Low Resistivity Tungsten Film via Krypton Sputtering
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Solution Overview
Problem
The miniaturization of bit lines in integrated circuits is limited by the resistivity of metal films, which can be affected by impurities in the sputtering process, leading to defects in the metallic interconnect layers and compromising the operational integrity of the circuits.
Innovation Solution
A method of sputter depositing a tungsten film with low resistivity by using a tungsten target with minimal carbon and oxygen impurities, combined with a titanium backing plate and aluminum bonding layer, in a plasma processing chamber with krypton gas, to form a low-resistivity thin film suitable for gate electrode stacks and bit lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional sputtering processes are used with standard tungsten targets, then metal films can be deposited, but the films exhibit high resistivity due to impurity incorporation
Solution Approach 1:
The patent changes the chemical composition parameters of the tungsten target by strictly controlling impurity levels (carbon ≤10 ppm, oxygen ≤10 ppm) and using specific bonding layers (aluminum with thickness 1-10 μm) to achieve low resistivity films (≤10 μohm-cm). This parameter optimization resolves the contradiction between film quality and deposition process feasibility.
Solution Approach 2:
The patent employs a composite target structure consisting of tungsten bonding layer (1-10 μm), aluminum bonding layer (1-10 μm), and tungsten bulk material. This composite structure prevents impurity diffusion from the target to the film while maintaining low resistivity, thereby resolving the contradiction between operational integrity and resistivity control.
2Productivity
If bit line miniaturization is pursued to increase circuit density, then more transistors can be integrated, but defects in metal films compromise operational integrity
Solution Approach 1:
The patent uses krypton gas as the sputtering atmosphere, which is chemically inert and prevents unwanted reactions that could introduce defects. This inert environment ensures high film quality with minimal defects, enabling both high circuit density and maintained operational integrity in miniaturized bit lines.
3Ease of manufacture
If standard tungsten targets are used in sputtering, then deposition can proceed, but carbon and oxygen impurities increase film resistivity
Solution Approach 1:
The patent performs preliminary purification by selecting tungsten targets with pre-controlled low impurity content (carbon ≤10 ppm, oxygen ≤10 ppm) and preparing aluminum bonding layers before deposition. This preliminary action prevents impurity incorporation during deposition, achieving both ease of manufacture and high film purity.
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 approach results in tungsten films with resistivity as low as 8.5 μohms-cm, enhancing the miniaturization capabilities and reducing defects in the bit lines, thereby improving the operational integrity of integrated circuits.
Implementation Method 1
exciting the krypton into a plasma to deposit, by sputtering, a tungsten film layer on a material layer of a substrate
Implementation Method 2
flowing krypton into the plasma processing chamber; and exciting the krypton into a plasma
Data Source
AI summary
Systems and methods for sputtering a layer of refractory metal layer onto a barrier layer disposed on a substrate are disclosed herein. In one or more embodiments, a method of sputter depositing a tungsten structure in an integrated circuit includes: moving a substrate into a plasma processing chamber and onto a substrate support in opposition to a sputter target assembly comprising a tungsten target having no more than ten parts per million of carbon and no more than ten parts per million of oxygen present as impurities; flowing krypton into the plasma processing chamber; and exciting the krypton into a plasma to deposit, by sputtering, a tungsten film layer on a material layer of a substrate supported by the substrate support. In some embodiments, the target assembly further includes a titanium backing plate and an aluminum bonding layer disposed between the titanium backing plate and the tungsten target.