Optical cable for interferometric endpoint detection

An endpoint detection system, comprising:

• a processing chamber having a ceiling, sidewalls, and a bottom defining an internal volume;
• a substrate support located in the internal volume configured to support a substrate thereon;
• an optical bundle disposed to emit light through a ceiling of the processing chamber, the optical bundle having a plurality of fibers arranged around a center, the plurality of fibers configured to transmit the light from a light source and receive light from the substrate, the plurality of fibers comprising:
• a first transmitting row comprising a plurality of first emitting fibers configured to transmit light from a light source towards the substrate;
• and
• a first receiving row comprising a plurality of first receiving fibers configured to receive reflected light originating from the transmitted light, the plurality of first receiving fibers configured to receive light emitted from the plurality of first emitting fibers, the plurality of first receiving fibers and the plurality of first emitting fibers are radially disposed about the center and each first emitting fiber of the plurality of first emitting fibers have a pairing angle from a respective first receiving fiber of the plurality of first receiving fibers wherein the pairing angle extends through the center, the pairing angle being between about 175 degrees and about 185 degrees.

A semiconductor processing system, comprising:

• an optical bundle disposed to emit light through a ceiling of a processing chamber, the optical bundle having a plurality of fibers disposed about a center and configured to transmit the light from a light source towards a substrate disposed in the processing chamber, the plurality of fibers comprising a first plurality of emitting fibers and a plurality of receiving fibers, wherein each receiving fiber of the plurality of receiving fibers is disposed at a pairing angle from a respective emitting fiber of the plurality of emitting fibers and wherein the pairing angle extends through the center at an angle between about 175 degrees and about 185 degrees;
• a non-transitory computer readable medium storing instructions, the instructions when executed by a processor cause a controller coupled to the light source to perform a method, the method comprising:
• emitting a first light from a first emitting fiber of the plurality of emitting fibers;
• receiving the first light at a respective first receiving fiber of the plurality of fibers, the respective first receiving fiber radially disposed at a pairing angle from the first emitting fiber;
• emitting a second light from a second emitting fiber of the plurality of emitting fibers;
• and
• receiving the second light at the second receiving fiber, the second receiving fiber radially disposed at the pairing angle from the second emitting fiber, the second receiving fiber configured to receive light originating from the second emitting fiber, wherein the pairing angle through the center is between about 175 degrees and about 185 degrees.