Multiple anode plasma for CVD in a hollow article
A method and apparatus for plasma enhanced chemical vapor deposition to an interior region of a hollow, tubular, high aspect ratio workpiece are disclosed. A plurality of anodes are disposed in axially spaced apart arrangement, to the interior of the workpiece. A process gas is introduced into the region. A respective individualized DC or pulsed DC bias is applied to each of the anodes. The bias excites the process gas into a plasma. The workpiece is biased in a hollow cathode arrangement. Pressure is controlled in the interior region to maintain the plasma. An elongated support tube arranges the anodes, and receives a process gas tube. A current splitter provides a respective selected proportion of a total current to each anode. One or more notch diffusers or chamber diffusers may diffuse the process gas or a plasma moderating gas. Plasma impedance and distribution may be controlled using various means.
1. An apparatus for plasma enhanced chemical vapor deposition to an elongated interior region of a hollow tubular workpiece ( 10 ) of high aspect ratio greater than or equal to about thirty to one, comprising:
the hollow tubular workpiece ( 10 ) of high aspect ratio greater than or equal to about thirty to one, said workpiece ( 10 ) having the elongated interior region;
a plurality of anodes ( 20 , 22 , 24 ) placed in an axial spaced apart arrangement, dimensioned to distribute along a lengthwise axis of the elongated interior region of the hollow 7 tubular conductive workpiece ( 10 ) of high aspect ratio greater than or equal to about thirty to one, wherein each anode comprises a shield surrounding said anode, each shield comprising at least one hole;
an elongated support tube ( 18 ) containing the plurality of anodes ( 20 , 22 , 24 ) and dimensioned to fit into the elongated interior region of the workpiece ( 10 ) and along the lengthwise axis, wherein a ratio of a spacing between the anodes to an interior diameter of the hollow 7 tubular workpiece is between about 20:1 and about 1:1, wherein the elongated support tube ( 18 ) has a plurality of holes disposed in the tube ( 18 ) and spaced in order to allow electron access to the plurality of anodes;
an electrical biasing circuit ( 14 ) connected to provide an individualized DC or pulsed DC bias to each of the plurality of anodes ( 20 , 22 , 24 ); and
a gas supply conduit ( 63 ) connectable to deliver a process gas to the interior region of the workpiece ( 10 ) at a pressure of the interior region of the workpiece ( 10 ) controlled to achieve a plasma.
2. The apparatus of claim 1 , further comprising at least one gas diffuser ( 58 ) that diffuses the process gas from the gas supply conduit ( 63 ), the at least one gas diffuser ( 58 ) including a gas chamber diffuser.
3. The apparatus of claim 1 , wherein:
the plurality of anodes ( 20 , 22 , 24 ) is in spaced apart arrangement along an interior of the elongated support tube ( 18 ), the elongated support tube ( 18 ) being operable to receive a process gas; and
a current splitter ( 30 ) is connected to the plurality of anodes ( 20 , 22 , 24 ) such that each anode ( 20 , 22 , 24 ) is provided the DC or pulsed DC bias at a respective selected proportion of a total current and the workpiece ( 10 ) is biased as a cathode.
4. The apparatus of claim 3 , comprising the gas supply conduit ( 63 ) connected to the support tube ( 18 ) and at least one gas chamber diffuser ( 58 ) fluidly connectable to the gas supply conduit ( 63 ), wherein the gas chamber diffuser ( 58 ) includes:
a chamber member ( 112 ); and
a diffuser member ( 114 ) having a plurality of through holes ( 128 ) fluidly, connecting the chamber member ( 122 ) to the interior region of the workpiece ( 10 );
wherein a majority or all of the plurality of through holes ( 128 ) are in a lower half of the diffuser member ( 114 ) in a horizontal orientation of the gas chamber diffuser ( 58 ).
5. The apparatus of claim 4 , wherein the elongated support tube ( 18 ) is further operable to receive a second gas supply line ( 61 ) that delivers a plasma moderating gas, the apparatus comprising at least one notch diffuser ( 60 ) fluidly connectable to the second gas supply line ( 61 ).
6. The apparatus of claim 5 , wherein the at least one notch diffuser ( 60 ) is attached to an upper half and a center region of the elongated support tube ( 18 ), the elongated support tube ( 18 ) being oriented horizontally.
7. The apparatus of claim 3 ,
wherein the plurality of holes disposed in the tube ( 18 ) are anode slots ( 50 ), each anode slot ( 50 ) is positioned relative to a respective tip of one of the plurality of anodes ( 20 , 22 , 24 ) so as to balance between an arcing condition and an excess DC voltage condition; and
wherein the elongated tube ( 18 ) further comprises a second plurality of holes ( 52 ) placed between the anode slots ( 50 ) to allow electron access between the plurality of anodes ( 20 , 22 , 24 ).
8. The apparatus of claim 3 , wherein the current splitter ( 30 ) includes a plurality of transformers ( 76 , 78 , 80 ) connected in a differential mode.
9. The apparatus of claim 3 , wherein the current splitter ( 30 ) includes a plurality of switches directing to each anode ( 20 , 22 , 24 ) the respective selected proportion of the total current.
10. The apparatus of claim 3 , further comprising a power supply connected to the current splitter ( 30 ) and providing a current that has a high frequency pulsing between about 10 kHz and 60 kHz that is burst during intervals at a low frequency less than about 20 Hz.