The ability to use plasma etching to produce high aspect ratio (HAR) features is becoming increasingly important as the market demands solid-state non-volatile memory storage. In order to minimize bowing and twisting defects in HAR features, precision control of the ion energy distribution function (IEDF) is required. Additionally, HAR etching requires longer processing time, and higher etch rates are needed to reduce overall cost, which requires higher power systems.
Eagle Harbor Technologies (EHT), Inc. has previously developed a rapid capacitor charger (Spartan) that can rapidly charge the wafer and stray capacitance to high voltage in tens of nanoseconds and operate at 400 kHz. This system can produce sheath voltage waveforms that are flatter than those produced with standard sinusoidal radio-frequency generators, which can improve control over the IEDFs and allow for greater process control. Additionally, this system can operate at up to 20 kW continuously when water cooled, potentially allowing higher etch rates. EHT is conducting an experimental and computational program to improve the understanding of the interaction between bias waveforms and plasma properties to commercialize this power system technology.
In the Phase I, EHT operated the Spartan on a small test chamber with an inductively coupled plasma source. EHT constructed a retarding field analyzer (RFA) and the associated electronics. EHT measured the source parameters with a Langmuir probe and RFA. Initial investigations with the RFA were conducted with the Spartan operating. In parallel, Sandia National Laboratories (SNL) used a 1D particle-in-cell code to model the plasma with the applied bias voltage.
EHT modified the chamber to a capacitively-coupled source, which is more relevant to the semiconductor tool industry and closer to the system that SNL modeled. EHT will continue to develop the high-voltage RFA and investigate other energy analyzers. These analyzers will be used with even higher-voltage bias waveforms. The Phase I principal investigator at SNL moved to North Carolina State University, and she will continue to provide computational support to better understand the experimental results.
The market for solid-state non-volatile memory storage is driving the demand NAND FLASH, which requires precision etching of HAR features with aspect ratios approaching 100:1. To overcome some of the challenges with manufacturing 2D NAND, the semiconductor processing industry is moving to 3D NAND. One of the major challenges with the production of HAR features for 3D NAND is controlling bowing and twisting of the holes. Improved control of the IEDF improve the quality of HAR features. Additionally, HAR etching requires longer processing time and higher etch rates are needed to reduce overall cost. EHT pulsed power systems have the potential to improve IEDF control while operating at the high power required to increase etching rates thereby reducing production time and lowering costs.
Key Words: plasma etch, ion energy distribution, IEDF, plasma bias, pulsed RF, pulsed power, semiconductor processing