Flow sensor, mass flow controller, and method for manufacturing flow sensor

A flow sensor comprising:

• a first substrate having a pair of thermosensitive films, a heater film located on a position between the pair of thermosensitive films, and a passage protective film having corrosion resistance and provided at a position other than positions of forming the thermosensitive films and the heater film in a passage forming region on a first main surface, the first substrate having a metal sealing film having corrosion resistance and provided in a region other than the passage forming region on the first main surface;
• and
• a second substrate having a groove formed in the passage forming region on a second main surface disposed opposite the first main surface and a side wall forming portion separating other regions other than the passage forming region from the groove and provided as protruding beyond the other regions, the second substrate being made of a material having corrosion resistance;
• and
• a fixing member configured to bond the first main surface to the second main surface so that the first main surface is faced to the second main surface and fix the first main surface to the second main surface,
• wherein the side wall forming portion of the second substrate is compression bonded so that the side wall forming portion is located on the metal sealing film of the first substrate.