Non‐Contact Surface Metrology and ZeGage Optical Profiler

John Fabio

Sam Banerjea

Zygo Corporation

©2014 Zygo Corporation. All rights reserved. About Zygo

• Zygo has 44 years experience in Metrology and Optical Systems. • Two main business divisions: – Metrology Solutions that provide process control for surface shape, surface texture, material characteristics, film thickness and feature position based on Zygo’s expertise in optical interferometry. – Optical Systems and Components ranging from meter-class plano optics to optical assemblies. • Publically traded (NASDAQ: ZIGO) since 1983. • Strong history of innovation and technology leadership with >300 patents issued.

2 How Zygo Measure Surfaces

•For –Form – Roughness – Waviness – Structure – Relationships to other surfaces • And we want to do it – Quantitatively – Quickly – Easily – Without damaging the part

3 Benefits of Optical Methods

• Full 3D topography scan • Picks up 1M+ data points • No damage to the surface • Fast scan speeds • Lower vertical noise

Mechanical stylus 3D Optical metrology

4 A Look at Interferometry

Several optical 3D metrology techniques are available today: • Vertical resolution down to nanometers, regardless of magnification • Fields of view from µm** to mm • Lateral feature size down to sub µm • High data density • Non contact, high speed • Machined, polished, burnished and ground surfaces • Complex surface structures

From Laser Focus World, 1995

** 1 micrometer = 39.37 microinches

5 3D Interference Microscopy

6 Interference Microscopy

• An interference microscope is a conventional microscope with the addition of a beam splitter and reference mirror • Most interference microscopes are near-equal path systems, using filtered incandescent or LED light sources

7 Scanning the White Light Fringes

• The two signals correspond to two camera pixels

• In an actual system, there are about a scan million pixels and individual scan signals

Signal A scan B A

Signal B Height difference

8 Michelson Interference Objective

• Equal path (usually) Pupil (location of source image) • Works with extended white light sources • Ideal for low-magnification objectives

Reference mirror Object

9 Mirau Objective

• Equal path (usually) • Works for white light • Requires an extended or off- axis source (because of central obscuration)

• Best for high-magnification Reference mirror objectives (central obscuration)

Beam splitter

Object

10 A Complete Interference Microscope System

• Designed for high precision on small objects • Includes staging, controls and software for surface texture analysis • Basic performance capabilities: – Surface topography repeatability – Lateral resolution – Measurement range – Correlation to stylus measurements – Vibration sensitivity

11 Wavelength and NA Set Optical Lateral Resolution

• Sparrow criterion limit = common specification for a microscope • At low mag ( <20X ), the camera can be as important as the optics, reducing the effective resolution by “pixelization”

Optical resolution at l = 560 nm

Magnification NA Sparrow criterion (micrometers **) 1X 0.03 9.50 2X 0.055 5.18 2.75X 0.08 3.56 5.5X 0.15 1.90 10X 0.30 0.95 20X 0.40 0.71 50X 0.55 0.52

** 1 micrometer = 39.37 microinches

12 Correlation to Stylus Measurements

• Evaluation using a ZeGage interference microscope at Zygo compared to a stylus instrument at UNCC Center for Precision Metrology • Rubert reference specimens – 4 random samples with

Ra= 0.02 µm … 0.15 µm – 8 sinusoidal samples with Ra = 0.1µm … 6.4 µm and pitch = 2.5 µm … 135 µm • Halle roughness standards – 2 samples with Ra= 0.024 µm and 0.22 µm

13 Summary of Ra: Random Specimens

Sample name Stylus ZeGage, 10X ZeGage, 20X ZeGage, 50X Rubert 501 0.015 µm ‐ 0.016 µm 0.012 µm Rubert 502 0.035 µm ‐ 0.036 µm 0.031 µm Rubert 503 0.067 µm ‐ 0.095 µm 0.076 µm Rubert 504 0.119 µm ‐ 0.150 µm 0.130 µm Halle 2070/03 0.0238 µm 0.0237 µm 0.0239 µm ‐ Halle 2058/01 0.216 µm 0.237 µm 0.215 µm ‐

Graphical Representation Direct Comparison of Stylus and Optical of the 50X Results Profiles at 50X for the 502 Specimen

R2=0.9964

14 Summary of Ra: Sinusoidal Specimens

Sample Name Pitch Stylus ZeGage with 20X ZeGage with 50X Rubert 543 2.5 µm 0.018 µm ‐ 0.021 µm Rubert 542 8 µm 0.060 µm 0.048 µm 0.051 µm Rubert 529 10 µm 0.097 µm 0.108 µm 0.090 µm Rubert 531 100 µm 0.315 µm 0.316 µm 0.315 µm Rubert 528 50 µm 0.507 µm 0.506 µm 0.515 µm Rubert 530 100 µm 1.009 µm 1.012 µm 1.050 µm Rubert 527 100 µm 2.995 µm 3.025 µm 3.066 µm Rubert 525 135 µm 6.389 µm ‐ 6.362 µm

Graphical Representation 2 R =0.9998 of the Above Results R2=1

Direct Comparison of Stylus and Optical Profiles at 20X for 528 Specimen

15 Comparing Scanning Methods

Interferometry Stylus scan

B A B A scan

16 Comparing Interferometry to Stylus Results

Interferometry Interferometry

Stylus Stylus

17 Potential Damage by Stylus

Measurement Taken on Paper

18 Potential Damage by Stylus

Measurement Taken on Paper

19 Common S Parameters

Sa = Average Roughness

Sq = Root Mean Square Roughness

•Sa and Sq represent an overall measure of the texture comprising the surface Plateau-like Surface

Sa = 16.03 nm • They are insensitive in differentiating peaks, Sq = 25.4 nm valleys and the spacing of the various texture features

• Used to indicate significant deviations in the texture characteristics

•Sa is primarily used for machined surfaces Surface with Peaks

Sa = 16.03 nm •Sq is typically used to specify optical surfaces Sq = 25.4 nm

20 Common S Parameters

Ssk = Skewness

Sku = Kurtosis

•Ssk and Sku represent symmetry and deviation from an ideal norm Surface with Multiple Peaks

Ssk = 3.20 S = 18.71 •Ssk indicates the predominance of peaks or ku valleys

•Sku shows inordinately high peaks/ deep valleys

•Ssk is useful for honed surfaces and wear conditions Periodic Texture

Ssk = 0.16 S = 1.63 •Sku is used to check presence of peaks and ku valleys

21 Common S Parameters

Sp = Max Peak Height

Sv = Max Valley Depth

Spv (or Sz) = Max Height of Surface Printed surface with deep valley structures •Sp, Sv, and Spv are evaluated from the absolute highest and lowest points found on the surface.

•Sp is the height of the highest point and Sv is the depth of the lowest point

•Sp is used for sliding contact applications

•Sv is related to fluid retention, lubrication or coatings

Polymer surface prepared with asperities •Spv is the difference between Sp and Sv and is used to Sp = 0.90 µm characterize sealing surfaces and coatings Sv = -15µm

22 S Parameters to R Parameter Correlation

Description Stylus ZeMaps Roughness Average Ra Sa Root Mean Square Rq Sq Peak Rp Sp Valley Rv Sv Total Height (Peak to Valley) Rt Spv (or Sz) Material Ratio Rmr Smr1 Smr2 Profile Height Pt PV Skewness Rsk Ssk Kurtosis Rku Sku Max Roughness Depth Rmax IsoSRmax Average Max Height Rz IsoSRz Base Roughness Depth R3z IsoSR3z Bearing Ratio (Core Roughness Depth) Rk MR-T-Sk Bearing Ratio (Reduced Peak Height) Rpk MR-T-Spk Bearing Ratio (Reduced Valley Depth) Rvk MR-T-Svk Bearing Ratio (Peak Material Component) Mr1 MR-T-Smr1 Bearing Ratio (Valley Material Component) Mr2 MR-T-Smr2 Waviness Parameters W Sa Waviness Height Wt PV Note: R parameters defined by ISO 4287, S parameters defined by ISO 25178-2

23 ISO 25178 : Geometric Product Specifications, Surface Texture: Areal

• Standard prepared by WG16 of the ISO technical committee TC213. • ISO 25178 means a collection of international standards relating to the analysis of 3D areal surface texture. • First international standard for specification and measurement of 3D surface texture. • Standard describes applicable measurement technologies, calibration methods, and calibration standards/software that are required. • Standard covers non-contact measurement.

24 Form, Roughness and Waviness Segmentation

• Segmentation is accomplished using Fourier transform methods… • … or more advanced spline-based methods • Cutoff limits (ls, lc, lf) are defined in standards: ISO 4287, ASME B46.1 (USA), JIS B0601 (Japan)

25 Calibration is Essential for Best Results

• Like all metrology tools, coherent scanning interferometer systems should be calibrated for the following: – Accurate XY metrology • Lateral calibration standard – System form bias •SiCFlat – Vertical height scale • Step height standard

26 Specialized Objectives with Long Working Distance

• For hard to reach areas, Michelson type objectives are available with 40 mm of working distance • Applications include measurements inside cones and cylinders using an auxiliary optic

3 mm Fold mirror

27 ZeGage Non-Contact Profiler

• Entry-level optical evaluation of 3D form and surface finish on precision machined or fabricated surfaces. • Takes measurements of ISO-compliant roughness parameters, form, step-height and material wear.

• Higher-precision alternative to traditional contact or touch-probe surface finish gages. • Vibration isolation elements built into the chassis. • Applications found in industrial manufacturing, R&D, quality inspection, failure analysis, wear analysis and more. • Markets served include medical, automotive, consumer electronics, military, and aerospace.

28 ZeGage Highlights

• Built for shop floor and lab usage • ≤ 3.5 nm vertical resolution independent of magnification or vertical scan length • SureScan™ Technology eliminates the need for an isolation table • Novel through-the-lens focus aid assists part setup at exactly the area of measurement • Easy to use and learn ZeMaps software with ISO 25178-2* compliant surface parameters • 1X – 50X objectives available

* ISO 25178-2:2012 - Geometrical Product Specifications - Surface texture: Areal -- Part 2: Terms, definitions and surface texture parameters

29 ZeGage Design Features

System Footprint: Z-Stage based scanner W: 525 mm enables scans up to 20 mm D: 525 mm Internal software Max H: 815 mm controlled focus aid illuminator Sealed Head cover has no manual controls or adjustments ZeMaps software on 64-bit Windows 7

Direct threaded Single objective standard. T-Slot Stage Top 4-position turret Plate optional

USB Puck stage 4x2 inch travel manual stage or 4x4 motorized controller stage with t-slot fixture compatibility

Integrated Base and Industrial worktable column hides electronics provides large and cables ergonomic work surface Only 3 cables from base: CAN, Camera, Power Built-in isolators + SureScan System ships fully eliminates the need for an assembled isolation system

30 ZeMaps Software

Measurement Analysis and Interactive 2D or Setup Display 3D Model Display Realtime Stage Toolbar Toolbar Position readout

Integrated Live Display Objective and Stage Speed Light Selector Extracted 2d profile Level with results & Slider calipers

31 Measurement Example: Step Height

Magnification: 10X Description: Area: 1.0 mm x 1.0 mm High aspect ratio resolution target PV: 400 µm

32 Measurement Example: Prosthetic Implant Surface Characterization

• Surface roughness and wear scar on the surface of a polished prosthetic implant surface • Measured using 20X Mirau objective • 100 µm scan on a significantly curved surface • Visible features include – Fine scratches – Material pullups – Deep and wide wear scar

• Approx. 30 nm Ra after form removal

33 Measurement Example: Silver Finger on PV cell

Magnification: 5X Description: Area: 1.4 mm x 1.1 mm Screen printed silver finger on a silicon

SPV : 35 µm Photovoltaic cell

34 Measurement Example: Polished Optical Window

Magnification: 10X Area: 0.70 mm x 0.53 mm Description:

SPV: 14 nm Surface finish of a polished optical flat Sa: 0.07 nm

35 Measurement Example: Single Point Diamond Turned Surfaces

Magnification: 50X Description: Area: 0.3 mm x 0.2 mm Surface finish of a single point diamond

Sa: 1 nm turned optical surface

36 Measurement Example: Ground Metal Surfaces

• Surface roughness on the surface of a ground metal component • Measured using 20X Mirau objective • 40 µm scan length • Visible features include – Fine scratches in multiple directions

• Approx. 0.46 µm Sa after form removal

37 Measurement Example: Laser Scribed Silicon

• Surface topography of a laser scribe on silicon • Measured using 10X Mirau objective • 65 µm scan length • 30 µm deep scribe – Molten debris visible at the edge of the scribe – Texture of the bare silicon also measurable at the same time

38 Consider the ZeGage Optical Profilometer

• A short coherence white light illumination source and long range scan devices allow reliable measurement of heights ranging from nanometer to 10’s of millimeters in height! • ZYGO provides the widest range of interferometric objectives available – 1X to 50X magnification range – 1X to 10X Long working distance configurations available • Patented and trusted algorithms for surface detection ensure consistent, repeatable, and accurate results – even in the most challenging metrology environments

39 The ZeGage for Your Applications

• No risk of damaging your part  No need for sampling lots • 3D Topography gives increased understanding of part surface  No line sampling interpretation required • Measures complicated parts and structures • Fast setup times and measurements Area measurements in seconds • Compact, portable design • Can be used anywhere without additional isolation

40 THANK YOU!

41