Ghost Feature Lithography for Gate CD Control
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Solution Overview
Problem
Conventional optical lithography struggles to accurately form gate lines with squared ends over non-rectangular active regions, leading to transistor leakage due to rounded ends and incomplete extension of gate lines beyond the active region.
Innovation Solution
A method involving a first mask to form features and ghost features beyond the edge of a non-rectangular active region, followed by a second mask to trim these features, ensuring gate lines have squared ends and extend fully, minimizing leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional optical lithography is used to form gate lines over non-rectangular active regions, then the manufacturing process is simple, but the gate lines have rounded ends and do not extend fully beyond the active region, causing transistor leakage
Solution Approach 1:
The patent applies preliminary action by forming ghost features adjacent to the active region before the final gate line formation. These ghost features serve as placeholders that define the extension points for the gate lines, ensuring they reach the required distance beyond the active region edges. The ghost features are formed in a first lithographic step, then used as references in subsequent steps to achieve precise gate line extension without relying on direct patterning at the critical dimension limit.
Solution Approach 2:
The patent segments the gate line formation process into multiple distinct steps: first forming ghost features adjacent to the active region, then forming gate lines that extend to these ghost features, and finally removing the ghost features. This segmentation allows each step to be optimized independently, with the ghost feature formation step establishing precise reference points that guide the subsequent gate line patterning, thereby achieving squared ends and proper extension.
2Manufacturing precision
If the gate lines are formed to extend beyond the active region using conventional methods, then the gate length is increased, but the ends become rounded and critical dimension control deteriorates
Solution Approach 1:
The patent introduces ghost features as intermediary elements that mediate between the active region and the gate lines. These ghost features act as intermediate reference structures that are easier to pattern with precise dimensions than the final gate lines themselves. By using the ghost features as intermediaries, the process achieves better critical dimension control for the gate line extension, as the ghost features can be formed with relaxed dimensional tolerances that still ensure proper gate line placement.
3Manufacturing precision
If ghost features are formed adjacent to the active region using a two-print-two-etch approach, then the gate line extension and squared ends are achieved, but the process complexity increases
Solution Approach 1:
The patent merges multiple functions into the ghost feature structures: they serve as reference markers for gate line extension, as etch stop references, and as features to be removed in a dedicated cleanup step. The two-print-two-etch approach combines the formation of ghost features and gate lines in an integrated sequence where the same lithographic and etching steps accomplish multiple objectives simultaneously, reducing the need for separate dedicated steps for each function.
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 forms semiconductor devices with gate lines that have squared ends and extend beyond the active region, reducing transistor leakage and improving critical dimension control.
Implementation Method 1
A stepper includes a light source and optics/lenses that project light coming through the reticle and images the circuit pattern... on a photoresist film formed on a silicon wafer
Implementation Method 2
The method further includes using a second mask to remove a portion of the plurality of first features extending beyond the edge of the non-rectangular shaped active region and the at least one ghost feature
Data Source
AI summary
In accordance with various embodiments, semiconductor devices and methods of forming semiconductor devices having non-rectangular active regions are provided. An exemplary method includes using a first mask to form a plurality of first features over a non-rectangular shaped active region and at least one ghost feature, wherein the plurality of first features extend beyond an edge of the non-rectangular shaped active region. The method further includes using a second mask to remove a portion of the plurality of first features extending beyond the edge of the non-rectangular shaped active region and the at least one ghost feature.