Ching-Nen Peng

A memory yield improvement scheme combining built-in self-repair and error correction codes

Error correction code (ECC) and built-in self-repair (BISR) schemes have been wildly used for improving the yield and reliability of memories. Many built-in redundancy-analysis (BIRA) algorithms and ECC schemes have been reported before. However, most of them focus on either BIRA algorithms or ECC schemes. In this paper, we propose an ECC-Enhanced Memory Repair (EEMR) scheme for yield improvement. Many modern memories are equipped with ECC in addition to BISR. We evaluate the back-end flow that combines both ECC and BIRA to determine whether yield can be improved by proper sequencing of the two steps. We also collect and identify important failure patterns and their distributions from over 100,000 sample memory instances, which are used to enhance the EEMR scheme that incorporates ECC. As ECC is failure pattern sensitive, careful evaluation from realistic failure bitmaps is necessary. We also verify the feasibility of implementing the proposed EEMR scheme by real test data. Experimental results from industrial 4Mb memory instances show that the proposed EEMR scheme gains over 2% instance yield on average, as compared with the traditional scheme. We also investigate the reliability of the EEMR scheme with different ECC specifications and BIRA algorithms.

Wafer Level Chip Scale Package copper pillar probing

This paper introduces a probing methodology for Integrated Fan Out Wafer Level Chip Scale Packaging (InFO WLCSP) which has the promise of being a very cost effective solution to achieve “More than Moores law” for mobile devices - more so than 3D integrated circuits (3DIC). InFO WLCSP can use either Aluminum (Al) pads or Copper (Cu) pillars as contact interfaces. Cu pillars without solder caps are selected as the contact interface due to their superior area and cost efficiency. However, there are some challenges due to Cu oxidation and its small size. In this paper we propose a novel methodology that leads to a very high precision test resulting in better yield for mass production of InFO WLCSP packages. We will show results on some industrial designs to validate our claims.

Redundancy architectures for channel-based 3D DRAM yield improvement

The three-dimensional integrated circuit (3D IC) is considered a promising approach that can obtain high data band-width and low power consumption for future electronic systems that require high integration level. One of the popular drivers for 3D IC is the integration of a memory stack and a logic die. Because the yield of a 3D IC is the product of respective yields of the mounted dies, the yields of the memory dies and logic die must be high enough, or the 3D IC will be too expensive to be manufactured. To obtain a high yield of 3D ICs, efficient test and repair methodologies for memories are necessary. In this paper, we target the channel-based 3D dynamic random access memory (DRAM) and propose two 3D redundancy architectures, i.e., Cubical Redundancy Architectures 1 and 2 (CRA1 and CRA2). We use Wide-IO DRAM as an example for discussion. In CRA1, spares are associated with each DRAM die as in a conventional 2D architecture. In CRA2, we use a static random access memory (SRAM) on the logic die as spares. Experimental results show that the CRA1 can achieve up to 18% higher stack yield than traditional redundancy architecture with the same area overhead. On the other hand, the CRA2 can achieve the same yield as the CRA1 with 40% less spares, but 1.3% higher area overhead.

Bandwidth enhancement in 3DIC CoWoS ™ test using direct probe technology

Three-dimensional integrated circuit (3DIC) technologies with the vertical stacking schemes offer the promising performances but are sensitive to the post-bond probe in the testing reliability. In order to overcome this test challenge, the direct probe interface is applied and the performances of chip are also demonstrated. By using the direct probe interface, the post-bond chips have gained with 48% bandwidth enhancement and the test cost is also reduced in the whole test flow due to the reusable characteristics.

A Built-Off Self-Repair Scheme for Channel-Based 3D Memories

Redundancy repair is a commonly used technique for memory yield improvement. In order to ensure high repair rate and final product yield, it is necessary to develop a repair scheme for the coming three-dimensional (3D) architecture of stacked DRAM. According to the JEDEC mobile memory technology roadmap, the interface of 3D DRAM, including the Wide I/O and High-Bandwidth Memory (HBM), is mainly classified as channel-based memories. In this paper, we propose a built-off self-test (BOSR) scheme at the controller level for channel-based 3D memory to enhance final product yield after the bonding of a memory cube to its corresponding logic die. The logic die contains the Channel controller, in which the BOSR circuit resides. Experimental results show that the repair rate is high with higher cluster failure ratio due to the flexible algorithm we choose. The area overhead is low and it decreases significantly when the memory size or channel count increases. The performance penalty is also low due to the parallel execution of address comparison and repair. Moreover, the manufacture cost is lower than conventional DRAM architecture due to allocator-based redundancies. Finally, the proposed scheme can easily be applied to other channel-based 3D memories.

Efficient probing schemes for fine-pitch pads of InFO wafer-level chip-scale package

With the increasing demand of super high scale of integration and small form factor in advanced semiconductor products, especially those that integrate DRAM and logic dies, 3D IC and Wafer-Level Chip-Scale Packaging (WLCSP) are considered promising approaches. In Integrated Fan-Out (InFO) WLCSP, a large number of fine-pitch pads, where neighboring pads cannot be probed simultaneously due to insufficient pitch, are used as the contact interfaces of inter-die interconnections. If the fine-pitch pads cannot be probed, the interconnections between the pads and boundary scan cells (BSCs) cannot be tested, which can lead to higher defect level. From industrial investigation, untested fine-pitch pads lead to 1-2% test coverage loss. To improve the overall test coverage, in this paper, we propose a pre-bond probing methodology for fine-pitch pads of InFO WLCSP. By the proposed probing schemes, open/short faults on the interconnects between the fine-pitch pads and BSCs can be all tested by the ATE. Moreover, for short faults that only occur between adjacent pads (interconnects), we propose a grouping method to determine the test patterns at each probing stage, which can minimize the test time. We also show that our method can achieve 100% test coverage of open/short faults.

A novel DFT architecture for 3DIC test, diagnosis and repair

Three-dimension ICs (3D-ICs) are the current trend due to their improvement in heterogeneous integration, performance, power consumption, silicon area, and form factors. However, the consequent new challenges are interconnects between dies, i.e., Through-Silicon-Vias (TSVs) and micro-bumps (μ-bumps). Therefore, many interconnect test, diagnosis, and repair schemes were proposed, such as double TSVs & double μ-bumps schemes. In this paper a novel DFT technique is presented based on the double resource schemes. Challenges to two-die, multi-tier, and numerous interconnects are handled by proposed testable, diag-nosable, repairable, and scalable element, structure, and flow.

Test Cost Reduction Methodology for InFO Wafer-Level Chip-Scale Package

Editor’s note: To reduce the manufacturing cost of heterogeneous 3-D integration, the Integrated Fan-Out Wafer-Level Chip-Scale Packaging (InFO WLCSP) is one of the emerging packaging technologies. In this article, the authors propose a cost model for InFO WLCSP, which can be used for analyzing the total test cost with respect to the test configuration and for optimizing the test configuration and procedure. —Jin-Fu Li, National Central University

A Local Parallel Search Approach for Memory Failure Pattern Identification

Due to more aggressive design rules adopted by memories than logic circuits, memories have been considered as the major technology driver of advanced logic circuits, so far as CMOS process technology is concerned. Memory failure pattern identification therefore is important, and is traditionally considered a key task that can help improve the efficiency of memory diagnosis and failure analysis. Critical failure patterns (that are the yield killers), however, may change in different memory designs and process technologies. It is difficult to identify critical failure patterns from high-volume memory failure bitmaps if they are not predefined. To solve this problem, we propose a local parallel search algorithm for efficient memory failure pattern identification. In addition, the proposed system integrates the defect-spectrum-based and coordinate-distance-based methods to identify critical memory failure patterns from a large amount of memory failure bitmaps automatically, even if they are not defined in advance. In our experiment for 132,488 4-MB memory failure bitmaps, the proposed system can automatically identify six critical yet undefined failure patterns in minutes, in addition to all known patterns. In comparison, the state-of-the-art commercial tools need manual inspection of the memory failure bitmaps to identify the same failure patterns.

Configurable Cubical Redundancy Schemes for Channel-Based 3-D DRAM Yield Improvement

Three-dimensional stacked memory stacking logic and memory dies are one of the most promising 3-D integration applications. This paper proposes two memory redundancy schemes to improve the yield of channel-based 3-D stacked DRAM by sharing spare memory across dies and satisfying channel constraints at the same time. The proposed schemes achieve much higher yield with very small area overhead than other memory redundancy schemes.