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cmos_manufacturing [2026/09/25 11:02] – [5.Microlens formation] mathieu.ludden.extcmos_manufacturing [2026/09/25 11:03] (current) – [5.Microlens formation] mathieu.ludden.ext
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 Direct methods do not require fabricating a mask or a mold insert containing 3D concave microstructures. The geometry of the lens is established directly, typically exploiting surface tension while the material is in a liquid or thermoplastic state, producing a super smooth surface finish with an arithmetic average roughnes $R_a < 1\text{ nm}$. Direct methods do not require fabricating a mask or a mold insert containing 3D concave microstructures. The geometry of the lens is established directly, typically exploiting surface tension while the material is in a liquid or thermoplastic state, producing a super smooth surface finish with an arithmetic average roughnes $R_a < 1\text{ nm}$.
-  *  Thermal Reflow Method: A photoresist layer is coated onto a substrate and exposed to UV light through a mask with circular array patterns. After development, isolated cylindrical photoresist structures are formed3. Heating these structures causes them to melt and form spherical microlenses due to surface tension. **This photolithography and reflow bake approach is a standard MEMS process used for CMOS image sensors.**+  *  **Thermal Reflow Method**: A photoresist layer is coated onto a substrate and exposed to UV light through a mask with circular array patterns. After development, isolated cylindrical photoresist structures are formed3. Heating these structures causes them to melt and form spherical microlenses due to surface tension. **This photolithography and reflow bake approach is a standard MEMS process used for CMOS image sensors.**
   * Microplastic Hot Embossing: A silicon mold insert featuring circular openings is first fabricated using deep reactive ion etching (DRIE). A polymer substrate is placed between heating plates and the mold insert, where external pressure is applied above the material's glass transition point to form the microlenses through partial filling. The substrate is then cooled as slowly as possible to reduce thermal stress and replication errors.   * Microplastic Hot Embossing: A silicon mold insert featuring circular openings is first fabricated using deep reactive ion etching (DRIE). A polymer substrate is placed between heating plates and the mold insert, where external pressure is applied above the material's glass transition point to form the microlenses through partial filling. The substrate is then cooled as slowly as possible to reduce thermal stress and replication errors.
   * Microdroplet Jetting (Inkjet Printing): Droplets of a UV-polymerizable liquid are ejected from a nozzle onto a substrate. Upon reaching the substrate, they are exposed to UV light, solidifying into smooth spherical shapes   * Microdroplet Jetting (Inkjet Printing): Droplets of a UV-polymerizable liquid are ejected from a nozzle onto a substrate. Upon reaching the substrate, they are exposed to UV light, solidifying into smooth spherical shapes