Due to the steady increase in substrate sizes for low-temperature poly-Si devices and LSIs, there are strong demands for larger substrate handling, more accurate positioning and shorter tact time for many processes such as laser crystallization scan exposure, , and dopant activation  and so on. In order to satisfy such demands, we have developed a high-performance scan-type stage for large substrates. In this paper, we describe the outline of the mechanical structure and also the performance of this stage.
The XY moving stage was installed on an air slider of planarized granite. Stroke sizes of the stage were more than 920 mm and 730 mm for scan and step directions, respectively; the stage size was matched to the large glass substrates (4th generation). The stroke in the vertical direction was more than 32 mm, and the stage could rotate for more than ±0.3 degree for alignment.
The stage is driven by a newly introduced shaft-type linear motor, which consists of a fixed stainless-steel pipe shaft and a moving cylindrical coil rounded around the shaft. There are thin annular permanent magnets stacked inside the shaft. Since this coaxially aligned structure of permanent magnets and the coil is a nearly ideal configuration for efficient magnetic coupling, this motor could generate a stronger driving force; this enabled rapid acceleration and deceleration of the stage. Since stacked magnets generate parallel and uniform magnetic field along the shaft surface but slight field for transverse direction, electromagnetic force slightly fluctuated along the shaft, independent of the pitch of the magnet plate. This introduced another important advantage of the shaft-type linear motor that cogging, which has a serious impact on processing, was almost eliminated. This fluctuation was further reduced by introducing a real-time feedback system. The shaft-type motor, however, had been said to have the serious difficulty of elongation since its own weight bends the shaft. This problem was solved by using new magnetic materials and an optimized design of physical dimensions of the motor.
Experiments have been conducted under stabilized temperature conditions. The maximum scan speed of the stage was more than 500 mm/s with a speed stability of 0.03%, about one order of magnitude better than the reported value of about 0.5%. Acceleration and deceleration times from the halt condition to the constant velocity condition and vise versa were 1.0 s; the scan time was as short as 1.8 s for a 920 mm stroke. The “straight extent” was always better than ±0.5 mm Projection optics is commercially available for shaping a 30-mm-long excimer laser light beam on a sample surface. If we combine this stage and such optics, the whole area of a 4th-generation substrate surface can be scanned within a little more than 1 minute; that is, extremely high throughput can be expected. For example, to grow arrays of large Si grains, two-dimensional position control is the most important subject.