Showing papers on "Proximity effect (electron beam lithography) published in 1997"

Dose modification proximity effect compensation (PEC) technique for electron beam lithography

Abstract: A method of compensating for proximity effects in electron beam lithography systems is disclosed. An uncorrected dose profile is obtained for the pattern features to be introduced into a layer of electron beam sensitive material, including a determination of the clearing dose for the electron beam sensitive resist and the dose height for each edge of the pattern feature. Thereafter the incident dose of exposure energy for introducing an image of the pattern into a layer of electron beam sensitive material is adjusted by designating the clearing dose for each edge of the pattern feature as a function of the dose height. The uncorrected dose profile for determining the dose height and the clearing dose is optionally obtained from a calibration step. Each feature is optionally partitioned into a plurality of subshapes and the incident dose of exposure energy is then adjusted for each edge of each subshape by designating the clearing dose for each edge of each subshape as a function of the dose height.

Dose, shape, and hybrid modifications for PYRAMID in electron beam proximity effect correction

Abstract: As the dimensions of circuit primitives are reduced, the proximity effect becomes an increasingly important limiting factor in the fabrication of high density integrated circuits using electron beam (e-beam) lithography. In the past, proximity effect correction schemes have in general utilized one of two different approaches: dose or shape modification. Previously, PYRAMID, a hierarchical, rule-based proximity effect correction scheme which has been demonstrated to be able to correct circuit patterns with a minimum feature size of 0.1 μm was successfully presented. Although PYRAMID has been implemented with a pattern shape modification technique, its correction algorithms are not limited to this approach. In this article, the two approaches are compared in details in terms of CD error (edge placement error) and edge contrast, using the two corresponding versions of PYRAMID. A hybrid approach, i.e., combination of dose and shape modifications, is also considered.

Method and device for electron beam lithography

Abstract: PROBLEM TO BE SOLVED: To minimize a dead time due to proximity effect correction calculation and improve the writing precision in the peripheral portion of a pattern, by carrying out proximity effect correction calculation during preliminary exposure at least with a minimum correction luminous exposure, and correction lithography for insufficient preliminary luminous exposure and actual proximity effect correction, thus performing exposure twice in total. SOLUTION: The writing coordinate, shot dimension, and standard luminous exposure outputted from a shot dissolving circuit ultimately drive a positioning deflection control circuit, a shaping deflection control circuit, and an irradiation time control circuit, respectively. An area density calculation circuit calculates the exposure area density corresponding to the writing coordinate from a shot dimension area and additionally writes it to a map memory circuit. In this case, lithography processing for area density correction calculation is carried out while preliminary exposure is carried out once for a constant irradiation time T1 with a minimum value of correction luminous exposure or less, and correction lithography is carried out again for an irradiation time T2 in accordance with the calculated area density distribution, thus carrying out lithography so that the sum of the variable irradiation time T2 and the previous constant irradiation time T1 is equal to an appropriate luminous exposure of corrected proximity effect.

Novel Proximity Effect Including Pattern-Dependent Resist Development in Electron Beam Nanolithography

Abstract: A novel proximity effect, which includes the effect due to secondary electron scattering to a range of less than a micron and the pattern dependence of resist development, has been found and investigated to develop a precise dose control method in electron beam nanolithography. Experiments and simulations including secondary electron scattering were performed for precise evaluation of the proximity effect. This result revealed that the proximity effect caused by secondary electron scattering to the range between 30 nm and a micron is not negligible for nano-patterns. In addition, from experimental estimation of the rate of development of patterns of various sizes, a significant decrease of the rate was found for patterns less than 30-nm wide. The difference of the rate is also modified by the background deposited energy due to surrounding patterns. Therefore, we have to be very careful about how we determine the proper dose for a given nano-pattern.

Low voltage electron-beam lithography based InGaAs/GaAs quantum dot arrays with 1 meV luminescence linewidths

Abstract: We have developed InGaAs/GaAs quantum dots with diameters down to about 50 nm on shallow quantum wells using low voltage electron-beam lithography and wet chemical etching. Due to the low energy of the e-beam of 2.5 keV the proximity effect is negligible and arrays of quantum dots with a homogeneous diameter could be fabricated. By using low excitation photoluminescence spectroscopy we observe a clear shift of the dot emission to higher energy due to lateral quantization that amounts to 6 meV in the smallest structures. The linewidth of the luminescence of the dot arrays of about 1.5 meV is almost independent of the dot size, i.e., the inhomogeneous broadening due to the patterning induced lateral size fluctuation is found to be negligible in the present structures.

Proximity effect correcting method in electron beam lithography technique

Abstract: PROBLEM TO BE SOLVED: To provide a proximity effect correcting method which can optimize the correction exposufe amount at the center of an unit division in a boundary region where the pattern area density sharply changes. SOLUTION: Firstly, (A) each unit division is subjected to bit map expansion, and the pattern area density in each of the unit divisions is calculated. (B) The pattern area density in each of the unit divisions is subjected to averaging process, and the pattern area density is calculated. (C) Stored energy caused by backward scattering is calculated on the basis of an EID(energy intensity distribution) function and the pattern area density. Secondly, (D) when the sum of square of the difference between the stored energy calculated in the above (C) and the stored energy caluculated on the basis of the pattern area density after the averaging process which is obtained in the above (B) is greater than or equal to a specified value, the pattern area density is corrected. The electron beam exposure amount in the unit division is corrected on the basis of the obtained pattern area density after correction.

Manufacture of mask pattern, manufacturing device of mask pattern, and mask manufacturing device

Abstract: PROBLEM TO BE SOLVED: To provide a manufacturing method of a mask pattern, a manufacturing device of the mask pattern, and a mask manufacturing device which are capable of adjusting an exposure, depending on variation of density of pattern area derived from a size adjustment of the writing pattern, increasing the tolerance in exposure size, satisfying an adjustment of proximity effect, and accurately adjusting the pattern. SOLUTION: A pattern size is changed by adjusting a size of writing pattern based on the pattern designed, using an offset means 100 (offset process). The exposure tolerance of an electron beam exposure is improved. The adjustment of proximity effect on the writing pattern adjusted in size is conducted, depending on the actual variation of the pattern area density resulted from the size adjustment by the adjusting means 200 of the proximity effect (adjusting process for proximity effect). The writing pattern with the proximity effect adjusted by the writing means 300 is drawn on the making substrate (drawing process).

Investigation of the proximity effect in amorphous AlF3 electron-beam resists

Abstract: A proximity effect occurs when two features having a close proximity are exposed using conventional organic electron-beam resists, subsequently causing overexposure of the region between the two features and ultimate broadening of the features. In this study, we employ probes of a through-focal series to irradiate amorphous AlF3 (a-AlF3) inorganic films. A proximity effect of a very different nature is also observed while employing the a-AlF3 films as self-developing electron-beam resists. Such an effect distorts the closely spaced features and sets a limit on the proximity of those nanometer-scaled features. According to the results of electron microscopy obtained while examining the peculiar behavior of the proximity effect, mass-transport phenomena are critical in the damaging behavior of the a-AlF3 films. Besides, our results presented herein demonstrated the ability of the through-focal probes to produce aluminum nanostructures of varying sizes in thin films containing a-AlF3 self-developing resists.

Mask pattern forming method capable of correcting errors by proximity effect and developing process

Abstract: In a method for forming a mask pattern which is exposed with light or electrons, a resist layer being exposed with light or electrons passed through said mask pattern to form a resist pattern, a light or electron beam intensity on the resist layer is calculated. Then, a deviation of a logarithmic value of the light intensity is calculated, and a ratio of a logarithmic value of a dissolving speed of the resist layer to a logarithmic value of the exposure is calculated. Then, a value is calculated by a 1/b . I where a is the deviation, b is the ratio, I is the intensity. Then, a size of the resist pattern is calculated by setting a contour having a predetermined value in a distribution of the value, and a difference between the mask pattern and the size of the resist pattern is calculated. Finally, the mask pattern is corrected in accordance with the difference.

Electron beam lithography data generating apparatus

Abstract: PROBLEM TO BE SOLVED: To provide an electron beam lithography data generating apparatus intended for the improvement of the dimensional accuracy of a resist pattern and reduction of the pattern forming time in electron beam lithography. SOLUTION: Data of an original pattern to be formed by the electron beam is converted into data of basic pattern into which a polygon composed of the marginal edges of the original pattern is divided so that the area of the inner pattern surrounded by a contour pattern having specified width is max. (S2, S3). Exposure data is so set that the inner pattern defined by the contour pattern of each basic pattern is exposes at specified quantity of exposure or less. This reduces the proximity effect of another pattern located near one pattern to be formed by the electron beam.

Electron ream exposure device

Abstract: PROBLEM TO BE SOLVED: To provide an electron beam exposure device capable correcting proximity effect without deteriorating the throughput, reduces blurs due to Coulomb effect, is easily to execute beam adjustment work, and the beam position of which is stable. SOLUTION: An aperture 18 is provided for a crossover position 19 on the upstream side from a mask 14. An opening angle at forming of an image of the mask 14 on a wafer 17 is determined by the aperture 18. Scattered electrons 23 and 24 generated from a part except for the pattern of the mask 14 pass through a transfer lens 15, and the end parts of then are cut by an aperture 21. They are image-formed on the wafer 17 with the opening angle decided by the size of the aperture 21. Since the opening angle of the scattered electrons 23 and 24 is several times as much as the opening angle of the electron beam 22 which passes through the pattern part of the mask 14, an image accompanied with blurs is obtained and makes accumulated energy distribution in resist on the wafer 17 flat. COPYRIGHT: (C)1999,JPO

Device and method for designing photomask pattern

Abstract: PROBLEM TO BE SOLVED: To provide a design fulfilling the design rule of a logic circuit and to easily obtain a photomask pattern including an optical proximity effect correction pattern where fine working accuracy is improved SOLUTION: This system is composed of the designing device possesses a pattern condition inputting part 2 used for the input of a pattern design rule which is a condition for extracting a photomask pattern part to be optimized at a usual photomask pattern, a pattern extracting part 7 extracting an optical proximity effect pre-correction pattern cell that is not suited to the pattern design rule and is corrected in terms of an optical proximity effect, a light intensity simulation part 9 repeatedly executing light intensity simulation for several times for a pre-optimizing pattern cell and a pattern optimizing part 10 optimizing the optical proximity effect pre-correction pattern cell based on plural simulation results COPYRIGHT: (C)1998,JPO

Method of transferring miniature pattern by using electron beam lithography system without proximity effect

Abstract: An electron beam lithography system radiates an electron beam uniform in beam current density through apertures formed in an aperture plate to an electron resist layer, and steps are formed in the outlet end portions of the apertures so as to decrease the beam current density of a peripheral portion of the incident electron beam, thereby preventing the electron resist layer from the proximity effect.

Pattern proximity effect correcting method, program and apparatus

Abstract: PROBLEM TO BE SOLVED: To provide a pattern proximity effect correcting method and apparatus for efficiently correcting the proximity effect, without depending on the skill of the designer SOLUTION: For forming a pattern on an object, using a beam pattern formed on the basis of a pattern data, the proximity effect of the pattern is corrected by computing an ideal beam intensity profile of the beam pattern for forming a pattern of desired shape on the object in the form of a continuously varying beam intensity profile(S1), dividing the edge of the pattern into segments according to the pattern data(S2), assigning displacement codes representing at least one of a first displacement along the normal direction of the segment and second displacement along the extending direction of the segment to the segments(S4), and changing the displacement code to displace the segments so that the beam intensity profile obtained from the pattern data approximates to the ideal one(S5)

On the way to 1 Gb: demonstration of e-beam proximity effect correction for mask making

Abstract: The e-beam proximity effect is well known as one of the limiting factors in e-beam lithography. As features get smaller the need for e-beam proximity effect correction increases. There exist different approaches to cover these effects by varying dose or shape of the pattern layout during the exposure step. Whichever algorithm is used, the question of proximity effect correction gets more and more a performance problem for forefront applications like the 256 megabit and 1 gigabit chips. The correction approach has to handle large data volume in reasonable time. Key to overcome this hurdle is to include hierarchial data handling into the proximity correction algorithm, which involves hierarchical data structures as well as hierarchy reorganization methods. The goal of the present work is to perform all necessary steps in order to guarantee the accuracy of the exposure result for the 1 gigabit memory chip. One step of the preparation is the e-beam proximity correction for raster scan machines. With respect to proximity effect correction, raster scan machines have a severe drawback. The scanning speed is constant while writing the layout, i.e., dose variation is not applicable to compensate for the proximity effect. There is, however, the geometry which can be exploited as degree of freedom. Geometrical variations of the layout underlie many constraints such as neighboring features, the exposure grid of the e-beam tool and, but not least, writing time. The paper presents how to solve some of the major problems occurring when proximity effect correction becomes an unavoidable step in the mask making process. Power and application limits of proximity effect correction for raster scan machines are investigated. The exposure has been carried out on a MEBES 4500 system. Process latitude and line width linearity are presented. In addition, practical questions like file size increase due to proximity correction are investigated. Exposure results of uncorrected and corrected pattern are compared to demonstrate the necessity of the correction as well as the improvement in pattern fidelity.

Resist Heating in Cell Projection Electron Beam Direct Writing

Abstract: Electron beam (EB) direct writing systems have often been used for fabricating sub-half-micron advanced devices because EB direct writing is the most practical method for making the required patterns. Recently, the cell projection (CP) method has become indispensable for increasing the writing throughput in the EB direct writing system. However, it is considered that resist heating may be seriously aggravated below the quarter-micron level when the CP method is used, because the total deposited energy, which is irradiated by one CP EB shot, is almost the same as that irradiated by one variably shaped (VS) EB maximum size shot. Resist heating in the case of the CP method is calculated by a finite element method using the ANSYS (Ver. 5.0A: ANSYS, Inc.) program. In particular, thermal diffusion calculation is mainly carried out under the conditions of 50 kV acceleration voltage and 10 A/cm2 current density for practical application to advanced device fabrication. The calculated results suggest that resist heating in the CP method is mainly caused by the horizontal thermal flux between plural EB shots within the area of one CP shot, by the same mechanism as proximity resist heating under the VS method. Therefore, CP EB writing causes horizontal-mode resist heating. In particular, when a low current density is used, this resist heating mode arises significantly. However, CP writing with high acceleration voltage causes a reduction in the rise of the resist temperature, which causes resist heating. When the EB irradiation time is longer than 1.0 µ s under practical EB writing conditions, the resist temperature increases proportionally to the decrease of writing pattern size in the case of the CP writing with a maximum shot size of 5.0×5.0 µ m. It is also shown that the larger the beam blur of an incident beam, the more serious is the resist heating. When a highly sensitive resist (10 µ C/cm2) is used under these practical conditions, however, resist heating in the CP method is prevented without writing throughput degradation regardless of the CP maximum shot size, because the resist temperature does not rise above the thermal denaturation temperature of standard EB resists. Accordingly, the maximum CP shot size, which affects the writing throughput, is determined by the proximity effect and the Coulomb interaction for fine pattern fabrication.

Method for correcting proximity effect

Abstract: PROBLEM TO BE SOLVED: To provide a method for correcting proximity effect which occurs in the case where a substrate patterned by a material having a large back-scattering electronic factor is subject to electron beam exposure. SOLUTION: A method is used to correct proximity effect during electron beam exposure, by emitting an energy beam to a sensitive substrate through a correction mask having a correction exposure aperture 31 in the case where present patterns 27, 28 and 29 are formed on the sensitive substrate in which a base pattern 43 is formed in advance, through electron beam exposure. The correction exposure aperture 31 where the area of the base pattern having a small back-scattering electronic factor within a small area 41 of the sensitive substrate is included is provided to the correction mask. COPYRIGHT: (C)1999,JPO

Method for forming mask pattern

Abstract: PROBLEM TO BE SOLVED: To provide a method for forming the mask pattern of a mask in which a pattern correction calculating time can be shortened, and an influence due to a light proximity effect can be precisely suppressed by suppressing the deterioration of the through-put of drawing. SOLUTION: In a mask pattern forming method at the time of forming a mask for an optical lithography by electron beam drawing, an exposure process by an electron beam is constituted of a first exposure process for operating exposure with constant exposure to the whole area of a pattern area 10, and a second exposure process for operating exposure with prescribed exposure to prescribed areas 100a-100d including edges 10a-10d. Thus, the correction of a light proximity effect in optical lithography can be precisely operated, and the deterioration of the through-put of pattern drawing can be suppressed by using the mask in which the mask pattern is formed. COPYRIGHT: (C)1998,JPO

Mask for exposing fine pattern and its manufacture

Abstract: PROBLEM TO BE SOLVED: To provide an exposing mask correcting the fine deviation of a pattern by proximity effect occurring when super-high resolution technique is used. SOLUTION: As to this exposing mask constituted of a phase shift film having an asymmetric hole pattern which has a second hole pattern 61 in the vicinity of a first hole pattern 6, and which does not have another hole pattern in the point-symmetric position of the pattern 61 with respect to the pattern 6 and a transparent base plate; the correction amount of the positions of the patterns 6 and 61 is calculated in accordance with pitch between the patterns 6 and 61, and the positions of the patterns 6 and 61 are corrected so as to avoid that the fine deviation of the pattern caused by the light proximity effect made stronger by the phase shift film 2. COPYRIGHT: (C)1999,JPO

Novel objective lens for low voltage electron beam imaging

Abstract: Low energy electron beams are increasingly being used in semiconductor manufacturing for wafer and mask inspection because of their low level of damage to the sample, and the reduced charging effects when the electron energy is close to EII where secondary electron yield is unity Also due to the short range of the electrons with the sample and the reduced proximity effect, electron beams with even lower energies are attractive for a variety of other applications such as surface studies, thin film microscopy, and lithography However, achieving high resolution and high secondary electron detection efficiency at 100 eV landing energy and below meets serious electron optical challenges To address this issue, we describe a low aberration objective lens that is combined with an efficient secondary electron detector The objective lens has a final electrode just in front of the sample to minimize the electric field at the sample surface We have optimized the design for minimum beam diameter and high secondar

Proximity effect correction method

Abstract: PROBLEM TO BE SOLVED: To enable a proximity effect to be accurately corrected even when negative photosensitive material is used. SOLUTION: The pattern region of a correction mask 6 is divided into a large number of small regions split at a pitch smaller than the spreading width of back scattering of an electron beam, and an opening which transmits an electron beam as large in size as an area obtained by subtracting a prescribed area from the non-exposed part of a region on a wafer 7 corresponding to the small region on the mask 6 is provided to each small region. An electron beam EB passing through the opening of a beam forming aperture 2 is made to irradiate the mask 6 through the intermediary of an object lens 3 and scan it by a main deflector 4 and an auxiliary deflector 5, and a wafer 7 is subjected to an exposure process by an electron beam EB which passes through the opening in each small region on the mask 6 as corrected on a proximity effect.

Pitch Dependence of Linewidth in the 0.25 µm Patterns Fabricated Using Positive Chemically Amplified Resist

Abstract: We investigated the proximity bias characteristic of 0.25 µ m patterns used with three types of positive chemically amplified resists of differing material and properties. To determine the proximity bias characteristics, we examined how the relationship between the pitch and the linewidth varies with post-exposure-bake (PEB) temperature and time. Our experiment revealed that each resist exhibits its own unique proximity bias characteristics. We also found that the proximity bias characteristics of the three resists depended to a large extent on the PEB temperature: the lower the PEB temperature, the greater the resemblance of the proximity bias characteristics to the optical characteristic. Considering this and using the pitch vs. linewidth curve with PEB time as a parameter, we concluded that the proximity bias characteristic of resists largely depends on the diffusion of acids and other thermal effects in the resists. These characteristics resemble optical characteristics as the PEB temperature decreases, the acids diffuse to a lesser extent, and the thermal effects decrease.

Determining method of critical dosage in electron beam writing

Abstract: PROBLEM TO BE SOLVED: To precisely determine critical dosage, by setting a specific value of dosage wherein, in a collective pattern written and developed by changing dosage, the pattern widths of the resist surface and the bottom surface become identical in the central part of the collective pattern, as the critical dosage SOLUTION: A collective pattern is constituted of the same rectangular repetition patterns which are arranged in a sufficiently wide region as compared with the spread of proximity effect in such a manner that the writing area ratio is 50% and translation symmetry is ensured The collective pattern is written Rectangles in one collective pattern are exposed with the identical dosage After the collective pattern is written and developed by changing the dosage, a value equal to one-half of the dosage wherein, the widths of the patterns of the resist surface and the bottom surface become identical in the central part of the collective pattern is set as the critical dosage

Fabrication and characterization of a regrown InP/GaInAs quantum point contact

Abstract: We demonstrate observation of quantized conductance of a regrown 90 nm wide quantum point contact (QPC) in InP/Ga/sub 0.25/In/sub 0.75/As at 10 K. The QPC is produced using high-resolution electron beam lithography and wet chemical etching to define the structure. PMMA was used as an etch mask during wet etching in HCl:CH/sub 3/COOH:H/sub 2/O/sub 2/ solution at 15/spl deg/C. Proximity effect due to mask exposure by backward scattered electrons decreases masking property of PMMA. To overcome a problem of insufficient masking ability of the resist, a post-development hard baking above the glass transition temperature (Tg) of PMMA was performed. Using this simple approach, we were able to produce the QPCs as small as 50 nm in width.

Practical implementation of top-surface imaging process by silylation to sub-0.20-μm lithography

Abstract: Top-surface imaging process by silylation (TIPS) has been suggested as an attractive solution to cope not only with limitation of resolution and process latitudes but also with line width variations due to reflections over steps. However this technique has not received a wide acceptance as a production worthy process until now, because of the stringent requirements on suitable silylation and dry development equipment that have good uniformity and good reproducibility. In a parametric study of TIPS dry development steps, we found the most important factors in the first step and the second step respectively. The optimized process demonstrated good etch rate uniformity and excellent 0.17 micrometer dense and isolated pattern of gate and islands pattern of capacitor in 1 G bit DRAM device. Their profiles were vertical and uniform within a wafer, while the proximity effect between dense and isolated pattern of gate remained 0.01 micrometer. In islands pattern, wider process margins of both local depth of focus (LDOF) and exposure latitude (EL) could be obtained and excellent 3(sigma) value of critical dimension (CD) uniformity within a wafer confirmed better applicability to 1 G bit DRAM and beyond. When silylated resist patten was transferred into substrate layer CD bias and uniformity could be controlled less than 0.02 micrometer. There were also no residues after both photoresist strip and induced polymer removal step. From these studies. TIPS process using cluster tool of silylation system made by LRC and TCP TM 9400 TM SE etcher for dry development was demonstrated a production worth process for the sub-0.20 micrometer lithography in terms of obtaining finer pattern without pattern problems and a reliable process for 1 G bit DRAM and beyond.