Multiple source deposition process

Abstract

A method for the deposition of a thin film of a pre-determined composition e.g. a phosphor, onto a substrate, in which the composition is a ternary, quaternary or higher composition, especially a composition selected from the group consisting of thioaluminates, thiogallates and thioindates of at least one element from Groups IIA and IIB of the Periodic Table. In the embodiment, the method comprises placing a pellet of at least one sulphide on a first source and placing a pellet of at least one sulphide on a second source, with one pellet containing dopant. Vapour deposition onto the substrate is effected with separate electron beams. The rate of vaporizing of the sulphides is monitored with separate shielded coating rate monitors. The temperature of the sources is controlled to obtain the composition on the substrate. The method is particularly used for deposition of ternary or quaternary phosphors on substantially opaque substrates in electroluminescent devices.

1 . A method for the deposition of a thin film of a pre-determined composition onto a substrate, said composition comprising a ternary, quaternary or higher composition, comprising the steps of: 
 (i) placing a pellet of at least one sulphide on a first source and placing a pellet of at least one sulphide on a second source, the sulphides on the first and second sources being different, said sulphides being the components of said composition, at least one of the pellets on the first and second sources additionally containing dopant for the composition;    (ii) effecting vapour deposition of said composition on said substrate by simultaneously vaporizing the pellets on the first and second sources with separate electron beams; and    (iii) monitoring the rate of vaporizing of sulphide from the first source with a first coating rate monitor and monitoring the rate of vaporizing of sulphide from the second source with a second coating rate monitor, said first coating rate monitor being shielded from deposition of sulphide from the second source and said second coating rate monitor being shielded from deposition of sulphide from the first source.    
     
     
         2 . The method of  claim 1  in which, in step (ii), the temperature of said first and second sources is controlled.  
     
     
         3 . The method of  claim 2  in which, in step (iii), the temperature of each of the first and second coating rate monitors is monitored and controlled.  
     
     
         4 . The method of  claim 1  in which the composition is a thin film phosphor.  
     
     
         5 . The method of  claim 3  in which said composition is selected from the group consisting of ternary, quaternary and higher compositions of at least one cation from Groups IIA and IIB of the Periodic Table.  
     
     
         6 . The method of  claim 1  in which said composition is selected from the group consisting of thioaluminates, thiogallates and thioindates of at least one cation from Groups IIA and IIB of the Periodic Table.  
     
     
         7 . The method of  claim 3  in which, in step (i), sulphide is located at a third source, said third source having a coating rate monitor that is screened from the first and second sources, said rate of coating from the third source being monitored and controlled.  
     
     
         8 . The method of  claim 3  in which, in step (i), the dopant is located at a third source, said third source having a coating rate monitor screened from the first and second sources, said rate of coating from the third source being monitored and controlled.  
     
     
         9 . The method of  claim 6  in which said substrate is opaque in the visible and infrared regions of the electromagnetic spectrum.  
     
     
         10 . The method of  claim 6  in which the composition is a ternary composition.  
     
     
         11 . The method of  claim 6  in which the composition is a quaternary composition.  
     
     
         12 . The method of  claim 3  in which, in step (iii), vapour deposition is carried out in an atmosphere of H 2 S.  
     
     
         13 . The method of  claim 6  in which said composition is of the formula Ba a Ca 1-a Al 2 S 4 :Eu, where “a” is the range of 0 to 1.  
     
     
         14 . The method of  claim 13  in which the composition is CaAl 2 S 4 :Eu.  
     
     
         15 . The method of  claim 6  in which the cation is selected from the group consisting of barium, calcium, strontium, magnesium, zinc and cadmium, and mixtures thereof.  
     
     
         16 . The method of  claim 3  in which the substrate temperature is monitored.  
     
     
         17 . The method of  claim 4  in which the composition deposited on the substrate is a single crystal phase.  
     
     
         18 . The method of  claim 4  in which the composition deposited on the substrate is more than one crystal phase.  
     
     
         19 . A composition deposited on a substrate, said composition comprising a thioaluminate, thiogallate or thioindate of at least one cation selected from Groups IIA and IIB of the Periodic Table, said composition having been formed by the method of  claim 1 .  
     
     
         20 . The composition of  claim 19  in which the composition is of the formula Ba a Ca 1-a Al 2 S 4 :Eu, where “a” is the range of 0 to 1.  
     
     
         21 . The composition of  claim 20  in which the composition is CaAl 2 S 4 :Eu.  
     
     
         22 . The composition of  claim 19  in which the composition is an alkaline earth thioaluminate.  
     
     
         23 . The composition of  claim 19  in which the cation is selected from the group consisting of barium, calcium, strontium, magnesium, zinc and cadmium, and mixtures thereof.  
     
     
         24 . A method for the deposition of a thin film of a pre-determined composition onto a substrate, said composition comprising a ternary, quaternary or higher composition, comprising the steps of: 
 (i) placing a first deposit at a first source of a vapour deposition apparatus and placing a second deposit at a second source of the vapour deposition apparatus, said first and second deposits being different, components of said first and second deposits in combination forming said pre-determined composition;    (ii) determining temporal variation of deposition of said components onto said substrate from said first and second sources; and    (iii) using said temporal variation for controlling said first and second sources so as to obtain homogeneous temporal deposition of said composition on the substrate by simultaneous vapour deposition from said sources.    
     
     
         25 . The method of  claim 24  in which said temporal variation is obtained by monitoring the rate of vaporizing from the first source with a first coating rate monitor and monitoring the rate of vaporizing from the second source with a second coating rate monitor, said first coating rate monitor being shielded from deposition from the second source and said second coating rate monitor being shielded from deposition from the first source.  
     
     
         26 . The method of  claim 25  in which said monitoring is used as the determining of temporal deposition of step (ii).  
     
     
         27 . The method of  claim 26  in which said monitoring of step (ii) is used in step (iii).  
     
     
         28 . The method of  claim 24  in which said composition is a thin film phosphor.  
     
     
         29 . The method of  claim 28  in which said composition is selected from the group consisting of thioaluminates, thiogallates and thioindates of at least one cation from Groups IIA and IIB of the Periodic Table.  
     
     
         30 . The method of  claim 24  in which the composition is a dielectric thin film.  
     
     
         31 . The method of  claim 30  in which there is the additional step of depositing a phosphor juxtaposed to said dielectric thin film.  
     
     
         32 . The method of  claim 24  in which the first and second deposits are sulphides.  
     
     
         33 . The method of  claim 24  in which a third deposit is placed at a third source, components of said third deposit forming part of said composition.  
     
     
         34 . The method of  claim 24  in which said substrate is opaque in the visible and infrared regions of the electromagnetic spectrum.  
     
     
         35 . The method of  claim 24  in which said composition is of the formula Ba a Ca 1-a Al 2 S 4 :Eu, where “a” is the range of 0 to 1.  
     
     
         36 . The method of  claim 24  in which the cation is selected from the group consisting of barium, calcium, strontium, magnesium, zinc and cadmium, and mixtures thereof.  
     
     
         37 . The method of  claim 24  in which vapour deposition is by sputtering.  
     
     
         38 . The method of  claim 37  in which the composition is a thin film.  
     
     
         39 . The method of  claim 24  in which vapour deposition is by electron beam.  
     
     
         40 . The method of  claim 39  in which temperature of said first and second sources is controlled.  
     
     
         41 . The method of  claim 24  in which vapour deposition is by thermal evaporation.  
     
     
         42 . The method of  claim 41  in which temperature of said first and second sources is controlled.  
     
     
         43 . The method of  claim 39  in which said composition is of the formula Ba a Ca 1-a Al 2 S 4 :Eu, where “a” is the range of 0 to 1.  
     
     
         44 . The method of  claim 39  in which the composition is CaAl 2 S 4 :Eu.