LOCOS Oxide Edge Control via Dual-Stage Segmentation
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Solution Overview
Problem
Conventional LOCOS processes face challenges in achieving smooth and consistent line edge roughness (LER) and critical dimension alignment in semiconductor integrated circuits, particularly in forming thick oxide regions for high-voltage transistors like LDMOS FETs, where existing methods often result in jagged or discontinuous edges.
Innovation Solution
A method involving the formation of a first oxygen diffusion barrier layer, an aperture, and subsequent LOCOS regions, with a polysilicon layer deposited at 570° C or less to form spacers, allowing for the creation of a second LOCOS region aligned to these spacers, thereby achieving improved line edge roughness and critical dimension accuracy through the use of amorphous polysilicon etching and oxidation processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional LOCOS process is used to form thick oxide regions, then oxide thickness can be achieved, but line edge roughness becomes jagged and discontinuous
Solution Approach 1:
The oxide formation process is divided into two distinct stages: first forming an initial LOCOS region, then forming a second LOCOS region. This segmentation allows each stage to contribute differently to the final structure, with the first stage establishing the base oxide and the second stage refining the edges to reduce roughness while adding thickness.
Solution Approach 2:
The first LOCOS region is formed in advance before the second LOCOS region. This preliminary action creates a foundation that guides the subsequent oxidation process, enabling the second stage to focus on edge refinement and thickness enhancement without compromising line edge quality.
2Volume of moving object
If conventional LOCOS process is used, then thick oxide can be formed, but critical dimension alignment deteriorates
Solution Approach 1:
By dividing the oxide formation into two stages, the process achieves better critical dimension alignment. The first LOCOS region establishes initial dimensions, and the second LOCOS region refines these dimensions with improved precision, resulting in overall better critical dimension control compared to a single-stage process.
Solution Approach 2:
The first LOCOS region acts as an intermediary structure between the substrate and the second LOCOS region. It provides a controlled interface that enables precise alignment for the second oxidation stage, thereby improving critical dimension alignment while achieving the required oxide thickness.
3Device complexity
If single-stage LOCOS oxidation is performed, then process simplicity is maintained, but edge smoothness and consistency are poor
Solution Approach 1:
The oxidation process is segmented into two stages: first LOCOS oxidation and second LOCOS oxidation. This segmentation increases process complexity but dramatically improves edge smoothness and consistency, as each stage contributes specific qualities to the final oxide structure that cannot be achieved in a single stage.
Solution Approach 2:
The two-stage LOCOS process maintains continuous useful action by sequentially building upon the previous stage's results. The second oxidation stage continuously refines and enhances the first stage's output, ensuring consistent edge quality throughout the process without interruption or reset.
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 thicker, more uniform LOCOS structure with improved line edge roughness and critical dimension alignment, enhancing the performance and reliability of high-voltage transistors by ensuring smooth and consistent edges, which is crucial for accurate transistor operation and integration with other semiconductor devices.
Implementation Method 1
some or all of the semiconductor substrate is covered with an oxygen diffusion barrier material, such as silicon nitride
Implementation Method 2
the exposed opening is exposed to oxygen (oxidation is performed), and the oxygen reacts with the silicon and transforms it into a silicon dioxide region
Data Source
AI summary
A method of forming an integrated circuit forms a first oxygen diffusion barrier layer in a fixed position relative to a semiconductor substrate and forms an aperture through the first oxygen diffusion barrier layer to expose a portion of the semiconductor substrate. The method also forms a first LOCOS region in an area of the aperture and a second oxygen diffusion barrier layer along the first LOCOS region and along at least a sidewall portion of the first oxygen diffusion barrier layer in the area of the aperture. The method also deposits a polysilicon layer, at a temperature of 570° C. or less, over the second oxygen diffusion barrier layer, etches the polysilicon layer and the second oxygen diffusion barrier layer to form a spacer in the area of the aperture, and forms a second LOCOS region in the area of the aperture and aligned to the spacer.