MM PLD
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Release status: Prototype validation
| Description | Fast prototyping tool for multiple material structures in the micrometer range
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Contents
Multi-Material, Sequentially Masked Pulsed Laser Deposition
Motivation
Current micro and nanofabrication processes rely on a vast set of tools and technical capabilities, which usually implies a considerable capital expense and severely limits accessibility to such capabilities in many regions of the world. Small research organizations may acquire some of the tools required, but the fabrication process for standard devices require a substantial number of difficult and error-prone steps which take enormous amounts of know-how and optimization procedures in order to perform with an acceptable rate of success.
General Idea
The main goal is to generate an affordable, and easy to use system which allows the deposition of a wide range of materials in a geometricaly controlled way, effectively enabling the creation of heterostructures with a wide range of functionality. Such a device may become a powerful tool for materials science research, and could also sustain interesting developments in distributed and participative manufacturing.
To implement such capabilities, the combination of the following techniques/ideas has been devised, with a particular twist ;)
Pulsed Laser Deposition
Pulsed Laser Deposition is a technique in which mass is transfered in a controlled atmosphere from a target to a substrate by means of irradiating the former with a high energy pulse of light. The energy transfered induces out of equilibrium thermal processes in the target, resulting in the formation of a plasma 'plume' which has a stoichiometry closely matched to the target composition.
While it's not the technique of choice for industrial device fabrication (mainly due to film quality and complications associated with large area deposition, see this section), the ability to deposit a wide range of materials has made it the workhorse for many research regarding complex materials (oxides, nitrates, dichalcogenides, etc) and the applications of some interesting effects (ferroelectricity, superconductivity, …) that they show. An often overlooked characteristic of this technique is the ease of coupling of the energy over the target: one can control with exquisite presicion the amount, rate, placement an timing of the energy transfered from the laser.
Shadow Mask Lithography
Stencil Lithography refers to the use of a usually solid mask with some defined apertures placed either in contact or some distance away from a substrate during a deposition process which effectively allows the spatially selective transfer of material. While this technique is seldom used in industry due to it’s practical resolution limitations, the spatial modulation of mass flow through an aperture is an inherently clean process which imposes very few limitations on the nature of the deposited species, as opposed to conventional resist based optical or e-beam lithography, where etching processes need to be carefully tailored to avoid undesired interactions, specially when there are underlying layers with very different physicochemical characteristics. [15] It offers a series of benefits such as mask reusability, ease of manipulation, avoidance of resist contamination, loose constraints associated with substrate characteristics and the relative ease of implementation of dynamic lithography schemes, where the pattern moves with respect to the substrate allowing a grater deal of flexibility and some unprecedented capabilities regarding spatially tailored thickness and compositional variations.
An example: Thin Film Transistor
So for illustrating how this may work, lets consider the fabrication of a bottom contacts, top gate thin film transistor.
Basically we have 3 different materials arranged in 4 layers, each with its particular pattern. Of course this is an enormous simplification of how an actual device ma be arranged, but bear with me for a while.
So in a standard fabrication flow, we may try something like this:(TODO)
While in the proposed system, we may load 3 different targets onto the carrousel and use a set of masks which are moved in front of the substrate for each of the targets in the following way:
Implementation
So the first implementation was a modification of an existing system. Since I don't think the configuration was very hobbyist friendly, I will only document it briefly in MM PLD - v0.
