CMOS-MEMS Testkey for Wafer-Level Mechanical Properties Extracting
Date Issued
2011
Date
2011
Author(s)
Chuang, Wan-Chun
Abstract
This research develops the technologies of mechanical characterization of CMOS-MEMS devices, and presents a robust algorithm for extracting mechanical properties, such as Young’s modulus, mean stress, and gradient stress, through the external electrical circuit behavior and pre-deformation of the micro test-key. First, an approximate analytical solution for the pull-in voltages of bridge-type testkey subjected to electrostatic loads and initial stress is derived based on the Euler’s beam model and the minimum energy method. Then one can use the aforesaid closed form solution of the pull-in voltage to extract the Young’s modulus and mean stress of the test structures. Second, according to the flexure formula and elastic curve of a cantilever beam, the gradient stress can be obtained by measuring the pre-deformation of the cantilever-type testkey utilizing White Light Interferometer. The test cases include the testkeys fabricated by TSMC 0.18 μm standard CMOS process, and the experimental results refer to Osterberg’s work about the pull-in voltage of single crystal silicone micro bridges. The extracting material properties calculated by the present algorithm are valid. Besides, this research study the robustness of this algorithm including sensitivity analysis for pull-in voltage measurement and dimension effects of testkeys. This mechanical properties extracting method is expected to be applicable to the wafer-level testing in micro-device manufacture and compatible with the wafer-level testing in IC industry since the test is non-destructive.
Subjects
pull-in voltage
Young’s modulus
mean stress
gradient stress
CMOS-MEMS
Type
thesis
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