Means to eliminate bubble entrapment during electrochemical processing of workpiece surface
Methods and systems are provided to eliminate bubble entrapment during electrochemical processing of a substrate, wherein a rigid plate with fluid openings allow process solution to flow between the front surface of the substrate and an electrode. The plate includes a protruding region. In operation, the protruding region causes a raised solution surface to touch the front surface of the wafer prior to complete immersion of the substrate in the solution. In other embodiments, the raised surface of the solution can be provided by applying pressure to a flexible pad or other workpiece surface influencing device (WSID).
This application claims the priority benefit under 35 U.S.C. § 119(e) of U.S. provisional application No. 60/635,112, filed Nov. 19, 2004, and is a continuation-in-part (CIP) of U.S. application Ser. No. 10/816,340, filed Mar. 31, 2004 (attorney docket No. ASMNUT.2DVCP1; NT-295), which is a CIP of U.S. application Ser. No. 10/252,793, filed May 23, 2002 (attorney docket No. ASMNUT.041DV1; NT-102D), which is a divisional of U.S. application Ser. No. 10/511,278, filed Feb. 23, 2000 (issued as U.S. Pat. No. 6,413,388, issued Jul. 2, 2002). This Application also claims priority to U.S. provisional application No. 60/462,919, filed Apr. 4, 2003 by way of application Ser. No. 10/816,340.
FIELDThe present invention generally relates to semiconductor integrated circuit technology and, more particularly, to a device for electrotreating or electrochemically processing a workpiece.
BACKGROUNDConventional semiconductor devices such as integrated circuits (IC) generally comprise a semiconductor substrate, usually a silicon substrate, and a plurality of conductive material layers separated by insulating material layers. Conductive material layers, or interconnects, form the wiring network of the integrated circuit. Each conductor in the wiring network is isolated from the neighboring conductors by the insulating layers, also known as interlayer or interlevel dielectrics (ILDs). One dielectric material that is commonly used in silicon integrated circuits is silicon dioxide, although there is now a trend to replace at least some of the standard dense silicon dioxide material in IC structures with low-k dielectric materials such as organic, inorganic, spin-on and CVD candidates.
Conventionally, IC interconnects are formed by filling a conductor such as copper in features or cavities etched into the dielectric interlayers by a metallization process. Copper is becoming the preferred conductor for interconnect applications because of its low electrical resistance and good electromigration property. The preferred method of copper metallization is electroplating. In an integrated circuit, multiple levels of interconnect networks laterally extend with respect to the substrate surface. Interconnects formed in sequential layers can be electrically connected using features such as vias or contacts. In a typical interconnect fabrication process, first an insulating layer is formed on the semiconductor substrate, and patterning and etching processes are then performed to form features or cavities such as trenches, vias, and pads etc., in the insulating layer. Then copper is electroplated to fill all the features. In such electroplating processes, the wafer is placed on a wafer carrier and a cathodic (−) voltage with respect to an electrode is applied to the wafer surface while a deposition electrolyte wets both the wafer surface and the electrode.
Once the plating is over, a material removal step such as a chemical mechanical polishing (CMP) process step is conducted to remove the excess copper layer, which is also called copper overburden, from the top surfaces (also called the field region) of the workpiece, leaving copper only in the features. An additional material removal step is then employed to remove the other conductive layers such as the barrier/glue layers that are on the field region. Fabrication in this manner results in copper deposits within features that are physically as well as electrically isolated from each other. Another important material removal technique, especially for wafers with low-k dielectrics, is the electrochemical polishing (electropolishing) or electrochemical etching process. In electropolishing, an anodic voltage is applied to the wafer surface with respect to a cathodic electrode in an electropolishing electrolyte. Excess conductor, such as overburden copper is removed without physically touching and stressing the interconnect structure. It is possible to perform electropolishing on a wafer surface while physically touching the surface with a pad material. Such techniques are called electrochemical mechanical polishing or etching methods.
One technique used for planar deposition and removal of materials is collectively referred to as Electrochemical Mechanical Processing (ECMPR), which term is used to include Electrochemical Mechanical Deposition (ECMD) processes as well as Electrochemical Mechanical Polishing (ECMP) (also known as Electrochemical Mechanical Etching (ECME)). It should be noted that in general both ECMD and ECMP processes are referred to as electrochemical mechanical processing (ECMPR) since both involve electrochemical processes and physical touching of, or mechanical action on, the workpiece surface. All electrochemical techniques for material deposition and removal may be referred to as “electrotreatment.”
In one aspect of an ECMPR method, a workpiece-surface-influencing-device (WSID) such as a mask, pad or a sweeper is used during at least a portion of the electrotreatment process when there is physical contact or close proximity and relative motion between the workpiece surface and the WSID. Descriptions of various planar deposition and planar etching methods and apparatus can be found in the following patents and pending applications, all commonly owned by the assignee of the present invention. U.S. Pat. No. 6,176,992, issued Jan. 23, 2001, entitled “Method and Apparatus for Electrochemical Mechanical Deposition.” U.S. Pat. No. 6,534,116, issued Mar. 18, 2003, entitled “Plating Method and Apparatus that Creates a Differential Between Additive Disposed on a Top Surface and a Cavity Surface of a Workpiece Using an External Influence,” filed on Dec. 18, 2000 and U.S. Pat. No. 6,951,551, issued Jul. 26, 2005, entitled “Plating Method and Apparatus for Controlling Deposition on Predetermined Portions of a Workpiece”. These methods can deposit metals in and over cavity sections on a workpiece in a planar manner. The disclosures of these patents are incorporated herein by reference. They also have the capability of yielding novel structures with excess amount of metals over the features irrespective of their size, if desired.
In ECMD methods, the surface of the workpiece is wetted by the electrolyte and is rendered cathodic with respect to an electrode, which is also wetted by the electrolyte. During ECMD, the wafer surface is pushed against or in close proximity to the surface of the WSID or vice versa when relative motion between the surface of the workpiece and the WSID results in sweeping of the workpiece surface. Planar deposition is achieved due to this sweeping action as described in the above-cited patent applications.
In ECMP methods, the surface of the workpiece is wetted by the electropolishing electrolyte or etching solution, but the polarity of the applied voltage is reversed, thus rendering the workpiece surface more anodic compared to the electrode. A WSID touches the surface during removal of the layer from the workpiece surface.
Very thin planar films can be obtained by first depositing a planar layer using an ECMD technique and then applying an ECMP technique on the planar film in the same electrolyte by reversing the applied voltage. Alternatively, the ECMP step can be carried out in a separate machine and a different etching electrolyte or electropolishing solution. This way the thickness of the deposit may be reduced in a planar manner. In fact, an ECMP technique may be continued until all the metal on the field regions is removed. It should be noted that a WSID may or may not be used during the electroetching process since substantially planar etching can be achieved either way as long as the starting layer surface is planar.
It should be noted that the electrode 26 is only schematically shown in
U.S. application Ser. No. 09/960,236 filed on Sep. 20, 2001, entitled “Mask Plate Design,” assigned to the assignee of the present invention, discloses various WSID embodiments. Also, U.S. application Ser. No. 10/155,828 filed on May 23, 2002, entitled Low Force Electrochemical Mechanical Deposition Method and Apparatus, also assigned to the same assignee of the present invention teaches means of applying force to the wafer surface by a WSID for ECMPR.
To this end, there is still a need for further development of high-throughput electrochemical processes and apparatus that can yield deposits with less defect and high yield, and methods and apparatus that provide more uniform material removal from workpiece surfaces.
SUMMARY OF THE INVENTIONIn accordance with one aspect of the invention, a method is provided for immersing a surface of a wafer in a solution for processing the surface. The method included flowing the solution through openings of a rigid plate having a protruding region to form a raised solution surface over the protruding region. A selected portion of the wafer surface is contacted with the raised solution surface. The wafer surface is immersed fully into the solution.
In accordance with another aspect of the invention, a system is provided for eliminating bubble entrapment under a surface of a wafer when the surface is immersed into a process solution to process the surface of a wafer. The system includes a rigid plate, having a protruded region and fluid openings. The plate is configured such that when the solution flows through the rigid plate, a raised solution surface forms over the protruded region. The system also includes a moving mechanism configured to move the wafer such that, as the wafer is moved towards the solution, a selected portion of the surface of the wafer contacts the raised solution surface before immersing the surface of the wafer fully into the solution.
In accordance with another aspect of the invention, a method of processing a conductive surface of a wafer using a process solution is provided. The method includes flowing the solution through openings of a plate having a protruding region to form a raised solution surface over the protruding region. A selected portion of the conductive surface is contacted with the raised solution surface. The conductive surface is fully immersed into the solution and the conductive surface is processed.
In accordance with another aspect of the invention, a system is provided for electroprocessing a conductive surface of a wafer using a process solution. The system includes an electrode configured to be placed in the process solution. A rigid plate, having a protruded region and fluid openings, is configured to be immersed in the solution and positioned between the electrode and the conductive surface. The plate is configured such that as the solution flows through the rigid plate, a raised solution surface forms over the protruded region. A moving mechanism is configured to move the wafer such that as the wafer moves towards the solution, a selected portion of the conductive surface contacts the raised solution surface before immersing the surface fully into the solution.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiments will now be described using the example of fabricating interconnects for integrated circuit applications. It should, however, be recognized that present invention can be used to operate on any workpiece with various electroplated materials such as Au, Ag, Ni, Pt, Pd, Fe, Sn, Cr, Pb, Zn, Co and their alloys with each other or other materials, for many different applications such as packaging, flat panel displays, magnetic heads and such. In the examples provided below, the example material that is electroplated or electropolished will be copper, but it will be understood that other materials can instead be used.
In electrochemical mechanical processing (ECMPR) such as electrochemical mechanical deposition (ECMD) and electrochemical mechanical polishing (ECMP) or etching (ECME), since the mechanical action on wafer surface assists planarization of the surface of the wafer, uniformity of this mechanical action is important to obtain uniform process results, such as a uniformly planarized wafer surface.
During ECMD and ECMP processes, wafers are typically rotated and may additionally be moved laterally. As can be appreciated, on a rotating wafer surface the linear velocity due to rotation is zero right at the center of the wafer and it increases linearly towards the edge of the wafer in proportion to the distance to the center. The linear velocity is highest right at the edge of the wafer and it is given by the relationship: V=(2πrR/60) cm/second, where “r” is the radius of the wafer in centimeters and “R” is the rotation in revolution per minute (rpm). As can be seen from this relationship, velocity “V” increases as the radius of the wafer “r” increases. Mechanical action delivered by a WSID (see
In another method, if the relative velocity between the WSID and the wafer surface is not constant, the force applied by the WSID is adjusted such that a higher force is applied onto certain surface regions, such as the central region of the wafer, where the relative velocity is low. As previously mentioned, in exemplary ECMD or ECMP processes, the wafer is rotated and also translated over a stationary WSID surface. If the velocity of the lateral motion is lower than the motion near the edge of the wafer due to rotation, velocity near the center of the wafer would be lower than at the edge. Therefore, additional force should be applied near the center of the wafer to improve process results.
There are various approaches that may be used to apply additional force on the wafer surface near its center. One such approach involves shaping of the wafer surface. When such shaped wafer surface is pushed against a pad structure, its center gets the highest force. An example of shaping wafer 100 while it is processed may be described in connection with
The WSID 204 may have a compressible layer 206 having a top surface 208. The top surface 208 may be made of a flexible material and may be abrasive or it may contain a polishing pad material. The top surface 208 is brought to physical contact with the front surface 101 of the wafer during the ECMD or ECMP processes. The WSID 204 comprises openings 210, such as holes with various geometrical shapes or slits with varying width, or may be made of a porous material that allows a process solution (not shown) to flow through the WSID and wet the surface of the wafer. The WSID 204 is supported by a support plate 212, which has a top surface 213 and a back surface 214. The WSID 204 is placed on the top surface 213 of the support plate 212. The support plate 212 is fixed on sidewalls 25 of a process chamber, which is not shown in
Referring to
As shown in
As shown in
Referring back to
One exemplary method of controlling force involves controlling the flow rate of the process solution. Depending on the porosity of the filter 218, as the flow rate of the process solution increases, the pressure under the filter 218 increases. Since the edges of the support plate 212 are fixed, the support plate 212 bows up under increased process solution flow as shown in
Another way of controlling the bowing and thus the force on the central region of the wafer involves controlling the porosity of the filter 218. At a given solution flow rate, filters with smaller pore size would give more bowing and thus more additional force would be applied to the central section of the wafer. As can be seen in the force-distance graph in
The force may also be controlled by shaping the WSID itself or by constructing the support plate to make it more or less compliant along the diameter of the wafer. Other stiffeners or flexural members can be added to WSID to produce a force curve of any desired shape for planarization, especially at the center region.
In this respect,
By varying the thickness of the support plate, the applied pressure and the size of the high-pressure interface may be changed.
The above-noted methods and structures may also be used for eliminating bubbles that may be trapped between the wafer surface and the process solution during electroplating and electropolishing processes. As shown in
As will be described more fully below, alternatively, from the foregoing bowed WSID surface principle, the surface of the support plate or solution supply plate through which the solution flows towards the workpiece surface can itself be given a profile to assist removal of bubbles in electrochemical processes without having a compressible layer or a pad on it, particularly in a non-contact ECMPR. Since in a non-contact ECMPR there is no need to touch the wafer surface with a WSID, there is no need for a pad, and the WSID may be formed as a rigid structure. In that respect, non-contact ECMPR may actually be called ECPR (electrochemical processing) since there is no mechanical action applied to the wafer surface during process.
The support plate may be a rigid plate having openings and a surface profile, which will be referred to as a plate hereinbelow. In this embodiment, a surface of the plate includes a protruding profile or region, which may be any curved or protruding surface or surface portion, including but not limited to, spherical, cylindrical, conical, pyramidal, rectangular, trapezoidal, or triangular surfaces. During the process, the plate is placed in a process solution and the solution is flowed through openings of the plate. The solution flowing through the protruding region of the plate conforms to the top surface profile and forms a raised solution surface over the protruding region. When a workpiece is lowered towards the process solution, the workpiece surface first touches the raised surface of the solution which corresponds to the location of the protruding region of the plate. If so configured, the central region of the workpiece may be wetted first by the process solution, and then the solution moves towards the periphery of the wafer, sweeping any bubbles out with it. This prevents bubble entrapment under the workpiece before the rest of the surface of the workpiece is wetted by the solution. This way, since the bubbles are eliminated or swept away from the center, and no bubble entrapment occurs.
The protruding region may be placed about the center of the plate surface or may extend along the length or width of the plate surface. As the workpiece surface moves towards the surface of the plate, a gap filled with solution is formed between the workpiece surface and the surface of the plate. Peripheral ends of the gap are unblocked so that the solution is moved laterally to the open ends of the gap as the pressure from the moving workpiece surface pushes the solution while the workpiece surface is getting closer to the surface of the plate. At the protruding region, the surface profile of the plate locally narrows the gap and applies more pressure to the adjacent solution. For example if a protrusion on the plate is placed across from the center of the workpiece surface, the gap between the two surfaces, i.e. the wafer surface and the plate surface, will be narrower at this location. Solution between the surface about the center of the wafer and the protruding region on the plate surface will be squeezed more than the solution in the rest of the gap, which will cause solution to flow outwardly into this low pressure zone. This outwardly flow also sweeps away any remaining or forming bubbles with the solution.
During the process, the front surface 510 of the wafer to be processed is placed across from a first surface 518 of the plate 500. Fluid openings 520 between the first surface 518 and the second surface 522 of the plate 500 allow the process solution 505 to flow between the front surface 510 of the wafer 503 and the electrode 506. The openings 520 may be shaped as holes or slits and may have any geometrical shape. The first surface 518 includes a protruding region 524 or a protruding surface or a bump to eliminate bubble entrapment under the front surface 510. The protruding region 524 may be a portion of the first surface or may be the entire first surface. The second surface 522 may be flat as shown in
As shown in
Although various preferred embodiments and the best mode of the present invention have been described in detail above, those skilled in the art will readily appreciate that many modifications of the exemplary embodiment are possible without materially departing from the novel teachings and advantages of this invention.
Claims
1. A method of immersing a surface of a wafer in a solution for processing the surface, comprising:
- flowing the solution through openings of a rigid plate having a protruding region to form a raised solution surface over the protruding region;
- contacting a selected portion of the wafer surface with the raised solution surface; and
- immersing the wafer surface fully into the solution.
2. The method of claim 1, further comprising rotating the wafer before contacting.
3. The method of claim 1, wherein the selected portion of the surface is a center of the surface of the wafer.
4. The method of claim 1, further comprising placing the rigid plate into the solution.
5. The method of claim 1, further comprising processing the surface of the wafer.
6. A system for eliminating bubble entrapment under a surface of a wafer when the surface is immersed into a process solution to process the surface of the wafer, comprising:
- a rigid plate, having a protruded region and fluid openings, wherein the plate is configured such that as the solution flows through the rigid plate, a raised solution surface forms over the protruded region; and
- a moving mechanism configured to move the wafer, wherein as the wafer is moved towards the solution, a selected portion of the surface of the wafer contacts the raised solution surface before immersing the surface fully into the solution.
7. The system of claim 6, wherein the protruded region forms a portion of a top surface of the rigid plate.
8. The system of claim 6, wherein the protruded region forms a top surface of the rigid plate.
9. The system of claim 6, further including an electrode placed in the process solution.
10. The system of claim 9, further including a power supply connected to the electrode and the surface of the wafer to apply a potential difference between the surface of the wafer and the electrode to process the surface.
11. The system of claim 9, wherein the rigid plate is placed between the electrode and the surface of the wafer.
12. The system of claim 6, wherein the rigid plate has a rectangular shape.
13. The system of claim 6, wherein the selected portion of the surface is a center of the surface of the wafer.
14. A method of processing a conductive surface of a wafer using a process solution, comprising:
- flowing the solution through openings of a plate having a protruding region to form a raised solution surface over the protruding region;
- contacting a selected portion of the conductive surface with the raised solution surface;
- immersing the conductive surface fully into the solution; and
- processing the conductive surface.
15. The method of claim 14, further comprising applying a potential difference between the conductive surface and an electrode.
16. The method of claim 15, wherein processing is electropolishing.
17. The method of claim 15, wherein processing is electrodeposition.
18. The method of claim 14, further comprising rotating the conductive surface before the step of contacting.
19. The method of claim 14, wherein the selected portion of the conductive surface is a center of the conductive surface of the wafer.
20. The method of claim 14, wherein the plate is rigid.
21. A system for electroprocessing a conductive surface of a wafer using a process solution, comprising:
- an electrode configured to be placed in the process solution;
- a rigid plate, having a protruded region and fluid openings, configured to be immersed in the solution and positioned between the electrode and the conductive surface, wherein the rigid plate is configured such that as the solution flows through the rigid plate, a raised solution surface forms over the protruded region; and
- a moving mechanism configured to move the wafer, wherein as the wafer is moved towards the solution, a selected portion of the conductive surface contacts the raised solution surface before immersing the surface fully into the solution.
22. The system of claim 21, wherein the rigid plate is placed between the electrode and the conductive surface of the wafer.
23. The system of claim 21, wherein the rigid plate has a rectangular shape.
24. The system of claim 21, wherein the selected portion of the conductive surface is s center of the conductive surface of the wafer.
25. The system of claim 21, wherein the protruded region forms a portion of a top surface of the rigid plate.
26. The system of claim 21, wherein the protruded region forms a top surface of the rigid plate.
27. The system of claim 21, further including a power supply connected to the electrode and the surface of the wafer to apply a potential difference between the conductive surface of the wafer and the electrode to process the conductive surface of the wafer.
Type: Application
Filed: Nov 18, 2005
Publication Date: Jun 22, 2006
Inventors: Jeffrey Bogart (Los Gatos, CA), Bulent Basol (Manhattan Beach, CA)
Application Number: 11/283,004
International Classification: C25D 7/12 (20060101);