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Specific Process Knowledge/Thin film deposition/Deposition of Silicon Nitride

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Silicon Nitride (Si₃N₄)

Silicon nitride (Si₃N₄) is a wide‑bandgap (~5 eV) ceramic prized for its high mechanical strength, low intrinsic stress, chemical inertness, and excellent dielectric properties, making it a workhorse insulator in microelectronics and MEMS. It is deposited by reactive magnetron sputtering for dense, low‑defect films, and by low‑pressure CVD (LPCVD) or plasma‑enhanced CVD (PECVD) to obtain highly uniform, conformal layers over large wafers or temperature‑sensitive substrates. Within semiconductor process flows, Si₃N₄ serves as a hard mask, etch stop, stress liner, diffusion barrier, gate or capacitor dielectric, shallow‑trench‑isolation liner, and robust passivation layer for logic, memory, and power devices. Optically, its moderate refractive index (~2.0) and low propagation loss enable high-Q integrated-photonics waveguides, resonators, frequency-comb sources, filters, and durable anti-reflection coatings spanning the visible to the mid-IR. Beyond electronics and photonics, Si₃N₄’s high fracture toughness, fatigue resistance, and chemical stability support MEMS pressure sensors, accelerometers, and resonators, as well as protective barriers in solar cells, Li‑ion batteries, and high‑temperature or corrosive‑environment components, underscoring its versatility across semiconductor, optical, and engineering applications.

Deposition of silicon nitride

Deposition of silicon nitride can be done by either LPCVD (Low Pressure Chemical Vapor Deposition) or PECVD (Plasma Enhanced Chemical Vapor Deposition). Stoichiometric nitride or silicon-rich (low stress) LPCVD nitride is deposited on a batch of wafers in an LPCVD nitride furnace. PECVD nitride (or oxynitride) is deposited on a few samples at a time in a PECVD system. LPCVD nitride has a good step coverage and a very good uniformity. Using PECVD, it is possible to deposit a much lower temperature and a thicker layer of nitride on different types of samples, but the nitride does not cover the sidewalls very well.

It is also possible to deposit silicon nitride and oxynitride by reactive sputtering.

Comparison of LPCVD, PECVD, and sputter systems for silicon nitride deposition

LPCVD PECVD Sputter-System Metal-Nitride(PC3) and Sputter-System Metal-Oxide(PC1) Lesker sputter system
Generel description
  • Low Pressure Chemical Vapour Deposition (LPCVD furnace process)
  • Plasma Enhanced Chemical Vapour Deposition (PECVD process)
  • Reactive sputtering
  • Pulsed DC reactive sputtering
  • Reactive HIPIMS (high-power impulse magnetron sputtering)
 *Reactive sputtering
Stoichiometry
  • Stoichiometric nitride, Si3N4
  • Silicon rich (low stress) nitride, SRN
  • SixNyHz
  • SixOyNzHv

Silicon nitride can be doped with boron or phosphorus

  • SixNy (Sputter-System Metal-Nitride(PC3))
  • SixOyNz (Sputter-System Metal-Oxide(PC1))

Tunable composition

  • Unknown
Film thickness
  • Stoichiometric nitride: ~5 nm - ~230 nm
  • Silicon rich (low stress) nitride: ~5 nm - ~335 nm

Thicker nitride layers can be deposited over more runs (maximum two)

  • ~40 nm - 10 µm
  • limited by process time.
  • Deposition rate likely faster than Sputter-System (Lesker)
  • limited by process time.
  • Deposition rate ~ 1-5 nm/min
Process temperature
  • Stoichiometric nitride: 780 °C - 800 °C
  • Silicon rich (low stress) nitride: 810 °C - 845 °C
  • 300 °C
  • Up to 600 °C
  • Up to 400 °C
Step coverage
  • Good
  • Less good
  • some step coverage possible, especially by HIPIMS
  • some step coverage possible but amount unknown
Film quality
  • Deposition on both sides og the substrate
  • Dense film
  • Few defects
  • Deposition on one side of the substrate
  • Less dense film
  • Incorporation of hydrogen in the film
  • Deposition on one side of the substrate
  • Less dense film
  • Properties including density tunable (requires process development)
  • Deposition on one side of the substrate
  • unknown quality
  • likely O-contamination
KOH etch rate (80 oC)
  • Expected <1 Å/min
  • Dependent on recipe: ~1-10 Å/min
  • Unknown
  • Unknown
BHF etch rate
  • Unknown
  • Unknown
Batch size
  • 1-15 100 mm wafers (4" furnace), 1-25 100 mm wafers (6" furnace)
  • 1-25 150 mm wafers (only 6" furnace)
  • Several smaller samples
  • 1-7 50 mm wafers
  • 1 100 mm wafers
  • 1 150 mm wafer

Depending on what PECVD you use

  • many smaller samples
  • Up to 10*100 mm or 150 mm wafers
  • Several smaller samples
  • 1-several 50 mm wafers
  • 1*100 mm wafers
  • 1*150 mm wafer
Allowed materials
  • Silicon
  • Silicon oxide
  • Silicon nitride
  • Pure quartz (fused silica)

Processed wafers have to be RCA cleaned

  • Silicon
  • Silicon oxide (with boron, phosphorous)
  • Silicon nitrides (with boron, phosphorous)
  • Pure quartz (fused silica)
  • III-V materials (in PECVD4)
  • Small amount of metals (in PECVD3)
  • Almost any as long as they do not outgas and are not very toxic, see cross-contamination sheets
  • Any





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