Papers by Keyword: TMAH

Abstract: Tetramethylammonium hydroxide (TMAH) and N-methyl pyrrolidinone (NMP) are commonly used in photoresist developing and stripping process, however, both of TMAH and NMP have been confirmed with CMR (Carcinogenic, Mutagenic and Reprotoxic) concerns. With more attention attracted to TMAH and NMP replacements, Huntsman developed a range of new quaternary amines products, including E-GRADE^® Choline OH (Choline Hydroxide), E-GRADE^® THEMAH (Tris (2-hydroxyethyl) methylammonium Hydroxide), XHE-125, XHE-128, XHE-138, XHE-145 and XHE-148, and solvents, E-GRADE^® MEOX (3-Methyl-2-oxazolidinone) and XHE-123, which have been evaluated in comparison with the performance of TMAH and NMP.

Abstract: Tetramethylammonium hydroxide (TMAH) is a metal-free strong alkaline solution which can etch poly-Si. The concentration of dissolved gas as well as the concentration of TMAH affects etching rate of poly-Si. The detailed kinetics of poly-Si etching in TMAH solution is investigated in this study. The effect of water and TMAH concentration on the etching kinetics of poly-Si was investigated by using various concentrations of TMAH solution. It is found that H₂O in TMAH solution plays an important role in etching poly-Si. Presence of dissolved CO₂ and O₂ in TMAH solution tends to inhibit etching of poly-Si. The concentration of dissolved CO₂ and O₂ in TMAH were reduced by Ar bubbling, thereby the poly-Si etching rate increased.

Abstract: In order to evaluate the effect of repeated cleaning on EUV reticles, specifically, on the etched Mo/Si multilayer, wafer-based test structures with a mimic of this etched Mo/Si multilayer (“black-border”) were fabricated. The resistance of Mo and Si towards alkaline chemistries was tested and quantified using these test structures. The initial passivating film on Mo seems to play a role in delaying the Mo to further oxidize and dissolve in alkaline solutions. For the cleaning times used (minutes) the Mo surface, and thus the black-border edges, will probably stay passivated by that protective oxide in alkaline solution (pH 11), with no or only very limited Mo loss. Stirring and the amount of oxygen or other oxidizing species like H2O2 in solution could increase the oxidation rate of the Mo and/or Mo oxides into soluble Mo(VI) species.

Abstract: Tetramethylammonium hydroxide (TMAH) is a common etchant for Sigma shape formation in IC manufacturing. The impact of oxygen dissolved in TMAH solution on process was studied in this paper. A novel O2 gas injector was developed to improve the process stabilization by control of the oxygen concentration in TMAH solution

Abstract: The anisotropic silicon etching characteristics of TMAH(tetramethyl ammonium hydroxide)+Triton at near the boiling point were investigated. The etch rate of Si {100}, the convex corners, and the roughness of the etched surface contact with the fabrication of bulk microstructures and thus micromechanical devices in silicon. This study presents that the etch rate of Si {100} in 25 wt.% TMAH with 0.1% Triton at near boiling point (112°C) is 1.37μm/min, it is three times higher than it at 80°C. The surface roughness and convex corners of Si {100} after etching at different temperature were investigated by optical microscope, scanning electron microscope (SEM) and atomic force microscope (AFM). The etching rate and smoothness of an etched surface can be improved simultaneously at near boiling point, meanwhile, the undercutting on convex corner should be accepted.

Abstract: As the demand for greater speed in semiconductor devices continues, a typical method of increasing charge mobility is to maximise the silicon strain at the depletion region in p-type transistors through the implementation of “Sigma Cavity” structures in the bulk silicon on either side of the gate structure. These structures, when filled, exhibit a uniaxial strain in the depletion region thus, increasing the charge transport speed [1]. The shape of the Sigma Cavity structure is important in maximising the strain in this region, thus strict control of the shape dimensions is imperative to the electrical performance of the device.

Abstract: Tetramethyl ammonium hydroxide (TMAH) has wide applications in semiconductor industry, including photoresist development, silica etching (especially Sigma etching), and wafer cleaning, etc. One of the critical areas of the photolithography process is the development of unexposed (negative) or exposed (positive) photoresists without pattern distortion. As a metal free, basic aqueous solution, TMAH is the most common positive photoresist developer providing no metal contaminations. The bath composition, especially the concentration of TMAH, is strictly controlled within the process specifications (~2.2 to 2.4 % (w/w)), since it greatly affects the developing rate and contrast [1]. Traditional monitoring of TMAH concentration does not suffice for the modern needs of a sub-20 nm IC fabrication process. Additional critical parameters include dissolved carbonate and proprietary surfactants.

Abstract: Anisotropic etching of silicon refers to the directional-dependent etching, usually by alkaline etchants like aqueous KOH, TMAH and other hydroxides like NaOH. With the strong dependence of the etch rate on crystal orientation and on etchant concentration and temperature, a large variety of silicon structures can be fabricated in a highly controllable and reproducible manner. Hence, anisotropic etching of <100> silicon has been a key process in common MEMS based technologies for realizing 3-D structures [1-4]. These structures include V-grooves for transistors, small holes for ink jets and diaphragms for MEMS pressure sensors as shown in Figure 1 [1]. The actual reaction mechanism has not been well understood and comprehensive physical and chemical models for the process have not yet been developed. With increasing numbers of MEMS applications, interest has grown in recent years for process modelling, simulation and software tools useful for the prediction of etched surface profiles [4-6].

Abstract: The effect of galvanic interaction between the evolving facets of the etch front on the Si {100} surface smoothness during wet anisotropic etching in surfactant-added tetramethylammonium hydroxide (TMAH) is studied by etching different mask patterns. Triton X-100, with formula C₁₄H₂₂O(C₂H₄O)_n, where n=9-10, is used as the surfactant. The different smoothness of wet etched Si {100} surfaces, evaluated by atomic force microscope (AFM) and optical microscope, indicates that the wet etched Si {100} surfaces could become extremely smooth after the onset of the electrochemical etching contribution. A model to account for the galvanic interaction between the evolving facets is proposed, demonstrating that the chemical etching can be significantly surpassed by the electrochemical etching when the relative area of the exposed {100} surfaces are relatively small in comparison to that of the developed {111} sidewalls. Additionally, silicon beams with smooth surfaces are presented in the fabrication of a sandwich micro accelerometer to avoid the risk of device invalidation. This study is useful for engineering applications where the fabrication of microstructures for high quality devices should contain smooth surfaces.

Abstract: Anisotropic wet etching of high resistivity silicon by TMAH for the fabrication of large area silicon radiation detectors is studied in this work. TMAH is widely applied in microelectronics and micromechanical fabrication etching low resistivity silicon, whereas the etching of high resistivity silicon was seldom studied by the industry. This work focused on the research of TMAH etching of high resistivity lager area silicon wafer aiming at its application in silicon radiation detector fabrication. We investigated the etching properties of TMAH of 4 inch (111) silicon wafers. Various parameters combinations were explored, such as TMAH solution concentration of 25wt%, 15wt% and 5wt%, and temperature of 95 °C, 90 °C and 85 °C. Etch rate, etch uniformity and silicon surface roughness were observed.