Study of the SiO2-to-Si3N4 etch selectivity mechanism in inductively coupled fluorocarbon plasmas and a comparison with the SiO2-to-Si mechanism

Abstract

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.

Dielectric Barrier, Etch Stop, and Metal Capping Materials for State of the Art and beyond Metal Interconnects

“…The primary drawbacks to this approach are the difficulty of achieving perfect selectivity in the presence of inevitable surface defects, compatibility of the selective metal caps with next metal layer patterning and cleaning steps, and the added cost associated with the additional processing step. Etch selectivity.-While significant effort has been focused on understanding the influence of plasma etch chemistry, [349][350][351][352][353][354][355][356] low-k ILD porosity, 394 and ILD composition 395 on the low-k ILD plasma etch mechanisms and profiles, most ILD/ES etch selectivity studies have focused on a singular a-SiN:H or a-SiC:H ES material. Relatively little work has been reported investigating in detail how the properties and composition of the low-k ES can influence etch selectivity.…”

“…More specifically, it is believed that deposited carbon is quickly returned to the gas phase via formation of volatile species such as CO, CO 2 , COF 2 on SiO 2 vs. CNF on Si 3 N 4 due to differences in bond strengths and the volatility of the etch by products. 352 Low-k a-SiC:H and a-SiCN:H ES/DB materials have also been reported to exhibit high etch selectivities (2-10) relative to SiO 2 and low-k a-SiOC:H ILD materials. 38,353,354 The high etch selectivity has been similarly attributed to differences in the thickness of a deposited CF x layer that forms on the various surfaces during plasma etching.…”

“…349 This selectivity has generally been attributed to differences in the thickness of a fluorinated carbon (CF x ) layer that forms during dry plasma etching of SiO 2 and Si 3 N 4 /a-SiN:H with SiO 2 surfaces exhibiting <1.5 nm thick films and Si 3 N 4 exhibiting film thicknesses ranging from 1.5-4 nm. 352 The differences in CF x film formation during fluorinated plasma etching have been attributed to differences in the ability of SiO 2 vs. Si 3 N 4 surfaces to consume deposited surface carbon during the etching reactions. More specifically, it is believed that deposited carbon is quickly returned to the gas phase via formation of volatile species such as CO, CO 2 , COF 2 on SiO 2 vs. CNF on Si 3 N 4 due to differences in bond strengths and the volatility of the etch by products.…”

Atomic Layer Etching at the Tipping Point: An Overview

“…fairly rapid etching for one material and slow etching or deposition for another material. [20][21][22][23][24][25][26] However, the thicknesses of these steady-state surface layers can be of the order of several nm. During the time needed for these to form, significant material loss can take place.…”

Challenges of Tailoring Surface Chemistry and Plasma/Surface Interactions to Advance Atomic Layer Etching

“…Subsequently, the reaction step would then have to enable removal of both Si and O atoms by volatilization of the complex fluorocarbon layer. However, since fluorocarbon layers usually take the form of CF, CF 2 and/or CF 3 groups, [40][41][42][43] it is possible that more than one reaction layer is required to volatilize silicon and oxygen, assuming the highest yielding volatilized species are SiF 4 and CO 2 .…”