Collection of unused precursors in ALD

1 . An ALD system, comprising an ALD reactor and a precursor trap coupled downstream of said ALD reactor via a valve assembly and configured to collect unused chemical precursors after reactions in said ALD reactor.

2 . The ALD system of claim 1 , wherein the valve assembly comprises a pair of valves configured to be time-phase operated such that a first one of the pair of valves opens during periods of a first precursor exposure and its purge, during which time a second one of the pair of valves is closed, permitting unused portions of the first precursor to be directed to the precursor trap.

3 . The ALD system of claim 2 wherein the first and second ones of the pair of valves are fast switching throttle valves.

4 . The ALD system of claim 1 , wherein the valve assembly is attached to effluent surface of said ALD reactor.

5 . The ALD system of claim 1 , wherein the valve assembly is actuated at a time later than initiation of a first precursor exposure time by a time interval substantially equal to a time for the first precursor to move between an upstream injecting valve and the downstream trap.

6 . A method, comprising time phase operating a pair of valves coupled downstream from an ALD reactor such that a first one of the pair of valves opens during periods of exposure of a first precursor and its purge while at substantially the same time a second one of the pair of valve is closed, so as to selectively permit unused portions of the first precursor to be collected by a precursor trap downstream of the ALD reactor.

7 . A method, comprising actuating a valve coupled downstream of an ALD reactor and upstream of a precursor trap at a time later than initiation of a first precursor exposure time by a time interval substantially equal to a residence time of the first precursor and its purge in the ALD reactor.