A chamber 25 comprises a support 45 for holding a substrate 20 and a sensor system 135 adapted to detect the presence or proper placement of the substrate 20 on the support 45. The support 45 comprises a window 155 that is transparent and adapted to transmit light therethrough. The sensor system 135...http://www.google.com.au/patents/US6592673?utm_source=gb-gplus-sharePatent US6592673 - Apparatus and method for detecting a presence or position of a substrate
