The fabrication of arrays of single ions in silicon via ion implantation

245 Pages·2014·12.81 MB·English

The fabrication of arrays of single ions in silicon
via ion implantation
Jessica van Donkelaar
Submitted in total fulfillment of the requirements of the degree
of Doctor of Philosophy
February 2014
School of Physics, Faculty of Science
The University of Melbourne

Abstract
Conventional computers are approaching fabrication limits where statistical
variation in the placement of single dopants greatly impacts device perfor-
mance. Additionally, practical modelling of more than a handful of atoms
while accounting for quantum properties can only be performed with a quan-
tum computer. Fabricating a solid state Si:P Kane architecture will require
deterministic doping; the ability to accurately place dopants within a sub-
strate.
We have implemented an apparatus for creating arrays of single P donor atoms
within Si. We model the fabrication of a three-donor device for demonstrat-
ing the coherent transfer by adiabatic passage transfer (CTAP) protocol and
show that it can be done with deterministic ion implantation through a 20nm
nanostencil stepped 30nm between implants to produce a yield of 1-in-7 well
placed arrays.
Single ion implantation is an established method of device fabrication that
involves detecting single 14keV P+ ions entering a substrate via the charge
induced as the ion collides with the lattice. We have tested various designs
for the single ion detector to evaluate the sources of good performance and
achieved 98 4% counting efficiency with the classic design in high purity sil-
±
icon.
We have fabricated 200nm think Si N nanostencils with slot and hole shaped
3 4
apertures as small as 20nm using the focusssed ion beam (FIB) technique of
0.0.0
back filling larger apertures with Pt. These adequately mask a 14keV P+ ion
to define the implant site.
We have built apparatus that employs a piezo-positioner to move the nanos-
tencil above the surface of a single ion detector. This system is LN cooled
2
within a high vacuum to implement deterministic doping. The fine alignment
of the nanostencil to the implant site is performed using the ion impact signals
as feedback over a patterned area of the detector and we have demonstrated
this concept to a precision of sub-100nm.
Declaration
This is to certify that:
1. The thesis comprises only my original work towards the PhD except
where indicated.
2. Due acknowledgment has been made in the text to all other material
used.
3. The thesis is less than 100,000 words in length, exclusive of tables, bib-
liographies, appendices and footnotes.
Jessica van Donkelaar

Preface
The Si substrate detectors we employ for single ion implantation are fabri-
cated at the Semiconductor Nanofabrication Facility (SNF) at the University
of New South Wales (UNSW) as a collaboration between nodes of the Centre
for Quantum Computer Technology (CQCT). The detectors produced during
the course of this work in particular were fabricated primarily by Nai Shyan
Lai and Fay Hudson.
PostdoctoralfellowAndrewAlvescollaboratedindesigningtheapparatusand
worked with me to get the MeV IBIC data of section 3.0.9 and the shadow
mask implants of section 5.2.

Acknowledgments
I would like to thank the many people who provided both technical assistance
and moral support during my PhD project. My sincere thanks go to Roland
Szymanski for showing me the inner workings of the pelletron and to Alberto
Cimmino similarly laying bare the colutron. I am grateful to Sergey Rubanov
for the training of the FIB/SEM system and assistance with the TEM. Thank
you Andy Greentree for CTAP advice, to Changyi Yang for all his invaluable
help in the lab and to Andrew Alves for working with me.
Thank you to my supervisor David Jamieson for his enthusiasm and attentive
guidance over the years.
And finally, thanks go to my family and friends for their support, especially
my parents Meryl & Patrick van Donkelaar and my husband David Perry.