AlN Substrates Research Articles

Designing the performance of a thick-film laser power detector by means of a heat-transfer analysis using finite-element method

Besides the usual application of thick-film technology to produce circuits of high reliability, this technology is also attractive for the fabrication of sensors. A laser power detector has been realized utilizing the thick-film technique. A special detector configuration provides an exact laser power measurement independent of the position of beam impingement on the detector area and independent of the intensity distribution of the laser beam. The detector, which actually operates as a heat-flow meter, consists of a thermopile circularly applied on an AlN substrate. The geometrical proportions of the detector have been accommodated to an NdYAG laser with a given specification by means of thermal heat-transfer analysis using the finite-element method (FEM). Based on the FEM simulation of steady state and transient temperature distributions on the detector area induced by laser beam impingement, the performance and the operating range of the detector have been specified.

Adhesion strength and microstructural evaluation in electroless Ni-P metallized AlN substrate

The adhesion strength of the electroless Ni (EN)-plated AlN substrates is studied through investigation of the microstructural morphologies at the AlN-EN interfaces. Etching sites around the Al-Y-O compounds on the etched AlN substrate provide the anchor acceptors for interlocking the EN film to achieve a high adhesion strength. Separation of the EN film from the AlN substrate under the action of force leaves the fracture cracks propagating along the AlN/EN interface, cutting through the anchors and making the fragmental EN films around the etching sites reside on the AlN fracture surface. However, the polished AlN substrate lacks the interlocking sites and fails to obstruct the cracks propagating along the AlN/EN interface, and thus results in a poor adhesion strength. An appropriate adhesion strength of 13.7 MPa with a small standard deviation (/spl plusmn/2.3 MPa) can be obtained for the previously etched and 10 /spl mu/m thick EN-plated AlN substrate.

イオンプレーティングによるＡｌＮのメタライジング 表面改質による窒化アルミニウムと金属の接合 （第２報）

Metallization method of AlN substrate by ion plating technique has been developed. Dual coating films of 5-10 μm thick nitrides (TiN, ZrN and CrN) and 10 μm thick copper were formed on the AlN substrate by ion plating. The functionally gradient films of TiN Ti were also deposited on the AlN substrate. The adherent strength of metallized films against AlN substrate was evaluated by the tensile test at room temperature. The morphologies of nitride films were quite sound and they were stuck AlN together well. Element analyses by EPMA and ESCA revealed that nitrides such as TiN, ZrN and CrN were hardly reacted with AlN substrate or Cu film. The adherent strength of TiN, ZrN, CrN coating film and the functionally gradient films indicated the average values of 50-60 MPa in any cases. The joint strength of TIN+Cu dual metallized AlN to copper soldered by Sn-38 mass%Pb solder was about 33 MPa.

Wetting and spreading of molten aluminium against AlN surfaces

Wetting and spreading of molten aluminium against AlN substrates were investigated between 1100 and 1290°C. The contact angles decreased linearly with time under isothermal conditions between 1100 and 1200°C. The isothermal rate of spreading of molten aluminium against AlN substrates was constant between 1220 and 1290°C and the rate increased exponentially with increasing temperature. Crystals of Al4C3 nucleated and grew on the substrate surface beneath the liquid. However, the formation of Al4C3 may not be solely responsible for the changes in contact angle and spreading. It is postulated that carbon contamination from the substrate and/or experimental equipment coupled with the low oxygen partial pressure of the chamber in the presence of graphite, were primarily responsible for the observed contact angle and spreading phenomena. The activation energy for the spreading process was 448 kJ mol-1, suggesting the presence of some chemical reaction at the interface. Carbon-rich aluminium may be initiating a continuous surface reaction with the AlN substrates by reducing the native oxide layer on the substrate surface.

Impurity Contamination of GaN Epitaxial Films From the Sapphire, SiC and ZnO Substrates

ABSTRACTLikely contamination of GaN films by impurities emanating from Al2O3, SiC and ZnO substrates during growth has been studied by secondary ion mass spectrometry analysis. The highly defective interfacial region allows impurities to incorporate more readily as comparedjo the equilibrium solubility in a perfect crystal at a given temperature as evidenced by increased impurity levels in that region as detected by SIMS. The SIMS measurements in GaN layers grown on SiC and sapphire showed large amounts of Si and O, respectively, within a region wider than the highly disordered interfacial region pointing to the possibility of impurity diffusion at growth temperatures. The qualitative trend observed is fairly clear and significant. These observations underscores the necessity for developing GaN and/or AlN substrates.

Effects of Substrate Orientation on the Valence Band Splittings and Valence Band Offsets in GaN and AlN Films

AbstractWe present a first-principles study of heteroepitaxial interfaces between GaN and both cubic as well as wurtzite AlN substrates oriented along main cubic or hexagonal directions and of stacking fault interfaces between cubic and wurtzite GaN. Our calculations show that all studied heterostructures are of type I. Valence band offsets for GaN/AlN are nearly independent of the substrate orientation and of the order of 0.8 eV. The valence and conduction band offsets for a stacking fault interface are predicted to be 40 meV and 175 meV, respectively.

Gold metallization for aluminum nitride

A metallization scheme for gold on AlN is investigated that incorporates three layers sputter-deposited in succession on the AlN substrate, without breaking vacuum: 20 nm of Ti to promote adhesion, a 100 nm thick TiSiN barrier layer, and 230 nm Au. The stability of the scheme was studied after annealing in vacuum up to 800 °C for 30 min and at 400 °C in Ar ambient for 300 h, using 2 MeV 4He ++ backscattering spectrometry, sheet resistance measurements, and adhesion tests. It is shown that the incorporation of the diffusion barrier prevents the interaction of the Ti from the adhesion layer with the gold layer and thereby preserves the integrity of the metallization scheme. This metallization scheme may be applicable to other substrate materials.

Reaction layer formation at the interface between Ti or Zr and AlN

Pure AlN substrate was prepared by hot-pressing to eliminate the influence of sintering-aid substances on interface reactions. Thin films of Ti or Zr were deposited on pure AlN substrate by e-gun evaporation. Thermally induced solid-state reactions of the metal films with the AlN substrate were investigated by Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD). TiAl 3 , TiN, and Ti 4 N 3-x , including Ti 2 N, were formed at the Ti/AlN interface in the temperature range of 600 to 800 °C. Only aluminides, including ZrAl 3 and ZrAl 2 , were formed at the Zr/AlN interface at temperatures above 300°C. Both Ti and Zr reacted with AlN to give a laminate structure and aluminides were formed adjacent to AlN.

Solid-state reaction of Ti and Ni thin films with aluminum nitride

Pure bulk AlN substrates were prepared by hot pressing to eliminate the influence of an aid-sintering substance on the interface reactions. AlN thin films were deposited on Si(111) substrates to decrease the influence of charging on the analyses of metal/AlN interfaces with x-ray photoelectron spectroscopy (XPS). Thin films of titanium and nickel were deposited on bulk AlN substrates by e-gun evaporation and ion-beam assisted deposition (IBAD) and deposited on AlN films in situ by e-gun evaporation. The samples of the evaporated Ti films on bulk AlN and Ni films on bulk AlN were annealed at temperatures from 600 to 800 °C and from 600 to 850 °C for 1 h, respectively. Solid-state reaction products between the metal films and bulk AlN substrates under annealing and IBAD were investigated by x-ray diffraction (XRD) and Ruthford backscattering spectroscopy (RBS). TiAl3, TiN, and Ti4N3−x including Ti2N were found at the interface between the Ti films and AlN substrates for the annealed samples and IBAD sample. No interaction phase was detected for the sample as-deposited by evaporation. However, XPS depth profile of the Ti/AlN/Si sample showed that Ti–N bonding existed at the interface between the AlN film and Ti film. In the Ni/bulk AlN system, NiAl3 and Ni3N were formed at the interface between the Ni thin film and bulk AlN substrate for the samples annealed above 600 °C for 1 h. No interaction phase was detected by XRD and RBS for as-deposited samples and no evidence for Ni–N or Ni–Al bonding was obtained by XPS depth profile of Ni/AlN/Si.

Metallurgical reactions at the interface of Sn/Pb solder and electroless copper-plated AlN substrate

Intermetallic formation between electroless-plated copper and Sn/Pb solder is investigated. An interlayer is formed between copper and solder, and segregation of Pb-rich and Sn-rich phases are observed. X-ray diffraction and EDX analysis results suggest that the major intermetallic formed in the interlayer is Cu/sub 6/Sn/sub 5/. For the as-plated sample, the adhesion strength of Cu to the AIN substrate after 150/spl deg/C aging is affected by both the recrystallization and the creep of copper. For the soldered specimen, the presence of intermetallic compound causes cracks to propagate along the intermetallic/Cu interface and results in a decrease of the adhesion strength.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

表面改質による窒化アルミニウムと金属の接合 （第１報） Ｔｉ＋Ｃｕ二層メタライズしたＡｌＮとＣｕのはんだ付

Soldering of surface-modified AIN to copper was investigated using Sn-38 mass%Pb solder. AlN substrate was dually metallized by Ti and Cu using ion plating technique as follows ; the 10μm thick Ti film was first plated on the AIN substrate, heat-treated in vacuum on various conditions and then the 5-10μm thick Cu film was plated on the heat-treated Ti film again. The thermal stress and heat conduction analyses suggested that the soldered joints could possess the superior properties when the thickness of soldering layer was kept less than 0.4 mm. Defects such as micro voids and cracks were occurred in Ti film after heat treatment, and the fraction of defects increased with increasing the treating temperature and time. The tensile strength of Ti+Cu dual metallized AlN to copper joint was approx. 20 MPa, and slightly decreased as the treating time of Ti film was increased. The Ti+Cu dual metallized AIN to copper soldered joint indicated the superior reliability for thermal fatigue and heat conduction.

On The Origin of Laser-Induced Surface Activation of Ceramics

ABSTRACTThe surfaces of Al2O3and AlN are modified by pulsed-laser irradiation This modification promotes the deposition of copper when the irradiated substrates are immersed in an electroless bath. In this paper the nature of the surface modification is analyzed using results from Auger Emission Spectroscopy (AES) and Cross Sectional Transmission Electron Microscopy (XTEM). During irradiation AlN thermally decomposes leaving a discontinuous metallic film on the surface. A film of Al2O3is detected at the surface of the irradiated AlN substrate, much thicker when the irradiation is performed in an oxidizing atmosphere than when done in a reducing one. Nanoparticles of metallic aluminum are generated during laser irradiation of Al2O3in a reducing atmosphere. When the irradiation of Al2O3is performed in an oxidizing atmosphere, regions containing aluminum or substoichiometric alumina are detected by AES. It is concluded that the presence of metallic aluminum is the main reason why electroless deposition can occur in both AlN and Al2O3. Deposition kinetics are completely consistent with this conclusion. It is very likely that also substoichiometric alumina helps to catalyze the electroless deposition.

Au/(Ti—W) and Au/Cr metallization of chemically vapor-deposited diamond substrates for multichip module applications

Since diamond obtained by chemical vapor deposition (CVD) has an extremely high thermal conductivity, it holds great promise in solving thermal management problems in high performance multichip modules (MCMs). Consequently, there is a need to develop a reliable metallization system for CVD diamond. Refractory metals such as Ti, Mo, Ta and W are known to form adhering carbide layers at high temperatures. Also, transition metals such as Cr, Ni and Ni—Cr are widely used in other MCM technologies involving Si, AlN, SiC and alumina substrates. In the work reported here, adherent Au/Cr and Au/(Ti—W) metallization systems were produced at low temperatures using d.c. magnetron sputtering and electron beam evaporation techniques. Adhesion at low temperature is essential since CVD diamond could lose its thermal and electrical properties at high temperatures. Furthermore, interaction between metal layers may cause an increase in conductor trace resistivity and delamination. Adhesion was measured using a Sebastian V-A thin film stud pull tester. The deposition parameters were optimized to give maximum adhesion using a statistical design software package, Echip. In the case of the sputtered metallization, pre-sputter cleaning of diamond surface improved adhesion significantly. Values above 9 klbf in−2 were obtained in the case of Au/(Ti—W) and 11.8 klbf in−2 in the case of Au/Cr. Post-deposition annealing was performed in nitrogen ambient to investigate the effect of post-metallization processing on adhesion and also to test for any possible interaction between the metals at high temperatures. Annealing temperatures were limited to 450 °C since MCM substrates are seldom exposed to temperatures higher than these. Energy-dispersive spectroscopy (EDS) analysis indicated outdiffusion of W through Au at 400 °C. No interdiffusion was observed in the case of Au/Cr as per optical microscopy and EDS analysis. Auger electron spectroscopy results indicate interaction between the metals in both Au/(Ti—W) and Au/Cr metallizations at 450 °C.

Oxygen Transport in Aluminum Nitride Substrates

The diffusion of oxygen in commercially available aluminum nitride substrates has been studied by performing interdiffusion‐type experiments. The diffusion of oxygen both within AlN grains and along grain boundaries was investigated. By using as‐received AlN substrates and an electron microprobe as an analytical tool, it was found that the rate of oxygen diffusion along grain boundaries was strongly influenced by the presence of impurities and/or other phases at these boundaries. The diffusion of oxygen within AlN grains was studied between 1600° and 1900°C in a flowing nitrogen atmosphere by using secondary ion mass spectrometry (SIMS) for determining oxygen concentration profiles. The chemical diffusion coefficient of oxygen in the AlN lattice as a function of temperature is described by the equation image The oxygen concentration profiles determined by SIMS also show a contribution from diffusion along grain boundaries. Therefore, it was possible to determine values for the product δD′o (δ= width of grain boundaries, D′o= grain boundary diffusion coefficient of oxygen).

Preparation of epitaxial AlN films by electron cyclotron resonance plasma-assisted chemical vapor deposition on Ir- and Pt-coated sapphire substrates

AlN epitaxial films have been fabricated on Ir- and Pt-coated α-Al2O3 substrates via electron cyclotron resonance plasma-assisted chemical vapor deposition (ECRPACVD) using an AlBr3-N2-H2-Ar gas system at substrate temperatures ranging from 500 to 700 °C. The epitaxial relationships between AlN films and substrates were determined by x-ray diffraction, x-ray pole figure, and reflection high-energy electron diffraction. The results are useful in practical applications, such as AlN/metal/α-Al2O3 structure in surface acoustic wave (SAW) devices.

窒化アルミニウムと金属の接合に関する研究（第１報） 活性金属法によるＡｌＮと金属の接合部組織

Brazing of AlN to metals was conducted at 1073-1293 K for 0-129.6 ks using active filler metals of Cu-22%Ti, Cu-10%Zr, Cu-15%Hf binary alloys and Ag-27%Cu-2%Ti ternary alloy. The reaction layer which was comprised of TiN, ZrN or HfN was formed at the bonding interface between AlN substrate and the brazing layer, and eutectic phases such as Cu-Cu4Ti were detected in the brazing layer when binary filler metals were used for AlN to copper joining. TiN was identified in the reaction layer of AlN-molybdenum joint brazed using ternary filler metal. The thermodynamic calculation suggested that TiN, ZrN and HfN were produced by the interfacial reaction between AlN and active metals in the melted binary filler metals.

Indirect bonding of Ni-electroless plated AlN and Cu by hot pressing method

The electroless Ni (EN) plating method was employed to metallize the AlN ceramic substrates. The EN-plated AlN substrate was bonded with the Cu foil to form a sandwich-like AlN-EN/Cu/EN-AlN assembly by hot pressing in vacuum with a pressure of 6.5 MPa for 30 min. For the bonding temperature below the Ni-P eutectic temperature of EN at 880/spl deg/C, the samples were bonded through solid state diffusion. On the other hand, the samples were bonded via a liquid phase media through both wetting and diffusion if the bonding temperature was above 880/spl deg/C. An optimum adhesion strength around 10 MPa occurred within bonding temperature range 600-700/spl deg/C. The fracture took place in the EN/Cu interface for samples bonded below 600/spl deg/C, while fracture took place in the AlN/EN interface above 700/spl deg/C, The increasing temperature enhanced interdiffusion of Cu and EN to form a strong bond, yet resulted in a large residual thermal stress in the AlN/EN interface. The bonded samples with as-received AM exhibited higher adhesion strength than those with polished AlN because there existed a residual compression perpendicular to the AlN/EN interface at surface irregularities in the as-received AlN, which resulted in an additional shear strength offset in the adhesion test. The adhesion strength of samples with etched AlN was the highest as compared to those of as-received and polished AlN, although the surface roughness of the etched AlN was the same as that of the as-received one. It is argued that the etched surface of AlN with micro-etched holes provides the anchor sites for interlocking with the EN film, which results in a good mechanical bonding in the joint. However, a mechanical trimming on the edges of bonded samples would damage the joint, and a low adhesion strength is instead observed. >

Excimer laser ablation and activation of SiOx and SiOx-ceramic couples for electroless copper plating

A XeCl (4.0 eV photon energy) pulsed excimer laser was used to study the ablation behavior of substoichiometric silicon oxide (SSO), SiOx with x∼1.0. The SSO ablation rate was quite high and its ablation threshold quite low (≤0.3 J/cm2), thereby making it an interesting material for pulsed laser patterning without the use of deep-UV radiation. Surface activation, as illustrated by subsequent copper deposition by the electroless process, was observed along well-defined narrow (∼10–20 μm) lines just beyond the edges of ablated trenches in SSO deposited on XeCl-transparent fused silica substrates. When a thin layer of SSO was deposited on polycrystalline Al2O3 or AlN substrates and subsequently laser treated, surface activation of these ceramics occurred on the laser-irradiated regions at much lower fluences and with fewer exposures than are required to activate the bare ceramic substrates. In both types of experiment, activation is believed to result from redeposition of elemental silicon, an ablation product.

Morphology and adhesion strength in electroless Cu metallized AlN substrate

The metallization of aluminum nitride substrates by electroless copper plating is investigated. The AlN substrate is etched by 4% NaOH to study the correlation between the adhesion strength and the surface roughness of etched AlN substrate. Both the as-received nonpolished and the polished AlN are studied. For the nonpolished substrate, the adhesion strength increases from 130 kg/cm/sup 2/ for the sample with an average surface roughness of 0.2 mu m to 230 kgf/cm/sup 2/ for one with an average surface roughness of 0.82 mu m. For the polished substrate, the adhesion strength reaches 271 kg/cm/sup 2/ with a surface roughness of 0.19 mu m. Mechanical interlocking is the major cause for the adhesion strength between the Cu and AlN substrates. The polished substrate that was subsequently etched could form fine cavities on the AlN surface, and the microetching effect resulted in a stronger mechanical interlocking, which increases the adhesion strength.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fabrication of Cofired ALN Multilayer Substrates at Low Temperature Sintering

AbstractIn order to lower the firing temperature of W cofired AlN multilayer substrates, sinterabilities of AlN substrate material and W conductor were investigated at low sintering temperatures around 1650 •C.In case of AIN substrate material, the effect of AIN powder properties on sinterability and thermal conductivity was evaluated. The powders, with specific surface area between 2.3 and 8.2m2• g−1 and oxygen content between 0.7 and 3.2 wt%, were sintered with CaO and Y2O3 as sintering additives. The finer powder promoted the densification below 1600°C and each powder was fully densified at 1650°C. However thermal conductivity sintered at 1650°C decreased with decreasing particle size due to increasing oxygen content inside AlN grains. The thermal conductivity of optimized AlN substrate sintered at 1650°C had over 100W • m−1 K−1.W conductor is required dense microstructure for high adhesion strength to AlN substrate. Shrinkage mismatch between AlN and W during sintering caused porous microstructure for coarse W powders or detaching for fine W powders. The optimized W paste was developed for low temperature sintering.