NiCrAl Thin Film Resistor Interface for Lower Etch Undercut
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Solution Overview
Problem
Thin film resistors (TFRs) using nickel chromium aluminum (NiCrAl) face issues such as undercut, line-edge roughness, and non-uniformity due to the wet etch process, as well as a high temperature coefficient of resistance, primarily due to inadequate bonding between the NiCrAl resistor body and the titanium tungsten (TiW) resistor heads.
Innovation Solution
The introduction of a thin interfacial layer, such as titanium (Ti) or titanium nitride (TiN), between the NiCrAl resistor body and the TiW resistor heads improves bonding, reducing undercut and line-edge roughness, and enhancing uniformity across the wafer, while also lowering the temperature coefficient of resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a wet etch process is used to structure the NiCrAl film, then the NiCrAl resistor can be formed, but undercut of the NiCrAl resistor beneath the hardmask occurs and line-edge roughness increases
Solution Approach 1:
A thin interfacial layer of titanium nitride (TiN) is introduced between the NiCrAl resistor body and the TiW hardmask. This interfacial layer acts as a mediator that modifies the etch interface, reducing the undercut of NiCrAl beneath the hardmask and improving line-edge roughness during the wet etch process
2Ease of manufacture
If TiW is used as the hardmask and resistor head material, then the resistor structure can be formed, but non-uniformity across the wafer occurs
Solution Approach 1:
The thin TiN interfacial layer serves as a uniform mediator across the entire wafer surface, providing consistent bonding and etch protection between the NiCrAl resistor body and TiW hardmask. This interfacial layer compensates for variations in the wet etch process, resulting in improved uniformity of resistor characteristics across the wafer
3Device complexity
If direct bonding is attempted between NiCrAl resistor body and TiW head material, then the structure can be formed, but the temperature coefficient of resistance remains undesirably high
Solution Approach 1:
The thin TiN interfacial layer acts as a thermal and electrical mediator between the NiCrAl resistor body and TiW head material. This interfacial layer improves the bonding interface quality and reduces the temperature coefficient of resistance by providing a more stable thermal and electrical transition zone, without significantly increasing device complexity
Solution Approach 2:
The resistor structure employs a composite material system consisting of NiCrAl resistor body, TiN interfacial layer, and TiW hardmask/resistor heads. This multi-material composite structure optimizes the bonding interface properties and thermal characteristics, achieving a lower temperature coefficient of resistance compared to direct NiCrAl-TiW bonding
Data Source
AI summary
An integrated circuit includes a thin film resistor body that is formed over a dielectric layer. An interfacial layer is formed on the thin film resistor body and resistor heads are formed on the interfacial layer. The thin film resistor body includes nickel chromium aluminum (NiCrAl) and the resistor heads include titanium tungsten (TiW).