Nanostructure

The elaboration of submicrometer magnetoresistive (MR) read heads and highly sensitive elements of nonvolatile memories (MRAM) requires patterning processes that are commonly used in the industry of semiconductors. Due to the continued increase in the bit density of magnetic recording, the current challenge consists in the replication of patterns with dimensions lower than 50 nm. The planar processes for thin films patterning are based on two main steps: (i) the pattern definition in a photon or electron sensitive polymer (resist) by lithography and (ii) the transfer of these nanostructures in the manganite film using dry etching (see Fig. 6 which depicts all the steps of the patterning process).

Conventional UV lithography is traditionally used to get patterns higher than 1 ¡m in size. Patterning at dimensions lower than 50 nm calls for high resolution techniques such as scanning electron beam lithography (SEBL), X-ray lithography (XRL), or nanoimprinting. Today theoretical ultimate resolution limits of SEBL and XRL are well known and replications below 20 nm in the high resolution PMMA (polymethylmethacrylate) resist have been demonstrated experimentally [76,77]. During SEBL (or XRL), the polymer chains are cut under sufficient electron (or X-rays) doses which reduce locally the molecular weight of the resist and the immersion in a selective solvent dissolves the

1/ Spinning of the resist

Resist (PMMA or

AZ)

CMR oxyde

Substrate (STO or

LAO)

4/ The metallic mask patterns after removal of the resist

Al or Ti

2/ After UV (or electron beam) lithography and development

0 0

Post a comment