Jay T. Scheuer

Advanced Charge Control for Single Wafer Implanters

Supplying low energy electrons to insure neutralization of implanted wafers requires an advanced charge control system. Some devices are extremely sensitive to low levels of metal contamination. We have designed a radio frequency (rf) plasma flood gun that eliminates the use of a hot filament. This makes this PFG more reliable and not susceptible to filament failures. We will present data showing that this advanced PFG has excellent charge control with an electron energy distribution that floods the wafer with an abundant supply of low energy electrons.

VIISta 810 dosimetry performance

Details of the dosimetry system for the Varian VIISta 810 medium current implanter are described. The system design provides improvements to the VSEA E-series implanters. The wafer scan velocity is variable, allowing a better match of the dose to the number of wafer scans, which in turn enables higher wafer throughput. Detailed vertical uniformity information is uploaded to the control system host computer enabling interrupted implants to be completed at another time, even on a different VIISta 810. Data is presented demonstrating the dosimetry performance for top off, glitched and high-tilt implants.

High-Uniformity Inductively Coupled Plasma Source With Magnetic Multicusp Confinement

A high-uniformity inductively coupled plasma source is presented. The plasma uniformity is improved with a magnetic multicusp structure that surrounds the plasma chamber. A picture showing the alternating bright and dark plasma regions along the perimeter of the plasma chamber-an effect of the magnetic confinement-is presented as well.

Reliability Tests of a Real Time Charge Monitor (RTCM)

Wafer charging effects that result from the ion implantation process are typically mitigated by employing a plasma flood gun to provide electrons to neutralize the positive ion beam as it strikes the wafer surface. As gate oxide thickness of semiconductor devices continues to shrink, control of the wafer charge‐up during ion implantation becomes critical. Varian Semiconductor Equipment Associates (VSEA) has designed and built a real time charge monitor (RTCM) for in situ measurement of the beam‐induced charging potential. Mounted close to the wafer and in the beam path, the RTCM continuously measures the deviation from quasi‐neutrality as the wafer passes through the beam. In this paper we present reliability tests of this device for high current implanters over varied implantation conditions and failure modes. When correlated with the yield of antenna device test wafers, it was found that the RTCM signal is a sensitive and reliable tool to predict charging damage to the semiconductor devices.

Optimized Autotuning for Single Wafer High‐Current and Medium‐Current Implanters

As semiconductor lot sizes decrease the impact of autotuning performance on productivity is increased. The dual magnet architecture of the VIISta series of single wafer ion implanters provides unparalleled defect prevention and beam control while presenting unique challenges for autotuning. We present data from field installations of high‐current and medium‐current VIISta implanters demonstrating excellent autotuning performance in terms of tuning speed and success rate.

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.

Reduction of charge exchange effects on the VIISta810

The VIISta810 medium current implanter can be used in a wide range of applications due to its good process performance, high productivity and low cost of ownership. However, tests have shown that at the elevated pressures characteristic of high energy, high dose applications, charge exchange effects can result in dose and uniformity issues. These pressures can be avoided by use of the end station pressure interlock, which, however, leads to a reduction in throughput. In moving from the VIISta810 to the VIISta810HP, additional cryo pumps were installed, one on the process chamber and one on the corrector magnet chamber, to improve the vacuum performance. Furthermore, the position of the closed-loop Faraday was moved upstream and an adjustable, conductance limiting aperture was installed. To test the repeatability and uniformity dependence on process parameters and photo resist coverage, 200 and 300 mm cross hair wafers were implanted with the VIISta810 and VIISta810HP vacuum configurations. Maximum energy and 80% of the maximum beam current for single and double charged ions of various species were applied. Sheet resistance measurements were performed and vacuum pressures and beam current variations were recorded. Test results have shown that the improvements lead to a distinct reduction of the charge exchange effects and their influence on dose. The upgraded vacuum configuration, provided good dose repeatability and uniformity on photoresist wafers, even in the high energy and high dose range, without reduction in throughput relative to bare wafers.