Abstract
The dynamic absorption coefficients of several chemically amplified resists (CAR) and non-CAR extreme ultraviolet (EUV) photoresists are measured experimentally using a specifically developed setup in transmission mode at the x-ray interference lithography beamline of the Swiss Light Source. The absorption coefficient α and the Dill parameters ABC were measured with unprecedented accuracy. In general, the α of resists match very closely with the theoretical value calculated from elemental densities and absorption coefficients, whereas exceptions are observed. In addition, through the direct measurements of the absorption coefficients and dose-to-clear values, we introduce a new figure of merit called chemical sensitivity to account for all the postabsorption chemical reaction ongoing in the resist, which also predicts a quantitative clearing volume and clearing radius, due to the photon absorption in the resist. These parameters may help provide deeper insight into the underlying mechanisms of the EUV concepts of clearing volume and clearing radius, which are then defined and quantitatively calculated.
Highlights
In photolithographic processing, the optimum absorption is determined by the tradeoff between efficiently harvesting the incoming light and the need to maintain a constant intensity throughout the film thickness
These resists were mostly based on diazonaphthoquinone and novolak resins (g-line and i-line) or chemically amplified resists (CAR) compounds (DUV), which yield an absorption coefficient (α) ranging from 0.5 to 1 μm−1.1,2 At these values of α, the intensity of light reaching the bottom of the resist layer is still about 80% of the intensity at the top, which guarantees both an adequate depth clearance and a limited sidewall slope
X-axis error bar, which indicates the uncertainty in the thickness measurement σd, and by the Y-axis error bar, which indicates the uncertainty in the transmittance σIo. (For those resists spin coated at only one thickness, we consider the line through the origin.) The measured α is summarized for all samples in Fig. 4; the error bar is calculated from the error-weighted linear fit of the TermsOfUse.aspx ln (TX) versus thickness plot
Summary
The optimum absorption is determined by the tradeoff between efficiently harvesting the incoming light (high absorption) and the need to maintain a constant intensity throughout the film thickness (low absorption). Photoresists for deep ultraviolet (DUV) and earlier technologies were designed to coat at 200- to 800-nm thickness These resists were mostly based on diazonaphthoquinone and novolak resins (g-line and i-line) or chemically amplified resists (CAR) compounds (DUV), which yield an absorption coefficient (α) ranging from 0.5 to 1 μm−1.1,2 At these values of α, the intensity of light reaching the bottom of the resist layer is still about 80% of the intensity at the top, which guarantees both an adequate depth clearance and a limited sidewall slope. Extreme ultraviolet (EUV) photoresists are designed to coat at
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