Browse Prior Art Database

PbFree C4/BLM with Annular Oxide Ring for Dimensional Control and Reliability

IP.com Disclosure Number: IPCOM000181689D
Original Publication Date: 2009-Apr-09
Included in the Prior Art Database: 2009-Apr-09
Document File: 5 page(s) / 103K

Publishing Venue

IBM

Abstract

This invention employs a novel final passivation scheme together with a unique dielectric mask step that is used to create annular rails or 'posts' with strategically placed 'tabs' or openings to allow for the metal electrical continuity that is required for electroplating.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 46% of the total text.

Page 1 of 5

PbFree C4/BLM with Annular Oxide Ring for Dimensional Control and Reliability

As C4 processing moves into PbFree bumping and "fine-pitch" placement (e.g. 3mil C4 on 6 mil pitch and "finer"), the BLM/UBM structure must protect the lower copper layer from inter-reaction with Sn and consumption in the formation of intermetallic SnCu. The current solution for this problem is using a Ni barrier layer above the Copper BLM layer, between the solder bump and the BLM copper. However, in the normal established processes used to fabricate the BLM and C4 structure, the edges of the BLM are exposed during processing. This recently was found to result in consumption of the entire Cu layer by reaction with Sn underneath the Ni barrier layer. Sn from the solder can actually find its way around the top of the nickel barrier to react continuously with underlying copper beginning at the edge and working it's way inward. This presents a serious reliability risk because when the Cu layer is fully reacted with Sn it no longer adheres to the underlying TiW layer, resulting in separation of the C4/BLM from the wafer at the TiW:Cu interface. A second concern has to do with edge attack of BLM films, particularly the copper beneath the Ni barrier, during BLM wet etch patterning, of the standard PbFree TiW-Cu-Ni-(Cu) BLM stack. ((Cu) on top is optional)

This invention employs a novel final passivation scheme together with a unique dielectric mask step that is used to create annular rails or 'posts' with strategically placed 'tabs' or openings to allow for the metal electrical continuity that is required for electroplating. After imaging of the dielectric 'post' mask, PSPI is applied up over the top of the 'posts' and imaged to form the final polyimide via (FV) that is then transferred by RIE through the underlying dielectric nitride level. The polyimide is cured, and shrinks to <50% of it's original thickness, now with a height that is well below that of the oxide 'posts' by on the order of 1 um. The embodiments shown in this article apply to the case of "no-TD" aluminum, but the invention could be adapted to accommodate a TD aluminum pad layer as well. The base BLM TiW-Cu layers are applied with PVD sputtering technology and are then removed over the oxide posts using a short chem-mechanical polish step. The TiW/Cu metal is now continuous only in the area of the "tabs" in the oxide post mask pattern, providing sufficient connection to allow for electroplating in the central region of the oxide rail structure where the solder ball will be centered. At this point, electroplating is used to deposit the nickel barrier film and any top-level copper that may be required, for example, in the case of C4NP methodology. Conventional C4NP or Electroplated C4 processing is used to create the PbFree solder ball. The C4 solder mask is designed such that the final placement of the solder ball will be with edges coincident with the...