Takashi Fuse

Defect inspection technology for a gloss-coated surface using patterned illumination

In this paper, we discuss the development of an inspection system for a gloss-coated surface using patterned illumination. The convex defect on a gloss-coated surface is caused by top-coating paint on a primary coating with minute particles such as dust remaining. Since the convex defect is transparent, it is difficult to observe it in conventional illumination. Thus, we developed an optical system with patterned illumination and an inspection system using imaging technology with a phase-shifting method given the behavior of specular reflection on a gloss surface. The inspected surface is illuminated with the patterned illumination by shifting the phase of a stripe pattern, and a camera takes multiple images of the specular reflection. By calculating the amplitude of the luminance modulation according to a phase-shifting method, the amplitude image can be obtained from the multiple images. The amplitude image means the distribution of the reflectance. The scratch and dirt as well as small convex defects on a gloss surface can be observed in the amplitude image. This inspection system can make an image of the shape and specular reflectance on a gloss surface and allows inspection of gloss coating, which was difficult in the conventional method.

High-speed solder bump inspection system using a laser scanner and CCD camera

We have developed technologies which inspect the shape of solder bumps. The bumps are used to solder an LSI to a printed wiring board in high-speed workstations. The inspection system developed can measure the height, diameter, and brightness of bumps at very high speed. The bump height is measured using triangulation, in which a laser beam scans the bumps, and reflected light is detected with a position sensitive detector (PSD). The diameter and the brightness are measured using a microscope and a CCD camera. The detected results are compared with CAD data. A height measurement accuracy of ±3 μm and a diameter measurement accuracy of ±5 μm were obtained. Practical inspection systems using these techniques have been created and they can inspect 2000 bumps in 60 seconds.

Development of high-speed 3D inspection system for solder bumps

We developed a high-speed 3D inspection system for solder bumps. The system applies laser-based triangulation with a laser diode, an acousto-optical deflector (AOD), and a position sensitive detector. The system scans LSI surfaces with a laser beam at a 15 m/s scanning speed, and can acquire height data at rate of up to 7 X 106 samples/sec with 0.8 micrometers resolution. For high-speed laser beam scanning with the AOD, we developed a technique to correct for the cylindrical lensing effect that causes astigmatism on a focal plane. Our correction method is unique in that it notices the scanning speed being constant in order for the dynamic deviation to be erased. This technique can suppress these deviations enough to enable accurate laser scanning. When installed on an LSI chip assembly line, the system can measure each bump height to within +/- 2 micrometers in 5 ms. This will allow for a 100% inspection to be achieved.

High-speed 3D inspection system for solder bumps

This paper discusses a high-speed 3-D inspection system for solder-bumps. The system uses a high-speed 3-D sensor system and an accurate measurement algorithm. Solder-bumps have recently been used for flip-chip bonding. Before bonding all bumps need their height and diameter inspected and if bumps are too big or too small, there is a danger of short or open circuits occurring after bonding on the substrate electrodes. Thus, a 100% inspection is required to assure high flip-chip bonding process yields. We developed a laser-based high- speed bump height capture system and an accurate bump height and diameter measurement algorithm. The inspection system takes 20 milliseconds to measure the height and diameter of a bump. It measures the bump height to an accuracy of plus or minus 3 micrometer, and the bump diameter to plus or minus 5 micrometer. Thus, this system is suitable for performing a 100% inspection of solder-bumps.

Observation of nanometer-scale crystal grain orientation in ferroelectric thin films using polarization near-field scanning optical microscopy (NSOM)

We developed an observation technique for crystal orientation in the nanometer-scale grain using polarization near-field scanning optical microscopy (NSOM), and applied it to Pb(Zr,Ti)O3 (PZT) ferroelectric thin films. PZT is a ferroelectric RAM material. Because ferroelectric RAM cell sizes have become smaller and are now, being measured in the submicron scale range, the grain sizes in PZT that constitute the cells are about 100 nm. The observation for crystal grain orientation of such ferroelectric RAM cells has been difficult with current methods such as X-ray diffraction method or micro-Raman spectroscopy. PZT is a uniaxial crystal because of its tetragonal structure and we found that the birefringence retardation of PZT depends on its crystal grain orientation. The nanometer-scale grain was observed by NSOM, which is not limited by the diffraction limit of conventional optical microscopy. To achieve the observation of birefringence retardation, NSOM and polarization optical elements were integrated. For this integration, the optical compensation of polarized light was indispensable because a near-field probe in NSOM might show birefringence. Then, a polarization compensation method at the tip of the near-field probe was developed. Using this polarization NSOM, a new technique for observing the crystal grain orientation by birefringence retardation was developed.