Number

328-EN

Section

General Section

Use

Abstract

Nitrogen trifluoride (NF₃) is used in the fast growing sector of photovoltaics manufacturing. It was initially used as an alternative to sulphur hexafluoride but the fast growth of the renewable energy sources lead to a level of NF₃ emissions that is already concerning since it is itself a greenhouse gas (GHG), even if less potent as the sulphur hexafluoride. Fluorine gas can be used as a replacement because it is not a GHG, but special protective and preventive measures have to be taken because this alternative has its own hazards.

Substituted substances

Alternative Substances

Reliability of information

Evidence of implementation: there is evidence that the solution was implemented and in use at time of publication
Divergent opinions: not all conclusions for similar cases are similar to the ones in this case study
Internet information: data are from an internet document and only a basic and partial evaluation could be performed

Reason substitution

skin/respiratory sensitizing
ecotoxicity

Hazard Assessment

Substance to be substituted: Nitrogen trifluoride has no harmonised classification according to Annex VI of Regulation (EC) No 1272/2008 (CLP Regulation). Its main hazard is related to a high Global Warming Potential (GWP) and an atmospheric lifetime over three thousand years. Alternative substance: Fluorine is an oxidiser, is fatal if inhaled, causes severe skin burns and eye damage. It reacts with moisture to form hydrogen fluoride (hydrofluoric acid) which is also highly hazardous. Fluorine has practically zero atmospheric lifetime and zero global warming potential. In USA the permissible exposure limit for eight hours -Time weighted average (TWA)- for fluorine is 10 ppm, while for nitrogen trifluoride is 1 ppm (see Further Information).

Description of Substitution

Thin-film silicon solar cell production needs periodical cleaning of silicone built up on the walls of the chamber for Enhanced Plasma Chemical Vapor Deposition (EPCVD). Gases able to provide fluorine radicals are used for these chemically resistant, unwanted deposits. Nitrogen trifluoride (NF3) is currently the most used gas and, though not climate neutral itself, it was introduced as a better alternative to sulphur hexafluoride, a very powerful greenhouse gas. There were claims that concentration of NF3 in the atmosphere is growing faster than expected, therefore other alternatives were researched. Fluorine was considered a good substitute. It is climate neutral, it provides quality results, has a cleaning rate 2.7 times that of NF3, and in the past years it became possible to produce it on the site. The low cost of ownership and the flexible modular capability making it adjustable to various production lines, are some advantages of fluorine generated on site. In situ generators use hydrofluoric acid hydrolysis to obtain molecular fluorine. Stringent safety measures are imperative to keep under control the risks of such reactive chemicals. According to one representative of the producer there has been no safety incident for the several tens of generators provided in the course of a decade. Fluorine gas is used at a pressure above the atmospheric one, but lower than required for nitrogen trifluoride. Fluorine above ambient pressure is protected by double containment. The lines connected to the cleaning site are double-contained, the outer line being filled with pressurised nitrogen. Pressure monitors detect breaches in the fluorine line. The generator has ventilated enclosures around all the components.

Case/substitution evaluation

It is hard to choose between long term climate effects and the impact on health and safety, which may be very severe (even fatal) and, by comparison, occurs much rapidly. Though the use of fluorine is increasing, there are concerns regarding the capacity of producers and users to insure a safe process. Even if the transportation of compressed fluorine in cylinders can be avoided when on-site generators are use, the problem of transporting hazardous substances still remains, since hydrofluoric acid is needed as raw material. On the other hand, reported growth in the atmospheric concentration of NF₃ is also concerning. It suggests that control and abatement measures are not efficient. NF₃ contribution to climate change is still modest, but it is used in a fast growing business. If NF₃ will be included in the Kyoto protocol the need for alternatives might favour the use of fluorine, with the required safety measures for normal conditions and in case of emergencies. If not, it is possible that some of the producer will continue to use NF3 and improve the abatement technologies and leak-proof their systems.

State of implementation

In use

Date and place of implementation

Germany, 2009

Availability ofAlternative

The alternative is available on the market.

Producer/Provider

http://www.linde-gas.com/en/index.html

Type of information supplier

Producer / distributor

Further information

NASA, 2008, Potent Greenhouse Gas More Common in Atmosphere Than Estimated http://www.nasa.gov/home/hqnews/2008/oct/HQ_08-268_Greenhouse_gas.html

Linde: Solar: Adding value to the global solar industry through leading integrated gases and chemical supply solutions

Download Fluorine Datasheet(PDF 656.0 KB)

Publication source: author, company, institute, year

The description is based on: Michael Matz, Climate-friendly thin- A new study suggests that fluorine gas is a compelling alter trifluoride, a potent greenhouse gas widely used by thin-film for PECVD chamber cleaning,  Photon International, November 2009.

Date, reviewed

November 26, 2021