Self assembly of block copolymers : applicability in microelectronics and gains for patterned media

Abstract

As device size decreases, conventional lithographic methods are finding it increasingly hard to keep up. Introduction of newer method such as E-beam, X-ray lithography etc. has demonstrated possibility of scaling to lower dimensions. However most of these methods are too expensive, too complex or too slow. Hence a method is required which can provide high resolutions at low cost, is easy to implement and can be integrated with current processing technologies. Block copolymer self assembly promises to do just that. An immiscible block copolymer will microphase separate into individual domains due to unfavorable mixing enthalpy. These microphase-separated blocks can have domain sizes of very low dimensions, to the order of 15-20 nms. By careful preparation, microphase-separated thin films of immiscible block copolymers can act as nanomasks for a variety of applications in electronic, optoelectronic and storage media fields. One such application is patterned media. With ever increasing areal densities, there is a limit to which the grain size within a bit can be decreased, for a conventional thin film media. Beyond a certain limit, which is dictated by the superparamagnetic effect, these grains will spontaneously reverse, resulting in undesired data loss. Patterned media has been proposed as an alternative to surpass this thermal instability criterion. In patterned media, lithographically defined nano-scale magnetic elements form single bits onto which the data is stored. Due to its unique structure in which each magnetic dots act as a single magnetic domain it can postpone the arrival of superparamagnetic effect beyond densities much higher than 10 Terabits/inch². However, very high resolutions and strict positioning control is required for its fabrication so as to attain a marketable 1Tb/inch² advantage.

(cont.) Block Copolymer self assembly holds great promise in fabrication of such devices requiring periodic, high resolution pattern generation. If issues such as long range order, pattern uniformity and placement accuracy of magnetic dots can be effectively resolved, block copolymer self assembly enabled lithography can quickly become the main stay of the multimillion dollar hard disk industry.