By refining the entire optical system in our LM7500 reticle inspection system, we have successfully improved the image
quality and inspection speed.
The LM7500 system uses a beam scanning method in which the inspection pixel size is switched by changing the
magnification ratio of the telescope in the section subsequent to the scanner's optical system. The telescope
magnification ratio is designed to meet the requirements of the light spot diameter and beam scanning width on a reticle,
and specifies the scanning speed. We have realized a smaller light spot diameter by improving the design of the section
prior to the optical system, including the AOD (acousto-optic deflector), which is the starting point of the scanner's
optics. This has led to faster scanning.
We have also succeeded in minimizing the adjustment error by optimizing the magnification ratio of the telescope, thus
increasing the adjustment margin of the incident light beam entering the section subsequent to the scanner's optical
system. This means that the difference in the X and Y directions of an image can be suppressed to a remarkable extent
for a beam scanning system.
Moreover, because the LM7500 scans both transmitted and reflected light simultaneously, pattern inspections, particle
inspections and even scribe-tri-tone inspections can be carried out at the same time. We have also succeeded in
increasing the inspection speed by 30% through optical system optimization.
Conventionally, pattern inspection is performed on completed reticles. In other words, the completed circuit pattern on a
reticle is inspected after etching and removing the resist. This pattern consists of the transmission region (Qz), half
transmission region (MoSi) and shading region (Cr). If the process stage where a detected defect occurred can be
specified, detection can be made at an earlier process stage, enabling an improvement in the process and/or yield.
When inspecting the resist pattern on a reticle before the etching process, points such as the endurance of the resist
against the inspection light beam and the effect of the gas that is generated by irradiation must be considered. In addition
to there being no damage to the resist pattern, there must also be no contamination of the optical elements caused by
outgases. To prevent contamination, therefore, we developed a cassette-type enclosure with gasproof windows in which
the reticle is set, thus shutting out outgases. Also, because the image of the resist pattern is very different from a normal
pattern, we needed to develop various functions, such as algorithms, to detect defects on the resist pattern.
This time, we have successfully developed a resist pattern inspection function for the LM7500 reticle inspection system.
This function enables both die-to-database and die-to-die inspection and features an inspection light wavelength of 266
nm, allowing the detection of smaller defects that could not be detected with an i-line (365 nm) inspection system.
A new DUV high-resolution reticle defect inspection platform has been developed. This platform is designed to meet the reticle qualification requirements of the 65-nm node and beyond. In this system, the transmitted and reflected inspection lights are collected simultaneously to produce reticle images at high speed. Transmitted and reflected inspections in the die-to-die (DD) and the die-to-database (DB) modes can be executed concurrently. Both images can be gathered at full synchronization with low noise. Basically, both inspection modes are needed to detect as many types of hard and soft defects as possible. Concurrent inspection saves time from using transmitted and reflected lights sequentially. In this presentation, results of DD and DB inspection using standard programmed defect test reticles as well as advanced 65-nm production reticles, are given, showing high-sensitivity and low-false-count detections being achieved with low operating cost.