Optimizing FPGA and Wafer Test Coverage with Spatial Sampling and Machine Learning

TL;DR

This paper introduces spatial sampling algorithms combined with machine learning to reduce testing costs in semiconductor manufacturing, achieving improved predictive accuracy for wafer and FPGA tests.

Contribution

The study proposes novel hybrid sampling strategies using Short Distance Elimination to enhance test data distribution and accuracy in predictive models.

Findings

K-SDE improves prediction accuracy by 16.26% for wafers.

S-SDE improves prediction accuracy by 16.49% for wafers.

Effective parameter settings identified for optimal RMSD minimization.

Abstract

In semiconductor manufacturing, testing costs remain significantly high, especially during wafer and FPGA testing. To reduce the number of required tests while maintaining predictive accuracy, this study investigates three baseline sampling strategies: Random Sampling, Stratified Sampling, and k-means Clustering Sampling. To further enhance these methods, this study proposes a novel algorithm that improves the sampling quality of each approach. This research is conducted using real industrial production data from wafer-level tests and silicon measurements from various FPGAs. This study introduces two hybrid strategies: Stratified with Short Distance Elimination (S-SDE) and k-means with Short Distance Elimination (K-SDE). Their performance is evaluated within the framework of Gaussian Process Regression (GPR) for predicting wafer and FPGA test data. At the core of our proposed approach is the Short Distance Elimination (SDE) algorithm, which excludes spatially proximate candidate points during sampling, thereby ensuring a more uniform distribution of training data across the physical domain. A parameter sweep was conducted over the (alpha, beta) thresholds, where alpha and beta are in the range {0, 1, 2, 3, 4} and not both zero, to identify the optimal combination that minimizes RMSD. Experimental results on a randomly selected wafer file reveal that (alpha, beta) equal (2, 2) yields the lowest RMSD. Accordingly, all subsequent experiments adopt this parameter configuration. The results demonstrate that the proposed SDE-based strategies enhance predictive accuracy: K-SDE improves upon k-means sampling by 16.26 percent (wafer) and 13.07 percent (FPGA), while S-SDE improves upon stratified sampling by 16.49 percent (wafer) and 8.84 percent (FPGA).