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3081 Zanker Road
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Phone: 408.943.6900, Fax: 408.943.7943
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Background Statement for SEMI Draft Document 5117A
REVISION TO SEMI MS2-1109, TEST METHOD FOR STEP-HEIGHT MEASUREMENTS OF THIN FILMS
Note: This background statement is not part of the balloted item. It is provided solely to assist the recipient in reaching an informed decision based on the rationale of the activity that preceded the creation of this document.
Note: Recipients of this document are invited to submit, with their comments, notification of any relevant patented technology or copyrighted items of which they are aware and to provide supporting documentation. In this context, “patented technology” is defined as technology for which a patent has issued or has been applied for. In the latter case, only publicly available information on the contents of the patent application is to be provided.
Background
SEMI MS2-1109 enables the determination of step height measurements of thin films. Step height measurements can be used to determine thin film thickness values. Thickness measurements are an aid in the design and fabrication of MEMS devices and can be used to obtain thin film material parameters, such as Young’s modulus.
SEMI MS2 became publicly available in March of 2007 without precision and bias data. The MEMS Young’s Modulus and Step Height Round Robin Experiment was held from December 2008 through April 2009. The SEMI MS2 standard was revised to include the round robin precision and bias data and was published in November 2009 after a successful reballot.
Standard reference materials (SRM 2494 and SRM 2495) are being developed to aid customer’s in their use of five documentary standard test methods (including SEMI MS2). During the review process of the standard reference materials, most sections of this test method were modified as reflected by the changes in this SEMI Document 5117, resulting in what can be considered a complete rewrite of this test method. Of particular note is the following:
1. Those definitions obtained from ASTM are modified,
2. The calibration procedure is updated and is similar to that used in draft Test Methods E 2244, E 2245, and E 2246 that are being balloted in ASTM,
3. Improved the round robin tables, and
4. The combined standard uncertainty equation is modified to include the incorporation of two additional uncertainty components in the combined standard uncertainty equation and added Table A1-1 to facilitate the understanding of this equation.
This SEMI Document 5117A is now being balloted and the complete set of changes can be seen in the redlined version of this document. SEMI Document 5117A was approved for letter balloting in July 2011.
This is a Draft Document of the SEMI International Standards program. No material on this page is to be construed as an official or adopted Standard or Safety Guideline. Permission is granted to reproduce and/or distribute this document, in whole or in part, only within the scope of SEMI International Standards committee (document development) activity. All other reproduction and/or distribution without the prior written consent of SEMI is prohibited.
Page 28 Doc. 5117A ã SEMIâ
Semiconductor Equipment and Materials International
3081 Zanker Road
San Jose, CA 95134-2127
Phone: 408.943.6900, Fax: 408.943.7943
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Review and Adjudication Information
Task Force Review / Committee AdjudicationGroup: / MEMS Materials Characterization TF / NA MEMS / NEMS Committee
Date: / Monday, October 24, 2011 / Monday, October 24, 2011
Time & Timezone: / 1:30 PM to 2:30 PM, Pacific Time / 3:00 PM to 5:00 PM, Pacific Time
Location: / SEMI Headquarters
3081 Zanker Road / SEMI Headquarters
3081 Zanker Road
City, State/Country: / San Jose, CA / San Jose, CA
Leader(s): / Janet Cassard (NIST, ) / Mark Crocket (MEMSMART, )
Win Baylies (BayTech Group, )
Standards Staff: / Paul Trio (SEMI NA)
408.943.7041 / / Paul Trio (SEMI NA)
408.943.7041 /
This meeting’s details are subject to change, and additional review sessions may be scheduled if necessary. Contact the task force leaders or Standards staff for confirmation.
Telephone and web information will be distributed to interested parties as the meeting date approaches. If you will not be able to attend these meetings in person but would like to participate by telephone/web, please contact Standards staff.
SEMI Draft Document 5117A
REVISION TO SEMI MS2-1109, TEST METHOD FOR STEP-HEIGHT MEASUREMENTS OF THIN FILMS
NOTICE: This document was completely rewritten in 2009.
1 Purpose
1.1 This test method enables the determination of step height measurements of thin films. Step height measurements can be used to determine thin film thickness values. Thickness measurements[1] are an aid in the design and fabrication of MEMS devices and can be used to obtain thin film material parameters, such as Young’s modulus.[2]
2 Scope
2.1 This test method presents a procedure for measuring step heights of thin films using step height test structures. It applies only to films, such as those found in microelectromechanical system (MEMS) materials, which can be accurately imaged using an optical interferometer (also called an interferometric microscope) or comparable instrument with the capability of obtaining topographical 2-D data traces.
NOTICE: This standard does not purport to address safety issues, if any, associated with its use. It is the responsibility of the users of this standard to establish appropriate safety and health practices and determine the applicability of regulatory or other limitations prior to use.
3 Limitations
3.1 For optical interferometry, all platforms involved in step height measurements must be reflective.
NOTE 1: If in doubt as to whether or not the platforms are sufficiently reflective, approximately 8 nm of chromium followed by approximately 150 nm of gold can be deposited on the top surface. The chromium serves as an adhesion layer for the gold while the gold coverage provides a smooth, reflective surface enabling accurate interferometric measurements. These additional layers are assumed to have a uniform thickness across the chip and, as such, do not enter into the calculations. This post-processing is considered outside the scope of this test method.
4 Referenced Standards and Documents
4.1 SEMI Standard
SEMI MS4 — Test Method for Young’s Modulus Measurements of Thin, Reflecting Films Based on the Frequency of Beams in Resonance
4.2 ASTM Standards[3]
ASTM E2244 — Standard Test Method for In-Plane Length Measurements of Thin, Reflecting Films Using an Optical Interferometer
ASTM E2245 — Standard Test Method for Residual Strain Measurements of Thin, Reflecting Films Using an Optical Interferometer
ASTM E2246 — Standard Test Method for Strain Gradient Measurements of Thin, Reflecting Films Using an Optical Interferometer
ASTM E2444 — Standard Terminology Relating to Measurements Taken on Thin, Reflecting Films
ASTM E2444 — Standard Terminology Relating to Measurements Taken on Thin, Reflecting Films[4]ASTM E2530 — Standard Practice for Calibrating the Z-Magnification of an Atomic Force Microscope at Subnanometer Displacement Levels Using Si (111) Monatomic Steps
NOTICE: Unless otherwise indicated, all documents cited shall be the latest published versions.
5 Terminology
5.1 Abbreviations and Acronyms
5.1.1 CMOS — complementary metal oxide semiconductor
5.1.2 FOV — field of view
5.1.3 MEMS — microelectromechanical systems
5.2 Definitions
Some of the following terms and definitions are similar to those found in ASTM E2444.
5.2.1 2-D data trace — a two-dimensional group of points that is parallel to the xz- or yz-plane of the instrument.
NOTE 2: For many instruments, the 2-D data trace is extracted from a 3-D data set.
5.2.2 3-D data set — a three-dimensional group of points with a topographical z-value for each (x, y) pixel location within the field of view of the instrument.
5.2.3 bulk micromachining — a MEMS fabrication process that removes where the substrate is removed at specified locations. [ASTM E2444]
5.2.4 interferometer — a non-contact optical instrument used to obtain topographical 3-D data (such as 3-D data sets and 2-D data traces). [ASTM E2444]
NOTE 3: The height of the sample is measured along the z-axis of the interferometer is used to measure the height of the sample. The interferometerinterferometric microscope’s x-axis is typically aligned parallel or perpendicular to the measured transitional edges to be measured.
5.2.5 microelectromechanical systems — ain general, this term is used to describe micron-scale structures, sensors, and actuators, and or the technologies used for their manufacturemanufacture (such as, silicon process technologies), or combinations thereofboth.
[ASTM E2444]
5.2.6 physical step height standard — the artifactstep height used to calibrate the optical interferometerinterferometric microscope or comparable instrument in the out-of-plane z-direction.
5.2.7 platform height — the distance in the z-direction that a flat, processed surface of interest is from a designated flat, processed reference surface.
5.2.8 reference platform — the flat, processed surface that is used to level and zero the measurements in the z-direction.
5.2.9 sacrificial layer — to allow freestanding microstructures, a single thickness of material that is intentionally deposited (or added) then removed (in whole or in part) during the micromachining micromachining process, to allow freestanding microstructures. [ASTM E2444]
5.2.10 step height — the distance in the z-direction that an initial, flat, processed surface (or platform) is to a final, flat, processed surface (or platform).
NOTE 4: It is recommended that the two platforms of interest be designed adjacent to each other.
5.2.11 step height test structure — a test structure from which step height measurements are obtained.
5.2.12 structural layer — a single thickness of material that is present in the final MEMS device. [ASTM E2444]
5.2.13 substrate — in a fabrication process, the thick, starting material (often single crystal silicon or glass) in a fabrication process that can be used to build MEMS devices. [ASTM E2444]
5.2.14 surface micromachining — a MEMS fabrication process where micron-scale components are formed on a substrate by the deposition (or addition) and removal (in whole or in part) of structural and sacrificial layers.
5.2.15
[ASTM E2444]
5.2.16 test structure — a fabricated component (such as, a fixed-fixed beam or cantilever) that is used to extract information (such as, the residual strain or the strain gradient of a layer) about thea fabrication process. [ASTM E2444]
5.2.17 thickness — the height in the z-direction of one or more designated thin film layers.
5.2.18 transitional edge — the side of a MEMS structure that is characterized by a distinctive out-of-plane vertical displacement as seen in a 2-D data trace.
5.2.19 Young’s modulus — a parameter indicative of material stiffness that is equal to the stress divided by the strain when the material is loaded in uniaxial tension, assuming the strain is small enough such that it does not irreversibly deform the material.
NOTE 5: It is also called the elastic modulus, the modulus of elasticity, and the tensile modulus.
5.3 Symbols
5.3.1 For Calibration
5.3.1.1 s6ave — the maximum of two uncalibrated values (σbefore and σafter) where σbefore is the standard deviation of the six step height measurements taken along the physical step height standard before the data session and σafter is the standard deviation of the six measurements taken along the physical step height standard after the data session.
5.3.1.2 s6same — the maximum of two uncalibrated values (σsame1 and σsame2) where σsame1 is the standard deviation of the six step height measurements taken at the same location on the physical step height standard before the data session and σsame2 is the standard deviation of the six measurements taken at this same location after the data session.
5.3.1.3 scert — the certified one sigma uncertainty of the certified physical step height standard used for calibration.
5.3.1.4 srepeat(samp) — the relative step height repeatability standard deviation as obtained from step height test structures fabricated in a process similar to that used to fabricate the sample.
5.3.1.5 calz — the z-calibration factor of the interferometerinterferometric microscope or comparable instrument.
5.3.1.6 cert — the certified value of the double-sided physical step height standard used for calibration.
5.3.1.7 zdrift — the uncalibrated positive difference between the average of the six calibration measurements taken before the data session (at the same location on the physical step height standardused for calibration) and the average of the six calibration measurements taken after the data session (at thise same location on the physical step height used for calibration).
5.3.1.8 zperclin — over the instrument’s total scan range, the maximum relativepercent deviation from linearity (typically less than 3 %), as quoted by the instrument manufacturer (typically less than 3%).
5.3.1.9 This pertains to most optical interferometers and therefore zperc may equal zero percent for other instruments.
5.3.1.10 zrepeat(shs) — the maximum of two uncalibrated values; one of which is the positive calibrated difference between the minimum and maximum values of the six calibration measurements taken before the data session (at the same location on the physical step height standardused for calibration) and the other is the positive calibrated difference between the minimum and maximum values of the six calibration measurements taken after the data session (at thise same location on the physical step height used for calibration)).
5.3.1.11 — the calibrated average of the twelve calibration measurements taken before and after the data session at the same location on the physical step height used for calibration.
5.3.1.12 — the uncalibrated average of the six calibration measurements that was used to determinefrom which zrepeat(shs) is found.
5.3.1.13 — the uncalibrated average of the six calibration measurements from which σ6ave is found.
5.3.1.14 — the uncalibrated average of the six calibration measurements used to determine σ6same.