Pulsed RF Selective Etching for Low-Damage Material Modification
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Solution Overview
Problem
Conventional etching processes in semiconductor manufacturing face challenges in achieving high selectivity and minimizing material deformation, particularly when dealing with constrained trenches and delicate structures, as they often result in substrate damage and reduced selectivity due to high plasma power and sputtering effects.
Innovation Solution
The use of a low-power RF plasma, pulsed at frequencies below 5,000 Hz with an RF bias power between 10 W and 100 W, and a pulsed DC power to generate priming particles, which reduces sputtering and enhances etch selectivity by up to an order of magnitude, allowing for precise material modification and selective etching of semiconductor substrates with exposed materials like silicon oxide, silicon nitride, and silicon carbide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional high-power plasma etching is used, then etching speed is improved, but substrate damage and material deformation increase
Solution Approach 1:
The patent applies pulsed plasma discharge where the plasma is turned on and off periodically. During the on-phase, etching occurs with controlled ion bombardment. During the off-phase, the substrate surface relaxes and any damaged layers are removed by subsequent chemical reactions. This periodic action allows faster etching than conventional continuous low-power methods while avoiding cumulative substrate damage from continuous high-power plasma.
Solution Approach 2:
The patent changes multiple plasma parameters simultaneously: power density, pressure, gas composition, and pulse duration. By optimizing these parameters together, the process achieves high etch rates through increased ion flux during the on-phase while controlling damage through reduced ion energy and shorter exposure time. The off-phase parameters allow surface recovery and selective chemical removal of damaged material.
2Duration of action of moving object
If conventional continuous plasma is used, then etching continues without interruption, but selectivity between materials decreases
Solution Approach 1:
The pulsed plasma process alternates between etching phases that remove material and relaxation phases that allow selective surface reactions. During the off-phase, volatile byproducts desorb and damaged surface layers are removed, exposing fresh material for the next etching pulse. This periodic cycle enhances selectivity by allowing different materials to respond differently to the repeated stress-relax cycles, with softer materials showing more pronounced relaxation effects.
Solution Approach 2:
Before the main etching pulses, the process includes a conditioning phase where the plasma is applied at lower power to prepare the surface. This preliminary action modifies surface chemistry and removes weakly bonded material, creating a more uniform starting surface for subsequent high-power etching pulses. This pre-treatment enhances selectivity by ensuring consistent surface conditions across different material regions.
3Quantity of substance
If high RF bias power is applied, then plasma density increases, but sputtering damage to delicate structures increases
Solution Approach 1:
The pulsed plasma process allows plasma density to build up during the on-phase at high power, providing sufficient reactive species for efficient etching. During the off-phase, the plasma density drops and ion bombardment ceases, allowing the substrate surface to relax without continuous sputtering damage. This temporal separation enables high plasma density when needed for etching while protecting structures during the relaxation phase.
Solution Approach 2:
The process dynamically adjusts plasma parameters including power, pressure, and gas flow rates during different phases of the pulse cycle. During the on-phase, parameters are optimized for high plasma density and etching rate. During the off-phase, parameters are adjusted to allow surface relaxation and removal of damaged material. This dynamic control enables the system to achieve high plasma density without permanent structural damage.
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
This approach improves etch selectivity and feature profiles by reducing sputtering and plasma-induced damage, enabling more precise control over the etching process and maintaining the integrity of materials intended to be preserved, thus enhancing overall semiconductor processing quality.
Implementation Method 1
forming a low-power plasma within a processing chamber housing the semiconductor substrate. The low-power plasma may be a radio-frequency ('RF') plasma, which may be at least partially formed by an RF bias power operating between about 10 W and about 100 W
Implementation Method 2
The RF bias power may also be pulsed at a frequency below about 5,000 Hz. forming a low-power plasma may also include utilizing a pulsed DC power. The pulsed DC power may be applied to a bipolar electrostatic chuck supporting the semiconductor substrate
Implementation Method 3
modifying a material on a semiconductor substrate. The substrate may have at least two exposed materials on a surface of the semiconductor substrate. The methods may include etching one of the at least two exposed materials on the surface of the semiconductor substrate at a higher etch rate than a second of the at least two exposed materials
Data Source
AI summary
Semiconductor systems and methods may include methods of performing selective etches that include modifying a material on a semiconductor substrate. The substrate may have at least two exposed materials on a surface of the semiconductor substrate. The methods may include forming a low-power plasma within a processing chamber housing the semiconductor substrate. The low-power plasma may be a radio-frequency (“RF”) plasma, which may be at least partially formed by an RF bias power operating between about 10 W and about 100 W in embodiments. The RF bias power may also be pulsed at a frequency below about 5,000 Hz. The methods may also include etching one of the at least two exposed materials on the surface of the semiconductor substrate at a higher etch rate than a second of the at least two exposed materials on the surface of the semiconductor substrate.