Gate Hard Mask Profile for Stable Source/Drain Trench Formation
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Solution Overview
Problem
The integration circuit (IC) industry faces issues with epitaxial merge between source/drain features due to over-etching, which causes instability in isolation structures and affects yield and wafer acceptance testing, primarily because existing methods result in excessive global etching that breaks down these structures.
Innovation Solution
The solution involves enlarging the hard mask profile to block excess global etching gas, forming source/drain trenches shallower and preventing breakage of isolation structures, thereby preventing undesired epitaxial merge by designing a Gate-All-Around (GAA) field effect transistor structure with a multi-etch process that includes a patterned hard mask and dummy gate layer with an uneven profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If existing etching methods are used to form source/drain trenches, then source/drain features can be formed, but over-etching occurs causing isolation structures to break off and become unstable
Solution Approach 1:
The patent applies preliminary action by forming a mandrel structure with protruding portions before the etching process. These protruding portions serve as pre-positioned barriers that prevent over-etching into the isolation structures. The mandrel is formed in advance with specific geometric features (protruding portions extending beyond the gate electrode edges) that will control the etching depth and protect isolation structures during the subsequent source/drain trench formation process.
Solution Approach 2:
The mandrel structure acts as an intermediary element between the gate electrode and the source/drain regions. The protruding portions of the mandrel mediate the etching process by physically blocking the etch front from reaching the isolation structures. This intermediary structure transfers the control function from direct gate-width-based etching to mandrel-protrusion-based etching, preventing isolation structure damage while enabling precise source/drain trench formation.
2Manufacturing precision
If over-etching occurs during source/drain trench formation, then source/drain features can be fully formed, but epitaxial merge between adjacent source/drain features occurs
Solution Approach 1:
The mandrel structure with protruding portions is formed in advance to establish physical boundaries that prevent excessive etching. The protruding portions extend beyond the gate electrode edges by a controlled amount (e.g., 5-20 nm), creating a predetermined etch stop that ensures source/drain trenches are formed completely while preventing etch damage that would lead to epitaxial merge during subsequent growth processes.
Solution Approach 2:
The mandrel protruding portions serve as intermediary barriers that control the etching process. They mediate between the need for complete source/drain trench formation and the need to prevent isolation structure damage. By positioning the mandrel protrusions at specific locations, the patent creates a buffer zone that allows complete trench formation while preventing the harmful side effect of isolation structure breakage that would cause epitaxial merge.
3Reliability
If the hard mask profile is enlarged to block excess global etching gas, then isolation structures are protected from breakage, but the device structure becomes more complex
Solution Approach 1:
The hard mask is segmented into distinct functional regions: a main body portion aligned with the gate electrode and protruding portions extending beyond the gate edges. This segmentation allows different parts of the hard mask to perform different functions - the main body defines the gate alignment while the protruding portions specifically protect the isolation structures. The segmentation transforms a single complex profile into manageable functional segments that can be formed and controlled independently.
Solution Approach 2:
The hard mask profile exhibits local quality variations with protruding portions having different dimensions and positions compared to the main body. The protruding portions are locally enlarged or extended only in the regions where isolation structure protection is needed, while the main body maintains standard dimensions for gate alignment. This local quality approach protects isolation structures without unnecessarily complicating the entire hard mask structure.
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 epitaxial merge by controlling the etching process, ensuring stable isolation structures and improving the yield and performance of semiconductor devices.
Implementation Method 1
performing an etching process to the hard mask layer and the dummy gate layer using the patterned photoresist, thereby forming patterned hard mask structures and patterned dummy gate structures
Data Source
AI summary
One aspect of the present disclosure pertains to a method of forming a semiconductor structure. The method includes forming an active region over a substrate, forming a dummy gate layer over the active region, forming a hard mask layer over the dummy gate layer, forming a patterned photoresist over the hard mask layer, and performing an etching process to the hard mask layer and the dummy gate layer using the patterned photoresist, thereby forming patterned hard mask structures and patterned dummy gate structures. The patterned hard mask structures are formed with an uneven profile having a protruding portion. The protruding portion of each of the patterned hard mask structures has a first width, wherein each of the patterned dummy gate structures has a second width, and the first width is greater than the second width.