MEEF (Mask Error Enhancement Factor) is the most representative index which CD (Critical Dimension) variation in wafer is amplified by real specific mask CD variation. Already, as it was announced through other papers, MEEF is increased by small k1 or pattern pitch. Illumination system, just like lens aberration or stage defocus affects directly MEEF value, but the leveling or species of substrate and the resist performance are also deeply related to MEEF value. Actually, when the engineers set up the photo process of shrink structure in current device makers, they established minimum shot uniformity target such as MEEF value within wafer uniformity and wafer to wafer uniformity, besides UDOF (Usable Depth of Focus) or EL (Exposure Latitude) margin.
We examined MEEF reduction by checking the difference in resist parameters and tried to correlate the results between experiment and simulation. Solid-C was used for simulation tool. The target node was dense L/S (Line/Space) of sub-80 nm and we fix the same illumination conditions. We calculated MEEF values by comparing to original mask uniformity through the optical parameters of each resist type. NILS (Normalized Image Log Slope) shows us some points of the saturation value with pupil mesh points and the aberration was not considered. We used four different type resists and changed resist optical properties (i.e. n, k refractive index; A, B, and C Dill exposure parameters). It was very difficult to measure the kinetic phenomenon, so we choose Fickian model in PEB (Post Exposure Bake) and Weiss model in development. In this paper, we tried to suggest another direction of photoresist improvement by comparing the resist parameters to MEEF value of different pitches.
We found a new polymer platform for ArF BARC that can be prepared by addition polymerization. This system not only improves resist pattern collapse, but also allows control of the optimum film thickness, and etch rate by combination of compounds, method of polymerization (molecular weight control), and additives. Moreover, these materials have the unique characteristic that the resist profiles change little even if the type of resist changes.
There are many considerations to the design of BARC materials. Among those many properties, one important property that can effect lithographic performance is BARC coating uniformity. In general, the basic coating property (conformal or planar) depends on basic characteristics of polymer (Mw, chemistry, etc). But another major factor to control the coating uniformity is the choice of solvent system in the formulation of the BARC. According to our experimental results, two major factors that can affect the coating uniformity of one BARC are the vapor pressure and the hydrophilicity of solvents. If any solvent has too high vapor pressure and high hydrophilicity relatively, polymer segregation occurs in BARC surface area in case of high humidity condition, resulted in bad coating uniformity.
In this paper, we will show basic evaluation results including the morphology change of BARC surface with several solvents which can be used in BARC formulation according to various humidity and temperature conditions. And also we will show the solution to overcome this problem in device manufacturing.
KEYWORDS: Diffusion, Photoresist materials, Line edge roughness, Polymers, Atomic force microscopy, Temperature metrology, Scanning electron microscopy, Photoresist developing, Lithography, Glasses
LER of an acetal-type photoresist (PR) and an annealing-type PR was measured by Atomic Force Microscopy, with which LER is more quantitatively measurable than using SEM. The annealing-type PR showed smaller LER than acetal-type did. Acid diffusion length measurement of these two types of KrF photoresists with a practical method that is a measurement of the thickness loss in a resist film after development which follows placement of exposed resist powder on the surface and applying PEB was also executed. The annealing-type PR has been found to show longer acid diffusion length than that of acetal-type PR. Considering deblocking temperature, acetal group is cleaved right upon exposure before PEB due to its relatively low activation energy. This means that there would be more hydroxystyrene units in acetal-type PR at the beginning of PEB than in annealing-type one. Tg of photoresist samples before and after deblocking reaction was also measured by DSC. After deblocking reaction, it was found that Tg of acetal-type PR is much higher than that of annealing-type PR. This relatively high Tg will make acetal-type PR to have shorter acid diffusion length in conjunction with relatively low PEB temperature comparing with annealing-type in general. The absolute Tg value and Tg change with deblocking reaction depending on types of PRs were correlated to explain the inherent difference in LER performance in different types of PRs.
The shrinkage of resist pattern during in-line SEM measurement has been argued and studied as one of the problems unsettled for manufacturing with ArF photolithography. Many of attempts to solve this problem have focused their attentions on the improvement of resist and inspection equipment. We bring up BARC (bottom anti-reflective coating) as a new impact factor on SEM shrinkage of resist. Practically, although the same resist was employed, our shrinkage tests gave the results depending on the kind of BARC. Feature size and depth of focus also affect SEM shrinkage of resist. Effect of reflectivity on SEM shrinkage was evaluated by changing thickness of BARCs and resultantly was somewhat significant. In this paper, the BARC-dependent results of SEM shrinkage are analyzed and discussed to provide a possibility that BARC may have another function of reducing SEM shrinkage.
The ArF resist has been evaluated focusing on resin character such as molecular weight, monomer composition and polydispersity (Pd). The resin properties were investigated to elucidate that which parameter was affected to the line edge roughness (LER). The Pd was correlated with LER. As the Pd was large, the LER was small. The resin molecular weight and monomer composition were affected to their vertical profile. Low molecular weight portion rich resin resulted in round and t-top profile, whilst high molecular weight rich resin resulted in square profile. The amount of lower molecular weight fraction was changed by purification method. The lower molecular weight resin caused severe tapered profile. It was concluded that 1) shift of Mw to smaller and 2) higher content of low molecular size fraction lead to rounded and tapered pattern profile. Lot-to-lot stable good pattern profile has achieved by controlling polymer molecular weight and content of low molecular size fraction in small variation range.
A frequent problem encountered by photoresists during the manufacturing of semiconductor device is that activating radiation is reflected back into the photoresist by the substrate. So, it is necessary that the light reflection is reduced from the substrate. One approach to reduce the light reflection is the use of bottom anti-reflective coating (BARC) applied to the substrate beneath the photoresist layer. The BARC technology has been utilized for a few years to minimize the reflectivity. As the chip size is reduced to sub 0.13-micron, the photoresist thickness has to decrease with the aspect ratio being less than 3.0. Therefore, new Organic BARC is strongly required which has the minimum reflectivity with thinner BARC thickness and higher etch selectivity towards resist. SAMSUNG Electronics has developed the advanced Organic BARC with Nissan Chemical Industries, Ltd. and Brewer Science, Inc. for achieving the above purpose. As a result, the suitable high performance SNAC2002 series KrF Organic BARCs were developed. Using CF4 gas as etchant, the plasma etch rate of SNAC2002 series is about 1.4 times higher than that of conventional KrF resists and 1.25 times higher than the existing product. The SNAC2002 series can minimize the substrate reflectivity at below 40nm BARC thickness, shows excellent litho performance and coating properties.
To reach the sub-0.3 micrometer contact hole pattern by i-line lithography, some advanced technology was introduced such as Phase Shift Mask (PSM) and/or photoresist (PR) flow process. It may be possible that the contact hole is patterned with 0.18 micrometer resolution by the PR flow process with PSM. However, PSM cause the Tg temperature of resist down at the phase shift area. And it also leads the bulk effect by the different pattern density at the cell edge. Thus, during the PSM + PR flow process, 'contact shift' and 'contact distortion' (so-called 'Eyebrow') defects are unavoidable. To repel these defects, we designed the new lithographic process; the UV-bake before thermal flow process. By the UV light at 130 +/- 10 degrees Celsius, the resist was cured at the resist surface. This surface-cured resist has the higher Tg temperature even the normal PSM reticle induces the Tg down. Top surface curing (hardening) also minimized the bulk effect. To maximize the UV bake effects, we developed new resist which was optimized to UV-bake process. By UV-bake process with new resist, the 0.2 micrometer contact hole was patterned. ET margin was 14 nm/10 mJ, and DOF margin was 0.6 micrometer at the mass fabrication device. The 'Eyebrow' and contact shift defects are not detected.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.