Repair of open stencil masks for ion projection lithography by E-beam induced metal deposition

For repairing clear defects on lithography masks of the open stencil type, physical holes have to be filled with absorber material. The deposition, therefore, has to start on an existing structure, followed by a lateral growth into the open gap. For this purpose, E-beam induced deposition from a W(CO)6 gas has been used as the repair technique. In order to minimize the repair time, a two step procedure is introduced. Each step has specific requirements which must be optimized separately. The speed of the first step, the bridge forming step, depends mainly on the available gas flux. Here, a lateral growth speed of 28 nm/s is obtained. During the second step, the absorber is reinforced to the required thickness. The deposited bars were characterized by their performance in ion projection lithography. They satisfy the requirements for contrast and stability against ion sputtering during pattern transfer. No microcharging caused by the deposits was observed. A resolution of 100 nm in PMMA was obtained by a 10:1 ion reduction exposure.