Optical methods for inline inspection
Challenge
Modern technology is producing increasingly complex devices containing hundreds of components, often fabricated by different techniques. These products may also be composed of multiple layers of different materials with nanometre-sized features, each requiring precise positioning for reliable performance. To ensure these devices are free from defects and imperfections manufacturers need quality checks at multiple stages of the production process. To increase competitiveness these measurements must be costeffective, high-speed, accurate, and capable of being performed inline during production to allow problems to be detected at an early stage.
Optical metrology techniques are an attractive solution that fulfills many of these criteria. In addition, light-based measurement methods are non-contact and have the potential to analyse the surface topology and the different layers of a sample simultaneously. However, such methods are currently limited due to measurement instrument sensitivity to features such as surface roughness, finish, or interference caused by reflected or refracted light. New technologies have the potential to overcome these problems but lack the calibration standards and methodologies to validate their use in modern production lines.
Solution
In the EMPIR project Metrology for highly-parallel manufacturing VTT, the National Metrology Institute of Finland, developed a method capable of measurements at the nanometre level – or better than 0.1% height- scale accuracy. This method was developed to characterise an optical sensor, the FocalSpec LCI1200 sensor. Based on patented Line Confocal Imaging (LCI) technology, the LCI1200 sensor illuminates a target with light that has height information encoded into different wavelengths, or ‘colours’, and the reflected or returned light provides information on the sample’s surface features. Characterisation was performed for factors known to affect optical measurements including the instrument’s resolution level and magnification scale, or sample properties such as slope angle, colour, and reflectivity. The methods developed, although used specifically to assess an LCI sensor, are applicable to a wide range of optical instrument types.
Impact
FocalSpec 3D Line Confocal sensors, such as the LCI1200, deliver high resolution 3D topography, tomography, and 2D intensity date for industrial use, mainly in the ‘3C’ sector - Computers, Communication, and Consumer electronics. FocalSpec sensors are capable of inline inspection of a range of high-tech items that would normally be problematic for monitoring by optical methods, such as curved or transparent materials or printed and flexible electronics.
The characterisation by VTT confirmed the accuracy of the LCI1200 and highlighted factors that can affect the performance of optical sensors, knowledge used to further improve the lineup of FocalSpec products. FocalSpec sensors now leverage the methods and reference plates validated in the project for fast, in-the-field calibration of their instruments, ensuring the stability and accuracy of their systems for customers at the point of use.
The new methods will help the introduction of optical sensors for rapid and cost-effective monitoring into European production lines, allowing them a competitive edge in the emerging field of highly-parallel manufacturing.
- Category
- EMRP,
- Industry,