Roughening of porous SiCOH materials in fluorocarbon plasmas

Low-k materials developed for ULSI interconnects should have sufficient resistance to processing plasma. CO 2 plasma is being considered as a promising candidate for low damage photoresist ash and as a surface activation chemistry for self-assembled monolayers and atomic layer deposition on low-k materials. This article explores the interaction of two organosilicate (OSG) based low-k materials with different k-values (OSG2.4 and OSG2.2) with CO 2 plasma in both CCP and ICP-remote plasma chambers. Time dependent exposure of the materials to CO 2 plasma revealed quick and effective sealing of OSG2.4 surface whereas it takes longer time for OSG2.2. The sealing reduces further plasma damage and leads to accumulation of CO 2 in the pores of both materials. The same behavior occurs in ICP-remote plasma but without a complete sealing of the surface. This suggests the important role of ion bombardment. Damage to low-k by conventional O 2 plasma was studied alongside and it was found that for t < 60 s, O 2 plasma exerts more damage on OSG2.2 than CO 2 . This trend is reversed at t > 60 s. Furthermore, lesser time exposure to CO 2 plasma was investigated with respect to source power at constant pressure and it was discovered that damage although small, increases with varying source power. The performance enhancement of electronic circuits was majorly centered on reducing the transistor sizes, increasing transistor speed and density. However, in advanced technology nodes the performance of the resulting integrated circuits (IC) is greatly hindered by the resistance -capacitance (RC) delay experienced during the signal propagation within the interconnects.1 In order to solve this problem, the traditional Al was replaced by Cu, which has lower resistivity and SiO 2 with k = 4.0 was replaced by low dielectric constants (low-k) materials. Organosilicate glasses (OSG) deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) and/or by Spin-on Glass technology (SOG) are presently the most popular low-k materials.Photoresist strip using O 2 based plasma is a conventionally used processing technique but this has been found to be severely damaging to porous low-k materials. The modifications to the porous low-k materials lead to increased k-values from densification and hydrophilization.2-5 The CO 2 -based plasma has been reported to be less damaging with respect to the O 2 counterpart. Fuller et al. proposed the use of CO 2 based RIE plasma for photoresist stripping. Ming-Shu Kuo et al. and Hualiang Shi extensively studied the surface modification of ultralow-k materials by CO 2 plasma and the results are published in their PhD dissertations 7,8 and in several papers. 9-13 They reported that i) CO 2 and O 2 plasma damage to ultralow-k films are comparable ii) there is lower atomic oxygen density in CO 2 discharge than O 2 discharge because of higher activation energy (11.5 eV) required to liberate atomic oxygen from CO 2 than from O 2 molecules (6 eV) -this is why there is supposedly a reduction in damage by CO 2 discharge wi...

Section: Resultsmentioning

confidence: 99%

Modification of Ultra Low-k Dielectric Films by O₂and CO₂Plasmas

Olawumi

Levrau

Krishtab

et al. 2014

“…38 During porous low-k etching, a strong surface roughness builds up at the etch front because of surface densification and material modification creating an uneven surface density and composition. 25,41 When polymerizing etching processes without oxygen are used, the plasma-induced damage can be minimized. In more recent years, special attention has been paid to the impact of V-UV only to the ULK physical properties.…”

Section: /[F] Ratio) or Less (For [C]/[f]mentioning

confidence: 99%

Toward Successful Integration of Porous Low-k Materials: Strategies Addressing Plasma Damage

Lionti

Volksen

Magbitang

et al. 2014

Self Cite

The increasing sensitivity of porous low dielectric constant materials to process damage constitutes a major roadblock to their implementation in back-end-of-the-line (BEOL) wiring structures for advanced technology nodes. In the early 2000s and in anticipation to future low-k related integration challenges, the semiconductor industry started to investigate the possibility to repair or prevent this damage. It is remarkable that the most disruptive solutions proposed today are inspired from the work initiated more than 10 years ago. In this review we first describe the accepted mechanisms for plasma damage, followed by a quick summary of the methods used to quantify its extent on both blanket films and patterned structures. We then report on the past and current strategies developed to mitigate the plasma damage of porous, low-k materials during damascene integration processes.

“…1,2,5,6 An alternative approach for improving the residue removal efficiency involves structural modification of the fluorocarbon polymer together with introduction of polar functional groups into the polymer backbone using ultraviolet (UV) irradiation followed by a wet clean step. The UV sources consisted of a narrow band, single-wavelength UV source with λ = 254 nm 4,7 or a broad band source of λ > 200 nm 8 or λ > 230 nm.…”

mentioning

confidence: 99%

“…4 A short plasma treatment carried out prior to the wet clean step enhances the polymer removal efficiency but also has a drawback of irreversibly damaging the porous dielectrics by material densification, carbon depletion, and increase of hydrophilicity. 1,2,5,6 An alternative approach for improving the residue removal efficiency involves structural modification of the fluorocarbon polymer together with introduction of polar functional groups into the polymer backbone using ultraviolet (UV) irradiation followed by a wet clean step. The UV sources consisted of a narrow band, single-wavelength UV source with λ = 254 nm 4,7 or a broad band source of λ > 200 nm 8 or λ > 230 nm.…”

mentioning

confidence: 99%

Characterization of Patterned Porous Low-kDielectrics: Surface Sealing and Residue Removal by Wet Processing/Cleaning

Le¹,

Kesters²,

Decoster³

et al. 2016

The results described in this paper first demonstrate key differences between a plasma-exposed blanket porous dielectric sample and a patterned structure in terms of surface sealing induced by the patterning plasma using ellipsometric porosimetry characterization. While the blanket CVD organosilicate glass (nominal k-value = 2.4, ∼20% of porosity) surface was sealed by the C 4 F 8 /CF 4 -based plasma, the surface of the analogous patterned structure of 45 nm 1/2 pitch was found to be completely open after the same patterning plasma process. Second, the surface composition of the patterned feature, type of the residues generated during the plasma etch, and the effect of a subsequent wet clean step are presented. The experimental results demonstrate that the use of a relevant patterned test structure and its characterization represent an appropriate approach for the optimization of the etch and cleaning processes. The removal efficiency of various wet clean solutions, including dilute HF, citric acid, tetramethylammonium hydroxide:H 2 O 2 :H 2 O mixture, and a slightly alkaline formulated mixture, with regard to polymer residues, CFx, and metal-containing residues, TiFx, can be clearly distinguished using the patterned porous low-k stack. In back-end of line (BEOL) processing of advanced microelectronic CMOS integrated circuits, conductor lines are made using a damascene approach. For this, dielectric layers are locally etched through a patterned photoresist or metal hardmask layer using plasmas and followed by electroplating of Cu inside the etched patterns. In order to ensure accurate profile control, etching anisotropy, and minimize degradation of the exposed porous dielectric during the plasma etch, polymerizing plasma chemistries are employed to deposit a thin layer of polymer on the exposed surface.1-3 A good balance between the polymerization and the dielectric etch rate allows the polymer film to passivate the sidewalls without affecting the vertical etch rate, resulting in a vertical etch profile. The polymer formed during the dry etch process ("post-etch polymer residues" or PER), mostly fluorocarbon polymers for fluorocarbon-containing plasmas, must be removed prior to deposition of subsequent layers (metal) in the etched features to achieve high adhesion and good coverage. Removal of these polymers is usually performed by a combination of a short plasma treatment and wet clean using chemical solutions, or by wet cleans alone. It is known that this type of fluorocarbon polymer is chemically inert to many existing wet clean solutions, including aqueous solutions such as fluoride ion-containing or highly alkaline solutions, and solvent mixtures.4 A short plasma treatment carried out prior to the wet clean step enhances the polymer removal efficiency but also has a drawback of irreversibly damaging the porous dielectrics by material densification, carbon depletion, and increase of hydrophilicity. 1,2,5,6 An alternative approach for improving the residue removal efficiency involves structural modification o...