Showing papers on "Proximity effect (electron beam lithography) published in 1983"

Proximity effect correction for electron beam lithography by equalization of background dose

Abstract: Compensation for the proximity effect in electron lithography can be achieved by equalization of the backscattered dose received by all pattern points. This is accomplished by exposing the reverse tone of the required pattern with a beam diameter dc=2σb ×(1+ηe)−1/4 and dose Qc=Qe ×[ηe/(1+ηe)], where σb is the radius of the Gaussian spatial distribution function of backscattered electrons at normally exposed pixels, ηe is the ratio of backscattered to forwardscattered energy, and Qe is the dose delivered to normally exposed pixels. This correction method has been confirmed to work for 500‐nm features by computer simulation of electron beam exposure and development and by experiment on a raster scan electron beam lithography system.

Method of compensating the proximity effect in electron beam projection systems

Abstract: For compensating scattering losses of electrons in photoresists (proximity effect) which influence electron beam lithography by altering the pattern geometry it is suggested to expose selected partial areas of a pattern to an additional irradiation dosage in a second exposure step. For that purpose, a specific mask with corresponding correction openings can be used which is applied with the same, or with a different electron beam intensity. In a particularly advantageous manner the correction of the proximity effect can be achieved when complementary masks are used; the correction openings for the partial areas of the one complementary mask are arranged in the other complementary mask. The proximity effect is then corrected without an additional exposure step. For measuring the proximity effect a photo-optical process is suggested where line patterns with decreasing ridge width in the photoresist are defined through electron beam projection, and where the developing process of the photoresist is discontinued prematurely. The ridge edges which in the presence of the proximity effect are asymmetrical can be easily detected under the microscope.

ELECTRON BEAM LITHOGRAPHY FROM 20 TO 120 kev WITH A HIGH QUALITY BEAM.

Abstract: We have performed electron beam lithography studies on thick substrates using beam energies of 20–120 keV and a nominal beam diameter of 2 nm in a Philips 400 electron microscope with scanning capability. Metal lines as narrow as 10 nm were fabricated on Si and GaAs substrates using liftoff of a single thin layer of resist. High resolution (approximately 10 nm) patterns could be written at all beam energies with an exposure latitude that remained approximately constant up to energies for which the range of the backscattered electrons became significantly larger than the pattern area. For large area patterns written with the small beam, the proximity effect is greatly reduced, even at 20 keV, because of the sharp edge of the exposure profile. At high beam energies, the range of backscattered electrons is large enough that they contribute only a slowly varying background dose, leading to a relatively simple proximity correction even for complex patterns.

An image processing approach to fast, efficient proximity correction for electron beam lithography

Abstract: A limitation on the quality of electron beam lithography is the proximity effect. This produces exposure of the resist at locations remote from the point of incidence of the electron beam. One of the techniques used to mitigate this problem is to precompensate the applied beam dose. Traditional approaches to this problem have required extensive calculations which occasionally fail to produce satisfactory results. However, the proximity correction problem is quite similar to the edge enhancement problem which arises in pattern recognition. Furthermore, the issue of data base compaction for the precompensated lithography is quite similar to bandwidth compression in image transmission. In this paper, we examine the application of image processing methods to the proximity correction problem. We find that, while the match between these disciplines is not perfect, the idea appears quite promising.

Method for correction of proximity effect in electron beam lithography

Abstract: PURPOSE: To unnecessitate the performance of calculation for correction and the addition of the memory storage for pattern data by a method wherein the lowering of resolution due to proximity effect is effectively compensated using an inverted field pattern exposure. CONSTITUTION: A circuit pattern region, consisting of regions KLMN and PQRSTU, is first exposed by electron beams. The intensity and width of the beams are adjusted in such a manner that the total energy distribution generating in respective image element to be irradiated will be highly approximated to the back scattering distribution. The inverted field pattern, consisting of regions A, B, C and D excluding the regions KLMN and PQRSTU, is exposed by an adjusted beam. Thus the total energy, which is the sum of the first and the second components, is generated. The first component is the ideal distribution generating when a circuit pattern alone is exposed. The second component is the almost constant energy distribution generated on the entire regions of A, B, C and D by the generation of all distribution approximate to the back scattering energy distribution. COPYRIGHT: (C)1984,JPO&Japio

Method for electron beam patterning

Abstract: PURPOSE:To reduce the adverse influence given to the demensional accuracy due to proximity effect by a method wherein a drawing pattern is divided into a center pattern and an outline pattern surrounding it, and the irradiation dose of an electron beam to be given to the center pattern is made smaller than that which will be given to the outline pattern. CONSTITUTION:In the case of a pattern of 6mum in width, it is divided into the outline pattern 15 of the width of 0.6mum and the center pattern 13, and in the case of the pattern 1mum in width, it is divided into the outline pattern 16 of the width of 0.2mum and the center pattern 14. Also, an isolated pattern 17 of 0.6mum square is not divided. At this time, the optimum ratio of irradiation dose to be given to each pattern is as follows when the pattern 13 is formed by the dose of 1.0: Pattern 13 is 1.0, pattern 14 is 1.3, pattern 15 is 2.1, pattern 16 is 2.3 and pattern 17 is 2.5. According to this constitution, the stored energy which is oozed out of the drawing pattern when an electron beam is made to irradiate can be reduced to the minimum, not only the dimensional accuracy of an isolated pattern can be remarkably improved, but also an enormous effect can be obtained by performing a simple correction even when a proximity effect correction is conducted.

Correction of proximity effect at electron beam exposure

Abstract: PURPOSE:To simplify the correction process concluding simply only with the figure data process when the correction of proximity effect is to be performed at electron beam exposure by a method wherein the proximity effect is divided into the proximity effect correction between patterns and the proximity effect correction inside of the patterns to give independence respectively. CONSTITUTION:Two figures 1, 2 are made to come nearby, and when lengthes (l1) and (l2) of two sides at the neighboring part of the figures thereof and length (l) out of (l1), (l2) came nearby actually are larger than the prescribed value (w), it is necessary to perform the narrowing process to the figures 1, 2 are shown respectively with oblique lines. Therefore the side (a1) of the figure 1 and the side (a2) of the figure 2 and the distance d between the figures 1, 2 to be made as the objects of the narrowing process are measured, and respective narrowing quantities delta1=delta(a1, d), delta2=delta(a2, d) are decided by a drawing test, etc. After then, the figures thereof are considered as the fundamental figures being isolated, and the exposure process is performed to the respective figures. Accordingly the proximity effect correction is performed according simply to the figure data process not according to change of distribution of exposure intensity, and the process is performed at a high speed.

Proximity effect correction on substrates of variable material composition

Abstract: The main contribution to the proximity effect in electron beam lithography on solid substrates results from electrons backscattered from the substrate. The range around the point of incidence of the primary beam over which these electrons affect the resist as well as their total number depends very much on the substrate material, in particular on the atomic number of the material. In the case of isolated lines it has been shown earlier that the resulting dose variation can be compensated for by modulating the incident dose in accordance with the backscattered electron signal detected during exposure. Shape‐to‐shape interaction in dense patterns is normally simulated numerically and corrected for on a pattern data level, and this simulation could, in principle, include variable substrate material compositions. The purpose of this paper is to show that a suitable combination of numerical dose compensation for constant substrate composition and real time feedback from the backscattered electron signal can yield significantly improved results compared to either correction alone.

Mask blank for drawing

Abstract: PURPOSE:To obtain a mask blank for electron beam drawing which holds a pattern size excellently and precisely, by reducing the influence of proximity effect and the fogging of an electron beam. CONSTITUTION:A mask blank basically uses glass, quartz, etc., or materials obtained by providing them with a chromium layer, a (chromium/chromium oxide) layer, or an iron oxide layer, etc., and has a metallic layer with a low atomic number as an outermost (top) layer. For example, the mask blank 15 consists of a glass substrate 11, a chronium layer 12, a chrominum oxide layer 13, and an aluminum layer 14. The substrate coated with resist 16 is irradiated with an electron beam EB to cause proximity effect. This effect, however, is reduced by providing as the top layer the metallic layer which has a small coefficient of electron beam reflection and a low atomic number, i.g. the aluminum layer 14 in this case.

Canyon lithography

Abstract: We describe a simple resist structure for implementing brushfire lithography (BFL) in electron-beam writing. The outlines of the pattern features are written as narrow deep openings formed in a single layer of positive electron resist. An oblique evaporation of a metal film onto the surface yields outlined electrically isolated metal copies of the features. These can be toned by selective electrically controlled etching. Transfer of the metal pattern to the underlying resist completes the structure.

Polysiloxane resist as a probe for energy deposited in electron beam exposed resists

Abstract: Polymeric resists based on the O–Si–O backbone, called polysiloxanes, have the extraordinary property that they are highly sensitive to various forms of energy, and at the same time they are highly resistant to etching in an oxygen plasma. Thus, thin layers of these materials on top of thick layers of carbon based polymers can be patterned and then used as masks for plasma etching of the bottom layer. The proximity effect parameters for electron beam exposure of such a system have been reported previously by Jones, Paraszczak, and Speth. In the present paper, the thin layer of polysiloxane is used for the energy which is deposited in the top layer of the resist system. The effect of electron beam potential upon the distribution of deposited energy in the resist film is determined experimentally, and compared with Monte Carlo simulations. The results are used to discuss the effect of electron beam potential on the dose contrast achievable in single and double layer resist systems.

High Voltage Electron Beam Writing for Submicron Design Rule VLSI Fabrications

Abstract: The advantages of high voltage electron beam lithography in submicron VLSI fabrications have been established. By electron beam lithography with 50 kV acceleration voltage, vertically walled PMMA pattern is obtained at a relatively low dose, 50 µC/cm2. This fact, combined with the increase in beam current, brings about the improvement of throughput in 50 kV writing by a factor of 5 over 20 kV writing. Proximity effect is markedly reduced in 50 kV writing. The pattern size variation due to the proximity effect is within 0.05 µm for line patterns ranging from 10 µm to 0.25 µm. Vertically walled PMMA pattern of 0.25 µm space, which is equal in size to the beam spot, is obtained at 50 µC/cm2 in 50 kV writing. In addition, it is shown that radiation damage of MOSFET's due to the 50 keV beam is essentially the same as that due to 20 keV beam.

Registration mark detection in electron beam proximity printing

Abstract: Electron beam proximity printing is a lithography method for high throughput exposure of repetitive patterns with submicron structures. An electron beam shadow projects the pattern contained in a transmission mask onto the wafer. Pattern registration in this projection printer is achieved by using the electron beam current absorbed in the wafer. Two registration steps are employed: one for wafer (or global) align, the other for chip (or local) align. The achieved registration accuracy is better than 0.1 μm using 10 keV electrons and 1.1 μm thick PMMA on the wafer registration marks.

X-Ray Lithography Using Synchrotron Radiation And Ion-Beam Shadow Printing

Abstract: In order to retain the simplicity of optical (400 nm) 1:1 shadow projection even in the case of sub-μm structures, the wavelength of the radiation employed has to be reduced drastically. The application of deep-UV radiation (e- 200 nm) only leads to an insignificant improvement in the Fresnel-limited resolution. Soft X-rays as well as high-energy ions are capable of replicating sub-μm features in shadow projection at reasonable proximity distances (>o 30 μm). X-ray lithography, the technique which is further developed at present, utilizes wavelengths between 0.5 and 5 nm, with structural resolution as good as 0.1 μm under certain conditions. The transition to soft X-rays requires the development of new intense sources as well as sensitive and process-stable resists, high-transmissive (optical light, X-rays) masks, and an appropriate alignment system with an accuracy below 0.1 μm. The type of X-ray source used is the most decisive parameter in determining the attainable resolution. (This is the reason why we only deal in this paper with the properties of the different X-ray sources, with strong emphasis on synchrotron sources. The use of X-ray tubes limits the minimum structure size to about 0.5 μm, even in the case of the tri-level technique.) Parallel and high-intensity synchrotron radiation makes the replication of patterns within the fresnel limit possible and provides a higher flexibility in choosing the suitable resist. Nevertheless, the two different approaches complement each other, since the first available X-ray systems will be equipped with low-cost conventional X-ray tubes which can be replaced later by compact synchrotron sources now under development. However, the technological basis, especially the mask technique, remains nearly unchanged. The technique of shadow projection using ions, as described here employs the dechanneling effect of a thin metal layer as well as the difference in energy loss between the random and the channeling directions. There are two advantageous features of ion-beam lithography in comparison to X-ray and E-beam lithography. Inexpensive ion sources with high intensities, in contrast to those for X-rays, are already available and no proximity effect occurs as in the case of electrons. Furthermore, the high energy-deposition density leads to a high sensitivity of resists. Mask problems, however, are more critical and the resolution is not as high as in the case of X-ray lithography.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Forming method for resist pattern

Abstract: PURPOSE:To obtain the resist pattern in which a resist does not remain in an end edge by using two masks each regulating the longitudinal and lateral sizes of a rectangular pattern. CONSTITUTION:Cr patterns 14, 15 are formed onto a glass substrate 13, and the masks 11, 12 regulating the longitudinal and lateral size of the patterns are manufactured. The masks of the rectangular patterns are superposed, and mask patterns according to a predetermined design are obtained. When the resist is exposed by the masks of the rectangular patterns, the edges of the patterns are hardly exposed by a proximity effect because exposure regions and non-exposure regions are in contact at the angles of 180 deg. in designed pattern sections. Accordingly, the edge sections of designed patterns are not exposed even through exposure by the mask 12 in succession to the mask 11, and the resist patterns for forming minute connecting holes can be formed through development.

Inspection of light exposure pattern

Abstract: PURPOSE:To be able to varify easily the results of compensation for proximity effect and thereby attempt increased accuracy of pattern by electron beam exposure by calculation all over the picture drawing area based on the light exposure data of the phenomenon energy intensity distribution in the case of light exposure to an electron beam and seeking an area that has a specified phenomenon energy intensity from the phenomenon energy intensity distribution. CONSTITUTION:Design pattern data is read out from a memory 2 by the instruction of a CPU1 to carry out compensation calculation based on compensation method that is beforehand determined in a compensation calculation circuit 3, and a value of compensation is calculated. For example, regarding each of patterns K-M a sample point is set up on each side to calculate the effects of individual patterns. The sample point is selected at the bisector point of each side, for example. Compensation is made by dividing a pattern into simple rectangular patterns for a pattern of complex shape as in a pattern L. By the instruction from CPU1, the logic calculation circuit 5 reads out exposure pattern data from a first buffer memory 4 and the design pattern data is read out from a main memory 2. Exclusive Or (EOR) of both readings is sought.

Electron beam exposure system

Abstract: PURPOSE:To suppress a proximity effect inside a pattern and between patterns in real time without lowering a throughput by a method wherein a direction of a track of scattering electrons is changed and an amount of reentry of the scattering electrons into an electron beam-sensitive resist is reduced. CONSTITUTION:Magnetic poles 5 of the strong excitation type are arranged between a lower-end part of an objective 1 and a wafer or a mask 6 as a specimen. A uniform magnetic field 21 which is parallel to a scanning direction 11 of a beam is formed on the surface of the wafer or the mask 6 by the magnetic poles 5. Normally, an electron beam-sensitive resist is coated on the surface of the wafer or the mask 6; accordingly, this magnetic fiels 21 is formed on the surface of a substrate which is situated directly under the resist. A semiconductor substrate 13 is irradiated with a beam 10 through a resist substratum film 12 coated on the surface of the semiconductor substrate 13 and through the electron beam-sensitive resist 14. While this incident beam 10 is scattered in a forward direction in this manner, it irradiates the electron beam-sensitive resist 14, the resist substratum film 12 and the semiconductor substrate 13. The beam is scattered in a backward direction in accordance with a rate which is proportional to an atomic number of the semiconductor substrate 13.

Electron-beam direct writing technology for LSI wiring process

Abstract: Electron-beam direct writing technology is described here for a fine pattern LSI wiring process. A new proximity effect correction algorithm that is capable of handling LSI patterns and which makes use of the exposure dose table is used to compensate for proximity effects. A New Positive Resist (NPR) is used which exhibits high resolution and high dry etching durability. Moreover a tri-level resist scheme is introduced for highly stepped substrates. This technology has been applied to fabrication of custom LSIs having a minimum feature size of 1 µm and chip size of 5 mm? Data processing time for the proximity effect correction is about 10 min/level. Results of the wiring process test indicate that this technology is useful for custom LSI wiring.

Electron beam lithograph proximity correction method

Abstract: Proximity effect is reduced or eliminated by breaking each shape of a lithographic exposure pattern into two parts, a perimeter part having a width on the order of the lithographic exposure pattern minimum linewidth and the remaining central part or parts (if any) which are completely surrounded by the perimeter part. Figure 2 shows the edge parts hatched and the centre part blank. The lithographic exposure pattern is then modified by moving or setting back the edges of each central part away from the perimeter part which surrounds it (similar to reducing the size of the central part) to form a nominally unexposed band separating each central part from the perimeter part which surrounds it. This is shown in Fig. 3. The width of the nominally unexposed band in the modified exposure pattern is preferably chosen as large as possible so long as the condition is met that upon developing a radiation sensitive layer directly exposed to the modified exposure pattern, the nominally unexposed band develops (i.e., dissolves, resists dissolution, or is otherwise modified) substantially as if it were also exposed. The nominally unexposed band is exposed, in fact, by electrons scattered from the directly exposed part(s) of the shape (the perimeter part plus the central part, if any). The width of the nominally unexposed band is preferably about twice the edge bias applied to outside edges of each shape.

The magnitude and significance of proximity effects in electron image projector defined layers

Abstract: Electron image projection is an attractive technique for making submicron integrated circuits (IC) but long and short range proximity effects cause some pattern distortion. Long range proximity effects have now been measured and the significance of long and short range effects to IC fabrication assessed. Long range proximity exposure effects due to re‐entrant electrons are sufficiently uniform for local corrections to be unnecessary. With automatic proximity correction IC patterns could be scaled down to below 0.5 μm (1 μm pitch) even with single level resist and 20 keV electrons.

Mask for pattern transfer and manufacture thereof

Abstract: PURPOSE:To avoid a decrease in resolution of a pattern peripheral section by proximity effect by a method wherein light transmittance at a narrow part is increased than that of the wide line breath part of a pattern section and the light transmittance of a peripheral section is increased than that of a central section at the wide part as well when a mask for pattern transfer used for electron beam transfer is made CONSTITUTION:Cr film 12 is coated on a quartz substrate 11 and selective etching is done in accordance with desired patterns and a plurality of mask patterns consisting of the films 12 are obtained Next, vapor deposition is done to metal thin films 13 from the upper left direction against the normal direction of the substrate 11 and films 13 having thin thickness at the central sections of exposure pattern sections and thick thickness at peripheral sections are obtained At that time, no thin films 13 do not grow at the pattern sections having narrow line breadth In this way, a mask for transfer is made and then CsI films 14 becoming desired photoelectric films are coated on the thin films 13 and the exposed section of the substrate 11