Buried Cavity Alignment via Lithography Radiation Attenuation
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Solution Overview
Problem
The challenge in integrated electronic circuit fabrication is producing circuit elements at defined locations relative to buried cavities in the substrate, which requires precise alignment of fabrication tools with alignment marks, making the process lengthy and cumbersome.
Innovation Solution
A method involving forming an open cavity in a substrate, heating it to close the cavity and create a surface depression, filling the depression with a material that attenuates lithography radiation, and using a resist layer exposed to a controlled radiation flux to create a mask aligned with the buried cavity, eliminating the need for precise alignment of tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If alignment marks are used on the substrate for precise positioning of circuit elements relative to buried cavities, then manufacturing precision is improved, but the fabrication process becomes lengthy and complex due to successive iterations and offset measurements
Solution Approach 1:
The invention creates a depression in the substrate surface at the location where the cavity opening was initially positioned, before subsequent fabrication steps. This depression serves as a pre-established reference feature that automatically defines the position for circuit elements, eliminating the need for time-consuming alignment iterations with traditional marks
Solution Approach 2:
The substrate itself provides the alignment reference through its own depression feature, rather than requiring external alignment marks. The depression is formed as a direct consequence of the cavity closure process, making the substrate self-referential for positioning purposes
2Manufacturing precision
If alignment marks and successive iterations are used for positioning, then manufacturing precision is improved, but device complexity increases due to multiple alignment operations
Solution Approach 1:
The invention extracts the alignment reference function from external alignment marks and integrates it directly into the substrate structure itself. The depression formed in the substrate serves as an inherent positioning feature, simplifying the overall fabrication process by eliminating separate alignment mark deposition and measurement steps
3Shape
If the substrate surface is fully reconstructed after cavity closure, then surface quality is improved, but the ability to provide alignment reference for buried cavities is lost
Solution Approach 1:
The substrate surface is reconstructed to be substantially planar over the entire region containing the cavity, while simultaneously maintaining a localized depression at the specific location where the cavity opening was initially positioned. This allows the surface to serve both as a high-quality planar surface for circuit fabrication and as a localized reference feature for positioning
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 method simplifies and accelerates the production of circuit elements by automatically aligning the resist mask with the buried cavity, is compatible with cavities of any dimensions, and allows for the creation of buried cavities that can be filled with conductive or heat-extracting materials, enhancing the fabrication process.
Implementation Method 1
The substrate is then heated so as to cause the cavity to close by deformation of the substrate. During this heating, part of the material of the substrate close to the surface of the latter moves around the opening of the cavity
Implementation Method 2
at least partly filling, the depression in the substrate surface with a portion of a material selected so that this portion attenuates a radiation reflected by the substrate
Data Source
AI summary
An integrated electronic circuit includes a cavity buried in a substrate. A surface of the substrate has a depression aligned above the buried cavity. The depression is filled with a material selected so that reflection of a lithography radiation on the substrate surface is attenuated. A resist layer is deposited on the circuit and then exposed to the radiation so that those resist portions which are located above the depression and those located away from the depression receive amounts of radiation that are below and above, respectively, the development threshold of the resist. An etching mask is therefore obtained on the circuit, which is aligned with respect to the cavity and its associated surface depression.