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CMOS-MEMS test-key for extracting wafer-level mechanical properties.

ABSTRACT: This paper develops the technologies of mechanical characterization of CMOS-MEMS devices, and presents a robust algorithm for extracting mechanical properties, such as Young's modulus, and mean stress, through the external electrical circuit behavior of the micro test-key. An approximate analytical solution for the pull-in voltage of bridge-type test-key subjected to electrostatic load and initial stress is derived based on 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. The test cases include the test-key fabricated by a TSMC 0.18 ?m standard CMOS process, and the experimental results refer to Osterberg's work on the pull-in voltage of single crystal silicone microbridges. The extracted material properties calculated by the present algorithm are valid. Besides, this paper also analyzes the robustness of this algorithm regarding the dimension effects of test-keys. 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 process is non-destructive.

SUBMITTER: Chuang WC

PROVIDER: S-EPMC3571828 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature

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CMOS-MEMS test-key for extracting wafer-level mechanical properties.

Chuang Wan-Chun WC Hu Yuh-Chung YC Chang Pei-Zen PZ

Sensors (Basel, Switzerland) 20121212 12

This paper develops the technologies of mechanical characterization of CMOS-MEMS devices, and presents a robust algorithm for extracting mechanical properties, such as Young's modulus, and mean stress, through the external electrical circuit behavior of the micro test-key. An approximate analytical solution for the pull-in voltage of bridge-type test-key subjected to electrostatic load and initial stress is derived based on Euler's beam model and the minimum energy method. Then one can use the a ...[more]

PMID: 23235449

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Project description:A wafer scale bulge testing system has been constructed to study the mechanical properties of thin films and microstructures. The custom built test stage was coupled with a pressure regulation system and optical profilometer which gives high accuracy three-dimensional topographic images collected on the time scale of seconds. Membrane deflection measurements can be made on the wafer scale (50-150 mm) with up to nanometer-scale vertical resolution. Gauge pressures up to 689 kPa (100 psi) are controlled using an electronic regulator with and accuracy of approximately 0.344 kPa (0.05 psi). Initial testing was performed on square diaphragms 350, 550, and 1200 microm in width comprised of 720+/-10 nm thick low pressure chemical vapor deposited silicon nitride with approximately 20 nm of e-beam evaporated aluminum. These initial experiments were focused on measuring the system limitations and used to determine what range of deflections and pressures can be accurately measured and controlled. Gauge pressures from 0 to approximately 8.3 kPa (1.2 psi) were initially applied to the bottom side of the diaphragms and their deflection was subsequently measured. The overall pressure resolution of the system is good (approximately 350 Pa) but small fluctuations existed at pressures below 5 kPa leading to a larger standard deviation between deflection measurements. Analytical calculations and computed finite element analysis deflections closely matched those empirically measured. Using an analytical solution that relates pressure deflection data for the square diaphragms the Young's modulus was estimated for the films assuming a Poisson's ratio of v=0.25. Calculations to determine Young's modulus for the smaller diaphragms proved difficult because the pressure deflection relationship remained in the linear regime over the tested pressure range. Hence, the calculations result in large error when used to estimate the Young's modulus for the smaller membranes. The deflection measurements of three 1200 x 1200 microm(2) Si(3)N(4-x) membranes were taken at increased pressures (>25 kPa) to increase nonlinearity and better determine Young's modulus. This pressure-deflection data were fit to an analytical solution and Young's modulus estimated to be 257+/-3 GPa, close to those previously reported in literature.

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CMOS-MEMS test-key for extracting wafer-level mechanical properties.

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CMOS-MEMS test-key for extracting wafer-level mechanical properties.

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