Ion Projector Research Articles

Evaluation of ion projection using heavy ions suitable for resistless patterning of thin magnetic films

The ion projector at the Fraunhofer Institute ISiT has been used for the development of patterned magnetic media for potential future use in magnetic hard disk drives. By 8.8 times demagnification of an open stencil mask, magnetic contrast is generated by ion intermixing of Co/Pt sandwich layers. In this application a resist process is not necessary and the surface roughness of magnetic media is not altered. Monte Carlo simulations of the intermixing process with the dynamic T-Dyn software for H, He, Ne, Ar and Au ions show that the exposure dose can be reduced by a factor of 100 by irradiation with Ar+ ions instead of He+. This has been confirmed by magnetic force microscopy of 200 nm magnetic dots irradiated at a dose of 6×1013 Ar+/cm2 at 73 keV energy. Sufficient stability of the ion optical system concerning resolution and drift has been demonstrated by exposures in developed and undeveloped (latent image) resist down to 60 nm dots.

White electroluminescent nanostructures in silicon fabricated using focused ion implantation

The use of an accelerator fed microbeam as an implanter enables highest flexibility in doping substrates. Dopant, implantation dose, and pattern can be chosen individually and adopted to sequentially implanted structures. On the other hand, high throughput of arbitrarily shaped and identically doped samples, as needed in semiconductor device fabrication, can be achieved in conjunction with the Bochum Ion Projector. This machine is capable of focusing an ion beam down to 300 nm and allows both, prototyping and small series production of devices without the need of a coating mask on the substrate surface. We report on a method for producing nanoscale white light emitting structures by focused ion beam implantation in crystalline silicon. Focused ion beam implantation of acceptor ions into n-type doped Si yields lateral npn-junctions. These junctions emit light from their nanoscale depletion zones if operated in (reverse biased) breakdown mode, depending on voltage polarity on either side of the implanted area. The actual ion beam diameter is not a limiting factor for the submicron width light sources because radiation originates only from depletion zones with lateral sizes in the order of 100 nm. Compatibility with standard silicon processing allows monolithic integration of such light sources in conventional circuit designs. Their emission spectrum covers the whole visible range without showing sharp peaks. However, three distinct maxima can be observed. Their positions and relative heights slightly vary with implantation dose and applied voltage.

Si-doped luminescence gratings

We report on the fabrication of ordered arrays of dots formed by Si implantation through a grid into SiO 2 using the Bochum high-energy ion projector. Arrays of Si-implanted dots with dimensions in the micrometer and submicrometer range have been made. The samples show a strong red photoluminescence at room temperature. By the combination of μ-photoluminescence measurements and atomic force microscopy investigations optical and structural characterization of the produced structures was possible. Additional investigations by high-resolution transmission electron microscopy, X-ray diffraction and temperature-dependent photoluminescence on conventionally implanted samples have been performed for comparison.

Resistless Patterning of Magnetic Storage Media Using Ion Projection Structuring

AbstractCo/Pt thin film multilayers with strong perpendicular anisotropy and out-of-plane coercivities of 5-11 kOe were magnetically altered in areas of local ion beam interaction. The ion irradiations were performed by ion projection through silicon stencil masks fabricated by silicon on insulator (SOI) membrane technology. The ion projector at the Fraunhofer Institute for Silicon Technology (ISiT) was operated at 73 keV ion energy and with a 8.7- fold demagnification. After exposure to 3 × 1014Ar+/ cm2 magnetic islands smaller than 100 nm in diameter were resolved in the Co/Pt multilayersby means of magnetic force microscopy. The impact of different ion species (He+, Ar+ and Xe+) and ion energies (10 – 200 keV) on the multilayer structure was evaluated using Monte Carlo simulations. The ballistic interface intermixing was used to predict magnetic coercivity changes for various irradiation conditions. The simulations revealed that with 73 keV Ar+ and Xe+ ions the irradiation dose could be reduced by a factor of 100 and 400 respectively in comparison to 73 keV He+which was verified in the experiments. X-ray reflectivity measurements confirmed that the Co/Pt superlattice structure is slightly weakened during the irradiation and that the surface smoothness of the media is preserved. Using the Ion Projection Process Development Tool (PDT) at IMS-Vienna concentric data tracks including head positioning servo informations were patterned onto a 1” IBM microdrive™ glass disk which was coated with Co/Pt multilayers. In a single exposure step several tracks within an exposure field of 17 mm in diameter were structured by 2 × 1015He+/ cm2 at 45 keV using a 4- fold demagnification set-up.

Ion projection lithography for resistless patterning of thin magnetic films

The ion projector at the Fraunhofer Institute in Berlin (manufactured by Ion Microfabrication Systems, IMS, Vienna) has been used to pattern thin magnetic films. Disordering of chemically ordered FePt films by patterned ion irradiation (dose: 10 16 He + ions/cm 2; 75 keV) without a resist mask on the sample is demonstrated. Magnetically altered areas have been investigated by magnetic force microscopy. Magnetic islands of 340 nm width could be detected, limited by the size of the open stencil mask holes. The projector is capable of 50 nm resolution which would result in a storage density of 64 Gb/in 2. In a second experiment the ion projector has been applied for structured ion milling with Xe + ions on thin metallic films also without a resist mask. In a polycrystalline Au film 130 nm lines and spaces with a depth of 8 nm could be produced by a dose of 10 15Xe +ions at 75 keV energy.

Synthesis of silicide structures by high energy ion projection

A new approach in ion beam synthesis of silicides is investigated. Using a heavy ion projector buried silicide structures were produced by high energy ion implantation in silicon. The ion projection allows to perform structured implantation with submicron lateral dimensions. Structured silicides as CoSi 2, Rh 3Si 4, CrSi 2 and MnSi 1.73 have been fabricated by hot implantation and subsequent annealing either by a furnace or rapid thermal annealing (RTA). RBS and spreading resistance measurements were performed to characterize the samples.

Status of Ion Projection Lithography

AbstractAs part of the European MEDEA project on Ion Projection Lithography (IPL), headed by Infineon Techologies, a process development tool (PDT) has been assembled at IMS, Vienna, with the final target of 50 nm resolution in a 12.5 mm exposure field at 4× demagnification. The ion-optical system (PDT-IOS) has been integrated, including the LEICA mask changer and a sophisticated metrology stage with in-situ diagnostics. In parallel, the LEICA wafer stage and the vacuum compatible off-axis ASML wafer alignment system have been realized. At the moment (Nov00) the He+ ion beam is aligned until the mask level. Ion beam proximity wafer exposures directly behind the mask show a performance of the illumination optics as predicted. 150 mm stencil masks with 125mm diameter, 3μm Si membranes, 50mm × 50mm design field, have been produced by IMS-Chips, Stuttgart. There is expectation to start the PDT-IOS test phase in Q1/01. Using the experimental ion projector at the Fraunhofer-Institute ISiT in Berlin recent resolution tests have demonstrated 50 nm lines and spaces without proximity effect in standard Shipley DUV resist UVIIHS at an exposure dose of 0.5 μC/cm2 for 75 keV He+ions. This was accomplished by 8.5 × demagnification of a new generation of stencil test masks from IMSChips. One further promising application of IPL is the resistless structuring of thin magnetic films to produce magnetic nano dots for future ≥ 100 G bit/in2 storage devices. A consortium of IBM Germany - Speichersysteme Mainz, Fraunhofer-ISiT, LEICA Jena and IMS-Chips in cooperation with IMS-Vienna has been formed to evaluate this technology.

Resolution improvement of ion projector with a low energy spread multicusp ion source

A new multicusp ion source developed by the Lawrence Berkeley Laboratory has been implemented into the ion projector of the Fraunhofer institute ISiT in Berlin. This source with low energy spread of ~ 2eV reduces chromatic aberration so that 50nm lines can be printed with an exposure dose of 0.3@mC/cm^2 of 75keV He^+ ions into standard 300nm thick DUV resist (Shipley UV II HS).

Stencil masks for high energy ion projection

A high energy ion projector under construction will allow mask controlled ion beam implantation at demagnification between 10× and 100×. For energetic ions the material of the mask must be chosen in view of the required values of the stopping power and heat conduction. Thermal expansion and sputter effects are to be minimised. In a first experiment a 16× reduced projection of a copper mask with 20 μm wide structures was realized. To improve the resolution to 250 nm on the target mask structures of 4μm are required.

Ion Projection Lithography for Nano Patterning

AbstractAs a result of continuous improvement of the resist process, the experimental ion projector in the Fraunhofer Institute in Berlin (manufactured by Ion Microfabrication Systems, IMS, Vienna) has been able to print 75 nm lines and spaces into 180 nm thick standard DUV resist UV II HS without pattern collapse. A new wafer flow process for more reliable open stencil mask making was developed by IMS –Chips, Stuttgart (Germany), based on SOT wafers. Resistless direct surface modification by He and Xe ions has been tested on metallic and magnetic films in the Berlin projector. This method opens up a new possibility for the production of patterned media for future magnetic storage disks.

DUV resist UV II HS applied to high resolution electron beam lithography and to masked ion beam proximity and reduction printing

The positive DUV-resist UV II HS from Shipley has been evaluated for 30keV e-beam and 75keV H + ion exposure. In the case of electrons the large area sensitivity of this chemically amplified resist was 5μC/cm 2. 100nm wide lines could be delineated into 1μm thick resist. Pattern transfer into SiO 2 was possible with an etch selectivity SiO 2/resist of > 5. In the case of H + ion exposure into UV II HS-0.6 resist the sensitivity was 0.15 μC/cm 2 which corresponds to 1×10 12 H + ions/cm 2. With 8.4 times demagnification of the mask, the ion projector in Berlin could expose 80nm wide features into 370nm thick resist with an exposure latitude of ±10%. The 1:1 ion beam proximity printer at IMS, Vienna delineated the smallest mask features (1μm) over a mask to wafer gap of 1mm with < 5nm pattern widening for ±10% overexposure.

High energy implantation by ion projection

A new type of ion projector is proposed to structurize a wafer at a resolution below 200 nm reducing the typically used lithography steps to a large extent. Basically, this technique aims to project a mask onto a wafer using an ion optical lens system allowing a demagnification up to 1:50 for ions with energies between 100 keV and some MeV. The center piece of this device is a single magnetic lens consisting of a superconducting solenoid. The achievable lateral resolution depends on lens errors, stability of the stencil mask and straggling of the implanted ions. A variation of the implantation energy would allow three dimensional structurization.

Chemically amplified deep ultraviolet resist for positive tone ion exposure

The positive tone deep ultraviolet resist UV II HS-0.6 (Shipley) has been evaluated for ion exposure in the ion projector at the Fraunhofer Institute in Berlin. The chemically amplified resist showed extremely high sensitivity of 1×1012 H+ ions/cm2 at an ion energy of 75 keV. The contrast number was 11. Smallest lines with 65 nm linewidth could be delineated in 140-nm-high resist. At higher resist thickness of 370 nm, lines down to 70 nm were stable showing aspect ratios of &amp;gt;4. The exposure latitude at 100 nm nominal linewidth was ±10% dose variation for a ±10% linewidth change.

Ion absorbing stencil mask coatings for ion beam lithography

The implantation of ions into the silicon membrane masks of ion beam lithography is known to create compressive stress which leads to very serious distortion after only a few tens of exposures. In this article, we describe a new, dimensionally stable, protective coating for silicon membranes which meets the exacting requirements of very large scale integrated manufacturing. The coating is formed by first depositing a low density, low stress graphitic carbon film which is subsequently amorphized by He+ ion bombardment with a dose of about 125 mC/cm2. We show that the stress of these bilayer membranes is stable to within experimental error (±1 MPa) for 20 keV He+ ion doses up to 0.53 C/cm2, corresponding to about 8.5 million exposures in a 4×-ion projector.

HPR 506 photoresist used as a positive tone ion resist

A positive tone photo resist HPR 506 (Olin Microelectronic Materials) has been investigated for its performance under ion exposure. Experiments have been conducted with light ions (H+ and He+) in the ion projector IPLM 02 (IMS; Vienna) at an energy of 75 keV. The resist resolution proved to be ∼180 nm which is not as good as the projector resolution of below 80 nm as demonstrated with Polymethylmetacrylate. The sensitivity of HPR 506 resist in positive tone amounts to 1.2×1013 H+ ions/cm2 and 6×1012 He+ ions/cm2 with contrast numbers of 3.3 and 3.2, respectively. The dose gap between positive and negative mode is sufficiently high (factor of 3) to guarantee a good process stability. The exposure latitude for He+ exposure has a value of 15 nm. The sensitivity does not oscillate with resist thickness like in optical lithography. These performance data confirm that HPR 506 resist can be used for mix and match exposure in ion projectors and i-line steppers.

Masked ion beam lithography for proximity printing

Optical and X-Ray proximity printing systems are resolution limited by diffraction and beam dispersion. Parallel dispersion free ion beam systems are therefore ideal to transfer stencil mask patterns onto all sorts of nonideal substrates. A feasibility study was performed with the existing Alpha ion projector of the Society for the Advancements of Microelectronics in Austria operated in the MIBL (Masked Ion Beam Lithography) mode with ≈ 10×10 mm2 exposure field. Structures as small as 0.2 μm in diameter could be transfered even with a gap of 1 mm between stencil mask and substrate. The widening of resist lines with 10% increase in dose was evaluated to be 14 nm for 2800 μm gap and 4 nm for 300 μm gap. This excellent exposure latitude favourably compares with synchrotron based X-ray lithography, where a widening of 20 nm with 10% overexposure has been reported for a 40 μm gap, and 10 nm for 10 μm gap. Promising applications of the MIBL technique include the fabrication of flat panel displays based on vacuum electronics (field emitter displays), surface acoustic wave and microoptic devices and - in combination with reactive ion etching - the fabrication of micro electro mechanical systems (MEMS). Prospects for MIBL steppers of printing fields > 100×100 mm2 are discussed.

Silicon stencil masks for masked ion beam lithography proximity printing

Silicon membranes with 2 μm to 6 μm thickness and ≈ 10×10 mm2 mask field have been fabricated with the help of electrochemical etch stop techniques. The Si foil was coated with 0.3 μm thick PECVD Si3N4. Shaped electron beam lithography was done in ARCH (OCG) positive resist. RIE etching into the nitride layer was done with CHF3/Ar/SF6. Silicon trench etching was based on Cl2/Ar/BCl3 plasma chemistry implementing gas chopping. Ion beam proximity printing of the Silicon stencil mask structures was done with 55 keV Helium ions into 0.4 μm thick AZ PN114 negative resist using the Alpha ion projector of the Society for the Advancements of Microelectronics in Austria in the MIBL (Masked Ion Beam Lithography) mode. Pattern transfer of a mask feature of less than 100 nm diameter (25:1 aspect ratio in the stencil mask) could be demonstrated even for a mask to wafer gap of 1 mm. The prospects of fabricating large area (> 100×100 mm2) Silicon stencil masks for MIBL printing of gate levels for FieldEmitterDisplays (FEDs) andMicro-Electro-Mechanical-Systems (MEMS) is discussed.

Experimental investigation of stochastic space charge effects on pattern resolution in ion projection lithography systems

Coulomb interactions in charged particle beams are known to blur beam profiles as the total current is increased. While this has been studied in single ion beam columns, similar studies have not been published, so far, for masked ion beam projection systems. Experiments were performed using highly transparent stencil grid masks of 40 mm×40 mm area with resolution test patterns in central and peripheral positions. Such grid test masks have been inserted into the ion projection lithography machine IPLM-02 and into the ‘‘Alpha ion projector’’ operated at 5× ion–optical reduction (Alpha-5×). A standard duoplasmatron ion source was used for both ion projectors. Operating the IPLM-02 at 8.7× demagnification with He+ ions of 73 keV ion energy at the wafer plane (about 50 keV at the crossover), no significant degradation in resolution was found changing the ion beam current through the column from 300 nA to 2 μA. Using the Alpha-5×, the total current through the column was changed either by varying the ion source emission or by blanking parts of the mask, using appropriate apertures. The special design of the Alpha ion projector with an ion energy of 5–7 keV at the crossover region between the imaging lenses is a sort of worst case scenario for space charge effects. Thus, the influence of stochastic space charge effects on resolution could be clearly identified. Using helium ions with 7 keV at the crossover the exposure latitude (change of linewidth in nm with 10% change of exposure dose) increased by 60 nm when changing the current through the column from 3 to 120 nA. Based on this experimental result with the Alpha ion projector and on well-known scaling laws, it can be stated that a newly designed ion projector (ALG-1000) with 200 keV ion energy at the crossover will allow sub-0.15-μm resolution for total ion beam currents through the column of 3 μA, as needed for future high volume production of dense patterns within ≥20 mm×20 mm exposure fields. Furthermore, improved designs of ion optical columns will allow a reduction of system length, thus reducing the influence of stochastic space charge effects. Consequently, ion projection lithography can be extended to the high volume fabrication of sub-0.10-μm feature patterns in large exposure fields.

Projection ion beam lithography

Demagnifying mask-to-wafer projection with ion beams is a potential lithographic technique for high volume device production with large process latitudes. Sub-0.1 μm resolution is possible with more than 10 μm depth of focus. Furthermore, there is the possibility of an electronic alignment on-line during chip exposure with nanometer precision: ‘‘pattern lock’’ may be achieved in feedback control loops by controlling X and Y position, rotation, scale, difference in X–Y scale and trapezoidal distortion of the projected ion image by dipole, quadrupole, and hexapole fields induced in an electrostatic multipole, by axial magnetic fields generated in a solenoid, and by the fine adjustment of lens voltages. Results obtained with an advanced research type ‘‘Alpha Ion Projector’’ are presented with the focus on recent exposure latitude evaluations. Further developments of ion projection lithography are discussed concentrating on electrostatic lens optics for the realization of large exposure fields (20×20 mm2–35×35 mm2) with less than 20 nm distortion. Results of a cost of ownership model for ion projection steppers are presented.

Ion projector distortion stability and wafer exposures under electronic alignment (“pattern lock”) conditions

Ion projector distortion stability and wafer exposures under electronic alignment (“pattern lock”) conditions