Contact Reliability Research Articles

High Temperature Reliability of Refractory Metal Ohmic Contacts to Diamond

Several metallization schemes using refractory metals have been demonstrated to produce ohmic contacts to diamond via a solid‐state reaction process. This process utilizes existing microelectronic techniques and provides strongly adherent contacts which exhibit low contact resistance. Measurements of the long‐term reliability of Mo/Au contacts formed by this process on a type II b diamond crystal are presented here for the temperature range 450 to 625°C. The measurements consist of the resistance between two contacts as a function of isothermal annealing time over time intervals in excess of 130 h in a purified inert ambient. The Mo/Au contacts appeared to be stable and reliable at these high temperatures with no indication of deterioration or degradation of performance.

Electromigration in multilayer metallization: Drift-controlled degradation and the electromigration threshold of Al-Si-Cu/TiNxOy/TiSi2 contacts

Metallizations that incorporate a conductive layer beneath an Al alloy (multilayers) are necessary for the improvement in electromigration performance required by the continued feature size reduction and increased integration of microelectronic devices. Degradation of contact structures that utilize multilayer metallization will result from electromigration-induced voiding of the Al layer. A detailed understanding of the mechanisms of voiding is required for the accurate prediction of contact reliability. We have examined electromigration voiding in Al-Si-Cu/TiNxOy/TiSi2 multilayer contacts. Accelerated testing reveals that a TiNxOy/TiSi2 layer formed by rapid thermal anneal of Ti is an effective Si diffusion barrier at operating temperatures (<125 °C) and eliminates electromigration-induced leakage failures. Contact degradation occurs by increased resistance due to voiding of the Al-Si-Cu layer. Voiding involves drift-controlled edge displacement where the Al-Si-Cu layer migrates out of positively biased contacts, leaving the TiNxOy/TiSi2 layer intact. For 1-μm-diam contacts, the drift velocity has a significant lattice diffusion component and failure times are expected to far exceed operation lifetimes of devices. Additionally, evidence is presented for an electromigation threshold that eliminates voiding degradation for contacts connected by stripes.

A reliability model for connector contacts

Connector contacts have a typical end-of-life behavior during accelerated life testing. A model that predicts the change in resistance ( Delta R) for an aging contact is developed based on that behavior. The model shows that the duration of accelerated life tests can sometimes be reduced by up to 50%, resulting in substantial time and cost savings. Analysis of the model leads to several unexpected conclusions. For example, the evaluation of contact reliability, using Delta R as a parameter, does not agree with a time-to-failure approach in which each individual contact is assumed to have a specific failure time. The agreement is restored by the use of change in conductance ( Delta G) ratios. The use of Delta G by itself leads directly to the conclusion that contact reliability evaluated at some point in a contact's life explicitly depends on the resistance of the contact when it was put into use.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Estimating the reliability of electrical connectors

Some current approaches to estimating the reliability of electrical contacts and connectors are discussed. These approaches center on the statistical analysis of test data and address the active degradation mechanisms, the determination of appropriate environmental tests with corresponding acceleration factors and exposures, the statistical analysis appropriate for the test data, and the establishment of appropriate acceptance criteria. Each of these issues is treated separately. Multiposition connectors and Mil-Hdbk-217 are discussed. The authors deprecate reliability predictions based on generic databases and failure rate models, such as Mil-Hdbk-217, and describe instead what should constitute a reliability qualification program. >

Electroplating of Thick and Ductile Palladium‐nickel Alloys

Electroplating of palladium‐nickel alloy is becoming widely used, mainly for interconnection applications in the electronics industry and for decorative purposes. Enhanced hardness and brightness combined with superior wear properties compared with hard gold deposits make this alloy desirable in many applications. Like pure palladium, palladium‐nickel is frequently covered with a thin layer of hard gold to improve contact reliability; this results in a much less expensive and longer‐lasting contact material than hard gold on its own. In response to the growing demand, the authors have developed a palladium‐nickel alloy electroplating process that can plate alloys of varying composition (10–50 w % Ni) at current densities ranging from <5 mA/cm to >500 mA/cm. This process produces specular, hard and ductile deposits up to a thickness of ‐25 ?m. The new palladium‐nickel alloy electroplating process is described with regard to its chemistry, operating conditions, bath maintenance and regeneration, diagnostic measures, and properties of the electrodeposits.

Optimization of ohmic contacts for reliable heterostructure GaAs materials

We studied silver barrier ohmic (Ni/AuGe/Ag/Au) contacts to the GaAs based HEMT structures and observed strong dependence of the cleaning procedures on the ohmic con-tact resistance (Rc), its stability and reliability. The chemical profiles of the metal con-tacts before and after alloying were measured by SIMS. Samples cleaned with the com-bined plasma O2 and NH4OH process exhibited excellent results:R c ∼ 0.1–0.12 ohm-mm when alloyed in the temperature range of 440–540° C and remained stable when subjected to a 200° C and 600mA/mm stress condition for 1000 hr.

Reliability of Ohmic Contacts for AlGaAs/GaAs HBTs

ABSTRACTThe reliability of ohmic contacts to thin, heavily doped layers of GaAs is investigated. Pd/Ge/Au contacts to n-type GaAs display excellent electrical stability over extended periods of thermal stress. The contact resistance stays below 0.50Ω-mim during a 2500h, 280°C bake. Reactive ion beam assisted evaporation of Ti with N forms TiN which is introduced as a barrier layer in Pt/TiN/Ti/Au contacts to a thin p+ layer. The TiN layer allows greater process latitude in the sintering process and improves long term stability of the ohmic contact. The microstructure of the p-type contacts is examined with TEM and Auger profiling at different instances of the 2500h, 280°C bake and compared to the contact resistance measurements.

Reliability of Ohmic Contacts for AlGaAs/GaAs HBTs

ABSTRACTThe reliability of ohmic contacts to thin, heavily doped layers of GaAs is investigated. Pd/Ge/Au contacts to n-type GaAs display excellent electrical stability over extended periods of thermal stress. The contact resistance stays below 0.5Ω-mm during a 2500h, 280°C bake. Reactive ion beam assisted evaporation of Ti with N forms TiN which is introduced as a barrier layer in Pt/TiN/Ti/Au contacts to a thin p+ layer. The TiN layer allows greater process latitude in the sintering process and improves long term stability of the ohmic contact. The microstructure of the p-type contacts is examined with TEM and Auger profiling at different instances of the 2500h, 280°C bake and compared to the contact resistance measurements.

Growth of oxide films on the surface of Cu contact and its effect on the contact resistance property

AbstractFrom the viewpoints of contact reliability for small‐sized contact components, growth processes of the oxide film on the Cu contact surface were analyzed by studying the film thickness and formation of films. This analysis of the film was conducted in detail by ellipsometry which scarcely applied to the contact phenomena, in combination with an electrochemical reduction method. Moreover, the effect of the growth of the film on the contact resistance property was studied. As a result, in the oxidation by heating in air, Cu2O film grows mainly at the initial stage of the film growth. As the film grows around 1000 Å, CuO appears on the surface of Cu2O.In this stage, the contact resistance increases sharply and contact failure occurs. Furthermore, it was found that the velocity of growth of the film is slowed which corresponds Co each stage of the oxidation: the initial, the middle, and the latter stage. By application of ellipsometry to the analysis of the contact surface, the measurement of the film thickness together with the possibility of discrimination for the formation of the film by using changes of the optical constants of the film were clarified.

A Reliability Study of Relay Suitable for Surface Mount Process Using High-Temperature-Resistant Plastics

The behavior of gas emissions generated from plastic materials with high resistance to heat was studied by gas chromatography and gas chromatograph-mass spectrometry. The results show the effects of these gas emissions on contact reliability and suggest appropriate means for reducing such emissions. Also, as a result of examination of the organic carbon on the contact surfaces by electron spectroscopy for chemical analysis, it was found that gas emissions generated from high-heat-resistant plastics do not form any organic membranes on the contact surface.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A reliability study of relay suitable for surface mount process using high-temperature-resistant plastics

The behavior of gas emissions generated from plastic materials with high resistance to heat was studied by gas chromatography and gas chromatograph-mass spectrometry. The results show the effects of these gas emissions on contact reliability and suggest appropriate means for reducing such emissions. Also, as a result of examination of the organic carbon on the contact surfaces by electron spectroscopy for chemical analysis, it was found that gas emissions generated from high-heat-resistant plastics do not form any organic membranes on the contact surface.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Improved Contacts in Glass-Encapsulated Capacitors

Ceramic chip capacitors hermetically sealed into glass sleeves are used extensively in the electronics industry. However, glass-encapsulated capacitors can loose contact at the termination lead wire. To improve the contact reliability, a brazing operation is suggested that coincides with the present sealing temperature of 720°C. For this purpose a nickel coating over the conventional termination and a braze paste for use in nitrogen was developed. It was found that an electroplated nickel coating and a braze paste consisting of "Incusil 15" were most satisfactory. However, the brazing operation increases the dissipation factor from 0.6 percent for conventional glass-encapsulated capacitors to about 1.8 percent for brazed and sealed capacitors. To test the contact reliability, the capacitors were temperature cycled between 30 and 210°C for up to 1000 times. In this test seven of the 36 conventional glass-encapsulated capacitors failed through loss of contact, whereas none of the 180 brazed and sealed capacitors failed. This result is a significant improvement in the contact reliability of glass-encapsulated capacitors.

The Effect of Dust Contamination on Electric contacts

Dust seriously influences the reliability of electric contacts. Evidence shows that failure of electric equipment is closely relaterl to this problem. Scanning electron microscope (SEM) photos investigating the morphology and size distribution of the dust particles are shown. The composition of the particles was examined by X-ray energy spectroscopy (XES). Electric contact experiments show that the contact resistance was not only affected by the geometry of the surface but also strongly dependent on the normal force and electric current effect which causes nonlinear and irreversible contact resistance. Theoretical explanation for these phenomena is given by means of the plastic deformation which is due to the load or the joule heating that causes dust particle embedding into the surface. Increasing load or electric current is not an acceptable solution. Future work for dust research is also briefly discussed.

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.

Dependence of ohmic contact quality on Au-Ge alloy-thickness for n-type GaAs

Abstract As a contribution towards a better understanding of the complex process of ohmic contact formation with Au-Ge-Ni, and to optimize the contact quality, contact resistivity and sheet resistivity under the contact have been determined for various metallization thicknesses. The surface morphology was observed by SEM and the characteristics of the surface analysed by means of an electron microprobe analyser. Temperature measurements were carried out to discover the conduction mechanism, and the reliability of the contacts was assessed by high-temperature ageing

A TaSi x barrier for low resistivity and high reliability of contacts to shallow diffusion regions in silicon

It is shown that a thin TaSi x layer underneath the aluminium-based metallization considerably improves the contacts from the metallization to shallow diffusion regions in silicon. TaSi x with x < 2 acts as a barrier against aluminium and silicon diffusion at the contacts and thus impedes aluminium spiking as well as silicon precipitates in the contacts. Furthermore the silicon erosion induced by high currents is reduced by one order of magnitude. The contact resistance to n + -Si is decreased by a factor of 3–5. Finally the TaSi x provides a low barrier Schottky diode on lightly doped n-Si and p-Si.

Electrical performance of high density probe array for testing Josephson circuit chips

An assembly has been constructed and successfully evaluated for contacting 228-pad Josephson test chips. Miniature spring contacts mate with the 228, 100 μm diameter pads arranged on 200 μm centers in a double row about the edge of a 6.35 mm chip. Measurements have been made at 4.2K of contact reliability, resistance, self and mutual inductances, and current capacity. Experimental values of electrical characteristics compare well with computer simulations. This probe array is being incorporated into a non-magnetic cryoinsert for Josephson chip testing. The design uses materials such as pyrex, molybdenum, silicon, machineable ceramic, and aluminum to be consistent with a microgauss ambient magnetic field.

Contact Reliability Studies on Lead‐Salt Diode Lasers

Deleterious changes in the electrical and optical properties of lead‐salt semiconductor diode lasers have been traced to the diffusion of In into the surface layer of the lead‐salt crystals. New contacting methods have been developed to eliminate this mode of degradation for and diode lasers.

Sputtered Ruthenium as a Contact Material for Sealed Reeds

Cobalt-hardened gold is used as a contact material on remreed sealed contacts. A possible change of material for contacts of this type has been studied. The contact material investigated consists of a thin film of ruthenium over a thicker film of hardened gold. Both films are deposited by dc sputtering. The advantages of this contact finish compared to electroplated hard gold are reviewed: lower erosion per arcing operation, reduced arcing, and better resistance stability due to lower foreign element comtamination. The reliability of ruthenium contacts is related to that of hard gold contacts. A small change of contact geometry (gap and overlap) is needed to maintain the contact resistance at the level found with hard gold. The reliability is better in low-voltage (~5 V) level operation, due to the elimination of carbonaceous contaminants. The ruthenium contacts exhibit longer life in erosion tests involving cable discharges. Ruthenium contacts can be sealed off in a water free atmosphere so they could be used at below-freezing temperatures. Ruthenium contacts are able to withstand magnetostrictive scrubbing without sticking failures. However, the life of the ruthenium contact when switching current of 100mA (make and break) at 50V in a resistive load does not show significant improvement over hard gold. This is explained in terms of bridge transfer due to chattering during the make operation of the contacts.

A Degradation Mechanism for Ohmic Contacts in GaAs Devices

Investigations have been conducted to study how reliability of ohmic contacts in GaAs devices is affected by a metal which is in contact with the ohmic contacts, such as a heat sink metal or a bonding pad metal. Ti and Pt, besides Cu, have been found to enhance electrical characteristics degradation of the contacts in aging tests. Metallurgy of the contact region upon aging is analysed with the aid of electron probe micro-analysis and is correlated with change in the electrical characteristics of the contacts. The degradation mechanism has been confirmed wherein the highly doped. GaAs surface layer, which is essential for “ohmic” contacts, is gradually consumed, due to GaAs reaction with the metal which is in contact with the ohmic contacts.