Study on defect reduction for high aspect ratio etch process
Increasing data needs much larger memory capacity. One of the Flash Memory Solution is Vertical NAND (V-NAND) Flash Memory. In order to fabricate this device, a high aspect ratio hole must be made in the channel hole through the etching process after multilayer thin film deposition. In order to obtain high aspect ratio etch, process condition should have high RF power, high flow rate of polymer gas, and long process time. This harsh etch condition results in high ion energy and lots of polymer production. It can create defects like fluorocarbon polymer and arcing. In this study, we studied arcing mechanism. Here we defined various margins for arcing-free and optimized the focus ring. And we improved pumping conductance for polymer discharge. This study removed defects and obtained arcing-free during V-NAND etch process.
Study of Plasma Arcing Mechanism in High Aspect Ratio Slit Trench Etching
The abnormal process issue, arcing, was met in recipe development of high aspect ratio (HAR) trench etching. The arcing mechanism is proposed by continuous growth of polymer upon hard-mask along pattern boundary during deep trench etching. It leads to excess charge trapped and high potential difference between polymer and substrate. Eventually, electrical field breakdown occurs and results in severe pattern damage. The arcing risk can be effectively monitored in advance by measuring the polymer thickness on bare-Si wafer. A critical thickness of polymer is observed because we seldom find out the occurrence of arcing on the wafer while the polymer thickness is less than 960nm. Low pressure, inert gas dilution and high ESC temperature provide the knobs to control the polymer thickness less than 960nm –the critical thickness, as well achieving acceptable vertical trench profile in HAR etching.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME