We created an optical design that fulfils the abovementioned characteristics. The imaging system design employs an optical arrangement of cylinders without using reflectors to limit degradation of the optical performance in surrounding areas that may be caused by assembling errors. The illumination system design employs a telecentric optical arrangement to ensure uniform illumination for bright-field observation and brightness for dark-field observation.
We employed a modular design for the lens tube design so that the function and quality may be maintained when the user changes the position of the observation cylinder or illumination tube, or if extra accessories are attached. We briefly explain this design below. In order to support the choice of camera orientation and the addition of accessories, the cylinder consists of three parts: (i) a camera tube, (ii) a middle tube, and (iii) a mirror house.
The user can separate/reassemble each part to freely change the position of the camera and illumination against the middle tube that has an installing reference.
Meanwhile, as equipment operations have become faster and installed cameras have become larger, microscope units are required to have high anti-G performance.
For this reason, we applied a flange-and-bolt connection method to the main three lens tubes and other common modules (objective mounts, camera mounts, and illumination tubes).

Figure 9. Cylinder structure and secure rigidity

To make full use of the WIDE VMU Series wide field observation capability, it is important to ensure uniform illumination within the field of view. Differences in visibility between the central and the outer areas of the field caused by uneven illumination can reduce the advantages of an enlarged image field.
Meanwhile, in order to make the positioning of illumination tubes adjustable, the illumination tubes have to move in a certain manner so that the angles between illumination mirrors in related modules stay within certain values. For this purpose, we invented a new method to fix and adjust the mirror-holding parts, and prepared tools for module-adjusting the illumination optical axes. Thus, both the adjustable positioning of illumination tubes was achieved while maintaining uniform illumination.

Figure 10. Changing the positioning of illumination tubes and ensuring illumination uniformity

Based on the newly developed WIDE VMU Series, the following applications can be recommended. Observation in the infrared range can be carried out by combining this system with the M Plan NIR Objective Lens Series or the LCD Plan NIR Objective Lens Series, both of which compensate chromatic aberration both in the visual and near-infrared ranges and have higher transmittance in the near-infrared. This can be applied to observation of the internal structure of a semiconductor device or failure analyses such as hot electron observation with an emission microscope^{1), 2)}

Figure 11. Example of an infrared observation image

Adding a processing optical path to the WIDE VMU enables it to carry out laser repair using a microscope-mounted YAG laser. In addition to the abovementioned NIR Series, the NUV Objective Lens Series or UV Objective Lens Series, which corrects the color aberration in the near-UV or the UV ranges, can be used to repair defects of semiconductor devices and photomasks^{1), 2)} using lasers of the near-infrared to UV ranges, as well as YAG lasers of the basic wavelength (1064 nm), the second harmonic (532 nm), the third harmonic (355 nm), or the fourth harmonic (266 nm).

Figure 12. Example of YAG laser-processing

This WIDE VMU Series is a wide-field microscope unit designed to be built-in equipment, supporting the diversification and increasing speed of inspection systems such as the AOI system.
As EMS manufacturers grow larger and larger in the near future, there will be increased demand for higher resolution and efficiency in the field of inspecting samples such as PCBs, FPDs, wafers, and multi-functional films.
We will continue to develop user-friendly products that flexibly respond to market needs.
〈References〉
1) Masashi Kurokawa, et al.: The Microscope Unit VMU for Being Built in Equipment and its Application in Multi-Wavelength Laser Processing, Proceedings of the Optical Measuring Technology Symposium 2001 (2001)
2) Hidekazu Sano, et al.: The Microscope for Inspection FS300 and its Systems, Proceedings of the Optical Measuring Technology Symposium 2000 (2000)
Source: the Transactions of Optical Measuring Technology Symposium 2015
The WIDE VMU Series received the Good Design Award in 2015.