Terry Sparks

The Use of Unsaturated Fluorocarbons for Dielectric Etch Applications

Six unsaturated fluorocarbon (UFC) gases as well as a fluorinated ether were examined for dielectric etch and global warming emissions performance and compared to three perfluorocompound (PFC) gases. All of the gases were capable of etch performance comparable to that of a typical C 3 F 8 process, while exhibiting superior global warming emissions performance compared to the PFCs. A low-flow hexafluoro-2-butyne process was found to have a significant emissions benefit, showing a normalized emissions reduction of 88.2% compared to the C 3 F 8 process. Two other C 4 F 6 isomers (hexafluoro-1,3-butadiene and hexafluorocyclobutene) also exhibited reductions greater than 80%, while hexafluoropropene and octafluorocyclopentene exhibited emissions reductions greater than 70% compared to the typical C 3 F 8 process. For the C 4 F 6 isomers, a large portion of the emissions were a result of CHF 3 formation with photoresist as the sole source of the hydrogen. An extended 4 min etch with hexafluoro-1,3-butadiene resulted in a deep via with an aspect ratio of 5:1, very high selectivity to photoresist, and no evidence of etch stopping.

Use of 2H-heptafluoropropane, 1-iodoheptafluoropropane, and 2-iodoheptafluoropropane for a high aspect ratio via etch in a high density plasma etch tool

An issue currently facing the semiconductor industry is the use and emission of perfluorocompounds (PFCs), gases which are believed to contribute to global warming, in a number of plasma processes used in integrated circuit manufacture, including wafer patterning. Several approaches to reducing emissions of these compounds are being considered, namely abatement, recapture/recovery, process optimization, as well as the development of alternative chemistries as PFC substitutes. The authors present here the results of an effort to test several alternatives in a silicon dioxide etch application (high aspect ratio via etch). 2H-heptafluoropropane, 1-iodoheptafluoropropane, and 2-iodoheptafluoropropane, were tested in an Applied Materials Centura 5300 high density plasma etch tool. Fourier transform infrared spectroscopy was used to analyze the process effluent. The process performance and emissions of the alternative etchants were compared to those of a standard chemistry on the Centura 5300 etch tool.

Use of Novel Hydrofluorocarbon and Iodofluorocarbon Chemistries for a High Aspect Ratio Via Etch in a High Density Plasma Etch Tool

This paper presents the results of an effort to test several novel chemistries for use as replacements for perfluoro-compounds in dielectric etch processes. Chemistries belonging to the hydrofluorocarbon and iodofluorocarbon families, namely, 2H-heptafluoropropane (CF 3 -CFH-CF 3 ), iodotrifluoromethane (CF 3 I),1-iodoheptafluoropropane (CF 2 I-CF 2 -CF 3 ), and 2-iodoheptafluoropropane (CF 3 -CFI-CF 3 ), were tested in an Applied Materials Centura 5300 HDP etch tool, using a high aspect ratio silicon dioxide via etch application as the test vehicle. Designed experiment methodology was used in the evaluation. Effluent was analyzed using Fourier transform infrared spectroscopy and quadrupole mass spectrometry. The performance of the alternative etchants in a high aspect ratio via etch process was compared to that of a standard chemistry on the Centura 5300 etch tool. Significant reductions in global warming emissions, relative to a perfluorinated baseline process, were found to be attainable with the alternative chemistries.

Evaluation of Oxalyl Fluoride for a Dielectric Etch Application in an Inductively Coupled Plasma Etch Tool

The goal of the work presented in this article was to provide a preliminary screening for a novel fluorinated compound, oxalyl fluoride, C 2 O 2 F 2 (F-(C=O)-(C=O)-F), as a potential replacement for perfluorocompounds in dielectric etch applications. Both process and emissions data were collected and the results were compared to those provided by a process utilizing a standard perfluorinated etch chemistry (C 2 F 6 ). In this evaluation, oxalyl fluoride produced very low quantities of global warming compounds under the conditions in which it was tested, as compared to the C 2 F 6 process A preliminary evaluation of the compounds process performance was also carried out. Patterned tetraethoxysilane-deposited silicon oxide masked with deep UV photoresist having 0.6, 0.45, and 0.35 μm via hole features was used as the test vehicle. Although C 2 O 2 F 2 was capable of etching silicon dioxide, low oxide etch rate and poor selectivity to the mask layer were observed. Finally, in addition to the experimental work performed, a set of ab initio quantum chemical calculations was undertaken to obtain enthalpies of dissociation for each of the bonds in the oxalyl fluoride molecule in order to better understand its dissociation pathways in plasma environments.

Modeling of photoresist erosion in plasma etching processes

A set of surface reaction mechanisms has been developed to predict photoresist (PR) erosion in a high density Ar-c-C/sub 4/F/sub 8/ plasma. The mechanisms include angle and energy dependent ion sputtering, ion activation, and atomic F etching of activated surface species. An integrated plasma equipment and feature profile model was used to simulate these mechanisms. The simulation results show faceted profile evolution for the PR due to preferential ion sputtering at the incident angle to the facet. The faceting also occurs on small defective surface pits, leading to expansion of the defect size. Comparison between simulated and experimental profiles shows good agreement.

Integrated equipment-feature modeling investigation of fluorocarbon plasma etching of SiO2 and photoresist

As the microelectronics industry continues to shrink feature size and increase feature density in the back-end of integrated circuits, the traditional empirical approach to plasma etch process development is becoming prohibitively expensive and time consuming. Fundamental physics based models can prove useful in driving down process development time and cost. In this article, an integrated equipment-feature scale modeling infrastructure for SiO2 and photoresist (PR) etching in fluorocarbon based plasma discharges is described. The model correlates process conditions with plasma properties, surface interactions, and etch results. A validated plasma chemistry for Ar/c–C4F8/CF4 and detailed plasma–surface reaction mechanisms for SiO2/PR etching have been incorporated in the model. Major surface reactions for SiO2 etching include neutral surface passivation, fluorocarbon radical polymerization, and ion assisted etching of volatile products. The mechanism for PR erosion includes energy/angle dependent ion sput...

The Evaluation of Hexafluorobenzene as an Environmentally Benign Dielectric Etch Chemistry

Hexafluorobenzene was evaluated as an alternative chemistry for dielectric etch applications in a high density plasma etch chamber with reduced global warming emissions. Processes based on hexafluorobenzene exhibited global warming emissions reductions as high as 97% compared to a C 3 F 8 -based process, which is the greatest reductions level of any alternative chemistry examined to date on this tool. Using hexafluorobenzene, it is possible to operate in a regime of high etch rate and high polymerization. There are several issues, however, that need to be addressed if this chemistry is to be used for high performance dielectric etching. This material is a liquid at room temperature, which makes it difficult to deliver process gas to the chamber. In addition, this chemistry is highly polymerizing, resulting in excess polymer deposition on chamber walls leading to significant process variability for standard chamber clean times Significantly longer chamber clean times were required between each etch to remove the excess polymer.

High density plasma oxide etching using nitrogen trifluoride and acetylene

The use of nitrogen trifluoride (NF3) and acetylene (C2H2) in the presence of helium has been examined for oxide etching in an inductively coupled, high density plasma etch tool. Oxide etch rates have been measured for blanket films and for patterned wafers with features of 0.6, 0.45, and 0.35 μm nominal critical dimension, while process performance has been assessed with cross-sectional scanning electron microscopy. Optical emission spectroscopy has been employed in situ to characterize the species present in the plasma, and quadrupole mass spectrometry has been used to analyze process effluent sampled between the chamber outlet and the turbo pump inlet. Polymer film deposited on the surface of the oxide layer has been studied with time-of-flight secondary ion mass spectrometry. Global warming emissions for a range of process conditions have been quantified using Fourier transform infrared spectroscopy, and are compared to emissions from more typical oxide etch processes on the same tool type. Results in...

Evaluation of Pentafluoroethane and 1,1-Difluoroethane for a Dielectric Etch Application in an Inductively Coupled Plasma Etch Tool

In this work, a combination of two hydrofluorocarbon compounds, pentafluoroethane (FC-125, C2HF5) and 1,1-difluoroethane (FC-152a, CF2H–CH3), was evaluated as a potential replacement for perfluorocompounds in dielectric etch applications. A high aspect ratio oxide via etch was used as the test vehicle for this study, which was conducted in a commercial inductively coupled high density plasma etch tool. Both process and emissions data were collected and compared to those provided by a process utilizing a standard perfluorinated etch chemistry (C2F6). Global warming (CF4, C2F6, CHF3) and hygroscopic gas (HF, SiF4) emissions were characterized using Fourier transform infrared (FTIR) spectroscopy. FC-125/FC-152a was found to produce significant reductions in global warming emissions, on the order of 68 to 76% relative to the reference process. Although etch stopping, caused by a high degree of polymer deposition inside the etched features, was observed, process data otherwise appeared promising for an initial study, with good resist selectivity and etch rates being achieved.

Characterization of iodoheptafluoropropane as a dielectric etchant. III. Effluent analysis

The work presented in this article represents the third and final part of a series of articles which present a systematic evaluation of iodoheptafluoropropane (C3F7I) as a potential replacement for perfluorocompound chemistries in dielectric etch applications. In the experiments discussed in this series, 1- and 2-iodoheptafluoropropane based etch processes had been employed in a via etch application in an inductively coupled high density plasma etch tool. Part I of this article discusses etch process behavior of 1- and 2-iodoheptafluoropropane, while Part II examines films deposited by the 1-iodo isomer. This article will focus on the composition of the process effluent stream, as characterized by Fourier transform infrared (FTIR) spectroscopy. Data generated by both isomers of the compound will be presented and compared to those generated by conventional (C3F8- and C2F6-based) etch processes. Significant reductions in global warming emission (on the order of 80%–85%) were obtained relative to the convent...