Ring Oscillator Measurement Circuit for Wafer Variation Mapping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing semiconductor wafer testing systems face challenges in effectively measuring ring oscillators due to their inability to cover all sources of process variation and decouple variation sources, requiring a scalable and robust infrastructure that produces trustworthy data.
Innovation Solution
A scalable digital infrastructure is implemented using a collection of ring oscillators with an instruction register, multiplexer, pulse counter, and data shift register to sequentially measure and count oscillations, ensuring robustness and scalability through non-overlapping clocks and balanced delay paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single ring oscillator is used for measurement, then the device complexity is low, but it cannot cover all sources of process variation and cannot decouple variation sources
Solution Approach 1:
The test infrastructure is segmented into multiple independent ring oscillator circuits distributed across the wafer, with one or more oscillators per chip. This segmentation allows each oscillator to independently measure local process variations, enabling comprehensive coverage of process variation sources while maintaining manageable complexity through modular architecture
Solution Approach 2:
The patent transitions from a single-point measurement approach to a multi-dimensional measurement infrastructure by distributing ring oscillators across multiple chips and locations on the wafer. This spatial dimensionality enables decoupling of different variation sources (e.g., within-chip vs. between-chip variations) and provides comprehensive process characterization
2Reliability
If multiple ring oscillators are measured simultaneously, then data coverage and reliability improve, but the measurement system complexity increases
Solution Approach 1:
The patent implements a universal test infrastructure that can measure multiple ring oscillators simultaneously using shared measurement resources including probe card channels, timing circuits, and data acquisition systems. This multi-functional approach enables reliable measurement of many oscillators without proportionally increasing system complexity
Solution Approach 2:
The measurement system uses identical ring oscillator circuit designs replicated across multiple chips and locations. This copying approach ensures that all oscillators are measured using the same proven methodology, thereby ensuring data trustworthiness and consistency while simplifying the measurement infrastructure through standardized procedures
3Ease of manufacture
If a simple test circuit is used, then the manufacturing process is easy, but it cannot provide comprehensive process variation data
Solution Approach 1:
The ring oscillator test circuits are designed to be self-contained and self-measuring, requiring minimal external test equipment. Each oscillator automatically generates its own test signal and can be measured using standard probe card connections, making the circuits easy to manufacture while providing rich process variation data through frequency measurements that reflect local process conditions
Data Source
AI summary
An apparatus has a collection of ring oscillators. An instruction register block is configured to sequentially address and activate each ring oscillator in the collection of ring oscillators. A multiplexer with input lines is connected to each ring oscillator in the collection of ring oscillators and an output line. A pulse counter is connected to the output line of the multiplexer to count the number of oscillations of a selected ring oscillator within a selected time period to form a multiple bit frequency count output signal. A data shift register receives the multiple bit frequency count output signal and produces a serial frequency count output signal.