Silicon etching by-products play a major role in silicon gate etching processes because they are the precursors to SiOClX passivation layer formation on feature sidewalls and on reactor walls. As a result, the understanding and modelling of these processes relies on the knowledge of the absolute value of SiClX (SiBrX) fluxes to the surfaces exposed to the plasma. However, only a few experimental data on the absolute concentration of SiClX etch byproducts are available in the literature. In this work, we show that broad band UV absorption spectroscopy can be used to measure the absolute densities of SiClX (X = 0–2), SiFX (X = 1–2) and SiO species, as well as to detect SiBr molecules. In addition, a new absorption spectrum has been observed and attributed to the SiClF radical. We have used a state of the art silicon gate etching process operating in a low pressure high density HBr/Cl2/O2/CF4 plasma etching a 200 mm diameter silicon wafer to produce the different radicals.The absorption bands of these species are all located in the 200–400 nm spectral region. Absorbances of 10−4 could be detected with a good signal to noise ratio in a few seconds exposure time using a Xe arc light source and a photodiode array detector. Details of the experimental procedure used to measure absorption spectra and to extract absolute concentrations from these spectra are presented, including a discussion concerning the influence of the monochromator spectral resolution on the absolute density determination for atomic species.
During plasma etching processes, organic or mineral layers are deposited on the chamber walls. In general, these layers cause large and uncontrolled shifts in the etch process, which is becoming a major issue in some of the plasma processes used in integrated circuit fabrication. The chemical nature of these layers and their deposition mechanisms remain poorly understood due to the lack of in situ surface diagnostics available to monitor the reactor walls. In this article, we present a simple technique using x-ray photoelectron spectroscopy (XPS) analyses to monitor the chemical composition of the layer deposited on a sample floating on top of a 200-mm-diam wafer where the layers deposited are identical to those deposited on the chamber walls. The principle of the technique is to stick a small Al2O3 sample onto the 200-mm-diam silicon wafer, with an air gap between the sample and the wafer. Providing that the air gap is thick enough, the Al2O3 surface will be electrically floating even when the silicon wafer is rf biased. During the etching process, the Al2O3 sample thus experiences exactly the same plasma conditions as the reactor walls. As the sample is physically clamped on the wafer, it can then be transferred under vacuum to an XPS analyzer, allowing quasi-in situ analyses of the deposited layers. The validity of the technique has been tested during silicon gate etching in HBr/Cl2/O2 plasmas, which are known to deposit silicon oxychloride layers on the chamber walls. The influence of CF4 addition in the plasma which has been recently introduced in gate etching manufacturing is also analyzed using the same technique. In a second step, we show that the presence of photoresist on the etched wafer profoundly affects the chemical nature of the layers formed on the chamber walls, mainly by significantly increasing the carbon concentration in the deposited layer.
Articles you may be interested inInfluence of the reactor wall composition on radicals' densities and total pressure in Cl 2 inductively coupled plasmas: II. During silicon etching Influence of ion mixing on the energy dependence of the ion-assisted chemical etch rate in reactive plasmas During silicon gate etching in low pressure high density HBr/Cl 2 /O 2 plasma, SiOCl x layers are deposited on the reactor walls. These layers are at the origin of process drifts. However their chemical composition, deposition mechanism and their influence on the plasma chemistry remains poorly understood. In this study, the chemical composition of this layer has been investigated by a ''plasma etching-sputtering'' technique: the silicon oxychloride layer deposited on the reactor walls during the etching of a 200 mm diam silicon wafer has been subsequently submitted to an Ar plasma with the addition of a few % SF 6 . During the slow etch process of this layer, time-resolved optical emission spectroscopy and mass spectrometry have been used to follow the time evolution of the gas phase concentration of different atoms and radicals, the etch products of the SiOCl x layer. The results give insight into the chemical nature of the deposited layer and of its variation as a function of the depth. In particular, it will be shown that these layers are chlorine-rich and not oxidelike. Also, their composition is not homogeneous through their depth. In a second set of experiments, the SiOCl x layer has been exposed to an Ar/O 2 plasma providing information on the oxidation mechanism of the Si-Cl bonds and thus on the SiOCl x film deposition mechanism in HBr/Cl 2 /O 2 plasmas. This oxidation mechanism is acting through the entire volume of the 10 nm thick layers and proceeds by substitution of Cl atoms of SiCl bonds by O atoms, resulting in desorption of a large amount of Cl atoms from the chamber walls during the layer oxidation. Finally, the layer on the chamber walls has been exposed to an Ar/Cl 2 plasma, demonstrating that SiOCl x layers are not etched significantly by Cl atoms.
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