The penetration limit of poly(4-vinyl phenol) thin films for etching via holes by inkjet printing

Abstract

Related ArticlesTiO2 nanoparticles and silicon nanowires hybrid device: Role of interface on electrical, dielectric, and photodetection properties Appl. Phys. Lett. 101, 253104 (2012) Strain relaxation in GaN nanopillars Appl. Phys. Lett. 101, 253102 (2012) Statistically modified surfaces: Experimental solutions for controlled scattered light J. Appl. Phys. 112, 114325 (2012) Digging up bulk band dispersion buried under a passivation layer Appl. Phys. Lett. 101, 242103 (2012) Influence of surface tension on cavitation noise spectra and particle removal efficiency in high frequency ultrasound fields J. Appl. Phys. 112, 114322 (2012) Additional information on Appl. Phys. Lett. 14 demonstrated using Ag ink with etching solvent to form the path by permeating poly(methyl methacrylate) (PMMA) and filling it simultaneously. Kawase et al. 15,16 etched via holes in a polymer dielectric layer for interconnection using inkjet printing for making all plastic transistor circuits, owing to the coffee ring effect, during which materials loaded in solvents are carried to the contact line. 16,20,21,23,24 Few have studied the limitation of using inkjet etching to produce via holes in polymer layers. Via hole formation in polymer films by inkjet etching is through polymer dissolution and re-deposition, which is different from etching holes in silicon dioxide reported by Lennon et al., 25 where chemical reaction is involved and the soluble product can be washed away afterwards in water. Since there is neither local removal of the dissolved polymer from inside the hole nor evaporation of the polymer, the dissolved polymer must re-occupy the space within the produced via hole during re-deposition. Therefore, a limit of penetration depth can be expected, thereby posing a barrier to making a through via hole. If the polymer layer is not completely etched through, subsequent filling with conductive materials in the holes will result in an electrical failure due to the residual insulating polymer. In this paper, we investigate the polymer penetration limit during the inkjet via hole etching process based on the experimental study. It is envisaged that the results may assist the optimum design of such via holes in microelectronic devices.Poly(4-vinyl phenol) (PVPh) was dissolved into isopropyl alcohol (IPA) to yield a transparent brown-colored solution, which was spin coated onto a glass substrate subsequently to produce a thin PVPh film. Multiple IPA drops were jetted using a Microfab Jetlab V R 4 printer onto the PVPh film to dissolve via holes so that no residual polymer existed and the glass substrate was exposed. The via hole dimensions, outer diameter (D out ), inner diameter (D in ), and depth (H d ) were measured by scanning the profile using a Zygo V R scanning white-light interferometry (SWLI) microscope. Figure 1 shows a typical inkjet-etched via hole that was created in this study and its profile.The relation between D out and via hole penetration is investigated using a polymer layer of a fixed thickness, wh...