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High resolution and energy filtering TEM study of interfacial structure and reaction in advanced materials processing
(1998-04-10)
Chang, HL
;
Chang, L
;
Chen, FR
;
Kai, JJ
;
Tzou, E
High resolution TEM becomes more powerful when coupled with a Gatan imaging filler (GIF). It gives both structural and compositional information simultaneously with subnanometer and nanometer resolution. respectively. By means of these combined techniques, the failure mechanism of diffusion barrier layers in IC devices, having the structure of Al-1%Si-0.5%CuiTiNITi/Si substrate, was investigated. In non-oxygen stuffed samples thermally stressed at 550 degrees C for 1 h serious Al spikes below contacts were observed where metal layer Ti also reacted with Si substrate to form C49-TiSi2 and was consumed completely. TiN and Al become unstable due to high temperature thermal stress and reacted into TiAl3 and AlN. Decomposition of TiN degraded the function of the barrier layer, and so a diffusion path at the weakest point of the contact corner was opened for metal Al alloy to diffuse through the barrier layer and to form a spike below the TiN layer. We also showed that the oxygen-stuffing processes after each TiN/Ti deposition enhances the barrier capability against Al/Si diffusion in thermal stress. It was found that Ti and TiN were oxidized to form titanium oxide which reacted with the Al alloy. As a result, Al2O3 and TiAl3 were found above the TiN layer. Therefore, it is concluded that oxidation during oxygen-stuffing processes provides a means to inhibit diffusion in thermal stress processes, and maintains integrity of the stack structure. (C) 1998 Acta Metallurgica Inc.
Microstructural investigation of oxidized Ni/Au ohmic contact to p-type GaN
(1999-01-01)
Chen, LC
;
Chen, FR
;
Kai, JJ
;
Chang, L
;
Ho, JK
The phase evolution of oxidized (10nm) Ni/(5nm) Au films on p-GaN was examined with a field emission gun transmission electron microscope in conjunction with composition analyses to explore the mechanism of formation of low resistance ohmic contact to p-GaN. The p-GaN/Ni/Au sample heat treated above 500 degreesC in air was mainly composed of a mixture of crystalline NiO, Au and amorphous Ni-Ga-O phases. Small voids adjacent to the p-GaN film were also found. Moreover, NiO partially contacts to p-GaN as well as Au islands and the amorphous Ni-Ga-O phases. The results suggest that the crystalline NiO and/or amorphous Ni-Ga-O phases may play a significant role in the formation of a low resistance ohmic contact to p-GaN.
Improvement of resolution by maximum entropy linear image restoration for NiSi2/Si interface
(1999)
Chen, FR
;
Kai, JJ
;
Chang, L
;
Wang, JY
;
Chen, WJ
A linear imaging constrained-maximum entropy method has been developed to extend the resolution from a series of defocused high-resolution images and one diffraction pattern. Our method is basically the Gerchberg-Saxton algorithm, which restores spatial information by imposing real space and Fourier space constraints cyclically. A constrained-maximum entropy method (constrained-MEM) was developed for real space constraints. This constrained-MEM finds an optimum solution of phases such that simulated images resemble the experimental image under some constraints in real space. These constraints include conservation of charge as well as a minimum of the chi(2) function, which is a measure of the level of satisfaction between simulated images and experimental images. For the Fourier space constraint, the square root intensities of diffraction spots were substituted. In this paper, we demonstrate that this method is able to extend the resolution from a series of high-resolution images and one diffraction pattern from a periodic NiSi2/Si interface. The atomic structure of the NiSi2/Si interface can be directly read out from the MEM image without a priori knowledge of the interface.
Microstructural investigation of oxidized Ni/Au ohmic contact to p-type GaN
(1999)
Chen, LC
;
Chen, FR
;
Kai, JJ
;
Chang, L
;
Ho, JK
The microstructure of oxidized Ni/Au films on p-GaN was examined to elucidate the formation of a low resistance ohmic contact to p-GaN with a field-emission gun transmission electron microscope in conjunction with composition analyses. The p-GaN/Ni/Au samples were heat treated at 500 degrees C in air mainly composed of a mixture of crystalline NiO, Au, and amorphous Ni-Ga-O phases. Small voids adjacent to the p-GaN film were also observed. The as-deposited Au film converted into discontinuous islands containing small amounts of Ni that connect with p-GaN. NiO formed a continuous film at the surface that covers the Au islands and the amorphous Ni-Ga-O phases. Moreover, NiO partially contacts p-GaN as well as Au islands and the amorphous Ni-Ga-O phase. The orientation relationship of the crystalline NiO, Au-rich islands, and p-GaN film was identified as NiO(111)//Au(11 (1) over bar)//GaN(0002) and NiO[1 (1) over bar 0]//Au[1 (1) over bar 0]//GaN[11 (2) over bar 0]. The results suggested that Ni atoms diffuse through the Au layer onto the surface and react with oxygen to form NiO, whereas Au atoms diffuse towards the inside to form a Au-Ni alloy. The microstructural examination indicated that the crystalline NiO and/or the amorphous Ni-Ga-O phases may significantly affect the low resistance ohmic contact to p-GaN. (C) 1999 American Institute of Physics. [S0021-8979(99)05219-6].
The effect of heat treatment on Ni/Au ohmic contacts to p-type GaN
(1999-11-16)
Chen, LC
;
Ho, JK
;
Chen, FR
;
Kai, JJ
;
Chang, L
The effect of heat treatment temperature on the microstructure and specific contact resistance of oxidized Ni(5 nm)/Au(5 nm) contacts to p-type GaN was investigated.,The: minimum specific contact resistance (Q(c)) obtained was 4 x 10(-6) Omega cm(2) after heat treating at 500 degrees C in air for 10 min. The cross-sectional microstructure of heat treated Ni/Au films on p-type GaN was examined with transmission electron microscope (TEM) in conjunction with compositional analyses. The high value of Q(c) for samples heat treated at lower temperatures (< 400 degrees C) was attributed to the fact that Au islands and crystalline NiO detached from the p-type GaN. When the temperature increased to 500 degrees C, NiO films and Au islands epitaxially constructed on p-type GaN matrix. The crystalline NiO may play a crucial role in the formation of low-resistance ohmic contact to p-GaN. Increasing the temperature further to 600 degrees C, large voids adjacent to p-GaN were observed which resulted in the reduction of contacting area deteriorating the contact resistance.
Deposition of heteroepitaxial diamond on 6H-SiC single crystal by bias-enhanced microwave plasma chemical vapor deposition
(2000-04-01)
Chang, L
;
Yan, JE
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Chen, FR
;
Kai, JJ
;
材料科學與工程學系
Deposition of heteroepitaxial diamond on substrates of 6H-SiC single crystal by a d.c. voltage biased-enhanced microwave plasma chemical vapor deposition method has been attempted. Various concentrations of methane (CH4) up to 10% in hydrogen (H-2) was used to evaluate its effect on epitaxy. Characterization of cross-sectional transmission electron microscopy with electron energy loss spectroscopy shows that an interlayer can form between diamond 6H-SiC, depending on the CH4 concentration. With low CH4 concentration, diamond was directly nucleated on 6H-SiC with an orientation relationship of diamond {111}//6H-SiC {0001} and diamond [110]//6H-SiC [11 (2) over bar 0]. (C) 2000 Elsevier Science S.A. All rights reserved.
Thermal stability of Cu/Ta/GaAs multilayers
(2000-11-20)
Chen, CY
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Chang, L
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Chang, EY
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Chen, SH
;
Chang, DF
Copper metallization for GaAs was evaluated by using Cu/Ta/GaAs multilayers for its thermal stability. A thin Ta layer of 40 nm was sputtered on the GaAs substrate as the diffusion barrier before copper film metallization. As judged from sheet resistance, x-ray diffraction, Auger electron spectroscopy and transmission electron microscopy, the Cu/Ta films with GaAs were very stable up to 500 degreesC without migration into GaAs. After 550 degreesC annealing, the interfacial mixing of Ta with GaAs substrate occurred, resulting in the formation of TaAs2. At 600 degreesC annealing, the reaction GaAs with Ta and Cu formed TaAs, TaAs2, and Cu3Ga, resulting from Cu migration and interfacial instability. (C) 2000 American Institute of Physics. [S0003-6951(00)03047-3].
Extension of HRTEM resolution by semi-blind deconvolution method and Gerchberg-Saxton algorithm: application to grain boundary and interface
(2001)
Chen, FR
;
Ichnose, H
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Kai, JJ
;
Chang, L
;
材料科學與工程學系
A generalized maximum entropy method coupled with Gerchberg-Saxton algorithm has been developed to extend the resolution from high-resolution TEM image(s) for weak objects. The Gerchberg-Saxton algorithm restores spatial resolution by operating real space and reciprocal space projections cyclically. in our methodology, a generalized maximum entropy method (Kullback-Leibler cross entropy) dealing with weak objects is used as a real space (P1) projection. After P1 projection, not only are the phases within the input spatial frequencies improved, but also the phases in the next higher frequencies are extrapolated. An example of semi-blind deconvolution (P1 project only) to improve the resolution in SiC twin boundary is shown. The nature of the bonding in this twin boundary is Si-C but it was rotated 180degrees along the boundary normal. The optimum solution from P1 projection can be further improved by a P2 projection. The square roots of diffraction intensities from a diffraction pattern are then substituted to complete a cycle operation of the Gerchberg-Saxton algorithm. Application examples of Gerchberg-Saxton algorithm to solve the atomic structure of defects (2 x 1 interfacial reconstruction and dislocation) in NiSi2 / Si interfaces will be shown also.
Four-dimensional dielectric property image obtained from electron spectroscopic imaging series
(2001)
Lo, SC
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Kai, JJ
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Chen, FR
;
Chang, L
;
Chen, LC
We have demonstrated a new quantitative method to characterize two- dimensional distributions of energy-dependent dielectric function of materials from low loss electron spectroscopic image (ESI) series. Two problems associated with extracted image-spectrum from the low-loss image series, under-sampling and loss of energy resolution, were overcome by using fast Fourier transformation (FFT) interpolation and maximum entropy deconvolution method. in this study, Black Diamond(TM)/Si3N4/SiO2/Si-substrate dielectric layer designed for copper metallization was used as the sample. We show that the reconstructed (FFT interpolated and maximum entropy deconvoluted) image-spectrum obtained from ESI series images can be quantified with the same accuracy as conventional electron energy-loss spectroscopy spectra. Since the analysis of the dielectric function is sensitive to the local thickness of the specimen using Kramers-Kronig analysis, we also developed a new method to quantitatively determine the dielectric constant for low-k materials. We have determined the thickness of the Black Diamond using the extrapolated thickness method from the materials of known dielectric constants. Using Kramers-Kronig formula, the dielectric function map can be deduced front two-dimensional reconstructed single scattering spectra with providing the information of thickness. We proposed a four-dimensional data presentation for revealing the uniformity of the energy dependent property. The accuracy of our methods depends on the thickness determination and on the quality of the reconstructed spectra from the image series.
Oxidation of Ta diffusion barrier layer for Cu metallization in thermal annealing
(2001-06-01)
Yin, KM
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Chang, L
;
Chen, FR
;
Kai, JJ
;
Chiang, CC
This work examines the thermal stability of Ta barrier layer for Cu metallization with the effect of oxygen. The Cu/Ta/SiO2/Si films were annealed at temperatures ranging from 400 to 600 degreesC under various vacuum conditions. Transmission electron microscopy has been performed to characterize the microstructure of the films after annealing. The results show that an amorphous interlayer of oxide between Cu and Ta can be formed at 400 degreesC in a vacuum of 10(-2) mbar. X-Ray energy dispersive spectroscopy and electron energy loss spectroscopy confirm that this interlayer is tantalum oxide. This interlayer transformed into a crystalline phase of Ta-Cu oxide at 600 degreesC. In addition, formation of tantalum oxide interlayer is more thermodynamically favorable than that of copper oxide layer at the Cu/Ta interface. Growth of the amorphous interlayer is atmosphere-dependent, as evidenced by the thickness of tantalum oxide being decreased with better vacuum or argon gas. This observation suggests that the oxidation source may arise from the annealing atmosphere rather than from interior SiO2. Furthermore, it has been observed that oxygen diffuses along grain boundaries in copper films to cause tantalum oxidation. (C) 2001 Elsevier Science B.V. All rights reserved.

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