| Method for making a semiconductor device having a high-k gate dielectric and a titanium carbide gate electrode -> Monitor Keywords |
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Method for making a semiconductor device having a high-k gate dielectric and a titanium carbide gate electrodeRelated Patent Categories: Semiconductor Device Manufacturing: Process, Coating With Electrically Or Thermally Conductive Material, To Form Ohmic Contact To Semiconductive Material, Contacting Multiple Semiconductive Regions (i.e., Interconnects), Multiple Metal Levels, Separated By Insulating Layer (i.e., Multiple Level Metallization), With Formation Of Opening (i.e., Viahole) In Insulative LayerMethod for making a semiconductor device having a high-k gate dielectric and a titanium carbide gate electrode description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060121727, Method for making a semiconductor device having a high-k gate dielectric and a titanium carbide gate electrode. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to methods for making semiconductor devices, in particular, those with titanium carbide containing gate electrodes or barrier layers. BACKGROUND OF THE INVENTION [0002] An MOS field-effect transistor may include a high-k gate dielectric and a metal gate electrode. The metal gate electrode may comprise a titanium carbide layer, which may be formed on the high-k gate dielectric using an atomic layer chemical vapor deposition ("ALCVD") process. Although an ALCVD process may be used to deposit such a layer on such a dielectric, it may be difficult to generate a titanium carbide layer with the desired thickness and workfunction using such a process. [0003] Accordingly, there is a need for an improved process for making a semiconductor device that includes a titanium carbide containing gate electrode or barrier layer. There is a need for an ALCVD process that may be tailored to produce a titanium carbide layer with the desired thickness and workfunction. The method of the present invention provides such a process. BRIEF DESCRIPTION OF THE DRAWINGS [0004] FIGS. 1a-1b represent cross-sections of structures that may be formed when carrying out an embodiment of the method of the present invention. [0005] FIGS. 2a-2i represent cross-sections of structures that may be formed when carrying out an embodiment of the method of the present invention to make a semiconductor device using a replacement metal gate process. [0006] Features shown in these figures are not intended to be drawn to scale. DETAILED DESCRIPTION OF THE PRESENT INVENTION [0007] A method for making a titanium carbide layer is described. That method comprises alternately introducing a carbon containing precursor and a titanium containing precursor at selected pulse times into a chemical vapor deposition reactor, while maintaining a substrate at a selected temperature. The reactor is operated for a sufficient time, and pulse times are selected for the carbon containing precursor and the titanium containing precursor, to form a titanium carbide layer of a desired thickness and workfunction on the substrate. [0008] In the following description, a number of details are set forth to provide a thorough understanding of the present invention. It will be apparent to those skilled in the art, however, that the invention may be practiced in many ways other than those expressly described here. The invention is thus not limited by the specific details disclosed below. [0009] FIGS. 1a-1b represent cross-sections of structures that may be formed when carrying out an embodiment of the method of the present invention. FIG. 1a represents substrate 100 upon which is formed high-k gate dielectric layer 101 and titanium carbide layer 102. Substrate 100 may comprise any material that may serve as a foundation upon which a semiconductor device may be built. Substrate 100 may, for example, comprise silicon and/or germanium. [0010] High-k gate dielectric layer 101 may comprise, for example, hafnium oxide, hafnium silicon oxide, lanthanum oxide, lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide, titanium oxide, tantalum oxide, barium strontium titanium oxide, barium titanium oxide, strontium titanium oxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, and lead zinc niobate. Particularly preferred are hafnium oxide, lanthanum oxide, zirconium oxide, and aluminum oxide. Although a few examples of materials that may be used to form high-k gate dielectric layer 101 are described here, that layer may be made from other materials that serve to reduce gate leakage. [0011] High-k gate dielectric layer 101 may be formed on substrate 100 using a conventional ALCVD process. In such a process, a metal oxide precursor (e.g., a metal chloride) and steam may be alternately fed at selected flow rates into a CVD reactor, which is operated at a selected pressure while substrate 100 is maintained at a selected temperature. The CVD reactor should be operated long enough to form a layer with the desired thickness. In most applications, dielectric layer 101 should be less than about 40 angstroms thick, and more preferably between about 5 angstroms and about 20 angstroms thick. [0012] In the method of the present invention, titanium carbide layer 102 is formed on high-k gate dielectric layer 101 by alternately introducing a carbon containing precursor and a titanium containing precursor into a CVD reactor, while substrate 100 is maintained at a selected temperature. Pulse times should be selected for the carbon containing precursor and the titanium containing precursor, and the reactor should be operated for a sufficient time, to generate a titanium carbide layer of a desired thickness and workfunction. [0013] The carbon containing precursor may comprise a metal alkyl or metalloid alkyl complex, such as trimethylaluminum ("TMA") or triethylboron. The titanium containing precursor may comprise a titanium halide, such as titanium tetrachloride ("TiCl.sub.4"). The pulse time for the carbon containing precursor for a given growth cycle, when introduced into the CVD reactor, may be less than about 1 second, on the order of 10 to 20 seconds, or somewhere in between--depending upon whether the desired titanium carbide layer will be a p-type, n-type, or mid-gap film. [0014] The pulse time for the titanium containing precursor should be sufficient to provide enough titanium to generate the desired titanium carbide layer. In many applications, a pulse time between about 2 and 3 seconds should be adequate. The substrate temperature preferably should be maintained at between about 100.degree. C. and about 700.degree. C. The optimum substrate temperature, like the optimum pulse time for the carbon containing precursor, may depend upon whether the desired titanium carbide layer will be a p-type, n-type, or mid-gap film. [0015] The method of the present invention may be tailored to produce titanium carbide layers with different thicknesses and workfunctions. For example, to form a p-type titanium carbide layer, the temperature of substrate 100 preferably should be maintained between about 100.degree. C. and about 250.degree. C. To form a p-type titanium carbide layer using a TMA precursor, that precursor preferably should be introduced into the reactor for a relatively short pulse time, e.g., a pulse time that is between about 0.5 seconds and about 1 second. As mentioned above, the titanium containing precursor (e.g., titanium tetrachloride) may have a pulse time that is between about 2 and 3 seconds. [0016] When titanium carbide layer 102 will set the workfunction for a PMOS gate electrode, titanium carbide layer 102 must be sufficiently thick to set the workfunction for the gate electrode. To form a sufficiently thick titanium carbide layer, a minimum number of growth cycles (each growth cycle comprising a TMA pulse followed by a purging gas pulse, and a TiCl.sub.4 pulse followed by a purging gas pulse) must be performed. After completing between about 20 and about 40 growth cycles using the operating conditions described above, a p-type titanium carbide layer that is between about 10 angstroms and about 20 angstroms thick, and that sets a workfunction that is between about 4.9 eV and about 5.2 eV, may result. [0017] If, alternatively, titanium carbide layer 102 should be an n-type layer, the temperature of substrate 100 preferably should be maintained above about 400.degree. C. (e.g., between about 400.degree. C. and about 700.degree. C.) when forming that layer. To form an n-type titanium carbide layer using a TMA precursor, that precursor preferably should be introduced into the reactor for a relatively long pulse time, e.g., a pulse time that is between about 10 seconds and about 20 seconds. In some embodiments, a single pulse of TMA per growth cycle may be preferred; whereas, in other embodiments, multiple pulses of TMA per growth cycle (e.g., four separate 5 second pulses per growth cycle instead of a single 20 second pulse per growth cycle) may be preferred. [0018] When forming an n-type titanium carbide layer using the method of the present invention, as when forming a p-type titanium carbide layer, the titanium containing precursor (e.g., titanium tetrachloride) may have a pulse time that is between about 2 and 3 seconds. One may form an n-type titanium carbide layer that is between about 50 angstroms and about 250 angstroms thick by completing between about 70 and about 250 growth cycles using these operating conditions. An n-type titanium carbide layer with that thickness may set a workfunction for an NMOS gate electrode that is between about 3.9 eV and about 4.3 eV. [0019] When forming a titanium carbide layer with a mid-gap workfunction using the method of the present invention, the temperature of substrate 100 preferably should be maintained between about 250.degree. C. and about 400.degree. C. To make such a mid-gap titanium carbide layer, the pulse time for the carbon containing precursor preferably lies between the pulse times that may be applied when making p-type or n-type titanium carbide layers. Similarly, the number of growth cycles that may be required to form a mid-gap titanium carbide layer of the desired thickness may lie between the number of growth cycles required to make p-type or n-type titanium carbide layers. [0020] FIG. 1b represents a semiconductor device that includes NMOS gate electrode 115 and PMOS gate electrode 120. NMOS gate electrode 115 comprises n-type titanium carbide layer 105. PMOS gate electrode 120 comprises p-type titanium carbide layer 110. N-type titanium carbide layer 105 and p-type titanium carbide layer 110 are each formed on high-k gate dielectric layer 101. Metal layer 121 is formed on n-type titanium carbide layer 105 and metal layer 118 is formed on p-type titanium carbide layer 110. Metal layers 121 and 118 may comprise, for example, titanium nitride. A replacement metal gate process, which may be used to form a structure like the one that FIG. 1b illustrates, is described in detail below. Continue reading about Method for making a semiconductor device having a high-k gate dielectric and a titanium carbide gate electrode... Full patent description for Method for making a semiconductor device having a high-k gate dielectric and a titanium carbide gate electrode Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method for making a semiconductor device having a high-k gate dielectric and a titanium carbide gate electrode patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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