Bottom anti-reflective coatings (BARCs) are essential for achieving the 65-nm node resolution target by minimizing the substrate reflectivity to less than 1% and by planarizing substrates. We believe that the developments in 157-nm BARC products are on track to make them available for timely application in 157-nm lithography. We have made some significant improvements in resist compatibility and etch selectivity in relation to the latest available 157-nm resists.
Two chromophores having desired high light absorbance at the 157-nm wavelength have been identified. The prototype BARC formulations basically meet the critical requirements for workable 157-nm BARCs, including optical properties, thermal stability, photo-stability, etch rate and selectivity, and compatibility with photoresists. The BARCs also show good coating quality and stripping resistance. Another essential feature of the BARCs is that they are formulated in industry-accepted safe solvents. The lithographic profiles of a benchmarked 157-nm photoresist on our prototype BARC LH157B show straight 60-nm L/S patterns. LH157B also exhibited excellent lithography performance as an ArF BARC. Optimization of the BARC formulations is in progress.
This paper presents our progress in developing spin-on, thermosetting hardmasks and bottom antireflective coatings (BARCs) for 193-nm trilayer usage. Binder materials that were used in preparing the silicon-containing hardmasks include polymers with pendant alkylsilane function and various polyhedral oligomeric silsesquioxane (POSS) substances, with the hardmasks being very transparent at both 193 and 248 nm. The second generation hardmasks (POSS-containing) offer significant improvements over earlier materials in oxygen (O2) plasma etching resistance. The etching selectivity (O2 plasma) for a trilayer BARC relative to the best-case hardmask is about 31.5:1 (15-second etch), with the selectivity numbers being much higher for longer etching times. The preferred hardmask is both spin-bowl and solution compatible. The new trilayer BARCs use binders that are rich in aromatic content for halogen plasma etching resistance, but the antireflective products also feature optical parameters that allow low reflectivity into the photoresist. The BARCs are very spin-bowl compatible. At about 500-nm film thickness, selected BARCs have provided 80-95% planarity over 200-nm topography. Combining the two thermosetting products (hardmask and BARC) with a thin 193-nm photoresist in a trilayer configuration has given excellent 80-nm L/S (1:1) after exposure and wet-development. A conventional resist has provided 100-nm L/S (1:1.4).
The 70-nm technology node is projected to go into manufacturing production by late 2004. The most promising technology for the 70-nm technology node of semiconductor devices is 157-nm lithography. Although advances in developing 157-nm technology have been hampered by greater challenges than originally expected, considerable progress has been made. Great efforts have been made to improve the exposure tool, the laser, the resist materials, the resist processing, the mask materials, and bottom anti-reflective coatings (BARCs). BARCs are essential in achieving the 70-nm-node resolution target by minimizing the substrate reflectivity to less than 1% and planarizing substrates. This paper will describe the various design considerations for a workable 157-nm BARC, including optical constants, thermal stability, photo stability, etch rate and selectivity, resist compatibility, film conformality, coating quality, and lithography profile. It will demonstrate that to maintain less than 1% reflectance for a 157-nm BARC, the value of refractive index n (real) must be from 1.3 to 1.8 and that of k (imaginary) must be from 0.26 to 0.6, determined by Prolith modeling. The refractive index ranges are set as optical constant targets for the design of BARCs formulations. The photoresist profiles from 157-nm lithography utilizing our developed BARCs will also be presented.
With the increasing drive towards smaller feature sizes in integrated circuits and the consequent use of shorter exposure wavelengths, the imaging resist layer and underlying bottom anti-reflective coating (BARC) layer are becoming thinner. At this scale, the performance of chemically amplified resists can be adversely affected by the BARC-resist interfacial interactions. These interactions can cause distortion of resist profiles and lead to footing, undercut, or pattern collapse. BARC components can immensely influence the deprotection and dissolution properties of the resist. A thorough understanding of the physico-chemical interactions at these interfaces is essential to design and develop new material platforms with minimal adverse interactions and maximum compatibility between BARC and resist. Results are reported from studies of (A) surface versus bulk chemistry of BARC materials as a function of cure temperature, (B) the dependence of the thickness and composition of the residual layer (resist material remaining on the surface of the BARC after development) on BARC components, as determined by formulating the BARC or resist with an excess of various BARC components, and (C) the dependence of the residual layer thickness on crosslink density, exposure does, and resist bake temperature. The BARC thin films and the interphase between BARC and resist were characterized with near edge x-ray absorption fine structure (NEXAFS) spectroscopy. Surface chemical properties of BARC films were derived from contact angle measurements of various liquids on these thin films. Preliminary results from these studies indicate that some BARC components may migrate to the BARC-resist interphase and act as dissolution inhibitors. Similarly, small molecule additives in the resist may migrate into the BARC layer, causing chemical modifications.
Previous generations of Bottom Anti-Reflective Coatings (BARCs) have had excellent optical properties but the etch performance for these BARC's were only 30% faster than the photoresist at best. A novel BARC chemistry has increased the capability of the photolithography process; this new chemistry has the capability to change etch and optical properties by the BARC bake process. This paper will present the bake process changes required to modify both etch characteristics and optical properties. Etch characteristics that were measured were bulk etch rate and etch selectivity to photoresist. Index of refraction and the absorption coefficients were measured for optical properties. Photolithography results focusing on Acetal and Hybrid photoresist types will be presented with specific attention to critical dimension control and focus latitude shifts, if any, associated with these BARC bake process changes.
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.
Plasma (dry) etching is a key step in semiconductor device manufacturing processes whereby the resist pattern is transferred to a substrate. As the resist thickness is reduced to meet stringent transparency requirements in photolithography, the usage of fast etching material as BARC is considered to be increasingly critical in minimizing resist thickness loss in pattern transfer steps. Several models emphasizing correlation between polymeric structure and etch resistance based on empirical parameters have been developed but are hard to generalize. We have examined the reactive ion etch (RIE) properties of a variety of polymer groups including natural polymers, poly(styrenic)s, poly(acrylate)s, poly(olefin)s, poly(ester)s and several polymers grafted with UV light absorbing chromophores. With the assumption that in the etching processes the reactive species from plasma attack the polymeric materials at a molecular level instead of an atomic level, we have developed a model based on the contribution of chemical bonds in the polymer structure to predict etch rates. The present study shows that this model revealed marked correlations across polymer families for three different etch processes. This model has also proved to be an effective tool in predicting the etch behavior of polymers for use in BARCs.
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.