Eishi Shiobara

Novel antireflective layer using polysilane for deep ultraviolet lithography

A bottom antireflective layer (ARL) is essential for deep ultraviolet (UV) lithography. We have just developed a polysilane antireflective layer (PSARL) process. PSARL can act as an antireflective layer due to the Si–Si bond which has absorption in the deep UV region, and it can be etched with high selectivity to resist under etch conditions that use a chlorine plasma which is a suitable inorganic silicon etchant. Similar to the conventional organic ARL process, PSARL can be simply spin coated onto the substrate, and removed with an asher using an O2/CF4 gas mixture. The partially cross-linked diphenylsilane copolymer was evaluated with a view to its application as an ARL material and the results obtained are presented in this article.

Resist edge roughness with reducing pattern size

Recently, resist edge roughness with reducing pattern size has become a serious problem. We investigated the roughness of chemically amplified, positive-tone resists, experimentally. To reduce the roughness, we added a quencher with strong basicity to the resist, and observed sub quarter micron nested lines. As a result, the roughness was improved with increasing the quencher concentration, especially in 0.15 micrometers nested line patterns. Adding quencher was not too much effective for the larger size patterns. The acid concentration in resist was increased by adding quencher, because the nominal dose became large by that. It was also indicated experimentally that generated acid concentration at pattern edge was nearly equal to that of quencher at nominal dose. The nominal dose was determined by quencher concentration. We defined effective acid concentration as remaining acid concentration after quenching. This effective acid concentration increased with increasing quencher concentration too. The roughness seemed to be generated when effective acid concentration profile was lowered. It is indicated that the resist edge roughness with reducing pattern size can be expected from its effective acid concentration profile.

Study of EUV outgassing spatial distribution toward witness plate in the EUV outgas tester

In the experiments to evaluate outgassing of EUV resists, it was found that the amount of PAG anion and/or Fluorine observed on the witness sample (WS) was different for the variety of WS location and direction in the testing chamber. The XPS measurements showed there were about 10 times of Fluorine atoms on the WS which were put to face the exposing position of the resist on the wafer compared to that were put to turn the back on the wafer. As the Fluorine is the component of photo-acid-generator (PAG) of resists used in the experiments, it is thought that the PAG anion and/or its decomposed species have high sticking coefficient to the WS. The simulation was performed to understand the directivity of outgassing from the exposing point, using the Direct Simulation Monte Carlo (DSMC) method. The results indicated that the sticking coefficient of PAG anion is about 0.8, suggesting that the position and direction of WS in the chamber relative to the wafer strongly affects the amounts of deposition of the species having big sticking coefficients.

Development of Tool for Contamination Layer Thickness Measurement Using High Power Extreme Ultraviolet Light and in Situ Ellipsometer

Extreme ultraviolet (EUV) lithographic exposure is performed in a vacuum environment. The Mo/Si multilayers used as imaging optics and a mask can be contaminated by carbon, which is originally an outgassing species of the hydrocarbons that decompose from the resist materials during EUV exposure. This carbon contamination reduces the total reflectivity of the imaging optics and mask, and affects the lithographic performance, including the throughput and resist pattern replication resolution. This contamination should be reduced to maintain the lithographic performance; thus, the relationship between the carbon contamination and the outgassing species should be clarified. We therefore developed a novel tool for in situ contamination layer thickness evaluation. The distinctive features of this tool are as follows: 1) exposure using a total power of in-band EUV light (267 mW/cm2) that is as high as that required for high-volume manufacturing (>100 mW/cm2), 2) the visible light beam of the in situ spectroscopic ellipsometry is focused on the Mo/Si multilayer witness sample to obtain the detection limit for measured thickness and that the limit was found to be 0.03 nm, and 3) the witness and 8-in. resist wafer sample stages have extremely low outgassing characteristics. Using this tool, a starting adhesion point was observed and the carbon contamination layer thickness was evaluated during the resist exposure. For 90 min resist exposure, no contamination adhered onto the Mo/Si witness sample until the exposure time reached 25 min, and after which, the contamination started to adhere to the witness sample.

Resist outgassing characterization for qualification in high power EUV lithography

For high volume manufacturing (HVM) utilizing extreme ultraviolet (EUV) lithography, practical resist outgassing qualification system is required. Witness sample (WS) testing systems using electron beam (EB) or low power EUV light have been proposed as candidates, however some issues remain on how these alternative light sources, in comparison to high power EUV, will affect resist chemical reactions and ultimately resist outgassing. In this paper, we have investigated resist induced optics contamination by utilizing two types of WS test systems of high power EUV light and EB sources. A correlation between these light sources is discussed, especially focusing on the resulting chemical phenomena depending on resist material properties.

Application of polysilanes for deep-UV antireflective coating

Application of polysilanes for a deep UV (DUV) bottom anti- reflective coating (BARC), in order to resolve the problem posed by the insufficient anti-reflection with thin conventional organic BARC applied on transparent dielectric film, is described. The newly developed polysilane anti- reflective coating has the real part of refractive index, n equals 2.00, and the imaginary part, k equals 0.23 at 248 nm. The polysilane coating is immiscible with a chemically amplified photoresist, and is not removable during normal wet development of photoresist. Etching rate of the polysilane is 2 times faster than that of DUV resist during BARC etching, and lower than that of DUV resist during dielectric film etching. The polysilane layer is easily removed by ashing using O2 gas process. Using thick polysilane coating, it can realize both the suppression of the interface reflection between the resist and BARC and good critical dimension control on dielectric film.

Resist outgassing characterization based on the resist compositions and process

For extreme ultraviolet (EUV) lithography, some critical issues concerning possible tool optics contamination due to resist outgassing remain to be resolved [1-4]. Before resists can be used on the ASML NXE:3100 and ASML NXE:3300 EUV scanners, they need to be tested in dedicated equipment and qualify according to the ASML NXE outgassing guidelines. In view of these guidelines, EIDEC has been working on an infrastructure set-up to enable resist outgassing testing. However, further investigations are still necessary to realize the application of the proposed outgassing evaluation method. Moreover, given the significant number of resists to be tested, fundamental studies to established concepts that reduce the number of resist outgassing tests are necessary. The application of these concepts focused on resist outgassing characterization based on resist composition and processes is presented. Moreover, a suggestion on how this fundamental information can be applied to reduce the total number of resist outgassing tests required for various EUV resists is discussed.

LWR reduction in low-k1 ArF-immersion lithography

Line width roughness (LWR) reduction is a critical issue for low k1 ArF immersion lithography. Various approaches such as materials, exposure technology and the track process have been performed for LWR reduction during lithography process. It was reported that the post-development bake process had good performance for LWR reduction (1). However, the post-development bake process induced large CD change owing to the degradation of large isolated resist pattern. Therefore post-development process with small iso-dense bias is required in low k1 ArF immersion lithography. The resist smoothing process is one of the candidates for LWR reduction with small iso-dense bias. This method whereby the resist pattern surface is partially melted in organic-solvent atmosphere was shown to have a significant LWR reduction effect on resist patterns. This paper reports on the application of the resist smoothing process to the ArF immersion resist pattern after development. It was found that the resist smoothing process was effective to reduce LWR for ArF immersion resist. As a result of LWR trace from after development to after the hard mask etching process, the effect of LWR reduction with the resist smoothing process continued after the hard mask etching process. Furthermore CD change of large isolated patterns with the smoothing process was smaller than in the case of post-development bake process. We confirmed that the resist smoothing process is an effective method for decreasing LWR in ArF immersion lithography.

Contribution of EUV resist components to the non-cleanable contaminations

The suppression of outgassing from extreme ultraviolet (EUV) resist needs to be addressed for realizing EUV lithography (EUVL) because outgassing is likely the main contributor to the contamination of mirror optics in EUV scanners, which results in reflectivity loss. Resist outgassing causes two types of contamination: cleanable contamination, involving hydrocarbon contaminants, and noncleanable contamination, involving noncarbon components. The relation of cleanable contamination between EUV- and electron beam (EB)-based evaluations is linear. However, the relation of noncleanable contamination is not clear. In this study, we investigated the contribution of EUV resist components to noncleanable contamination using different photoacid generator components. The cleanability of noncleanable elements (sulfur, iodine, chlorine, and bromine) in contamination films was measured and compared for the EUV- and EB-based outgas testers. The result suggested that the chlorine and bromine contaminants were completely removed after cleaning. On the other hand, sulfur and iodine remained even after cleaning. This suggested that the careful use of iodine in resist materials is necessary due to its high photoabsorption and low cleanability. In addition, the cleaning rate and noncleanability of contaminants in the EUV-based test were larger than in the EB-based test. This suggests that the contamination film in the EUV-based test is more porous than that in the EB-based test.

A New Stacked-Mask Process Utilizing Spun-on Carbon Film for Sub-130-nm Etching

A novel stacked-mask process (S-MAP) was developed for sub-130-nm etching. The S-MAP consists of a tri-layer with a top layer of thin resist for patterning, a spin-on-glass (SOG) interlayer, and a newly developed spun-on carbon-film bottom layer. The spun-on carbon film was synthesized, in particular to have high carbon and low oxygen contents, and showed an etching resistivity 1.3 times higher than that of conventional resist films. An S-MAP utilizing this spun-on carbon film provides improved critical dimension (CD) control and enables etching of high-aspect-ratio holes. Via first dual damascene (DD) formation employing S-MAP eliminated the undesirable SiO2 fence around the top of the via holes, whereas the conventional process does not.