Plasma deposition
An apparatus for depositing a group III metal nitride film on a substrate, the apparatus comprising a plasma generator to generate a nitrogen plasma from a nitrogen source, a reaction chamber in which to react a reagent comprising a group III metal with a reactive nitrogen species derived from the nitrogen plasma so as to deposit a group III metal nitride on the substrate, a plasma inlet to facilitate the passage of nitrogen plasma from the plasma generator into the reaction chamber and a baffle having one or more flow channels for passage of the nitrogen plasma. The baffle is located between the plasma inlet and the substrate and prevents a direct line of passage for nitrogen plasma between the plasma inlet and the substrate.
1. An apparatus for depositing a group III metal nitride film on a substrate, the apparatus comprising:
(a) a plasma generator to generate a nitrogen plasma from a nitrogen source;
(b) a reaction chamber in which to react a reagent comprising a group III metal with a reactive nitrogen species derived from the nitrogen plasma so as to deposit a group III metal nitride on the substrate;
(c) a plasma inlet to facilitate the passage of nitrogen plasma from the plasma generator into the reaction chamber; and
(d) a baffle having one or more flow channels for passage of the nitrogen plasma, the baffle located between the plasma inlet and the substrate and the baffle comprising a plurality of distribution members located above a blocking member, each distribution member defining an aperture and being spaced from adjacent distribution members and the blocking member, wherein the apertures defined by the distribution members are progressively smaller upon approaching the blocking member, and
wherein the baffle prevents a straight line of passage for nitrogen plasma between the plasma inlet and the substrate.
2. The apparatus of claim 1 wherein consecutive distribution members and the blocking member are at least partially overlapping.
3. The apparatus of claim 1 wherein adjacent distribution members and the blocking member are connected by one or more circumferentially disposed connecting members.
4. The apparatus of claim 1 wherein each circumferentially disposed connecting member is circumferentially offset from those connecting members located immediately above and below.
5. The apparatus of claim 1 wherein the plurality of distribution members are rings and the blocking member is a solid disc and wherein the rings are of progressively smaller diameter with the smallest diameter ring located adjacent the solid disc.
6. The apparatus of claim 5 wherein the rings are substantially parallel to one another.
7. The apparatus of claim 6 wherein the parallel rings are disposed in a plane substantially perpendicular to the direction of flow of nitrogen plasma from the plasma inlet.
8. The apparatus of claim 1 wherein one or more of the distribution members comprise a projection to direct the nitrogen plasma in a substantially vertical downwards direction.
9. The apparatus of claim 1 wherein the group III metal nitride film is a gallium nitride film.
10. The apparatus of claim 1 wherein the baffle filters out high energy unwanted reactive nitrogen plasma species to prevent their contacting the substrate.