Plasma enhanced chemical vapor deposition

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Plasma enhanced chemical vapor deposition
PECVD chamber diagram.jpg
Technology Details
Other Names PECVD  
Technology CVD
Equipment List of PECVD equipment
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Plasma enhanced chemical vapor deposition (PECVD) is a chemical vapor deposition technology that utilizes a plasma to provide some of the energy for the deposition reaction to take place. This provides an advantage of lower temperature processing compared with purely thermal processing methods like low pressure chemical vapor deposition (LPCVD). PECVD processing temperatures range between 200-400°C. LPCVD processes range between 425-900°C.

Method of operation

Reactant (and dilution) gases flow into process chamber through a shower head which is a large perforated metal plate located above the sample. The shower head helps to provide a more uniform distribution of reactant gas flow over the sample surface. An RF potential is applied to the shower head to generate a plasma. Energetic electrons in the plasma ionize or dissociate (“crack”) reactant gases to generate more chemically reactive radicals. These radicals react to form the thin film of deposition material on top of the sample. The energy supplied by plasma provides the key advantage of reduced process temperatures for PECVD vs. LPCVD where all of the energy for reaction is supplied thermally.

Parameters

RF Power

High Frequency (HF) RF Power 13.56 MHz

  • RF power has a strong effect on film stress.

Low Frequency (LF) RF Power 420 kHz (GSI PECVD only)

  • Use of low frequency RF causes more ion bombardment of the sample surface.
  • This provides another input parameter for modifying film stress.
  • Ion bombardment can also improve step coverage of film deposition into trench features.

Gas Flow Rates

  • In general, higher gas flow rates will cause higher deposition rates unless the reaction is limited by another reactant gas.

Chamber Pressure

  • Chamber pressure is optimized to provide good within wafer uniformity.

Temperature

  • Higher temperatures provide higher quality films. The highest temperature that can be used for the LNF PECVD equipment is between 350 to 400°C depending on the tool.
  • Higher temperature films have lower hydrogen content and will have slower etch rates in wet etches and dry plasma etches.
  • At lower temperatures, films are also more prone to have pinholes.

Shower head to susceptor spacing

  • Adjusting the gap between showerhead and the sample and susceptor provides another input parameter for adjusting within wafer uniformity.
  • Larger spacing reduces deposition rate.
  • Spacing can also modulate film stress.
  • For the LNF PECVD tools, shower head to susceptor spacing can only be adjusted for the P5000 PECVD tool


Applications

Plasma Enhanced Chemical Vapor Deposition is used in nanofabrication for deposition of thin films. PECVD deposition temperatures are between 200 to 400°C. It is used rather than LPCVD or thermal oxidation of silicon when lower temperature processing is necessary due to thermal cycle concerns or material limitations. PECVD films are typically of lower quality than the higher temperature LPCVD films. PECVD films tend to have higher etch rates, higher hydrogen content, and pinholes (especially for thinner films (<~4000Å)). However, PECVD can provide higher deposition rates. For example, deposition rates for silicon nitride (Si3N4) are: P5000 PECVD @400C = 130Å/sec vs. LPCVD @800C = 48Å/min (~160x faster).

Materials

PECVD deposition materials available in the LNF include: silicon dioxide (SiO2), silicon nitride (Si3N4), silicon oxynitride SiOxNy, and Amorphous silicon.

Equipment

P5000 PECVD

Main article: P5000 PECVD
  • For processing of pieces up to 150mm wafers
  • This is a Semi-clean tool and is the most restrictive PECVD tool in regard to substrate materials and materials present on samples that are allowed into the tool.

GSI PECVD

Main article: GSI PECVD
  • For processing of pieces up to 100mm wafers
  • Offers Low Frequency RF for film stress tuning
  • This is also a Semi-clean tool but has a more relaxed policy on substrate materials that are allowed into the tool including glass wafers, glass slides, and GaAs.

Plasmatherm 790

Main article: Plasmatherm 790
  • For processing of pieces up to 150mm wafers
  • This tool is in the metals material classification and is the least restrictive for materials that are allowed into the tool.


Complete tool list


References


Further reading