Wafer electroplating apparatus for improving process uniformity

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application claims priority under 35 U.S.C. §119 to Korean Patent Application 2004-115407 filed on Dec. 29, 2004, the entire contents of which is incorporated by reference herein.

BACKGROUND

The invention relates to wafer electroplating apparatuses; more specifically, a wafer electroplating apparatus for enhancing the uniformity of metal film deposition of the wafer electroplating process, and a method thereof. There are numerous electroplating methods used for depositing metal films on wafers; such as chemical vapor deposition, physical vapor deposition and electrochemical reactions. However, electroplating methods using electrochemical reactions are currently more prevalent since these methods produce better quality of metal deposition on the wafers than the other techniques.

FIG. 1 shows a sectional view of a conventional wafer electroplating apparatus. The wafer electroplating apparatus 10 includes an electroplating bath 11 containing a plating solution 14, an anode 13 located inside the bottom portion of the electroplating bath 11, and a ring-shaped cathode 12 on which a wafer W is directly mounted. A power source is directly connected between and applied to anode 13 and the cathode 12. In this conventional electroplating arrangement, the metal (for example, copper) is electrochemically reduced and deposited as a film on to the wafer surface.

FIG. 2A shows the top view of a conventional planar ring type cathode 12. This shape has disadvantages because of probable misalignment of the wafer W supported atop the cathode leading to insufficient contact of the wafer with the cathode; including contamination with possible impurities on the wafer. These instances can lead to both inefficient and insufficient metal film deposition on the wafer.

Similarly, in FIG. 2B, the sites a (area on wafer not in contact with cathode) and β (area on the wafer with less metal film deposit) may occur as a result of the instances stated above.

These problems exist in the prior art which lead to irregularities in metal film deposition on the wafers.

SUMMARY OF THE INVENTION

In an embodiment of the invention, a wafer electroplating apparatus is configured wherein an electrode is in direct contact with both the face and front edges of the wafer.

According to an embodiment of the invention, a wafer electroplating apparatus comprises an electroplating bath, an electroplating solution, an anode located inside the base portion of the electroplating bath, and a cathode, which is installed on top of the electroplating bath, atop of which a wafer is mounted. The cathode further comprises: a first portion electrically connected to an edge of the wafer; and a second portion extending from the first portion and electrically connected to a side of the wafer.

In an embodiment of the invention, the second portion of the cathode structurally matches the side of the wafer.

In an embodiment of the invention, the second portion of the cathode is concave shaped to match the convex edge of the wafer.

In an embodiment of the invention, the cathode further comprises a third portion for aligning the wafer, wherein said third portion extends in a planar direction from the second portion.

In an embodiment of the invention, the third portion of the cathode slants upwards and outwards of the top edge of the electroplating bath.

In another embodiment of the invention, the cathode is ring shaped and electrically connected to the entire edge of the wafer. The cathode is preferably an electroconductive material.

According to still another embodiment of the invention, a wafer electroplating apparatus comprises: an electroplating bath containing an electroplating solution; an anode located inside the base portion of the electroplating bath; and a cathode installed at the top of the electroplating bath, wherein the cathode is in direct contact with a wafer. Preferably, the cathode includes: a plane portion in contact with a side of the wafer; a concave portion extending from the plane portion which structurally matches the convex edge of the wafer; and a slanting portion which extends from the concave portion and inclined upwards and outwards of the top edge of the electroplating bath.

In another embodiment of the invention, the electroplating bath comprises: an inlet through which the electrolyte solution is supplied into the electroplating bath; and an outlet from which the spent electrolyte drains out of the electroplating bath.

In an embodiment of the invention, the cathode is of any shape, but most preferably structurally shaped to be in contact with both the side and edges of the wafer; thus allowing a uniform distribution of an electrical current on the wafer; thereby, allowing equivalent areas of attraction for a metal to deposit. Consequently, a metal film depositing on to the wafer is of uniform thickness.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings show illustrative embodiments of the present invention and, together with the description, serve to explain principles of the present invention. In the drawings:

FIG. 1 is a sectional view showing the structure of a conventional wafer electroplating apparatus;

FIG. 2A and FIG. 2B are top and sectional views illustrating the conventional wafer electroplating apparatus;

FIG. 3 is a sectional view illustrating a wafer electroplating apparatus in accordance with an embodiment of the invention;

FIG. 4 is a sectional view further illustrating the wafer electroplating apparatus in accordance with an embodiment of the invention;

FIG. 5 is a sectional view illustrating the enlargement of a cathode in the wafer electroplating apparatus according to an embodiment of the invention; and,

FIG. 6 is a perspective sectional view illustrating the partial enlargement of the cathode in the wafer electroplating apparatus according to an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention are described below with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be constructed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will fully convey the scope of the invention to those skilled in the art. Like numerals refer to like elements throughout the specification.

FIG. 3 is a sectional view illustrating a wafer electroplating apparatus in accordance with an embodiment of the invention. FIG. 3 shows a wafer electroplating apparatus 100. FIG. 3 shows the principle of electroplating via electrolysis in a wafer electroplating apparatus, where a metal ion is reduced to an elemental metal and deposited as a film on a wafer. The wafer electroplating apparatus 100 comprises an electroplating bath 110, which contains an electroplating solution 140, an electrode 130 located inside the electroplating bath 110, and an electrode 120 on which a wafer W is mounted.

The plating solution 140 contained in the electroplating bath 110 is an electrolytic solution, which consists of an aqueous solution of metallic salts. For example, an aqueous copper sulfate (CuSO₄) solution may be used for electroplating a copper film on to the surface of the wafer W.

In another embodiment of the invention shown in FIG. 4, the electroplating bath 110 may further comprise an inlet 150 for supplying the electrolytic solution and an outlet 160 to drain out the used electrolytic solution.

As shown in FIG. 3, the electrode 130 is located inside the base portion of the electroplating bath 110, and acts as the anode or the positive electrode where electrochemical oxidation occurs. While electrode 120 acts as the cathode or negative electrode, is located at the top of the electroplating bath 110 where reduction occurs.

The anode 130 is preferably a metal or material similar thereto. As illustrated in FIG. 3, the anode 130 is made out of copper. Similarly, the cathode 120 is preferably made of an electroconductive material.

When electrical current is applied, the current is carried by the movement of electrons from the anode 130 to the cathode 120 and in the solution 140 by the movement of ions. The movement of positively charged cations in the solution towards the direction of the cathode 120 is equivalent electrically to the movement of negatively charged electrons in the opposite direction from the anode 130 to the cathode 120. The positively charged ions in the solution 140 migrate to electrode 120, where they are reduced and deposited as elemental metal. Consequently, a metal film is deposited on to the surface of the electrically-charged wafer W, since the wafer is directly mounted on the cathode 120.

Simultaneously, at the electrode 130, with the passage of electrical current, the metal, for example, copper, in the anode 130 is oxidized to copper ions with the release of two electrons for each atom of copper. Ideally, the anode 130 loses mass and the cathode 120 gains an equal mass, as copper is transferred from the anode into solution 140 and from solution 140 to the cathode 120.

The cathode 120, can be of any shape; but is preferably shaped in a ring pattern and is configured to support the circular wafer W while contacting to an outer circle of the wafer W. The direct contact of cathode 120 with wafer W ensures the electrical conduction of the wafer W. The cathode 120 may be formed of any metal; but most preferably a metal containing a stainless steel (SUS). The wafer W is mounted on the cathode 120 where the outer circle face of the front face W1 (see FIG. 5) thereof is laid on the cathode 120; and the front face WI is in direct contact with the cathode 120.

FIG. 5 is a sectional view illustrating the enlargement of a cathode in the wafer electroplating apparatus according to an embodiment of the invention, and FIG. 6 is a perspective sectional view illustrating the partial enlargement of the cathode in the wafer electroplating apparatus according to an embodiment of the invention.

Referring to FIG. 5 and FIG. 6, the cathode 120 is constructed to include a plane portion 120a to contact with the flattened edge of the front face W1 of the wafer W, and concave portion 120b to contact with the convex side face W2 of the wafer W. When electrical power is applied to the electrodes, current flows evenly through both the front face W1, and through the side face W2 of the wafer W. Consequently, the application of current in the side face W2 ensures that the wafer is still electrically charged; even when front face W1 has impurities. Subsequently, the metal film will still be deposited uniformly on the surface of the wafer.

In another embodiment of the invention, the cathode 120 may be installed to have any elastic force distributed uniformly toward the wafer W ; but most preferably, an elastic force, which maintains the aligned position of the wafer W relative to the cathode 120.

Furthermore, in another embodiment of the invention, the cathode 120 comprises a slanted portion 120c inclined upwards and outwards to the top of the electroplating bath 110. The slanted portion 120c enables the wafer W to be properly mounted on and aligned with the cathode 120 for an efficacious electroplating process.

In an embodiment of this invention, the cathode 120 acts as the negative electrode. The cathode 120, further, provides a uniform electrical conduction state of the wafer, since portion 120a is in direct contact with the side face W1 and slanted portion 120b is in direct contact with edge W2. However, the shape of cathode 120can be modified according to the shape of the edge or side face W2 of the wafer W.

The description that follows is the operation of the wafer electroplating apparatus 100 with the aforementioned elements. An illustrative example is shown in FIG. 4, where an aqueous copper sulfate (CuSO₄) solution is the electrolyte 140 used in plating a copper film on the front face W1 of the wafer W.

The wafer W is mounted on the cathode 120 and properly positioned to allow the edge of the front face W1 to be in direct contact with the cathode 120. In this holding position, the side face or edge W2 is also allowed to be in direct contact with cathode 120. Next, the power is applied to the electrodes 120 and 130, consequently rendering the wafer W to be electrically conductive.

In solution, the copper sulfate ionizes into copper ions CU²⁺, sulfate ions So₄²⁻, hydrogen ions H⁺, hydroxyl ions OH⁻and hydronium ions H₃⁺.

Simultaneously, at the positive electrode 130, the oxidation reaction generates electrons e⁻, according the half-reaction:
Cu(s)→Cu2+(aq)+2e−.

Copper ions in the solution migrate to the negative electrode 120, where they are reduced and deposited as elemental copper, according to the half-reaction:
Cu2+(aq)+2e→Cu(s).

Since side face or edge W2, and front face W1 of wafer W are in direct contact with cathode 120 by the plane portion 120a, curved portion 120b and slanted portion 120c, the conduction state with an electrical field is uniformly distributed on wafer W. Hence, this configuration, which is an embodiment of the invention, alleviates irregular coverage during the electroplating process.

Although the present invention has been described in connection with the embodiment of the present invention, and illustrated in the accompanying drawings, it is not limited thereto. It will be apparent to those skilled in the art that various substitutions, modifications and changes may be made thereto, without departing from the scope and spirit of the invention.