Role of Initial Precursor Chemisorption on Incubation Delay for Molybdenum Oxide Atomic Layer Deposition
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- 作者：Charith E. Nanayakkara ; Abraham Vega ; Guo Liu ; Charles L. Dezelah ; Ravindra K. Kanjolia ; Yves J. Chabal
- 刊名：Chemistry of Materials
- 出版年：2016
- 出版时间：December 13, 2016
- 年：2016
- 卷：28
- 期：23
- 页码：8591-8597
- 全文大小：537K
- ISSN：1520-5002
文摘
In an effort to grow metal oxide films (e.g., MoO3) at low temperatures, a novel molybdenum precursor, Si(CH3)3CpMo(CO)2(η3-2-methylallyl) or MOTSMA, is used with ozone as the coreactant. As is often observed in atomic layer deposition (ALD) processes, the deposition of molybdenum trioxide displays an incubation period (∼15 cycles at 250 °C). In situ FTIR spectroscopy reveals that ligand exchange reactions can be activated at 300 °C, leading to a shorter incubation periods (e.g., ∼ 9 cycles). Specifically, the reaction of MOTSMA with OH-terminated silicon oxide surfaces appears to be the rate limiting step, requiring a higher temperature activation (350 °C) than the subsequent ALD process itself, for which 250 °C is adequate. Therefore, in order to overcome the nucleation delay, the MOTSMA precursor is initially grafted at 350 °C, with spectroscopic evidence of surface reaction, and the substrate temperature then lowered to 250 or 300 °C for the rest of the ALD process. After this initial activation, a standard ligand exchange is observed with formation of surface Si(CH3)3CpMo(η3-2-methylallyl) after precursor and its removal after ozone exposures, resulting in Mo(═O)2 formation. Under these conditions, the ALD process proceeds with no nucleation delay at both temperatures. Postdeposition X-ray photoelectron spectroscopy spectra confirm that the film composition is MoO3. This work highlights the critical role of precursor grafting to the substrate as essential to eliminate the nucleation delay for ultrathin ALD grown film deposition.