CVD Titanium Silicide for Contract Hole Plugs

(1) FIELD OF THE INVENTION

This invention relates to methods of filling contact holes in dielectric layers with conducting metal plugs and more specifically to methods of using chemical vapor deposition of titanium silicide to form conducting metal plugs.

(2) DESCRIPTION OF THE RELATED ART

Contact holes in dielectric layers formed on integrated circuit wafers are typically filled by forming layers of titanium and titanium nitride using sequential sputtering forming layers of titanium and titanium nitride on the sidewalls and bottoms of the via holes. The wafer is then thermally processed to form titanium silicide at those points where the titanium is in contact with silicon. A blanket deposition of tungsten or other metal is then used to fill the contact holes.

U.S. Pat. No. 5,534,730 to Mori et al. describes contact holes with thin oxide at the bottom. Titanium silicide, TiSi.sub.x, is deposited in the contact hole using chemical vapor deposition. As the TiSi.sub.x film is formed the oxide is reduced and the titanium silicide forms a conductive contact to the silicon below the oxide.

U.S. Pat. No. 5,376,405 to Doan et al. describes a method of using chemical vapor deposition for depositing titanium silicide on a an integrated circuit wafer.

U.S. Pat. No. 5,066,612 to Ohba et al. describes the use of multilayer insulating layers for activating selective metal growth in filling contact holes with metal.

This invention describes methods of filling contact holes in dielectric layers formed on an integrated circuit wafer using chemical vapor deposition of titanium silicide.

In the manufacture of integrated circuit wafers a layer of dielectric is formed over the wafer after the devices have been formed in the wafer and some electrodes, usually polysilicon electrodes have been formed. It is necessary to form contact or via holes in this dielectric layer and to fill these contact or via holes with conductor metal so that electrical patterns formed on the dielectric layer have electrical connection to the appropriate points of the devices formed in the wafer and electrodes formed on the wafer.

FIG. 1A shows a cross section view of a part of an integrated circuit wafer showing the semiconductor wafer 10, a diffused region 14 formed in the wafer 10, and a field oxide isolation region 12. A polysilicon electrode 16 is shown formed on the field oxide region 12. A dielectric layer 18, usually silicon dioxide, is formed on the integrated circuit wafer and contact holes 20 are formed in the dielectric layer 18.

A conventional method of filling the contact holes with conductor metal is shown in FIGS. 1B and 1C. As shown in FIG. 1B layers of titanium 22 and titanium nitride 24 are sequentially sputter deposited on the wafer forming layers of titanium 22 and titanium nitride 24 on the sidewalls and bottom of the via holes. The wafer is then thermally processed to form titanium silicide at those points 21 where the titanium is in contact with silicon. As shown in FIG. 1B the step coverage of the titanium nitride layer at the edge of the contact holes 23 is poor. As shown in FIG. 1C a blanket layer of tungsten 26 is deposited on the wafer to fill the contact holes. As shown in FIG. 1C the poor step coverage of the titanium nitride can cause voids 28 to form in the tungsten filling the via. The tungsten is then etched back to leave tungsten only in the contact holes, not shown.

The conventional method described above is a complex process and the poor step coverage of the titanium/titanium nitride layer causes reliability and other problems in the tungsten, or other metal, plug filling the contact hole. These problems become more severe as the diameters of the contact holes decrease, as happens with increasing circuit density.

It is a principle objective of this invention to provide simplified methods for filling contact holes with conducting metal plugs.

It is another principle objective of this invention to provide methods for filling contact holes with conducting metal plugs which result in improved quality and reliability of the conducting metal plugs.

These objectives are achieved by using blanket deposition of titanium silicide to completely fill the contact holes, by selective deposition of titanium silicide to completely fill the contact holes, or by depositing a titanium silicide adhesion layer on the sidewalls and bottom of the contact holes and filling the contact holes with titanium silicide, tungsten, aluminum, or copper. The titanium silicide, tungsten, aluminum, and copper are deposited using chemical vapor deposition.

FIG. 1A shows a cross section view of an integrated circuit wafer having devices formed therein, a dielectric layer formed thereon, and contact holes formed in the dielectric layer.

FIG. 1B shows a cross section view of the integrated circuit wafer of FIG. 1A with blanket layers of titanium and titanium nitride deposited on the wafer.

FIG. 1C shows a cross section view of the integrated circuit wafer of FIG. 1A with a blanket layer of tungsten formed on the layers of titanium and titanium nitride.

FIG. 2 shows a cross section view of an integrated circuit wafer having devices formed therein and a dielectric layer formed thereon.

FIG. 3 shows a cross section view of the integrated circuit wafer of FIG. 2 with contact holes formed in the dielectric layer.

FIG. 4 shows a cross section view of the integrated circuit wafer of FIG. 3 with a blanket layer of titanium silicide formed on the wafer.

FIG. 5 shows a cross section view of the integrated circuit wafer of FIG. 4 after the titanium silicide has been etched back to the surface of the dielectric layer.

FIG. 6 shows a cross section view of the integrated circuit wafer of FIG. 3 with titanium silicide selectively deposited on the wafer.

FIG. 7 shows curves of the titanium silicide growth rate on silicon and silicon dioxide as a function of the silane to titanium tetrachloride flow ratio. The curves in FIG. 7 are taken from the Journal of the Electrochemical Society, Vol. 139, No. 4, 1992, page 1159.

FIG. 8 shows a cross section view of the integrated circuit wafer of FIG. 6 after the titanium silicide has been etched back, using reactive ion etching, or polished back, using chemical mechanical polishing, to the surface of the dielectric layer.

FIG. 9 shows a cross section view of the integrated circuit wafer of FIG. 3 with a titanium silicide adhesion layer formed on the wafer.

FIG. 10 shows a cross section view of the integrated circuit wafer of FIG. 9 after the titanium silicide adhesion layer has been etched back to the surface of the dielectric layer.

FIG. 11 shows a cross section view of the integrated circuit wafer of FIG. 10 after conductor metal has been selectively deposited on the titanium silicide layer.

Refer now to FIGS. 2-5 for a preferred embodiment of the method of this invention. FIG. 2 shows a cross section view of a part of an integrated circuit wafer showing the semiconductor wafer 10, a diffused region 14 formed in the wafer 10, and a field oxide isolation region 12. A polysilicon electrode 16 is shown formed on the field oxide region 12. A dielectric layer 18 is formed on the integrated circuit wafer. In this example the dielectric layer is silicon dioxide having a thickness of between about 0.7 and 1.0 micrometers. This example, and the examples that follow, show a particular part of the integrated circuit wafer. Those skilled in the art will readily recognize that polysilicon electrodes can be formed at other locations of the wafer and that the invention will work equally well for other parts of the integrated circuit wafer.

As shown in FIG. 3, contact holes 20 are then formed in the dielectric layer 18. In this example the contact holes 20 are formed using reactive ion etching and have a diameter of between about 0.2 and 0.5 micrometers. FIG. 3 shows one contact hole 20 exposing part of a silicon junction region and one contact hole 21 exposing part of a polysilicon electrode.

Next, as shown in FIG. 4, a blanket layer of titanium silicide, TiSi.sub.2, is deposited on the wafer thereby completely filling the contact holes. The blanket layer of titanium silicide is deposited using chemical vapor deposition, CVD, from a combination of silane gas, SiH.sub.4, and titanium tetrachloride gas, TiCl.sub.4. The chemical vapor deposition used is either plasma enhanced chemical vapor deposition, PE-CVD, rapid thermal chemical vapor deposition, RT-CVD, or low pressure chemical vapor deposition, LP-CVD. The titanium silicide fills the contact holes completely, has good adhesion to the sidewalls of the contact holes, and forms a low resistance silicide contact with the silicon at the bottoms of the contact holes.

Next, as shown in FIG. 5, that part of the titanium silicide above the plane of the top surface of the dielectric layer 31 is removed using reactive ion etching or chemical mechanical polishing leaving titanium silicide plugs 30 in the contact holes. If reactive ion etching is used the reactive ion etching can be carried out in-situ after depositing the titanium without opening the chamber used for depositing the titanium silicide or, if vacuum was used for deposition of the titanium silicide, without breaking the vacuum. The reactive ion etching can also be carried out ex-situ with the wafer removed from the chamber used to deposit the titanium silicide. If chemical mechanical polishing is used the wafer must be removed from the chamber used to deposit the titanium silicide.

Refer now to FIGS. 2, 3, and 6-8 for another preferred embodiment of the method of this invention. FIG. 2 shows a cross section view of a part of an integrated circuit wafer showing the semiconductor wafer 10, a diffused region 14 formed in the wafer 10, and a field oxide isolation region 12. A polysilicon electrode 16 is shown formed on the field oxide region 12. A dielectric layer 18 is formed on the integrated circuit wafer. In this example the dielectric layer is silicon dioxide having a thickness of between about 0.7 and 1.0 micrometers.

As shown in FIG. 3, contact holes 20 are then formed in the dielectric layer 18. In this example the contact holes 20 are formed using reactive ion etching and have a diameter of between about 0.2 and 0.5 micrometers. FIG. 3 shows one contact hole 20 exposing part of a silicon junction region and one contact hole 21 exposing part of a polysilicon electrode.

Next, as shown in FIG. 6, titanium silicide 32, TiSi.sub.2, is deposited selectively in the contact holes thereby completely filling the contact holes. The titanium silicide is deposited using chemical vapor deposition, CVD, from a combination of silane gas, SiH.sub.4, gas and titanium tetrachloride gas, TiCl.sub.4, and selectivity is achieved by adjusting the ratio of the flow rate of the SiH.sub.4 to the flow rate of the TiCl.sub.4. Titanium silicide can also be deposited using a combination of SiH.sub.2 Cl.sub.2 gas and titanium tetrachloride gas, TiCl.sub.4, and selectivity is achieved by adjusting the flow rate of the SiH.sub.2 Cl.sub.2 to the flow rate of the TiCl.sub.4.

FIG. 7 shows curves of the titanium silicide growth rate on silicon 42 and on silicon dioxide 44 as a function of the ratio of the flow rate of the SiH.sub.4 to the flow rate of the TiCl.sub.4, for the case where titanium silicide is deposited using SiH.sub.4 and TiCl.sub.4. The curves of FIG. 7 are taken from the Journal of the Electrochemical Society, Vol. 139, No. 4, 1992, page 1159. Since the bottoms of the contact holes are either silicon or polysilicon the flow rates of the SiH.sub.4 and TiCl.sub.4, or the flow rates of the SiH.sub.2 Cl.sub.2 and TiCl.sub.4, can be adjusted to provide a much greater titanium silicide deposition rate on the silicon at the bottoms of the contact holes than on the silicon dioxide so that the deposition of the titanium silicide fills the holes but does not deposit on the silicon dioxide. The selectivity is maintained by using a deposit/etch/deposit process wherein the deposition of the titanium silicide is interrupted by periods of in-situ reactive ion etching to remove any titanium silicide deposited on the top surface of the silicon dioxide layer followed by continued deposition of titanium silicide. The deposition and etching steps of the deposit/etch/deposit process can be repeated as often as necessary. Even though the titanium silicide deposits more readily on silicon compared to silicon dioxide, the titanium silicide has good adhesion to the sidewalls of the contact holes in the silicon dioxide layer. As in the preceding embodiment the chemical vapor deposition used is either plasma enhanced chemical vapor deposition, PE-CVD, rapid thermal chemical vapor deposition, RT-CVD, or low pressure chemical vapor deposition, LP-CVD.

Next, as shown in FIG. 8, that part of the titanium silicide above the plane of the top surface of the dielectric layer 31 is removed using reactive ion etching or chemical mechanical polishing leaving titanium silicide plugs 32 in the contact holes. If reactive ion etching is used the reactive ion etching can be carried out in-situ after depositing the titanium without opening the chamber used for depositing the titanium silicide or, if vacuum was used for deposition of the titanium silicide, without breaking the vacuum. The reactive ion etching can also be carried out ex-situ with the wafer removed from the chamber used to deposit the titanium silicide. If chemical mechanical polishing is used the wafer must be removed from the chamber used to deposit the titanium silicide.

Refer now to FIGS. 2, 3, 7, and 9-11 for still another preferred embodiment of the method of this invention. FIG. 2 shows a cross section view of a part of an integrated circuit wafer showing the semiconductor wafer 10, a diffused region 14 formed in the wafer 10, and a field oxide isolation region 12. A polysilicon electrode 16 is shown formed on the field oxide region 12. A dielectric layer 18 is formed on the integrated circuit wafer. In this example the dielectric layer is silicon dioxide having a thickness of between about 0.7 and 1.0 micrometers.

As shown in FIG. 3, contact holes 20 are then formed in the dielectric layer 18. In this example the contact holes 20 are formed using reactive ion etching and have a diameter of between about 0.2 and 0.5 micrometers. FIG. 3 shows one contact hole 20 exposing part of a silicon junction region and one contact hole 21 exposing part of a polysilicon electrode.

Next as shown in FIG. 9 a thin titanium silicide adhesion layer 34 is deposited on the wafer using chemical vapor deposition thereby forming an adhesion layer of titanium silicide on the top surface of the silicon dioxide, the sidewalls of the contact holes, and the bottoms of the contact holes but dot filling the holes. As can be seen from FIG. 7, the deposition rate of titanium silicide is greater on the silicon at the bottoms of the contact holes than on the silicon dioxide at the sidewalls of the contact holes and the top surface of the silicon dioxide layer. The deposition rates for this embodiment are adjusted so that the difference in deposition rates is less than in the selective deposition used in the preceding embodiment. This difference in deposition rates results in a thicker deposit of the titanium silicide adhesion layer at the bottoms of the contact holes than on the sidewalls of the contact holes or on the top surface of the silicon dioxide layer, as shown in FIG. 9.

Next, as shown in FIG. 10, the titanium silicide adhesion layer 34 is etched back using in-situ or ex-situ reactive ion etching following the titanium silicide deposition so that titanium silicide adhesion layer 34 is left only on the sidewalls and bottoms of the contact holes.

Next, as shown in FIG. 11, a conductor metal 36 is selectively deposited on the titanium silicide adhesion layer 34 on the sidewalls and bottoms of the contact holes using selective chemical vapor deposition, thereby filling the contact holes with a plug of conductor metal 36. The conductor metal in this example is titanium silicide, tungsten, aluminum, or copper. Selectivity is achieved by adjusting the chemical deposition parameters and by using the deposit/etch/deposit process described earlier where the deposition is interrupted with periods of in-situ reactive ion etching.

While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.