Dry etch characteristics of Al-Nd films for TFT-LCD

In this study, Al-Nd thin films deposited on glass were etched using magnetized inductively coupled plasmas and their etch characteristics were investigated as a function of gas combination of Cl2/BCl3 and HBr/BCl3, inductive power, bias voltage and pressure. When Cl2/BCl3 gas mixtures were used to etch Al-Nd films, low etch rates close to 1/3 of that of pure Al and etch selectivities over photoresist less than 0.9 were obtained due to the non-volatile Nd in Al-Nd thin films. Also, some residues originating from the remaining Nd were observed on the surface of glass and side wall of the Al-Nd lines after the etching of Al-Nd. However, the use of HBr/BCl3 gas mixtures increased Al-Nd etch rates and etch selectivities over photoresist, and the highest Al-Nd etch rate close to 140 nm/min and etch selectivity close to 1.1 could be obtained with 50% HBr/50% BCl3. In addition, barely no residues and no critical dimensional loss could be found with this etch condition. X-Ray photoelectron spectrometry (XPS) showed preferential removal of Nd by HBr during the Al-Nd etching and preferential removal of Al by Cl2 and BCl3. Therefore, the highest Al-Nd etch rate at 50% HBr/50% BCl3 appears to be related to the optimal combination of Nd etching with HBr and Al etching with BCl3.