Study on contact distortion during high aspect ratio contact SiO2 etching

Abstract

As pattern density is increased in semiconductor integrated circuits (ICs) and pattern sizes are decreased to nanometer scale, high aspect ratio contact etching has become one of the most difficult processes in nanoscale IC fabrication. The increase in aspect ratio of the contact oxide etching raises problems such as low mask selectivity, microloading, pattern degradation, and etch stops. In this study, the authors investigated the effect of various oxide etch conditions such as mask materials, mask thickness, and oxide etch processes, on contact profile degradation. The results showed that greater contact pattern distortion occurred as the aspect ratio of the etched oxide was increased. The use of amorphous carbon instead of amorphous silicon as the etch mask, and the use of a more carbon-rich gas composition, lessened pattern distortion. The polymer deposited at the interface between the mask layer and the oxide layer appeared to significantly affect the degree of contact pattern distortion. By adding an in-situ polymer removal step during the overetch of a multistep contact oxide etch process with a 20:1 aspect ratio, about a 7% improvement in pattern distortion could be obtained without changing other conditions. V

Plasma etching of high aspect ratio features in SiO2 using Ar/C4F8/O2 mixtures: A computational investigation

“…Feature distortion includes line (or contact) etch roughness, twisting, and producing noncircular vias. 3,9,56 The latter feature distortion is shown in Fig. 21, where horizontal sections of the feature are shown (with and without charging) at different heights in the feature.…”

“…2,6 Maintaining CDU requires minimizing pattern distortion, in which an initially circular mask opening is not preserved through the depth of the feature, evolving into ellipses or other noncircular shapes. [7][8][9] CER originates from nonuniformities in the mask due to stochastic processes during etching or from the lithography-development process. These nonuniformities are then imprinted into the sidewalls of the feature by anisotropic delivery of activation energy.…”

“…These nonuniformities are then imprinted into the sidewalls of the feature by anisotropic delivery of activation energy. 9,10 Maintaining CDU also requires minimizing twisting, where the etch does not proceed strictly normal to the surface but deviates from the normal, and avoiding feature-to-feature variations in the total etch depth. 6,11 Many of these problems associated with CDU can be attributed to the stochastic nature of fluxes of radicals and ions incident into adjacent features.…”

Role of Oxygen in Amorphous Carbon Hard Mask Plasma Etching

“…The application of amorphous carbon as an alternative hard mask for conductive or dielectric underlayer HAR etching has been introduced as a means of addressing the limitations associated with conventional single-layer hard masks based on silicon. − The utilization of an amorphous carbon layer (ACL) as an etching mask in nanoscale plasma etching patterning is facilitated by its impressive physical properties, including a high melting point, exceptional hardness, and resistance to corrosion and etching in Cl- or F-containing gases. Additionally, in both current and next-generation semiconductor processing, the ACL hard mask, in conjunction with a complex gas mixed plasma, can be leveraged to achieve high etching selectivity in HAR etching. − In industrial semiconductor plasma etching, three or more complex gas mixtures, which are based on inert gases such as argon and composed of a combination of oxygen, C x F y , and C x H y F z gases, are used to control the etch profile and selectivity. , In a complex gas mixture, inert gas is injected to control the plasma density and degree of dissociation rate, and a trace amount of oxygen gas is injected to control the degree of precursors and deposited polymers produced in the plasma. , However, the high removability of the ACL by oxygen can result in unwanted sidewall etching of the ACL hard mask when exposed to a processing plasma containing oxygen gas, leading to a distorted etch profile and increased pattern opening. Thus, it is imperative to analyze and regulate the etching characteristics of the ACL when using oxygen gas as the profile of the hard mask holds a significant influence on the profile of the bottom layer to be etched, and thus greatly impacts the device quality and performance.. , …”

Analysis of formation mechanism of deposited film in a high-aspect-ratio hole during dry etching using fluorocarbon gas plasmas

“…[6][7][8][9][10][11] In the RIE process with FC gas, a suitable thickness of amorphous-CF x (a-CF x ) film deposited on the mask or sidewalls of the hole by CF x radicals plays an important role in protecting the structures from ion bombardment, leading to high selectivity and reduction of side etching. Nevertheless, it has been reported that excessive or lack of a-CF x film deposition leads to various hole profile issues, such as bowing (increased hole diameter near the middle of a hole [12][13][14] ), distortion, 15,16) and striation (vertical scratches on the sidewall 17) ). Furthermore, the conductivity of a-CF x films has also been reported, where associated features may induce charging at the bottoms of the high-AR holes during the RIE process.…”