3D Source Contact Structure for Reduced-Pitch Power MOSFETs
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Solution Overview
Problem
Existing methodologies for reducing the cell pitch in high-power MOSFETs, such as VDMOSFET and UMOSFET, face limitations due to increased process complexity and alignment errors, leading to uneven contact resistances and degraded device reliability.
Innovation Solution
A novel process method involving a silicon carbide shallow trench process and lateral etching is employed to form a three-dimensional source contact structure, allowing for reduced cell pitch and maintaining equal contact areas on both sides of the source region, thereby reducing process complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the contact width of the source and metal is reduced to shorten cell pitch, then the cell density increases, but the contact resistance increases
Solution Approach 1:
The patent transitions from a planar two-dimensional contact structure to a three-dimensional contact structure by forming a trench in the dielectric layer and filling it with metal. This vertical dimension addition increases the contact area between source and metal without increasing the lateral cell pitch, thereby maintaining low contact resistance while achieving high cell density.
2Productivity
If the contact window width is reduced to shorten cell pitch, then the cell density increases, but the process complexity increases
Solution Approach 1:
The patent employs self-aligned processes where the metal contact window is automatically positioned relative to the source region through the trench formation and filling process. This self-alignment mechanism eliminates the need for separate alignment steps and reduces process complexity while achieving the desired contact geometry for high cell density.
3Productivity
If the contact window width is reduced to shorten cell pitch, then the cell density increases, but the alignment precision requirements increase
Solution Approach 1:
The patent introduces a dielectric layer with a trench as an intermediary structure between the source region and the metal contact. This intermediary trench structure serves as a self-aligned template that automatically defines the metal contact window position, eliminating the need for high-precision alignment between separate lithography steps and reducing alignment precision requirements.
4Reliability
If the overlapping length of contact window and source region is increased to reduce contact resistance, then the contact resistance decreases, but the cell pitch increases
Solution Approach 1:
The patent resolves this contradiction by adding a vertical dimension through trench formation. The increased contact area is achieved through the depth of the trench rather than increasing the lateral overlapping length, thus reducing contact resistance without increasing the horizontal cell pitch.
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
The method effectively reduces cell pitch by 10-20% while maintaining consistent contact areas, enhancing horizontal and vertical contact surfaces for improved device performance and reliability.
Implementation Method 1
a silicon carbide shallow trench process along the metal contact window is performed to divide the source heavily doped area into a first heavily doped region and a second heavily doped region
Implementation Method 2
a lateral etching process to the inter-layer dielectric wherein the spacing is formed is performed to expose the first metal-source surface contact region and the second metal-source surface contact region
Implementation Method 3
source contact metal is deposited such that the source contact metal covers at least the first metal-source surface contact region, the second metal-source surface contact region, a longitudinal surface along the first heavily doped region and the second heavily doped region, and an interval surface between the first heavily doped region and the second heavily doped region
Data Source
AI summary
A process method for fabricating a three-dimensional source contact structure is provided, which is applicable to form a step-like three-dimensional source contact structure in a MOSFET of a power device. The proposed method sequentially adopts a lithography process and a shallow trench process to form a metal contact window. And a lateral etching process, or spacers which will be removed eventually, can be alternatively provided for increasing horizontal surface contact when depositing a source contact metal. Meanwhile, a longitudinal surface exposed by the shallow trench process is also beneficial to increase vertical contact when depositing the source contact metal. As a result, a step-like three-dimensional source contact structure can be formed by employing the present invention. It is believed that the present invention achieves in reducing cell pitch effectively and can be widely applied to various power devices having MOSFET structure thereof.