Residue-free plasma etching of polyimide coatings for small pitch vias with improved step coverage

Abstract

The authors have found that patterning polyimide coatings containing organosilane adhesion promoter using pure oxygen plasma resulted in a thin silicon-rich residue layer. They show in this paper that adding small amounts of fluorine-containing gas to the etching gas mixture is necessary in order to achieve residue-free polyimide plasma etching. They report residue-free plasma etching of polyimide coatings with both isotropic and anisotropic profiles, using either metal or oxide hard masks. These etching methods are however not sufficient for the fabrication of high density metal filled vias in 10 lm thick polyimide coatings. In order to improve the metal step coverage over the vias while keeping the pitch as small as possible, the authors have developed a two-step etching recipe combining both isotropic and anisotropic profiles, resulting in wine-glass shaped vias.

Investigation of “fur-like” residues post dry etching of polyimide using aluminum hard etch mask

“…These residues were arbitrary in shape, and appeared light in texture, and for ease of understanding will be referred to as fur-like residues in this paper. Similar residues have been reported in the literature [11][12],…”

Flex-to-Rigid (F2R): A Generic Platform for the Fabrication and Assembly of Flexible Sensors for Minimally Invasive Instruments

“…Because of the large difference in thickness between the 250 nm thick Al/Si 1% hard mask and the 1 μm thick Al/Si 1% bondpad and re-routing layer, it is possible to remove the thin fronside layer in a timed wet-etching step using a PES-type etchant solution. Replacing the 250 nm thick Al/Si 1% hard mask by a 500 nm thick PECVD SiO 2 layer has also been reported as a possible alternative [22]. In this case, the SiO 2 hard mask is removed together with the 1 μm thick thermal SiO 2 layer using a wetetch selective toward aluminum.…”

“…Etching of small pitch, residue-free vias for subsequent metallization in the first polyimide layer has been studied in [22]. We present here the etching optimization of the second polyimide layer.…”

“…A 250 nm thick Al/Si 1% layer is sputtered and patterned and used as a hard mask for the polyimide dry etching. A small amount of carbon tetrafluoride (CF 4 ) or sulfur hexafluoride (SF 6 ) is added to the oxygen gas mixture for the etching of the polyimide layer in order to remove any residue due to the silicon containing adhesion promotor incorporated in the polyimide [22]. The Al/Si 1% mask is removed after the etching using a PES-type etchant.…”

Wirebond Process Improvement through Silicon Die Polyimide Removal

“…In this case, different types of etching are required for the fabrication of electrical bias running through the polyimide layer [5]. Several studies have been published on the characterization of polyimide dry etching using different plasma chemistries, etching methods, and parameters [6][7][8]. However, the capability and availability of plasma machine in semiconductor is a factor but this was not become an excuse to have a reliable ball shear data during evaluation of the device.…”