Etch Residue Research Articles

Characterization of Low-k Dielectric Etch Residue on the Sidewall by Chemical Force Microscope

Atomic force microscope (AFM) with inclined sample measurement and hydrophobic functionalized AFM probe was used to visualize the sidewall of low-k pattern and allowed to characterize the hydrophobic characteristics on the sidewall after low-k etch. To functionalized the AFM probe, 1H,1H,2H,2H-Perfluorodecyltrichlorosilane (FDTS) as a hydrophobic film was coated on an AFM probe. Because of the magnitude of the phobic-phobic interaction force and the tip forced to make a phase shift. Using this technique the visualization and characterization of the etch residue on the low-k sidewall can be successfully performed. It is shown that the investigation toward an effective chemical clean for the etch residue removal could be applicable.

Improved Cleaning Process for Etch Residue Removal in an Advanced Copper/Low-k Device without the Use of DMAC (Dimethylacetamide)

Plasma dry etching processes are commonly used to fabricate sidewalls of trenches and vias for copper / low-k dual damascene devices. Typically, some polymers remain in the trench and at the via top and sidewall. Other particulate etch residues are may remained in the bottom and on the sidewalls of vias. Generally, the particulate consists of mixtures of copper oxide with polymers. The polymers on the sidewalls and the particulate residues at the bottom of vias must be removed prior to the next process step. Small amounts of polymer are intentionally left on the sidewalls of trenches and vias during the etching in order to achieve a vertical profile and to protect the low-k materials under the etching mask. Until now, the industry has relied mainly on organic solvent containing mixtures to clean etch / ash residues from such devices. The effectiveness of available residue removers varies with the specific process and also depends on which new integration materials are used. New materials typically include Cu, TaN, low-k dielectrics and others [1-. Solvent content is thought to aid the removal of polymer residues and particulates produced during plasma dry etching processes. Therefore, in the past we have used a residue remover which contains DMAC (dimethylacetamide). But the use of DMAC is banned in microelectronic fabrication facilities in Europe because of its toxicity. Thus we wanted to find and evaluate a DMAC-free residue remover for removing polymer residues while maintaining high selectivity to the copper and ILD films.

Optimized Wetting Behavior of Water-Based Cleaning Solutions for Plasma Etch Residue Removal by Application of Surfactants

Wet chemical plasma etch residue removal is a promising alternative to low-k dielectric degrading plasma cleaning processes. With decreasing feature dimensions the wetting behavior of the liquid on low energetic surfaces present after dielectric patterning will be an important issue in developing wet cleaning solutions. High surface energy liquids may not only be unable to wet low energetic surfaces, but can also cause nonwetting of small structures or pattern collapse. The improvement of the wetting behavior of a cleaning liquid by lowering its surface energy by the addition of surfactants is the strategy followed in this study. We show that with choosing the appropriate rinsing solution a wet chemical process using surfactant aided cleaning solutions compatible to the materials used in BEOL (porous low-k, copper, barriers) can be found. The results show a distinct improvement of the wetting behavior of the modified solutions on several low energetic solid surfaces like copper or polymers deposited during dry etching.

TiN Metal Hardmask Etch Residue Removal on Advanced Porous Low-k and Cu Device with Corner Rounding Scheme

A novel wet cleaning formulation approach was developed with a TiN etch rate of more than 30 Å/min at room temperature and more than 100 Å/min at 50°C. The chemicals are compatible with Cu and low-k materials, and are suitable for Cu dual damascene interconnect 28 nm and smaller technology node applications. The chemicals offer a route to in situ controlled TiN pullback or even complete removal of the TiN mask during the cleaning process in single wafer tool applications. The chemicals do not contain NH4OH or TMAH and so are very user-friendly.

TiN Metal Hardmask Etch Residues Removal for Cu Dual Damascene Devices with TiN Mask Corner Rounding Scheme

A novel wet cleaning non-fluoride formulation approach was developed with a TiN etch rate of more than 100 Aå/min at 55 ºC. The chemicals are compatible with Cu and low-k materials, and are suitable for Cu dual damascene interconnect 20 nm and smaller technology node applications. The chemicals offer a route to in situ controlled TiN pullback or even complete removal of the TiN mask during the cleaning process in single wafer tool applications. Additionally, development progress for recent formulations with greater than 250 Aå/min at 50 ºC TiN etch rates is reported.

Controllable chemical vapor deposition of large area uniform nanocrystalline graphene directly on silicon dioxide

Metal-catalyst-free chemical vapor deposition (CVD) of large area uniform nanocrystalline graphene on oxidized silicon substrates is demonstrated. The material grows slowly, allowing for thickness control down to monolayer graphene. The as-grown thin films are continuous with no observable pinholes, and are smooth and uniform across whole wafers, as inspected by optical-, scanning electron-, and atomic force microscopy. The sp2 hybridized carbon structure is confirmed by Raman spectroscopy. Room temperature electrical measurements show ohmic behavior (sheet resistance similar to exfoliated graphene) and up to 13% of electric-field effect. The Hall mobility is ∼40 cm2/Vs, which is an order of magnitude higher than previously reported values for nanocrystalline graphene. Transmission electron microscopy, Raman spectroscopy, and transport measurements indicate a graphene crystalline domain size ∼10 nm. The absence of transfer to another substrate allows avoidance of wrinkles, holes, and etching residues which are usually detrimental to device performance. This work provides a broader perspective of graphene CVD and shows a viable route toward applications involving transparent electrodes.

Etch Process Optimization and Electrical Improvement in TiN Hard Mask Ultra-Low K Interconnection

ABSTRACTAs critical dimensions decrease, key dimension-related dielectric etch challenges emerge, including via and trench uniformity and etch depth profile. The transition to ultra-low-k films such as BDIII (Black Diamond; k=2.55) dielectrics requires consideration of film sensitivity to compositional modification, polymer interactions at pores, and the effect of diffusion. Use of N2/O2 plasma at 60 ˚C to modify the M1 trench profile has been demonstrated to lower the RC delay by 14% as compared to traditional CO2 plasmas at 60˚C. Use of a DHF solution to clean the etching residue in the dual damascene structure results in >97% yield with a tight range of via chain resistance.

High density plasma reactive ion etching of CoFeB magnetic thin films using a CH4/Ar plasma

In this study, high density plasma reactive ion etching of CoFeB magnetic thin films was investigated using CH4/Ar and CH4/O2/Ar gas mixes. The etch rate, etch selectivity and etch profile of CoFeB thin films were obtained as a function of gas concentration and etch parameters. The etch rate of CoFeB thin films and Ti hard mask gradually decreased with increasing CH4 or O2 concentrations. As the CH4 gas was added to Ar gas, the etch profile of the CoFeB thin films improved. The addition of O2 gas into the CH4/Ar gas mix also led to anisotropic etching of the CoFeB thin films. With an increase in the dc-bias voltage supplied to the substrate and a decrease in gas pressure, the etch rates increased and the etch profile became vertical without any redepositions or etch residues. Based on the etch characteristics and surface analysis of the etched films by X-ray photoelectron spectroscopy, it can be concluded that the etch mechanism of CoFeB thin films in CH4/Ar and CH4/O2/Ar plasmas does not follow the reactive ion etch mechanism but rather a chemically assisted physical sputtering mechanism.

Characterization of Post Etch Residues on Patterned Porous Low-k Dielectric Using Multiple Internal Reflection Infrared Spectroscopy

Plasma etching and ashing processes on intricate porous low-k dielectrics are known to introduce high levels of defects that may cause serious reliability issues. Post etch cleans to remove polymer residues could also further damage the porous low-k dielectrics. Compounding the difficulty of handling weak porous ULK materials, a lack of sensitive metrology to evaluate such damage is a serious hindrance to systematic development of plasma etching, restoration and cleaning processes. In this paper, a new metrology tool using Multiple Internal Reflection Infrared Spectroscopy (MIR-IR) was developed and tested using silicon wafer based IR waveguides. Our data demonstrates the capability of MIR-IR spectroscopy to monitor removal of thin polymeric post-plasma etch residues from porous low-k dielectrics and characterize plasma-induced dielectric damage.

Inductively coupled plasma etching of graded-refractive-index layers of TiO2 and SiO2 using an ITO hard mask

Transparent dielectric layers with varying compositions of TiO2 and SiO2, and ITO are deposited on sapphire and Si substrates by using an RF sputter system. Inductively coupled plasma (ICP) reactive ion etching (RIE) of the ITO hard mask is examined under H2, CH4, and Cl2 chemical environments. The slope of the sidewall and the etch residue on the sidewall of the ITO hard mask are controlled by the flow rates of H2, CH4, and Cl2. ICP-RIE dry etch of TiO2 and SiO2 is investigated under fluorinated environments. Comparable etch rates of TiO2 and SiO2 (ratio ≈ 2:1) and high selectivity ≫ 1 over ITO are found. Graded-refractive-index (GRIN) layers, made up of multiple dielectric layers of TiO2 and SiO2, are patterned to form cylindrical pillars by ICP etching using the ITO hard mask. Fluorine containing residues are identified on the TiO2 and SiO2 surfaces. Various etch chemistries are investigated to obtain smooth, vertical, and residue-free sidewalls of the GRIN pillars.

Characterization of Post Etch Residues on Patterned Porous Low-k Using Multiple Internal Reflection Infrared Spectroscopy

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Post Plasma Etch Residue Removal in Dilute HF Solutions

Effectiveness of dilute HF solutions in selectively removing fluorine based plasma etch residue films (PER) with respect to copper has been investigated. PER films were generated by CF4/O2 etching of cresol novolak based photoresist films that were spin coated on copper. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) studies were performed to investigate the PER removal using dilute HF solutions (0.05–0.2 vol. %) and the removal was further confirmed using electrochemical impedance spectroscopy. PER removal rate of ∼60 Å/min was obtained using 0.2 vol % HF (pH 2.8). Higher selectivity of PER/Cu was achieved under deaerated conditions compared to aerated conditions.

Effects of Postetching Treatment on Molecular-Pore-Stacking/Cu Interconnects for 28 nm Node and Beyond

The effects of postetching treatment (PET) using carbon-containing gas on molecular-pore-stacking (MPS)/Cu interconnects were investigated. By using this technology, a 5% reduction in wiring capacitance was obtained as a result of the hardening of exposed MPS at the trench bottom. Via-chain yield improvement was also confirmed as a result of eliminating of etching residues in via-holes. These results indicate that high production yield and reliability can be obtained by PET for 28-nm-node complementary metal oxide semiconductor (CMOS) devices and beyond.

Effects of Postetching Treatment on Molecular-Pore-Stacking/Cu Interconnects for 28 nm Node and Beyond

The effects of postetching treatment (PET) using carbon-containing gas on molecular-pore-stacking (MPS)/Cu interconnects were investigated. By using this technology, a 5% reduction in wiring capacitance was obtained as a result of the hardening of exposed MPS at the trench bottom. Via-chain yield improvement was also confirmed as a result of eliminating of etching residues in via-holes. These results indicate that high production yield and reliability can be obtained by PET for 28-nm-node complementary metal oxide semiconductor (CMOS) devices and beyond.

Correlation Between Film Properties and Anhydrous HF Vapor Etching Behavior of Silicon Oxide Deposited by CVD Methods

The anhydrous HF vapor etching of sacrificial silicon dioxide films grown by plasma-enhanced and low-pressure chemical vapor deposition (PECVD and LPCVD) methods was studied. The film compositions and etch residue were analyzed as part of the study. The effects of the oxide deposition method, precursors, annealing and oxide composition on the etch rate are discussed. Annealing decreases the etch rate and removes water and other hydrogen-containing residue from the films. Films grown using a tetraethoxysilane (TEOS) precursor etch fast, unannealed films even 30 times faster than thermal oxide and they also contain more OH–species than films from SiH4 precursors even after annealing. The etch rate of all CVD films is close to that of thermal oxide after annealing at 1000 °C, around 0.1 µm/min. Etch rate differences between CVD films are much larger than those observed during wet HF etching.

Wet Etching and Surface Analysis of Chemically Treated InGaN Films

This paper discusses the performance of different wet chemical etchants on InGaN. It is shown that certain etchants can be used to chemically etch and remove appreciable amounts of InGaN even though the etch rate is not as high as observed for other III-V materials. The performance of etchants studied here were (i) two different ratios of HF, HNO3, (ii) cyclic usage of NH4OH followed by HCl, (iii) hot H2SO4 and H3PO4 mixture, and (iv) conc. NH4OH. The etched surfaces have then been analyzed by x-ray photoelectron spectroscopy (XPS). Different etch residues were observed on the top surface. These results suggest an alternative to reactive plasma etching or photo-enhanced electrochemical etching of InGaN type materials. Based on the observed performance of the etchants studied, it was also possible to segregate the surface cleaning protocols and etchants.

Etch characteristics of FePt magnetic thin films using inductively coupled plasma reactive ion etching

Etch characteristics of L10 FePt thin films masked with TiN films were investigated using an inductively coupled plasma (ICP) reactive ion etching in a CH 3OH/Ar plasma. As the CH 3OH gas was added to Ar, the etch rates of FePt thin films and TiN hard mask gradually decreased, and the etch profile of FePt films improved with high degree of anisotropy. With increasing ICP rf power and dc-bias voltage to substrate and decreasing gas pressure, the etch rate increased and the etch profile becomes vertical without any redepositions or etch residues. Based on the etch characteristics and surface analysis of the films by X-ray photoelectron spectroscopy, it can be concluded that the etch mechanism of FePt thin films in a CH 3OH/Ar gas does not follow the reactive ion etch mechanism but the chemically assisted sputter etching mechanism, due to the chemical reaction of FePt film with CH 3OH gas.

Prevention of AlCu Line Galvanic Corrosion after Fluoride Containing Stripper Cleaning: A Case Study

In this paper, the status of galvanic corrosion on AlCu lines during the AlCu post etch and ashing residue removal process is studied with a fluoride containing stripper in details, including DIW rinse condition and dry process. The experimental data show that galvanic corrosion on AlCu lines is not observed in the chemical cleaning process, but inclined to be caused by the rinse and dry processes in this case. Different scenarios in the rinse process, such as overflow or quick dump rinse (QDR), the times of quick dump rinse cycles, CO2 bubbled DIW and metal protection solution rinse, are studied. At the same time, two kinds of dry processes are also evaluated. The results show the optimized rinse and dry processes can eliminate the galvanic corrosion on AlCu lines without the change of wafer manufacture prevenient process and cleaning solution.

Etch-stop technique for patterning of tunnel junctions for a magnetic field sensor

Spin-dependent tunnelling devices, e.g. magnetic random access memories and highly sensitive tunnelling magnetoresistance (TMR) sensors, often consist of a large number of magnetic tunnel junctions (MTJs) of uniform quality over the whole device. The uniformity and yield of the fabrication of such a device are therefore very important. A major source of yield loss is the short-circuiting of junctions by redeposition of etch residues. This can be prevented by terminating of the etch in the typically 1 nm thick tunnelling barrier. Here, electron spectroscopy for chemical analysis for monitoring the etching semi-continuously is proposed. The fabrication scheme employs Ar ion milling for etching the MTJs, and photoelectron spectroscopy for analysing the composition of the etched surface in situ. Junctions etched either to or through the barrier were used for this. The quality of the etch stop was investigated using transmission electron microscopy (TEM), and it was confirmed that the etch could be stopped in the MgO barrier. The TEM imaging also showed clear signs of redeposition. Such redeposition was attributed to being partly caused by the reduction of the TMR ratio of the junctions etched through the barrier, which was only 15% as compared with 150% for junctions etched to the barrier. Also, the latter junctions exhibited 2.7 times less noise in the low-frequency regime, resulting in a 27 times improvement of the signal-to-noise ratio with the etch stop. The barrier also proved effective in protecting the bottom contact from oxidation during the capping and contacting of the junctions.

Thick benzocyclobutene etching using high density SF6/O2 plasmas

Etching of thick nonphotosensitive benzocyclobutene (BCB) was investigated using a high density SF6/O2 plasma with an inductively coupled plasma (ICP) etcher. The effects of SF6 concentration on etching characteristics, including etching rate, anisotropy, and residue, are fully discussed in this article. Moreover, experiments were designed and carried out to study the causes of BCB etching residue. A grasslike etching residue was observed for low SF6 concentration at the bottom of BCB patterns with a SiO2/SixN layer and the BCB patterns cured on a N2-purged hotplate, while residue-free etching is obtained for the BCB patterns cured in a N2-purged vacuum chamber. A high SF6 concentration and exclusion of O2 during hard curing are important to prevent the grasslike etching residue. A highly anisotropic and residue-free etching of thick (∼13 μm) BCB is achieved for BCB cured in a N2-purged vacuum chamber at 250 °C for 1 h and with a pure SF6 plasma under etching conditions of 700 W ICP power, 100 W reactive ...