Patterned media – getting closer
Imprint watchers are watching and waiting for news that patterned media has come of age….the question is … is there a technical barrier, or are manufacturers just waiting for the existing solution to run out of steam ?
When I ask my contacts “if your boss said I want to buy a factory, can I pull the switch”…. the consistent answer is “we are not ready yet”. Reading and writing at 1 Tera-bit per squ. in. or 25 nm pitch has been demonstrated, but all process steps still need work. The biggest technology gap is in making the imprint mold. Everyone is using Directed Self-Assembly (DSA) so they can write a sparse pattern and then fill in the blanks using a block copolymer. The problem is that at the target feature size, the best behaved block copolymers do not have enough resolution, so there is a material development challenge.
At SPIE Advanced Lithography in the spring, HGST showed a different strategy to create a square feature with a larger area of magnetic material for a given pitch. They do this by making the mold from two imprint lithography steps, one to create a set of rings and the other to create a fan. At the intersection, a rectangular “spot” is formed. A subtle advantage of this strategy is that they can now add another doubling technique. After writing sparse rings and a fan, DSA with current materials is used to fill in the pattern to half the target density. Then the well-known technique of side wall spacer doubling can be used to double the rings and double the fan, and finally these are then combined to create the squares. All this sounds like a “tour de force” of advanced lithography, but they only need one to get started in replicating copies. No one has yet made a full area mold, once they have then it will be time to pull the switch.
There was other interesting news on the patterned media front. Seagate have reported that they can detect a small change of 0.1 nm per clean in mold dimensions after 60 cleans. Given that at an atom is worth around 0.3nm, they are definitely tracking sub atomic effects ! Apparently, HGST do not see a dimension loss during clean.
Seagate also showed results with features sizes of 7 nm. Molecular Imprints (MII) showed that to create a 13 nm spot on a 20 nm pitch, they had to imprint holes, because the pillars fell over. The web connecting the holes provided the needed mechanical stability. They then image reverse the pattern in order to create pillars in the magnetic material. MII claimed that they can do patterning at this level for 35 cents a double sided disk, a cost point well within the numbers that the industry has said it needs.
HGST showed how they can manage the non-regular patterns, such as chevrons that occur in the various alignment patterns on today’s disks. This was a key step towards full read write demonstration.
My take is that there is no shortage of energy being committed by the major players to make patterned media happen. It is pretty clear that they are still a year or two from pulling the switch on mass production of the world’s smallest features.
About the author
Mike Watts has been patterning since 1 um was the critical barrier, in other words for a longtime. I am a tall limey who is failing to develop a Texas accent here in Austin. I have a consulting shingle at www.impattern.com.
My blog “ImPattering” will focus on the latest developments in the business and technology of patterning. I am particularly interested in trying to identify how the latest commercial applications evolve.