Dual-Thickness LOCOS Formation Without Photolithography Masks
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Solution Overview
Problem
Existing methods for forming local oxidation of silicon (LOCOS) structures with different thicknesses on a semiconductor substrate require multiple mask levels, increasing production costs and cycle time.
Innovation Solution
A method that uses a blanket etch of a sacrificial layer to protect one LOCOS structure while allowing the other to grow in thickness, eliminating the need for a mask level by employing an oxygen diffusion barrier (ODB) layer and a polysilicon layer to control the etching process, allowing for the formation of LOCOS structures with different thicknesses without photolithography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mask levels are used to form LOCOS structures with different thicknesses, then manufacturing precision is improved, but device complexity and production cost increase
Solution Approach 1:
The patent extracts and removes the mask layer from the fabrication process entirely. Instead of using photolithography masks to define regions for different LOCOS thicknesses, the invention uses a blanket etch process with a sacrificial layer that is selectively removed to expose only the regions requiring thicker oxidation, thereby eliminating mask-related complexity while maintaining precision
Solution Approach 2:
The patent applies preliminary action by forming a sacrificial layer before the oxidation process. This sacrificial layer is deposited conformally and then selectively removed through blanket etching to create the necessary openings. The preliminary preparation of the sacrificial layer structure enables subsequent selective oxidation without requiring masks during the critical oxidation step
2Manufacturing precision
If mask levels are used to form LOCOS structures with different thicknesses, then manufacturing precision is improved, but production cycle time increases
Solution Approach 1:
By removing the mask deposition, alignment, and photolithography steps from the process flow, the patent eliminates the time-consuming sequential operations associated with multiple mask levels. The blanket etch approach allows parallel processing of the entire wafer surface simultaneously, reducing overall cycle time while maintaining the ability to produce different LOCOS thicknesses
Solution Approach 2:
The patent enables continuous useful action by using a blanket etch process that operates across the entire wafer surface in one continuous operation, rather than requiring multiple discrete mask alignment and exposure steps. The sacrificial layer removal proceeds uniformly across all regions, maintaining continuous processing without interruption for mask changes
3Ease of manufacture
If blanket etch is used instead of patterned etch, then ease of manufacture is improved, but manufacturing precision may worsen
Solution Approach 1:
The precision required for opening width control is achieved through preliminary action in the form of conformal sacrificial layer deposition. The sacrificial layer is deposited to a precisely controlled thickness that determines the final opening dimensions after blanket etching. This preliminary thickness control, combined with the known etch rate, enables precise opening width definition without requiring complex mask patterns
Solution Approach 2:
The patent controls manufacturing precision through parameter changes in the sacrificial layer deposition process. By adjusting the sacrificial layer thickness, deposition rate, and etch conditions, the opening widths are precisely controlled. The relationship between sacrificial layer thickness and final opening width is established through controlled experimentation and incorporated into process parameters
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 reduces production costs and cycle time by eliminating the need for mask levels and enables efficient fabrication of integrated circuits with dual thickness LOCOS structures, improving manufacturability and allowing for different operating voltages in MOS transistors.
Implementation Method 1
the first LOCOS structure can be covered by an oxygen diffusion barrier (ODB) layer
Implementation Method 2
A wafer on which the LOCOS structures are formed is then subjected to an oxidation process, allowing the second LOCOS structure to grow to a greater thickness
Implementation Method 3
performing a blanket etch of the polysilicon layer, thereby removing at least a portion of the polysilicon layer over the second LOCOS structure
Data Source
AI summary
A method of fabricating an integrated circuit includes forming a first opening having a first width and a second opening having a second width in a first dielectric layer over a silicon substrate. The openings expose the silicon substrate and the exposed silicon substrate is oxidized to form first and second LOCOS structures having a first thickness. A polysilicon layer is formed over the silicon substrate, so that the polysilicon layer fills the first and second openings. A blanket etch of the polysilicon layer is performed to remove at least a portion of the polysilicon layer over the second LOCOS structure while leaving the first LOCOS structure protected by the polysilicon layer. The silicon substrate under the second LOCOS structure is further oxidized such that the second LOCOS structure has a second thickness greater than the first thickness.