Laser scanning inspection of the mask film's penetration and uniformity

In the aspect of transmittance inspection, UV spectrograph is usually used to measure the transmittance of the film and its uniformity. In addition, it needs to consider the background interference and spectral resolution caused by stray light (ie, the optical shutter (Bandwidth), and the angle of incident light from the UV spectrometer to Pellicle. Although for some thin film suppliers, products may occasionally exceed specifications, the penetration rate of each film is usually measured, so the penetration rate is generally no problem.

The uniformity of transmitted light is a mercury or xenon lamp that is checked by a monochromatic light source and is usually green. With the help of monochromatic light, because the film is a spin coating process, these uneven spots on the film can be easily tested. Similarly, MLI used a reflective laser inspection machine to check the uniformity of the uncoated film. The thickness of the uncoated film can be calculated by the penetration and reflectance of the UV spectrometer, or it can be generally commercialized. Film thickness measuring machine.

Inspection of fine dust on the membrane

It is very important to verify the accuracy of the machine using the fine dust standard to calibrate the dust, especially the 1 μm, 0.5 μm and 0.3 μm standard dust samples for correction of the pellicle dust test tool. These dust standards should even be regularly taught to on-line operators for visual inspection to ensure inspection accuracy.

At present, there are three ways to check the dust on the film—inspectors, laser scanning, and image photography inspections. Human eyesight is very keen, MLI found with the appropriate light source, 0.3 μm size dust can also be checked out (in the standard plastic film on the film to correct and verify with a laser scanning machine). However, the human eye test cannot be quantified because there are many factors that make quantification difficult, such as the eyesight of the tester, the ability to focus, the position and angle of the test, the distance between the film and the eye, the incident and background light intensity, and the pupil of the human eye. The response to the background light and so on. Therefore, fine dust below 1 μm is also examined. Different inspectors may have different sizes of judgments.

Even with machine inspections, there is no way to get good repeat measurements. For laser scanning inspection of fine dust, the best reproducibility is about +/- 20%. Its bottleneck is mainly controlled by the overlap of scan lines and the stability of the scan lines, and the stability of the scan lines can be detected by the optical scanning system. The shock is limited. In general, laser scanning can detect fine dust less than 0.3 μm.

Photographic inspection can detect micro dust less than 0.3 μm easily under the appropriate lighting system. With today's high-speed computer camera systems and image processing, this is the best way to measure the dust on the film.

Each of the above three inspection methods has its own limitations. Eyesight, laser scanning, and image photography inspections detect the scattered light instead of the actual size of the dust. The actual size of the dust may be larger than the size of the scattered light, sometimes 10 times the detected size. In addition, the limitation of laser inspection is the inability to detect about 2-3 mm of film dust on the edge of the frame. The size of this area depends on the angle of laser scanning, the intensity of the laser spot, the height of the frame, and the degree of light scattering at the edge of the frame.

Compared with eye inspection, the advantages of laser scanning and image photography inspection are high repeatability. Moreover, eye inspection under strong light is not a comfortable working environment for personnel. However, personnel testing still has considerable advantages such as good sensitivity, rapidity, inspection to the edge of the frame, and even judging whether the relatively large dust particles are on the outside or inside of the film, and so on.