Through the wafer optical transmission sensor

In a method for controlling the manufacture of devices which manufacture includes the step of wet eching within a chamber a material having a metal layer to remove selected portions of said metal layer and determining the extent of removal of said metal layer the combination of directing a light beam through said material and detecting the light transmitted through said material using apparatus positioned within said wet etching chamber and remaining in such chamber during the wet etching process, the following steps

• fixedly positioning a unitary assembly within said wet etching chamber said assembly consisting of a distal portion positioned above said material and substantially out of the wet etching spray pattern, containing a light source for emitting light at a pre-selected wavelength, a window to permit light generated by said light source to exit said distal portion of said assembly, and lens for directing said light source toward said material;
• and
• a proximal portion positioned below said material, containing a window positioned to receive light transmitted through said material, optical filter means selected to transmit the light generated from the source and passing through said material and to reject ambient light, and detector means for collecting said transmitted light and transmitting signals generated by said light to signal processing means for controlling said wet etching process.