Thin Film Resistor Cap Layer Etch Stop Hardmask
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Solution Overview
Problem
Conventional thin film resistor (TFR) integration in semiconductor IC devices faces challenges such as high temperature annealing affecting aluminum interconnects, increased sheet resistance, and polymer residue formation, which complicates the fabrication process and can lead to electromigration issues and electrical shorts.
Innovation Solution
Forming the TFR before the first metal/interconnect layer allows for optimal annealing at higher temperatures without damaging the aluminum interconnects, and using a nitride or oxide cap layer as an etch stop and hardmask to reduce the number of photomask processes and prevent polymer residue formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TFR annealing is performed at high temperature (≥500°C) to optimize TCR, then TCR is improved, but aluminum interconnect is damaged
Solution Approach 1:
The TFR annealing process is performed at high temperature (≥500°C) before the aluminum interconnect layer is deposited. This preliminary action allows the TFR to achieve optimal TCR values through high-temperature annealing without subsequently damaging the aluminum interconnect, which would form TiAl3 intermetallic compounds and increase sheet resistance if annealed after deposition
2Manufacturing precision
If photomask processes are used for TFR formation, then patterning precision is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent extracts the hardmask function from the photomask process by using a deposited cap layer (such as silicon nitride or silicon oxide) as the hardmask material. This eliminates the need for separate photomask deposition and patterning steps, reducing manufacturing complexity while maintaining patterning precision through standard photolithography processes
Solution Approach 2:
The cap layer serves multiple functions: it acts as an etch stop layer to protect underlying structures, serves as a hardmask for TFR patterning, and provides a release layer for stress management. This multi-functionality reduces the total number of process steps compared to using separate dedicated layers for each function
3Object-generated harmful factors
If chemical clean process is used to remove polymer residue, then polymer residue is removed, but sensitive structures are damaged
Solution Approach 1:
The patent converts the potentially harmful chemical clean process into a beneficial selective cleaning operation by using the cap layer as a protective mask. The cap layer prevents the chemical clean from damaging sensitive structures like tungsten vias and contacts, while still allowing effective removal of polymer residue from exposed areas. The cap layer itself is designed to be resistant to the cleaning chemistry
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, minimizes polymer residue, and prevents electrical shorts, enabling cost-effective integration of TFRs with aluminum interconnects while maintaining precise resistance values and stable operation over a wide temperature range.
Implementation Method 1
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 first etch process is performed to remove selected portions of the TFR etch stop cap layer and underlying portions of the TFR film layer, thereby defining an etch stop cap and underlying TFR element
Data Source
AI summary
A method 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. At least one TFR cap layer is formed, and a TFR etch defines a TFR element from the TFR film. A TFR contact etch forms TFR contact openings 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. The TFR cap layer(s), e.g., SiN cap and/or oxide cap formed over the TFR film, may (a) provide an etch stop during the TFR contact etch and/or (b) provide a hardmask during the TFR etch, which may eliminate the use of a photomask and thereby eliminate post-etch removal of photomask polymer.