Hostname: page-component-78c5997874-v9fdk Total loading time: 0 Render date: 2024-11-03T08:50:09.161Z Has data issue: false hasContentIssue false
  • English
  • Français

Thin Film Polymer Stress Measurement Using Piezoresistive Anisotropically Etched Pressure Sensors

Published online by Cambridge University Press:  15 February 2011

G. Bitko ,
R. Harries ,
J. Matldn ,
A. C. McNeil ,
D. J. Monk ,
M. Shah  and
J. Wertz
G. Bitko
Affiliation:
Motorola, Semiconductor Products Sector, Sensor Products Division, M/D D138, 5005 E. McDowell Rd., Phoenix, AZ 85008
R. Harries
Affiliation:
Motorola, Semiconductor Products Sector, Sensor Products Division, M/D D138, 5005 E. McDowell Rd., Phoenix, AZ 85008
J. Matldn
Affiliation:
Motorola, Semiconductor Products Sector, Sensor Products Division, M/D D138, 5005 E. McDowell Rd., Phoenix, AZ 85008
A. C. McNeil
Affiliation:
Motorola, Semiconductor Products Sector, Sensor Products Division, M/D D138, 5005 E. McDowell Rd., Phoenix, AZ 85008
D. J. Monk
Affiliation:
Motorola, Semiconductor Products Sector, Sensor Products Division, M/D D138, 5005 E. McDowell Rd., Phoenix, AZ 85008
M. Shah
Affiliation:
Motorola, Semiconductor Products Sector, Sensor Products Division, M/D D138, 5005 E. McDowell Rd., Phoenix, AZ 85008
J. Wertz
Affiliation:
Motorola, Semiconductor Products Sector, Sensor Products Division, M/D D138, 5005 E. McDowell Rd., Phoenix, AZ 85008
Get access

Abstract

Silicon bulk micromachined piezoresistive pressure sensors are very sensitive to applied stresses: that is, applied pressure and/or packaging-related stresses. Device encapsulation has been observed to affect the electrical output of the pressure sensor significantly. The magnitude of the zero applied pressure output voltage (i.e., the offset voltage) that can be attributed to a thin film encapsulant is proportional to the magnitude of the roomtemperature thermal stress of that film. Parylene C coatings have been used as encapsulants in this work. Finite element and analytical modeling techniques were used to evaluate the effect of material property variation on the offset of a pressure sensor. A simple, linear expression of offset as a function of a material property parametric group, that includes: parylene thickness, parylene biaxial modulus, parylene CTE, silicon thickness, and annealing temperature; has been established. Experimental analysis of parylene coated pressure sensors and parylene coated silicon and gallium arsenide wafers was performed to confirm the resulting model. Known variations in parylene material properties caused by processing (i.e., uncontrolled deposition, annealing, and high temperature storage) have been used as an experimental vehicle for this purpose. An empirical relationship between offset voltage on parylene coated devices and room-temperature thermal stress on parylene coated wafers that have been exposed to the same processing is a linear expression with a similar slope to the modeling results. Furthermore, stress measurements from parylene coated silicon wafers and parylene coated gallium arsenide wafers have been used to estimate the parylene biaxial modulus (approximately 5000 MPa) and the parylene CTE (approximately 50 ppm/°C) independently. These material properties were observed to shift following parylene annealing and high temperature storage exposure experiments in a manner that is consistent with the established model.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 436: Symposium CC – Thin Films Stresses and Mechanical Properties VI , 1996 , 365
Copyright
Copyright © Materials Research Society 1997

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

[1] Townsend, P. H., Weihs, T. P., Sanchez, J., E., J., and Børgesen, P., ”Thin Films: Stresses and Mechanical Properties IV,” Materials Research Society Symposium Proceedings, vol.308. Pittsburgh, PA: MRS, 1993.Google Scholar
[2] Monk, D. J. and Shah, M., ”Thin Film Polymer Stress Measurement Using Piezoresistive Anisotropically Etched Pressure Sensors,” Mat. Res. Soc. Symp. Proc., San Francisco, CA, pp. 103–109, 1995.Google Scholar
[3] Monk, D. J., Maudie, T., Stanerson, D., Wertz, J., Bitko, G., Matkin, J., and Petrovic, S., ”Media Compatible Packaging and Environmental Testing of Barrier Coating Encapsulated Silicon Pressure Sensors,” 1996 Solid- State Sensors and Actuators Workshop, Hilton Head, SC, to be published, 1996.Google Scholar
[4] Noble, M., ”Environmental Concerns for Integrated Circuit Sensors,” Measurement + Control, vol.19, pp. 210–213, 1986.Google Scholar
[5] Petersen, K. E., ”Silicon as a Mechanical Material,” Proc. IEEE, vol.70, pp. 420–457, 1982.Google Scholar
[6] Sulouff, R. E., Jr., ”Silicon Sensors for Automotive Applications,” International Conference on Solid-State Sensors and Actuators: Transducers ‘91, San Francisco, CA, pp. 170–176, 1991.Google Scholar
[7] Shah, M. K., McNeil, A. C., Summers, M. D., and Meyer, B. D., ”Application of Finite Element Analysis to Predict the Performance of Piezo-resistive Pressure Sensor,” Sensors in Electronic Packaging, MEDVol. 3/EEP-Vol.14, 1995 ASME International Mechanical Engineering Congress and Exposition, San Francisco, pp. 79–85, 1995.Google Scholar
[8] Young, W. C. and Roark, R. J., Formulas for Stress and Strain, 5th ed. New York: McGraw-Hill, 1982.Google Scholar
[9] Gorham, W. F., ”A New, General Synthetic Method for the Preparation of Linear Poly-p-xylylenes,” J. Polym. Sc., vol.4, pp. 3027–3039, 1966.Google Scholar
[10] Bachman, B. J., ”Poly-P-Xylylene as a Dielectric Material,” 1st International SAMPE Electronics Conference, Santa Clara, CA, pp. 431–440, 1987.Google Scholar
[11] Niegisch, W. D. and Gorham, W. F., ”Xylylene Polymers,” in Encyclopedia of Polymer Science and Technology, vol.15. New York: John Wiley & Sons, Inc., pp. 98–124, 1971.Google Scholar
[12] Bitko, G., Monk, D. J., Toh, H. S., and Wertz, J., ”Annealing Thin Film Parylene Coatings for Media Compatible Pressure Sensors”, Motorola Technical Developments, to be published, 1995.Google Scholar
[13] Wu, P. K., Yang, G.-R., Mcdonald, J. F., and Lu, T.-M., ”Surface Reaction and Stability of Parylene N and F Thin Films at Elevated Temperatures,” J. Elect. Mati., vol.24, pp. 53–58, 1995.Google Scholar
[14] Monk, D. J., Toh, H. S., and Wertz, J., ”Oxidative Degradation of Parylene C (Poly (monochloro-para-xylylene)) Thin Films on Bulk Micromachined Piezoresistive Silicon Pressure Sensors,” Sensors and Materials, to be published, 1996.Google Scholar
[15] Sabeti, R., Charlson, E. M., and Charlson, E. J., ”Selective Deposition of Parylene,” Poly. Comm., vol.30, pp. 166–169, 1989.Google Scholar
[ 16] Brantley, W. A., ”Calculated Elastic Constants for Stress Problems Associated with Semiconductor Devices,” J. Appl. Phys., vol.44, pp. 534–535, 1973.Google Scholar
[17] Hu, J. M. and Pecht, M., ”Temperature Dependence of the Mechanical Properties of GaAs Wafers,” J Elect. Packaging, vol.113, pp. 331–336, 1991.Google Scholar
[18] Dabral, S., Zhang, X., Wang, B., Yang, G.-R., Lu, T.-M., and McDonald, J. F., ”Metal-Parylene Interconnection Systems,” Materials Research Society Symposium Proceedings: Low-Dielectric Constant Materials—Synthesis and Applications in Microelectronics, San Francisco, pp. 205–215, 1995.Google Scholar