Self-Aligned Stressor Formation via Substrate Reflow
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Solution Overview
Problem
Existing methods for forming MOS transistors with stressors often separate the stressor regions from the channel, which can limit the effectiveness of stress application and carrier mobility improvement.
Innovation Solution
A method involving the formation of recesses in the substrate adjacent to spacers, with the substrate material reflowed to align the recess top with the spacer boundary, allowing for self-aligned stressor regions filled with materials like SiGe or SiC that apply compressive or tensile stress directly to the channel, eliminating the need for additional photomasks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If sidewall spacers are formed and ion implants are performed to create stressor regions, then stressor regions can be formed in source/drain regions, but the stressor regions become separated from the channel region, reducing stress application effectiveness
Solution Approach 1:
The spacer structure serves a dual function: it acts as both the stressor material and the self-aligning mask for defining the stressor region boundaries. The spacer material itself (e.g., SiGe or SiC) provides the stress, eliminating the need for separate stressor formation steps and ensuring precise alignment with the channel region.
Solution Approach 2:
The patent combines the functions of the self-aligning mask and the stressor into a single structure. The spacer that is traditionally used only for alignment purposes during ion implantation is instead made from stressor material, merging the alignment function and stress application function into one integrated component.
2Ease of manufacture
If conventional ion implantation methods are used to form stressors, then stressor regions can be created, but additional photomasks are required, increasing process complexity
Solution Approach 1:
The spacer structure serves as its own definition for the stressor region boundaries. The spacer width and position, already established from previous gate formation steps, automatically define where the stressor regions should be located, eliminating the need for additional photomask alignment steps.
Solution Approach 2:
The spacer performs multiple functions: it serves as the stressor material, acts as the self-aligning mask for defining stressor boundaries, and determines the precise location and dimensions of the stressor regions. This multi-functionality eliminates the need for separate photomask steps.
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 enhances carrier mobility and reduces parasitic resistance by ensuring stressor regions are closely aligned with the channel, improving transistor performance by 10% and reducing Rsd by 15% compared to traditional methods.
Implementation Method 1
The substrate material beneath the first portion of the first spacer is reflowed, so that a top portion of the first sidewall of the substrate material defining the recess is substantially aligned with a boundary between the gate dielectric film and the first spacer
Data Source
AI summary
A method includes providing a substrate comprising a substrate material, a gate dielectric film above the substrate, and a first spacer adjacent the gate dielectric film. The spacer has a first portion in contact with a surface of the substrate and a second portion in contact with a side of the gate dielectric film. A recess is formed in a region of the substrate adjacent to the spacer. The recess is defined by a first sidewall of the substrate material. At least a portion of the first sidewall underlies at least a portion of the spacer. The substrate material beneath the first portion of the spacer is reflowed, so that a top portion of the first sidewall of the substrate material defining the recess is substantially aligned with a boundary between the gate dielectric film and the spacer. The recess is filled with a stressor material.