The 45-nm node will require the use of thinner photoresists, which necessitates the use of multilayer pattern transfer
schemes. One common multilayer approach is the use of a silicon-rich anti-reflective hardmask (Si BARC) with a
carbon-rich pattern transfer underlayer (spin-on carbon, or SOC). The combination of the two layers provides a highly
planar platform for a thin resist, and provides a route to etch substrates due to the alternating plasma etch selectivities of
the organic resist, inorganic Si BARC, and organic SOC. Yet such schemes will need to be optimized both for pattern
transfer and optics. Optimizing optics under hyper-NA immersion conditions is more complicated than with standard
(that is, NA<1) lithography. A rigorous calculation technique is used to evaluate and compare standard lithography to a
hyper-NA case using a multilayer stack. An example of such a stack is shown to have reasonable lithographic
The 65nm half pitch node will require 193nm wavelength in combination with NA > 0.9 to keep k1 above 0.3. With such high angles of diffracted light the relative amount of TE (or s) polarization that contributes to image formation increases. Unfortunately, the swing curve for TE polarization is higher than normal for traditional BARC materials. This study explores new advanced bottom anti-reflective coating (BARC) materials dedicated to ultra-high NA imaging. The improvements in imaging performance over traditional BARCs are shown through simulations and experimental results with the latest high NA TWINSCAN XT:1400 exposure systems. Simulations will show the relation between various BARC and top anti-reflective coating (TARC) material approaches and high NA imaging performance. This was done, among other things, as function of illumination settings. These simulations are accompanied by experimental results with the different suggested BARC strategies as multi-layer BARCs and tunable reflective index materials. Initial experiments were done on the TWINSCAN XT:1250 with 0.85NA. After analyzing these results, further tests were done on the TWINSCAN XT:1400 NA=0.93 exposure system. These results verify the feasibility of the newly developed BARC materials.
As the semiconductor industry constantly increases the information density and the speed of integrated circuits, the control over the shrinking critical dimension (CD) becomes increasingly important. Soon the current 248 nm exposure tools will be insufficient to meet the needs of the shrinking CD. Shorter wavelengths, such as 193 nm, will be required to progress to smaller feature size. However decreasing the exposure wavelength makes the control of the feature size even more difficult, due in part to a sharp increase in substrate reflectivity with decreasing wavelength. Controlling this reflectivity through the use of bottom antireflective coatings (BARCs) will play an important role in the success of upcoming lithographic technologies. While there are successful spindon organic BARCs for 193 nm lithography, continuing improvements in resist and process technology demand continuing improvements in BARCs. Described herein are the chemistry, methods, and performance of a highly versatile polymer for use as a future generation 193 nm spin-on thin film organic BARC. The versatility of the polymer functionality allows for cross-linking while baking by either a strong acid catalyzed thermal reaction without an additional cross-linking molecule, or an uncatalyzed thermal reaction with a cross-linker, both without off gassing. Attachment of a variety of chromophores is easily accomplished by a thermal reaction either to the polymer in solution or while on the wafer during baking. The versatility of having one polymer with functionality that allows for multiple modes of cross-linking, varied choice of chromophore, and method of chromophore attachment, provides a platform that can be easily tailored to meet the needs of the emerging 193 nm technology.
The need for constant reduction in critical dimensions (CD) of integrated circuits to make them faster has been the driving force for next generation lithography. Currently KrF (248nm) is the shortest wavelength of light being used by IC manufacturers to mass produce devices. If the semiconductor industry continues at the same pace of packing more information on a chip, shorter wavelength (193nm) (ArF Excimer laser) will soon be introduced in production. Shorter wavelengths mean larger swing ratios, CD variations, reflective notching and standing waves due to sharp increase in reflectivity. Therefore some mechanism to reduce reflectivity becomes increasingly important at shorter wavelengths. Bottom antireflective coatings (BARCs) will play an important role in this endeavor. This paper discusses the chemistry and performance of two new spin-on organic 193nm BARCs (ARC 27 and ARC 28) optimized for their use at 1st reflectivity minimum thickness (30-40nm). The optical values of ARC 27 (n= 1.7, k= 0.56) measured by ellipsometer at 193nm give 0% reflectivity at the 1st reflectivity minimum with the optimum thickness of the BARC being 30nm. Lithographic studies with 193nm photoresist show good performance down to 90nm with isolated line (PAR705) and 100nm with dense line photoresist (PAR710,718). The optical properties of ARC 28 are 1.53 and 0.54 and a nominal thickness of 40nm on silicon is recommended to achieve 0% reflectivity. It shows good resolution at 110nm L/S and broad photoresist compatibility.
Semiconductor companies have been successful in introducing new process technology generations every two years. In order to maintain this accelerated pace, 157nm technology is schedule to be introduced in late 2003. Although there are still several obstacles to achieving this goal, there has been considerable progress in the 157nm program. The solution to 157nm technology is however, not complete without an antireflective coating. This paper describes in detail the various design considerations for an antireflective layer for 157nm lithography. These considerations involve a) multilayer system vs. single layer, b) optical constants, c) screening of chromophore, d) etch rate, and e) lithography. This paper will show the optical constants necessary to maintain less than 2% reflectance for single layer systems (1st and 2nd min) and bilayer systems (3rd and 4th min). Additionally, it will demonstrate that it is possible to control k value of the antireflective layer in the range of 0.2 to 0.5. It will be shown that materials with both high k value and etch selectivity >1 can be designed for 1st min single layer applications. Lastly, resist profiles were generated using currently available 157nm photoresist and a commercial BARC.
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.
Two organic, spin-on BARCs are in the small scale manufacturing phase -- with the goal being a 193-nm product optimized for commercialization. Chemistries of the BARCs are shown in this paper and performance of the two products relative to industry accepted needs is discussed. The thermoset BARCs, EXP98090B and EXP99001D, are prepared from hydroxy-functional, dye-attached acrylic polymers by adding an aminoplast and sulfonic acid catalyst. With select 193-nm resists, the BARCs give resolution of L/S pairs down to 0.12 micrometer. Plasma etch rates of both BARCs are comparable to those of 193-nm photoresists. Other BARC performance parameters that are discussed for the two products include: film and optical properties, conformality, simulated reflectance curves, spin-bowl compatibility, metals content, and defects.
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.
This paper presents the chemistries and properties of organic, spin-on, bottom antireflective coatings (BARCs) that are designed for 193 nm lithography. All of the BARCs are thermosetting and use dye-attached/incorporated polymers. A first generation product, NEXT, will soon be commercialized. NEXT is built form i-line and deep-UV chemistries with the polymeric constituent being a substitute novolac. This product provide outstanding resolution of 0.16 micrometers L/S with several 193 nm photoresists. Second generation chemical platforms under study include acrylics, polyesters, and polyethers with the 193 nm absorbing chromophore being an aromatic function. The performance of selected BARCs from the four platforms is described, including: optical properties, 193 nm litho, plasma etch rates, Prolith modeling data, spin-bowl and waste line compatibility, and ambient stability.
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.