Specific Process Knowledge/Lithography/Aligners/Aligner: Maskless 02 processing

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Exposure technology

Aligner: Maskless 02 is not a direct writer. In the maskless aligner, the exposure light is passed through a spatial light modulator, much like in a video projector, and projected onto the substrate, thus exposing an area of the design at a time. The substrate is exposed by scanning the exposure field across the substrate in a succession of stripes.

The light source is a laser diode (array) with a wavelength of 375nm (2.8W) or 405nm (8W). The spacial light modulator is a digital micro-mirror device. The individual mirrors of the DMD are switched in order to represent the design, and the laser is flashed in order to yield the desired exposure dose. This image is projected onto the substrate through a lens(system). The projected image yields a pixel size of 160nm X 160nm at wafer scale. The image is scanned across the substrate, in order to expose the entire design, each stripe overlapping (2 or 4 times) in order to minimize uniformity effects and stitching errors.

The writing head of the Aligner: Maskless 02 moves only in the z-direction. Using an optical (or pneumatic) focusing system, the maskless aligner is able to do real-time autofocus. The defocus process parameter is used to compensate offsets in the focusing mechanism, and to optimize printing quality in different resists and varying thicknesses. The stage of the Aligner: Maskless 02 moves only in x and y. It has no theta-axis. All rotation during alignment is thus accomplished by transformation of the input design.

Process Parameters

• 5206E 0.5µm 375nm (fast + quality)
• 5214E 1.5µm 405nm (fast)
• 5214E 1.5µm 375nm (fast)
• MiR 701 1.5µm 405nm (fast)
• MiR 701 1.5µm 375nm (fast + quality)
• nLOF 2020 2µm 375nm (fast + quality)

• Substrate centering + flat alignment test

Exposure mode

(high quality, fast)

High Aspect Ratio mode

• Intensity vs. aperture (405nm + 375nm)
• Dose test for 1.5µm MiR (405nm + 375nm)

Writing speed

• Speed vs. area (375nm)
  • Online
  • Offline

The writing speed of Aligner: Maskless 02 as a function of the exposure area

• Speed vs. dose (375nm + 405nm)

The writing speed of Aligner: Maskless 01 as a function of the exposure dose

Substrate centring and flat alignment

During substrate detection, the sample is scanned along the X- and Y-axes, as well as diagonally. From these measurements, the size (diameter) of the substrate is calculated, as well as the stage position matching the center of the substrate. This stage position will be the default origin for the subsequent exposure.

At the end of substrate detection, the sample is scanned twice along the bottom edge (flat), in order to determine the substrate rotation. This angle will be presented in the exposure panel along with the option to expose the design rotated in order to compensate for this angle, i.e. aligned to the flat/edge of the substrate.

Alignment

Top Side Alignment

• 4 marks (before final installation)
• Scaling (375nm, high res camera)

Advanced Field alignment (TSA)

• 4 marks, 25 fields (375nm, high res camera)
• Scaling, 10 fields (375nm, high res camera)