Silicon hardmask (Si-HM) materials used in lithography processes play a critical role in transferring patterns to desired substrates. In addition, these materials allow for the tuning of optical properties such as reflectivity and optical distribution for better lithography. Si-HM materials also need to possess good compatibility with photoresists before and after optical exposure, during which the photoresist in the exposed area may change polarity. Therefore, Si-HM materials may benefit from adaptive or amphiphilic capabilities to keep both exposed and unexposed photoresist compatible with the substrate. In this work, we will demonstrate that Si-HM surfaces may be adaptive or amphiphilic through both experiments and computer simulation. Specifically, we will demonstrate that the functional groups (polar and nonpolar) at the Si-HM surface may be switchable, and the surface will be dictated by the environment to which the Si-HM is exposed. Knowing the adaptive capability of Si-HM materials will greatly facilitate the development of better underlayer materials for improved lithography.
Measuring properties of ultrathin optical films is based on optical interference. Ultrathin films are very challenging to test, because their thicknesses are far smaller than the measuring wavelength, so very little phase shift can be detected. In this work, test sensitivity and accuracy are improved by a rigorous algorithm in which all unknowns {n,k,t} in their full space are fit together without approximations and presumptions. As a result, a software for variable-angle spectroscopic ellipsometer (VASE) data fitting was developed. It gives very reliable ultrathin-film measurement down to 2.5 nanometers. The software not only improves the reliability, accuracy of {n,k,t} measurement, but it also extends VASE capabilities to characterize a film’s optical quality.
A variable-angle spectroscopic ellipsometer (VASE) is an essential tool for measuring the thickness of a thin film, as well as its n and k optical parameters. However, for films thinner than 10 nm, precise measurement is very challenging. In this paper, the root causes of these measurement complexities are discussed, and a new approach is proposed to improve measurement accuracy and reliability as the VASE approaches its fundamental limits, that is, the limitations of the system’s mechanical accuracy and optical coherence. Specifically, twelve different polymer thin films were tested, each with 16 test points. The measured thicknesses (ranging from 3 nm to 19 nm) and n- and k-values strongly depended on test settings and on the data fitting algorithm, incident angle, and wavelength selection. Fitting using equal thickness and n-value of multiple test points was applied as additional criteria to evaluate the consistency of the test results. With this technique, reasonable n-values and thickness values were obtained from films that were as thin as 3 nm. To improve the efficiency of the model fitting, film thickness and n-value are associated to allow these two-dimensional parameters to be fitted into a quasi-one-dimensional model, which reduces central processing unit (CPU) utilization.
We have designed and tested a prototype TRL4 radio-frequency (RF) sensing platform containing a transceiver that interrogates a passive carbon nanotube (CNT)–based sensor platform. The transceiver can be interfaced to a server technology such as a Bluetooth® or Wi-Fi device for further connectivity. The novelty of a very-low-frequency (VLF) implementation in the transceiver design will ultimately enable deep penetration into the ground or metal structures to communicate with buried sensing platforms. The sensor platform generally consists of printed electronic devices made of CNTs on flexible poly(ethylene terephthalate) (PET) and Kapton® substrates. This novel remote sensing system can be integrated with both passive and active sensing platforms. It offers unique characteristics suitable for a variety of sensing applications. The proposed sensing platforms can take on different form factors and the RF output of the sensing platforms could be modulated by humidity, temperature, pressure, strain, or vibration signals. Resonant structures were designed and constructed to operate in the very-high-frequency (VHF) and VLF ranges. In this presentation, we will report results of our continued effort to develop a commercially viable transceiver capable of interrogating the conformally mounted sensing platforms made from CNTs or silver-based nanomaterials on polyimide substrates over a broad range of frequencies. The overall performance of the sensing system with different sensing elements and at different frequency ranges will be discussed.
As the critical dimensions for the feature sizes shrink, the thickness of the photoresist layer decreases to enable patterning without collapse of the photoresist structure. Simultaneously, the use of an antireflective coating underneath the photoresist layer becomes imperative for achieving good critical dimension control. The thickness of the bottom antireflective coating (BARC) and its etch rate relative to the photoresist determine how much resist is lost during the dry etch step. In order to minimize resist loss during BARC etch, we have designed BARC compositions that have high etch selectivity and optical constants (high n and high k) that make it possible for the BARC to be used much thinner than the existing BARCs. Furthermore, the new BARC compositions are single component systems and are therefore relatively simple to produce compared to typical BARCs. The polymer that forms the coating has high absorbance at 248nm and is also capable of crosslinking in the presence of an acid catalyst at elevated temperatures. These organic coatings are immiscible with photoresists and are not affected by the base developer. In this paper, we will report the etch properties, optical properties and compatibility with photoresists of these new coatings.
Among the variety of dual damascene (DD) processes, the via- first approach has drawn much attention because of its reduced process steps and improved photolithography process window. The via-first process requires a layer of via-fill material to be applied beneath the photoresist layer. The primary function of this via-fill materials is to act as an etch-block at the base of the vias to prevent over-etching and punch-through of the bottom barrier layer during the trench-etch process. However, such materials also help to planarize the substrate and may limit back reflection from the substrate as well, helping to control the critical dimension (CD) of the printed features. Based on this understanding, our research efforts have been focused on the advancement of DD-applicable bottom antireflective coatings (BARCs). A series of novel planarizing DUV BARCs with full- via-fill properties and enhanced etching selectivity to resists have been developed. They showed good full-fill, void-free performance in 0.20micrometers vias having an aspect ratio of five, also sufficient top coverage i.e., enough coating thickness, low surface variation, and little thickness bias of isolated-via (1:10) area versus dense-via (1:1) area. The resist sidewall profiles with features sizes less than 0.20micrometers indicated that there was good compatibility of the BARCs with the resists. The thin film etching selectivity to commercial resists was about 1.2:1 under an Hbr/O2 atmosphere. A study of the BARCs described in this report allows further discussion of the impact of pattern density, feature size, and processing conditions on BARC coating performance.
The work outlines a solution to the challenge of integrating a planarizing BARC into the via first dual damascene manufacturing process. We report the initial problems encountered in attempting the planarizing process and the resulting investigation into the coating process. We identify the critical parameters relating to the via fill performance of the material which relate not only to the process conditions, but also to the chemical make-up of the BARC. As a direct result of this study, a low molecular weight component within the DUV BARC has been identified which may be the key component to planarizing behavior. Cooperation from both supplier and user was necessary, as the availability of alternative test structures, with equivalent topography/surface chemistry, as device wafers was not possible. This resulted in considerable investment [from the user] of sacrificing product wafers for the analysis of the planarizing performance.
Dual Damascene (DD) process has been implemented in manufacturing semiconductor devices with smaller feature sizes (<EQ 0.20 micrometer), due to increased use of copper as a metal of choice for interconnects. Copper is preferred over aluminum due to its lower resistance which helps to minimize the effects of interconnect delays. Via first DD process is the most commonly used process for manufacturing semiconductor devices since it requires less number of processing steps and also it can make use of a via fill material to minimize the resist thickness variations in the trench patterning photolithography step. Absence of via fill material results in non-uniform fill of vias (in isolated and dense via regions) thus leading to non-uniform focus and dose for exposure of the resist in the deep vias. This results in poor resolution and poor critical dimension (CD) control in the trench-patterning step. When a via fill organic material such as a bottom anti- reflective coating (BARC) is used, then the resist thickness variations are minimized thus enhancing the resolution and CD control in trench patterning. Via fill organic BARC materials can also act as etch blocks at the base of the via to protect the substrate from over etch. In this paper we review the important role of via fill organic BARCs in improving the efficiency of via first DD process now being implemented in semiconductor manufacturing.
A fast-etching broad band bottom anti-reflective coating (BARC) for photoresist applications at the wavelength of 365nm, 248nm and 193nm was developed. The new BARC formulated in safe solvents such as ethyl lactate and PGME exhibits wide spin bowl compatibility with various photoresists, and can be processed with common edge bead removal solvents. The optical properties of the new BARC are tailored for high contrast resist systems, with film optical density exceeding 4.2 micrometers at 365 nm, 7.5 micrometers at 248 nm and 8.5 micrometers at 193 nm. Most importantly, we have demonstrated plasma etch rates of the new coating in excess of 1.5-2.0 times that of conventional i-line and DUV photoresist. The compatibility of this material with multi resists at all three wavelengths will be discussed as well as trade-offs versus dedicated single wavelength BARC systems.
A new bottom antireflective coating (BARC) for 248 nm lithography is described. The new coating has an optical density of approximately 10/micrometers (k equals 0.41 and n equals 1.482) and plasma etches at rates higher than that of DUV resists depending on the etch conditions. Coating conformality is superior to older generation BARCs, also contributing to improved etch dynamics. Excellent 0.25 micrometers features have been obtained with ESCAP, Acetal and t-BOC type photoresists. The new BARC is spin coated from safe solvents and is spin bowl compatible with EBR and photoresist solvents.
This paper reports on an optimization methodology for BARC/resist processes in order to obtain best CD-control on various substrate topographies. A selection of resist and BARC materials is studied by means of simulations and experiments. Two BARC properties, turned out to be of major importance: planarization effects on topography and etch behavior. The topography itself is very important too: step height and lateral dimensions have a severe influence on CD control. Based on a new evaluation technique, the use of topographical swing curves, the optimum thickness of the BARC layer and of the resist layer are determined.
We report here the development of a fast-etching i-line bottom anti-reflective coating (BARC): EXP97002B. The new BARC is applied from a safe solvent system, exhibits wide spin bowl compatibility with photoresists, and may be processed with common edge bead removal solvents. The optical density of the new BARC is 6.15/micrometer at 365 nm (n equals 1.71, k equals 0.39). We have demonstrated plasma etch rates for the new coating in excess of 1.5 - 2.0 times that of conventional i- line photoresists. The coating system planarizes substrate topography, reducing resist film thickness variations and, thereby, resist swing. Feature coverage is still excellent, as evidenced by the ability of the new BARC to coat 0.7 micrometer vertical topography. The practical issues for implementing the new BARC in a manufacturing environment is also discussed.
The properties of a new anti-reflective coating for 248 nm lithography are described. It is formed by thermally cross-linking a spin-on organic coating, and has an absorbance greater than 12/micrometers. It is compatible with UVIIHS and APEX-E photoresists. Thin films (less than 600 angstrom over silicon substrates) are found to completely suppress standing waves, to reduce EO swing curves to less than 3%, and to offer good CD control over typical field oxide topography. The etch rate was found to be comparable to that of the APEX-E photoresist.
Thin film interference effects in photoresist are the most serious issues for device production in sub-half micron patterning. These effects change the fraction of the energy available for photoresist absorption and subsequently cause serious line width fluctuation. One of the most realistic candidates from the point of view of the device mass production is the development of an organic bottom anti-reflective coating (ARC). Because organic ARC has high absorption characteristics of incident light, the standing wave in photoresist could be diminished. However, up to now, organic ARC still has some issues in resist profile (i.e. footing). Usually, the processes of organic ARC is optimized by tuning its thickness. Very little effort has been done on the optimization of post exposure bake. In this paper, the effects of post exposure bake temperature on resist profile and process windows, including energy latitude and focus latitude, of single line and dense line features will be discussed. The swing ratio is improved from 15.5 percent for the case without BARC to 1.2 percent for the case with ZHRi BARC of thickness 1010A (at top of reflectance curve). In term of PEB effect, PEB temperature of 90 degrees C is better than other conditions except it still has slight standing wave. With BARC, it can not only improve DOF process window from nothing to 0.8 micrometers of 0.35 micrometers dense and single line features but also reduce its proximity effect. Comparing the resist profile between BARC at top and bottom of reflective swing curve, the footing is much severe for the case of BARC with thickness at bottom of swing curve in HRi or XHRi material.
In this paper, we describe the results of experiments performed using wafers having either phosphorous (POCl3) doped polysilicon, LPCVD silicon nitride, LPCVD silicon dioxide, LPCVD silicon dioxide over POCl3 doped polysilicon, evaporated aluminum, or CVD tungsten thin films, patterned with and without the use of deep UV anti-reflective coatings. The parameters of reflectance control, critical dimension control, focus/exposure latitude, and resist profiles were studied for line/space gratings and contacts. Incorporation of anti-reflective coatings was shown to be very beneficial for reducing the impact of highly reflective substrates, grainy surfaces, and topographical features encountered during deep UV imaging. The ARC process is independent of the substrate's reflectivity, allowing the same exposure dose for all substrates studied. Without ARC the optimum exposure dose for the same substrates varied over a 35% range. ARC also provides slightly increased exposure and focus windows for some substrates, and was shown to significantly improve linewidth control on rough substrates such as POCl3 doped polysilicon and tungsten. The grainy surface of the tungsten wafers was nearly impossible to pattern without the use of an anti-reflective coating; without ARC, there was virtually no process window (approximately 2 mJ/cm2) for retention of 0.50 micrometers features.
This paper discusses issues concerning the use of a thin absorbing organic anti-reflective (AR) coating for 0.5 micrometers excimer laser lithography. Linewidth profiles, CD control, substrate dependence and etching are all affected by the presence of the AR coating. The advantages of implementing highly absorbing organic AR coatings are that CD control with resist thickness (swing curve) is improved, substrate reflectivity effects becomes negligible, adhesion is improved and reflective notching is decreased, leading to better CD control over topography. For example, the swing curve was reduced from 0.18 micrometers to 0.04 micrometers by using an absorbing AR film. Exposure/focus latitudes were modeled using Obelisk software. This gave an exposure dose of 26 mJ/cm2 for printing 0.5 micrometers dense lines on aluminum, poly- silicon, oxide, nitride and tungsten. In addition, the exposure latitudes for these substrates was found to be +/- 10% when the total depth of focus was 1.2 micrometers . Statistically designed experiments were used to optimize resist profiles of the SNR248 resist images on AR coating. Issues relating to implementing organic AR coatings under a 1300 angstrom absorbing AR coating reduced reflectivity variation on poly-silicon from 38% to 6% over a resist thickness range of 350 angstrom. By using the AR coating the swing curve variation was reduced from 0.18 micrometers to 0.04 micrometers .
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