Volatile Imidazoles and Group 2 Imidazole Based Metal Precursors

Abstract

Sterically hindered imidazolate ligands are described, along with their synthesis, which are capable of coordinating to Group 2 metals, such as: calcium, magnesium, strontium, in an eta-5 coordination mode which permits the formation of monomeric or dimeric volatile complexes. A compound comprising one or more polysubstituted imidazolate anions coordinated to a metal selected from the group consisting of barium, strontium, magnesium, radium or calcium or mixtures thereof. Alternatively, one anion can be substituted with and a second non-imidazolate anion. Synthesis of the novel compounds and their use to form BST films is also contemplated

1 . A method of depositing a metal containing film comprising reacting an imidazolate structure selected from the group consisting of: 
       
         
           
           
               
               
           
         
       
       wherein
 R 1 , R 2 , R 3  and are each individually bulky groups selected from the group consisting of: C 1 -C 10  tertiary alkyl; C 1 -C 10  tertiary alkoxy; C 1 -C 10  tertiary alkylamine; C 1 -C 10  tertiary alkyl functionalized with a heteroatom substituted ring structure; C 1 -C 10  tertiary alkyl functionalized with an amide group; C 1 -C 10  tertiary alkyl functionalized with an ester group, and mixtures thereof; 
 (L) is a neutral ligand selected from the group consisting of aliphatic C 3 -C 20  ether or polyether, crown ether, amine, poly amine, amide, poly amide, ester, polyester, aromatic ether, aromatic ester, aromatic amide, aromatic amine, pyridine, imidazole, pyridine, pyrazine, furan, pyrrole, and mixtures thereof; 
 n=0-4; and 
 M=Ba, Sr, Ca, Ra, Mg, or mixtures thereof, 
 
       with an oxidant selected from the group consisting of water, alcohol, oxygen, ozone, nitrous oxide, nitrogen dioxide, hydrogen peroxide, or combinations thereof either in the presence or absence of an applied plasma discharge to grow a metal-containing film selected from the group consisting of barium oxide, strontium oxide, magnesium oxide, calcium oxide or radium oxide and mixtures thereof, using a reactor pressure between 0.001-1000 Torr and a temperature from 0-1000° C. 
     
     
         2 . The method of  claim 1  wherein the metal-containing film is barium oxide grown at a rate of >1 Angstrom per cycle. 
     
     
         3 . The method of  claim 2  where the rate >1.5 Angstrom per cycle. 
     
     
         4 . The method of  claim 3  where the rate is >2 Angstrom per cycle. 
     
     
         5 . The method of  claim 1  where the metal-containing film is strontium oxide grown at a rate of >1 Angstrom per cycle. 
     
     
         6 . The method of  claim 5  where the rate is >1.5 Angstrom per cycle. 
     
     
         7 . The method of  claim 6  where the rate is >2 Angstrom per cycle. 
     
     
         8 . The method of  claim 1  wherein the compound is selected from the group consisting of: Di-barium tetra(2,4,5-tris-t-butylimidazolate); Di-barium tetra(2-tert-butyl-4,5-di-(1,1-dimethylpropyl)imidazolate); Di-barium tetra(2-(1,1-dimethylbutyl)-4,5-di-tert-butylimidazolate); and Di-barium tetra(2-(1,1-dimethylbutyl)-4,5-di-(1,1-dimethylpropyl)imidazolate). 
     
     
         9 . The method of  claim 1  wherein the compound is selected from the group consisting of: Di-strontium tetra(2,4,5-tris-t-butylimidazolate); Di-strontium tetra(2-tert-butyl-4,5-di-(1,1-dimethylpropyl)imidazolate); Di-strontium tetra(2-(1,1-dimethylbutyl)-4,5-di-tert-butylimidazolate); and, Di-strontium tetra(2-(1,1-dimethylbutyl)-4,5-di-(1,1-dimethylpropyl)imidazolate). 
     
     
         10 . The method of  claim 1  wherein R 1 , R 2 , and R 3  of each imidazolate anion are the same bulky group. 
     
     
         11 . The method of  claim 1  wherein at least one of R 1 , R 2 , and R 3  of one imidazolate anion is joined to at least one of the R 1 , R 2 , and R 3  of another imidazolate anion to connect the two imidazolate anions. 
     
     
         12 . A method of forming a barium strontium titanium film, a strontium titanium film, or a barium titanium film, comprising reacting an imidazolate structure selected from the group consisting of: 
       
         
           
           
               
               
           
         
       
       wherein
 R 1 , R 2 , R 3  and are each individually bulky groups selected from the group consisting of: C 1 -C 10  tertiary alkyl; C 1 -C 10  tertiary alkoxy; C 1 -C 10  tertiary alkylamine; C 1 -C 10  tertiary alkyl functionalized with a heteroatom substituted ring structure; C 1 -C 10  tertiary alkyl functionalized with an amide group; C 1 -C 10  tertiary alkyl functionalized with an ester group, and mixtures thereof; 
 (L) is a neutral ligand selected from the group consisting of aliphatic C 3 -C 20  ether or polyether, crown ether, amine, poly amine, amide, poly amide, ester, polyester, aromatic ether, aromatic ester, aromatic amide, aromatic amine, pyridine, imidazole, pyridine, pyrazine, furan, pyrrole, and mixtures thereof; 
 n=0-4; and 
 M=Ba, Sr or mixtures thereof, 
 
       with alternating pulses of titanium precursors selected from the group consisting of titanium alkoxide, titanium alkoxide/diketonate, titanium cyclopentadienyl, titanium amide, titanium imidazolate and mixtures thereof in an ALD or pulsed CVD mode to grow the barium strontium titanium film.