Page 21 - 3_Chemical industry

Sum parameter – Total Organic Carbon
TOC – Determination in diluted hydrofluoric
acid
SCA-130-310
Hydrofluoric acid is the only acid that attacks
glass (glass etching). Because of this
chemical property, it plays a distinct role in
several industrial processes, for instance in
the manufacturing of solar cells and wafers
as well as in microchip production.
Hydrofluoric acid is the most widely used
etching agent in the semiconductor industry.
When carrying out etching processes, it is
important to ensure that the etching agent
used will etch the respective layers and not
leave any contaminants.
This raises questions on the impurities of
etching agents, where both the purity of the
starting acid and that of the etching solutions
after the etching process are of interest.
To determine the degree of contamination,
the TOC parameter is particularly suitable, as
it is a sum parameter that detects all organic
carbon compounds.
■ TOC determination
In the following measurement, a 4%
hydrofluoric acid was manually diluted to 1:10
with water and measured using the TOC-
L CPH. Given the acidity of the hydrofluoric
acid, the IC content can be neglected. With
regard to the dilution, the solution was slightly
acidified and sparged for 3 minutes. The
NPOC was subsequently determined by
means of combustion oxidation.
An aliquot of the sample is injected onto a hot
(680 °C) platinum catalyst. The organic
substances are converted to CO 2 and
detected via an NDIR detector.
■ Calibration
Due to mostly working in a small measuring
range, calibration was carried out in a range
of 0.25 mg/L – 5.0 mg/L. For dilutions, the
automatic dilution function of the TOC-L
system was applied. The injection volume
was 150 µL respectively.
Kal. Kurve
69,047
60
50
40
Fläche
30
20
10
0 0 1 2 3 4 5 5,5
Konz[mg/L]
Figure: Calibration curve, TC 5 mg/L.