Thompson G B, Miller M K, Fraser H L
Department of Metallurgical and Materials Engineering, University of Alabama, A129 Bevill Building, P.O. Box 87020, Tuscaloosa, AL 35487, USA.
Ultramicroscopy. 2004 Jul;100(1-2):25-34. doi: 10.1016/j.ultramic.2004.01.010.
Some of the factors in the preparation of atom probe specimens of metallic multilayer thin films have been investigated. A series of Ti/Nb multilayer films were sputtered deposited on n-doped Si [001] substrates with either 5 or 0.05Omega cm resistivity. Each wafer was pre-fabricated into a series of 5 microm x 5 microm x approximately 80 microm island posts by photolithography and reactive ion etching. Once the film was grown on the wafer, a Si post was mounted to either a tungsten or stainless steel fine tip needle that was mechanically crimped to a Cu tube for handling. The specimen was then loaded into a Focus Ion Beam instrument where a sacrificial Pt cap was in situ deposited onto the surface of the film and subsequently annularly ion milled into the appropriate geometry. The Pt cap was found to be an effective method in reducing Ga ion damage and implantation into the film during milling. The multilayers deposited on the high resistivity Si exhibited uncontrolled field evaporation which lead to high mass tails in the mass spectra, a reduction in the mass resolution, high background noise, propensity for "flash-failure", and a variation in the apparent layer thickness as the experiment elapsed in time. The multilayers deposited on lower resistivity Si did not suffer from these artifacts.
对金属多层薄膜原子探针样品制备中的一些因素进行了研究。一系列Ti/Nb多层膜被溅射沉积在电阻率为5或0.05Ω·cm的n型掺杂Si[001]衬底上。通过光刻和反应离子蚀刻将每个晶圆预先制成一系列5μm×5μm×约80μm的岛状柱体。一旦薄膜在晶圆上生长，将一个Si柱体安装到机械压接到用于操作的Cu管上的钨或不锈钢细尖针上。然后将样品加载到聚焦离子束仪器中，在那里将牺牲性Pt帽原位沉积在薄膜表面，随后环形离子铣削成合适的几何形状。发现Pt帽是减少铣削过程中Ga离子对薄膜的损伤和注入的有效方法。沉积在高电阻率Si上的多层膜表现出不受控制的场蒸发，这导致质谱中出现高质量拖尾、质量分辨率降低、高背景噪声、“闪断”倾向以及随着实验时间的推移表观层厚度的变化。沉积在较低电阻率Si上的多层膜没有这些假象。
