Multi-station sequential curing of dielectric films

Abstract

The present invention addresses provides improved methods of preparing a low-k dielectric material on a substrate. The methods involve multiple operation ultraviolet curing processes in which UV intensity, wafer substrate temperature and other conditions may be independently modulated in each operation. In certain embodiments, a film containing a structure former and a porogen is exposed to UV radiation in a first operation to facilitate removal of the porogen and create a porous dielectric film. In a second operation, the film is exposed to UV radiation to increase cross-linking within the porous film. In certain embodiments, the curing takes place in a multi-station UV chamber wherein UV intensity and substrate temperature may be independently controlled at each station.

1 . A method of processing a semiconductor wafer, the method comprising:
 performing a plurality of exposure operations providing wafer exposure characteristics on a wafer, wherein:   at least two of the exposure operations differ with respect to at least one of the wafer exposure characteristics selected from the group consisting of: radiation intensity, radiation wavelength, and wafer support temperature,   each exposure operation of the plurality of exposure operations is performed in a common processing chamber, and   at least two of the exposure operations are performed in different stations of the common processing chamber.   
     
     
         2 . The method of  claim 1 , wherein the plurality of exposure operations is two operations. 
     
     
         3 . The method of  claim 2 , wherein the common processing chamber comprises 3 or more stations and two or more of the stations are used to provide wafer exposure characteristics that are the same. 
     
     
         4 . The method of  claim 3 , wherein light sources used to provide the exposure operations at each of the two or more stations providing wafer exposure characteristics that are the same are oriented at different relative orientations with respect to the wafer. 
     
     
         5 . The method of  claim 4 , wherein the common processing chamber comprises 4 or more stations and two or more of the stations are used to provide wafer exposure characteristics that are the same. 
     
     
         6 . The method of  claim 5 , wherein light sources used to provide the exposure operations at each of the two or more stations providing wafer exposure characteristics that are the same are oriented at different relative orientations with respect to the wafer. 
     
     
         7 . The method of  claim 1 , wherein a first exposure operation of the plurality of exposure operations is to evolve a gaseous by-product from a dielectric film and a second exposure operation of the plurality of exposure operations is to increase cross-linking in the film to harden the dielectric film. 
     
     
         8 . The method of  claim 7 , wherein a porous ULK film on the wafer is subjected to the plurality of exposure operations to remove porogens and to increase cross-linking. 
     
     
         9 . The method of  claim 7 , wherein a spin-on ULK film on the wafer is subjected to the plurality of exposure operations to evolve solvent and to increase cross-linking. 
     
     
         10 . The method of  claim 1 , wherein a nitride film on the wafer is subjected to the plurality of exposure operations to increase tensile stress. 
     
     
         11 . The method of  claim 1 , further comprising depositing a dielectric film on the wafer. 
     
     
         12 . The method of  claim 1 , wherein:
 a first exposure operation of the plurality of exposure operations is to ultraviolet (UV) radiation and the wafer exposure characteristics of the first exposure operation are selected to cause porogens in the wafer to be removed,   a second exposure operation of the plurality of exposure operations is to UV radiation and the wafer exposure characteristics of the second exposure operation are selected to increase cross-linking in the wafer, and   the second exposure operation is performed after the first exposure operation.   
     
     
         13 . The method of  claim 12 , wherein:
 the wafer temperature during the first exposure operation is held at between approximately 250° C. and 450° C.,   the wafer temperature during the second exposure operation is held at approximately 400° C. or greater, and   the wafer temperature during the second exposure operation is maintained at a higher temperature than the wafer temperature during the first exposure operation.   
     
     
         14 . The method of  claim 12 , wherein the radiation intensity during the first exposure operation is held to approximately 50% to 90% of the radiation intensity of the second exposure operation. 
     
     
         15 . The method of  claim 12 , wherein:
 the radiation wavelength and the radiation intensity during the first exposure operation are biased towards one or more absorption wavelength peaks of the porogens, and   the radiation wavelength and the radiation intensity during the second exposure operation are biased towards one or more absorption wavelength peaks of the wafer.   
     
     
         16 . The method of  claim 15 , wherein the first exposure operation is performed in an inert environment. 
     
     
         17 . The method of  claim 12 , wherein:
 the first exposure operation is performed while flowing oxygen gas into the station where the first exposure operation is performed and the radiation wavelength and radiation intensity during the first exposure operation are tuned for activating the oxygen, and   the radiation wavelength and radiation intensity during the second exposure operation are biased towards one or more absorption wavelength peaks of the wafer.   
     
     
         18 . The method of  claim 1 , wherein:
 a first exposure operation of the plurality of exposure operations has a radiation intensity of zero and non-zero wafer support temperature,   a second exposure operation of the plurality of exposure operations is to ultraviolet radiation and the wafer exposure characteristics of the second exposure operation are selected to increase cross-linking in the wafer, and   the second exposure operation is performed after the first exposure operation.   
     
     
         19 . The method of  claim 18 , wherein:
 the first exposure operation has a wafer support temperature between approximately 300° C. and 450° C.