Photoresist characterization and linearization procedure for the gray-scale fabrication of diffractive optical elements

LeCompte, Marion R.; Gao, Xiang; Prather, Dennis W.

doi:10.1364/ao.40.005921

Cited by 34 publications

(15 citation statements)

References 18 publications

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“…The Gaussian approximation method presented in the next sections will outline the method by which an optimum pixel may be selected for each pixel location to accurately re-create any desired profile, including but not limited to, the PFL profile defined in equation (3.5). Alternate gray-scale photoresist linearization schemes have been investigated [43]. Linear gratings with 8 levels were fabricated, however the authors did not demonstrate arbitrary profiles, nor did the model facilitate integration into complicated structure designs.…”

Section: Gaussian Approximation Methodsmentioning

confidence: 99%

Development of a Deep Silicon Phase Fresnel Lens Using Gray-Scale Lithography and Deep Reactive Ion Etching

Morgan

Waits

Krizmanic

et al. 2004

J. Microelectromech. Syst.

127

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A phase Fresnel lens (PFL) could achieve higher sensitivity and angular resolution in astronomical observations than the current generation of gamma and hard x-ray instruments. For ground tests of a PFL system, silicon lenses must be fabricated on the micro-scale with controlled profiles to enable high lens efficiency. Thus, two MEMS-based technologies, gray-scale lithography and deep reactive ion etching (DRIE), are extended to create multiple controlled step heights in silicon on the necessary scale.A Gaussian approximation is introduced as a method of predicting a photoresist gray level height given the amount of transmitted light through a grayscale optical mask. Etch selectivity during DRIE is then accurately controlled by introducing an oxygen-only step to a standard Bosch cycle to produce the desired scaling factor between the photoresist and silicon profiles. Finally, a profile evaluation method is developed to calculate the expected efficiency of measured silicon profiles. Calculated efficiencies above 87% have been achieved.

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Section: Gaussian Approximation Methodsmentioning

confidence: 99%

Development of a Deep Silicon Phase Fresnel Lens Using Gray-Scale Lithography and Deep Reactive Ion Etching

Morgan

Waits

Krizmanic

et al. 2004

J. Microelectromech. Syst.

127

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“…Nevertheless, most photoresists have nonlinear response to UV light exposure so a gray-scale photomask pattern with linear transmittance distribution will not give us a linear photoresist profile, as shown in Fig.3a. A mathematical model is adopted here to characterize and linearize our final photoresist profile [10]. In the model, the original total percentage of unexposed photoresist is normalized as 1, and the percentage of exposed photoresist is denoted as E(t), which is generated after exposure to UV light within a period of time, t. It is further assumed that the changing rate of exposed photoresist,…”

Section: Sloped Photoresistmentioning

confidence: 99%

Cracking pressure control of parylene checkvalve using slanted tensile tethers

Lin

Tai

2010

2010 IEEE 23rd International Conference on Micro Electro Mechanical Systems (MEMS)

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MEMS check valves with fixed cracking pressures are important in micro-fluidic applications where the pressure, flow directions and flow rates all need to be carefully controlled. This work presents a new surface-micromachined parylene check valve that uses residual thermal stress in the parylene to control its cracking pressure. The new check valve uses slanted tethers to allow the parylene tensile stress to apply a net downward force on the valving seat against the orifice. The angle of the slanted tethers is made using a gray-scale mask to create a sloped sacrificial photoresist with the following tether parylene deposition. The resulted check valves have both the cracking pressures and flow profiles agreeable well with our theoretical analysis.

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“…This feature is convenient for maintaining process repeatability without needing to adjust the exposure time manually, but makes it very difficult to know the actual dose used for the exposure. As a solution, the entire process is calibrated using normalized values as demonstrated previously [28,[39][40][41].…”

Section: Photoresist Heightmentioning

confidence: 99%

Double-Exposure Grayscale Photolithography

Mosher

Waits

Morgan

et al. 2009

J. Microelectromech. Syst.

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Three-dimensional (3D) photoresist structures may be realized by controlling the transmitted UV light intensity in a process termed gray-scale photolithography.Light modulation is accomplished by diffraction through sub-resolution pixels on a photomask. The number of photoresist levels is determined by the number of different pixel sizes on the mask, which is restricted by mask fabrication. This drawback prevents the use of gray-scale photolithography for applications that need a high vertical resolution.The double-exposure gray-scale photolithography technique was developed to improve the vertical resolution without increasing the number of pixel sizes. This is achieved by using two gray-scale exposures prior to development. The resulting overlay produces an exposure dose that is a combination of both exposures.Calibration is utilized to relate the pixel sizes and exposure times to the photoresist height. This calibration enables automated mask design for arbitrary 3D structures and investigation of other effects, such as misalignment between the exposures.

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Photoresist characterization and linearization procedure for the gray-scale fabrication of diffractive optical elements

Cited by 34 publications

References 18 publications

Development of a Deep Silicon Phase Fresnel Lens Using Gray-Scale Lithography and Deep Reactive Ion Etching

Development of a Deep Silicon Phase Fresnel Lens Using Gray-Scale Lithography and Deep Reactive Ion Etching

Cracking pressure control of parylene checkvalve using slanted tensile tethers

Double-Exposure Grayscale Photolithography

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