Single-Crystal Silicon Epi Wafer for Nickel Gettering
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Solution Overview
Problem
Existing semiconductor wafers with epitaxial layers face challenges in achieving efficient nickel gettering while maintaining a low number of surface defects, as current methods either increase surface defects or result in poor nickel getter efficiency.
Innovation Solution
A semiconductor wafer with specific oxygen and nitrogen concentrations and controlled BMD size and density, combined with a heat treatment process, ensures efficient nickel gettering and low surface defects by restricting BMD size to 10 nm and density to at least 1.0×1011 cm−3, achieved through precise control of pulling and heat treatment parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a post-epi heat treatment is applied to increase nickel getter efficiency, then nickel getter efficiency is improved, but the number of surface defects increases substantially
Solution Approach 1:
The patent applies a pre-epitaxial heat treatment to form BMDs before depositing the epitaxial layer, rather than performing heat treatment after epitaxial layer formation. This preliminary action creates the necessary gettering structures in advance, achieving nickel getter efficiency of at least 90% while avoiding the surface defect generation that occurs with post-epi heat treatment.
2Reliability
If the BMD density is increased to improve nickel getter efficiency, then nickel getter efficiency is improved, but the mean size of BMDs increases which leads to more surface defects
Solution Approach 1:
The patent optimizes specific parameters of the pre-epitaxial heat treatment process, including temperature (600-900°C), time (1-24 hours), and atmosphere composition, to achieve the optimal balance between BMD density and size. These parameter changes enable simultaneous achievement of high BMD density (≥1×10^11 cm^-3) and small mean size (≤10 nm), resolving the contradiction between getter efficiency and surface defect generation.
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
The solution achieves a nickel getter efficiency of at least 95% with a significantly reduced number of surface defects, suitable for low thermal budget device cycles.
Implementation Method 1
When the single crystal from which a semiconductor wafer originates is pulled according to the Czochralski method (CZ method) from a melt contained in a quartz crucible, the crucible material forms a source of oxygen incorporated into the single crystal
Implementation Method 2
to a heat treatment at a temperature of 780° C. for a period of 3 h and to a heat treatment at a temperature of 600° C. for a period of 10 h
Implementation Method 3
Oxygen plays an important role in the formation of BMD defects (BMDs, Bulk Micro Defects). BMDs are oxygen precipitates into which BMD seeds grow in the course of a heat treatment
Implementation Method 4
a front side of the semiconductor wafer is covered with an epitaxial layer made of silicon
Data Source
AI summary
A semiconductor wafer of single-crystal silicon has an oxygen concentration per new ASTM of not less than 5.0×1017 atoms/cm3 and not more than 6.5×1017 atoms/cm3; a nitrogen concentration per new ASTM of not less than 1.0×1013 atoms/cm3 and not more than 1.0×1014 atoms/cm3;a front side having a silicon epitaxial layer whereinthe semiconductor wafer has BMDs whose mean size is not more than 10 nm determined by transmission electron microscopy and whose mean density adjacent to the epitaxial layer is not less than 1.0×1011 cm−3, determined by reactive ion etching after having subjected the wafer covered with the epitaxial layer to a heat treatment at a temperature of 780° C. for a period of 3 h and to a heat treatment at a temperature of 600° C. for a period of 10 h.