Polysilicon Control Gate Void Prevention via Nitrogen Doping
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Solution Overview
Problem
The reduction in gap size between memory cells in nonvolatile memory devices makes it difficult to form a control gate with uniform grain size, leading to voids that affect electrical properties and coupling ratios, causing abnormal cell distribution and reliability issues.
Innovation Solution
Incorporating a nitrogen source gas in the polysilicon deposition process for forming the control gate, along with a silicon source gas and impurity doping gas, to inhibit grain size increase and prevent void formation, while performing thermal nitrification of the dielectric layer to ensure uniform grain size and electrical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If polysilicon is grown and formed on the dielectric layer to form the control gate, then the control gate can be formed, but large and uniform grain size of polysilicon generates voids between grains
Solution Approach 1:
The patent changes the chemical composition parameters of the deposition environment by introducing nitrogen source gas (NH3, N2O, or NO) along with silicon source gas and impurity doping gas. This parameter change in the gas composition during polysilicon deposition modifies the grain growth characteristics, resulting in smaller and more uniform grain sizes that prevent void formation while maintaining electrical property consistency
Solution Approach 2:
The patent creates a composite deposition environment by combining multiple gas sources (nitrogen source gas, silicon source gas, and impurity doping gas) in specific flow rate ratios. This composite gas mixture produces polysilicon with modified microstructural properties, achieving fine-grained uniform structure without voids while maintaining the necessary electrical characteristics for control gate functionality
2Productivity
If the gap between memory cells is reduced to increase integration density, then device integration increases, but forming the control gate becomes more difficult
Solution Approach 1:
By modifying the deposition parameters through nitrogen source gas addition, the patent achieves better polysilicon film quality (smaller, uniform grains without voids) that is more suitable for narrow gaps. This parameter change improves the ease of control gate formation in high-density configurations where traditional polysilicon deposition would fail due to void formation
3Manufacturing precision
If voids are generated in the control gate, then grain size appears uniform, but electrical properties differ between memory cells
Solution Approach 1:
The patent converts the potential harm of grain boundary formation into a benefit by controlling the deposition conditions with nitrogen source gas. Instead of allowing large grains to form with voids at boundaries, the modified deposition environment promotes fine-grained uniform structure where grain boundaries are minimized and void-free, transforming what could be a defect mechanism into a quality improvement
4Reliability
If voids in the control gate adhere to the dielectric layer, then coupling ratio decreases, but this effect is difficult to control
Solution Approach 1:
The patent applies preliminary action by modifying the polysilicon deposition process itself to prevent void formation before it can occur. By introducing nitrogen source gas during the deposition stage, the process proactively creates void-free polysilicon structure, eliminating the subsequent problem of void adhesion to the dielectric layer and coupling ratio degradation without requiring additional corrective process steps
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 prevents voids in the control gate, maintains uniform electrical properties, and enhances the reliability of nonvolatile memory devices by ensuring consistent coupling between the floating and control gates, thereby improving the overall performance and distribution characteristics.
Implementation Method 1
forming a polysilicon layer over the dielectric layer through a polysilicon deposition process using a nitrogen source gas, a silicon source gas, and an impurity doping gas
Implementation Method 2
nitrifying a surface of the dielectric layer through a thermal nitrification process using the nitrogen source gas after forming the dielectric layer
Data Source
AI summary
A method of manufacturing a nonvolatile memory device comprises providing a semiconductor substrate defining active regions and isolation regions with a gate insulating layer and a floating gate formed over each active region and isolation layer formed in the respective isolation regions, forming a dielectric layer on a surface of the isolation layers and the floating gates, forming a polysilicon layer over the dielectric layer through a polysilicon deposition process using a nitrogen source gas, a silicon source gas, and an impurity doping gas, and patterning the polysilicon layer to form a control gate.