M-TEST: A test chip for MEMS material property measurement using electrostatically actuated test structures

A set of electrostatically actuated microelectromechanical test structures is presented that meets the emerging need for microelectromechanical systems (MEMS) process monitoring and material property measurement at the wafer level during both process development and manufacturing. When implemented as a test chip or drop-in pattern for MEMS processes, M-Test becomes analogous to the electrical MOSFET test structures (often called E-Test) used for extraction of MOS device parameters. The principle of M-Test is the electrostatic pull-in of three sets of test structures [cantilever beams (CB's), fixed-fixed beams (FB's), and clamped circular diaphragms (CD's)] followed by the extraction of two intermediate quantities (the S and B parameters) that depend on the product of material properties and test structure geometry. The S and B parameters give a direct measure of the process uniformity across an individual wafer and process repeatability between wafers and lots. The extraction of material properties (e.g., Young's modulus, plate modulus, and residual stress) from these S and B parameters is then accomplished using geometric metrology data. Experimental demonstration of M-Test is presented using results from MIT's dielectrically isolated wafer-bonded silicon process. This yielded silicon plate modulus results which agreed with literature values to within /spl plusmn/4%. Guidelines for adapting the method to other MEMS process technologies are presented.

[1]  S. Timoshenko,et al.  THEORY OF PLATES AND SHELLS , 1959 .

[2]  W. Brantley.  Calculated elastic constants for stress problems associated with semiconductor devices , 1973 .

[3]  K. Petersen.  Dynamic micromechanics on silicon: Techniques and devices , 1978, IEEE Transactions on Electron Devices.

[4]  R. Howe,et al.  Microfabricated structures for the in situ measurement of residual stress, Young’s modulus, and ultimate strain of thin films , 1987 .

[5]  Mark G. Allen,et al.  Calibrated measurements of elastic limit, modulus, and the residual stress of thin films using micromachined suspended structures , 1988, IEEE Technical Digest on Solid-State Sensor and Actuator Workshop.

[6]  K. Najafi,et al.  A novel technique and structure for the measurement of intrinsic stress and Young's modulus of thin films , 1989, IEEE Micro Electro Mechanical Systems, , Proceedings, 'An Investigation of Micro Structures, Sensors, Actuators, Machines and Robots'.

[7]  Jan-Åke Schweitz,et al.  mechanical Characterization of Thin Films by Micromechanical Techniques , 1992 .

[8]  Khalil Najafi,et al.  Electronic Determination of the Modulus of Elasticity and Intrinsic Stress of Thin Films using Capacitive Bridges , 1992 .

[9]  Jacob K. White,et al.  Implementation of MEMCAD system for electrostatic and mechanical analysis of complex structures from mask descriptions , 1993, [1993] Proceedings IEEE Micro Electro Mechanical Systems.

[10]  S. Senturia,et al.  Self-consistent simulation and modelling of electrostatically deformed diaphragms , 1994, Proceedings IEEE Micro Electro Mechanical Systems An Investigation of Micro Structures, Sensors, Actuators, Machines and Robotic Systems.

[11]  M. Schmidt,et al.  Monitoring plasma over-etching of Wafer-bonded Microstructures , 1995, Proceedings of the International Solid-State Sensors and Actuators Conference - TRANSDUCERS '95.

[12]  S. Senturia,et al.  3D coupled electro-mechanics for MEMS: applications of CoSolve-EM , 1995, Proceedings IEEE Micro Electro Mechanical Systems. 1995.