Atomic layer deposition of metal carbide films using aluminum hydrocarbon compounds

Abstract

Methods of forming metal carbide films are provided. In some embodiments, a substrate is exposed to alternating pulses of a transition metal species and an aluminum hydrocarbon compound, such as TMA, DMAH, or TEA. The aluminum hydrocarbon compound is selected to achieve the desired properties of the metal carbide film, such as aluminum concentration, resistivity, adhesion and oxidation resistance. In some embodiments, the methods are used to form a metal carbide layer that determines the work function of a control gate in a flash memory.

1 . An atomic layer deposition process for forming a metal carbide thin film on a substrate in a reaction space, comprising:
 alternately and sequentially contacting the substrate with vapor phase pulses of a first metal precursor and a first aluminum hydrocarbon compound, such that a metal carbide film comprising from about  6  to about  16 % aluminum is formed.   
   
   
       2 . The method of  claim 1 , wherein alternately and sequentially contacting the substrate with vapor phase pulses of a metal precursor and an aluminum hydrocarbon compound comprises a thermal ALD cycle comprising:
 providing the first metal precursor to the reaction space;   removing excess metal compound and reaction byproducts;   providing the first aluminum hydrocarbon compound to the reaction space; and   removing excess aluminum hydrocarbon compound and reaction byproducts from the reaction space.   
   
   
       3 . The method of  claim 2 , further comprising a plasma ALD cycle comprising providing a plasma-excited species to the reaction space. 
   
   
       4 . The method of  claim 3 , wherein the plasma excited species comprises hydrogen radicals. 
   
   
       5 . The method of  claim 3 , wherein the thermal ALD cycle and plasma ALD cycle are performed in a ratio of about 5:1 to about 1:5. 
   
   
       6 . The method of  claim 1 , wherein the metal precursor is a metal halide. 
   
   
       7 . The method of  claim 6 , wherein the metal halide is a tantalum halide. 
   
   
       8 . The method of  claim 7 , wherein the metal halide is TaCl 5 . 
   
   
       9 . The method of  claim 1 , wherein the aluminum hydrocarbon compound is selected from the group consisting of alkanes, alkenes and alkynes. 
   
   
       10 . The method of  claim 9 , wherein the aluminum hydrocarbon compound is selected from the group consisting of trimethyl aluminum (TMA), triethyl aluminum (TEA), and dimethylaluminumhydride (DMAH). 
   
   
       11 . The method of  claim 2 , further comprising a second thermal ALD cycle comprising providing a second aluminum hydrocarbon compound to the reaction space, wherein the second aluminum hydrocarbon compound is different from the first aluminum hydrocarbon. 
   
   
       12 . The method of  claim 10 , wherein the thermal ALD cycle and second ALD cycle are performed in a ratio of about 5:1 to about 1:5. 
   
   
       13 . The method of  claim 1 , wherein the metal carbide is tantalum carbide. 
   
   
       14 . The method of  claim 1 , wherein the metal carbide is deposited to a thickness of about 1 to about 1000 Å. 
   
   
       15 . The method of  claim 14 , wherein the metal carbide is deposited to a thickness of about 100 to about 200 Å. 
   
   
       16 . The method of  claim 1 , wherein the atomic layer deposition process is carried out at a temperature of about 150° to about 550° C. 
   
   
       17 . The method of  claim 16 , wherein the atomic layer deposition process is carried out at a temperature of about 350° to about 400° C. 
   
   
       18 . The method of  claim 1 , wherein the atomic layer deposition process is carried out at a pressure of about 2 to 5 Torr. 
   
   
       19 . The method of  claim 1 , wherein the metal carbide thin film serves as a control gate in a flash memory. 
   
   
       20 . The method of  claim 19 , wherein the work function of the control gate is determined by the metal carbide. 
   
   
       21 . The method of  claim 1 , wherein the metal carbide thin film serves as a gate metal for a gate electrode in a CMOS transistor. 
   
   
       22 . The method of  claim 21 , wherein the metal carbide thin film sets the work function of the gate electrode. 
   
   
       23 . The method of  claim 1 , further comprising annealing the thin film at a substrate temperature greater than 500° C. 
   
   
       24 . A control gate in a flash memory structure comprising a tantalum carbide layer, wherein the tantalum carbide layer comprises aluminum and wherein the work function of the control gate is determined by the work function of the tantalum carbide layer. 
   
   
       25 . The flash memory structure of  claim 24 , wherein the tantalum carbide layer comprises from about 6 to about 16% aluminum. 
   
   
       26 . The flash memory structure of  claim 24 , wherein the tantalum carbide layer is from about 25 to about 200 Å thick. 
   
   
       27 . A method for forming a flash memory on a substrate comprising:
 forming a dielectric layer on the substrate;   forming a charge trap layer directly over and adjacent to the dielectric layer;   forming a barrier oxide directly over and adjacent to the charge trap layer:   forming a metal carbide control gate over the barrier oxide;   etching the dielectric layer, charge trap layer, barrier oxide and control gate to form a flash structure; and   passivating the flash structure by depositing SiO 2 ,   wherein the metal carbide control gate comprises aluminum and during the deposition of SiO 2  the aluminum in the metal carbide reacts with oxygen to self-passivate the control gate.   
   
   
       28 . The method of  claim 27 , wherein the metal carbide comprises from about 6 to about 16% aluminum. 
   
   
       29 . The method of  claim 27 , wherein the metal carbide control gate is from about 25 to about 200 Å thick. 
   
   
       30 . The method of  claim 27 , wherein the metal carbide control gate is formed by an atomic layer deposition process comprising alternately and sequentially contacting the substrate with a vapor phase pulse of a metal halide and an aluminum hydrocarbon compound. 
   
   
       31 . The method of  claim 27 , wherein the aluminum hydrocarbon compound is selected from the group consisting of trimethyl aluminum (TMA), triethyl aluminum (TEA), and dimethylaluminumhydride (DMAH). 
   
   
       32 . The method of  claim 27 , wherein the metal halide is a tantalum halide. 
   
   
       33 . The method of  claim 27 , wherein the tantalum halide is TaCl 5 . 
   
   
       34 . A method of forming a metal carbide thin film with a desired level of oxidation resistance comprising:
 depositing a metal carbide thin film by alternately and sequentially contacting a substrate with vapor phase pulses of a metal precursor and an aluminum hydrocarbon compound, wherein one or more reaction conditions are selected to produce a desired concentration of aluminum in the metal carbide thin film, and wherein the concentration of aluminum in the metal carbide is from about 1 to about 30%.   
   
   
       35 . The method of  claim 34 , wherein the metal carbide thin film comprises from about 6 to about 16% aluminum. 
   
   
       36 . The method of  claim 34 , wherein the one or more reaction conditions are selected from the nature of the aluminum hydrocarbon compound, the reaction temperature, the reaction pressure, the pulse time of the metal precursor, the pulse time of the aluminum hydrocarbon compound, use of a reactant comprising plasma, the pulsing sequence and post deposition annealing. 
   
   
       37 . The method of  claim 34 , wherein the metal precursor is a metal halide. 
   
   
       38 . The method of  claim 34 , wherein the aluminum hydrocarbon compound is selected from the group consisting of alkanes, alkenes and alkynes. 
   
   
       39 . The method of  claim 38 , wherein the aluminum hydrocarbon compound is selected from the group consisting of trimethyl aluminum (TMA), triethyl aluminum (TEA), and dimethylaluminumhydride (DMAH). 
   
   
       40 . The method of  claim 39 , wherein multiple aluminum hydrocarbon compounds are used. 
   
   
       41 . The method of  claim 39 , wherein the ratio between the multiple aluminum hydrocarbon compounds is selected to produce a desired concentration of aluminum in the metal carbide thin film. 
   
   
       42 . The method of  claim 34 , wherein the metal carbide is tantalum carbide. 
   
   
       43 . The method of  claim 34 , wherein the metal carbide is deposited to a thickness of about 1 to about 1000 Å. 
   
   
       44 . The method of  claim 34 , wherein the metal carbide thin film serves as a control gate in a flash memory. 
   
   
       45 . The method of  claim 44 , wherein the work function of the control gate is determined by the metal carbide. 
   
   
       46 . The method of  claim 34 , wherein the atomic layer deposition process is carried out at a pressure of about 0.5 to 10 Torr. 
   
   
       47 . The method of  claim 34 , wherein the atomic layer deposition process is carried out at a temperature of about 150° to about 550° C.