Reducing damage to ulk dielectric during cross-linked polymer removal

#1. Technical Field

#The present invention relates generally to semiconductor fabrication, and more particularly, to methods for reducing damage to an ultra low dielectric constant (ULK) dielectric during removal of a crosslinked polymer.

#2. Related Art

#The embodiments of this invention will be described in detail, with reference to the following figures, wherein like designations denote like elements, and wherein:

#FIGS. 1A-C show an illustrative conventional method for removing a crosslinked polymer.

#FIGS. 2A-2D show a method according to one embodiment of the invention for reducing damage to an opening in a dielectric during removal of a planarizing layer therefrom.

#With reference to the accompanying drawings, FIGS. 2A-2D show methods for forming an integrated circuit and reducing damage to a dielectric during removal of a crosslinked polymer therefrom. FIG. 2A, as will be described, shows a number of steps combined for brevity. As shown in FIG. 2A, an introductory structure 108 includes, for example, a metal 110 in a substrate 112, a hardmask layer 114, a cap layer 116 and a dielectric 118. In one embodiment, dielectric 118 includes an ultra low dielectric constant (ULK) dielectric. The ULK dielectric may include any now known or later developed dielectric having a dielectric constant lower than 3.9, i.e., the dielectric constant of silicon dioxide (SiO2). Structure 108 may further include a hydrogenated silicon oxycarbide (SICOH) hardmask layer 120 and a sacrificial hard mask 122 (e.g., tetraethyl orthosilicate Si(OC2H5)4 (TEOS)). An initial step includes forming an opening 160, e.g., a via opening, in dielectric 118 by, for example, using a reactive ion etch (RIE), followed by a stripping step comprising a plasma containing oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), nitrogen (N2), hydrogen (H2), ammonia (NH3), argon (Ar), helium (He) or other gases capable of removing organic layers, including combinations thereof.

#Next, in order to hide opening 160 during other processing, a bi-layer planarizing structure is formed according to one embodiment of the invention. In one embodiment, this step includes at least partially filling opening 160 with an at most lightly crosslinked polymer 162, and then forming a planarizing layer 164 over polymer 162. As shown in FIG. 2A, in one embodiment, polymer 162 fills only a portion of opening 160, and planarizing layer 164 fills at least any remaining portion of opening 160. In this case, the at most lightly crosslinked polymer 162 may simply be deposited in a portion of opening 160, or polymer 162 may fill the entire opening 160 and then an etching can be performed to remove polymer 162 except in a lower portion of opening 160. As shown in an alternative embodiment in FIG. 3, where the at most lightly crosslinked polymer 162 overfills opening 160, planarizing layer 164 is formed over the overfilled portion of polymer 162, i.e., the etching step may be omitted.

#In one embodiment, at most lightly crosslinked polymer 162 may include an un-crosslinked polymer or a lightly crosslinked polymer. Preferably, an un-crosslinked polymer is used because it can be removed more readily. In one embodiment, an un-crosslinked polymer such as a cyclic olefin selected from the group consisting of: Norbornene-hexafluoro alcohol (Norbornene-HFA), Norbornene-sulfonomide and Poly-Norbornene Acetate, is used. However, it may be advantageous to use a lightly crosslinked polymer such as polymethyl methacrylate vinyl benzene cyclobutene (PMMA-VBCB) to prevent any potential dissolving of at most lightly crosslinked polymer 162 when planarizing layer 164 is subsequently formed with its own solvent, which may dissolve polymer 162.