In high-end industries such as semiconductor manufacturing, new displays, and new energy, precise control of film thickness directly determines product performance and yield. From photoresist coatings for wafer level packaging to ITO conductive films for OLED displays, from anti reflection films for solar cells to Parelin coatings for medical devices, nanometer level thickness deviations can all lead to the scrapping of entire batches of products.Accuracy of thickness gaugeAs a core indicator for measuring the performance of optical film thickness gauges, it has become a key parameter that cannot be ignored in the field of precision manufacturing.
1、 Analysis of Precision Parameters of Mainstream Optical Film Thickness Meters
At present, the mainstream optical film thickness gauge on the market is based on the principle of spectral reflection interference, which calculates the thickness of thin films by analyzing the interference spectra of reflected light at different interfaces. The accuracy of the thickness gauge has generally reached the nanometer level. Taking the Filmetrics series automatic optical film thickness measuring instrument from Nikon as an example, different models achieve a balance between accuracy and range for different application scenarios.
The single point portable film thickness gauge is suitable for rapid laboratory testing and on-site sampling. Its thickness gauge accuracy can reach 0.02nm, with an accuracy of 1nm or 0.2% (whichever is greater), stability as low as 0.05nm, and a measurement range covering 15nm to 70 μ m, which can meet most basic thin film measurement needs. The automatic Mapping film thickness measuring instrument is designed for batch production testing, supporting multi-point automatic measurement and thickness distribution map generation. While maintaining an accuracy of 0.02nm, it expands the measurement range to 5nm to 2mm, and the measurement speed can reach 2 points per second.
The Filmetrics F54-XY-200 automatic optical film thickness gauge from Younikon is designed specifically for 200mm × 200mm samples, with five configurations covering a measurement range of 4nm to 120 μ m. The spot size can be flexibly selected between 2 μ m and 100 μ m, and the wavelength range can be configured from 190-1700nm. The accuracy of the thickness gauge is consistent with the entire series of products, and it supports pattern recognition, autofocus, and tilt correction functions, perfectly adapting to the batch inspection needs of patterned wafers.
2、 Core technical support for the accuracy of nanoscale thickness gauges
The optical film thickness gauge can achieve nanometer level thickness measurement accuracy without the dual guarantee of hardware configuration and software algorithm. At the hardware level, high-precision spectrometers and stable light sources are the foundation. The combination of tungsten halogen lamp and deuterium lamp light source can provide stable output over a wide wavelength range, ensuring that different film materials can obtain clear interference spectra; High resolution CCD detectors can capture extremely weak spectral changes, providing reliable data for thickness calculations.
In terms of software algorithms, advanced spectral matching techniques and fast Fourier transform (FFT) analysis modes can effectively eliminate noise interference and improve the accuracy of measurement results. Built in optical constant database for thousands of materials, it can quickly match the refractive index and extinction coefficient of the tested film layer, avoiding thickness deviation caused by material parameter errors. For multi-layer film structures, algorithms can analyze the thickness and optical properties of each film layer layer by layer, even for complex film systems with more than ten layers, accurate measurements can be achieved.
In addition, automated hardware design further enhances the consistency of thickness gauge accuracy. The electric XY worktable is driven by high-precision ball screws and servo motors, with a positioning error of less than 1 μ m, ensuring that each measurement accurately falls on the preset point; The autofocus and tilt correction functions can eliminate measurement errors caused by uneven sample surfaces, ensuring comparability of measurement results at different positions.
3、 Key factors affecting the accuracy and stability of thickness gauges
Although the optical film thickness gauge itself has extremely high thickness measurement accuracy, the actual usage environment and operation mode still have a significant impact on the measurement results. Environmental vibration is one of the most common interference factors, and small ground vibrations can cause optical path deviation, resulting in spectral noise. In severe cases, it can even cause measurement results to deviate by tens of nanometers. To address this issue, the use of an active shock absorber can effectively isolate low-frequency vibrations ranging from 1-200Hz, with a vibration suppression rate exceeding 98%, providing a stable environmental foundation for high-precision measurements.
The surface condition of the sample can also affect the accuracy of the thickness gauge. Scratches, stains, or excessive roughness on the surface of the sample can cause light scattering, reducing reflected light intensity and signal-to-noise ratio; The back reflection of the transparent sample may also interfere with the reflected light of the positive facial mask layer, interfering with the measurement results. Therefore, it is necessary to clean the sample before measurement and eliminate the influence of back reflection through software algorithms.
Regular calibration is a necessary measure to maintain the long-term stability of thickness gauge accuracy. It is recommended to use nationally certified standard thickness sheets for monthly calibration, covering commonly used measurement wavelengths and thickness ranges during the calibration process to ensure that the equipment can maintain accurate measurement results across the entire range.
4、 How to choose an optical film thickness gauge that meets accuracy requirements
When choosing an optical film thickness gauge, the accuracy of the gauge is the primary consideration, but it also needs to be evaluated comprehensively based on measurement range, sample size, automation requirements, and other factors. For laboratory research and small batch testing, a single point portable film thickness gauge can meet the needs. It has a small size, easy installation, and can be measured in just a few minutes; For batch production testing, the automatic Mapping film thickness measuring instrument can significantly improve testing efficiency and reduce manual errors; For large-sized or patterned samples, specialized equipment that supports autofocus and pattern recognition should be selected.
In addition, a comprehensive after-sales service system is also crucial. A professional technical support team can provide full process services from sample testing, equipment selection to installation and debugging, and personnel training, timely solving problems encountered during use and ensuring the long-term stability of thickness gauge accuracy.
With the continuous development of high-end manufacturing, the requirements for thin film measurement accuracy will continue to increase. Every improvement in the accuracy of thickness gauges will drive technological progress in industries such as semiconductors, displays, and new energy. As a professional provider of precision thin film measurement solutions, Unicon Technology, with years of industry experience and high-quality product services, provides high-precision and high reliability optical film thickness gauges and supporting solutions to our customers, helping to upgrade China's precision manufacturing industry.
