Replacement Gate Spacer Structure for MOS Spacer Spike Removal
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The poly depletion effect in Metal-Oxide-Semiconductor (MOS) devices, caused by depletion layers forming in gate regions, increases the effective gate dielectric thickness, making it difficult to generate an inversion layer at the semiconductor surface, and the formation of metal gates is challenging due to the formation of spacer spikes during the dummy gate stack removal process.
Innovation Solution
The method involves forming replacement gate spacers to act as an etching mask, etching the spacer spikes, and replacing the top portions of gate spacers with a different material to prevent adverse etching of the gate spacers, using anisotropic etching processes to remove spacer spikes while protecting the underlying structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If anisotropic etching process is used to remove spacer spikes, then spacer spikes are effectively removed, but the gate spacers are adversely etched
Solution Approach 1:
The gate spacer is segmented into two distinct parts: the lower portion made of first material and the upper portion made of second material. This segmentation allows differential etching where the anisotropic etching process selectively removes spacer spikes and first material while preserving the second material portion, thus protecting the gate spacer structure.
Solution Approach 2:
Different materials are used for different portions of the gate spacer to create local quality variations. The first material (e.g., silicon nitride) has high etch selectivity against silicon dioxide, making it resistant to anisotropic etching, while the second material (e.g., silicon oxide) is more easily etched. This allows the upper portion to be removed while protecting the lower portion.
2Ease of manufacture
If dummy gate stacks are removed to form trenches, then metal gates can be formed, but spacer spikes are formed that complicate the process
Solution Approach 1:
The gate spacer is formed with a two-material structure before the dummy gate stack removal process. This preliminary structuring ensures that when spacer spikes form during subsequent processing, they are already differentiated in material composition, enabling selective removal later without affecting the main gate spacer body.
Solution Approach 2:
The problematic spacer spikes are selectively extracted from the structure through anisotropic etching that targets the first material while leaving the second material intact. This extraction removes the harmful spacer spikes that would otherwise complicate the metal gate formation process.
3Device complexity
If conventional polysilicon gates are used, then device structure is simple, but poly depletion effect increases effective gate dielectric thickness
Solution Approach 1:
The gate structure transitions from conventional single-material polysilicon gates to composite metal gate structures with multiple layers (e.g., tungsten, cobalt, titanium nitride, tantalum nitride). These composite structures eliminate poly depletion effects by using metals that do not form depletion layers, while maintaining controllable effective gate dielectric thickness through precise layer thickness control.
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 removes spacer spikes without adversely affecting the gate spacers, ensuring precise formation of metal gates that mitigate the poly depletion effect, enhancing the performance of MOS devices.
Implementation Method 1
performing a second etching process to remove the spacer spike, wherein the second etching process is an anisotropic etching process
Data Source
AI summary
A method includes forming a dummy gate electrode on a semiconductor region, forming a first gate spacer on a sidewall of the dummy gate electrode, and removing an upper portion of the first gate spacer to form a recess, wherein a lower portion of the first gate spacer remains, filling the recess with a second gate spacer, removing the dummy gate electrode to form a trench, and forming a replacement gate electrode in the trench.