Independent Electron and Ion Energy Distribution Control for Semiconductor Processing

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. To minimize defects in HAR features and produce higher aspect ratio features, precision and independent control of the ion and electron energy distribution functions (IED and EED) is required. Additionally, HAR etching requires longer processing time and higher etch rates are needed to reduce overall cost, which requires higher power systems. EHT has developed an industrially-relevant bipolar pulse generator that allows for independent control over the positive and negative pulses. This system has the potential to independently control the IED and EED at the wafer surface, which can reduce charging effects that produce defects in HAR features. To commercialize this power system in the semiconductor capital equipment market, independent control must be validated experimentally and connected with improved etching results. The goal of the SBIR program is to develop an understanding of the complex power system-plasma dynamics through a combined experimental and computational program. In the Phase I program, EHT modified the existing plasma chamber to enable use of electronegative plasmas, demonstrated the ability to make EED measurements, and began to investigate bipolar pulsing for IED/EED control. On the computational side, EHT engineers were trained on the usage of the University of Michigan modeling code. Additionally, preliminary simulations of the EHT chamber were conducted. In the Phase II program, EHT and UM will continue to experimentally and computationally investigate the impact of bipolar pulsing on IED/EED control. The major focus will be on the electrons, especially those produced by the high energy electrons and ions impacting the chamber components, including the wafer. The baselined model enables us to explore the plasma-power system connection on a time and length scale that would be challenging or impossible to measure experimentally. Additionally, the modelling will allow us to connect the plasma-power system effects with the IEAD/EEAD and ultimately to etch results. The market for solid-state, non-volatile memory storage is driving the demand for NAND flash. To overcome some of the challenges with manufacturing 2D NAND, the semiconductor processing industry has largely transitioned to 3D NAND, which requires precision etching of HAR features with aspect ratios exceeding 100:1. Improved control of the IEAD and EEAD improves the quality of HAR features. HAR etching requires longer processing time and higher etch rates are needed to reduce overall cost. EHT’s new bipolar pulse generator for wafer bias has the potential to provide independent control of the IEAD and EEAD to improve the quality of HAR features while operating at the high power required to increase etching rates thereby reducing production time, lowering costs and increasing yield.