Stencil lithography

The main deposition method used with stencil lithography is physical vapor deposition. This includes thermal and electron beam physical vapor deposition, molecular beam epitaxy, sputtering, and pulsed laser deposition. The more directional the material flux is, the more accurate the pattern is transferred from the stencil to the substrate.

Reactive ion etching is based on ionized, accelerated particles that etch both chemically and physically the substrate. The stencil in this case is used as a hard mask, protecting the covered regions of the substrate, while allowing the substrate under the stencil apertures to be etched.

Here the thickness of the membrane has to be greater than the penetration length of the ions in the membrane material. The ions will then implant only under the stencil apertures, into the substrate.

In the static mode, the stencil is aligned (if necessary) and fixed to a substrate. The stencil-substrate pair is placed in the evaporation/etching/ion implantation machine, and after the processing is done, the stencil is simply removed from the now patterned substrate.

In the quasi-dynamic mode (or step-and-repeat), the stencil moves relative to the substrate in between depositions, without breaking the vacuum.

In the dynamic mode, the stencil moves relative to the substrate during deposition, allowing the fabrication of patterns with variable height profiles by changing the stencil speed during a constant material deposition rate. For motion in one-dimension, the deposited material has a height profile ${\displaystyle h(x)}$ given by the convolution

${\displaystyle h(x)=c\int t(x')M(x-x')dx'}$

where ${\displaystyle t(x)}$ is the time the mask resides at longitudinal position ${\displaystyle x}$, and ${\displaystyle c}$ is the constant deposition rate. ${\displaystyle M(x)}$ represents the height profile that would be produced by a static immobile mask (inclusive of any blurring). Programmable-height nanostructures as small as 10nm can be produced.[2]