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Spectral Imaging Microscopy

IP.com Disclosure Number: IPCOM000246038D
Publication Date: 2016-Apr-27
Document File: 2 page(s) / 162K

Publishing Venue

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Abstract

This paper describes an instrument and system that combines a microscope and a spectral imaging camera to measure thickness of one or more structured coatings that may be microscopic.

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Page 01 of 2

Spectral Imaging Microscopy Abstract

This paper describes an instrument and system that combines a microscope and a spectral imaging camera to measure thickness of one or more structured coatings that may be microscopic.

Introduction

Spectral imaging technology can be used to measure online coating thickness using white light interferometry principles. When integrated with a microscope-like optical system, it may also measure thickness of one or more structured coatings that could be microscopic. Herein, the instrument will be referred to as a spectral imaging microscope although the optics are different from a standard microscope.

Conventional and commercial instruments that measure thicknesses are mostly scanning-based techniques. Figure 1 shows the principle of a 3D white light interferometry profiler based on scanning technology [1].

Figure 1: 3D White Light Interferometry

Typically, a camera acquires images from a microscope using a scanning interferometric objective. The scan motion, in the direction normal to the surface, generates the optical path difference required to calculate the thickness or distance at each point of the image. The white light source or broadband light source goes through an interference objective that includes a reference mirror. A portion of the light is then directly reflected to the camera and the other portion is transmitted through the objective and reflected by the sample. The reference beam is directly reflected by the reference mirror within the objective and the reflected beam from the sample will combine and interfere at the camera. A scanner vertically moves the objective up and down to vary the optical path difference and generates an interference pattern at each location imaged by the microscope.

An immediate disadvantage is the difficulty to implement these techniques in an online environment. Furthermore, these commercially available measurement instruments are generally bulky and expensive. Advantages include: vibration-free, mechanically robust, and perfectly suited for topography of complex 3D surfaces. The instruments also show a very high spatial and thickness resolution. However, for the type of applications envisioned, this technology is over-engineered and the advantages do not overcome the disadvantages.

This profiler is perfectly suited for 3D metrology. However, it is over complicated for measuring thickness of one or more structured microscopic layers.

Implementation

The spectral imaging microscope measures thickness of structured layers that can be microscopic. It leverages spectral imaging cameras in combination with a microscopic system that operate without a reference and do not require any scanning. Refer to Figure 2.

Figure 2: Spectral Imaging Microscope System


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These attributes make it possible to integrate into roll-to-roll processes for online measur...