Removing bubbles from plating cell

An electroplating apparatus comprising:

• an electrode arranged along a bottom of a chamber;
• an ionically resistive element with through holes arranged along a top of the chamber;
• a membrane arranged between the electrode and the ionically resistive element;
• one or more panels forming a plurality of regions between the membrane and the ionically resistive element;
• a substrate holder arranged above the ionically resistive element;
• a seal arranged between peripheries of the ionically resistive element and the substrate holder;
• a manifold formed between a bottom of the substrate holder and a top surface of the ionically resistive element to laterally flow an electrolyte during electroplating, portions of the electrolyte descending from the manifold into the plurality of regions and ascending from the plurality of regions into the manifold via the through holes of ionically resistive element;
• and
• a substrate arranged along the bottom of the substrate holder, the substrate including with a protuberance extending along a chord of the substrate, the protuberance contacting the top surface of the ionically resistive element above a first region of the plurality of regions, and the protuberance arranged across the top surface of the ionically resistive element along one of the panels forming the first region.