Li Min, Jin Zhi-Xian, Zhang Wei, Bai Yu-Hang, Cao Yan-Qiang, Li Wei-Ming, Wu Di, Li Ai-Dong
National Laboratory of Solid State Microstructures, Department of Materials Science and Engineering, College of Engineering and Applied Sciences, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, 210093, People's Republic of China.
Sci Rep. 2019 Jul 18;9(1):10438. doi: 10.1038/s41598-019-47049-z.
The wide applications of ultrathin group IV metal oxide films (TiO, ZrO and HfO) probably expose materials to potentially reactive etchants and solvents, appealing for extraordinary chemical stability and corrosion resistance property. In this paper, TiO ultrathin films were deposited on Si at 200 °C while ZrO and HfO were grown at 250 °C to fit their growth temperature window, by thermal atomic layer deposition (TALD) and plasma-enhanced ALD (PEALD). A variety of chemical liquid media including 1 mol/L HSO, 1 mol/L HCl, 1 mol/L KOH, 1 mol/L KCl, and 18 MΩ deionized water were used to test and compare chemical stability of all these as-deposited group IV metal oxides thin films, as well as post-annealed samples at various temperatures. Among these metal oxides, TALD/PEALD HfO ultrathin films exhibit the best chemical stability and anti-corrosion property without any change in thickness after long time immersion into acidic, alkaline and neutral solutions. As-deposited TALD ZrO ultrathin films have slow etch rate of 1.06 nm/day in 1 mol/L HCl, however other PEALD ZrO ultrathin films and annealed TALD ones show better anti-acid stability, indicating the role of introduction of plasma O in PEALD and post-thermal treatment. As-deposited TiO ultrathin films by TALD and PEALD are found to be etched slowly in acidic solutions, but the PEALD can decrease the etching rate of TiO by ~41%. After post-annealing, TiO ultrathin films have satisfactory corrosion resistance, which is ascribed to the crystallization transition from amorphous to anatase phase and the formation of 5% Si-doped TiO ultrathin layers on sample surfaces, i.e. Ti-silicate. ZrO, and TiO ultrathin films show excellent corrosion endurance property in basic and neutral solutions. Simultaneously, 304 stainless steel coated with PEALD-HfO is found to have a lower corrosion rate than that with TALD-HfO by means of electrochemical measurement. The pre-treatment of plasma H to 304 stainless steel can effectively reduce interfacial impurities and porosity of overlayers with significantly enhanced corrosion endurance. Above all, the chemical stability and anti-corrosion properties of IV group metal oxide coatings can be improved by using PEALD technique, post-annealing process and plasma H pre-treatment to substrates.
超薄IV族金属氧化物薄膜（TiO、ZrO和HfO）的广泛应用可能使材料暴露于具有潜在反应活性的蚀刻剂和溶剂中，因此需要其具有卓越的化学稳定性和耐腐蚀性。在本文中，通过热原子层沉积（TALD）和等离子体增强原子层沉积（PEALD），在200 °C下于Si上沉积TiO超薄薄膜，而在250 °C下生长ZrO和HfO薄膜以适应其生长温度窗口。使用包括1 mol/L H₂SO₄、1 mol/L HCl、1 mol/L KOH、1 mol/L KCl和18 MΩ去离子水在内的多种化学液体介质，来测试和比较所有这些沉积态IV族金属氧化物薄膜以及不同温度下退火后的样品的化学稳定性。在这些金属氧化物中，TALD/PEALD HfO超薄薄膜表现出最佳的化学稳定性和抗腐蚀性能，在长时间浸入酸性、碱性和中性溶液后厚度没有任何变化。沉积态的TALD ZrO超薄薄膜在1 mol/L HCl中的蚀刻速率为1.06 nm/天，然而其他PEALD ZrO超薄薄膜和退火后的TALD ZrO薄膜表现出更好的抗酸稳定性，这表明了PEALD中引入等离子体O以及后热处理的作用。通过TALD和PEALD沉积的TiO超薄薄膜在酸性溶液中蚀刻缓慢，但PEALD可使TiO的蚀刻速率降低约41%。退火后，TiO超薄薄膜具有令人满意的耐腐蚀性，这归因于从非晶态到锐钛矿相的结晶转变以及在样品表面形成5% Si掺杂的TiO超薄层，即钛硅酸盐。ZrO和TiO超薄薄膜在碱性和中性溶液中表现出优异的耐腐蚀性能。同时，通过电化学测量发现，涂覆有PEALD-HfO的304不锈钢比涂覆有TALD-HfO的304不锈钢具有更低的腐蚀速率。对304不锈钢进行等离子体H预处理可有效减少覆盖层的界面杂质和孔隙率，并显著提高耐腐蚀性能。最重要的是，通过使用PEALD技术、后退火工艺以及对衬底进行等离子体H预处理，可以提高IV族金属氧化物涂层的化学稳定性和抗腐蚀性能。
