Study of Ti/W/Cu,Ti/Co/Cu,and Ti/Mo/Cu multilayer structures as schottky metals for GaAs diodes

Schottky structures with copper and refractory metals as diffusion barrier for GaAs Schottky diodes were evaluated. These structures have lower series resistances than the conventionally used Ti/Pt/Au structure. Based on the electrical and material characteristics, the Ti/W/Cu and Ti/Mo/Cu Schottky structures are thermally stable up to 400°C; the Ti/Co/Cu Schottky structure is thermally stable up to 300°C. Overall, the copper-metallized Schottky structures have excellent electrical characteristics and thermal stability, and can be used as the Schottky metals for GaAs devices.     

Etching of As- and P-based III–V semiconductors in a planar inductively coupled BCl<Subscript>3</Subscript>/Ar plasma

A parametric study of the etch characteristics of Ga-based (GaAs, GaSb, and AlGaAs) and In-based (InGaP, InP, InAs, and InGaAsP) compound semiconductors in BCl₃/Ar planar inductively coupled plasmas (ICPs) was performed. The Ga-based materials etched at significantly higher rates, as expected from the higher volatilities of the As, Ga, and Al trichloride, etch products relative to InCl₃. The ratio of BCl₃ to Ar proved critical in determining the anisotropy of the etching for GaAs and AlGaAs, through its effect on sidewall passivation. The etched features in In-based materials tended to have sloped sidewalls and much rougher surfaces than for GaAs and AlGaAs. The etched surfaces of both AlGaAs and GaAs have comparable root-mean-square (RMS) roughness and similar stoichiometry to their unetched control samples, while the surfaces of In-based materials are degraded by the etching. The practical effect of the Ar addition is found to be the ability to operate the ICP source over a broader range of pressures and to still maintain acceptable etch rates.     

Reliability characteristics of ohmic contacts for AlGaAs/GaAs HBTs

The thermal stability of ohmic contacts for AlGaAs/GaAs HBTs is presented. Ti/Pt/Au, Ti/Pt/Au and Cr/Pt/Au, and AuGe/Ni/Ti/Pt/Au were investigated for emitter, base, and collector contacts, respectively. As a result of 200 degrees C storage tests, it was found that these contacts did not limit the reliability of AlGaAs/GaAs HBTs.<>     

Use of a TiN barrier to improve GaAs FET ohmic contact reliability

We have used a reactively sputtered TiN diffusion barrier to prevent interpenetration of a (Ni)GeAuPt ohmic contact layer and Ti/Pt/Au overlay on GaAs devices baked at 250-300°C in air. Planar GaAs MESFET's and TLM patterns were fabricated and iteratively tested and baked. Devices without TiN showed severe degradation in morphology and dc and RF performance. Devices with TiN remained essentially unchanged.     

Improvedn-type GaAs ohmic contacts compatible with a chlorine-based dry-etch process

We report the use of a Mo barrier layer within Ni/Au-Ge based ohmic contacts to GaAs for eliminating an etch stop reaction that occurs during Cl-based dry etching of heterojunction bipolar transistors. With conventional Ni/Au-Ge/Ag ohmic contacts, chlorinecontaining discharges produce a passivating layer of AgCl on the semiconductor surface, preventing further etching. This layer is absent when the Ag in the contact is replaced with Mo. The Mo has several advantages over other diffusion barrier layers and yields contacts with excellent adhesion, smooth morphology, and sharp edge definition. The average contact resistivity of these contacts ton ⁺-GaAs(n = 6 × 10¹⁸ cm^-3) was 0.074 ohm-mm, which is lower than the typical contact resistivity of conventional Ni/Au-Ge/ Ag metallization (0.11 ohm-mm).     

Gallium–Indium–Zinc-Oxide-Based Thin-Film Transistors: Influence of the Source/Drain Material

During the last years, oxide semiconductors have shown that they will have a key role in the future of electronics. In fact, several research groups have already presented working devices with remarkable electrical and optical properties based on these materials, mainly thin-film transistors (TFTs). Most of these TFTs use indium-tin oxide (ITO) as the material for source/drain electrodes. This paper focuses on the investigation of different materials to replace ITO in inverted-staggered TFTs based on gallium-indium-zinc oxide (GIZO) semiconductor. The analyzed electrode materials were indium-zinc oxide, Ti, Al, Mo, and Ti/Au, with each of these materials used in two different kinds of devices: one was annealed after GIZO channel deposition but prior to source/drain deposition, and the other was annealed at the end of device production. The results show an improvement on the electrical properties when the annealing is performed at the end (for instance, with Ti/Au electrodes, mobility rises from 19 to 25 cm²/V ldr s, and turn-on voltage drops from 4 to 2 V). Using time-of-flight secondary ion mass spectrometry (TOF-SIMS), we could confirm that some diffusion exists in the source/drain electrodes/semiconductor interface, which is in close agreement with the obtained electrical properties. In addition to TOF-SIMS results for relevant elements, electrical characterization is presented for each kind of device, including the extraction of source/drain series resistances and TFT intrinsic parameters, such as (intrinsic mobility) and VT_i (intrinsic threshold voltage).     

Rapid isothermal processing of Pt/Ti contacts to p-type III-Vbinary and related ternary materials

Results of an extensive study of the interfacial intermixing and interaction of the Pt/Ti bilayer metallization to seven III-V binary and related ternary compound semiconductor systems, as well as the contact electrical properties, are given. Pt/Ti contact to InAs and In_0.53 Ga_0.47As were ohmic as deposited, while the same metallization scheme on GaAs, GaP, InP, In_0.52Al_0.48 As, and Ga_0.7Al_0.3As provided a rectifying contact as-deposited. The latter group of contacts, with the exception of InP and GaP, were transformed to an ohmic contact as a result of rapid thermal processing (RTP) at the temperature range of 300 to 450°C. A linear correlation between the semiconductor bandgap value and the Schottky-barrier height, measured in the Pt/Ti contacts, was observed     

Reliability of AuGe/Pt and AuGe/Ni ohmic contacts on GaAs

The reliability of AuGe/Pt and AuGe/Ni ohmic contacts with and without overlay metal (Ti/Au, Ti/Pt/Au or TiW/Au) has been studied. AuGe/Ni contacts have proved superior and more reliable than AuGe/Pt contacts with or without overlay. AuGe/Pt contacts are stable without overlay but degrade rapidly with overlay. AuGe/Ni contacts exhibit thermal stability after 1000 hours' aging at 250°C.     

Ti,W,Mo,TiW膜的阻挡性能比较

介绍了Ｔｉ－Ａｕ，Ｔｉ－Ｗ－Ｐｔ－Ａｕ，Ｍｏ－Ａｕ，ＴｉＷ－Ａｕ，ＴｉＷ－Ｐｔ－Ａｕ等多种金属膜分别在４００，４２５，４５０，４７５和５００℃，３０分钟等时退火后的显微镜观察结果和典型样品的俄歇能谱分析结果。结果表明，Ｔｉ由于在Ａｕ中扩散太快，阻挡性能较差，而Ｗ，Ｍｏ，ＴｉＷ都有较好的阻挡性能。结合实际应用，ＴｉＷ－Ｐｔ－Ａｕ应是硅微波功率管的金属化的较佳选择。     

Structural characterization of Ti and Pt thin films on GaAs(100) substrate

In an attempt to understand the Schottky barrier behavior of Ti/Pt/GaAs and Pt/Ti/ GaAs bimetal Schottky diodes, we have investigated the interfacial morphology of Ti and Pt thin films on GaAs(l00) substrate. The characterization was based on coverage profiling of Auger electron spectroscopy in conjunction with transmission electron microscopy. Emphasis was placed on film uniformity and atomic interdiffusion. The results showed Ga and As outdiffusion in Pt/GaAs interface and some oxygen incorporated in Ti film, but no evidence of clustering for both metal/GaAs systems.     

Stability of metal/GaAs-lnterfaces: A phase diagram survey

Calculated phase diagrams of ternary Ga-As-metal systems for the metals Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Re, Os, Rh, Ir, Ni, Pd, Pt, Cu, Ag and Au are presented. The predictive calculations are based on the following simplifications: Ternary phases and solid solubilities are disregarded and the Gibbs energy of formation of binary compounds is estimated by the enthalpy of formation and calculated from Miedema’s model. The predicted diagrams agree surprisingly well with experimental data and they may be useful for the many cases where data are lacking or fragmentary. The phase diagrams and the thermodynamic data are shown to be a powerful tool for the understanding of interface reactions of metallic contacts to GaAs and hence for the development of improved contact materials.     

Dry etching of III-V semiconductors in IBr/Ar electron cyclotron resonance plasmas

IBr/Ar plasmas were found to be promising candidates for room temperature dry etch processing of the III-V semiconductors GaAs, AlGaAs, GaSb, InP, InGaAs, and InSb. Results showed fast etch rates (～3,000Å/min) at high microwave power (1000W) and good surface morphology (typical root mean square roughness ～2 nm), while retaining the near-surface stoichiometry. There was little variation of surface smoothness over a wide range of plasma compositions for Gacontaining materials. By contrast, there was a plasma composition window of about 25–50% of IBr in IBr/Ar plasmas for maintaining good morphology of Incontaining semiconductors like InP. Etch rates of the semiconductors generally increased with microwave power (400-1000 W) and rf power (50-250 W), whereas there was little dependence of the rates on the increasing percentage of IBr in the IBr/Ar plasma composition above 30% IBr for In-based, and 50% IBr for Ga-based materials. Those results show the etch rates over 30% of IBr in IBr/ Ar are desorption-limited. Photoresist masks do not hold up well to the IBr under ECR conditions, resulting in poor profile control, whereas SiN_x offers much better etch resistance.     

Carrier waves in semiconductors I: Zero temperature theory

A detailed treatment of the space-charge waves or carrier waves which are associated with drifting carriers in a semiconductor is given. These waves have a phase velocity comparable to that of the drifting carriers, but normally have very high loss. This dielectric relaxation loss may be radically decreased by utilizing the interaction between two sets of carriers, working with semiconductors of small cross section, or semiconductors placed against high permittivity materials. Gain may be obtained by using special materials such as GaAs, or by the use of interactions between two sets of carriers in the presence of a magnetic field. The treatment given neglects the effect of diffusion so as to keep the mathematics simple and emphasize the physics of the problem. In a later paper, methods of taking diffusion into account will be given.     

增强型InGaP/AlGaAs/InGaAs PHEMT栅退火工艺

针对InGaP/AlGaAs/lnGaAs PHEMT器件,进行了Ti/Pt/Au和Pt/Ti/Pt/Au两种栅金属结构的退火实验,通过实验研究比较,得到了更适用于增强型器件的退火工艺,利用Ti/Pt/Au结构,在320℃退火40min,使器件阈值电压正向移动大约200mV,从而成功制作了高成品率的稳定一致的增强型器件,保证了增强型器件阈值电压在零以上.     

Metal contacts to n-type GaN

Contacts consisting of various single layer metals to n-type GaN have been formed and characterized. The current-voltage characteristics were measured for 17 different metals (Sc, Hf, Zr, Ag, Al, V, Nb, Ti, Cr, W, Mo, Cu, Co, Au, Pd, Ni, and Pt) deposited on the same epitaxial growth layer. The barrier height, ideality factor, breakdown voltage, and effective Richardson coefficients were measured from those metals which exhibited strong rectifying behavior. The barrier heights for these metal contacts were measured using current-voltage-temperature and capacitance-voltage techniques. It was found that an increase in metal work function correlated with an increase in the barrier height. The surface state density of GaN was approximated to be very similar to CdS and almost a factor of ten less than GaAs.     

Electrical contacts for II-VI semiconducting devices

High resistivity II-VI semiconductors in general and CdTe and its associated materials like CdZnTe and CdMnTe in particular are suffering from ohmic contacting problem due to their high electron affinity and consequently large work function. Ni, Au, Pt and Pd have large work function and have possibility to match with the above materials. However, except Ni other materials have problems in large-scale commercial applications. In order to overcome the ohmic contacting problem to these semiconductors the following studies has been conducted in the text of the present paper. These are: (i) Work function engineering to modulate the work function through combination materials like, Cu, Au, Mo, W and Co. (ii) Introduction of a charge diluting intermediate semiconducting layer media in between the metal and CdTe to neutralize the bound polarized charges. These two aspects were applied in case of thin film CdTe-CdS solar cells to evaluate their contacting performances and their influences in solar cell parameters. Both cell performances and the contact characteristics of these contacting technologies were studied at depth and indicated their applicability in semiconducting devices.     

Development ot ohmic contacts for GaAs devices using epitaxial Ge films

Ohmic contacts to n-type GaAs have been developed using epitaxial Ge films on GaAs alloyed with Ni overlayers by solid-state diffusion at temperatures of 450/spl deg/C-650/spl deg/C. These contacts have applications to high reliability, high temperature microwave devices. Reflection electron diffraction of the Ge layers prior to deposition of the Ni overlayers reveals the presence of high quality single-crystalline films. Even after sintering, there is very little penetration of Ge into GaAs in the absence of Ni. With the presence of a Ni overlayer, significant interdiffusion between Ge and GaAs is revealed by Auger electron spectroscopic profiles. These results, together with the current-voltage characteristics of similar contacts prepared on p-type GaAs, indicate the presence of a Ge-doped n/SUP +/ layer at the Ni/Ge-GaAs interface. Ohmic contacts using epitaxial Ge films with Ta and Mo overlayers have also been investigated.     

Monolithic microwave amplifiers formed by ion implantation into LEC gallium arsenide substrates

A fabrication procedure for broad-band monolithic power GaAs integrated circuits has been demonstrated which includes formation of via holes through the 100-µm-thick GaAs substrate. A selective implant of²⁹Si ions into the GaAs substrate is used to dope the FET channel region to 1.2 × 10¹⁷cm^-3. The ohmic contacts are AuGe/Ni/Pt and the gates are Ti/Pt/Au. A 1.5-µm-thick circuit pattern is achieved using metal rejection assited by chlorobenzene treatment of AZ1350J photoresist. Using undoped Czochralski wafers of GaAs pulled from a pyrolytic boron nitride crucible, integrated amplifiers have been produced which deliver 28 ± 0.7 dBm from 5.7 to 11 GHz. These chips are 2 mm × 4.75 mm × 0.1 mm thick.     

用于半导体激光器热沉的金刚石膜/Ti/Ni/Au金属化体系的研究

提出了一种用于半导体激光器热沉的金刚石膜/ Ti/ Ni/ Au金属化体系.采用金属化前期预处理、电子束蒸镀技术和后续低温真空热处理,金属层和金刚石膜之间获得了良好的结合强度.AES分析表明Ti/ Ni/ Au金刚石膜金属化体系中,Ni层起到了良好的阻挡效果;XRD显示预处理过的金刚石膜,镀膜后经过6 73K,2 h低温真空热处理,Ti/金刚石膜界面形成Ti O和Ti C;RBS分析进一步证实该金属化体系在6 73K,1h真空加热条件下具有良好的热稳定性.采用完全相同的半导体激光器结构,金刚石膜热沉的热阻仅为氮化铝热沉的4 0 % .     

Improvement of the field emission characteristics of an oxidized porous polysilicon using annealed Pt/Ti surface emitter electrode

The field emission characteristics of an oxidized porous polysilicon were investigated with different annealing temperatures. Pt/Ti, Ir, and Au/NiCr were used as surface emitter electrodes, and Pt/Ti emitter showed highly efficient and stable electron emission characteristic compared with the conventional Au/NiCr electrode. Thin Ti layer played an important role in promotion of adhesion of Pt to SiO₂ surface and uniform distribution of electric field on the OPPS surface. Additionally, the Ti layer efficiently blocked the diffusion of emitter metal, which resulted in more reliable emission characteristics. Pt/Ti emitter annealed at 350 °C/1 h showed the highest efficiency of 3.36% at V_ps=16 V, which resulted from the improvement of interfacial contact characteristics of thin emitter metal to an oxidized porous polysilicon. Annealing above 400 °C showed that Pt/Ti and Ir emitter electrode were thermally more stable than Au/NiCr emitter.