Juergen Schloeffel

On Acceleration of SAT-Based ATPG for Industrial Designs

Due to the rapidly growing size of integrated circuits, there is a need for new algorithms for automatic test pattern generation (ATPG). While classical algorithms reach their limit, there have been recent advances in algorithms to solve Boolean Satisfiability (SAT). Because Boolean SAT solvers are working on conjunctive normal forms (CNFs), the problem has to be transformed. During transformation, relevant information about the problem might get lost and, therefore, is not available in the solving process. In this paper, we present a technique that applies structural knowledge about the circuit during the transformation. As a result, the size of the problem instances decreases, as well as the run time of the ATPG process. The technique was implemented, and experimental results are presented. The approach was combined with the ATPG framework of NXP Semiconductors. It is shown that the overall performance of an industrial framework can significantly be improved. Further experiments show the benefits with regard to the efficiency and robustness of the combined approach.

Programmable deterministic Built-In Self-Test

In this paper, we propose a new programmable deterministic built-in self-Test (BIST) method that requires significantly lower storage for deterministic patterns than existing programmable methods and provides high flexibility for test engineering in both internal and external test. Theoretical analysis suggests that significantly more care bits can be encoded in the seed of a linear feedback shift register (LFSR), if a limited number of conflicting equations is ignored in the employed linear equation system. The ignored care bits are separately embedded into the LFSR pattern. In contrast to known deterministic BIST schemes based on test set embedding, the embedding logic function is not hardwired. Instead, this information is stored in memory using a special compression and decompression method. Experiments for benchmark circuits and industrial designs demonstrate that the approach has considerably higher overall coding efficiency than the existing methods.

Cell-Aware Test

This paper describes the new cell-aware test (CAT) approach, which enables a transistor-level and defect-based ATPG on full CMOS-based designs to significantly reduce the defect rate of manufactured ICs, including FinFET technologies. We present results from a defect-oriented CAT fault model generation for 1,940 standard library cells, as well as the application of CAT to several industrial designs. We present high volume production test results from a 32 nm notebook processor and from a 350 nm automotive design, including the achieved defect rate reduction in defective-parts-per-million. We also present CAT diagnosis and physical failure analysis results from one failing part and give an outlook for using the functionality for quickly ramping up the yield in advanced technology nodes.

Defect-oriented cell-aware ATPG and fault simulation for industrial cell libraries and designs

Industry is facing increasingly tougher quality requirements for more complex ICs. To meet these quality requirements we need to improve the defect coverage. This paper presents a new methodology to significantly increase the defect coverage of the test patterns generated by ATPG tools. The fault model used during the ATPG is enhanced to directly target layout-based intra-cell faults. In contrast to previous techniques, such as Gate-Exhaustive, N-Detect, or Embedded-Multi-Detect, which either are too complex for real-world designs or merely improve the probability of detecting intra-cell defects, the new approach targets the actual root causes of intra-cell defects. The newly proposed Cell-Aware-methodology has been evaluated for 90nm and 65nm technologies on 1671 library cells and on 10 real industrial designs with up to 50 million faults. The experimental results show an average increase of 1.2% in defect coverage and a reduction of 420ppm in escape rate for a 50mm2 design.

Cell-aware Production test results from a 32-nm notebook processor

This paper describes a new approach for significantly improving overall defect coverage for CMOS-based designs. We present results from a defect-oriented cell-aware (CA) library characterization and pattern-generation flow and its application to 1,900 cells of a 32-nm technology. The CA flow enabled us to detect cell-internal bridges and opens that caused static, gross-delay, and small-delay defects. We present highvolume production test results from a 32-nm notebook processor to which CA test patterns were applied, including the defect rate reduction in PPM that was achieved after testing 800,000 parts. We also present cell-internal diagnosis and physical failure analysis results from one failing part.

Deterministic Logic BIST for Transition Fault Testing

BIST is an attractive approach to detect delay faults due to its inherent support for at-speed test. Deterministic logic BIST (DLBIST) is a technique which was successfully applied to stuck-at fault testing. As delay faults have lower random pattern testability than stuck-at faults, the need for DLBIST schemes is increased. Nevertheless, an extension to delay fault testing is not trivial, since this necessitates the application of pattern pairs. Consequently, delay fault testing is expected to require a larger mapping effort and logic overhead than stuck-at fault testing. In this paper, we consider the so-called transition fault model, which is widely used for complexity reasons. We present an extension of a DLBIST scheme for transition fault testing. Functional justification is used to generate the required pattern pairs. The efficiency of the extended scheme is investigated by using industrial benchmark circuits.

Defect-oriented cell-internal testing

Industry is facing very high quality requirements for todays and tomorrows ICs. Especially in the automotive market these quality requirements need to be fulfilled. To achieve this we need to improve currently used test methods and fault models to improve the overall defect coverage. This paper presents two new methodologies to significantly improve this situation. One method will focus on cell-internal Bridges over a wide range of Bridge resistor values and the second method concentrates on library cell-internal high-resistive Open defects. The fault models used during the ATPG are enhanced to directly target the layout-based intra-cell Open and Bridge defects. Both methods have been evaluated on 1500 library cells of a 65nm technology. In addition the wide range of intracell Bridges has been evaluated on 10 real industrial designs with up to 60 million faults. Various results are presented from all 1500 library cells and from the 10 industrial designs as well.

Cell-aware analysis for small-delay effects and production test results from different fault models

This paper focuses on a new approach to significantly improve the overall defect coverage for CMOS-based designs with the final goal to eliminate any system-level test. This methodology describes the pattern generation flow for detecting cell-internal small-delay defects caused by cell-internal resistive bridges. Results have been evaluated on 1,900 library cells of a 32-nm technology. First production test results are presented from evaluating additional defect detections achieved with different fault models on a 45-nm design.

SUPERB: Simulator utilizing parallel evaluation of resistive bridges

A high-performance resistive bridging fault simulator SUPERB (Simulator Utilizing Parallel Evaluation of Resistive Bridges) is proposed. It is based on fault sectioning in combination with parallel-pattern or parallel-fault multiple- stuck-at simulation. It outperforms a conventional interval-based resistive bridging fault simulator by 60times to 120times while delivering identical results. Further competing tools are out-performed by several orders of magnitude.

ABCD modeling of crosstalk coupling noise to analyze the signal integrity losses on the victim interconnect in DSM chips

The paper proposes an ABCD modeling approach to model the crosstalk coupling noise on the victim interconnect due to single/multiple aggressor(s) in deep sub-micron (DSM) chips. After the order reduction the crosstalk model is utilized for the analysis of crosstalk coupling noise on the victims far end signal. Various timing issues related to signal waveform such as, delay time, overshoot and undershoot occurrence time etc., that in effect help to ensure in prior the desired signal integrity (SI) and performance reliability of the SoCs, can be estimated analytically using the reduced order crosstalk model. It has been observed that the crosstalk coupling noise introduces the delay in the victims far end signal which can be significant enough or even unacceptable if many aggressors simultaneously couple energy to the victim line, or the line spacing between the aggressor and victim is reduced due to manufacturing defect such as under-etching or even, length of the victim interconnect is increased due to improper layouts of / routings between cores and devices on chips. Influences of other interconnect parasitics on the victims far end signal can also be analyzed using the same model. Simulation results obtained with the proposed reduced order model is found to be quite comparable to the accuracy of the PSPICE simulation.