Backside Contact Structure for Void-Free Power Rail Filling
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Solution Overview
Problem
Existing semiconductor device structures face issues with metal void formation in backside contact areas due to tapered shapes, leading to increased resistance and potential circuit damage.
Innovation Solution
The implementation of a backside contact structure with a positive slope profile, comprising an initial cylindrical portion and a series of truncated-cone shaped portions, utilizing a double SiGe etch stop layer to enhance metal filling and reduce void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a tapered backside contact area shape is used, then the contact area can be formed in the substrate, but metal voids are generated in the hole or trench leading to increased resistance and potential circuit damage
Solution Approach 1:
The patent inverts the conventional tapered profile by implementing a positive slope profile where the contact area widens toward the metal filling layer rather than narrowing. This inversion of the traditional approach prevents metal void formation during the filling process, as the widening profile allows metal to flow in smoothly without trapping voids, thereby improving reliability while maintaining manufacturability
Solution Approach 2:
The patent changes the geometric parameters of the backside contact area by transitioning from a negative slope (tapered) profile to a positive slope profile. This parameter change in the contact area geometry fundamentally alters the metal filling behavior, enabling complete metal deposition without void formation and resolving the contradiction between manufacturing feasibility and reliability
2Ease of manufacture
If a direct backside contact structure is implemented, then process capability and dimension limitations are improved, but profile improvement of the backside contact area is needed to prevent metal voids
Solution Approach 1:
The patent applies preliminary action by forming the positive slope profile of the backside contact area before the metal filling process. This pre-established profile ensures that subsequent metal deposition will proceed without void formation, combining the ease of direct backside contact manufacturing with the precision needed to prevent defects
Solution Approach 2:
The patent introduces an intermediary etch stop layer that facilitates the formation of the positive slope profile. This intermediary layer enables precise control over the contact area geometry during etching, allowing the transition from conventional tapered profiles to the improved positive slope profile that prevents metal voids while maintaining manufacturing simplicity
Data Source
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Figure 3A~3C
Figure 4A~4C
AI summary
Provided is a device comprising a semiconductor device on a substrate, the semiconductor device having at least two sides and including a bottom dielectric isolation; a channel structure and a gate at least partially surrounding the channel structure; a plurality of source/drain structures on opposing sides of the channel structure; and one or more metal signal routing layers disposed on an opposite side of the semiconductor device than the substrate, wherein the substrate is on a first side of the semiconductor device and includes: a backside power rail, BPR; a backside contact structure, the backside contact structure vertically between the backside power rail and a first source/drain structure, wherein the backside contact structure comprises a first portion contacting the first source/drain structure, having a positive slope, wherein the backside contact structure further comprises a second portion adjacent to the first portion having no slope, extending from the first portion to a distance further distal from the first source/drain structure.