Ion injector and lens system for ion beam milling
The embodiments herein relate to methods and apparatus for performing ion etching on a semiconductor substrate, as well as methods for forming such apparatus. In some embodiments, an electrode assembly may be fabricated, the electrode assembly including a plurality of electrodes having different purposes, with each electrode secured to the next in a mechanically stable manner. Apertures may be formed in each electrode after the electrodes are secured together, thereby ensuring that the apertures are well-aligned between neighboring electrodes. In some cases, the electrodes are made from degeneratively doped silicon, and the electrode assembly is secured together through electrostatic bonding. Other electrode materials and methods of securing may also be used. The electrode assembly may include a hollow cathode emitter electrode in some cases, which may have a frustoconical or other non-cylindrical aperture shape. A chamber liner and/or reflector may also be present in some cases.
1. An apparatus for etching a substrate, the apparatus comprising: a reaction chamber; a substrate support;
an inlet for supplying one or more gases or plasma to the reaction chamber;
a first electrode, a second electrode, and a third electrode, each having a plurality of apertures therein, wherein the second electrode is positioned below the first electrode, and wherein the third electrode is positioned below the second electrode;
a hollow cathode emitter electrode comprising a plurality of hollow cathode emitters, wherein the hollow cathode emitters are aligned with the apertures in the first, second, and third electrodes, each of the hollow cathode emitters having a width that is wider at a top portion than at a bottom portion, and wherein the hollow cathode emitter electrode is positioned above the first electrode;
one or more RF sources configured to generate a plasma above the hollow cathode emitter electrode and/or in the hollow cathode emitter electrode, and configured to extract ions from the plasma by applying a bias to the first electrode and/or second electrode; and
further comprising a controller configured with instructions to cyclically rotate the substrate support in a first direction at a first average rotation rate and in a second direction at a second average rotation rate during etching, the first direction being opposite the second direction, and wherein the first and the second average rotation rates are different and first direction being opposite the second direction.
2. The apparatus of claim 1 , further comprising a rotation mechanism configured to rotate and tilt the substrate support with an accuracy of about 2° or better.
3. The apparatus of claim 1 , further comprising a reflector positioned below the third electrode and above the substrate support, wherein the reflector is operable to neutralize ions passing through the apertures in the first, second, and third electrodes during etching.
4. The apparatus of claim 1 , wherein each of the hollow cathode emitters comprises an electrically conductive tube having a frustoconical geometry.
5. The apparatus of claim 4 , further comprising a gas pathway that prevents formation of an excess pressure differential across the first, second, and third electrodes during times of high gas flow or during pump down.
6. The apparatus of claim 1 , wherein the plurality of apertures are formed by:
providing and securing a first inter-electrode layer such that it is immobilized between the first electrode and the second electrode, and providing and securing a second inter-electrode layer such that it is immobilized between the second electrode and the third electrode, wherein the first electrode, second electrode, third electrode, first inter-electrode layer, and second inter-electrode layer are substantially vertically aligned with one another to form an electrode assembly; and
forming the plurality of apertures in the first electrode, second electrode, and third electrode while the first inter-electrode layer and the second inter-electrode layer are immobilized in the electrode assembly.
7. The apparatus of claim 1 , further comprising a rotation mechanism configured to rotate the substrate support with an accuracy of about 2° or better.
8. The apparatus of claim 7 , wherein the controller is configured with instructions to cause rotating the substrate support about ±215° as measured from a central starting position.
9. The apparatus of claim 7 , wherein the controller is configured to cause (i) applying a first bias to the first electrode, (ii) applying a second bias to the second electrode, and (iii) supplying the plasma above the first electrode such that the extracted ions pass through the apertures in the first electrode, second electrode, and third electrode toward a surface of the substrate.
10. An apparatus for etching a substrate, the apparatus comprising:
a reaction chamber;
a substrate support;
an inlet for supplying one or more gases or plasma to the reaction chamber;
a rotation mechanism configured to rotate the substrate at an accuracy of about 2° or better;
a first electrode and a second electrode positioned in the reaction chamber, each of the first and second electrodes being made from degeneratively doped silicon, each of the first and second electrodes comprising a plurality of apertures therein;
further comprising a hollow cathode emitter electrode with plurality of apertures and positioned above the first and second electrodes; and
a controller configured with instructions to perform the following operations:
positioning the substrate on the substrate support in the reaction chamber,
applying a first bias to the first electrode and a second bias to the second electrode, and supplying plasma above the first and second electrodes such that ions pass through the plurality of apertures in the first and second electrodes toward a surface of the substrate,
while supplying the plasma, cyclically rotating the substrate and substrate support in a first direction at a first average rotation rate and in a second direction that is opposite the first direction at a second average rotation rate, wherein the first and second average rotation rates are different, and
etching the substrate as a result of ions traveling toward the surface of the substrate while the substrate is rotated.
11. The apparatus of claim 10 , wherein the controller is configured with instructions to cause rotating the substrate and substrate support about ±215° or less as measured from a central starting position.
12. The apparatus of claim 11 , wherein the controller is configured with instructions to cause rotating the substrate and substrate support about ±180° or less as measured from the central starting position.
13. The apparatus of claim 10 , further comprising a reflector positioned below the first and second electrodes, wherein the controller is configured to cause impacting the ions on the reflector to thereby neutralize the ions to form particles, wherein the particles etch the substrate.
14. The apparatus of claim 10 , wherein the plurality of apertures in the first and second electrodes are formed by:
providing and securing an inter-electrode structure such that it is immobilized between the first electrode and the second electrode, wherein the first electrode, second electrode, and inter-electrode structure are substantially vertically aligned with one another to form an electrode assembly; and
forming the plurality of apertures in the first and second electrodes while the inter-electrode structure is immobilized between the first and second electrodes in the electrode assembly.