Fig. 1. Process flow for a 4-level master FZL fabrication.

Fig. 2. Process flow for a membrane FZL replication.

Fig. 3. Schematic of an on-substrate prefixing fixture.

Fig. 4. Phase distribution of a 4-level diffractive element.

Fig. 5. (a) Phase distribution of a 4-level element with etching depth errors, and (b) relationship between etching depth errors and diffraction efficiency.

Fig. 6. (a) Phase distribution of a 4-level element with overlay registration errors, and (b) relationship between overlay registration errors and diffraction efficiency.

Fig. 7. (a) Phase distribution of a 4-level element with linewidth errors, and (b) relationship between linewidth errors and diffraction efficiency.

Fig. 8. Phase distribution of a 4-level membrane FZL with width transfer errors.

Fig. 9. Phase distribution of a 4-level membrane FZL with depth transfer errors.

Fig. 10. Relationship between transfer errors and diffraction efficiency.

Fig. 11. Photo of 4-step level membrane FZL.

Fig. 12. (a)–(b) Micrographs of two observations in 200× magnification, (c) cross-section profile at the outermost period of diffractive membrane, and (d) 3D scanning result.

Fig. 13. (a) Linewidths on membrane and (b) test result of each step depth on the membrane.

Fig. 14. Distribution map of different diffractive orders.