In this paper we demonstrate the development and optimization of an 800 nm-thick Plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiN) photonic platform on a 300-mm silicon wafer. The implementation of ArF immersion lithography contributes to superior manufacturing processes, as it provides excellent critical dimension (CD) uniformity inter- and intra-wafers, make it an optimal platform of production of integrated circuits and nanoscale devices.
We introduce well-developed optical proximity correction (OPC) techniques to the metasurface-based flat optics manufacturing process. Flat optics, formed by subwavelength scale nanostructure pillar (nanopillar) array, so called metasurface, has become promising substitutes for conventional bulky optical components. For its manufacturing, photolithography is preferable rather than the electron beam lithography (EBL) technique because of its time and cost effectiveness for mass manufacturing. However, the required feature size and pitch of the metasurface for the visible light is approaching the process limit of the ArF immersion lithography. It results in critical dimension (CD) errors due to optical proximity effect and could result in efficiency degradation of the flat optics. In the semiconductor manufacturing industry, OPC based on process modelling and numerical computation has been developed for the last few decades to control the CD on the wafer. Here, a machine learning (ML) model is constructed to avoid the time consumption of the conventional OPC method without losing the accuracy. Various pitches of flat optics metalens, from 465 nm to 160 nm, has been studied for the implementation of the ML OPC. The root mean square (RMS) CD errors < 1 nm and the CD accuracies < 6 nm can be achieved. The CD error percentages over the pillar diameters < 6 % is observed and the improvement of CD error and CD accuracy compared to rule based OPC in small pitches of metalens is demonstrated.
We present the optical and electrical properties of AlN-based and 12% doped ScAlN-based pyroelectric detectors fabricated on 8-inch wafers respectively. Both AlN and ScAlN materials are deposited at a temperature of ~200oC, making them potential candidates for CMOS compatible MEMS pyroelectric detectors. FTIR spectroscopy is used to measure the absorption of these pyroelectric detectors over the wavelength range of ~2–14 μm and the results show absorption improvement up to ~75% for ScAlN-based pyroelectric detectors compared to that of AlN-based pyroelectric detectors at the wavelength of 4.26 μm where CO2 gas absorption of IR radiation is anticipated. Higher output current (~3-fold increase) is also observed from ScAlN-based pyroelectric detectors. Other than pyroelectric coefficient that contributes to improved performance for ScAlN-based pyroelectric detectors, we believe that absorptivity of the device also plays a major role in the performance of pyroelectric IR detectors. The results obtained from the study of the electrical and optical properties of AlN-based and ScAlN-based CMOS compatible MEMS pyroelectric detectors will bring forth potential applications of these detectors onto multi-functional integrable and monolithic platforms.
We experimentally demonstrate a switchable metamaterial absorber for infrared spectral region using MEMS technology. In order to achieve active tunability; air gap is introduced as the part of dielectric spacer layer and is electrostatically actuated. As the air gap is decreased, the peak absorption wavelength will blue shift accordingly. The tuning range is approximately 700 nm for 300 nm air gap change. Complementary cross is used as the metamaterial unit cell pattern. Owing to the π/2 rotational symmetry of the metamaterial unit cell geometry and out of plane actuation direction of the metamaterial layer, the resultant absorption retains the polarization insensitive characteristics at different actuation states. Additionally high temperature stable materials such as, molybdenum and silicon-di-oxide are used as structural materials for potential use in rugged applications.
In this paper, the issue of intensity imbalance in an alternating phase shift mask has been studied for hole patterns with pitches 300 nm and below. A method of processing is developed, which would nullify the effects of phase errors that cause focus dependent difference in the sizes of holes belonging to opposite phases. This method uses two exposures with opposite foci. Using this method, the effect of the focus on the difference in the size of holes from opposite phases could be totally eliminated. It also changes the nature of the focus curve, bringing a significant improvement in the depth of focus without affecting exposure latitude and mask error enhancement factor. The method works quite effectively for all the via pitches, however, some constant size difference existed across focus, that is easily correctable by biasing one phase with respect to the other. It was also found that this technique could bring remarkable immunity against the lens aberrations such as defocus and astigmatism.
This paper studies the concept of and challenges in patterning trenches using hybrid phase shift mask. Our hybrid mask consists of alternating, chrome-less and 20% attenuated phase shift features on the same reticle. Using this mask, we could pattern across-pitch 120 nm trenches on 0.68-NA, KrF lithography scanner, which is equivalent to K1 of 0.33. However, many challenging issues like unequal best focus for different duty ratios of the same technique and same duty ratio of different techniques, variation in the dose requirements despite aerial image CD matching and the pitch dependent variation in the critical dimension imbalance of the zero and π phased trenches are observed. These issues, that are question marks on the viability of hybrid mask, are presented in this paper. Hybrid mask manufacturing and characterization data is also included to justify that the issues are not because of the mask manufacturing process.
One of the contributions to pattern placement/misalignment may come from the mask making process itself, in chromeless masks. This contribution will be important at 90 nm and smaller nodes. Hence it is necessary to estimate this contribution and find ways to minimize this. In this paper an effort has been made to measure this misalignment accurately. A series of box in box structures for overlay measurement, on KLA and CD SEM, were designed on the reticle. The structures had an outer box of etched chrome and an inner box with 180 degree phase. The edge of the chrome was used as the edge of the outer box. The line printed at the phase intersection was used as the edge of the inner box. Each of these structures were put in with a pre-determined value of X and Y misregistrations. The CD SEM structures were smaller in size but designed the same way as KLA structures. Such structures were put at 4 corners of the die. Overlay measurements were carried out using the optical overlay machine as well as CD SEM. An average misalignment of 11 nm and 1 nm were found in the X and Y directions respectively. When the results from each die corner was analyzed, it was found that the X misalignment had two different distributions. Also, exposure parameters such as focus and partial coherence for best misalignment measurement points were investigated. It is concluded that for obtaining accurate misalignment data, measurements should be conducted at a focus where the two opposite phase edges pattern at similar width. Also, a higher partial coherence is recommended as aberrations such a coma have more profound influence at lower partial coherence and this could contaminate the true misalignment data.
A method to fabricate a very thin channel body Fin-FET and Tri-gate MOSFET is presented. 8% Attenuated Phase-shift mask (APSM) and single phase chrome-less mask (CLM) techniques are evaluated to pattern fins in sub-50 nm regime using KrF lithography scanner with a maximum numerical aperture of 0.68. Some of the issues of single phase CLM technique with respect to fin patterning are highlighted. Dual Exposure With Shift (DEWS)’ is introduced to pattern gate lines down to 80 nm using binary mask.
Scattering bars have been an essential component of the reticle layout design to increase process yields for devices with design rules that are 0.18 um and below. These are sub-resolution features and make semi isolated and isolated features to be imaged like dense features as the illumination conditions are always decided by most dense pitch. With the use of scattering bars the depth of focus and iso-dense matching get improved. This results in better critical dimension (CD) control in the wafer fabs. Scattering bar has been helpful in extending the limit of optical lithography. This paper describes the effect of scattering bars width and separation on the printed feature size. Trench patterning is studied at different partial coherence and lens numerical aperture (NA). Also, the effects are compared for binary and 8% attenuated phase shift mask (APSM). The patterned feature size is found to be more sensitive to scattering bar parameters at small NA and low partial coherence. The CD of the feature has strong dependence on scattering bar separation than size and also influenced by the NA and sigma. An interesting phenomenon at low partial coherence is the presence of deep valley or 'V' shaped CD trend in scattering bar separation versus CD curve. CD dip is more on APSM as compare to binary mask.
This paper studies the alignment performance of dual damascene patterning using two different integration schemes. These schemes cater to two different low K materials. The via first scheme is used for CVD type material while the dual hardmask trench first is used for spin on low K material. The alignment and exposure is performed on Nikon scanner S203B using LSA (Laser Step Alignment; a scattering based system) and FIA (Field Interferometer Alignment; a contrast-based system) systems while the overlay is measured on KLA 5200XP.
Many different mark designs were evaluated for both the schemes. The effect of resist coat was found to be different on different mark types. Difference was also seen in the signal strengths in X and Y directions. Process optimisation for scanner was done by varying the slice level, signal processing algorithms, and focus. The initial alignment mark evaluations were done by studying the signals obtained from such marks and comparison of Static Random Factor (SRF) and Dynamic Random Factor (DRF) obtained from the scanner. The best marks were then applied to the lot splits and the final performance was evaluated by measuring the total overlay results. Results showed that SRF and DRF evaluation could be used for screening to find out the best marks for a certain level. It can also be concluded that dual damascene alignment is possible with trench first scheme that has small step height using the LSA window mark or the FIA narrow island mark. For both schemes the best performer was the FIA Narrow Island Mark. Hence it can be concluded that better alignment performance could be obtained by special alignment mark designs for a specific level.
Attenuated Phase Shift Masks (att PSM) have become very popular in the industry for printing contact holes. Higher transmission att PSM generally tends to give a better depth of focus and exposure latitude. However, the main drawbacks of using higher transmission masks are side lobes, printing of unnecessary patterns and resist erosion. The side lobbing is strongly dependent on the feature size, pitch, coherency of exposure radiation, illumination type and the transmission of the mask being used. Along with these factors, the other most important factor is the resist contrast. In this paper the effect of pitch, feature size, and resist sensitivity were evaluated on side lobes and rings formation for via holes designed down to 180 nm. Six different pitches were studied (1:1 to 1:5). Two different types of resists were used and the mask transmission used for the study was 8%. Simulations were carried out using PROLITH 3D version 7.1 from KLA Tencor while the experimental verifications were done at Nikon 248 nm step and scan tool. The experimental results were found in accordance with the simulation data. The effect of NA & (sigma) have also been studied on resolution, exposure latitude and depth of focus.
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