关键词: 半导体存储器, 3D NAND, 刻蚀, 氮化硅, 二氧化硅, 硅酸

Abstract:

As one of the most significant memory chips in semiconductor market, NAND has been developed from two-dimension (2D) to three-dimension (3D). Due to the three-dimensional memory structure of 3D NAND, the capacity density, read-write speed and reliability of memory chips have been greatly improved, as well as the reduction of power dissipation. It is by nitride-oxide selective etching process in the alternate stacked structure of 3D NAND that the inter-dielectric layers can be obtained. The more stack layers, the better performance of chips will be. Meanwhile, however, silicon dioxide (SiO₂) would regrow on the corner of oxide layers, the phenomenon called regrowth, which directly makes damage to the stack structure. If the deposition is so thick that becomes adhesive together, the stack structure will collapse, severely affecting the performance of devices. Preventing SiO₂ regrowth is imperative for higher stacked layers, meaning that the key point is to figure out the specific process of regrowth and its impact factors. Due to the rapid development of this field, the existing information is such a mess that there is a lack of sorted information and systematic research dealing with the problem of regrowth. This paper briefly reviewes developing situation and existing research results of silicon nitride selective etching process in 3D NAND manufacture procedure, with emphases in the significance of controlling silicon concentration to avoid regrowth. Furthermore, relative theoretical models are introduced to provide simulation and prediction for regrowth process. In order to analyze the chemical reaction in regrowth, this paper summarizes the relative solution chemistry of silica and the impact of polysilicic acid formation, and suggests that the gel curve can reflect its aggregation behavior. Accordingly, researches on how to avoid regrowth can be guided theoretically by discovering the influence factors of silicic acid aggregation or the deposition behaviors of polysilicic acid on oxide layers.

Key words: semiconductor memory, 3D NAND, etching, silicon nitride, silica, silicic acid