摘要:

Diffractive lenses are becoming the optical elements of choice for many applications. One type of diffractive lens, the binary zone plate, has already demonstrated high‐resolution performance experimentally. However, in order to increase the diffraction efficiency of these zone plates, a blazed grating profile must be used. This can best be approximated by a staircase grating profile, created by multilevel exposures. Using x‐ray lithograph, we fabricated for the first time circular, linear bi‐ and trilevel zone plates, with gold structures 0.75 μm thick (per level), on silicon nitride substrates. The zone plates were designed for use at a wavelength of 1.54 Å, and had a theoretical efficiency of 68.5% for bilevel and 81.5% for trilevel zone plates. Due to the large depth of focus and high resolution inherent to x‐ray lithography, the finished zone plate exhibits very steep sidewall profiles, with linewidth resolution down to 0.25 μm. Such vertical sidewalls are essential for achieving high lens efficiency. Fabrication errors, such as thickness variation in the electroplated gold and misalignment, were considered, and their effect on the optical efficiency of the zone plate was estimated. Alignment errors between levels were minimized, achieving a best result of 25 nm (3σ). In fabricating the zone plates, we employed standard integrated device tools, such as a Leica Cambridge Electron Beam microfabricator (EBMF) 10cs/120 electron‐beam writer for the x‐ray mask fabrication, and a Suss 200 x‐ray stepper for the multilevel exposures. Thus, we have shown that it will be possible to fabricate many lenses, with a variety of optical characteristics, in one wafer.  

ISSN:0734-211X    

DOI:10.1116/1.587414

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

In the energy range of interest for x‐ray lithography, absorption of x rays by atoms results in the emission of photoelectrons and Auger secondary electrons, as well as a shower of low energy electrons. The development of accurate image formation models in x‐ray lithography requires that these mechanisms be included. The photoelectron processes produce a redistribution of the x‐ray energy over a finite volume. The interaction of the electrons with the medium is complex and can be treated in the framework of a response theory (dielectric function). A simulation code, based on the Monte Carlo method (lesis), has been developed to study the photon energy redistribution in resists, in the vicinity of resist–substrate interfaces and overlayers. The low computational efficiency of the Monte Carlo method motivates the need to parametrize the energy redistribution results of the simulation. This parametrization was performed for a polymethyl‐methacrylate/Si interface, as a function of the photon energy. The parametrization can be interpreted as the weighted sum of individual electron responses. The effects on the resist of photoelectrons generated in the substrate are discussed. These effects have been incorporated in an effective dose model that can be used to compute complex interface geometries. The results are particularly relevant for the nanolithography domain (<100 nm).

ISSN:0734-211X    

DOI:10.1116/1.587415

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

In‐plane distortion of a fiducial array was used as a metric to compare the relative responses to heat treatments of x‐ray masks doped with different brightener levels. Samples plated from gold‐sulfite baths containing 0, 2, and 75 ppm Tl all distorted by more than 50 nm after annealing at 100 °C. Quenching in liquid nitrogen fully relieved the stress of the undoped sample only. Room temperature stress relaxation behavior after storage of the gold samples for 2.5 years is detailed. Gold samples doped to any level with a thallium‐based brightener gradually relax, if initially stressed, and remain at a zero stress state. Behavior is explained in terms of room temperature grain growth and plastic deformation.

ISSN:0734-211X    

DOI:10.1116/1.587416

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The effect of antireflection (AR) coating on optical transparency for SiC membrane and the accelerated radiation damage of thicker AR film of 0.4 μm in thickness on a 2‐μm‐thick SiC membrane have been investigated in detail using SiO2, Al2O3, and ITO (indium tin oxide) films. SiO2, Al2O3, and ITO films were suitable for obtaining higher optical transparency and reducing the amplitude of interference fringes. The transmittance above 80% at 633 nm was achieved for 1‐μm‐thick as‐deposited SiC membrane with these AR films on both sides. AR films showed film stress change toward the compressive direction by synchrotron radiation (SR) irradiation. ITO film was found to have the strongest durability against SR irradiation among the AR films studied. The measured maximum and 3σ values forXandYcoordinates of the SR‐induced displacement of the SiC membrane with 0.4‐μm‐thick ITO film on one side were 30 nm andX=11 andY=39 nm, respectively, after irradiation of 191 kJ/cm2. Optical transparency of the mask membrane with ITO film was not changed after SR irradiation.

ISSN:0734-211X    

DOI:10.1116/1.587417

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

In order to achieve precise control for the internal stress of x‐ray absorber films, we have controlled the sputtering‐gas (Xe) pressure within ±0.002 Pa (at 0.5 Pa) using a newly developed ultrahigh‐vacuum sputtering system, but we found that it was difficult to reproducibly obtain sufficiently low‐stress Ta films over the long term. We therefore investigated the relationship between the internal stress and substrate temperature at a low deposition pressure (0.45 Pa). It was found that internal stress changes basically toward tensile with increasing substrate temperature because of the bimetal effect, but at substrate temperature from 205 to 220 °C, the internal stress changes toward compressive with increasing temperature. We characterized Ta films deposited at various temperatures using x‐ray diffraction and secondary electron microscopy and found that a film deposited at 205 °C was columnar‐structure β‐Ta and that one deposited at 240 °C was fibrous‐structured β‐Ta. Films deposited at temperatures higher than 270 °C were rough‐surfaced α‐Ta. For films deposited at pressures lower than 0.8 Pa and at a substrate temperature of 240 °C, the internal stress was almost constant regardless of gas pressure fluctuation. Thus, at 240 °C and 0.45 Pa, we can deposit low‐stress (<5×107N/m2) Ta films with excellent long‐term reproducibility.

ISSN:0734-211X    

DOI:10.1116/1.587418

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

A new technique for measuring effective lithographic contrast based on its definition is presented. Results obtained at the IBM Advanced Lithography Facility using the Helios storage ring are compared with conventional ways of determining mask contrast. In addition, a method to decrease the effects of multiple exposures in adjacent fields during the step and repeat operation of an x‐ray lithography stepper is presented.

ISSN:0734-211X    

DOI:10.1116/1.587419

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Deep etch x‐ray lithography permits the manufacture of very accurate high‐aspect‐ratio microstructures, which can be used as master templates for subsequent replication by electroforming and/or molding processes. This allows for mass production of three‐dimensional microstructures in a variety of materials. In this article we report on the first results using x rays from the Advanced Light Source (ALS) at the Lawrence Berkeley Laboratory, as well as on the processing and technology developed to produce high‐aspect‐ratio microstructures. The first masks used were simple stencil masks chemically or laser etched in thick metal sheets. For resist, we used commercial acrylic cast sheets. Microstructures 840 μm thick were fabricated by deep x‐ray lithography and used as templates for copper electroforming. A technology for the high contrast masks required to work at these short wavelengths is being developed and a deep etch x‐ray lithography facility is under construction at the ALS.

ISSN:0734-211X    

DOI:10.1116/1.587420

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

This article studies the effect of mirror misalignment on run‐out overlay errors in a synchrotron radiation based x‐ray lithography system. Using the ES‐5 beam‐line installation at the CXrL as an example, we found that the current beamline mirror alignment method, which relies on the final beam shape and orientation at the mask‐wafer plane, is insensitive to the mirror grazing incident angle alignment. Simulations using the ray‐tracing programshadowindicate that a smaller than ±0.5‐mrad mirror grazing angle misalignment consumes the required run‐out overlay error budget of the beamline. A direct beamline run‐out overlay measurement technique based on the Hartmann method was developed for the beamline mirror alignment. This measurement technique was applied to our ES‐5 beamline mirror alignment procedure. The measurement results show that the beamline induced run‐out error of the installed ES‐5 beamline is less than 0.014 μm in both horizontal and vertical direction for a 25‐mm exposure field with a mask‐wafer gap of 40 μm. The across field run‐out error distribution is also compared withshadowsimulation results. The good agreement between measurement and simulation data indicates that our measurement technique provides a sensitive, practical, and accurate method for x‐ray lithography beamline mirror alignment and evaluation.

ISSN:0734-211X    

DOI:10.1116/1.587421

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

In proximity x‐ray lithography (XRL), two types of illumination are used: full field and scanning. We describe a single mirror condenser for XRL beam lines which provides a high flux of soft x rays. The surface is generally aspheric, designed using numerical methods, and described by polynomials. The flexible design approach can be used to find a result with specific imaging characteristics according to the various requirements of the beam line, and thus is of more general application. The performance of the designed condenser is verified with ray tracing. For advanced submicron applications, mirror scanning is preferred because of its higher scanning speed. However, with figured mirrors, a small change of grazing angle may cause a large variation of image shape, so that to provide a uniform beam, the scanning of the mirror is compensated by a lateral shift. A uniform exposure of 50×50 mm2field can be achieved.

ISSN:0734-211X    

DOI:10.1116/1.587422

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

When x‐ray absorbers such as W are sputtered directly onto x‐ray mask membranes a large temperature gradient is set up due to the power input from the plasma, and the very inefficient thermal conduction in the plane of the thin membrane. To obtain absorber stresses sufficiently low that pattern distortion is negligible, the temperature gradient across the membrane must be no greater than a few degrees. To achieve this we introduce He at about 665 Pa (5 Torr) between the back surface of the membrane and an Al heat sink heated to 200 °C, separated by 1 mm. Uniform stress is easily achieved. The He gas also allows one to implement aninsitustress control feedback system based on an array of optically based gap sensors which can determine stress of the deposited film from the change in the pressure‐induced bulge of the membrane.

ISSN:0734-211X    

DOI:10.1116/1.587423

出版商:American Vacuum Society    

年代:1994

数据来源: AIP