Thin-Film Resistor Fabrication Under Metal Layer
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Solution Overview
Problem
The existing methods for manufacturing thin-film resistors (TFRs) in semiconductor integrated circuits require multiple mask layers, making them costly and difficult to anneal at high temperatures, and often result in variations in resistance value due to the formation of ridges at the edges of the TFR elements, which affect the temperature coefficient of resistance (TCR).
Innovation Solution
The TFR elements are formed underneath the TFR heads/contacts using a damascene CMP approach with a single mask layer, allowing for annealing at high temperatures without affecting the later-formed structures and eliminating ridges through a cleaning and wet etch process, thereby reducing the number of mask layers needed and improving TCR performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional TFR fabrication processes are used with multiple mask layers, then TFR heads and contacts can be formed, but the manufacturing complexity and cost increase significantly
Solution Approach 1:
The TFR element is formed first before the TFR heads and contacts. By performing the TFR element formation in advance using a single mask layer defining the TFR heads, the subsequent head and contact formation becomes simpler and does not require additional mask layers, thus reducing overall manufacturing complexity
Solution Approach 2:
The first mask layer serves multiple functions: it defines both the TFR heads and the TFR element regions. This multi-functional mask layer eliminates the need for separate mask layers that would traditionally be required for defining TFR heads, TFR elements, and contacts in conventional processes
2Reliability
If TFRs are formed with conventional processes, then TFR structures can be created, but high-temperature annealing becomes difficult without affecting other structures
Solution Approach 1:
The TFR element is formed and annealed before the TFR heads and contacts are created. This preliminary formation allows the TFR element to undergo high-temperature annealing (up to 500°C or higher) to achieve desired electrical properties without affecting the TFR heads and contacts, which are formed later and would be damaged by such high temperatures
Solution Approach 2:
The fabrication process is segmented into distinct stages where the TFR element is formed and processed separately from the TFR heads and contacts. This temporal and spatial segmentation allows independent optimization of annealing conditions for the TFR element without constraining the formation of subsequent structures
3Manufacturing precision
If TFR elements are formed with conventional methods, then resistance values can be achieved, but variations in resistance occur due to ridge formation at edges
Solution Approach 1:
The problematic ridges that form at the edges of TFR elements during conventional fabrication are completely removed through selective etching processes. By extracting these harmful ridge structures, the resistance value variations and TCR performance instability caused by ridge presence are eliminated, leading to more precise and reliable TFR characteristics
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 mask layers required, enables high-temperature annealing to achieve near 0 ppm TCR, and improves the stability and consistency of TCR performance by removing ridges, resulting in more reliable and cost-effective TFR modules.
Implementation Method 1
allowing for annealing at high temperatures without affecting the later-formed structures
Implementation Method 2
eliminating ridges through a cleaning and wet etch process
Implementation Method 3
A chemical-mechanical planarization (CMP) process may then be used to remove any excessive copper and barrier
Data Source
AI summary
A method for manufacturing a thin film resistor (TFR) module includes forming a TFR element over a substrate; annealing the TFR element to reduce the temperature coefficient of resistance (TCR) of the TFR element; and after forming and annealing the TFR element, forming a pair of conductive TFR heads in contact with the TFR element. By forming the TFR element before the TFR heads, the TFR element may be annealed without affecting the TFR heads, and thus may be formed from various materials with different annealing properties, e.g., SiCCr and SiCr. Thus, the TFR element may be annealed to achieve a near 0 ppm TCR, without affecting the later-formed TFR heads. The TFR module may be formed using a damascene CMP approach and using only a single added mask layer. Further, vertically-extending “ridges” at edges of the TFR element may be removed or eliminated to further improve the TCR performance.