Aluminum based conductor for via fill and interconnect

A semiconductor device including a dielectric layer having a opening form therein having a cross-sectional area of less than 1 μm2 and a PVD aluminum base conductor filled in the opening.

FIELD OF THE INVENTION

The present invention relates to semiconductor devices and methods of making the same, and more particularly to semiconductor devices and methods using aluminum for via fill in interconnects.

BACKGROUND OF THE INVENTION

Clevenger et al., U.S. Pat. No. 6,448,173, issued Sep. 10, 2002, discloses a dual damascene process capable of reliably producing aluminum interconnects that exhibit improved electromigration characteristics over aluminum interconnects produced by conventional RIE techniques. The dual damascene process relies on a PVD-Ti/CVD-TiN barrier layer that produces aluminum lines that exhibit significantly reduced saturation resistance levels and/or suppressed electromigration, particularly in lines longer than 100 micrometers.

Bothra, U.S. Pat. No. 6,297,557, issued Oct. 2, 2001, discloses an aluminum filled via hole for use in a semiconductor interconnect structure. The aluminum filled via hole in a semiconductor interconnect structure includes a first patterned metallization layer lying over a first dielectric layer. A second dielectric layer overlying the first patterned metallization layer and the first dielectric layer. An aluminum filled via hole defined through the second dielectric layer and in contact with the first patterned metallization layer. The aluminum filled via hole has an electromigration barrier cap over a top most portion of the aluminum filled via hole that is substantially level with the second dielectric layer. The electromigration barrier cap has a thickness of between about 500 angstroms and about 2500 angstroms. An electromigration barrier layer is deposited over the second dielectric layer and within the recess gap. The electromigration barrier is preferably a titanium tungsten, a tungsten, or tungsten silicide layer deposited using a sputter process or CVD process to a thickness of about 1000 angstroms to about 300 angstroms.

It is heretofore been known to combine CVD aluminum technology with an overlayer of PVD aluminum deposited to fill small geometries.

Heretofore it has also been known to use CVD aluminum plugs to deposit the plug fill and interconnect in the same deposition step. Chemical vapor deposition of aluminum plugs using MOCVD precursors such as dimethyl aluminum hydride has been known to offer a means for forming plugs and interconnects with high quality aluminum films at process temperatures below 200° C.

Heretofore it has also been known to utilize an unsequential deposition of thin CVD aluminum film and PVD Al (Cu). The chemical vapor deposition aluminum is deposited at low temperatures using dimethyl-aluminum hydride.

Chio et al., U.S. Pat. No. 5,629,238, issued May 13, 1997, discloses a method of forming a conductive line using a fluorine doped oxide layer as an insulating layer between conductive lines. The method comprises the steps of: (a) forming a fluorine doped oxide layer on a semiconductor substrate on which a lower structure is formed; (b) etching the oxide layer of the region where a conductive line is to be formed, followed by forming a trench; (c) forming an insulating layer over the overall surface of the resultant substrate; (d) depositing conductive material on the resulting substrate; and (e) etching back the conductive material so that the conductive material is left on the trench only, thereby forming a conductive line. The conductive line is formed of aluminum-containing material and the insulating layer is formed of silicon dioxide. The insulating layer is interposed between the fluorine doped oxide layer and the aluminum-containing conductive line and the conductive line is free from corrosion.

Lee et al., U.S. Pat. No. 5,843,843, issued Dec. 1, 1998, discloses metal wiring structures for integrated circuits including a seed layer formed on an integrated circuit substrate and a wetting layer formed on the seed layer opposite the integrated circuit substrate. The metal wiring layer is formed on the wetting layer opposite the seed layer. The seed layer and the metal wiring layer have the same crystal orientation. In a preferred embodiment, the seed layer is an aluminum layer having a (111) crystal orientation and the metal wiring layer has an aluminum having (111) crystal orientation. The metal wiring layer may be aluminum or an aluminum alloy. The wetting layer preferably is titanium.

The present invention provides alternatives to the prior art.

SUMMARY OF THE INVENTION

One embodiment of the invention includes a semiconductor device including a dielectric layer having an opening form therein having a cross-sectional area of less than 1 μm2and a PVD aluminum base conductor filled in the opening.

Another embodiment of the invention includes a semiconductor device comprising at least two levels of aluminum-based intermetal connections, an aluminum base conductor via between each level; and wherein the aspect ratio of the via is no less than 1.5.

Another embodiment of the invention includes a semiconductor device comprising a stacked metal pad, comprising an aluminum base conductor for metal pads and having a plurality of aluminum based vias formed in the stacked metal pad.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now toFIGS. 1A-G, a semiconductor device according to the present invention may be made by forming a first dielectric layer14over a substrate12so that the first dielectric layer14includes openings15therethrough exposing a portion of the substrate12or another semiconductor layer. The substrate12may be any semiconductor material known to those skilled in the art including, but not limited to, silicon, germanium, silicon and germanium, gallium arsenate, silicon carbide, and silicon germanium. The first dielectric layer14may be any dielectric material known to those skilled in the art including silicon dioxide, but preferably, the first dielectric layer14is a low dielectric constant material having a dielectric constant no greater than about 3.7 such as, but not limited to, carbon dopped silicon oxide (eg. SiOxCy, 5≧(x, y)>0), fluorine dopped silicon oxide (eg. SiOxFy, 5≧(x, y)>0), silicon carbine (eg. SiCx, 3≧x>0), nitrogen containing silicon carbine (eg. SiCxNy, 5>(x, y)>0). The openings15in the first dielectric layer14may be made by any method known to those skilled in the art including using standard photolithographic techniques. The openings15in the first dielectric layer14may expose a portion of a metallization or bond or metal pad on the substrate12or an electrically conductive area of the substrate12.

Referring now toFIG. 1B, if desired, a barrier layer or adhesion layer16may be formed over a portion of the first dielectric layer14and the substrate12, especially when the dielectric constant of the first dielectric layer14is less than about 3.7. The barrier layer or adhesion layer is a material to avoid impurity diffusion from the first dielectric layer14into the first plug portion18and vice versa, which may result in an unstable dielectric constant value of the first dielectric layer14. Also, the barrier layer or adhesion layer form a good transition layer for the first dielectric layer14and the first plug portion18integration. The first barrier layer16extends down into the opening15formed in the first dielectric layer14and contacts the substrate12. However, it is not necessary for the first barrier layer16to be present to practice the present invention. The first barrier layer16may include Ti, TiNx(2≧x>0), TiWx(3≧x>0), TiSix(3≧x>0), Ta, TaNx(2≧x>0) and may have a thickness of about 50-650 angstroms. Preferably, the barrier layer or adhesion layer is formed by a low power physical vapor, deposition or a chemical vapor deposition (eg. MOCVD, atomic layer CVD) to avoid surface damage of the first dielectric layer14. In a feature size of an integrated circuit device having transistor node less than 0.13 um, the size of the opening15in the first dielectric layer14is less than about 2 μm2, while an optimized pattern density of the opening15of the wafer and on the bond pad or metal pad is crucial to achieve a substantially void-free and a flat surface of the first plug portion18. The pattern density of the opening15is no less than 30% of the wafer. The aspect ratio of the opening15is no less than 1.5. In one embodiment of the invention the depth as indicated by arrow A inFIG. 1Granges from about 1500-8000 angstroms.

Referring now toFIG. 1C, a first plug portion18is formed in the opening15in the first dielectric layer14and contacts the first barrier layer16, if present, or directly contacts the substrate12. The first plug portion18includes aluminum. The first plug portion18may include only aluminum or aluminum alloys such as AlCux(2≧x>0). In one embodiment of the invention, the grain size of the metal of the first plug portion18is no greater than 200 nm. By using a relatively short grain size for the metal in the first plug portion18, the opening15(via) in the first dielectric layer14can be completely filled without voids despite having a relatively narrow cross-sectional area and relatively large aspect ratio. In one embodiment of the invention the first plug portion18is formed by physical vapor deposition of an aluminum base material which has substantially the same grain size as the material deposited in the opening15of the first dielectric layer14. The important deposition parameters include a substrate bias for the first plug portion resputtering (the resputtering fraction is about 40%˜80%), a substrate temperature during deposition, around 20° C. to about 200°0C. (bias dependent), and a product of sputter gas pressure (P in Pa) and a distance of target to substrate (D in mm), the product value (P*D) is about 150 to about 750 mm*Pa. For a higher P*D would result in smaller grain size and a more compressive film. As will be appreciated fromFIG. 1C, in one embodiment, the material for the first plug portion18may be deposited so that it covers also a portion of the first barrier layer16overlying the first dielectric layer14. Alternatively, the deposition process may be stopped when the first plug portion18substantially fills the opening15in the first dielectric layer14. Alternatively, the excess material as shown inFIG. 1C, may be etched back or planarized stopping on the first barrier layer16, if present, or on the first dielectric layer14as shown inFIG. 1D. Preferably, the excess material as shown inFIG. 1Cis directly patterned as a portion of interconnect to form good adhesion between he first plug portion18and the interconnect.

Referring now toFIG. 1E, thereafter, a first interconnect portion20is deposited over the first plug portion18and the first barrier layer16, if present. The first interconnect portion20comprises aluminum or aluminum alloys such as AlCux(2≧x>0) . The material of the first interconnect portion20is substantially the same as the plug portion18to strengthen the mechanical properties (eg. Shear force, bonding energy, etc.) between the plug portion and the first interconnect portion. In one embodiment of the invention the ratio of the average grain size of the first plug portion18material and the first interconnect portion20material ranges from about 0.4-1. In one embodiment of the invention, the thickness of the first interconnect portion20is less than the height of the first plug portion18. In one embodiment of the invention, the height of the first plug portion18ranges from 100 nm -2000 nm, which is dependent on a design of the pattern density and the aspect ratio of the opening15. In one embodiment of the invention, the thickness of the first interconnect portion20is no less than about 200 nm. In one embodiment of the invention the height/thickness ratio of the first plug portion18to the first interconnect portion20is about 1-6. In one embodiment of the invention, the first interconnect portion20material is (111) perpendicular to the substrate12surface. In one embodiment of the invention, the first interconnect portion20extends horizontally and overlies two spaced apart first plug portions18.

Referring now toFIG. 1F, if desired, a second barrier22may be formed over the first interconnect portion20. A second dielectric layer24is formed over the structure ofFIG. 1Eand includes opening26therein exposing a portion of the second barrier layer22, if present, or the first interconnect portion20. The second dielectric layer24may be of a similar material as the first dielectric layer including low dielectric constant materials. The openings26formed in the second dielectric layer24preferably are not aligned with the first plug portion18. In one embodiment of the invention, the pattern density of the openings26in the second dielectric layer24are no less than about 50 percent of the bond pad or metal pad to strengthen the mechanical properties during assembly, especially when the first or the second dielectric layer is of low dielectric constant materials. As will be appreciated fromFIG. 1F, there are three openings26in the second dielectric layer24for every two openings15in the first dielectric layer14. The openings26may be formed in the second dielectric layer24by any method known to those skilled in the art including, but not limited to, known photolithographic techniques.

Referring now toFIG. 1G. a second metallization structure may be formed in a similar manner as previously described wherein a third barrier layer30may be formed over a portion of the second dielectric layer24and down into the openings26formed therein and contacting, the second barrier layer22, if present, or the first interconnect portion20. The second plug portion32and the opening26in the second dielectric24are substantially the same as those for the opening15in the first dielectric layer14and the first plug portion18. A second interconnect portion34may be formed over the second plug portion32in substantially the same manner as described with respect to the first interconnect portion20. If desired, a fourth barrier layer36may be formed over the second interconnection portion34. Again, in a feature size of integrated circuit device having a transistor node less than 0.13 um, a smooth. topography of metallization is crucial for photolithography. The smooth topography of metallization could be achieved by means of physical or chemical removal techniques such as etched back or chemical mechanical planarization stopping on a determined thickness of the first or second interconnect portion20or34. However, as will be appreciated fromFIG. 1G. both the first interconnect portion20(and the second barrier layer22if present) include a hollow (surface depression)28aligned with the first plug portion18. In one embodiment of the invention, the ratio of the depth of the hollow28and the thickness of the first interconnect portion20is less than ⅓. In one embodiment of the invention the depth of the hollow28is less than 600 angstroms. In one embodiment of the invention the size of the hollow28is less than ⅓ of the size of the opening15in the first dielectric layer14. In one embodiment of the invention the outer cross-sectional area of the opening is less than 1 μm2. A similar hollow28is formed in the second interconnect portion34. In one embodiment of the invention, an anti-reflection coating, silicon oxynitride, is preferred forming over the metallization for a better resolution of the opening15and32. As will be appreciated fromFIG. 1G. one embodiment of the invention includes a semiconductor device including a stacked metal pad which improves degradation resistance of the conductor and includes an aluminum base conductor pads20,34and a plurality of aluminum based vias18,32to form the stacked metal pad. The second interconnect portion34(and first interconnect portion20) may be formed by physical vapor deposition of a aluminum base material target having a grain size substantially the same as that desired to be present in the deposited interconnect portions. This may be accomplished by forming the second plug portion32using a first target having a grain size ranging from about 50 nm to less than 200 nm (including the same process to form the first plug portion18) and changing the target to a second aluminum base material having a grain size greater than the grain size of the plug portions18,32and at least 200 nm to deposit the interconnect portions20,34. InFIG. 1G. the thickness of the first interconnect portion20is indicated by arrow B and the height of the first plug portion18is indicated by the arrow A and the cross-sectional area of the first plug portion is measured generally at arrow C.

When the terms “over”, “overlie”, “overlies”, or “overlying” are used herein with respect to the relative position of a first component to a second component, the same shall mean that the first component may be in direct contact with the second component or that additional layer or layers may be interposed between the first component and the second component. Similarly, when the terms “under”, “underlie”, “underlies”, or “underlying” are used herein with respect to the relative position of a first component to a second component, the same shall mean that the first component may be in direct contact with the second component or that additional layer or layers may be interposed between the first and the second component.