Mitigation of the etch-induced intra-field overlay contribution

Improving the on-product overlay performance after optimization of the etch-induced contributions

“…Smaller overlay is possibly due to a flatter sheath due to a denser plasma. Unlike increasing pressure, increasing HF only slightly increases intra-field fingerprint [9].…”

“…The stack and overlay measurement methodology to isolate etch contribution is shown in Figure 3. As explained in our previous publication [9], we use the Super Nova 2 process stack which is representative for an N7 LE 3 Metal 1 BEOL process patterning process at IMEC. In the original Litho-Etch (LE) flow, the M1A, M1B, and M1C patterns are first etched into a 20-nm thick SiO2 memorizing layer.…”

“…We show only the relevant conditions which belongs to the critical SOG etch step. There are more etch settings and more layers which went through etch [7,9].…”

“…This length scale corresponds to die level which repeats at each exposure field where we have reported an extensive study on both etch-induced [7,9] and stress related intra-field overlay [10]. Interestingly, the etch-induced intra-field overlay fingerprints were similar for wafers at different stress types and levels including no stress [7,9,10]. The common part was the Spin-On-Glass (SOG) anti-reflecting coating layer.…”

“…Despite the continuous improvements on scanner side, due to tighter requirements, handling high spatial frequency overlay penalties at small length scales (sub-mm level) becomes more challenging [8]. This length scale corresponds to die level which repeats at each exposure field where we have reported an extensive study on both etch-induced [7,9] and stress related intra-field overlay [10]. Interestingly, the etch-induced intra-field overlay fingerprints were similar for wafers at different stress types and levels including no stress [7,9,10].…”