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Yellow luminescence in n-type GaN epitaxial films
(1997-09-15)
Chen, HM
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Chen, YF
;
Lee, MC
;
Feng, MS
;
材料科學與工程學系
Photoluminescence, resonant Raman scattering, and photoconductivity measurements have been employed to study the yellow; emission in undoped n-type and a set of Se-doped GaN epitaxial films. It is best described by a transition from the conduction-band edge to a deep acceptor. Unlike the donors and accepters used in most previous studies that substitute Ga sires, Se atoms can replace N sites. With this unique fact, we identify that the origin of the yellow emission involves the nitrogen antisite. In addition, it is found that persistent photoconductivity can be observed after the yellow; band excitation, We further suggest that the nitrogen antisite exhibits a metastable behavior similar to the arsenic antisite in GaAs.
Growth of MgWO4 phosphor by RF magnetron sputtering
(1998-05-01)
Chu, JP
;
Hsieh, IJ
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Chen, JT
;
Feng, MS
;
材料科學與工程學系
Magnesium tungstate (MgWO4) thin film phosphors prepared by radio frequency (RF) magnetron sputter deposition were characterized. alpha- and beta-MgWO4 were determined as the major phases in the films studied. Since the deposition rates of film were influenced by RF power. working pressure as well as oxygen content, these processing parameters played an important role in affecting the phase present in the as-deposited films. It is found that the formation of alpha-MgWO4 phase was favorable for the films grown at low deposition rates (<40 Angstrom min(-1)) whereas beta-MgWO4 was a dominant phase at high deposition rates. Substrate temperatures showed no detectable effects on the deposition rates and thus the beta-MgWO4 was the only phase present for the substrate temperature range examined. A phase formation mechanism due to the deposition rate difference is described. Post-deposition annealing significantly improved the cathodoluminescence (CL) properties of films, with annealing temperatures at 750 degrees C or above being the most effective. CL property improvement appeared to he attributed to the enhancement of crystallinity and the transformation to the stable beta-MgWO4 phase during the annealing. Annealing-induced film delamination and blisters. however, resulted in deterioration of low voltage CL properties. (C) 1998 Elsevier Science S.A. All lights reserved.
Process optimization of plasma-enhanced chemical vapor deposited passivation thin films for improving nonvolatile memory IC performance
(1998-12-01)
Lin, CF
;
Tseng, WT
;
Feng, MS
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Characteristics of plasma-enhanced chemical vapor deposited (PECVD) SiO2/SiNx passivation layers are modified to improve and optimize electrical performances such as program/erase cycle and hot carrier reliability of floating-gate nonvolatile memory devices. SiH4/N2O gas mixtures are utilized as precursors for oxide CVD process. Higher SiH4/N2O flow rate ratios render the resulting oxide films more silicon-rich, as manifested by their higher refractive index (RI) and wet etch rates. These modifications in film characteristics also correspond to increased program/erase cycles and lower % hot-carrier linear drain current (I-dlin) degradation An increase in RI from 1.520 to 1.675 translates to a rise in program/erase cycles from 17.3 K to 32 K and a fall in I-dlin from 8.2% to 4.9%. Further improvement in device performance is fulfilled by modifying the stoichiometry of the overlying nitride passivation layer. Water diffusion from oxide and hydrogen release from nitride are both responsible for hot carrier drain current degradation and loss in program/erase cycles. The utilization of a high-RI oxide in conjunction with a low hydrogen content nitride would give rise to the optimal device reliability.
Optimization of multilayer thin film passivation processes for improving cache memory device performance
(1999-04-01)
Lin, CF
;
Tseng, WT
;
Feng, MS
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A multilayer thin film passivation structure based on alternating plasma-enhanced chemical vapor deposited (PECVD) SiOx-SiNx layers are prepared and characterized, in order to improve and optimize the electrical performance and hot carrier reliability of polyload resistors in 4-transistor (4-T) cache static random access memory devices. SiH4-N2O gas mixtures are utilized as precursors for oxide CVD process. Adopting a higher SiH4/N2O flow rate ratio during deposition renders the resulting oxide films more silicon rich, as manifested by their higher refractive index (RI) and wet etch rates. These modifications in film characteristics are also accompanied by enhanced resistance of polyload resistor and lower percentage hot-carrier linear drain current (I-dlin) degradation. An increase in RI from 1.46 to 1.67 translates to a rise in resistance of polyload resistor from 98 to 225 G Omega and a fall in I-dlin from 5.8 to 4.5%. Further improvement in device performance can be realized by modifying the stoichiometry of the overlying nitride passivation layer. This is achieved by increasing bias power while reducing the SiH4/NH3 gas flow rate ratio during the PECVD nitride deposition process. The nitride thus thus deposited contain lower Si-H bond density, and exhibit lower buffered oxide etch rates and compressive stress. Passivation structures based on the combination of a high RI oxide and a low Si-H content nitride layers yield the most promising device performance and reliability. Defect species in the oxide passivation layer are identified and their charge trapping mechanisms clarified. Impact of moisture and hydrogen from the passivation on polygate and load resistor are both held responsible for device degradation. Interfacial defect reactions involving both hydrogen and moisture are proposed to account for the carrier trapping mechanisms responsible for device failure. (C) 1999 The Electrochemical Society. S0013-4651(98)02-078-3. All rights reserved.
Process optimization and integration for silicon oxide intermetal dielectric planarized by chemical mechanical polish
(1999-05-01)
Lin, CF
;
Tseng, WT
;
Feng, MS
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The chemical mechanical planarization (CMP) characteristics of silicon oxide films are studied systematically for the optimization of planarization for intermetal dielectric (IMD) processes. By way of orthogonal array experimental design, the influences of physical parameters during CMP upon the polishing behaviors of silicon oxide dielectric materials are investigated. Polishing results with a removal rate greater than 200 nm/min and a within-wafer nonuniformity less than 4% can be achieved and an optimized polish process is derived from parametric experiments, which are based on the summarized trends from orthogonal array experimental results. The optimized polish process is applied to planarize patterned IMD wafers with different metal line pitch and IMD thickness. Incorporating the IMD geometric factors and CMP polishing performance, a rule including the integral nonuniformity, thickness of dielectric, efficiency of planarization, geometry of device, removal rate, and its variation for CMP time estimation (INTEGRATE) is proposed to approximate the required IMD thickness and CMP polish time for ImD process integration. High efficiency of the planarization process and excellent planarity are both achieved based on the rule of INTEGRATE. (C) 1999 The Electrochemical Society. S0013-4651(98)09-059-4. All rights reserved.
A ULSI shallow trench isolation process through the integration of multilayered dielectric process and chemical-mechanical planarization
(1999-06-22)
Lin, CF
;
Tseng, WT
;
Feng, MS
;
Wang, YL
;
材料科學與工程學系
A multilayer thin film structure (SiO2/SiNx/SiO2) with a one-step chemical-mechanical polish (CMP) process is developed for shallow trench filling and planarization for ULSI devices in the quarter micron regime. By fine-tuning the plasma-enhanced chemical vapor deposition (PECVD) conditions we successfully modified the stoichiometry and other characteristics of the as-deposited SiNx and oxide films. As these film characteristics are changed, the CMP removal rate selectivity between sacrificial oxide and nitride stopper layer can also be adjusted. Correspondingly, the CMP process latitude for shallow trench isolation in 0.25 mu m memory devices can be broadened by sequentially depositing multilayered oxide and nitride films with adjustable characteristics and CMP removal rates. Dishing-free wide trench areas with excellent planarity can be achieved through the integration of the proposed multilayered PECVD oxide/nitride scheme and the one-step CMP process. (C) 1999 Elsevier Science S.A. All rights reserved.
Effects of O-2- and N2O-plasma treatments on properties of plasma-enhanced-chemical-vapor-deposition tetraethylorthosilicate oxide
(1999-07-01)
Chen, YC
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Yang, MZ
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Tung, IC
;
Chen, MP
;
Feng, MS
The high quality silicon oxide films were prepared by plasma-enhanced chemical vapor deposition (PECVD) using tetraethylorthosilicate (TEOS)-oxygen based chemistry. The O-2- or N2O-plasma treatments were performed on the as-deposited films as an attempt to improve the properties of the TEOS oxide films. TEOS oxide film deposited at lower pressure had lower Si-OH content, less carbon impurity, and flatter surface, and hence had better electrical properties. Both O-2- and N2O-plasma would decrease the oxygen content of the oxide film, which led the composition of the film to deviate from the stoichiometric SiO2. The O-2-plasma treatment did not show the encouraging effect on the chemical structure and electrical properties of the TEOS oxide films. In contrast, the N2O-plasma treatment could be a promising means to improve the breakdown field and leakage current density of the TEOS oxide films, which was accomplished by the N2O-plasma effect to facilitate the passivation of dangling bonds, linking reaction of Si-OH bonds, nitridation reaction and densification of the amorphous silicon oxide network.
The novel improvement of low dielectric constant methylsilsesquioxane by N2O plasma treatment
(1999-10-01)
Chang, TC
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Liu, PT
;
Mor, YS
;
Sze, SM
;
Yang, YL
The organic silsesquioxane, methylsilsesquioxane (MSQ), has a low dielectric constant because of its lower film density compared to thermal oxide. However. the quality of MSQ film is degraded by the damage of oxygen plasma and hygroscopic behavior during photoresist stripping. In this work, we studied the N2O plasma treatment for improving the quality of MSQ. The leakage current of MSQ decreases as the N2O plasma treatment time is increased. The dielectric constant of N2O plasma-treated sample remains constant (similar to 2.7). In addition, the thermal stability of MSQ film can be enhanced. The role of N2O plasma is to convert the surface layer of organic MSQ into inorganic type by decomposition of the alkyl group and thus form a passivation layer. The inert passivation layer enhances the resistance to moisture uptake and O-2 plasma attack. Therefore, N2O plasma-treatment greatly improves the quality of low k MSQ film and removes the issue of photoresist stripping in the integrated process. (C) 1999 The Electrochemical Society. S0013-4651(98)10-071-X. All rights reserved.
Nitric acid-based slurry with citric acid as an inhibitor for copper chemical mechanical polishing
(1999-10-15)
Hu, TC
;
Chiu, SY
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Dai, BT
;
Tsai, MS
;
Tung, IC
A novel inhibitor, citric acid, was introduced in the HNO3-based slurry for copper chemical mechanical polishing. It was anticipated that a passivation layer could be formed on the copper surface in the presence of citric acid. In a 3 vol.% HNO3 solution, the passivation effect derived from citric acid saturated as the citric acid concentration reached ca. 0.01 M. The polishing rate was found to decrease with the addition of citric acid. The results showed that the HNO3-based slurry with citric acid as an inhibitor could achieve good surface planarity for copper chemical mechanical polishing. (C) 1999 Published by Elsevier Science S.A. All rights reserved.
Effects of methyl silsesquioxane electron-beam curing on device characteristics of logic and four-transistor static random-access memory
(1999-11-01)
Lin, CF
;
Tung, IC
;
Feng, MS
;
材料科學與工程學系
;
Department of Materials Science and Engineering
The as-spun methyl silsesquioxane (MSQ) film cured by an electron beam (e-beam) did not show water absorption after a five-day exposure to ambient ail: MSQ was applied to the triple-level metal (TLM) Logic and double-level metal (DLM) foul-transistor (4-T) static random-access memory (SRAM) as intermetal dielectric by means of the non-etchback process. When MSQ treatment conditions were properly controlled, the top layer of the as-spun films was cured by e-beam exposure while the bottom layer of the film was thermally cured for a short period of time. The as-cured MSQ offered good surface planarity. In addition, neither via poisoning, bowing nor cracking was observed. The results showed that, by the application of the e-beam cured MSQ in the fabrication of intel connect structures, the cache time of DLM 4-T SRAM could be improved to 10 ns compared with 11.5 ns for the SRAM fabricated using the conventional furnace cure spin-on-glass (SOG) process (400 degrees C annealing for one hour). E-beam exposure has little effect on n-channel metal-oxide-semiconductor (NMOS) device characteristics, such as saturation current threshold voltage and channel length. In contrast, e-beam exposure has a significant effect on p-channel MOS (PMOS) device characteristics, resulting in a shift of the threshold voltage as well as an increase in the channel length. It is notable that the e-beam exposure almost did not affect NMOS device characteristics in the 4-T SRAM, since the polysilicon load resistor could serve as a shield against electron bombardment. In such a case, the resistance of the polysilicon load resistor was significantly decreased.

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