Semiconductor Wafer Contamination Identification via Junction Leakage
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Solution Overview
Problem
Current methods for evaluating semiconductor wafers require time-consuming measurements of junction leakage currents at multiple temperatures and are not accurate enough to identify contamination metals causing leakage, especially in high-quality wafers for devices like CCDs and CMOS sensors.
Innovation Solution
A method involving a reference wafer with known contamination, where p-n junction cells are formed and junction leakage currents are measured to create a distribution associated with specific contamination elements, allowing for the identification of contamination elements in measured wafers based on this association.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If junction leakage currents are measured at multiple temperatures to identify contamination metals, then identification accuracy is improved, but measurement time increases
Solution Approach 1:
The patent applies preliminary action by pre-establishing a database that correlates contamination metal types with their characteristic junction leakage current distributions at multiple temperatures. Instead of performing multi-temperature measurements for every wafer evaluation, the system pre-processes reference data during device fabrication or calibration phases, storing the relationships between metal contamination types and their electrical signatures. This allows rapid identification during actual evaluation by comparing measured distributions against the pre-built database, dramatically reducing measurement time while maintaining identification accuracy.
2Measurement precision
If multiple levels are formed for different contamination elements, then identification accuracy is improved, but measurement complexity increases
Solution Approach 1:
The patent applies copying by creating simplified representations of complex contamination signatures. Instead of directly measuring and analyzing multiple contamination levels simultaneously, the system creates a reference database containing copied or simulated leakage current distributions for each individual metal type at various temperatures. During evaluation, the measured distribution is decomposed and matched against these pre-created copies, transforming a complex multi-level identification problem into a series of simpler pattern-matching operations that reduce measurement and analysis complexity.
3Difficulty of detecting and measuring
If junction leakage current distribution is measured to identify contamination, then contamination identification capability is improved, but evaluation time increases
Solution Approach 1:
The patent applies parameter changes by transforming the measurement approach from time-consuming multi-temperature junction leakage current measurements to a simplified single-point or reduced-point measurement method. The system measures junction leakage current at a single reference temperature and uses a pre-established database to map this single parameter measurement to contamination metal identification. This parameter reduction technique maintains contamination identification capability by leveraging the unique electrical signatures stored in the database, while dramatically reducing evaluation time by eliminating the need for multiple temperature measurements.
Data Source
AI summary
A method for evaluating a semiconductor wafer including preparing a reference wafer in which contamination element and amount of contamination are known, forming a plurality of cells including p-n junctions on the reference wafer, measuring junction leakage currents in the plurality of cells on the reference wafer to acquire a distribution of the junction leakage currents of the reference wafer, associating the distribution of the junction leakage currents of the reference wafer with a contamination element, forming a plurality of cells including p-n junctions on a wafer to be measured, measuring junction leakage currents in the plurality of cells on the wafer to be measured to acquire a distribution of the junction leakage currents of the wafer to be measured, and identifying a contamination element of the wafer to be measured based on the association.