Showing papers on "Proximity effect (electron beam lithography) published in 1994"

Proximity effect compensation in scattering-mask lithographic projection systems and apparatus therefore

Abstract: In electron beam lithography, formation of micron and submicron size features is complicated by undesired nonuniform (pattern-density dependent) resist exposure from electrons backscattered from the underlying substrate. The disclosed technique uses a combination of a scattering mask and a scattering filter to add a leveling background exposure automatically and thus provide uniform contrast across the entire exposure pattern.

Method for fabricating InP diffraction grating and distributed feedback laser

Abstract: A method for fabricating an InP diffraction grating for a distributed feedback semiconductor laser includes the steps of applying an electron beam resist on a semiconductor substrate, giving electron beam exposure to the electron beam resist and controlling heights of resist patterns by using fixed electron beam diameters but by varying incident electron doses. The semiconductor substrate is dry-etched. The electron beam exposure is such that the incident electron doses are made larger at a center portion than at portions towards two sides of the diffraction grating. Due to the proximity effect, the resist patterns after development will have a lower height and a narrower width at portions at which the incident electron doses are increased and, conversely, a higher height and a wider width at portions at which the incident electron doses are decreased. In a method of fabricating a distributed feedback laser using a substrate of the InP diffraction grating fabricated as above, the method includes the step of sequentially growing on the substrate a waveguide layer, an active layer and a cladding layer. The method enables to fabricate a low distortion distributed feedback laser for analog modulation having non-uniform diffraction gratings.

Application of Proximity Effect Correction Using Pattern-Area Density to Patterning on a Heavy-Metal Substrate and the Cell-Projection Exposure

Abstract: Proximity effect correction for electron beam (EB) direct writing is studied in this paper. An iterative calculation of exposure-dose modulation by equalizing the deposited energy of all figures requires an extremely long calculation time, especially in the case of high EB acceleration voltage. Therefore it is not practical for the correction of LSI. The correction method using pattern-area density, however, could realize the high-speed proximity effect correction. In this paper, this method is first investigated from the standpoint of the correction accuracy. Next, the applicability of this method to two critical cases is examined. One is the patterning on a heavy-metal substrate, on which backscattering yield of electrons is high. The other is the application to the cell-projection exposure, in which it is impossible to modulate exposure dose inside the cell. Lastly, the calculation time of the proximity effect correction is evaluated for 64 Mbit dynamic random access memories (MbDRAMs).

Comparative evaluation of chemically amplified resists for electron‐beeam top surface imaging use

Abstract: The ultimate lithographic performance of e‐beam direct writing can only be achieved if the proximity effect is reduced by a top surface imaging resist technology. The capability of some commercial and experimental chemically amplified resists for an e‐beam‐sensitive top surface imaging process were evaluated. Analogous to the resist contrast, a silicon contrast was defined, which characterizes the silylation property of the resists very well and enables a comparison of the evaluated resists. The influence of bake and silylation conditions on the silicon contrast was investigated. The patterning results prove that the proximity effect was reduced dramatically. One of the evaluated resists was applied to structuring the metal layers of a 0.8‐μm‐CMOS technology.

Proximity effects in dry developed lithography for sub-0.35-μm application

Abstract: When printing at the resolution limit of the steppers, optical proximity effects become increasingly important and might limit the useful resist processing window. In this paper proximity effects have been studied for processes based on surface imaging and dry development. Proximity effect resulted in both linewidth and profile differences between dense and isolated lines at 0.35 micrometers and below. Proximity is partly due to optical effects (NA, (sigma) , wavelength, mask tonality) and partly due to processing conditions (silylation and development). To study the optical effects, aerial image simulations have been performed and a comparison with experimental results was carried out. Reduction in proximity is realized by a reduction in 'process offset', improvements in silylation contrast and a reduction in microloading effects during dry development. Positive tone resist processes show a reduced proximity effect as compared to negative tone resist processes and the feasibility for 0.30 micrometers dimensions has been shown. At 0.25 micrometers level, the process optimization should be accompanied with optical solutions in the form of selective mask biasing.

PBS resist profile studies for submicron mask lithography

Abstract: Design rules for 250 nm devices and optical proximity correction (OPC) enhancement techniques require improved resolution. Resolution requirements for these applications extend into the 500 nm realm. The most widely used resist for e-beam generated masks is PBS. Difficulties have been reported when using PBS for features smaller than 2.0 micrometers . These have included poor resolution and CD linearity anomalies at

Improved Proximity Effect Correction Technique Suitable for Cell Projection Electron Beam Direct Writing System

Abstract: Electron beam (EB) direct writing is expected to play an important role in the field of lithography for manufacturing future advanced ULSIs. Cell projection techniques are of particular interest, which may make the EB direct writing system practical for use in ULSI memories with many repeated patterns. However, the proximity effect of such systems disturbs the formation of fine 0.2 µ m level patterns throughout the patterning area. In order to solve this problem, we have developed an improved proximity effect correction technique suitable for use in a cell projection EB direct writing system. This technique makes use of smaller cell projection shot (CPS) size in the edge region than in the center region in the EB direct writing area with dose compensation between CPSs, based on the self-consistent method. Utilizing this technique, we can obtain fine 0.2 µ m patterns with 0.02 µ m critical dimension (CD) control patterns, which are required to manufacture 1Gbit dynamic random access memories (DRAMs).

Electron source and electron beam drawing method and device

Abstract: PURPOSE: To speed up proximity effect compensation by providing a controller which can control the amount of radiation of electron for each electron source in an electron beam drawing for transferring the image of an array electron source onto a sample. CONSTITUTION: An electron beam 2 which is discharged from an array electron source 1 and has a section in the shape of an accelerated pattern to be drawn is transferred onto a sample 5 which is projected by a projection lens 4 and where a sensitized agent is applied for drawing. At this time, the position of the electron beam 2 is determined by a deflector 3. Only a region which can be drawn by the array electron source 1 from a control computer 6 is cut and is accumulated at a pattern data storage 7. Proximity effect compensation operation is performed to the pattern data based on the sensitivity of a known sensitizing agent by an operation device 8 and is returned to the pattern data storage 7 again. An array electron source controller 9 controls the array electron source 1 according to the content and radiates the electron beam 2 in a shape where the amount of application is compensated, thus speedily compensating proximity effect and achieving drawing accurately. COPYRIGHT: (C)1995,JPO

Critical Dimension Control of Poly-Butene-Sulfone Resist in Electron Beam Lithography

Abstract: Critical dimension uniformity is one of the key parameters to define the performance of electron beam lithography as well as the other lithography technologies. The characteristics of poly-butene-sulfone (PBS), a positive-type electron resist, have been investigated from the view-point of critical dimension control, using two types of electron beam lithography systems which use Gaussian spot and variable-shaped beams. It has been elucidated that the sensitivity of the PBS has a strong relationship with humidity during development. When the humidity changes from 30% to 32%, the sensitivity increases corresponding to the increase of 1 µ C/cm2 dosage. A very good critical dimension uniformity of less than 0.04 µ m has been attained using a variable-shaped beam at 30% humidity. The spot beam can also obtain a good pattern width uniformity at 32% humidity and 4.5 µ C/cm2 dosage. It is expected to correct the proximity effect in PBS by selecting the electron dosage related to humidity.

Surface imaging by silylation for low voltage electron-beam lithography

Abstract: Electron‐beam lithography with low voltage electrons offers a number of advantages. Low voltage electrons have short penetration depths. Therefore, backscattering from the substrate which causes the proximity effect as well as radiation damage in the substrate are potentially minimized or excluded. As a consequence, a top surface imaging resist technology should be applied. The surface imaging by silylation was combined with low voltage electron exposure using 1.8‐, 3‐, and 5‐keV electrons. Resist structures down to 50 nm are shown.

Electron beam drawing device and method therefor

Abstract: PURPOSE:To draw a pattern with a high dimensional accuracy also for an extremely thin and dense device pattern by setting an exposure evaluation point to a non-irradiation region of an electron beam and then reviewing its proximity effect compensation. CONSTITUTION:A data conversion means 11 for converting design data DIN to exposure data DOUT, an electron beam drawing means 12 for performing electron beam drawing processing based on the exposure data DOUT, and a control means 13 for controlling the input/output of the data conversion means 11 and the electron beam drawing means 12 are provided and the data conversion means 11 sets a first evaluation point (t) to a non-irradiation part Pa of a graphic target 14 to be exposed which is created based on the design data DIN. Also, a second evaluation point Sn is set to the irradiation part Pb and then the proximity effect compensation of the graphic target 14 to be exposed is subjected to review control based on the exposure intensity of the non- irradiation part Pa and the exposure intensity of the irradiation part Pb.

Proximity Effect Correction for 1:1 X-Ray Mask Fabrication

Abstract: This article describes the improvement of a self-consistent proximity effect correction to fabricate 1:1 X-ray masks. The present method has two features; the first is the change of sampling point from pattern edges to the center. This is effictive in saving on the calculation time, and it is theoretically shown that the deposited energy intensity at the edge is equal to that obtained with the conventional method. The other is to combine the pattern shape and additional dose modulations for finer patterns (?4? f, ? f is the forward scattering range of electrons) with the ordinary dose modulation method. The algorithm is verified by experiments and simulations, and is found to be effective in reproducing 0.1 ? m patterns with high accuracy.

Electron beam lithography system

Abstract: PURPOSE:To properly correct proximity effect even when performing a self- projection type drawing. CONSTITUTION:On a stencil mask, a pattern 20-2 of Lc in width for reduction copying and a shielding area 22 of Lc/2 in width between patterns 20-1 and 20-3 adjoining thereto are formed. An image 23G drawn by electron beam in preceding step is horizontally slid to the area 22 in order to irradiate only a part of the pattern 20-2 and a part of the pattern image is drawn on a target while changing dosage.

Quantitive analysis of the proximity effect in optical lithographic process

Abstract: As the density of VLSI circuits increases, the proximity effect has been one of the critical issues in optical lithography. In general, the linewidth difference between dense and isolated patterns corresponds to 0.08 micrometers when a conventional i-line single resist process using a 0.54 NA is applied to the half-micron geometry on a flat wafer. Therefore, this linewidth difference has significantly affected the process stability in the real process applications. This paper describes the dependency of the proximity effects on the pattern size, line and space duty ratio, kinds of substrate film, defocus effect during exposure, and resist process conditions related to the variation of the resist thickness and develop time. Critical dimension (CD) deviation caused by the different latent image contrast is also experimentally monitored using two different photoresists. A simulation is performed for the purpose of obtaining the optimum resist thickness to reduce CD difference caused by the variations of resist thickness in the real topography.

Method and device for electronic beam pattern generation

Abstract: PURPOSE:To provide an electronic beam pattern generation method and a device thereof which can prevent generation of graphic pattern separation, double exposure data, etc., and enables proper correction processing of proximity effect without lowering through-put even when processing data of a device pattern exceeding capacity of buffer memory. CONSTITUTION:The title device prepares exposure data from design data 1 and carries out exposure based on the exposure data. It is provided with an output means 15 which outputs exposure data by dividing the data into a plurality of exposure data files 5-1 to 5-n not exceeding capacity of a buffer memory 7 provided to the electronic beam pattern generation device after specified conversion processings 11 and 13 are performed for the design data 1.

Proximity effect on patterning characteristics of hole patterns in synchrotron radiation lithography

Abstract: This paper reports the results of analyzing the proximity effect on the patterning characteristics for plural neighboring hole patterns in synchrotron radiation lithography. Fresnel diffraction simulation was used and pattern replication experiments were performed with pattern pitch, proximity gap, and mask contrast as parameters. Even when the pattern pitch (hole:space) is 1:1, pattern sizes down to 0.2 ? m can be replicated with a large dose margin under a large proximity gap condition up to 40 ? m, irrespective of the mask contrast. A low-contrast (2.5) mask has an advantage over the conventional-contrast (7) mask in that it allows the use of a larger proximity gap when replicating hole patterns with a size of 0.1?0.2 ? m. Moreover, the phase-shifting mask we previously proposed improves the exposure latitude and widens the proximity gap, so that it is possible to use a 20-? m gap to replicate 0.1-? m hole patterns for a pitch of 1:1 and to use a 30-? m gap for a pitch of 1:2.

Investigation of proximity effects for a rim phase-shifting mask printed with annular illumination

Abstract: Resolution enhancement techniques have been explored extensively in the last few years in attempts to reliably extend optical lithography to smaller features. Off-axis illumination has shown remarkable success improving the depth of focus for dense lines and spaces. However, the depth of focus for isolated lines is degraded. This paper shows experimental results of 0.22 micrometers lines at varying pitch printed with a rim phase-shifting mask on a GCA DUV stepper with 0.53 NA and annular illumination of 0.6 - 0.7 (sigma) . Although the results demonstrate a depth of focus of greater than 1.0 micrometers , there are severe proximity effects which cause a 60 nm difference between the dimension of dense versus isolated lines. We hypothesize that this proximity effect is caused by three physical phenomena, the aerial image itself, reflections from the silicon substrate, and acid diffusion in the APEX-E (IBM) resist. Simulation results are presented which show that of the 60 nm linewidth difference, 10 nm is due to the image, 10 nm is caused by substrate reflections, and 40 nm is the result of acid diffusion in the resist.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Electron beam lithography with background exposure in a neighbouring region

Abstract: A method of forming a pattern, notably a grating for semiconductor lasers, on the substrate of an integrated circuit by means of electron beam lithography. The adverse effects of the known proximity effect are prevented by additional exposure of the substrate in regions adjacent the region in which the pattern is to be written. Such additional exposure can take place with a resolution which is substantially less than that within the pattern, so that a substantial gain in time is realised relative to customary "ghost" exposure methods. Moreover, the proximity effect can thus be utilized to impose the longitudinal variation desired for laser use on the duty cycle of the grating.

Formation of semiconductor fine configuration, manufacture of inp diffraction grating, and manufacture of distributed feedback type laser

Abstract: PURPOSE:To manufacture a low distortion distributed feedback type laser for analog modulation which has an ununiform diffraction grating CONSTITUTION:Electron beam resist 1 is uniformly spread on an InP substrate 2 Electron beam exposure is so performed that the electron beam dosage in the central part is larger than at both of the end portions In this case, the resist diffraction grating pattern formed in the electron beam resist by proximity effect is low and narrow in the region where the electron beam dosage is large in the central part, and high and wide in the region where the electron beam dosage is small in both of the end portions In the central part of the diffraction grating, a lambda/4 phase shift 3 is formed This resist pattern is subjected to dry etching using Cl2 based gas, and transferred on the InP substrate 2 Thus a diffraction grating having an ununiform shape is obtained A distributed feedback type laser is manufactured by growing in order an optical guide layer, an active layer and a clad layer on the substrate