The etching of Si, SiO 2 , Si 3 N 4 , and SiCH in fluorocarbon plasmas is accompanied by the formation of a thin steady-state fluorocarbon film at the substrate surface. The thickness of this film and the substrate etch rate have often been related. In the present work, this film has been characterized for a wide range of processing conditions in a high-density plasma reactor. It was found that the thickness of this fluorocarbon film is not necessarily the main parameter controlling the substrate etch rate. When varying the self-bias voltage, for example, we found a weak correlation between the etch rate of the substrate and the fluorocarbon film thickness. Instead, for a wide range of processing conditions, it was found that ion-induced defluorination of the fluorocarbon film plays a major role in the etching process. We therefore suggest that the fluorocarbon film can be an important source of fluorine and is not necessarily an etch-inhibiting film.

Articles you may be interested inDegradation mechanism of Schottky diodes on inductively coupled plasma-etched n-type 4H-SiCThe mechanisms underlying selective etching of a SiO 2 layer over a Si or Si 3 N 4 underlayer, a process of vital importance to modern integrated circuit fabrication technology, has been studied. Selective etching of SiO 2 -to-Si 3 N 4 in various inductively coupled fluorocarbon plasmas (CHF 3 , C 2 F 6 /C 3 F 6 , and C 3 F 6 /H 2 ) was performed, and the results compared to selective SiO 2 -to-Si etching. A fluorocarbon film is present on the surfaces of all investigated substrate materials during steady state etching conditions. A general trend is that the substrate etch rate is inversely proportional to the thickness of this fluorocarbon film. Oxide substrates are covered with a thin fluorocarbon film ͑Ͻ1.5 nm͒ during steady-state etching and at sufficiently high self-bias voltages, the oxide etch rates are found to be roughly independent of the feedgas chemistry. The fluorocarbon film thicknesses on silicon, on the other hand, are strongly dependent on the feedgas chemistry and range from ϳ2 to ϳ7 nm in the investigated process regime. The fluorocarbon film thickness on nitride is found to be intermediate between the oxide and silicon cases. The fluorocarbon film thicknesses on nitride range from ϳ1 to ϳ4 nm and the etch rates appear to be dependent on the feedgas chemistry only for specific conditions. The differences in etching behavior of SiO 2 , Si 3 N 4 , and Si are suggested to be related to a substrate-specific ability to consume carbon during etching reactions. Carbon consumption affects the balance between fluorocarbon deposition and fluorocarbon etching, which controls the fluorocarbon steady-state thickness and ultimately the substrate etching.

It has been found that in the etching of SiO2 using CHF3 in an inductively coupled plasma reactor of the planarized coil design, a thin steady state fluorocarbon film can play an important role in determining the rate of etching. This etching is encountered as the amount of bias power used in the SiO2 etching process is increased, and a transition from fluorocarbon film growth on the SiO2 to an oxide etching rate which is consistent with reactive sputtering theory is made. The observed presence of an intermediate region where etching occurs, although a steady state fluorocarbon film suppresses the etch rate from that expected for a reactive sputtering process, has been referred to as the fluorocarbon suppression regime. This work demonstrates the role of the steady state fluorocarbon film present on silicon dioxide during etching within the fluorocarbon suppression regime. X-ray photoelectron spectroscopy studies of the surfaces of partially etched SiO2 have shown a thinning of this film with increasing rf bias power, as well as a decrease in the fluorine content of the surface film as a function of increasing rf bias power. We have found that slight variations in the film thickness, on the order of 1 nm, can result in large variations, approximately 400 nm/min, in the silicon dioxide etch rate. The presence of the film within the suppression regime appears to be due to the overwhelming polymerization ability of high density plasmas, coupled with the inability of the oxide to react sufficiently with the total fluorocarbon particle flux in order to completely remove this film. For this reason these types of reactors exhibit a regime where oxide etching occurs in the presence of a surface film. The film appears to be directly responsible for the observed suppression of the oxide etch rate from that expected for a reactive sputtering process by dissipating the bombarding ion energy, and thereby suppressing the energy flux arriving at the oxide surface.

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. For various fluorocarbon processing chemistries in an inductively coupled plasma reactor, we have observed relatively thick ͑2-7 nm͒ fluorocarbon layers that exist on the surface during steady state etching of silicon. In steady state, the etch rate and the surface modifications of silicon do not change as a function of time. The surface modifications were characterized by in situ ellipsometry and x-ray photoelectron spectroscopy. The contribution of direct ion impact on the silicon substrate to the etching mechanism is reduced with increasing fluorocarbon layer thickness. Therefore, we consider that the silicon etch rate is controlled by a neutral etchant flux through the layer. Our experimental data show, however, that ions play an import role in the transport of silicon etching precursors through the layer. A model is developed that describes the etch kinetics through a fluorocarbon layer based on a fluorine diffusion transport mechanism. The model is consistent with the data when one or two of the following roles of the ions on the etching process are assumed. The first role is an enhancement in the diffusivity of fluorine atoms through the fluorocarbon layer and an enhancement in the reaction probability of fluorine in the fluorocarbon layer. In this case the fluorine is assumed to originate from the gas phase. The second role includes ion fragmentation and dissociation of the fluorocarbon surface molecules.

The influence of reactor wall conditions on the characteristics of high density fluorocarbon plasma etch processes has been studied. Results obtained during the etching of oxide, nitride, and silicon in an inductively coupled plasma source fed with various feedgases, such as CHF 3 , C 3 F 6 , and C 3 F 6 /H 2 , indicate that the reactor wall temperature is an important parameter in the etch process. Adequate temperature control can increase oxide etch selectivity over nitride and silicon. The loss of fluorocarbon species from the plasma to the walls is reduced as the wall temperature increased. The fluorocarbon deposition on a cooled substrate surface increases concomitantly, resulting in a more efficient suppression of silicon and nitride etch rates, whereas oxide etch rates remain nearly constant.