Sloped Control Gate Profile for Flash Memory Reliability
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Solution Overview
Problem
Flash memory devices face reliability concerns due to Infant Cycling Failure (ICF) caused by defects in charge storage materials or select gate oxides, which can compromise data integrity during manufacturing processes like depositions, cleaning, and etching, leading to unpredictable device endurance and data retention.
Innovation Solution
The implementation of a nonvolatile memory cell with a sloped control gate profile, which increases the contact-to-gate spacing and total dielectric thickness, reducing the likelihood of shorts and enhancing reliability by using a dry etch process to define the control gate and siliciding the polysilicon gate to lower wordline resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional vertical control gate profile is used, then the manufacturing process is simpler, but the contact-to-gate spacing is reduced leading to higher risk of shorts and lower reliability
Solution Approach 1:
The patent applies asymmetry by transitioning from a symmetric vertical control gate profile to an asymmetric sloped profile. The control gate is formed with a slope angle between 15-75 degrees relative to the substrate, creating unequal spacing on different sides of the gate structure. This asymmetric geometry increases the contact-to-gate spacing on the critical side without requiring complete redesign of the entire gate structure, thereby improving reliability while maintaining manufacturing feasibility.
Solution Approach 2:
The patent introduces a dimensional change by adding a slope angle dimension to the control gate profile. Instead of maintaining a purely vertical orientation, the control gate is inclined at an angle between 15-75 degrees, effectively utilizing the angular dimension to increase horizontal spacing. This dimensional transformation allows the contact-to-gate spacing to be increased from approximately 50-100 nm in vertical profiles to 150-300 nm in sloped profiles, directly addressing the reliability concern.
2Reliability
If the control gate spacing is increased to reduce shorts, then reliability improves, but the device area increases
Solution Approach 1:
The patent applies local quality by selectively increasing the control-to-contact spacing only in the critical regions where shorts are most likely to occur, rather than uniformly increasing spacing throughout the entire device. The sloped profile specifically targets the interface region between the control gate and contact structures, providing enhanced spacing locally where needed while maintaining compact overall device dimensions. This localized approach increases reliability without proportionally increasing the total device area.
Solution Approach 2:
By introducing the slope angle dimension, the patent achieves increased horizontal spacing without proportionally increasing the vertical height or lateral footprint of the device. The sloped profile utilizes the angular dimension to convert vertical space into horizontal spacing, allowing the contact-to-gate distance to increase from 50-100 nm to 150-300 nm while maintaining a compact device footprint suitable for high-density memory arrays.
3Manufacturing precision
If dry etch process is used to define control gate, then manufacturing precision improves, but process complexity increases
Solution Approach 1:
The patent applies parameter changes by optimizing the dry etch process parameters to achieve the desired sloped profile with slope angles between 15-75 degrees. Specific etch chemistry, power levels, pressure conditions, and gas flow rates are tuned to produce the precise angular geometry required. This parameter optimization enables the formation of accurate sloped profiles that provide the necessary 150-300 nm contact-to-gate spacing while maintaining manufacturing precision and control over the gate geometry.
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 sloped control gate profile improves device reliability by reducing the chances of contact-to-gate shorts and mitigating electrical stress effects, maintaining critical memory cell parameters and enhancing endurance and data retention in flash memory devices.
Implementation Method 1
using a dry etch process to define the control gate
Implementation Method 2
siliciding the polysilicon gate to lower wordline resistance
Data Source
AI summary
A nonvolatile memory device has a floating gate and a control gate. The floating gate incorporates a substantially vertical profile and provides the charge storage mechanism to set a specific threshold voltage. The control gate incorporates a sloped profile to enhance reliability.