Thermal Atomic Layer Deposition of Ultrathin LiPON at a 200 mm Wafer-Scale

Over the past decade, LiPON solid electrolyte has been recognized as a good candidate for portable energy solutions. Meanwhile, the miniaturization of devices has led to intricate architectures that pose significant challenges for thin-film deposition, particularly in achieving conformal coatings with precise thickness control. In this paper, we assess the deposition process of an ultrathin LiPON layer by thermal atomic layer deposition (ALD) from the precursors, lithium bis(trimethylsilyl)amide (also known as lithium hexamethyldisilazide, LiHMDS) and diethyl phosphoramidate (DEPA). This process exhibits a growth-per-cycle (GPC) around 0.6 Å/cycle between 290 and 330 °C. X-ray photoelectron spectroscopy (XPS) analyses show an N/P atomic ratio ∼1 over the whole temperature range. However, material properties are not constant, with significant concentration changes for the two nitrogen bonding states. A metal–electrolyte–metal (MEM) stack is used to confirm electrochemical functionality of an ultrathin 13 nm LiPON film deposited at 330 °C. We achieve process parameters that result in ultrathin, conformal, smooth, and continuous films, appearing well adapted for further integrations. Finally, we demonstrate homogeneous material features at a 200 mm wafer-scale displaying the process maturity in readiness for industrial transfer.