| dc.description.abstract | Nanoscale thin films exhibit unique properties and functionalities and are significant in a wide variety of applications and various sectors such as microelectronics, energy harvesting and storage applications, optoelectronics, sensing, and various other emerging technologies such as flexible electronics, 2D materials, quantum computing, micro electromechanical systems (MEMS), and packaging. Atomic Layer Deposition (ALD) is one method for producing thin films; its advantages include atomic-scale precision and control over film properties, which are vital for these applications. On the other hand, ALD is carried out under vacuum and therefore the process is expensive and slow. Atmospheric-Pressure Spatial Atomic Layer Deposition (AP-SALD) is an advanced technique for fabrication of thin films with properties similar to ALD but under atmospheric conditions and up to 2 orders of magnitude faster than ALD.
AP-SALD is advantageous for its ability to deposit uniform, conformal and pinhole-free thin films. However, formation of powder can be observed during deposition using lab-scale and industrial-scale AP-SALD systems. A major reason for the formation of airborne powder particulates is due to intermixing of precursor gases. This can be a disadvantage as it can lead to non-uniform film growth, an increase in surface roughness and poor adhesion, film quality and properties. Moreover, formation of powder around the perimeter of the AP-SALD reactor head and the channels due to undesired material deposition can affect the performance and efficiency of the system. In addition to unwanted powder formation, AP-SALD is a coating technique that deposits a film over the entire substrate area, whereas selective deposition of a patterned film is sometimes desired. To overcome these challenges, methods to control the location of material deposited by AP-SALD are crucial. Therefore, the objective of this work includes developing methods to (1) either prevent or minimize the powder formation on 3D-printed AP-SALD reactor heads and (2) control what parts of the substrate are coated by depositing thin films at specific regions on the substrate.
Several advanced strategies revolving around exhaust systems, in-situ monitoring and process optimization are being explored at the Functional Nanomaterials Group to prevent powder formation and effective removal of powders. In addition to these methods, coating the AP-SALD reactor head with materials that passivate the surface against gas-phase reactions may reduce powder formation on the reactor head. Area-selective atomic layer deposition (AS-ALD) by area deactivation is a technique in which thin films are selectively deposited on specific regions or patterns of a substrate (growth area) by coating the undesired regions (non-growth area) with growth inhibitors. In this work, the effect of dip-coating a custom AP-SALD reactor head with growth inhibitors to prevent material nucleation and powder formation is studied. Samples made of the same material as the reactor head are dip-coated with various growth inhibitors: polymers including poly(methyl methacrylate) (PMMA) and poly(vinyl pyrrolidone) (PVP) and self-assembled monolayers including octadecylphosphonic acid (ODPA) and dodecanethiol (DDT) for different durations up to 6 hours and 53 hours 30 minutes, respectively. Then AP-SALD depositions are performed on the samples to assess the effectiveness of the inhibitors. Some of the selected inhibitors demonstrate a clear ability to limit film growth on the 3D-printed samples. When 3D-printed reactors are coated with the promising growth inhibitors PVP and ODPA, powder formation is still observed on the reactor after performing depositions, although slightly less powder formation is observed when the reactor was coated with ODPA.
Using 3D printing, AP-SALD reactors with complex channels that cannot be fabricated with conventional manufacturing methods can be fabricated. Fabricating custom reactor heads with channels that deliver precursors at desired locations on the substrate can enable direct selective deposition. In this work, novel area-selective AP-SALD reactors are developed to selectively deposit thin-film patterns on a silicon substrate. Two types of reactors are designed and tested; to deposit wide and narrow patterns separated by a small and large gap, respectively. Using the former type of reactor, a pattern is visually observed after depositions, however film growth with approximately half the thickness of the patterns is observed in the gaps due to precursor leakage and intermixing. Closely spaced narrow patterns are deposited using the latter type of reactor by slightly offsetting the reactor head relative to the substrate in subsequent depositions. This method can also be extended to depositing wide patterns and represents a significant advancement in the ability to deposit high-throughput patterned films by AP-SALD. | en |
