Method for fabrication and structure for high aspect ratio vias

DETAILED DESCRIPTION The present invention discloses method for fabrication and structure for high aspect ratio vias.
According to the invention's method, a via is first etched in a dielectric.
Then a conformal layer is deposited over the dielectric and the via.
The conformal layer reduces an initial width of the via to a target width.
A trench is then etched in the dielectric and the conformal layer.
Since the width of the via is reduced from the initial width to the target width, the resulting final via has a high aspect ratio, while the fabrication of the final high aspect ratio via has been made much easier as compared to the conventional fabrication methods.
The via and the trench are then filled with metal which contacts an interconnect metal situated below the via.
In one embodiment of the invention copper is used to fill the via and the trench and also as the interconnect metal below the via.
In one embodiment of the invention, the dielectric is silicon dioxide or fluorinated silicon dioxide and the conformal layer is silicon dioxide.
In another embodiment of the invention, the dielectric is silicon dioxide or fluorinated silicon dioxide while the conformal layer is silicon nitride.
In order to etch the trench in the dielectric and the conformal layer, a timed exposure to a carbon fluoride based plasma is employed.
Alternatively, instead of timing the exposure to plasma, a suitable etch stop layer is used.
In the embodiment of the invention where silicon nitride is used as the conformal layer, the silicon nitride remaining on the dielectric is removed using either chemical mechanical polishing or a carbon fluoride based plasma.
The invention's final structure is a via and a trench where the via's side walls are covered by the conformal layer while the trench's side walls are not covered by the conformal layer.