Post-etch Cleaning Research Articles

Optimization of waveguide fabrication processes in lithium-niobate-on-insulator platform.

Lithium niobate (LN) is used in diverse applications such as spectroscopy, remote sensing, and quantum communications. The emergence of lithium-niobate-on-insulator (LNOI) technology and its commercial accessibility represent significant milestones. This technology aids in harnessing the full potential of LN's properties, such as achieving tight mode confinement and strong overlap with applied electric fields, which has enabled LNOI-based electro-optic modulators to have ultra-broad bandwidths with low-voltage operation and low power consumption. Consequently, LNOI devices are emerging as competitive contenders in the integrated photonics landscape. However, the nanofabrication, particularly LN etching, presents a notable challenge. LN is hard, dense, and chemically inert. It has anisotropic etch behavior and a propensity to produce material redeposition during the reactive-ion plasma etch process. These factors make fabricating low-loss LNOI waveguides (WGs) challenging. Recognizing the pivotal role of addressing these fabrication challenges for obtaining low-loss WGs, our research focuses on a systematic study of various process steps in fabricating LNOI WGs and other photonic structures. In particular, our study involves (i) careful selection of hard mask materials, (ii) optimization of inductively coupled plasma etch parameters, and finally, (iii) determining the optimal post-etch cleaning approach to remove redeposited material on the sidewalls of the etched photonic structures. Using the recipe established, we realized optical WGs with total (propagation and coupling) loss value of -10.5 dB, comparable to established values found in the literature. Our findings broaden our understanding of optimizing fabrication processes for low-loss lithium-niobate waveguides and can serve as an accessible resource in advancing LNOI technology.

Effect of Post-Etch Wet Cleaning on GaAs Surfaces

In this study, we investigated the effect of the post-etch cleaning of GaAs surfaces. We found that a plasma damage layer was formed on GaAs surfaces by dry etching, and an As-rich layer remained after post-etch cleaning. The As rich layer needs to be removed because it is replaced by micron-sized particles when stored in an air. We also found that a pure GaAs surface can be obtained by performing additional cleaning consisting of oxide formation and removal.

Influence of silane type and application time on the bond strength to leucite reinforced ceramics

Introduction All-ceramic restorations currently dominate the market of indirect restorative materials due to their biocompatibility, longevity and superior aesthetics [1]. Silica-based ceramics, such as leucite, carry the advantage of being receptive to surface treatments, making them bondable to tooth substrates [2]. However, a standardised application protocol regarding silane coupling agents is lacking. Such step is critical to ensure durability of the restoration placed in situ. Post-etch cleaning and silane application have been proven to increase bond strength, however, this step varies for each material [3]. The aim of this research was to assess the influence of different types of silane coupling agents and respective application times on the bond strength of the ceramic-resin interface. Materials and methods Ten leucite reinforced glass ceramic blocks (IPS Empress CAD LT BL4/C 14) were divided into equal halves. Of the samples obtained, 6 were randomly divided into three groups according to the silane used: G1 BIS-Silane (Bisco, Schaumburg, IL, USA); G2 ESPE Sil Silane Coupling Agent (3 M ESPE AG, Seefeld, Germany); G3 Monobond Plus (Ivoclar-Vivadent, Schaan, Liechtenstein). Each was then divided into two subgroups, according to the surface conditioning time: T1 (1 min.) or T2 (5 min.). Each block was acid etched (HF 9.5% − 1 min), post-etching cleaned (OPA 37.5% − 1 min; ultrasonication − 2 min.) and silanized. Heat treatment was carried out at 100 °C (1 min.). Then a thin layer of Optibond FL (Kerr) adhesive was applied and each block was adhered to pre-heated resin at 55 °C. The samples were light cured for 40 s on each side (1200 mW/cm2). Samples were sectioned into microspecimens (1 ± 0.2 mm2) that were subjected to aging (10,000 thermocycles − 5 and 55 °C). The microspecimens were tested in tension at a crosshead speed of 0.5 mm/min, until they debonded. Data analysis was carried out by a two-way ANOVA, at a significance level of 5%. Results The group featuring BIS-Silane with longer application time (G1T2) presented a mean µTBS value (32.4 ± 19.6 MPa) significantly higher to all other groups (p < .001). Monobond Plus registered the lowest mean µTBS value (G3T1 − 18.5 ± 7.3 MPa) and (G3T2 − 17.3 ± 5.8 MPa). The type of silane coupling agent has shown to have a significant influence on the microtensile bond strength (p = .001; η 2=0.16). Discussion and conclusions Some authors have previously suggested that silanization could benefit from longer application times, but seldom research has been found featuring this variation protocol [3,4]. Silanes require a hydrolysation process in order to establish chemical bonds. Two-bottle systems show the highest bond strength results and may benefit from longer application times. The addition of 10-MDP seems to have no significant advantage over traditional silane coupling agents.

Process Parameter Control for BEOL TiN Hard Mask Etch-Back

In this paper we demonstrate an effective process control mechanism to significantly improve on the process performance of a BEOL post-etch cleaning process with an integrated partial or complete removal of the TiN HM (hard mask) layer by so called formulated chemistries on a single wafer processing tool. The novel process control mechanism enables a 50% reduction in chemical consumption while achieving an at least equivalent TiN etch uniformity.

Rinsing of High-Aspect-Ratio Features on Patterned Wafers

A comprehensive process model is developed to simulate the mechanism and the dynamics of rinsing and cleaning of deep and narrow structures on patterned substrates. This process is critical in a number of applications such as post-etch cleaning of patterned wafers during the manufacturing of semiconductor devices. The model takes into account various mass transport mechanisms including convection and diffusion/dispersion that occur simultaneously with various surface interactions such as adsorption and desorption of impurities on the substrate surfaces. The influences of charged species in the bulk and on the surface, and their induced electric field that affect both transport and surface interactions, are included in this paper. The results of this paper illustrate the model usefulness and potentials to predict the change in the rinse time and efficiency with changes in the key operational parameters such as temperature, concentration, flow rate, and mass transfer on the wafer surface. Ammonium hydroxide on SiO 2 surface is used as the model system in this study because of its wide application; however, the model can be used for analyzing the rinsing of other impurities by simply changing the model parameter inputs.

Influence of post-etch cleaning and silane heat treatment on resin bond strength to silica-based leucite: an in vitro study

Adhesive cementation of bonded all-ceramic restorations is critical for their long-term clinical performance. The objective of this study was to evaluate the role of post-etch cleaning (PEC) and silane heat treatment on the micro-tensile bond strength of silica-based leucite (SBLE) ceramic when bonded to composite resin. Twenty-four blocks of SBLE ceramic (HeraCeram Press®, Heraeus Kulzer GmbH Grüner Weg 11 63450 Hanau) were fabricated and bonding surfaces were etched using 9.5% hydrofluoric acid. Six experimental groups were made from the various surface treatment combinations including: PEC (37.5% phosphoric acid for 1 min, rinsed with water for 20 s and ultrasonic bath immersion), silane application and silane heat treatment (100 °C for 5 min). An adhesive resin and a light-cured restorative composite were used to bond the ceramic and composite resin blocks under standard conditions. Three hundred and sixty specimen sticks (8 × 1 mm²) were subjected to micro-tensile testing. The means of the micro-tensile bond strength (μ-TBS) were analysed with ANOVA and Tukey–Kramer multiple comparison test. The specimens tested were assessed for mode of failure using scanning electron microscopy. The highest μ-TBS value (38.25 ± 3.40 MPa) of the specimen was achieved by PEC and heated silane. PEC and silane application showed statistically significant improvements in the μ-TBS (p < 0.01). The mean maximum difference was due to PEC (18.91 ± 3.70 MPa). In the surface treatment of SBLE ceramics, PEC had the most significant factor which affected the μ-TBS of resin composite.

Exploration of Chemical Bonding Transformation Mapping to Assist Low-k Dielectric Nanostructure Fabrication

In leading edge integrated circuit manufacturing, reduction of RC time delay by incorporation of porous ultra low-k interlayer dielectrics into Cu interconnect nanostructure continues to pose major integration challenges. The main challenge is that porous structure renders interlayer dielectrics mechanically weak, chemically unstable and more susceptible to the RIE plasma etching damages. Besides the challenge of handling weak porous ultra low-k materials, a lack of sensitive metrology to guide systematic development of plasma etching, restoration and cleaning processes is the major stumbling block. We explored Multiple Internal Reflection Infrared Spectroscopy and associated IR techniques as a sensitive (sub-5 nm) characterization tool to investigate chemical bonding modification across fluorocarbon etch residues and low-k dielectric interface after plasma etching, ashing, UV curing and post-etch cleaning. The new insights on chemical bonding transformation mapping can effectively guide the development of clean-friendly plasma etch for creating ultra low-k dielectric nanostructures with minimal dielectric damages.

Exploration of Chemical Bonding Transformation Mapping to Assist Low-k Dielectric Nanostructure Fabrication

In leading edge integrated circuit manufacture, reduction of RC time delay by incorporation of porous ultra-low k (ULK) interlayer dielectrics (ILD) into Cu interconnect nanostructure continues to pose major integration challenges. The main challenge is porosity induced to lower the dielectric constant of the ILD has the undesirable side effect of compromising its mechanical and chemical stability. As a result, these materials are more susceptible to the damages caused by RIE plasma etching processes. Besides the challenge of handling weak porous ULK materials, a lack of sensitive metrology to guide systematic development of plasma etching, restoration and cleaning processes is the major stumbling block. To assist in the overall integration effort, we have been actively exploring Multiple Internal Reflection Infrared Spectroscopy (MIR-IR) and associated IR spectroscopic techniques as a sensitive (sub-5nm) characterization tool to assist the fabrication process of ULK nanostructure with targeted critical dimension. In this paper, we will report new findings obtained on chemical bonding modification across fluorocarbon etch residues and low-k dielectric interface after manufacture relevant processing treatments including plasma etching, ashing, UV curing and post-etch cleaning. MIR-IR metrology showed useful spectroscopic details of chemical bonding transformations taking place during plasma etch and strip processing on both blanket and dielectric trench structures. The observed increase of Si-OH and C=O and the decrease of Si-CH3 IR absorption bands correlated well with increasing plasma induced damage, K increases verified by MIS structure, especially for more aggressive stripping process. With functional group-specific chemical derivatization, chemical bonding structure of 1-2 nm post-etch residue on porous low-k trench structure was established. UV-induced modification of fluorocarbon polymer residue to improve its subsequent wet cleaning removal was studied by FTIR, XPS and SEM. The overall goal is to apply new insights on chemical bonding transformation mapping to achieve cleans-friendly plasma etches on creating ULK dielectric nanostructures with minimal dielectric damages.

Wetting behavior of plasma treated low-k films in dHF cleans solutions

Post-ash and post-etch cleaning of low-k structures require significant wetting of their surfaces. This work focuses on the interactions between dilute HF cleaning chemistries (dHF—1:50 to 1:1000) on porous low-k surfaces (k=2.3) as a function of time. Wetting of these solutions was measured by a contact angle goniometer within a high humidity environment. Because ashing low-k films can change their surface chemistry and structure, the contact angles of dHF on N2/H2 and O2 ashed porous low-k films were measured as well. Ellipsometry has shown that 1:50 HF removes an ash-damaged layer from the low-k. Based on thickness loss measurements (ellipsometry and profilometry), the composition of the dilute HF droplet changes minimally as it etches the dielectric surface. Under more concentrated dHF solutions, changes in contact angle, droplet radius, and volume indicate that the droplet spreads for an initial period and then reaches a steady state, perhaps due to the creation of an etch inclusion on the surface. The steady state volume changes show volume loss rates similar to those expected from evaporation; however, the total volume losses are less than expected from only evaporative processes.

Dynamics of Interactions Between HF and Hafnium Oxide During Surface Preparation of High-K Dielectrics

The interactions of HF with hafnium oxide are important aspects of the post-etch cleaning of high-k dielectrics. The dynamics of these interactions during typical wafer rinsing are studied using a quartz crystal microbalance (QCM) equipped with a flow-through cell. A process model is developed showing that the overall rinse process consists of three simultaneous steps: adsorption, desorption, and etching involving fluoride species. The model is validated using the experimental data obtained in QCM. The key parameters of these process steps, namely, adsorption, desorption, and etch rate coefficients are determined using the combined experimental measurement and process modeling.

"Damage Free" Cleaning for Advanced BEOL Interconnections

For the 32nm logic technology and beyond, more stringent specifications in terms of dimensions and materials integrity continue to drive the cleaning process improvements. In this paper, post-etch wet cleaning was optimized in order to address CD loss issues and metal hard mask cleaning improvement in a Trench First Hard Mask (TFHM) backend architecture. Based on materials compatibility tests and electrical results, this wet clean process should also be fully compatible with a Via First Trench Last (VFTL) architecture.

Determining the Fundamental Kinetic Parameters for Rinsing and Cleaning of Hafnium-Based High-k Materials

The interactions of HF with hafnium oxide are important during post-etch cleaning of high-k dielectrics. The dynamics of these interactions during the rinse process are studied using a quartz crystal microbalance (QCM) equipped with a flow-through cell. A process model is developed showing that the overall process consists of three simultaneous process steps: adsorption, desorption and etching involving fluoride species. The model was validated using the experimental data obtained in QCM. The key parameters of these process steps namely adsorption, desorption and etch rate coefficients were determined using the combined experimental measurement and process modeling.

Effect of Pattern Layout and Dissolved Oxygen in CO2 Rinse Water on Cu Corrosion during Post-Etch Cleaning

When post-etch cleaning was carried out in Cu dual-damascene process, Cu at the bottom of isolated via was etched out especially in the wafer edge, and this would become a critical issue as device scale is shrunk. The corrosion was caused in the rinse step rather than chemical cleaning step because dissolved oxygen in rinse water from the air increased oxidation–reduction potential (ORP) and CO2 included in the rinse water for preventing wafer electrification decreased pH. The corrosion was found to be suppressed by increasing dummy pattern density and by controlling atmosphere and pH of the rinse water.

Two step optimized process for scanning tunneling microscopy tip fabrication

Fabrication of ultrasharp tips for scanning tunneling microscopy is inherently a two-step procedure, typically involving an etch process and postetch cleaning. From the myriad of etching parameters available in literature a procedure is presented that allows quantitative optimization and the routine production of tips with 3–10 nm radius of curvature. These ideally shaped tips require final oxide removal. Utilizing a custom designed e-beam heater element, oxide removal without localized melting is realized.

Nonoxidative Aqueous Cleaning Solutions for Tungsten Layers

Aqueous cleaning solutions were developed for postetch cleaning of tungsten layers to replace the amine-based organic strippers. They are composed of tetramethylammonium hydroxide, HF, and two additives. Even the cleaning recipes without a strong oxidant, such as hydrogen peroxide, could remove postetch residues formed by reactive ion etching and they also had the same particle removal efficiency compared to ammonium and hydrogen peroxide mixture known as RCA Standard Clean. The concentration of metal ion on the wafer surface after cleaning by them was under . The effects of the cleaning could be explained by applying Pan’s double-layer model [ J. Electrochem. Soc. , 148 , G315 (2001) ]. In fact, these cleaning solutions made it possible to decrease the resistances of tungsten bit lines and metal contacts and contributed to yield enhancement.

Borderless via Clean Study for Minimizing Al-Cu Loss in 58nm Flash Devices

The borderless (BDL) vias landing on the metal lines were demanded in high-density flash memory devices due to the reduced die size, compared with non-borderless (NBDL) vias. IMD material recess in un-landed via dry etching and the Al-Cu metal line undercut caused by post-etch cleaning may lead to via resistance Rv high and EM reliability issue. In this work, the Al-Cu loss mechanism in BDL-via cleaning by using amine- and fluoride-based chemicals were studied in 58nm flash devices. We found that the Al-Cu undercut can be minimized in HDA containing solvent by controlling the formation of Al2O3/Al/HDA gel-like material to the less amounts; the shorter HDA processing time with sufficient IPA rinse generated the thinner gel-like layer leading to the less Al-Cu undercut in DIW rinse step. For TMAH/H2O2-containing semi-aqueous solution, the metal contained etched-residues can be removed by reaction of OH- with Al to form dissolved Al(OH)4-; addition of H2O2 will form a oxidized passivation layer on the metal surface to prevent from metal corrosion. On the other hand, the Al/Al2O3 contained polymer was removed by fluoride-based solvent or DSP+ through the reaction with [F-] to form the DIW-dissolved AlFx by-products; while the dilute H2SO4 and H2O2 in DSP+ will oxidize Al to form Al2O3 that will be further etched by HF, the severe Al-Cu undercut was found in DSP+.

Characterization of Post Etch Residues Depending on Resist Removal Processes after Aluminum Etch

The subject of this report is the characterization of plasma etch residues after a metal etch process with Cl2/BCl3 etch gases. One of the interactive factors in the removability of the residues is the photo-mask removal process (DSQ). Depending on the DSQ process the molecular structure of the residues will differ. For our findings, we used laser spectroscopy and Fourier-transformed infrared spectroscopy to obtain information about the degree of the cross-linking of the molecular structure of residues in a post-metal etch cleaning process. The post-etch cleaning is important for removing residues remaining after the metal structuring process. The main goal is to use emission spectroscopy for studying the compounds of the dry-etch related residues. Finally, it was shown that small variations in wafer treatment directly after dry-etching results in different solubilities of residues in HDA (hydroxylamine) based solutions. [1]

Optimization of a SC CO&lt;sub&gt;2&lt;/sub&gt; Post-Etch Cleaning for Copper Interconnections

Optimization of a SC CO&lt;sub&gt;2&lt;/sub&gt; Post-Etch Cleaning for Copper Interconnections

Electrochemical Behavior of Copper in Post-Etch Cleaning Solutions

not Available.

Porosity and structure evolution of a SiOCH low k material during post-etch cleaning process

In the back end of line (BEOL) interconnections for 65 nm and beyond technology nodes, the integration of porous dielectric materials is now needed to improve signal propagation. In order to develop and optimize etching and cleaning process steps that may degrade the dielectric material, the characterization of ultra-low k porosity becomes mandatory. In this paper, the impact of wet cleaning with diluted HF solution was characterized depending on several plasma treatments. In particular, we focused on pore sealing effects after plasma and its persistency after wet treatments. It was demonstrated that methyl silsesquioxane (MSQ) thin film dissolution in diluted HF is not linear with process time, meaning that the material is not homogeneous. Depending on the plasma treatment, the thin layer created on the top surface is porous and does not protect the material from chemical dissolution. On contrary, some plasma treatment creates a thin layer with a very low permeability (sealed porosity) that acts as a protective coating against dissolution in diluted HF. Moreover, its porosity remains sealed, and pore sealing effect is not impacted by this cleaning process.