Electrolytic Cell with Electrically Neutral and Conductive Sieve

Abstract

An electrochemical deposition fountain reactor for processing spinning semiconductor wafers can include a perforated ionic membrane near the wafer surface through which electrolyte flows. This allows high velocity electrolyte jets to impinge the wafer surface at low bulk flow rates, which reduces the boundary layer at the wafer surface and allows for better replenishment of ions at the wafer surface.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No. 18/504,648, filed Nov. 8, 2023, the disclosure of which is hereby incorporated in its entirety by reference herein.

TECHNICAL FIELD

This disclosure relates to electrochemical deposition manufacturing equipment.

BACKGROUND

Electrochemical deposition is a process used to deposit various materials onto a substrate, such as silicon wafers. This technique is commonly employed in the semiconductor industry to create thin films, coatings, or patterns on silicon wafers.

Before deposition, the silicon wafer surface may need to be cleaned and prepared to ensure good adhesion of deposited material. This typically involves cleaning steps to remove any contaminants or oxides from the silicon's surface.

An electrochemical cell is set up with the silicon wafer serving as the cathode (negatively charged electrode). The material to be deposited, often a metal or alloy, is placed in the electrolyte solution. This solution contains ions of the desired material. A potential difference is applied between the silicon wafer (cathode) and an anode (usually made of the same material as the deposition target). As the electric current passes through the electrolyte, metal ions in the solution are reduced at the silicon wafer's surface. This reduction process causes the metal ions to bond with the silicon substrate, forming a plated metal layer. The deposition process can be controlled by adjusting parameters such as current density, deposition time, and bath composition to achieve the desired film thickness.

After the deposition, additional processes may be performed, such as annealing, to improve the quality and adhesion of the deposited material. Photolithography and etching processes are often used to pattern the deposited material, creating specific structures on the silicon wafer.

SUMMARY

An electrolytic cell has an electrochemical reactor including a housing defining a chamber and an electrically neutral conductive sieve mounted within the chamber that directs jets of electrolyte toward a workpiece that rotates within the chamber.

An electrochemical deposition apparatus includes a disk-shaped electrically neutral and conductive sieve that can be mounted within an electrochemical reactor in a spaced relationship from a rotating semiconductor wafer associated with the electrochemical reactor, and that defines a plurality of perforations that direct jets of electrolyte toward the rotating semiconductor wafer to disrupt a boundary layer of electrolyte at a surface of the rotating semiconductor wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded assembly view of an electrolytic cell.

FIG. 2 is a perspective view, in cross-section, of the electrolytic cell of FIG. 1.

FIG. 3 is a perspective view, in cross-section, of portions of the electrolytic cell of FIG. 1.

FIG. 4 is a schematic view, in cross-section, of portions of the electrolytic cell of FIG. 1.

FIGS. 5 and 6 are plan views of electrically neutral and conductive sieves.

DETAILED DESCRIPTION

Embodiments are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The figures are not necessarily to scale. Some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art.

Various features illustrated and described with reference to any one of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.

Uniformity of electrochemically deposited plated material is of importance both for performance and waste reduction. Performance is key to enable companies to make their products smaller and more powerful. The need for waste prevention is due to the common use of precious metals.

The two main components that control uniformity are the distribution of the electric field and mass transfer at the wafer surface. The electric field is mainly controlled by the hardware, such as reactor shape. For many applications, mass transfer is dealt with using a combination of hardware and chemical additives that counteract the inclinations of metal ions. Certain processes, such as those that use gold, rely more heavily on hardware developments to control mass transfer due to ion size and limitations of ion concentration in the bath. A focus of this disclosure is on the control of mass transfer.

A second issue is that the overall rate of plating on a wafer is subject to these two components as well. Increasing the electric field can be accomplished by applying a greater charge to the system. Limitations occur, however, in the form of deprived ions at the wafer surface due to mass transfer. By increasing the overall mass transfer (ions available at the wafer surface), faster plating can be achieved.

According to boundary layer physics, the faster a fluid moves across a surface the thinner the boundary layer. Ions must traverse this layer by diffusion, so the thickness of this layer directly affects the rate at which a metal can be plated. If the boundary layer is non-uniform in a way that repeats relative to the wafer surface, non-uniform plating occurs. Ideally the boundary layer is exactly uniform across the entire wafer, but this is difficult to achieve in a dynamic system.

Some existing techniques include a single diffuser that controls both electric field and fluid vectors, motorized louvers within the reactor, localized delivery and return of the electrolyte, or localized fluid jets through an ionically resistive element. In the first instance, the device is simple and static. Coupling the fluid dynamics with the same device that controls the electric field, however, inherently limits the ability to optimize either's effect. There is no intrinsic connection between the manipulation of these two factors that enables co-optimization of both parameters simultaneously.

The second utilizes louvres within the reactor to create non-repeating fluid dynamics. The louvres are moved by an external motor run by software that ensures the movement is random. This is mechanically complicated. Additionally, these louvres are not transparent to the electric field and therefore interfere with it.

The third uses jets at the wafer surface along with return ports around the jet. This system is geared toward square substrates and does not rotate. Instead the substrate shifts in a cartesian coordinate so that every point on the plating surface encounters the jets.

The fourth is a dielectric fixture proximal to the wafer surface with holes therein to direct fluid jets at the wafer surface. It provides the bulk of the electrolyte flow above this fixture across the wafer surface, and obtains similar results in terms of reducing boundary layer. Being ionically resistive however, it faces the issue of not being able to decouple manipulation of the boundary layer from manipulation of the electric field.

A compromise the proposed arrangement obtains is a non-uniform boundary across the wafer, but in a way that is randomized relative to the wafer. The plating surface experiences two main components of fluid flow: impinging flow and lateral flow. The fluid is pumped perpendicularly toward the plating surface with its outlet around the perimeter. This impinging flow creates lateral flow (enhanced by the spinning of the plating surface) which causes repeating fluid vectors across the wafer.

An electrochemical deposition fountain reactor in which semiconductor wafers are processed as spinning disc electrodes is thus proposed. It includes a perforated ionic substrate (e.g., membrane) near the wafer surface through which the electrolyte flows. This allows high velocity electrolyte jets to impinge the wafer surface at low bulk flow rates. These jets reduce the boundary layer at the wafer surface, allowing for better replenishment of ions at the wafer surface and therefore faster, more uniform plating. Being an ionic substrate, it manipulates the flow path but not the electric field. The size and distribution of the perforations are configurable to accommodate various wafer sizes and mask types. A corresponding support is likewise configurable in order to not disrupt the fluid dynamics.

Referring to FIGS. 1, 2, 3, and 4 an electrolytic cell arrangement 10 includes an electrochemical reactor 12, an electrically neutral and conductive sieve 14 (e.g., a perforated ionic membrane), a support 16 (e.g., a grate, struts, rings, etc.), a workpiece 18 (e.g., a semiconductor wafer), and a wafer carrier 20. When assembled, the sieve 14 is disposed between the reactor 12 and support 16, and the support 16 is disposed between the sieve 14 and wafer 18.

The carrier 20 is arranged in typical fashion to rotate relative to the reactor 12, sieve 14, and support 16. This rotation can be achieved using various mechanisms. A common method employs a mechanical arm or spindle that holds and rotates the carrier 20. This can allow for the controlled and precise rotation of the wafer 18 during electrochemical deposition. The specific design of the rotation mechanism can vary depending on the equipment and process used in semiconductor manufacturing.

The reactor 12 defines a ledge 22 on which the sieve 14 and support 16 are mounted, and a cavity 24 to hold electrolyte. The ledge 22 defines, in this example, a plurality of threaded bores 26.

The sieve 14 includes a plurality of perforations 28 configured to permit jets of electrolyte from the cavity 24 to flow therethrough and impinge against the wafer 18 as it rotates, and a plurality of holes 30. When assembled, the bores 26 are in registration with the holes 30.

The support 16, in this example, is a grate in direct areal contact with the sieve 14, constrains movement of the sieve 14, and defines a plurality of holes 32. When assembled, the bores 26 are in registration with the holes 30, 32. Threaded fasteners (not shown) can thus be used to secure the sieve 14 and support 16 to the reactor 12. Other mounting techniques are also contemplated.

Referring to FIGS. 2 and 3, the reactor 12 includes an anode 34 mounted at a bottom of the cavity 24, and further defines a return port 36 in fluid communication with a corresponding tank, an outer bowl 38 arranged to drain electrolyte therein to the tank via the return port 36, a weir 40 arranged to capture and direct electrolyte overflow to the outer bowl 38, and an exhaust ring 42 arranged to capture gas resulting from the deposition process for removal from the reactor 12. The reactor 12 further defines an electrolyte supply port (not shown) underneath the anode 34 in fluid communication with the tank. A pump may be used to move electrolyte through the system.

As the wafer 18 and wafer carrier 20 spin while submerged in the electrolyte, a boundary layer at the wafer surface will form with some thickness. The thickness of this layer will depend on the angular velocity of the wafer 18, among other factors. A thicker boundary layer means slower replenishment of ions at the wafer surface, and therefore slower and/or poorer quality plating. Wafer angular velocity has the inherent effect of adjusting the boundary layer differently based on radius: slower angular velocity in the center resulting in a thicker boundary layer thereon, faster angular velocity at the edge resulting in a thinner boundary layer thereon.

Referring to FIG. 4, electrolyte vertically flows through the cavity 24, bottom to top at low velocity. It is compressed through the perforations 28, increasing velocity toward the wafer surface (jets). This high velocity electrolyte impinges the wafer surface, disrupting the boundary layer and providing a higher replenishment of ions at the wafer surface. In other words, it disrupts the thick boundary layer caused by spinning the wafer 18. Since the perforations 28 are defined by the electrically neutral and conductive sieve 14, the structure that forms the jets is invisible to the electric field.

Testing results indicate that a 5 liter per minute electrolyte flow rate with the sieve 14 yields the same plating rate as a 60 liter per minute electrolyte flow rate without the sieve 14.

As mentioned above, perforations of the sieve 14 can be of different sizes and/or shapes to account for the above described phenomenon. Referring to FIG. 5, an electrically neutral and conductive sieve 44 includes a plurality of perforations 46 of radially increasing size and a plurality of holes 48. Referring to FIG. 6, an electrically neutral and conductive sieve 50 includes a plurality of perforations 52 of slot-like configuration and a plurality of holes 54. Other configurations are also possible.

While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of these disclosed materials.

As previously described, the features of various embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to strength, durability, marketability, appearance, packaging, size, serviceability, weight, manufacturability, case of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.

Claims

1. An electrolytic cell comprising:

an electrochemical reactor including a housing defining a chamber and an electrically neutral and conductive sieve mounted within the chamber and configured to direct jets of electrolyte toward a workpiece that is configured to rotate within the chamber.

2. The electrolytic cell of claim 1, wherein the electrically neutral and conductive sieve is a perforated ionic membrane.

3. The electrolytic cell of claim 2, wherein perforations of the perforated ionic membrane are of different size.

4. The electrolytic cell of claim 2, wherein perforations of the perforated ionic membrane are of different shape.

5. The electrolytic cell of claim 1, wherein the electrically neutral and conductive sieve is arranged parallel to and spaced away from the workpiece.

6. The electrolytic cell of claim 1, wherein the electrically neutral and conductive sieve is disk shaped.

7. The electrolytic cell of claim 1 further comprising a support mounted within the chamber between the electrically neutral and conductive sieve and the workpiece and in direct areal contact with the electrically neutral and conductive sieve.

8. The electrolytic cell of claim 7, wherein the support is a grate.

9. An electrochemical deposition apparatus comprising:

a disk-shaped electrically neutral and conductive sieve configured to be mounted within an electrochemical reactor in a spaced relationship from a rotating semiconductor wafer associated with the electrochemical reactor, and defining a plurality of perforations configured to direct jets of electrolyte toward the rotating semiconductor wafer that disrupt a boundary layer of electrolyte at a surface of the rotating semiconductor wafer.

10. The apparatus of claim 9, wherein the disk-shaped electrically neutral and conductive sieve is a perforated ionic membrane.

11. The apparatus of claim 10, wherein perforations of the perforated ionic membrane are of different size.

12. The apparatus of claim 10, wherein perforations of the perforated ionic membrane are of different shape.

13. The apparatus of claim 9, wherein the disk-shaped electrically neutral and conductive sieve is arranged parallel to and spaced away from the rotating semiconductor wafer.

14. The apparatus of claim 9 further comprising a support configured to be mounted within the electrochemical reactor between the disk-shaped electrically neutral and conductive sieve and the rotating semiconductor wafer and in direct areal contact with the disk-shaped electrically neutral and conductive sieve.

15. The apparatus of claim 14, wherein the support is a grate.