Robert B. Simonton

Overview of the Eaton NV-8200P high beam purity, parallel scanning implanter

Eaton has developed a medium current ion implanter to meet the requirements of emerging advanced semiconductor processes. Hybrid scanning with a novel electrostatic scan angle correction lens is used to control beam incidence. To insure repeatability of processes requiring true beam incidence control, in-situ beam profiling and two axis divergence measurement provide input to the auto-tuning system. The direction of the mechanical axis of scan is always parallel to the wafer surface so that the distance from the wafer to the various optical elements is constant for all wafer tilt and twist combinations. This feature reduces variation in beam spot size and divergence across the surface of the wafer. Specific techniques for addressing all the various forms of beam and wafer contamination are also discussed. Two beam energy filters are utilized, including one immediately before the target, to maximize energy purity when multi-charged, decelerated, or molecular beam species are implanted. The vacuum system is designed to enhance beam purity and for ease of maintenance. The system provides useful beams over the energy range of 3 to 750 keV. The control system and ion source technology are based on that used in the companys high current implantation systems.

Flux Dependence of Amorphous Layer Formation and Damage Annealing in Room Temperature Implantation of Boron into Silicon

We implanted silicon 200mm wafers with 20keV 11 B + to a fluence of 5×10 15 atoms/ cm 2 using beam currents from 1-7mA, which produced flux of about 50-350µA/cm 2 . The implant temperature of all wafers rose no more than five degrees above room temperature, regardless of flux. Cross sectional TEM images (as-implanted) of the highest flux samples revealed a continuous amorphous layer from the implanted surface to a depth of about 530A. The high flux and 1 . We observed a strong dependence of as-implanted damage on boron flux, as previously reported by Eisen and Welch 2 . After 900°C, 20 sec RTA, the highest flux samples had 50% lower sheet resistance than the lowest flux samples, due to better activation, as observed in SRP. When a 1050°C, 15 sec RTA was employed, this sheet resistance and activation dependence on flux disappeared. Cross sectional TEM images revealed that the size and number of the Type II end of range defects , which were centered near the amorphous and crystalline as-implanted interface, in the highest flux samples were smaller than the Type 1 dislocation loops centered about the peak disorder in the lowest flux samples after RTA. SIMS and SRP profiles indicated that transient enhanced diffusion during the 900°C, 20 sec RTA may have been reduced in the highest flux samples. Based on these observations and on previous reports, we conclude that sufficiently high flux during room temperature boron implantation will produce a continuous amorphous layer with doses that are appropriate for p-type source/drain formation. The amorphous layer will produce improved activation and damage annealing behavior in subsequent RTA, particularly as the RTA temperature is reduced.

THE EFFECT OF DOSE RATE ON ION IMPLANTED IMPURITY PROFILES IN SILICON

Abstract In this paper is reported a systematic study of the effect of dose rate (ion beam current) on ion implanted impurity profiles in single-crystal silicon. A close examination of the effect of dose rate on as-implanted profiles reveals that for both boron and arsenic implantation, for beam currents ranging from 0.4 mA to 12 mA, dose rate has a small but clearly observable effect on channeling tails with higher beam currents producing shallower profiles. The effect is greater for on-axis (0° tilt/0° rotation) implants than for off-axis (8–9° tilt/30° rotation) implants. Lower mass (boron) implants have a more significant dose rate effect than do higher mass (arsenic) implants.

An accurate and computationally efficient semi-empirical model for arsenic implants into single-crystal (100) silicon

In this paper is reported an accurate and computationally efficient semiempirical model based on an extensive set of experimental data for arsenic implants into (100) single-crystal silicon. Experimental and model development details are given, and issues of the measurements are discussed. The newly developed model has explicit dependence on tilt angle, rotation angle, and dose, in addition to energy. Comparisons between the model predictions and experimental data are made in order to demonstrate the accuracy of this model.

An Examination of the Effect of Dose Rate on Ion Implanted Impurity Profiles in Silicon

The effect of dose rate on ion implanted impurity profiles in single-crystal silicon has been carefully and systematically examined. It is found that for both boron (light mass) and arsenic (heavy mass), the dose rate has a small but clearly observable effect on channeling tails with higher beam currents producing shallower profiles in the channeling tail. The effect is greater for on-axis (0{degree} tilt/0{degree} rotation) implantation than for off-axis (8 to 9{degree} tilt/30{degree} rotation) implantation, for which there is a clear indication of a dose rate effect for boron, but the effect is negligible for arsenic. Lower mass (boron) implants have a more significant dose rate effect than do higher mass (arsenic) implants. The possible mechanisms that result in this interesting dose rate effect are discussed.

Sources of variation in therma wave measurements of ion implanted wafers

In this article we report measurements of Therma Wave gauge repeatability over short, medium, and long time intervals, Therma Wave variations due to damage relaxation “decay”, and the effect that wafer temperature during implant has on the TW value. Measurements over short time intervals (several hours) were found to give the best gauge repeatability. We observed that under certain conditions the TW decay compensation mode may actually increase the noise level of the measurement, which has been reported by previous investigators [1,2]. Significant changes in Therma Wave units (∼ 5%) were observed for small changes (40°C) in wafer temperature during implant.

High Miller index channeling in silicon substrates

Abstract We investigated the effect of several high Miller index axial and planar channels on implant profiles of boron at several energies. Wafers were implanted with electrostatic scanning at orientations that resulted in the ion beam sweeping through alignment with these channels. Therma-Wave maps identified channeled and de-channeled locations, which were analyzed with SIMS and compared. We conclude that the {620} planar channels and the 〈12X〉 and 〈13X〉 axial channels, which may be encountered during implantation at 7° tilt, have no measurable effect on as-implanted boron profiles. However, the 〈125〉 axial channel at 24.1° tilt 18.4° twist produced measurable channeling effects.

Channeling control for large tilt angle implantation in Si 〈100〉

Abstract This investigation will present measurements of silicon 〈100〉 wafers, implanted with tilt angles in the range 7–60°, which identify combinations of tilt and azimuthal (twist) angles that avoid major channeling zones. The orientations identified in this study minimize channeling effects even for very low dose implantation. A stereographic projection demonstrates that all major variations in observed channeling behavior are explained by channeling in the six major (low Miller index) crystallographic axes and planes. The implanted wafers were characterized using modulated reflectance and SIMS measurements. We investigated the relative severity of ion channeling in major poles and planes and the effect of energy and species variations on channeling behavior. The physical basis for the observed variations is explained by employing the concepts of critical channeling angles and average distance traveled within a channel.

The Detailed Variation of Boron and Fluorine Profiles with Tilt and Rotation Angles for BF 2 + ION Implantation in (100) Silicon

Over 250 boron and over 250 fluorine profiles have been obtained from BF 2 + implants over a wide range of implant energies, doses, tilt angles, and rotation angles. A detailed study has been conducted on the boron and fluorine profile variations with the tilt and rotation angles over the available range of energies and doses. Channeling through a few low index axial and planar channels in (100) silicon has been found to account for the observed profile variations with implant angle. Tilt and rotation angle combinations which minimize channeling and ensure process uniformity have been deduced.

Modification of time dependence in thermal wave signal from ion implanted wafers

Abstract The thermal wave signal from ion implanted silicon wafers exhibits gradual change as a function of time after implant. This change in thermal wave signal can affect the long term repeatability of measurements made on implant monitors. This paper describes a method for reducing, and in many cases eliminating, the time dependence of the thermal wave signal. Wafers implanted with B+, P+, and As+ at doses ranging from 1011 to 1014 ions/cm2 and energies from 60–100 keV were subjected to l temperature anneals for varying times. The decay factor was studied as a function of anneal temperature and time. The effect of exposure of the wafers to UV radiation is also discussed.