Corrugated membranes for improved pattern definition with micro/nanostencil lithography

Abstract

We present a MEMS process for the fabrication of arbitrary (adaptable to specific aperture geometries) stabilization of silicon nitride membranes to be used as miniature shadow masks or (nano) stencils. Stabilization was realized by the fabrication of silicon nitride corrugated support structures integrated into large-area thin-film solid-state membranes. These corrugated support structures are aimed to reduce the membrane deformation due to the deposition-induced stress and thus to improve the dimensional control over the surface patterns created by stencil lithography. We have performed physical vapor deposition (PVD) of chromium on unstabilized (standard) stencil membranes and on stabilized (corrugated) stencil membranes to test the proposed stabilization geometry. Both the membrane deformation and the surface structures were analyzed, showing reduced deformation and improved pattern definition for the stabilized stencil membranes. The structures have been modeled using a commercial finite element method (FEM) software tool. The simulation and experimental results confirm that introducing stabilization structures in the membrane can significantly (up to 94%) reduce out-of-plane deformations of the membrane. The results of this study can be applied as a guideline for the design and fabrication of mechanically stable, complex stencil membranes for direct deposition.

Stretchable Conductors Fabricated by Stencil Lithography and Centrifugal Force-Assisted Patterning of Liquid Metal

“…The optical images of the sample taken during the process indicate that the blurring underneath the microbridges in the stencil allows for a continuous metal pattern on the substrate surface ( Figure 4 b(i)) and enable a continuous LM pattern across the entire serpentine structure ( Figure 4 b(ii,iii)). Compared to the reported strategy of using a corrugated SiN 39 or an electroplated Cu 24 membrane to increase its mechanical robustness, the proposed microbridge stencil enables a wider variety of designs in the micrometer scale without introducing additional processes.…”

“…By introducing corrugations in the SiN membrane, the moment of inertia of the membrane can be greatly increased which reduces the stress-induced stencil bending and thereby greatly improves the pattern definition. 39 Producing the corrugated membrane requires another fabrication process, which increases the overall stencil fabrication time and costs. Furthermore, a long serpentine or interdigitated structure has not been demonstrated yet by using the reported corrugated membrane.…”

Patterning of parallel nanobridge structures by reverse nanostencil lithography using an edge-patterned stencil

“…A nanobridge in the stencil (figure 4(a)) was first transferred as a nanogap structure by the normal stencil process ( figure 4(b)) and then reversed to the final nanobridge pattern on the Si substrate ( figure 4(c)). As indicated in figures 4(a) and (b), the width of the nanogap in the primary Cr pattern (∼85 nm) was narrower than the initial width of the stencil nanobridge (∼115 nm), which was caused by the pattern blurring during the stencil deposition [19,20]. The blurring effect, which is induced by a non-zero size of the evaporation source and a gap between the stencil and substrate, makes the deposited pattern larger than the original aperture size [19,20].…”

“…In the normal stencil process, we need to minimize the blurring to keep the width of a bridge pattern as small as possible, close to that of the original slit in the stencil. In the reverse process, although it still remains as a challenge to control the amount of blurring and obtain a high uniformity over a large substrate area [20,21], we can utilize the blurring for reducing the pattern width even further because a bridge structure of the stencil is first transferred as a narrower gap on the oxide layer. During the following steps transferring the gap to the reversed bridge pattern there was little change in the pattern size (figures 4(b), (c)).…”

Etching of sub-micrometer structures through Stencil

“…The fabrication process flow can be found in details elsewhere [12][13][14]. Basically, it starts with a double sided polished Silicon wafer (100 mm in diameter) (Figure 1.a) where a layer of low stress silicon nitride (LS-SiN) is deposited (Figure 1.b).…”