Effects of Temperature on the Etching Properties of Bi 4-xLaxTi3O12 Thin Films

Abstract

Non-volatile ferroelectric random access memories (FRAMs) have widely studied for communication products and smart cards due to low operating voltage, fast switching speed, and nonvolatility. In recent years, high permittivity dielectrics have been studied intensively for ferroelectric random access memories (FRAM) owing to low operating voltage and fast switching speed and nonvolatility. Bi-layered Bi4-xLaxTi3O 12 (BLT) has been intensively studied because it shows low leakage current, low coercive field and lack of fatigue with simple Pt electrodes and repeated polarization reversals with electric field cycling. In addition, BLT exhibits low crystallization temperature, good resistance of fatigue and a medium polarization. For the integration of ferroelectric thin films into high-density memories, anisotropic etching process should be developed. In recent years, most dry etching of semiconductor materials has been performed in high-density plasmas. Among high-density plasmas, inductively coupled plasma (ICP) etching systems posses of good properties such as superior uniformity and easy control of incident ion energy to the bottom electrode. However, there is only a few reports about etching mechanism and characteristics of BLT thin films in terms of gas chemistry such as Cl2/Ar and CF4/Ar. In this study, the etching properties of BLT in Cl2/Ar plasma was studied in terms of etch rate and selectivity as functions of substrate temperature. We obtained the maximum etch rate of 803 Å/min at 20% Cl 2 addition into Ar plasma. As the substrate temperature increased, the etch rate increased. The increase of etch rate can be explained by the enhancement of chemical etching effect. The variation of ion current density and of volume density for Cl and Ar atoms are measured by the Langmuir probe and optical emission spectroscopy (OES). The etch products are measured with quadruple mass spectroscopy (QMS). The etching profiles of samples are evaluated with scanning electron microscopy (SEM). The etch mechanism of BLT can be explained as follows; 1) the etch rate of BLT increased and made nonvolatile etch products with increasing substrate temperature due to increasing of chemical etching effect. 2) nonvolatile etch products (La-Cl x) can be desorbed only by the ion bombardment.