1 Physical Measurement Laboratory Semiconductor and Dimensional Metrology Division Nanoscale Metrology Group MEMS Measurement Science and Standards Project MEMS 5-in-1 RM Slide Set #10 Reference Materials 8096 and 8097 The MEMS 5-in-1 Test Chips – Thickness Measurements (for RM 8097) Photo taken by Curt Suplee, NIST

2 List of MEMS 5-in-1 RM Slide Sets Slide Set #Title of Slide Set 1OVERVIEW OF THE MEMS 5-IN-1 RMs 2PRELIMINARY DETAILS THE MEASUREMENTS: 3 Young’s modulus measurements 4 Residual strain measurements 5 Strain gradient measurements 6 Step height measurements 7 In-plane length measurements 8 Residual stress and stress gradient calculations 9 Thickness measurements (for RM 8096) 10 Thickness measurements (for RM 8097) 11REMAINING DETAILS

3 Outline for Thickness Measurements (for RM 8097) 1References to consult 2Thickness for RM 8097 a. Overview b. Equation used c. Data sheet uncertainty equations d. ROI uncertainty equation 3Location of test structure on RM chip 4Test structure description 5Calibration procedure 6Measurement procedure 7Using the data sheet 8Using the MEMS 5-in-1 to verify measurements

4 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 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 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 , March 21, User’s guide (Section 8, pp ) 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 , February 2013 ( Standard 5. SEMI MS2-1113, “Test Method for Step Height Measurements of Thin Films,” November (Visit for ordering information.) Thickness article 6. J.C. Marshall, “New Optomechanical Technique for Measuring Layer Thickness in MEMS Processes,” J. of Microelectromechanical Systems, Vol. 10, No. 1, pp , March Fabrication 7. The RM 8097 chips were fabricated at MEMSCAP using MUMPs-Plus! (PolyMUMPs with a backside etch). The URL for the MEMSCAP website is 1. References to Consult

5 2a. Thickness (for RM 8097) Overview Description: The height of one or more thin-film layers Purpose: Used in the determination of thin film material parameters, such as Young’s modulus Test structure: Cantilever exhibiting stiction Instrument: Interferometric microscope, stylus profilometer, or comparable instrument(s) Method: Calculated from step height measurements of: a) the height of the anchor to the underlying layer (A), b) the height of the stuck portion of the cantilever to the anchor (B), and/or c) the height of the stuck portion of the cantilever to the underlying layer (C) C

6 where Aheight from the underlying layer to the anchor Bheight from the anchor to the top of the stuck portion of the cantilever C calc calculated height from the underlying layer to the top of the stuck portion of the cantilever Hanchor etch depth Jheight from the top of the underlying layer to the bottom of the stuck portion of the cantilever that takes into consideration the roughness of the surfaces, any residue present between the layers and a tilting component 2b-2c. P1 or P2 Thickness Equations and Data Sheet Uncertainty Equations (for RM 8097)

7 Determine the thickness, α, three different ways: Choose the value for α (i.e., α i, α ii, or α iii ) that has the smallest uncertainty unless the value for α has been preselected The data sheet (DS) expanded uncertainty equation is where k=2 is used to approximate a 95 % level of confidence 2b-2c. P1 or P2 Thickness Equations and Data Sheet Uncertainty Equations (for RM 8097)

8 U ROI expanded uncertainty recorded on the Report of Investigation (ROI) U DS expanded uncertainty as obtained from the data sheet (DS) U stability stability expanded uncertainty 2d. ROI Uncertainty Equation

9 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 Lot 95 Lot Location of Cantilever on RM 8097 (The RM 8097 Chips)

10 3. Location of Cantilever on RM 8097 For RM 8097 Layerpoly1 or poly2 W ( µm) 20 L ( µm) Thickness cantilevers: 600 (poly1 only), 650, 700, 750, and 800 In-plane length cantilevers: 24, 80, 200, 500, and 1000 OrientationThickness: 0 º In-plane length: 0 º (poly1 only) and 90 º Quantity of cantilevers 3 of each length for each orientation Thickness: 15 poly1 and 12 poly2 In-plane length: 30 poly1 and 15 poly2 10 Locate the cantilever in one of these groups given the information on the NIST-supplied data sheet Top view of thickness test structure

11 4. Test Structure Description (For RM 8097) Top view of thickness test structure

12 4. Test Structure Description For RM 8097 p2 Top view of cantilevers in in- plane length group p1 Unconventional anchor design Same anchor design as in thickness test structures Top view of thickness test structures p1 p2

13 Calibrate instrument in the z-direction –As specified for step height calibrations 5. Calibration Procedure

14 Measure A (using a stylus profilometer) – optional –Obtain 3 data traces –Level the data with respect to the poly0 layer –From platX Obtain platXa1, platXb1, and platXc1 Obtain s platXa1, s platXb1, and s platXc1 –From platY Obtain platYa1, platYb1, and platYc1 Obtain s platYa1, s platYb1, and s platYc1 Measure C (using an optical interferometer) –Use a high magnification objective –Obtain 3 data traces (typically perpendicular to the beam and crossing the pegged portion of the beam) –Level the data with respect to the poly0 layer –From platZ Obtain platZa2, platZb2, and platZc2 Obtain s platZa2, s platZb2, and s platZc2 –From platX Obtain platXa2, platXb2, and platXc2 Obtain s platXa2, s platXb2, and s platXc2 6. Measurement Procedure C

15 Obtain –From the NIST-supplied data sheet:  repeat(samp)N relative step height repeatability standard deviation H anchor etch depth  H range of the anchor etch depth J est estimated value for the dimension J u cJest estimate for the combined standard uncertainty of J est –s roughX smallest of all the values obtained for s platXt1 and s platXt2 –s roughY = s roughZ smallest of all the values obtained for s platYt1 and s platZt2 Typically, choose –Fate of A =  1to disregard  i as a possible thickness –Fate of B =  1to disregard  ii as a possible thickness –Fate of C > 0if > 0, to force the selection of  iii (calculated using C and J est ) as the thickness if = 0, to let the software determine the thickness by the smallest uncertainty value 6. Measurement Procedure (continued) C

16 Find Data Sheet T.3.a –On the MEMS Calculator website (Standard Reference Database 166) accessible via the NIST Data 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 T.3.a –Click “Reset this form” –Supply INPUTS to Tables 1 through 4 –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 7. Using the Data Sheet

17 If your criterion for acceptance is: where D α positive difference between the thickness value of the customer, α (customer), and that appearing on the ROI, α U α(customer) thickness expanded uncertainty of the customer U α thickness expanded uncertainty on the ROI, U ROI 8. Using the MEMS 5-in-1 To Verify RM 8097 Thickness Measurements Then can assume measuring the poly1 (or poly2) thickness according to SEMI MS2 according to your criterion for acceptance if: –Criteria above satisfied and –No pertinent “wait” statements at the bottom of your Data Sheet T.3.a