LowTemperature MEMS Process Using Plasma Activated SiliconOnSilicon SOS Bonding

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Low-Temperature MEMS Process Using Plasma
Activated Silicon-On-Silicon (SOS) Bonding

• MSc report
• Yungming Sun

Tzeno Galchev, Warren C. Welch III, and Khalil
Najafi, Low-Temperature MEMS Process Using Plasma
Activated Silicon-On-Silicon (SOS) Bonding , 2007
MEMS Conference
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Outline

• Abstract
• Introduction
• Fabrication
• Discussion

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Abstract

• Dielectric Barrier Discharge (DBD)
• High Aspect-Ratio MEMS
• Silicon-On-Silicon (SOS)

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Introduction - 1

• Problem in Silicon-On-Glass (SOG)
• Build up of heat during etching.
• Not strong enough to the pressure from Helium

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Introduction - 2

• Problem in Deep Reactive Ion Etch (DRIE)
• Footing or Notching when a buried dielectric
  is used as the etch stop.

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Introduction - 3

• SOS processing has 6 advantages, when
• compared to SOG and SOI
• Oxide is patterned before DRIE, footing problem
  can be minimized.
• Carrier wafer is silicon, not only is backing
  wafer not needed, but also heating during etching
  is reduced.

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Introduction - 4

• Carrier wafer can undergo standard
  micro-fabrication technologies before bonding.
• Thermal mismatch between silicon and glass in SOG
  process is eliminated in SOS process.

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Introduction - 5

• Low-temperature process allows the formation of
  buried feedthroughs using a variety of materials,
  including metals.
• Offer the opportunity of achieving full
  integration because all process steps are CMOS
  compatible.

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Fabrication - 1
Figure 1. Silicon-On Silicon process flow
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Fabrication - 2
Figure 2. SEM of fabrication SOS die
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Fabrication - 3
Figure 3. Close up photograph of one of the
Pirani gauges made using SOG (a) and SOS (b).
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Fabrication - 4
Figure 4. SEM of the bottom of comb fingers made
using SOG (a) and SOS (b).
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Discussion - 1
Figure 5. DBD creates a uniform plasma discharge
due to a high AC voltage applied between two
electrodes.
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Discussion - 2

• Discharge is too short to generate heat, and so
  sensitive substrates can be protected.
• Unlike low-pressure glow discharge, there is
  little surface bombardment of wafer by energetic
  species.

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Discussion - 3
Figure 6. The diameter of a water bubble on the
surface of silicon and oxide as plasma power is
varied.
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Discussion - 4
Figure 7. The diameter of a water bubble on the
surface of silicon and oxide as electrode gap is
varied.
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Discussion - 5
Figure 8. The diameter of a water bubble on the
surface of silicon and oxide as number of
treatements is varied.
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Discussion - 6
Figure 9. The diameter of a water bubble on the
surface of silicon and oxide as scan speed is
varied.
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