Stencil lithography

Marc Antonius Friedrich van den Boogaart
EPFL, 2006
Thèse EPFL

Résumé

This work describes the advancements made in micro and nano patterning via stencil lithography. Stencil lithography is a resist-less and direct pattern technique where a controlled amount of material is deposited through apertures on to a substrate in a vacuum environment. This unique approach enables large scale micro and nano structuring of unconventional materials and on a large range of substrates otherwise not possible using conventional photolithography. A theoretical approach is presented for correct implementation of stencil lithography with the aim of giving the reader sufficient insight in stencil lithography and associated phenomena, such as the deposition method, stencil aperture clogging, and the resulting pattern distortion (blurring). The developed "zone theory" allows the reader to estimate the size of the resulting surface patterns and pattern uniformity over a large area. The fabrication of thin-film stencils consist of a few basic process steps such as the choice of membrane material. The motivation for use of specific materials or processes are described followed by the description of a basic planar stencil fabrication scheme. A detailed fabrication description for a 100 mm stencil containing a large number of membranes with apertures ranging from 200 nm up to several 100 μm is given. The utilization of stencils show that the patterns are accurately transferred on to a substrate and that the size of the resulting structures is correctly approximated using the "zone theory". However, deposition of material with a high residual stress through mechanically unfavorable membrane geometries results in stencil membrane deformation and loss of pattern resolution. Two additional fabrication schemes for mechanically reinforced stencil membranes are presented. The utilization of improved stencils shows increased membrane stability, while comparisons of deposited patterns through planar and improved stencils show that the patterns deposited through improved stencils have better pattern resolution and definition. A Finite Element Method model is successfully used to predict stencil deformation under influence of deposited, high stressed material. This model allows the determination of optimum stabilization structures and there placement, enabling a shorter design and fabrication delay. The full integration stencil lithography into existing and established processes requires not only a precise transfer but also a precise pattern registration. A stencil alignment procedure is presented which enables a sub-micrometer alignment accuracy. A set of application examples is given where stencil lithography can be useful or even necessary for successful device fabrication. These examples show the potential of stencil lithography for use as a reliable micro and nano patterning technology in a large range of applications fields. Furthermore, a new approach for the dynamic utilization of stencils is given where the presented system might be useful for rapid prototyping of micro- and nano-patterns. This system has a low-tech threshold and enables nanopatterning without the need for a cleanroom environment.

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https://infoscience.epfl.ch/record/86075?ln=fr

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Marc Antonius Friedrich van den Boogaart
EPFL, 2006
Thèse EPFL

Résumé

Official source

https://infoscience.epfl.ch/record/86075?ln=fr

À propos de ce résultat

Concepts associés (21)

Concepts associés

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Publications associées (17)

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Stencil lithography (SL) is a shadow mask based technique which allows parallel, resistless, micro- and nano-patterning of material through apertures in a membrane (stencil) onto a substrate [1]. The stencils are usually made of LPCVD low-stress SiN due to its outstanding physical and chemical stability. However, limitations are found in some special designs, where membranes could be distorted because of the deformations induced by stress from the deposited materials. To solve this problem, the fabrication process has to become more complex by introducing corrugations on the membranes for reinforcement [2]. Here we report on a recently developed PECVD SiC based shadow mask for applications in SL. The SiC stencil demonstrated a better performance than the shadow mask made of SiN in terms of robustness to deformation and resistance to etching. The SiC was grown by PECVD at temperatures below 400 oC. The intrinsic stress of SiC can be tuned from compressive to tensile by varying the annealing time to fulfill the low stress requirement for the stencil membrane. During this process, the amorphous SiC is starting to crystallize and thus enhance its robustness, which translates into a higher Young’s modulus [3]. The fabrication of the SiC stencil (Fig 1a-d) started from a Si wafer with 540 nm thick PECVD SiC on the front side and 200 nm thick PECVD SiN on the backside. SiC was patterned by dry etching in AMS 200 DSE, following by a DRIE process on the backside to open the membrane windows. The residual 50 m thick Si left after the DRIE process was etched away by KOH. Fig 1e shows the SEM image of a released 1 mm x 1 mm area SiC membrane. The SiC stencil was then placed on a Si substrate for metal deposition. Fig 2 shows the SiC stencil and the accurately duplicated corresponding patterns on the substrate after 5 nm Ti and 50 nm Au deposition in an ebeam evaporator. The results are comparable to those from SiN stencil deposition, where the main challenge is the enlargement of the pattern, known as blurring [4]. The robustness was compared between the low-stress (110 MPa) SiC and the low-stress (200 MPa) SiN by depositing Cr film, which has a high tensile stress. Fig 3 shows the different bending behaviors of cantilever structures in the membranes when coated with 25 nm Cr. The SiC cantilevers bend 75% less than the SiN ones by measuring the maximum deformation, providing a wider possibility for the choice of the deposited material. The higher robustness to deformation of the SiC membrane indicates the possibility of having in general a more precise pattern duplication from the stencil to the substrate. Another advantage of SiC is its high chemical inertness, enabling it to be a good mask for both dry and wet etching. The SiC stencil was used as a mask to etch 500 nm SiO2 by RIE without any metal protection layer on the membrane due to its high etching selectivity (Fig 4a). By comparison, a metal protection layer is essential for SiN stencil under similar conditions for dry etching [5]. The transferred patterns (Fig 4b) show a sub 100 nm loss in diameter for a 3 m diameter aperture, as shown in Fig 4c and d. There is no evident damage to the SiC stencil after the dry etching.

Microelectronic Engineering2011

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Deep-ultraviolet-microelectromechanicaI systems stencils for high-throughput resistless. patterning of mesoscopic structures

Jürgen Brugger, Marc Antonius Friedrich van den Boogaart

We describe a combination of 100-mm wafer scale deep-ultraviolet (DUV) exposure and a microelectromechanical systems (MEMS) process to fabricate silicon nitride membranes with submicrometer apertures to be used as miniature shadow masks or nanostencils. Apertures down to a lateral resolution of 200 nm were made in a 500-nm-thick membrane by DUV exposure and dry plasma etching. The membranes were released by a combination of wet silicon etching using potassium hydroxide (KOH) and dry silicon etching using a plasma process. The millimeter-size stencils were used for single-step, local deposition of metal micro- and nano-patterns without the need for photoresist process steps. We have performed stencil deposition on full wafer scale for micro- and nano-patterns in a variety of metals (e.g. Al, Au, Ni, etc.). Dry under-etching of the nanowires resulted in free-standing cantilevered nanoelectromechanical systems (NEMS) structures with resonance frequencies in the megahertz range. The resistless method allows us to pattern micrometer and nanometer scale patterns in a single step without any further processing. It is promising for the surface processing of MEMS/NEMS devices having sensitive or fragile surfaces, such as biochips, organic polymer layers, and self-assembled monolayers. (C) 2004 American Vacuum Society.

2004

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Deep-ultraviolet–microelectromechanical systems stencils for high-throughput resistless patterning of mesoscopic structures

Jürgen Brugger, Marc Antonius Friedrich van den Boogaart

2004

Chargement

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Microelectronic Engineering2011