Ramp-up Rate Research Articles

Characterisation of Low Energy Boron Implantation and Fast Ramp-Up Rapid Thermal Annealing

ABSTRACTThe effects of ramp-up rate during rapid thermal processing of ultra-shallow boron implants have been investigated. Ramp-up rates were varied between 25 °C and 200 °C for two types of anneals: soak anneals and spike anneals. It was found that the ramp-up rate had very little influence on junction depth or electrical activation for both types of anneals. Spike anneals did produce shallower profiles than soak anneal for a comparable electrical activation and may be an option for future processes.

Simulation of External Ion Injection, Cooling and Extraction Processes with SIMION 6.0 for the Ion Trap/Reflectron Time-of-flight Mass Spectrometer

In this work we have developed a PC-based simulation to study ion injection, cooling and extraction processes for multiple ions in an trap/reflectron time-of-flight (IT/reTOF) system. This simulation is based upon SIMION 6.0 with user written programs in which a 3D collision model is used to describe ion--buffer gas molecule interactions. The results of various simulations describing the relation between the trapping efficiency for external injection of ions into the trap and the RF phase, and the effects of initial kinetic energy and ramp-up rate on dynamic trapping of externally produced ions are discussed. Further, single-pulsing and bipolar-pulsing schemes for ejecting ions from the trap are examined. The simulations show that bipolar pulsing can markedly improve the resolution. In the bipolar ejection mode the relation between resolution and the extraction voltages and RF ramp-off rate are studied.

The viscosity of germanium during substrate relaxation upon thermal anneal

Thin-film heterostructures experience structural relaxation when subjected to post-deposition thermal heat treatment. The rate of relaxation, elastic effects, and inelastic effects on the stress and deformation of the structure are determined by the physical properties of the materials, in particular, the solid-phase viscosity. During relaxation, movement of defects causes an increase of viscosity with time at a constant rate as these defects are annihilated. Experimental anneals have been performed on structures with polycrystalline silicon films on (111) germanium substrates, in which the substrate relaxes during thermal annealing. A numerical analysis of the experimental results has determined values for the viscosity and viscosity rate of (111) germanium wafers. In addition, four zones of the relaxation process have been identified, and results indicate that the increasing viscosity with time has a larger effect at lower furnace ramp-up rates.

A Novel Technique For Rtp Annealing Of Compound Semiconductors

AbstractWe introduce for the first time a novel rapid thermal processing (RTP) unit called ZapperTM, which has recently been developed by MHI Inc. and the University of Florida for high temperature thermal processing of semiconductors. This ZapperTM unit is capable of reaching much higher temperatures (>1500 °C) than conventional tungsten-halogen lamp RTP equipment and achieving high ramp-up and ramp-down rates. We have conducted implant activation annealing studies of Si+-implanted GaN thin films (with and without an AIN encapsulation layer) using the ZapperTM unit at temperatures up to 1500 °C. The electrical property measurements of such annealed samples have led to the conclusion that high annealing temperatures and AIN encapsulation are needed for the optimum activation efficiency of Si+ implants in GaN. It has clearly been demonstrated that the ZapperTM unit has tremendous potential for RTP annealing of semiconductor materials, especially for wide bandgap compound semiconductors that require very high processing temperatures.

A pulsed magnetic field test facility for conductors and joints

A pulsed magnetic field test facility is under construction at Massachusetts Institute of Technology for testing large scale cable-in-conduit superconductor and joint samples. Separate, demountable split-pair solenoid and saddle coils provide a combination of fields which can be either transverse or parallel to the sample axis. The solenoid and saddle magnets together can provide transverse peak fields as high as 8.4 T. Peak parallel fields of 6.6 T can be generated with the solenoid alone. Ramp-up rates of 1.5 T/s and ramp-down rates of 20 T/s are possible. Sample currents up to 50 kA are provided by a superconducting current transformer. The sample is connected to the transformer secondary through a pair of low resistance joints. Supercritical helium is provided to the sample at flow rates up to 20 g/s, pressures up to 1 MPa, and temperatures from 4.7 to 10 K. Programmable logic controllers provide coordination of the magnetic field, sample current, and helium flow rate and temperature in the sample. Sample and facility instrumentation signals are processed and data is stored on a workstation-based data acquisition system with comprehensive data reduction capability. Facility details and status are described.

Volume expansion and loss of sample due to initial self-heating in capillary electroseparation (CES) systems

The application of a high voltage, V, in capillary electroseparations following sample injection, can cause loss of analyte if the rate of thermal expansion of the liquid in the capillary (due to ohmic heating) is more rapid than the rate of electro-migration of the slowest moving analyte into the column. We show that the limiting condition for avoidance of this undesirable effect requires that the ramp-up rate for the applied voltage is below a critical value. This critical (maximum) value is given to a good approximation by a simple formula (Eq. (30)). Limiting values of dV/dt are in the region of 1000 V s−1 when the power loss in the capillary is around 3 W m−1 (e.g. with a field of 30,000 V m−1 and a current of 100 μA). A detailed mathematical analysis which takes full account of the thermal dependence of key variables, indicates that thermal explosion will occur at fields above a critical value (Eq. (21)). We recommend that commercial CES instrumentation incorporates manual or software led ramp-up voltage control.

Very thin CoSi2 films by Co sputtering

The structure, resistivity, and thermal stability of CoSi2 films ranging in thickness from ∼11 to 52 nm were investigated. Both the bulk and the surface components of the resistivity were extracted. The films exhibited good thermal stability. The thermal stability and the silicidation temperature which gave the minimum film sheet resistance were found to increase with the sputtered film thickness. The sheet resistance was independent of the ramp-up rate (3–20 °C/s), prolonged exposure of the Co film to air, and the presence of native oxides on the Si surface prior to Co deposition.

Novel magneto-optical recording materials: Bi-substituted garnet films

For future high density magneto-optical recording materials, a Bi-substituted garnet film ((BiDy)3(FeGa)5O12) is an attractive candidate since it has strong magneto-optic effect at short wavelengths less than 600 nm. The signal in read back performance at 500 nm using a garnet film can be an order of magnitude higher than a current rare earth-transition metal amorphous film. However, the granularity and surface roughness of such crystalline garnet films are the key to control for minimizing media noise.We have demonstrated a new technique to fabricate a garnet film which has much smaller grain size and smoother surfaces than those annealed in a conventional oven. This method employs a high ramp-up rate annealing (Γ = 50 ~ 100 C/s) in nitrogen atmosphere. Fig.1 shows a typical microstruture of a Bi-susbtituted garnet film deposited by r.f. sputtering and then subsequently crystallized by a rapid thermal annealing technique at Γ = 50 C/s at 650 °C for 2 min. The structure is a single phase of garnet, and a grain size is about 300A.

Magnetic and magneto-optic properties of rapid thermally crystallized garnet films (invited)

A new technique to improve the morphology of sputter-deposited bismuth garnet films for optical storage is discussed. This technique employs high ramp-up rate annealing in a nitrogen atmosphere, which leads to a smaller grain size and smoother surface than a conventional oven annealing or in situ crystallization process during film growth. By utilizing this technique, the films can be successfully crystallized to the grain size of about 200–300 Å, and a high coercivity (≳kOe). Multilayer films of garnets with other additions such as Cr and SiOx are also discussed. These multilayer films can provide better morphology and high coercivity.

Study of plasma disruptions and their suppression by a fast-ramping current in the STOR-1M tokamak

Minor and major disruptions, preceded by the growth of m = 2 and m = 3 modes, are observed during normal discharges on the STOR-1M tokamak, when the plasma safety factor on the plasma surface, q(a), becomes lower than 3 or with strong gas-puffing. It has been demonstrated that stable low-q discharges, with q(a) as low as 1.6 can be obtained and maintained for durations longer than the growth time for resistive tearing modes, if the plasma current is ramped up rapidly through a disruptive q region defined by 1.85 < q(a) < 2.1. The boundaries of the disruptive q region do not change when the maximum current ramp-up rate is varied between 0.5–2 kA μs−1.

Large m=3/n=l locked mode in JT-60 and its stabilization

An m=3/n=l locked mode has been observed in JT-60 at safety factors slightly below three during the current ramp-up phase of high plasma current discharges. The locked mode grows suddenly and there is no Mirnov oscillation just before the onset of this mode. The maximum plasma current of Ohmic discharges is restricted to approximately 2.4 — 2.45 MA by disruptions, which are preceded by a large m=3/n=l locked mode. The locked mode is stabilized by high power neutral beam injection. The stabilizing effect depends on neutral beam heating power, plasma density, plasma current ramp-up rate and divertor/limiter configuration.

Modelling of start-up assist by electron cyclotron waves for large-size tokamaks

This paper presents a model describing the plasma production in a tokamak by means of electron cyclotron microwave power and the initial ohmic current ramp-up. A zero-dimensional code is applied to the case of large-size, high magnetic field tokamaks and, in particular, to the case of the INTOR/NET tokamak. It is shown that the r.f. plasma can be produced and heated to temperatures of a few hundred eV with power densities of the order of 50 kW/m3. Detailed results are given for a case in which 4 MW of electron cyclotron power is used to create a plasma whose steady-state temperature is well above the impurity radiation barriers. For the plasma inductance assumed and a current ramp-up rate of 0.625 MA/s, the ohmic current can be initiated in such a plasma with a total-loop voltageVL<20 V. The resistive contribution to the loop voltage is of the order of 1 V.

Plasma current ramp-up and Ohmic-heating transformer recharging experiments using lower-hybrid waves on a tokamak

Plasma current ramp-up by lower-hybrid waves in a high-density regime (n̄e≳1×1019 m−3) is investigated on the Alcator C tokamak [Nucl. Fusion 25, 1127 (1985)]. A time-averaged conversion efficiency (Ẇ−Pext)/Prf of over 15% has been obtained at a density of n̄e ≂1×1019 m−3, where W is the poloidal field energy and Pext is the external inductive power. The maximum conversion efficiency obtainable is lower at higher densities. Ramp-up rates of over 1 MA/sec were obtained when rf current ramp-up is applied to an Ohmically maintained plasma. Lower-hybrid current drive can also be used to maintain the plasma while recharging the Ohmic-heating transformer. The conversion efficiency of 10% obtained during recharging is found to be comparable to that obtained during ramp-up under similar conditions.

Lower hybrid current drive in the presence of a DC electric field

A code for numerical modelling of lower hybrid current drive has been developed which takes into account the DC electric field. The model is based on the Fokker-Planck equation, the plasma circuit equation and the power balance equations. The flow of power supplied by the RF waves and the OH coil (transformer) is investigated. Also studied are the current drive efficiency and the ramp-up efficiency, which is the ratio of RF energy to plasma electromagnetic energy. The ramp-up rate of the plasma current is slower and the RF power required for recharging the OH coil is higher when the DC electric field is taken into account than when it is neglected. The simulation results agree well with the results of Alcator C experiments. The RF energy and the time for ramp-up and recharge required for the next-generation tokamak are estimated.

Plasma current generation and sustainment by electron cyclotron waves, in the WT-2 tokamak.

By injection of microwave power ${P}_{\mathrm{EC}}$ near the electron cyclotron (EC) frequency into an Ohmically heated (OH) plasma in the WT-2 tokamak after OH power is shut off, the plasma current is sustained and ramped up by the EC wave only, without OH power. Here, EC-driven current is generated by EC heating of the suprathermal electron beam in OH plasma. Further, when ${P}_{\mathrm{EC}}$ is injected into plasma sustained by lower-hybrid- (LH-) driven current, the plasma current and its rampup rate increase. Here, EC-driven current is generated by EC heating of the mildly relativistic electrons in LH-driven plasma.

Oxide Growth Using the Water-Wall Arc Lamp

ABSTRACTThe uses of Rapid Thermal Annealing or Rapid Thermal Processing (RTP) have been expanding beyond the original post implant annealing. RTP has been used to reflow low temperature oxides (PSG or BPSG), anneal silicides and to sinter contacts. One application of RTP which is beginning to receive attention is the growth of oxides or nitrides of silicon.This paper will examine the use of a commercial rapid thermal processing system based on a very high power water-wall DC arc lamp to grow oxides on silicon wafers. The work includes a study of the growth rates of oxides at different temperatures. Direct feedback control of wafer temperature and high ramp-up and cool-down rates are used to minimize the effects of temperature errors or “tails” in the temperature/time profiles. Ellipsometry is used as the primary measurement tool to characterize the oxide films.In addition to using a pure, dry oxygen atmosphere, several oxygen-argon mixtures are used. The effects of atmosphere on the growth rate of the oxide film are reported.In order to become a practical application of RTP, oxide growth must be accomplished uniformly and reproducibly. These characteristics are machine-dependent. The uniformity of films grown in this system are discussed. The growth of oxide films and the uniformity measurements are used as an indirect technique to characterize the uniformity of the system. The reproducibility of film thickness is also examined.