Buried Split Word Line Fabrication via Oxide Spacer Patterning
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Solution Overview
Problem
The existing methods for fabricating buried split word line structures in semiconductor memory cells face challenges in achieving consistent dimensions due to variability in etching processes, affecting the height and width of the split word lines, which is critical for the performance of access FETs in memory cells.
Innovation Solution
A method involving the formation of a U-shaped gate conductor within trenches, where a first insulating layer is etched back to a specific depth, followed by a conductive material etched to a second depth, and then a second insulating layer is deposited, allowing for precise control of the split word line dimensions by dynamically adjusting the etching depths, ensuring consistent dimensions regardless of manufacturing equipment capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional etching processes are used to form buried split word lines, then the fabrication process is simple, but the dimensions (height and width) of the split word lines vary greatly due to equipment variability
Solution Approach 1:
The patent applies preliminary action by forming oxide spacers before depositing the conductive material. The oxide spacers are deposited and patterned in advance to define the precise width and position of the split word lines. This preliminary structuring ensures that subsequent conductive material deposition occurs at predetermined locations, eliminating dimension variability caused by etching equipment differences.
Solution Approach 2:
The patent uses oxide spacers as intermediary structures that mediate between the trench formation and the final conductive word line formation. These spacers serve as temporary placeholders that define the geometric parameters of the split word lines. The conductive material is then deposited conformally over these spacers, ensuring precise dimensional control without direct reliance on etching process variability.
2Manufacturing precision
If the etched depth of glue layer and conductive layer is increased to control split word line height, then height control improves, but equipment capability requirements increase
Solution Approach 1:
The patent applies self-service by using conformal deposition processes that automatically self-align to the oxide spacer structures. The conductive material deposits conformally over the spacers, and the resulting split word line dimensions are determined by the spacer geometry rather than by controlling etch depth. This self-aligning mechanism eliminates the need for high-precision depth control equipment.
Solution Approach 2:
The patent changes the controlling parameter from etch depth (which requires precise equipment control) to oxide spacer thickness (which can be controlled by deposition processes). By shifting the critical dimension control to the deposition stage where thickness control is more achievable and equipment-independent, the patent reduces equipment capability requirements while maintaining manufacturing precision.
3Manufacturing precision
If oxide spacer thickness and lateral etching rate are controlled to achieve precise split word line width, then width precision improves, but process control difficulty increases
Solution Approach 1:
The patent uses preliminary patterning to define the split word line width through oxide spacer deposition and patterning before conductive material formation. The spacer width, defined by deposition thickness and pattern geometry, directly determines the final word line width. This preliminary definition eliminates the need for precise control of lateral etching rates during subsequent processing steps.
Solution Approach 2:
The patent extracts the width control function from the etching process and places it in the deposition and patterning process. By separating the width definition step (oxide spacer formation) from the conductive material formation step, the patent makes width control independent of etching process variables, thereby reducing process control complexity.
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 results in a more stable and consistent dimension of the buried split word line structure, reducing variability and enhancing the reliability of memory cell performance by independently controlling the height and width of the split word lines.
Implementation Method 1
a conductive material conformal to the trench is formed
Implementation Method 2
a first insulating layer within the trench adjacent the conductive material is deposited. Next, the first insulating layer is etched back to a first etched depth. The conductive material is etched back to a second etched depth
Data Source
AI summary
A method for forming a buried split word line structure is provided. The method comprises the following steps. At first, a substrate having a trench therein is provided. Two liners are formed to a first thickness on sidewalls of the trench. Then, the trench is filled with a first insulating layer to a first height. The two liners are removed. Finally, a conductive material is deposited to a second height between and adjacent to the first insulating layer and the trench. Here, the first height is greater than the second height.