Method of forming conductive connections

[0002] This invention relates to methods of forming a conductive connection on a substrate between a first region and a second region, to methods of forming a conductive interface to be received between a first region and a second region, to methods of forming a conductive contact, and to methods of forming a conductive line.

[0003] In the processing of integrated circuits, electrical contact is typically made to isolated active device regions formed within a wafer substrate typically comprising monocrystalline silicon. The active device regions are connected by high electrically conductive paths or lines which are fabricated above insulative material which covers the substrate surface. To provide electrical connection between the conductive paths, and active-device regions, an opening in the insulative material is typically provided to enable conductive films to make electrical connection with desired regions. Such openings are typically referred to as contact openings, or simply “contacts”.

[0004] As transistor-active area dimensions approached one micron in diameter, conventional process parameters resulted in intolerable increased resistance between the active region or area and the conductive layer. One way of reducing such contact resistance is by formation of a metal silicide atop the active area prior to application of conductive material which will partially or fully fill the remaining contact opening and/or other material which will be utilized to form the conductive runner. One common metal silicide material formed is TiSi_x, where “x” is predominantly “2”.

[0005] Ultimately, an electrically conductive contact-filling material, such as tungsten, would be provided for making electrical connection to the contact with the active area. However, tungsten adheres poorly to titanium silicide. Additionally, it is desirable to prevent intermixing of the contact-filling material with the silicide and underlying silicon. Accordingly, an intervening layer is typically provided to prevent diffusion of the silicon and silicide with the plug-filling metal, and to effectively adhere the plug-filling metal to the underlying substrate. Such material is, accordingly, also electrically conductive and commonly referred to as a “barrier layer” due to its anti-diffusion properties. One material of choice for use as a glue/diffusion barrier layer is titanium nitride. This is an attractive material as a contact diffusion barrier in silicon integrated circuits because it behaves as an impermeable barrier to silicon, and because the activation energy for diffusion of other impurities is very high. Titanium nitride is also chemically thermodynamically very stable, and it has low electrical resistance.

[0006] Titanium silicide and titanium nitride can be formed in a number of different manners. One prior art process for forming titanium silicide and titanium nitride barrier contacts comprises first depositing an elemental titanium layer by physical vapor deposition (i.e., sputtering) to within a contact opening over a silicon containing region. Subsequently, the wafer is moved from the physical vapor deposition chamber to a chemical vapor deposition chamber. There, titanium nitride is chemical vapor deposited from an organic titanium containing precursor, such as tetrakisdimethylamido titanium (TDMAT). The wafer is subsequently exposed to suitable annealing conditions to transform titanium at the base of the contact into a titanium silicide. Tungsten or some other conductive material (for example, conductively doped semiconductor materials) is then deposited to fill the remaining contact opening. A planarizing process, such as chemical-mechanical polishing, is then utilized to isolate the conductive plug-filling material within the contact opening.

[0007] In another process, titanium is chemical vapor deposited utilizing TiCl₄and H₂as precursors at sub-atmospheric pressure, at a temperature of around 635° C., and in the presence of plasma. Deposition under these conditions, principally because of the temperature, will cause the titanium which deposits immediately over the silicon-containing active region to constitute titanium silicide. The titanium overlying insulative material will deposit as elemental titanium. The wafer is then moved from the TiCl₄deposition chamber to an organic chemical vapor deposition chamber where the above-described TDMAT is utilized to deposit a TiN layer. The processing then continues as otherwise described above.

[0008] This invention was principally motivated in addressing problems associated with contact plug formation involving titanium silicide and titanium nitride interface materials between a silicon-containing region and an overlying conductive plug-filling material, such as tungsten. The artisan will, however, appreciate applicability of the invention to any other aspect of semiconductor wafer processing whereby a conductive connection is formed on a substrate between a first region comprising silicon and some second region, with the invention only being limited by the accompanying claims appropriately interpreted in accordance with the Doctrine of Equivalents.

[0009] The invention comprises methods of forming a conductive connection on a substrate between a first region and a second region, methods of forming a conductive interface to be received between a first region and a second region, methods of forming a conductive contact, and methods of forming a conductive line.

[0010] In one aspect, a method of forming a conductive connection on a substrate between a first region and a second region, includes forming a first titanium comprising layer over and in electrical connection with the first region. The first layer is exposed to a nitrogen containing plasma effective to transform at least an outer portion of the first layer into a second layer comprising titanium nitride. Titanium is deposited to form an elemental titanium comprising third layer over the second layer. The third layer is exposed to a nitrogen containing plasma effective to transform at least an outer portion of the third layer into a layer comprising titanium nitride. The second region is formed over and in electrical connection with the transformed third layer.

[0011] In one aspect, the invention comprises a method of forming a conductive line. A conductively doped silicon comprising semiconductive material is formed over a substrate. Titanium is deposited over the semiconductive material to form a first layer in electrical connection with the semiconductive material. The first layer is exposed to a nitrogen containing plasma effective to transform at least an outer portion of the first layer into a second layer comprising titanium nitride. Titanium is deposited to form an elemental titanium comprising third layer over the second layer. The third layer is exposed to a nitrogen containing plasma effective to transform at least an outer portion of the third layer into a layer comprising titanium nitride. A metal is deposited over and in electrical connection with the transformed third layer. The semiconductive first layer, second layer, third layer, transformed third layer and metal materials are formed into a conductive line.

[0012] Preferred embodiments of the invention are described below with reference to the following accompanying drawings.

[0013] FIG. 1 is a diagrammatic sectional view of a semiconductor wafer fragment at one processing step in accordance with the invention.

[0014] FIG. 2 is a view of the FIG. 1 wafer at a processing step after that depicted by FIG. 1.

[0015] FIG. 3 is a view of the FIG. 1 wafer at a processing step after that depicted by FIG. 2.

[0016] FIG. 4 is a view of the FIG. 1 wafer at a processing step after that depicted by FIG. 3.

[0017] FIG. 5 is a view of the FIG. 1 wafer at a processing step after that depicted by FIG. 4.

[0018] FIG. 6 is a view of the FIG. 1 wafer at a processing step after that depicted by FIG. 5.

[0019] FIG. 7 is a view of the FIG. 1 wafer at a processing step after that depicted by FIG. 6.

[0020] FIG. 8 is a diagrammatic sectional view of an alternate embodiment semiconductor wafer fragment at one processing step in accordance with the invention.

[0021] FIG. 9 is a view of the FIG. 8 wafer at a processing step after that depicted by FIG. 8.

[0022] FIG. 10 is a view of the FIG. 8 wafer at a processing step after that depicted by FIG. 9.

[0023] FIG. 11 is a view of the FIG. 8 wafer at a processing step after that depicted by FIG. 10.

[0024] FIG. 12 is a view of the FIG. 8 wafer at a processing step after that depicted by FIG. 11

[0025] FIG. 13 is a view of the FIG. 8 wafer at a processing step after that depicted by FIG. 12.

[0026] FIG. 14 is a view of the FIG. 8 wafer at a processing step after that depicted by FIG. 13.

[0027] This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8).

[0028] One method of forming a conductive connection on a substrate between a first region comprising silicon and a second region is described with reference to FIGS. 1-8, and another is described with reference to FIGS. 9-14. The exemplary implementation of FIGS. 1-8 forms a conductive contact. The exemplary implementation with respect to FIGS. 9-14 forms a conductive line. Any other conductive connections on a substrate between a first region comprising silicon and a second region are contemplated.

[0029] Referring initially to FIG. 1, a semiconductor wafer fragment in process is indicated generally with reference numeral 10. Such comprises a bulk monocrystalline silicon substrate 12 having a diffusion region 14 formed therein. Alternate silicon comprising substrates from monocrystalline silicon are, of course, contemplated. By way of example only, polycrystalline or monocrystalline comprising layers, plugs and devices are exemplary possible silicon comprising substrates. Region 14 in this example can be considered as a first region comprising silicon to which electrical connection is to be made. An insulative material 16, such as doped or undoped silicon dioxide, is formed over silicon comprising substrate 12. A contact opening 18 is formed within insulative material 16 to extend to at least proximate region 14, and preferably all the way to outwardly expose region 14 as shown. Region 14 may or may not include a native oxide formed thereover.

[0030] Referring to FIG. 2, titanium is deposited over insulative material 16 to within contact opening 18, and accordingly over first region 14, to form a first layer 20 in electrical connection with first region 14. An example and preferred process for depositing layer 20 comprises chemical vapor deposition in a suitable chamber, for example a plasma-enhanced chemical vapor deposition chamber, preferably using an inorganic titanium containing precursor. Preferably, the depositing to form first layer 20 is at a temperature effective to form titanium silicide during the first layer depositing from silicon of first region 14 and the titanium being deposited thereover. Alternately but less preferred, the layer could be deposited as substantially elemental titanium, with subsequent suitable high temperature processing forming titanium silicide after the deposition. Where the preferred silicide is ultimately formed, all of the titanium of first layer 20 immediately over first region 14 might constitute titanium silicide (shown), or only an inner portion thereof comprising silicide with an outer portion thereof comprising elemental titanium (not shown). An example preferred process for forming layer 20 is to combine TiCl₄and H₂in a capacitively coupled plasma-enhanced chemical vapor deposition chamber powered at 700 watts, a wafer chuck temperature of 635° C., and a pressure of 4 Torr. Such deposited titanium at a rate of 2.5 Angstroms per second, with a titanium silicide layer being produced at such temperature. Alternately by way of example only but less preferred, layer 20 can be formed as titanium silicide by chemical vapor deposition using titanium and silicon containing precursors. A 4 preferred thickness for layer 20 over region 14 is from 100 Angstroms to 250 Angstroms.

[0031] Referring to FIG. 3, first layer 20 has been exposed to a nitrogen containing plasma effective to transform at least an outer portion (only an outer portion as shown) of first layer 20 into a second layer 22 comprising titanium nitride. Such processing most preferably occurs in the same chamber within which layer 20 was initially formed. Layer 22 is preferably formed to a thickness of from about 5 Angstroms to about 50 Angstroms. Such exposing preferably includes both nitrogen and hydrogen components in the plasma. Examples include NH₃, or N₂and H₂. A preferred example is plasma power at from 100 to 750 watts, wafer chuck temperature maintained at from 600° C. to 680° C., and reactor pressure being maintained from 500 mTorr to 400 Torr. A specific example is 200 watts, 635° C., and 1 Torr. N₂and H₂flow to the reactor is preferably such that the flow of H₂exceeds that of N₂. A specific example under the above conditions includes an H₂flow of 600 sccm in a N₂flow of 400 sccm. Accordingly if first layer 20 comprises an outer elemental titanium portion, at least an outer portion thereof will be transformed to titanium nitride during such exposing. Alternately where first layer comprises an outer titanium silicide portion, an outermost portion thereof would be transformed to titanium nitride during the above exposing.

[0032] Referring to FIG. 4, titanium is deposited to form an elemental titanium comprising third layer 24 over second layer 22. Again, the preferred deposition is chemical vapor deposition utilizing the same chamber within which the first deposition and plasma exposure occurred. Further, formation of layer 24 also preferably occurs under plasma conditions. Preferred and exemplary processing is as described above with respect to deposited first layer 20. Intervening titanium nitride comprising layer 22 over silicide comprising layer 20 immediately over region 14 advantageously prevents deposited layer 24 from being transformed during or after deposition to a silicide. A preferred thickness for layer 24 is from 100 Angstroms to 150 Angstroms.

[0033] Referring to FIG. 5, third layer 24 is exposed to a nitrogen containing plasma effective to transform at least an outer portion (only an outer portion as shown) of third layer 24 into a layer 26 comprising titanium nitride. Again, such exposing most preferably occurs in the same chamber which the first exposing and depositions occurred. Further, substrate 10 is preferably not removed from such chamber from start of the first layer 20 depositing until after the exposing to transform at least the outer portion of third layer 24 into titanium nitride comprising layer 26. A preferred thickness for layer 26 is from about 100 Angstroms to about 200 Angstroms. A further preferred embodiment results in complete transformation of titanium layer 24 into a titanium nitride comprising layer (not shown). Preferably, the exposing of layer 26 is similar to the nitrogen plasma exposing of layer 20, as described above. Preferably, a greater quantity of nitrogen is present in the exposing of third layer 24 than in the exposing of first layer 20. Further, where N₂and H₂are utilized, there is preferably a greater quantity of H₂than N₂in the exposing of the first layer, and a greater quantity of N₂than H₂in the exposing of the third layer. A specific example is such as that described above, with differing N₂and H₂flows of 600 sccm and 400 sccm, respectively.

[0034] After the exposing of third layer 24 to a nitrogen plasma to transform at least an outer portion thereof into a titanium nitride comprising layer, such transformed outer portion is preferably exposed to a nitrogen containing atmosphere at a pressure of at least 50 Torr before any subsequent deposition. Such atmosphere is preferably void of plasma and the exposure conducted before removing the substrate from the chamber within which the nitrogen plasma exposure occurred. A preferred processing step here is at 60 Torr in a 100% N₂or NH₃atmosphere at 635° C. for about 35 seconds. Such has been discovered to further reduce contact resistant.

[0035] Referring to FIG. 6, a conductive material or layer 28, such as for example elemental tungsten or conductive poly, is deposited over insulative material 16 to within contact opening 18 over transformed layer 26. Such comprises or constitutes an exemplary second region, whereby an interface or electrical connection is being made between a second region 28 and a first region 14.

[0036] Referring to FIG. 7, remaining first layer, second layer, third layer, transformed third layer, and metal materials are removed from over insulative material 16 to form an insulative conductive contact or contact plug 30 within contact opening 18 in electrical connection with silicon comprising substrate 12. An example and preferred processing is chemical-mechanical polishing.

[0037] The above is but one example of a method of forming a conductive connection on a substrate between a first region and a second region. But one other example of such a method whereby such occurs in the formation of a conductive line is next described with reference to FIGS. 8-14. Like numerals from the first described embodiment have been utilized where appropriate for analogous layers, with differences being indicated with different numerals.

[0038] FIG. 8 indicates a semiconductor wafer fragment 36 comprising a bulk monocrystalline silicon substrate 12. Exemplary fabrication is described with reference to formation of a transistor gate. A gate oxide layer 38 is formed over substrate 12. A conductively doped semiconductive material layer 40 is formed over layer 38.

[0039] Referring to FIG. 9, titanium is deposited over semiconductive material 40 to form a first layer 20 in electrical connection with semiconductive material 40. Material and processing is preferably the same as described above for layer 20 with respect to the first described embodiment. Alternately by way of example only but less preferred, layer 20 can be formed as titanium silicide by chemical vapor deposition using titanium and silicon containing precursors.

[0040] Referring to FIG. 10, first layer 20 is exposed to a nitrogen containing plasma effective to transform at least an outer portion thereof into a second layer 22 comprising titanium nitride. Example materials and processing are again as described above with respect to formation of layer 22 in the first-described embodiment.

[0041] Referring to FIG. 11, titanium is deposited to form an elemental titanium comprising third layer 24 over second layer 22. Processing is again preferably as described above with respect to the first embodiment relative to forming layer 24.

[0042] Referring to FIG. 12, third layer 24 is exposed to a nitrogen containing plasma effective to transform at least an outer portion thereof into a layer 26 comprising titanium nitride. Processing and materials are again preferably as described above with respect to layer 26 in the first described embodiment.

[0043] Referring to FIG. 13, a metal layer 44, for example elemental tungsten, is deposited over and in electrical connection with layer 26.

[0044] Referring to FIG. 14, the semiconductive first layer, second layer, third layer, transformed outer portion of the third layer, and metal materials are formed into a conductive line. Such forming most preferably comprises etching all of said layers using a common masking step at the conclusion of formation of all such layers, as shown.

[0045] Preferably, all such depositings and exposings occur in the same plasma-enhanced chemical vapor deposition chamber.

[0046] In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.