Etching Selectivity via Intermediate Layer Segmentation
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Solution Overview
Problem
Etching processes for thick layers with high non-uniformity require long over-etching and high selectivity, which is difficult to achieve with conventional methods, especially when contamination and stress limitations restrict the thickness of stop layers like titanium nitride, making secure stopping challenging.
Innovation Solution
Introducing an intermediate layer between the etch layer and the stop layer, using two distinct etching processes with high selectivities, where the first etchant has a selectivity of at least 5:1 with respect to the etch layer and intermediate layer, and the second etchant has a selectivity of at least 5:1 with respect to the intermediate and stop layers, thereby multiplying the overall selectivity and ensuring secure stopping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single etching process with high selectivity (more than 40:1) is used to ensure secure stopping on the stop layer, then the etching precision is improved, but the device complexity increases and the ease of manufacture deteriorates
Solution Approach 1:
The patent divides the etching process into two separate steps with different etchants. The first etching step uses a first etchant to etch the etch layer with selectivity of at least 5:1 relative to the intermediate layer. The second etching step uses a second etchant to etch the intermediate layer with selectivity of at least 5:1 relative to the stop layer. This segmentation achieves an overall selectivity exceeding 100:1 without requiring a single highly selective etching process, thereby simplifying manufacturing.
2Reliability
If the stop layer thickness is increased to prevent etching through, then the reliability is improved, but the stress constraints worsen due to layer stress limitations
Solution Approach 1:
The patent introduces an intermediate layer between the etch layer and the stop layer. This intermediate layer acts as a mediator that enables the etching process to stop securely without requiring a thick stop layer. The intermediate layer has specific material properties that allow it to be etched selectively by the second etchant with selectivity of at least 5:1 relative to the stop layer, thereby preventing etching through the stop layer while maintaining acceptable stress levels.
3Productivity
If a single etching process is used, then the productivity is improved, but the manufacturing precision deteriorates due to inability to achieve sufficient selectivity
Solution Approach 1:
The patent segments the etching process into two distinct steps using different etchants. The first etching step removes the etch layer with the first etchant, and the second etching step removes the intermediate layer with the second etchant. Each step has a selectivity of at least 5:1, resulting in an overall selectivity exceeding 100:1. This segmentation achieves high manufacturing precision while maintaining productivity by using standard etching processes rather than requiring a single highly selective process.
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 achieves selectivities exceeding 100:1, allowing for secure control of non-uniformities and preventing etching through the stop layer, even with limited stop layer thickness, thus ensuring reliable manufacturing of devices like via contacts.
Implementation Method 1
a first step of etching the etch layer with a first etchant, the first etchant comprising a first etch selectivity of at least 5:1 with respect to the etch layer and the intermediate layer
Implementation Method 2
a second step of etching the intermediate layer with a second etchant, the second etchant comprising a second etch selectivity of at least 5:1 with respect to the intermediate layer and the stop layer
Data Source
AI summary
A method for etching a layer assembly, the layer assembly including an intermediate layer sandwiched between an etch layer and a stop layer, the method including a step of etching the etch layer using a first etchant and a step of etching the intermediate layer using a second etchant. The first etchant includes a first etch selectivity of at least 5:1 with respect to the etch layer and the intermediate layer. The second etchant includes a second etch selectivity of at least 5:1 with respect to the intermediate layer and the stop layer. The first etchant being is different from the second etchant.