Metal Gate Contact Undercut for Reduced Resistance
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Solution Overview
Problem
The challenge in semiconductor device fabrication lies in the shrinking size of gate structures in MOSFET devices and the integration of high-k dielectric materials with metal gates, requiring improved methods for trench formation and metal gate replacement to enhance contact efficiency and reduce power consumption.
Innovation Solution
The method involves forming a substrate with a polysilicon gate structure, followed by doping and replacing it with a metal gate, and using a combination of dry and wet etch processes to create undercuts and fill trenches with conductive materials, such as tungsten, to increase contact area and reduce contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a standard anisotropic etch process is used to create a trench in the dielectric, then the trench can be formed with good vertical profile, but the contact area with the metal gate structure is limited
Solution Approach 1:
The patent transitions from a purely vertical trench etch to a two-stage process that creates both vertical walls and lateral undercuts. The first anisotropic etch establishes the vertical trench profile, while the second isotropic etch adds lateral dimensions by forming undercuts beneath the metal gate structure. This dimensional expansion significantly increases the contact surface area between the conductive material and metal gate without compromising the vertical alignment established in the first stage.
2Productivity
If the gate structure size is shrunk to increase density, then device density and power reduction are achieved, but contact resistance increases due to reduced contact area
Solution Approach 1:
The patent applies local quality by creating region-specific etching characteristics. The anisotropic etch provides precise vertical walls in the upper dielectric region, while the isotropic etch creates lateral undercuts in the lower dielectric region beneath the metal gate. This localized differentiation of etching behavior allows the contact structure to expand laterally at the bottom while maintaining vertical precision at the top, thereby increasing contact area and reducing contact resistance even in scaled devices.
3Area of moving object
If only a single anisotropic etch process is used, then the process is simple and fast, but the contact area with metal gate structure is insufficient
Solution Approach 1:
The etch process is segmented into two distinct stages with different characteristics. The first stage uses an anisotropic etch to create the initial vertical trench with good profile control. The second stage uses an isotropic etch to form lateral undercuts that expand the contact area. By dividing the etching operation into these two specialized segments, each optimized for its specific function, the process achieves superior contact area without requiring complete process redesign.
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 results in reduced contact resistance and improved surface contact between gate contacts and metal gate stacks, enhancing the performance and density of integrated circuit devices.
Implementation Method 1
a wet etch process forms an undercut near the top surface of the metal gate structure
Implementation Method 2
a dry etch process forms a trench in the ILD to a top surface of the metal gate structure
Data Source
AI summary
An integrated circuit includes a semiconductor substrate including a source region and a drain region and a gate dielectric over the semiconductor substrate. A metal gate structure is over the semiconductor substrate and the gate dielectric and between the source and drain regions. The integrated circuit further includes an interlayer dielectric (ILD) over the semiconductor substrate. First and second contacts extend through the ILD and adjacent the source and drain regions, respectively, and a third contact extends through the ILD and adjacent a top surface of the metal gate structure. The third contact further extends into an undercut region of the metal gate structure.