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Investigation of Optical Probe Techniques for Interface Characterisation

Objective

In the foreseeable future most microelectronic semiconductor materials for IT devices will be produced by thin-film growth techniques under vacuum conditions and from gas, liquid and solid processes. Perfecting the thin-layer interface is very important in making possible higher quality device performance.
This Action has developed a new field of surface and interface characterisation called "epioptics". This has submonolayer resolution and is accurate enough to distinguish single atomic layers of crystals. Epioptics, using light as both probe and signal, enables growth to be characterised in situ and, uniquely, in all growth environments.
New techniques for determining the properties of materials used in information technology devices have been developed. Light is used both as a probe and a signal (epioptics) and extremely high resolution can be obtained. In contrast to existing techniques, epioptics can be used in situ, while growing the crystals, in all the environments employed for this purpose. Applying epioptics to various processes provides new insights into the growth mechanisms involved, thus increasing yield and quality.

The project has shown that light can indeed be used to characterize surface and interface structure, with submonolayer resolution, due to advances in instrumental design, symmetry rules which forbid bulk response, and the discovery of strong, resonant surface contributions at particular wavelengths of light. Carefully chosen systems, which have been thoroughly characterized by conventional surface probes, have been used to establish the credibility of the new techniques from both an experimental and theoretical viewpoint.

Reflection anisotropy spectroscopy (RAS) has been shown to be the most promising all optical technique for real time growth monitoring on commercial reactors. At the end of the project the growth of indium arsenic on gallium arsenic in an molecular beam epitaxy (MBE) growth reactor was monitored layer by layer, in situ, in real time. An additional spin off from the project was that RAS was show to provide a quick and easy method for checking silicon wafer orientation.
APPROACH AND METHODS
Epitaxial layers, including As, Ga, GaAs and Sb were grown on silicon substrates by molecular beam epitaxy (MBE), and As and GaAs by photo-enhanced metal organic vapour phase epitaxy (photo-MOVPE). The material was extensively characterised using conventional techniques. A number of purely optical techniques providing complementary information were then used to investigate and characterise the surface and interface of the material with submonolayer resolution in situ. The techniques used were polarisation-dependent reflectivity (spectroscopic ellipsometry, reflection difference spectroscopy and reflection anisotropy), Raman spectroscopy, laser-induced fluorescence and optical second harmonic generation.
A strong cooperative theoretical effort underpinned the experimental work. The Action involved experts in the field of epitaxial growth, materials characterisation by optical techniques, and the theory of the optical response of interfaces.
PROGRESS AND RESULTS
This Action has shown that light can indeed be used to characterise surface and interface structure, with sub-monolayer resolution, due to advances in instrumental design, symmetry rules which forbid bulk response, and the discovery of strong, resonant surface contributions at particular wavelengths of light. Carefully chosen systems, which have been thoroughly characterised by conventional surface probes, have been used to establish the credibility of the new techniques from both an experimental and theoretical viewpoint.
Reflection anisotropy spectroscopy (RAS) has been shown to be the most promising all-optical technique for real-time growth monitorig on commercial reactors. At the end of the Action the growth of InAs on GaAs(100) in an MBE growth reactor was monitored layer-by-layer, in situ, in real time. An additional spin-off from the Action was that RAS was shown to provide a quick and easy method for checking Si wafer orientation (Siemens-TU Berlin joint patent P4127704.4).
POTENTIAL
This Action has demonstrated the feasibility of using optical probes to monitor growth of thin-film IT materials with submonolayer resolution in situ and under all growth conditions. Implementation of these new characterisation techniques should result inimproved materials and higher yields for the fabrication of future IT semiconductor devices.

Coordinator

University of Dublin
Address
Trinity College
Dublin 2
Ireland

Participants (6)

Defence Research Agency (DRA)
United Kingdom
Address
St Andrews Road
WR14 3PS Malvern
TECHNISCHE UNIVERSITÄT BERLIN
Germany
Address
Straße Des 17 Juni 135
10623 Berlin
THE UNIVERSITY OF LIVERPOOL
United Kingdom
Address
Oxford Street
L69 7ZE Liverpool
University of Wales, Cardiff
United Kingdom
Address

CF1 1XL Cardiff
Università degli Studi di Messina
Italy
Address
Salita Sperone 31
98166 Sant'agata Di Messina
Università degli Studi di Roma Tor Vergata
Italy
Address
Via Orazio Raimondo 1
00173 Roma