Rf device and method with trench under bond pad feature

A method for forming an electronic element incorporating a composite dielectric region (CDR) under a bonding pad coupled to an active device, comprising:

• providing a semiconductor substrate of a first material having a first thermal expansion coefficient (TEC) and having a first surface, wherein the substrate has therein a first region adapted to receive the active device and a second region adapted to receive the bonding pad;
• forming a mask on the second region, the mask having spaced-apart openings of a first width;
• etching space-apart trenches of substantially the first width to a first depth in the substrate, leaving columns of substantially undisturbed substrate material between the trenches and other portions of the substrate material beneath the trenches;
• forming dielectric having a second TEC in the trenches so that a substantially centrally located void is present in the dielectric extending from the first surface into the trench but not extending to other portions of the substrate material beneath the trench;
• filling the trench with an inclusion material electrically floating with respect to the substrate and having a third TEC less than the second TEC, wherein the combination of the dielectric and the electrically floating inclusion material therein forms the composite dielectric region adapted to support the bonding pad;
• forming the active device in an active device region proximate the composite dielectric region wherein the active device has a first terminal;
• forming the bonding pad on the composite dielectric region above the dielectric and inclusion material electrically isolated from the inclusion material;
• and
• electrically coupling the bonding pad to the first terminal of the active device.

An electronic device comprising:

• a semiconductor substrate having therein a bonding pad region and an active device region;
• a bonding pad electrically isolated from the substrate;
• a composite dielectric region on the substrate in the bonding pad region and underlying the bonding pad, wherein the composite dielectric region comprises insulating dielectric regions and non-single crystal semiconductor inclusion regions, the inclusion regions being electrically isolated from the bonding pad and the substrate by portions of the insulating dielectric regions;
• and
• an active device in the active device region electrically coupled to the bonding pad by an interconnection.