Showing papers on "Contact resistance published in 1982"

Obtaining the specific contact resistance from transmission line model measurements

Abstract: In characterizing ohmic contacts using the transmission line model, it is necessary to make a measurement referred to as the contact end resistance, as a result of modification to the sheet resistance under the contact. In this article we show that this contact end resistance and the consequent specific contact resistance can be deduced from simple resistance measurements carried out between contacts on a standard, transmission line model test pattern.

The effects of contact size and non-zero metal resistance on the determination of specific contact resistance

Abstract: This paper presents theoretical and experimental results concerning two sources of error in the determination of specific contact resistance of ohmic contacts to semiconductor device structures that utilize circular test patterns with varying gap length. It is shown that the potential drop vs gap length data cannot be usually represented by a straight line and a non-zero metal overlay sheet resistance can significantly alter the effective contact resistance value.

A direct measurement of interfacial contact resistance

Abstract: A method is described for directly measuring interfacial contact resistance and estimating the degree of uniformity of the interfacial layer in metal-semiconductor contacts. A two-dimensional resistor network model is used to obtain a relationship between the specific contact resistance and the measured interfacial contact resistance for contacts with a homogeneous interfacial layer. Measurement results are given for 98.5% Al/1.5% Si and 100 % Al contacts on n-type silicon.

Characteristics of AuGeNi ohmic contacts to GaAs

Abstract: We have studied AuGeNi ohmic contacts to n-type MBE grown GaAs epitaxial-layer with doping in the (1016−1019) cm−3 range, and found several new effects: (a) Contact resistivity exhibit a weak dependence on carrier concentration (much weaker than 1/ND depencence); (b) We find evidence for a high resistivity layer under the contact at least several thousands angstroms deep, which dominate the contact resistance in most cases; (c) We find a peripheral zone around the contact, about 1 μm wide which differs chemically from the GaAs epi-layer; (d) SIMS analysis reveals a deep diffusion into the GaAs of Ni and Ge; (e) Correlation between density of GeNi clusters in the contact and the contact resistivity are found; (f) Temperature measurements justify that tunneling is responsible for the ohmic contact. We discuss also the validity of the transmission line method and the commonly accepted model of the contact.

A transmission line model for silicided diffusions: Impact on the performance of VLSI circuits

Abstract: In scaled technologies, performance improvements become increasingly limited by interconnect parasitics. The increased emphasis in the literature on low-resistance replacements for, or supplements to, polysilicon-gate technologies verifies the importance of parasitic limitations. Further, the role of the series source and drain resistance as well as contact resistance in limiting device performance has also been addressed by several authors. This role is further enhanced by the actual much more rapid increase in sheet resistivity with decreasing junction depth than previously assumed by other workers. In fact, it can be anticipated that metallurgical advances, such as silicides, will be required to compensate for the increased sheet resistance of source and drain diffusions. In the present work, a theoretical development of a transmission line model for a totally silicided diffusion is presented. Both the silicide and the diffusion sheet resistivities ρ S and ρ D , and the specific contact resistivity ρ c , are incorporated, unlike earlier models for contact holes only in which ρ S = 0. This model is applied to specific typical MOS structures, including single-section and three-section structures, to calculate the contact resistance contribution to total resistance. These results are used in conjunction with device equations addressing the device and circuit performance of small-geometry MOSFET's. Both n- and p-channel devices are considered as well as various scaling scenarios (constant field, constant voltage, etc.). These results show that for n-channel devices with a gate length of 1 µm, a-factor-of-two increase in circuit performance can be expected when using silicides. However, for p-channel devices, the expected performance gain as a result of using silicides is a factor of ten.

Volatile component loss and contact resistance of metals on GaAs and GaP during annealing

Abstract: This work is devoted to a mass spectrometric study of volatile component loss and in situ measurement of the resistance of metallized GaAs and GaP samples during heat treatment. Arsenic losses during heat treatment have been determined quantitatively with a quadrupole mass spectrometer. A relation was found between the arsenic loss and the specific contact resistance of the metallized sample. The associated activation energy was found to be similar to the case of thin film diffusion.

Platinum silicide ohmic contacts to shallow junctions in silicon

Abstract: Ohmic contact to shallow pn+ and np+ junctions in silicon were studied. Thin layers (∼200 A) of platinum were sputter deposited and reacted with the silicon substrate at 590 °C to result in the stable PtSi silicide. In a self‐registered process, aqua regia was used to etch the unreacted platinum. An Al‐0.9% Si alloy has been used for final metallization. A small contact area of 3×3 μm2 was chosen so as to be in accordance with the current level of integration. A four‐terminal Kelvin‐resistor structure has been utilized to accurately measure the contact resistance. The effect due to the dopant concentration was studied at the implant dose range of 1–8×1015 cm−2. Van der Pauw sheet resistance measurements, secondary ion mass spectroscopy, and Rutherford backscattering experiments were all performed in order to characterize the shallow junctions and the silicide‐silicon interface. Predeposition and in‐situ etching resulted in considerable improvement in the measured specific contact resistance. Values well w...

Method of making CMOS by twin-tub process integrated with a vertical bipolar transistor

Abstract: A process for forming high performance npn bipolar transistors in an enhanced CMOS process using only one additional mask level. The bipolar transistor is formed using a low dose blanket implant to form the base in the substrate n-well, then applying arsenic-implanted polysilicon to form the emitter. The emitter formation involves forming a blanket polysilicon layer over the wafer, then using the additional photomask to confine the subsequent arsenic implant to the emitter, n + and polysilicon contact regions, prior to application of aluminum metallization. The arsenic implanted polysilicon technique provides state-of-the-art bipolar processing as well as improved contact characteristics. The combined polysilicon-aluminum metallization improves step coverage, circuit reliability, and reduces the possibility of aluminum diffusion (spiking) through junctions. The n-type contact resistance is improved by virtue of being implanted with arsenic; the p-type contact resistance is controlled by the diffusion from the p + regions which dope the polysilicon during the emitter drive-in cycle.

Effect of Fretting on the Contact Resistance of Palladium

Abstract: The fretting of palladium contacts was studied at conditions relevant to their use in separable electronic connectors. Wrought, clad, and electroplated palladium mated to wrought palladium develop high contact resistance due to the formation of friction polymer. This can occur in ordinary room air which contains traces of organic air pollutants. Contact resistance changes diminish as force is increased. Static contact resistance measurements were made in small steps along wear tracks during fretting tests. It was found that the contact resistance increases were greatest at or near the ends due to the accumulation of polymer, and that the numbers of fretting cycles required to produce high contact resistance diminish sharply as track length is increased from 10 to 160 #m. Thin coatings of a polyphenyl ether contact lubricant significantly improve the stability of contact resistance, and contacts flooded with this fluid showed little degradation. This is attributable to its ability to disperse the polymer which is formed. Likewise, palladium contacts immersed in toluene, a polymer precursor commonly used in laboratory studies of friction polymerization, display stable contact resistance. These findings are compared to those of previous studies of the contact resistance of palladium during fretting, and it is shown that differences in interpretation of results are due to variations in the apparatus which were used.

Structural study of alloyed gold metallization contacts on InGaAsP/InP layers

Abstract: Specific contact resistance of gold metallization on In1−xGaxAsyP1−y has been measured as a function of composition from InP to In0.53Ga0.47As. The alloy formation of the contacts was investigated in the temperature range 130°–550°C, using temperature dependent in situ x‐ray diffraction. The thermodynamics of the solid state reactions are discussed. The electrical contact behavior can be explained in terms of the alloys which form at various temperatures. In the ternary Au/InGaAs/InP contact polycrystalline GaAs and a thin layer of Au3In2 form at lower temperatures (150°–250 °C) and remain stable up to 550 °C. This is consistent with the measured low contact resistance which is comparable to that of the Au/GaAs contact.

Thermal contact correlations

Abstract: The theoretical relationships for determining contact, gap, and joint conductances are developed for conforming rough surfaces for first loading. The dimensionless conductances are functions of the relative contact pressure, surface parameters, conductivity ratio, and a fluid parameter which depends upon several gas and surface characteristics. The proposed conductance correlations are supported quantitatively

Electrical Properties of Conductive Elastomer as Electrical Contact Material

Abstract: The conductive elastomer has both electrical and elastic properties. When the conductive elastomer is considered as an electrical contact material, it is possible to obtain conductive and elastic properties in one simple material. Therefore, the concept of metallic electrical contact can be changed to the elastomeric contact. Moreover due to excellent properties of facile shape formation, corrosion resistance, and air tight contact interface, the conductive elastomer is suitable for high density microsized connectors. However as it is very difficult to obtain as low a resistivity as in metals, the effectiveness of the elastomeric contacts is limited. The present study has been conducted to determine the electrical conduction mechanism and to find low resistivity materials. The specimen silicone rubber, in which electrical conductive particles such as carbon and metals were dispersed, was investigated. The resistivity versus conductive particle content, voltage versus current characteristics, resisitivity change in range of room temperature to liquid nitrogen temperature, and conduction mechanisms were discussed. In conclusion the conduction mechanism changes with the conductive particle content. For large content current paths were established by contact of particles, and for small content conduction electrons pass through the gap between particles by the Schottky conduction. Therefore, the resistance of the elastomer consisted of particle resistance, constriction resistance of the contact interface between particles, and the gap resistance.

Field Studies of Contact Materials: Contact Resistance Behavior of Some Base and Noble Metals

Abstract: The contact resistance of various metals was determined after exposure of from three months to four years in telephone central offices and in nonair-conditioned locations. The logarithm of median contact resistance was stable for some materials, but with most it increased on aging according to linear, parabolic, or logarithmic time relationships. The kinetics of contact resistance change depended on the intrinsic chemical reactivity of the material, the air pollutants which were present in the exposure site, and especially on the relative humidity. Contact resistance-force behaviors were affected also by the topographic and hardness characteristics of the metals. The overall ranking in central offices on the basis of stability of contact resistance from best to worst was 1) gold; 2)high gold-silver alloys, palladium, high palladium-silver alloys, 60Sn40Pb, and tin; 3) copper, high copper alloys, and nickel; and 4) silver. Where relative humidity was only slightly less well-contro11ed, as in a nonair-conditioned room in an urban central office building, except for gold the contact resistances of all materials were from one and two orders of magnitude greater after 40 months of exposure, and often displayed different kinetic behaviors. Palladium was exposed in a total of 18 sites and its contact resistance was found to be highly variable, even exceeding 1000 \Omega in less than 1 year when relative humidity was high and reactive chlorine-containing air pollutants were present. Pore corrosion of gold electrodeposits and creep of tarnish films from adjacent base metals did not occur in central offices except when the substrate was silver and the level of sulfiding pollutants was high.

Neutral electrode for radio-frequency surgery

Abstract: A neutral electrode is described for radio-frequency surgery, which electrode is used to dissipate the radio-frequency surgery current from a patient, with a contact resistance which is as small as possible. The neutral electrode consists of two electrode partial surfaces which are electrically insulated from one another in order to allow monitoring of the electrically conductive connection to the patient by means of a low-frequency monitoring current, using one monitoring circuit. The first electrode partial surface is provided as the main electrode for dissipating the radio-frequency surgery current, and thus has a contact resistance which is as low as possible. This main electrode is surrounded by a second electrode partial surface, which is used only as the monitoring electrode and consists, for example, of a plurality of small contact surfaces, connected in parallel, with a diameter of a few mm. The contact resistance of the monitoring electrode, which is thus not used for dissipating the radio-frequency surgery current, is orders of magnitude greater than the contact resistance of the main electrode to the patient's skin.

Contact resistance of polysilicon silicon interconnections

Abstract: Electrical contacts to poly are an important part of current silicon technology. In this letter we present a method of calculating the electrical characteristics for a planar poly to silicon contact. An interesting and significant result that is derived and discussed is a minimum contact resistance that is a strong function not only of the specific contact resistance of the contact interface but also of the contact geometry.

New explanation of ND-1 dependence of specific contact resistance for n-GaAs

Abstract: A new model of the ohmic contact to n-GaAs is proposed. It assumes that the contact resistance is due to the n+/n-barrier between the contact region (n+) and the semiconductor bulk (n = ND) as long as the bulk concentration is smaller than the effective density of states. Then the contact resistance is inversely proportional to the dopant concentration.

Low-resistance ohmic contacts to p-InP

Abstract: A new method for making low-resistance ohmic contacts to p-InP is described. Using layer-by-layer evaporated Au-Zn (25 wt% net Zn)/Cr/Au metallisation, specific contact resistance as low as 4.5 × 10?5 ?cm2 was obtained for p-InP with carrier concentration 2 × 1018 cm?3. The effects of annealing temperature and time on the contact resistances were investigated.

Au/Be ohmic contacts to p-type indium phosphide

Abstract: The use of evaporated layers of Au and Be for alloyed ohmic contacts to p -type InP with 10 17 –10 18 cm −3 doping has been examined. It was found that the Au/Be ratio influences the optimum heat-treatment time and temperature but not the value of the specific contact resistance. The minimum value of the contact resistance for the Au/Be contact, as well as other Au-based alloy contacts to p -type InP, was found to be inversely proportional to substrate doping. A possible explanation for this result is the formation of small, localized p + regions during the Au/InP alloying process.

A Transmission Line Model for Silicided Diffusions: Impact on the Performance of VLSI Circuits

Abstract: In sealed technologies, performance improvements become increasingly tilted by interconnect parasitic. The increased emphasis in the literature on low-resistance replacements for, or supplements to, polysilicon-gate technologies verifies the importance of parasitic limitations. Further, the role of the series source and drain resistance as well as contact resistance in limiting device performance has also been addressed by several authors. This role is further enhanced by the actual much more rapid increase in sheet resistivity with decreasing junction depth than previously assumed by other workers. In fact, it can be anticipated that metallurgical advances, such as silicides, will be required to compensate for the increased sheet resistance of source and drain diffusions. In the present work, a theoretical development of a transmission line model for a totally silicided diffusion is presented. Both the silicide and the diffusion sheet resistivities/spl rho//sub S/ and /spl rho//sub D/, and the specific contact resistivity /spl rho//sub c/, are incorporated, unlike earlier models for contact holes only in which /spl rho//sub S/ =0. This model is applied to specific typical MOS structures, including single-section and three-section structures, to calculate the contact resistance contribution to total resistance. These results are used in conjunction with device equations addressing the device and circuit performance of small-geometry MOSFET's. Both n- and p-channel devices are considered as well as various scaling scenarios (constant field, constant voltage, etc.). These results show that for n-channel devices with a gate length of 1 /spl mu/m, a-factor-of two increase in circuit performance can be expected when using silicides. However, for p-channel devices, the expected performance gain as a result of using silicides is a factor of ten.

Failure and Overheating of Aluminum-Wired Twist-On Connections

Abstract: In this investigation, twist-on connectors of the type used for branch circuit wiring in buildings have been tested with solid aluminum and copper conductors. The connector and conductor combinations tested are approved in both the United States and Canada. All of the twist-on connections were made in accordance with the connector manufacturers' instructions. Testing consisted of on-off cycling at 90 percent of rated current and 13 percent duty cycle. Failures, involving increasing connection resistance and abnormal heating, have occurred in less than a year in a substantial number of the aluminum-wired connections. The failures involve both the electrical conductor (EC) and alloy aluminum conductors. In contrast the copper-wired connections have low resistance and are stable. The temperature of many of the overheating aluminum-wired connections has been high enough to cause hazardous deterioration of the conductor insulation. The difference in performance between the copper and aluminum conductors is determined to be due to failure to achieve and sustain low resistance conductor-to-conductor contact in the aluminum-wired connections. This results in the greater portion of the current flowing through the connector spring rather than directly from conductor to conductor. The connector spring is plated steel and is not suited to be the major part of the current path. Degradation of the contacts between the aluminum wires and connector spring follows by several well-known mechanisms, leading to increasing connection resistance and the resulting heat generation and high temperatures.

Thin-film silicon solar cell

Abstract: PURPOSE:To obtain a thin-film Si solar cell, contact resistance between a metallic electrode and an amorphous Si layer therein is small, by previously forming the zone of the Si layer being in contact with the electrode by microcrystalline amorphous Si when the amorphous Si layer with a junction is formed on a light- transmitting insulating substrate through a transparent electrode and the metallic electrode is formed on the Si layer. CONSTITUTION:The light-transmitting insulating substrate 1 consisting of glass, etc. is coated with the transparent electrode 2 composed of an ITO film, an SnO2 film, etc., and the PIN junctions of the amorphous Si layers 3-5 consisting of a P type, an I type and an N type from the electrode 2 side are deposited on the electrode 2. The metallic electrode 6 is formed on the layer 5, but an N type microcrystalline amorphous Si layer 7 is interposed between the electrode 6 and the layer 5 without directly bringing the electrode 6 into contact with the layer 5. The layer 7 can be prepared easily by increasing high-frequency discharge power on the formation of glow discharge by a high-frequency input. Accordingly, the geometry factor of the layer 7 is enlarged with the increase of output power, and contact resistance is reduced.

Ion selective electrode

Abstract: PURPOSE:To lower the electrode resistance of a silver halide electrode by forming a film prepd by adding silver sulfide to silver halide on the surface of an electrode base body CONSTITUTION:Silver sulfide is mixed at 5-20mol% with silver chloride, and the mixture is heated to melt An electrode base body is dipped in this uniform molten liquid phase and is pulled up, the melt is then allowed to solidify at ordinary temp, thereby forming the film of silver chloride and silver sulfide on the surface of the electrode base body The silver halide electrode constituted in this way is low in resistance of the electrode per se and is the thin film in contact with an electrode base body 2 over the entire surface of the electrode and this results in decreased contact resistance between the electrode and a lead-out conductor and decreased overall electric resistance Practically, this silver chloride electrode is sensitive to the activity of the Cl-ions in a sample soln 1 The body 2 (copper) has the film of AgCl+Ag2S formed on the surface thereof, that is, an electrode layer 3 The liquid connecting part 5 of a standard electrode 4 is inserted in the soln 1 and the potential difference between the base body 2 and the lead wire of the electrode 2 is measured

Effects of Processing Methods on the Contact Performance Parameters for Silver-Tungsten Composite Materials

Abstract: A comparative study of electrical, mechanical, and microstructural properties of silver-tungsten contact materials (49 and 64 volume percent Ag) prepared by two different processing methods, namely press-sinter (PS) and press-sinter-infiltrate (PSI), is reported Even with the same elemental composition, tungsten particle size and distribution, the two different techniques of preparation have resulted in no difference in electrical contact resistance, minor differences in microhardness, transverse rupture strength and thermal expansion, and significant differences in contact life and arc erosion properties Oxidation weight gains at 600°C and 700°C are similar but the oxide layer morphology is quite different at 700°C The oxidation rate at 700°C is more than ten times of that at 600°C Silver tungstate is found to be absent at 700°C High contact resistance is due to the formation of porous tungsten oxides and a porous tungsten layer where silver is removed by the electric arc The arc erosion is dependent on crack formation and propagation which are not fully understood

Test contact resistance of dry circuit contacts

Abstract: In the testing of dry circuit contacts, a constant current source is applied to the contacts The open circuit voltage of the source is set to a predetermined maximum value and then the short circuit current at the contacts measured If the current value is below a predetermined maximum value, the voltage of the source is increased to bring the short-circuit current to the predetermined value The voltage drop across the contacts is then measured and the contact resistance calculated This arrangement makes adjustments to take into account variations in the test circuit, such as different lead lengths and other variables, without subjecting the contacts at any time to an open circuit voltage or short circuit current above maximum values