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3D NAND gets fabrication boost with etch equipment

Posted: 09 Jul 2014     Print Version  Bookmark and Share

Keywords:3D NAND  etch  deposition  Lam Research 

Greater process control is needed to reduce cost as memory makers ramp up chip production. Stepping up to the task, Lam Research Corp. unveiled its latest thin film deposition and plasma etch products addressing the need for three of the most critical steps in forming 3D NAND memory cells: stack deposition, vertical channel etching, and tungsten wordline deposition.

The 3D NAND memory structures now moving to production involve numerous pairs of stacked films. Process variability on both the horizontal and vertical planes must be minimised for critical steps so that each memory cell in the final device delivers similar performance. Otherwise, variation in one step can be transferred and multiplied in subsequent steps, compounding errors and leading to poor device performance and low product yield. With 40 or more pairs of films in the stack, carefully managing even slight process fluctuations is essential. Lam's new products address these stringent control requirements.

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The 3D structures—used to increase device density for more storage capacity—involve creating numerous memory levels at the same time where small errors can be magnified greatly, and therefore exceptional precision and process repeatability control are needed. Source: Lam Research

The VECTOR Q Strata PECVD (plasma enhanced chemical vapour deposition) system is used for depositing multi-layer film stacks. For this step, the system can perform both oxide/nitride and oxide/polysilicon film stack deposition. To deposit the ultra-smooth, uniform films required to avoid compounding errors, the system's matched chambers deliver superior defectivity, film stress, and wafer bow performance. In addition, the VECTOR Q Strata also provides industry-leading productivity with the highest throughput per square metre of fab area available today. As the number of layers in these stacks continues to grow, high productivity is increasingly important for cost-effective production.

Once the stack of paired films is deposited, Lam's 2300 Flex F Series dielectric etch product is used to create a vertical channel through the stack. The new system can etch through high aspect ratio structures with minimal distortion or sidewall damage, while also tightly controlling etch profile uniformity across the wafer. This capability is critical since even small deviations can cause channel dimensions to differ from cell to cell, resulting in device performance variation. A proprietary high ion energy source with modulation of energies enables these results.

The latest in Lam's market-leading tungsten deposition product line, the ALTUS Max ICEFill system controls variability by providing void-free fill of the geometrically complex 3D NAND wordlines. Using a proprietary filling technique, the new system creates the tungsten wordlines with an inside-out ALD process. The ICEFill process completely fills the lateral (horizontal) lines without any voids, while at the same time minimising deposition in the vertical channel area. As a result, both electrical performance and yield are enhanced.

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