Bon-Woong Koo

Plasma doping for the fabrication of ultra-shallow junctions

Pulsed plasma doping (P 2 LAD) is an alternate doping technique for the formation of ultra-shallow junctions in silicon wafers. In the P 2 LAD technique, a pulsed negative voltage applied to the silicon substrate creates a plasma containing the desired dopant species and also accelerates the positive dopant ions from the plasma toward the substrate, where they are implanted. BF 3 plasmas have been used to form p + -n junctions, while AsH 3 and PH 3 plasmas have been used for the formation of n + -p junctions. This paper will review the characteristics of ultra-shallow junctions formed by P 2 LAD. As-implanted and annealed profiles have been obtained by secondary ion mass spectrometry and compared with analogous profiles produced by B + , BF + 2 and As + ion implantation. Good sheet resistance uniformity, charging performance, structural quality, and photoresist integrity have been observed. In addition, junctions have been made which offer trade-offs between sheet resistance and junction depth that are better than those achieved with beamline implants. Finally, sub-0.2 μm pMOSFET devices have been fabricated with P 2 LAD and exhibit device characteristics that are similar to or better than beamline-implanted ones.

Ion energy distributions in a pulsed plasma doping system

Discharge parameters in a pulsed dc plasma doping system have been studied using measurements of time-resolved ion energy distributions, relative ion density, plasma potential, and electron temperature in BF3 and Ar plasmas during active discharge and afterglow periods. Negative plasma potentials are observed when using a hollow cathode to create a plasma while implanting at ultralow energies (<500eV). The kinetics of ion generation and decay in BF3 during the pulse on and off periods have been discussed.

Plasma diagnostics in pulsed plasma doping (P/sup 2/LAD) system

As semiconductor devices continue to shrink in size, demands for the formation of ultra-shallow junctions (USJ) are increasing. Pulsed plasma doping (P/sup 2/LAD) has emerged as a scaleable and cost effective solution to dopant delivery, since it is capable of high dose rates at ultra-low energies (0.02-20 kV). In P/sup 2/LAD, a pulsed plasma is generated adjacent to the silicon wafer using pulsed biases. Typical pulse widths range between 5 and 50 /spl mu/s, and pulse repetition rates are between 100 and 10000 Hz. Time-resolved Langmuir probe measurements showed that cold plasma is present during the afterglow period, which may play an important role in process control. Probe measurements also showed the presence of primary electron and electron beams during the initial pulse-on stage in both Ar and BF/sub 3/ plasmas. Ion mass and energy analysis indicated that BF/sub 2//sup +/ is the dominant ion species in the BF/sub 3/ plasmas, with BF/sup +/ as the second-most abundant ion species.

Plasma characterization of a plasma doping system for semiconductor device fabrication

Plasma characterization in a pulsed plasma doping system for semiconductor ion implantation has been carried out. The wafer to be implanted is placed directly on a platen in the pulsed plasma and then biased to a negative potential to accelerate the positive ion, from the plasma into the wafer. A wafer bias between 0 V and -4.5 kV with BF/sub 3/ source gas was used to implant boron ions into 200 mm-diameter silicon wafers. An ion mass and energy analyzer was used to measure the ion species and ion energy distribution during the plasma doping. The time-resolved Langmuir probe measurement technique was also used to determine the doping plasma conditions such as plasma density and electron temperature. The ion mass analysis result shows that BF/sub 2//sup +/ is the dominant ion species in the BF/sub 3/ bulk plasma and BF/sup +/ is the second important dopant species. The time-resolved Langmuir probe measurement shows the presence of energetic primary electrons, and the fast decay of electron temperature during the afterglow period is observed.

UpTime® Si2H6/SiF4 Mix for High Productivity Si Implant

Abstract- There is a need to improve the performance of Si+ implant dopant source for several emerging high dose low energy precision material modification implant applications. Beam current and source life obtained from SiF4, the currently available dopant source is not able to meet either the beam current or the ion source life desired to enable the adoption of such applications. This paper presents a novel silicon dopant gas source based on mixture of Si2H6 and SiF4, which delivers 15% higher beam current for Si in comparison to SiF4, thus enabling the process owners to implement these emerging Si implant applications. In addition this new dopant source mitigates halogen cycle effects associated with SiF4, offers long ion source life and reduces beam glitching which is a critical requirement for these applications. Additionally, the benefit of the UpTime® sub-atmospheric system used in the delivery of dopant gas mixtures to the implanter and enhancing the safety of implant operation is highlighted.

Ultra-low-energy BF/sub 3/ plasma doping characterization by ion mass and energy spectrometry

Summary form only given. Pulsed plasma doping (P/sup 2/LAD) provides controllable and cost effective solutions to dopant delivery in semiconductor device fabrication. In the P/sup 2/LAD system under investigation here, plasma is ignited with each negative voltage pulse applied to the cathode electrodes, including the silicon wafer. During the pulse-on period, positive ions are accelerated across the sheath and implanted within the wafer. This process has been studied using a Hiden EQP mass spectrometer installed within the pulsed electrode for in-situ detection of implant process parameters. Previous work, employing time-averaged mass spectrometry, indicated that BF/sub 2//sup +/ is the dominant ion species in the BF/sub 3/ plasmas, with BF/sup +/ as the second most abundant ion species. In this paper, we report time-resolved ion mass and energy distributions for various BF/sub 3/ doping voltage in the sub kilovolt range, at constant gas pressure, pulse frequency and duty ratio. These experiments have led to the better understanding of the gas phase phenomena, resulting in an improved optimization of the boron doping process.

Plasma diagnostics in pulsed plasma doping system

Summary form only given, as follows. As semiconductor devices continue to shrink in size, demands for the formation of ultra-shallow-junctions (USJ) are increasing. Pulsed plasma doping (P/sup 2/LAD) has emerged as a scaleable and cost effective solution to dopant delivery, since it is capable of high dose rates at ultra low energies (0.05-10 keV). When combined with rapid thermal annealing (RTA), laser annealing and other diffusionless methods, this technique is able to produce scaleable shallow doping profiles outside of the productive operating envelope of conventional ion implanters. In P/sup 2/LAD, a pulsed plasma is generated adjacent to the silicon wafer using pulsed biases, typically ranging between -200 V and -5.0 kV. Typical pulse widths range between 5 and 50 /spl mu/s, and pulse repetition rates between 100 and 5000 Hz. Time-resolved Langmuir-probe measurement showed that cold plasma is present during the afterglow period, which may play an important role for process control, e.g. charge neutralization and minimal etching. It also showed the presence of primary electron and electron beams during the initial pulse-on stage in both Ar and BF/sub 3/ plasmas while they are stronger in BF/sub 3/ plasma. Also, time averaged ion mass/energy analysis indicated that BF/sub 2//sup +/ is the dominant ion species in the BF/sub 3/ plasmas (>90 %), and BF/sup +/ is the second most abundant ion species. In this study, we propose time-resolved ion mass/energy measurements in various doping conditions.

Study of pulsed plasma doping by Langmuir probe diagnostics and ion mass-energy analyzer

Summary form only given. Pulsed plasma diagnostics in a plasma doping system for semiconductor device fabrication have been carried out. Pulsed plasma was generated adjacent to the silicon wafer using pulsed biases. The source gases were BF/sub 3/ and N/sub 2/. An ion mass and energy analyzer was mounted with a small aperture open to the plasma. Bias voltages between 0 and -5.0 kV were applied to the aperture to measure the ion species and ion energy distribution during the plasma doping. Time-resolved Langmuir probe measurements were used to determine the doping plasma conditions such as plasma density and electron temperature. Preliminary ion mass analysis results show that BF/sup 2+/ is the dominant ion species in the BF/sub 3/ plasmas, and BF/sup +/ is the second most abundant dopant species. The time-resolved Langmuir probe data indicate that during a 20 ps long implant pulse the plasma density is in the order of 10/sup 8/ - 10/sup 10/ cm/sup -3/ and the electron temperature is 2-15 eV. Between the pulses, the density decays exponentially at first and then reaches a non-zero value, which demonstrates the existence of residual plasma between pulses. The effects of electron beams, primary electron bombardment, secondary electron emission, and the fast decay of electron temperature during the afterglow period were observed. Increase of plasma density with cathode voltage and pressure, and decay with time were also observed.