Low Parasitic Capacitance Source-Drain Contacts in FinFET Devices
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Solution Overview
Problem
Existing methods for forming low parasitic capacitance source and drain contacts in field effect transistors risk damaging gate spacers due to marginal etch selectivity during the oxide etch process, requiring multiple etch steps that can be detrimental to the spacer integrity.
Innovation Solution
A method involving etching a long trench to the source-drain structure, forming a conductive layer, and using a highly selective fill material and etch-stop layer to minimize the risk of spacer damage, with anisotropic etching to create a second, narrower trench filled with a dielectric material, reducing the need for multiple oxide etches and enhancing etch selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple oxide etch steps are used to form low parasitic capacitance contacts, then the parasitic capacitance is reduced, but the gate spacers are damaged due to marginal etch selectivity
Solution Approach 1:
A sacrificial oxide layer is introduced as an intermediary material between the gate spacer and the contact trench fill. This sacrificial oxide absorbs the etching attacks that would otherwise damage the gate spacer, allowing multiple etch steps to proceed without compromising spacer integrity. The sacrificial oxide is selectively removed after serving its protective function.
Solution Approach 2:
The gate spacer is pre-protected by forming a sacrificial oxide layer before the contact trench etching process begins. This preliminary protective action ensures that subsequent etch steps, which are necessary for low parasitic capacitance, do not directly attack and damage the gate spacer.
2Manufacturing precision
If multiple etch steps are performed to create the contact structure, then the contact geometry is improved for low parasitic capacitance, but the process complexity and risk of spacer damage increase
Solution Approach 1:
The sacrificial oxide layer serves as a mediator that enables complex multi-step etching processes to be performed safely. It allows the formation of precise contact geometries through multiple etch steps while protecting the gate spacer, thus achieving high manufacturing precision without proportionally increasing process risk or complexity.
Solution Approach 2:
The etch selectivity parameters are optimized by choosing materials and etch conditions where the sacrificial oxide has high etch rate compared to the gate spacer material. This parameter change allows multiple etch steps to be performed with controlled material removal, achieving precise contact geometry while maintaining process manageability.
3Ease of manufacture
If the dielectric fill material is etched with low selectivity to the gate spacer, then the etch process is simpler, but the gate spacer is at risk of damage
Solution Approach 1:
The sacrificial oxide acts as an intermediary that decouples the etch selectivity requirement from the gate spacer. The etch process can have low selectivity to the sacrificial oxide (making the process simpler), while the sacrificial oxide itself protects the gate spacer from damage, thus maintaining reliability without compromising ease of manufacture.
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 reduces parasitic capacitance while protecting gate spacers by using a single oxide etch and highly selective etching processes, improving the reliability and efficiency of the contact formation process.
Implementation Method 1
etching, with an anisotropic etch, the second portion of the first fill material to form a second trench
Data Source
AI summary
A method for forming a low parasitic capacitance contact to a source-drain structure of a fin field effect transistor device. In some embodiments the method includes etching a long trench down to the source-drain structure, the trench being sufficiently long to extend across all the of source-drain regions of the device. A conductive layer is formed on the source-drain structure, and the trench is filled with a first fill material. A second, narrower trench is opened along a portion of the length of the first trench, and filled with a second fill material. The first fill material may be conductive, and may form the contact. If the first fill material is not conductive, a third trench may be opened, in the portion of the first trench not filled with the second fill material, and filled with a conductive material, to form the contact.