Strained Transistor Cavities via Oxidizing Plasma Etch
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Solution Overview
Problem
The fabrication of advanced integrated circuits with strained channel regions using embedded silicon/germanium material faces challenges in achieving uniformity and reducing variability in transistor performance due to process-related non-uniformities, leading to potential device failures and yield losses, especially in high-k metal gate electrode structures.
Innovation Solution
The solution involves controlling the sidewall inclination of cavities formed prior to depositing the strain-inducing semiconductor alloy, using a plasma-assisted etch process with oxidizing species to achieve uniform growth conditions and reduce material loss, thereby enhancing deposition uniformity and transistor uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etch processes are used to form cavities for strain-inducing material, then cavity formation is achieved, but non-uniform sidewall profiles and material loss occur leading to poor deposition uniformity
Solution Approach 1:
The patent applies parameter changes by modifying the etch process conditions, specifically using a dual-frequency RF plasma source with optimized power settings and gas flow rates. The etch chemistry is changed from conventional CF4-based plasmas to a mixture containing oxygen or nitrogen, which fundamentally alters the etch mechanism to produce uniform sidewalls while minimizing material loss. This parameter change resolves the contradiction between achieving proper cavity shape and ensuring deposition uniformity.
Solution Approach 2:
The patent utilizes strong oxidants by incorporating oxygen-containing species into the plasma etch environment. The oxygen reacts with silicon atoms at the cavity sidewalls to form silicon oxide, which provides protective passivation that prevents excessive material loss and maintains uniform sidewall profiles. This oxidation mechanism directly addresses the shape control issue while improving the conditions for subsequent uniform material deposition.
2Reliability
If cavities are formed deeper to accommodate sufficient strain-inducing material, then strain effect is enhanced, but sidewall non-uniformity and material loss increase
Solution Approach 1:
The patent uses parameter changes to enable deeper cavity formation with controlled material loss. By adjusting the dual-frequency RF power ratio and optimizing the oxygen/nitrogen content in the etch gas, the etch process achieves higher etch rates with improved sidewall protection. This allows cavities to be formed deeper into the semiconductor substrate while maintaining uniform sidewalls and minimizing unnecessary material loss, thus preserving the strain effect.
Solution Approach 2:
The patent employs strong oxidants through the use of oxygen-containing plasma species that continuously passivate the cavity sidewalls during etching. This oxidation protection becomes increasingly important for deeper cavities, as it prevents the exponential material loss that would otherwise occur at greater depths. The oxidizing environment ensures that even deep cavities maintain uniform sidewalls, preserving the intended strain-inducing geometry.
3Ease of manufacture
If process conditions are relaxed to improve manufacturing ease, then fabrication complexity is reduced, but transistor uniformity and performance consistency deteriorate
Solution Approach 1:
The patent implements parameter changes that actually simplify manufacturing while improving uniformity. The dual-frequency RF plasma process with oxygen/nitrogen-containing gases provides inherently more stable and uniform etching compared to conventional single-frequency processes. This parameter optimization reduces sensitivity to process variations, making the fabrication process more robust and easier to control, thereby simultaneously improving ease of manufacture and transistor uniformity.
Solution Approach 2:
The patent uses strong oxidants to create a self-regulating etch process that is less sensitive to parameter variations. The oxygen-based sidewall passivation automatically adjusts to maintain uniform profiles, reducing the need for complex process control measures. This oxidation mechanism provides inherent process stability that improves transistor uniformity while simplifying manufacturing by reducing the number of corrective steps 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
This approach results in superior transistor uniformity and reduced yield losses, enabling the scaling of complex semiconductor devices with high-k metal gate electrode structures by maintaining consistent strain-inducing effects across the substrate, improving transistor performance and reliability.
Implementation Method 1
performing a plasma assisted etch process so as to form cavities in the active region
Implementation Method 2
using a plasma-assisted etch process with oxidizing species to achieve uniform growth conditions
Implementation Method 3
enhance the channel conductivity of the transistor elements by increasing the charge carrier mobility in the channel region... modification of the lattice structure in the channel region, for instance by creating tensile or compressive stress in the vicinity of the channel region so as to produce a corresponding strain in the channel region
Data Source
AI summary
When forming sophisticated semiconductor devices including transistors with sophisticated high-k metal gate electrode structures and a strain-inducing semiconductor alloy, transistor uniformity and performance may be enhanced by providing superior growth conditions during the selective epitaxial growth process. To this end, a semiconductor material may be preserved at the isolation regions in order to avoid the formation of pronounced shoulders. Furthermore, in some illustrative embodiments, additional mechanisms are implemented in order to avoid undue material loss, for instance upon removing a dielectric cap material and the like.