in thin crystalline silicon on insulator
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Image of FIG. 1.
FIG. 1.

TEM cross section micrograph of the sample before implantation. Silicon overlayer was thinned from 85 nm to 26 nm by dry oxidation at 1000 °C and subsequent wet etching.

Image of FIG. 2.
FIG. 2.

(a) Damage distribution, in terms of displacements per atom, produced by a 20 keV Ga+ beam (single-shot) with a standard deviation of about 5 nm, as computed by Monte Carlo simulation; (b) multi-shot pattern performed by Raith ionLiNE for a 20 nm diameter dot. To implant the whole region 27 single-shots are delivered. They are distributed along concentric circles of 20 nm (16 shots), 12 nm (9 shots) and 4 nm (2 shots) diameter, respectively.

Image of FIG. 3.
FIG. 3.

TEM micrographs, plan-views, of (a) a single-shot (145 ions) pattern and (b) a single-shot magnification. Damage is associated to the white spots.

Image of FIG. 4.
FIG. 4.

Monte Carlo simulations of 20 keV Ga+ ion trajectories in a silicon matrix, projected on the surface of the irradiated sample. Simulation has been performed using the SRIM code. The thick red lines indicate the ion paths, where the dotted green lines refer to the trajectories of the primary, secondary, tertiary, etc., knock-on substrate atoms.

Image of FIG. 5.
FIG. 5.

(a) Bidimensional DPA distribution for a 20 nm-5 × 1014 ions/cm2 implanted region and (b) its relative cut-line (y = 0). The plot reports all the displacements occurred along the 26 nm film thickness.

Image of FIG. 6.
FIG. 6.

(a) Plan-view TEM micrograph of a 20 nm-5 × 1014 ions/cm2 implanted region and (b) the relative simulated equi-damage contour plots overlapped to it. According to the simulation the region in which the displacements per atom are higher than 0.3 (dashed light blue line), i.e., the theoretical lower limit for the formation of an amorphous region, is roughly a circle of 32 nm diameter, correspondent to the area where the TEM contrast is bright and quite uniform.

Image of FIG. 7.
FIG. 7.

HRTEM of a 20 nm nominal diameter area implanted at a dose of 5 × 1014/cm2. Insets show FT calculated in several regions. FT indicates the presence of an amorphous region (fuzzy rings in FT at the center of the dot), extending about 30 nm. In the near contiguous zones, some diffraction spots appear indicating the presence of still crystalline regions embedded in amorphous material.

Image of FIG. 8.
FIG. 8.

TEM micrographs of 50 nm nominal diameter dots implanted at a dose of (a) 3 × 1014 ions/cm2 and (b) 5 × 1014 ions/cm2.

Image of FIG. 9.
FIG. 9.

TEM micrographs of a 50 nm dot implanted at the dose of 3 × 1014 ions/cm2, (a) before and (b) after in situ 4 min of heating at 470 °C. Thermal process anneals out the very lateral filamentary disordered regions and the damaged area becomes more regular in shape.

Image of FIG. 10.
FIG. 10.

(a) TEM micrographs of 50 nm diameter dot, implanted at a dose of 3 × 1014 ions/cm2, annealed at 500 °C for 24 min. With respect to Fig. 9(a) , further annealing causes only a small reduction in diameter, the interface with the surrounded single crystal becomes sharper with a clear evidence of the formation of straight lines corresponding to (100) and (110) planes, as shown by (b) the selected area diffraction of (a).

Image of FIG. 11.
FIG. 11.

(a) Selected area diffraction pattern of a recrystallized spot, 50 nm in diameter implanted with a dose of 3 × 1014 ions/cm2, characterized by the extra spots associated to the twins (light blue dotted circles); (b) dark field image obtained with the diffraction beam of the twin indicated by the arrow.

Image of FIG. 12.
FIG. 12.

Typical TEM micrograph of a 50 nm dot, implanted at a dose of 5 × 1014 ions/cm2, after a rapid thermal annealing at 890 °C for 10 s.

Image of FIG. 13.
FIG. 13.

(a) The derivate of the capacitance with respect to the applied voltage, dC/dV, as a function of the position on the sample surface for a 50 nm array implanted at a dose of 3 × 1014 ions/cm2 and annealed at 580 °C. (b) A line scan of (a) along a [110] direction. Line scan shows that high differential capacitance regions are typically located at a distance of 430 nm, very close to the pattern step.


Generic image for table
Table I.

Nano-focused ion beam Raith ionLiNE parameters used to perform dot implantation. Each shot was provided by a Ga+ ion beam, with about 5 nm standard deviation.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Maskless implants of 20 keV Ga+ in thin crystalline silicon on insulator