Abstract:
A process for removing a substance from a substrate, includes: (1) providing the substrate, wherein: (a) the substrate is at least partially coated with the substance; (b) the substance is a transition metal oxide, a transition metal silicate, a Group 13 metal oxide, a Group 13 metal silicate, or mixtures thereof; and (c) the substance has a dielectric constant greater than silicon dioxide; (2) reacting the substance with a reactive gas to form a volatile product, wherein the reactive gas comprises chlorine; and (3) removing the volatile product from the substrate to thereby remove the substance from the substrate, provided that when the substance is Al 2 O 3  and the substrate is a semiconductor from which the substance is being selectively etched, the process is conducted in the absence of a plasma having a density greater than 10 11  cm −3 . The process is particularly suitable for etching semiconductors and for cleaning reaction chambers.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to a method to etch high-k dielectric materials deposited on a substrate, and a method to clean residues from the internal surfaces of a reactor in which these high-k dielectric films are deposited. More specifically, this invention relates to etching and/or cleaning metal-oxide high-k dielectric materials such as Al 2 O 3 , HfO 2 , ZrO 2 , etc. and mixtures thereof, and metal silicate high-k dielectric materials such as HfSi x O y , ZrSi x O y , etc. and mixtures thereof.  
           [0002]    In the manufacture of semiconductor integrated circuits (IC), dielectric materials such as silicon dioxide (SiO 2 ), silicon nitride (Si 3 N 4 ), and silicon oxynitride (SiON) have been widely used as insulators for transistor gates. Such insulators are often called gate dielectrics. As IC device geometry shrinks, gate dielectric layers have become progressively thinner. When the gate dielectric layer approaches thicknesses of a few nanometers or less, conventional SiO 2 , Si 3 N 4 , and SiON materials undergo electric breakdown and no longer provide insulation. To maintain adequate breakdown voltage at very small thickness (≦10 nm), high dielectric constant materials (i.e., high-k materials, which for present purposes are defined as materials where k is greater than about 4.42, the k of silicon dioxide) must be used as the gate insulating layer. The IC industry has experimented with many high-k materials. The latest and most promising high-k materials are metal oxides such as Al 2 O 3 , HfO 2 , ZrO 2 , and mixtures thereof, and metal silicates such as HfSi x O y , ZrSiO 4 , and mixtures thereof.  
           [0003]    High-k materials such as Al 2 O 3 , HfO 2 , and ZrO 2  are very stable and resistive against most of the etching reactions, which has led to their use as etch stop layers and hard mask layers in plasma etching of other materials. See, e.g., K. K. Shih et al., “Hafnium dioxide etch-stop layer for phase-shifting masks”, J. Vac. Sci. Technol. B 11(6), pp. 2130-2131 (1993); J. A. Britten, et al., “Etch-stop characteristics of Sc 2 O 3  and HfO 2  films for multilayer dielectric grating applications”, J. Vac. Sci. Technol. A 14(5), pp. 2973-2975 (1996); J. Hong et al., “Comparison of Cl 2  and F 2  based chemistries for the inductively coupled plasma etching of NiMnSb thin films”, J. Vac. Sci. Technol. A 17(4), pp. 1326-1330 (1999); U.S. Pat. No. 5,972,722 to Visokay et al.; U.S. Pat. No. 6,211,035 B1 to Moise et al., U.S. patent application Publication US2001/0055852 A1 to Moise et al.; and EP 1,001,459 A2 to Moise et al.  
           [0004]    These high-k materials are typically deposited from chemical precursors that are reacted in a deposition chamber to form films in a chemical vapor deposition (CVD) process. In some instances, these high-k materials are deposited onto semiconductor substrates (wafers) by atomic layer deposition (ALD), in which the films are deposited in controlled, nearly monoatomic layers. Apparatus and processes for performing ALD are disclosed in, e.g., U.S. Pat. No. 5,879,459 to Gadgil et al., U.S. Pat. No. 6,174,377 B1 to Doering et al., U.S. patent application Publication US2001/0011526 A1 to Doering et al., U.S. Pat. No. 6,387,185 B2 to Doering et al., WO 00/40772 to Doering et al. and WO 00/79019 Al to Gadgil et al. This family of patents assigned to Genus, Inc. teaches that “In situ plasma cleans allow the realization of a very long time between maintenance cleaning.” (See, e.g., U.S. Pat. No. 6,387,185 B2 at column 7, lines 27-28.) However, no details of any process for plasma cleaning of ALD chambers were given in the above family of disclosures.  
           [0005]    Plasma sources have been used to enhance atomic layer deposition processes (PE-ALD). For example, Pomarede et al. in WO 02/43115 A2 teach the use of plasma sources to generate excited reactive species that prepare/activate the substrate surface to facilitate subsequent ALD. Nguyen et al. in WO 02/43114 A2 teach the use of a pulsing plasma to enact ALD processes instead of alternating precursor chemical flows. Again, these publications do not disclose any method to clean the ALD residues after the wafers have been processed.  
           [0006]    Although the aforementioned high-k materials are excellent gate insulators, it is very difficult to dry etch these films for pattern transfer. While the deposition process desirably generates high-k films on a substrate (typically a silicon wafer), the reactions that form these films also occur non-productively on other exposed surfaces inside of the deposition chamber. Accumulation of deposition residues results in particle shedding, degradation of deposition uniformity, and processing drifts. These effects can lead to wafer defects and subsequent device failure. Therefore, all CVD chambers, and specifically ALD chambers, must be periodically cleaned.  
           [0007]    Due to their extreme chemical inertness, there have been few attempts to dry etch these high-k materials. J. W. Lee et al. in “Electron cyclotron resonance plasma etching of oxides and SrS and ZnS-based electroluminescent materials for flat panel displays”, J. Vac. Sci. Technol. A 16(3), pp. 1944-1948, reported several chemistries to etch various metal oxides and sulfides. The authors used very powerful plasma conditions (800 W of microwave source power, up to 450 W of RF chuck bias power, and chamber pressure of 1.5 mTorr). The result of such process conditions is very high chuck bias voltage (up to −535 V). High chuck bias voltage can greatly enhance energetic ion sputtering and sputtering induced etching. The authors used Cl 2 /Ar, BCl 3 /Ar, and SF 6 /Ar mixture under the extreme plasma conditions to etch various materials. Al 2 O 3  showed the slowest etch rates. In most of their experiments, Al 2 O 3  etch rates were less than 20% of the ZnS etch rates under identical conditions. The authors also noted “Fairly similar trends were seen with BCl 3 /Ar discharges, with the absolute rates being ˜20% lower than that for Cl 2 /Ar.” While the authors&#39; method may be used for anisotropic etching of flat panel display devices, high power plasma sputtering cannot be achieved on grounded chamber surfaces. Therefore, the authors&#39; methods cannot be extended to clean deposition residues in ALD chambers.  
           [0008]    Williams et al. in U.S. Pat. No. 6,238,582 B1 teach a reactive ion beam etching (RIBE) method to etch thin film head materials such as Al 2 O 3 . The patentees used a CHF 3/ Ar plasma as the ion source. Collimated reactive ion beam then impinged upon the wafer substrate to etch thin film materials. Such collimated ion beams cannot be used to clean deposition residues from ALD chambers.  
           [0009]    Lagendijk et al. in U.S. Pat. Nos. 5,298,075 and 5,288,662 teach a “process for thermal oxidation of silicon or cleaning of furnace tubes . . . by exposing the silicon or tube to temperatures above 700° C. while flowing a carrier gas containing oxygen and a chlorohydrocarbon having a general formula C x H x Cl x  where x is 2, 3, or 4 over the silicon or tube. The chlorohydrocarbon is selected to readily and completely oxidize at temperature.” (See Abstract.) Oxidation of silicon into SiO 2  and gettering metal contaminants (such as Na and Fe) in oxidation or diffusion furnaces is a completely different process than etching/cleaning high-k materials.  
           [0010]    In view of the dearth of art disclosing dry etching/cleaning of high-k materials, ALD reactors have typically been cleaned by mechanical means (scrubbing or blasting) to clean up the deposition residues from the internal surfaces of the chamber and downstream equipment (e.g. pump headers and exhaust manifolds). However, mechanical cleaning methods are time-consuming and labor-intensive.  
           [0011]    Fluorine-containing plasma-based dry cleaning is commonly used to clean up residues of silicon compounds (such as polycrystalline silicon, SiO 2 , SiON, and Si 3 N 4 ) and tungsten in chemical vapor deposition (CVD) reactors. However, fluorine-based chemistry is ineffective to remove the high-k dielectric materials discussed above. See, e.g., J. Hong et al., J. Vac. Sci. Technol. A, Vol. 17, pp1326-1330, 1999, wherein the authors exposed Al 2 O 3  coated wafers to NF 3/ Ar based inductively coupled plasmas, and found that “the greater concentration of atomic F available at high source power contributed to thicker fluorinated surfaces, leading to the net deposition rather than etching.” 
           [0012]    Thus, there is an urgent need for a process to chemically dry clean high-k residues, such as Al 2 O 3 , HfO 2 , ZrO 2 , HfSi x O y , ZrSi x O y  and mixtures thereof from ALD chambers without venting/opening up the chamber. An effective chemical dry cleaning method will significantly increase the productivity and lower the cost-of-ownership (CoO) of ALD reactors.  
           [0013]    All references cited herein are incorporated herein by reference in their entireties.  
         BRIEF SUMMARY OF THE INVENTION  
         [0014]    Accordingly, the invention provides a process for removing a substance from a substrate, said process comprising:  
           [0015]    providing the substrate, wherein: (a) the substrate is at least partially coated with a film of the substance; (b) the substance is at least one member selected from the group consisting of a transition metal oxide, a transition metal silicate, a Group 13 metal oxide and a Group 13 metal silicate; and (c) the substance has a dielectric constant greater than that of silicon dioxide;  
           [0016]    reacting the substance with a reactive gas to form a volatile product, wherein the reactive gas comprises chlorine; and  
           [0017]    removing the volatile product from the substrate to thereby remove the substance from the substrate,  
           [0018]    provided that when the substance is Al 2 O 3  and the substrate is a semiconductor from which the substance is being selectively etched, the process is conducted in the absence of a plasma having a density greater than 10 11  cm −3 .  
           [0019]    Further provided is a process for removing a substance from a substrate, said process comprising:  
           [0020]    providing the substrate, wherein: (a) the substrate is at least partially coated with a film of the substance; (b) the substance is at least one member selected from the group consisting of a transition metal oxide and a transition metal silicate; and (c) the substance has a dielectric constant greater than that of silicon dioxide;  
           [0021]    reacting the substance with a reactive gas to form a volatile product, wherein the reactive gas comprises chlorine; and  
           [0022]    removing the volatile product from the substrate to thereby remove the substance from the substrate.  
           [0023]    Still further provided is a process for cleaning a substance from a reactor surface, said process comprising:  
           [0024]    providing a reactor containing the reactor surface, wherein: (a) the reactor surface is at least partially coated with a film of the substance; (b) the substance is at least one member selected from the group consisting of a transition metal oxide, a transition metal silicate, a Group 13 metal oxide and a Group 13 metal silicate; and (c) the substance has a dielectric constant greater than that of silicon dioxide;  
           [0025]    reacting the substance with a reactive gas to form a volatile product, wherein the reactive gas comprises chlorine; and  
           [0026]    removing the volatile product from the reactor to thereby remove the substance from the substrate.  
       
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS  
       [0027]    The invention will be described in conjunction with FIG. 1, which shows a schematic view of an apparatus for performing a process of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]    The inventive process is useful for dry-etching high-k materials and dry-cleaning chemical vapor deposition (CVD) chambers (and more specifically, ALD chambers) used to deposit high-k materials onto wafer surfaces. The material to be removed from the surface being etched or cleaned is converted from a solid non-volatile material into species that have higher volatility than the high-k materials and, are subsequently removed by reactor vacuum pumps. Thus, in preferred embodiments, the invention removes a substance from a substrate using a reactive gas to volatilize the substance. Unlike wet-etching and wet-cleaning processes, dry-etching and dry-cleaning processes do not immerse the substrate in or expose the substrate to liquid chemical solutions.  
         [0029]    The substance to be removed is a transition metal oxide, a transition metal silicate, a Group 13 metal oxide or a Group 13 metal silicate (in accordance with the IUPAC Nomenclature of Inorganic Chemistry, Recommendations 1990, Group 13 metals include Al, Ga, In and TI, and the transition metals occupy Groups 3-12). The substance is a high-k material having a dielectric constant greater than that of silicon dioxide (i.e., greater than about 4.42), more preferably greater than 5, even more preferably at least 7. Preferably, the substance is at least one member selected from the group consisting of Al 2 O 3 , HfO 2 , ZrO 2 , HfSi x O y , ZrSi x O y , and mixtures thereof. Those skilled in the art will appreciate that the formula HfSi x O y  (and the formula ZrSi x O y ) represents a mixture of HfO 2  (ZrO 2 ) and SiO 2 , where x is greater than 0 and y is 2×+2.  
         [0030]    Since the chlorides of these metals (such as AlCl 3 , HfCl 4 , ZrCl 4 , and SiCl 4 ) are more volatile, it is preferred to convert these high-k substances into chlorides. This conversion is accomplished by contacting the substance to be removed with a reactive gas containing chlorine. Preferred examples of chlorine-containing reactive gases include BCl 3 , COCl 2 , HCl, Cl 2 , ClF 3 , and NF x Cl 3−x , where x is 0 to 2, and chlorocarbons and chlorohydrocarbons (such as C x H y C z  where x=1-6, y=0-13, and z=1-14). Chlorine-containing reactive gases that also contain oxygen-getter functions, such as Bl 3,  COCl 2 , and chlorocarbons and chlorohydrocarbons (such as C x H y Cl z  where x=1-6, y=0-13, and z=1-14) are more preferred because the oxygen-getter component (B, CO, C, or H) in these molecules extracts oxygen from the high-k materials and hence enhances the conversion of metal oxides and metal silicates into metal chlorides. Among the chlorine-containing and oxygen-getter gases, BCl 3  is the most preferred one. In embodiments employing COCl 2  as the reactive gas it can be provided in prepared form or formed by an in situ reaction of CO and Cl 2 . In embodiments for removing metal silicates, the reactive gas can comprise a chlorine-containing gas and a fluorine-containing gas (e.g., BCl 3  and BF 3 ), or a gas containing both fluorine and chlorine such as ClF 3 , and NF x Cl 3−x , where x is 0 to 2. The reactive gases can be delivered by a variety of means, such as conventional cylinders, safe delivery systems, vacuum delivery systems, solid or liquid-based generators that create the reactive gas at the point of use.  
         [0031]    In addition to the reactive gases described here, inert diluent gases such as nitrogen, CO2, helium, neon, argon, krypton, and xenon etc. can also be added. Inert diluent gases can modify the plasma characteristics and cleaning processes to better suit some specific applications. The concentration of the inert gases can be 0-99%.  
         [0032]    The process of the invention is useful for etching semiconductors and cleaning deposition chambers for semiconductor manufacturing. Thus, suitable substrates for the etching embodiments of the invention include, e.g., semiconductor wafers and the like, while suitable substrates for the cleaning embodiments of the invention include, e.g., surfaces of deposition chambers for CVD and/or ALD.  
         [0033]    Thermal or plasma activation and/or enhancement can significantly impact the efficacy of chloro-compound-based etching and cleaning of high-k materials. For thermal activation, the substrate can be heated up to 600° C., more preferably up to 400° C., and even more preferably up to 300° C. The pressure range is generally 10 mTorr to 760 Torr, more preferably 1 Torr to 760 Torr.  
         [0034]    For in situ plasma activation, one can generate the plasma with a 13.56 MHz RF power supply, with RF power density at least 0.2 W/cm 2 , more preferably at least 0.5 W/cm 2 , even more preferably at least 1 W/cm 2 . One can also operate the in situ plasma at RF frequencies lower than 13.56 MHz to enhance ion assisted cleaning of grounded ALD chamber walls. The operating pressure is generally in the range of 2.5 mTorr to 100 Torr, more preferably 5 mTorr to 50 Torr, even more preferably 10 mTorr to 20 Torr. Optionally, one can also combine thermal and plasma enhancement for more effective cleaning of ALD chamber walls.  
         [0035]    One can also use remote plasma source to replace in situ plasma to generate more reactive species. The remote plasma source can be generated by either an RF or a microwave source. In addition, reactions between remote plasma generated reactive species and high-k materials can be activated/enhanced by heating ALD reactor components to elevated temperatures up to 600° C., more preferably up to 400° C., and even more preferably up to 300° C.  
         [0036]    Other means of activation and enhancement to the cleaning processes can also be employed. For example, one can use photon induced chemical reactions to generate reactive species and enhance the etching/cleaning reactions.  
         [0037]    The following tables show thermochemical calculations for preferred reactions for volatilizing the substance to be removed from the substrate. In these tables, K eq  represents the equilibrium constant for the reaction as written; so that the larger this value is, the more favorable the reaction will be to proceed.  
                                                           TABLE 1                           Al 2 O 3  reaction with BCl 3 : Al 2 O 3  + 2BCl 3 (g)           B 2 O 3  + 2AlCl 3 (g)            Temperature (° C.)   ΔH (Kcal)   ΔS (Cal)   ΔG (Kcal)   K eq                      0.000   9.561   12.274   6.208   1.078E−005       100.000   9.547   12.249   4.976   1.217E−003       200.000   9.424   11.959   3.766   1.822E−002       300.000   9.299   11.719   2.582   1.036E−001       400.000   9.196   11.553   1.419   3.461E−001       500.000   15.123   19.739   −0.138   1.094E+000       600.000   15.476   20.169   −2.135   3.422E+000       700.000   15.748   20.464   −4.167   8.629E+000       800.000   15.951   20.664   −6.224   1.852E+001       900.000   16.097   20.794   −8.298   3.515E+001       1000.000   16.190   20.871   −10.381   6.056E+001                  
 
         [0038]    [0038]                                                           TABLE 2                           HfO 2  reaction with BCl 3 : 1.5HfO 2  + 2BCl 3 (g)           1.5HfCl 4 (g) + B 2 O 3              Temperature (° C.)   ΔH (Kcal)   ΔS (Cal)   ΔG (Kcal)   K eq                      0.000   −17.999   −12.638   −14.547   4.367E+011       25.000   −18.003   −12.653   −14.231   2.707E+010       50.000   −18.025   −12.721   −13.914   2.576E+009       75.000   −18.057   −12.817   −13.595   3.426E+008       100.000   −18.096   −12.924   −13.273   5.950E+007       125.000   −18.138   −13.034   −12.948   1.283E+007       150.000   −18.182   −13.141   −12.621   3.305E+006       175.000   −18.226   −13.242   −12.291   9.879E+005       200.000   −18.268   −13.335   −11.959   3.346E+005                    
         [0039]    [0039]                                                           TABLE 3                           ZrO 2  reaction with BCl 3 : 1.5ZrO 2  + 2BCl 3 (g)           1.5ZrCl 4 (g) + B 2 O 3              Temperature (° C.)   ΔH (Kcal)   ΔS (Cal)   ΔG (Kcal)   K eq                      0.000   −29.845   −12.107   −26.538   1.717E+021       25.000   −29.825   −12.038   −26.236   1.710E+019       50.000   −29.822   −12.026   −25.935   3.481E+017       75.000   −29.828   −12.047   −25.634   1.239E+016       100.000   −29.842   −12.083   −25.333   6.891E+014       125.000   −29.858   −12.126   −25.030   5.502E+013       150.000   −29.875   −12.168   −24.726   5.913E+012       175.000   −29.892   −12.207   −24.422   8.142E+011       200.000   −29.908   −12.240   −24.116   1.381E+011                    
         [0040]    [0040]                                                           TABLE 4                           HfO 2  reaction with COCl 2 : HfO 2  + 2COCl 2 (g)           HfCl 4 (g) + 2CO 2 (g)            Temperature (° C.)   ΔH (Kcal)   ΔS (Cal)   ΔG (Kcal)   K eq                      0.000   −20.643   41.960   −32.105   4.890E+025       25.000   −20.649   41.940   −33.153   2.014E+024       50.000   −20.668   41.878   −34.201   1.357E+023       75.000   −20.699   41.787   −35.247   1.343E+022       100.000   −20.739   41.677   −36.290   1.806E+021       125.000   −20.786   41.554   −37.331   3.112E+020       150.000   −20.840   41.423   −38.368   6.578E+019       175.000   −20.900   41.285   −39.402   1.647E+019       200.000   −20.965   41.144   −40.432   4.757E+018                    
         [0041]    [0041]                                                           TABLE 5                           ZrO 2  reaction with COCl 2 : ZrO 2  + 2COCl 2 (g)           ZrCl 4 (g) + 2CO 2 (g)            Temperature (° C.)   ΔH (Kcal)   ΔS (Cal)   ΔG (Kcal)   K eq                      0.000   −28.540   42.313   −40.098   1.218E+032       25.000   −28.530   42.350   −41.157   1.483E+030       50.000   −28.533   42.341   −42.215   3.573E+028       75.000   −28.547   42.300   −43.273   1.469E+027       100.000   −28.569   42.238   −44.330   9.244E+025       125.000   −28.599   42.160   −45.385   8.215E+024       150.000   −28.636   42.071   −46.438   9.694E+023       175.000   −28.678   41.975   −47.489   1.448E+023       200.000   −28.724   41.873   −48.537   2.638E+022                    
         [0042]    [0042]                                                           TABLE 6                           ZrSiO 4  reaction with BCl 3 :       ZrSiO 4  + 2.667BCl 3 (g)           ZrCl 4 (g) + 1.333B 2 O 3              Temperature (° C.)   ΔH (Kcal)   ΔS (Cal)   ΔG (Kcal)   K eq                      0.000   −31.065   −21.096   −25.303   1.764E+020       25.000   −31.003   −20.879   −24.778   1.460E+018       50.000   −30.962   −20.747   −24.258   2.554E+016       75.000   −30.935   −20.665   −23.740   8.020E+014       100.000   −30.916   −20.613   −23.224   4.013E+013       125.000   −30.902   −20.577   −22.710   2.928E+012       150.000   −30.891   −20.549   −22.196   2.914E+011       175.000   −30.879   −20.523   −21.682   3.755E+010       200.000   −30.867   −20.496   −21.169   6.012E+009       225.000   −30.852   −20.466   −20.657   1.158E+009       250.000   −30.835   −20.432   −20.146   2.612E+008       275.000   −30.814   −20.393   −19.636   6.754E+007       300.000   −30.790   −20.349   −19.127   1.967E+007       325.000   −30.761   −20.300   −18.618   6.358E+006       350.000   −30.729   −20.247   −18.112   2.252E+006       375.000   −30.692   −20.190   −17.606   8.652E+005       400.000   −30.652   −20.130   −17.102   3.572E+005       425.000   −30.608   −20.066   −16.600   1.573E+005       450.000   −22.891   −9.391   −16.100   7.349E+004       475.000   −22.663   −9.081   −15.869   4.327E+004       500.000   −22.443   −8.791   −15.646   2.649E+004                    
         [0043]    [0043]                                                           TABLE 7                           ZrSiO 4  reaction with BF 3  and BCl 3 :       ZrSiO 4  + 1.333BF 3 (g) + 1.333BCl 3 (g)           SiF 4 (g) + ZrCl 4 (g) + 1.333B 2 O 3              Temperature (° C.)   ΔH (Kcal)   ΔS (Cal)   ΔG (Kcal)   K eq                      0.000   −25.010   −21.014   −19.270   2.627E+015       25.000   −24.951   −20.807   −18.748   5.540E+013       50.000   −24.912   −20.681   −18.229   2.136E+012       75.000   −24.885   −20.600   −17.713   1.319E+011       100.000   −24.865   −20.545   −17.199   1.186E+010       125.000   −24.849   −20.502   −16.686   1.445E+009       150.000   −24.833   −20.463   −16.174   2.260E+008       175.000   −24.816   −20.423   −15.663   4.354E+007       200.000   −24.796   −20.380   −15.153   9.992E+006       225.000   −24.772   −20.332   −14.644   2.661E+006       250.000   −24.745   −20.278   −14.136   8.053E+005       275.000   −24.712   −20.218   −13.630   2.721E+005       300.000   −24.675   −20.152   −13.125   1.012E+005       325.000   −24.633   −20.080   −12.622   4.095E+004       350.000   −24.586   −20.003   −12.121   1.784E+004       375.000   −24.535   −19.922   −11.622   8.303E+003       400.000   −24.478   −19.837   −11.125   4.095E+003       425.000   −24.418   −19.749   −10.630   2.128E+003       450.000   −16.684   −9.050   −10.139   1.160E+003       475.000   −16.439   −8.717   −9.917   7.894E+002       500.000   −16.201   −8.405   −9.703   5.535E+002                    
         [0044]    Tables 1-7 show that BCl 3  and COCl 2  can be used as the etchants for dry etching and cleaning of the high-k materials. BCl 3  (boron trichloride) is a liquefied gas at room temperature and can be readily delivered into ALD reactors for chamber cleaning. COCl 2  (phosgene) is preferably provided in situ in etch or deposition reactors by reacting carbon monoxide and chlorine to form phosgene assisted by an external energy source (e.g. plasma):  
         CO (g)+Cl 2  (g)→COCl 2    
         [0045]    The above thermochemical calculations are illustrations of limiting cases for those chemical reactions. In addition to the limiting case reaction products such as B 2 O 3 , intermediate reaction products such as boron oxychloride (BOCl) can also be formed in reactions between high-k materials and BCl 3 . Intermediate reaction products such as BOCl have higher volatility, thus may further enhance the removal of high-k materials.  
         [0046]    In addition to being thermodynamically favorable, a chemical reaction often requires external energy source to overcome an activation energy barrier so that the reaction can proceed. The external energy source can be either from thermal heating or plasma activation. Higher temperature can accelerate chemical reactions, and make reaction byproducts more volatile. However, there may be practical limitations on temperature in production deposition chambers. Plasmas can generate more reactive species to facilitate reactions. Ions in the plasmas are accelerated by the electric field in the plasma sheath to gain energy. Energetic ions impinging upon surfaces can provide the energy needed to overcome reaction activation energy barrier. Ion bombardment also helps to volatize and removes reaction byproducts. These are common mechanisms in plasma etching/cleaning and reactive ion etching. Optionally, one can combine both thermal and plasma activation mechanisms to enhance the desired reactions for dry etching/cleaning of high-k materials. As an alternative to in situ plasma cleaning, one can use remote plasma source to generate more reactive species for cleaning high-k material residues from the deposition chambers. In addition, reactions between remote plasma generated reactive species and high-k materials can be activated/enhanced by heating CVD or ALD reactor components to elevated temperatures up to 600° C., more preferably up to 400° C., and even more preferably up to 300° C.  
       EXAMPLES  
       [0047]    The invention will be illustrated in more detail with reference to the following Examples, but it should be understood that the present invention is not deemed to be limited thereto.  
         [0048]    The following are experimental examples of utilizing the above chemistries for dry etching/cleaning of high-k materials. All the experiments were done in a parallel plate capacitively coupled RF plasma reactor. FIG. 1 is a schematic of the setup. Sample coupons were prepared from wafers coated with high-k dielectric materials Al 2 O 3 , HfO 2 , and ZrO 2  deposited by atomic layer deposition. For each experimental run, a sample coupon was put onto a carrier wafer and loaded onto the reactor chuck through a loadlock. Process gases were fed into the reactor from a top mounted showerhead. The chuck was then powered by a 13.56 MHz RF power source to generate the plasma. The thickness of the high-k film on a coupon was measured by ellipsometry both before and after a timed exposure of the processing plasma. Change in high-k film thickness after plasma processing is used to calculate the etch rate. In addition to etch rate, plasma dc self bias voltage (V dc ) was also measured. In all of the examples here, both the wafer and the chamber walls were kept at room temperature.  
       Example 1  
       [0049]    Etching/Cleaning of Al 2 O 3  Samples  
         [0050]    Since power is one of the key processing parameters in plasma etching/cleaning, we evaluated power dependence of Al 2 O 3  etching by BCl 3  plasma. The results are listed in Table 8 below.  
                                                           TABLE 8                           RF power dependence of Al 2 O 3  etching by BCl 3  plasma                Power density   Pressure   Al 2 O 3  etch rate           Power (W)   (W/cm 2 )   (mTorr)   (nm/min)   V dc  (V)                    50   0.27   500   0.0   −16       100   0.55   500   3.0   −35       200   1.10   500   9.8   −58                  
 
         [0051]    Apparently there is threshold power density of 0.55 W/cm 2  or threshold V dc  of −35 V for etching Al 2 O 3 . Higher power density and higher V dc  resulted in higher etch rate.  
         [0052]    Next, we investigated chamber pressure dependence of Al 2 O 3  etching by BCl 3  plasma. The results are listed in Table 9 below.  
                                                           TABLE 9                           Chamber pressure dependence of Al 2 O 3  etching by BCl 3  plasma                Power density   Pressure   Al 2 O 3  etch rate           Power (W)   (W/cm 2 )   (mTorr)   (nm/min)   V dc  (V)                    100   0.55   50   7.2   −91       100   0.55   500   3.0   −35       100   0.55   1000   0.8   −4                  
 
         [0053]    Higher etch rate was achieved at reduced pressure. There are two factors favor the etch reactions at reduced pressure. First, higher V dc  at lower pressure leads to more energetic ion bombardment to help the etch reactions to overcome activation energy barrier. Second, lower pressure leads to faster desorption and diffusion of reaction byproducts. Higher V dc  also enhances physical sputtering by energetic ions. To delineate the contributions from reactive ion etching and physical sputtering, we conducted comparison runs using pure argon plasma. The results are listed in Table 10 below.  
                                                           TABLE 10                           Argon plasma etching of Al 2 O 3                  Power density   Pressure   Al 2 O 3  etch rate           Power (W)   (W/cm 2 )   (mTorr)   (nm/min)   V dc  (V)                    200   1.10   5   0.6   −173       200   1.10   50   1.0   −189       200   1.10   500   −0.4   −185                  
 
         [0054]    The data showed that pure argon plasma essentially did not etch Al 2 O 3  even with very high power and much higher V dc  than that of BCl 3  plasmas. This clarifies that physical sputtering is not the primary mechanism to etch Al 2 O 3 . Instead, ion bombardment enhanced chemical etching, or reactive ion etching (RIE) is the primary mechanism.  
         [0055]    Tables 8 and 9 showed that higher power and lower pressure can increase V dc , which in turn enhances chemical etching of high-k materials. Once can also operate the RF plasma at lower frequencies. Ions transiting through a plasma sheath often exhibit bi-modal energy distribution at lower frequencies. Bimodal ion energy distribution results in a large fraction of the ions impinging onto reactor surfaces. This can be an effective strategy to enhance plasma cleaning of high-k deposition residues from grounded ALD chamber surfaces. At a fixed RF excitation frequency (such as 13.56 MHz), the data in Tables 8 and 9 shows that higher power and lower pressure can increase V dc , which in turn enhances chemical etching of high-k materials. Lower pressure and higher power is particularly effective to enhance plasma etching of substrates coated with high-k films. For ALD chamber cleaning, one must balance the requirements between RF powered reactor components and ground reactor components (such as chamber walls). We chose chamber pressure of 500 mTorr for other examples illustrated here.  
       Example 2  
       [0056]    Etching/Cleaning of HfO 2  Samples  
         [0057]    At 500 mTorr pressure, etching of HfO 2  was achieved at all power levels between 50 and 200 W. The results are listed in Table 11 below.  
                                                           TABLE 11                           BCl 3  plasma etching of HfO 2                  Power density   Pressure   HfO 2  etch rate           Power (W)   (W/cm 2 )   (mTorr)   (nm/min)   V dc  (V)                    50   0.27   500   1.6   −14       50   0.27   500   1.4   −16       100   0.55   500   4.7   −34       200   1.10   500   14.7   −63                  
 
       Example 3  
       [0058]    Etching/Cleaning of ZrO 2  Samples  
         [0059]    Several experiments were conducted with ZrO 2  samples. The results are listed in Table 12 below.  
                                                           TABLE 12                           BCl 3  plasma etching of HfO 2                  Power density   Pressure   ZrO 2  etch rate           Power (W)   (W/cm 2 )   (mTorr)   (nm/min)   V dc  (V)                    50   0.27   500   0.3   −16       100   0.55   500   −3.8*   −32       100   0.55   500   −2.5*   −45       200   1.10   500   7.1   −65                          
 
         [0060]    While the invention has been described in detail and with reference to specific examples thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.