TSV Formation via Via-Last Approach with Mandrel Etch Stop
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Solution Overview
Problem
The via-last approach in TSV formation, where TSVs are created from the backside of a wafer, faces issues with lateral etching that widens ILD openings and risks etching through thin metal pads, complicating the formation of isolation layers and potentially damaging metal layers.
Innovation Solution
The method involves forming M0 metal pads with a conductive barrier layer and inner region within STI pads, stopping the etch at an intermediate level to prevent STI pad etching, and then forming TSVs that land on these pads, ensuring reliable coupling and minimizing damage to subsequent metal layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If TSVs are formed using the via-last approach from the backside of the wafer, then the TSVs can be formed after all metal layers and passivation layers are formed, but serious lateral etching occurs in the ILD causing the TSV openings to be wider than the openings in the semiconductor substrate
Solution Approach 1:
The patent applies local quality by forming a mandrel structure with different material properties in different regions. The mandrel includes a first portion with a first material and a second portion with a second material, where each material is selectively etched by different etchants. This allows precise control of the TSV opening width at different levels (in the substrate versus in the ILD) by selectively removing specific portions of the mandrel, thereby resolving the lateral etching issue while maintaining the via-last approach flexibility.
2Adaptability or versatility
If TSVs are formed using the via-last approach, then TSVs can be formed after metal layers are formed, but the metal pads in the bottom metal layer may be undesirably etched or etched through during TSV opening formation
Solution Approach 1:
The mandrel structure is designed with local quality variations where specific portions are made of materials resistant to the etchants used for TSV formation. This protects the underlying metal pads from being etched or etched through during the TSV opening process, while still allowing the via-last approach to be implemented after metal layers are formed.
Solution Approach 2:
The mandrel acts as an intermediary structure that mediates between the etching process and the metal pads. It provides a protective barrier during TSV formation, allowing the etch to proceed through the ILD and into the substrate without directly contacting and damaging the metal pads underneath.
3Adaptability or versatility
If TSVs are formed using the via-last approach, then TSVs can be formed after metal layers are formed, but difficulty occurs in the formation of isolation layers on the sidewall of the TSV openings
Solution Approach 1:
The mandrel structure provides well-defined sidewalls with controlled geometry throughout the etching process. This creates uniform TSV openings with consistent width and shape, making it easier to form isolation layers on the sidewalls. The selective etching of different mandrel portions ensures that the opening geometry is optimized for subsequent isolation layer deposition.
Data Source
AI summary
A device includes a semiconductor substrate having a front surface and a back surface opposite the front surface. An insulation region extends from the front surface into the semiconductor substrate. An inter-layer dielectric (ILD) is over the insulation region. A landing pad extends from a top surface of the ILD into the insulation region. A through-substrate via (TSV) extends from the back surface of the semiconductor substrate to the landing pad.