Novel Approaches to Nanopatterning: From Surface Monolayer Initiated Polymerization to Hybrid Organometallic-Organic Bilayers

Abstract

The extendability of conventional subtractive lithographic processing using spin-coated polymeric single layer resists (SLR) faces many challenges as feature sizes in microelectronics push below 100 nm. In addition, the opacity of the polymeric materials traditionally used as SLR resins to future exposure sources presents new challenges as the radiation penetration depth decreases (e.g. 157 nm, EUVL, low keV e-beam). One solution to these problems is the use of surface imaging materials and processes. In such surface imaging methods, exposure in only a thin surface layer is used to create a pattern in a substantially thicker etch barrier layer. Conventional surface imaging approaches have mainly focused on silylation techniques which have experienced a variety of problems. This paper presents an update on two novel surface imaging methods under investigation: (1) surface monolayer initiated polymerization (SMIP) and (2) organometallic-organic bilayer resists.The SMIP process involves using a monolayer that contains a polymerization initiator functionality. Exposure of the monolayer to radiation can deactivate the initiators in selected areas and the remaining initiators can subsequently be used to directly grow patterned polymer structures. This process allows complete decoupling of the imaging properties of the monolayer from the etch properties of the polymer etch barrier. In essence, the polymerization process is used to amplify the pattern initially formed in the monolayer. Recent results are presented that demonstrate the use of x-ray photoelectron spectroscopy in conjunction with dose array experiments to analyze the sensitivity of the initiators used for this process.The other novel surface imaging method presented in this work uses organometallic-organic bilayers. In these systems, thin films of radiation sensitive organometallic precursors are used as an imaging layer in conjunction with thick organic etch barrier layers. Upon exposure, the organometallic precursor film is selectively converted to metal oxide. After exposure, the unexposed regions of the film can be developed away. Subsequent dry pattern transfer in an oxygen plasma can be used to transfer the pattern defined in the thin oxide layer through the organic etch barrier layer. Organometallic precursor films with sensitivities on the order of 70 μC/cm2 are demonstrated which result in oxide films that possess an etch selectivity of 100:1 with respect to novolac in oxygen plasmas. 500 nm line-space patterns are demonstrated as a first lithographic imaging proof-of-concept.

Patterned grafting of polymer brushes onto flexible polymer substrates

“…These sites are often created by binding or deposition of specific starter molecules or precursors thereof which are then activated in a subsequent step. [1][2][3][4] The spatially resolved activation or deactivation of such reactive sites has been demonstrated as a means to create patterns of polymer brushes on specially prepared surfaces. On gold or silicon surfaces, self-assembled monolayers (SAMs) of precursor molecules were first deposited, followed by chemical derivatization to give the surface-bound initiators for the subsequent grafting reaction.…”

“…Using focused electron beams for selective deactivation of the initiators, grafting of structures with a lateral resolution in the 50 nm range has been demonstrated. 2,3 Due to the chemical amplification through the grafting reaction, such grafted patterns may find application as high resolution photoresists. 4 However, this technique has some drawbacks including the limited choice of support materials that allow the formation of SAMs, and the potentially weak adhesion of the grafted material, which relies on the interaction between the SAMforming molecules and the base material.…”

Preparation of Micro- and Nanopatterns of Polymer Chains Grafted onto Flexible Polymer Substrates

“…Grafting of polymers on specially prepared reactive surfaces has been described recently. , Lateral resolution in the 50 nm range has been achieved by selective activation or deactivation of surface functional groups using e-beams . Nonetheless, there are significant limitations in these methods.…”