Fast and large-field electron-beam exposure by CSEL

We have developed a Crestec Surface Electron emission Lithography (CSEL) for mass production of semiconductor devices. CSEL system is 1:1 electron projection lithography using surface electron emitter. In first report, we confirmed that a test bench of CSEL resolved below 30 nm pattern over 0.2 um square area. Practical resolution of the system is limited by the chromatic aberration. We improved the resolution of the prototype CSEL system by reducing the initial energy spread of electrons and/or by increasing the electric field intensity. An energy spread of emitted electrons of a nanosilicon planar ballistic electron emitter (PBE) is very small. After that, the prototype CSEL system exposed sub-micron patterns distributed over 3 mm square area in last report. In this study, we examine the prototype CSEL system exposed deep sub-micron pattern over full-field for practical use. The experimental column of the system is composed of the PBE and a stage as a collector electrode that is parallel to the electron source. An accelerating voltage of about -5 kV is applied to the electron source with respect to the collector. The target wafer and PBE are set between two magnets. The two magnets generate vertical magnetic field of 0.5 T to the surface of the target wafer. A gap between the electron source and the target wafer is adjusted to a focus length depending on electron trajectories in the electromagnetic field in the system. The electron source projects a patterned electron image on the target since the patterned mask was formed on the surface electrode of the electron source. The electrons are emitted from openings of the mask. When a pulsed bias voltage is applied to the electron source, the electron source emits a patterned surface electron beam. The beam strikes the resist film coated on the target wafer and make replica of the pattern. We indicate the system exposes line patterns of about 200 nm in width over large area. An advantage of CSEL is high resolution due to small chromatic aberration, and another advantage is potentially high throughput because the coulomb blur is small without any crossover in the electron optics. When we get sufficient current from the electron source the throughput can be more than 100 wafers/hour.