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MEMS 5-in-1 RM Slide Set #7: In-Plane Length Measurements

Reference Materials 8096 and 8097 for MEMS 5-in-1 Test Chips for In-Plane Length Measurements in the Nanoscale Metrology Group of NIST.

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MEMS 5-in-1 RM Slide Set #7: In-Plane Length Measurements

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  1. MEMS 5-in-1 RM Slide Set #7 Reference Materials 8096 and 8097 The MEMS 5-in-1 Test Chips – In-Plane Length Measurements Physical Measurement Laboratory Semiconductor and Dimensional Metrology Division Nanoscale Metrology Group MEMS Measurement Science and Standards Project Photo taken by Curt Suplee, NIST

  2. List of MEMS 5-in-1 RM Slide Sets

  3. Outline for In-Plane Length Measurements

  4. 1. References to Consult • Overview 1. J. Cassard, J. Geist, and J. Kramar, “Reference Materials 8096 and 8097 – The Microelectromechanical Systems 5-in-1 Reference Materials: Homogeneous and Stable,” More-Than-Moore Issue of ECS Transactions, Vol. 61, May 2014. 2. J. Cassard, J. Geist, C. McGray, R. A. Allen, M. Afridi, B. Nablo, M. Gaitan, and D. G. Seiler, “The MEMS 5-in-1 Test Chips (Reference Materials 8096 and 8097),” Frontiers of Characterization and Metrology for Nanoelectronics: 2013, NIST, Gaithersburg, MD, March 25-28, 2013, pp. 179-182. 3. J. Cassard, J. Geist, M. Gaitan, and D. G. Seiler, “The MEMS 5-in-1 Reference Materials (RM 8096 and 8097),” Proceedings of the 2012 International Conference on Microelectronic Test Structures, ICMTS 2012, San Diego, CA, pp. 211-216, March 21, 2012. • User’s guide (Section 6, pp. 114-131) 4. J.M. Cassard, J. Geist, T.V. Vorburger, D.T. Read, M. Gaitan, and D.G. Seiler, “Standard Reference Materials: User’s Guide for RM 8096 and 8097: The MEMS 5-in-1, 2013 Edition,” NIST SP 260-177, February 2013 (http://dx.doi.org/10.6028/NIST.SP.260-177). • Standard 5. ASTM E 2244-11e1, “Standard Test Method for In-Plane Length Measurements of Thin, Reflecting Films Using an Optical Interferometer,” September 2013. (Visit http://www.astm.org for ordering information.) • Fabrication 6. The RM 8096 chips were fabricated through MOSIS on the 1.5 µm On Semiconductor (formerly AMIS) CMOS process. The URL for the MOSIS website is http://www.mosis.com. The bulk-micromachining was performed at NIST. 7. The RM 8097 chips were fabricated at MEMSCAP using MUMPs-Plus! (PolyMUMPs with a backside etch). The URL for the MEMSCAP website is http://www.memscap.com.

  5. 2a. In-Plane Length Overview L • Definition: The straight-line distance between two transitional edges • Purpose: For use when interferometric measurements are preferred over using the design dimensions (e.g., when measuring in-plane deflections and when measuring lengths in an unproven fabrication process) • Test structure: In-plane length test structure • Instrument: Interferometric microscope or comparable instrument • Method: Multiple key corner points are identified and recorded along with their uncertainties for an in-plane length calculation, taking into account offset and misalignment 5

  6. 2b. In-Plane Length Equation (for one trace) where Lmeasured in-plane length Lmeasmeasured in-plane length used to calculate Lalign Lmeastmeasured in-plane length from trace “t” Lalignmeasured in-plane length after correcting for misalignment Loffsetmeasurement-specific in-plane length correction term x1uppertx-value that locates the upper corner associated with Edge 1 in Trace “t” x2uppertx-value that locates the upper corner associated with Edge 2 in Trace “t” calxx-calibration factor (to account for misalignment) (including a correction term)

  7. 2c. Data Sheet Uncertainty Equations • In-plane length combined standard uncertainty, ucL, equation where uLdue to uncertainty in the calculated length urepeat(L)due to uncertainty in the in-plane length measurement from four data traces uxcaldue to uncertainty in the x-calibration ualigndue to alignment uncertainty uoffsetdue to uncertainty of the value for Loffset urepeat(samp)due to repeatability • The data sheet (DS) expanded uncertainty equation is where k=2 is used to approximate a 95 % level of confidence

  8. 2c. Data Sheet Uncertainty Equations and • For RMs 8096 and 8097, Loffset due to: • Edges facing each other • For 8096, it also corrects for measuring the edges of the covering oxide (as opposed to the m2 edges) • Averaging of pixels

  9. 2d. ROI Uncertainty Equation UROI expanded uncertainty recorded on the Report of Investigation (ROI) UDS expanded uncertainty as obtained from the data sheet (DS) Ustability stability expanded uncertainty

  10. 3. Location of Structure on RM Chip (The 2 Types of Chips) • RM 8097 • Fabricated using a polysilicon multi-user surface-micromachining MEMS process with a backside etch • Material properties of the first or second polysilicon layer are reported • Chip dimensions: 1 cm x 1 cm • RM 8096 • Fabricated on a multi-user 1.5 µm CMOS process followed by a bulk-micromachining etch • Material properties of the composite oxide layer are reported • Chip dimensions: 4600 µm x 4700 µm Lot 95 Lot 98

  11. 3a. Location of Structure on RM 8096 Loo Lii Lio Top view of in-plane length test structures Locate the structure in this group given the information on the NIST-supplied data sheet

  12. 3b. Location of Structure on RM 8097 Top view of in-plane length test structure p1 Locate the structure in one of these arrays given the information on the NIST-supplied data sheet p2

  13. L a΄ a e e΄ m2 Edge 4 Edge 3 Edge 3 Edge 4 y x 4a. Test Structure Description (For RM 8096) Top view of in-plane length test structures

  14. y x L poly0 a΄ a q p poly1 poly1 anchor to poly0 e e΄ Edge 1 Edge 2 Edge 5 4b. Test Structure Description (For RM 8097) Top view of in-plane length test structure

  15. 5. Calibration Procedure • Calibrate instrument in the z-direction to obtain calz • As specified for step-height calibrations • Calibrate instrument in the x- and y-directions • On a yearly basis, or after the instrument as been serviced • A 10 µm grid (or finer grid) ruler is used • Orient the ruler in the x-direction • Record rulerx as the maximum FOV in the x-direction (as measured on the screen of the interferometric microscope) • Estimate xcal (standard deviation in a ruler measurement) • Calculate calx (the x-calibration factor) • Record xres • Repeat the above in the y-direction to obtain caly • Supply the following inputs to the data sheet: • calx, rulerx, xcal, xres, caly, and calz scopex = the maximum x-value obtained from an extracted 2D data trace

  16. y x L poly0 a΄ a q p poly1 poly1 anchor to poly0 e e΄ Edge 1 Edge 2 Edge 5 6. Measurement Procedure • Four 2D data traces are extracted from a 3D data set • For Traces a, a, e, and e • Enter into the data sheet: • The uncalibrated values (x1uppert and x2uppert) for Edge 1 and Edge 2 • To find xupper: • Examine the x values between Point “p” and Point “q” (as shown in figure for Trace a Edge 1) • The x value that most appropriately locates the upper corner of the transitional edge is called xupper or x1upperain this case • The values for n1t and n2t • The maximum uncertainty associated with the identification of xupperis ntxrescalx • If it is easy to identify one point, nt = 1 • For a less obvious point that locates the upper corner, nt> 1 • The uncalibrated values for ya and ye • DetermineLmeas t indicates the data trace (a, a, e, or e) xres = uncalibrated resolution in x-direction

  17. Lmeas α Lalign (x2uppera΄, ya΄) (x1uppera΄, ya΄) Lmeasa΄ Trace a΄ Δx1 α2 Δy Edge 1 Edge 2 α1 Lmease΄ Δx2 Trace e΄ (x2uppere΄, ye΄) (x1uppere΄, ye΄) 6. Measurement Procedure (continued) • Determine Lalign if , then and and if , then and

  18. m2 Loo Lii y x 6. Measurement Procedure (continued) • Determine Loffset • Obtain 12 3D data sets • Lalignis calculated for each data set • Calculate Lalignave • Loffset = Ldes – Lalignave • Or, obtain 4 3D data sets • Determine Lalign for both Lii and Loo • Calculate Liialignave • Calculate Looalignave • Loffset = (Looalignave – Liialignave)/2 • Determine L • L = Lalign + Loffset Edge 1 Edge 2 Edge 4 Edge 3

  19. 7. Using the Data Sheet • Find Data Sheet L.0 • On the MEMS Calculator website (Standard Reference Database 166) accessible via the NIST Data Gateway (http://srdata.nist.gov/gateway/) with the keyword “MEMS Calculator” • Note the symbol next to this data sheet. This symbol denotes items used with the MEMS 5-in-1 RMs. • Using Data Sheet L.0 • Click “Reset this form” • Supply INPUTS to Tables 1 and 2 • Click “Calculate and Verify” • At the bottom of the data sheet, make sure all the pertinent boxes say “ok.” If a pertinent box says “wait,” address the issue and “recalculate.” • Compare both the inputs and outputs with the NIST-supplied values

  20. 8. Using the MEMS 5-in-1To Verify In-Plane Length Measurements • If your criterion for acceptance is: where DL positive difference between the in-plane length value of the customer, L(customer), and that appearing on the ROI, L UL(customer) in-plane length expanded uncertainty of the customer UL in-plane length expanded uncertainty on the ROI, UROI • Then can assume measuring in-plane length according to ASTM E2244 according to your criterion for acceptance if: • Criteria above satisfied and • No pertinent “wait” statements at the bottom of your Data Sheet L.0

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