AbstractThe patterning of nanometre-scale features over large scales (wafer) is commonly performed with stepper equipment that is expensive to both purchase and maintain. Low-cost alternative lithography techniques for larger feature sizes such as nanoimprinting and direct laser writer lithography have been developed over the last few decades. They have been used for many niche areas in research as a bridge to industrialization patterning.
Displacement Talbot Lithography (DTL) is one of the recently developed technique. This attractive system, insensitive to the gap distance by integrating the Talbot pattern spatially over a certain distance, allows the patterning of rough and bowed surface within minutes without the need for expensive equipment. Areas up to 6-8 inch can be patterned
with the current technology.
As DTL technology is a new lithography method, the impact of the experimental conditions on the process was still, at the beginning of the thesis, open to investigation. The different parameters impacting the process can be isolated
into three categories:
1. The DTL PhableR machine by itself provided by Eulitha. The integration distance, type of integration laser power, polarisation can be modified. However, the 375 nm wavelength of the laser source and the equipment capabilities
cannot be changed.
2. The type of masks, their design and their impact on the quality of the process.
3. And finally the substrate, the anti-reflective coating and the type of resist used.
A literature review of the most common patterning techniques available within industry and research is first performed to compare DTL’s capability with conventional approaches. It is followed by the presentation of the Talbot
effect and its use in lithography and other disciplines. Then, the chemistry mechanics, fundamental limits of the resist, and equipment are described. Thanks to this, broad questions can be asked on the DTL technology: What is the
minimum feature size obtainable? Which conditions are required to obtain such feature sizes? And how do the mask type and feature size of the mask influence the shape of the Talbot carpet?
In the first results chapter, with a scalar-approximation of the light propagation, a study of the impact of the mask topology on the resolution is performed. The conditions to achieve the best resolution, both theoretically and practically, are stated and discussed.
An in-depth study of the Talbot effect itself showed that the contrast and resolution were controllable thanks to the adjustment of the contribution of the harmonics appearing in the Talbot spectrum. In a new chapter, a link between
the domination of the smaller harmonic and improved resolution is stated.
A new question appeared after these two studies: Could the resolution be further enhanced through mask design? It is not possible with standard mask design. However, a new type of mask allowing a better resolution and the use
of larger pitch with the machine has been created and studied: quasi-periodic masks. Indeed, the smaller harmonic presence is notably strengthened with this new type of mask.
Finally, a last question has been explored: can DTL create any feature shapes? With conventional processes, the displacement blurs the illumination, restricting the range of feature shape. To bypass this issue, DTL has been combined
with a lateral nanopositioning system to create a large-area (2-inch wafer) patterning technique with the flexibility of a direct-write system. A vast number of shapes impossible to achieve before with DTL is then reported. Furthermore, the development of a modelling tool allowed the prediction and exploration of the pattern shape achievable.
|Date of Award||28 Apr 2021|
|Supervisor||Cathryn Mitchell (Supervisor) & Philip Shields (Supervisor)|