Graham G. Arthur

Development and characterization of nitride and oxide based composite materials for sub 0.18 mm attenuated phase shift masking

Abstract Results are presented from investigations into the UV properties of various oxide, nitride, and intermetallic materials for application as attenuated phase shift masking films for 248 and 193 nm wavelengths. There are several materials which are potential candidates as attenuating phase shifting films at short UV wavelengths. None of these, however, are elemental films or stoichiometric compounds. Non-stoichiometric alloys, cermets, and composite materials do though allow for phase shift mask solutions. Through modeling of free electron and bound electron behavior of metals, dielectrics, and semiconductors, predications can be made about the optical properties of their combinations. By adjusting the material stoichiometry through control of sputter deposition parameters, films can be tailored for specific optical applications. Through use of extinction coefficient/refractive index plots ( k-n plots), evaluation of phase shifting films is made possible. Details on four classes of materials are presented: a tantalum silicon oxide (TaSiO), an aluminum rich aluminum nitride ( Al AlN ), a molybdenum silicon oxide (MoSiO), and non-stoichiometric silicon nitride (Si x N y ). Attenuated phase shifting films have been produced based on all four classes. Optical properties and RIE etch processes for materials are compared.

The effect of excimer laser etching on thin film diamond

Excimer laser projection patterning with an ArF (193 nm) source has been employed in the irradiation of thin diamond films. The effect of a number of process parameters including laser fluence and processing ambient on the quality of the etch product has been investigated; scanning electron microscopy shows that good control of etch quality may be achieved with excellent lateral reproduction of images down to 2 μm. Raman scattering and Auger electron spectroscopy of irradiated films have been correlated, and modifications in the diamond surface have been quantified according to processing parameters. Electrical tests on laser modified surfaces show that the reactivities of metals have a major role in the performance of contact metallizations on such a material. The viability of excimer laser etching of diamond as a manufacturing technique is considered.

Laser projection patterning for the formation of thin film diamond microstructures

Abstract Projection patterned excimer laser radiation at 193 nm has been used to etch free-standing polycrystalline diamond films. Excellent lateral reproduction of images down to 2 μm has been achieved, but features evolve with a side wall that slopes at around 25 ° to the normal; this limits the depth of each feature in relation to its lateral dimension. However, three-dimensional microgears, with a diameter of 930 μm, have been successfully fabricated using this technique. Patterning in air gives rise to etch rates as high as 31 nm per laser pulse, but in an evacuated environment this is reduced to around 0.6 nm; furthermore, Raman spectra indicate that patterning in vacuo leaves strongly modified surfaces, whilst air processing causes little degradation to the diamond film.

Deep UV optics for excimer laser systems

Abstract The high irradiance at short wavelengths provided by Excimer Lasers has applications in conventional lithography, micromachining and laser chemical processing. In each case a new generation and type of projection optics will be required. In this paper, the problems of lens design in the deep uv for each of the above areas are reviewed. Emphasis is given to the practical designs actually constructed and results achieved at the Rutherford Appleton Laboratory. For some designs, diffraction limited imagery over large fields is shown to be possible. The theoretical and practical work reported here shows that certain catadioptric systems are sufficiently broadband to obviate the need to line-narrow the laser.

LIGA: a fabrication technology for industry?

LIGA is a technology that offers significant advantages where high accuracy, high aspect ratio microstructures are required. The application of LIGA to the manufacture of real products has been delayed by technical problems that exist with the individual process steps and the limited availability of integrated facilities, enabling users to subcontract the complete manufacturing process. These problems have been dominated by the limited availability of high quality masks, long and expensive exposure at synchrotron radiation sources and the electrodeposition of thick stress-free layers. This paper describes the practical solutions developed at the Central Microstructure Facility, RAL, for the key process steps of manufacturing high precision gold-on- beryllium masks, exposure of SU-8 resist using a 2 GeV synchrotron, electrodeposition of deep (

Investigation of photoresist-specific optical proximity effect

GTR 500 mm), stress-free metal layers and resist stripping procedures fro 3 micrometers minimum features up to 500 mm deep on 4-6 inch wafers. A cost model shows that the reduction in the exposure time using SU-8 instead of PMMA resist may enable x-ray LIGA to be cost competitive with other techniques such as uv LIGA, DRIE or direct laser ablation.

Analysing the dissolution characteristics of deep UV chemically amplified photoresist

Abstract Optical proximity effects arising from individual resist characteristics are investigated. The parameters studied are those used in photoresist exposure and development simulation using the SOLID and Prolith/2 programs. The optical proximity effect is found to be independent of the exposure parameters but greatly affected by the development process and is shown to be a function of the Mack parameter, n, which is related to the resist contrast, γ. Finally, in order to put this effect into perspective with other resist selection criteria, the development parameter, n, is also shown to be related to wall angle and depth-of-focus (DOF). The results of this investigation will therefore enable the user to select the most appropriate photoresist for a specific application.

LIGA for Boomerang

Abstract The dissolution characteristics of poly(hydroxystyrene)-based, chemically amplified (CA) photoresists for the deep uv are examined. It is shown that recently reported characteristics1 found in DNQ/novolac-based conventional resists are also present in PHS-based, CA resist, including the so-called development notch and the variation of dissolution characteristics as a function of depth into resist film. Inclusion of these anomalies into the development step of the optical lithography simulator, PROLITH/22, gives improved simulation accuracy. Simulation of CA e-beam resists3 which utilise the same chemistry should also benefit from the improvements described.

Optimization of dielectric antireflective coatings on a transparent substrate in sub-half-micron CMOS technology

Boomerang is a 3GeV synchrotron radiation accelerator, currently being constructed in the State of Victoria, Australia. The outline design of two beamlines, suitable for the fabrication of MEMS devices using the LIGA process, is presented, along with an estimate of the exposure doses throughout the resist. The most commonly used resist is PMMA, which requires a minimum dose of about 4500 J/cm3 for accurate microstructure definition. Exposure with such a dose, in resist thicknesses of several hundred microns, can take hours. Fortunately, SU-8 resist is becoming more widely used as the minimum dosage required is about 35 J/cm3, leading to exposure times of only a few minutes. Although Boomerang will shorten exposure times due to its higher irradiance at the substrate, the full benefits may not be realizable due to excessive resist heating. Heating effects have been simulated and suggest that helium cooling will be essential if the glass transition temperature of the resist (100°C for PMMA, 50°C for SU-8) and thermal distortion of the mask are to be avoided. The parameters chosen in this study of the future performance of Boomerang have been inserted into a cost model. The model shows that Boomerang exposure can become competitive with other exposure methods, particularly where large quantities of devices with deep structures are required.

Swing curve phase and amplitude effects in optical lithography

The optimization of a dielectric anti-reflective coating (ARC) on a transparent substrate with significant topography is described. Supporting theory is provided and although it is not possible to obtain the ultimate performance of an ARC over planar film stacks and flat substrates, the critical dimension (CD) swing ratio is greatly reduced and a manufactureable solution achieved using response surface modeling (RSM) in combination with data generated form the lithography simulation tool, PROLITH/2.