Strained Source-Drain Structure via Multi-Step Etching
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Solution Overview
Problem
The proximity limitation imposed by dry etching in semiconductor devices restricts the size of the implant region, hindering device performance due to the thickness of spacers formed on gate structures.
Innovation Solution
A method involving the formation of a high-performance strained source-drain structure through a multi-step etching process, including a dry etch, a wet etch, and a thermal etch, to create a recess with specific contours, followed by the deposition of Silicon-Germanium (SiGe) material, which allows for enhanced source-drain structure formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If dry etching is used to form the implant region, then the process is simple and direct, but the proximity limitation reduces the overall size of the implant region
Solution Approach 1:
The single dry etching process is segmented into three sequential etching steps: dry etching, wet etching, and thermal etching. Each step contributes differently to the final recess shape, with the dry etch providing the initial contour, the wet etch enlarging the recess with vertical sidewalls, and the thermal etch further enlarging it with angled sidewalls. This segmentation allows the implant region to exceed the spacer thickness limitation while maintaining process control.
Solution Approach 2:
The patent employs a composite etching approach combining three different etching chemistries and mechanisms (dry plasma etching, wet chemical etching, and thermal vapor HF etching). Each etching method has distinct characteristics that complement the others, enabling the formation of a complex recess profile that cannot be achieved with a single etching process.
2Manufacturing precision
If spacers are formed on the sides of gate structures, then gate definition is improved, but the proximity limitation is imposed on the implant region
Solution Approach 1:
Instead of forming the implant region first and then adding spacers (which would limit implant region size), the patent inverts the sequence by first forming spacers for precise gate definition, then using those spacers as reference structures to form a larger implant region that extends beyond the spacer boundaries through the multi-step etching process.
Solution Approach 2:
The patent transitions from a two-dimensional implant region constrained by spacer width to a three-dimensional recess structure with varying cross-sectional dimensions. The recess has different widths at different depths, with the upper portion being wider than the spacer width, thereby overcoming the proximity limitation in the lateral dimension while maintaining precise gate definition.
3Device complexity
If a single etch process is used to form the recess, then the process is simpler, but the recess contour cannot be optimized for source-drain structure formation
Solution Approach 1:
The etching process is divided into three distinct segments, each with specific process parameters and chemistry optimized for a particular portion of the recess profile. The dry etch creates the initial recess with controlled depth, the wet etch enlarges it with vertical walls, and the thermal etch further enlarges it with angled walls. This segmentation enables precise control over the final recess contour.
Solution Approach 2:
Each etching step targets a specific local quality or characteristic of the recess: the dry etch establishes the basic geometry and depth, the wet etch creates vertical sidewalls in the middle region, and the thermal etch forms angled sidewalls in the upper region. This local optimization of etching characteristics at different positions within the recess enables the complex multi-faceted contour required for optimal source-drain structure formation.
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 device boosting and drain-induced barrier lowering (DIBL) control by creating a novel strain source drain (SSD) profile closer to the channel, improving performance without the need for LDD implantation, thus overcoming the limitations of dry etching.
Implementation Method 1
A dry etch forms a recess with a first contour
Implementation Method 2
a wet etch enlarge the recess to a second contour
Implementation Method 3
a thermal etch enlarges the recess to a third contour
Implementation Method 4
A source-drain structure is formed in the enlarged recess having the third contour by depositing a semiconductor material such as Silicon-Germanium (SiGe)
Data Source
AI summary
A method for forming a high performance strained source-drain structure includes forming a gate structure on a substrate and forming a pocket implant region proximate to the gate structure. Spacers are formed adjacent to the gate structure. A dry etch forms a recess with a first contour; a wet etch enlarge the recess to a second contour; and a thermal etch enlarges the recess to a third contour. The source-drain structure is then formed in the recess having the third contour.