Margret Harms

Improved tungsten absorber technology for sub-half-micron X-ray lithography

Abstract This paper reports on a novel absorber technology for X-ray stepper masks based on a stabilized tungsten layer. Effective stress reduction (σ⩽10 7 N/m 2 ) and excellent long term stability (Δσ 6 N/m 2 ) are being obtained by sputtering the 0.8 μm thick tungsten layers in the presence of oxygen, and subsequently annealing them in an oxidizing atmosphere. Investigations with respect to microstructure and composition indicate a highly textures W 3 O layer, having grain sizes in the order of 60 nm. For etching the W pattern a CF 4 based RIE process has been optimized. In this case a beam lithography in combination with a tri-level system (HPR/SiN/PM15) is being used. W pattern with sub-half micrometer dimensions have been etched with steep edges.

Status And Prospects Of Sic-Masks For Synchrotron Based X-Ray Lithography

This paper deals with the development of an X-ray stepper mask technology based on a rigid SiC.-membrane and a stress compensated W-absorber system. The SiC-mask blanks are being fabricated using batch processes like CVD-deposition and selective thin etching. As a result of extensive process optimization the polycristalline membranes can be fabricated with a smooth surface (< 40 nm) and a Youngs modulus as high as the bulk value (4.6*10 11 N/m 2). Membranes of 2.7 μm in thickness are being prepared routinely with excellent transparency for synchrotron and optical radiation. For a high X-ray absorption and low thermal expansion sputter deposited tungsten has been applied. Ihe proposed stress compensating technique enables absorber stresses of less than 1*107 N/m , resulting in a mask distortion of < 100 nm. Precise sub-0.5-micron pattern with steep profiles have been generated by use of e-beam lithography and RIE techniques. High doses SOR experiments indicate an excellent long-term stability of SiC-W-masks.

High contrast synchrotron X-ray lithography by means of silicon based masks and magnesium beam windows

Abstract This paper deals with the investigation of novel beam line windows based on magnesium in combination with silicon X-ray masks. Mg enables, because of the distinct absorption edge at 10A, an effective contrast enhancement in synchrotron lithography. In regard to BESSY radiation and PMMA resist the contrast of Si-masks can be increased more than sixfold by use of Mg-beam windows instead of silicon/kapton windows. In comparison to Be-beam windows the contrast can be threefold enhanced. The prospects of a one-to-one submicron mask technology based on a thin absorbing layer are being discussed in view of exposure experiments with only 0.3 μm thick Au patterns on Si-masks. It turned out that also by adjusting a reliable proximity distance of 30 μm between mask and wafer 0.1 μm features can be replicated in 1 μm thick resist. This offers the important possibility of copying Si master masks having very thin absorbing layers by means of synchrotron lithography after inspection and elimination of faults.