Versatile Tools for Advanced Manufacturing: 3D Optical Metrology

General discussion in the metrology field tends to revolve around the relative merits of non-contact or contact measurement solutions. However, demand now exists in almost every industry for more compact, complex components that are at high risk of contamination or damage through even minimum contact with a probe.

Non-contact optical metrology solutions are generally the best option for such exacting applications, thanks to the technology’s high precision and measurement repeatability - essential characteristics when mere nanometers may be the difference between a test passing or failing.

Non-contact optical metrology solutions do not typically damage parts during measurement. They are also much more rapid than conventional contact systems, making them ideal for applications involving high sampling rates and complex products.

3D optical metrology tools can be incorporated ‘in process,’ and this approach is very much the future of metrology for advanced manufacturing scenarios. Measurement systems continue to relocate from the quality control department and dedicated metrology rooms to be closer to, or even on, the production floor itself.

No alternative metrology solution is considered close to 3D optical metrology in terms of its capacity to rapidly and precisely evaluate a large number of data points quickly. As manufacturers call for increasingly advanced functionality with minimal effort and cost, 3D optical metrology solutions have become a cornerstone of competitiveness in today’s market.

Some sectors continue to exhibit a reluctance towards deploying optical measurement systems, and this is partly due to misconceptions around reliability, a lack of first-hand experience, or simply because potential users have investigated out-dated metrology tools rather than current, next-generation optical metrology solutions.

Recent developments in high-resolution sensors, computers, optics, and data processing capabilities have led to optical metrology becoming standard practice in industry sectors as diverse as aerospace, consumer electronics, medical, semiconductors, and automotive manufacturing.

Process Control,

Quality control is central to efficient and cost-effective manufacturing and competitive success and, as such, sub-standard metrology solutions can have genuine and substantial cost implications.

There is an increasing demand for automated, non-contact metrology systems that can offer high-frequency part inspection as part of an existing production line. Traceability, improved productivity, and global expansion is also becoming increasingly important, with key production decisions being made from geographically spread out manufacturing facilities.

Ultimately, the industry requires absolutely precise, accurate metrology on every part produced, and 3D optical metrology solutions can offer the potential to meet these exacting process control requirements.

ZYGO & Optical Metrology

ZYGO was founded half a century ago with the aim of providing precision engineering systems and custom optics for optics fabrication. The company quickly became synonymous with metrology for surface analysis and positioning – a natural extension of its work in optics manufacturing. Around 70% of ZYGO's current business involves the manufacture of laser interferometers, 3D optical profilers, and nano-position sensors.

ZYGO's ultra-precise optical metrology instruments have been designed specifically for high-value applications in consumer electronics, semiconductor lithography, optical testing, and precision manufacturing. High-performance three-dimensional metrology is central to both process development and manufacturing yield in each of these areas.

Many users of high-precision metrology tools are demanding greater data density in increasingly complex applications. Metrology is often performed in extremely challenging environments in which factors such as vibration or turbulence would cause numerous problems for traditional metrology tools. Being able to extract the maximum data from each individual scan is also essential in facilitating superior metrology on the broadest set of samples.

ZYGO has developed its SureScan™ technology for vibration robust metrology on its 3D optical profilers in order to help alleviate the demand on metrology tool manufacturers to maintain flexibility and measurement precision in such challenging environments.

This, and other tools, offer users a multitude of capabilities, including High Dynamic Range scans and oversampling. Furthermore, industry-leading signal processing techniques form the foundations of ZYGO's "MoreData™" technologies, which maximize data capability and quality.

These advanced technologies are shifting the locations of instruments, bringing them closer to the production floor, stimulating in-process metrology applications, and enabling measurement of almost any surface, whether it be very smooth, very rough, very flat, or highly sloped.

Metrology and Smart Phone Components

The manufacture of mobile phones provides an ideal example of industry demand for highly accurate metrology with greater data density. Mobile phone manufacture has metrology demands across the component spectrum, with applications including flexible circuits, camera modules, and mechanical components all requiring critical metrology.

Lenses

Smartphone camera lenses are partially comprised of aspheric lens elements. Manufacturing yield for smartphone lens assembly typically depends on the shape of these complex aspheres as well as on the array of built-in features enabling individual lenses to fall into alignment when they are assembled in a lens barrel.

As images captured by smartphone cameras continue to increase in quality, lens design tolerances become tighter, and characterization requirements become broader. Advanced camera designs also require complex surface geometries.

Approximately 40 million microlenses are manufactured daily, meaning that there is significant demand for rapid, reliable, high-quality metrology to properly support the sheer scale of these precision manufacturing processes.

Lens manufacturers require highly detailed information on lens surfaces and the interlocking alignment features, and this information must be provided rapidly and with high confidence.

ZYGO developed its COMPASS™ 3D optical profiler system with this application in mind. The system offers a combination of interference microscopy, multi-axis staging, and dedicated software, making it ideal for the evaluation of both lens molds and individual production lenses.

COMPASS™ uses full-surface 3D metrology to characterize these complex surfaces without conceding accuracy or precision. The system can identify a range of defects, including deviation from design, process asymmetries, and manufacturing errors that would normally be missed. The presence of any of these defects would be highly detrimental to image quality and lens performance, so proper identification and quantification of these defects will provide manufacturers with valuable insight into their processes. (Figure 1)

A typical COMPASS texture map of a full mobile phone camera lens mold pin. One can clearly see the circular tooling marks from the diamond turning as well as the radial waviness arising from small vibrations on the cutting tool when the pin was manufactured.

Figure 1. A typical COMPASS texture map of a full mobile phone camera lens mold pin. One can clearly see the circular tooling marks from the diamond turning as well as the radial waviness arising from small vibrations on the cutting tool when the pin was manufactured. Image Credit: Zygo Corporation

Flexible Circuits

Flexible circuits are used to connect many of the internal components of a modern smartphone. This helps save space, reduce weight, and improve the efficiency of energy consumption. Flexible circuits are able to fit a large number of connections into a relatively small area, so even minor flaws in these small, inexpensive components can lead to a high-value device that is ultimately unusable.

The critical lateral dimensions and topography of these components (usually electrical traces) used in such flexible circuits should be thoroughly evaluated. This would have traditionally been undertaken using two different metrology systems, but ZYGO optical profilers have successfully combined both vertical and lateral metrology tasks into a single, fully automated solution. Not only does this save time and valuable space in the factory, but it is also key to enabling more efficient workflows. (Figure 2)

Flexible circuit microelectronics are inspected to verify proper feature height, width, spacing, and continuity using ZYGO

Figure 2. Flexible circuit microelectronics are inspected to verify proper feature height, width, spacing, and continuity using ZYGO's ZeGage, NewView, and Nexview optical profilers. Image Credit: Zygo Corporation

Mechanical Components

Critical metrology is also useful in evaluating the topography features, surface finish, and lateral dimensions of mechanical components, such as the barrels that camera lenses are fitted into or the outer casing that contains the numerous parts of a mobile phone.

Surface finish is essential where cosmetic parts must maintain a consistent aesthetic across devices, despite often being manufactured in various locations and even by multiple vendors. ZYGO instruments such as the Nexview NX2, NewView 9000, and ZeGage Pro optical profilers can be integrated into R&D, manufacturing, and quality control applications where these parameters must be monitored (Figure 3).

CSI measures texture on a variety of materials and surface finishing techniques including (left) polishing, (center) grinding, and (right) diamond turning left to right.

Figure 3. CSI measures texture on a variety of materials and surface finishing techniques including (right) polishing, (center) grinding, and (left) diamond turning left to right. Image Credit: Zygo Corporation

ZYGO's proprietary Mx™ software powers all its optical metrology instruments, providing a comprehensive suite of measurement results which would have previously required two or even three traditional metrology instruments to achieve.

Mx™ offers complete system control, with data analysis features including intuitive navigation, interactive 3D maps, and quantitative topography data. The software also features built-in statistical process control (SPC) with control charting, statistics, and pass/fail limits.

Utilizing a common, internally developed platform like Mx™ offers a truly streamlined workflow. For example, applications developed in an R&D lab on one platform may be deployed worldwide on any of the available platforms, ensuring compatibility as manufacturers select the right equipment and options for their organization.

The ever-increasing demand for advanced manufacturing technology in consumer electronics necessitates the use of metrology instruments that operate at the speed of the industry. ZYGO's range of optical profiler systems like NewView 9000, ZeGage Pro, Nexview NX2, and COMPASS can rise to this challenge, offering the best mix of configuration options, performance, capability, and price for any given application.

Consumer electronics products will continue to become more complex, meaning that a precise, versatile, and powerful surface metrology system is vital in keeping pace with these rapid developments.

Summary

The choice of high precision metrology solutions must be made carefully, and solutions must represent the best fit for a specific industrial application. Non-contact optical metrology solutions are the only viable option for the reliable, accurate, and cost-effective measurement of increasingly complex or difficult to measure components and parts across a growing number of applications.

Optical metrology tools are central to the shift towards in-process automated metrology, but OEMs should also note that not all optical measurement solutions are equal.

It is imperative that a potential technology solution provider can offer sufficiently sophisticated hardware and software capabilities to accommodate truly intelligent and in-depth data acquisition and analysis.

A potential technology solution provider should also be able to offer metrology tools that are able to fulfill the sub-nanometer accuracy and repeatability needs of contemporary, cutting edge industrial applications.

This information has been sourced, reviewed and adapted from materials provided by Zygo Corporation.

For more information on this source, please visit Zygo Corporation.

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