Method for forming thin film with a gas cluster ion beam

Abstract

A method of forming a thin film on the surface of a substrate such as silicon, in which a gas cluster (which is a massive atomic or molecular group of a reactive substance taking the gaseous form at room temperature under atmospheric pressure) is formed and then ionized, and the cluster ions are then irradiated onto a substrate surface under an acceleration voltage to cause a reaction. It is possible to form a high quality ultra-thin film having a very smooth interface, without causing any damage to the substrate, even at room temperature.

What is claimed is:  
     
         1 . A method for forming a thin film on the surface of a substrate with a gas cluster ion beam, which comprises the step of irradiating the surface of a substrate with ions of a gas cluster (which is a massive group of atoms or molecules of a reactive substance taking the gseous form at room temperature under atmospheric pressure) to cause a reaction with the surface of a substrate and thereby form a thin film on the substrate surface.  
     
     
         2 . A method as claimed in  claim 1 , wherein the said reactive substance is oxygen, an oxide, nitrogen, a nitride, a carbide, a sulfide, a halide, a hydride, an organo metallic compound, a mixture thereof or a mixture thereof with an inert gas.  
     
     
         3 . A method as claimed in  claim 1 , wherein the gas cluster ions are selected in terms of the number of component molecules.  
     
     
         4 . A method as claimed in  1 , wherein impurities present on the substrate are removed by the irradiation with the gas cluster ion beam, thereby forming a thin film with a low content of impurities.  
     
     
         5 . A method as claimed in  claim 1 , wherein the substrate surface is planarized (made flat) by the irradiation with the gas cluster ions, at the same time as the formation of the thisn film.  
     
     
         6 . A method as claimed in  claim 1 , wherein the thin film formed is an oxide.  
     
     
         7 . A method as claimed in  claim 1 , wherein the substrate is silicon.  
     
     
         8 . A method as claimed in  claim 1 , wherein the reactive substance is oxygen, an oxide of carbon, an oxide of nitrogen, a mixture thereof, or a mixture thereof with a rare (inert) gas, and the thin film formed is an oxide film.  
     
     
         9 . A method as claimed in  claim 1 , wherein the gas cluster is generated by supplying a pressurized gas to an expansion type nozzle cooled by a coolant.  
     
     
         10 . A method as claimed in  claim 1 , which includes the steps of 
 (i) forming a gas cluster from a substance which is reactive with the surface of the substrate and is a gas at room temperature and atmospheric pressure,    (ii) ionizing the gas cluster, and    (iii) irradiating the surface of the substrate with a beam of gas cluster ions.    
     
     
         11 . A method for generating gas cluster ions, which comprises the steps of generating a gas cluster with an expansion type nozzle cooled by a coolant and ionizing the resultant cluster.