Two-Step Gap-Fill Process for High Aspect Ratio Memory Cell Stacks

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Solution Overview

Problem

As semiconductor memory devices integrate more densely and patterns shrink, the large aspect ratio of memory cell stacks poses challenges in effectively filling gaps between cell stacks without forming seams or voids, which affects the structural stability and performance of the devices.

Innovation Solution

A two-step gap-fill process is employed, using a first source gas with a high volume ratio of a flowable precursor for the lower gap-fill process and a second source gas with a lower volume ratio of the same precursor for the upper gap-fill process, followed by curing and planarization to form a gap-fill insulator, ensuring adequate filling and conformality between cell stacks.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If a single-step gap-fill process is used, then the process complexity is low, but the filling capability in high aspect ratio gaps is insufficient and seams or voids form

Engineering Contradiction:

Improvefilling capabilityVSAvoidprocess complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The gap-fill process is divided into two distinct steps: a lower gap-fill process using a first source gas with high flowable precursor content to fill the bottom portion of high aspect ratio gaps, and an upper gap-fill process using a second source gas with lower flowable precursor content to fill the upper portion. This segmentation allows each step to be optimized for its specific region, eliminating seams and voids that would form with a single-step process.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different source gases with different precursor compositions are used for different regions of the gap-fill process. The first source gas with high flowable precursor content (ratio greater than 15:1) is applied to the lower region where better flow is needed to reach the bottom of high aspect ratio gaps, while the second source gas with lower flowable precursor content (ratio less than 15:1) is used for the upper region. This local optimization ensures complete filling throughout the entire gap height.

Inventive Principle:

Principle #3Local quality

2Productivity

If the aspect ratio of memory cell stacks increases due to higher integration, then the device density improves, but the difficulty of filling gaps without seams or voids increases

Engineering Contradiction:

Improvedevice densityVSAvoidgap filling quality

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The gap-fill process uses dynamic adjustment of precursor composition and deposition conditions between the two steps. The first step uses highly flowable precursor conditions to ensure material reaches the bottom of high aspect ratio gaps, while the second step adjusts to less flowable conditions for controlled upper region filling. This dynamic adaptation allows the process to handle varying aspect ratios effectively.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The process changes key parameters including precursor type, precursor ratio in source gas, and deposition conditions between the two gap-fill steps. The first step uses a high ratio of flowable precursor (greater than 15:1) while the second step uses a lower ratio (less than 15:1). These parameter changes enable the process to maintain filling quality as aspect ratios increase with higher device integration.

Inventive Principle:

Principle #35Parameter changes

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

This approach enhances the filling capability of gaps with high aspect ratios, reduces seams and voids, and improves the structural stability of cell stacks, ensuring reliable device performance.

Implementation Method 1

performing a lower gap-fill process to form a lower gap-fill insulator in the gaps... The lower gap-fill process may be performed using a first source gas that includes a first precursor and a second precursor

Methodology Applied

Scientific EffectChemical Vapour Deposition: Chemical Vapour Deposition

Implementation Method 2

performing an upper gap-fill process to form an upper gap-fill insulator on the lower gap-fill insulator... The upper gap-fill process may be performed using a second source gas that includes the first precursor and the second precursor

Methodology Applied

Scientific EffectChemical Vapour Deposition: Chemical Vapour Deposition

Implementation Method 3

curing the lower gap-fill insulator and the upper gap-fill insulator to form a gap-fill insulator

Methodology Applied

Scientific EffectCuring:

Data Source

PatentUS11063218B2Method of fabricating semiconductor devices using a two-step gap-fill process

Publication Date: 2021.07.13 SAMSUNG ELECTRONICS CO LTD

AI summary

A method of fabricating a memory device includes forming word lines and cell stacks with gaps between the cell stacks, forming a lower gap-fill insulator in the gaps, forming an upper gap-fill insulator on the lower gap-fill insulator, curing the lower gap-fill insulator and the upper gap-fill insulator to form a gap-fill insulator, and forming bit lines on the cell stacks and the gap-fill insulator. The lower gap-fill process may be performed using a first source gas that includes first and second precursors, and the upper gap-fill process may be performed using a second source gas that includes the first and second precursors, a volume ratio of the first precursor to the second precursor in the first source gas may be greater than 15:1, and a volume ratio of the first precursor to the second precursor in the second source gas may be less than 15:1.