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Laser assisted chemical micro-machining and replication


A workstation for the hot embossing of microstructures into polymers together with the necessary technology has been developed. Different approaches for the heating/cooling system, for the alignment of upper and lower tool as well as technology changes have been investigated. Finally, the cycle time for an average micro embossing process has been reduced from approximately 30 minutes down to 5 minutes. Some standard processes for different materials have been developed, allowing an easy adaptation to different designs to be embossed. The achieved alignment accuracy is sufficient for the most applications. Several developed features and tools, e.g. de-embossing aid, anti sticking pre-treatment, proved to simplify the process and to enhance the reliability and accuracy of the technology.
A gas reaction cell has been developed that will allow UV laser photochemical surface processing to take place. The substrate is mounted on a heated chuck and the reaction gas flowed over the surface via a nozzle. A second nozzle delivers a shield gas to protect the cell window. The cell is mounted on XY stages and the system is designed to have full movement under vacuum and partial pressure. The base vacuum is 10{-6}torr. The cell has applications in laser processing, but the design has relevance to any high vacuum system that requires XY stage movement. The cell has been commissioned and tested.
A high resolution lens images the required patterns on a photo-mask plate onto the workpiece inside the gas reaction cell. The lens should be designed for use with 193 nm wavelength, be achromatised and telecentric, and suitable for use with beam homogenisers and for the fluences required by the photochemical etching process. Moreover, the lens needs to be corrected for imaging through the quartz window that separates the gas process cell environment from the outside world. Two designs have been produced. Both have a numerical aperture of 0.25, and one has an image field size of 2.5mm diameter and the other has an image field of 12mm diameter. Both designs are currently undergoing detailed tests in ray-tracing software before the decision is taken with which design to proceed with fabrication. These lenses have wider applications than just gas phase laser chemical etching; such as direct 193nm laser ablation. In complexity, both designs approach that of full field lithography lenses used in the semiconductor industry, and their use for laser industrial processing is new.
The diffractive connector is a patented architecture that associates a diffractive optical element and a MT connector for various applications. In the LAMAR project, the aim is the connectorisation of opto-electronic interconnect modules that ensure the integrity of optical data transmission over the largest possible distance when light is coming out of the fibber ribbon. Other applications are possible since modifying the optical function encoded by the DOE is independent on the architecture and assembly. Implementation of a specific function for each single voice of the fibber ribbon is also possible.
The software is aimed at diffractive optical elements (DOEs) calculation and simulation. It is based on a Gerchberg-Saxton algorithm for phase calculation of multi-surface levels planar diffractive elements. It is a fast-converging iterative algorithm relying on successive Fast Fourier Transforms. An additional module allows DOEs simulation with different variable parameters (for example type of incoming wavefront) or different DOEs description (imbedding, multiplexing, oversampling of DOEs). The software is graphically interfaced for windows environment.
The potential of the usability of a micro gripper depends significantly on the material and surface quality that its tip consists of. Current models fabricated by Bartels Mikrotechnik already make the use of Nickel-Titanium, but they still suffer from certain problems due to insufficient surface quality and heat inducement. By using a novel process, it is expected that these process problems will be eliminated. The surface quality of the gripper tip is expected to be greatly enhanced, so that it can be used in a wide variety of applications (from assembly to minimally invasive surgery). Also, the fabrication time is expected to be comparable to other processes (such as wire erosion). At this time, a partner is fabricating a simple test structure, so that the impact can be quantified more easily. Studies of the surface quality and a comparison of fabrication techniques, regarding the former situation, have been produced. We expect to open up markets especially in the medical sector, as well as the possibility of developing other products on the base of good surface micromachined NiTi-samples.
A liquid phase etching process has been developed and optimised for laser thermochemical surface processing of metals and metallic alloys. Novel etchants using compositions of different acids with addition of metallic salts were developed to enhance the process with respect to speed and quality of machining. As a technological relevant demonstration, temperature sensitive superelastic NiTi alloys were machined with high quality, i.e. low thermal and mechanical loading of the structured part as well as a treatment without debris and low surface roughness, using a cw Nd:YAG laser. The achieved surface roughness was less than 0.3µm and the cutting angle less than 3 degrees obtained in foils of at least 200µm thickness. The development of the laser-assisted liquid phase etching process broadens the technical potential and contributes to the dissemination of this new technology. The flexible and direct micromachining with high precision and low costs of equipment offers the possibility for an economic fabrication of prototypes or small series production of metallic microparts even for SMEs. These results can be applied for new products or enhance the quality of existing products.
Paper designs for RF inductors making use of high aspect ratio conductors have been produced. These designs have been produced as a result of a design study conducted using analytical design equation and numerical simulation tools. Currently these designs have been circulated to the other partners responsible for their fabrication. RF inductors find application in almost all of today's wireless communications equipment, such as cellular phones, pagers, wireless LAN, GPS systems etc. The end users for these components are therefore likely to be component manufacturers or wireless communication equipment manufacturers. The main requirements for components used in these applications are small size, high quality factor, tight tolerance, and high operating frequencies. Currently most RF inductors are fabricated using one of four technologies, wire winding, multi-layer ceramic, thin film, or the recently introduced laser patterning. In general wire wound inductors offer the highest quality factors, but tight tolerance is achieved by screening of the components. In contrast to this thin film technology can produce tight tolerance components, but the inductance achievable in any chip size is more limited. High aspect ration inductors fabricated using the LAMAR process should hopefully offer the tight tolerance of this film technology. Also the results of this design study for the high aspect ratio inductors predict that the quality factor of the high aspect ratio inductors are 20-30% greater than those of commercially available thin film inductors and therefore match the Q-factors achievable from wire-wound inductors. Potential Barriers to the adoption of component fabricated using the LAMAR process include: - The tolerance achievable (tolerances of better that 2% on the inductance value are required). - Increasing trend towards the integration of inductors on chip and hence the elimination of the discrete component.
A liquid phase etching cell has been developed for laser thermochemical surface processing. The cell consists of two parts, a co-axial nozzle assembly and a basin, which are connected to each other by means of elastomer bellows. The nozzle can be adjusted laterally and in height with respect to the laser beam focus. The etch liquid enters the nozzle tip, which can easily be replaced, in such a way that a swirl is given the liquid flow, and also such that the flowing liquid into the nozzle does not intersect the laser beam directly. The basin holds the workpiece, submerged into the etch liquid the level of which in the basin can be controlled. The basin is mounted onto x-y-z stages allowing a relative movement of the nozzle over a 100x100mm² area to position the workpiece with respect to the laser beam. The cell has applications in laser processing, wherever a co-axial injection of reactive or non-reactive liquids with respect to the laser beam directly into the laser irradiated area is required. The advantages are found to be constant flow rates over large processing areas, efficient mass transport and cooling leading to better quality and reproducibility.
A halftone mask has been manufactured for the ablation and etching of diffractive optical elements. Half-tone mask technology makes use of sub-diffraction limit features in the mask in order to produce genuine grey-scale levels in the exposure intensity, resulting in a varying ablation depth controlled by the grey-level. This technique can be used in the production of microstructures where different ablation depth in different positions is required. The advantage is that one mask can produce the complete component, rather that a set of masks which will have to be overlaid with very high precision. Apart from diffractive optical elements, the technology has a much wider potential use in excimer laser ablation of microstructures varying depth.