(Invited) Characterization of Wetting Behavior on High Aspect Ratio Multilayer Structure
Authors: Kim Tae-Gon , Kim Donggyu , Kim G. , Park Jingoo 
Published: July 2022

The miniaturization and complexity of semiconductor structures increase to improve device performance and functionality. In particular, the latest high-performance semiconductor architectures are formed of high-aspect-ratio structures composed of multilayer thin films. In the case of logic devices, it is reported that the gate-all-around(GAA) structure will become the mainstream, and in the 3D NAND flash memory, it will have a structure with more than 168 layers and a high aspect ratio of 50 or more. In order to form such a structure, the manufacturing process becomes complicated and various challenges to be solved occur. One of the challenges facing is efficiently removing contaminants generated while forming structures having a complex and high aspect ratio structure without damaging the structures. In the case of a wet cleaning process, a technology capable of removing only contaminants without pattern collapse and material loss is required.

In order to develop a wet cleaning process for effective contaminant removal and precise control in cleaning process on a high aspect ratio multilayer structure, it is necessary to understand the chemical reaction characteristics between the material and the cleaning chemicals. In particular, it is important to understand the wettability of the cleaning liquid in the structures for damage-free cleaning process development.

The wettability of HAR nanostructures was studied using the FTIR-ATR measurement technique. Studies have shown that FTIR-ATR is a reasonable method for studying the wettability properties in HAR structures made of Si. We performed similar experiments and similar experimental results were obtained. However, the FTIR-ATR analysis method is difficult to apply to a HAR multilayer structure. In this structure in which thin films with different optical properties are stacked, the IR signal did not reach the detector sufficiently, making measurement impossible. In this paper, we introduce a new measurement method for analyzing the wettability in the HAR multilayer structures.

To evaluate the wettability of various chemicals in HAR multilayer structures, the trench pattern with a width of 200 nm and a depth of 9500 nm, the aspect ratio of 47.5 was used. This sample was immersed in a 20 nm silica particle solution to observe the arrival depth of the particles in the trench. To visualize the particle arrival depth, the sidewall of the trench was exposed by cutting and the sidewall surfaces were characterized by atomic force microscope (AFM, NX-20, Park Systems, Korea). Furthermore, an organic thin film which was carried out to form a hydrophobic surface was deposited on the samples to observe the wetting behavior according to the various wettability of the trench surface. A hydrophobic surface with a water contact angle of 95° was formed on the sample by depositing an organic thin film to observe the wetting behavior according to various wetting properties of the trench surface. The surface tensions of the particle solutions were varied by adding SDS surfactant.

The change in the sidewall surface of the trench using AFM was visualized successfully, and the observation explained the wetting behavior of the liquid. The experimental results agreed with the values calculated by the Wenzel & Cassie-Baxter model. The visualization of the trench sidewall using AFM could help understand the wetting behavior in the HAR multilayer structure.