Selective Epitaxy Process Control via Alternating Deposition and Etching
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Solution Overview
Problem
Current selective epitaxy processes for depositing silicon-containing materials in electronic devices face challenges such as the need for precise temperature control, potential over-etching, and low growth rates, especially at temperatures below 800°C, which can lead to increased series resistance and uncontrolled nitridation reactions.
Innovation Solution
A method involving an alternating gas supply process where a substrate with a monocrystalline and dielectric surface is exposed to a silicon-containing deposition gas at low pressure, followed by an etchant gas at higher pressure to selectively form epitaxial layers, with controlled gas flow ratios and pressures to maintain selectivity and high growth rates while keeping the process temperature below 800°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high reaction temperature (above 800°C) is used to maintain selectivity and achieve adequate growth rates, then deposition selectivity and growth rate are improved, but thermal budget is exceeded and uncontrolled nitridation reactions occur
Solution Approach 1:
The patent employs periodic alternation between deposition and etching cycles. During deposition cycles, silicon is deposited on both monocrystalline and polycrystalline surfaces. During subsequent etching cycles, the polycrystalline layer is selectively removed while the epitaxial layer on monocrystalline silicon is preserved. This periodic action enables selective growth at lower temperatures without requiring continuous high temperature processing
Solution Approach 2:
The patent changes process parameters by alternating between deposition conditions (lower temperature, silicon precursor flow) and etching conditions (higher temperature, etchant gas flow). This dynamic parameter adjustment allows the process to achieve selective epitaxial growth at lower average temperatures while maintaining adequate growth rates through optimized cycle timing and gas flow rates
2Productivity
If low pressure is used during deposition to achieve fast growth rates, then deposition speed is improved, but process control and selectivity become more difficult
Solution Approach 1:
The patent uses periodic alternation between low-pressure deposition and higher-pressure etching cycles. During deposition at low pressure, fast growth rates are achieved. During subsequent etching at higher pressure, selectivity is enhanced. This periodic switching allows the process to benefit from both low-pressure fast deposition and high-pressure selective etching
Solution Approach 2:
The patent dynamically adjusts pressure between deposition and etching cycles. Pressure is lowered during deposition to maximize growth rate, then raised during etching to enhance selectivity. This dynamic pressure adjustment optimizes both productivity and manufacturing precision at different stages of the alternating cycle
3Manufacturing precision
If etchant gas concentration is increased to remove polycrystalline material, then selectivity is improved, but over-etching of substrate features occurs
Solution Approach 1:
The patent employs periodic alternation between deposition and etching cycles with carefully controlled timing. The etching cycle is limited in duration to remove polycrystalline material while preventing over-etching of the epitaxial layer. Subsequent deposition cycles replenish material on monocrystalline surfaces. This periodic action with controlled cycle ratios achieves high selectivity while minimizing substrate damage
Solution Approach 2:
The alternating deposition-etching process provides inherent feedback control. The deposition step replenishes material on desired surfaces, while the etching step selectively removes material from undesired surfaces. By adjusting the ratio and duration of deposition versus etching cycles, the process self-regulates to achieve the desired net selective growth without excessive etching
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 enables efficient and selective deposition of silicon-containing materials with varied elemental concentrations, reducing series resistance and minimizing substrate damage, while maintaining a fast deposition rate and controlling the process temperature effectively.
Implementation Method 1
exposing the substrate to a silicon-containing deposition gas and maintaining the pressure in the process chamber below about 50 Torr to form an epitaxial layer on the monocrystalline surface
Implementation Method 2
exposing the substrate to an etchant gas to maintain a relatively high etchant gas partial pressure and to etch the second material
Data Source
AI summary
Methods of selectively and epitaxially forming a silicon-containing material on a substrate surface contained within a process chamber are provided. In one or more embodiments, the pressure in the process chamber is reduced during deposition of material on the substrate and increased during etching of material from the substrate. According to an embodiment, process gases are flowed into the chamber through first zone and a second zone to provide a ratio of the amount of gas flowed to the first zone and the amount of gas flowed to the second zone. In one or more embodiments, the first zone is an inner radial zone and the second zone is an outer radial zone, and ratio of inner zone gas flow to outer zone gas flow is less during deposition than during etching. According to one or more embodiments, the selective epitaxial process includes repeating a cycle of a deposition and then an etching process, and an optional purge until the desired thickness of an epitaxial layer is grown.