u00b0 the rotational distance to move a second end effector and a second wafer 1007 clockwise to face process module 1011 is shown as roughly 90 120 u00b0 thus wafer insertion into process module 1008 may commence slightly before wafer insertion into process module 1011 u2014 this necessitates asynchronous operation of the two end effectors of the dual wafer robot later sections of this description discuss the cam mechanism used to control the heights of the end effectors to ensure proper insertion of wafers into the process modules loading of process modules 1009 and 1010 requires loading third and fourth wafers from loadlock 1001 onto the two end effectors of dual water robot 1006 depending on details of the design of loadlock 1001 which are not critical to the present invention a collective z motion of the dual wafer robot may be necessary as described below in the illustration a pass through module 1012 is shown with two chambers in an above below orientation with respect to one another in one embodiment of the present invention one chamber of the pass through module is configured for wafer pre heating and the other chamber for wafer cool down in general a pass through module may be used in two modes 1 as a pass through module illustrated for a six chamber system in fig2 a b or for an eight chamber system as shown in fig3 a b in this mode one or two wafers would be loaded into the pre heat chamber of pass through module 1012 and then after pre heating a second robot illustrated in fig2 a 3b would remove the wafers for insertion into two process modules not shown u2014 see fig2 a 3b similarly after processing the wafers would be inserted by the second.