Substrate temperature control in an ALD reactor

1. A method for controlling the temperature of a substrate in an atomic layer deposition (ALD) process chamber comprising:

retaining a substrate on an electrostatic chuck assembly by electrostatic attraction, said substrate, when retained by said chuck assembly, forming a backside gas volume bounded by a backside surface of said substrate, a surface of the chuck assembly, and an annular seal;

providing a single backside gas inlet into the electrostatic chuck assembly connected to a backside gas source;

providing a backside gas by a first gas outlet arrangement leading to the backside gas volume for supplying said backside gas under pressure to said backside gas volume, said backside gas providing a heat transfer medium between said chuck assembly and said backside surface of said substrate, the first gas outlet arrangement receiving gas from the single backside gas inlet; and

creating a pressure gradient across an edge of said substrate by a second gas outlet arrangement, coupled to the backside gas source, to prevent reactive gases from causing deposition on a backside surface of said substrate or deposition on a surface of said chuck assembly, the second gas outlet arrangement comprising a first plurality of gas openings arranged in a ring surrounding the first gas outlet arrangement and surrounding the backside gas volume outside of the annular seal, the second gas outlet arrangement receiving gas from the single backside gas inlet, said step of creating a pressure gradient across an edge of said substrate comprising outputting a gas from said first plurality of gas openings to create a pressure gradient along an edge of said substrate to reduce the partial pressure of reactive gases along said edge.

2. The method of claim 1 further comprising supplying at least one gas into said process chamber for reacting with a frontside surface of said substrate in said atomic layer deposition process to form a layer on said frontside surface.

3. The method of claim 1 wherein said first gas outlet arrangement comprises a gas channel in said chuck assembly having a second plurality of gas openings arranged in a ring within the first plurality of gas openings, said method further comprising outputting a gas from said first plurality of gas openings to create a pressure gradient along an edge of said substrate to reduce the partial pressure of reactive gases along said edge and to prevent reactive gases from causing deposition on a backside surface of said substrate or deposition on a surface or edge of said chuck assembly.

4. The method of claim 1 further comprising:

detecting a temperature corresponding to a temperature of said substrate; and

controlling a chuck assembly heater, controlling coolant flowing through a coolant channel thermally coupled to said chuck assembly, and controlling said backside gas to regulate a temperature of said substrate.

5. The method of claim 4 wherein said detecting said temperature is performed by optically measuring a temperature of said backside surface of said substrate.

6. The method of claim 4 wherein said detecting said temperature is performed by a thermocouple that measures a temperature of said chuck assembly.

7. The method of claim 4 wherein said controlling said chuck assembly heater comprises controlling a resistive heater formed as part of said chuck assembly.

8. The method of claim 4 wherein said controlling said chuck assembly heater comprises controlling a plasma.

9. The method of claim 1 wherein said backside gas includes one of Ar, He, and H.

10. The method of claim 1 wherein said backside gas provides a backside gas pressure between 3-20 torr.

11. The method of claim 1 wherein said backside gas provides a backside gas pressure between 6-10 torr.