Thin Film Resistor Oxide Cap Hardmask Etch Process
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Solution Overview
Problem
Conventional thin film resistor (TFR) integration in semiconductor IC devices faces challenges such as the need for multiple expensive photomask processes, potential damage to aluminum interconnect layers due to high annealing temperatures, and difficulties in removing polymer residue from photomask etching, which can lead to electromigration issues and electrical shorts.
Innovation Solution
Forming TFRs before the first metal/interconnect layer, allowing for optimal annealing at temperatures above 500°C, using an oxide cap as a hardmask to reduce photomask usage and polymer residue, and forming spacer oxide edge spacers to prevent electrical shorts by encapsulating lateral edges of the TFR element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TFR annealing is performed at high temperatures (above 500°C) to optimize TCR, then TCR precision is improved, but aluminum interconnect layers are damaged
Solution Approach 1:
The TFR annealing process is performed at high temperatures (500-525°C) before the aluminum interconnect layers are formed. This preliminary action allows the TCR to be optimized to near-zero values without subsequently damaging the aluminum interconnects, as the aluminum layers are deposited after the high-temperature annealing is complete
Solution Approach 2:
The fabrication process is segmented into distinct stages: TFR formation and annealing occurs in an earlier stage before aluminum interconnect deposition. This temporal segmentation separates the high-temperature TFR processing from the aluminum interconnect formation, allowing each process to occur at its optimal conditions without interfering with the other
2Manufacturing precision
If polymer photomask is used for TFR etch, then patterning precision is improved, but polymer residue is generated causing electrical shorts
Solution Approach 1:
The harmful polymer residue is extracted and removed through a chemical clean process using oxygen plasma. This extraction step eliminates the polymer contamination that would otherwise cause electrical shorts and electromigration issues, while the patterning precision achieved by the polymer photomask is preserved
Solution Approach 2:
The polymer residue, initially a harmful byproduct, is converted into a removable contaminant through controlled chemical cleaning. The oxygen plasma treatment transforms the polymer into volatile products that can be evacuated, turning the harmful residue into a temporary intermediate that can be cleanly removed without damaging underlying structures
3Loss of substance
If chemical clean process is used to remove polymer residue, then polymer removal is improved, but IC element contacts are damaged
Solution Approach 1:
The chemical clean process is applied with spatial selectivity, targeting only areas with polymer residue while protecting IC element contacts. The cleaning conditions (oxygen plasma parameters, temperature, duration) are locally optimized to remove polymer from TFR regions without exposing sensitive contact structures to damaging conditions
4Manufacturing precision
If multiple photomask processes are used for TFR fabrication, then manufacturing precision is improved, but process complexity increases
Solution Approach 1:
Multiple photomask processes are merged into a single photomask step that patterns both the TFR and aluminum interconnect layers simultaneously. This consolidation reduces the total number of photomask processes from multiple sequential steps to one integrated patterning operation, simplifying the overall fabrication process while maintaining the necessary patterning precision through carefully designed mask layouts
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 reduces the number of photomask processes, prevents damage to aluminum interconnects, eliminates the need for chemical cleans, and minimizes electrical shorts, thereby enhancing the integration of TFRs in IC devices while maintaining precise resistance values and stability across a wide temperature range.
Implementation Method 1
A TFR may include any suitable resistive film formed on or in an insulating substrate... A TFR anneal may be performed at above 500° C., e.g., in the range of 500-525° C., to optimize the TCR value
Implementation Method 2
A TFR oxide cap layer is formed over the annealed TFR film layer... an oxide cap etch process is performed to remove selected portions of the TFR oxide cap layer... a TFR etch process is performed, using the TFR oxide cap as a hardmask
Data Source
AI summary
A process is provided for forming a thin film resistor (TFR) in an integrated circuit (IC) device. A TFR film is formed and annealed over an IC structure including IC elements and IC element contacts. An oxide cap is formed over the TFR film, which acts as a hardmask during a TFR etch of the TFR film to define a TFR element, which may eliminate the use of a photomask and thereby eliminate post-etch removal of photomask polymer. TFR edge spacers may be formed over lateral edges of the TFR element to insulate such TFR element edges. TFR contact openings are etched in the oxide cap over the TFR element, and a metal layer is formed over the IC structure and extending into the TFR contact openings to form metal contacts to the IC element contacts and the TFR element.