There's a new kid on the block in vapor deposition technology. The easily scalable, atmospheric-pressure process could become the preferred method for creating large-area thin-film and flexible devices.
The process, spatial atomic layer deposition (sALD), delivers semiconductor layers with better performance than physical vapor deposition (PVD) at the same, and potentially, higher throughputs.
So claim researchers with Holst Centre, a Netherlands-based R&D campus that develops generic technologies for wireless autonomous sensor technologies and flexible electronics.
PROCESS BORROWS FROM PVD SPUTTER DEPOSITION
A key step in producing next-generation ultra-high definition displays is the creation of a highly uniform layer of an amorphous oxide semiconductor like indium-gallium zinc oxide (IGZO).
This is accomplished using a PVD technique known as sputter deposition.
"Sputtering's an old and versatile thin film deposition process," says BCC Research analyst Andrew McWilliams in Physical Vapor Deposition (PVD): Global Markets.
"The goal of the deposition process is to impart specific properties to a surface to change or alter its characteristics. A material may be deposited on a surface to protect it from corrosion, wear, and abrasion; to improve its adhesive properties; make it more conductive; to protect it from light and air, or to make possible denser storage of data," Williams says.
He explains that the sputtering process involves, literally, sputtering material onto a substrate. For example, many metallizing operations sputter conductive or resistive materials onto a variety of substrates. Sputtering's also used in the microelectronics industry for semiconductor fabrication, and in the information storage industries for the production of disc media.
But sputtering requires expensive vacuum equipment and can also prove difficult to correctly control material composition and thickness over large areas. This results in variable transistor performance, particularly in thin film applications such as displays.
According Holst Centre, sALD offers an industry-compatible alternative which improves display performance while also cutting production costs.
The team has used the technique to create semiconductor layers with charge carrier mobilities (a key measure of semiconductor performance) of 30 to 45cm2/Vs. This compares to typical mobilities around 10cm2/Vs for sputtering.
The sALD layers also exhibited low off current, switch-on voltages around 0V and excellent bias stress stability.
“Spatial ALD offers all the performance advantages of traditional ALD—superior control of layer thickness and composition, large-scale uniformity and unparalleled conformability—but at 10-100 times the speed," says Paul Poodt, a program manager at Holst Centre. "So a typical 50nm thick layer can be produced within the standard one-minute window demanded by today’s industrial processes."
"The performance of sALD means semiconductor layers could become much thinner, enabling even higher throughputs and lower material consumption," says Gerwin Gelinick, a program director at Holst Centre.
Gelnick notes that performance characteristics of sALD are preserved even when scaling down the semiconductor thickness to less than 5 nm. This capability can lead to novel semiconductor structures, such as super-lattices, with even higher electron mobilities, he adds.
According to Holst Centre, its team and partners are working towards the upscaling and commercialization of sALD processes and related equipment.