Showing papers on "Proximity effect (electron beam lithography) published in 1989"

Electron beam lithography method and apparatus

Abstract: A charged beam lithography writes a pattern with charged beams on a sample. The pattern involves various shapes. For every position in the shapes in the pattern, degree of exposure due to a proximity effect caused by backward scattering charged from the shapes surrounding the position is calculated. A charged beam emission quantity corresponding to the calculated degree of exposure is subtracted from a set emission quantity to compensate the proximity effect and obtain an optimum charged beam emission quantity for the position. With charged beams of the optimum emission quantities thus obtained, the pattern is written with high dimensional accuracy.

Single Level Dry Developable Resist Systems, Based On Gas Phase Silylation

Abstract: In this paper various single level resist systems are presented that combine gas phase silylation with dry development. For novolak-diazoquinone type resists it is shown that the photoselectivity of the silylation process is determined, to a large extent, by the presence of hydrogen bonds between the resin and the un-exposed sensitizer. Upon irradiation these physical crosslinks are replaced by weaker hydrogen bonds between the resin and the indene-carboxylic acid. The effect of the presilylation bake temperature and decarboxylation are discussed. Also the influence of decomposition of the photoactive compound on the selectivity is shown. Other systems presented in this paper are based on chemical crosslinking of the resist. SUPER (SUbmicron Positive dry Etch Resist) is based on the combination of acid-catalyzed crosslinking and gas phase silylation. Because of the chemistry that is used, SUPER can be an interesting candidate for DUV-lithography. Crosslinking of, novolak-diazoquinone type photoresists is another possibility to create a selectivity for the silylation process. A system based on electron beam lithography is presented. Sub-half-micron features, without problems with the proximity effect, are shown.

Proximity effect correction for high‐voltage electron beam lithography

Abstract: A new proximity effect correction method using an approximate dose correction formula has been developed. The method is especially effective for a high acceleration voltage. In the case of an acceleration voltage of 40 kV, the correction error for the energy deposition in the resist was estimated analytically to be less than ±7%. The deviations of the line and space pattern dimensions were also evaluated experimentally to be less than ±0.03 μm. The calculation time for correcting a 4‐Mbit dynamic random access memory (DRAM) was only 0.7 h using a large‐scale computer of 15 MIPS (mega instructions per second). Even if the LSI patterns have no hierarchical structure, in an application specific integrated circuit (ASIC) pattern the calculation time would be 1 h or so. A 4‐Mbit DRAM pattern can be written using the electron beam direct‐writing system EX‐7 with sufficient accuracy. These results suggest that the method is practical.

Simulation of electron beam exposure of submicron patterns

Abstract: Analytical and Monte Carlo electron beam radial exposure distributions (REDs) are compared for accuracy in predicting proximity effects in submicron lithographic patterns. A proximity effect simulation tool (PRESTO) has been developed to convolve the desired pattern with the RED obtained from a companion Monte Carlo program for the simulation of electron energy loss (SEEL) or an empirical RED which is an analytical fit to experimental results. Together, SEEL and PRESTO are shown to simulate the electron beam exposure of submicron size patterns using a focused Gaussian electron beam system. PRESTO generates the electron distribution for the pattern by simulating the exposure of the resist for each pixel. Once the energy distribution has been determined equienergy density contours for the exposure of a given shape can be plotted. The ability of PRESTO and SEEL to accurately simulate the exposure of patterns with 0.25 μm design rules is demonstrated. Comparisons are made of the simulation results obtained wh...

Theory and practice of proximity correction by secondary exposure

Abstract: This article examines the theory and practice of correcting proximity effect in direct write electron beam lithography by the introduction of a second diffuse, image‐complement exposure. The common point‐spread function for energy deposition in the substrate is used in formulating a solution to the inverse scattering problem, and the solution is expressed as a power series in the backscatter coefficient. The ghost technique is shown to constitute an approximation to this solution. This mathematical exposition clearly indicates the power of the technique for providing very accurate, point‐by‐point correction of proximity effect. Application of the procedure to nonlinear resists in a shaped‐beam exposure tool is given.

On the Monte Carlo simulation program “RESIS” for electron exposure of resists

Abstract: Some of the results of the simulation program “RESIS” for modeling the electron exposure of resist PMMA are presented. As an example, the electron energy dissipation distribution at different depths in 0.8 μm resist on silicon substrate is given for a 20 keV single electron line source. The resist profiles in near-micron line patterns before and after proximity exposure compensation are simulated using the energy threshold criterion and the time dependent development process. The proposed proximity exposure compensation scheme based on dose correction technique leads to the ideal compensation of proximity exposure in electron beam lithography. Finally the comparison of resist edge slope and line width variation before and after proximity exposure compensation is made.

Computer Aided Proximity Effect Correction System in Photolithography

Abstract: Reflected light from step coverage causes fatal pattern defects in photolithography. The resist pattern defects are caused by the extra exposure from the highly reflective stepped substrate, such as breaks in the pattern of the aluminum layer. The problem is significant when the patterns in the different layers are near each other. We named this problem the proximity effect. The specific design rules such as the space between the resist pattern and the steps on the substrate are evaluated by simulation and experiment. Based on the evaluated results, we propose a computer aided proximity effect correction system to verify the pattern layout and eliminate the proximity effect. The effectiveness of the system is confirmed experimentally.

Resist Pattern Analysis For Submicron Feature Size Using 3-D Photolithography Simulator

Abstract: Photolithography has been used for manufacturing LSIs for a long time and it also becomes a key technology for submicrometer VLSIs. Three dimensional photolithography simulator, RESPROT, has been developed, and reported its concept and application data at the last SPIE's symposium, Vol : 922-02. In this paper RESPROT was improved to simulate optical aberrations, proximity effects and repeatable reticle defects which are remarkably important process factors on submicrometer pattern transfer. And resist pattern printability or fidelity were studied. At first three dimensional simulator, RESPROT, was improved for the quantitative calculation of higher order reduction lens aberrations and contrast enhance layer, CEL, for resist images. It was confirmed by the calculations that there is existent sixth order aberration and critical dimension loss was decreased by using of CEL. For proximity effect it is slightly improved by higher numerical aperture, NA, but resist images are deformed on defocusing. Printability of submicron reticle defects are depend on the defect type ; clear or dark defects. Both defects decrease imaged resist sizes on defocusing, but these are transferred more clearly on higher NA imaging. Also reticle defects are printed with more faithful by optical aberrations.

Device for editing mask pattern input

Abstract: PURPOSE:To efficiently obtain a corrected mask pattern by composing a mask pattern input editor of electron beam exposing mask pattern input editing means used for manufacturing a VLSI, calculating means for energy distribution of electrons irradiated through the pattern, lost in a resist, and display means therefor. CONSTITUTION:A mask pattern input editor 1 inputs new input of position information of a mask pattern, new position information for input mask pattern, corrects and stores position information of the mask pattern information. An energy distribution calculator 2 calculates energy distribution stored in a resist from the trace of incident electrons by a Monte-Carlo method on the basis of mask information input and edited in the editor 1. A display unit 3 simultaneously displays the pattern edited by the editor 1 and the calculated result obtained by the calculator 2. Thus, a proximity effect in the fine mask pattern is suitably corrected while predicting it in advance.

Proximity correction for electron‐beam patterning on x‐ray mask blanks

Abstract: A limiting factor in electron‐beam (e‐beam) lithography is the proximity effect. In the special case of x‐ray mask making, Monte Carlo calculations and resist profile simulations show that the proximity effect can be almost entirely eliminated by using 100 keV electrons for the resist exposure. To verify the theoretical results of the simulation, experiments with available electron energies of 20 and 50 keV were conducted, with good agreement. The poor efficiency of 100 keV electrons results in decreasing resist sensitivity. Electrons passing through the membrane hit holder parts behind it. The x‐ray radiation generated in this way was able to expose the resist from the backside of the membrane. A diffuse image of the holder parts could be seen in the resist.

Electron Beam Metrology For Integrated Circuit Structures: Predictions And Experiments

Abstract: A Monte Carlo program named SEEL (Simulation of Electron Energy Loss) was developed to simulate electron trajectories in arbitrary line geometries. Submicron scale electronic structures were fabricated in order to compare the simulation with experimental results. SEEL was used to determine the radial exposure distribution for electron energy dissipated in resist during electron beam lithography. A companion program called PRESTO (PRoximity Effect Simulation TOO was developed to predict the exposure of submicron scale patterns. Exposures were made for the purpose of comparing the experimental patterns with simulations.

Mask pattern input and editing device

Abstract: PURPOSE:To correct a mask pattern by deriving the exposure intensity of a light beam which transmits through a mask and radiated to a resist, by position information of the mask pattern, and displaying it together with the mask pattern to predict correctly a complicated proximity effect. CONSTITUTION:A position and a shape of a mask pattern which has been inputted and edited are sent to a display part 3 from a pattern position information storage and editing device 12. An exposure intensity distribution calculating part 2 derives an exposure intensity distribution in accordance with a theory of Hopkins by a mask pattern shape and position information from the pattern position information storage and editing device 12. A graphic display part 3 receives the mask pattern and information of the exposure intensity distribution from the pattern position information storage and editing device 12 and the exposure intensity distribution calculating part 2, and displays them simultaneously by a graphic display device 13. In such a way, while predicting beforehand a proximity effect in a minute mask pattern, the mask pattern to which a modification and a correction have been performed appropriately can be generated.

Electron beam exposure method

Abstract: PURPOSE:To suppress the influence of electrons of an electron beam reflected from a substrate and form a dense, fine pattern where no proximity effect is recognized by preparing a resist having a sensitivity which is inferior to that of an upper layer resist at a lower layer, thereby making the resist have a two-layer resist structure; namely lower and upper layer resists CONSTITUTION:Lower and upper layer resists 2 and 3 are coated on a silicon substrate 1 It is preferable for the lower layer resist to have sensitivity that is inferior to that of the upper layer resist Once the resist is irradiated by an electron beam, the upper layer resist is sufficiently exposed to the electron beam but the lower resist is not exposed to its beam Then the electron beam is reflected to the silicon substrate and even the lower resist is also exposed to its beam Being different from the case of a single layer resist 3 the arrangement of another resist 2 having inferior sensitivity makes the influence of reflected electrons small The resultant cross section obtained after its development exhibits a large undercut in the case of the single layer resist as shown by dotted lines 5 but a small undercut in the case of the two-layer resist as shown by solid lines 6

Computer Aided Proximity Effect Correction System in Photolithography : Lithography Technology

Abstract: Reflected light from step coverage causes fatal pattern defects in photolithography. The resist pattern defects are caused by the extra exposure from the highly reflective stepped substrate, such as breaks in the pattern of the aluminum layer. The problem is significant when the patterns in the different layers are near each other. We named this problem the proximity effect. The specific design rules such as the space between the resist pattern and the steps on the substrate are evaluated by simulation and experiment. Based on the evaluated results, we propose a computer aided proximity effect correction system to verify the pattern layout and eliminate the proximity effect. The effectiveness of the system is confirmed experimentally.

An E-beam direct write process for 16M-Bit DRAMs

Abstract: For obtaining a very fine wafer pattern below half micron, direct write EB lithography has charging and proximity effect problems. A method of compensating for the charging problem is to use a 40 kV proton shower irradiation process which decreases the bottom layer resistance of the trilayer resist. The charge of the electron beam is dissipated through the bottom-layer resist. As for the proximity effect, we developed a proximity effect correction software system by dosage modification. The theoretical and experimental results showed that in a 2.2-micron-thick trilayer planarizing resist system, a 0.5-micron isolated line, 0.5-micron isolated space, and 0.5-micron contact holes were simultaneously resolved in a half-micron-thick top-layer resist. The resultant half-micron-rule 16M-bit DRAM patterns were successfully obtained on uneven topography of the processed wafer using EB direct write.