Details of Grant 

EPSRC Reference:	GR/H43106/01
Title:	NANOLITHOGRAPHY WITH SILICON OXIDE LAYERS
Principal Investigator:	Broers, Lord A
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department:	Engineering
Organisation:	University of Cambridge
Scheme:	Standard Research (Pre-FEC)
Starts:	31 July 1992	Ends:	30 July 1995	Value (£):	142,587
EPSRC Research Topic Classifications:	Materials Processing
EPSRC Industrial Sector Classifications:
Related Grants:
Panel History:
Summary on Grant Application Form
To use our capability in ultra-high resolution nanofabrication to develop the full potential of directly patterned SiO2 for fabricating devices with dimensions of 10 nm and below. To build a reactive ion etcher specifically for nanostructure etching, and apply it to the investigation of silicon oxide dry development and pattern transfer processes. To examine the exposure mechanism(s) involved in the exposure process of SiO2 by direct electron beam irradiation, and consequently to understand the source of resolution limits of this process.Progress:During the early stages of the project, a heating stage was fitted to the high resolution electron beam fabrication system and experiments completed in which arrays of lines with a centre to centre spacing of 10.8 nm were resolved. This is the highest resolution achieved with the SiO2 process and, to the best of our knowledge, is the highest resolution produced in a material of practicable value for device fabrication. As part of our earlier work to develop the potential of silicon oxide as a practical nanometer scale resist, we have built an etcher that was specifically designed for nanostructure etching. Samples are etched using a reactive plasma generated by an electron cyclotron resonance (ECR) plasma source. This type of plasma source is able to deliver a collimated stream of low energy ions and reactive species to the sample, so allowing highly selective and anisotropic etching of samples with nanometer scale masks. Following characterisation of the equipment using Langmuir probes, differentially pumped mass spectrometry and etch rate measurements, the etcher has been used to etch silicon samples masked by thin oxide layers. At first, it was found that the system was very sensitive to contamination by water vapour. This contamination resulted in uncontrolled etch rates and the formation of silicon oxide deposits on samples. The problem was solved by careful elimination of water vapour from the process. To achieve this we introduced samples through a load lock and optimised the process gas purity. Subsequently, a process using a plasma of argon and SF6 gas was developed that etched silicon anisotropically with a selectivity of over 15:1 with respect to silicon oxide. The process has been used to etch silicon wires with a width and spacing of 100 nm and a depth of 300 nm. These structures were masked by 20 nm thick silicon oxide, thermally grown. An important feature of the recipe that is made possible by the use of an ECR plasma is the low ion energy (20 eV) used: The use of low energy ions decreases the etching induced damage in resulting nanostructures. Further experiments are underway to investigate the characteristics of dry development of electron beam exposed silicon oxide. The conditions in the etcher allow anisotropic etching in the absence of physical sputtering, and will allow us to maximise any chemical selectivity between exposed and unexposed silicon oxide. The aim is to exceed the selectivity of 3:1 currently found during development by wet etching while maintaining the high resolution previously found.
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