As a chemically amplified resist, UVN30 has been evaluated for mask use in high density pattern rapid fabrication by
electron beam lithography. This resist displays excellent sensitivity and reasonable resolution for dense features. At
optimum conditions proximity effect is eliminated and 75 nm and 150 nm dense lines resolved in a 300 nm thick film
with writing field of 1mm2. With UVN30 mask, Si nanostructures are etched by non-switch DRIE etch chemistry
developed in this work, which achieves high etch rate and smooth sidewall. This method is a promising technique for fast
speed fabrication of nanophotonics, nanochannels and Si master stamps for nanoimprint.
Pattern placement error (or pattern distortion) caused by different thermal expansions between templates and substrates in nanoimprint lithography is experimentally investigated. Using fabricated nanorulers, placement errors are quantitatively measured. Our results prove that nanoimprint lithography (NIL) with a heat cycle does have considerable error of pattern placement. But that is not the case with imprints at room temperature. This indicates that low-temperature or room-temperature imprints should be effective solutions.
This paper proposes to apply nanoimprint and soft lithography to the manufacture of large area planar chiral photonic meta-materials. Both dielectric and metallic chiral structures in nanometre order were replicated by nanoimprint lithography (NIL). To carry out the NIL, a nanofabrication process for imprint templates with chiral features was developed. For the dielectric chiral structures, a single layer of thick hydrogen silsequioxane (HSQ) was used, and for metallic chiral ones a bi-layer PMMA/HSQ technique was employed. The polarization conversion capabilities of planar chiral structures (PCS) imprinted in dielectric materials have been experimentally observed. This indicates that the developed nanoimprint processes in this work have the prospect of manufacturing planar photonic meta-media in high volume at low cost. A hybrid lithography combing nanoimprint and soft lithography is proposed for the constructions of chiral cavities inside dielectric materials.
Development of microfabrication technologies for MEMS and MOEMS has been reviewed. Depending on the materials, the fabrication technologies are grouped into silicon and non-silicon processes. Inherited from semiconductor industry, silicon process technology is the dominant technology in manufacturing MEMS and MOEMS. Past and present progresses in silicon micromachining have been described. However, there is a growing trend for non-silicon materials in MEMS and MOEMS devices and systems. Variety of materials can be used, including metals, polymers, glass, ceramics, etc. They often offer better performance and low cost of manufacturing than silicon. Although in research community new microfabrication technologies are constantly being developed, the industry requires as few as possible processing technologies so that the complexity and cost of manufacturing can be greatly reduced. MEMS industry needs standardization so that it can prosper like the semiconductor industry. However, there are great hurdles in standardizing MEMS fabrication technology. The fragmented market and diversity of applications make the standardization much more difficult than the semiconductor industry. One formula of standardization is the establishment of foundries. It has been a magic formula for semiconductor industry, but has not been so magic to the MEMS industry.
Aiming at correcting chromatic aberrations in a far-infrared band, the fabrication of a hybrid microlens array with one-step lithography is proposed, by using a coding grey-level mask. The designed hybrid microlens consists of a refractive microlens and a diffractive microlens in physics. Its structure parameters, in order to achieve the best correction of chromatic aberrations, are evaluated and optimized with the software OSLO to design the layout the grey-level mask. Based on the theory of partial coherent light, the photoresist exposure model and development model, the profile of hybrid microlens in the photoresist have been simulated, the nonlinear errors in the lithography process can be pre-compensated by correcting the mask design. A hybrid microlens array is fabricated through use of the designed mask.
The advance in microlithography has greatly helped the development of microoptical elements. Large array of microlenses can now be fabricated in the same fashion as manufacturing of integrated circuits. Because most of the microoptical elements require well-defined and continuous surface relief profile, special methods are needed to supplement to the normal microlithography to produce those relief structures. One of the techniques is greyscale lithography, including electron and laser beam direct write and greyscale photolithography. In this paper, the development of greyscale photolithography is reviewed, in comparison with the direct write techniques. The new development in coding method for greyscale mask is introduced. The importance of correcting non linearity in optical imaging and resist development is discussed. A discussing is also devoted to practical issues in mask fabrication, thick resist patterning and pattern transfer process.
Polymerase chain reaction (PCR) microvessel, capillary electrophoresis (CE) microchannel and impedance electrodes were integrated in a monolithic biochip. This paper reports on the detailed designs and fabrications of the PCR-CE-detector integrated biochip. The CE microchannel and PCR microvessel were fabricated with PDMS poured on a master made by SU-8 photoresist. The electrode plate was integrated with Au heater and temperature sensor for PCR amplification, electrodes for CE separation and impedance detection. The structure of the microfluidic channel was introduced and the impedance of microelectrodes on the chip was simulated.
The beam sampling grating is one of the important diffractive optical elements used in the field of laser sampling. It can be considered as an off-axis, binary phase, Fresnel zone plate. Base don the theory of interference, the principle of the variable period grating formation process is analyzed perfectly and the transmissive function of the BSG is obtained. This paper repots to fabricate the BSG with electron-beam direct writing. Compared with the holographic method, the new method is simpler, cheaper, and more efficient to manufacture elements on a large scale.
A new technique to fabricate arbitrarily shaped microstructures by using LCD (liquid crystal display) real- time mask is reported in this paper. Its principle and design method are explained. Based on partial coherent imaging theory, the process to fabricate micro-axicon array and zigzag grating has been simulated. The experiment using a color LCD as real-time mask has been set up. Micro-axicon array and zigzag grating has been fabricated by the LCD real-time mask technique. The 3D surface relief structures were made on pan chromatic silver-halide sensitized gelatin (Kodak-131) with trypsinase etching. The pitch size of zigzag grating is 46.26micrometers . The caliber of axicon is 118.7micrometers , and the etching depth is 1.332micrometers .
There are considerable interests in integrating Polymerase chain reaction (PCR) on a microchip can have much fast heating and cooling rate, the delicacy in its structure makes the PCR experiment difficult and cracks often occur particularly for the thin membrane type of PCR chips. Design study and experiment of silicon PCR chips are presented with the aim of identifying the problems encountered in experiment and finding an optimum chip structure. Heating characteristics of four different heater designs have been compared, so have the PCR chambers with fixed frame and with suspended frame. The thermal stress analysis has shown that the structure and heater design can make a significant difference in heating characteristics and in reducing the failure of PCR chips. Different solutions to reduce PCR chip failure have been proposed. One of the solutions was implemented in the experiment, confirming the design study results. Silicon PCR chips have been fabricated. Thermal cycling and initial DNA amplification results are presented.
In this paper, we present a new method to improve the image quality and resolution of photolithography by filtering in fractional Fourier domain. Introducing a filter into fractional Fourier domain can not only increase the flexibility of the filtering operation, but also enhance the image quality and the depth of focus in photolithography. The corresponding simulation results are illustrated.
FEA modeling of a thermally-excited silicon beam resonant pressure sensor is presented. The sensor consists of two bonded silicon chips, one with an etched beam and another with an etched diaphragm. FEA modeling is carried out on temperature distribution, resonant frequency shift due to thermal stress, effect of heater/detector elements on the natural resonance frequency, design of diaphragm geometry, and sensitivity of pressure measurement. The resonant pressure sensor samples are realized by silicon micromachining are measured. There is a satisfactory agreement between theory and experiments.
The PCR amplification is based on multiple temperature cycles of DNA synthesis; each includes denaturation of the template, annealing of the primers to complementary sites in the template and primer extension. The key technique of PCR amplification is the heating control in design and fabrication of its chip form. The specifications of the chip are heat properties. In this paper the heat properties of a micro PCR vessel integration heater and temperature sensor was introduced. The temperature distribution of the vessel was simulated with software tool IntelliSuite. The temperatures cycles were measured and the time response of the chip was discussed. It is found that the integrate micro vessel is a very useful tool not only for DNA synthesis but also as a biochemical reactor for many other biological and chemical analyses.
Simulation of photomask patterning process and optical lithography at wafer level has been combined to investigate the influence of a distorted photomask feature on final photoresist image. Unlike the previous optical lithography simulations which were based on ideal mask designs, the optical lithography simulation presented in this paper is based on distorted masks. The distorted mask comes from electron beam lithography simulation or laser direct write simulation. Proximity effects in e-beam lithography or laser direct write has been taken into account. The results have shown that optical proximity effect is worsened if a distorted mask is used in the optical lithography simulation, instead of an ideal mask.
Polymerase chain reaction (PCR) on a microchip has drawn considerable attention in recent years. Although a microchip can have must fast heating and cooling rate, the delicacy in its structure makes the PCR experiment difficult and cracks often occurs particularly for the thin membrane type of PCR chips. Electrothermal modeling of PCR chips is presented using commercial MEMS software tool IntelliSuiteTM, with the aim of identifying the problems encountered in experiment and finding an optimum chip structure. Heating characteristics of four different heater designs have been compared, so have the PCR chambers with fixed frame and with suspended frame. The thermal stress analysis has shown that the structure and heater design can make significant difference in heating characteristics and in reducing the failure of PCR chips. The computer simulation has confirmed what has been found in experiment the reason of membrane cracks. Improvement in PCR chip design has been proposed.
Patterning of thick layer SU-8 photoresist has been investigated with different radiation sources, including electron beam, X-ray, i-line stepper, UV mercury lamp with collimator, as well as two different types of UV contact maskaligner. Feature profiles with thickness up to 1 mm have been compared. Among all the radiation sources, x-ray exposure from a synchrotron radiation source is found to produce the best feature dimension control and has the highest feature aspect ratio. I-line stepper can also produce features with steep side wall but is limited to less than 200 micrometers resist thickness. The illumination parallelism is the key to control the resist profile, no matter what radiation sources are used. Other issues such as process condition become important when resist layer thickness is over 500 micrometers . Conditions for better profile control with thicker layer SU-8 photoresist are suggested.
Distortion effect in optical proximity corrected (OPC) masks on wafer level image has been investigated using combined simulation of photomask patterning process and projection optical lithography. Unlike the previous simulation of optical proximity effect, which were based on ideal mask design, the simulation presented in this paper is based on distorted mask features. The mask feature distortion comes from simulation of electron beam lithography or laser scanning lithography. Proximity effects in e-beam lithography or laser direct write has been taken into account for the generation of mask features. The simulation has demonstrated that the OPC compensation features are significantly distorted at mask level. Such distortions have noticeable impact on the wafer level resist images.
A new type pressure sensor based upon an electro-thermally driven and piezo-resistively sensed SiN-beam resonator is presented. A finite element analysis (FEA) method is involved to analyze the relationship between the excitation power, thermal stress, applied pressure and the resonant frequencies of the beam. The sensor is fabricated using silicon micro- machined technology and fusion bonding. Measurements yield a fundamental frequency of about 85 kHz and Q-factor of 1000 in air at atmospheric pressure, rising to over 40,000 in high vacuum (<0.01 Pa). A special close-loop detecting technology is employed to measure the response of the resonant frequency at different applied pressure loads. A 0 - 400 kPa sensor has a good linear frequency/pressure relationship. The span is about 10 kHz over the full pressure sweep, and the pressure sensitivity is about 23.8 Hz/kPa.
Modelling of a silicon resonator as a pressure sensor is presented. The resonator is electrothermally excited and the resonance frequency shift is detected by a piezoresistive thin film detector. Computer simulation using commercial MEMS software tool IntelliSuiteTM is compared with analytical model. Various design aspects, such as the pressure sensitivity, electrothermal heating of vibrating beam, influence of detection current and damping effect are investigated. Silicon resonator sensor have been fabricated and measured. The characteristics predicted by computer simulation has been confirmed by experimental results.
A new method has been developed to fabricate refractive microlens by etching ammonium dichromate gelatin (ADG) with enzyme solution. Unlike previous methods which are used to fabricate refractive microlens with photoresist, the process of fabricating microlens by etching ADG with enzyme solution doesn't require the use of expensive equipment, and it isn't sophisticated and time consuming. The light exposes ADG through a high contrast binary mask, then the exposed parts of ADS generate cross- linking reaction. Usually, the relief achieved by water developing is very shallow (<1um) when nonpre-harden gelatin is used, so we compound a certain concentration enzyme solution, and because of surface tension, ADG turns to spherical structure after developing. The optimum technique parameters of this process are presented. Results are presented for experiments and evaluated by profile meter and interference microscope.
Based on the energy conservation law, a modified proximity function is proposed to describe the absorbed energy distribution in photoresist during laser writing. The measured data for photoresist absorbing energy are fitted well to the modified proximity function. We analyze the proximity effect in laser writing by using the new model, it is helpful to further develop the precompensation and multi- exposure methods to correct proximity effects in laser direct writing.
Generally, a laser direct writing lithography system can only produce feature sizes larger than its beam spot size. When the feature size is comparable to its spot size, corner rounding and line shortening appears. This is caused by optical proximity effect. The effect is mainly due to light intensity spread in a laser beam which causes the spread of photon energy in resist layer. A new pre-compensation method has been developed to correct the optical proximity effect. The method has been implemented in the ISI-2802 laser direct write system. Feature size down to 0.6 micrometers has been produced with the system which normally can only produce 1 micrometers lithography without proximity correction.
Electron beam lithography is favored as one of the options for microlithography of ICs at below 150 nm resolution regime. To assist lithography process development, computer simulations are widely used. Current simulation packages for electron beam lithography are only able to offer simple solutions. A new simulation package MOCASEL is presented in this paper which offers a total solution to many issues encountered in current and future application of e-beam lithography. A number of modules have been built into the package, which can simulate not only 2D and 3D resist profiles on a flat substrate but on a topographical substrate. Proximity effect correction can be simulated to check its effectiveness. Signals from alignment mark detection can be calculated. Heating effect due to e-beam irradiation of resist can be estimated. All these modules are explained in the paper with simulation examples in the form of 2D and 3D resists profiles.
In this paper, a new method has been proposed to realize fine OPC with gray-tone coding mask instead of gray-tone mask. The relationships of the gray-tone coding mask and gray-tone mask have been discussed, and OPC simulation results are given with the gray-tone coding mask.
A new method is proposed to design gray-tone masks for fabrication of surface relief microstructures. Unlike previous methods which modulate the light intensity by changing the cell size or cell pitch only, the method relays on adjusting both the shape and position of a cell which gives an extra freedom to control the design accuracy. Using the new method a gray-tone mask has been designed to produce a hemispherical shape relief structure. Based on the theory of partial coherent light and the resist development model, the intensity distribution through the gray-tone mask and exposure of photoresist have been simulated. Nonlinear effects in aerial image and resist development have been taken into account to correct the mask design. The accuracy of the gray-tone mask design has been confirmed by simulation of 3D resist profiles.
Based on analysis of physical mechanics on optical proximity effect, we present a new method for fine correction of optical proximity effect and point out that the optimum of amplitude distribution on mask can improve distribution of spatial frequency spectrum, so intensity distribution of printed image near ideal distribution can be obtained. The simulation results show that deviation between contour of image after OPC and contour of ideal image is less than 0.009.
A new software package TEMP has been developed to simulate resist heating effects in high throughput e-beam lithography for photomask manufacturing. The TEMP package is based entirely on numerical methods. It consists of three simulators; the energy deposition simulator by 3D Monte Carlo method, the thermal diffusion simulator by 3D finite difference method and the resist development simulator by 3D cell removal method. A new double-cell numerical scheme was developed to achieve high accuracy of temperature information for fine pattern structures without high demand on computer memory. The change of resist sensitivity due to heating was experimentally characterized by a heating stage constructed inside an e-beam lithography system. The resist layer was exposed while it was being heated at different temperature. The measured sensitivity variations due to heating were fitted into an empirical model and is employed in the resist development simulator, so that the 3D developed resist images with heating effects can be simulated.
A new micro deflection scheme has been proposed for pixel addressing in color field emission display devices. With a pair of in-plane micro deflectors, three color pixels in an image call can be illuminated by a single field emitter array instead of three field emitter arrays in the conventional pixel addressing scheme. The feasibility of micro deflection concept is confirmed by 3-D computer simulation using a charge density method. The new scheme offers four times higher display resolution than conventional pixel addressing scheme without losing image brightness. The fabrication of micro deflectors and driving circuitry are comparable to the conventional addressing scheme.
The difficulty of using focused ion beam (FIB) tools for embedded phase shift mask repair is the removal of gallium ion stain. Conventional anti-staining techniques, such as post-repair plasma etch or XeF2 assisted FIB sputtering, is not applicable to embedded phase shift masks because of the phase shifting error introduced by additional substrate etch. A novel techniques, focused ion beam biased repair, has been developed to eliminate the post-repair residual defects caused by gallium ion staining. The biased repair involves sputter removal of an opaque defect to an area larger than its original size. The reduction of light transmission due to gallium stain is then effectively compensated by the enlarged repair. The concept of introducing a bias is also extended for clear defect repair, which makes it possible to repair a clear defect by using simple FIB induced carbon deposition with no need to create a proper transmission and phase shift. The new technique has been confirmed by both computer simulations and experimental repairs of MoSi and CrON embedded phase shift masks.
Chemically amplified resist AZPN114 from Hoechst has been extensively investigated for electron beam lithography at 150 nm resolution and below, using commercial e-beam lithography systems. Experimental design method was used to study the combined effect of pre and post exposure bake conditions on the performance of AZPN114 at 150 nm nominal linewidth. The effects of scanning field size of an e-beam system, the exposure energy, the resist thickness an pattern density, development conditions and post exposure delay have been investigated on resist sensitivity and resolution capability. One hundred nm resist lines with 7:1 aspect ratio and 50 nm resolution have been achieved using AZPN114 with optimized exposure and process conditions.
The reduction of image intensity in a rim phase shift mask (PSM) for contact holes has been investigated by computer simulation and experimental lithography. The reduction occurs at contact hole size below 1.0(lambda) /NA. The smaller the size the severer the reduction. A new design of rim PSM called partial rim PSM, is proposed to overcome the problem. Computer simulation of aerial images has shown that the partial rim PSM can enhance image intensity. The enhancement is more significant for smaller size of contact holes while the degradation of image quality is much less than a biased rim PSM proposed previously. The partial rim PSM has been fabricated using the same self-aligned process as for conventional rim PSM fabrication. The contact holes with partial rims and with conventional rims have been printed on a wafer by a g-line stepper. The experimental result has confirmed the improvement in image intensity achieved by the partial rim PSM.
Rim and attenuated phase shift masks can extend the range of i-line optical stepper lithography to 0.4 micrometers with enhanced depth of field. The repair of defects through subtractive and additive methods using focused ion beams is critical to the future success of the technology. Printability tests and simulation studies demonstrate the hierarchy of defects in which both rPSM and aPSM types are less tolerant of absorbing/attenuating defects, but more tolerant of clear defects than the corresponding conventional BIM. Repair trials reveal the existence of a new type of post repair defect - the phase trench - but also clearly demonstrate the feasibility of repair using FIB methods.
Proc. SPIE. 2437, Electron-Beam, X-Ray, EUV, and Ion-Beam Submicrometer Lithographies for Manufacturing V
KEYWORDS: Software, Lithography, Electron beam lithography, Electron beams, Polymethylmethacrylate, Data modeling, Scattering, Laser scattering, Scanning electron microscopy, Critical dimension metrology
The computer aided proximity effect correction program CAPROX has been used to correct structures written at 20 keV electron beam energy. A new method has been developed to determine proximity parameters for a given e-beam/resist/substrate system. Proximity parameters for PMMA and EBR-9 and chemically amplified negative resist AZPN114 have been determined, and compared with those obtained from the established 'doughnut method'. The new method provides more reliable and accurate values, particularly for the forward scattering range. The dependence of (alpha) , (beta) and (eta) on resist thickness was also measured and the sensitivity of proximity correction using CAPROX to variation in all three scattering parameters was demonstrated. The new method improves CD linewidth linearity and accuracy in the range 0.1 approximately equals 4.0 micrometers , achieving linewidth for both lines and gaps within 100 nm of designed size.
Rim and attenuated phase shift masks (PSMs) are the most promising candidates for mass ASIC production. Computer simulations have been carried out to compare their merits and limitations. It has been shown that both rim and attenuated PSMs improve the exposure latitude and depth of focus compared with a conventional binary intensity mask. An attenuated PSM demonstrates a higher exposure level and better defocus performance than a rim PSM, especially for sub-half micron contact holes. The comparison is based on a combination of criteria, since it is found that different conclusions may arise from computer simulations based on the analysis of an aerial image, if different evaluation criteria, such as log-intensity slope, image contrast or exposure-defocus tree, are applied independently. Examples illustrate the importance of choice of evaluation criteria. The superior performance of the attenuated PSM over conventional masks is confirmed by i-line experimental lithography.