Plasma Ashing Process Research Articles

Removal of post-etch photoresist and sidewall residues using organic solvent and additive combined with physical forces

The effect of tetramethyl ammonium hydroxide (TMAH) used as additive in organic solvent ( N-methyl pyrrolidone, NMP) on removal efficiency of post-etch photoresist was investigated on both blanket substrate and single damascene structures. In contrast to plasma ashing, photoresist removal using NMP/TMAH combined with megasonics showed no carbon depletion and no significant change in k-value. Mixing TMAH with NMP enhanced photoresist removal efficiency with respect to pure NMP. Photoresist removal using NMP/TMAH resulted in lower low- k capacitance (lower k-value) compared with that of plasma ashing process, due to the removal of the damaged layer generated during plasma etching. As a consequence of the removal of the damaged layer, a CD change was observed. The CD loss was estimated to be about 7 nm for 1% TMAH, and became negligible for 0.1% TMAH. Analysis of low- k sidewall using angle-resolved X-ray photoelectron spectroscopy showed that solvent mixture containing TMAH also removed sidewall residues generated by the etch plasma.

Nanometer-scaled triangular platinum islands fabricated using the bridge phenomenon of polystyrene beads

The authors optimized the fabrication of nanometer-scaled triangular platinum islands using the bridge phenomenon of polystyrene beads. Both the mixture ratio of polystyrene beads and the spin coating process were optimized to array a uniform monolayer of polystyrene beads at a high density over a large area. The length of the bridge between the adjacent polystyrene beads as well as the size of polystyrene beads could be controlled using the oxygen plasma ashing process with an adjustment in the ashing time. Platinum was deposited on the ashed polystyrene beads with the bridges as a mask, and the hexagonally arrayed triangular platinum islands were obtained through the dense and uniform triangular structures surrounded by the polystyrene bead bridges with dimensions of less than 45nm2 on the silicon substrate.

Copper cleaning in supercritical CO 2 for the microprocessor interconnects

In this study we report the efficiency of cleaning process in supercritical CO 2 for the removal of the post-etch residues and oxidized copper formed in the via after SiOC-based porous materials etching and photoresist plasma ashing processes. The cleaning solutions contain a sulfonic acid and chelating agents with different chemical configurations. X-ray reflectometry and scanning electron microscopy are used to estimate the oxidized copper dissolution and copper surface aspect (pitting corrosion and residues). The results show that the sulfonic acid dissolves cuprous oxide (Cu 2O) and copper hydroxide (Cu(OH) 2) and consequently allows to remove the residues located at the oxidized copper surface whereas the symmetric β-diketones remove only the copper hydroxide. The mixture of sulfonic acid and β-diketone does not lead to pits at the copper surface. This phenomenon could be due to a complex formation between copper and β-diketones facilitating the oxidized copper dissolution by the acid or could be due to copper surface protection by the adsorbed β-diketones.

Effect of CH4 Plasma Treatment on O2 Plasma Ashed Organosilicate Low-k Dielectrics

ABSTRACTDuring an O2 plasma ashing process, carbon depletion and subsequent moisture uptake caused increase of keff and the leakage current in an organosilicate (OSG) low-k dielectric. For dielectric restoration, additional CH4 plasma treatment on the O2 plasma ashed OSG low-k dielectric was investigated using angle resolved x-ray photoelectron spectroscopy (ARXPS), XPS depth profiling, x-ray reflectivity (XRR), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and contact angle goniometer. After CH4 plasma treatment on the O2 plasma ashed OSG, the surface carbon concentration and surface hydrophobicity were partially recovered. A dense surface layer containing C=C bonds was found to have formed on the top of the damaged OSG. The C-V hysteresis and the leakage current were reduced as a result of the CH4 plasma treatment. XPS depth profiling revealed that the recovery effect was limited to the surface region.

Damage of ultralow k materials during photoresist mask stripping process

Plasma-based ashing of photoresist masks after pattern transfer is a common processing step in the fabrication of integrated circuits. In this work we investigated damage mechanisms of nanoporous ultra low k (ULK) materials with different overall porosities due to the ashing process. Oxygen-, nitrogen- and hydrogen-based photoresiststripping using direct and remote plasma processes were examined. Ellipsometry, x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and transmission electron microscopy were utilized to study the damage layer thickness, physical (pore morphology), and chemical modifications of the nanoporous silica thin films after exposure to the O2-, N2- or H2-based ashing processes. As a result of the plasma exposure, carbon groups in nanoporous silica can be removed from the ULK layers which is also accompanied by material densification. We find severe ashing damage of ULK materials after O2-based ashing using both direct and remote discharges. N2 and H2 discharges also damage ultralow k materials for direct plasma ashing processes which are accompanied by low energy ion bombardment of the substrates. The introduction rate and degree of the ULK materials modifications correlates with the overall porosity. We show that the pore interconnectivity is one of the key parameters that determine ashing damage. ULK damage is greatly reduced for remote N2 or H2 discharges, but the resist removal rates are impractically low if the substrate is at room temperature. We show that both acceptable photoresist stripping rates and ULK damage levels can be achieved for remote H2 plasma ashing processes if the substrate temperature is 250°C and higher.

Formation of nanometer-scale gap electrodes based on a plasma ashing technique

We propose a new and reproducible method to fabricate metal electrodes with a nanometer-scale gap and width, which have been considered as one of the basic building blocks for future nano-devices. The techniques used in this study were the conventional photolithography, e-beam lithography and plasma ashing techniques. Specifically, the plasma ashing process was used to easily form the nanometer-sized gap (10 nm or less) that is difficult to realize by e-beam lithography only. Using the method investigated in this work, we demonstrated that Au electrodes with a nanometer-sized gap and width could be easily fabricated.

Heat, moisture and chemical resistance on low dielectric constant (low- k) film using Diethoxymethylsilane (DEMS) prepared by plasma enhanced chemical vapor deposition

Resistance of low dielectric constant (low- k) dielectrics, deposited using Diethoxymethylsilane (DEMS) precursor and helium (He) carrier gas with or without oxygen (O 2) reaction gas, against heat, moisture stress and chemical treatment is clarified. The low dielectric constant organosilicate glass (OSG) films deposited using DEMS and O 2 is shown to be the most reliable: the dielectric constant are stable even after a heating test at 700 °C and a pressure cooker test (PCT) for 168 h. This stability is high enough to ensure the low- k properties throughout fabricating multilevel interconnects and long-term reliability after the fabrication. This is due to the stability of Si–CH 3 bonds and more Si–C–Si– bonds, which has high degree of cross-linking. However, the degradation of the dielectric constant occurs after O 2 plasma ashing process. The nitrogen plasma treatment is proposed to prevent the damage from O 2 attack in the low- k films deposited using DEMS precursor.

Wet-etch release process for silicon-micromachined structures using polystyrene microspheres for improved yield

One of the final steps in fabricating microelectromechanical devices often involves a liquid-etch release process. Capillary forces during the liquid evaporation stage after the wet-etch process can pull two surfaces together resulting in adhesion of suspended microstructures to the supporting substrate. This release-related adhesion can greatly reduce yields. In this paper, we present a wet-etch release method that uses polystyrene microspheres in the final rinse liquid. The polystyrene microspheres act as physical barriers between the substrate and suspended microstructures during the final liquid evaporation phase. A plasma-ashing process is utilized to completely remove the polystyrene microspheres from the microstructure surfaces. Using this process, release yields >90% were achieved, as compared to yields of 20-50% when the polystyrene microspheres were not included. This release process is inexpensive, easy to implement, and is effective for both single-crystal and polycrystalline silicon MEMS devices.

Dry Etching of Cr2O3/Cr Stacked Film during Resist Ashing by Oxygen Plasma

Stacked films of chromium oxide and chromium (Cr2O3/Cr) have been commonly used as a photomask for the lithographic process of integrated circuit fabrication. It has been found, however, that the Cr2O3/Cr films were etched during the oxygen plasma ashing process, which is applied for the resist removal after the Cr2O3/Cr patterning. In order to solve this problem, we investigated the mechanisms of the Cr2O3/Cr film etching during the ashing process. As a result, it was found that the Cr2O3/Cr film is oxidized during the ashing process to generate CrOx (2≤x≤3) in which Cr has a higher valence than Cr2O3, and that the CrOx (2≤x≤3) evaporates. It was confirmed by means of a plasma shielding experiment that not only oxygen plasma but also oxygen radicals oxidize the Cr2O3/Cr. It has been found that keeping the photomask temperature below 200°C during the ashing process solves the Cr2O3/Cr etching problem.

04/01822 Method and equipment for production of activated carbon: Kashiwagi, Y. Jpn. Kokai Tokkyo Koho JP 2003 226,551 (Cl. C01B3/08), 12 Aug 2003, Appl. 2002/30,463. (In Japanese)

The petrology, mineralogy, and inorganic geochemistry of two contrasting high-sulfur, vitrinite-rich subbituminous to bituminous coals from the North Eastern Region (NER) of India have been studied using a combination of optical microscopy, quantitative X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM/SAED), and chemical analysis techniques. The study reveals that the Fe nano-particles are present in Indian high-sulfur Tertiary coals including nano-pyrite, Fe-oxyhydroxides and a small amount of sphalerite. The pyrite is present as framboids and unsymmetrical cubic crystals (rhombohedral). They contain potentially hazardous elements viz. As, Pb, and Se measured by EDS techniques. Mineral-matter residues isolated from the coals by low-temperature oxygen-plasma ashing are dominated by carbonate minerals (calcite, dolomite, ankerite), pyrite and pyrite oxidation products (jarosite and coquimbite), kaolinite, illite, and quartz. Sulfate-bearing phases such as tschermigite, bassanite and gypsum are also present, probably as artifacts of the plasma-ashing process.

Formation of Molecular Templates for Fabricating On-Chip Biosensing Devices

Formation of organosilane monolayers having various functional groups on silicon oxide surfaces for fabricating on-chip biosensing devices was investigated. Alkyl and perfluoro-alkyl functionalized monolayers were prepared by a chemical vapor deposition, and amino functionalized monolayers were formed by a liquid phase reaction. Each monolayer was confirmed to be closely packed and composed of single moiety species. A molecular patterning process using these organic monolayers was performed. The monolayer patterns were uniformly formed on the substrate by using ultraviolet light patterning and oxygen plasma ashing processes. The pH responsibility at the liquid/modified electrode interface was examined by using capacitor profiles of the structure of monolayer/silicon oxide/silicon. The amino modified surface showed good pH sensitivity of −44 mV/pH. This value was similar to that of the silicon nitride surface. On the other hand, the potential was not changed in any pH solutions in the case of the alkyl and perfluoro-alkyl monolayer-modified surface. It was demonstrated that the pH response of these surfaces was greatly affected by the variation of the functional group. Furthermore, by using the patterned monolayers, fabrication of a multichannel electrode for multiple detection of pH response was achieved.

플라즈마 애싱 공정에 의한 표면미세가공 MEMS 구조물의 변형 분석

플라즈마 애싱 공정에 의한 표면미세가공 MEMS 구조물의 변형 분석

Effect of ion energy and incident angle on the modification of a porous low dielectric-constant material in an O 2 plasma ashing process

A porous silica film was treated in an O 2 reactive ion etching (RIE) process, and changes in the film property with ion energy and incident angle were compared with those observed in a conventional ashing process. The production of hydroxyl (–OH) groups, which always occurs in a conventional ashing, was suppressed when the bias voltage was higher than a threshold value in an O 2 RIE process. This means that the formation of an oxide-like dense layer at the film surface, which is known to inhibit the diffusion of oxygen radicals into the film, requires an ion energy above the threshold value. Conversely, the hydroxyl groups were produced even at bias voltages higher than the threshold value in an O 2 RIE process, when the ion incident angle was higher than a threshold angle. The threshold angle increased with an increase in the bias voltage. Consequently, nearly vertical sidewalls can be fabricated without degradation in their dielectric properties due to the production of hydroxyl groups by employing high bias voltages in an O 2 RIE process.

Characteristics of Polymer Residues Formed at the Via Hole and Photoresist Ashing Properties of Remote Oxygen/Nitrogen Plasma

The low-temperature remote oxygen/nitrogen plasma ashing process that removes both the photoresist and polymer residues containing carbon and fluorine after reactive ion etching (RIE) process was investigated. The fluorocarbon residue was distributed with a depth of several tens of angstroms from the surface with a relatively homogeneous spatial distribution after the RIE process. X-ray photoelectron spectroscopy (XPS) analysis also showed the formation of fluorocarbon films during RIE with mainly C–C, C–CFx (x=1,2,3), CF, and CF2 bonds. The ashing rate increased with increasing amount of nitrogen addition to oxygen gas and showed saturation at approximately 10% of nitrogen addition. Mass spectrometry measurement revealed that the amount of atomic oxygen increased with the addition of nitrogen to oxygen gas. This study revealed that atomic oxygen is the primary reactive species responsible for removal of photoresist in the remote oxygen/nitrogen ashing process.

Trimethylchlorosilane Treatment of Ultralow Dielectric Constant Material after Photoresist Removal Processing

The dielectric properties of organic-porous silica films deteriorate after photoresist removal processing. plasma ashing has been commonly used to remove photoresist. Nevertheless, the plasma will destroy the functional groups and induce moisture uptake in porous silica films. In this study, trimethylchlorosilane (TMCS) is used to repair the damage to porous silica caused by the plasma ashing process. The leakage current and dielectric constant will decrease significantly after the TMCS treatment is applied to damaged porous silica. These experimental results show that the TMCS treatment is a promising technique to repair the damage to porous silica during photoresist removal processing. © 2002 The Electrochemical Society. All rights reserved.

The Effects of Plasma Induced Damage on The Channel Layers of Ion Implanted GaAs MESFETs during Reactive Ion Etching(RIE) and Plasma Ashing Processes

AbstractThe gate length of GaAs MESFETs is required to be shorter for higher microwave frequency applications. The side-wall process using silicon nitride is one of the effective processes to fabricate short gate length GaAs MESFETs. The side-wall process consists of deposition and anisotropic etching of silicon nitride and delivers plasma induced damages on the channel layers of the devices. In this study, the effects of plasma induced damage on the channel layers of ion implanted GaAs MESFETs during reactive ion etching and plasma ashing processes have been investigated. The plasma induced damage was characterized by sheet resistance measurement, Xray photoelectron spectroscopy(XPS) and auger electron spectroscopy(AES) of different etched surfaces, compared with a chemically wet-etched reference surface. Also the effect of the plasma induced damage on the device performance was investigated. As a result, plasma ashing can deteriorate the plasma-induced damage by RIE.

A new simulation model for plasma ashing process-induced oxide degradation in MOSFET

Plasma ashing process-induced oxide damage is studied quantitatively in this paper. To simulate thin gate-oxide damage due to the plasma ashing process, a new equivalent circuit model is proposed by including a differential capacitance, a parasitic resistance, an offset flatband voltage, and the effects of feedback on the interface-state and trapped oxide charge densities generated during the plasma ashing process. According to this new model, computation of gate oxide charging current is performed by correlating to the latent interface-state density. The test n-MOSFET devices, including different antenna-ratios are measured, and excellent agreement is obtained as compared with measured results. Moreover, the deficiency of the previous model is stated and compared. In addition, the effects of substrate doping concentration on plasma-induced oxide damage are also investigated as well as those of plasma ion density, plasma uniformity, thin gate-oxide thickness. Therefore, the relationships between interface states/oxide traps and antenna ratio are linked to provide a guideline for circuit designers and the plasma ashing process-induced damage can be predicted.

Characterization and Removal of Trace Heavy Metal Contamination on Si-Surface Resulted from CHF3/C2F6 Reactive Ion Etching

The characteristics of removal of trace heavy metal contamination on the silicon surface resulted from CHF3/ C2F6 reactive ion etching (RIE) was studied using total reflection X-ray fluorescence spectroscopy (TRXRF). In order to investigate the depth profile of metallic contaminants near the surface, TRXRF measurements containing glancing angle scans were performed after slightly etching of silicon surface by repeating the cleaning procedures that diluted HF (DHF) removed the oxide grown by the mixture of H2SO4 and H2O2 (SPM) or O2 plasma ashing treatment. RIE and O2 plasma ashing processes resulted in metal contamination such as Fe, Ni, Zn, etc. They were present as both of plate-type and bulk-type, and the large part of plate-type contamination was removed easily. Especially, Fe resulted from RIE was the most abundant contaminant and its concentration was ∼1011 atoms/ cm2. Fe was mainly distributed within ∼2 nm from silicon surface and could be effectively reduced below ∼2×1010 atoms/ cm2 by etching of ∼2.5 nm depth of the silicon substrate.

Photoresist Ashing by Atmospheric Pressure Glow Plasma.

We investigated the mechanism and application of photoresist ashing by means of atmospheric pressure glow (APG) plasma. APG plasma using a mixture gas of He and O2 could ash the photoresist with a rate of about 1μm•min-1, which was roughly the same value as that of O2 plasma ashing at a low pressure. The dependences of etch-rate on O2 gas flow rate, discharge power and substrate temperature suggested that the APG plasma ashing process was mainly the oxidation of the photoresist by oxygen radicals. The XPS and optical emission spectroscopy suggested that excited helium promoted the desorption of oxides on the surface of the photoresist. To reduce cost, we tried to use Ar, acetone (Ac) and O2 mixture gas instead of He and O2 mixture gas. Ar/Ac/O2 plasma could etch the photoresist as fast as He /O2 plasma, although the O2 content was one sixth of that of He/O2 plasma. Minute area ashing using a pray type discharge tube was also investigated. Its ashing rate was the fastest, about 4.0μm•min-1, when Ar/O2 mixture gas was used.

Observation of oxide films on reactive ion etch processed InP mesa sidewalls and surfaces

Oxide films observed on InP mesa sidewalls (about 30 nm thick) and horizontal surfaces (about 10 nm thick) after reactive ion etching (RIE) and subsequent plasma ashing were characterized in detail. Auger electron spectroscopy and x-ray microanalysis in transmission electron microscopy suggested that the films are In - Si - P oxides containing more In than P, which is only partially consistent with previous reports. The films presented a serious barrier during subsequent fabrication processes such as regrowth and chemical cleaning, but could be effectively removed by cleaning in a diluted HF solution. It was proposed that Si in the film was incorporated as a result of mask erosion, excess In was due to the preferential evaporation of P during the RIE, and oxidation of the elements occurred during the subsequent oxygen plasma ashing process.