Drive for size

Combination lithography and block copolymers could lead to efficient mass-production of higher-capacity chip memory. Siobhan Wagner reports.

A new manufacturing technique could overcome the technological limitations currently facing the microelectronics and data-storage industries, and pave the way for smaller electronic devices and higher-capacity hard drives.

Researchers at the University of Wisconsin and Hitachi Global Storage Technologies have developed a technology that combines lithography techniques traditionally used to print, or pattern, microelectronic circuits with self-assembling materials called block copolymers. These consist of two or more chemically different polymer segments, or blocks, connected by a junction point.

When added to a lithographically-printed surface, the copolymers’ long molecular chains spontaneously assemble into the designated arrangements.

‘The block of polymer molecules are half of one chemistry make-up and half of another, and the molecules want to be with their own kind,’ explained Juan de Pablo, co-director of the University of Wisconsin-Madison Nanoscale Science and Engineering Centre (NSEC).

‘So one half goes one way and one half goes the other, and to be able to meet the constraints of these two pieces of the molecule they self-assemble into ordered structures.’

Paul Nealey, the director of the NSEC, said that the information encoded in the molecules results in getting certain size and spacing of features with desirable properties. ‘Thermodynamic driving forces make the structures more uniform in size and higher density than can be obtained with the traditional materials,’ he claimed.

The block copolymers print the resulting array down to the molecular level, offering a precision unattainable by traditional lithography-based methods alone. Such nanoscale control also allows the researchers to create higher-resolution arrays capable of holding more information than those produced today.

Also, the self-assembling block copolymers need only a quarter of the patterning information as traditional materials to form the desired molecular architecture, which makes the process more efficient, said Nealey. ‘If you only have to pattern every fourth spot, you can write those patterns at a fraction of the time and expense,’ he said.

In its current form, this method is suited for designing hard drives and other data-storage devices, which need uniformly-patterned templates —exactly the types of arrangements the block copolymers form most readily. With additional advances, the approach may also be useful for designing more complex patterns, such as microchips.

‘These results have profound implications for advancing the performance and capabilities of lithographic materials and processes beyond current limits,’ said Nealey.

He added that extrapolating existing lithography to smaller and smaller dimensions may become prohibitively expensive. His group hopes that this new approach will be both commercially viable and capable of meeting the industry’s highly-demanding quality control standards. The technique has the potential to offer performance improvements over existing methods, while reducing the time and cost of manufacturing.

Richard New, director of research at Hitachi Global Storage Technologies, shares this hope. ‘The research addresses one of the most significant challenges to delivering patterned media — the mass production of disks in high volume, at a reasonable cost,’ he said.

‘The large potential gains in density offered by patterned media makes it one of the most promising technologies on the horizon for future hard drives.’

The project received funding from the US National Science Foundation and the Semiconductor Research Corporation.