Self-Aligned MOS Contacts Using an Insulator Cap Etch Stop
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Solution Overview
Problem
The formation of contact-to-gate shorts in metal-oxide-semiconductor (MOS) transistors becomes prevalent as transistor gate pitches scale down, with existing methods struggling to maintain precise registration and critical dimensions, leading to increased parasitic capacitance and yield loss.
Innovation Solution
The implementation of an insulator-cap layer atop the gate electrode and within spacers in MOS transistors, which electrically isolates the gate from the contact, allowing for self-aligned contact formation and reducing the likelihood of shorts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional contact formation methods are used, then manufacturing process is simple, but contact-to-gate shorts occur frequently due to misalignment
Solution Approach 1:
An insulator cap layer is introduced as an intermediary structure between the gate electrode and the contact opening. This mediator provides electrical isolation and physical protection, preventing direct contact between conductive elements even when alignment is imperfect, thereby resolving the contradiction between reliability and structural simplicity.
Solution Approach 2:
The insulator cap layer is formed on the gate electrode before contact opening formation. This preliminary action prepares the gate structure in advance to withstand potential misalignment during subsequent contact formation, eliminating the need for extremely precise alignment while maintaining reliability.
2Area of moving object
If gate pitch is scaled down to increase density, then transistor density improves, but registration control and critical dimension control become much harder
Solution Approach 1:
The insulator cap layer serves a dual function: it provides electrical isolation (protective function) and acts as an etch stop layer that defines the contact opening boundary (alignment function). This self-service capability allows the structure to self-align during contact formation, reducing dependence on external registration control and enabling successful fabrication even with relaxed alignment tolerances.
Solution Approach 2:
The insulator cap layer acts as a cushioning layer that absorbs the impact of potential misalignment. By providing a buffer zone between the gate electrode and contact opening, it tolerates larger dimensional variations and registration errors, enabling gate pitch scaling while maintaining manufacturing feasibility.
3Manufacturing precision
If tighter critical dimension control is implemented, then contact alignment improves, but manufacturing complexity and cost increase
Solution Approach 1:
The insulator cap layer creates a self-aligned contact formation process where the contact opening naturally aligns to the gate electrode through the etch stop function of the cap layer, eliminating the need for complex external alignment control mechanisms and reducing manufacturing complexity.
Solution Approach 2:
The patent combines multiple functions into the insulator cap layer structure: electrical isolation, etch stop, and alignment reference. This merging of functions into a single structure simplifies the overall manufacturing process by reducing the number of separate control steps required, thereby reducing manufacturing complexity while maintaining precision.
Data Source
AI summary
A transistor comprises a substrate, a pair of spacers on the substrate, a gate dielectric layer on the substrate and between the pair of spacers, a gate electrode layer on the gate dielectric layer and between the pair of spacers, an insulating cap layer on the gate electrode layer and between the pair of spacers, and a pair of diffusion regions adjacent to the pair of spacers. The insulating cap layer forms an etch stop structure that is self aligned to the gate and prevents the contact etch from exposing the gate electrode, thereby preventing a short between the gate and contact. The insulator-cap layer enables self-aligned contacts, allowing initial patterning of wider contacts that are more robust to patterning limitations.