Highlights

The use of synchrotron radiation deep lithography or deep X-ray lithography has become a powerful tool for advanced fabrication in the last three decades. Most notably, it has been applied to micro/nanofabrication. Deep X-ray lithography has the advantage of producing large areas filled with fine patterns in combination with tall structures as compared to optical or deep ultraviolet (DUV) lithography which is the current commercial method for micro/nanofabrication, in particular, in the field of semiconductor manufacturing. Currently, micro/nanofabrication using deep X-ray lithography is aimed at fields such as micromechanics, biotechnology, X-ray optics and micro-optics.

Owing to the strong concentration of high-tech industry combined with the high level of scientific research and education, Singapore is conducive for the development of synchrotron radiation applications. The Singapore Synchrotron Light Source (SSLS), headed by Professor Herbert Moser of the Department of Physics, offers a user facility providing synchrotron radiation services. SSLS expertise in the production of high-aspect-ratio (structures that are much taller than wide) plastic moulds through the method of synchrotron radiation deep lithography has not gone unnoticed. In fact, SSLS is the only centre in Asia to have been contracted by Micromotion GmbH, a German high-tech company, to be one of its privileged plastic moulds suppliers.

In explaining the choice of Singapore, Dr Udo Kirsch, Head of Microstructuring at Micromotion, said that SSLS was selected because it can produce the high-aspect-ratio plastic micro moulds in both high quality and large quantity.

Micromotion, located at Mainz-Gonsenheim near Frankfurt in Germany, is specialised in the development and manufacture of microgears and microactuators using the Micro Harmonic Drive principle. The Micro Harmonic Drive is suited for precision positioning applications in a wide range of compact machines and portable devices. The products offer a new generation of miniaturised products in a wide range of application areas such as semiconductor manufacturing, medical equipment, automation, optical communication and laser technology.

Besides synchrotron radiation deep lithography, technology developed by SSLS has applications in many other fields -- including the assessment of structure, geometry and chemistry of materials. For instance, SSLS was commissioned by an art connoisseur to evaluate a Thai Buddha statue. Using X-ray fluorescence spectroscopy, it was shown that the top was made of brass while the body was made of bronze. Traditional methods of analysing the statue would have damaged the artefact.

Another area of expertise of SSLS includes the Infrared Spectro/Microscopy beamline (ISMI) which involves the study of molecules, low energy electron excitations in solids and electromagnetic metamaterials. Commissioned by the Prime Ministers Office in collaboration with the Singapore Police Force, SSLS used ISMI to determine the nature of explosives after an explosion had occurred. The ISMI offers a non-destructive means of analysing explosives residues to establish, within two hours, the type of explosives used.

SSLS has also collaborated with industry partners like Chartered Semiconductor, Sony Singapore as well as ST Microelectronics.

SSLS has made its first X-ray proximity lithography exposures at the LiMiNT beam line using a test mask provided by SSLS' strategic partner CAMD, Baton Rouge, Louisiana. LiMiNT stands for Lithography for Micro- and Nanotechnology. Beam line and scanner were delivered and installed by Oxford Danfysik in December 2001. The full white spectrum of Helios 2 is used, only filtered by two Be windows of total thickness of 400 µm. There are no mirrors in the beam line. The useful spectral flux at the sample covers a bandwidth from 2 to 10 keV delivering a power of 0.9 W to the 4" wafer at an electron current of 300 mA.
The picture shows various cylindrical test devices made in 200 µm high SU-8 resist. Aspect ratio is up to 50.
SSLS is working with groups from local and overseas universities and institutes as well as industry on several projects in the fields of biotechnology, polymer processing, X-ray and microoptics, and microfluidics.

The 3rd International Conference on Synchrotron Radiation in Materials Science (SRMS-3) was hosted and organised by SSLS from 21 to 24 January 2002 in Singapore. 190 participants from 24 countries and 4 continents gathered in the Shangri-La Hotel to present 170 papers, 30 of them invited. The broad range of topics covered was another demonstration of the almost ubiquitous use of synchrotron radiation methods. It spanned from high-energy diffraction to far infrared spectroscopy, from magnetic scattering to industrial applications, from the latest on 3rd generation storage ring sources to X-ray Free Electron laser projects, and from large to small storage rings. Synchrotron radiation based materials science is obviously in good shape.

Using the Phase Contrast Imaging beam line at SSLS a group lead by Dr. Yeukuang Hwu of Academia Sinica, Taiwan, has produced first images of various samples including insects, plants, and foodstuff. The beam line provides the white spectrum of Helios 2 (characteristic photon energy 1.5 keV) filtered by a Be window of 400 µm thickness. On passing through the sample the spatial intensity distribution of the X-ray beam over its cross section is modulated. X-rays are then converted to visible light by a scintillator foil and recorded by means of a high-resolution CCD camera. The picture shows a local insect.
SSLS is developing the PCI facility to deliver time-resolved microscopic images of the bulk of samples that are sufficiently transparent for the up to 10 keV photons of Helios 2. Current areas of interest are the medical and biosciences, microtechnology, polymer processing, and food science and technology.

SSLS received a new grant from Science and Engineering Research Council (SERC), National Science and Technology Board (NSTB).

- build a new beam line for infrared spectro/microscopy,
- set up process equipment needed for micro/nano manufacturing and
- cover for the infrastructure embedding beam lines and experimental systems.

This will go a long way in speeding up research and development at SSLS significantly.