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150mm Wafer Transfer

150mm Wafer Transfer. Keith Warner, Andy Loomis April 7, 2000. Transfer Process Goals. Adhesive-based wafer-to-wafer bonding 2 – 5 µm bondline thickness, thermal limits on post-transfer processing, +/- 2 µm alignment accuracy with existing tools

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150mm Wafer Transfer

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  1. 150mm Wafer Transfer Keith Warner, Andy Loomis April 7, 2000

  2. Transfer Process Goals Adhesive-based wafer-to-wafer bonding 2 – 5 µm bondline thickness, thermal limits on post-transfer processing, +/- 2 µm alignment accuracy with existing tools Complete transfer of NU processes, also useful for other device types Oxide fusion bonding (Adopt existing process from CCD work) < 1 µm bond layer, post-transfer processing ~400°C (Tungsten CVD plugs, “hot” Al), +/- 1 µm alignment with tool to be purchased Determine technology limits on this program Sub-micron via placement with oxide bonding Build/specify tools using stepper technology techniques

  3. Wafer Bonding - Voids • Voids are formed after the SOI handle wafer is removed • Particulate - Cleaning, clean area, inspection, filtration • Pinholes and oxide quality - Starting material • Adhesion – Cleaning • Bubbles – Vacuum outgassing of epoxy

  4. Wafer Bonding - Voids (After wafer thinning decorative etch) 12/16/99 3/2/00 Void – free wafer transfer achieved

  5. Wafer Bonding - Alignment • Alignment method – depends on type of tool • Early work used Research Devices flip-chip bonder • Limitations of optical system restricted accuracy to +/- 5 µm

  6. Wafer Bonding - Alignment • Karl Süss mask aligner with infrared optics • Better than +/- 2 µm accuracy, repeatable

  7. Wafer Bonding - Alignment (Same wafer without voids) Accurate alignment achieved

  8. Wafer Bonding – Bondline Uniformity (2-5 µm required across wafer) • Wafer flatness – Double side polished ultra-flat wafers • Adhesive curing cycle – Experiments started (Research Devices tool is not designed for wafer-to-wafer bonding; available pressure is inadequate) • Spacers – Latex microspheres • Particulate – Cleaning, inspection, filtration Still working on optimization

  9. Wafer Bonding Apparatus and Operation

  10. Status • Void-free transfer successful • Alignment accuracy adequate for devices currently available (“North2”) • Method identified to meet bondline requirements – experiments are underway • Full-time effort has started

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