Concepts for protecting the mask from particle contamination: (a) mask inside container; (b) with cover plate to reduce the volume from where particles can reach the mask; (c) critical surface facing down to avoid gravitational settling of particles onto the mask, thermal and electrical gradient between mask and cover plate to facilitate thermophoresis and electrophoresis; (d) with particle trap around the mask to deposit particles entering from the side before they reach the mask. It is adapted from Ref. 5.
Modeling situation. Particle approaching the critical surface of an upside-down mask with an initial velocity . Forces acting on the particle are gravity , drag force , and thermophoretic force . It is adapted from Refs. 7 and 14.
Schematic diagram of the particle injection system for a low-pressure chamber to evaluate the thermophoretic effect on mask protection with velocity-controlled particles. It is adapted from Ref. 8.
Deposition results of 125 and 220 nm PSL particles with particle injection velocities of 31 and 18 m/s for the 2 cm gap distance under no temperature gradient and with 10 K/cm temperature gradient at 100 mTorr. The number of particles added for each case is shown next to the wafer maps. It is adapted from Ref. 9.
Deposition results for 125 nm PSL particles having 25 m/s injection velocity at a chamber pressure of 50 mTorr with no reverse flow (left) and with reverse flow for 115 mTorr inside the cap (right). It is adapted from Ref. 10.
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