Development, installation, and performance of the x-ray stepper JSAL 5C^a)

We show the first results from a newly-operation advanced x-ray stepper, and describe an improved type of x-ray mask for use on it. The Mod 5C is the newest x-ray stepper developed by JMAR (JSAL Nanolithography). It is configured for installation at the Center for NanoTechnology (CNTech) on a synchrotron radiation port of the Aladdin storage ring. The alignment system is based on a new IBBI detection system with demonstrated subnanometer resolution. For this system, three microscopes are used for detecting the misalignment between wafer and mask marks with the error signal fed back in the mask positioning stage with the mask locked to the wafer stage through the use of a high-resolution laser interferometer. Both field-by-field and global alignment techniques are possible, and multiple wafer sizes can be used with a NIST format mask held in a kinematic mount, with a gap setting capable of adjustment between 2 and $50microns$⁠. A novel beam scanning system was installed to deliver a uniform exposure over a field of $35×35mm2$ field. The high power from the storage ring allows exposure times in chemically amplified resists of $5–10s$ for the CNTech-designed beamline; shorter exposure times could be achieved with a refocusing beamline, and the stepper can be configured for an x-ray point source. To achieve sub-$35nm$ resolution requires very small gaps. A new type of mask had to be developed, on the basis of the mesa mask originally developed at MIT. A very high flatness is required to maintain a parallel mask-wafer exposure environment. Currently, for low cost and easy manufacturing, we employ gold-plated absorber masks with a silicon nitride membrane. From the initial exposures, the resolution achieved is below $50nm$ with exposure conditions described. The issues of the resolution of the exposure tool are addressed and compared to the outcomes from detailed modeling.