In situmeasurements of HCl during plasma etching of poly-silicon using a diode laser absorption sensor

Abstract

Tunable diode laser absorption spectroscopy is used to monitor hydrogen chloride (HCl) concentration in a commercial, high-density, low-pressure plasma reactor during plasma etching. A near-infrared diode laser is used to scan the P(4) transition in the first overtone of HCl near 1.79 µm to measure changes in HCl levels. A variety of HBr and Cl 2 feedstock recipes are investigated at a process pressure of 10 mTorr as a function of rf power transformer coupled plasma, bias power and the total flow rate. Using 50 ms averaging and a signal modulation technique, we estimate a minimum detectivity of 4 × 10 −6 in peak absorbance, which corresponds to an HCl number density of ∼2 × 10 11 cm −3. The diode-laser based HCl sensor is sufficiently sensitive to detect small concentration variations and HCl concentration correlates with poly-Si etch rate for the conditions studied. These measurements demonstrate the feasibility of a real-time diode laser-based sensor for etch rate monitoring and the potential for process control.

HCl ppb-level detection based on QEPAS sensor using a low resonance frequency quartz tuning fork

“…HCl is not only a source of dioxin and acid rain, but also has been identified as hazardous in industrial workplaces, with a short period exposure limit of 5 ppm. Furthermore, HCl has performed an important role in photochemistry [3] and plasma etching [4]. Hence, there is a significant need for sensitive detection of HCl gas concentrations at sub-ppm levels.…”

“…Laser absorption spectroscopy (LAS) has the advantages that include fast response, non-invasive, highly sensitive and selective detectio compared with chemical sensors which are currently widely used for HCl detection [5]. Tunable diode laser absorption spectroscopy (TDLAS) was adopted for HCl measurements [4,6] and a minimum detection limit (MDL) of 45 ppm was obtained [6]. In order to further improve the detection sensitivity, a multi-pass gas cell (MPGC) is usually used in the TDLAS technique, where the effective optical path length is typically tens and even hundreds of meters in order to reach a detection limit of the analyte trace gas species at ppb concentration levels [7][8][9].…”

Optical Absorption Measurements of Hydrogen Chloride at High Temperature and High Concentration in the Presence of Water Using a Tunable Diode Laser System for Application in Pyrohydrolysis Non-Ferrous Industrial Process Control

“…Hydrogen chloride (HCl) gas is an important chemical compound that is present in several industrial processes. Some of these include chemical vapor deposition for coatings, 1 plasma etching of semiconductors, 2 and measurement of toxic gases during the combustion of plastics such as polyvinyl-chloride. 3 In the non-ferrous metallurgy sector, as described in equation where M is metal, HCl can be used for pickling metal (removing oxide through hydrochlorination), and the HCl is recovered through pyrohydrolysis of the resulting metal chloride.…”

Vacuum UV broad-band absorption spectroscopy: a powerful diagnostic tool for reactive plasma monitoring

“…often small polyatomic radicals. For instance, the detection of larger, closed shell molecules is impossible and relies on the use of more sophisticated laser absorption techniques in the infrared region 8,9,10,11 or on mass spectrometry 12,13 . However, many molecules have Rydberg states or pre-dissociated continuums which absorb in the Vacuum-UV (VUV) spectral range.…”

“…It is not straightforward to deduce the absolute density of Br 2 from this spectrum since for the same reasons than already mentioned for HBr, the absorption on rotational lines of Br 2 must be saturated and unfortunately it is not permitted to introduce Br 2 , which is liquid at room temperature, into the chamber. However, it is possible to produce known amounts of Br 2 molecules by mixing HBr and Cl 2 gases, which react totally together to form HCl and Br 2 9,21.…”