Front Via Structure for Backside Power Rail Connection Without Voids
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Solution Overview
Problem
The formation of high-aspect-ratio via structures in semiconductor devices is challenging due to difficulties in patterning and etching, often resulting in incomplete filling and voids at the bottom of the via holes, which deteriorate the connection performance between the front side and back side power distribution networks.
Innovation Solution
A semiconductor device with a front via structure formed in a via hole composed of a lower and upper via hole connected vertically, where the lower via hole has a higher aspect ratio than the upper via hole, and a connection surface is formed between them, potentially including a silicide layer, to facilitate better connection between the front side source/drain region contact plug and the back side buried power rail.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-aspect-ratio via hole is formed to connect front side structure to back side BSPDN structure, then the connection between front side and back side is achieved, but the via hole cannot be completely filled and voids are generated at the bottom portion
Solution Approach 1:
The via hole formation process is segmented into two distinct stages: first forming an initial via hole through the isolation layer to reach the BSPDN structure, then forming a second via hole through the first via hole to create the final front via. This segmentation allows each etching step to work with a lower aspect ratio, improving etching quality and material filling completeness while maintaining the overall high-aspect-ratio connection capability.
Solution Approach 2:
The first via hole is formed in advance as a preliminary structure that facilitates the subsequent formation of the second via hole. This preliminary action creates a guided pathway that enables better control over the final via hole formation and filling process, ensuring complete material deposition without voids at the bottom portion.
2Reliability
If a high-aspect-ratio via hole is formed to connect front side structure to back side BSPDN structure, then the connection between front side and back side is achieved, but patterning and etching become extremely difficult
Solution Approach 1:
The complex high-aspect-ratio via hole patterning and etching process is divided into two simpler sequential processes. The first process forms a via hole with moderate aspect ratio through the isolation layer, and the second process forms another via hole through the first via hole. This segmentation makes each patterning and etching step more manageable and controllable, reducing manufacturing difficulty while achieving the required connection.
Solution Approach 2:
The via hole formation is approached by adding a temporal dimension to the process - forming via holes in two distinct time steps rather than attempting to form the complete high-aspect-ratio via in a single step. This dimensional change in the process flow transforms an intractable single-step problem into two manageable sequential steps.
Data Source
Figure 1
Figure 2A~2B
Figure 2C~2D
AI summary
Provided is a semiconductor device that includes: at least one transistor, a front side structure, and a back side structure, the front side structure being disposed opposite to the back side structure with respect to the transistor; and a front via formed at a side of the transistor and connecting the front side structure to the back side structure, wherein the front via is formed in a via hole formed of a lower via hole and an upper via hole vertically connected to each other, and wherein the via hole has a bent structure at a side surface thereof where the lower via hole is connected to the upper via hole.