Method of forming a semiconductor device

A method of forming a semiconductor device comprising a plurality of stacked transistor devices each comprising a bottom transistor device and a top transistor device, the method comprising:

• forming a plurality of parallel fin structures on a substrate, each of the fin structures comprising a bottom device sub-stack comprising a number of bottom channel layers and a top device sub-stack comprising a number of top channel layers;
• forming a sacrificial gate across the fin structures;
• forming bottom source/drain bodies for each bottom transistor device by epitaxy;
• forming a bottom dummy contact layer covering the bottom source/drain bodies, comprising depositing a dummy material over the bottom source/drain bodies, and removing a top portion of the dummy material by an etch back process such that a bottom portion of the dummy material remains to cover the bottom source/drain bodies;
• forming top source/drain bodies for each top transistor device over the bottom dummy contact layer by epitaxy;
• depositing an insulating material over the bottom dummy contact layer and the top source/drain bodies;
• subsequent to depositing the insulating material, replacing the sacrificial gate with a functional gate stack by a replacement metal gate process;
• subsequent to the replacement metal gate process, patterning holes extending through the insulating material, each hole exposing an upper surface portion of the bottom dummy contact layer;
• replacing the bottom dummy contact layer with one or more contact metals, comprising etching the dummy material via the holes and thereafter depositing the one or more contact metals via the holes;
• etching cuts through the contact metal via the holes, thereby forming bottom source/drain contacts for the bottom transistor devices;
• and
• filling the cuts and holes with an insulating material.