Copper interconnect
The damascene process is like his development of the dual- damascene process, a manufacturing process of the semiconductor industry, which is mainly used in integrated circuits ( microchips ) with copper interconnects. The name " damascene " comes from an ancient ornament technology, Tauschierung (also Damaszierung, English damascening ).
Background
In the early years of Microelectronics ( until early 2000s ) only aluminum was used as a wiring material. For the preparation of so-called metallization (consisting of a structured layer of the intermediate contact and a further layer with the proper circuit traces ), the aluminum is first deposited over the entire surface and then patterned by a dry etching method. Since copper is no comparable etching process available, this procedure was not adopted in the early 2000s the so-called copper technology, in which the aluminum was replaced as head of web material by copper with the transition of some companies.
As an alternative production method of the damascene process and its development of the dual damascene process has been developed. In contrast to the damascene process are the dual damascene process, the VIA (English vertical interconnect access, contact joints between two metallization ) and the overlying metallization stuffed together in one process step with copper. Thus, even a copper CMP step is necessary, wherein the supernatant after the electro-deposition of copper is planarized.
Method
Starting from an existing substrate, such as silicon or already deposited metallization, an insulating layer ( dielectric), frequently silicon dioxide (SiO2 ) is first deposited over the entire surface. Followed by a photolithographic structuring, which means that it is a photoresist is applied and patterned. Now the present patterned photoresist layer serves as a mask for the following dry etching process, with the subsequent contact holes (vias ) and interconnects are etched. Etching terminates on the dielectric located below the dielectric copper diffusion barrier ( such as silicon nitride ) that serves as an etch stop. After the etching, the photoresist residue is removed.
After this structure is followed by the filling of the etched trenches with an electrically conductive material such as copper or tungsten (actually, only in the first metallization layer in contact with the silicon substrate). Since copper diffuses easily into the dielectrics ( intermetallic dielectric, IMD, and interlayer dielectric ILD ), it is necessary before the deposition of copper diffusion barrier coat. This diffusion barrier must be electrically conductive, since the barrier is also the bottom of the vias, that is, applied at the contact point of two metallization levels. In addition, the thickness of the barrier layer reduces the effective diameter of Viaslöcher thereby increasing their electric resistance. Also for this effect to minimize an electrically conductive barrier is effective.
The copper deposition can be performed, both by electrochemical deposition or metal organic chemical vapor deposition ( MOCVD). Both processes take place again over the whole area, also are the trenches " crowded ", so should be ensured that no voids to the next metallization; the electrical contact would not be ensured or would have a higher resistance. The excess copper is then removed by chemical mechanical polishing ( CMP) and leveled.
Finally done once the deposition of a barrier layer, otherwise the copper could easily migrate to higher levels. Since the barrier layer is again not further structured over the whole area and it must consist of a non-conductive material (eg, silicon nitride). Doing so may cause a short circuit between the interconnects a metallization. Unlike aluminum it forms but no protective oxide. Therefore, the barrier layer also serves as a passivation layer, that is, it protects the copper from the environment. This is necessary because copper would easily oxidized and thus increase the electrical resistance to a higher metallization. The copper oxide is pervious to water and oxygen, so that with time, the copper would continuously oxidize whereby the conductors are unusable. In addition, the barrier layer serves as an etch stop for a subsequent damascene process.