Sub-10-nm Si lines fabricated using shifted mask patterns controlled with electron beam lithography and KOH anisotropic etching

We developed a new method for Si nanofabrication that provides sub-10-nm resolution using electron beam lithography combined with KOH anisotropic etching of a Si(1(1) over bar0$) substrate. The method, called shifted mask pattern method, uses two shifted mask patterns to reduce the Si linewidth. The two shifted mask patterns delineated in the [11(2) over bar] direction are used as a KOH etching mask where the masks are shifted vertically to each other in the [11(2) over bar] direction. During KOH anisotropic etching, Si linewidth under the shifted part of the masks is reduced due to the etching's smoothing resulting from the low etching rate of the Si(111) plane. The linewidth can be controlled by changing the mask shift. An image reversal process using electron cyclotron resonance (ECR) plasma oxidation mas used to form a plasma oxide mask for KOH etching. This mask was obtained by ECR oxygen plasma irradiation using a ZEP520 resist mask pattern. Highly accurate position and linewidth control was achieved with a 70-kV electron beam nanolithography system that has a minimum deflection step of 3 nm. The variation of pattern position and linewidth was about 1 nm. Using this method, we have been able to fabricate lines as narrow as 2 nm.