Damascene metal interconnects using highly directional deposition of barrier and/or seed layers including (III) filling metal

[0002] As semiconductor device geometries continue to scale down below 0.5 um and approach 0.18 um minimum feature size, the metal interconnect lines which carry current between devices on a chip begin to dominate the overall circuit speed. In order to enhance interconnect speed and reliability, the semiconductor industry is moving away from blanket deposition and etch of aluminum-based metalizations, and towards damascene and dual-damascene interconnect structures with copper-based metalizations. One reason for this movement is that copper is a lower resistivity metal than aluminum, which results in a lower RC interconnect delay. Copper has also been shown to have superior electromigration performance compared to aluminum. However, copper is more difficult to process, primarily because it is more difficult to etch and it acts as a deep level trap in silicon-based devices.

[0003] The typical way to process copper interconnects in a semiconductor device is to (i) etch a trench or via into a dielectric material, (ii) deposit the interconnect metalization to fill the trench or via, and then (iii) polish the metal back to remove any metal from the field (i.e., the surface of the semiconductor wafer). The resulting metal-filled trenches or vias form the electrical interconnect. Forming an interconnect structure by filling a trench or via with metal is known as a “damascene” process. If a trench and underlying via are filled simultaneously, it is known as a dual-damascene process.

[0004] The crystallographic texture of metal interconnects can correlate very strongly to electromigration reliability. Aluminum and copper-based metal lines with strong (111) texture show better electromigration performance. Strong texture can be obtained by using, a refractory underlying metal. For example, titanium is often used a barrier/shunt layer under aluminum metalizations because the (0002) texture of the titanium induces a strong (111) texture in the overlaying aluminum-based film. In a similar way, the (0002) texture of tantalum can improve the (111) texture of copper-based metalizations. Copper interconnects with (111) texture thus show a tenfold increase in electromigration reliability as compared to randomly oriented or (100) textured copper lines.

[0005] A refractory metal such as titanium, titanium nitride, tantalum, tantalum nitride, or tungsten nitride is typically deposited prior to the deposition of aluminum or copper-based metalizations in damascene processing. This barrier layer prevents copper diffusion into the surrounding dielectric and improves the quality of the metal/dielectric interface. In order to obtain adequate step coverage in high aspect ratio trenches and vias, several deposition techniques have been developed to give very directional deposition including, for example, the use of Ionized Metal Plasma, high target-to-substrate distance, or Hollow Cathode Magnetron. Typically, these deposition techniques are optimized to give the maximum step coverage on all surfaces inside the damascene structure.

[0006] The (111) texture of aluminum-based and copper-based damascene interconnects, however, degrades with decreasing line width. Narrow lines show a (100) component which can be attributed to (111) oriented grains growing from the side of the damascene trench, such that the (100) grain orientation is parallel to the top surface of the trench. Interconnect reliability is negatively affected by the presence of these non-(111) grains. What is lacking in the art is the use of a highly directional barrier metal deposition technique to enhance the texture of the subsequently deposited metalization from only the bottom of a damascene structure (and on the field or surface of the dielectric).

[0007] In view of the above, an improved damascene metal interconnect, and method for forming the improved damascene metal interconnect, is provided. According to the method of the invention, a damascene structure is first etched into a dielectric material. A first barrier material is then deposited over the damascene structure in a manner to ensure maximized bottom and side wall coverage. A second barrier material is then deposited using a highly directional deposition technique to provide very little side wall coverage. A metalization layer is then deposited over the damascene structure, and a chemical mechanical polish is used to form the interconnect structure. The metalization layer can be either aluminum or copper-based.

[0008] The improved damascene metal interconnect includes a dielectric material, and a damascene structure etched in the dielectric material. A first barrier material is deposited on the damascene structure to ensure maximized bottom and side wall coverage. A second barrier material is applied to the first barrier material using a highly directional deposition technique to provide very little side wall coverage. A metalization layer is then deposited over the damascene structure, which can be polished using a chemical mechanical polish. The metalization layer can comprise either aluminum or copper-based metal.

[0009] The present invention provides improved texture of damascene interconnects, which can be correlated to improved electromigration reliability. In addition, the invention provides improvements to via contact resistance (analogous to graded ARC) with minimum impact on via diameter. These and other features and advantages of the invention will become apparent upon a review of the following detailed description of the presently preferred embodiments of the invention taken in conjunction with the appended drawings.

[0010] FIG. 1 shows a damascene structure etched into a dielectric material.

[0011] FIG. 2 shows a barrier material deposited on the damascene structure shown in FIG. 1, with maximized bottom and side wall coverage.

[0012] FIG. 3 shows a second barrier material deposited on the damascene structure shown in FIG. 2, where FIG. 3(a) shows an overhang on the sides of the damascene structure, and FIG. 3(b) shows the use of a barrel shaped structure.

[0013] FIG. 4 shows aluminum or copper-based metalization deposited on the structure shown in FIG. 3.

[0014] FIG. 5 shows the damascene interconnect structure shown in FIG. 4 after chemical mechanical polish has been applied.

[0015] FIG. 6 shows an alternative damascene interconnect structure.

[0016] Referring now to the drawings, where like elements are designated by like reference numerals throughout, a damascene structure 12 etched in a dielectric material 10 is shown in FIG. 1. As those skilled in the art will appreciate, the dielectric material 10 can comprise silicon dioxide or any other suitable materials that insulate metal lines from each other. A barrier material layer 14 is deposited in a manner generally known in the art, as shown in FIG. 2, to provide maximized bottom 16 and side wall 18 coverage. This barrier material 14 is preferably chosen to have good diffusion barrier properties, but poor texture enhancement properties. Examples of such barrier materials 14 may include titanium nitride (TiN), tantalum nitride (TaN), and tungsten nitride (WN).

[0017] As shown in FIG. 3, a second barrier material 20 is then deposited using a highly directional deposition technique. By using the highly directional deposition technique, very little coverage is achieved along the side walls 18 of the damascene structure 12. The lack of side wall 18 coverage can further be enhanced by varying certain process conditions such as power, pressure, etc. Results of such variations can yield an overhang 24 condition over the side walls 18 of the damascene structure 12 (see FIG. 3(a)), or an overall ‘barrel shaped’ 26 appearance to the damascene structure 12 (see FIG. 3(b)).

[0018] An aluminum or copper-based metalization 28 is deposited into the damascene structure 12 to provide the electrical connection necessary to the structure. Metalization can be deposited by a PVD, CVD, electroplating, or electroless plating process, or a combination of these techniques. The deposited metalization layer 28 is shown in FIG. 4. In addition, some of these techniques can be used to achieve enhanced fill from the bottom 16 of the damascene structure 12, thereby increasing the effect of the (111) texture from the bottom 16 of the structure.

[0019] Chemical mechanical polish (CMP) is then used to etch excess metalization 28 in a manner generally known in the art, as shown in FIG. 5. A passivation layer (not shown) can also be applied with the next level of dielectric material (not shown). The (111) texture of the resulting damascene structure can further be enhanced by annealing techniques. An alternative, equivalent structure is shown in FIG. 6. This alternate structure can be formed by depositing the directional, texture-forming metal 20 first, and then depositing the barrier metal 14 within the damascene structure 12. The remaining steps described above would not be altered.

[0020] As those skilled in the art will appreciate, several further extensions or modifications to the damascene structure 12 described above are also contemplated. Two examples include:

[0021] 1. The copper metalization 28 (see FIG. 4) can alternatively be deposited using a PVD copper seed (not shown) followed by copper electroplating. Preferably, the PVD copper seed is highly directional, such that there is very little side wall coverage. As a result, the copper seed can be used to enhance the texture of the interconnect line in one of two ways. If the barrier metal 14 on the side wall 18 does not itself act as a seed for copper plating, but does conduct current to the bottom 16 of the via, the electroplated copper can be grown primarily from the bottom 16 of the damascene structure 12 with (111) oriented texture. The barrier metal 14 thus provides a good interface with the copper (after annealing for example) to maintain good reliability. Alternatively, if the barrier metal 14 on the side wall 18 does act as a suitable seed for copper plating, the electroplated copper will be grown from both the bottom 16 of the damascene structure 12 with (111) oriented texture, as well as from the side walls 18 of the damascene structure 12 typically with random texture. After annealing, the preferred (111) texture in the damascene structure 12 is produced.

[0022] 2. In shallow damascene structures, the copper metalization can be deposited by PVD techniques only. If this is done in a highly directional manner, the result can yield growth primarily from the bottom 16 of the damascene structure 12. This further provides strong (111) texture induced by the underlying barrier metal 14.

[0023] It is to be understood that a wide range of changes and modifications to the embodiments described above will be apparent to those skilled in the art and are contemplated. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of the invention.