Cryogenic Ruthenium Etching for Smoother BEOL Interconnect Sidewalls
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Solution Overview
Problem
Current subtractive etching methods for ruthenium (Ru) in back-end-of-line (BEOL) interconnects at room temperature result in inconsistent roughness and high electrical resistance, making them unsuitable for smaller technology nodes.
Innovation Solution
Etching Ru at cryogenic temperatures using a halogen-containing gas and an oxygen-containing gas, such as Cl2 and O2, with a controlled temperature range of -90°C to 20°C, and maintaining specific gas ratios and pressures to enhance passivation and reduce roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If room temperature etching is used, then the etching process is simple and fast, but the sidewall roughness is high and electrical resistance is high
Solution Approach 1:
The patent applies parameter changes by transitioning from room temperature to cryogenic temperature range (-90°C to 20°C) for the etching process. This temperature parameter modification fundamentally changes the etching mechanism, enabling smoother sidewalls and reduced roughness while maintaining process effectiveness through controlled thermal conditions.
Solution Approach 2:
The patent implements periodic action through alternating exposure to halogen-containing gas and oxygen-containing gas during the etching process. This periodic gas switching creates controlled oxidation and etching cycles that progressively smooth the sidewalls while removing material, achieving high precision without requiring continuously complex equipment.
2Productivity
If room temperature etching is used, then the etching rate is high, but the electrical resistance of interconnects is high
Solution Approach 1:
The patent modifies the temperature parameter to cryogenic ranges while simultaneously optimizing gas composition parameters (halogen-to-oxygen ratios). This dual parameter change achieves a new operating regime where etching proceeds at acceptable rates while producing smooth, low-resistance interconnects, resolving the contradiction between productivity and reliability.
Solution Approach 2:
The patent uses composite gas chemistry combining halogen-containing gases (for etching) and oxygen-containing gases (for passivation and smoothing). This composite approach allows simultaneous achievement of material removal and surface quality improvement, maintaining etching rate while reducing electrical resistance through controlled chemical interactions.
3Manufacturing precision
If cryogenic temperature etching is used, then the sidewall roughness is reduced, but the process complexity increases
Solution Approach 1:
The patent establishes a broad but controlled temperature window (-90°C to 20°C) that achieves smooth sidewalls without requiring extreme precision. This parameter range optimization balances manufacturing precision with practical temperature control complexity, making cryogenic etching feasible with standard equipment.
Solution Approach 2:
The periodic switching between halogen and oxygen gases creates self-regulating chemical cycles that compensate for temperature variations. This temporal control mechanism reduces the burden on spatial temperature uniformity, allowing smooth sidewalls to be achieved even with moderate temperature control capabilities.
4Manufacturing precision
If halogen and oxygen gas mixture is used, then the passivation is enhanced and roughness is reduced, but the process complexity increases
Solution Approach 1:
The patent employs periodic alternation of halogen-containing gas and oxygen-containing gas flows during etching. This temporal separation of chemical functions (etching vs. passivation) simplifies flow control requirements compared to simultaneous multi-gas delivery, while still achieving enhanced passivation and reduced roughness through cyclic chemical action.
Solution Approach 2:
The patent optimizes the ratio parameters of halogen-to-oxygen gas flows to achieve effective passivation and smoothing. By establishing specific ratio ranges rather than requiring precise absolute flow rates, the process reduces gas flow control complexity while maintaining surface quality improvements.
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
The method achieves smoother sidewalls and improved etching rates, reducing roughness and electrical resistance, leading to better device quality and process efficiency.
Implementation Method 1
exposing a portion of a substrate containing an exposed Ru layer to a processing gas comprising a halogen containing gas and an oxygen containing gas
Implementation Method 2
exposing the portion of the Ru layer to the halogen containing gas
Implementation Method 3
maintaining a temperature of the substrate support between -90° C. and 20° C. while exposing the portion of the Ru layer to the halogen containing gas
Data Source
AI summary
Disclosed herein are methods for etching ruthenium (Ru) at low temperatures, and a processing chamber for performing the same. In one example, a method for etching ruthenium (Ru), includes exposing a portion of a substrate containing an exposed Ru layer to a processing gas comprising a halogen containing gas and an oxygen containing gas, wherein the substrate is disposed on a substrate support in a processing chamber; and maintaining a temperature of the substrate support between −90° C. and 20° C. while exposing the portion of the Ru layer to the halogen containing gas.