Sputtering chamber having auxiliary backside magnet to improve etch uniformity and magnetron producing sustained self sputtering of ruthenium and tantalum
A plasma sputter chamber and process for sputtering ruthenium and tantalum at low pressure or with self-sustained sputtering (SSS). The source magnetron is strongly unbalanced and of sufficient size to project the unbalanced magnetic field toward the wafer to increase the ionization probability. Sputter etch uniformity is increased by the use of an auxiliary magnet system rotating with the source magnetron but placed towards the center of rotation. It may be a larger, nearly balanced auxiliary magnetron with an outer polarity matching that of the source magnetron or an array of magnets of that polarity. An integrated process includes a directional deposition of the refractory metal and its nitride, a sputter etch, and a flash deposition.
1. A magnet system for a plasma sputter chamber, comprising:
a source magnetron having
an outer magnet assembly comprising magnets of a first magnetic polarity that is oriented along a first direction and
an inner magnet assembly comprising at least one magnet of an opposed second magnetic polarity that is oriented opposite the first direction, surrounded by the outer magnet assembly, and separated therefrom by a closed first gap,
wherein a first ratio of the magnetic strength of the outer magnet assembly to the magnetic strength of the inner magnet assembly of the source magnetron is at least three, and
wherein the source magnetron is rotated in back of a target assembly about the central axis; and
an auxiliary magnetron disposed away and spaced from an outer side of the source magnetron in a second direction from the inner pole toward the central axis, overlying the central axis, and having an outer magnet assembly comprising magnets of the first magnetic polarity that is oriented along the first direction, surrounding an inner magnet assembly comprising at least one magnet of the second magnetic polarity that is oriented opposite the first direction, and separated therefrom by a closed second gap, wherein the inner and outer magnet assemblies of the auxiliary magnetron have substantially equal magnetic strengths.
2. The system of claim 1 , wherein the second gap is wider than the first gap.
3. A magnet system configured to be disposed on a back of a target assembly of a plasma sputter chamber for influencing a production of particles sputtered from a front of the target assembly and consisting of:
a source magnetron consisting of
an outer pole of first magnetic polarity oriented along a first direction and
an inner pole of an opposed second magnetic polarity oriented opposite the first direction, surrounded by the outer pole, and separated therefrom by a closed first gap,
wherein the source magnetron is rotated in back of the target assembly about the central axis; and
an auxiliary magnet arrangement disposed on an outer side of the source magnetron in a direction from the inner pole toward the central axis, at least partially disposed at a position between the central axis and the outer pole, and consisting of at least one magnet of the first magnetic polarity oriented along the first direction.
4. The magnet system of claim 3 , wherein the auxiliary magnet arrangement is spaced outside of and away from the source magnetron.
5. The magnet system of claim 3 , wherein the auxiliary magnet arrangement consists of an arc-shaped array of magnets, the array having a shape following a shape of a portion of the outer pole separated therefrom by a second gap.
6. The magnet system of claim 5 , further comprising at least one arc-shaped pole piece capturing the magnets of the auxiliary magnet arrangement.
7. The system of claim 1 , wherein a second ratio of the magnetic strength of the outer magnet assembly of the auxiliary magnetron to the magnetic strength of the inner magnet assembly of the auxiliary magnetron is less than 1.5.
8. The system of claim 1 , wherein the outer magnet assembly of the source magnetron includes a pole piece having a flattened aperture having a major axis between 15 and 20% longer than a minor axis thereof.
9. The system of claim 8 , wherein the minor axis is arranged along a radius from the central axis.
10. The system of claim 9 , wherein the second gap includes two opposed straight portions extending perpendicularly to the radius.