Ion Implantation and Ion Beam Analysis
Ion Implantation and Ion Beam Analysis
Ion Implantation
With more than twenty years experience in the field of ion
implantation we offer a very wide range of services. Now acknowledged as a European
Centre of Excellence, the Central Facility was originally formed in 1978 by the then
Science Research Council. The Facility's primary task was to support research in the
U.K. investigating applications of ion beams to semiconductor processing. Since that
time the S.E.R.C. has awarded over 100 full grants to users of the Facility.

(Right) 0.2mA beam of argon
being deflected into the beam line. Doubly charged and neutral beams are faintly
visible. Flourescence was obtained by a deliberately poor vacuum.
Current research includes ion beam synthesis of compounds, control of implantation
profiles by multiple ion implants and ion beam mixing of quantum wells for the
fabrication of opto-electronic devices. We were the first to use rapid thermal
annealing for dopant activation in ion implanted GaAs, and have also been closely
involved with the development of SIMOX material, a oxide produced by implanting oxygen
into silicon. Our new 2MV implanter will support growing interest in deep device
structures in both silicon and III-V technology.
Processing
Rapid Thermal Annealing was developed at Surrey in the mid
seventies and forms a basis for thermal treatment of samples after implantation. A
newly installed R.T.A. furnace also capable of 1300 C for 6 hours can be seen. Such
systems are complemented by more conventional flow furnaces and encapsulation systems
for use with III-V materials. A PECVD rig for depositing silicon nitride encapsulants
can be seen.
Multi-target sputtering (DC or RF) and evaporation systems are available for the
deposition of thin films, with ellipsometry and Talystep available for thickness
measurements.
Electrical and optical equipment is available to measure Hall effect, CV, IV and
photoluminescence spectra at temperatures from 4K to 500K. Stripping Hall effect and
CV are also available to provide depth resolved carrier concentration and mobility
profiles, with a four point probe wafer mapper available for assessing process
uniformity.
To provide the Facility for either selective area implantation or pilot device
fabrication, photolithography and wet and dry processing are available in house, for
dimensions down to one micron. Probe stations for testing completed devices are also
available.
Ion Beam Analysis
Rutherford backscattering is a powerful method of depth
profiling of sub-micron films. High energy light ion beams are used. The information
is in the energy of particles scattered in backward direction. The required dose is
quite small and does little damage to most samples. With channelling the beam
can be aligned on a single crystal to give a depth profile of disorder and strain.

The example shown is of a metal bilayer being
investigated for use as an ohmic contact resistant to high temperatures. 1.5MeV He+
RBS data taking 5 mins to collect after annealing at 350 C. Box shows unannealed
structure.
Various related techniques can often be used simultaneously with RBS. Trace element
analysis is available by detecting the characteristic X-rays. Good lateral resolution
down to 0.01 mm is obtainable with the microbeam. Light elements can often be detected
with nuclear reactions, and hydrogen can be detected in a forward scattering geometry.

Elemental depth profile calculated from the raw data
above using the data reduction program SQUEAKIE.
Use Ion Beam Analysis to charaterise your thin films.
Simulation of Ion Implantation
Many computer simulation packages are
available for the calculation of ion implantation effects, from implantation range
profiles to full cascade calculations. Different calculation techniques can be
employed. Analytical calculations are used in SUSPRE and Monte Carlo trajectory
simulations in TRIM and CRYSTAL. Many body calculations, using full many body
potentials, are used in Molecular Dynamics programs to study low energy implantation.

Monte Carlo cascade simulation of 11 separated
ion impacts for 150 keV Arsenic implantation into a silicon substrate. Different
colours represent different recoil generations. The edge of the box is 250nm.

A full Molecular Dynamics simulation of a 200 eV
copper ion cascade in a copper target. The cascade is shown at different times as the
energy is dissipated through the target. Colours represent increasing particle
energies - white, red, green, blue.
Details of Accelerator Facilities Available
Implantation
There are three implanters giving range of currents,
energies and ions: - 50-500 kV general purpose implanter, 20 years old but much
modified. Usually delivers beam current of a few uA
- 35-350 kV medium current (<mA) implanter, use restricted to ion beam
synthesis.
- 500-2000 kV Van de Graaff HVE implanter installed in 1991. Air lock
source exchange mechanism for rapid operation.
Doubly charged species are often available giving implantation energies up to 4 MV
with reduced beam current.
Very flexible sample handling, including whole wafers, as available at various
implantation temperatures.

Ion Beam Analysis
There is a 2 MV Van de Graaff accelerator with several beam
lines and various techniques available often simultaneously:
- Rutherford backscattering for rapid elemental depth profiling. RBS
is most sensitive to high mass elements in a low mass matrix. Light elements are often
accessible to analysis by RBS with lower sensitivity. Non-Rutherford elastic
scattering or nuclear reaction analysis (NRA) for selected elements give higher
sensitivity. Diffused deuterium profiles in polymers down to about 10um are obtained
with a 3He+ beam, for example. Hydrogen can be analysed by elastic recoil detection
(ERD) in a forward scattering geometry.
- Channelling for damage analysis in single crystals. Angular scans
in various crystal directions give information on impurity location.
- Particle Induced X-ray Emission (PIXE) for trace element analysis.
Comparable to electron microprobe, but with better sensitivity.
- Microbeam analysis giving 3D multiple elemental maps down to 10um
lateral resolution.
- High Resolution Depth Profiling using glancing entrance or exit
geometry to give surface depth resolution better than 5nm.
Processing
Dielectric/metals deposition, annealing including RTP, optical and
electrical characterisation, lithography, wet & dry etching.
C.Jeynes@ee.surrey.ac.uk - Facility Liason
B.Sealy@ee.surrey.ac.uk - Research group leader
30th May, 1995