Angled Ion Implantation for Cavity Sidewall Shape Control
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Solution Overview
Problem
Existing methods for forming embedded structures in CMOS devices, such as eSiGe and eSi:C, face challenges in protecting extension regions during cavity formation, as the wet etch process can undesirably affect device properties by removing material from these regions.
Innovation Solution
The method involves directing ions at a non-normal angle of incidence to alter the etchability of cavity sidewalls, creating amorphized or boron-doped regions that protect extension areas from subsequent wet etching, allowing for the formation of embedded stressors with enhanced device performance by controlling the shape and etch rate of cavities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a wet etch process is used to form cavities with sigma-shaped sidewalls, then the cavity shape is improved for proximity to the gate, but the extension regions are undesirably etched away
Solution Approach 1:
The patent applies preliminary ion implantation to the extension regions before the wet etch process. This pre-treatment modifies the extension region material (e.g., amorphization or boron doping) to make it resistant to subsequent wet etching, thereby preventing material loss while allowing the cavity to achieve its desired sigma-shaped profile
Solution Approach 2:
The patent introduces local quality changes by selectively treating only the extension regions with ion implantation, while leaving the cavity regions untreated. This creates a spatially differentiated structure where extension regions become etch-resistant while cavity regions remain etchable, enabling selective protection during the wet etch process
2Reliability
If ions are directed at normal incidence to amorphize extension regions, then protection from wet etching is achieved, but thermal processing recrystallizes the amorphous regions losing protection
Solution Approach 1:
The patent changes the ion incidence angle parameter from normal (perpendicular) to oblique (angled). This parameter change fundamentally alters the ion penetration depth and damage distribution, creating a modified structure that remains resistant to wet etching even after thermal recrystallization, thereby maintaining protection reliability through composition stability
Solution Approach 2:
The patent creates a composite structure by introducing boron-doped regions into the extension areas through oblique ion implantation. This composite material (silicon with boron doping) provides enhanced etch resistance that is maintained after thermal processing, combining the benefits of structural modification with chemical doping for stable protection
3Manufacturing precision
If conventional ion implantation is used to protect extension regions, then etch resistance is improved, but additional process steps are required to maintain the amorphous structure
Solution Approach 1:
The patent performs the protective modification (oblique ion implantation) as a preliminary step before cavity formation and embedded structure growth. This single pre-treatment step establishes etch resistance that persists through subsequent thermal processing, eliminating the need for additional protective measures or process steps to maintain the protected state
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 effectively prevents the unwanted etching of extension regions, enabling the growth of embedded stressors like SiGe or Si:C within cavities while maintaining the integrity of the substrate, thereby improving transistor performance by reducing etch rate and preserving device properties.
Implementation Method 1
directing ions toward the substrate at a non-normal angle of incidence, wherein the ions strike an upper portion of a cavity sidewall
Implementation Method 2
forming amorphous regions 26 between gates 24 that overlap extension regions 18
Data Source
AI summary
A method of modifying a shape of a cavity in a substrate. The method includes forming one or more cavities on a surface of the substrate between adjacent relief structures. The method also includes directing ions toward the substrate at a non-normal angle of incidence, wherein the ions strike an upper portion of a cavity sidewall, and wherein the ions do not strike a lower portion of the cavity sidewall. The method further includes etching the one or more cavities wherein the upper portion of a cavity sidewall etches more slowly than the lower portion of the sidewall cavity.