SFIL Multi Imprint Machine

A multi-imprint Step and Flash Lithography machine that can perform repeated imprints on 200 mm wafers was developed for the purpose of defect analysis, and is shown in Figure 1. This machine can imprint high resolution (sub-100 nm) features from quartz templates using a step-and-repeat process. Multiple imprints are performed by moving an 8” wafer to various X-Y positions while holding a template stationary. For the multi-imprint process, it is necessary to have the compliant flexure affixed to the template since a rigid template and compliant wafer stage can lead to an unstable configuration for imprinting away from the center of the substrate.1 The orientation stage design that can tilt a template about the two “remote axes” that lie on the template-wafer interface was developed and described here.  Two flexures are mounted orthogonal to each other in order to generate two tilting motions, about the a and b axes.
a) b)
Figure 1: Multi imprint apparatus construction. (a) Stripped-down Ultratech 1700 (II) stepper, and (b) the completed SFIL stepper in its current form.
The major machine components include the following: (i) a micro-resolution Z-stage that controls the average distance between the template and the substrate and the imprinting force; (ii) an automated X-Y stage for step and repeat positioning; (iii) a pre-calibration stage that enables attainment of parallel alignment between the template and substrate by compensating for orientation errors introduced during template installation; (iv) a fine-orientation flexure stage that provides a highly accurate, automatic parallel alignment of the template and wafer to the order of tens of nanometers across an inch; (v) a flexure-based wafer calibration stage that orients the top of the wafer surface parallel with respect to the plane of the XY-stage; (vi) an exposure source that is used to cure the etch barrier; (vii) an automated fluid delivery system that accurately dispenses known amounts of the liquid etch barrier; and  (viii) load cells that provide both imprinting and separation force data. An exploded view of the calibration stage is shown in Figure 2.
Figure 2. Exploded view of calibration stage assembly.
The multi-imprint apparatus is currently configured to handle 1-in. square templates. It is used to produce more than 20 imprints on 200 mm wafers for defect studies.  The installation of the template and the loading and unloading of the wafer are performed manually. The printing operations, including X-Y positioning of the wafer, dispensing of etch barrier liquid, Z-translation of the template to close the gap between the template and wafer, UV curing of etch barrier, and controlled separation are all automated. These unit processes are controlled by a LabVIEW interface.
For a short movie showing the Multi Imprint Machine in action, click HERE.
1. Tan, H., A. Gilbertson, and S.Y. Chou. J. Vac. Sci. Tech. B, 16(6) (1998) 3926.