Silicon dioxide

Silicon dioxide, SiO2, is a common dielectric material used in semi-conductor processing. It can be both grown on silicon substrates using wet or dry techniques and deposited on a wide variety of substrates using techniques such as LPCVD, PECVD, Sputtering, and Evaporation. It is also easily etched. Common names include silicon oxide, silicon dioxide, silica, SiO2, HTO (high temperature oxide), LTO (low temperature oxide).

The growth and deposition technique used will affect the quality and dielectric strength of the silicon dioxide. Generally the higher the process temperature the higher the quality. HF etch rate also gives a window into the film quality with higher quality films etching between 900-1000Å/min and lower quality films etching significantly faster.

Processing Equipment

Deposition/Growth Equipment

• Low temperature deposition
  • Lab 18-1
  • PVD 75
  • Angstrom Engineering Evovac Evaporator
  • SJ-26 Evaporator
• Medium temperature deposition
  • Veeco Fiji ALD
  • P5000 PECVD
  • GSI PECVD
  • Plasmatherm 790
  • Tempress S1T2 - LTO 4"
  • Tempress S1T4 - LTO 6"
• High temperature deposition
  • Tempress S4T4 - TEOS 4"
  • Tempress S2T2 - Nitride-HTO 6"
  • Tempress S2T3 - Nitride-HTO-OxyNitride 4"
  • Tempress S3T1 - Dry Oxide
  • Tempress S3T2 - Wet Oxide
  • Tempress S5T2 - Phosphorous Anneal Oxidation
  • Tempress S5T4 - Boron Anneal Oxidation

Etching Equipment

• Wet Etching
  • Acid Bench 02
  • Acid Bench 12
  • Acid Bench 73
  • Acid Bench 82
• RIE
  • P5000 RIE
  • LAM 9400
  • STS APS DGRIE
  • Plasmatherm 790

Characterization Equipment

• Material Properties
  • Woollam M-2000 Ellipsometer
  • NanoSpec 6100
  • Flexus 2320-S
  • Rame-Hart Goniometer

Applications

Common uses of silicon dixode include:

• Dielectric
• Sacrificial Layer
• Structural Layer
• Hard Mask for RIE etching
• Thermal or LPCVD silicon dixoide can be used as a mask for KOH etching

Processes

Deposition/Growth Processes

At the LNF there are multiple ways of growing or depositing an Silicon Dioxide film. The processes are listed from highest to lowest temperature. This generally relates to film quality.

• Thermal oxidation
  • Dry Oxidation
  • Wet Oxidation
• Low-Pressure Chemical Vapor Deposition (LPCVD)
  • High Temperature Oxide (HTO) is conformal and has a BHF etch rate comparable to Thermal Oxide.
  • Low Temperature Oxide (LTO) is NOT conformal and has a BHF etch rate comparable to PECVD oxide.
• Atomic Layer Deposition (ALD)
• Plasma Enhanced Chemical Vapor Deposition (PECVD)
  • Optical and etch properties of the deposited film will be dependent on tool and recipe selected.
• Physical vapor deposition PVD)
  • E-beam evaporation
  • Sputter deposition
  • SiO2 films deposited with these methods are likely to have pinhole and high etch rates.

Etch Processes

Silicon dioxide is usually patterned using an etching process. The LNF has wet and dry etching capabilities.

• Wet etching*
  • Silicon Oxide can be etched with Hydrofluoric acid based solutions.
  • The etch rate of the silicon dixoid depends on the quality of the oxide. The lower the etch rates indicate better film quality. *You can get a good estimate of etch Silicon Dioxide etch rates from ["Etch rates for micromachining processing"] and ["Etch rates for micromachining processing-Part II"]

• RIE Etch*
  • Tool material restriction must be considered when selecting an RIE tool as it will impact what tools you can use for future process steps.
  • RIE will give straighter sidewalls and less undercut than wet etching.

Characterization Processes

• Optical
  • The optical properties of the tool will vary depending on the deposition method used.
  • The optical techniques can be used to find the thickness of the film.
  • Elipsomentry can be used to find the n and k values.
• Stress
  • The Flexus 2320-S can be used to find the stress of the film.
  • Curvature of the wafer must be measured before deposition.
  • If film is deposited on both sides it must be removed from the backside before the second measurement is taken.

References

• Etch rates for micromachining processing
• Etch rates for micromachining processing-Part II
• Wikipedia: Silicon dioxide