SEAL RINGS IN ELECTROCHEMICAL PROCESSORS
A seal ring for an electrochemical processor does not slip or deflect laterally when pressed against a wafer surface. The seal ring may be on a rotor of the processor, with the seal ring having an outer wall joined to a tip arc through an end. The outer wall may be a straight wall. A relatively rigid support ring may be attached to the seal ring, to provide a more precise sealing dimension. Knife edge seal rings that slip or deflect laterally on the wafer surface may also be used. In these designs, the slipping is substantially uniform and consistent, resulting in improved performance.
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Production of semiconductor integrated circuits and other micro-scale devices typically requires formation of multiple metal layers on a wafer or other substrate. By electroplating metals layers in combination with other steps, such as planarizing, etching and photolithography, patterned metal layers forming the micro-scale devices are created.
Electroplating is performed with the substrate, or one side of the substrate, in a bath of liquid electrolyte, and with electrical contacts touching a conductive layer on the substrate surface. Electrical current is passed through the electrolyte and the conductive layer. Metal ions in the electrolyte deposit or plate out onto the substrate, creating a metal layer on the substrate. The metal ions also tend to plate out onto the electrical contacts as well. This affect, referred to as “plate-up” changes the electric field around the contacts, causing non-uniform plating. The metal plated onto the electrical contacts consequently must be removed, adding to the time requirements and complexity of the manufacturing process.
So called dry or closed contact rings have been developed to avoid plate-up of the contacts. In these designs, a seal ring seals the electrolyte away from the electrical contacts. The electrical contacts touch the conductive layer on the substrate at the perimeter of the substrate. The seal ring contacts the substrate surface radially inwardly of the electrical contacts, so that the contacts remain isolated from the electrolyte.
Although the use of a seal in a dry contact ring solves the plate-up problem, dry contact rings have their own disadvantages. Initially, the seal of a dry contact ring necessarily contacts or covers an annular shaped area on the substrate surface, which area cannot be used to form devices. Hence, a fraction of the useable substrate surface must be sacrificed if a seal is used. The seal must also not unduly disturb the electric field around the edge of the wafer, or electroplating quality will be degraded. In some processors, the seal can also plate up (i.e., metal gets plated onto the seal) over successive wafer plating cycles. Avoiding seal plate up is also significant in providing uniform high quality metal plated wafers. The seal must also perform reliably and consistently over a large number of plating cycles, without leaking and with minimal sticking to the wafer after the plating cycle.
SUMMARY OF THE INVENTIONA new seal ring for an electrochemical processor has now been invented. In one design, the new seal ring does not slip when sealed against a wafer surface. The seal ring may be on a rotor of the processor, with the seal ring having an outer wall joined to a tip arc. The outer wall may be a straight wall. A relatively rigid support ring may be attached to the seal ring, to provide a more precise sealing dimension. The seal may optionally be molded onto the e.g., metal support ring. Knife edge seal rings that slip or deflect laterally on the wafer surface may also be used. In these designs, the slipping is substantially uniform and consistent, resulting in improved performance. The present seal rings also have minimal area of contact with the wafer, which improves yield.
In the drawings, the same reference number indicates the same element in each of the views.
As shown in
A membrane 60 may optionally included, with anolyte in a lower chamber below the membrane and with catholyte in an upper chamber above the membrane 60. Electric current passes from the electrodes through the electrolyte to a conductive surface on the wafer, as is well known in the art. A motor 28 in the head may be used to rotate the wafer during electroplating. As shown in
Various seal designs have been used in electrochemical processors.
A typical o-ring may naturally have no slip if it is clamped between two sealing surfaces. However, a clamped o-ring seal design in an electroplating processor would require a very tall structure which would interfere with electric field and mass-transfer at the edge of the wafer, and also tend to trap bubbles. As a result, in electroplating processors, seals are typically an elastomer at the tip/rim of a beam-like or cantilever structure, such as shown in
The inventors' analysis and mathematical modeling of seal behavior reveals that the seal tip can slip or deflect radially inward or outward when engaging the wafer as shown in
However, known seals or varying designs may or may not slip when used with different electrolytes and wafer surfaces. For example, a seal might not slip on copper seed wafers, yet slip on photoresist coated wafers, giving inconsistent results on various processes. Since nominal wafer engagement forces for a 12 inch wafer are about 30-50 lbs, there could be a significant variation in seal compliance and edge-exclusion if the seal slipped on some wafers and not on others. Perhaps, even more inconsistent results might result if the seal slips to varying degree on the same wafer (i.e. if the seal slips on only one side of the wafer).
The inventors have discovered that improved seal performance may be achieved by designing a seal that consistently and uniformly slides on various wafer surfaces. The inventors have also discovered that improved weal performance may be achieved by designing a seal that successfully resists sliding entirely, with the seal tip compressing or deforming without sliding during engagement onto the wafer.
Referring still to
The end radius 118 may range from 0.001 to 0.005 or 0.001 to 0.003 inches. The tip arc 116 may have a radius ranging from 0.010 to 0.30 or 0.015 to 0.025 inches. Dimension HH, in
The seal ring 102 shown in
The dimensions of different sections of the seal may be selected to achieve a low or zero-slip design. In use, one section or area of the seal structure (i.e. the ring 104 and the elastomer beyond the structure around the arc section 110) deflects slightly up and moves the tip radially inward, while another section (i.e. the tip arc 116 and the wall 120) deflect radially outward. The seal may be designed so that the radially inward motion on one part of the seal structure is matched by the radially outward motion of another part of the structure. The result is then that the net sliding motion at the end 118 is minimal, e.g., less than 0.5 mm, 0.25 mm, 0.2 min, 0.1 mm, 0.05 mm, or even zero.
The contact force applied to the seal ring 102 may vary from about 40 to 120 pounds, for an 11.62 ID seal ring. The contact force causes the end 118 and the tip arc 116 to deform, with little or no sliding. This no-slip design, coupled with using a relatively rigid metal support ring 104, gives a more precise sealing dimension, which improves yield as the patterns are moved closer to the edge of the wafer. The no-slip seal ring 102 has compliance and a small amount of deflection at given force without the seal end 118 tending to move in the lateral direction as the seal engages the wafer. This avoids the possibility of the end 118 rolling under itself and affecting the seal performance.
In use, the knife edge of the seal ring 130 engages the wafer at the inner-radius. The seal ring 130 will deflect more for a specified applied contact force. However, the deflection of slip is uniform. Referring to
The seal ring 150 has relatively high local compliance like the knife-edge seal ring 130. The seal ring 150 can also help shield the plating rate directly at the seal-wafer interface. This may help reduce seal failure due to plate-up of the seal material for some chemistries. Both seal rings 130 and 150 seal with less surface area than conventional designs. The seal ring 130 seals at the very I.D. of the seal. The seal ring 150 pulls the seal lip inboard to the seal (closer to the edge of the wafer). The lower surface which creates the point of the seal lip is now at the front of the seal. This creates an over hang that shields the seal lip from the high current densities. The overhang 162 may reduce the local plating rate at the seal/wafer contact and may reduce the tendency for seal plate up.
The dimensions and angles discussed above are provided as examples and are not critical to the performance of the seal rings. Dimensions outside of the given ranges may be used in alternative designs. The term wafer here means any substrate on which micro-scale devices may be formed. Micro-scale devices include microelectronic, micromechanical, microelectro-mechanical, micro-optical and micro-fluidic devices, whether formed on semiconductor or other substrate materials.
Thus, novel designs and methods have been shown and described. Various changes and substitutions may of course be made without departing from the spirit and scope of the invention. The invention, therefore, should not be limited except to the following claims and their equivalents.
Claims
1. An electrochemical processor, comprising:
- a vessel;
- a rotor engageable with the vessel;
- the rotor having a seal ring that does not slip when sealed against a wafer surface.
2. An electrochemical processor, comprising:
- a vessel;
- a rotor engageable with the vessel;
- a seal ring on the rotor having an outer wall joined to a tip arc through an end.
3. The electrochemical processor of claim 2 with the outer wall comprising a straight wall.
4. The electrochemical processor of claim 2 with the end having a radius of less than 0.01 inches and the tip arc has a radius of less than 0.03 inches.
5. The electrochemical processor of claim 2 with the seal ring having an upper end for engaging a wafer, with the upper end formed via a straight wall and a radius.
6. The electrochemical processor of claim 5 further including a support ring attached to the seal ring.
7. The electrochemical processor of claim 6 with seal ring comprising a fluoroelastomer and the support ring comprising a metal.
8. A seal ring for use in an electrochemical processor, comprising:
- a material having a straight vertical outer wall intersected by a curved surface to form an edge having a radius of less than 0.005 inches.
9. The seal ring of claim 8 with the material comprising a fluoroelastomer.
10. The seal ring of claim 8 with the curved surface comprising a radius of less than 0.03 inches.
11. The seal ring of claim 8 further including a slot in the material, and a metal support ring having an inner edge inserted into the slot.
12. A seal ring for use in an electrochemical processor, comprising:
- a material having a first surface and a second surface forming a knife edge with the second surface, with the knife edge at an inner diameter of the material, and with the knife edge having a radius of less than 0.002 inches.
13. The seal ring of claim 12 with first and second surfaces comprising straight and flat surfaces forming an angle of 15 to 25 degrees between them.
14. A seal ring for use in an electrochemical processor, comprising:
- a material having a first surface and a second surface forming a knife edge with the second surface, with the second surface forming a shielded overhang space between a wafer surface and the material, when the seal ring is engaged onto a wafer.
15. The seal ring of claim 14 with the second surface forming an angle of 90 to 130 degrees to the first surface.
16. A seal ring for use in an electrochemical processor, comprising:
- a tip that contacts a workpiece;
- a first section that deflects radially inwardly on the workpiece as the tip contacts the workpiece;
- a second section that deflects radially outwardly on the workpiece as the tip contacts the workpiece; and with the radially inward movement of the first section substantially equal to the radially outward movement of the second section, resulting in substantially no net sliding movement of the tip on the workpiece.
17. The seal ring of claim 16 wherein the first section comprises an arc section and the second section comprises a wall section.
18. The seal ring of claim 16 wherein the net sliding movement of the tip is less than 0.5 mm.
Type: Application
Filed: May 17, 2012
Publication Date: Nov 21, 2013
Applicant: APPLIED MATERIALS, INC. (Santa Clara, CA)
Inventors: Nolan L. Zimmerman (Kalispell, MT), George Mattinger (Cupertino, CA), Gregory J. Wilson (Kalispell, MT), Eric A. Englhardt (Palo Alto, CA), Balamurugan Ramasamy (Bangalore)
Application Number: 13/474,533
International Classification: C25D 17/00 (20060101);