Sheet Resistance Test Structure for Over-Etch Quantification
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Solution Overview
Problem
The manufacturing of Digital Micromirror Devices (DMDs) faces challenges with over-etching of conductive features, which can lead to post failure and under-etching issues, and conventional etch-stop layers are not typically used in DMD structures.
Innovation Solution
A method is developed to quantify over-etch of conductive features by forming a sheet resistance test structure and using a common etch process to measure changes in sheet resistance values, allowing for precise calculation of over-etch amounts through the comparison of initial and final sheet resistance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a common etch process is used to etch the conductive feature, then the etching speed is improved, but over-etching occurs leading to post failure
Solution Approach 1:
A sheet resistance test structure is formed alongside the conductive feature before etching. This test structure serves as a sacrificial element that is etched first, allowing the main conductive feature to be etched subsequently with controlled depth, preventing over-etching that would compromise post reliability.
Solution Approach 2:
The sheet resistance test structure acts as an intermediary between the etch process and the conductive feature. By measuring the sheet resistance of the test structure before and after etching, the etch depth can be quantified and controlled, ensuring the conductive feature is etched to the correct depth without damaging underlying posts.
2Manufacturing precision
If the etch depth is increased to remove sufficient material, then the manufacturing precision is improved, but over-etching into the conductive feature occurs
Solution Approach 1:
The mechanical/physical etching process is supplemented with an electrical measurement system. By measuring the sheet resistance of the test structure, the etch depth is determined through electrical properties rather than relying solely on mechanical timing or physical depth measurement, enabling precise control without over-etching.
Solution Approach 2:
The sheet resistance of the test structure changes as etching progresses. By monitoring this parameter (sheet resistance) before and after etching, the etch depth can be precisely controlled. The change in sheet resistance provides a quantitative measure of etch depth, allowing the process to stop at the optimal point without over-etching.
3Reliability
If conventional etch-stop layers are used to prevent over-etching, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The etch-stop function is extracted from the main device structure and placed in a separate test structure. Instead of incorporating an etch-stop layer within the conductive feature itself (which would increase complexity), a dedicated test structure is created that serves solely as an etch depth reference, keeping the main device simple while providing over-etch protection.
Solution Approach 2:
A copy of the conductive feature is created in the form of the sheet resistance test structure. This test structure replicates the electrical properties of the conductive feature but is designed specifically for measurement purposes. By etching both simultaneously and measuring the test structure's sheet resistance, the etch depth of the main feature is controlled without adding complexity to the functional device.
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 enables timely detection and correction of over-etch issues, improving the reliability and operation of DMDs by accurately quantifying over-etch and preventing post failure, without the need for conventional etch-stop layers.
Implementation Method 1
etching the sheet resistance test structure and etching the conductive feature through the one or more openings in the photoresist spacer layer using a common etch process
Implementation Method 2
A second sheet resistance value of the sheet resistance test structure is obtained after the etching, and an amount of over-etch into the conductive feature using the first and second sheet resistance values is quantified
Data Source
AI summary
The invention provides a method for quantifying over-etch of a conductive feature. In one embodiment, this method includes forming a conductive feature over a substrate, the conductive feature having a sheet resistance test structure associated therewith, the sheet resistance test structure having a first sheet resistance value. This method may further include etching the conductive feature and the sheet resistance test structure using a common etch process, obtaining a second sheet resistance value of the sheet resistance test structure after the etching, and quantifying an amount of over-etch into the conductive feature using the first and second sheet resistance values.