Ziwei Fang

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.

Plasma doping for shallow junctions

In this article we review the characteristics of ultrashallow junctions produced by plasma doping (PLAD). PLAD is one of the alternate doping techniques being developed for sub-0.18 μm devices. Here, we describe results from a wide range of experiments aimed at the production of ultrashallow junctions. For the results shown here, a BF3 plasma was used to provide the dopant ions that were implanted into 150 and 200 mm Si substrates using wafer biases ranging from −0.14 to −5.0 kV. The ultrashallow junctions formed with this technique have been examined with both secondary ion mass spectrometry and electrical profiling techniques. Good sheet resistance uniformity, charging performance, structural quality, and photoresist integrity have been obtained. When PLAD is used in the production of sub-0.2 μm gate length p-metal–oxide–semiconductor field effect transistors, one finds subthreshold swing, off-state leakage, and hot-carrier reliability that are similar to beamline-implanted ones. In addition, higher dri...

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 doping implant depth profile calculation based on ion energy distribution measurementsa)

In traditional beamline implantation, the incident ion mass and energy are well known parameters and simulation programs are available to predict the implant profiles. In plasma based ion implantation, all ionized species present in the plasma are extracted and implanted by applying negative voltage pulses to the wafer. Therefore, prediction of implant profile is more complicated since it requires the knowledge of relative abundance of each ion species as well as their energy distribution prior to entering the wafer surface. This information is not readily available using conventional plasma characterization techniques because most of them measure plasma bulk properties. In order to collect the information needed for predicting plasma implant profiles, an ion mass and energy spectrometer is installed at the wafer level to allow in situ measurement of ion mass and energy distribution. In this paper, BF3 plasma in the pressure range from 30to250mTorr is studied. The relative flux and energy distribution of ...

Implant dosimetry results for plasma doping

A system for accurate and repeatable implant dose measurement for plasma doping architectures must circumvent a number of possible pitfalls. Such a system must accurately count ions crossing the pulsed plasma sheath to the wafer surface, while that surface is typically at high potential and immersed in the ambient plasma environment of the wafer. The effects of secondary electrons and the capacitive displacement current must be suppressed and the measurement itself must not alter the plasma or be affected by the high potential of the wafer bias. Traditional Faraday systems do not address these requirements. A new dose measurement system has been developed to meet the needs of pulsed plasma doping and the performance of that system for dose accuracy, repeatability, and uniformity is described.

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.

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

Plasma diagnostics in a pulsed plasma doping system, for semiconductor applications, have been carried out. An ion mass and energy analyzer was used to measure the ion species and ion energy distribution in the plasma doping process. Time-resolved Langmuir probe measurements were carried out to determine the plasma parameters. Preliminary results show that BF2+ is the dominant ion species in the BF3 plasma, and other molecular fragments also exist. The Langmuir probe data in Ar plasma indicate that during a 20 μs long implant pulse the plasma density is in the order of 109∼1010 cm-3 and the electron temperature is 0.4-14 eV. Between the pulses, the density decays exponentially at first and then reaches a nonzero value. The existence of electron beams, hot electrons, fast decay of electron temperature, and residual plasma were observed in both Ar and BF3 plasmas.

Contamination control in a pulsed plasma doping tool

Pulsed plasma doping offers a number of compelling benefits for low energy implantation, such as throughput, simplicity and low risk to wafers. The compromise to plasma-based doping systems is the absence of mass selection and increased sensitivity to system contaminants. To quantify the level of contamination present, secondary ion mass spectroscopy (SIMS) measurements of boron and arsenic implantation for sub-keV energies up to 5 keV are presented. Preliminary data show the depth profile of contaminants is consistent with surface contamination from nonionized sputtered material. Initial results for particulate contamination measurements are also described.

Process Control in Production‐Worthy Plasma Doping Technology

As the semiconductor industry continues to scale devices of smaller dimensions and improved performance, many ion implantation processes require lower energy and higher doses. Achieving these high doses (in some cases ∼1×1016 ions/cm2) at low energies (<3 keV) while maintaining throughput is increasingly challenging for traditional beamline implant tools because of space‐charge effects that limit achievable beam density at low energies. Plasma doping is recognized as a technology which can overcome this problem. In this paper, we highlight the technology available to achieve process control for all implant parameters associated with modem semiconductor manufacturing.