Joined body and electrostatic chuck

A joined body comprising:

• a flat plate-shaped first member;
• a flat plate-shaped second member;
• and
• a joining portion disposed between the first member and the second member and joining the first member and the second member together,
• wherein the joining portion includes a first joining layer formed of a first joining material and disposed on a side toward the first member, a second joining layer formed of a second joining material and disposed on a side toward the second member, and a flat plate-shaped metal layer disposed between the first joining layer and the second joining layer and having a plurality of holes communicating with one another,
• the metal layer including a first-joining-material-impregnated layer which is disposed on a side toward the first joining layer and in which the plurality of holes are impregnated with the first joining material, a second-joining-material-impregnated layer which is disposed on a side toward the second joining layer and in which the plurality of holes are impregnated with the second joining material, and an unfilled hole layer which is disposed between the first-joining-material-impregnated layer and the second-joining-material-impregnated layer and in which the plurality of holes are void;
• wherein the metal layer is formed of felt of metal fibers;
• wherein a relation of t≥0.07 log(S)−0.1 is satisfied, where S is an average area (mm2) of an area of junction between the metal layer and the first joining layer and an area of junction between the metal layer and the second joining layer, and t is a thickness (mm) of the metal layer;
• wherein 1.0≤t≤3.0;
• and
• wherein the metal layer has a void fraction of 50% or greater and 90% or less.