[0034] The present invention has particularly beneficial utility in the electrochemical plating of copper or other metal onto a semiconductor wafer substrate in the fabrication of semiconductor integrated circuits. However, the invention is more generally applicable to the electrochemical plating of metals including but not limited to copper on substrates in a variety of industrial applications, including but not limited to semiconductor fabrication.
[0035] The present invention is generally directed to a novel electroplating apparatus which enhances uniformity in the thickness of a metal layer deposited on a semiconductor wafer. The apparatus facilitates the electroplating of a metal layer having substantially uniform thickness across the entire wafer surface, particularly between the center and edge regions of the wafer. The apparatus includes a bath container having a reservoir for containing an electrolytic fluid. A cathode and an anode immersed in the electrolytic fluid are connected to an electroplating current source. The wafer is provided in electrical contact with the cathode, in the electrolytic fluid. A shield is provided between the cathode and anode to modify the electrical characteristics of the electrolytic fluid and provide a substantially uniform thickness of the metal electroplated onto the center and edge regions of the wafer.
[0036] The shield may be ring-shaped or plate-shaped and may be electrically non-conductive or electrically-conductive. In one embodiment of the apparatus, the shield is either electrically conductive or non-conductive and alters the electric pathway between the anode and cathode in the electrolytic fluid. This alters the distribution of metal ions in the electrolytic fluid in such a manner that the thickness of a metal layer deposited onto the wafer is substantially the same across the edge region and center region on the wafer.
[0037] In another embodiment of the apparatus, the shield is electrically-conductive and may be connected to a shield current source. A switch may be provided between the shield current source and the shield. When the switch is manipulated to apply a negative charge to the shield, the shield acts as a cathode and reduces metal cations in the electrolytic fluid in the area adjacent to the edge region of the wafer. This reduces the quantity of metal cations in the electrolytic fluid in the area adjacent to the edge region as compared to the area adjacent to the center region of the wafer. Consequently, the electroplating metal deposition rate at the edge region of the wafer is reduced to compensate for the normally lower metal deposition rate at the center region of the wafer. This enhances the overall thickness uniformity of the electroplated metal across the entire surface of the wafer.
[0038] Upon application of a positive charge to the shield by manipulation of the switch, the shield acts as an anode. Accordingly, the concentration of metal cations in the electrolytic fluid in the area adjacent to the edge region of the wafer is increased, to increase the electroplating deposition rate of the metal onto the edge region of the wafer, as needed. By the alternating application of positive and negative charges to the wafer by manipulation of the switch, the thickness of metal electroplated onto the edge region of the wafer can be precisely controlled to provide a layer of electroplated metal having a substantially uniform thickness across the entire surface of the wafer.
[0039] The electroplating apparatus may further include a mechanism to control the relative position of the shield with respect to the wafer in the electrolytic fluid. By movement of the negatively-charged cathode/shield toward the wafer, the deposition rate of the metal onto the edge region of the wafer is reduced correspondingly. By movement of the negatively-charged cathode/shield away from the wafer, the deposition rate of the metal onto the edge region of the wafer is increased. This mechanism can be used in combination with the switch to facilitate precise control of the relative thickness of metal electroplated onto the center and edge regions of the wafer.
[0040] The electroplating apparatus of the present invention may be used with any formulation for the electrolytic fluid, such as copper, aluminum, nickel, chromium, zinc, tin, gold, silver, lead and cadmium electroplating baths. The present invention is also suitable for use with electroplating baths containing mixtures of metals to be plated onto a substrate. It is preferred that the electrolytic fluid be a copper alloy electroplating bath, and more preferably, a copper electroplating bath. Typical copper electroplating bath formulations are well known to those skilled in the art and include, but are not limited to, an electrolyte and one or more sources of copper ions.
[0041] Suitable electrolytes include, but are not limited to, sulfuric acid, acetic acid, fluoroboric acid, methane sulfonic acid, ethane sulfonic acid, trifluormethane sulfonic acid, phenyl sulfonic acid, methyl sulfonic acid, p-toluenesulfonic acid, hydrochloric acid, phosphoric acid and the like. The acids are typically present in the bath in a concentration in the range of from about 1 to about 300 g/L. The acids may further include a source of halide ions such as chloride ions. Suitable sources of copper ions include, but are not limited to, copper sulfate, copper chloride, copper acetate, copper nitrate, copper fluoroborate, copper methane sulfonate, copper phenyl sulfonate and copper p-toluene sulfonate. Such copper ion sources are typically present in a concentration in the range of from about 10 to about 300 g/L of electroplating solution.
[0042] Other electrochemical plating process conditions suitable for implementation of the present invention include a plating rpm of from typically about 0 rpm to about 500 rpm; a plating current of from typically about 0.2 mA/cm2 to about 20 mA/cm2; a plating voltage of typically about 2 volts and a bath temperature of from typically about 10 degrees C. to about 35 degrees C. In cases in which planarity of the electroplated metal through chemical mechanical planarization (CMP) is necessary, a leveling agent may be added to the electroplating bath solution at a concentration of from typically about 5 mmol/L to about 5 mol/L.
[0043] Referring to FIG. 2, an illustrative embodiment of an electroplating apparatus 30 of the present invention is shown. The apparatus 30 may be conventional and includes a standard electroplating cell having an adjustable electroplating current source 32, a bath container 34 having an interior bath reservoir 35, a typically copper anode 36 and a cathode 38. A contact ring 40 holds a semiconductor wafer 42 that is to be electroplated with metal, against the cathode 38.
[0044] The anode 36 and cathode 38 are connected to the current source 32 by means of suitable wiring 33. The bath container 34 holds an electrolytic fluid or electroplating bath solution 44. The apparatus 30 may further include a mechanism (not shown) for rotating the wafer 42 in the electrolytic fluid 44 during the electroplating process, as is known by those skilled in the art.
[0045] A shield 46 is mounted in the bath container 34, beneath the contact ring 40, according to techniques known by those skilled in the art. In a preferred embodiment, the shield 46 is mounted on a positional adjustment arm 60 which is engaged by a positional adjustment motor 58. The positional adjustment motor 58 is operated to adjust the vertical position of the shield 46 in the bath container 34, and thus, the proximity of the shield 46 to the contact ring 24.
[0046] As shown in FIGS. 3 and 4, the shield 46 typically includes a ring-shaped shield body 48 having a central shield opening 50. The shield body 48 may be an electrically-conductive metal or a non-conductive material such as plastic or ceramic, for example. In the case of a non-conductive shield body 48, an electrically-conductive material 51 covers the surfaces of the shield body 48. Preferably, the electrically-conductive material 51 is copper.
[0047] As shown in FIGS. 3 and 4, typical dimensions for the ring-shaped shield 46 include a diameter 64 of typically about 150˜200 mm; a ring width 65 of typically about 3˜5 cm; and a thickness 66 of typically about 30˜50 mm. These dimensions are compatible with an electroplating apparatus 30 which is sized for the processing of 300 mm wafers. However, it is understood that these dimensions may vary depending on the diameter of wafers to be processed in the electroplating apparatus 30.
[0048] An electrical contact 52, such as suitable wiring, for example, is electrically connected to the shield 46. A switch 54 is connected to the electrical contact 52. The switch 54 provides selective electrical connection between a positive terminal 56a and a negative terminal 56b of a shield current source 56. Accordingly, in operation of the apparatus 30 as hereinafter described, a positive charge is selectively applied to the shield 46 by establishing electrical communication between the positive terminal 56a and the shield 46 through the switch 54, as indicated by the phantom lines in FIG. 2. Conversely, a negative charge is selectively applied to the shield 46 by establishing electrical communication between the negative terminal 56b and the shield 46 through the switch 54.
[0049] Referring to FIGS. 5-7, an alternative embodiment of the present invention is shown wherein an electroplating apparatus 70 includes a shield 72 having a plate-shaped shield body 74, as shown in FIGS. 6 and 7. The shield body 74 may be an electrically-conductive metal or a non-conductive material such as plastic or ceramic, for example. In the case of a non-conductive shield body 74, an electrically-conductive material 76 covers the surfaces of the shield body 74. Preferably, the electrically-conductive material 76 is copper.
[0050] Referring again to FIG. 2, in operation of the electroplating apparatus 30, an electrolytic fluid 44 is placed in the bath reservoir 35 of the bath container 34, with the anode 36 immersed in the electrolytic fluid 44. The wafer 42, having a metal seed layer 43 deposited thereon, is attached to the cathode 38, typically using the contact ring 40, and immersed in the electrolytic fluid 44. The electroplating current source 32 is energized to apply a negative voltage to the cathode 38 and a positive voltage to the anode 36.
[0051] At the wafer 42, metal cations such as copper in the electrolyte fluid 44 are reduced to form metal atoms, which are electroplated onto the seed layer 43. However, due to the presence of the contact ring 40, the current density is higher in the area of the electrolyte fluid 44 which is adjacent to the edge region of the wafer 42 than in the area of the electrolyte fluid 44 which is adjacent to the center region of the wafer 42. Consequently, the metal deposition rate is typically higher at the edge region than at the center region of the wafer 42.
[0052] To reduce the electroplating rate at the edge of the wafer 42, the switch 54 is manipulated to establish electrical communication between the shield 46 and the negative terminal 56b of the shield current source 56. This imparts a negative charge to the shield 46, causing the shield to act as a cathode in the electrolytic fluid 44. Accordingly, metal cations adjacent to the shield 46 are reduced, forming metal atoms that are electroplated onto the shield 46. The concentration of metal cations in the electrolyte fluid 44 adjacent to the edge region of the wafer 42 is therefore reduced, thus lowering the electroplating deposition rate of the metal onto the edge region of the wafer 42.
[0053] In the event that it is deemed necessary to increase the electroplating rate at the edge region of the wafer 42, the switch 54 can be manipulated to establish electrical communication between the shield 46 and the positive terminal 56a of the shield current source 56. This imparts a positive charge to the shield 46, causing the shield 46 to act as an anode. Accordingly, metal from the electrically-conductive material 51 (FIG. 4) of the shield 46 is oxidized, causing metal cations to enter the electrolytic fluid 44. This increases the concentration of metal cations at the edge region of the wafer 42, thereby accelerating the electroplating deposition rate at the edge region of the wafer 42.
[0054] The electroplating deposition rate of metal onto the edge region of the wafer 42 can be further controlled by adjusting the proximity of the shield 46 with respect to the wafer 42. Thus, when the switch 54 applies a negative charge to the cathode/shield 46, the electroplating deposition rate at the edge region of the wafer 42 can be decreased, as needed, by moving the shield 46 into closer proximity to the contact ring 40. Conversely, when the switch 54 applies a positive charge to the anode/shield 46, the electroplating deposition rate at the edge region of the wafer 42 can be increased, as needed, by moving the shield 46 into closer proximity to the contact ring 40. Positional adjustment of the shield 46 in the electrolyte fluid 44 is accomplished by actuation of the positional adjustment motor 58 and positional adjustment arm 60.
[0055] Referring next to FIG. 8, in an electroplating apparatus 80 of still another embodiment of the present invention, the electrical contact 52, switch 54 and shield current source 56 of the embodiments of FIGS. 2 and 5 are omitted. The electroplating apparatus 80 includes a shield 82 which is interposed between the anode 36 and the cathode 38. The position of the shield 82 may typically be adjusted in the electrolyte fluid 44 by actuation of a positional adjustment motor 58 and positional adjustment arm 60, as heretofore described with respect to the embodiments of FIGS. 2 and 5.
[0056] The shield 82 may be an electrically non-conductive material such as plastic or ceramic, for example. Alternatively, the shield 82 may be an electrically-conductive material such as copper. Still further in the alternative, the shield 82 may include an electrically non-conductive shield body (not shown) which is covered with an electrically-conductive material, as heretofore described with respect to the embodiment of FIGS. 2 and 5. Furthermore, the shield 82 may have either a ring-shaped configuration or a plate-shaped configuration.
[0057] In operation of the electroplating apparatus 80, the shield 82 changes the distribution of metal cations in the electrolytic fluid 44, between the anode 36 and the wafer 42, in such a manner that the electroplating deposition rate at the edge region of the wafer 42 is slowed down to substantially equal the electroplating deposition rate at the center region of the wafer 42. Consequently, the thickness of a metal layer deposited onto the seed layer 43 on the wafer 42 is substantially uniform between the edge and center regions of the wafer 42. The electro deposition rate at the edge region of the wafer 42 can be increased, as needed, by moving the shield 82 into closer proximity to the wafer 42 by operation of the positional adjustment motor 58.
[0058] While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.
