A wafer mapping technique for residual stress in surface micromachined films
A wafer mapping technique for residual stress in surface micromachined films
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DOI：
10.1088/0960-1317/26/9/095013
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发表时间：
2016-09-01
影响因子：
2.3
通讯作者：
Walton, A. J.
中科院分区：
文献类型：
--
作者：
Schiavone, G.;Murray, J.;Walton, A. J.
采用可移动结构的 MEMS 器件的设计在很大程度上取决于沉积材料的机械行为。因此，能够充分表征微机械薄膜并自信地预测图案结构的机械性能非常重要。本文提出了一种表征技术，通过使用表面微加工释放的微结构，能够在晶圆级映射 MEMS 薄膜中的残余应力。这些专用 MEMS 测试结构和相关测量技术用于提取有关所研究薄膜的应变和杨氏模量的局部信息。然后通过将该数据与结构的有限元分析进行数值耦合来确定残余应力。本文阐述了测量程序，并通过使用电化学沉积的镍铁合金的案例研究进行了演示，特别容易产生高水平的残余应力。结果表明，该技术能够绘制薄膜不均匀性的晶圆图并识别晶圆之间的差异。通过映射技术与传统晶圆弓形测量获得的结果之间的比较凸显了使用针对不均匀、图案化和表面微机械加工的薄膜定制的程序的优势，而不是简单的标准应力提取方法。所提出的技术揭示了使用传统应力提取方法（例如晶片弓形测量）时通常未探索的详细信息。
The design of MEMS devices employing movable structures is crucially dependant on the mechanical behaviour of the deposited materials. It is therefore important to be able to fully characterize the micromachined films and predict with confidence the mechanical properties of patterned structures. This paper presents a characterization technique that enables the residual stress in MEMS films to be mapped at the wafer level by using microstructures released by surface micromachining. These dedicated MEMS test structures and the associated measurement techniques are used to extract localized information on the strain and Young's modulus of the film under investigation. The residual stress is then determined by numerically coupling this data with a finite element analysis of the structure. This paper illustrates the measurement routine and demonstrates it with a case study using electrochemically deposited alloys of nickel and iron, particularly prone to develop high levels of residual stress. The results show that the technique enables wafer mapping of film non-uniformities and identifies wafer-to-wafer differences. A comparison between the results obtained from the mapping technique and conventional wafer bow measurements highlights the benefits of using a procedure tailored to films that are non-uniform, patterned and surface-micromachined, as opposed to simple standard stress extraction methods. The presented technique reveals detailed information that is generally unexplored when using conventional stress extraction methods such as wafer bow measurements.