BiCMOS Dummy Windows for Etch Endpoint Detection
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Solution Overview
Problem
In the production of integrated BiCMOS semiconductor circuits, the detection of the endpoint in anisotropic plasma etching processes for small structures is challenging due to inaccuracies in layer thickness and etchant composition, leading to potential over-etching or under-cutting, which can result in increased emitter-base leakage and variability in bipolar parameters.
Innovation Solution
The introduction of dummy window structures with geometrical dimensions and shapes similar to active window structures within dummy moat areas increases the total surface area exposed to the etchant, allowing for precise endpoint detection during etching, thereby preventing over-etching and under-cutting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dummy surfaces are used for etch endpoint detection, then the etch endpoint signal can be detected, but the etch endpoint signal occurs prematurely due to higher etch-rate of large areas, so that the optimum moment in time when the etching process should be terminated cannot be determined with sufficient precision
Solution Approach 1:
The patent creates dummy window structures that are identical copies of the active window structures in terms of geometry, material composition, and etching characteristics. These dummy structures serve as surrogates for endpoint detection, providing an accurate signal that reflects the actual etching state of the small active structures without the premature signaling problem of large dummy surfaces.
Solution Approach 2:
The patent changes the parameter of dummy structure size from large areas (which cause premature endpoint signals) to small structures matching the active window dimensions. This parameter change ensures that the dummy structures exhibit the same etch-rate and endpoint characteristics as the active structures, enabling precise endpoint detection.
2Manufacturing precision
If the window structures to be etched are very small and delicate, then high precision etching is required, but detection of the endpoint of the etching process becomes no longer possible with conventional approaches
Solution Approach 1:
The patent creates dummy window structures that are identical copies of the active window structures in terms of geometry, material composition, and etching characteristics. These dummy structures serve as surrogates for endpoint detection, providing an accurate signal that reflects the actual etching state of the small active structures without the premature signaling problem of large dummy surfaces.
Solution Approach 2:
The dummy window structures act as intermediaries between the etching process and the endpoint detection system. They provide a measurable signal that indirectly indicates the etching state of the active structures, making the detection of endpoint for very small structures feasible through optical emission spectroscopy or other detection methods.
3Manufacturing precision
If anisotropic plasma etching is used for fine structures, then precise etching can be achieved, but inaccuracies in layer thickness and etchant composition lead to over-etching or under-cutting
Solution Approach 1:
The patent implements real-time feedback control by monitoring the etching process through endpoint detection methods (optical emission spectroscopy, plasma characteristics, or reflection properties). The dummy window structures provide a reliable feedback signal that indicates when the etching reaches the desired endpoint, allowing dynamic adjustment of the etching duration to compensate for variations in layer thickness and etchant composition.
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 reliable and precise etch endpoint detection for very small structures, reducing emitter-base leakage and variability in bipolar parameters, ensuring high precision in manufacturing integrated BiCMOS semiconductor circuits.
Implementation Method 1
Anisotropic plasma etching is used for the etching of fine structures
Implementation Method 2
the endpoint of the etching process can be detected by a change in the composition of the optical radiation by optical emission spectroscopy
Implementation Method 3
These deep depressions 6 become a problem when performing a process of chemical mechanical polishing (CMP) on a layer
Data Source
AI summary
An integrated BiCMOS semiconductor circuit has active moat areas in silicon. The active moat areas include electrically active components of the semiconductor circuit, which comprise active window structures for base and/or emitter windows. The integrated BiCMOS semiconductor circuit has zones where silicon is left to form dummy moat areas which do not include electrically active components, and has isolation trenches to separate the active moat areas from each other and from the dummy moat areas. The dummy moat areas comprise dummy window structures having geometrical dimensions and shapes similar to those of the active window structures for the base and/or emitter windows.