Combination CVD/ALD method, source and pulse profile modification
The present invention relates generally to methods and apparatus for the controlled growing of material on substrates. According to embodiments of the present invention, a precursor feed is controlled in order to provide an optimal pulse profile. This may be accomplished by splitting the feed into two paths. One of the paths is restricted in a continuous manner. The other path is restricted in a periodic manner. The output of the two paths converges at a point prior to entry of the reactor. Therefore, a single precursor source is able to fed precursor in to a reactor under two different conditions, one which can be seen as mimicking ALD conditions and one which can be seen as mimicking CVD conditions. This allows for an otherwise single mode reactor to be operated in a plurality of modes including one or more ALD/CVD combination modes. Additionally, the pulse profile of each pulse can be modified. The pulse profile can be modified to create a low or very low partial pressure pulse profile at the beginning of a pulse.
1. A method of operating a system having a reactor configured to deposit thin films, said method comprising the steps of:
dividing a flow of a reactant from a reactant source vessel in to two separate paths,
substantially restricting the flow of a first path of the two separate paths in a periodic manner,
substantially restricting the flow of a second path of the two separate paths in a periodic manner, and
combining the flow from the second path with the flow from the first path at a point after restriction and prior to entry of a reaction space.
2. A method according to claim 1 , wherein a combined flow comprising at least a portion from each path is fed to the reaction space during at least one period of time during operation of the system.
3. A method according to claim 1 , wherein a pulse profile of the combined flow entering the reaction space for each pulse of reactant includes less than half of the total amount of precursor within the first half of the pulse.
4. A method according to claim 3 , wherein the pulse profile is controlled by during the substantially restricting steps of the first and second paths of flow of the reactant.
5. A method according to claim 1 , wherein when either or both of the first or second paths are substantially restricted, there is no flow of reactant from said corresponding path entering the reaction space.
6. A method according to claim 1 , wherein the period in restricting the flow of a first path in a periodic manner comprises a purge step.
7. A method according to claim 1 , wherein the period in restricting the flow of a first path in a periodic manner comprises a purge step of an ALO process.
8. A method according to claim 1 , wherein the reactor configured to deposit thin films is performing an ALO process.
9. A method according to claim 1 , wherein the flow in the first path is restricted by passing through a needle valve or a mass flow controller.
10. A method according to claim 1 , wherein the first and second paths are combined at a four-way valve including the first and second paths, a path for a purge gas and a path to the reaction space.
11. A method according to claim 1 , further comprising performing an ALD process in the reactor.