Application of Refractory-Metal Oxides to Electron-Beam Lithography

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1. Selective masking effects of a WO_3 electron resist have been investigated on phosphorus and boron diffusion to silicon. Though the diffusion coefficient of phosphorus in the WO_3 layer is about twice as that in the SiO_2 layer, the WO_3 resist is useful as a masking film for phosphorus diffusion at elevated temperatures around 1000 C. 2. It was found that an etching rate of MoO_3 in alkaline solution after electron exposure depend on the deposition conditions such as the rf sputtering power and the pressure of Ar gas. The MoO_3 film of two layers, of which the upper layer is harder to dissolve in the alkaline solution than the lower layer, results in the under-cutting structure after chemical etching. This structure serves as a suitable mask for the formation of lift-off pattern of subsequently deposited layers. using the MoO_3 resist of this property, we have succeeded in fabricating a lift-off pattern of SiO_2. The above method is simple and applicable to other materials. 3. We also found that the rate of Ar sputter-etching of the MoO_3 layer is 1/5 of that of Au layer. Using the MoO_3 mask of this property, Au fine patterns can be delineated by the Ar sputter-etching. The resistance to the sputter-etching suggests that the MoO_3 and WO_3 films will be applicable as selective masks to ionimplantation and other dry-etching processes.