Robert W. Murto

Ultra-short pulse current-voltage characterization of the intrinsic characteristics of high-κ devices

An ultra-short pulse current–voltage (I–V) measurement technique has been applied to high-κ gate transistors to investigate the effects of fast transient charging. It is shown that the fast electron trapping may contribute to the degradation of transistor performance (i.e., low mobility) observed with direct current (DC) characterization methods, as well as pulse techniques in the tens of microseconds range and above. In particular, in the samples with significant electron trapping, the drain current in the saturation regime is shown to improve by up to 40% from its DC values when the characterization is performed with pulse I–V measurements in the nanosecond range.

Charge trapping and device performance degradation in MOCVD hafnium-based gate dielectric stack structures

Electron trapping data obtained with the pulsed I/sub d/-V/sub g/ measurement suggests that the trapping effectively occurs in the bulk of the high-k film rather than only at the interface of the high-k dielectric and interfacial oxide. This leads to less trapping in physically thinner high-k gate stacks. Carrier mobility of thinner hybrid stacks corrected for the inversion charge loss due to electron trapping is found to be approaching the universal high field electron mobility.

An investigation of species dependence in germanium pre-amorphized and laser thermal annealed ultra-shallow abrupt junctions

An earlier study of the activation and deactivation characteristics of p- and n-type dopant materials in shallow pre-amorphized silicon layers showed varying melt depth for a constant laser energy with varying dopant species. Possible causes of this variation could be attributed to either laser repeatability issues on early test equipment or a species-related laser absorption effects. Species dependence process windows are of serious concern for minimizing process complexity in CMOS wafer manufacturing. This paper reports the results of an investigation into the dependence of laser annealed junction depth in germanium pre-amorphized silicon layers on varying doses of boron, arsenic: and phosphorus dopant species. A 10 keV, 1/spl times/10/sup 15/ ions/cm/sup 2/ germanium implant was used to amorphize the silicon surface and set the laser annealed junction depth. Low energy implantation was used to introduce 1 keV boron, 2 keV phosphorus and 5 keV arsenic at doses of 1/spl times/10/sup 15/ and 3/spl times/10/sup 15/ ions/cm/sup 2/ into the amorphous region. Laser thermal annealing was performed at energies from 0.3 to 0.68 J/cm/sup 2/. Four-point probe and secondary ion mass spectrometry analysis data are presented.

Boron diffusion upon annealing of laser thermal processed silicon

In order to investigate the role of the end of range damage on dopant motion during post-laser thermal processing (LTP) anneals, a 15 keV, 1/spl times/10/sup 15/ ions/cm/sup 2/ Si/sup +/ implant was used to amorphize the silicon surface. Low energy implantation was used to introduce 1 keV B/sup +/ at a dose of 4/spl times/10/sup 15/ ions/cm/sup 2/ into the amorphous region. LTP was performed at energies from 0.625 to 0.825 J/cm/sup 2/. After LTP, conventional RTA was performed for 30 sec at temperatures between 700/spl deg/C and 1000/spl deg/C. SIMS analysis showed a significant pile-up of boron in the end of range region of the implant, as well as dose loss and enhanced diffusion of the boron. Qualitative agreement between the defect location and the gettered peak was observed but strong quantitative agreement between the density of the extended defects and the dose of gettered boron was not observed. At higher LTP powers (>0.75 J/cm/sup 2/) over-melting of the amorphous layer occurs, the density of EOR defects and the gettered boron dose decreases. In addition to gettering, post LTP annealing results in enhanced diffusion of the boron. It is unclear if this is transient enhanced diffusion (TED) but the enhancement is comparable to TED. The enhanced diffusion may result from the EOR damage however it is observed even for the highest LTP power. At this power the melting of the crystalline Si is observed and thus a significant fraction of the EOR region is removed. Thus the enhanced diffusion may be associated with quenched in interstitials after the laser melting process.

Boron Activation During Solid Phase Epitaxial Regrowth

To continue scaling dimensions of transistors, higher dopant concentration levels are needed for ultra-shallow contacts. Therefore studies of dopant activation have been performed in preamorphized silicon wafers with various boron implant conditions to determine the maximum achievable dopant concentrations after Solid Phase Epitaxial Regrowth (SPER) alone. In the first experiment a silicon piece was preamorphized with a 30 keV, 1×10 15 cm −2 and 90 keV, 1×10 15 cm −2 Si + implant followed by a 30 keV, 1×10 15 cm −2 B + implant. Solid phase epitaxial regrowth at 500 °C indicates that boron can be activated at low temperatures. Ultra Low Energy (ULE) implants were studied in the second experiment. Silicon wafers were implanted with 2.5 keV, 1×10 15 cm −2 Si + to amorphize and then B+ was implanted at 0.5 keV in the dose range of 1×10 15 to 9×10 15 cm −2 . Samples were annealed in the temperature range of 500 to 650 °C. High concentrations of boron make it difficult to fully regrow amorphous layers and thus yield marginal electrical properties. Much of the boron remains inactive, particularly at the higher dose implants. In both experiments Variable Angle Spectroscopic Ellipsometry (VASE) is used to measure amorphous layer thickness and Hall effect measures active boron dose. For the first experiment, Secondary Ion Mass Spectrometry (SIMS) data compares chemical dose to active dose during the regrowth process. Sheet resistance data is obtained from a four point probe for the ULE implant experiment.

Implementation of a universal exhaust solution for implanter fire prevention

In ion implanters, toxic and pyrophoric vapors pumped from the source region can leave deposits along the inner walls of the non-conductive pipe across the high voltage gap. The subsequent distortion in the electrical field across this gap can result in arcing across the high voltage gap that may ignite some of this residue. The ignition of this residue causes exhaust fires which result in possible damage to the ion implanter, the exhaust system, and the wafer fab itself. In August 1995, Texas Instruments sponsored a workshop with SEMATECH, Applied Materials, Eaten Corporation, and Varian Associates to determine a hardware-based universal solution to this problem. This report describes the objectives of the Implant Exhaust Workshop, the universal solution agreed to by the implanter manufacturers, and the implementation of these systems as a requirement on all new ion implanters purchased by Texas Instruments.