Ion Projection Lithography Research Articles

Characterization of silicon open stencil masks in an ion projection lithography machine

Silicon open stencil masks, realized in a 2 μm thick membrane, were investigated with respect to their stress quality, the resistivity against sputter erosion by ion impingement and their response to temperature variations. In a test pattern of an area 20 x 21 mm2 an average distortion of 0.15μm was obtained. The sputter erosion in a nitride top layer under the operating conditions of the projector was found to be 1.5 nm/h.

Silicon Membrane Mask Blanks for X-Ray and Ion Projection Lithography

In the subquarter-micron range, X-ray lithography and demagnifying ion projection are promising printing techniques. For both methods special designed masks are needed which have to fulfil strong requirements including flatness, stabiltiy, defect density, transparency, and surface properties. In this paper we would like to demonstrate that silicon membrane based mask blanks are well suited to meet most of these demands. Furthermore, silicon as membrane material offers the advantage to make use of the experience in semiconductor process technology. A fabrication sequence has been developed, based on silicon epitaxial growing, clean-room compatible wet etching and anodic bonding techniques. Highly boron doped silicon layers with germanium as counter-dopant offer the possibility of stress engineering. An etching process on the base of KOH/IPA is applied in a clean-room environment to decrease the particle density during etching. A very comfortable bonding process for fixing silicon membranes on glass ring carriers was optimized and yieds super flat mask blanks. The application of this process and the results of the blank characterization are presented and discussed.

Fabrication of low-stress silicon stencil masks for ion beam lithography

This paper describes the fabrication of stencil masks in large area, low-stress (10 MPa), n-type silicon membranes for demagnifying (4×) ion projection lithography (IPL) and proximity printing. The projection masks have a silicon foil area 95 mm in diameter, thicknesses between 2 and 5 μm, and resolution of 0.6 μm. Proximity printing masks have a 1 cm square membrane area, 0.8 μm thickness, and 80 nm resolution. Measured distortion (3σ) in the IPL masks ranges between 0.23 and 0.65 μm, with an experimental error of 0.20 μm.

Resist materials for sub-0.5-μm pattern transfer with demagnifying ion projection lithography (IPL)

Different kinds of resist materials were used to prove the high versatility of Ion Projection Lithography (IPL). With standard exposure and developing conditions test structures in the sub-0.5-μm range were obtained routinely. A new dry development process is presented which included helium ion exposure to polyimide and, subsequently, photoablation by an excimer laser.

Sub-0.5-μm lithography with a new ion projection lithography machine using silicon open stencil masks

An ion projection lithography system was equipped with an open stencil mask manufactured by applying silicon technology. By exposing poly(methylmethacrylate) and SiO2 to He+ ions, the pattern, transferred with a 9.5:1 reduction, showed structures with a minimum linewidth of 0.25 μm. The emphasis of this work concentrated on the various effects which produce distortion of the mask. Whereas linear dilation of the foil caused by compressive stress and enhanced by the network structure could be offset by means of the ion optical system, anisotropic distortion which resulted from the unequally distributed openings in the pattern had to be minimized by applying a suitable design. With a field effect transistor test pattern, an average distortion of 0.15 μm has been obtained in a 20×21 mm2 area of the mask. Only minor contributions to pattern deviations were expected from the temperature increase and sputter erosion.

Preliminary experimental study of the multiple ion beam machine

The multiple ion beam machine (MIBM) that we are developing for nanolithography offers important advantages over other nanolithography machines. A focused ion beam machine [R. L. Seliger, R. D. Olney, J. W. Ward, and V. Wang, J. Vac. Sci. Technol. 16, 1610 (1979)] uses a single ion beam to write the pattern. As a result, each chip on a wafer must be written individually thus leading to low throughput for high-volume production. On the other hand, an ion projection lithography machine (G. Stengel, H. Löshner, and J. J. Muray, Solid State Technol. 1986, 119) has a high throughput; however, it is inconvenient in that it requires a special mask to be made for each lithographic pattern. The MIBM uses multiple focused ion beams, which are deflected and blanked in synchronism, each beam being used to write a single chip. Thus, the exposure time for the whole wafer is the same as is required to write a single chip, resulting in a high throughput.

Ion projection lithography for sub-micron modification of materials

Ion projection lithography (IPL) uses demagnifying ion-optics for reduction printing of open stencil masks at 5 x or 10 x scale. A feasibility study with a research type Ion projection lithography machine (IPLM-01) demonstrates sub-0.1 Jim resolution combined with a high depth of focus and the possibility of an electronic alignment of the projected ion image in X, Y, rotation and scale and an electronic adjustment of intrafield distortion. The IPL technique combines lithography with direct submicron technique for ion beam modification of materials.

Ion projection lithography in (in)organic resist layers

Ion Projection Lithography (IPL) was applied for structuring organic and inorganic resists. To prove the feasibility of Ion Projection Lithography for printing submicron features the pattern transfer characteristics was determined in PMMA and SiO 2 resist layers. Furthermore, Response Surface Methodology (RSM) was used to evaluate the dependence of the obtained results on various process parameters. By application of RSM the machine setup was optimized and process latitudes were established.

The Stability of Ion Projection Lithography Masks

ABSTRACTIon projection lithography (IPL) has demonstrated the ability to replicate high resolution patterns with very short exposure times. Computer modeling of masks used in a hypothetical IPL system Is accomplished to estimate mask distortion during fabrication and exposure. Radiation cooling is shown to play an important role in temperature control. Two different methods of mask temperature control are examined. Results suggest a high degree of pattern stability can be expected from this type of mask.

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 demagnifying projection an IMBS enables the production of gratings with sub-0.2-μm periodicity and adjusted scale.

Fabrication of submicron deep ultraviolet masks by ion microprojection

Photolithographic masks with submicron resolution have been produced in a one-step process by 1:10 ion microprojection of a stencil mask pattern into polymethyl methacrylate resist material. In the implanted pattern areas, light transmission is reduced for wavelengths extending into deep ultraviolet (DUV); thus, these patterns can be replicated into UV-sensitive photoresists using, e.g., excimer laser radiation. In the present ion projection lithography machine a 2.5-mm-diam mask was produced using a single 2-s exposure with 82 keV He+ ions. Replication in poly(butene-1-sulfone) resist was performed by single or double shot exposure using a KrF excimer laser (wavelength 248 nm). Resolutions exceeding 800 lp/mm were obtained in the replicated structures.

Submicron lithography and DUV-master masks made by ion projection lithography

Ion beam induced changes of the physical and chemical properties of PMMA have been performed in a locally selective mode with an Ion Projection Lithography Machine IPLM-01. Sub 0.5 μm resolution has been achieved using PMMA as positive or negative (image reversal) ion sensitive resist. UV- and DUV-transmission loss of thin PMMA films on quartz due to ion implantation has been shown to yield a mask fabrication process for UV and DUV lithography. Excimer laser exposure of PBS through these direct implanted masks gives submicron resolution.

Ion-Projection Lithography for Submicron Modification of Materials

ABSTRACTIon-Projection Lithography (IPL) is a future production technique for submicron electronic devices, wich combines the advantages of e-beam and X-ray lithography without having their disadvantages. Like electrons, ions can be accelerated, focused and deflected, and as is the case with X-rays, scattering in resist layers is less pronounced as for e-beams. Experimental results of IPL obtained with an Ion-Projection-Lithography-Machine IPLM-01 are presented: Ion images of self supporting masks ten times demagnified with a geometrical resolution < 0.25 μm printed into organic and inorganic resist layers in high volume production oriented times.