Silicon Wafer Thermal Treatment for LSA Dislocation Prevention
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Solution Overview
Problem
The challenge is to prevent dislocation in silicon wafers, particularly those doped with high concentrations of nitrogen or boron, during Laser Spike Anneal (LSA) treatment, as existing methods are ineffective in managing the strong thermal stress and plate-like oxygen precipitates that form, leading to alignment errors and overlay issues in semiconductor device manufacturing.
Innovation Solution
A silicon wafer with a nitrogen concentration of 1×10^12 atoms/cm^3 or more or specific resistance of 20 mΩ·cm or less, featuring an epitaxial layer, undergoes a thermal treatment at 750° C. for 4 hours and then at 1,000° C. for 4 hours to promote the growth of polyhedron oxygen precipitates over plate-like ones, reducing the likelihood of dislocation during LSA treatment by controlling the temperature and thermal history.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If LSA treatment is performed to achieve ultra-shallow junction with steep impurity profile, then manufacturing precision is improved, but strong thermal stress causes dislocation and overlay errors
Solution Approach 1:
The patent applies preliminary thermal treatment at 750°C for 4 hours before LSA to form fine precipitates that will serve as nuclei for polyhedron-shaped oxygen precipitates. This preliminary action prepares the wafer structure to withstand the subsequent strong thermal stress of LSA treatment, preventing dislocation while maintaining the ability to achieve ultra-shallow junction.
Solution Approach 2:
The patent changes the thermal treatment parameters by heating at a rate of 5°C per minute or more within the temperature range of 800°C or higher, and heating at 1,050°C or higher for 5 minutes or more. This parameter change transforms the shape of oxygen precipitates from plate-like to polyhedron-shaped, which have lower stress concentration and prevent dislocation during LSA treatment.
2Productivity
If high concentrations of nitrogen or boron are contained in the wafer to increase gettering ability, then productivity is improved, but plate-like oxygen precipitates are easily formed causing dislocation
Solution Approach 1:
The patent changes the thermal parameters by heating at 750°C for 4 hours followed by heating at 1,050°C or higher for 5 minutes or more. This parameter change transforms plate-like oxygen precipitates into polyhedron-shaped precipitates in wafers with high nitrogen or boron concentrations, preventing dislocation while maintaining the gettering ability provided by these dopants.
Solution Approach 2:
The patent applies preliminary thermal treatment at 750°C for 4 hours to form fine precipitates that serve as nuclei. This preliminary action controls the morphology of oxygen precipitates in wafers doped with high concentrations of nitrogen or boron, ensuring they become polyhedron-shaped rather than plate-like, thus preventing dislocation while preserving gettering functionality.
3Reliability
If thermal treatment is performed to form oxygen precipitates for preventing dislocation, then reliability is improved, but manufacturing time increases
Solution Approach 1:
The patent changes the thermal treatment parameters by heating at a rate of 5°C per minute or more within the temperature range of 800°C or higher, and maintaining 1,050°C or higher for at least 5 minutes. This parameter change accelerates the formation of polyhedron-shaped oxygen precipitates, reducing the total thermal treatment time compared to conventional slow heating methods while ensuring dislocation prevention.
Solution Approach 2:
The patent uses a two-stage thermal treatment process: first heating at 750°C for 4 hours to form fine precipitates, then heating at 1,050°C or higher for 5 minutes or more to transform them into polyhedron-shaped precipitates. This periodic action with distinct temperature stages efficiently creates the desired precipitate structure while minimizing total processing time.
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 effectively prevents dislocation triggered by oxygen precipitates, ensuring accurate alignment and reducing overlay errors in semiconductor device processes, even under the high thermal stress of LSA treatment.
Implementation Method 1
thermal treatment is performed on the wafer at 750° C. for 4 hours and then at 1,000° C. for 4 hours
Implementation Method 2
a steep temperature gradient is formed not only in the thickness direction of the wafer but also in the in-plane direction, causing strong thermal stress inside the wafer
Implementation Method 3
scanning the wafer with a laser beam whose beam diameter is about several millimeters. As a result, a region irradiated with the laser beam reaches, on the order of milliseconds or less, a temperature that is greater than or equal to 1,000° C.
Implementation Method 4
oxygen precipitates could be a trigger for dislocation
Data Source
AI summary
An object of the present invention is to provide an epitaxial wafer on which dislocation is preventable even when a LSA treatment is performed in device processes. An epitaxial wafer according to the present invention includes a wafer 11 whose nitrogen concentration is 1×1012 atoms/cm3 or more or whose specific resistance is 20 mΩ·cm or less by boron doping, and an epitaxial layer 12 provided on the wafer 11. On the wafer 11, if a thermal treatment is performed at 750° C. for 4 hours and then at 1,000° C. for 4 hours, polyhedron oxygen precipitates grow predominantly over plate-like oxygen precipitates. Therefore, in the device processes, plate-like oxygen precipitates cannot be easily formed. As a result, even when the LSA treatment is performed after various thermal histories in the device processes, it is possible to prevent the dislocation, which is triggered by oxygen precipitates, from generating.