Kevin J. Morris

PMMA as an X-ray resist for micro-machining application: latent image formation and thickness losses

Abstract This paper reports preliminary results of direct observation of a latent image formed in thick PMMA resist after X-ray exposure.

Transfer mask for high-aspect-ratio microlithography

For conventional patterning (optical or x-ray microlithography and micromachining) a mask with a substrate reasonably transparent to desired radiation is used. A new technique - transfer mask or sacrificial patterning - is described in this paper. The technique is based on forming absorber pattern directly on the surface of the sample. This method is suitable for any radiation (visible light, UV, X-rays, electron and ion beams) and allows use of a conventional master masks (optical or x-ray) with low, medium, high (submicron) resolution to achieve patterns with desired aspect ratio. Multiple exposures and sequential developments can produce patterns with extremely high aspect ratio. New lithography techniques, such as in-situ development, UV and x-ray radiation assisted chemistry (etching and deposition), can be easily realized by using this transfer mask technique. Forming the transfer mask directly on the sample opens new possibilities not available with the conventional masks: exposure of samples with curved surfaces and dynamic deformation of the sample surfaces during the exposure, etc.

Multilevel 3D patterning of stacked PMMA sheets for x-ray microlithography

This paper presents a novel technique for fabricating 3D patterns in a thick layered resist and describes an alignment aide designed for the specific application of thick resist x-ray micromachining. In this technique, a PMMA layer of desired thickness is formed on a substrate by spinning or solvent bonding. The layer is exposed with X- rays to generate a latent image. A second layer of PMMA is bonded over the first layer and is exposed with an appropriate mask, generating a latent image in the second layer. This process can be repeated several times creating a 3D latent image. Simultaneous development forms a true 3D pattern in the PMMA resist.

X-ray microlithography exposure system for high aspect ratio micromachining

A new x-ray micro-lithography exposure system has been designed and built at CAMD to meet specific demands of synchrotron radiation assisted high aspect ratio micromachining. The system consists of a broad-band transmission (1.2 angstroms to 6.5 angstroms) beamline and a multi-chamber X-ray Exposure Station. The beam line accepts radiation emitted in a bending magnet of the CAMD 1.3 - 1.5 GeV synchrotron storage ring. The beam line is approximately 10 m long and terminates with 125 micrometers thick Be window which defines an X-ray beam of 50 X 10 mm2 at the exposure plane. The beam line is configured to provide 1.0 W/cm2 at 1.5 GeV and 100 mA storage ring operation. The Exposure Station is designed to control different exposure conditions and can handle a variety of mask/sample assemblies. The first camber of the exposure tool is designated as a radiation filter, it controls x-ray spectra using foils and inert gases, and optimizes dose delivered to a sample with a thick resist (in excess of 1 mm). The second chamber is equipped with a multi-axes scanning mechanism to provide designed orientation and exposure of the mask/sample assembly. The two chamber can be separated by a thin foil to facilitate the use of reactive atmospheres for radiation induced chemical processes during exposure. An expansion of the Exposure Station providing large area exposures (up to 300 X 300 mm2) is described.

Temperature rise in thick PMMA resists during x-ray exposure

Temperature measurements of thick PMMA resist during X-ray (1 to 5 keV) exposure are presented in this paper. Thin metal (gold) film thermal sensors were fabricated directly on the resist surface and on the resist/substrate interface using micro-lithography methods. The temperature measurements were conducted in vacuum (< 10-4 Torr) and in 1 to 25 Torr helium pressure--conditions corresponding to typically X-ray lithography exposure. The results of temperature rise measurements performed with thermal sensors and with miniature conventional thermocouples are compared.

X-ray microfabrication of multi-level structures and 3-D patterning

Abstract Preliminary results of a novel techinique for producing true three-dimensional patterns in thick resits are presented in this work.

A New Tomography Beamline at a Wiggler Port at the Center for Advanced Microstructures and Devices (CAMD) Storage Ring

A new tomography beamline has been built and commissioned at the 7 T wiggler of the CAMD storage ring. This beamline is equipped with two monochromators that can be used interchangeably for X‐ray absorption spectroscopy or high resolution X‐ray tomography, at best 2–3 μm pixel size. The high‐flux double multilayer‐mirror monochromator (W‐B4C multilayers) can be used in the energy range from 6 to 35 keV with a resolution (ΔE/E ) between 0.01–0.03. The second is a channel‐cut Si(311)‐crystal monochromator with a range of 15 to 36 keV and resolution of ca. 10−4, this is not yet tested. Tomography has the potential for high‐throughput materials analysis; however, there are some significant obstacles to be overcome in the areas of data acquisition, reconstruction, visualization and analysis. Data acquisition is facilitated by the multilayer monochromator as this provides high photon flux, thus reducing measurement time. At the beamline, Matlab© routines provide simple x,y,z fly‐throughs of the sample. Off‐beam...

Thin metal film thermal microsensors

Design, fabrication, and testing of thermal micro-sensors suitable for miniature and microscopic systems, for application on thin films (free standing or on substrates) as temperature sensors are presented in this paper. The sensors utilize the electrical resistivity temperature dependence of a metal. Using micro-lithography methods, several sets of gold resistors were fabricated in the form of flat 30 to 250 nm thick wires, 7 - 10 micrometers wide, and several cm long in a serpentine shape covering approximately 1.0 mm2. These sensors have demonstrated better than 0.001 degree(s) C sensitivity. The electrical resistivity and its thermal coefficient of a thin gold metal film were compared with those of bulk material. Temperature measurements on Si wafers were performed in situations corresponding to x-ray lithography exposure conditions suitable for micromachining. The temperature rise and relaxation time of a silicon wafer during x-ray exposure were measured in vacuum and different He gas pressures.