摘要
Titanium nitride (TiN) is a robust ceramic material extensively used in semiconductor manufacturing due to its exceptional hardness, chemical resistance, and thermal stability. These properties make TiN an ideal choice for applications such as gate electrodes and diffusion barriers. Additionally, TiN serves as a hard mask in semiconductor fabrication, providing high chemical resistance and compatibility with high-aspect-ratio patterning.However, the intrinsic hardness and chemical inertness of TiN necessitate the development of effective etching techniques. Conventional methods such as plasma etching, atomic layer etching (ALE), and chemical mechanical polishing (CMP) provide precise control but are often impeded by slow processing speeds, high operational costs, and the potential for material damage. Additionally, achieving high selectivity against copper (Cu) and dielectric materials remains a significant challenge. Plasma etching frequently suffers from low selectivity for Cu and the risk of metal damage; while ALE offers improved process control, it still requires protective strategies for Cu. CMP, on the other hand, lacks material selectivity and may induce mechanical damage to both Cu and dielectric layers. In contrast, wet etching has emerged as a promising technique for TiN removal due to its superior selectivity over dielectric materials and its ability to minimize substrate damage. Furthermore, wet etching presents advantages in terms of lower equipment complexity and reduced operational costs, making it economically favorable for large-scale semiconductor manufacturing.To enhance etching efficiency in wet etching processes, this study proposes two distinct approaches. The first approach is inspired by the commercially used Standard Clean 1 (SC1) solution, an alkaline mixture composed of H₂O, NH₄OH, and H₂O₂. In the SC1 system, hydrogen peroxide (H₂O₂) acts as an oxidizing agent, decomposing under alkaline conditions to generate hydroperoxide ions (HO₂⁻). These reactive species facilitate the formation of soluble titanium complexes through interactions with Ti ions, thereby promoting material removal(Figure1). Building upon this mechanism, we propose substituting water with an organic solvent to reduce the surface tension of the etching solution. A lower surface tension enhances the wettability of the solution on TiN surfaces, improving its ability to penetrate surface features and interact with the TiN layer. This improved interfacial compatibility is expected to enhance removal efficiency. Preliminary experimental results demonstrate that replacing water with 70 wt% ethyl acetate in an SC1-like solution significantly increases the etching rate, from 5.66 nm/min to 9.88 nm/min, as shown in Figure 3.The second approach draws inspiration from mechanisms reported in the selective wet etching of silicon nitride (Si₃N₄), where SN1- and SN2-like reactions are employed. In this system, H₂PO₄⁻, a weak nucleophile derived from H₃PO₄, substitutes the NH₂ group on the Si₃N₄ surface via an SN1-like mechanism. This is followed by the hydrolysis of Si–N bonds through an SN2-like attack by water, ultimately forming Si–OH and facilitating removal. Analogously, we explore a chlorination-based strategy, as illustrated in Figure 2, wherein the chlorinating agent, trichloroisocyanuric acid (TCCA), is utilized to generate electrophilic chlorine species (Cl⁺) or chlorine radicals (Cl•) capable of reacting with TiN. This reaction pathway facilitates the formation of volatile titanium tetrachloride (TiCl₄), which can be easily removed from the substrate surface. Prior studies have confirmed the efficacy of such chlorination reactions in gas-phase plasma environments. In our wet chemical system, this chlorination approach similarly enhances the etching rate, with results showing an increase from 1.12 nm/min to 9.34 nm/min in the presence of chlorinating reagents, as shown in Figure 4.To elucidate the fundamental etching mechanisms underlying these two approaches, systematic investigations into the effects of etchant concentration, temperature, and oxidizing agent presence on the etching rate and material selectivity are being conducted. High-performance liquid chromatography–mass spectrometry (HPLC-MS) and nuclear magnetic resonance (NMR) spectroscopy were employed to identify and confirm the formation of titanium-containing etching byproducts. Additionally, post-etching surface morphology and chemical bonding alterations were analyzed by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. Through comprehensive mechanistic understanding and parameter optimization, this study aims to establish a controllable and efficient TiN wet etching process suitable for advanced semiconductor manufacturing applications. Keywords: Titanium nitride, wet etching, organic solvent, chlorination Figure 1