Wafer presence sensor for detecting quartz wafers

A method of detecting the presence of substrates, comprising:

• providing a linear array of chambers adapted to clean and/or dry substrates;
• providing a transport mechanism adapted to lower the substrates into and to raise the substrates from the chambers, the substrates being raised and lowered while held in a vertical orientation, the raising and lowering of a respective substrate with respect to each chamber defining a respective vertical plane;
• using respective acoustic transmitter/receiver pairs to define a plurality of acoustic signal paths, each of the acoustic signal paths intersecting a respective one of the vertical planes at an acute angle;
• and
• detecting the presence of the substrates by detecting interruption of the acoustic signal paths.

A substrate detection apparatus, comprising:

• a linear array of chambers adapted to clean and/or dry substrates;
• a transport mechanism adapted to lower the substrates into and to raise the substrates from the chambers, the transport mechanism raising and lowering the substrates while holding the substrates in a vertical orientation, the raising and lowering of a respective substrate with respect to each chamber defining a respective vertical plane;
• and
• a plurality of transmitter/receiver pairs each adapted to define respective signal paths, each of the signal paths intersecting a respective one of the vertical planes at an acute angle.