High Aspect Ratio Contact Filling in Power MOSFETs
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Solution Overview
Problem
As semiconductor technology advances to smaller geometries, forming and properly filling high aspect ratio contact openings in power MOSFETs becomes increasingly difficult, necessitating new techniques for effective metal contact to source and heavy body regions.
Innovation Solution
The implementation of a seed layer at the bottom of contact openings to promote growth of conductive fill material, combined with dielectric spacers along lower sidewalls to prevent contact with body regions, and an interconnect layer that contacts the source regions along upper sidewalls, allowing for void-free filling of high aspect ratio contact openings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If contact openings are made smaller to support smaller geometries, then device density is improved, but filling reliability deteriorates due to high aspect ratio forming difficulties
Solution Approach 1:
A seed layer is deposited at the bottom of contact openings before filling with conductive material. This preliminary action provides a nucleation site that promotes reliable growth of conductive fill material, solving the filling reliability issue while maintaining small contact opening dimensions for high device density
Solution Approach 2:
Dielectric spacers are introduced as an intermediary material lining the lower sidewalls of contact openings. These spacers prevent direct contact between conductive fill material and body regions, enabling reliable filling of high aspect ratio openings while maintaining proper electrical isolation and small opening sizes
2Reliability
If contact openings have high aspect ratio to maintain electrical isolation, then device performance is improved, but manufacturing difficulty increases
Solution Approach 1:
The contact opening structure is segmented into distinct functional zones: dielectric spacers line the lower sidewalls to provide electrical isolation, while the upper portion remains open for conductive material filling. This segmentation enables high aspect ratio openings to be manufactured reliably by separating the isolation function from the filling function
Solution Approach 2:
Different regions of the contact opening are assigned different properties: dielectric material is placed specifically at the lower sidewalls for electrical isolation, while the upper portion and bottom are prepared with seed layers for conductive filling. This local differentiation resolves the manufacturing difficulty by addressing each region's specific requirements
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 enables reliable and efficient filling of high aspect ratio contact openings in power MOSFETs, reducing the formation of keyholes or voids and ensuring proper electrical contact, thereby improving the performance and reliability of semiconductor devices.
Implementation Method 1
The seed layer serves as a nucleation site for promoting growth of conductive fill material
Implementation Method 2
The step of filling a lower portion of each contact opening is carried out using electro-less plating
Data Source
AI summary
A field effect transistor (FET) includes body regions of a first conductivity type over a semiconductor region of a second conductivity type. Source regions of the second conductivity type extend over the body regions. Gate electrodes extend adjacent to but are insulated from the body regions by a gate dielectric layer. Contact openings extend into the body regions between adjacent gate electrodes. A seed layer extends along the bottom of each contact opening. The seed layer serves as a nucleation site for promoting growth of conductive fill material. A conductive fill material fills a lower portion of each contact opening. An interconnect layer fills an upper portion of each contact opening and is in direct contact with the conductive fill material. The interconnect layer is also in direct contact with corresponding source regions along upper sidewalls of the contact openings.