Cleaning stack of wafers

The invention provides apparatus for cleaning wafers in a stack (10) comprising a multiplicity of wafers, and comprising a generally horizontal trough (17) into which the stack of wafers is to be placed, the axis of the trough being perpendicular to the planes of the individual wafers, supports (12) within the trough to hold the wafers off lower parts of the trough, a fixed support (14) for one end of the stack and sufficient space in a direction away from this end of the stack to allow the wafers to separate by a distance such that capillary action between them is broken, in which there is provision (16) to introduce jets of liquid upwardly from lower parts of the trough (17), whereby those jets of liquid maintain the wafers clear of direct contact with the supports (12) to hold the wafers off the lower parts of the tough, and separate the wafers laterally in a direction parallel to the axis of the trough so moving the wafers in a direction away from the fixed support (14), and those jets of liquid also clea