摘要:

The recent progress in the development of the lithographic processes within the LIGA technique is reported, which is based on deep‐etch synchrotron radiation lithography, electroforming, and molding processes (in German: lithografie, galvanoformung, abformung). Mask blanks for high‐contrast x‐ray masks for 0.2 nm wavelength are fabricated from titanium and beryllium membranes produced by physical vapor deposition techniques. Absorber patterns on these masks can be produced by 50‐keV electron‐beam pattern generation in 3–5‐μm‐thick polymethylmethacrylate (PMMA) resists, because the use of beryllium strongly reduces the otherwise marked influence of electrons backscattered from the substrates on the resist profiles. To comply with the requirements of deep‐etch lithography cross‐linked PMMA resists and suitable multicomponent developers have been formulated. The casting resin‐based resists are polymerized directly on the substrate which results in extremely low internal stresses to prevent stress corrosion of the resist structure during development.

ISSN:1071-1023    

DOI:10.1116/1.584039

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The radiation stability of x‐ray membranes is of major importance for future development of x‐ray lithography and x‐ray microscopy. The primary concern in this respect is loss of dimensional stability due to the radiation damage. The dose required to introduce sensible distortion of the pattern on a membrane is far below that necessary for the radiolysis of the membrane material. The ability of a material to resist generation and accumulation of the radiation defects is related to its band structure. Mechanisms of radiation defect generation, protective mechanisms, and possible ways to control the radiation resistance are discussed.

ISSN:1071-1023    

DOI:10.1116/1.584040

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

A variety of source technologies are currently being proposed for x‐ray lithography. Some are broadband sources, producing a continuum spectrum or a broad distribution of wavelengths. The performance of a system using a broadband source is strongly affected by the vacuum window, mask substrate, and resist composition because of the wavelength‐selective transmission and absorption of these layers. A desired ‘‘optimum’’ spectrum of energy deposited in the resist can be obtained by proper choice of source parameters, vacuum window, and mask substrate. The calculated performances of different source technologies are compared, using source parameters appropriate to each technology. The effect of vacuum window and mask substrate on performance is shown for a representative broadband source spectrum. The feasibility of x‐ray lithography sources for manufacturing use should be viewed in terms of theoretical 0.25‐μm patterning capability, which is found to depend principally on three factors: power, geometry (isotropic or collimated), and whether a vacuum window is required.

ISSN:1071-1023    

DOI:10.1116/1.584041

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The reliable beamline structure for synchrotron radiation lithography has been investigated using the Photon Factory storage ring (2.5 GeV). The recently built beamline aims at attaining system reliability and safety. This beamline, one of three branch lines split from a basic beamline, is a 10−7Pa ultrahigh‐vacuum system with an oscillating mirror. In addition to a 40 ms fast closing valve (FCV) and an acoustic delay line (ADL), installed in the basic beamline, a<15 ms FCV and 40 ms ADL were set up to protect the storage ring from accidental breakdown. The FCV and ADL were placed far upstream of the oscillating mirror, to cope with accidental gas leakage caused by the oscillating mechanism. A vacuum breakdown test demonstrated that the FCV and ADL are greatly effective in vacuum protection. In order to protect operators from x‐ray exposure, two auxiliary shutters made of tantalum were placed upstream of the oscillating mirror. The oscillating mirror, driven through bellows by a combination of a direct current servomotor and a cam mechanism, enabled a highly reliable oscillation. A double‐structured bellows was adopted to provide against gas leakage. In addition, a silicon carbide plane mirror (40×17×4 cm) was employed because of its high‐heat‐resistance capability.

ISSN:1071-1023    

DOI:10.1116/1.584043

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

A bright and reliable x‐ray source for lithography has been developed using plasma focus. Discharge with constant pressure gas, one of the features of plasma focus, makes the x‐ray source system simple and lengthens lifetime. A fine ceramic insulator made of alumina in place of a conventional Pyrex glass insulator improves system reliability. The system operates for more than 105discharges without maintenance. The lifetime of the system is ten times longer than that of a conventional plasma focus device. The resolution of a pattern printed by multishot exposure depends not only on the diameter of pinched plasma but also on the variation of source position. A new spherical electrode surrounding the plasma‐focusing space is added to stabilize the location of the spot on the axis by eddy currents which exert the Lorentz force on the plasma. The spot position deviation has become negligibly small as compared with the pinched plasma diameter. The x‐ray source size for neon is 1 mm in diameter and 10 mm in length. Consequently, 0.4‐μm fine pattern has been printed with this source. Neon radiates intense x rays in opposite voltage polarity to that of a conventional plasma focus. Polarity inversion enables a very thin beryllium window to be located on the axis with the assistance of magnetic deflector and plasma stop. An x‐ray intensity of 5 mJ/cm2/shot 25 cm from the source with an irradiance of 10 mW/cm2at the 2‐Hz repetition rate has been obtained. The plasma focus is a promising x‐ray source for lithography from the viewpoint of intensity, resolution, and lifetime.

ISSN:1071-1023    

DOI:10.1116/1.584044

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

A variable spot‐shaping system using an electrostatic quadrupole triplet has been developed to provide a more flexible pattern generation without loss of beam current accompanying a change of dimension of the shaped beam. The quadrupole electron‐beam lithography system (QEBS) consists of a LaB6electron gun, magnetic illuminating lenses, square apertures, an electrostatic quadrupole triplet, and an octopole deflector. The high precision electrostatic quadrupole triplet has been newly developed for this system. The length of the shaped beam can be varied from 0.3 to 30 μm for a rectangular beam and from 1 to 200 μm for a linear beam by adjusting the excitation voltages of the second and the third quadrupoles. The excitation voltages of the quadrupole triplet are controlled by floating digital/analog (D/A) converters with high voltage amplifiers and high‐precision dc voltage sources. Preliminary parttern exposures demonstrate that the QEBS is suitable for forming fine line patterns.

ISSN:1071-1023    

DOI:10.1116/1.584003

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

We have developed an electron‐beam (e‐beam) lithography system named ‘‘NOWEL’’ which utilizes very accurate pattern writing method and high‐speed data processing. Accordingly NOWEL makes it possible to manufacture reticles for 16‐Mbit dynamic random access memories (DRAM’s) or more densely integrated very large scale integrated circuits (VLSI’s). The NOWEL system has three key features: (1) Vertical landing deflection system. This consists of three yokes in series and one short‐working‐distance lens (M=0.86). The landing angle at the corner of the 5‐mm2main field is<0.0025 rad. Therefore the butting error arising from a 10‐μ height variation of the substrate is<0.05 μ. Deflection aberration is about 0.2 μ. (2) Double exposure method called ‘‘A/B mode.’’ We adopted a variable shaped beam. The first exposure is made by serial writing with constant‐size rectangular spots, and the second one is made on the previously exposed area by shifting the beam position and reshaping the beam spots. One‐half dosage is given in each exposure. By this method the edge roughness of each pattern is improved to be<0.05 μ. (3) Pattern data compression. A hierarchical pattern data structure was developed. In the memory cell area the data can be divided into only a few pattern data for cell units and their repetition data, i.e., start positions, pitch data, and numbers of cell units in the cell area. According to the repetition data in the main field the main deflector moves the positions of cell units, written by the subdeflector, with the same pattern data. We call this exposure method ‘‘main deflection matrix mode.’’ For fine positioning especially in this mode we developed a 20‐bit digital‐analog convertor (0.005‐μ least significant bit). These reduction techniques should compress the amount of total pattern data to 1/10 for a 16‐Mbit DRAM. By using NOWEL we made a test reticle which contained 16‐Mbit cell patterns with total accuracy within 0.1 μ. In this simplest case only one cell unit with the patterns for 128‐bit cells and their repetition data were needed.

ISSN:1071-1023    

DOI:10.1116/1.584005

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

The electron optical column is designed for the electron‐beam (EB) exposure system EX‐7 employing a vector scanned variably shaped beam (VSB) on a continuously moving stage. The column, which utilizes a high current density of 200 A/cm2and a high voltage of 50 kV, has been designed for a 0.25 μm patterning. Generation of triangular shapes in addition to rectangular shapes reduces shot numbers to enhance throughput. An octapole deflector with small deflection distortion, has been developed for beam shaping. The ray tracing method using an analytical expression for the electric and magnetic field was used to design the objective focusing and deflection system, which is composed of a magnetic lens and dual channel electrostatic octapole deflectors. Beam edge resolution including the electron‐beam interaction effect is about 0.12 μm and distortion is<0.01 μm at the final beam convergence semiangle of 8 mrad and field size of 600 μm square. As a result, a 0.25 μm resist pattern has been obtained over 600 μm field. Main deflection field stitching error was<±0.04 μm (3σ) without deflection distortion correction.

ISSN:1071-1023    

DOI:10.1116/1.584006

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

As integrated circuit (IC) feature sizes shrink, correspondingly greater demands are put on the reticle writing systems for pattern placement accuracy. In raster‐scanned electron‐beam exposure systems such as MEBES which build up the pattern as a mosaic of stripes, quite small placement errors at the stripe boundaries can have serious consequences in terms of the electrical performance of the finished IC. The specifications of butting error for these exposure systems is typically 0.1 μm for a 0.25‐μm address size. While this is in itself not a serious error for most features, it can be troublesome if it shows up as a linewidth error for a submicron gate electrode. Here we have demonstrated that this error can be substantially reduced by using multiple exposures or scans to build up the pattern data so that in each exposure the stripe boundary is offset within the pattern from the remainder of the exposures. Thus, forNexposures, only 1/Nof the total dose at any one stripe boundary includes the placement error from stripe butting. Consequently, the butting error is significantly reduced in the exposed resist image. We have implemented this procedure using a novolak resist which is exposed with a scan or exposure count of 3; the reduction of the placement error by a factor better than 4 is demonstrated by metrology techniques.

ISSN:1071-1023    

DOI:10.1116/1.584007

出版商:American Vacuum Society    

年代:1988

数据来源: AIP

摘要:

Holographic lithography, in which the interference pattern of two coherent waves is used to expose a resist film, is the preferred technique for producing large‐area gratings with low distortion. The spatial period of a pattern produced by holographic lithography is directly proportional to the wavelength of the radiation and inversely proportional to the sine of one‐half the angle between the incoming beams. To expose gratings with periods ≊100 nm (50‐nm‐nominal linewidth) the source wavelength must be ≊200 nm. Since coherent deep‐ultraviolet sources are not readily available, we have investigated an achromatic holographic configuration which permits the use of incoherent sources (e.g., CdXe arc lamp) or short‐coherence‐length (≊10 μm) excimer lasers. The configuration consists of two gratings, one acting as a beamsplitter, the other as a recombiner. The beam from the source is split into plus and minus first‐order beams by the beamsplitter grating, and the zero order is subsequently blocked. The plus and minus first‐order beams are again diffracted by the recombiner grating onto the substrate. The intensity recorded at the substrate has a spatial period one‐half that of the beamsplitter grating. An analysis of this configuration shows that the intensity pattern on the substrate is independent of both the source wavelength and the angle of incidence (i.e., spatial coherence). For the configuration to be truly achromatic with high contrast the two interferometer arms must have equal path lengths within a small ‘‘window.’’ Tests of this configuration with parent gratings of 540 nm period and a Hg arc lamp produce good contrast photoresist patterns at 270 nm period, and tests with an ArF excimer laser and 250‐nm‐period parent gratings produce 125‐nm‐period patterns in polymethylmethacrylate (PMMA). This achromatic deep UV setup is similar to a proposed x‐ray interferometer and serves as a test bed for solving problems of alignment.

ISSN:1071-1023    

DOI:10.1116/1.584008

出版商:American Vacuum Society    

年代:1988

数据来源: AIP