Deep Hole Etching Simulation for Advanced NAND Flash Memory
Introduction
The NAND Flash memory cell has been refined to reduce the bit cost, but the limit of its miniaturization has been reached due to the high electric field problem and the difficulty of lithography. On that account, three-dimensional stack cell structures have been adopted to achieve mass storage devices [1-3]. It has already been reported that the fabrication of 256Gbit NAND Flash memory with 48 stacked layers started on August in 2015 [4, 5]. For the fabrication of the stack structures, it is necessary to realize etching of deep holes. For examples, if using 30nm design rules and one layer thickness is 40nm, its depth becomes 1.92um. If the holes diameter is 100 nm, its aspect ratio becomes 19.2. Then, in the next generation, the 512 Gbit flash memory cell will need the deep hole with the aspect ratio of 38.4 for 3.84um-depth. For investigating more suitable process conditions or optimum etched topography, accurate three-dimensional etching simulation is required, but it takes a very long time to simulate this deep hole etching accurately if using usual simulation methods like the Monte-Carlo method, because the aspect ratio of this deep hole is very large and therefore, the flux calculation effort of enhancing ions and neutral radical species is enourmous for a reactive enhanced ion etching (RIE) model.
We have demonstrated the deep hole etching simulation with practical calculation times even for 3D, using the multi-dimensional process simulator Victory Process, which extensively and efficiently uses parallel processing. In this article, we show its simulation result with the ion enhanced chemical etching model and a good performance scaling of the parallel processing.
