William G. En

Comparison of experimental target currents with analytical model results for plasma immersion ion implantation

An analytical model of the voltage and current characteristics of a remote plasma is presented. The model simulates, the ion, electron and secondary electron currents induced before, during and after a high voltage negative pulse is applied to a target immersed in a plasma. The model also includes analytical relations that describe the sheath expansion and collapse due to negative high voltage pulses. The sheath collapse is found to be important for high repetition rate pulses. Good correlation is shown between the model and experiment for a wide variety of voltage pulses and plasma conditions. >

ANALYTICAL MODELING OF PLASMA IMMERSION ION IMPLANTATION TARGET CURRENT USING THE SPICE CIRCUIT SIMULATOR

Plasma immersion ion implantation applies a series of negative high‐voltage pulses to a target immersed in a plasma. An analytical model of the currents and potentials induced before, during, and after the negative bias in a planar geometry is presented. The effect of multiple pulses on the results is also studied. The model determines the time‐varying ion current, electron current, total current, total dose, and sheath thickness for a piecewise linear voltage pulse. The sheath collapse is found to be important for high repetition rate pulses. Implementation of the model is done in SPICE, a circuit simulator. Comparison with experimental data has demonstrated the accuracy of the model.

Modeling of oxide charging effects in plasma processing

An analytical model of oxide charging in plasma processing is presented. The model simulates the interactions of the plasma with semiconductor device structures on the wafer and the substrate bias to determine the charging induced in thin gate oxides. This model agrees well with experimental data for pulsed substrate bias. The simulation shows that a lower plasma electron temperature can reduce the charging damage. Well structures modulate the charging damage, with p wells charging more negatively and n wells charging more positively than an identical case without a well structure. Two‐dimensional charging effects such as plasma nonuniformities and antenna structures have also been successfully modeled. Antenna‐type device structures are shown to enhance the charging damage in both capacitor and well structures.

A new method for determining the secondary electron yield dependence on ion energy for plasma exposed surfaces

A new experimental method for determining the secondary electron yield for plasma exposed surfaces is described. From the measurement of the plasma condition and the total current generated when a voltage pulse is applied to a target material exposed to a plasma, the dependence of the secondary electron yield of that target on ion energy can be extracted. The secondary electron yield is determined by an analytical model of the plasma ion, electron, and displacement currents. Experimental results for an aluminum target correlate well with previous secondary electron measurements which used a traditional technique. Secondary electrons yield data of other materials: single crystal silicon, aluminum, titanium nitride, and silicon dioxide are also extracted.

Anomalous behavior of shallow BF3 plasma immersion ion implantation

Plasma immersion ion implantation (PIII) with BF3 and SiF4 plasmas is used to fabricate shallow P+/N junctions in Si. Exposure to the plasma and accelerated ions can lead to simultaneous etching and deposition on the substrate during implantation. A simple mathematical model for this process is presented and applied to the case of shallow implantation of BF3. Etching rates of SiO2 are seen to vary with power and pressure of the process gas. Etching rates of Si, SiO2, and CoSi2 are studied by spectrophotometry and Rutherford backscattering spectrometry. The roughness of Si substrates and SiO2 and CoSi2 films before and after PIII is monitored by atomic force microscopy.

Plasma immersion ion implantation reactor design considerations for oxide charging

The effects of wafer bias and plasma parameters on thin oxide charging during plasma immersion ion implantation (PIII) are simulated. The simulator has been shown to determine accurately the charging currents generated during PIII. The dependence of the plasma electron temperature, ion density and plasma uniformity on charging damage in metal oxide semiconductor capacitor structures is investigated. A lower plasma electron temperature is shown to reduce charging damage. Simulation and experimental results show that for a given voltage pulse waveform there is a range of bias repetition rates allowed by limiting the charging damage below a threshold value. Within this range there exists a switch-over repetition rate that minimizes the charging damage.

A plasma immersion implantation system for materials modification

Abstract A plasma immersion ion implantation (PIII) system is described which provides the capability to bridge the range between research exploration and commercial applications for materials modification of electronic materials, with a particular focus on layer transfer processes. The Silicon Genesis PIII system is capable of operation at high plasma densities (≈5×10 11 ions/cm 3 at the wafer) with high purity, mono-species ionization (>99% H + ions with a hydrogen plasma). The first generation of Silicon Genesis PIII systems is equipped to use 200-mm wafers (through an automated loadlock) and pulsed potentials up to 50 kV. Use of the mono-species ionization characteristic of the Silicon Genesis PIII system provides the capability to precisely vary the characteristics of surface layers through implantation of atoms and damage creation at well-controlled depths in the materials of choice. The Silicon Genesis PIII system is designed for efficient production of SOI and other layer transfer-generated materials and can be adapted for materials modification of more complex structures and work pieces.

Modelling of charging effects in plasma immersion ion implantation

Abstract The charging effects of plasma immersion ion implantation on several device structures is simulated. The simulations use an analytical model which couples the interaction of the plasma and IC devices during plasma implantation. The plasma model is implemented within the circuit simulator SPICE, which allows the model to uses all of the IC device models existing within SPICE. The model of the Fowler-Nordheim tunneling current through thin gate oxides of MOS devices is demonstrated, and shown how it can be used to quantify the damage induced. Charging damage is shown to be strongly affected by the device structure.

Nondestructive, in-line characterization of device performance parameters of shallow junction processes

Deep submicron transistor source–drain structures require a challenging combination of ultrashallow depth and low series resistance. Because these factors affect off-state leakage, drive current, and threshold voltage, it is important to maintain tight control of junction depth and depth uniformity over the full wafer diameter. A method for nondestructive, small area, high throughput characterization of ultrashallow junctions, called Carrier Illumination™ (CI) has recently been developed. It offers the potential for in-line monitoring of critical parameters associated with shallow junction processes. The CI method measures the active doping depth of shallow implants such as source/drain extensions on product wafers. Recent results demonstrate the ability of CI measurements to indicate junction depth variation due to implant dose, energy, and annealing temperature and time. This article presents correlation of in-line CI junction depth measurements to end-of-the line electrical properties of n metal–oxide–...

Effect of antenna structures on charging damage in PIII

Antenna structures are shown to enhance charging damage in MOSFET devices during Plasma Immersion Ion Implantation (PIII). The antenna structure increases the total charge per pulse induced on the floating gate oxide, enhancing the charge by up to several orders of magnitude. Using a coupled analytical model of the plasma, device structure and substrate bias, the dependence of the antenna structure on the induced charge per pulse is found. From the simulation, the phase space of antenna ratio and charge per pulse is mapped into three regions: no charging damage, device degradation, and oxide failure. Experimental results using three different antenna ratios (5 k:1, 11 k:1, 44 k:1) correlate well with simulation results.