Variable Dummy Shape Overlap for RTA Temperature Uniformity
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Solution Overview
Problem
Rapid Thermal Anneal (RTA) processes in semiconductor manufacturing suffer from large systematic across-field threshold voltage variations due to local variations in wafer surface reflectivity, which degrade device characteristics more severely than Across Chip Linewidth Variation (ACLV), and existing dummy fill shapes cannot independently control Shallow Trench Isolation (STI) density without affecting diffusion or polysilicon feature densities.
Innovation Solution
The method involves determining the reflectivity of diffusion fill shapes and polysilicon conductor fill shapes in one portion of a wafer and active circuit structures in another, then adjusting the overlap, size, or shape of the fill shapes, and inserting or removing films to balance reflectivity and temperature across the wafer, allowing for controlled STI density without altering the density of active features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dummy fill shapes are used to reduce variation in local density for RX and PC features, then manufacturing process window is improved, but STI density variations cannot be reduced without affecting RX or PC local density
Solution Approach 1:
The patent segments the dummy fill shapes into two distinct types: RX fill shapes and PC fill shapes. By separating the functions of density control for different feature types, the patent can independently adjust STI density without compromising the density requirements for RX or PC features. This segmentation allows selective placement and overlapping of fill shapes to achieve uniform STI density while maintaining proper RX and PC feature densities.
Solution Approach 2:
The patent applies local quality by allowing different regions of the wafer to have different densities of dummy fill shapes. Specifically, it enables variable overlap between RX and PC fill shapes in different local regions to compensate for STI density variations. This local adjustment of fill shape density achieves uniform reflectivity and temperature distribution during RTA without requiring uniform density across the entire wafer.
2Temperature
If STI density is adjusted to improve RTA uniformity, then temperature uniformity during rapid thermal anneal is improved, but density of diffusion or polysilicon features is affected
Solution Approach 1:
The patent introduces dummy fill shapes as intermediary elements that mediate between the conflicting requirements of STI density control and feature density maintenance. These fill shapes act as placeholders that can be strategically placed and overlapped to adjust STI density without directly interfering with the density of RX or PC features. The intermediary fill shapes absorb the adjustment needs, allowing independent control of STI density for RTA uniformity while preserving feature density.
Solution Approach 2:
The patent uses dummy fill shapes as copies or replicas of actual features that serve the same structural purpose but without the functional constraints of real features. These copied structures can be freely adjusted in density and placement to achieve uniform STI regions for improved RTA performance, while the actual RX and PC features maintain their required densities for proper device functionality.
3Manufacturing precision
If infrared RTA processes are used to apply spike anneal, then sharp and shallow junctions are achieved, but local variations in reflectivity cause large systematic across field Vt variation
Solution Approach 1:
The patent applies equipotentiality by creating uniform reflectivity conditions across the wafer surface through strategic placement of dummy fill shapes. By ensuring that all regions have similar STI density and thus similar optical properties, the patent eliminates potential differences in temperature distribution during infrared RTA. This equipotential surface of uniform reflectivity ensures that all regions receive equivalent thermal energy, achieving consistent threshold voltage across the field while maintaining the sharp and shallow junctions enabled by spike anneal.
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 achieves uniform temperatures during RTA, reducing long-range RTA variations by modulating STI density without affecting critical diffusion or polysilicon feature densities, thereby improving semiconductor device characteristics.
Implementation Method 1
Local variations in the reflectivity of the surface of a wafer affect the amount of radiated light absorbed by the wafer
Implementation Method 2
the amount of radiated light absorbed by the wafer, which in turn affects the maximum temperature and the time at temperature
Implementation Method 3
Infrared RTA processes are commonly used apply this sort of spike anneal
Implementation Method 4
RTA variations are known to operate over fairly large distances, typically 4 mm radius, because of the high thermal conductivity of a standard semiconductor wafer
Data Source
AI summary
Embodiments of the invention provide a method, structure, service, etc. for variable overlap of dummy shapes for improved rapid thermal anneal uniformity. A method of providing uniform temperatures across a limited region of a wafer during a rapid thermal anneal process comprises determining a first reflectivity in a first portion of the limited region by measuring a density of first structures in the first portion. Next, the method determines a second reflectivity in a second portion of the limited region by measuring a density of second structures in the second portion. Specifically, the first structures comprise diffusion fill shapes and polysilicon conductor fill shapes (non-active dummy structures); and, the second structures comprise active circuit structures.