Patent ID: 7963736

Claim:
A semiconductor-processing apparatus comprising: a wafer handling chamber; at least one wafer processing chamber, each connected to the wafer handling chamber; a wafer handling device disposed in the wafer handling chamber for loading a wafer in the wafer processing chamber, said wafer handling device comprising an end effector for placing a wafer thereon, said end effector being movable from a ready-to-load position to the wafer processing chamber in an x-axis direction which is a wafer loading direction and in a y-axis which is perpendicular to the x-axis direction on a wafer loading plane; at least one first photosensor disposed in the wafer handling chamber in front of the wafer processing chamber at a position where the wafer placed on the end effector partially blocks light received by the first photosensor at the ready-to-load position and entirely blocks light received by the first photosensor when the wafer moves from the ready-to-load position toward the wafer processing chamber in the x-axis direction; and at least one second photosensor disposed in the wafer handling chamber in front of the wafer processing chamber at a position where the wafer placed on the end effector does not block light received by the second photosensor at the ready-to-load position and partially blocks but never entirely blocks light received by the second photosensor when the wafer moves from the ready-to-load position toward the wafer processing chamber in the x-axis direction, wherein the first photosensor is adapted to output a first analogue signal indicative of quantity of light sensed by the first photosensor at the ready-to-load position, and the second photosensor is adapted to output a second analogue signal indicative of lowest quantity of light sensed by the second photosensor when the wafer moves from the ready-to-load position toward the wafer processing chamber, wherein the first and second photosensors are disposed at positions such that an amount of a wafer deviation, a, in the x-axis direction is determinable by the equation a=a ′+( R −√{square root over (( R 2 −b 2 ))}) wherein a′ is an amount of a wafer deviation detected by the first photosensor, b is an amount of a wafer deviation detected by the second photosensor, and R is a radius of the wafer.