Nathan W. Cheung

Extraction of Schottky diode parameters from forward current‐voltage characteristics

It is shown that by using the forward current density‐voltage (J‐V) characteristics of a Schottky diode, a plot of d(V)/d(ln J) vs J and a plot of the function H(J) vs J, where H(J)≡V−n(kT/q)ln(J/A**T2), will each give a straight line. The ideality factor n, the barrier height φB, and the series resistance R of the Schottky diode can be determined with one single I‐V measurement. This procedure has been used successfully to study thermal annealing effects of W/GaAs Schottky contacts.

Plasma immersion ion implantation—a fledgling technique for semiconductor processing

Abstract Plasma immersion ion implantation (PIII) is a cluster compatible doping and processing tool offering many inherent advantages over conventional beamline ion implantation. When first introduced in the late 1980s, the technique was primarily used to enhance the surface mechanical properties of metals. Recently, a substantial amount of research activities have focused on microelectronics and have led to a number of very interesting applications, such as the formation of shallow junction, synthesis of silicon-on-insulator, large area implantation, trench doping, conformal deposition, and so on. In this paper, we will review the principles of PIII, the dynamic sheath model for various kinds of plasma, reactor designs, recent applications in the area of microelectronics, as well as the future of PIII pertaining to semiconductor materials and processing.

Damage-free separation of GaN thin films from sapphire substrates

Gallium nitride thin films grown on sapphire substrates were successfully separated and transferred onto Si substrates using single 38 ns KrF excimer laser pulses directed through the transparent substrate at fluences in the range of 400–600 mJ/cm2. The absorption of the 248 nm radiation by the GaN at the interface induces rapid thermal decomposition of the interfacial layer, yielding metallic Ga and N2 gas. The substrate is easily removed by heating above the Ga melting point of 30 °C. Scanning electron microscopy and x-ray diffraction of the GaN films before and after lift-off demonstrate that the structural quality of the GaN films is not altered by the separation and transfer process.

Fabrication of thin-film InGaN light-emitting diode membranes by laser lift-off

Indium–gallium nitride (InGaN) multiple-quantum-well (MQW) light-emitting diode (LED) membranes, prefabricated on sapphire growth substrates, were created using pulsed-excimer laser processing. The thin-film InGaN MQW LED structures, grown on sapphire substrates, were first bonded onto a Si support substrate with an ethyl cyanoacrylate-based adhesive. A single 600 mJ/cm2, 38 ns KrF (248 nm) excimer laser pulse was directed through the transparent sapphire, followed by a low-temperature heat treatment to remove the substrate. Free-standing InGaN LED membranes were then fabricated by immersing the InGaN LED/adhesive/Si structure in acetone to release the device from the supporting Si substrate. The current–voltage characteristics and room-temperature emission spectrum of the LEDs before and after laser lift-off were unchanged.

InxGa1−xN light emitting diodes on Si substrates fabricated by Pd–In metal bonding and laser lift-off

Indium–gallium nitride (InxGa1−xN) single-quantum-well (SQW) light emitting diodes (LEDs), grown by metalorganic chemical vapor deposition on sapphire, were transferred onto Si substrates. The thin-film InxGa1−xN SQW LED structures were first bonded onto a n+-Si substrate using a transient-liquid-phase Pd–In wafer-bonding process followed by a laser lift-off technique to remove the sapphire growth substrate. Individual, 250×250 μm2, LEDs with a backside contact through the n+-Si substrate were then fabricated. The LEDs had a typical turn-on voltage of 2.5 V and a forward current of 100 mA at 5.4 V. The room-temperature emission peak for the InxGa1−xN SQW LEDs was centered at 455 nm with a full width at half maximum of 19 nm.

Proximity gettering with mega‐electron‐volt carbon and oxygen implantations

We have demonstrated that a buried gettering layer can be formed with a single MeV ion implantation without damaging the top device region. The strong gettering efficiency of carbon implant and its linear dependence on dose are confirmed. A surprising feature of the carbon implanted layers is that no extended defects are formed after annealing for implant doses up to 2×1016 cm−2 at 3 MeV, compared to a layer of small precipitates and dislocations in the case of oxygen implantation. It is suggested that the carbon‐related gettering centers are point defects or their clusters.

Plasma immersion ion implantation for ULSI processing

Abstract With a high ion-density plasma produced by electron cyclotron resonance (ECR) sources, the space charge region between the plasma and a negatively biased target can sustain a potential difference up to 50 kV, with an implantation flux as high as 10 16 /cm 2 s. Other unique features of this plasma immersion ion implantation (PIII) technique include: no ion mass selection, no beam transport optics, and the ion energy and angular distributions controlled by the plasma gas pressure and the applied bias waveforms. By adding a sputtering electrode into the plasma which is powered by a separate voltage supply (i.e., a triode configuration) the implantation chamber can also be converted into an ion-assisted physical vapor deposition system. In this review paper, we outline the physical mechanisms and operation modes of PIII and discuss applications of PIIIs unique features for ultra-large-scale integrated circuit fabrication. Recent successes of using PIII for conformal doping of nonplanar device structures, sub-100-nm p + /n junction formation, backside damage impurities gettering, and selective electroless plating of metal interconnects are presented.

Electromigration characteristics of copper interconnects

The electromigration characteristics of electroless plated copper interconnects have been investigated under DC and time-varying current stressing. A scheme for selected electroless Cu plating by using 150-AA Co as the seeding layer is reported. The Cu DC and pulse-DC lifetimes are found to be one and two orders of magnitude longer than that of Al-4% Cu/TiW and Al-2% Si interconnects at 275 degrees C, and the extracted Cu lifetime at 75 degrees C is about three and five orders of magnitude longer than that of Al-4% Cu/TiW and Al-2% Si, respectively. As previously reported for Al metallization, the Cu bipolar lifetimes were found to be orders of magnitude longer than their DC lifetimes under the same peak stressing current density because of the partial recovery of electromigration damage during the opposing phases of bipolar stressing.<<ETX>>

Projecting interconnect electromigration lifetime for arbitrary current waveforms

A vacancy-relaxation model is proposed. It predicts the DC lifetime, pulse DC (arbitrary unidirectional waveform) lifetime, pure AC lifetime, and AC-plus-DC-bias lifetime for all waveforms and all frequencies above 1 kHz. The predictions are verified by experiments and significantly raise the projected lifetimes beyond the widely assumed A/sub dc/ T/J/sub rms//sup m/. The pure AC lifetimes of aluminum interconnect are experimentally found to be more than 10/sup 3/ times larger than DC lifetime for the same current density. In addition, AC stress lifetimes are observed to follow the same dependences on current magnitude and temperature, for T >

Plasma immersion ion implantation for semiconductor processing

Abstract Plasma immersion ion implantation (PIII) is a technique which promises high dose rate implantation and compatibility with large-area processing. When a large negative bias is applied to the substrate which is immersed inside a high ion-density plasma, all ion species present will be implanted without ion mass selection. Innovations of this techniques include: implantation time independent of implantation area, capability to perform concomitant deposition and implantation, and simplicity of machine design and maintenance. This paper reports the modeling of PIII plasma dynamics and several demonstrated semiconductor processing applications such as plasma doping, subsurface material synthesis, ion beam mixing, microcavity engineering, and surface modifications. Several processing issues such as substrate charging and dosimetry will also be discussed.