In advanced industries such as semiconductor and liquid crystal display manufacturing, there is a growing need for higher-accuracy, larger-diameter silicon wafers and liquid crystal substrates for device miniaturization and productivity enhancement. With the increasing use in basic sciences of ultra-high-accuracy optical devices such as astronomical telescope mirrors and X-ray focusing mirrors for synchrotron radiation facilities, there is an ever-growing demand for highly accurate surface profile. A Fizeau interferometer is commonly used for measuring highly accurate surface profile of large-diameter planar substrates. This technique allows a three-dimensional surface profile to be obtained using a single process and nanometer-level resolution to be achieved. Using this method, the difference between the object surface and a reference plane (or sphere) is measured. The absolute accuracy of measurement is therefore limited by the accuracy of the reference plane, making it difficult to achieve nanometer-level absolute accuracy. A major problem is that the larger the reference plane, the more likely it is to be deformed by gravity.

The researchers have, for the first time in the world, developed a surface profiler for planar substrates with a diameter of up to 600 mm that can measure surface irregularities with nanometer-level absolute accuracy. A Fizeau interferometer is commonly used for measuring highly accurate surface profile. The measurement principle is based on comparison with a reference plane, and the accuracy of measurement is of the order of λ/20 (about 32 nm), depending on the accuracy of the reference plane. The developed profiler directly measures the surface profile without the need for a reference plane, making it possible to measure the profile of planar substrates with a diameter of up to 600 mm to an absolute accuracy of 5 nm or less. This accuracy is equivalent to identifying a surface irregularity of less than the thickness of a 10-yen coin (1.5 mm) on the Kanto Plain (17,000 km²).