Patent DE-19935558-A1 (DE)
Title: Electrostatic nano-imprint press, sandwiches polymer film between molding and substrate platens, controlling electrostatic force applied, degree of closure and temperature
Inventor: KOOPS HANS WILFRIED PETER
IPC: B29C59/04
Filed: 1999-07-30
Abstract: Two electrically-conducting workpieces sandwich a thin, thermoplastically-deformable polymer. One, the master, is surface-structured; the other is an unstructured substrate. Electrical field is generated between the substrate and the resultant electrostatic force is exerted onto the polymer. Master and/or substrate are free to move or press together while the polymer is heated. The polymer takes the form of the master as it is deformed during heating. Preferred Features: Impressing is controlled over time. A high frequency technique, based on measurement of capacity, determines and controls workpiece separation, integrated over their area. Hence the thickness of the intervening polymer is measured and the process of molding is carried out under computerized control and monitoring. The master is made from mechanically-stable, transparent or opaque material. In a slight variant, the master differs only in having a non-conductive structured surface on a metallic, electrically-conducting intermediate layer, to which a potential is applied. Surface structures of the master are digital or analog, with various structural geometries sized between a few nanometers and 1 mm. Structures other than for molding, are carried. These assist precise registration between different structuring processes, carried out one above another. They also assist process execution. The substrate has a conductive surface, transparent conductive surface or a metallic surface. Onto this is applied a suitable thickness of a given polymer layer or matrix material, for molding. The pressure profile is independent of surface area. No increase in voltage is required, when scaling up the process to any size. Local pressure is approximately constant and independent of local contact area, even when there is only one contact point over the raised master structure, so that the force transferred is largely independent of local structural geometry. A high frequency capacity bridge measurement circuit is employed. Determination of the capacity during impressing over a known contact area, is used to measure platen (master, substrate) spacing and hence molding force. Thus viscosity behavior of the polymer to be structured is measured accurately and used for pre-adjustment. Irregularities present in polymer layer thickness are detected and compensated, to achieve optimal molding. Feedback of capacity measurements, more precisely define start and end of the process, and controls the course of the process. On completion, the same polarity and charge are applied to the platens; they repel normally and separate with the polymer between, minimizing processing time. There is no mechanical transverse shearing during separation. Around the pressing assembly, further surfaces are arranged, to influence the electrical edge potential of the pressing area. Essentially these control pressure distribution to the edges, keeping it the same as in the middle (avoidance of edge effects). Reduced potential and forces can be used in marking- and alignment stages, especially in multilayer structuring. Reliable molding of the very smallest particles applied to a conductive master support structure is achieved, by control of force distribution, spacing and process execution, with the aid of capacitance measurement. Master, substrate and polymer form three separate components. The polymer is a thin continuous film, or is applied by pressing onto the substrate. This enables covering and structuring of the largest areas. The master is from a continuous roll, used in a similar process. The potential applied is DC with superimposed AC (or HF). This modifies polymer viscosity effectively by alternating mechanical loading (vibro-pressing), improving the impression.