Single Work Function Metal Gate for Low Resistance MOSFETs
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Solution Overview
Problem
The existing replacement metal gate process for MOSFETs faces challenges in achieving low gate resistance due to the need for multiple work function metals, which complicates the filling process and results in high gate resistance, threshold voltage shifts, and variability, especially with shrinking gate sizes.
Innovation Solution
The method involves forming oppositely doped high-k dielectric gates with a shared, thin work function metal, allowing for a significant bulk fill material in the gate opening, which reduces gate resistance while maintaining correct work functions for N-FETs and P-FETs, by using a 'high-k first' or 'high-k last' process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple work function metals are used in the gate opening, then the correct work functions for N-FET and P-FET can be achieved, but the gate opening becomes difficult to fill and gate resistance increases
Solution Approach 1:
The patent extracts the work function metal from the bulk fill position and places it only as a thin lining layer on the sidewalls and bottom of the gate opening. This allows the bulk fill material to be a single low-resistance material while the work function is provided by the thin metal lining, resolving the contradiction between achieving correct work functions and enabling easy filling with low gate resistance.
Solution Approach 2:
The gate structure uses a composite configuration combining a thin work function metal layer with a bulk fill material. The work function metal provides the necessary electrical work function properties, while the bulk fill material provides low resistance, achieving both requirements simultaneously through material composition rather than using multiple thick metal layers.
2Ease of manufacture
If work function metal recess is performed to create more space for bulk fill material, then gate resistance can be reduced, but the process complexity increases and threshold voltage shifts occur
Solution Approach 1:
The work function metal is deposited as a thin lining layer before the bulk fill material is deposited. This preliminary action of creating the work function metal lining first allows subsequent bulk fill material to be deposited without requiring complex recess processes, simplifying the overall manufacturing process while still providing space for adequate bulk fill material.
3Ease of manufacture
If work function metal recess is performed, then more space for bulk fill material is created, but repeatability and uniformity deteriorate
Solution Approach 1:
By extracting the work function metal to a thin lining configuration rather than using thick bulk layers, the process becomes less sensitive to variations in deposition and etching parameters. This thin lining approach provides better repeatability and uniformity across wafers and through the manufacturing process while still providing adequate space for bulk fill material to achieve low gate resistance.
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 simplifies the process, reduces gate resistance, and improves repeatability and uniformity, allowing for a substantial bulk fill material in the gate opening, even at small gate sizes, while setting the correct work functions for N-FETs and P-FETs, thereby enhancing device performance.
Implementation Method 1
doping of a high-k dielectric film of the gates allows both the N-FET and P-FET gates to share the same, thin, work function metal
Data Source
AI summary
A method for forming a replacement metal gate structure sharing a single work function metal for both the N-FET and the P-FET gates. The method oppositely dopes a high-k material of the N-FET and P-FET gate, respectively, using a single lithography step. The doping allows use of a single work function metal which in turn provides more space in the metal gate opening so that a bulk fill material may occupy more volume of the opening resulting in a lower resistance gate.