Angelika Bruns

A study of catalytically transformed negative X-ray resists, based on aqueous base developable resin, an acid generator and a crosslinker

Abstract Negative working X-ray resists, based on phenolic resin, an acid generator and a crosslinker are described. First the sensitivities of various activators are compared by using a proton scavenger, that produces a colour upon protonation. Although diphenyliodonium hexafluorophosphate and chlorinated triazine derivatives appear to be the most sensitive ones, the difference with naphthoquinone diazides and CBr4 is not very pronounced. Subsequently it is shown that those activators that produce strong acids can induce acid catalyzed condensation reactions in resist films that consist of a phenolic resin and polyfunctional alkylating agents. As only very small amounts of acid are needed to render the phenolic resin insoluble in aqueous base developer, a very high sensitivity can be reached. Preliminary results with some experimental resists show a sensitivity of 20 mJ/cm2.

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.

X-ray mask technology: precise etching of sub-half-micron tungsten absorber features

Abstract A RIE technique for the fabrication of sub-0.5 μm W absorber patterns has been developed based on a SF 6 /CH 3 /Ar gas system. Upon extensive optimization of particularly CHF 3 content and bias voltage precise pattern with vertical profiles can be etched in 0.8 μm thick W layers on top of a rigid SiC-membrane. Features down to 0.2 μm dimensions have been fabricated with a linewidth homogenity of less than 50 nm. Due to proximity corrected e-beam writing and almost stress free W layers, a pattern placement accuracy of better than 100 nm (3σ) has been obtained for different absorber coverages (Step field 25x25 mm 2 ).

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.