Patent Application
20070184652
The present invention is directed, in general, to a method for preparing a metal feature and, more specifically, to a method for preparing a metal feature surface prior to electroless metal deposition.
The continual demand for enhanced integrated circuit performance has resulted in, among other things, a dramatic reduction of semiconductor device geometries, and continual efforts to optimize the performance of every substructure within any semiconductor device. A number of improvements and innovations in fabrication processes, material composition, and layout of the active circuit levels of a semiconductor device have resulted in very high-density circuit designs. Increasingly dense circuit design has not only improved a number of performance characteristics, it has also increased the importance of, and attention to, semiconductor material properties and behaviors.
The increased packing density of the integrated circuit generates numerous challenges to the semiconductor manufacturing process. Every device should be smaller without damaging the operating characteristics thereof. High packing density, low heat generation, and low power consumption, with good reliability and long operation life must be maintained without any functional device degradation. Increased packing density of integrated circuits is usually accompanied by smaller feature size.
As integrated circuits become denser, the widths of interconnect layers that connect transistors and other semiconductor devices of the integrated circuit are reduced. As the widths of interconnect layers and semiconductor devices decrease, their resistance increases. Accordingly, semiconductor manufacturers seek to create smaller and faster devices by using, for example, a copper interconnect instead of a traditional aluminum interconnect. Unfortunately, copper is very difficult to etch in most semiconductor process flows. Therefore, damascene processes have been proposed and implemented to form copper interconnects.
Damascene methods usually involve forming a trench and/or an opening in a dielectric layer that lies beneath and on either side of the copper-containing structures. Once the trenches or openings are formed, a blanket layer of the copper-containing material is formed over the entire device. Electrochemical deposition (ECD) is typically the only practical method to form a blanket layer of copper. The thickness of such a layer must be at least as thick as the deepest trench or opening. After the trenches or openings are filled with the copper-containing material, the copper-containing material over them is removed, e.g., by chemical-mechanical polishing (CMP), so as to leave the copper-containing material in the trenches and openings (e.g., forming an interconnect) but not over the dielectric or over the uppermost portion of the trench or opening.
After forming the copper interconnect, a capping layer may be formed thereover. The capping layer is designed to act as a diffusion barrier between the copper in the interconnect and other features located thereby, as well as an etch stop layer for subsequent interconnects. Electroless cobalt plating may be used to selectively deposit a cobalt alloy capping layer on top of the copper interconnect after CMP. This process is catalyzed by the copper interconnect surface, which allows the cobalt alloy capping layer to selectively deposit on the copper interconnect (e.g., it does not deposit on the surrounding dielectric).
The electroless cobalt plating, however, currently has certain drawbacks. One such drawback is the lack of coverage of the copper interconnect that results after the electroless cobalt plating. This lack of coverage may, and often will, negatively affect the electrical performance of the interconnect. Other problems may also result.
Accordingly, what is needed in the art is a method for manufacturing an interconnect that does not experience the aforementioned problems of the prior art.
To address the above-discussed deficiencies of the prior art, the present invention provides a method for manufacturing an interconnect and an integrated circuit. The method for manufacturing the interconnect, in one embodiment, includes forming a first metal feature over or within a substrate, subjecting the first metal feature to a hydrogen containing plasma, the hydrogen containing plasma configured to remove organic residue from an exposed surface of the first metal feature, and electroless depositing a second metal feature on the first metal feature having been subjected to the hydrogen containing plasma. The method for manufacturing the integrated circuit, in addition to the formation of the interconnect, includes forming one or more transistors over a substrate, the interconnect configured to connect the one or more transistors and form an operational integrated circuit.
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
The present invention is based, at least in part, on the acknowledgement that organic residue on an upper surface of a metal feature may inhibit the electroless metal deposition of a second metal feature thereon. Having made this acknowledgement, the present invention further acknowledges that conventional wet cleans are ineffective at removing the organic residue without extreme damage to the metal feature. Based upon the aforementioned recognitions, as well as substantial experimentation, the present invention recognizes that a hydrogen containing plasma could be used to remove a substantial portion, if not all, of the organic residue from the metal feature prior to the electroless metal deposition of the second metal feature. The present invention further recognizes that the hydrogen containing plasma can be conducted without severe damage to the metal feature.
Turning now to
Conventionally formed within the opening 115 in the embodiment shown are a barrier layer 120 and seed layer 130. In the illustrative embodiment shown, the barrier layer 120 and seed layer 130 are also formed over an upper surface of the dielectric layer 110. As those skilled in the art appreciate, the barrier layer 120 is configured to substantially reduce, if not prevent, a metal located within the opening 115 in the dielectric layer 110 from diffusing into nearby structures. Similarly, as those skilled in the art appreciate, the seed layer 130 is configured to provide a surface upon which a subsequent metal layer can easily be deposited.
The materials chosen for the barrier layer 120 and seed layer 130 are generally dependent on the particular material being used for the first metal layer 210 (
Turning now to
In the illustrative embodiment shown in
Turning to
It has been observed that the conventional process used to polish the first metal layer 210, seed layer 130 and barrier layer 120 often includes a corrosion inhibitor additive therein to prevent corrosion of the first metal layer 210 during the polishing thereof. The present invention has recognized that this corrosion inhibitor (e.g., in one instance Benzotriazole (BTA)) often remains on the upper surface of the first metal feature 310 as organic residue 320 after completing the polishing of the first metal layer 210. As mentioned above, the organic residue 320 on the first metal feature 310 inhibits the electroless metal deposition of a second metal feature 510 (
Turning now to
The hydrogen containing plasma 410 illustrated in
Similarly, the hydrogen containing plasma 410 may be generated with a variety of different conditions. For example, the hydrogen containing plasma 410 might use an RF power ranging from about 50 watts to about 5000 watts, a pressure ranging from about 50 mTorr to about 3000 mTorr, and a temperature ranging from about 25° C. to about 350° C., among others. Additionally, the hydrogen containing plasma 410 may use hydrogen gas, ammonia, or another hydrogen source to provide the hydrogen thereto. In the instance wherein hydrogen gas is used, the gas flow of hydrogen might range from about 2 sccm to about 3000 sccm. In the instance wherein ammonia gas is used as the hydrogen source, the gas flow of ammonia might range from about 2 sccm to about 3000 sccm. Other gases, such as argon, helium or nitrogen, could also be included with the hydrogen source. While many different ranges have been given for the hydrogen containing plasma, the present invention should not be limited to any specific ranges.
Turning now to
Preferably, the second metal feature 510 includes cobalt or a cobalt alloy. For example, useful cobalt alloys include cobalt-tungsten alloys, cobalt-phosphorus alloys, cobalt-tin alloys, cobalt-boron alloys, and ternary alloys, such as cobalt-tungsten-phosphorus and cobalt-tungsten-boron. The second metal feature 510 may also include, however, other metals, metal alloys and dopants, such as nickel, tin, titanium, tantalum, tungsten, molybdenum, platinum, iron, niobium, palladium, nickel cobalt alloys, doped cobalt, doped nickel alloys, nickel iron alloys, boron, phosphorous, and combinations thereof. The second metal feature 510 may be deposited to have a thickness of about 5000 nm or less, such as between about 50 nm and about 2000 nm. However, other thicknesses could be used.
Cobalt alloys, such as cobalt-tungsten, may be deposited by adding tungstic acid or tungstate salts, such as sodium tungstate, ammonium tungstate, and combinations thereof. Phosphorus for the cobalt-tungsten-phosphorus deposition may be obtained by using phosphorus-containing reducing agents, such as hypophosphite. Cobalt alloys, such as cobalt-tin, may be deposited by adding stannate salts including stannic sulfate, stannic chloride, and combinations thereof. The metals salts may be in the electroless solution at a concentration between about 0.5 g/L and about 30 g/L, among others.
In one aspect, the second metal feature 510 is deposited from a metallic electroless solution containing at least one metal salt and at least one reducing agent. Suitable metal salts include chlorides, sulfates, sulfamates, or combinations thereof. One example of a metal salt is cobalt chloride. The metal salt may be in the electroless solution at a concentration between about 0.5 g/L and about 30 g/L.
Suitable reducing agents include sodium hypophosphite, hydrazine, formaldehyde, and combinations thereof. The reducing agents may also include borane-containing reducing agents, such as dimethylamine borane and sodium borohydride. The reducing agents may, without limitation, have a concentration between about 1 g/L and about 30 g/L of the electroless solution.
The electroless solution may further include between about 0.01 g/L and about 50 g/L of one or more additives to improve deposition of the metal. Additives may include surfactants, complexing agents (carboxylic acids, such as sodium citrate and sodium succinate), pH adjusting agents (sodium hydroxide, potassium hydroxide), stabilizers (thiourea, glycolic acid), and combinations thereof.
In general, the metallic electroless solution may be applied to the first metal feature 310 surface at a rate between about 50 ml/min and about 2,000 ml/min, such as between about 700 ml/min and about 900 ml/min. The metallic electroless solution may be applied for about 30 seconds to about 180 seconds at a temperature between about 60° C. and about 90° C., among others.
In one aspect, a cobalt electroless composition for forming the second metal feature 510 may include about 20 g/L of cobalt sulfate, about 50 g/L of sodium citrate, about 20 g/L of sodium hypophosphite, and a sufficient amount of potassium hydroxide to provide a pH of between about 9 and about 11. This electroless composition may be applied to the substrate surface for about 120 seconds at a flow rate of about 750 ml/min and at a temperature of about 80° C. In another aspect, a cobalt-tungsten layer may be deposited by the addition of about 10 g/L of sodium tungstate.
It should be noted that the subjecting of the first metal feature 310 to the hydrogen containing plasma 410 and the formation of the second metal feature 510 might be performed in the same processing tool. For instance, a clustering tool could be used wherein the subjecting of the first metal feature 310 to the hydrogen containing plasma 410 occurs in a chamber of the clustering tool, and the formation of the second metal feature 510 occurs in a different chamber of the same clustering tool. Alternatively, however, the subjecting of the first metal feature 310 to the hydrogen containing plasma 410 and the formation of the second metal feature 510 may be performed in completely separate processing tools.
Referring finally to
Although the present invention has been described in detail, those skilled in the art should understand that they could make various changes or substitutions herein without departing from the spirit and scope of the invention in its broadest form.
