Abstract

In order to study (i) how the in-plane stress develops in alkoxide-derived oxide gel films on heating and (ii) how the residual stress changes with firing temperature, we prepared titania and silica gel films on Si(100) wafers from alkoxide solutions. The intrinsic stress was previously measured in situ during heating up to 500 °C for the gel films, where the stress was calculated from the radius of curvature of the substrate bending. Because the commercialized apparatus that measures the substrate bending has an upper limitation of temperature at 500 °C, we devised a method for estimating the intrinsic stress over 500 °C in the present work. The gel films were heated from 100 °C up to 900 or 1000 °C successively and cumulatively. Then we estimated the intrinsic stress over 500 °C by monitoring the changes in stress in situ during heating and cooling for the cumulatively fired films. Combining the estimated data over 500 °C with those measured below 500 °C, we found that the intrinsic stress increases and then decreases around to zero with temperature for both titania and silica gel films, which we recognized as a general trend in alkoxide-derived oxide thin films in conjunction with our previous work on yttria stabilized zirconia (YSZ) films. Regarding the residual stress, the titania and silica films exhibited different behaviors. The titania film showed an increase followed by a slight decrease, and finally a significant increase in residual tensile stress with increasing firing temperature. The silica films also exhibited an increase and a decrease in residual tensile stress with increasing firing temperature, but the stress continued to decrease and turned into compressive one at ca 800 °C. The last decrease in residual tensile stress that turned into compressive one resulted from the development of compressive thermal stress during cooling, which is due to the smaller thermal expansion coefficient of silica than silicon. It was thus clarified that the difference in thermal expansion coefficient between the film and the substrate becomes prominent in residual stress when the films are fired at high temperatures like 800 °C. Thus we could successfully obtain a general view on how the residual stress changes with firing temperature as well as on how the in-plane stress develops during heating thanks to the information on the stress development in the sol–gel-derived titania and silica films that was added to the information on the YSZ films.

中文翻译：

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Si（100）衬底上溶胶-凝胶衍生的二氧化钛和二氧化硅薄膜中的面内应力发展

抽象的

为了研究（i）加热时醇盐衍生的氧化物凝胶薄膜的面内应力如何发展，以及（ii）焙烧温度下残余应力如何变化，我们在Si（100）晶片上制备了二氧化钛和硅胶膜醇盐溶液。固有应力是在加热到500°C的凝胶膜之前预先测量的，其中应力是根据基材弯曲的曲率半径计算得出的。因为测量衬底弯曲的商业化设备在500°C下具有温度的上限，所以在本工作中，我们设计了一种方法来估算500°C以上的固有应力。依次将凝胶薄膜从100°C连续加热到900或1000°C。然后，我们通过监测累积烧制的薄膜在加热和冷却过程中的原位应力变化来估计500°C以上的固有应力。将超过500°C的估计数据与低于500°C的测量数据相结合，我们发现二氧化钛和硅胶膜的内应力随温度的升高先升高后降低至零，这被我们认为是醇盐衍生的总体趋势氧化物薄膜以及我们之前在氧化钇稳定的氧化锆（YSZ）薄膜上的工作。关于残余应力，二氧化钛和二氧化硅膜表现出不同的行为。二氧化钛膜显示出增加，随后略有下降，最后随着烧成温度的增加，残余拉伸应力显着增加。二氧化硅膜还随着焙烧温度的升高而表现出残余拉伸应力的增加和减少，但应力持续降低并在约800°C时变成压缩应力。残余拉伸应力最终变为压缩应力的最后一个减少是由于冷却过程中压缩热应力的产生，这是由于二氧化硅的热膨胀系数小于硅的热膨胀系数。因此明确了，当在诸如800℃的高温下烧制膜时，膜与基板之间的热膨胀系数的差异在残余应力中变得显着。