Practical DUV lithography for the optoelectronics market

The rapidly emerging Optoelectronics market is bringing new challenges to the lithographer. The production of very large devices, such as waveguides, has historically utilised contact printers to manufacture many devices with both large field size and relatively large dimensions. However, the devices being manufactured today have dimension requirements well below that possible on either contact or projection aligners. As a result of this, i-line lithography is now seen as almost standard, with some leading edge companies producing devices with dimensions that require DUV lithography. An obvious outcome of this is the need to stitch fields together in order to print these relatively large devices, further complicated where i-line and DUV lithography solutions are used, due to the majority of i-line tools being 5X reduction steppers whereas most DUV tools are 4X reduction scanners. In this paper we show results from stitching of multiple reticle fields on i-line steppers and DUV scannners as well as the interdependence between scanner and stepper fields. Experimental results will show that, through various techniques such as field rotation or field magnification, the stitch accuracy can be adjusted. We will also show that this can be applied not only to the complete length of the stitched field, but also to a specific part that may encompass only the device being stitched. Data will show the ability to stitch successfully 5X to 5X, 4X to 4X, and 5X to 4X. In order to measure the accuracy of the stitched field, an overlay tool using box in box structures is normally used. We will show that an exposure tool can use its self-metrology to measure the accuracy of the stitch. The accuracy and repeatability of these measurements as well as a comparison to a typical overlay tool will be given.