Dummy Contacts Mitigate Plasma Charging Damage in MOS Gate Dielectrics
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Plasma charging damage to the gate dielectric during the manufacturing of metal-oxide-semiconductor (MOS) devices, particularly during plasma etching, leads to yield and reliability issues due to the accumulation of excess electrical charge, which can cause dielectric breakdown.
Innovation Solution
The introduction of dummy contacts (DCs) in the metal 1 contact reticle design increases contact density in the active area, mitigating plasma charging damage without requiring changes to the fabrication process, by ensuring that dummy contacts are strategically placed to connect with dummy polysilicon on field oxide, dummy active areas, or between polysilicon features, and are not electrically connected to MOS transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If plasma etching is used to etch metal 1 layer, then etch rate and tool throughput are improved, but plasma charging damage accumulates on isolated metal pieces causing gate dielectric breakdown
Solution Approach 1:
The patent applies preliminary action by adding dummy contacts to the contact reticle design before fabrication. These dummy contacts are strategically placed in the active area to ensure that during plasma etching, charge can be dissipated before it accumulates to dangerous levels. The dummy contacts connect to dummy polysilicon regions, creating predetermined charge dissipation paths that prevent dielectric breakdown while maintaining normal etching conditions.
Solution Approach 2:
The dummy contacts serve as an intermediary element between the plasma etching process and the gate dielectric. By introducing these dummy contacts that connect to dummy polysilicon, the patent creates an intermediate charge dissipation mechanism that protects the gate dielectric from direct plasma charging damage. The dummy contacts act as a buffer that intercepts and dissipates charge before it can reach critical levels that would cause breakdown.
2Reliability
If RF power is lowered to mitigate plasma charging damage, then gate dielectric protection is improved, but etch rate and tool throughput are reduced
Solution Approach 1:
The dummy contacts serve as an intermediary element between the plasma etching process and the gate dielectric. By introducing these dummy contacts that connect to dummy polysilicon, the patent creates an intermediate charge dissipation mechanism that protects the gate dielectric from direct plasma charging damage. The dummy contacts act as a buffer that intercepts and dissipates charge before it can reach critical levels that would cause breakdown.
Solution Approach 2:
The patent extracts the charge dissipation function from the normal metal interconnect structure and places it in dedicated dummy contact regions. By separating the charge dissipation function into distinct dummy contacts that connect to dummy polysilicon, the patent allows the main metal 1 layer to focus on its primary function of signal transmission while the dummy contacts handle charge dissipation, preventing interference with normal etching operations.
3Reliability
If contact density is increased by adding dummy contacts, then plasma charging damage is mitigated, but device complexity increases
Solution Approach 1:
The patent applies local quality by concentrating dummy contacts in specific regions where they are most needed - the active area - rather than uniformly distributing them across the entire chip. The dummy contacts are placed in locations where they can effectively dissipate charge from isolated metal pieces, while leaving other regions unchanged. This localized approach provides targeted protection without unnecessarily increasing overall device complexity.
Solution Approach 2:
The dummy contacts serve multiple functions: they provide charge dissipation paths during plasma etching, maintain contact density requirements, and connect to dummy polysilicon regions that already exist in the design. By making the dummy contacts multi-functional, the patent reduces the need for separate structures dedicated solely to charge dissipation, thereby minimizing the increase in device complexity while achieving reliable plasma charging damage mitigation.
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 effectively eliminates plasma charging damage to the gate dielectric, as evidenced by a significant reduction in gate oxide leakage and failure rates, with no antenna fails observed across 22 wafers, compared to a 15-20% failure rate without the dummy contacts, while maintaining etch tool throughput.
Implementation Method 1
Plasma charging damage to the gate dielectric during the manufacturing of metal-oxide-semiconductor (MOS) devices, particularly during plasma etching, leads to yield and reliability issues due to the accumulation of excess electrical charge
Data Source
AI summary
A method of limiting plasma charging damage on ICs. A die includes gate stacks on active areas defined by a field dielectric. A pre-metal dielectric (PMD) layer is over the gate electrode. A contact masking material pattern is defined on the PMD layer including first contact defining features for forming active contacts and second contact defining features for forming dummy contacts (DC's) including over active areas and gate electrodes. Contacts are etched through the PMD layer using the contact masking material pattern to form active contacts and DC's. A patterned metal 1 (M1) layer is formed including first M1 portions over the active contacts and dummy M1 portions over the DC's. Metallization processing follows including forming interconnects so that the active contacts are connected to MOS transistors on the IC, and the DC's are not electrically connected to the MOS transistors.