Elpida Memory, Inc has developed a 90nm process technology with a view to using it for mass-production of large-volume, high-performance DRAMs.

The technology is applicable to DRAMs with a capacity of 512Mb or 1Gb and a maximum data rate of 667Mbps. The company is planning to use the process rule in its production of 512Mb DDR2 synchronous DRAMs and other products. Elpida's previous products have used 100nm process rule thus far.

To start volume production soon, the company tried to miniaturize its process rule to 90nm with the yields unchanged. Elpida decided to continue to use the existing manufacturing process for 100nm rule, to take over the facilities, which can immediately start mass-production. The exposure system, for example, uses 248nm KrF excimer laser, a technology broadly applied in the current DRAM production.

To prevent the yields from degrading due to the 90nm miniaturization, the company also adopted optical proximity correction (OPC) for correction and printing of mask patterns, and a contact solution with low resistance.

The width of wires and the distance between wires in and around a memory cell in 90nm products are approximately 90% of those in 100nm products. Accordingly, Elpida had been concerned that defects such as shorts and breaks in wires might increase, until it introduced OPC. The company said the number of such defects per wafer is equivalent to that which occurs with 100nm products.

In addition, a contact hole in 90nm products is about 80% of that in 100nm products. Because of this, contact resistance at holes might rise and interfere with the memory's high performance. Elpida has lowered contact resistance by using its proprietary silicide (Si-metal alloy) in such holes.

The company explained that the 90nm miniaturization would boost productivity per wafer by more than 20%, compared to the conventional 100nm products, given the smaller size of a chip.

By: DocMemory
Copyright © 2023 CST, Inc. All Rights Reserved