Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: Schematics of the polymer-based air-gap packaging performed on (a) a surface-micromachined MEMS device and (b) a bulk-micromachined MEMS device, both with planar feedthroughs

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: Polymer-based air-gap formation process flows for (a) RIE process and (b) direct photopatterning process

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: TGA results of neat and purified PPC: (a) Novomer 160 K and (b) QPAC 40 141 K

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: The chemical structure of PPC with carbon and hydrogen atoms labeled for referencing to NMR signals. The left part shows polycarbonate part, and the right part shows the polyether part. The polycarbonate parts predominate in the PPC structure. The uppercase letters label the carbon atoms in the polycarbonate part. The lowercase letters label the hydrogen atoms in both polycarbonate and polyether parts.

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: 13C-NMR spectra for neat QPAC 40 141 K (top), neat Novomer 160 K (middle), and purified Novomer 160 K PPC (bottom). The left column includes full spectra, and the right column includes the close-up spectra at the carbonate region.

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: 1H-NMR spectra for neat QPAC 40 141 K (top), neat Novomer 160 K (middle), and purified Novomer PPC 160 K (bottom)

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: Kinetic comparison between BCB curing and PPC decomposition processes at (a) 170 °C, (b) 190 °C, and (c) 210 °C

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: The Dektak profiles of the air-gap structures obtained using (a) 60% BCB cure, (b) 70% BCB cure, and (c) 80% BCB cure at 180–190 °C. The PPC decomposition was done at 240 °C for 4 hrs. The Dektak profiles are leveled with respect to the BCB. The solid line corresponds to the profile obtained before the BCB cap is removed, and the dotted line corresponds to the profile obtained after the BCB cap is removed.

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: Top-view optical image of wrinkles observed on BCB cap in 80% BCB cure air-gap sample. The BCB curing was done at temperatures between 180 and 190 °C, the PPC decomposition was done at 240 °C for 4 hrs. The Dektak profile of the shown BCB cap is given in Fig. 8(c), where the wrinkles are small height changes.

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: Top-view optical images and Dektak line-scan profiles of a 2.5 × 3.2 mm air-gap feature obtained from the middle of a medium thick nonphotosensitive PPC sample subjected to two-step thermal treatment of 1.3 hrs at 190 °C and 11 hrs at 240 °C. All data were acquired after PPC decomposition. The optical image and Dektak profile on top were acquired before removal of BCB cap, and the optical image and Dektak profile at the bottom were obtained after removal of BCB cap. Dektak profile on top was leveled with respect to overcoat BCB layer, and Dektak profile at the bottom was leveled with respect to Si surface. The inset schematics on each Dektak profile show the cross section of the features from which the Dektak profiles were obtained. Around 5 μm of BCB thickness was lost over the air-gap due to curing of the overcoat BCB layer and pattern-transfer BCB layer (which was casted from a diluted BCB solution), and overetching of the pattern-transfer BCB layer in RIE as explained in the Experimental Procedure section (∼3 μm loss of initially 12.3 μm thick overcoat BCB layer measured before thermal treatment as shown in BCB processing data sheet [21], ∼2 μm loss of initially 2.5 μm thick pattern-transfer BCB layer measured before RIE due to combined overetching and thermal treatment). Considering the losses in BCB thickness over the air-gap and process variation in BCB and PPC thicknesses, the air-gap thickness can be inferred as around 18–19 μm from the Dektak profiles above, which is in agreement with the thickness of PPC used in medium PPC sample.

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: An SEM image of the silicon surface of a medium PPC sample after the BCB cap was removed (the sample was tilted by 55 degrees in SEM tool for image acquisition)

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: Cross-sectional SEM images of an air-gap structure obtained on a thin PPC sample: (a) complete air-gap structure (b) close-up image of the small rectangle in (a). The residues sitting on BCB were due to BCB parts broken due to cross sectioning.

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: An XPS depth profile obtained from the air-gap region of a medium thick nonphotosensitive PPC sample with initial PPC thickness of 19.3 μm subjected to a two-step thermal treatment of 1.3 hrs at 190 °C and 13 hrs at 240 °C

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: The configurations of two-layer PPC film for direct photopatterning process, where (a) photosensitive PPC layer is at the bottom and (b) photosensitive PPC layer is on top

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: An XPS depth profile obtained from the air-gap region of a two-layer PPC sample with initial photosensitive (PAG-loaded) PPC at the bottom (2.8 μm), and nonphotosensitive PPC on top (23.5 μm) subjected to a three-step thermal treatment of 30 hrs at 150 °C, 30 hrs at 180 °C, and 11 hrs at 240 °C

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: High-resolution XPS scan, peak fit and peak deconvolution of C1s peaks obtained from (a) nonphotosensitive PPC residue and (b) photosensitive PPC residue

Date of download: 10/15/2017 Copyright © ASME. All rights reserved. From: Size-Compatible, Polymer-Based Air-Gap Formation Processes, and Polymer Residue Analysis for Wafer-Level MEMS Packaging Applications J. Electron. Packag. 2015;137(4):041001-041001-13. doi:10.1115/1.4030952 Figure Legend: A schematic showing the nanoindentation experiment done on (a) an air-gap structure and (b) on BCB-only region, both on the same sample