SRAM Strap Cell Stress Reduction via Segmented Contacts
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional SRAM strap cells experience mechanical stress during high-temperature fabrication, leading to stress-induced diffusion of Copper and electrical shorts, which compromises data storage reliability.
Innovation Solution
Incorporating multiple supply contacts in the Nwell tap and non-active gates in the Pwell tap of SRAM strap cells to reduce mechanical stress, thereby preventing stress fields and Copper diffusion, and ensuring even charge distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SRAM strap cells are fabricated with single supply contacts, then device complexity is reduced, but mechanical stress increases leading to Copper diffusion and electrical shorts
Solution Approach 1:
The patent divides the single supply contact into multiple supply contacts (first supply contact and second supply contact) within the Nwell tap and Pwell tap. This segmentation reduces mechanical stress concentration and prevents Copper diffusion from the backside of the die, thereby improving data storage reliability while maintaining manageable device complexity through systematic structural division.
2Object-affected harmful factors
If multiple supply contacts are used in Nwell tap and Pwell tap, then mechanical stress is reduced preventing Copper diffusion, but device complexity increases
Solution Approach 1:
The supply contact structure is segmented into multiple discrete contacts (first supply contact coupled to Nwell, second supply contact coupled to Pwell) rather than a single continuous contact. This segmentation distributes mechanical stress across multiple points, preventing the formation of stress fields that would drive Copper diffusion, while the modular nature of the segmentation keeps the added complexity manageable.
Solution Approach 2:
Different regions of the strap cell are given different structural qualities: the Nwell tap receives a first supply contact configured to reduce tensile stress, while the Pwell tap receives a second supply contact configured to reduce compressive stress. This local differentiation addresses specific mechanical stress conditions in different areas, effectively preventing Copper diffusion without requiring uniform complexity throughout the entire device.
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 solution effectively reduces mechanical stress and prevents electrical shorts, enhancing the reliability of data storage by maintaining uniform charge distribution and preventing Copper diffusion from the backside of the die.
Implementation Method 1
The N-type doped material regions are coupled to a positive voltage source and the P-type doped material regions are coupled to a negative voltage source. Coupling the voltage sources to the SRAM strap cell in this manner results in the substrate of the corresponding SRAM bit cell row having a more uniform charge distribution
Implementation Method 2
fabricating conventional SRAM strap cells includes exposing the corresponding die to temperatures exceeding 150 degrees Celsius (C). However, it has been observed that portions of an SRAM strap cell suffer from relatively high levels of mechanical stress under such temperature conditions. The mechanical stress can create stress fields within the die, which allows Copper (Cu) to diffuse (i.e., stress-induced diffusion) from the backside of the die
Data Source
AI summary
Aspects for reducing or avoiding mechanical stress in static random access memory (SRAM) strap cells are disclosed herein. An exemplary SRAM strap cell includes a P-type doped well (Pwell) tap electrically coupled to a first supply rail to distribute a first supply voltage to a Pwell region of corresponding SRAM bit cell rows. The SRAM strap cell also includes an N-type doped well (Nwell) tap electrically coupled to a second supply rail to distribute a second supply voltage to an Nwell region of corresponding SRAM bit cell rows. In one exemplary aspect, the Nwell tap can include multiple supply contacts used to couple the second supply rail to the SRAM strap cell to reduce mechanical stress in the Nwell tap. In another exemplary aspect, the Pwell tap can include non-active gates disposed across multiple Fins to stabilize the Fins and reduce or avoid mechanical stress in the Pwell tap.