Plasma-Therm Versaline PECVD now available

The nanoFAB is pleased to announce that the new Plasma-Therm Versaline PECVD (Plasma-Enhanced Chemical Vapour Deposition) system is fully commissioned and available for user training.

Thin films available for deposition include:

  • a-Si (amorphous silicon)
  • SiNx (Si-rich and stoichiometric nitride)
  • SiO2 (silicon dioxide)
  • SiOxNy (silicon oxynitride)

Through its user-friendly software, the Plasma-Therm Versaline PECVD offers robust recipe control for tuning parameters such as refractive index, composition, and film stress. Currently available process and carrier gases are: SiH4 (100%), NH3, N2O, H2, Ar, He, and N2.

System features of the Plasma-Therm Versaline PECVD:

  • Conformal films with high uniformity
  • Low particulate generation
  • Increased productivity through short clean cycles
  • Endpoint capabilities through Plasma-Therm’s EndpointWorks software

EndpointWorks is a multi-functional endpoint detection package for optical emission interferometry (OEI) and optical emission spectroscopy (OES) recipe control. OEI provides real-time deposition rate information and thickness control, while OES uses spectral information in the plasma to decrease the time required for clean cycles.

Typical uniformity results and optical constants for standard recipes/materials

Thickness maps acquired by Filmetrics F50-UV, optical constants measured by VASE Ellipsometer.


Recipe name: a-Si Dep

Silicon nitride

Recipe name: Stoichiometric Nitride Dep

Recipe name: Si-rich nitride Dep


Recipe name: SiO2 Dep

Film modification and process trends

Plasma-Therm boasts an extensive process library, which may be consulted to aid users in the modification of our standard recipes for specific applications. Some trends within the typical parameter space for these recipes are shown below.

a-Si trends

While the nanoFAB standard a-Si film is reasonable for most applications, Plasma-Therm has provided the nanoFAB with a second a-Si recipe based on He-dilution that can be tuned to easily adjust the deposited film stress. See the table below for a brief comparison between the process parameters of this recipe and the nanoFAB standard recipe (a-Si dep):

Parameter a-Si dep He-dilution
RF power (W) 20 25
Deposition pressure (mTorr) 600 900 to 1200
SiH4 flow rate (sccm) 25 50
He flow rate (sccm) 0 1000
Ar flow rate (sccm) 1400 0
Lower electrode temperature (°C) 250 140
Upper electrode temperature (°C) 175 140


This He-dilution recipe exhibits the following process trends:

  • Film stress that can be modulated from compressive (negative) to tensile (positive) by increasing the deposition pressure.
  • Deposition rate that increases with increasing pressure.

If you are interested in using this a-Si deposition recipe, please contact the primary tool trainer, Tim Harrison (, for details.

Please note that regardless of the a-Si deposition recipe used, OEI for endpoint detection does not work well due to the high optical absorption of a-Si.

SiON trends

The typical reactions used in the Plasma-Therm Versaline PECVD for the deposition of nitride films allows for the deposition of a silicon oxynitride (SiOxNy) by the modification of gas ratios and other deposition parameters. Oxynitride is a promising material that has been investigated for the development of optical components such as integrated waveguides, anti-reflective coatings, interferometers, filters, couplers, and splitters due to its tunable optical and mechanical properties. Such properties can be tailored by simultaneously adjusting both the N2O / SiH4 and N2O / NH3 ratios when depositing a film using a plasma chemistry of SiH4, N2O, and NH3. Depending on the application, films that are nearly pure silicon, primarily oxides, or even stoichiometric nitrides can be deposited. These films follow the general trends below:

  • Si-rich film
    • Very low N2O / SiH4 ratio.
  • Nitride-like film
    • Low N2O / SiH4 ratio.
    • Low N2O / NH3 ratio
  • Oxide-like film
    • High N2O / SiH4 ratio.
    • High N2O / NH3 ratio.
  • Meanwhile, the film stress is tied to the refractive index of the film (i.e. how oxide-like or nitride-like the film is):

SiO2 trends

By utilizing a similar gas chemistry to that used for oxynitrides, a pure oxide film can be deposited. Such films have many uses in semiconductor and micro-optics including use as insulating layers for integrated circuits, low refractive index optical films, encapsulation, passivation layers, and more. Each application tends to emphasize different film properties, including (but not limited to) uniformity, deposition rate, film stress, refractive index, and wet etch rate, which can be tuned in the deposited film by the adjustment of process parameters.

For the Plasma-Therm Versaline PECVD deposited oxide:

  • The deposition rate of the film can be increased by increasing the RF power and the relative SiH4 concentration (i.e. decreasing the N2O / SiH4 ratio).
  • Deposition rates potentially as high as 4500 Å/min can be achieved.

  • As with oxynitride films, an increased N2O /SiH4 ratio will decrease the refractive index to a minimum of ~1.46 at 632.8 nm.


The addition of the Plasma-Therm Versaline PECVD offers the nanoFAB community the ability to produce high quality SiNx films by depositions performed at lower temperatures and over much shorter timescales than typical Low Pressure Chemical Vapour Deposition (LPCVD). The Plasma-Therm Versaline PECVD is also capable of producing low-stress stoichiometric nitrides that are nearly impossible to produce via LPCVD. Shown below are comparisons between the typical optical constants of the films produced by the Tystar LPCVD Tube furnace (Tube 2) and those produced by the Plasma-Therm Versaline PECVD. Typical uniformity maps for LPCVD nitrides are also given for comparison to the uniformity maps shown above for Plasma-Therm deposited films.



Method Recipe Typical stress (MPa) Uniformity over 100 mm Ø wafer (%)
LPCVD Stoichiometric 1000 1.1
PECVD Stoichiometric -15 to -40 0.8
LPCVD Low-stress 100 to 250 1.0
PECVD Si-rich 200 1.7

Stress convention is as above: negative (compressive), positive (tensile).

Basic training on the Plasma-Therm Versaline PECVD is now available to all nanoFAB users via training requests submitted on LMACS. If you have any questions about the capabilities of the Plasma-Therm Versaline PECVD, please do not hesitate to contact Tim Harrison ( or Aaron Hryciw (