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Shape Evaluation of Photomask Lens Arrays Molded with a Gray-Scale Mask/Noncontact 3D surface profile measurement using a laser microscope


1. Application

Gray-scale masks is a technology used to fabricate molds for complex-shaped micro lenses or other products that are comprised of high-quality 3D microstructures. The gray-scale mask is used for 3D patterning; a resist coating is irradiated with a multiple-gradation laser to create the 3D pattern (Figure 1). Measuring the 3D shape of the resist after irradiation is essential for quality control. Since the 3D pattern is easily damaged, noncontact measurement is required to verify its integrity.

2. Olympus' solution

Olympus' LEXT 3D laser scanning microscope enables noncontact, three-dimensional imaging of the concave or convex shape of a gray-scale mask with high resolution and high contrast. Thanks to objective lenses with high numerical apertures and an optical system designed to obtain maximum performance from the 405 nm laser, the LEXT microscope can capture the profile of irregular slopes accurately, leading to reproducible, reliable 3D profiles (Figure 1). In addition to measuring the shape of samples, users can also clearly visualize minor irregularities using laser differential interference.

Concave pattern
Gray scale mask 凹 ob50×
Objective lens: 50x 50X, Zoom 1x
Gray scale mask 凹 ob50× 3D
Objective lens: 50x 50X, Zoom 1x
Gray scale mask 凹 ob100× 3D
Objective lens: 100x 100X, Zoom 1x
Convex pattern
Gray scale mask 凸 ob50×
Objective lens: 50x 50X, Zoom 1x
Gray scale mask 凸 ob50× 3D
Objective lens: 50x 50X, Zoom 1x
Gray scale mask 凸 ob100× 3D
Objective lens: 100x 100X, Zoom 1x

Figure 1. Imaging concave and convex patterns using the LEXT microscope

Figure 2. The lens fabrication process using a gray-scale mask.

Step 1

  1. Resist coating
    Resist coating
    Apply resist onto the glass.
     
  2. Drawing (laser irradiation)
    Drawing (laser irradiation)
    Irradiate the resist with a multiple-scale laser beam to create a positive resist.
    The irradiated area is exposed and softened.
     
  3. Soak in the developer
    Soak in the developer
    Develop the resist and strip away unnecessary regions. 3D profile evaluation during this phase is key to quality management.

Step 2

  1. Electroplating
    Electroplating
    Apply plating to the resist.
     
  2. Etching
    Etching
    Dissolve the resist through etching and flip the plating over to complete the original (metal mold).

Step 3

  1. Use thermo-compression to bond the film to the metal mold.
    Use thermo-compression to bond the film to the metal mold
     
  2. Imprint
    Imprint
    Peel the film off the metal mold and flip it over.
     
  3. Resin molding
    Resin molding
    Pour resin into the film.
     
  4. Finish
    Finish
    Solidify the resin and remove it from the film mold to complete the lens.
Olympus IMS

Products Used for This Application

The LEXT™ OLS5100 laser scanning microscope combines exceptional accuracy and optical performance with smart tools that make the system easy to use. The tasks of precisely measuring shape and surface roughness at the submicron level are fast and efficient, simplifying your workflow and delivering high-quality data you can trust.

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