Gettering Sites in Semiconductor Substrate via Ion Implantation
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Solution Overview
Problem
Existing gettering methods for semiconductor substrates are ineffective for slow diffusing impurities and require long processing times or high thermal budgets, and are not suitable for silicon on insulator (SOI) wafers due to the buried oxide layer acting as a diffusion barrier, and previous methods are complex or obsolete.
Innovation Solution
The method involves producing gettering sites at specific depths in the substrate layer using ion implantation followed by thermal processing to drive impurities to these sites, which are then removed during trench formation, allowing for efficient impurity removal without extending into active device areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gettering sites are created at the backside of the substrate using ion implantation or metal film deposition, then metallic impurities can be removed from active device areas, but the method requires very long processing times and high thermal budgets since impurities must travel through the entire wafer thickness
Solution Approach 1:
The invention transitions from creating gettering sites at the backside (one-dimensional approach requiring impurities to traverse full wafer thickness) to creating gettering sites within the bulk substrate at specific depths (adding a depth dimension). This allows impurities to be captured at proximity locations without requiring long-distance diffusion through the entire wafer, thereby reducing processing time while maintaining impurity removal effectiveness.
Solution Approach 2:
The invention introduces trenches as intermediary structures that serve dual purposes: they define the locations where gettering sites are created and they provide pathways for removing both the gettering sites and captured impurities from the substrate. This intermediary mechanism enables efficient impurity extraction without requiring extended thermal processing times.
2Reliability
If gettering sites are created at the backside of the substrate, then metallic impurities can be removed, but the method is not effective for silicon on insulator (SOI) type wafers where the buried oxide layer acts as a diffusion barrier
Solution Approach 1:
The invention moves from a backside-only gettering approach (which fails in SOI wafers due to the oxide barrier) to a bulk substrate approach where gettering sites are created at controlled depths within the substrate using ion implantation. This depth-dimension approach allows impurity capture to occur above the buried oxide layer in SOI wafers, enabling the method to work effectively across both bulk and SOI substrate types.
3Loss of time
If proximity gettering sites are created close to device regions, then processing time is reduced, but the method requires complicated processing with additional steps and very precise control of gettering site size to prevent extension into device active area
Solution Approach 1:
The invention combines the gettering site creation process with the trench isolation formation process. The same masking layers and etching steps used to define trench locations are also used to define gettering site locations. This merging of processes eliminates additional processing steps while maintaining precise control over gettering site dimensions and locations, thereby reducing overall process complexity.
Solution Approach 2:
The trenches serve multiple functions: they act as isolation structures between devices, they define the locations where gettering sites are created, and they provide removal pathways for both the gettering sites and captured impurities. This multi-functionality reduces the need for separate dedicated gettering process steps, simplifying the overall fabrication flow while maintaining effective impurity removal.
4Reliability
If gettering sites are created deep inside the substrate using ion implantation through etched trench isolation structures, then impurities can be removed, but the gettering sites remain in the wafer and generate charged carriers that can reach active device areas during high temperature processing
Solution Approach 1:
The invention extracts both the gettering sites and the captured impurities from the substrate by utilizing the trenches as removal pathways. After impurities are captured at the gettering sites, the same trenches are used to physically remove the gettering sites along with the trapped impurities. This extraction eliminates the source of charged carrier generation while maintaining the impurity removal benefit.
Solution Approach 2:
The gettering sites are designed as temporary structures that serve their impurity capture function and then are discarded through the trench removal process. The trenches provide a mechanism to discard both the gettering sites and the captured impurities together, eliminating any potential harmful effects from remaining gettering sites while recovering the impurity removal benefit.
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 enables effective gettering of impurities, including slow diffusing ones, at lower temperatures and with reduced processing time, suitable for SOI wafers, and integrates seamlessly with trench isolation processes without complicating the fabrication flow.
Implementation Method 1
Ions are then implanted into the substrate layer to produce gettering sites in the substrate layer
Implementation Method 2
the impurities driven to the gettering sites by thermally processing (heating) the substrate layer
Data Source
AI summary
A method for forming gettering sites and gettering impurities in a substrate layer includes producing a first masking layer over the substrate layer and patterning the masking layer to define openings at locations where trenches will be formed in the substrate layer at a later time. Ions are then implanted into the substrate layer to produce gettering sites. The gettering sites are disposed at a depth in the substrate layer such that the sites are removed when the trenches are formed. The first masking layer is removed and impurities driven to the gettering sites by thermally processing the substrate layer. A second masking layer is then produced over the substrate layer and patterned to define openings at locations where the trenches will be formed. The substrate layer is etched to produce the trenches. The gettering sites and gettered impurities are removed when the trenches are etched into the substrate layer.