The Research On Yield Enhancement Of 3D Memories

In order to meet the increasing demand of per unit area storage capacity of memory, the three-dimensional memories(3D memories) based on Through Silicon Via(TSV) has been widely used and further developed. But the problem of low yield of the three dimensional memories always restricts the application and development of the three-dimensional memories. The loss of the yield is mainly due to the existence of the fault units in the three-dimensional memories structure. The existence of fault cells which can not be repaired in the three-dimensional memories structure makes the whole three dimensional memories be discarded for it can’t work properly, resulting in the decrease of yield. The repair of fault cells in three-dimensional memories is to improve the yield of three-dimensional memories by appropriate repair method. The methods of yield enhancement for three dimensional memories proposed in this thesis are as follows: 1.Bad-Die Recycling Technique for Yield Enhancement of Three-Dimensional MemoriesUsing redundancy to repair the fault cell is an effective way for yield enhancement of three-dimensional memories. However, previous techniques cannot take full advantage of bad dies, leading a large amount of bad dies to be discarded. In order to make the best of the discarded bad dies, a yield enhancement technique by bad-die recycling for three-dimensional memories is proposed. In the presented technique, each block is divided into several sub-blocks firstly. After that, every die must go through the process of pre-bond test to get the fault information of blocks in a die, and then counting the number of the faulty sub-blocks in a die. Finally a fault-free block is chosen as global redundancy, and the sub-blocks in the global redundancy are used to repair faulty sub-blocks. The experimental results show that the proposed methodology is effective for yield enhancement of the three-dimensional memories. 2.Yield Enhancement for Three-Dimensional Memories with local shared and global shared hybrid schemeIn order to reduce the TSVs which are used to achieve the redundancy sharing. A novel method is proposed for yield enhancement in 3D memories by partial redundancy fixed allocation with local shared and global shared hybrid scheme. The first step is to obtain the distribution of each fault cells through pre-bound test. According to the fault cells’ information in the die, the required redundant units can be determined. Thus all the memory dies are classified according to the demanded redundant units of each die. Then choosing the appropriate memory dies to compose 3D memories according to the above algorithm. In three dimensional memories, the redundant rows and columns can be only be used to repair the faults in which the redundant rows or columns resides. Thus making these redundant rows and columns can be shared for the whole 3D memories without providing TSV connectivity. So that the used number of TSV can be reduced and the number of fault TSV can be reduced. The experimental result shows that the proposed method can effectively improve the yield of 3D memories.