Pulsed Plasma Mode for Low Dose Implant Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
PLAD systems face challenges in achieving low dose, conformal doping with adequate process control and wafer-to-wafer repeatability due to high ion concentration and short implant times, particularly in applications requiring ion concentrations much lower than typical PLAD systems can provide.
Innovation Solution
Implementing a pulsed plasma mode in PLAD systems by varying RF power levels and bias voltages to reduce ion concentration and extend implant time, allowing for controlled low dose implantation and improved uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If continuous wave RF power is used to generate plasma in a PLAD system, then high ion concentration is achieved enabling rapid implantation, but the implant time becomes too short (about 0.5 seconds) to allow adequate process control and wafer-to-wafer repeatability
Solution Approach 1:
The patent applies periodic action by transitioning from continuous wave RF power to pulsed RF power with alternating high and low power levels. The RF power is pulsed at a frequency that creates periodic plasma density variations, allowing the plasma to maintain high ion concentration during high power phases while providing sufficient overall implant time through the cycling action. This periodic modulation resolves the contradiction by enabling both rapid implantation during high plasma density phases and adequate process control through the extended cyclic operation.
Solution Approach 2:
The patent implements dynamics by making the RF power level variable rather than static. The system dynamically adjusts RF power between high and low levels in response to plasma conditions, allowing real-time optimization of ion concentration. This dynamic control enables the system to maintain high productivity when needed while providing sufficient time for process control and repeatability through the variable power modulation, directly resolving the contradiction between fast implantation and reliable process control.
2Quantity of substance
If high concentration of charged species is used in the plasma, then high dose implantation (1E16 to 1E17 ions per square centimeter) is achieved in short time, but low dose applications (1E13 ions per square centimeter) require extremely short implant times that prevent adequate process control
Solution Approach 1:
The patent uses periodic action to modulate plasma density through alternating high and low RF power levels. During high power phases, high ion concentration is achieved for effective implantation, while low power phases provide time for process control and stability. This periodic variation in plasma density allows the system to achieve both high ion concentration when needed and sufficient implant time for process control by cycling between the two states.
Solution Approach 2:
The patent applies parameter changes by varying the RF power level between high and low states, which directly changes the plasma ion concentration. This parameter modulation allows the system to achieve high ion concentration (1E16 to 1E17 ions per square centimeter) during high power phases for effective implantation, while the low power phases provide extended time for process control, thereby resolving the contradiction between high ion concentration and sufficient implant duration.
3Quantity of substance
If high RF power is continuously applied to maintain plasma, then adequate plasma density is maintained, but dopant deposition occurs on the wafer surface during periods when bias voltage is off but plasma is on
Solution Approach 1:
The patent applies periodic action by synchronizing RF power pulses with bias voltage pulses. The RF power is pulsed at the same frequency and phase as the bias voltage, creating coordinated high and low power phases. During low RF power phases when bias voltage is off, plasma density is reduced, minimizing dopant deposition. During high RF power phases when bias voltage is on, dopant implantation occurs. This synchronized periodic action resolves the contradiction by maintaining adequate plasma density during implantation while reducing deposition during non-implantation periods.
Solution Approach 2:
The patent implements dynamics by making RF power variable and synchronized with bias voltage application. The RF power level dynamically adjusts in response to bias voltage state, being high when bias is on and low when bias is off. This dynamic control allows the system to maintain adequate plasma density during implantation periods while reducing plasma activity during non-implantation periods, thereby preventing dopant deposition while maintaining plasma density when needed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The pulsed plasma mode reduces ion dose per pulse, increases implant time, and enhances wafer-to-wafer repeatability, enabling conformal doping at lower ion concentrations, such as 1E13, by modulating RF power and bias voltage in PLAD systems.
Implementation Method 1
These gasses are energized into a plasma through the use of radio frequency (RF) or other forms of energy, such as by utilizing one or more RF antennas or coils
Implementation Method 2
When the platen is negatively biased, the positively charged species, or ions, from within the plasma accelerate toward the workpiece, thereby implanting the dopant species in the workpiece
Implementation Method 3
transitioning the CW RF power to a pulsed RF power after the first predetermined period to reduce a concentration of ions in the plasma, wherein at least a first RF power level and a second lower RF power level, are repeatedly generated, causing the plasma to vary in ion concentration as a function of time
Data Source
AI summary
Methods of decreasing the dose per pulse implanted into a workpiece disposed in a process chamber are disclosed. According to one embodiment, the plasma is generated by a RF power supply. This RF power supply may have two different modes, a first, referred to as continuous wave mode, where the RF power supply is continuously outputting a voltage. This mode allows creation of the plasma within the process chamber. During the second mode, referred to as pulsed plasma mode, the RF power supply outputs two different power levels. The platen bias voltage may be a more negative value when the lower RF power level is being applied. This pulsed (or multi-setpoint) plasma also assists in reducing dopant deposition on the wafer during the time when CW plasma is on but the bias voltage pulse is in the off-state. In a further embodiment, a delay is introduced between the transition to the pulsed plasma mode and the initiation of the implanting process. In yet another embodiment the plasma is generated at a location in the chamber more judicious to reducing the dose impinging on the wafer, thereby increasing the process time to allow adequate control of the process.