New “self-immolating” or “unzipping” polymers, materials that depolymerize in response to irradiation, were designed and prepared successfully. We studied several candidate polymers and ultimately chose two of them for further development. One is a polyester that aromatizes upon depolymerization. The unzipping reaction initiated by UV exposure in solution was confirmed. The polymer was then studied in thin films to assess its potential for use in formulating photoresists. The neat polymer was tested as a blend with novolac resin. The effect of unzipping polyester loading in novolac on the rate of dissolution of films in TMAH was studied. Inhibition occurs at 20−30% loading. The films were exposed with DUV light and patterning was observed. The sensitivity of the unzipping polyester formulation is low in part due to the low absorption of the polymer for UV light. However, the polymer showed higher sensitivity with EUV exposure and first contrast curves show sensitivity in the range of 20−25mJ/cm<sup>2</sup>.
Out of band (OoB) radiation has been regarded as one of the key issues on Extreme Ultra Violet
Lithography (EUVL). OoB light especially in the deep ultraviolet (DUV) region have a negative
impact on image contrast and resist profile, since general photo acid generator (PAG) used in chemically
amplified EUV resist are also sensitive for DUV. It is reported that a Spectral Purify Filter (SPF) would
eliminate OoB radiation. However it expense a large reduction in EUV power and hence throughput, so
it is reported that HVM EUV exposure tool would not employ SPF.
Therefore, both EUV sensitive and DUV insensitive are required property to overcome OoB radiation
issue by resist material itself. Consideration of PAG cation structure was proceeded to control
absorption for DUV. Based on the concept, OoB insensitivity was investigated both on blend resist
platform and Polymer Bound PAG (PBP) platform. OoB insensitive concept was confirmed with UV
spectrum and sensitivity for KrF and ArF. The OoB insensitive PAG cation worked well on PBP, while
dark loss are seen on blend resist platform due to lack of inhibition effect. Lithographic performance
would be exhibited using Alpha Demo Tool (ADT) and NXE3100. Outgassing property on witness
sample (WS) and Residual Gas Analysis (RGA ) will be also discussed.
The concept of nonlinear acid diffusion coefficient would be emphasized to achieve better latent image
quality, resulting in better lithographic performance. Focusing on realizing the concept, we
previously reported about a main chain decomposable star shaped polymer (STAR polymer).STAR polymer consists of a core unit and several arm units which connect to the core unit with easily
acid cleavable bonding. (Fig.1) The main chain decomposition system is ideal to achieve promoted acid
diffusion at exposed area because it accompanies great molecular weight reduction at exposed area. The
significance of the STAR system had been confirmed for partially protected poly(p-hydroxystyrene)
(PHS) considering arm length and core structure.
Employing p-hydroxy-α-methylstylene (PHOMS) for arm structure, novel STAR polymer with
appropriate glass transition temperature (T<sub>g</sub>) could be realized. (Fig.2) Poly PHOMS is known to
undergo acid-catalyzed decomposition from the polymer end. Lithographic performance comparison
between the STAR polymer and the linear polymer as a control using a Micro Exposure Tool (MET)
would be exhibited.
Thermal property change with exposure and dissolution charactersitic will be also discussed. Moreover
main chain decomposition mechanism was investigated with flood EB irradiation.
In current optical lithography, resolution is required to reach for 45 nm half-pitch and a chemically amplified resist
(CAR) is used for a wide variety of applications. For ArF lithography beyond the 45 nm half-pitch, it is important to
control pattern quality. The molecular design of a photo acid generator (PAG) is very important in the study to
control not only acid strength but also acid diffusion length. Various novel PAGs that have different characteristics
were synthesized for resist performance improvement. Acid molecular size was determined by molecular orbital
(MO) calculation, and the acid diffusion coefficients <i>(D)</i> of these PAGs were evaluated by a bilayer method. As a
result, it was found that acid diffusion coefficient <i>(D)</i> could not be controlled simply by adjusting anion molecular size.
It may be presumed that the molecular interaction between acid generated by the exposure and polymer matrix areas is
one of the most important key factors for controlling acid diffusion.