Polymer layers by initiated chemical vapor deposition for thin film gas barrier encapsulation D.A. Spee a, ⁎, R. Bakker a , C.H.M. van der Werf a , M.J. van Steenbergen b , J.K. Rath a , R.E.I. Schropp a a Utrecht University, Debye Institute for Nanomaterials Science, Nanophotonics — Physics of Devices, Princetonplein 5, 3584 CC Utrecht, The Netherlands b Utrecht University, Faculty of Science, Pharmaceutics, Sorbonnelaan 16, 3508 TB Utrecht, The Netherlands abstract article info Available online 2 February 2011 Keywords: Initiated CVD Polymer film Atomic hydrogen Inorganic/organic barrier layer A combination of SiN x and polymer layers, in our case poly(glycidyl methacrylate) (PGMA) is very suitable as a permeation barrier layer on sensitive electronic devices. Our experiments thus far concentrate on increasing the stability and deposition rate of the polymer layers. To reach the thermal stability needed for the deposition of SiN x on PGMA by HWCVD, the PGMA chain length must be large. PGMA with a very high molecular weight (M W ) (78,000 Da, ~548 monomers) was deposited at a high deposition rate (N 60 nm/min). To mimic the reactive atomic H ambient during SiN x deposition conditions during HWCVD, the polymer layers were exposed to an atomic hydrogen environment for 0 to 550 s. Surprisingly, the most important factor for stability under these conditions was the filament temperature which was used during PGMA deposition, rather than the expected parameters such as M W or surface roughness. Using lower filament temperatures for PGMA deposition, the layers were much more stable in atomic H ambient. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Permeation of oxygen and water vapor into the active layers of electronic devices can lead to deterioration of their performance. This is an issue especially for devices made on flexible substrates, which, contrary to glass or metals, have a very high permeability to water vapor and oxygen. Thus, permeation barrier films deposited on flexible substrates are needed for many applications, such as flexible solar cells, organic light emitting diodes (OLEDs) and rollable displays [1–3]. Hybrid barrier layers consisting of alternating inorganic/organic layers have proved to show sufficiently low permeation rates [4]. A combination of SiN x and polymer is very suitable to create such a multilayer [5]. In our case the polymer is poly(glycidyl methacrylate) (PGMA). Both layers can be deposited using a continuous process: SiN x using hot wire chemical vapor deposition (HWCVD) and PGMA using initiated chemical vapor deposition (iCVD), where an initiator is dissociated into two radicals at a hot filament and starts the polymerization process. Since both techniques use long wires, they allow for a continuous roll to roll process. The wires provide a linear source of radicals, which will result in a homogenous deposition along the wire direction. By moving the substrate perpendicular to the wire, the deposition will be homogeneous in both dimensions. These barrier layers can even be deposited on sensitive organic layers, since in these techniques no energetic ions are present, which could possibly damage them. Our first experiments concentrated on increasing the deposition rate (r dep ) of PGMA, to make it a feasible option for a large scale processing, and the stability of the polymer. To reach the thermal stability needed for the deposition of SiN x on PGMA by HWCVD, the PGMA chain length (or molecular weight, M W ) must be large [6–9]. Under SiN x deposition conditions, besides high temperature, highly reactive atomic hydrogen is also present. To investigate the stability of PGMA under these conditions, the PGMA layers were exposed to an atomic hydrogen environment, mimicking the reactive conditions during SiN x deposition. 2. Experimental details 2.1. iCVD of PGMA Layers of PGMA were deposited in a home built reactor (PANDA), inspired by the reactor at MIT [10], on mono-crystalline wafers. The cylindrically shaped reactor has an internal diameter of 25 cm and a height of 5 cm. The monomer, GMA (97%, Aldrich) and initiator, tert- butyl peroxide (TBPO) (98%, Aldrich) were fed into the reactor through a line which was heated to 90 °C, in which they were mixed. The GMA was heated in a glass jar to 60 °C. Both flows were controlled by metering valves. The GMA flow was kept at 3 SCCM and the initiator flow was changed between 0.5 and 0.7 SCCM, changing the initiator/monomer (I/M) ratio from 1:6 to 1:4.3. The TBPO was thermally decomposed at a parallel array of nichrome wires, 3 cm above the substrate and heated to 250 or 220 °C. Thin Solid Films 519 (2011) 4479–4482 ⁎ Corresponding author. E-mail address: d.a.spee@uu.nl (D.A. Spee). 0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.01.297 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf