Silicon-rich nickel-silicide ohmic contacts for SiC semiconductor devices

Abstract

A method of producing an ohmic contact and a resulting ohmic contact structure are disclosed. The method includes the steps of forming a deposited film of nickel and silicon on a silicon carbide surface at a temperature below which either element will react with silicon carbide and in respective proportions so that the atomic fraction of silicon in the deposited film is greater than the atomic fraction of nickel, and heating the deposited film of nickel and silicon to a temperature at which nickel-silicon compounds will form with an atomic fraction of silicon greater than the atomic fraction of nickel but below the temperature at which either element will react with silicon carbide. The method can further include the step of annealing the nickel-silicon compound to a temperature higher than the heating temperature for the deposited film, and within a region of the phase diagram at which free carbon does not exist.

1 . A method of producing an ohmic contact to silicon carbide comprising: 
 forming a deposited film of nickel and silicon on a silicon carbide surface at a temperature below which either element will react with silicon carbide and in respective proportions so that the atomic fraction of silicon in the deposited film is greater than the atomic fraction of nickel; and    heating the deposited film of nickel and silicon to a temperature at which nickel-silicon compounds will form with an atomic fraction of silicon greater than the atomic fraction of nickel but below the temperature at which either element will react with silicon carbide.    
   
   
       2 . A method according to  claim 1  comprising: 
 forming the deposited film with an atomic fraction of silicon that is greater than 0.50 and no more than about 0.67; and    heating the deposited film to form a nickel-silicon compound with an atomic fraction of silicon that is greater than 0.50 and no more than about 0.67.    
   
   
       3 . A method according to  claim 1  further comprising annealing the nickel-silicon compound to a temperature higher than the heating temperature for the deposited film, and within a region of the phase diagram at which free carbon does not exist.  
   
   
       4 . A method according to  claim 1  wherein the step of heating the deposited film comprises heating the deposit to form a compound having the formula Ni 1-x Si x  where 0.5<x<0.67:  
   
   
       5 . A method according to  claim 1  comprising heating the deposited film at a temperature of between about 200 and 500° C.  
   
   
       6 . A method according to  claim 3  comprising annealing the nickel-silicon compound to a temperature of between about 400 and 850° C.  
   
   
       7 . A method according to  claim 1  comprising doping the silicon carbide to a concentration of about 10 19  cm −3  prior to the step of depositing the nickel and the silicon.  
   
   
       8 . A method according to  claim 1  wherein the step of forming the deposited film comprises depositing a layer of nickel and a layer of silicon in respective proportional thicknesses to produce the greater atomic fraction of silicon in the deposited film.  
   
   
       9 . A method according to  claim 8  comprising depositing the nickel and silicon in a ratio of silicon layer thickness to nickel layer thickness of between about 1.81 and 3.65.  
   
   
       10 . A method according to  claim 1  wherein the step of forming the deposited film comprises depositing a plurality of nickel layers and a plurality of silicon layers in respective proportional thicknesses to produce the greater atomic fraction of silicon in the deposited film.  
   
   
       11 . A method according to  claim 10  comprising depositing the respective nickel and silicon layers in a ratio of total thickness of silicon to total thickness of nickel of between about 1.81 and 3.65.  
   
   
       12 . A method according to  claim 8  comprising depositing the silicon layer on the silicon carbide surface and thereafter depositing the nickel layer on the silicon layer.  
   
   
       13 . A method according to  claim 1  wherein the step of forming the deposited film comprises sputter depositing a nickel-silicon layer in the desired proportion of nickel and silicon on the silicon carbide surface.  
   
   
       14 . A method according to  claim 1  comprising forming the deposited film on a doped silicon carbide surface.  
   
   
       15 . A method according to  claim 1  comprising forming the deposited film on a silicon carbide surface selected from the group consisting of bulk single crystals of silicon carbide and epitaxial layers of silicon carbide.  
   
   
       16 . A method according to  claim 1  comprising forming the deposited film on a silicon carbide surface having a polytype selected from the group consisting of the  4 H and  6 H polytypes of silicon carbide.  
   
   
       17 . A deposited film of silicon and nickel comprising a layer of nickel and a layer of silicon on a silicon carbide surface in which the ratio of the silicon film thickness to the nickel film thickness is between about 1.81 and 3.65.  
   
   
       18 . A deposited film of silicon and nickel according to  claim 17  comprising a plurality of layers of silicon and a plurality of layers of nickel in which the ratio of the total thickness of the silicon film layers to the total thickness of the nickel film layers is between about 1.81 and 3.65.  
   
   
       19 . A deposited film of silicon and nickel according to  claim 17  comprising a doped silicon carbide surface.  
   
   
       20 . A deposited film of silicon and nickel according to  claim 17  wherein the silicon layer is on the silicon carbide surface and the nickel layer is on the silicon layer.  
   
   
       21 . A deposited film of silicon and nickel according to  claim 19  wherein the first layer on the silicon carbide surface is a layer of silicon.  
   
   
       22 . A deposited film of silicon and nickel according to  claim 17  wherein said silicon carbide surface comprises an epitaxial layer.  
   
   
       23 . A deposited film of silicon and nickel according to  claim 17  wherein said silicon carbide surface comprises a bulk single crystal.  
   
   
       24 . A deposited film of silicon and nickel according to  claim 17  wherein said silicon carbide has a polytype selected from the group consisting of the 4H and 6H polytypes of silicon carbide.  
   
   
       25 . A semiconductor structure comprising: 
 a layer of silicon carbide; and    a contact on said silicon carbide layer and demonstrating ohmic character, said contact being formed of a composition having the formula Ni 1-x Si x  where 0.5<x<0.67.    
   
   
       26 . A semiconductor structure according to  claim 25  wherein said contact has the formula Ni 0.48 Si 0.52    
   
   
       27 . A semiconductor structure according to  claim 25  wherein said silicon carbide has a polytype selected from the group consisting of the 4H and 6H polytypes of silicon carbide.  
   
   
       28 . A semiconductor structure according to  claim 25  wherein said silicon carbide comprises an epitaxial layer.  
   
   
       29 . A semiconductor structure according to  claim 25  wherein said silicon carbide surface comprises a bulk single crystal.  
   
   
       30 . A semiconductor structure according to  claim 25  wherein said silicon carbide is p-type.  
   
   
       31 . A semiconductor structure according to  claim 25  wherein said silicon carbide is n-type.  
   
   
       32 . A semiconductor structure according to  claim 25  having a resistivity of between about 10 −3  and 10 −5  ohm-cm 2 .  
   
   
       33 . A semiconductor structure according to  claim 25  having a resistivity of between about 10 −5  and 10 −7  ohm-cm 2 .  
   
   
       34 . A semiconductor device comprising: 
 a layer of silicon carbide;    a contact on said silicon carbide layer and demonstrating ohmic character, said contact being formed of a composition having the formula Ni 1-x Si x  where 0.5<x<0.67;    said ohmic contact having a resistivity of at least about 10 −4  ohm-cm 2 ; and    a metallization layer on said ohmic contact.    
   
   
       35 . A semiconductor device according to  claim 34  wherein said ohmic contact has a resistivity of between about 10 −5  and 10 −6  ohm-cm 2    
   
   
       36 . An ohmic contact on an n-type silicon carbide surface, said ohmic contact having the composition Ni 1-x Si x  where 0.5<x<0.67 and a specific contact resistance of between about 3×10 −6  and 4×10 −6  ohm-cm 2 .  
   
   
       37 . An ohmic contact according to  claim 36  having a specific contact resistance of about 3.4×10 −6  ohm-cm 2  with a standard deviation of 1.4×10 −7  and an R-squared fit to the TLM model of 0.99999.  
   
   
       38 . An ohmic contact on a p-type silicon carbide surface, said ohmic contact having the composition Ni 1-x Si x  where 0.5<x<0.67 and a specific contact resistance of between about 2×10 −3  and 3×10 −3  ohm-cm 2 .  
   
   
       39 . An ohmic contact according to  claim 38  having a specific contact resistance of about 2.4×10 −3  ohm-cm 2  with a standard deviation of 1.0×10 −4  and an R-squared fit to the TLM model of 0.99985