Optimization of ohmic contact and adhesion on polysilicon in MEMS-NEMS wet etching process

This paper presents the optimization of polysilicon doping and metallization to form ohmic contact with etching resistance. Indeed, polysilicon doped by ion implantation and ohmic contacts are an important and interesting part of integrated circuit technology or MEMS and NEMS. LPCVD-polysilicon doping parameters, such as ion energy, dose, and annealing were investigated. In particular a superficial implantation realized after a deep implantation enables one to slightly decrease the polysilicon resistivity while the contact resistance is reduced. And ohmic contacts with wet etching resistance were realized by depositing the different metallization stacks. We demonstrate that ohmic contact pad Cr/Pt/Au has provided a good adhesion on LPCVD-polysilicon after wet etching.     

Effect of Pt barrier on thermal stability of Ti/Al/Pt/Au in ohmic contact with Si-implanted n-type GaN layers

We report the effect of the Pt barrier on the thermal stability of Ti/Al/Pt/Au in ohmic contact with Si-implanted n-type GaN layers. Ti/Al/Au (25/100/200 nm) and Ti/Al/Pt/Au (25/100/50/200 nm) multilayers were, respectively, deposited on as-implanted and recovered Si-implanted n-type GaN samples. The associated dependence of the specific contact resistance on the annealing time at various temperatures was compared. The long-term ohmic stability of a Ti/Al/Pt/Au multilayer in contact with a Si-implanted n-type GaN layer was much better than that of the Ti/Al/Au multilayer. This superior stability is attributed to the barrier function of the Pt interlayer. The Pt/Au bilayer can also passivate the propensity of oxidation for the conventional Ti/Al bilayer in contact with n-type GaN layers at elevated temperatures.     

退火参数对p型GaAs欧姆接触性能的影响

采用磁控溅射的方法在p型GaAs衬底上沉积了Ti/Pt/Au金属薄膜,研究了退火工艺参数(温度和时间)对p-GaAs/Ti/Pt/Au欧姆接触性能的影响。结果表明:p-GaAs上制作的Ti/Pt/Au金属系统能在很短的退火时间(60 s)内形成很好的欧姆接触。过分延长退火时间,并不能改善系统的欧姆接触性能。退火温度在400~450℃时均可得到较好的欧姆接触。当退火温度为420℃,退火时间为120 s时,比接触电阻率达到最低,为1.41×10–6.cm2。     

Low resistance, thermally stable Au/Pt/Ti/WSiN ohmic contacts on n+-InGaAs/n-GaAs layer systems

The electrical properties of the ohmic contact systems Au/Pt/Ti/WSiN and Au/Pt/Ti to n⁺-InGaAs/GaAs layers grown by metalorganic vapor phase epitaxy were investigated and compared to each other. The thermal stability properties of these contact systems were characterized by accelerated stress tests at elevated temperatures and by complementary thin film x-ray diffraction analysis to evaluate the microstructural properties of degraded and nondegraded structures. The goal of these efforts was to develop stable, homogeneous emitter contacts for power heterojunction bipolar transistors. It was found that for both contact systems the best (specific) contact resistance R_c (ρ _c) is about 0.05 Ωmm (2 × 10⁻⁷ Ωcm²) in the as-deposited state. Au/Pt/Ti/WSiN contacts show no degradation after aging at 400°C for more than 20 h. This is in contrast to standard Au/Pt/Ti contacts which significantly degrade even after short time annealing at 400°C. The good long-time stability of the Au/Pt/Ti/WSiN system is related to the advantageous properties of the reactively sputtered WSiN barrier layer.     

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.     

The ohmic contact formation mechanism of Au/Pt/Pd ohmic contact to p-ZnTe

The ohmic contact formation mechanism and the role of Pt layer of Au(500Å) Pt(500Å)/Pd(100Å) ohmic contact to p-ZnTe were investigated. The specific contact resistance of Au/Pt/Pd contact depended strongly on the annealing temperature. As the annealing temperature increased, the specific contact resistance decreased and reached a minimum value of 6×10^?6 Θcm² at 200°C. From the Hall measurement, the hole concentration increased with the annealing temperature and reached a maximum value of 2.3×10¹⁹ cm^?3 at 300°C. The Schottky barrier height decreased with the increase of annealing temperature and reached a minimum value of 0.34 eV at 200°C and it was due to the interfacial reaction of Pd and ZnTe. Therefore, the decrease of contact resistance was due to the increase of doping concentration as well as the decrease of Schottky barrier height by the interfacial reaction of Pd ZnTe. The specific contact resistances of Au Pd, Au/Pt/Pd and Au/Mo/Pd as a function of annealing time was investigated to clarify the role of Pt layer.     

Metallurgical stability of ohmic contacts on thin baseInP/InGaAs/InP HBT's

The metallurgical stability of ohmic contacts: Pt, Pt/Ti, Au/Ti, Au/Pt/Ti, and Au/Pt/Ti/W, on a 500 Å thick p⁺-InGaAs base of InP/InGaAs/InP HBTs have been investigated as a function of anneal temperature. All contacts were stable after a 300°C-30 s anneal. Pt contact failed at 350°C whereas Pt/Ti, Au/Ti, and Au/Pt/Ti contacts failed at 400°C. The failure mechanism was a collector leakage short owing to the penetration of Pt or Ti through the thin base. Only HBTs with Au/Pt/Ti/W contact were still functional after a 400°C anneal with no apparent shift in the turn-on voltage for the emitter and collector junctions     

非故意掺杂GaN上Ti/Al/Ni/Au欧姆接触研究

基于圆形传输线模型,研究了背景载流子浓度为71016cm3的非故意掺杂GaN与Ti/Al/Ni/Au多层金属之间欧姆接触的形成。样品在N2气氛中,分别经过温度450,550,700,800,900℃的1 min快速热退火处理后发现,当退火温度高于700℃欧姆接触开始形成,随着温度升高欧姆接触电阻持续下降,在900℃时获得了最低比接触电阻6.6106O·cm2。研究表明,要获得低的欧姆接触电阻,需要Al与Ti发生充分固相反应,并穿透Ti层到达GaN表面;同时,GaN中N外扩散到金属中,在GaN表面产生N空位起施主作用,可提高界面掺杂浓度,从而有助于电子隧穿界面而形成良好欧姆接触。     

Fabrication and characterization of nonalloyed Cr/Au ohmic contacts to n- and p-type In0.53Ga0.47As

Ion implantation and rapid thermal annealing have been used to selectively produce thin high carrier concentration n- and p-type layers on In0.53Ga0.47As, and nonalloyed ohmic contacts with excellent properties have been achieved by depositing layers of Cr and Au on the implanted regions. The Cr/Au metallization is used to produce ohmic contacts on both p-type and n-type material in the same deposition. A series of electrical test patterns based on the transmission line model and four terminal structure were used to characterize the contact resistance of both alloyed and nonalloyed ohmic contact metallizations on In0.53Ga0.47As. The nonalloyed contacts to n-type material are superior to conventional alloyed contacts made in this study, while the nonalloyed contacts to p-type material are a factor of 5 higher resistance.     

Au and non-Au based rare earth metal-silicide ohmic contacts to p-InGaAs

The aim of this study is to improve the electrical properties of ohmic contacts that plays crucial role on the performance of optoelectronic devices such as laser diodes (LDs), light emitting diodes (LEDs) and photodetectors (PDs). The conventional (Pd/Ir/Au, Ti/Pt/Au and Pt/Ti/Pt/Au), Au and non-Au based rare earth metal-silicide ohmic contacts (Gd/Si/Ti/Au, Gd/Si/Pt/Au and Gd/Si/Pt) to p-InGaAs were investigated and compared each other. To calculate the specific contact resistivities the Transmission Line Model (TLM) was used. Minimum specific contact resistivity of the conventional contacts was found as 0.111 × 10⁻⁶ Ω cm² for Pt/Ti/Pt/Au contact at 400 °C annealing temperature. For the rare earth metal-silicide ohmic contacts, the non-Au based Gd/Si/Pt has the minimum value of 4.410 × 10⁻⁶ Ω cm² at 300 °C annealing temperature. As a result, non-Au based Gd/Si/Pt contact shows the best ohmic contact behavior at a relatively low annealing temperature among the rare earth metal-silicide ohmic contacts. Although the Au based conventional ohmic contacts are thermally stable and have lower noise in electronic circuits, by using the non-Au based rare earth metal-silicide ohmic contacts may overcome the problems of Au-based ohmic contacts such as higher cost, poorer reliability, weaker thermal stability, and the device degradation due to relatively higher alloying temperatures. To the best of our knowledge, the Au and non-Au based rare earth metal-silicide (GdSi_x) ohmic contacts to p-InGaAs have been proposed for the first time.     

Power Device Packaging Technologies for Extreme Environments

Silicon carbide is a wide-bandgap semiconductor capable of operation at temperatures in excess of 300degC. However, high-temperature packaging to interface with the other elements of the electrical system is required. Die attach, wire bonding, and passivation materials and techniques have been demonstrated for use at 300degC. Transient liquid phase bonding has been developed with Au:Sn/Au, yielding high die shear strength after 2000 h at 400degC. Large diameter (250 mum) gold and platinum wire bonding was evaluated for top side electrical contact. Au wire was reliable after 2000 h at 300degC with Ti/Ti:W/Au pads over passivation on the SiC. However, Au wire on Ti/Pt/Au and Pt wire on both Ti/Tl:W/Au and Ti/Pt/Au exhibited passivation fracture with aging. Polyimide has been demonstrated for 2000 h at 300degC in air as a high-voltage passivation layer.     

一种基于Ag-Sn等温凝固的圆片键合技术

研究了用Ag-Sn作为键合中间层的圆片健合。相对于成熟的Au-Sn键合系统(典型键合温度是280℃),该系统可以提供更低成本、更高键合后分离(De-Bonding)温度的圆片级键合方案。使用直径为100mm硅片,盖板硅片上溅射多层金属Ti/Ni/Sn/Au,利用Lift-off工艺来形成图形。基板硅片上溅射Ti/Ni/Au/Ag。硅片制备好后,将盖板和基板叠放在一起送入键合机进行键合。键合过程在N2气氛中进行,键合过程中不需要使用助焊剂。研究了不同键合参数,如键合压力、温度等对键合结果的影响。剪切强度测试表明样品的剪切强度平均在55.17MPa。TMA测试表明键合后分离温度可以控制在500℃左右。He泄漏测试证明封接的气密性极好。     

Thermally stable Ge/Ag/Ni Ohmic contact for InAlAs/InGaAs/InP HEMTs

Excellent annealed ohmic contacts based on Ge/Ag/Ni metallization have been realized in a temperature range between 385 and 500/spl deg/C, with a minimum contact resistance of 0.06 /spl Omega//spl middot/mm and a specific contact resistivity of 2.62 /spl times/10/sup -7/ /spl Omega//spl middot/cm/sup 2/ obtained at an annealing temperature of 425/spl deg/C for 60 s in a rapid thermal annealing (RTA) system. Thermal storage tests at temperatures of 215 and 250/spl deg/C in a nitrogen ambient showed that the Ge/Ag/Ni based ohmic contacts with an overlay of Ti/Pt/Au had far superior thermal stabilities than the conventional annealed AuGe/Ni ohmic contacts for InAlAs/InGaAs high electron mobility transistors (HEMTs). During the storage test at 215/spl deg/C, the ohmic contacts showed no degradation after 200 h. At 250/spl deg/C, the contact resistance value of the Ge/Ag/Ni ohmic contact increased only to a value of 0.1 /spl Omega//spl middot/mm over a 250-h period. Depletion-mode HEMTs (D-HEMTs) with a gate length of 0.2 /spl mu/m fabricated using Ge/Ag/Ni ohmic contacts with an overlay of Ti/Pt/Au demonstrated excellent dc and RF characteristics.     

Effect of annealing temperature on Ti/Al/Ni/Au ohmic contacts on undoped AlN films

The Ti/Al/Ni/Au metals were deposited on undoped AlN films by electron beam evaporation. The influence of annealing temperature on the properties of contacts was investigated. When the annealing temperatures were between 800 and 950℃, the AlN-Ti/Al/Ni/Au contacts became ohmic contacts and the resistance decreased with the increase of annealing temperature. A lowest specific contacts resistance of 0.379 Ω·cm² was obtained for the sample annealed at 950℃. In this work, we confirmed that the formation mechanism of ohmic contacts on AlN was due to the formation of Al-Au, Au-Ti and Al-Ni alloys, and reduction of the specific contacts resistance could originate from the formation of Au₂Ti and AlAu₂ alloys. This result provided a possibility for the preparation of AlN-based high-frequency, high-power devices and deep ultraviolet devices.     

Long-term thermal stability of Ti/Al/Mo/Au ohmic contacts on n-GaN

Improved performance of the ohmic contacts on n-GaN has been demonstrated with the use of MoAu as the capping layer on TiAl metallization. Contact resistance as low as 0.13 Θ-mm was achieved in these ohmic contacts when annealed at 850°C for 30 sec. We have studied the long-term thermal stability of these contacts at 500°C, 600°C, 750°C, and 850°C, respectively. The Ti/Al/Mo/Au metallization forms low contact-resistance ohmic contacts on n-GaN that are stable at 500°C and 600°C after 25 h of thermal treatment. The ohmic-contact performance degrades after 10 h of thermal treatment at 750°C, while the contacts exhibit nonlinear current-voltage (I-V) characteristics after 1 h of thermal treatment at 850°C with the formation of oxide on the surface of the contacts accompanied by surface discoloration. The intermetallic reactions taking place in the contacts during the long-term thermal treatments were studied using Auger electron spectroscopy (AES), and the surface morphology was characterized using atomic force microscopy (AFM).     

Au/Ge/Pd ohmic contacts to n-GaAs with the Mo/Ti diffusion barrier

The influences of the As-outdiffusion and Au-indiffusion on the performances of the Au/Ge/Pd/n-GaAs ohmic metallization systems are clarified by investigating three different types of barrier metal structures Au/Ge/Pd/GaAs, Au/Ti/Ge/Pd/ GaAs, and Au/Mo/Ti/Ge/Pd/GaAs. The results indicate that As-outdiffusion leads to higher specific contact resistivity, whereas Au-indiffusion contributes to the turnaround of the contact resistivity at even higher annealing temperature. For Au/Mo/Ti/Ge/Pd/n-GaAs samples, they exhibit the smoothest surface and the lowest specific contact resistivity with the widest available annealing temperature range. Moreover, Auger electron spectroscopy depth profiles show that the existing Ti oxide for the Mo/Ti bilayer can very effectively retard Au-indiffusion, reflecting the onset of the turnaround point at much higher annealing temperature.     

Structural properties of alloyed Ti/Al/Ti/Au and Ti/Al/Mo/Au ohmic contacts to AlGaN/GaN

Two alloyed ohmic contact structures for AlGaN/GaN–Ti/Al/Ti/Au and Ti/Al/Mo/Au were studied. Both structures were optimized for minimum ohmic contact resistance. Structures grown on sapphire and SiC substrates were used to investigate structural properties of ohmic contacts to AlGaN/GaN. Ohmic contacts to AlGaN/GaN on SiC showed higher contact resistance values compared to contacts to AlGaN/GaN on sapphire. Ohmic contact metals were etched on samples after annealing. The alloyed interface was studied with backside illumination under an optical microscope. Alloyed inclusions associated with threading dislocations were observed on the surface. For the AlGaN/GaN on SiC sample the inclusion density was an order of magnitude lower than for the sample on sapphire. Conductive atomic force microscopy with carbon nanotube tip was used to investigate topography and conductivity profile of the surface after ohmic contact metal removal by etching.     

台面型InP/InGaAs PIN光伏探测器的p-InP低阻欧姆接触

研究了电子束蒸发淀积的非合金膜系Au/Pt/Ti/p-InP(2×1018cm-3)接触的物理特性,通过450℃、4 min的快速退火,获得了欧姆接触,其比接触电阻为7.3×10-5 Wcm2.接触电极退火后,采用离子溅射法淀积加厚电极Cr/Au.利用俄歇电子能谱(AES)进行深度剖面分析,表明Pt层能够相对有效地阻挡...     

n-GaN/Ti/Al/Ni/Au欧姆接触温度特性及微结构研究

主要对n-GaN/Ti/Al/Ni/Au欧姆接触在高温下(500℃)的特性进行了研究,发现在所测温度范围内,接触电阻率随测量温度的升高呈现出增加的趋势,接触开始退化。同时分析研究了在不同高温、不同时间范围内(24h)欧姆接触高温存储前后的变化,分析发现对于温度不高于500℃、在24h内存储温度升高,接触电阻率增加。当样品被施加500℃,24h的热应力后,其接触电阻率表现出不可恢复性增加。通过X射线衍射能谱分析了高温前后欧姆接触内部结构的变化机理,经过500℃的高温后,Ti层原子穿过Al层与Ni层原子发生固相反应。