H. Löschner

Ion Beam Lithography

Abstract Ion beam lithography (IBL) is still in the hands of researchers. The immediate aim is to investigate the production of micro-circuits with 0.1 μm line spacings in commercial prototypes. However such instruments can also be used for mask repair. The present paper, intended as an introduction to the more specialised contributions to IBL in these Proceedings, concentrates on basic physical principles. While ion sources of different types are covered, particular attention is paid to liquid metal ion sources, in view of their popularity and potential for a variety of applications in focused ion beam technology.Apparatus and method for projection ion beam lithography are described which allow formation of low distortion, large field, reduced images of a mask pattern at a wafer plane using an optical column of practical size. The column shown is comprised of an accelerating Einzel lens followed by a gap lens, with numerous cooperating features. By coordinated selection of the parameters of the optical column, lens distortion and chromatic blurring are simultaneously minimized. Real time measurement of the position of the image field with respect to the existing pattern on the wafer is employed before and during the time of exposure of the new field and means are provided to match the new field to the existing pattern even when the latter has been distorted by processing. A metrology system enables convenient calibration and adjustment of the apparatus.

Reactive ion etching for microelectrical mechanical system fabrication

The suitability of reactive ion etching for the fabrication of microelectro mechanical systems (MEMS) has been evaluated by characterizing the change of lateral dimensions versus depth in etching deep structures in silicon. Fluorine, chlorine, and bromine containing gases have provided the basis for this investigation. A conventional planar RIE (reactive ion etching) reactor has been used, in some cases with magnetic field enhancement or an inductive coupled plasma source and low substrate temperature. For RIE based on Cl2 or Cl2/HBr plasma a slightly ‘‘positive’’ (top wider than bottom) slope is achieved when etching structures with a depth of several 10 μm, whereas a ‘‘negative’’ slope is obtained when etching with an SF6 /CCl2F2‐based plasma. A pattern transfer with vertical walls is obtained for RIE based on SF6 (with O2 added) when maintaining the substrate at low temperature (≊−70 °C). Further optimization of plasma chemistries and RIE procedures should result in runouts on the order of 0.1/100 μm d...

Ion projection lithography: International development program

Ion projection lithography (IPL) has demonstrated not only the resolution required for next-generation lithography (50 nm resolution at >4:1 aspect ratio) [Bruenger et al., Microelectron Eng. 46, 477 (1999)] but also cost advantages with respect to other competing technologies [Gross et al., J. Vac. Sci. Technol. B 16, 3150 (1998)]. This article reports on the progress of a worldwide development program, with the target to manufacture a process development tool and create the necessary mask infrastructure to demonstrate that IPL is a viable industrial lithography technology for the future. An overview of papers, reporting on the progress in critical areas, is given and new, experimentally validated, simulations of complementary mask stitching are shown for the first time. Longitudinal and lateral offsets of up to 32 nm for 100 nm critical dimensions are possible with linewidth variations less than 11 nm. Our concept for beta tools, based on a powerful new stitcher strategy, is described. This will lead to...

SOI wafer flow process for stencil mask fabrication

A high yield fabrication process for stencil mask using SOI material is presented. Membranes and masks from different base materials have been fabricated. The stress of the membrane, depending on the doping level, has been determined. Initial pattern displacement measurements have been performed.

Ion projection lithography machine IPLM‐01: A new tool for sub‐0.5‐micron modification of materials

An ion projection lithography machine uses ions as the information carrier in a demagnifying step‐and‐repeat exposure system. With an IPLM sub‐0.2‐micron resolution can be obtained combined with an extremely high depth of focus—more than 100 μm. The use of a reliable and stable duoplasmatron ion source with high brightness and high angular current density is significant for this machine. A preprojective lens octupole permits an electrostatic shift of the ion image in x and y directions, and a solenoid at this site enables a rotation of the ion image through the action of the axial magnetic field. Furthermore, the scale of the projected ion image can be adjusted electronically within ±3%. Thus fine adjustment for die‐by‐die alignment can be done without mechanical movements. An ion projection lithography machine IPLM‐01 with a total height of 2.5 m and a floor space of 2 m2 has been built. By inserting a mask consisting of a grid of pinholes an ion multibeam scanning tool (IMBS) is generated. Using demagni...

Ion Projection Lithography

In spite of the comparatively modest level of effort devoted to ion projection lithography, the results obtained so far indicate that the technology is highly promising. Accordingly, a

Directly sputtered stress-compensated carbon protective layer for silicon stencil masks

36M program has been launched in Europe to develop a full field, IPL process tool.

p-n junction-based wafer flow process for stencil mask fabrication

Silicon stencil masks for ion beam projection lithography have a protective layer stopping the ions and thus preventing a change in the Si membrane stress. This is needed to maintain extremely tight pattern placement specifications even when they are irradiated with high exposure doses. The fabrication of carbon protective layers by indirect sputter coating which are suitable for helium ion beam exposure has already been reported. This article describes a method of forming very low stress carbon protective layers based on direct radio frequency sputter coating with nitrogen added to the argon sputter gas and in situ thermal treatment using commercially available equipment. The carbon layers thus produced are stable in conventional environments. The article deals also with the physical characterization of carbon layers and the protection performances of these coatings under helium ion beam exposure using accelerated lifetime testing.

Ion projection lithography: Status of the MEDEA project and United States/European cooperation

The development of stencil masks is considered to be critical to the success of the new ion projection lithography technology. We present here a p-n junction wafer flow process where all fabrication steps are realized on a bulk Si wafer except the final trench etching through the 2–4-μm-thick Si membrane. Stencil masks were produced in a conventional complementary metal-oxide-semiconductor 150 mm wafer line, using an e-beam direct writing tool for patterning. The resist patterns were transferred by standard reactive ion etching (RIE) into a stress-controlled SiON hard mask layer. Subsequent to depositing an Al metal layer for contact to the n-doped wafer surface, the membrane was realized by a wet chemical etch which implemented well established reverse biased p-n junction etch stop techniques. Then, openings through the Si membrane were etched by RIE or inductively coupled plasma etching. Finally, the remaining hard mask layer was removed in BHF. The realized Si membrane diameter was 120 mm with a stenci...

Novel electrostatic column for ion projection lithography

Structure and targets of the European MEDEA project on ion projection lithography as well as related U.S./European cooperation are explained. By assuming 10 μm virtual source size and 1 eV (full width half maximum) energy spread calculations for a multielectrode electrostatic ion–optical system (1.25 m between ion source and stencil mask, ≈1.8 m between mask and wafer) we realize the possibility of 100 nm resolution (line and space) over an exposure field of 22×22 mm2 even when using the MONTEC model for calculating the stochastic blur and when running 3.3 μA He+ ion beam current through the ion–optical column, thus more than twice exceeding target specifications. Thus, for 100 nm resolution and 50% pattern density the raw throughput is ≈12 cm2/s corresponding to >75 WPH (pattern within 80% of 300 mm wafer area).