Dennis E. Kamenitsa

Beam parallelism in the 8250 medium current implanter

Small variations in beam angle across the wafer can affect the apparent dose uniformity and implant depth under conditions where channeling of the implanted ions is possible. The depth profile of the implanted species can vary significantly under certain crystal orientations even with beam angle variations as small as /spl plusmn/0.5 degrees. This leads to non-uniformity in the measurements made with thermal wave or sheet resistance probes. The 8250 uses a second-generation design of the electrostatic scanning and parallelizing lens to produce a horizontally scanned beam in which the average beam angle at any point on the wafer is typically the same within 0.2 degrees. This paper describes the method of measurement of the beam angles and shows the effect of small angle variation on implanted wafers.

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.

Beam energy purity in the Eaton NV-8200P ion implanter

Abstract SIMS analysis has been characterized as a tool for the study of energy contamination and used to investigate the contaminant energies most likely to be present in the NV-8200P. By purposely contaminating implants with known amounts of specific off-energy ions, we have been able to demonstrate that for the chosen combinations of desired energy and possible contaminant, the SIMS technique has a resolution of less than 1.0% for the higher energy conditions investigated and less than 0.05% for the lower conditions. All of the lower energy conditions used deceleration. Under these conditions the NV-8200P shows no indication of beam energy contamination. We present the results of the SIMS analysis and describe the technique used in this analysis.

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.

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.

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.

A technique for determining beam parallelism on a medium current implanter using the Therma-Wave Therma-Probe

A technique has been developed using the Therma-Wave Therma-Probe which allows the quantification of the angle of incidence of the ion beam to the wafer crystal structure in a parallel scanned implanter. A Therma-Wave value vs. incident angle calibration curve is developed from an electrostatically scanned implanter where the variation in beam incident angle varies significantly over the wafer and is well characterized. This calibration curve is then applied to maps of wafers implanted in a parallel scanned implanter, the Eaton NV-8200P. Changes in the measured Therma-Wave value are then correlated to variations in the ion beams angle of incidence to the wafer crystal structure. The sensitivities and accuracy of this technique, along with possible limitations, are discussed.

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.

Higher charge state ion beam purity in the Eaton medium current implanter

Abstract An Eaton NV-6200 operating with the new “SKM” modified hot filament Freeman ion source technology has been characterized using multiply charged ions of phosphorus, boron, and arsenic. The improvements in ionization efficiency of the Freeman-type ion source offered by the Eaton SKM modification provide substantially increased currents of doubly charged ions and useful amounts of certain triply charged ions. We have investigated the ion beam purity of these higher charge state beams; we present quantitative data which describe the energy purity and determine whether contaminants created by charge exchange reactions during transport through the beamline are present. The process quality of high charge state implants is investigated by examining the implanted dopant concentration profile using SIMS. The energy analysis and implant profile data demonstrate that the higher charge state ions generated by the SKM ion source are transported with useful ion beam purity to the target substrate.

Process control issues for ion implantation using large tilt angles

Abstract Using large tilt angles (7°–60°) and wafer rotational repositioning during ion implantation results in several effects which can compromise process control. These effects include: (1) tilt-related nonuniformity, (2) effective dose reduction from decreased ion flux density, (3) effective ion energy decrease, (4) effective dose reduction from dopant loss by surface scattering, and (5) effective surface film thickness increase. In this paper we characterize these effects and explain their physical basis.