Optimal Aluminum Doping Method in PEALD for Designing Outstandingly Stable InAlZnO TFT

Abstract

In particular, the high mobility of oxide semiconductors compared to amorphous Si (a-Si) is suitable for achieving highresolution, high-driving frequency displays, and the amorphous phase of oxide semiconductors can solve the issues caused by grain boundaries, which is a fatal problem of low-temperature poly-Si (LTPS). [3][4][5][6] In addition, because oxide semiconductors have high back-end-ofline (BEOL) compatibility, research on their application in memory devices is also actively progressing. [7] The extremely low off-current of oxide semiconductors can improve the retention of dynamic random-access memory (DRAM) [8,9] by lowering the charge loss through the transistor, and oxide semiconductors exhibit good compatibility with various insulating layers, allowing them to be used as semiconductor materials for NAND flash [10,11] or ferroelectric random-access memory (FeRAM). [12] For these various applications of oxide semiconductors, it is important to understand the role of the elements in oxide semiconductors to optimize the characteristics of thin films and devices. In particular, the characteristics of the devices can vary dramatically depending on the ratio of the cations in the oxide semiconductors. In the case of InGaZnO (IGZO), a representative quaternary oxide semiconductor, the role of each cation composition is already known, and studies are being conducted to determine their optimal composition. [4,[13][14][15][16] In is known to form a path for electrons to move through a large sphere-shaped 5s orbital. [14] Therefore, as the composition ratio of In increases, mobility increases; however, stability can be degraded owing to weak bonding between In and O. Moreover, Zn contributes to the formation of a network of oxide semiconductors. Finally, Ga is known as a carrier suppressor and long-range stabilizer of IGZO. [1] Ga 3+ forms a stronger chemical bond with O 2− than with Zn 2+ or In 3+ ; therefore, the oxygen vacancy (V o ), which is one of the reasons for carrier formation and instability, can be suppressed. [17] However, several issues with IGZO arise from this Ga composition. For a carrier suppressor, the binding energy between Ga and O is weak, and IGZO has a relatively narrow band gap, which causes instability under illumination. [18,19] Additionally, inexpensive carrier suppressor elements that can replace relatively expensive Ga are required. From these points of view, research on InAlZnO (IAZO) using Al as a replacement element for Ga is being conducted. [20][21][22] Oxide semiconductors are promising semiconducting materials for next-generation thin-film transistors (TFTs). The role of the cations should be considered in the design of oxide semiconductors suitable for various applications. Ga has been widely used as a carrier suppressor in oxide semiconductors; however, research has recently been conducted to replace it with Al, which is cheaper and forms a stronger bond with O. Deposition using plasmaenhanced atomic layer deposition (PEALD) is very useful for controlling the composition of...