Experimental Mechanics

, Volume 39, Issue 3, pp 162–170 | Cite as

Tensile testing of polysilicon

  • W. N. SharpeJr.
  • K. T. Turner
  • R. L. Edwards
Article

Abstract

Tensile specimens of polysilicon are deposited on a silicon wafer; one end remains affixed to the wafer and the other end has a relatively large paddle that can be gripped by an electrostatic probe. The overall length of the specimen is less than 2 mm, but the smooth tensile portion can be as small as 1.5×2μm in cross section and 50μm long. The specimen is pulled by a computer-controlled translation stage. Force is recorded with a 100-g load cell, whereas displacement is recorded with a capacitance-based transducer. Strain can be measured directly on wider specimens with laser-based interferometry from two small gold markers deposited on the smooth portion of the specimen. The strength of this linear and brittle material is measured with relative ease. Young's modulus measurement is more difficult; it can be determined from either the stress-strain curve, the record of force versus displacement or the comparison of the records of two specimens of different sizes. Specimens of different sizes—thicknesses of 1.5 or 3.5 μm, widths from 2 to 50 μm and lengths from 50 to 500 μm—were tested. The average tensile strength of this polysilicon is 1.45±0.19 GPa (210 ±28 ksi) for the 27 specimens that could be broken with electrostatic gripping. The average Young's modulus from force displacement records of 43 specimens is 162±14 GPa (23.5 ±2.0×103 ksi). This single value is misleading because the modulus values tend to increase with decreasing specimen width; that is not the case for the strength. The three methods for determining the modulus agree in general, although the scatter can be large.

Key Words

Microelectromechanical systems Young's modulus strength polysilicon tensile tests 

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References

  1. 1.
    Sharpe, W.N., Jr., Yuan, B., and Edwards, R.L., “Variations in Mechanical Properties of Polysilicon,” Proceedings of the 43rd International Symposium of the Instrumentation Society of America, Orlando, FL, 179–188 (1997).Google Scholar
  2. 2.
    Koskinen, J., Steinwall, E., Soave, R. andJohnson, H.H., “Microtensile Testing of Free-standing Polysilicon Fibers of Various Grain Sizes”.J. Micromech. Microeng.,35,13–17 (1993).Google Scholar
  3. 3.
    Biebl, M. and Philipsborn, H.V., “Fracture Strength of Doped and Undoped Polysilicon,” Transducers '95-Eurosensors IX, Proceedings of the 8th International Conference on Solid-State Sensors and Actuators, and Eurosensors IX, Stockholm, 72–75 (1995).Google Scholar
  4. 4.
    Read, D.T. andMarshall, J.C., “Measurements of Fracture Strength and Young's Modulus of Surface-micromachined Polysilicon,”Microlithography and Metrology in Micromachining II,SPIE 2880,56–63 (1966).Google Scholar
  5. 5.
    Tsuchiya, T., Tabata, T., Sakata, S., and Tagi, Y., “Specimen Size Effect on Tensile Strength of Surface Micromachined Polycrystalline Silicon Thin Films,” Proceedings of the Tenth IEEE International Workshop on Microelectromechanical Systems, Nagoya Japan, 529–534 (1997).Google Scholar
  6. 6.
    Greek, S. andJohansson, S., “Tensile Testing of Thin Film Microstructures,”Micromachined Devices and Components III,SPIE3224,344–351 (1997).Google Scholar
  7. 7.
    Sharpe, W.N. Jr., Yuan B. andEdwards, R.L., “A New Technique for Measuring the Mechanical Properties of Thin Films,”J. Microelectromech. Sys.,6,193–199 (1997).Google Scholar
  8. 8.
    Sharpe, W.N., Jr., Yuan, B., Edwards, R.L., and Vaidyanathan, R., “Measurements of Young's Modulus, Poisson's Ratio, and Tensile Strength of Polysilicon,” Proceedings of the Tenth IEEE International Workshop on Microelectromechanical Systems, Nagoya, Japan, 424–429 (1997).Google Scholar
  9. 9.
    Sharpe, W.N., Jr., “An Interferometric Strain/Displacement Measurement System,” NASA Technical Memorandum 101638 (1989).Google Scholar
  10. 10.
    Chasiotis, I. andKnauss, W., “Mechanical Properties of Thin Polysilicon Films by Means of Probe Microscopy,”Materials and Device Characterization in Micromachining,SPIE 3512,66–75 (1998).Google Scholar
  11. 11.
    ASTM Standard E-111, “Standard Test Method for Young's Modulus, Tangent Modulus, and Chord Modulus,” Annual Book of ASTM Standards, American Society for Testing and Materials, Philadelphia (1998).Google Scholar
  12. 12.
    Sharpe, W.N., Jr., Turner, K.T. andEdwards, R.L., “Polysilicon Tensile Testing with Electrostatic Gripping,”Microelectromechanical Structures for Materials Research, Materials Research Society,518,191–196 (1998).Google Scholar
  13. 13.
    Sharpe, W.N. Jr., Brown, S., Johnson, G.C., andKnauss, W.Round-robin Tests of Modulus and Strength of Polysilicon,”Microelectromechanical Structures for Materials Research, Materials Research Society 518,57–65 (1998).Google Scholar

Copyright information

© Society for Experimental Mechanics, Inc. 1999

Authors and Affiliations

  • W. N. SharpeJr.
    • 1
  • K. T. Turner
    • 1
  • R. L. Edwards
    • 2
  1. 1.Department of Mechanical EngineeringJohns Hopkins UniversityBaltimore
  2. 2.Applied Physics LaboratoryJohns Hopkins UniversityLaurel

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