China Northern Huachuang Technology Group said it has developed a new etching method that can help China transition to 3D DRAM production. The company says it has learned to handle the 64-layer stack evenly, avoiding some of the problems with legacy technology.
The proposed process consists of two stages. First, neutral fluorine radicals act on the silicon germanium (SiGe) layer and have little effect on the adjacent silicon layer. In this case, a germanium fluoride protective film is formed on the silicon surface. Plasma purification then removes by-products and reduces micro-stress effects that can cause etch depth variations between structural regions.
Naura said the new method can provide Si to SiGe etch selectivity greater than 500:1. In other words, SiGe’s removal rate is more than 500 times faster than silicon. This is especially important for 3D DRAM, where alternating layers of material must be processed to great depths without damaging adjacent structures. The technology may help China’s Changxin Storage develop vertical memory layouts and partially overcome the limitations of DUV lithography technology, which does not have the capabilities of modern EUV systems.