Non-Contact Optical Measurement for Detecting Film Thickness

Non-Contact Optical Measurement for Detecting Film Thickness

For the produced thin film, among its many properties, the thickness and uniformity of the film are the most critical parameters. Therefore, monitoring and controlling the thickness and uniformity of thin films has become an important and indispensable part of industrial production. If you need it, PAM-XIAMEN can supply semiconductor wafers with optical measurement services. Take the LiNbO3 film on Silicon Wafer for example.

1. LiNbO3 Film Thickness Tested by Optical Based Measurement

We produce the wafer and test the film thickness for our customers. The data shown as the figure below is tested by optical measurement technology. For specific test methods, please email at [email protected].

LiNbO3 Film Thickness Tested by Optical Measurement

Thickness of LiNbO3 Film Tested by Optical Measurement

2. Non-Contact Optical Measurement Systems

Among the various methods for detecting film thickness, the optical measurement is one of the most widely used methods due to the non-contact, high sensitivity, high precision and the two-dimensional metrology of optical images. In addition, it has the advantages of being fast, accurate and not damaging the film compared with other methods.

From the theoretical point of view, according to the optical principle on which the measurement method is based, it can be classified into interference, diffraction, transmission, reflection, polarization and other methods. Therein, the optical measurement techniques include Newton’s ring interference fringes, Michelson interferometer, ellipsometry, white light interference and other methods. To know the method better, the advantages and disadvantages of these methods are listed in the table.

  Disadvantage Advantage
Newton’s rings The actual measurement is difficult Instrument is simple and portable
Michelson interferometer Manual number loops are easy to cause large errors It has the potential to be developed into a lightweight, portable automated measurement of film thickness
Ellipsometer It is affected by factors such as the interface layer, a complex mathematical model is required to solve the thickness It has higher sensitivity
White light interferometer Deuterium-halogen tungsten light is weak and easily affected by the environment It has high precision, enabling online monitoring of film thickness


We specifically introduce the optical measurement system of ellipsometry and white light interferometry as follows:

2.1 Ellipsometry to Measure Thin Film Thickness

Ellipsometry is an optical method to study the phenomenon of light at the interface of two media and the characteristics of the medium. Its principle is to use the change of polarization state that occurs when polarized light is reflected or transmitted at the interface.

Ellipsometry has a wide range of applications, such as the study of optical properties such as semiconductors, optical masks, wafers, metals, dielectric films, glass (or coatings), laser mirrors, large-area optical films, organic films, etc. It also can be used for measurements of electricity, amorphous semiconductors, polymer films, and real-time monitoring of film growth processes. Combined with a computer, it has the advantages of manually changing the incident angle, real-time measurement, and fast data acquisition.

2.2 Measurement of Film Thickness by White Light Interferometry

An interferometer is an optical instrument that uses the principle of interference to measure the difference in optical paths to determine related physical quantities. Any change in the optical path difference between two coherent beams will very sensitively lead to the movement of the interference fringes, and the optical path change of a certain beam of coherent light is caused by the geometric path it travels or the change in the refractive index of the medium, so through the interference Movement changes in the fringes measure small changes in geometric length or refractive index, thereby other physical quantities related to this are measured.

The measurement accuracy is determined by the accuracy of measuring the optical path difference. Every time the interference fringes move by one fringe spacing, the optical path difference changes by one wavelength (~10-7 meters), so the interferometer measures the optical path difference in units of light wavelengths. The high measurement accuracy is unmatched by any other measurement method.

Using the optical measurement equipment based on the principle of white light interference to determine the thickness of the optical film, the thickness of the film that can be measured is 10nm ~ 50um and the resolution is 1nm.

For more information, please contact us email at [email protected] and [email protected].

Share this post